Methodical Development of Modular Product Families: Developing High Product Diversity in a Manageable Way 3662656795, 9783662656792

Table of contents :
Contents
About the Authors
List of Figures
List of Tables
1: Introduction and Motivation
1.1 Megatrends and their Impact on Product Development
1.1.1 A New Level of Individualization
1.1.2 Globalisation 2.0
1.1.3 New Consumption Structure
1.1.4 Technology Convergence and Stronger Innovation Dynamics
1.2 Consequences for Businesses
1.3 Resulting Challenges for Product Development
1.4 Modular Product Structures as a Solution Strategy
1.5 Aim and Structure of This Book
1.5.1 Target Audience
1.5.2 Focus
1.5.3 Objectives and Key Messages
1.5.4 Overview and Structure
Literature
2: Interrelationships and Effects of Product Variety
2.1 Causes of Variety
2.1.1 External Causes
2.1.2 Internal Causes
2.1.2.1 Overarching Internal Causes of Product Variety
2.1.2.2 Causes of Internal Product Variety in Product Planning and Sales
2.1.2.3 Causes of Internal Product Variety in Product Development
2.1.2.4 Other Causes of Internal Product Variety
2.2 External Product Variety and Its Effects
2.2.1 External Product Variety
2.2.2 Impact of a High External Product Variety
2.3 Internal Product Variety and Its Effects
2.3.1 Internal Product Variety
2.3.2 Resulting Complicacy and Complexity
2.3.2.1 Complicacy
2.3.2.2 Complexity
2.3.2.3 Variant-Induced Complexity
2.3.2.4 Complexity from a Product Development Perspective
2.3.3 Overarching Effects Over the Life Phases
2.3.3.1 Effects in Product Development
2.3.3.2 Effects of Product Variety in Purchasing
2.3.3.3 Effects in Production
2.3.3.4 Effects in Distribution
2.3.3.5 Effects in Service and Maintenance
2.3.3.6 Effects in Recycling and Disposal
2.3.4 Separate Occurrence of Cause and Effect
2.3.5 Delayed and Gradual Occurrence
2.3.6 Cost Stickiness (Asymmetric Dynamic)
2.4 Resulting Costs of Product Variety
2.4.1 Overview of Cost Categories
2.4.2 Cost Effects of High Internal Variety
2.5 Possible Strategies
2.5.1 Reducing the Diversity of Supply
2.5.2 Increasing Product Benefits
2.5.3 Reduction of Complexity
2.5.4 Avoiding Complexity
2.5.5 Configuration of New Product Variants
2.6 Possibilities of Cost Assessment
Literature
3: Basics and Terms
3.1 The Product Program and Its Structure
3.2 Terms of Product Architecture
3.2.1 Requirements, Properties and Technical Characteristics
3.2.2 Functions and Functional Structures
3.2.3 Product Structure
3.2.4 Product Architecture
3.3 Modes of Construction
3.3.1 Integral and Differential Mode of Construction
3.3.2 Distinction from Modular Mode of Construction
Literature
4: The Potential of Modular Product Families
4.1 Views on Modularity in Research
4.1.1 View of Coupling, Decoupling, and Interfaces
4.1.2 Technical View
4.1.3 Functional Approaches
4.1.4 Process and Organizational View
4.1.5 Product-Strategical View
4.2 Definition of Modularity
4.3 Characteristics of Modularity
4.3.1 Decoupling
4.3.2 Commonal Use
4.3.3 Combinability
4.3.4 Interface Standardization
4.3.5 Function Binding
4.4 Potentials of Modular Product Structures
4.4.1 Concept of the Life Phases
4.4.2 Product Development
4.4.3 Procurement
4.4.4 Production and Assembly
4.4.5 Sales and Distribution
4.4.6 Product Use and Maintenance
4.4.7 Maintenance
4.4.8 Recycling
4.4.9 Summarizing the Concept of Module Drivers
4.5 Risks of Modularization
4.6 Design for Variety
4.6.1 Differentiation of Standard and Variant Components
4.6.2 Reduction of Variant Components
4.6.3 One-to-One Mapping
4.6.4 Decoupling of Components
Literature
5: Modular Product Structure Strategies
5.1 Overview of Modular Product Structure Strategies
5.1.1 Generic Procedure of Modularization
5.1.2 Definition of Product Structure Strategy
5.1.3 “Solution Space” of Product Structure Strategies
5.2 Specific Details of the Product Structure Strategy
5.2.1 Comprehensive Multiple Use of Modules/Common Module Strategy
5.2.2 Size Range Series
5.2.3 Modular Kit Strategy
5.2.4 Platform Strategy
5.3 Development of a Product Structure Strategy
Literature
6: Methods for the Development of Modular Product Families
6.1 Terms of Processes, Methods and Tools
6.2 Methods for Program Planning
6.2.1 Forward Planning
6.2.2 Market Analysis
6.2.3 Program Planning
6.3 Product Variety Management and Design-for-Variety
6.3.1 Design-for-Variety
6.3.2 Key Figures for Variety-Optimized Product Design
6.4 Modularization
6.4.1 Basic Procedure of Modularization
6.4.2 Modularization According to Technical-Functional Aspects
6.4.3 Modularization According to Organizational and Process Aspects
6.4.4 Product Strategic and Integrative Modularization Methods
6.4.5 Key Figures for Modularity
6.5 Evaluation Procedures
6.5.1 Material Number Cost Methods (Average Cost Methods)
6.5.2 Time Driven Activity-Based Costing
6.5.3 Complexity Cost Prognosis and Complexity Cost Evaluation for Modular Product Family Concepts
6.6 The Integrated PKT Approach for the Development of Modular Product Families
6.6.1 Motivation and Objectives of the Integrated PKT Approach
6.6.2 Basic Strategy of the Approach
6.6.3 Overview of the Method Units of the Approach
6.6.4 Presentation of Selected Method Units of the Integrated PKT Approach
6.6.4.1 System Analysis
6.6.4.2 Analysis of the External Variety
6.6.4.3 Analysis of the Internal Variety
6.6.4.4 Analysis of the Variety-Orientation
6.6.4.5 Improving the Design-for-Variety
6.6.4.6 Evaluation
6.6.4.7 Technical-Functional Modularization
6.6.4.8 Strategic Product Modularization
6.6.4.9 Consolidation of the Technical-Functional and Product-Strategic Modular Concepts
6.6.4.10 Concept Evaluation and Selection
6.6.4.11 Derivation of the Modular Product Structure
6.6.5 Application Studies on the Approach
Literature
7: Effects on Product Development Processes and Future Trends
7.1 Classification of Modularization in the Processes of Product Development
7.1.1 Process Models of Product Development
7.1.2 Necessary Activities for the Sustainability of Modular and Variant Products
7.2 Product Individualization and Personalization
7.3 Demographic Change and the Development of Ageing-Appropriate Products
7.4 Modular Lightweight Design Products
Literature
8: Glossary
Literature

Citation preview

Dieter Krause · Nicolas Gebhardt

Methodical Development of Modular Product Families Developing High Product Diversity in a Manageable Way

Methodical Development of Modular Product Families

Dieter Krause • Nicolas Gebhardt

Methodical Development of Modular Product Families Developing High Product Diversity in a Manageable Way

Dieter Krause Technische Universität Hamburg-Harburg Hamburg, Germany

Nicolas Gebhardt Technische Universität Hamburg-Harburg Hamburg, Germany

ISBN 978-3-662-65679-2    ISBN 978-3-662-65680-8 (eBook) https://doi.org/10.1007/978-3-662-65680-8 © Springer-Verlag GmbH Germany, part of Springer Nature 2023 This book is a translation of the original German edition „Methodische Entwicklung modularer Produktfamilien“ by Krause, Dieter, published by Springer-Verlag GmbH, DE in 2018. The translation was done with the help of artificial intelligence (machine translation by the service DeepL.com). A subsequent human revision was done primarily in terms of content, so that the book will read stylistically differently from a conventional translation. Springer Nature works continuously to further the development of tools for the production of books and on the related technologies to support the authors. This work is subject to copyright. All rights are reserved by the Publisher, whether the whole or part of the material is concerned, specifically the rights of reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors, and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, expressed or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. This Springer imprint is published by the registered company Springer-Verlag GmbH, DE, part of Springer Nature. The registered company address is: Heidelberger Platz 3, 14197 Berlin, Germany

Contents

1 Introduction and Motivation   1 1.1 Megatrends and Their Impact on Product Development������������������������������   1 1.1.1 A New Level of Individualization����������������������������������������������������   2 1.1.2 Globalisation 2.0 ������������������������������������������������������������������������������   3 1.1.3 New Consumption Structure������������������������������������������������������������   5 1.1.4 Technology Convergence and Stronger Innovation Dynamics��������   5 1.2 Consequences for Businesses ����������������������������������������������������������������������   5 1.3 Resulting Challenges for Product Development������������������������������������������   8 1.4 Modular Product Structures as a Solution Strategy��������������������������������������   9 1.5 Aim and Structure of This Book ������������������������������������������������������������������  11 1.5.1 Target Audience��������������������������������������������������������������������������������  11 1.5.2 Focus ������������������������������������������������������������������������������������������������  11 1.5.3 Objectives and Key Messages����������������������������������������������������������  12 1.5.4 Overview and Structure��������������������������������������������������������������������  13 Literature����������������������������������������������������������������������������������������������������������������  14 2 Interrelationships  and Effects of Product Variety  17 2.1 Causes of Variety������������������������������������������������������������������������������������������  17 2.1.1 External Causes��������������������������������������������������������������������������������  17 2.1.2 Internal Causes����������������������������������������������������������������������������������  20 2.2 External Product Variety and Its Effects ������������������������������������������������������  26 2.2.1 External Product Variety ������������������������������������������������������������������  26 2.2.2 Impact of a High External Product Variety��������������������������������������  28 2.3 Internal Product Variety and Its Effects��������������������������������������������������������  30 2.3.1 Internal Product Variety��������������������������������������������������������������������  30 2.3.2 Resulting Complicacy and Complexity��������������������������������������������  31 2.3.3 Overarching Effects Over the Life Phases����������������������������������������  36 2.3.4 Separate Occurrence of Cause and Effect����������������������������������������  40 2.3.5 Delayed and Gradual Occurrence ����������������������������������������������������  41 2.3.6 Cost Stickiness (Asymmetric Dynamic)������������������������������������������  43 2.4 Resulting Costs of Product Variety ��������������������������������������������������������������  44 v

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2.4.1 Overview of Cost Categories������������������������������������������������������������  44 2.4.2 Cost Effects of High Internal Variety������������������������������������������������  45 2.5 Possible Strategies����������������������������������������������������������������������������������������  47 2.5.1 Reducing the Diversity of Supply����������������������������������������������������  48 2.5.2 Increasing Product Benefits��������������������������������������������������������������  50 2.5.3 Reduction of Complexity������������������������������������������������������������������  51 2.5.4 Avoiding Complexity������������������������������������������������������������������������  52 2.5.5 Configuration of New Product Variants��������������������������������������������  52 2.6 Possibilities of Cost Assessment������������������������������������������������������������������  53 Literature����������������������������������������������������������������������������������������������������������������  56 3 Basics and Terms  61 3.1 The Product Program and Its Structure��������������������������������������������������������  62 3.2 Terms of Product Architecture����������������������������������������������������������������������  65 3.2.1 Requirements, Properties and Technical Characteristics������������������  66 3.2.2 Functions and Functional Structures������������������������������������������������  68 3.2.3 Product Structure������������������������������������������������������������������������������  72 3.2.4 Product Architecture ������������������������������������������������������������������������  73 3.3 Modes of Construction����������������������������������������������������������������������������������  75 3.3.1 Integral and Differential Mode of Construction ������������������������������  75 3.3.2 Distinction from Modular Mode of Construction����������������������������  78 Literature����������������������������������������������������������������������������������������������������������������  79 4 The  Potential of Modular Product Families  81 4.1 Views on Modularity in Research����������������������������������������������������������������  82 4.1.1 View of Coupling, Decoupling, and Interfaces��������������������������������  82 4.1.2 Technical View����������������������������������������������������������������������������������  85 4.1.3 Functional Approaches���������������������������������������������������������������������  86 4.1.4 Process and Organizational View������������������������������������������������������  87 4.1.5 Product-Strategical View������������������������������������������������������������������  90 4.2 Definition of Modularity ������������������������������������������������������������������������������  90 4.3 Characteristics of Modularity ����������������������������������������������������������������������  92 4.3.1 Decoupling����������������������������������������������������������������������������������������  92 4.3.2 Commonal Use���������������������������������������������������������������������������������  93 4.3.3 Combinability ����������������������������������������������������������������������������������  93 4.3.4 Interface Standardization������������������������������������������������������������������  94 4.3.5 Function Binding������������������������������������������������������������������������������  94 4.4 Potentials of Modular Product Structures ����������������������������������������������������  96 4.4.1 Concept of the Life Phases ��������������������������������������������������������������  96 4.4.2 Product Development������������������������������������������������������������������������  98 4.4.3 Procurement�������������������������������������������������������������������������������������� 100 4.4.4 Production and Assembly ���������������������������������������������������������������� 100 4.4.5 Sales and Distribution ���������������������������������������������������������������������� 101

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4.4.6 Product Use and Maintenance���������������������������������������������������������� 102 4.4.7 Maintenance�������������������������������������������������������������������������������������� 103 4.4.8 Recycling������������������������������������������������������������������������������������������ 104 4.4.9 Summarizing the Concept of Module Drivers���������������������������������� 104 4.5 Risks of Modularisation�������������������������������������������������������������������������������� 105 4.6 Design for Variety ���������������������������������������������������������������������������������������� 107 4.6.1 Differentiation of Standard and Variant Components���������������������� 109 4.6.2 Reduction of Variant Components���������������������������������������������������� 109 4.6.3 One-to-One Mapping������������������������������������������������������������������������ 111 4.6.4 Decoupling of Components�������������������������������������������������������������� 112 Literature���������������������������������������������������������������������������������������������������������������� 113 5 Modular  Product Structure Strategies 117 5.1 Overview of Modular Product Structure Strategies�������������������������������������� 118 5.1.1 Generic Procedure of Modularization���������������������������������������������� 119 5.1.2 Definition of Product Structure Strategy������������������������������������������ 123 5.1.3 “Solution Space” of Product Structure Strategies���������������������������� 124 5.2 Specific Details of the Product Structure Strategy���������������������������������������� 129 5.2.1 Comprehensive Multiple Use of Modules/Common Module Strategy �������������������������������������������������������������������������������������������� 130 5.2.2 Size Range Series������������������������������������������������������������������������������ 132 5.2.3 Modular Kit Strategy������������������������������������������������������������������������ 133 5.2.4 Platform Strategy������������������������������������������������������������������������������ 137 5.3 Development of a Product Structure Strategy���������������������������������������������� 140 Literature���������������������������������������������������������������������������������������������������������������� 141 6 Methods  for the Development of Modular Product Families 143 6.1 Terms of Processes, Methods and Tools ������������������������������������������������������ 144 6.2 Methods for Program Planning�������������������������������������������������������������������� 145 6.2.1 Forward Planning������������������������������������������������������������������������������ 146 6.2.2 Market Analysis�������������������������������������������������������������������������������� 150 6.2.3 Program Planning����������������������������������������������������������������������������� 152 6.3 Product Variety Management and Design-for-Variety���������������������������������� 153 6.3.1 Design-for-Variety���������������������������������������������������������������������������� 155 6.3.2 Key Figures for Variety-Optimized Product Design ������������������������ 160 6.4 Modularization���������������������������������������������������������������������������������������������� 166 6.4.1 Basic Procedure of Modularization�������������������������������������������������� 167 6.4.2 Modularization According to Technical-Functional Aspects������������ 167 6.4.3 Modularization According to Organizational and Process Aspects�� 173 6.4.4 Product Strategic and Integrative Modularization Methods ������������ 176 6.4.5 Key Figures for Modularity�������������������������������������������������������������� 182 6.5 Evaluation Procedures���������������������������������������������������������������������������������� 185 6.5.1 Material Number Cost Methods (Average Cost Methods) �������������� 186

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6.5.2 Time Driven Activity-Based Costing������������������������������������������������ 187 6.5.3 Complexity Cost Prognosis and Complexity Cost Evaluation for Modular Product Family Concepts �������������������������������������������������� 188 6.6 The Integrated PKT Approach for the Development of Modular Product Families�������������������������������������������������������������������������������������������������������� 190 6.6.1 Motivation and Objectives of the Integrated PKT Approach������������ 191 6.6.2 Basic Strategy of the Approach�������������������������������������������������������� 192 6.6.3 Overview of the Method Units of the Approach������������������������������ 196 6.6.4 Presentation of Selected Method Units of the Integrated PKT Approach������������������������������������������������������������������������������������������ 199 6.6.5 Application Studies on the Approach ���������������������������������������������� 216 Literature���������������������������������������������������������������������������������������������������������������� 217 7 Effects  on Product Development Processes and Future Trends 223 7.1 Classification of Modularization in the Processes of Product Development ������������������������������������������������������������������������������������������������ 224 7.1.1 Process Models of Product Development ���������������������������������������� 225 7.1.2 Necessary Activities for the Sustainability of Modular and Variant Products�������������������������������������������������������������������������������������������� 230 7.2 Product Individualization and Personalization �������������������������������������������� 233 7.3 Demographic Change and the Development of Ageing-Appropriate Products�������������������������������������������������������������������������������������������������������� 236 7.4 Modular Lightweight Design Products�������������������������������������������������������� 237 Literature���������������������������������������������������������������������������������������������������������������� 240 8 Glossary 243 Literature���������������������������������������������������������������������������������������������������������������� 260

About the Authors

Dieter Krause  studied production engineering/mechanical engineering and received his doctorate from the Friedrich-Alexander University of Erlangen-Nuremberg. This was followed by leading positions as chief designer, technical director, and managing director in mechanical and plant engineering companies. Since 2005, he is Head of the Institute of Product Development and Mechanical Engineering Design at Hamburg University of Technology. He is a member and speaker of the Scientific Society for Product Development (WiGeP) and is a member and advisory board member of the international Design Society. Nicolas  Gebhardt  studied product development/mechanical engineering at Hamburg University of Technology and received his doctorate on the use of graphics and visualizations in product development at the Institute for Product Development and Mechanical Engineering Design. As a research assistant, he conducted several research and development projects for modular products and product development processes. Since 2017, he has been working as a complexity manager and product architect in the German industry.

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Fig. 1.1 Current, global megatrends with a significant influence on product development������������������������������������������������������������������������������������������������������ 2 Fig. 1.2 Example products for the trend of modularization and individualization�������� 3 Fig. 1.3 Challenges for companies due to current megatrends�������������������������������������� 6 Fig. 1.4 Diversification strategy as a reaction of many companies and their danger of self-­reinforcement�������������������������������������������������������������������� 7 Fig. 1.5 Examples of the importance of product development with regard to the costs of subsequent product life phases�������������������������������������������������� 9 Fig. 1.6 Area of influence of product development in the above described vicious circle of the diversification strategy������������������������������������������������������ 9 Fig. 1.7 Possibility of action in product development concerning growing internal diversity of components and processes by using modular product structures to “break the vicious circle” (Compare Fig. 1.4 and 1.8)�������������� 10 Fig. 2.1 Company external (top) and internal (bottom) causes of the increasing product variety ������������������������������������������������������������������������������ 18 Fig. 2.2 Main external causes of high product variety ������������������������������������������������ 19 Fig. 2.3 Main internal causes of high product variety. (According to [7, 13, 20, 28, 40, 55])������������������������������������������������������������������������������������ 21 Fig. 2.4 Danger of miscalculation with a particularly wide range of offers and conventional cost accounting methods. (Based on [44, 55])�������������������� 24 Fig. 2.5 Examples of the external variety of products offered by various companies (excerpts from the respective product ranges)������������������������������ 27 Fig. 2.6 Examples for the visualization of the external product variety. (With friendly permission of Hilti Entwicklungsgesellschaft mbH and Lutz Aufzüge)���������������������������������������������������������������������������������� 27 Fig. 2.7 The differentiation of existing and overlapping product variety based on a product range of floor cleaning robots (fictitious example based on the iRobot floor cleaning robots)������������������������������������ 28

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Fig. 2.8 Reduction of the internal variety necessary to provide the external variety of offers as a core task of product development. (Based on [30]) �������������������������������������������������������������������������������������������� 31 Fig. 2.9 Number of elements, their connections and cycles as a partial aspect of complexity, according to [13]�������������������������������������������������������� 33 Fig. 2.10 Variety of elements and connections as a partial aspect of complexity, according to [13]������������������������������������������������������������������������������������������ 33 Fig. 2.11 Information content and uncertainty as partial aspects of complexity �������� 34 Fig. 2.12 Combinatorial variety as a partial aspect of complexity������������������������������ 34 Fig. 2.13 Scope of the system description as a partial aspect of complexity, according to [17]������������������������������������������������������������������������������������������ 34 Fig. 2.14 Dependence of perception based on personal knowledge as a partial aspect of complexity, explanation in the text, after [12]������������ 35 Fig. 2.15 Product development views of the internal complexity of the company����������� 36 Fig. 2.16 Overarching effects in the company due to increased product variety�����������������37 Fig. 2.17 Effects of increased product variety in the product life phases. (After [1, 8, 13, 20, 27, 33, 40, 55])�������������������������������������������������������������� 38 Fig. 2.18 Separate causation and effects of product variety in the company �������������� 41 Fig. 2.19 Delayed and gradual increase in costs due to increasing product variety according to [27, 28]������������������������������������������������������������������������ 42 Fig. 2.20 Cost stickiness in measures to reduce internal complexity [40]������������������ 43 Fig. 2.21 Overview of the cost types considered and their classification according to [9]�������������������������������������������������������������������������������������������� 44 Fig. 2.22 Overview of cost types and their contribution to complexity costs, left to [9], right [16]���������������������������������������������������������������������������� 45 Fig. 2.23 Qualitative progression of sales and costs over an increasing product variety [2, 40] �������������������������������������������������������������������������������� 46 Fig. 2.24 Qualitative progression of sales over external product variety (left), costs over internal product variety (right) and the different strategies for improvement, according to [41]�������������������������������������������������������������� 47 Fig. 2.25 Reduction of the variety of offers as a measure to increase profits, according to [41]������������������������������������������������������������������������������ 48 Fig. 2.26 Risk in reducing the external product variety as a measure to increase profits [41]�������������������������������������������������������������������������������������� 49 Fig. 2.27 Increasing product benefits with the same product variety as a measure to increase profits, [41]������������������������������������������������������������ 50 Fig. 2.28 Cost reduction by reducing the internal variety of components (1) and a downstream reduction of complexity in the company (2), [41] �������������������������������������������������������������������������������������������������������� 51 Fig. 2.29 Cost reduction by avoiding unnecessary product and component variety, [41]�������������������������������������������������������������������������������������������������� 52

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Fig. 2.30 Expansion of the product range by configuring new product variants from existing modules, according to [41] �������������������������������������� 53 Fig. 2.31 Considered evaluation factors of a conventional concept evaluation, for the explanation, see text, [16] ���������������������������������������������������������������� 54 Fig. 2.32 Extended concept evaluation with consideration of complexity costs as a dimension of economic value [16] ���������������������������������������������� 55 Fig. 2.33 Evaluation level plane consisting of production and complexity cost savings �������������������������������������������������������������������������������������������������� 56 Fig. 3.1 Schematic classification of a product program with product lines and product families ���������������������������������������������������������������������������� 62 Fig. 3.2 Example of a product program using the iRobot floor cleaning robots������������� 63 Fig. 3.3 Variants, alternatives and versions of products in product development and the product program. (Based on [17])������������������������������ 64 Fig. 3.4 Example of variants and version based on a product family of floor cleaning robots�������������������������������������������������������������������������������� 65 Fig. 3.5 Description principle for requirements with necessary and optional parts, according to [9] ���������������������������������������������������������������������������������� 67 Fig. 3.6 shows an example of a differentiated description according to product properties and technical characteristics of a floor cleaning robot �������������� 67 Fig. 3.7 Function “loosen dirt from the floor” of the floor cleaning robot and the corresponding implementation as an example for solution-neutral and solution-specific description������������������������������������������������������������������ 69 Fig. 3.8 Principle of a hierarchical function structure������������������������������������������������ 69 Fig. 3.9 Principle of flow-oriented function structure with states, functions and outputs, [5] �������������������������������������������������������������������������������������������� 70 Fig. 3.10 Example of a hierarchical functional structure of a floor cleaning robot ��������� 70 Fig. 3.11 Example of a flow-oriented functional structure of the floor cleaning robot (same functional range as in Fig. 3.10) ���������������������������������������������� 71 Fig. 3.12 Different levels of detail of a flow-oriented function structure [5]�������������� 71 Fig. 3.13 Basic classification in a product structure [15]�������������������������������������������� 72 Fig. 3.14 Section of the product structure of the floor cleaning robot ������������������������ 73 Fig. 3.15 A basic structure of a product architecture consisting of function structure, product structure and the assignment of functions to the executing components������������������������������������������������������������������������ 73 Fig. 3.16 The product architecture of the floor cleaning robot������������������������������������ 74 Fig. 3.17 Basic distinction between integral and differential mode of construction, according to [6]������������������������������������������������������������������ 76 Fig. 3.18 Qualitative representation of the suitability of integral and differential mode of construction for different numbers of units [7]������������������������������ 77

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Fig. 3.19 Integral and differential mode of construction as functionally oriented modes compared to total and partial mode of construction, according to [12] �������������������������������������������������������������������� 77 Fig. 4.1 Different views on the modularity of a product, based on [7, 30, 41]������������������������������������������������������������������������������������������������ 83 Fig. 4.2 Illustration of the decoupling of modules and the coupling of components within the modules �������������������������������������������������������������� 84 Fig. 4.3 View of coupling and decoupling on modularity������������������������������������������ 86 Fig. 4.4 Functional view of the modularity of a product ������������������������������������������ 87 Fig. 4.5 Structure of flows within a product from a modularity perspective ������������ 87 Fig. 4.6 View of the configuration of product variants on modularity���������������������� 88 Fig. 4.7 Resource-oriented view of product modularity (left: competencies, right: institutions)������������������������������������������������������������������������������������������ 89 Fig. 4.8 Characteristics of modular products according to [7, 41]���������������������������� 92 Fig. 4.9 The components inside the modules have a stronger coupling than those outside the module���������������������������������������������������������������������� 93 Fig. 4.10 Principle of commonal use of modules (here module “M1”) in several products���������������������������������������������������������������������������������������� 94 Fig. 4.11 Combinability of modules for the configuration of different products�������� 95 Fig. 4.12 Principles of standardized module interfaces ���������������������������������������������� 95 Fig. 4.13 Principles of module function binding �������������������������������������������������������� 95 Fig. 4.14 Generic overview of product life phases for different procurement strategies, based on [1]��������������������������������������������������������������������������������� 97 Fig. 4.15 Potentials and limits of a modular product structure in different product life phases, based on [7, 18, 35, 39]������������������������������������������������ 99 Fig. 4.16 Example of a modular product structure designed for easy product variant configuration of an herbicide sprayer product family. (Courtesy of Mantis ULV GmbH)�������������������������������������������������������������� 102 Fig. 4.17 Generic overview of typical module drivers, according to [7, 15] ������������ 105 Fig. 4.18 Conflict of objectives between standardization and differentiation [14]��������� 106 Fig. 4.19 Properties of the product structure of a product family that is ideally suited to variants, according to [27]�������������������������������������������� 108 Fig. 4.20 Example of a modular product family of aircraft galleys with standard components (lower part) and variant components (upper part)������������������ 110 Fig. 4.21 Example of the reduced design of a variant component, according to [27]���������������������������������������������������������������������������������������� 112 Fig. 5.1 General procedure of a modularization [8]������������������������������������������������ 120 Fig. 5.2 Decomposition of the existing product structure as the first step of modularization���������������������������������������������������������������������������������������� 121 Fig. 5.3 Analysis of the components as the second step of modularization������������ 122 Fig. 5.4 Definition of new modules as the third step of modularization������������������ 123

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Fig. 5.5 Definition of a new, modular product structure as the fourth step of modularization�������������������������������������������������������������������������������� 123 Fig. 5.6 Qualitative classification of key product structure strategies, by Gebhardt et al. [8]���������������������������������������������������������������������������������� 125 Fig. 5.7 Examples of product structuring measures at different levels of the product structure, according to Gebhardt et al. [8], Kipp [11] �������� 126 Fig. 5.8 Examples of product structuring measures across different scopes of the product range������������������������������������������������������������������������ 127 Fig. 5.9 Examples of product structuring measures with varying degrees of commonality. (Example on the right, courtesy of ROCCAT GmbH)������������127 Fig. 5.10 Different types of module commonality���������������������������������������������������� 128 Fig. 5.11 Example of multiple use of modules, according to Leichnitz and Eilmus [14]������������������������������������������������������������������������������������������ 131 Fig. 5.12 Principle of the size range series applied to a module (left) and a complete product (right) ������������������������������������������������������������������ 133 Fig. 5.13 Example of a size range series of pressure control valves. (Courtesy of Mankenberg GmbH)�������������������������������������������������������������� 134 Fig. 5.14 Example of a modular kit for the configuration of variant elevator cars. (Courtesy of Lutz Aufzüge)���������������������������������������������������������������� 135 Fig. 5.15 Examples of open and closed or user and manufacturer modular kits. (Examples courtesy of Lutz Aufzüge & Co KG, Mantis ULV Sprühgeräte GmbH and Jungheinrich AG) ������������������������������������������������ 136 Fig. 5.16 Basic principle of a platform strategy�������������������������������������������������������� 137 Fig. 5.17 Example of a platform strategy for a family of aircraft galleys, according to Jonas [10]������������������������������������������������������������������������������ 139 Fig. 5.18 Overview of the typical product structure strategy according to the granularity of modularization, according to Eilmus [5] ������������������ 141 Fig. 6.1 Systematics of processes (top) and methods (bottom)�������������������������������� 144 Fig. 6.2 Different methods of forward planning (methods presented here in bold), according to Fink and Siebe [22], Jonas [40]���������������������� 146 Fig. 6.3 Procedure of the scenario technique according to Gausemeier et al. [25]���������������������������������������������������������������������������������������������������� 147 Fig. 6.4 Principle of a roadmap for planning the product program and development projects �������������������������������������������������������������������������� 148 Fig. 6.5 Principle of SWOT analysis as a comparison of strengths and weaknesses versus opportunities and risks������������������������������������������ 149 Fig. 6.6 Example of a market share – market growth portfolio, according to Kotler et al. [49]�������������������������������������������������������������������� 151 Fig. 6.7 Tasks of Product Variety Management along the product cycle, according to Wildemann [87], Heina [33]�������������������������������������������������� 153 Fig. 6.8 Example of visualizations used in the Radical Simplification via Design [60] ������������������������������������������������������������������������������������������ 156

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Fig. 6.9 Procedure of the Integrated Framework for Product Family Design with the visualizations product, differentiation and commonality plan as working tools, according to Simpson et al. [78]�������������������������������������������������������������������������������������� 157 Fig. 6.10 Procedure diagram of Variety Mode and Effects Analysis (VMEA) and the variant tree as the main tool of the procedure, according to Caesar [11]���������������������������������������������������������������������������� 158 Fig. 6.11 Overview of the Variety-optimized design method, according to Firchau [23], Franke [24]������������������������������������������������������������������������ 159 Fig. 6.12 Collection of helpful design guidelines for the variety-optimized design of product families, according to Kipp and Krause [45])��������������� 161 Fig. 6.13 Collection of helpful design guidelines. (Continued Fig. 6.12) ���������������� 162 Fig. 6.14 Collection of helpful design guidelines. (Continued Fig. 6.13) ���������������� 163 Fig. 6.15 Basic procedure for modularization (see also Sect. 5.1.1) ������������������������ 167 Fig. 6.16 Module definition by the heuristic Dominant Flow, according to Stone [82])���������������������������������������������������������������������������������������������� 168 Fig. 6.17 Module definition by the heuristics Branching Flow (left) and Conversion Transmission (right), according to [82])�������������������������� 168 Fig. 6.18 Coupling graph, coupling matrix and compatibility matrix using the example of a desk lamp, according to Kusiak and Chun-Che Huang [53]�������������������������������������������������������������������������������� 170 Fig. 6.19 Example of a Design Structure Matrix (DSM)������������������������������������������ 171 Fig. 6.20 Presentation of product architecture (functional and building structure) and project organization in the Methodical Support of System Formation [30]���������������������������������������������������������������������������� 175 Fig. 6.21 Completed Module Indication Matrix (MIM) of the Modular Function Deployment, according to Erixon [21])������������������������������������������������������ 178 Fig. 6.22 Reordered Module Indication Matrix (MIM) for module formation in Modular Function Deployment, according to Erixon [21]), compare Fig. 6.21 �������������������������������������������������������������������������������������� 179 Fig. 6.23 Example of the merging of Design Structure Matrix and Modular Indication Matrix, according to Lanner and Malmqvist [54]����������� 180 Fig. 6.24 Example of different matrices and graphs for the structural analysis of technical systems in the Structural Complexity Management, from Lindemann et al. [55]���������������������������������������������������������������������������������� 181 Fig. 6.25 Example of a part number cost calculation, see text for explanation, according to Eilmus et al. [19])���������������������������������������������� 187 Fig. 6.26 Procedure for cost-based selection of modular product structures (Ripperda 2015)������������������������������������������������������������������������������������������ 188 Fig. 6.27 Overview of the cost forecast, for explanation see text (Ripperda 2015)������� 189 Fig. 6.28 Predicted costs using the example of a product family of floor cleaning robots (Ripperda 2015) ������������������������������������������������������������������������������ 190

List of Figures

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Fig. 6.29 Internal component variety should only be aligned with the variety of customer demand������������������������������������������������������������������������������������ 191 Fig. 6.30 Increased complexity should be reduced by reducing internal variety first before the variety of offered products on the market is reduced���������������������������������������������������������������������������������������������������� 193 Fig. 6.31 Example of a modular process over the product life phases as seen in an herbicide sprayer product family (see Fig. 4.16) ���������������������� 194 Fig. 6.32 The moderated integration of stakeholders from all product life phases and expert knowledge as an essential success factor for modularization�������������������������������������������������������������������������������������� 194 Fig. 6.33 Examples of analysis models used in the integrated PKT approach [52]���������������������������������������������������������������������������������������������� 196 Fig. 6.34 Use of special visual aids in the method modules of the integrated PKT approach [26] ������������������������������������������������������������������������������������ 196 Fig. 6.35 Objective of the Integrated PKT Approach for the development of modular product families as a reduction of internal variety for the provision of external product variety [50]�������������������������������������������� 197 Fig. 6.36 Process steps of the method for Strategic Planning of Modular Product Programs, according to Jonas [40])���������������������������������������������� 200 Fig. 6.37 The Program Structuring Model (PSM) as one of the central visual tools of the method unit for the Strategic Planning of Modular Product Programs according to Jonas [40]) ���������������������������������������������� 200 Fig. 6.38 Process steps of the Development of Product Programs with high Commonality, according to Eilmus [17])���������������������������������������������������� 201 Fig. 6.39 Extract from a Carry-over Chart as the central tool of the method unit, according to Eilmus [17])������������������������������������������������������������������ 202 Fig. 6.40 An example of a portfolio diagram of the components of a product family with their variety and the effects on variety-induced problems in a company, according to Kipp [44]���������������������������������������� 203 Fig. 6.41 Tree of external Variety of an exemplary product family of herbicide sprayers for visualizing and planning the variety of the product family, according to Kipp [44]������������������������������������������������������ 204 Fig. 6.42 Identification of variant functions in a Product Family Function Structure (PFS), here as a section of the herbicide sprayer product family shown above using the rotation atomizer, according to Kipp [44]������������������������������������������������������������������������������������������������ 205 Fig. 6.43 Module Interface Graph (MIG) using the herbicide sprayer product family as an example for the visualization of component variety [29] based on [6]���������������������������������������������������������������������������� 206 Fig. 6.44 Section of a Variety Allocation Model (VAM) as the central analysis and working tool for Design-for-Variety, using the example of herbicide sprayers, according to Kipp [44]������������������������������ 206

xviii

List of Figures

Fig. 6.45 Section of a simplified Variety Allocation Model (VAM) with technical characteristics as an alternative to the description of internal product variety (see Fig. 6.44)�������������������������������������������������� 207 Fig. 6.46 Schematic representation of the actual state (left) and ideal image (right) of a variety-­oriented product family structure in the VAM, according to Kipp [44] ���������������������������������������������������������� 208 Fig. 6.47 Recommended procedure in the VAM with increasing degree of novelty for the improvement of a Design-for-Variety project, according to Kipp [44]�������������������������������������������������������������������������������� 208 Fig. 6.48 General solution approaches by analyzing the flow-oriented Product Family Function Structure (PFS) on the basis of the variety of the functions, according to Kipp [44]���������������������������������������� 210 Fig. 6.49 Example of a variant-oriented product family concept for herbicide sprayers with simple modules for configuring the range of products, according to Kipp [44]������������������������������������������������������������ 210 Fig. 6.50 Module heuristics for technical-functional modularization according to Stone applied to the components of a product family using the Module Interface Graph (MIG) [6, 29] �������������������������� 212 Fig. 6.51 Use of network graphs and MIG for the development of life phase specific modularization concepts, here for the life phase of product development, according to [6]�������������������������������������������������� 213 Fig. 6.52 Extract from a Module Process Chart (MPC) for the coordination of life-phase-specific modularization concepts, according to Blees [6]�������� 214 Fig. 6.53 Identification and handling of conflicts in module definition along the product life phases, after [6])���������������������������������������������������������������������� 214 Fig. 6.54 Coordinated module formation for assembly process and product structure using the integral Product and Assembly Structure (iPAS), here using the example of a computer mouse [32] ������������������������������������ 216 Fig. 6.55 Results of a comparative study of seven use cases of the integrated PKT Approach for the Development of modular Product Families in industry [18]���������������������������������������������������������������������������� 217 Fig. 7.1 Classification of the essential work steps of a product family development using the integrated PKT approach in the workflow of VDI 2221������������������������������������������������������������������������������������������������ 226 Fig. 7.2 Process model of the integrated Product Engineering Model (iPEM) with the activities of VDI 2221 (left) [1]�������������������������������������� 227 Fig. 7.3 V-model for the development of mechatronic systems, according to VDI Guideline 2206 [31]������������������������������������������������������������������������ 228 Fig. 7.4 The Model of Architecting Steps as a reference process for the development of modular product families according to Otto et al. [22]���������������������������������������������������������������������������������������� 229

List of Figures

xix

Fig. 7.5 Overview of different business production strategies by decoupling point of the customer orders (compare Fig. 4.14), according to Beckmann [5]���������������������������������������������������������������������������������������������� 230 Fig. 7.6 Business production strategy for extended services (extended according to [5]) ���������������������������������������������������������������������������������������� 230 Fig. 7.7 Process landscape for modular product families in SMEs, according to Bahns et al. [3]���������������������������������������������������������������������������������������� 232 Fig. 7.8 Maintenance process for modular system (see Fig. 7.7), according to Bahns et al. [3]���������������������������������������������������������������������������������������� 233 Fig. 7.9 Field of tension in the development of modular lightweight products [18]���������������������������������������������������������������������������������������������� 238 Fig. 7.10 Using the modules of a product family of aircraft galleys to configure the product variants (compare Fig. 5.17) [10]���������������������������� 239 Fig. 7.11 Principle of the “test pyramid” of material, structural and component tests and the reduction of the number of necessary tests in a product family [18]���������������������������������������������������������������������� 240

List of Tables

Table 4.1 Properties of ideal standard components and variant components ������������ 111 Table 6.1 Generic module drivers after Modular Function Deployment [21]������������ 177 Table 6.2 List of generic module drivers [6] based on Erixon [21]���������������������������� 212

xxi

1

Introduction and Motivation

1.1 Megatrends and their Impact on Product Development Megatrends are defined as trends which are long-lasting, have effects in all areas of society, and are at the same time global and sustainable [12]. Consequently, megatrends also have a long-term impact on the business models of manufacturing companies and influence the entrepreneurial activities of these companies. New business areas will emerge as a result of new requirements and technologies or new needs of future buyers. The companies themselves will also have to change and adapt – and so will their products and product development. For the sake of explanation, only individualization, globalization, new patterns of consumption, and the knowledge society and technology convergence are presented here, as these megatrends have a strong influence on product development and on the subject of this book on mastering variety with the help of modular product structures. These megatrends are highlighted in Fig. 1.1. They place high demand on product development. As the products themselves become more and more extensive and complicated, product variety will continue to increase, the number and technical demands of used technologies are constantly growing, and product development is distributed over various locations and carried out jointly by an extensive network of suppliers. Today’s product development must meet these increased requirements. Most megatrends stem from fundamental social and technicalinnovations, such as improved communication, falling transport costs, easier world trade, declining population growth rates with simultaneous saturation of the consumer markets in the industrialised countries and, finally, the rapid growth of a global middle class. These causes and their effects are described in greater detail below.

© Springer-Verlag GmbH Germany, part of Springer Nature 2023 D. Krause, N. Gebhardt, Methodical Development of Modular Product Families, https://doi.org/10.1007/978-3-662-65680-8_1

1

2

1  Introduction and Motivation

Learning from nature Demographic change

Business Ecosystems

Globalization

Change in the world of work New political world order

Climate change and environmental pollution

Convergence of technologies Women on the advance

Cultural diversity

New mobility patterns

New consumption patterns Booming

Individualization Knowledge-based economy

Growing global security threat

Change of direction for energy and resources

Technology Convergence

health

Distributed intelligence

Digital life

Fig. 1.1  Current, global megatrends with a significant influence on product development

1.1.1 A New Level of Individualization As far back as 1982, Naisbitt expressed the rise of the individual as a “detachment from traditional social bonds” [12], and we still see this process continuing in the present day. Conventional role models give way to individual life plans. The trend towards individualization of demand is being promoted by the new information and advertising possibilities on the Internet. Individualism is certainly a global phenomenon and, at least in the long term, is not limited to the western industrialised countries. Mass markets are thus increasingly changing into micro-markets [24]. Through mass production, basic needs can be covered as widely as possible, so that well-informed, critical and price-conscious buyers are increasingly determining market developments today. Suppliers must make greater efforts to win the favor of buyers [23]. The expansion of technical products to include services, the development of which is already being intensively coordinated, plays a key role in this process. Well-known examples of such Product Service Systems (PSS) are car sharing, leased aircraft engines, or rental bicycles [11]. For end customers, the availability and flexibility this provides, compared to owning the product with its cumbersome capital commitment, is becoming increasingly important. The reputation of such services, which are often more sustainable, is also catching up in society as a status symbol vis-à-vis ownership [25]. Particularly interesting against the background of individualization are the new additive manufacturing processes (AM, often also called 3D printing), which allow greater degrees of freedom in component design compared to conventional technologies. In this process, an element-specific or layer-specific hardening of mostly shapeless material is used to produce almost any desired geometry [19]. Properly integrated into the processes of product development, product adaptation and creation, additive manufacturing enables the individualization and even personalization of products in large quantities [9, 16] (Fig. 1.2).

1.1  Megatrends and Their Impact on Product Development

3

Fig. 1.2  Example products for the trend of modularization and individualization (from left to right: Siemens FLENDER gear unit, Mamiya 645 camera system, LG G5 Modular Phone). (Picture sources from left to right siemens.de/getriebe, Eric Gaba, LG Electronics)

1.1.2 Globalisation 2.0 The causes of globalisation are mainly to be found in new means of communication, improved transport facilities, more liberal trading conditions and simplified transactions. Globalisation is by no means a new phenomenon. However, since the industrial revolution, a continuous increase in economic growth and the multinationality of companies, as well as an increasingly complicated and worldwide division of labour and denser networks of goods flows and exchange relationships can be observed [5, 8]. Moreover, the so-called globalisation 2.0 is not only be characterised by the internationalization of the movement of goods, services, and payments that has been observed so far, but also increasingly by the shift in the balance of power in international relations away from Western nations towards new focal points – above all in Asia. The technical development of new means of communication, especially the Internet, has led to much faster and better networking of supply and demand. As an extreme example, telecommunication costs fell by about 99% between 1970 and 2005 [2]. Only eight countries were connected to the Internet in 1988. Since 2000 all nations have been connected [6]. We can easily see that within just a few decades, a large number of buyers have thus been allowed quick access to a global market and suppliers on the other hand have a tool for supra-regional marketing. Falling transport costs are an essential prerequisite and driver of globalisation. Sea freight costs are currently low due to standardised container shipping since the 1960s and the increasing deadweight tonnage of the ships. The disadvantage of overseas transport is the comparatively long transport time with the resulting loss of flexibility and tied capital. However, if this can be accepted, the transport costs for goods from overseas are almost negligible. As examples, the transport cost from Australia to Europe for one ton of iron ore is about 12 US dollars, while the transport of a television set from Asia to Europe accounts for only about 1.4% of product costs. In conjunction with the significantly improved communication possibilities and trading conditions, product creation can be made ever more diverse and global. Many emerging nations in the Asian region offer more and more suitable industries for this.

4

1  Introduction and Motivation

In addition to better opportunities for global communication and transport, the liberalization of world trade supports the growing volume of international procurement of goods and products. Between 1988 and 2007, average customs duties were more than halved, which significantly promoted cross-border trade [17]. In addition, international and regional trading agreements have been concluded. A major motivation for this is the increasing scarcity of raw materials, as a result of which international cooperation is gaining in importance [1]. Other reasons for globalisation are the domestic economy’s need for new sales markets and favourable procurement sources. Even if a counter-trend has recently become apparent, it can currently be assumed that the megatrend of increasing globalisation will continue. In 2016, Germany, as the world champion exporter, proved once again that global trade is a mainstay of our prosperity and certainly a pillar of the German economy. The obstacles within international payment transactions, which were caused by legal regulations and transfer technology, previously hindering globalization, have been greatly reduced [8]; The opportunities for capital transfer and investment have thus increased and the associated transaction costs have fallen. Even if critically in terms of political economy, the potential for action by companies worldwide has increased and globalisation in its current form has only become possible by these new opportunities. The consequences of globalization for manufacturing companies are considerable [22]. On the purchasing market side, companies increasingly produce and procure globally. Corporate cooperation is becoming more and more international and the fragmentation of value chains is increasing. In general, there are better export conditions and opportunities for marketing across nations. Sales markets are being expanded, above all by a growing, consumer-oriented middle class in the emerging markets. The international sourcing of goods is also becoming more and more a matter of course for end consumers. In addition to the number of goods purchased, quality requirements are also increasing. This is being exploited to maintain market share, although the variety of goods on offer is also being greatly expanded. 60% of the German mechanical and plant engineering industry customers are already outside Western Europe [20]. At the same time, there are new competitors emerging as a result of globalisation. Product quality, which has been the strongest competitive advantage of German companies to date, is also increasing significantly in other nations. Further more, foreign companies can exploit their labour cost advantages for the most part. Simple products can increasingly be sourced locally and also exported. The import share of sophisticated machinery and equipment is growing so that the innovative and technological lead is becoming increasingly important for Germany as a business location [21]. The demands on each company’s products are becoming more diverse, which leads to a significant increase in internal complexity.

1.2  Consequences for Businesses

5

1.1.3 New Consumption Structure Consumer behaviour follows very different regional patterns, although these are becoming even more diverse overall. After a long phase of rising demand, western nations are focusing increasingly on quality and sustainability (green consumption) instead of quantity, and at the same time on individualised products [25]. In contrast, developing countries with rising purchasing power are opening up supra-regional consumer markets [21]. This is creating new, large middle classes that will experience the consumption patterns of Western countries in the near future [25]. The Asia-Pacific region’s share of global consumer spending alone will rise from 23% in 2009 to around 59% by 2030 [7]. Sales of consumer goods could increase tenfold with the increasing prosperity in the emerging markets [25]. Digital sales channels and good transport conditions are promoting this development. The opposing currents of these two groups of the world’s population, in turn, create diversification of demand and thus more and different product requirements.

1.1.4 Technology Convergence and Stronger Innovation Dynamics The exponential increase in available knowledge means that new technologies can be integrated into marketable products more quickly than before. Today’s products combine modes of action from increasingly diverse and specialized technological domains. Mechatronic products impressively illustrate the resulting challenges in the integrated development of mechanics, electronics and information technology – as has recently been the case with nano, bio and information technologies [25]. So-called cyber-physical systems (CPS) are characterized by products with the ability to make decisions, engage in communication, and trigger actions in their environment [11]. These systems consist of independent actors, networked through the Internet or comparable networks, such as remote-controlled smart homes or networked, decentralized energy production. Accordingly, the possibilities for collecting, storing, and exploiting data and information are increasing rapidly. These developments reinforce the trend of ever-shorter innovation cycles. The increasing frequency of innovation, along with more intense competition and changing consumption patterns, strengthens the megatrend of ever-shorter product life cycles.

1.2 Consequences for Businesses For manufacturing companies, the megatrends described above lead to many changes and challenges (see Fig. 1.3). The simple possibilities of international transport, but also the improved communication possibilities and trading conditions lead to a more globally oriented, more intensive competition and thus to stronger cost pressure. For companies, megatrends are leading to

6

1  Introduction and Motivation

Globalization

Individualiazation

New consumption patterns

Technology convergence

 Decreasing transport costs

 Switch to buyer markets

 Conscious consumption

 Cyber-Physical-Systems

 Improved communication

 Individual consumption

 New middle class

 Internet of things and services

 Mobility of capital

 Personalization

 Quality and sustainability (green consumption)

 Higher innovation frequencies

Global competitors

Global range of customers

Strong cost pressure

Individual demand

Dynamic requirements

Fig. 1.3  Challenges for companies due to current megatrends

increasingly individualized demand. The emerging middle classes of many rapidly developing countries, on the other hand, will not catch up with this megatrend to individualism until some time in the future, but they are strengthening this diversity of demand through their growing purchasing power. The change from seller’s to buyer’s markets increases the importance of individual performance. Large groups of customers in the industrialised nations are now much more quality oriented in their consumption behaviour. To continue generating demand, new products, functionalities and services are offered more frequently in such markets. The frequency of innovation is thus becoming increasingly important alongside price and quality. The increasing frequency with which new technological developments reach market maturity reinforces this trend of ever shorter product cycles. Together with the trend towards individualisation, this results in significantly more dynamic requirements from the company’s point of view. As a reaction of many companies to the above-mentioned developments and their resulting challenges, a diversification of the range of products on offer can often be observed. The megatrends described above are causing a decline in competitiveness for many companies due to strong cost pressure (see Fig. 1.4, left). In order to increase capacity utilization, many companies are reacting to the increasingly individual and dynamic demand by expanding their range of products (diversification strategy) in order to open up new applications and market niches with new product variants and generate more sales (see Fig. 1.4, left). As a result, the variety of product ranges of many companies is constantly increasing and more special requests from customers have to be served by new product variants. This means that external variance in different product variants, as well as in services and support, must be controlled internally. The external variety of offers initially induces an increase in the variety of components within the company (see Fig. 1.4, right). The number of different products and components increases, accompanied by corresponding fixed costs, for example through additional design effort or maintenance of more part numbers. The frequency of repetition and reuse decreases, as more different components are kept in stock and the search for existing components becomes more and more confusing and thus

1.2  Consequences for Businesses

Strong cost pressure

START

Increasing unit costs of production

Reduction of transparency

7

Declining competitveness

THE VICIOUS CIRCLE OF THE DIVERSIFICATION STRATEGY

Increase of complexity in the company

Demand for better Capacity utilization

Expansion of the range of products

Dynamic requirements

Individual demand

Increased component variety

New product variants

Increased process diversity

Fig. 1.4  Diversification strategy as a reaction of many companies and their danger of self-­ reinforcement (vicious circle of the diversification strategy, based on [14], Franke, Waldmann)

more time-consuming. As a result, the development effort increases and it becomes more difficult to keep track of the ever-larger parts master. In accordance with the variety of components, there is also an increased process variety in product development. The number of exceptions and special processes is increasing. The logistics of the various components are becoming more complex, inventories are increasing, batch sizes are getting smaller and assembly processes are becoming more complicated. In general, the increasing diversity in the company reduces the transparency of components and processes and the complexity of order processing increases in the company as a whole. The various cost-related effects, such as maintaining more part numbers, new investments in production equipment or training expenses for service and maintenance, can hardly be transferred to new product variants in a way that is appropriate to the cause. The challenges that arise from offering an ever wider range of products are spread over all phases of the product life cycle. They occur separately in terms of time and are largely not sufficiently taken into account in the standard calculation of surcharges. The unit costs therefore increase much more than calculated for the new product variants. This is aggravated by the fact that the new product variants for diversification of the range are usually tightly calculated and are offered in less attractive market segments compared to the existing products. Furthermore, it is not always guaranteed that the new product variants will appeal to new buyers. Under certain circumstances, only existing customers may switch to the new product variants so that sales do not increase (cannibalisation effect). The result is that, without intending it, the company ends up offering its new product variants at low margins, so the desired increase in profit does not occur and thus the company’s competitiveness effectively decreases (see Fig. 1.4) [14]. In the mid term this leads to lower sales and causes companies to look for further market niches in order to increase

8

1  Introduction and Motivation

capacity utilization. Thus the vicious circle of diversification starts again without any real improvement for the company. The increasing variety of products is a widespread trend  – it is inevitable for many companies to maintain their competitiveness. The resulting additional effort not only causes additional costs – it also poses significant challenges, as it can sometimes become a risk factor. A possible reaction to this may be to reduce the variety of products on offer and to specialise in a few products. However, in the long term this is often not an alternative. Rarely is it possible to reduce the variety of offers without a loss of image for the customer. Large parts of the investments once made to build up the diversity of offerings are remanent and thus permanently tied up capital (see Sect. 2.3.6). Reducing the diversity of offerings alone, for example by eliminating variants with low sales numbers, may reduce internal expenses in the short term, but it can rarely provide a lasting solution to the described problem of increasing product diversity (see Sect. 2.5.1). Completely avoiding the development shown in Fig. 1.4, therefore, is usually not possible. However, product development can significantly reduce the negative effects on the company by means of an appropriate, modular product structuring, as explained below. Modular product structure strategies offer particular advantages here.

1.3 Resulting Challenges for Product Development Within the current megatrends described above and the challenge of increasing product diversity, product development plays a special role. By defining the product, product development determines a large part of the effort and scope of the corporate processes that follow later in the product creation process (see Fig. 1.5). For example, the choice of module structure and interfaces can essentially determine the expenditures of maintainability and maintenance in advance, since important components can be reached and exchanged differently. The assembly processes can also only be planned within the limits of the predefined module structures. Product development must therefore be able to grasp the different requirements and transfer them to the design of the products. In doing so, it assumes an important function between the source of the variety of offerings in sales or product planning and the costs of the variance, which arise primarily in the downstream business processes of procurement, production, assembly, maintenance and repair. In the context of the effects of product diversity described above (vicious cycle), product development can exert influence by attempting to develop the required product diversity with a minimum of internal variety of components and processes (see Fig. 1.6). The aim here is not to transfer the planned variety of offers one-to-one to the internal variety of components and processes, but to simplify the configuration of the product variety demanded by the market.

1.4  Modular Product Structures as a Solution Strategy

9

Simple variant configuration time-to-market 100%

Production costs

22%

5%

7% 18%

80%

Number and variance of suppliers

% 70% 60%

38%

... Necessary QA tests

40%

28%

New tools N l ...

20%

Fixed costs Occurring costs

Assembly process 9%

0%

Product development

Example of decision effects

3% Production planning

Production

Materials management

Distribution

Fig. 1.5  Examples of the importance of product development with regard to the costs of subsequent product life phases [4, 18] Strong cost pressure

START

Increasing unit costs of production

Reduction of transparency

Declining competitiveness

THE VICIOUS CIRCLE OF THE DIVERSIFICATION STRATEGY

Increase of complexity in the company

Demand for better capacity utilization

Expansion of the range of products

Dynamicr requirements

Individual demand

Increased component variety

New product variants

Increased process diversity

Area of influence of product development

Fig. 1.6  Area of influence of product development in the above described vicious circle of the diversification strategy (see Fig. 1.4)

1.4 Modular Product Structures as a Solution Strategy From a product development’s point of view, modular product structure strategies offer very good potential for providing an externally required variety of products with the help of the smallest possible internal variety of components and processes for their manufac-

10

1  Introduction and Motivation

ture. At the same time, further advantages can be realized in all phases of the lifecycle. Product structuring is understood to be the goal-oriented design of the product structure with its modularity and interfaces according to technical-functional and/or product-­ strategic aspects. Modules have comparatively simple interfaces to other modules and components of the product and fulfil one (or few) clearly defined functions. They are well suited for simple creation of product variants by combination and can be manufactured in higher quantities by using them in several products, which can bring about savings through economies of scale and better familiarity with curve effects. The aim is to use modular product structures to provide the market with a wide range of products by reducing the internal variety of components and processes (see Fig. 1.7). Within the context of the megatrends described above, overarching planning of product structures beyond the individual development contracts is indispensable for many companies if the long-term risk of internal corporate complexity is to be avoided. However, the necessary capacities for this are usually not provided for, as product development often results in a bottleneck for product creation due to increasingly rapid market cycles. If the product range is viewed across the board beyond a product family, modular product structuring can open up great potential. The focus here is on savings through commonality – that is, exploiting the commonalities of different products to reduce internal variance within the company. In this context, the joint use of components or modules between different product families or even product lines can lead to major savings through economies of scale. This is usually the most important aspect to consider. Different innovation cycles can be better addressed with a modular product structure [3]. The reduction of internal variety and the simplified configuration of product variants are the main advantages that targeted modularization can provide. In addition to the Declining competitiveness

START

Demand for better capacity utilization

Increasing unit costs of production

THETEUFELSKREIS VICIOUS CIRCLE DER OF DIVERSIFIZIERUNGSSTRATEGIE THE DIVERSIFICATION Reduction of transperancy

Increase of complexity in the company

STRATEGY

Expansion of the range of products

Reduced component variety

Modular product families Increased component variety New product variants

Reduced process variety

Increased process diversity

Increase of complexity in the company

Improved competitiveness

Lower costs and error rates

Fig. 1.7  Possibility of action in product development concerning growing internal diversity of components and processes by using modular product structures to “break the vicious circle” (Compare Fig. 1.4 and 1.8)

1.5  Aim and Structure of This Book

11

reduction of internal variety, modular product structuring can generate further advantages for all product life cycle phases (see Sect. 4.4). It is important to note that the aim of modularization is not necessarily to achieve the highest possible modularity of the product structure. Rather, the aim is to achieve a product structure that is optimal in the strategic, company- and product-specific terms, in which module boundaries are purposefully and skilfully defined to achieve advantages in all product life phases. An individually developed modular strategy thus helps every company, regardless of the number of units or individuality of the products, and is currently seen as one of the key fields of action for ensuring the competitiveness of German companies [10, 15, 21].

1.5 Aim and Structure of This Book 1.5.1 Target Audience This book is written for product developers and decision-makers in practice. Since terms used in the development of modular product families vary widely in practice, we have provided a clear and concise glossary of terms. The basics, potentials and possible solutions are conveyed. This book intends to be a helpful reference work for science and research through basic chapters, examples and glossary. At the same time, it summarizes a decade of research in the field of developing modular product families at the Institute for Product Development and Design Technology (PKT) at the Hamburg University of Technology (TUHH). Interested students of the engineering sciences and especially of product development can dive into the development of modular product families based on the basics of a bachelor’s degree and find the necessary basics and examples.

1.5.2 Focus This book focuses on the development of modular product families and thus primarily addresses the aspects of modularization or modularity as well as variant diversity and reduction. It is therefore geared towards the development of products with a large number of variants and a modular product structure. The contents are to be understood as a supplement to the common product development methodology. The necessary basics of modularity and variety are addressed in Chaps. 2–4, the corresponding methods are explored in Chaps. 5 and 6, and their processes of product development in Chap. 7.

12

1  Introduction and Motivation

1.5.3 Objectives and Key Messages –– Overview of modular product structure strategies – Various product structure strategies, such as modular kits, platforms or common parts strategy, have been frequently and very differently described in the media and technical literature in the recent past. At the same time, they are not strict alternatives in product structuring, but rather basic principles that can be used in a very diverse and scalable manner for a company and a product. The costs and benefits of modularisation are therefore scalable. –– Definition of terms – Strongly differing understandings of the basic terms in the topic often make implementation in practice difficult. In this book, definitions are proposed and clearly presented by a glossary in Chap. 8. –– Modularization – According to the authors’ understanding, modularization means the development of a modular product structure to suit all requirements (module drivers) from all product life cycle phases. Through modularization, the components of a product family are organized in modules for all product life cycle phases and decoupled from each other using clearly defined interfaces. The goal of product modularization is not to maximize modularity, but to optimize the modular product structure for all product life cycle phases [13]. The modules are used for the simple configuration of product variants demanded by the market and can be used internally as simple organisational units. A modular product structure always represents a compromise. Modularisation is therefore not a purely technical task. Rather, the people must be involved in the development of that compromise so that it is supported in the long term. In practice, many of the influencing factors cannot be taken into account mathematically, so a purely mathematical optimization of product structures or architectures will not lead to a sustainable result. –– Awareness of complexity costs as an additional basis for decision-making  – The increasing variety of products causes high complexity costs in the company, which are difficult to estimate due to their delayed and interdepartmental occurrence. Decisions in product development are simultaneously made in many companies with a strong focus on manufacturing costs (if not limited to them). Awareness of complexity costs and understanding of the effects of component variety are far from sufficient in many companies. Decisions in product design must not focus solely on the manufacturing cost as an economic indicator. It is important that complexity costs are taken into account as another important indicator in order to limit the internal increase in complexity in the long term. –– Simplified illustration of external and internal complexity (analysis models) – The required variety of offers, the resulting internal complexity as well as the various effects of modularization and its module drivers are extremely extensive and complicated interrelationships. Especially in scientific literature, approaches are often presented to transfer this complexity almost completely from reality into models, in order to subsequently carry out analyses with these models and develop solutions. In practice these approaches often fail due to the principle of mapping the complexity in the company as

1.5  Aim and Structure of This Book

13

completely as possible in models in order to carry out mathematical optimizations. The book follows the basic strategy of collecting necessary information for each question and analyzing only this information. From an overall model, only the data necessary to perform a specific analysis are derived into so-called analysis models. –– Communication and interdisciplinarity – It is assumed that in connection with modularization, necessary information cannot be efficiently mapped in analysis models, for example, in corporate strategy. Therefore, a purely analytical or simulative approach is not sufficient. The knowledge of people must be skillfully included in the decision and thus in the methodological procedures, and they must be involved in the decision-­ making process. Workshop-based procedure concepts and visualizations as tools for communication and networking in product development are the essentials, with which the interdisciplinary nature of the development of modular product families can be mastered. –– Cross sectoral issue of variant management – modularization is one key aspect for mastering, reducing and avoiding internal variance. If implemented comprehensively, all departments within the product development process are involved. Only this holistic approach can lead to the desired result. If all effects of both internal and external variance are considered, the topic must be perceived as a superordinate cross-sectional task and organized in variant management, comparable to quality management.

1.5.4 Overview and Structure Chapter 2 – Interrelationships and Effects of Variety This chapter explains the basic relationships and effects of product variaty. Chapter 2 is therefore primarily aimed at people in decision-making situations about product variety and concepts for product structuring – but it is a good introduction to the motives behind the topic for all those interested. Readers who are not familiar with the terminology of product variety are advised to read Chap. 3, as it explains the basics and terms. Chapter 3 – Basics and Terms Chapter 3 is particularly suitable as an introduction to the topic but can also be a good reference for experts. Moreover, it provides a conceptual basis for the following chapters. Chapter 4 – Potentials of Modular Product Families As a basic procedure, modularization can provide a multitude of potentials for all product life phases. As a transition between the current challenges of product development and the concrete solution possibilities within the framework of product structuring, Chap. 4 provides the essential core of modular product families development and is thereby aimed at every reader.

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1  Introduction and Motivation

Chapter 5 – Modular Product Structure Strategies Terms such as platforms, modular kits or common parts strategies are used more and more frequently in literature and practice, and are often understood and implemented in very different ways. This makes it increasingly difficult to achieve transparency regarding the possibilities of product structuring. Chapter 5 offers an overview of the solution space of product structure strategies as well as parameters for their classification. Chapter 6 – Methods for the Development of Modular Product Families The development and implementation of modular product structures involves a multitude of very different methods and tools. Chapter 6 gives an overview of these methods and tools, highlighting the most important ones. It is aimed directly at product developers. Chapter 7 – Effects on Product Development Processes and Future Trends The task of modularization is best carried out across, parallel, and in coordination with existing organizational units of product development. It is a task with special demands on the product developer. Chapter 7 describes how these tasks can be embedded in development. As a concluding outlook, a selection of current research topics is highlighted with their effects and potentials concerning modularization. These include individualization and personalization, the trend towards additive manufacturing, demographic change, the trend towards cyber-physical systems (CPS) and the modularization of lightweight products. Chapter 8 – Glossary The glossary was created because terms are often defined differently. In addition, some terms are used differently in practice than in science, and are even understood differently in different companies. In order to facilitate a clear understanding of the use of terms in this book, a reference is reproduced in Chap. 8, which was created through many years of research work at the PKT Institute and has been compiled specifically for this book.

Literature 1. Borchardt K (2001) Globalisierung in historischer Perspektive – Vorgetragen in der Gesamtsitzung vom 1. Juni 2001. Verlag der Bayerischen Akademie der Wissenschaft, München 2. Busse M (2002) HWWA Discussion Paper Nr. 116 – Bundesverband der Deutschen Industrie (BDI): Außenwirtschafts-Report 04/2002 3. Dirzus D, Bartles D (2017) IIoT – wo stehen wir? Das Magazin für das digitale Unternehmen, pp 13–15 4. Ehrlenspiel K, Kiewert A, Lindemann U, Mörtl M (2007) Kostengünstig Entwickeln und Konstruieren – Kostenmanagement bei der integrierten Produktentwicklung. Springer, Berlin/ Heidelberg 5. Hirst P, Thompson G, Bromley S (2009) Globalization in question. Polity, Cambridge University Press

Literature

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6. International Telecommunication Union, OECD (2008) The global information society: a statistical view, Geneva 7. Kharas H (2010) The emerging middle class in developing countries. OECD Development Centre. www.oecd.org/dev/44457738.pdf. Zugegriffen: 05 August 2016 8. Kisker KP (2005) Internationale Kapitalmobilität  – Verschärfung der Ausbeutung in der Ersten und Dritten Welt. In: Baum-Ceisig A, Faber A (Hrsg) Soziales Europa? Perspektiven des Wohlfahrtsstaates im Kontext von Europäisierung und Globalisierung. Festschrift für Klaus Busch. VS Verlag für Sozialwissenschaften, Wiesbaden, pp 45–62 9. Ko H, Moon SK, Hwang J (2015) Design for additive manufacturing in customized products. Int J Precis Eng Manuf 16:2369–2375 10. Kortmann D, Klink H, Wüpping J (2009) Strategien zur profitablen Variantenkonfiguration. International Journal of Interoperability in Business Information Systems 9:57–60 11. Lindemann U (2015) Von der Mechatronik zu Cyber-Physical-Systems. In: Lindemann U (Hrsg) Handbuch Produktentwicklung. Hanser, München, pp 869–875 12. Naisbitt J (1982) Megatrends  – ten new directions transforming our lives. Warner Books, New York 13. Pahl G, Beitz W, Feldhusen J, Grote K-H (2007) Konstruktionslehre – Grundlagen erfolgreicher Produktentwicklung; Methoden und Anwendung. Springer, Berlin/Heidelberg 14. Rathnow PJ (1993) Integriertes Variantenmanagement- Bestimmung, Realisierung und Sicherung der optimalen Produktvielfalt. Vandenhoeck & Ruprecht, Göttingen 15. Roland Berger Strategy Consultants (2012) Modular Products- How to leverage modular product kits for growth and globalization 16. Spallek J, Sabkowski O, Krause D (2016) Influences of additive manufacturing on design processes for customised products. In: Marjanović D, Storga M, Pavković N and Bojčetić N (Hrsg) Proceedings of the DESIGN 2016 14th International Design Conference, Zagreb 17. United Nations Conference on Trade and Development UNCTAD (2008) Development and Globalization: Facts and Figures 18. VDI-Gesellschaft Produkt- und Prozessgestaltung (1987) VDI 2235 Wirtschaftliche Entscheidungen beim Konstruieren; Methoden und Hilfen. Beuth Verlag, Düsseldorf 19. VDI-Gesellschaft Produktion und Logistik (2014) VDI 3405 Additive Fertigungsverfahren  – Grundlagen, Begriffe, Verfahrensbeschreibungen. Beuth Verlag, Düsseldorf 20. VDMA (2015) Investieren in die Zukunft- Gemeinsame wirtschaftspolitische Positionen des deutschen Maschinen- und Anlagenbaus 2015. Frankfurt am Main 21. Verband Deutscher Maschinen- und Anlagenbau e.V. (2014) Zukunftsperspektive deutscher Maschinenbau. http://www.vdma.org/documents/ 22. Wiendahl H-P, Gausemeier J (2010) Wertschöpfung und Beschäftigung in Deutschland. acatech Veranstaltung am 14. September 2010 im PZH der Universität, Hannover 23. Wünsche M (2015) Wirtschafts- und Sozialkunde (IHK) – Prüfungstraining für kaufmännische und kaufmannsnahe Berufe. Springer, Gabler/Wiesbaden 24. Z_punkt GmbH (2011) Megatrends  – Update. http://www.z-­punkt.de/de/studien/studie/ megatrends-­2020plus/21, Zugegriffen: 12.4.2017 25. Z-punkt GmbH (2014) Unternehmer positionen Nord. Megatrends 2020plus – Herausforderungen und Chancen für Unternehmer

2

Interrelationships and Effects of Product Variety

2.1 Causes of Variety The megatrends of globalization, new consumption patterns and technologies, and individualization presented in Chap. 1 form the main external causes of product variety. They cannot be directly influenced by the company and are therefore largely unavoidable. In addition to these external causes of product variety, however, there are other, internal causes of product variety in the form of deficits in strategies, processes and organization, which create unnecessary variety of components and processes (see Fig. 2.1). Drivers that are company internal occur on average at shorter notice and are usually easier to influence than causes that are company external. The goal of manufacturing companies must be to map a high level of external product variety demanded by the market with as little internal variety as possible in order to cover the market requirements and at a reasonable cost. For this reason, it is important to know the causes and interrelationships of variety and to distinguish clearly between external and internal causes and effects. In the following sections, the external and internal causes of product variety are explained in more detail.

2.1.1 External Causes The causes of high product variety, which affect the company from the outside (see Fig. 2.2), cannot usually be influenced and their effect on the product range can only be avoided to a limited extent. Most of them have already been presented in Chap. 1 as essential motivations for strategies to reduce internal product variety, while at the same time offering a broad range of products enabled by modular product structuring. In addition to

© Springer-Verlag GmbH Germany, part of Springer Nature 2023 D. Krause, N. Gebhardt, Methodical Development of Modular Product Families, https://doi.org/10.1007/978-3-662-65680-8_2

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2  Interrelationships and Effects of Product Variety

Technology convergence Individualization

Standards and Norms

Globalization Laws

New consumption patterns

...

Increasing diversity of demand

...

Product planning/Sales Diversity of products

Product development Internal diversity of components and processes

Unsuitable evaluation and information systems

Deficits in methods

... ...

...

Lack of communication

Fig. 2.1  Company external (top) and internal (bottom) causes of the increasing product variety

the increasing diversity of demand and frequency of new technological achievements, there are other external causes, which are described below. As shown in Chap. 1, the variety of products is constantly increasing. Sales markets are becoming increasingly global due to better information and transport possibilities. Many populous countries, such as China or India, are catching up rapidly in terms of quantity and quality of industrial products and purchasing power. At the same time, Western societies are developing an increasingly quality-oriented consumer behavior. Companies in industrialized nations especially are facing more saturated markets with diverse and dynamic requirements. The challenge here is to offer an ever-broader product range in the face of increasing competitive pressure. Increased supply variety improves sales if it is well geared towards the market and covers the required variety. Many companies are therefore reacting by diversifying their own product range and differentiating it from that of their competitors (see Sect. 1.2). There is hardly any alternative to the differentiation strategy, especially when it comes to having a cost disadvantage [10]. The aim is to increase sales by serving additional markets and niches with products offering unique customer benefits. Increasing demand for customer-specific solutions is one of the most important trends, offering unique opportunities in the mechanical and plant engineering industry [51]. The

2.1  Causes of Variety

Individualization

Globalization

 Diversity of demand and competition lead to strategies of differentiation and diversification  Change of demographic structures

19

New consumption patterns

Technology convergence

 Global sales opportunities

 Technology convergence and  Faster product cycles

Fig. 2.2  Main external causes of high product variety

automotive industry is a well-known example of an increasingly individualized performance fulfillment with simultaneous mass customization. For example, it has been common practice for some time now to offer high product variety due to choices and options that cannot be sold in all variants until the model range is discontinued [21]. In addition, a self-sustaining effect of product variety is the interplay of offers, price calculations, and customers [52]. By diversifying the product range, the supplier is increasingly perceived as a one-stop-provider in the market, for standard as well as for special and complete solutions, which leads to requests for further “exotics”. The costs of increased variety in the company due to new product variants are difficult to determine in advance. Due to the surcharge calculation normally used to determine the cost price, the exotics are often offered at too low a price. The result is that the market demands further variants, thus additionally increasing the diversity of demand. For many products, the frequency of innovation is becoming increasingly as important as price and quality, creating additional incentives to buy in otherwise saturated markets. New technologies mean that products can now be offered with new functionalities or at lower prices. As a result, product life cycles are becoming shorter and shorter in many industries. Rapid reaction to new market requirements is becoming increasingly important if customers and thus sales are not to be lost permanently [54]. Indirectly, this also increases internal

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2  Interrelationships and Effects of Product Variety

variety, since significantly more product generations exist simultaneously over the market cycle with associated maintenance and service. Increased efficiency in product development is essential for the implementation of ever shorter product life cycles. The need for reducing internal complexity (see Sect. 2.3.1 Definition of terms) to accommodate increasing product variety, is an important prerequisite. In addition, there are intrinsic effects at the customer’s end depending on a broad product range. Even if the individual customer does not use the entire range of products, it gives him or her the security of being able to select a product variant that is ideally suited to his or her needs or, in case of doubt, to later switch to a better-suited product. Such a wide range of offers creates an additional indirect benefit for the customer and an image gain for the provider [24]. The effect of the so-called “paradox of choice,” however, must be duly considered [45]: If the range of products is too large or appears too confusing to the customer, uncertainty and fear of wrong decisions can arise, so that customers could switch to suppliers with a product range more clearly defined or presented [7]. In addition to more individual customer requirements, there are also more frequent adjustments of products to changing boundary conditions during the product use phase to be made. This, too, must be considered in advance in the product development phase.

2.1.2 Internal Causes The external product variety required by the market must be mapped with as little internal variety as possible in order to keep internal costs low. However, there are other causes and effects within the company that can counteract a lean supply of product variety and increase the internal variety of components and processes. This creeping but avoidable generation of variety has many different causes, as shown in Fig. 2.3. Essentially, the processes in sales and product planning are decisive for external variety. In product development, the internal product and component variety is defined on this basis. In contrast, the processes of the other product life phases implement the internal variety defined by product management, sales and development. However, they determine the efficiency with which this is done and whether additional complexity is created, for example, if special processes are required to produce the variants. All product life phases together are subject to the overarching, internal causes of product variety described in the following section.

2.1.2.1 Overarching Internal Causes of Product Variety The lack of information available for product variants with their essential characteristics, functions, usage, validity and releases is often problematic, since the corresponding documentation is not always primarily required for order fulfillment. The necessary information is usually very extensive and distributed across different departments and software systems. This makes it more difficult to find the information, which means that all variant

2.1  Causes of Variety

21 General causes         

Product planning and sales

Insufficient availability of information on product variants lack of transparency due to the diversity of components and processes irregular, inconsistent phase out of variants unclear separation between standard and non-standard business Insufficient accounting methods lacking strategy for alignment and control of variants lack of coordination of the product life phases with regard to product variety lack of awareness of the negative effects of product variety no suiting incentive systems and employee reviews

Product development

Purchsase

Procurement

Application & After Sales

Realisation of Product Variety Definition of Product Variety

 Diversification strategy (development of niche products) and differentiation strategies (unique services and products) with individual customer orientation  Focus on sales despite cost in-transparency  Sales of specific local variants  Establishement of full product ranges as barriers to market entry  Risk diversification and compensation of market fluctuations through a wide range of products  Dominance of sales with a strong focus on volumes

     

Multi-supplier strategy in procurement Focus on production costs Strive for problem-specific optimal solutions Poor traceabilityof existing solutions Faulty organizational structures Long-term replenishment and service contracts

Fig. 2.3  Main internal causes of high product variety. (According to [7, 13, 20, 28, 40, 55])

management tasks (see Sect. 6.3) – especially sales and design – are limited in their efficacy from the outset. The increasing variety of different components within the company quickly leads to a lack of transparency. Since the processes required to create all product variants are also becoming more extensive in all product life cycle phases and have more exception steps and regulations, it is becoming increasingly difficult to maintain a general overview. Particularly in the case of exotic variants, it is often assumed that these will not be in demand in significant quantities in the future. The corresponding information is therefore often not filed with the usual care. A further major problem with internal variety is the effort and importance of irregular and non-stop variant cleansing. In this context, the variety of components and their use must be systematically reviewed at regular intervals to determine their relevance to the current product range and adjusted if necessary. Due to the hindered availability of information, many companies can hardly carry out this task effectively and comprehensively. In many cases, the use of a component (see Sect. 3.2.4) cannot be determined with reasonable effort, so that continuously postponed. A frequent phenomenon is an unclear separation between standard and special business and the subsequent inclusion of special solutions in the variety of offers. After development, customer orders with special requirements are quickly incorporated into the general range of services in order to make further use of the development services provided. This usually happens regardless of the long-term oriented product program planning and thus possibly generates new internal components and processes which are not in demand sufficiently frequently in the medium term to cover the expenses. Together with the

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2  Interrelationships and Effects of Product Variety

insufficient adjustment of product and component variants, this has resulted in a historically grown product variety whose sales effectiveness is no longer a given. Improved work technology systems make it easier to handle a wide variety of products in all areas of the company, such as modern PDM systems and configurators or flexible manufacturing systems [14, 20]. However, one can only marginally reduce the cost to the organization of delivering this product variety through improved manageability and visibility, so much of the effort is still generated. Furthermore, the variety of products may have a role as a personally motivated end in itself. The increased product variety resulting from product planning, marketing and sales tends to require additional efforts and new sets of responsibilities, teams, or entire departments. Thus, the variety of products can lead to the raison d’être of jobs or even entire teams. This also applies to investments in operating resources and equipment for handling a variety of products. If, for example, new jobs are created for complexity management or new product configuration software is procured, these investments will initially be designed with overcapacities in anticipation of a further increase in product variety. Subsequently, the existence of these new capacities and the general desire to make good use of them may lead to an increase in the number of variants. Once such investments have been made, it is much more difficult to argue for and to implement a reduction in the number of variants in the company, as this is measured against the previous level of investment ([28] after [36]). Particularly serious in all product life cycle phases is the divergence of causes and effects of high product variety in terms of timing and company departments (see also Sects. 2.4 and 2.5). High product variety costs are incurred in all product life phases with no definable reference to the product variants. For these reasons, they cannot be calculated adequately. These costs are easy to underestimate, which leads to a lack of awareness of the significant impact of technical solutions on the complexity costs in the company. Therefore in decision-making situations, there is often a preference for solutions which promise savings in manufacturing costs, but which can be compensated for in the mid-­ term by increased complexity costs in the company and which can even generate losses. In many cases, there is no overriding, clear strategy for dealing with product variety in the company. In most cases, top management gives instructions on the orientation of product variety, but rarely on the handling of product variety within the company [15]. This topic is often the provenance of department heads and is usually not coordinated across the board. Due to the problems that occur widely over the product life phases as a result of high product variety, intensive coordination of the product life phases with regard to variant management is urgently required. Only this way is it possible to develop and produce products with many variants. Variant management should be set up across departments. The fundamental interrelationships between the diversity of offers and indirect costs to the company have been known for some time. In practice, however, it is only in recent years that product variety has been seen as a key driver of internal corporate complexity. As a result, a lack of awareness of the negative effects of increasing product variety is often another internal cause of additional variety.

2.1  Causes of Variety

23

Incentive systems and employee appraisals rarely integrate aspects for avoiding product variety, but rather conceal or even encourage it in some cases [20]. The sales department may try to reduce the variety of incoming orders, but usually pursues the goal of achieving the highest possible volume in incoming orders. Development is mainly incentivized by the development time, the production costs, and the fulfilment of requirements. In the long term, the reduction of the variety of parts supports the first two development goals above the others. However, since the assessment of target achievement and revision usually occurs earlier than the savings from reduced internal product variety, this is usually given lower priority.

2.1.2.2 Causes of Internal Product Variety in Product Planning and Sales In the transition from external to internal causes of high product variety, the customer orientation and differentiation or diversification strategies already described in Sect. 2.1.1 are at the forefront. Product planning and distribution are faced with more diverse market demands and increased competition and often react by expanding the range of products on offer (see Sect. 1.3). A focused turnover approach in sales can create unnecessary, profit-­ reducing variants by trying to place orders with a focus on fulfilling any and all special requests. This effect is often intensified by the fact that the responsibility for the costs of the consequences of high product variety is not attributed to sales or product planning. The lack of possibilities for a cost allocation based on causes makes it difficult for the sales department to gain an overview of the characteristics of offers that have a strong influence on internal company expenses. Variants that are rather exotic in the product range are therefore underestimated in terms of their additional cost and are offered at too low a price (see Fig. 2.4). The dependency between sales volume and calculation accuracy shown here can only be regarded as qualitative, since rarely sold product variants are not always technically exotic and automatically cause high hidden complexity costs. Sales abroad also entail a high degree of internal variety. When goods cross national borders, there are various legal requirements and standards which must be met. The documentation and often the product itself must be adapted, which results in the creation of country-specific product variants. Additional expenses are incurred not only in the development of country-specific product variants – there are also country-specific conditions in distribution and logistics, as well as in legal and regulatory matters. Due to different price expectations of customers for a certain product, it is possible to achieve more sales and thus economies of scale by reducing the variety of products offered with only minor variations in different price levels. Offering many product variants with comparatively small technical differences, but which at the same time are perceived by the customer as very different in terms of their characteristics, makes a direct price comparison difficult. In the ideal case, this results in higher prices, because the customer is less able to optimize his selection [50]. A wide variety of products can also be actively used by product planning as a strategy for creating barriers to market entry for potential competitors. By offering a full range of products including all necessary services, customers in many industries can be better

2  Interrelationships and Effects of Product Variety

Sales volume, costs and prices

24

Actual cost distribution

loss

profit

Calculated cost distribution through convential cost calculation methods

Initial distribution of sales

Product variants in order of sales volume

Diversification Complexity costs

Exotic product

Standard product Price

Loss Profit Production costs

Calculated costs

Actual costs

Calculated costs

(qualitative depiction)

Actual costs

Fig. 2.4  Danger of miscalculation with a particularly wide range of offers and conventional cost accounting methods. (Based on [44, 55])

bound to the company [43]. In addition, a wide variety of products and the servicing of different industries can be used to spread risk and compensate for market fluctuations. Finally, it should also be mentioned that the variety of offers is seldomly fully and appropriately matched to the variety of demand. Due to the remaining differences between the supply and demand spectrums, further product variants may be requested and must be developed accordingly [19].

2.1.2.3 Causes of Internal Product Variety in Product Development Product development is the link between the external product variety and the internal component variety that is necessary to provide a variety of offerings (see Fig. 2.1). A particular challenge here is the lack of awareness of the negative effects, already described as overarching causes. In product development, time and cost pressure can lead to new developments of similar or even identical components, resulting in a further increase in the component variety. In decision-making situations manufacturing costs and technical valence are usually used to evaluate alternative concepts. These are comparatively accurate and can be determined with reasonable effort, but do not include consideration of the negative effects of alternatives with higher internal variety. Thus, solutions are often chosen which allow for savings in production costs, but at the same time further increase internal variety (see also Sect. 2.6).

2.1  Causes of Variety

25

Developers often strive for problem-specific optimal solutions and generate new component variants in the process. In many cases, however, already existing solutions could be reused or solutions could be developed that may be reused in the future. This problem, described by Lindemann as the “dominance of creative developers”, is not only not balanced out, but is in some cases even supported by the incentive systems and employee appraisals typically used [32]. The sheer quantity of technical solutions and part numbers can be so massive, that companies will not be able to see existing solutions or find new ones due to insufficient information availability. Corresponding search systems are available, but are often costly and time-consuming in their acquisition, support, and application. Due to the difficulty of finding existing solutions, searches are abandoned prematurely, and preference is given to parts being redesigned quickly – with all the resulting costs in the subsequent product life phases. An additional complicating factor is that the risk-free applicability of existing solutions for a new design is not always guaranteed. Clear regulations and release procedures for the creation of new parts and variants as well as clearly structured and quickly usable search systems can prevent this from happening in the long term. In terms of organization, product development is often categorized according to product lines and product families (see Sect. 3.1). Even if developers, as specialists in technical disciplines such as mechanics, electronics, software, etc., are not directly assigned to specific product lines and work in a matrix organization, the responsible product managers and project managers are usually firmly responsible for specific products. Due to the organizational and temporal separation of product families in product development, similar requirements can rarely be recognized and implemented in the joint development of technical solutions. The result is multiple development of parts, although the multiple uses of identical parts would have been possible. The matrix organization with a two-dimensional, organizational allocation according to corporate function and products or assemblies helps to exploit additional synergies – but cannot completely solve the problem.

2.1.2.4 Other Causes of Internal Product Variety Production is generally aimed at keeping the variety of parts as small as possible. Nevertheless, production and development have very different views on product variety. Modern, flexible production plants can operate more reliably if a certain variety of parts allows for alternatives in the event of fluctuations in demand and failures [18, 25]. On the one hand, this is the only way to redirect orders and resources to other work systems. On the other hand, with the help of varying work contents in production control, sequence reversal algorithms can be applied, thus reducing downtimes [11]. Design measures to avoid mix-ups in assembly, such as the shape coding of interfaces or quick recognition of assembly positions according to Poka Yoke, may also make additional part variants necessary (Federal Statistical Office 2011). Here, technologies such as RFID, barcodes or position monitoring could also be used to avoid increasing the variety of parts. For procurement purposes, it can make sense to distribute certain modules and services amongst several suppliers in order to gain a stronger negotiating position or to be better

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2  Interrelationships and Effects of Product Variety

prepared for delivery failures. Differences between the suppliers and the modules concerned can in turn lead to new component variants with corresponding expenses to the company. Depending on the sector, comparatively long-term assurances are also often given for the supply reliability of products, maintenance and services, which can severely restrict any subsequent reduction in internal variety ([47]).

2.2 External Product Variety and Its Effects External product variety encompasses a company’s range of products and services and describes the variety of products offered to customers. It thus represents the company to the customer in a significant way.

2.2.1 External Product Variety External variety (sometimes also called “exogenous variety”) describes the range of product variants offered to the customer [5]. For it to contribute to the fulfilment of customer wishes and to influence sales, it must be recognizable to the customer, must at least include the essential selection criteria in the purchase decision and must cover these criteria in their necessary manifestations. It must therefore be a significant subset of the variety of demand. In addition, it should be clearly communicated to the customer to keep the selection of a product variant sufficiently simple [13]. Variants are technical systems with similar function and structure, and usually with a high proportion of identical components. They differ in at least one relationship or characteristic from the customer’s point of view. Even though the term “external variety” can also include other, external views (such as the diversity of suppliers or development partners), here it is only referred to in terms of the diversity of supply. Figure  2.5 shows examples of the external variety of services offered by selected companies. To describe external variety, the customer-relevant characteristics of a product can be used for physical products. From the customer’s point of view, customer-relevant properties differentiate the variants of a product and are used to select between product variants [53] (see also Sect. 3.2.1). Typically, external variety is documented in portfolio presentations of the product range, in websites and catalogues. The representations differ greatly depending on the purpose of the external presentation, advertising and purchase selection, or the internal overview, development, and administration (see Fig. 2.6). The requirements placed on a product by the customer can be divided into mandatory, optional, and desired requirements (see Sect. 3.2). Mandatory requirements are essential for the basic applicability of the product as viewed by the customer, and thus is a desired specification for aiding purchase decisions. Variations of these requirements over the

2.2  External Product Variety and Its Effects

27

Fig. 2.5  Examples of the external variety of products offered by various companies (excerpts from the respective product ranges)

Customer

Company

Web-based selection guides and configuration

(Hilti Entwicklungsgesellschaft mbH)

Production catalog and samples

Variety trees

(Institut für Produktentwicklung und Konstruktionstechnik)

Variant lists vehicle

If left

Front wall for left

(Hans Lutz Maschinenfabrik GmbH & Co. KG)

Front wall

Steering If right

Front wall for right

(Schichtel 2002)

Fig. 2.6  Examples for the visualization of the external product variety. (With friendly permission of Hilti Entwicklungsgesellschaft mbH and Lutz Aufzüge)

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2  Interrelationships and Effects of Product Variety

Fig. 2.7  The differentiation of existing and overlapping product variety based on a product range of floor cleaning robots (fictitious example based on the iRobot floor cleaning robots)

different customers pose the mandatory-variance. The optional-variance describes the different preferences of the customer regarding the product. They are influential in customer purchase decision and price willingness, but do not necessarily need to be fulfilled. Optional variants also include additional options with which the product can be expanded. Besides the subdivision into optional- and mandatory-variance, the characteristics of external variety can also be described by the categories fit, quality and taste [42, 50]. While the fit is synonymous with mandatory-variance, taste correspondences to optional-­ variance. The different forms of the fit- and taste-properties are also summarized as the so-called “vertical variance”. The category quality includes requirements on the reliability or service life of the products. They are often identified by different variant names such as starter, basic, advanced, or premium and also referred to as “horizontal variance”. In addition to the execution of the range of products in its breadth of different products and their variants, the chronological order of external product variety and its planning is of great importance. Therefore, an additional distinction is made between existing and intergenerational variety [35] (see Fig.  2.7). The characteristics in demand can be difficult to plan.

2.2.2 Impact of a High External Product Variety A large variety of offers can have both positive and negative effects on the company’s goals. The primary goal for increasing external variety is to attract new customer groups and retain existing customers [40] in order to improve sales and profits.

2.2  External Product Variety and Its Effects

29

The product range and its variety have a significant influence on the customer’s perception and the image of the company. If the external variety in the product range is recognizable by the customer, and contributes to the fulfilment of individual wishes and increase in product benefit, it has a positive effect on sales [13]. A wider range of offers and more alternatives to choose from in the purchase decision process, should therefore attract new customers and generate additional sales [20]. In saturated markets, however, there is a risk that no additional market share will be gained by increasing the variety of products on offer, as existing customers will switch to the new product variants, but no new buyers will be attracted, a phenomenon known as the cannibalization effect or the substitution effect. The supposed additional sales of new variants happen at the expense of the products offered so far. In most cases, both effects exist simultaneously, although there is a general risk that the cannibalization effect will dominate. This risk is particularly acute if the new product variants are not sufficiently geared to market segments and applications [20]. It is important to note that a greater variety of offers suggests a higher level of product performance to the customer, but at the same time also means greater effort in the selection process [7]. The latter aspect, especially in the case of products with a comparatively low price, can lead to customers shying away from the high expected effort in the selection process and preferring a supplier with a more manageable product range [45]. It is therefore important to present the product variants in a sensible sequence with understandable and comparable properties that provide the customer with a simple reference to the application [7]. According to [31], the following should be taken into account when determining the variety of offers • • • • •

visibility, clarity, and acceptance of the product variety by the customer what sales growth can be expected by offering additional variants, what is the market share and how strong is the competition which economies of scale can be used in all phases of product development and what market strategy is being pursued (for example, the creation of a market entry barrier).

Ideally, the choice of supply diversity should be harmonized with production processes and supply chain design [39]. Theoretically, each customer can be provided with an individual product without expected economies of scale through the standardization of components and processes. However, since economies of scale can be exploited in all phases of the product life cycle, there is almost always scope for savings in practice. In any case, when a new variant is introduced, the individual customer benefit must be clearly evident so that it contributes to higher sales. The possible effects of a high level of supply diversity on the market have already been described in Sect. 2.1.1 and are therefore summarized below (from [1, 50]).

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• Acquisition of further customers through a broader product range • Retaining existing customers by offering all necessary products and services from a single source • Differentiation from the competition • Creation of a market entry barrier through the placement of product variants in many application areas • Avoiding a price war by focusing the market on individual performance

2.3 Internal Product Variety and Its Effects Product development takes on an important function between the “source” of the variety of products on offer and the costs accrued from the resulting internal variety. The following practical example should illustrate this.

2.3.1 Internal Product Variety Negative Impact of a New Product Variety The customer’s request for a one-time execution of a plant in special painting at a company from the plant construction sector was examined at short notice and approved by the sales department, as no negative effects were expected from this new color variant of the existing aluminum frames, neither technically nor economically. Due to the fact that the material is difficult to paint, it was decided to use steel profiles instead of the standardized aluminum profiles that were to be painted afterwards. This unexpected material change required a one-time special process, which included the procurement of the special material and the commissioning of the painting, resulting in considerable additional costs and delays in the order. The design specifications in product development are responsible for a large part of the costs that will be incurred in the later phases of the product life cycle. This can include an increased number of different variant components with associated fixed costs, due for example, to additional design work, additional tests, machines, or storage locations. Every variance in the components potentially increases complexity in the processes through new work steps, process variants, special processes, decreasing batch sizes, an increasing number of required operating resources, new error possibilities, and other effects. Internal Variety Internal variety (partly also “endogenous variety”) describes the variety of components, assemblies, products, and processes – and by extension documents, competences or production, and resources – that occurs during order processing within a company. It is essentially accepted as a cost driver for the provision of a diversity of supply and should therefore be avoided and reduced unless it is absolutely necessary for the provision

High due to individual customer requirements

Reduction of inner variety due to methodical product development, design-for-variety and modularisation

31

Internal variety

Market variety

Product variety

2.3  Internal Product Variety and Its Effects

Internal variety

Fig. 2.8  Reduction of the internal variety necessary to provide the external variety of offers as a core task of product development. (Based on [30])

of a diversity of supply. It increases the complexity within the company, reduces the transparency of company processes and increases overhead costs. Internal product variety can be described as the variety of components of the product. A distinction is made between the component and part variants, in which components are stored in different variants and installed depending on the product variant, structure variants, for which the components of a product are combined in different structures to create a product variant, and quantity variants, which differ in the number of certain components [38]. Avoiding internal variety is the goal of design-for-variety and a core task of product development (see Fig. 2.8) (see also Sects. 1.3 and 1.4).

2.3.2 Resulting Complicacy and Complexity 2.3.2.1 Complicacy The described increase in product variety has the effect of an increasing number of objects (artifacts) in the company. Objects can represent all objects of daily work, such as documents, components, assemblies, products, orders, people, or processes. The objects are linked to each other in terms of content, for example, by the uses of an assembly in different product variants. An increased variety of products leads to an increase in the number of these relationships in addition to the number of objects. This makes the overview and handling of the product range more complicated for all product life phases. Complicacy The complicacy of a system consists of the number, variety, and relationships of the system elements and their states. It is a subset of complexity, but unlike the former, it describes deterministic, safe, and static systems. A complicated system has comparatively many elements and relationships, but also a deterministic behavior.

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In this book, the term complicacy is used to designate complexity that arises from the number and variety of components, products, or processes. There are other partial aspects of complexity, such as in the design or due to a complex manufacturing process – these are not considered in this book, however, but the complexity is only used in relation to the product variety.

2.3.2.2 Complexity The term complexity is used today in many contexts with different definitions [3]. The term differentiates strongly across individual scientific disciplines. It is actually the everyday use of the term that deviates from scientific definitions. In the context of product variety, the term is often already used to refer only to the increase in complicacy of the product structure (see Sect. 3.2.3) and the additional expenditure in the product development process. By definition, however, complexity can only be spoken of when a minimum of dynamism, unpredictability and uncontrollability is added to the aspects of complicacy. Complexity Complexity describes the number, variety, and relationships of system elements as well as their states and variability. A system can be described as complex if it is • non-deterministic • insecure and • variable over time (dynamic). If the aspect of temporal variability is missing, the term complexity is used. Since subjectively speaking, increasing complexity always increases complexity, this distinction is often not used in practice. For example, the development of a product family is only complex if unforeseen dynamic changes occur during development, which is reflected in practice (see Sect. 3.2.3). The described distinction between complexity and complicacy is widespread in the literature. On the one hand, complexity is measurable in its objective partial aspects, but on the other hand, its subjective perception depends on the frame and point of view. It has a negative impact on the company through increased expenditure and information requirements, but can also have positive effects in some cases, for example in its effect as a market entry barrier. The effects of complexity are often underestimated, as they can occur after they have been caused and also in completely different areas of the company. Complexity is formed by various aspects, which are explained below (summarized after [37, 49] and [1] by [6]). Number of Elements, Connections and Circuits Complexity can be understood as the number of elements of a system, its internal connections and the circular connections contained therein (see Fig.  2.9), which is a common

2.3  Internal Product Variety and Its Effects Fig. 2.9  Number of elements, their connections and cycles as a partial aspect of complexity, according to [13]

33 Increasing complexity Number of elements

Number of dependencies Number of cycles

Fig. 2.10  Variety of elements and connections as a partial aspect of complexity, according to [13]

Increasing complexity Number of different elements Number of different connections

Directed connections

description in business administration [27]. Advantageous is the quantifiability of this aspect, given by the reduction in the number of elements and compounds. Variety of Elements and Compounds An essential aspect of complexity, which distinguishes it from complexity, is the variability of a system (see Fig. 2.10), that is, the dynamic changes in the interconnections between the system elements and the types of elements [4]. Information Content and Uncertainty A special approach to complexity is the entropy of the system. This is often used in information theory to describe the average information content of a system. Essential here is the uncertainty regarding missing information – the more information is available, the less uncertainty remains (see Fig. 2.11) [46]. Combinatorial Variety The combinatorial variety of a system describes how many different states the system can reach [34]. The combinatorial variety of a system with three bulbs (see Fig. 2.12), each with two states “on” or “off”, gives 23 = 8 states. With 25 light bulbs, there are already 33,554,432 states. This partial aspect is particularly relevant for modular product families, where the product variants are created by combining individual modules.

34

2  Interrelationships and Effects of Product Variety

Fig. 2.11  Information content and uncertainty as partial aspects of complexity

Fig. 2.12 Combinatorial variety as a partial aspect of complexity

V1 V2 V3 V4 V5 V6 V7 V8

25 light bulbs

7

3

6 4

V = 23= 8 states

V = 33.554.432 states

Increasing complexity

1

2

Light bulb off Light bulb on

5

All dots are connected

Dot 1 is connected with dot 2 Dot 1 is connected with dot 3 Dot 1 is connected with dot 4 …

Fig. 2.13  Scope of the system description as a partial aspect of complexity, according to [17]

Scope of the System Description The perception and effect of the complexity of a system is essentially determined by the length of the description used. In computer science, the number of words necessary to describe a system is used for this purpose [17]. However, the length of the description used is strongly dependent on the description language chosen, as illustrated in Fig. 2.13 by two alternative descriptions with significantly different description scopes. Dependence of Perception In addition to the length of the description used, there is also the personal perception of complexity. This is based on the experience and knowledge of the observer. For example, without the knowledge of the system description, the subjective assessment of the complexity in the numerical series shown in Fig. 2.14 can be significantly different. Knowing that the number series (2) is sorted alphabetically in English (eight, five, four etc.), it appears as complex as the number series (1) [12].

2.3  Internal Product Variety and Its Effects

Rows of numbers

35

(1): { 1, 2, 3, 4, 5, 6, 7, 8, 9 } (2): { 8, 5, 4, 9, 1, 7, 6, 3, 2 }

Fig. 2.14  Dependence of perception based on personal knowledge as a partial aspect of complexity, explanation in the text, after [12]

The above definition of complexity is closely related to the definition of variant diversity, which describes the number and variety of different variants of a component, product or process. Due to its market dynamics, the diversity of variants can be understood as a partial aspect of complexity [6]. In the context of the development of modular product families, the diversity of variants is a major cause of internal company complexity. In the following, complexity is therefore understood primarily as the proportion induced by variety. This is also referred to as variant-induced complexity.

2.3.2.3 Variant-Induced Complexity The complexity considered here therefore results only from the number and variety of product variants and their variability over time. These can also be comparatively “simple” products, which become increasingly complicated due to the variance. Complicated products that vary by a simple product property, such as color, do not have variety-induced complexity. Such cases are not considered complex in this sense here. Variety Induced Complexity Variety-induced complexity is understood as the proportion of internal company complexity that results from product variety with its number and variance of objects, such as components, products, or processes. It describes the additional efforts, the use of additional resources and the increased need for information within order processing, which is due to an increased variety of products [1].

2.3.2.4 Complexity from a Product Development Perspective In product development, on the other hand, the question arises of how the product variety-­ induced complexity in the company can be controlled and reduced by product structuring and design. Four different views of complexity can be defined for product development, which are listed below (summarized by [6], see Fig. 2.15). • The constructional properties describe the number and variety of system elements and their relationships and thus also the combinatorial variety including its variability. • The appearances of complexity can objectively include the number of elements and connections and subjectively the perception of complexity by an observer. The former so-called “structural complexity” can be quantified and evaluated. The latter is strongly dependent on the respective viewer and his or her goals (also called individual or functional complexity) [29, 55].

36

2  Interrelationships and Effects of Product Variety Constructive properties Number and diversity of system elements Variability of relations

Manifestations

Product development Four different perspectives

Complexity

Objective

(1): { 1, 2, 3, 4, 5, 6, 7, 8, 9 }

Subjective

(2): { 8, 5, 4, 9, 1, 7, 6, 3, 2 }

Reference objects Level of description detail

Effect Relevance for business management Positive und negative consequences

Fig. 2.15  Product development views of the internal complexity of the company

• The reference objects are essential for the complexity. For example, an industry with few competing companies appears at first glance to be less complex. However, a detailed examination of the individual companies reveals the possibly extremely complex interrelationships between them. Statements about complexity can therefore only be made with regard to their reference object [22]. • The effect of complexity in the company can vary in type and relevance. There are both negative and positive effects (for example as a unique selling proposition) [55]. In the context of this book, complexity always refers to the variety-induced aspect of complexity.

2.3.3 Overarching Effects Over the Life Phases Producing companies and their departments are geared towards product development and thus influenced by a high product variety in all corporate divisions. Cross-sectional functions, such as IT or quality assurance/control, are also affected at least indirectly by an increased number of components, process steps or higher resource requirements. Due to the availability of larger amounts of data, IT also requires regular maintenance and investment in order to keep the increasing variety of products manageable. By breaking down the effects on many departments and thus cost centers, the overall effect of variety-induced complexity on the company is often underestimated [40], which further complicates the difficulties described in allocating these costs (see also Sect. 2.5). Increasing product variety triggers various effects in the company, which ultimately lead to additional costs in the individual product life phases (see Fig. 2.16).

2.3  Internal Product Variety and Its Effects

37

 

Fig. 2.16  Overarching effects in the company due to increased product variety

In general, more product variants must be developed, produced and distributed. Thus, for all departments in the company, the work content becomes more extensive and diverse. A direct consequence is an increased amount of necessary documentation and data storage. The most serious effects are usually the decreasing scale and learning curve effects, caused by the greater variety of work steps with lower repetition frequencies, which prevent the potential savings from being realized by routinizing the work steps. As the number of components and products produced increases, so do their variety and the interdependencies of the elements. The work content is therefore not only becoming more extensive but also more complicated, making it increasingly difficult to keep track of the work content and less likely that standardized and proven work procedures can be applied. Due to the increased number of different components and processes in the company, the number of special solutions, process exceptions and finally the number of possible errors is increasing. Due to the more difficult overview and the more intensive interdependencies of the products, components and processes, the impact of errors become greater and can no longer be easily anticipated. For a given number of product variants, however, a simultaneous subjectively perceived great variety of product can help to better differentiate between them and to handle them with fewer errors during the product life phases after development [7]. The described, overarching mechanisms of high product variety have an effect in all product life phases in the company, but cause different additional costs at different points in the market cycle of the respective products (see Fig. 2.17). The concrete effects of high product variety in the product life phases are described below.

38

2  Interrelationships and Effects of Product Variety

Fig. 2.17  Effects of increased product variety in the product life phases. (After [1, 8, 13, 20, 27, 33, 40, 55])

2.3.3.1 Effects in Product Development When new components are developed, they can be intended for later use in other products if the specifications are sufficiently similar. If these existing solutions cannot be found quickly and reliably enough, they are often overlooked and developed anew. The master data in companies can reach large dimensions with many thousands of part numbers, often rendering access to parts, functions, validity, and releases impossible within a reasonable timeframe. The result is worker overtime and functionally similar or even redundant components in the parts master, which further increases internal variety and further reduces transparency. With new variant parts, additional expenditure is incurred in development, such as for the modification or new design of tools and devices. For each new part number (variant) the corresponding documents, such as production drawings and parts lists, must be created, released and managed. If necessary, further documentation, such as user manuals, must also be created and kept available. Internal approvals and, above all, sector-specific approvals can be partially related to a basic variant, whereby a worst-case scenario and/or a standard configuration are used to derive the release of further variants from this. Such variant approval is costly and is in many cases not possible due to the deviation of the new variants from already approved products. This in turn results in high approval costs for the new product variants, even though they were derived from existing products. The main cause of significant additional expenditure in product development due to new product variants is an increasing number of necessary changes as well as their greater scope and more confusing effects. If, for example, new technologies are introduced or existing errors in the designs have to be eliminated, in the worst case this has to be done in each product variant individually.

2.3  Internal Product Variety and Its Effects

39

2.3.3.2 Effects of Product Variety in Purchasing In purchasing, the search for and acquisition of new suppliers may also be necessary on top of the costs for the acquisition of new parts and procurement processes through new variants. The number of ordering processes increases due to the higher number of part variants, so that additional work is incurred, discounts may be lost, and, in the worst case, lower quantity surcharges may have to be accepted. The exact forecast of requirements is made more difficult because the more variants there are, the less it is possible to calculate on the basis of total sales. Even with the same or increasing total volume, the relevance of one’s own company from the supplier’s point of view may decrease due to greater variety, shorter reaction times and poorer planning. The difficulty of forecasting demand may also result in increased Stockpiling. 2.3.3.3 Effects in Production In production, similar to procurement, the decreasing batch sizes and the wider range of parts are mainly responsible for the fact that performance values decrease with increasing product variety. The main effect here is the economies of scale and learning curves, which can no longer be sufficiently exploited even with increasing sales due to the broader range of products on offer. An increased variety of parts increases the machining spectrum and reduces the batch sizes. Even if a certain processing variety provides advantages through sequence reversal and diversification between work systems through more even utilization of the work systems, the existing variety of parts is usually higher and causes additional work. Due to the decreasing batch sizes, the number of set-up procedures increases and the automation of production processes becomes more difficult. There is also a greater possibility for errors due to an increasing number of different production processes, working materials, and work steps. Additional production trials and pilot series may become necessary if new product variants result in new work steps in production. Process planning efforts, consumption forecasts, part requirement determination, and material requirement planning are made more difficult. As the number of variants increases, the material flows become more complicated and lead to increasing inventories and fluctuating processing and assembly times. 2.3.3.4 Effects in Distribution For the sales department, new increased product variety means above all better opportunities for order acquisition. Provided that the diversity of supply is well adapted to the diversity of demand, more suitable products can be put together for individual customers. For an extended product range, new or at least adapted documents, such as product brochures, calculations or order lists, must be created accordingly. With a large variety of products, the price calculation is generally more difficult, as different components and services cannot be calculated so easily on a flat-rate basis. A larger and more varied product range also means greater training effort for the sales staff in order to maintain a sufficient overview of the products themselves and to be able to configure the right product variant for the customer. It must also be ensured that

40

2  Interrelationships and Effects of Product Variety

customers are able to access the product range sufficiently well and quickly, otherwise, motivation and certainty in the purchase decision can quickly decline [7].

2.3.3.5 Effects in Service and Maintenance Just like sales, product services must also be able to maintain an overview of the product variants to be able to process the various maintenance and service tasks sufficiently quickly. In many industries, service is linked with the customer and the products for the longest time, compared to other company departments. Therefore, it must be possible to work with most different products, due to the versions and variants on the market, and documentation and know-how must be available accordingly. This entails the creation and handling of many operating instructions, spare parts lists, and repair manuals. Service staff must be able to request this information quickly and must be trained in servicing the relevant variants with their different technical solutions. Technically, the procurement and stockpiling of more spare parts can generate a lot of effort over long periods of time. Information and material procurement in the service department, made more difficult by high product variety, can quickly drive up repair costs. This is the case, for example, if it is not sufficiently traceable which part variants and versions are installed in the product for a maintenance order or which version of the control software is available. Customers in the B2B business especially tend to strongly orient their purchasing decisions on reliability and life cycle costs. As a result, such customers sometimes prefer suppliers with a less diverse product range if they are looking for more reliable solutions or easy maintainability through standardized solutions. 2.3.3.6 Effects in Recycling and Disposal The recycling of products is increasingly the responsibility of manufacturers. Against the backdrop of increasing environmental pollution and dwindling resources, recycling is becoming more and more important. More important than the variety of products here are the dismantlability, material separation and the choice of material. Increasing product variety, however, can lead more quickly to problems in product recycling.

2.3.4 Separate Occurrence of Cause and Effect Based on the causes of product variety described in Sect. 2.1 and the effects over all product life phases mentioned in the last section, the separation of cause and effect becomes apparent. Typically, the operational focus of causation is in sales or product planning (see Fig. 2.18). There is often a risk that, from the point of view of the sales department, customer enquiries seem to deviate only slightly from existing product variants and are therefore acceptable. The additional expenditure for the new variant is comparably low in sales and the expected benefit is high. The complexity of the newly defined variant is underestimated or accepted for acquisition. The necessary arguments to convince development and

2.3  Internal Product Variety and Its Effects

41

Fig. 2.18  Separate causation and effects of product variety in the company

production are usually given – especially in cases of diversification strategy, as described in Chap. 1. It also underlies comparable risks in the series business when product planning attempts to cover market niches and increase sales with the help of new variants. The manifold effects on the departments involved in the entire product development process only become visible in the execution. They are therefore rarely sufficiently considered when the decision for a new variant is made. The total costs arising in the long term often exceed the initially estimated costs, especially since large parts of the costs of new variants cannot be recorded at all and cannot be allocated to the order or variant (see Sect. 2.6). A similar separation of cause and effect can also be observed in product development. For example, in development, the redesign of a component may require less cost and time than the search for a suitable, already existing part. But what is not considered is that this leads to the creation of new part numbers, order processes, NC programs, and storage spaces. The additional expenditures can easily exceed the avoided additional development costs many times over. This may also affect the spare parts inventory and thus service and maintenance during the service life, provided it is a standardized spare or wearing part. In all phases of life, therefore, there are additional expenses incurred which, as experience shows, are not sufficiently transparent in their full effect or not known at all. The complexity of the variance in the product development process is underestimated because its cause and its effects do not coincide in the same life cycle phase.

2.3.5 Delayed and Gradual Occurrence Due to the overlapping occurrence of the consequences of high product variety over the product life phases, the resulting costs occur with a considerable time delay. Many

42

2  Interrelationships and Effects of Product Variety Variant-specific complexity costs

costs

Variant-specific general costs

Fixed costs

investments

Internal variety Fig. 2.19  Delayed and gradual increase in costs due to increasing product variety according to [27, 28]

recurring additional expenses, for example, due to reduced batch sizes or increased error possibilities, will occur permanently until the product family is discontinued. Depending on the industry, additional costs for servicing and spare parts may continue to be incurred, even a long time after a product variant has been phased out of production. The corporate departments are affected to varying degrees by the variety of a product family at different points in the market cycle, depending on their responsibility for product development and support. The costs of increasing product variety happen in “jumps” due to the sudden need for additional investments. These investments may be necessary for the expansion of the infrastructural capacities for handling product variety (see Fig. 2.19) [26, 40]. In the event of an increase in variety, the additional burden can initially be borne by the available resources. No discernible cost increases have yet been objectively identified. Only when the increasing variety of products can no longer be controlled with current resources, and concrete problems such as supply bottlenecks threaten to happen, will measures be taken and investments be made, such as hiring additional personnel, expansion of storage capacities, more efficient IT systems or more flexible production facilities. The increasing number of variants thus gradually leads to additional fixed costs. These investment leaps occur with a delay due to the described waiting and implementation periods of the measures, so that the costs cannot be attributed to specific product variants. Steinfatt and Schuh figuratively speak of an “incubation period until the outbreak of the variety disease” [48].

2.3  Internal Product Variety and Its Effects

43

Investments in improved manageability of increased product variety are often initially designed with overcapacity in mind in anticipation of a further increase in the variety of products on offer. With the motivation to make better use of this free overcapacity, it is possible that after such an investment the product variety will increase again (also Sect. 2.1.2 Internal causes of product variety). The costs incurred are independent of changes in production volumes and product range and can therefore only be reduced in the long term or not at all, as described in the following section.

2.3.6 Cost Stickiness (Asymmetric Dynamic) Another important relationship is called cost stickiness, also called hysteresis effect or asymmetric-dynamic cost behavior (see Fig. 2.20). If rising overheads or other indicators show that the complexity built up has become too high, an attempt is made to reduce this complexity again, for example by reducing the variety offered. However, it is no longer possible to achieve the original cost level as it existed before the complexity was built up, since investments, such as new production systems, new warehouses, or expanded IT, are generally no longer reversible [40]. A subsequent reduction in complexity cannot release such one-off costs and will therefore not reach the original cost level ([47]).

cost stickiness

costs

Fixed costs

Internal variety Fig. 2.20  Cost stickiness in measures to reduce internal complexity [40]

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2  Interrelationships and Effects of Product Variety

2.4 Resulting Costs of Product Variety This section has been created under the co-authorship of Mr. Sebastian Ripperda. The variety of products and services required to ensure competitiveness induces a variety of components and processes as well as a resulting complexity in the company. This has a negative effect on all areas of the company, for example through batch size reduction, extended throughput and delivery times and problems with quality assurance (see Sect. 2.3.3). This section uses a cost model to present the cost effects of product variant-induced complexity in the company.

2.4.1 Overview of Cost Categories The life cycle costs of a product consist of the prime costs for the manufacturing company and the costs of the product user (see Fig. 2.21). The costs for the product user will not be considered further here. The prime costs are subdivided into the material- and production costs which are among the manufacturing costs as well as other company-specific cost types, such as development-, administration-, test- and distribution costs. All cost elements can be divided into their individual or overhead costs, fixed and variable as well as non-recurring and recurring shares [9] (see Fig. 2.21). Individual costs include, compared to the overheads, all expenses which are directly attributable to a single product. Fixed costs are assumed in the company to be unchangeable in the short term. Variable costs are directly dependent on the quantity produced and can therefore be influenced at short notice. The different cost elements hold

Type of costs Consumer costs

Development Administration

Cost structure

Life cycle costs

Structure of different cost types

unique

Purchase price

Tests Sales ...

Human resources

Costs of production indirect

direct

Stock

recurrent

Fig. 2.21  Overview of the cost types considered and their classification according to [9]

2.4  Resulting Costs of Product Variety

45

different shares in individual or overhead costs, fixed and variable, and non-recurrent and recurring costs. The next section describes the effects of a high degree of internal variety on the individual components of the cost model and the complexity costs.

2.4.2 Cost Effects of High Internal Variety The diversity of variants has a much smaller effect on manufacturing costs than is often expected but has a much greater impact on overhead costs. Activities that used to occur once for each product family must now be performed more and more for each variant. The variety significantly increases overhead costs in all areas involved in the product creation process, such as development and design, sales, purchasing, production, quality assurance, logistics, and accounting. These cost categories proportionately conceal the so-called complexity costs (see fig. 2.22). These arise largely from the effects of the internal variety of the product range in all phases of the company’s life. These shares are referred to as product variety-induced complexity costs. The cost effects of high product variety result from the effects within the company described in Sect. 2.4. In product development, variety leads to increased costs due to the design of new components, the modification of existing designs, the creation and administration of documentation, and additionally necessary tests and verifications. For procurement, the low number of units per component associated with high variety leads to higher material costs. The variety of components can result in increased costs due to the necessary search for and negotiations with suppliers. Larger warehouses, as well as complex logistics planning and control for external and internal transport processes, become necessary. In production, product variety increases the necessary expenditures for planning and set-up costs by smaller quantities, which can also lead to increased error rates, process

Manufacturing costs Material costs

Production costs

Manufacturing Costs

Logistic costs

... Disposal costs ... Costs of the product user

Investment costs Operating costs

Complexity costs

Life cycle costs

Development costs Administration costs

have a share in

Production costs

Higher inventories

Production control

extended delivery times Cannibalization effects

COMPLEXITY COSTS

Additional tests Additional documentations and maintenance Higher risk of complaints Increasing set up times due to smaller quantities Additional supplier search

Fluctuations in capacity utilization Time consuming logistics Risk of parallel developments Increasing number of order transactions High efforts regarding staff training

Design effort for new components

Increasing error probability in manufacturing

Fig. 2.22  Overview of cost types and their contribution to complexity costs, left to [9], right [16]

46

2  Interrelationships and Effects of Product Variety

times and throughput times. In addition, fewer repetitions may result in less or no learning curve effects. Expenditure on training and equipping sales staff rises as the number of variants increases. Large stocks must be maintained to maintain the readiness for delivery. In addition, the time and effort required to prepare quotations increases, and errors occur in order processing. During product use, more different spare parts are needed and additional handling and documentation effort is required for customer service. The risk of complaints also increases [23]. How high the shares of complexity costs are in the individual life cycle phases must be examined on a company-specific basis. In the example of automobile manufacturers, it has been shown that 15–20% of total costs are caused by product variety-induced complexity [8]. The total costs of a product family can increase by about 20–30% by doubling the number of variants according to Adam [2], which is due to the complexity costs. Nowadays, it can be assumed that, if we take a more precise, company-specific approach, a significantly higher proportion of complexity costs is caused by product variety. In Fig. 2.22, this is illustrated by the striking metaphor of an iceberg, with a small proportion of visible costs and a large proportion of costs which remain invisible. Based on conventional cost accounting methods, the overhead costs cannot usually be allocated to individual product variants as their origin. They are transferred at a flat rate to all products or at least to larger parts of the product range. This systematically distorts the additional costs of new product variants in the direction of existing products and underestimates them, making new product variants appear more profitable [44] (see Fig. 2.23). This creates the risk that cost-driving product variants are not identified and that the costs of creating and especially managing the variants are actually higher than the subsequent profit. With an increasing number of product variants and components, complexity increases in all areas of the company, which results in a corresponding increase in organizational effort. The expected cost increase with increasing product variety is therefore often significantly lower than the costs actually incurred later. Fig. 2.23 Qualitative progression of sales and costs over an increasing product variety [2, 40]

Costs / turnover

initial situation

Profit

Variety

2.5  Possible Strategies

47

In situations of declining profits, the range of products on offer is often expanded to secure market share. Special orders are accepted or new product variants are generated to serve niche applications. As exotics in the product range, these new variants are quickly offered at too low a price, since, as described above, the costs incurred are usually underestimated, so that in the medium term, instead of the hoped-for increase in profits, further losses are actually incurred. The company can thus enter a cycle of increasing variant diversity and further competitive disadvantages (see also “Vicious circle of diversification strategy” in Sect. 1.2). The qualitative relationship between the number of variants and the resulting costs is shown in Fig. 2.23. The diagram shows qualitatively the degressive increase in sales and the progressively rising costs with increasing product variety. This has a delayed, step-by-­ step nature, since only when the company’s capacities for handling product variety threaten to be exceeded will they be expanded (see Sect. 2.3.4). It should be noted that disproportionately rising costs are by a disproportionately low revenue growth.

2.5 Possible Strategies

Profit

Sales

Costs

For a better understanding of the impact of product variety on the resulting costs, the external variety of offered products and the internal variety of components and processes required to produce them can be considered as individual variables (see Fig. 2.24). External variety enables higher sales of product variants – internal variety causes costs in the company. The external variety of offers causes the internal complexity of the company.

External variety (variety of offerings)

Internal variety in the company

Fig. 2.24  Qualitative progression of sales over external product variety (left), costs over internal product variety (right) and the different strategies for improvement, compare Fig.  2.23, according to [41]

48

2  Interrelationships and Effects of Product Variety

However, in product development, the necessary internal variety and thus costs can be significantly reduced with the help of suitable, modular product structure strategies and thus coordinated processes throughout the entire product creation process. Between external and internal variety there is thus the control lever shown in Fig. 2.24 below, which represents the main motivation of variety management. The complexity and costs resulting from an increased internal product variety cause many companies to implement strategies for improvement. The external variety of offers is often reduced in order to achieve a better cost-benefit ratio (Case 1 in Fig. 2.24). Another possibility is to increase the product benefit in order to achieve higher prices while maintaining the same internal complexity (Case 2). A third strategy is to try to reduce or avoid internal complexity in order to achieve higher revenues again. Since the variety of offers on the market and the implementation of the corresponding variety of components and processes in the company show strong interdependencies, a significant and sustainable reduction of complexity costs in the company can only be achieved through coordinated measures in all fields of action. For the sake of simplification, the fields of action are nevertheless explained separately below.

2.5.1 Reducing the Diversity of Supply

costs

Turnover

An obvious and frequent measure in the event of a threatened decline in profits due to excessive product variety is to reduce the existing range of products. To this end, unprofitable product variants will be sold and no longer offered. In most cases, product variants with sales below a certain threshold are removed from the offer – regardless of their contribution to internal complexity. The aim is that the capacity freed up as a result should reduce the costs of manufacturing the products that will continue to be offered to such an extent that the reduced sales are compensated (see Fig. 2.25).

External variety (variety of offerings)

Internal variety in the company

Fig. 2.25  Reduction of the variety of offers as a measure to increase profits, according to [41]

49

costs

turnover

2.5  Possible Strategies

External variety (variety of offerings)

Internal variety in the company

Fig. 2.26  Risk in reducing the external product variety as a measure to increase profits (see Fig. 2.25), [41]

It must be possible to reduce a sufficient proportion of the complexity costs built up for this purpose, and dispensing with some special variants must reduce turnover not more than marginally. The adjustment of the product range for product variants with low sales should be carried out regularly by, or in close coordination with, Product Planning, and represent an instrument of variant adjustment as part of continuous variant management (see Sect. 6.3). However, there is a great danger that a reduction in the external product variety, if it is used as the main measure to reduce complexity. This is due to the effects on sales and costs of such a measure. Initially, the decline in sales is often underestimated in the event of a reduction in the offered product variety (see Fig. 2.26, left, red curve). The product range and its variety have a significant influence on the perception of the customer. A reduction in the variety of offers can therefore influence the image of the company with the customer. In some circumstances, existing buyers of the cancelled product variants will not reorient themselves in the company’s product range but will shift to other suppliers [20]. On the other hand, the potential reduction in costs can also be quickly overestimated (see Fig. 2.26, right, red curve). Experience has shown that the savings achieved by eliminating a few variants are smaller than planned, especially when compared with the investments made in capacities to handle an increased product variety. However, it is precisely these investments that account for a substantial proportion of the complexity costs, although only a small proportion of the cost remanence described in Sect. 2.5.5 can be recovered. In addition, obligations for warranty, service and maintenance can result in unplanned expenses long after product variants have been discontinued. In the worst case, this may lead to a reduction of the remaining profit, that is, to the opposite of the actual objective of the measure.

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A reduction in the variety of products on offer alone, for example by eliminating C-variants with low sales, may reduce internal expenses for a short time, but it can rarely provide a sustainable solution to the described problem of increasing product variety. If the product variety is to be reduced, then those product variants should be examined which have contributed disproportionately to the increase in complexity costs. Another more drastic measure would be to significantly reduce the variety of products on offer, for example by eliminating a product family or unprofitable production processes that offer corresponding cost-saving potential. However, the described problems on the market side should not be ignored.

2.5.2 Increasing Product Benefits

costs

turnover

The alignment of the offered product variety with the diversity of demand on the market largely determines product sales. The product range and its variety have a significant influence on the perception of the customer and the image of the company. It must be recognizable to the customer to cover at least the essential selection criteria for the purchase decision and to cover these in their necessary manifestations. It is important to adapt the offered product variety with its property profiles precisely to the market segments and applications as well as their presentation for the customer during the purchase decision process – that is, visibility, clarity and acceptance. Possible improvements of existing products regarding these aspects make it possible to increase sales of the existing range of products (see Fig. 2.27). Measures to improve existing product variants, such as improved functionalities, higher performance or new technologies, also broaden the sales curve, enabling higher profits to be achieved while

External variety (variety in offerings)

Internal variety in the company

Fig. 2.27  Increasing product benefits with the same product variety as a measure to increase profits, [41]

2.5  Possible Strategies

51

maintaining the same product variety. At the same time, however, there will also be additional costs that must be weighed. This relationship is shown in Fig. 2.27. The additional benefit for customers and the associated turnover must be greater than the additional costs required for implementation.

2.5.3 Reduction of Complexity

costs

turnover

Measures to reduce complexity are aimed at improving the development and production of the defined variety of offered products in order to keep the resulting complexity costs low. Product development in particular can offer great potential for savings here since the provision of product variants can be significantly simplified by an appropriately designed modular product structure (see Chap. 5). By reducing internal variety while maintaining external variety, complexity costs can be reduced, which lowers the cost trend and thus increases profits (see Fig. 2.28, step 1). If the product life phases, such as sales, purchasing, production, assembly and after-­ sales, continue to show possibilities for process improvement, they can further reduce the effort required to provide reduced internal variety (see Fig. 2.28, step 2). These include process strategies of postponement, communality, or flexibility, which can be used to further reduce costs. The existing internal variety can be managed more efficiently, and an increase in profits can be achieved. This leads to an offset of the entire cost curve (see Fig. 2.28 right, green curve).

1 2

External variety (variety in offerings)

Internal variety in the company

Production and processes, tailored to variety

Fig. 2.28  Cost reduction by reducing the internal variety of components (1) and a downstream reduction of complexity in the company (2), [41]

2  Interrelationships and Effects of Product Variety

costs

turnover

52

Avoided unnecessary variety

External variety (variety in offerings)

Internal variety in the company

Fig. 2.29  Cost reduction by avoiding unnecessary product and component variety, [41]

2.5.4 Avoiding Complexity Strategies to avoid variety aim to prevent new complexity. On the one hand, they aim the optimal positioning of product variants in market segments and areas of application when planning the product variety (see Fig. 2.29). On the other hand, they try to anticipate and reduce the emergence of new internal variety at an early stage through coordinated development of the product range, products, and processes, as well as modular product structure strategies. On the market side, not all conceivable product variants can be planned for, so it is best to focus on those that cause a small or, in the best case, no increase in internal variety – as shown in the next chapter (see Fig. 2.29, right-hand side). The emergence of new internal variety should, as far as possible, be decoupled from increasing external product variety [47, 55].

2.5.5 Configuration of New Product Variants Product variants, especially those based on modular product structure strategies, can be offered with a significantly reduced effort. Depending on the industry and product range, new product variants beyond the current range of products can be generated by combining existing modules (see Fig. 2.30, left curve). The offers can be extended without significant additional effort. With an appropriate product structure strategy, the effort required to expand the product range by adding new variants can be significantly reduced by deriving new product variants on the basis of the modular concepts, which are largely built up from existing modules.

53

costs

turnover

2.6  Possibilities of Cost Assessment

External variety (variety of offerings)

Internal variety in the company

Fig. 2.30  Expansion of the product range by configuring new product variants from existing modules, according to [41]

2.6 Possibilities of Cost Assessment This section has been created under the co-authorship of Mr. Sebastian Ripperda. In product development, product variety-induced complexity and the resulting complexity costs can be reduced by means of targeted product structuring. However, estimating the possible complexity costs is a major challenge in the evaluation and decision of which product structure concepts to pursue. As described in Sects. 2.3 and 2.4, these costs are, to a large extent, occurring across departments and at different point in time, and are therefore difficult to anticipate. Conventional methods of cost evaluation therefore have significant disadvantages in determining the cost effects of products with a high diversity of products [20, 32, 40]. When evaluating alternative product concepts, technical value and economic evaluation criteria are used. In Fig. 2.31, the evaluations of three different, alternative product structure concepts are shown in a diagram on the left as an example. Often economic evaluation is reduced to a consideration of the manufacturing costs, since these can generally be anticipated with comparatively little effort and good accuracy using empirical values and calculation tools (see Fig. 2.31, right). With this reduced consideration, preference is given to solutions that cause the lowest possible manufacturing costs and combine these with a good technical-functional solution. The cause-related allocation of complexity costs is usually not sufficiently

54

2  Interrelationships and Effects of Product Variety

Technical quality ranking

EEconomical conom miical al quality qu q uality ranking ran nkkiing ng Reduction of production costs

Legend Better rated solutions

Worse rated solution

alternative product structure concepts

Fig. 2.31  Considered evaluation factors of a conventional concept evaluation, for the explanation, see text, [16]

considered in the economic evaluation of product concepts. If corresponding criteria are taken into account, this is often only done by expert estimates or flat-rate overheads – that is, comparatively uncertain and subjective. Figure 2.32 schematically shows a valuation portfolio which once again considers the economic value divided into possible savings potentials of production costs and complexity costs as separate dimensions. The resulting evaluation plane of the economic value spread over manufacturing and complexity cost savings is shown as an excerpt in Fig.  2.33 and is explained in the following. The often neglected consideration of complexity effects in the evaluation of technical product concepts can cause two typical types of wrong decision making. • Solutions that would cause higher production costs but allow large savings potential in terms of complexity costs are prematurely discarded (see Fig. 2.33, green area “discarded potential”). In the long term, these product concepts can offset their higher manufacturing costs through savings in complexity costs and have a positive overall

2.6  Possibilities of Cost Assessment

55

Technical quality rating

Reduction of complexity costs

Reduction of production costs

Legend better rated solutions

worse rated solutions

Fig. 2.32  Extended concept evaluation with consideration of complexity costs as a dimension of economic value [16]

balance. If, for example, fewer size stages are provided for in a series, the necessary oversizing can increase the manufacturing costs per unit, which can be compensated for, for example, by economies of scale in other life phases. Due to the lack of short-­ term production cost savings, such solutions are sometimes unjustifiably rejected. If the potential complexity cost savings are seen, there is a risk that they will be underestimated due to their medium to the long-term occurrence. • Solutions can be chosen that would save production costs but cause significantly higher complexity costs (see Fig. 2.33, red area “complexity cycle”) and thus have a negative overall balance. Such concepts are often chosen because of the manufacturing cost savings – with long-term negative effects on the company. However, usable indicators for complexity costs conflict with reasonable evaluation effort and sufficient accuracy. Selecting only the most important complexity drivers specific to a company and product with comparatively manageable creation effort and sufficient traceability for decision-makers can integrate initial estimates of complexity costs into the concept evaluation.

56

2  Interrelationships and Effects of Product Variety Reduction of complexity costs

profit

Reduction of manufacturing costs current product family

loss

Legende Rejected potential

Complexity spiral

Alternative production concepts

Fig. 2.33  Evaluation level plane consisting of production and complexity cost savings (extract from Fig. 2.32, for explanation see text)

Selected cost assessment methods are presented in Sect. 6.5. By estimating the material number costs in the so-called average cost method, the selection of alternative concepts in product development can be supported and, in a first step, a forecast of the effects on complexity costs can be given. The process requires comparatively little effort and provides initial insights into the optimum variety of components. Nevertheless, the average cost method disregards many effects of the resulting complexity, for example significantly different technical solution concepts.

Literature 1. Abdelkafi N (2008) Variety-induced complexity in mass customization. Dissertation, Technische Universität Hamburg-Harburg 2. Adam D (1998) Produktions-management. Gabler, Wiesbaden 3. Andreasen MM (2009) Complexity of industrial practice and design research contributions- we need consolidation. In: Meerkamm H (Hrsg) Design for X. 20. Symposium Neukirchen, TuTech Verlag, Erlangen, 24 September 2009 4. Ashby WR, Huber JA (1974) Einführung in die Kybernetik. Suhrkamp, Frankfurt am Main 5. Bartuschat M (1995) Beitrag zur Beherrschung der Variantenvielfalt in der Serienfertigung. Dissertation, Technische Universität Braunschweig 6. Brosch M (2015) Eine Methode zur Reduzierung der produktvarianteninduzierten Komplexität. Dissertation, Technische Universität Hamburg-Harburg

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27. Kersten W, Rall K, Meyer CM, Dalhöfer J (2006) Complexity management in logistics and ETO supply chains. In: Blecker T, Kersten W, Huang GQ (Hrsg) Operations and technology management. ESV, Berlin, pp 325–342 28. Kesper, H (2012) Gestaltung von Produktvariantenspektren mittels matrixbasierter Methoden. Dissertation, Technischen Universität München 29. Kirchhof R (2003) Ganzheitliches Komplexitätsmanagement – Grundlagen und Methodik des Umgangs mit Komplexität im Unternehmen. Dissertation, Technischen Universität Cottbus 30. Kortmann D, Klink H, Wüpping J (2009) Strategien zur profitablen Variantenkonfiguration. IJBIS 9:57–60 31. Lancaster KJ (1990) The economics of product variety – a survey. Mark Sci 9:189–206 32. Lindemann U (2009) Methodische Entwicklung technischer Produkte. Springer, Berlin/ Heidelberg 33. Lindemann U, Reichwald R, Zäh MF (2006) Individualisierte Produkte  – Komplexität beherrschen in Entwicklung und Produktion. Springer, Berlin/Heidelberg 34. Malik F (2008) Strategie des Managements komplexer Systeme – Ein Beitrag zur Management-­ Kybernetik evolutionärer Systeme. Haupt-Verlag, Bern 35. Martin M, Ishii K (2002) Design for variety: developing standardized and modularized product platform architectures. Res Eng Des 13:213–235 36. Meboldt M (2008) Mentale und formale Modellbildung in der Produktentstehung als Beitrag zum integrierten Produktentstehungs-Modell (iPeM). Dissertation, Technische Universität Karlsruhe 37. Meyer CM (2007) Integration des Komplexitätsmanagements in den strategischen Führungsprozess der Logistik. Dissertation, Technische Universität Hamburg-Harburg 38. Pepels W (2006) Produktmanagement – Produktinnovation, Markenpolitik, Programmplanung, Prozessorganisation. Oldenbourg, München/Wien 39. Randall T, Terwiesch C, Ulrich KT (2007) User design of customized products. Mar Sci 26:268–280 40. Rathnow PJ (1993) Integriertes Variantenmanagement  – Bestimmung, Realisierung und Sicherung der optimalen Produktvielfalt. Vandenhoeck & Ruprecht, Göttingen 41. Ripperda S, Krause D (2017) Cost effects of modular product family structures – methods and quantification of impacts to support decision making. J Mech Des:139:12 S 42. Rosenberg O (1997) Kostensenkung durch Komplexitätsmanagement. In: Franz K-P (Hrsg) Kostenmanagement  – Wettbewerbsvorteile durch systematische Kostensteuerung. Schäffer-­ Poeschel, Stuttgart, pp 185–206 43. Schmalensee R (1978) Entry deterrence in the ready-to-eat breakfast cereal industry. Bell J Econ 9:305–327 44. Schuh G (2005) Produktkomplexität managen – Strategien – Methoden – Tools. Hanser-Verlag, München/Wien 45. Schwartz B (2007) The paradox of choice – why more is less. Harper Perennial, New York 46. Shannon CE, Weaver W (1949) The mathematical theory of communication. University of Illinois Press, Urbana 47. Bundesamt S (ed) (2011) Bevölkerungs- und Haushaltsentwicklung im Bund und in den Ländern. Statistisches Bundesamt, Wiesbaden 48. Steinfatt E, Schuh G (1992) Variantenvielfalt als Krankheit  – Differenzierte Produktkostenprognose. Technische Rundschau:58–64 49. Ulrich K (1995) The role of product architecture in the manufacturing firm. Res Policy 24:419–440 50. Ulrich KT (2011) Design  – creation of artifacts in society. University of Pennsylvania, Philadelphia

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3

Basics and Terms

The important terms of product structuring, modular design and variant management are often known, but understood differently. Misunderstanding the terms can have a serious impact on the quality of results in modularization projects. For this reason, a clarification of terms is necessary and essential. Furthermore, terms such as module, platform or modular kit have become very well known in the recent past through high-profile projects of large companies. However, they are rarely explained in detail in the corresponding publications, but are presented in their respective interpretation and execution and are often even used synonymously, which has greatly increased the difference of opinions as to their meaning. This is an introductory chapter for this topic, but together with the glossary in Chap. 8, it can also serve as a handy reference for experts. In addition, it provides the conceptual basis for the following chapters. The models and terms shown in this chapter have proven itself in numerous projects for the development of modular product families at the PKT Institute. In order to establish a uniform understanding, this chapter explains the basic terms relating to the topics product program in Sect. 3.1, product structure in Sect. 3.2 and modes of construction in Sect. 3.3. For the sake of simplicity, the more advanced topics of modularity, modularization and product variety are explained in Chap. 4. Common part strategy, size ranges, modular system and platform as essential principles for the implementation of a modular product structure are explained in Sect. 5.2.

© Springer-Verlag GmbH Germany, part of Springer Nature 2023 D. Krause, N. Gebhardt, Methodical Development of Modular Product Families, https://doi.org/10.1007/978-3-662-65680-8_3

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3.1 The Product Program and Its Structure The product program of a manufacturing company is the highest level of the hierarchy and refers to the totality of all products and services that a company offers on the market. Product programs are usually divided into different hierarchical levels. A clear definition of these levels is important for the development and handling of modular product structures and the planning and control of product variety. In practice, there are very different classifications, for example, according to market segments, product functions, or employed technologies. Classification levels, such as product line or product family, are often used differently in different companies, and terms such as models, series or types are also used. Classification systems based on several dimensions are also used simultaneously. The purpose of the product program classification system is to achieve a clear structure within the company and to give the customer a clear overview of the product program (see also Sect. 4.4.5). cc Product Program Consisting of Product Lines, Product Families and Product Variants  The product program is the totality of the products offered by a company [16]. It consists of the company’s own production program, the purchased products, which are offered on the market as merchandise without substantial changes, and services (see Fig. 3.1). The production program is usually further divided into product lines and product families. The product line represents a set of products as a subset of the product program which have similar application areas, functions or production processes and whose combination into a product line makes sense from a business and organizational perspective. Product lines represent groups of product families from an organizational point of view. These are usually company-specific ([10], based on [16]).

Fig. 3.1  Schematic classification of a product program with product lines and product families

3.1 The Product Program and Its Structure

63

A product family refers to a set of product variants that have similar functional principles, technologies and the same areas of application or production processes [14]. A product family comprises all variants in which a product is offered. Product variants are products with very similar form and/or function and usually a high proportion of identical groups or parts. They are technical systems with the same purpose, which have the same basic functionality but differ in at least one characteristic [7]. Ideally, these characteristics are relevant for the customer when making a purchase decision, so that the customer can choose the product variant that suits him. An example of a possible classification of the product program is shown in Fig. 3.2, in which a possible classification of the product program has been made based on a floor cleaning robot. On a product line level, a rough classification according to markets is important, whereas on the product family level the different application scenarios determine the classification. The product variants of the floor cleaner product family differ in terms of customer-relevant features or characteristics. The structured division into product lines and families simplifies the implementation of product development projects by providing a better overview and simplifying the assignment of tasks. On the other hand, the exploitation of synergies through common product structures and carry-over components is made more difficult, since the division usually determines an organizational separation into different teams and projects. Matrix organizations with cross- functions groups for the development of common components improve synergies across the product program. Different versions of product requirements or their use in different products is important for optimal organizational handling of products and their components, both in the context of their development as well as their validity over different periods of time. In development projects, different solutions are usually developed at the same time, so that a Product range Producon program Household robots

Profi robots

vacuum cleaning

Roomba 866

Roomba 886

accessories

dusng

Roomba 605

Product line

Product family

Product variants

Fig. 3.2  Example of a product program using the iRobot floor cleaning robots

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selection decision can only be made at a later point in time with better knowledge of a more advanced stage of development. In order to be able to distinguish between these different objects, the terms variant, alternative, and version are used (Fig. 3.3). The terms variant and alternative are often used interchangeably, which makes the following differentiation important. cc Variant, Alternative and Version  Variants are simultaneously implemented technical systems with high similarity and the same basic functionality. They differ in at least one relevant characteristic. Variants are designed to cover different requirement areas and exist simultaneously. A related set of product variants forms a product family. Alternatives are different technical systems or concepts with identical requirements, which are developed in parallel as different (partial) solutions within product development – but from which only one alternative is ultimately pursued (see Fig. 3.3). Alternatives are different solutions to a task. They fulfill the same requirements but are different in concept. They are developed parallel to each other as different (partial) solutions within the scope of product development and are reduced to a final solution in an evaluation and selection process. An alternative is chosen or the contents and findings from several alternatives are merged into a concept to be developed further. A version is a precisely defined temporal state of an object within the scope of its life cycle. A version is created at a defined point in time and is linked to its predecessor and successor in a chronological sequence [17]. This means that only one version of an object exists at any point in time, but there may be several variants.

variant III

versions

III.1

variant II

Product variants

II.1

II.2

I.3

I.4

II.3

variant I I.1

I.2

Product Program Development Projects Development project

2. generation

Legend 3. generation

Alternatives in the product development process

variant

version

I.1

4. generation

Fig. 3.3  Variants, alternatives and versions of products in product development and the product program. (Based on [17])

3.1 The Product Program and Its Structure

65

However, the use of the terms variant and alternative depends on the point of view. The variants of the product family of a supplier (vendor) thus represent component alternatives for a customer or a developer, from which later must ultimately select a solution for use in the overall system. The terms variant, alternative and version can be used for entire products, but also components or processes. It is especially important to distinguish clearly between product and component variants. Product variants are visible and distinguishable for the customer. Component variants are used to configure product variants and are therefore often not visible or understandable for the customer [1]. Product and component variants are part of the external or internal variety, which makes terminological differentiation important (Fig. 3.4). In processes, the different demands on company resources are used as to distinguish between variants, alternatives and versions [7].

3.2 Terms of Product Architecture The structure of a product can be described by its functional elements or its physical components, for which product and functional structures are used. The term product architecture covers both views of the product and the relationships between the functions and the components. In addition to these technical and functional product models, the product family requirements, which represent the initial data of a development project, are another important product description.

Fig. 3.4  Example of variants and version based on a product family of floor cleaning robots

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In the following sections, the relevant definitions and basics of requirements, functional structures, product structures and product architectures are presented in the context of the development of modular product families.

3.2.1 Requirements, Properties and Technical Characteristics cc Requirements  A requirement is a specified, presupposed and mandatory demand with regard to a characteristic of a product. Requirements are either needed or desired by a stakeholder and thus describe a benefit or need. Requirements are typically recorded and documented during the definition of a development project on the basis of a list of requirements, quantified as concretely as possible and divided into fixed requirements, minimum requirements or wishes. Requirements concern the market and the product use by the customer, but also come from different areas of the company or legal requirements [11, 13]. Special importance is attached to the formulation of requirements from the customer’s point of view and in a solution-neutral form. This is the only way to ensure that customer requirements are met and good technical solutions are not prematurely ruled out. Furthermore, requirements should be clearly and concisely formulated and identifiable. Different interpretation possibilities and inconsistencies are to be avoided. Requirements must include clear objectives, the achievement of which must be measurable at a later stage with a reasonable amount of effort. The description of the requirements should be as solution-neutral as possible and follow the structure described in Fig. 3.5. All tasks of recording and managing requirements are summarized under the term requirements management. In addition to the description of the requirements for a product, the differentiated description of a product or a product family according to properties and characteristics has proven to be a useful principle (see Fig. 3.6). This system was described as Characteristics-­Properties Modeling (CPM) by Weber [21]. The Domain Theory according to Andreasen [3] or the Axiomatic Design according to Jiao and Tseng [2] also structure a product differentiated according to its internal and external attributes and the relationships between them [8]. cc Properties and Characteristics  Properties describe the behavior of a product, such as reliability, safety, aesthetics, weight, but also producibility or environmental effects. The product properties –– –– –– ––

reflect the customer perception of the product, are not directly influenceable by the developer and can often not be quantified. Customer requirements are therefore requirements for certain product properties.

3.2 Terms of Product Architecture

67 behaviour

system

modal verb:

Condition

product

shall (shall not) must (must not) / may/ can

ability verb

restriction property

components

goal Examples „If there is no carpet, ....

... the vacuum-cleaning robot....

... must ...

... be able to take up…

... at least 80 percent of the dust.“

„On smooth surfaces...

... the vacuum-cleaning rbot....

... must ...

... achieve ...

... a dust absorption of 70 ± 5 percent ...

... during one pass over the surface.“

Fig. 3.5  Description principle for requirements with necessary and optional parts, according to [9] Characteristics (designer‘s view)  bearing around vertical axis  battery capacity  rear wheels with single g wheel control

Properties (customer‘s view)  quiet operation  low maintenace effords  small turning circle  driving under furniture

 material selection

 ground clearance rance  low height

Fig. 3.6  shows an example of a differentiated description according to product properties and technical characteristics of a floor cleaning robot

Characteristics describe the structure, shape and nature of a product, such as its forms, dimensions, materials or surfaces. Characteristics –– are determined directly by the developer and –– are quantifiable. Ultimately, the customer only perceives a small number of product characteristics directly, as many do not directly relate to customer needs [21].

Product Properties and Technical Characteristics In the case of the floor cleaning robot, the interaction of specific technical characteristics, such as the choice of material, the geometry of the nose wheel or the battery capacity, enable the product to function properly (Fig. 3.6 left). However, the characteristics themselves have no direct significance for the customer, as the customer only perceives the product properties, such as reliability, weight, effectiveness, noise or price (Fig. 3.6 right). These result from the sum of the technical characteristics.

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DIN 2330 makes a similar division and further divides the external product properties according to the purpose of a product and its relations to other systems [4]. Further definitions of the properties and characteristics, as well as other terms such as attributes or specifications, can be found in the literature. An alternative definition as a trio of terms “property, characteristic, value” is for example represented by [13]. According to this, a property consists of a characteristic and a value. For example, a property of an internal combustion engine would be the characteristic “displacement” with the specification “1.6 l”. However, “1.8 l” would be a different property, since the specification as a component of the property differs [1]. In this logic and the use of the term “characteristic”, this definition contradicts the above definition of property and characteristic used here. Regardless of which terminology is used in a company, however, a clear separation of the terms used for the description of internal and external viewpoint is important, as these can be very different and misinterpretations can quickly arise. The differentiation according to (external) product properties and (internal) technical characteristics offers the advantage for the development of product families with many variants that the variety of a product family on the market can be described using selected product properties and the internal component variety by technical characteristics [8, 21]. The goal is to optimally align the product program to the market and at the same time to realize this with the lowest possible internal variety (see also Sects. 4.4 and 6.3.1).

3.2.2 Functions and Functional Structures The functionality of a product and its development plays a central role in many reference processes for product development, such as VDI 2221 or VDI 2206 [19], VDI Guideline 2206 [20]. The main motivation here is the abstract and solution-neutral description of a development task in the sense of a “black box view” in order to obtain the largest possible solution space. cc Function  A function is an intentional connection between the input and output of a technical (sub)system to fulfil a task. Functions, like requirements, are formulated as solution-neutral as possible in order not to anticipate technical solution possibilities when defining and solving development tasks. They are described by a subject and verb phrase (e.g. “increase pressure”, “direct torque” or “reduce speed”) and classified according to energy, material and information flows. As far as possible, this information should be supplemented or specified by the physical quantities involved. In any case, functions are to be described as solution-neutral as possible. Using the function “loosen dirt from the floor” of the floor cleaning robot, Fig. 3.7 shows the change from solution-neutral to a solution-specific description based on function and working principle.

functions

design

solution principle/ effect

69

finding a solution

3.2 Terms of Product Architecture

Functional carriers / components

Fig. 3.7  Function “loosen dirt from the floor” of the floor cleaning robot and the corresponding implementation as an example for solution-neutral and solution-specific description

Overall funcon Main funcons Subfuncons

Fig. 3.8  Principle of a hierarchical function structure

There are two different approaches to describing the functionality of a product, often used in combination. The first is the hierarchical function structure, which describes the overall function starting with one or a few main functions and dividing them over several levels into subfunctions that are not further subdivided. These subfunctions are later realized by concrete, technical solutions. In contrast, the flow-oriented function structure is oriented towards the flows within the product of material (matter), energy and information. cc Functional Structure  Functions can be represented for a product in their interaction and can be differentiated into main functions, sub-functions and auxiliary functions. This is done in a flow-oriented function structure or a hierarchical function structure. Hierarchical function structures represent the subdivision of functions into further subfunctions and are usually represented as a tree structure (see Fig. 3.8). Flow-oriented function structures are based on the energy, material and information flows in the product and show the conversions of these flows with the help of functions in the form of a block diagram (see Fig. 3.9). States and functions strictly alternate in a floworiented function structure.

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Function

Input state

Output state

Legend Function

State

Material flow

Energy flow

Information flow

Fig. 3.9  Principle of flow-oriented function structure with states, functions and outputs, [5] Cleaning the floor

Cleaning

Seperate dirt from floor

Absorb dirt

...

...

Filtering dirt

Moving robot

Store dirt

Empty dirt

Driving robot

Controlling robot

Navigating robot

Detecting dirt

Seperate & empty dirt container

Store electrical energy

Converting electrical energy into motion

Measure distance

Fig. 3.10  Example of a hierarchical functional structure of a floor cleaning robot

As an example, the Fig. 3.10 shows a section of the hierarchical functional structure of the floor cleaning robot. For comparison, Fig.  3.11 shows the same section as a flow-­ oriented function structure. In the case of flow-oriented function structures, main flows that fulfil the essential main function of the product can be marked in the graphic. Flows are also described that enter the product and leave it, in a transformed manner if necessary. Information flows are mostly used to control product functions and influence the function parameters during use. If a closer look is needed, information flows can be further divided into signals and data. In more complicated systems, flow-oriented function structures can become very large. The Basic Scheme of Mechatronic Systems according to VDI 2206 assists in this respect by assigning the arrangement of functions to the three areas of mechanical engineering, electrical engineering and information technology [20]. In addition, related functions can be combined in a flow-oriented function structure comparable to the abstraction levels of a hierarchical function structure, so that large systems can be presented more clearly with the help of mixed modeling of flow-oriented and hierarchical function structure (see Fig. 3.12).

3.2 Terms of Product Architecture

Device loaded

Electrical energy

Store electrical energy

71

Converting electrical energy into motion

Robot moves

Measure distance

Converting electrical energy into rotation

Generate airflow

Rotation energy

Detecting the amount of dirt Dirt on floor

Loose dirt on floor

Seperate dirt from floor

Conducting airflow with dirt

Dirt with air in the device

Dirt in the device

Filtering dirt

Seperate & empty dirt container

air

Disposal of dirt

air

Legend Material flow

Information flow

Energy flow

State

Function

Fig. 3.11  Example of a flow-oriented functional structure of the floor cleaning robot (same functional range as in Fig. 3.10)

Fig. 3.12  Different levels of detail of a flow-oriented function structure [5]

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3.2.3 Product Structure While functional structures describe a product on a functional level, product structures show the physical structure of a product. Product structures thus illustrate the way a product is made up of its components. cc Product Structure  The product structure describes the physical, hierarchical breakdown of a product into its components and their physical relationships. Within the product structure, further individual parts and (sub)assemblies are grouped in assemblies at a lower level (see Fig. 3.13) [15]. The product structure is of decisive importance for creating variants.  In product development, product structures are described in BOMs and in Product Data Management systems, which define the hierarchical product structure. Product structures are often referred to as building structures because it is often based on the assembly sequence. The design of a product structure strongly influences the subsequent product life cycle phases, such as procurement or production. For example, a product assembly process is already largely influenced by the assemblies that are created in a product structure. The structure of a product is also an important tool for creating variants since clever structuring simplifies the configuration of variants. Experience has shown that this involves considerably less effort than designing each variant individually. For the successful development of products, a product structure that matches company objectives is therefore a fundamental requirement. Figure 3.14 shows the product structure of the floor cleaning robot as an example section, which is also used in Sect. 3.2.4 as an example of product architecture.

Product

...

Assembly

e.g. housing

Assembly

e.g. motor control

subassembly

subassembly

part

part

part

part

part

part

e.g. sensor

part

part

...

...

...

Fig. 3.13  Basic classification in a product structure [15]

...

3.2 Terms of Product Architecture

73

...

Housing

Cleaning module

Drive

Control panel screen Push button

…

Collection container

gear boxes

brushes

fan

engine

engine

filter

wheel

gear box

…

bearings

…

…

…

battery

Housing panels

…

… …

Fig. 3.14  Section of the product structure of the floor cleaning robot

Functional structure

Sub-function A Overall function

Sub-function B

Assembly structure Sub-function A1

Component A1

Sub-function A2

Component A2

Sub-function A3

Component BC

Sub-function B1

Component C1

Sub-function B2

Component C2

Assembly A

Assembly B

Product

Assembly C

Fig. 3.15  A basic structure of a product architecture consisting of function structure, product structure and the assignment of functions to the executing components

3.2.4 Product Architecture For many tasks in product development, the components must be considered together with their functions and link with other components. Common modeling of product structure and function structure is the core idea of product architecture. The structure of the assignment between components and functions is of particular interest (see Fig. 3.15).

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cc Product Architecture  Product architectures combine product structures as the physical structure and functional structures as the functional description of a product and relate their elements to each other (see Fig. 3.15). Product architectures are the totality of the functional and physical descriptions of a product [18]. Product architectures define which components of a product (combined to form a module) fulfill which sub-function of a product. With the product architecture, the functional reference of modules can be represented very well by trying to assign each function to one or several modules unambiguously. Thus, function-oriented solutions can be searched for and the corresponding modules can be used in other products. For the functional structure and product structure sections of the floor cleaning robot shown in Figs. 3.10, 3.11, 3.14, the corresponding product architecture section is shown in Fig. 3.16. Product architectures are of particular interest for the simple configuration of product variants or the derivation of new variants for product families. For this purpose, the term product structure can be extended to include the aspect of product breakdown structures. cc Product Breakdown Structure  In a product family, the product breakdown is the constant part of the product structure that roughly outlines the product [17]. In this way, the same fundamental components can always be assigned to different product variants, such as the chassis, body and drive system of a car. The components arranged hierarchically below, such as axles or wheels, are variable and thus form the product variants. The term aims to standardize parts of the product structure and not necessarily to standardize the components used.

…

…

…

Fig. 3.16  The product architecture of the floor cleaning robot (compare Figs. 3.10, 3.14, 3.15)

3.3 Modes of Construction

75

An essential term in the course of modularization projects is that of the component. cc Component  The term component is often used synonymously with the terms single part or component [15], but can also describe an assembly. The term is usually not used as a fixed term in product documentation, such as in bills of materials. In the context of modularization, on the other hand, components are derived by what is known as decomposition, i.e. the breakdown of the product structure. The project-related use of the term offers the advantages of being able to define a suitable level of detail and to be able to break down and optimize the existing product structure more easily. This definition of a component is very important for the successful development of a modular product structure, as it is the starting point for restructuring the product structure (see Sect. 6.4.1).  The term component is used both in the literature and in practice for an item in the product structure or even as a fixed level in the product structure. However, the terms assembly, sub-assembly, and individual part are here retained for the levels of product structure. These already imply structure levels just due to their meaning. The more relative term “component” can thus be used individually within projects for product structuring as the smallest units considered (for further explanation Sect. 6.4.1).

3.3 Modes of Construction With regard to product structure, modes of construction describe certain design principles according to which the product structure can be aligned. They pursue different goals, and the product structure is designed to help achieve these goals. The term mode of construction has been used to describe many different design principles [12]. Many modes of construction, such as fiber reinforced composites, sandwich construction, or hybrid design, therefore, only have a minor influence on the product structure and are not the focus here. When it comes to product structuring, the integral, differential, or modular modes of construction are much more interesting. The latter has a great influence on the basic product structure strategy and is therefore described in more detail with the possible implementation forms, such as a modular kit or a platform in Sect. 5.2. The use of the terms integral, differential, modular, and platform design is inconsistent and sometimes contradictory both in practice and theory. Different meanings of the terms in German and English language are an aggravating factor. In this section a definition and delimitation of terms is given.

3.3.1 Integral and Differential Mode of Construction The differentiation between a more integral or differential mode of construction has long been used in product development to describe alternative design principles [12, 15]. Both modes of construction represent two opposites (see Fig. 3.17). The decisive factor is the

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3  Basics and Terms

Integral

physical desintegration physical integration

Differential

“… too big in production…“ “… large parts too complicated to procure…“ “… too little design freedom…“ …

“… lightweight design…” “… too many interfaces…” “… too many assembly steps…” …

Fig. 3.17  Basic distinction between integral and differential mode of construction, according to [6]

physical integration or differentiation of a product (an assembly, a component) into one or more individual parts. cc Integral and Differential Mode of Construction  The integral mode of construction describes the design principle of designing components or even entire products from as few individual parts as possible (see Fig. 3.17, left). The goal is often to combine several functions on one component. Reasons for an integral design are, for example, the reduction of part numbers, the reduction of weight, the improvement of stiffness, the saving of interfaces or assembly steps and production resources. In many cases, product optimization aims at a cost-effective transfer of several functions to one workpiece. It is often used for mass-produced products. The differential mode of construction, on the other hand, describes the design principle of dividing components or even entire products into more parts (see Fig.  3.17, right). Drivers for a differential design can be easier handling of smaller components in production and transport, reuse of existing parts or greater freedom in material selection and component design. They are more likely to be used for single products or small batches. Dividing into several smaller parts also aims to increase the number of parts in use by allowing them to be used more than once. The spectrum, whether a product structure is more integral or differential, is primarily oriented towards possible improvements in the product design and production as well as the product life cycle, with the goal of cost savings. Products often contain mixed forms, in which certain assemblies can be built in a more differential design and others according to the integral mode of construction. Higher quantities are more in favor of an integral mode of construction and vice versa, since many of the advantages and disadvantages of both modes are determined by economies of scale (see Fig. 3.18).

3.3 Modes of Construction

77

volume suitability high

medium

low

integral

differential

Fig. 3.18  Qualitative representation of the suitability of integral and differential mode of construction for different numbers of units [7]

Principle multiple functions

dividing Differential design

spring

spring holder Total design

one function

Focus

merging Integral design

cam turned

holder Partial design

cam as sheet metal package

Fig. 3.19  Integral and differential mode of construction as functionally oriented modes compared to total and partial mode of construction, according to [12]

Where integral and differential mode of construction are concerned, there is a further possibility of function-driven conceptual subdivision [12]. For example, if a function is performed by one or more components at the same time, Koller speaks of “a total mode of construction” and of “a partial mode of construction,” if it is divided among several components (see Fig. 3.19). If, on the other hand, several functions are fulfilled by one component, this is called an “integral mode of construction.” A contrasting concept to this is the distribution of the functions to one component at a time in differential mode of construction. These terms have not become generally accepted in practice, but they are interesting with regard to the distinction between the terms integral and differential mode of construction.

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3.3.2 Distinction from Modular Mode of Construction The principles of a modular kit are often referred to as modular mode of construction, but go far beyond the motives of a construction method. In contrast to most modes of construction, modular design and also platform strategies include the basic design of the product structure. Essential extensions in contrast to the differential mode of construction are the focus clearly beyond a product on the entire product family, product line or product range with preplanned use of the modules also in other product variants or product families. cc Modular Mode of Construction  The modular mode of construction – also known as modular kit – is a product structure strategy in which different modules are used to create product variants by combining them, to achieve savings through increased commonality or to achieve further technical-functional and/or product-strategic advantages for all product life phases. The creation of different product variants through the combination of modules is essential. Modules consist of one or more components that are particularly strongly coupled to each other compared to their coupling to other components. The terms pairs modular kit – module or building kit – building block are often used synonymously. However, modules independently fulfill a function or a limited set of functions. A differentiation of the terms differential mode of construction and modular mode of construction, as presented here, has become widely established in German design science. In international, English-language literature, however, this distinction is often not made and only the terms Integral Design Principle and Modular Design Principle are used. Likewise, the term product platform design is often used synonymously for modular mode of construction. In German-speaking countries, however, a distinction is made between a modular strategy and a platform strategy and the term modular kit is often used in addition. This term can be assigned different contents, which is explained in more detail in Chap. 5. The module boundaries are defined within the framework of modularization specifically for the technical improvement of function fulfillment and according to other motives, the so-called module drivers (see also Sect. 4.4). Examples are the simple configuration of product variants by combining modules, the outsourcing of modules to external development partners or simplified maintenance by easily accessible and easily exchangeable modules, to name just a few examples. Modularization can be done specifically according to only one or more module drivers. One often tries to consider several module drivers from one or different product life cycle phases when creating a modular product structure and thus goes far beyond the design decision of a more integral or differential mode of construction. Due to the significantly expanded motivations of modularization compared to the integral and differential modes of construction and the focus on other levels of the product structure, the spectra “integral to differential” and “non-modular to highly modular” are not comparable with each other.

Literature

79

Ideally, all relevant module drivers from all product life cycle phases should be integrated into a holistic approach to the development of modular product structures in order to achieve sustainable module formation and for use across departmental boundaries. A detailed description of this context is presented in Sect. 6.6.

Literature 1. Bundesamt S (ed) (2011) Bevölkerungs- und Haushaltsentwicklung im Bund und in den Ländern. Statistisches Bundesamt, Wiesbaden 2. Abdelkafi N (2008) Variety-induced complexity in mass customization. Dissertation, Technische Universität Hamburg-Harburg 3. Andreasen MM, Hansen CT, Cash P (2015) Conceptual design. Springer International Publishing, Cham 4. Deutsches Institut für Normung (1974) DIN 2330 Begriffe und Benennungen  – Allgemeine Grundsätze. Beuth-Verlag, Berlin 5. Ehrlenspiel K, Meerkamm H (2013) Integrierte Produktentwicklung  – Denkabläufe, Methodeneinsatz, Zusammenarbeit. Hanser-Verlag, München 6. Ehrlenspiel K, Kiewert A, Lindemann U, Mörtl M (2007) Kostengünstig Entwickeln und Konstruieren – Kostenmanagement bei der integrierten Produktentwicklung. Springer, B ­ erlin/ Heidelberg 7. Franke H-J (ed) (2002) Variantenmanagement in der Einzel- und Kleinserienfertigung – Mit 33 Tabellen. Hanser-Verlag, München/Wien 8. Gebhardt N, Malone K, Krause D (2012) Nutzung von “Merkmalen” und “Eigenschaften” zur Beschreibung und Analyse von Produktvarianz. In: Pätzold K, Wartzack S (ed) Krause definition. Design for X 2012. Beiträge zum 23. DfX-Symposium Oktober 2012. TuTech-Verlag, Hamburg 9. Internationale Organisation für Normung (2011) ISO/IEC/IEEE 29148:2011 Systems and software engineering – life cycle processes – requirements engineering. Genf 10. Jonas H (2014) Eine Methode zur strategischen Planung modularer Produktprogramme. Dissertation, Technische Universität Hamburg-Harburg 11. Ko H, Moon SK, Otto KN (2015) Design knowledge representation to support personalised additive manufacturing. Virtual Phys Prototyp 10:217–226 12. Koller R (1998) Konstruktionslehre für den Maschinenbau- Grundlagen zur Neu- und Weiterentwicklung technischer Produkte mit Beispielen. Springer, Berlin/Heidelberg 13. Lindemann U (2009) Methodische Entwicklung technischer Produkte. Springer, Berlin/ Heidelberg 14. Meyer M (1997) Revitalize your product lines through continuous platform renewal. Res Technol Manag 40:17–28 15. Pahl G, Beitz W, Feldhusen J, Grote K-H (2007) Konstruktionslehre – Grundlagen erfolgreicher Produktentwicklung; Methoden und Anwendung. Springer, Berlin/Heidelberg 16. Rupp MA (1988) Produkt-, Markt-Strategien- Handbuch zur marktsicheren Produkt- und Sortimentsplanung in Klein- und Mittelunternehmungen der Investitionsgüterindustrie. Verlag Industrielle Organisation, Zürich 17. Schichtel M (2002) Produktdatenmodellierung in der Praxis. Hanser-Verlag, München/Wien 18. Ulrich KT, Eppinger SD (2012) Product design and development. McGraw-Hill Irwin, New York

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19. Verein Deutscher Ingenieure (1993) VDI-Richtlinie 2221  – Methodik zum Entwickeln und Konstruieren technischer Systeme und Produkte. Beuth-Verlag, Berlin 20. Verein Deutscher Ingenieure, VDI 2206 (2004) Entwicklungsmethodik für mechatronische Systeme. Beuth-Verlag, Berlin 21. Weber C (2007) Looking at “DFX” and “product maturity” from the perspective of a new approach to modelling product and product development processes. In: Krause F-L (Hrsg) The future of product development. Proceedings of the 17th CIRP design conference. Springer, Berlin/Heidelberg, pp 85–104

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The product structure describes the inherent and hierarchical structure of a product from its components. Modularization involves the targeted development of a modular product structure by grouping together certain components of the product into modules according to various criteria. Such a modular structure has a significant influence on all processes involved in product development. A cleverly designed modular product structure has the potential to streamline and simplify all related processes. The goal of modularization is to achieve this effect in the best possible way by developing an easy-to-handle, modular product structure while reducing complexity within the company and achieving significant advantages and cost-reductions for all product life phases. Modularity is an abstract characteristic of product structure. In recent years, the terms modularity and modularization have increasingly found their way into various disciplines of industry and science, sometimes carrying different meanings. Even within individual companies and departments, there are different ways of understanding these concepts, which inevitably leads to communication problems. Such circumstances make a clear definition of terms a necessity, so as to provide a basis for understanding the material given in the later chapters of this book and offer a consensus of terms for product development. Both points are addressed in this section. First, the concept of modularity is explained from various scientific perspectives in Sect. 4.1. Building on this, a definition of modularity as a characteristic of product structure is introduced in Sect. 4.2 and characteristics of modularity are presented in Sect. 4.3. A suitable modular product structure offers potential for all life phases of the product. The various motives for the formation of modules are called module drivers and are explained in Sect. 4.4. Possible effects of a modular product structure in the respective product life phases are described in Sect. 4.5. The reduction of internal complexity by structuring the products in clear and variety-oriented modules represents an important measure across all life phases and is therefore dealt with separately in Sect. 4.6.

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4.1 Views on Modularity in Research When it comes to product modularity, we see a variety of views and definitions presented in the corresponding literature, (see Fig. 4.1). Since the modularity of a product has effects and potentials in all product life phases, many approaches with very different modularization goals in mind, have heretofore been developed, and many industry-specific definitions have been coined. The motivations for modularization have expanded considerably over time. The different views are not independent of each other. Instead, they influence each other and pursue different focal points within this topic. Many authors combine several of the views in their approaches so that no clear assignment can be made. Both Salvador and Gershenson provide a comprehensive overview of the different views and approaches, on which this section will build [30, 41]. To this day, the definition of modularity and its partial aspects remain a much-discussed topic [29]. The section below provides an overview of the views on modularity of products in the corresponding literature. In the following Sect. 4.2, a summary definition of modularity is given.

4.1.1 View of Coupling, Decoupling, and Interfaces The most widespread view of modularity across different scientific disciplines is that of coupling and decoupling [5, 30, 41]. A module is seen as a set of (system) components that are much more strongly coupled to each other than to other components of the system (see Fig. 4.2). cc Decoupling  The decoupling of modules of a product describes the state of a product structure in which the modules are largely independent on each other. Such dependencies can be structural connections, but also of information, material or energy exchange (see Fig. 4.2).  The decoupling of modules is a key characteristic of modularity. Modules are based on decoupling because modules are only created by concentrating couplings within a module (intramodular) and decoupling it from the rest of the product structure (intermodular). From this point of view, the ratio of the intensities of inter- and intramodular couplings determines the modularity of the technical system. For this purpose, modules with defined interfaces for an exchange of information, material or energy must be spatially delimitable [13]. Salvador argues that every product consists entirely of modules [41] and describes their separability in terms of the decoupling described above as important characteristic since he regards modules as essential units for the formation of product variants through combination (see also Sect. 4.1.3). Similarly, a module can represent a unit that can be easily removed from the product without the product incurring any damage.

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Comparably, modular systems are described in terms of the strength of the relationships between their subsystems, which can be understood as modules. Here, the ratio of the intensities of inter- and intramodular couplings does not decide between a modular or a non-modular structure but is rather a transitional property. Since this ratio can be different for each module in a system, different parts of one system can be differently modular. Coupling Types The types of coupling considered are decisive for a view of the modularity of a product that is characterized by the coupling intensities. Physical connections between the components, such as the use of a screw fastener for the realization of a force flow, are obvious. Additional relevance is held by the exchange of materials, information, or energy [22]. Coupling Intensities When assessing modularity on the basis of coupling intensities, the question of quantifying these couplings arises. The number and type of couplings can be used comparatively easily for assessing coupling intensity. Various approaches attempt to describe coupling intensities by technical quantities, such as transmitted forces or power, but this is not always sufficiently meaningful or reproducible. Another approach is characterized by the motivation to avoid the effects of necessary product adaptations on other components of the product by forming suitable modules [33]. For this purpose, the potential change impact is used as a criterion for the coupling intensities of modules. The less likely it is that a module will need to be changed due to the modifications of other modules, the more the module is seen as “decoupled”.

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Interfaces As a key property of a module is to have significantly simpler and clearer couplings to the outside of other modules, the connections between modules are of particular importance. The term interface is often used to describe the couplings between modules [30]. The term was intensely used by IT technology [41]. cc Interface  An interface is a space of interaction between two (sub)systems or, in our case, between modules of a product. The interaction can be spatial, can involve the exchange of energy or forces, or that of substance or information. If an interface is used more frequently in its design, or if it is used for the interchangeability or multiple uses of modules, it makes sense to standardize and, above all, document it accordingly. The term interface is often used in general language to describe particularly important couplings in the product, which are relevant, for example, for assembly, the configuration of variants, or information exchange. Due to their special requirements for performance and interchangeability, interfaces are often standardized. Interfaces can be open, for example for connection with third-party products, or they can be designed as proprietary. An interface-oriented view of modularity is therefore also strategic, since proprietary interfaces restrict the circle of manufacturers whose modules can be coupled via the interface [25] (see Sect. 4.1.5).

4.1.2 Technical View The individual components of a product interact with each other to enable the overall function of the product. Usually a certain arrangement and coupling of the components is technically useful [8]. This is mainly determined by –– the necessary connections between the various components, –– a need to separate certain components that should not be located close to each other during operation, such as several heat sources or electromagnetically sensitive sensors, and –– further boundary conditions of the spatial arrangement of certain components, such as accessibility by the user. This technical view is based on the analysis of the flows of force, energy, material, and information and helps shape how certain modules are formed. As described before, modules are groups of components that have significantly more and stronger couplings to each other than to components outside their group (see Fig. 4.3). Amongst to more technical approaches to defining a module are mainly [21], the Design Structure System according to Steward [45], and the Integration Analysis Methodology according to Pimmler and

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Eppinger [37] (see Sect. 6.4). The latter integrate the separation of the considered couplings into physical connections and the exchange of media, energy and information as presented in Sect. 4.1.1.

4.1.3 Functional Approaches Functions allow for a complete description of a product without anticipating technical solutions (see also Sect. 3.2.2). They describe the working structure of a product and are an essential part of the product architecture. Many approaches have emerged that consider the modularity of a product primarily in connection with the product functions and the direct relationships of these functions to the modules. Assignment of Functions and Modules Different approaches use functions to describe modularity. Almost all approaches emphasize the advantages of assigning functions to product modules as unambiguously as possible (see Fig. 4.4), for example [8, 26, 31, 46; Krause and Paetzold 2010]. Pahl and Beitz classify modularity by the functional and physical independence of product components [35]. Although the different approaches to describing modularity through functions are similar, the motivations for choosing such an approach are very diverse. They include good product functionality, easy assignment to function-oriented development teams, and good design changeability. Aspects such as assembly can also be simplified by a clear assignment of functions and modules. Many approaches go much further, addressing, for example, a simplified update of the product in the market phase or a simple transfer of modules to a new product generation. The simplified configuration of product variants on the principle of individual modules is also mentioned. Many of the approaches are thus additionally strategic or resource-oriented (see Sects. 4.1.4 and 4.1.5). However, they use the general guideline of an unambiguous assignment of functions to modules for simplified application. Flows within the Product Flow-oriented approaches to the description of modularity extend the coupling-oriented view by considering the flows of forces, media, energy, and information through a product itself. The Modular Design Methodology (MDM) according to Stone [46] offers an important representative of this view. Individual modules are provided for the conduction,

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conversion and branching of these flows (see Fig. 4.5). These simplified rules for module design have similar motivations as the one-to-one-mapping of functions and modules presented above. Configuration of Product Variants Among many other authors, Otto et al., for example, argue that the product variants within a product family can be built on a common, modular basis [34]. The development, production, and distribution of product variants is one of the most important views on modularity, because the variations are limited to just a few modules and the product variants can be configured by combining them (see Fig. 4.6) (see also [8, 12, 19, 23, 27, 39, 41, 42, 50]). Building on those approaches which view the configuration of different functions through the lens of module combination, more recent approaches go a step further and focus on the configuration of customer-relevant properties of product variants through the combination of modules, such as the Methodical Support of Design for Variety [27] or Variety Mode and Effect Analysis [11]. The company department for Product Planning and Marketing plans different scopes of the product range in advance and derives requirements for the product variants. It also has a motivation in the configuration of future product variants. North American sources especially often tend to focus on the development of modular product families to cover broad market areas. Many authors treat the product structure strategies of the platform and those of a modular kit as very similar.

4.1.4 Process and Organizational View A major motivation for the formation of modules lies in the basic problem-solving strategy (based on cybernetics) of initially viewing extensive and complicated systems in a

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structured way and dividing them into several subsystems in order to gain a better understanding of these systems [48]. The same applies to extensive and complicated tasks, such as the development of the aforementioned systems, which are first broken down into smaller sub-tasks before these are solved individually and the results reintegrated. Decoupling can also be achieved from a process point of view, if individual components can be treated separately along with the product life phases. Components or modules can be decoupled, for example, to be able to develop, procure, produce, or maintain them separately from the rest of the product structure (see Sect. 4.1.2). The consequence of this view is the division of a product into meaningful and clear modules to simplify its complexity, general understandability, and workability, [8, 48]. With the help of modules, systems and their structure can be described with a comparatively low total amount of information [17]. This strategy of modular product structuring also makes it easier to organize the processes of the entire product creation process. Many product development procedures integrate this strategy. This is particularly evident in the V-Model, which depicts the division into subsystems (modules) and their subsequent integration [43]. VDI 2221 provides for the work section “Formation of feasible modules” in the “General procedure for development and design” [48]. Among other motives, this primarily addresses the division of the development task “before the labor-­ intensive design steps”. However, the parallel development of several product variants or a modular product family is neglected, since the guideline strongly addresses the development methodology of individual products (see also Sect. 7.1.1). For the breakdown into simple subtasks, a separability and later integration of the corresponding sub-scopes of the product is necessary, which is reflected in the decoupling of modules described above. From a process- and resource-oriented point of view, the modularity of a product is, therefore, an essential prerequisite for the simple execution of tasks. Interestingly, not only physical couplings have to be considered: Newcomb et al. describe a module as a physical or conceptual grouping of components with certain commonalities, which can be treated as a logical unit (Newcomb et al.).

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Improving Resource Use by Matching Task and Resource From a process and organizational design perspective, the profile of each module’s resource load is relevant for module formation [7, 15, 40]. The basic strategy is to mutually align the work content of tasks with the executing resources to improve resource utilization [2]. The type of resource to which the modularity is geared may include people, their skills, or facilities, such as plants or machines. The basic approach is to adapt the work content to the resources they work on. For example, if work tasks in product development that require special know-how (see Fig., 4.7 left) or parts with production steps using special machines (see Fig. 4.7, right) are bundled in modules, this greatly facilitates process organization. One benefit of the separability of modules from the product and the coordination of modules with the processes and organizational units of the product life phases is the possibility of using modules for the parallelization of tasks [8]. In all phases of product development, processes can be streamlined by forming modules (for example, according to ordering procedures, manufacturing operations, or pre-­ assembly groups) in order to structure the overall task and make it manageable [41]. Different approaches to module formation, therefore, are based on the view of different product life phases, such as purchasing, production at different locations, assembly [20, 35], maintenance through replacement modules, recycling [44] and many more. Some authors also summarize these views of product life phases on modularity in design, production, and usage modularities – [10, 21, 24, 40]. The integration of module views of different product life phases is addressed by ([15]; [7]) (see Sects. 6.4.4 and 6.6.4), and (Koppenhagen 1981), among others. Use of Commonalities One motivating factor of modularity, which was shaped comparatively early in science, is that of commonality as an economic and product-strategic factor [41, 49]. The higher quantities of production volumes resulting from using the same modules as often as possible can trigger economies of scale and learning curve effects – it is this aspect that is a key driver of modularization.

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cc Commonality  Commonality refers to “similarity”, “similarities”, or “sharing of common features” and stands for the use of commonalities of variant products to reduce the internal variety of the products and the associated complexity in the company. The commonality of modules is a partial parameter of modularity as well as a gradual and relative property of variant products [14, 24, 41]. The term is often further specified and used, for example for –– –– –– ––

functional commonality as similarity of requirements and solution principles, component commonality or technical commonality as physical similarity, structural commonality as similarity of product structures or process commonality as similarity of used processes.

The design of a product range as an essential part of the product strategy is geared to market requirements by diversifying the product range. Such program planning results in requirements for the product lines, families, and variants to be developed, and shows where there is potential for commonality of modules.

4.1.5 Product-Strategical View Product strategy comprises the contribution of the products to the corporate strategy or the application of the corporate strategy to the products. It is designed for the medium to long term and primarily entails the successful positioning of the product and its variants on the market, further product innovations, the market life cycle, and the continued development of new product versions and generations. The strategic options for a product are closely linked to the modular structure of that product. The modular structure as well as the scope and properties of the modules are decisive for the implementation of the strategic goals [25]. For example, new product variants or the integration of new technologies into the product can be realized by developing new modules. Decoupling these modules as much as possible from the rest of the product simplifies planning and implementation. From the point of view of product strategy, the modularity of a product is therefore interesting with regard to the feasibility of medium and long-term product planning. The product strategy perspective shows that modularity should not be limited to a single product [41]. Configuration through modules or the multiple use of modules in different product families or lines are essential and the main motivation to use a modular design in products with many variants across the entire product range to achieve long-term success in the market.

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4.2 Definition of Modularity This section was co-authored by Erik Greve. As can be seen from the sources and views of modularity listed in Sect. 4.1, the literature, when defining modularity, largely refers to the strengthening of the couplings of components within a module and the decoupling of modules from each other. However, this description alone is not sufficient for many cases. The following summarizing definition therefore considers other properties as well (see Fig. 4.8). The decoupling of modules is an essential prerequisite for the modularity of a product structure, as it is the only way to create separable modules. The characteristics of commonal use, combinability, interface standardization, and function binding describe the implementation of modularity in more concrete terms. The criteria used for decoupling are determined by the respective goals of modularization (see also Sect. 4.4). The five mentioned characteristics have become established in the literature. They are used for the following definition of the term modularity and are described in more detail in the following subchapter. cc Modularity  Modularity is a gradual characteristic of the product structure. An essential part of this structure is the concentration of component couplings within the modules. These show stronger couplings to each other than to other components or modules. Modules comprise components with certain common features, which can thus be treated as a logical unit. Modularity is specifically designed to meet the requirements of all product life phases. Particularly noteworthy here are –– Commonal use – modules are used in various products to enable savings through economies of scale. –– Combinability – By combining the modules, different product variants can be configured. Essential measures for implementation are interface standardization and function binding. For the latter, the modules fulfill exactly one function or a defined set of functions [7, 8, 41]. Just like modularity itself, the five characteristics of modularity are also considered gradual. They describe the modularity of a product structure in its entirety. The aim of developing modular structures is not necessary to achieve a product structure that is as modular as possible. Rather, the modular characteristics are to be developed in such a way as to encourage the greatest possible number of company- and product-specific advantages in all life phases of the product family and reduce the process- and product-related variety. By configuring product variants, it is possible to achieve a significant reduction in internal variety while at the same time offering a wide range of products. Since this configuration is usually carried out via several product variants, it is possible to consider a single product within the framework of modularization, but this usually falls far short of the

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Fig. 4.8  Characteristics of modular products according to [7, 41]

possible savings. Therefore, modularity is a characteristic that should be seen and developed across several product variants or product families. Modularity is often strongly linked to functions. If possible, a module should completely fulfill one or a defined set of a few product functions. Changing product functions is thus simplified and only involves changing one or a few modules. However, if modules are formed solely according to function-specific aspects, many of the potentials of modular product structures cannot be fully exploited. For example, customer needs are not addressed exclusively via the functions but are rather described by product characteristics (e.g. different performance values). An implementation of non-function-driven module drivers should therefore be considered (see Sect. 4.4).

4.3 Characteristics of Modularity This section was co-authored by Erik Greve. The modularity characteristics shown in Fig. 4.8 are described in detail in the following sections.

4.3.1 Decoupling The components of a product can, for example, be physically connected or linked via information flows. Depending on the intensity of this coupling, the components are more or less independent of each other and have strong or weak relationships with each other. The modular characteristic of decoupling builds on this way of thinking, but refers to the modules of a product and describes the interactions of the modules with each other. The couplings within a module are much more pronounced than the couplings to other modules (see Fig. 4.9). Which components are to be separated or coupled, and to what

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extent, depends on the requirements of the product structure to be developed and the objectives of the modularization. The degree of decoupling of the individual modules should therefore always be adapted rather than just maximized. A simple example are battery modules, which in many products are strongly decoupled from the rest of the product structure and are very easy to disconnect. Exchangeability and rechargeability of the batteries are significantly facilitated by this decoupling. Separate development or a pre-assembled purchase is also advantageous.

4.3.2 Commonal Use In terms of modularity, the term “commonal” can therefore be understood as “similar”, “same” or even “standardized”. In general, this characteristic is understood to mean the standardization of modules so that they can be reused in as many product variants, families or lines as possible (see Fig. 4.10) and economies of scale can be achieved through the higher quantities, for example as shorter development times, learning curve effects or lower procurement costs. Thus, the possibilities of commonal use are not limited to physical modules, but also include processes. Designing the processes in the development of variant components on a commonal basis often yields greater savings than simply increasing the proportion of parts taken over. In the commonal use of modules, care must be taken to ensure that the necessary product differentiation towards the customer is sufficiently maintained. Oversizing the modules for use in products with different performance values can also lead to an increase in the manufacturing costs for products with lower performance requirements. However, the savings from multiple-use of modules often more than outweigh this (see Sect. 2.4). The degree and implementation of commonality must always be adapted to the application.

4.3.3 Combinability Just like commonality, the characteristic of combinability is an essential goal of modularization. The modules are used to configure different product variants by combining them (see Fig. 4.11). A prerequisite here is also the decoupling of the modules. M1

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A wide variety can be created with relatively little effort by combining modules. The configuration process is usually much easier to implement than the separate development and production of the individual variants. In some cases, configuration is deliberately outsourced to the customer, who can put together the product himself (for example, in the case of modular kitchen systems or hydraulic work systems). This aspect can be an important competitive factor in times of constantly increasing product individualization.

4.3.4 Interface Standardization The characteristic of interface standardization focuses on the technical implementation of modularization. Interfaces are areas of interaction between two modules (see Fig. 4.12). This interaction can generally be a structural connection or the exchange of energy, material or information. If an interface is used more frequently in its design or is designed for exchangeability or multiple uses of modules, it is useful to design it as simple as possible and to document it as such. The main advantage is that the modules can be combined with little effort thanks to a defined interface that spans the product family. Particular care must be taken in interface standardization to avoid excessive over- or mis-sizing and lack of product differentiation, as well as to decide on an open or proprietary interface (see also Sect. 4.1.1).

4.3.5 Function Binding Function binding describes the property of modules each fulfilling only one sub-function or a fixed set of a few sub-functions (see Fig. 4.13). Just like interface standardization, this characteristic is also a helpful design principle of the modular product structure, so that modules can be combined more easily and in a more targeted manner to form product variants. Often there are further advantages of function binding, such as easier product modification by changing, adding, or omitting a new function one module at a time. For product families with many variants, the orientation of the modules to the differentiating product properties are particularly decisive from the customer’s point of view. This determines how easily the different product variants can be configured by the modules.

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As shown in the previous sections, the five characteristics of modularity can be at very different levels compared to each other. The more pronounced they are, the greater will be the modularity of the product family. There is no fixed point at which one can speak of a modular product. Rather, a system is more or less modular in its structure. Product ranges with a large number of variants can be significantly improved in terms of their internal variety by configuring the product variants from individual modules. Therefore, modularity is a characteristic that should be seen and developed across several product variants or product families and should not be limited to a purely function-­oriented module structure. In order to achieve the desired technical and strategic goals of modularization, the above-mentioned characteristics are specifically developed to generate advantages for all product life phases through the modular product structure. The following section describes, how each of these advantages can be achieved.

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4.4 Potentials of Modular Product Structures This section was co-authored by Erik Greve. The way a product is structured has different effects on different aspects along the entire value chain. It is possible to directly influence the essential strategic objectives such as time, costs, quality or flexibility. The success of a product can therefore be significantly improved by its modular structure. This is especially true for products with a large number of variants since the internal complexity of a large variety of products can be significantly reduced by means of modular product families. For this reason, both potentials and risks must be specifically considered in the context of product structuring. This section presents the potential of modularization. The concept of product life phases is presented and used to ensure a clear classification of effects. Finally, the potential of modular product structures are summarized and the avoidance of risks during implementation and realization is discussed.

4.4.1 Concept of the Life Phases Skilful modularization can generate savings in all product life phases. The effects are described below for each life phase. cc Product Life Phase  A product life phase represents a corporate function along with the product development, production or the use or recycling of a product. There is typically a specialist department or division within a company responsible for implementing requirements and thus tapping the product structure potential for each product life phase. The generic life phases include product development, procurement, production, sales and distribution, use, and recycling/disposal. However, these must be adapted to the specific needs of the company (see Fig. 4.14). In the context of modularization, the term product life phase was coined primarily by Erixon within the framework of the Modular Function Deployment method (see Sect. 6.5.3) [15]. Often, the life phases are also based on the cost centers of a company, which can help to define the individual phases. These product life phases should not be confused with the product life cycle. The latter describes the typical sales process of a product from development to market launch, growth, maturity, and saturation through to market phasing [32]. The effects of a modular design of the product structure and the associated targeted reduction of internal product variety can be traced through all product life phases. This usually follows from a reduction of the part numbers and the corresponding optimization of both the learning curve and the economies of scale. In addition, further specific advantages can be implemented for individual life cycle phases through targeted product structuring.

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It is important here that there is not necessarily a single correct modular structure for all phases of life, but that there is a structure that can be adapted for each phase according to the respective objectives. This basic idea is followed by several modularization methods that aim to harmonize the product structure according to the different objectives of the product life phases. These are presented in Sect. 6.4.4. Now the potentials of modular product structures are presented for the various product life phases, which are shown together with the limits to be observed as an overview in Fig. 4.15.

4.4.2 Product Development In product development, one benefit can be achieved by the developed of several, strongly decoupled modules in parallel in separate teams. This also makes it easier to award development contracts to external service providers. In many companies, development projects are planned according to individual products or manageable product families with their respective favorable times of market launch. The advantage of such an development planning is clear organization based on individual products. However, this also has the disadvantage that potential synergies between the individual development projects are more difficult to identify and implement. This is due on one hand to the temporal, personnel, and financial separation of the projects, and on the other hand to the difficulty of having an overview of all products. A more modular view of a product range significantly improves the ability to implement module developments independently of individual products. Individual modules can be pre-developed and then used for several products. The advantages are better work load planning in development and shorter development times or the more flexible allocation of specialist developers. The prerequisite is that corresponding modules need to be identified and decoupled within the product range. This is supported if the interfaces of these modules are designed as simply and clearly as possible. If employed functions and technologies are bundled in one or a few modules, the personnel allocation of development experts is simplified, and the coordination effort among the teams is reduced. Possible disadvantages include the additional effort of modularization, as well as the more complicated coordination of development projects and the coordination of interfaces. However, these disadvantages can often be more than compensated by the above-mentioned advantages and the exploitation of synergies in product development. The repeated use of modules also increases production batch sizes. The task of modularization is to organize the product structures within the product range into suitable modules so that they can be better implemented. A further advantage of modular product structures may be improved robustness of the product structure against design changes that may become necessary, for example, due to new regulations or technological developments. These adjustments can be better limited to individual, self-­ contained modules.

Loss of knowhowthrough outsourcing

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Fig. 4.15  Potentials and limits of a modular product structure in different product life phases, based on [7, 18, 35, 39]

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Proven modules can be more easily adopted from previous product generations or other product families. This also reduces the effort for documentation, since it can be created and managed per module.

4.4.3 Procurement In the life phase of procurement, activities are organized to supply the company with goods or services that the company cannot produce itself. This is where we can see a major advantage of modular product structures in the ordering of pre-assembled modules. The purchase of externally developed and tested units can also be simplified. This can significantly reduce the workload in procurement and the number of different purchase orders and suppliers. The use of modules for several products increases the volumes of procurement orders so that in most cases better purchasing conditions can be achieved. Goods receipt tests can also be simplified if the modules are selected and designed accordingly. Particularly with complicated products, it is helpful to purchase additional modules in order to reduce one’s own administrative expenses and to keep them manageable for all parties involved in the supply chain [4].

4.4.4 Production and Assembly In production and assembly, the procured materials are processed into usable economic or consumer goods using production resources. As in the previous phases, potential can be tapped by reusing components and modules. If standardized modules are produced in increased quantities, unit costs can generally be reduced. The set-up work and the need for tools and assembly devices can be reduced [36]; learning curve and economies of scale can be better exploited and lead times can also be reduced. A further advantage is the possibility to provide special test modules. These allow modules to be tested separately from other production and assembly processes, so that errors can be detected early while other processes run in parallel. Reducing these test modules to only those components necessary for the testing cuts down on the amount of capital tied up or lost in case of errors. Coordinating the modular product structure and the manufacturing organization results in parallelizing processes, which subsequently results in shorter lead times. Production planning can be made easier by structuring the processes hierarchically. The production system and the resulting processes can be divided into main line and secondary lines in accordance with the modular product structure [38].

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While the individual modules are produced on the secondary lines, the overall product is manufactured by feeding and integrating the modules on the mainline. The separation allows the individual assembly lines to be viewed separately as self-contained systems. Such streamlining significantly supports customer-specific mass production, since customer-­specific adaptation is limited to secondary production lines and takes place as late as possible in the production process according to the principle of postponement. In this way, the entire assembly process can be divided into less complex individual sections that can be optimally adapted to their respective production processes, and the material flow-compatible arrangement can be improved. Standardized interfaces can also enable easy testing of modules that have been specially adapted to a customer. Modified designs also have less impact on the production or assembly lines, as they can potentially be limited to one or a few modules, thereby increasing flexibility. The self-contained sub-processes allow for a clear assignment of tasks and responsibilities, thus simplifying documentation and process control. The auxiliary lines are not structurally tied to the main assembly line and are more likely to be reused after production is discontinued. For the variant-independent assembly scopes, this results in a constant assembly time with variant-neutral lead time and thus better planning reliability. By relocating the variant-­creating modules to the end of the mainline, the so-called postponement, a quick reaction to new orders and changes is made possible.

4.4.5 Sales and Distribution In sales, the product to be sold is made available to the customer or end-user using (marketing) strategies. Depending on the strategic orientation of the company, this life phase can be at the beginning of the product lifecycle in the case of an engineer-to-order (ETO) strategy or after production in the case of a make-to-stock (MTO) strategy (see Sect. 4.4.1). In sales, one great benefit of modular product structures lies in the simple creation of product variants through the configuration of modules. A clear alignment of distinguishing features of the product variants from the customer’s point of view on the variant modules is particularly important for a variant-oriented configuration with the help of a modular product structure (see Sect. 4.6). If this is the case, the variants can be configured quickly and based on a small internal product variety from different modules without exerting great influence on the development and manufacturing process [39]. A simple configuration can often shorten delivery times or improve availability, which is an important competitive advantage in many industries. New sales strategies can also be derived from the self-contained nature of the modules, such as later product updates, product extensions or adaptations. Modular product structures are a measure excellently suited to reducing the internal complexity of a company through product development throughout all phases of the

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product life cycle. Against the background that a large part of this complexity is caused by an increasing offered variety, it is particularly important to consider the interests of sales in the development of modular product structures. The product families of herbicide sprayers shown in Fig. 4.16 are a good example of a modular product structure that has been designed to allow easy configuration of product variants [27]. Based on a platform module (see Fig. 4.16 left), the different variants can be generated by mounting simple modules. The selection of the necessary modules is easy to carry out because one or less variant product properties are represented by a module from the customer’s point of view. By means of simple and safe to install interfaces, customers can purchase only the platform and configuration modules and then install them themselves (see Fig. 4.16 middle).

4.4.6 Product Use and Maintenance In the usage phase, functionality from the customer’s point of view is the main focus. The structuring of the product into individual modules can make its use much easier and make many product functions possible in the first place. For instance, operating units can be decoupled spatially and treated as separate units from the rest of the product and can only be coupled with other modules via a robust and contactless radio or infrared interface. During the customer’s usage phase, conditions and requirements also change, so that subsequent retrofitting of functions or other updates can be marketed. On the one hand, these measures are intended to enable the customer to continue using the product and thus strengthen customer loyalty, and on the other hand to convey the advantage of a later adaptation already at the time of the purchase decision. The interchangeability of corresponding modules is an important factor for product adaptations and extensions. The product can be upgraded by using higher quality modules or adapted to the respective application Arrangement (central, lateral)

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Fig. 4.16  Example of a modular product structure designed for easy product variant configuration of an herbicide sprayer product family. (Courtesy of Mantis ULV GmbH)

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and environmental conditions [7]. The limitation to a module exchange reduces the effort and can partly be done by the customer himself. Any changes must be planned in advance at the product development stage. These can be changes in the employed technology (e.g. new energy storage or communication systems), the market, or the legal situation. With the help of product range planning methods (see Sect. 6.2), certain trends can be derived and already included in the development of the modular product structure. In addition, maintenance and repair processes carried out on the product during its use are also supported by the corresponding modularization for maintenance and replacement. The exchange of modules is of great importance in this context [47]. Wearing parts and consumables can be grouped together in modules that are easy to remove, thus making maintenance work much easier. Depending on the service strategy, this process may be outsourced to the customer due to the simplification of module replacement. Ease of replacement is also an important factor for repair work. Here, fault-prone parts or components with a similar service life can be grouped together in modules so that damage can be localized more easily. In addition, repairs can be carried out on site and under unfavorable conditions if necessary. Replacement modules can be kept in stock, thus reducing product downtime. By using transfer modules across several product variants and families, the reduced variety of parts can further reduce inventory costs for the service department. For easier maintenance and cleaning, a floor cleaning robot has a dirt container module which is decoupled from the rest of the product and can therefore be easily removed and emptied by a simple click mechanism. This prevents the entire product from being lifted over a waste bin. The cleaning brushes can also be easily removed as a whole module, making it easier to clean the brushes or replace them after they wear out. ◄ Retrofitting through the subsequent purchase of modules is also planned. A so-called lighthouse module extends the product function, as it enables the robot to identify and clean several rooms separately. For reasons of functional expandability, a certain degree of oversizing was accepted here, since the sensors for recording the signals of the lighthouse and the corresponding control algorithm are always present in the robot. ◄

4.4.7 Maintenance After market entry, a modular product structure must be continuously adapted to changing conditions (see also Sect. 7.1.2) [3]. These changes may have already been planned in advance within the framework of product family development or may become necessary unexpectedly. Examples are planned facelifts, the integration of newly available technology into the product family, and the derivation of a new product variant due to new or legal requirements. Modular product structures are ideally suited to facilitate product maintenance activities. For already planned or probable changes, decoupled modules can be provided in a targeted manner to simplify later development and integration into the supply chain and processes.

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4.4.8 Recycling This phase aims to break down the product into its waste products, which can either be reused, recycled or disposed of. In order to be able to ensure that the dismantling is as easy as possible, the formation of modules is motivated by the use of components of similar materials [9]. These recycling or disposal modules often do not need to be further disassembled and can even be disposed of or reused in their entirety. Thus, the modular product structure enables economic and environmentally friendly recycling.

4.4.9 Summarizing the Concept of Module Drivers As shown in the previous sections, modular product structures enable the exploitation of potentials in all product life phases. In the development of a modular product structure, it is necessary to take up the company- and product-specific requirements of the individual product life phases with regard to the modularity of the product structure, to integrate them into the product development and thus to exploit the described potentials in the best possible way. The approach of module drivers was developed based on the potential of modular product structures [15]. The objectives of each product life cycle phase are recorded in the form of so-called module drivers. cc Module Driver  Module drivers are technical or product-strategic reasons for creating modules within a product structure. Examples include: outsourcing development, special production processes, the configuration of product variants, or simple maintenance. These are individually specified within a concrete modularization project in so-called module driver specifications, such as sub-projects in development the test of components, replacement parts, or maintenance.  The module drivers and their characteristics thus represent specific goals of each individual product life phase (see Fig. 4.17). Various methods of product development are devoted to modularizing the product structure from the perspective of a single life phase, based on individual module drivers (see Sect. 6.4). As mentioned at the beginning of this section, there is usually no single superordinate module structure that can be adopted in all product life phases. For this reason, methodological approaches to modularization exist for harmonizing these modular product structures, which are specific to each product life phase. These are presented in Sect. 6.4. By integrating all module drivers into the development of a modular product structure, a company-specific product structure strategy can be developed, in order to avoid potential risks. Typical risks in the development and implementation of a modular product structure are, for example, a higher weight, more quality checks and assembly steps due to more interfaces, additional costs due to oversizing of modules or effects of product cannibalization on the market due to strong multiple use of modules. It must be ensured that the described potentials of modular product structuring outweigh the initial additional effort in developing the module structure. However, the

4.4 Potentials of Modular Product Structures Technical functional module drivers  Herbizide flow  Mechanical structure  Electrical power Carry-over parts  Transfer nozzle Temporal variance

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Recycling/ Disposal Product recycling  Reuse of pump Material recycling  Plastics  Battery  Metall Thermal recycling Diplosal

Fig. 4.17  Generic overview of typical module drivers, according to [7, 15]

significant reduction of the overall, internal company complexity in the development of a modular product structure, including the module drivers of all product life phases, means that this is usually the case – even if the corresponding reduction in complexity costs is difficult to measure using conventional cost accounting methods (see Sects. 2.4, 2.5, 2.6).

4.5 Risks of Modularization This section was co-authored by Jennifer Hackl. In the previous section, the potential in the various product life phases that can be achieved by modularizing product families or product ranges was shown. In practical application, however, there is the challenge of realizing a modular product structure that is clearly manageable and can implement the potentials without further negative effects. It often must be considered whether a too fine-grained modularity does not also present certain disadvantages. First, differing views of individual departments may lead to conflicting demands on the modularity of the product structure. In addition, potential side effects from individual modularization measures must be known and safeguarded against. One of the challenges in the development of modular product families lies in the interaction of the modules in different product life phases along the product creation process timeline (see Sect. 4.4.1). Since the organization, processes, and operations in the individual product life phases can be very different, the achievable potential through modularization (see Sect. 4.4) and the resulting requirements for the modular product structure can vary greatly. The diverse potentials of modularization for the product life phase thus result in very different requirements for the modularity of the product structure. It follows that there can be no single, optimal modular product structure. Rather, a compromise must be found that is reasonable for all the life cycle phases involved and that is comprehensible and acceptable to all (see also Sect. 6.6). Only this compromise solution

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makes it possible for the modular product structures to be accepted by all stakeholders involved and to be permanently anchored in the company. Conflicts of Modularization Over the Product Life Phases The potential for conflict in modular product structuring often lies in the lack of communication between departments and the goal of optimizing one’s own processes without having an eye for the best overall solution. If, for example, in sales, the configurability of the product is intended for the customer by selecting individual sales modules, the corresponding modules must be provided individually and be available for the customer. If, however, these modules have to be tested in production in interaction with other modules, it may lead to a potential conflict: in the worst case the modules have to be assembled, tested and then disassembled again. The function to be tested should be performed by only one of the modules alone so that this can be tested separately. An intense common use of modules across many different product variants or families can usually not be achieved without either oversizing or undersizing these modules. Oversizing occurs when a module is designed for the maximum requirements of its applications. In the case of undersizing, a module is designed for the average requirements of its applications and a non-optimal performance is accepted, which is only possible in the case of optional requirements (see Sect. 3.2.1). Advantageous economies of scale in development, procurement, and production through common use, must be weighed against the negative effects of such incorrect dimensioning as more installation space and weight, or less differentiation of product variants from one another. Starting with individual performance parameters, such oversizing can also include entire functions in the module, which are only required in some product variants. At the same time, this can also result in increased production and assembly costs for the variants with lower requirements. In this case, it must be estimated to what extent this additional expenditure is offset or exceeded by savings due to economies of scale, such as uniform processes or a shorter set-up time. Figure 4.18 shows a selection of possible arguments with regard to the standardization of modules and their common use as well as an increased differentiation of the modules

Standardization

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Fig. 4.18  Conflict of objectives between standardization and differentiation [14]

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with a better fulfillment of specific customer requirements. In this conflict, the individual degrees of differentiation of all modules must be considered. Increased common use of modules makes it more difficult to differentiate between product variants from the customer’s point of view, which can have a negative impact on the perceived quality and individuality of the product for the customer.

4.6 Design for Variety This section was co-authored by Erik Greve. In Sect. 4.4, various potentials of modular structured products were presented from the perspectives of the individual product life phases. The product structure strategy of modular product families offers a significant advantage across all product life phases by reducing complexity throughout the entire company  – particularly so in regard to an ever-­increasing variety of demand in many manufacturing sectors shown in Chap. 2. As already described in Sects. 4.4 and 4.5, modular product structuring offers great advantages when configuring product variants using a few modules. In many companies with a high level of product variety, the variety of components and processes makes the activities of all product life phases more complex. Modular structuring of products across product ranges can therefore bring about particularly large savings by reducing internal variety. The basis for this is a variant-oriented product structure, which can – ideally – directly configure each variant product property from the customer’s point of view by using one module with a small scope. Due to its strong potential of enabling savings across various life phases, the concept of Design for variety is introduced and explained in more detail here. The aforementioned internal variety is caused by a variety of external and internal drivers. However, the only thing that affects sales is the variety in product properties that the customer perceives, and the value when selecting a product variant. The alignment of internal company variety with the variety of demand is an essential aspect of product structuring that is variety-oriented and thus also an essential prerequisite for modular product structuring. The suitability of a product family for variety is essentially determined by a variant-oriented component design and the product structure based on it. cc Variety-Oriented Design  In the context of product structuring, the term variety-­ oriented design describes the property of a product structure to enable the configuration of a defined external variety of offers with a minimum internal variety of components and processes [27]. According to Kipp, the product structure of an ideally variant-oriented product family can be summarized in four basic characteristics [28]. In an abstract model of a product family in Fig. 4.19, these are shown as relationships between the external variety of products (see Fig.  4.19, above, formulated as customer-relevant product properties) and the internal variety of components (see Fig. 4.19, below).

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Fig. 4.19  Properties of the product structure of a product family that is ideally suited to variants, according to [27]

A product family consists of different components. Some of them can be used in all variants of the product families and are therefore called standard components. Others must be available for configuring product variants, deriving new variants or customizing a product variant. These are referred to as variant components. Variant components allow the product to be differentiated from the customer’s point of view in one or more product properties. They can be installed either in variants optionally, or in different numbers to create the product variants. The properties of a product structure that is ideally suited to a variety-oriented design are shown in 4.19. These describe a hypothetical ideal state – that is, they cannot always be achieved in reality – and serve as a target image for variety-oriented product structuring and design. According to [27], the four defining properties of this ideal variety-oriented product family are –– differentiation of standard and variant components, –– reduction of variant components, –– one-to-one mapping of variant components and differentiating product properties as well as the –– decoupling of the components. These are described in detail below and their practical use is demonstrated.

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4.6.1 Differentiation of Standard and Variant Components This property describes the clear and consistent differentiation of standard and variant components (see Fig.  4.19, point 1). The fewer variant components exist, the more the number of components and complexity in the company decreases. For this reason, a clear separation between the two component classes is particularly important. Furthermore, a high number and value proportion of standard components in the product structure is desirable. Consequently, variant components should have a lower proportional value in the product, that is, they should be inexpensive to manufacture, easy to procure and to be stored [16]. The differentiation into standard and variant components is fulfilled if each component of the product family can be clearly assigned to one of the two classes. The variant components must allow a product property to be differentiated that is desired as being selectable from the customer’s point of view. This rule is often contradicted insidiously and goes unnoticed due to subsequent changes. In order to achieve a clear differentiation between variant and standard components, all components without reference to a differentiating product property must be standardized and, if necessary, integrated into a standard module or the platform of the product family (see Fig. 4.19 Components B and D). The variant components should directly define a variant and customer-relevant product property. Differentiation of Standard and Variant Components Aircraft galleys are available in many different variants, as they have to be adapted to the respective aircraft models, functional requirements, passenger numbers and airlines. In particular, they often differ in the various plug-in modules, which can themselves vary in function, size and shape (Fig. 4.20). Since the connections and thus the interfaces to the load-bearing wall behind the compartments differ due to the different slide-in components, the load-bearing wall is variant but has no direct reference to a differentiating product property from the customer’s point of view. It is not noticed by the customer and therefore its variety does not directly add value to the overall product. In this context, a differentiation between standard and variant components provides for standardization of the connections for all drawer variants, so that only one standardized support wall has to be provided.

4.6.2 Reduction of Variant Components According to this criterion, the variant components according to the above definition (see Table 4.1) ought to be reduced to the geometry that is essential to differentiate the relevant variant product property. An attempt must be made to separate all standard parts from

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Fig. 4.20  Example of a modular product family of aircraft galleys with standard components (lower part) and variant components (upper part)

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Table 4.1  Properties of ideal standard components and variant components Ideal standard components Only used unchanged

Installed in every product variant of the product family High proportion of use in the product family

Ideal variant components Direct reference and significant contribution to a differentiating product property from the customer’s point of view Low proportional value in the product and the product family Inexpensive to manufacture, easy to procure and store

variant components, so that each element and each geometry of a variant component serves to differentiate a variant product property that must be selectable and relevant from the customer’s point of view. The benefit in doing this lies in the fact that the resulting variant components can provide the variety required by the customer, but due to their reduction, they will potentially cause significantly less effort in handling, modification and care in all product life phases. They can be provided, adapted and configured more easily in different specifications. Reduction of Variant Components A supplier manufactures and sells various drive shafts. Since the customers use different drive trains, up to now a separate shaft variant was produced for each connection variant, stored in the product data management system with its own article number and manufactured in differing work steps. Due to these changing manufacturing processes, the intransparency, set-up times, tool demand and risk of failure was increased. To reduce the number of variant components, the drive shafts were separated from the connection geometries. Parameters such as diameter, length and material of the shafts could be standardized. In this case, the variant property “connection geometry” with its high variety was separated into a new variant component. The rest of the drive shaft is standardized (see Fig. 4.21). A standardized interface was used to connect this new, reduced variant component like an adapter.

4.6.3 One-to-One Mapping The variant components are used to configure the planned range of product variants. Ideally, exactly one variant component differentiates exactly one variant product property (see Fig. 4.21, on the far right). This one-to-one mapping avoids the proliferation of variant product properties resulting in increasing amounts of new component variants. Due to this multiplication effect, the number of necessary variant components is often greatly increased. These effects can be significantly reduced and many part numbers can be saved, if a variant product property is realized by only one variant component.

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Fig. 4.21  Example of the reduced design of a variant component, according to [27]

Desktop computers, for example, are offered in countless variations. The variant product properties from the customer’s point of view, such as memory capacity and computing speed, can be combined to a large extent in individual modules and via standardized interfaces.

4.6.4 Decoupling of Components The best possible decoupling is related in particular to the variant components, which should be separated from each other as widely as possible. In practice, complete decoupling is not possible, since in this case any interaction between the components of the product would no longer work. In this respect, this property of an ideally variety-oriented product family is to be understood as a theoretical idea with sole reference to a Design for Variety. An ideally decoupled product structure contains only components that have very few interfaces. The motivation behind this is based on the fact that changes are easier be realized if potential effects of these changes are limited. In the case of product families, additional product variants are often generated or existing ones changed in later phases of a development project or after market launch. A product structure that is as decoupled as possible offers better robustness against these changes, since the change of one component is less likely to require changes of other components. The corresponding effort for this change is significantly lower. The variant components, in particular, should therefore be decoupled as far as possible [27].

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In comparing the characteristics of an ideal variety-oriented product family with those of modular product structures (see Sect. 4.2), it becomes clear that these are particularly well suited for realizing Design for Variety for a product family. Differentiation, reduction, one-to-one mapping and decoupling are the main criteria that must be taken into account when developing modular product families to meet variant requirements. The methodological support of Design for Variety according to Kipp integrates these principles into a procedure for variety-oriented redesign and development of a modular product structure, geared to the simple configuration of product variants and the reduction of the internal variety of components (see Sect. 6.3.1) [27]. We have provided a number of instructions and design guidelines for the constructive implementation of a variant-oriented product structure (see Sect. 6.3.1). By improving the Design for Variety, it is also possible to achieve or at least support a significant reduction in internal company processes and ultimately the overall complexity in the company.

Literature 1. Abdelkafi N (2008) Variety-induced complexity in mass customization. Dissertation, Technische Universität Hamburg-Harburg 2. Andreasen MM, Hansen CT, Cash P (2015) Conceptual design. Springer International Publishing, Cham 3. Bahns T, Beckmann G, Gebhardt N, Krause D (2015) Sustainability of modular product families. In: Weber C, Husung S, et al. (eds) The 20th international conference on engineering design, pp 185–194 4. Baldwin C, Clark K (1993) The benefits and limitations of structured design methodologies. Manuf Rev:221–220 5. Beckmann G, Gebhardt N, Bahns T, Krause D (2016) Approach to transfer methods for developing modular product families into practice. In: Marjanović D, Štorga M, et al. (eds) Proceedings of the DESIGN 2016 14th international design conference, pp 16–19 6. Bender B (2016) VDI 2221 – Die neue Richtlinie. In: Krause D, Paetzold K, Wartzack S (eds) Design for X. Beiträge zum 27. DfX-Symposium. Oktober 2016, Hamburg 7. Blees C (2011) Eine Methode zur Entwicklung modularer Produktfamilien. Dissertation, Technische Universität Hamburg-Harburg 8. Blees C, Jonas H, Krause D (2009) Perspective-based development of modular product architectures. In: Proceedings of the ICED09 – 17th international conference on engineering design. Stanford University, California, pp 95–106 9. Bönker T (1999) Beitrag zum Produktrecycling  – Entwicklung einer modularen Bewertungsund Planungssystematik. Shaker-Verlag, Aachen 10. Brökel K, Feldhusen J, Grote K-H, Rieg F, Stelzer R (2008) Nachhaltige und effiziente Produktentwicklung- 6. Gemeinsames Kolloquium Konstruktionstechnik, 9–10 Oktober, Shaker, Aachen 11. Caesar C (1991) Kostenorientierte Gestaltungsmethodik für variantenreiche Serienprodukte  – Variant mode and effects analysis (VMEA). Dissertation, Technische Hochschule Aachen 12. Deutschen Instituts für Normung e. V (2002) DIN 199–1:2002–03 Technische Produktdokumentation. Beuth-Verlag, Berlin

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13. Eckert C, Clarkson J, Zanker W (2004) Change and customisation in complex engineering domains. Res Eng Des 15:1–21 14. Eilmus S (2016) Methodische Unterstützung der Entwicklung von Produktprogrammen mit hoher Kommunalität. Dissertation, Technische Universität Hamburg-Harburg 15. Erixon G (1998) Modular function deployment  – a method for product modularisation. Dissertation, The Royal Institute of Technology, Stockholm 16. Franke H-J (ed) (2002) Variantenmanagement in der Einzel- und Kleinserienfertigung – Mit 33 Tabellen. Hanser-Verlag, München/Wien 17. Gebhardt N, Beckmann G, Krause D (2009) Product family models and knowledge transfer support for the development of modular product families. In: Proceedings of the 9th Norddesign conference, Aalborg 18. Gebhardt N, Kruse M, Krause D (2015) Gleichteile-, Modul- und Plattformstrategie. In: Lindemann U (ed) Handbuch Produktentwicklung. Hanser, München, pp 111–149 19. Gershenson JK, Prasad GJ, Zhang Y (2003) Product modularity – definitions and benefits. J Eng Des 14:295–313 20. Halfmann N (2015) Montagegerechtes Produktstrukturieren im Kontext einer Lebensphasenmodularisierung. Dissertation, Technische Universität Hamburg-Harburg 21. Huang C-C, Kusiak A (1998) Modularity in design of products and systems. IEEE Trans Syst Man Cybern A 28:66–77 22. Hubka V, Eder WE (1988) Theory of technical systems – a Total concept theory for engineering design. Springer, Berlin/Heidelberg 23. Internationalen Organisation für Normung (2015) DIN EN ISO 9000:2015–11 Qualitätsmanagementsysteme – Grundlagen und Begriffe. Beuth, Berlin 24. Jiao J, Tseng MM (2000) Fundamentals of product family architecture. Integr Manuf Syst 11:469–483 25. Jonas H, Gebhardt N, Krause D (2012) Towards a strategic development of modular product programs. In: Marjanović D et al. (eds) DESIGN 2012. Proceedings of the 12th international design conference, Dubrovnik, May 21–24, 2012, pp 959–968 26. Kaplan RS, Anderson SR (2007) Time-driven activity-based costing – a simpler and more powerful path to higher profits. Harvard Business School Press, Boston 27. Kipp T (2008) Methodische Unterstützung der variantengerechten Produktgestaltung. Dissertation, Technische Universität Hamburg-Harburg 28. Kipp T, Krause D (2008) Design for variety  – efficient support for design engineers. In: Marjanović D et  al. (eds). Proceedings of the 10th international design conference design, Dubrovnik, pp 425–432 29. Kirchhof R (2003) Ganzheitliches Komplexitätsmanagement – Grundlagen und Methodik des Umgangs mit Komplexität im Unternehmen. Dissertation, Technische Universität Cottbus 30. Krause D, Kipp T, Blees C (2012) Modulare Produktstrukturierung. In: Rieg F, Steinhilper R (eds) Handbuch Konstruktion. Hanser-Verlag, München, pp 657–678 31. Kusiak A, Huang C-C (1996) Development of modular products. IEEE Trans Compon Packag Manuf Technol 19:523–538 32. Lindemann U (2009) Methodische Entwicklung technischer Produkte. Springer, Berlin/ Heidelberg 33. Martin M, Ishii K (2002) Design for variety: developing standardized and modularized product platform architectures. Res Eng Des 2002:213–235 34. Otto K, Hölttä-Otto K, Simpson TW, Krause D, Ripperda S, Ki Moon S (2016) Global views on modular design research  – linking alternative methods to support modular product family concept development. J Mech Des 138:71101

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35. Pahl G, Beitz W, Feldhusen J, Grote K-H (2007) Konstruktionslehre- Grundlagen erfolgreicher Produktentwicklung; Methoden und Anwendung. Springer, Berlin/Heidelberg 36. Piller FT, Waringer D (1999) Modularisierung in der Automobilindustrie – Neue Formen und Prinzipien; Modular Sourcing, Plattformkonzept und Fertigungssegmentierung als Mittel des Komplexitätsmanagements. Shaker, Aachen 37. Pimmler TU, Eppinger SD (1994) Integration analysis of product decompositions. In: ASME conference on design theory and methodology, Minneapolis, pp 343–351 38. Pine BJ (1994) Maßgeschneiderte Massenfertigung  – Neue Dimensionen im Wettbewerb. Wirtschaftsverlag Überreuter, Wien 39. Rathnow PJ (1993) Integriertes Variantenmanagement- Bestimmung, Realisierung und Sicherung der optimalen Produktvielfalt. Vandenhoeck & Ruprecht, Göttingen 40. Ripperda S, Krause D (2013) An assessment of methodical approaches to support the development of modular product families. In: Lindemann U, Venkataraman S et al. (eds) Proceedings of the 19th International Conference on Engineering Design (ICED13). Lightning Source Inc., La Vergne 41. Salvador F (2007) Toward a product system modularity construct – literature review and reconceptualization. IEEE Trans Eng Manag 54:219–240 42. Schuh G (2005) Produktkomplexität managen – Strategien – Methoden – Tools. Hanser-Verlag, München/Wien 43. Shannon CE, Weaver W (1949) The mathematical theory of communication. University of Illinois Press, Urbana 44. Simpson TW, Bobuk A, Slingerland LA, Brennan S, Logan D, Reichard K (2012) From user requirements to commonality specifications – an integrated approach to product family design. Res Eng Des 23:141–153 45. Steward DV (1981) The design structure system – a method for managing the design of complex systems. IEEE Trans Eng Manag 28:71–74 46. Stone RB (1997) Toward a theory of modular design. Dissertation, The University of Texas at Austin 47. Ulrich K (1995) The role of product architecture in the manufacturing firm. Res Policy 24:419–440 48. Verein Deutscher Ingenieure (1993) VDI-Richtlinie 2221  – Methodik zum Entwickeln und Konstruieren technischer Systeme und Produkte. Beuth-Verlag, Berlin 49. Verein Deutscher Ingenieure, VDI 2206 (2004) Entwicklungsmethodik für mechatronische Systeme. Beuth-Verlag, Berlin 50. Zamirowski E, Otto K (1999) Identifying product portfolio architecture modularity using function and variety heuristics. In: ASME design engineering technical conference

5

Modular Product Structure Strategies

A strategically oriented development of modular product structures is an effective measure to avoid, reduce and master the complexity arising from a variety of products and processes in the company. The aim is to ensure that the planned variety of products is not transferred one-to-one to the internal variety of components and processes. At the same time, as described in Sect. 4.4, many other advantages can be achieved in all product life phases by identifying these potentials and aligning product structures accordingly. Modules make excellent product structure order units, and decoupling them serves to reduce complexity in all life phases. The aim of modularization is to precisely define the modules in a way that is coordinated over the product life phases and not necessarily to create a product that is as modular as possible. Terms such as platform, modular system or common parts strategy are used more and more frequently in the media, technical literature, and practice. These product structure strategies are often understood and implemented very differently. Transparency about the basics and possibilities of product structuring is thus becoming increasingly difficult. The aim of this chapter is therefore to provide an overview of the solution space of the product structure strategies and at the same time to provide support in the fundamental decision making process of the product structure strategy. It is important to be able to develop the appropriate product structures for your own products in a targeted and scalable way, and to be able to combine the basic product structure strategies as principles. These are presented here. In this chapter, an overview of various product structure strategies is given in Sect. 5.1 as an Introduction. Common strategies such as platform, modular kit, or equal module strategy are then presented in Sect. 5.2 and differentiated from each other.

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However, these product structure strategies do not represent separate alternatives. Rather, they describe individual, fundamental ideas for structuring products. A product will rarely be structured according to only one of these strategies. Instead, the strategies can be scaled and combined in different ways. The parameters according to which this can be done and the scope for doing so are shown in Sect. 5.3.

5.1 Overview of Modular Product Structure Strategies The product structure describes the physical and hierarchical composition of a product from its components and their relationships. Modular product structuring is based on the definition of modules, that is, the combination of components of the product and their decoupling from the rest of the product (see Sect. 4.2). The advantages that can be achieved in this way can enable potential savings in all phases of the product life cycle (see Sect. 4.4). Methods of modularization are presented later in Sect. 6.4. The general procedure of modularization is first explained in Sect. 5.1.1. The goal of modularization is to develop an ideal modular product structure. This does not only consider the structuring of the product alone: it is closely linked to the variety of the product range and the processes and resources of all product life phases, including the user application (see Sect. 4.1). This results in different potentials, which can be made possible by clever module definition within the product structure, with special consideration of both the various product life phases and the product lines up to the entire product range. Product structuring is strategically important to a company, which is why this book presents general product structure strategies. The term is defined in Sect. 5.1.2. Section 5.1.3 shows the different options available for designing a modular product structure strategy. Certain strategies for product structuring have proven to be particularly useful and have become known through best practice examples from the industry. Essential here are the platform strategy, the modular kit [strategy?], and the common module strategy, which are explained in Sect. 5.2. These represent individual lighthouses in the solution space of various strategies of modular product structuring and at the same time showcase the basic principles of product structures. Different sources give altering differentiations of essential strategies for product structuring, e.g. according to Schuh the platform with module variants, basic modules with module variants, generic and free modularisation [19] or according to Pine the component sharing, cut-to-fit, component swapping, bus, mix, sectional or slot modularity [16], based on [21]. This conceptual distinction, however, is based solely on a different granularity of the modules and is too difficult to distinguish for a strategic selection and development of a modular product structure strategy.

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It should be noted here that the product structure strategies platform, modular kit and common module presented in this chapter represent individual “beacons” in the solution space of the product structure strategies. However, these are not to be understood as categorical alternatives, but can be combined with each other as basic principles of modular product structuring.

5.1.1 Generic Procedure of Modularization cc Modularization and Product Structuring  Modularization is the goal-oriented development of the modularity of the product structure with the concrete specification of modules and their interfaces (see Sect. 4.2). For this purpose, the product structure is broken down into suitable components (decomposition) depending on the respective objective, the scope and boundary conditions. The components are then analyzed and grouped in new modules according to technical-functional and/or product-strategic aspects (see Fig. 5.1). The new modular product structure is developed and designed. It is essential that the goal of modularization is not necessarily to achieve the highest possible modularity of the product structure, but rather a modular product structure that is optimized strategically, company-specifically, and product-specifically to achieve advantages in all product life phases. The terms modularization and product structuring can be understood synonymously, as modularization is the basic definition of the product structure. Various approaches for the modularization of a product structure have been developed as a result of differing objectives (see Sects. 4.1 and 6.4). The general procedure, however, is very similar among all approaches (see Fig. 5.1). This is explained below. Step 1 – Decomposition of the Existing Product Structure An existing product structure has been created in its grouping of assemblies, sub-­ assemblies and components, usually over a long period of time for various reasons and often in a relatively unstructured way. It is documented in the form of bills of material and is closely linked to the existing process flows. In the process of modularization, this existing product structure should be broken down and rearranged in a streamlined way. The first step must therefore be to define the product scope to be considered and its decomposition into the smallest units to be considered (see Fig. 5.2). Existing assemblies are seldom suitable for this, since they already define a structure for the product. Individual parts are also usually not the appropriate level of consideration since many of them can already be meaningfully regarded as inseparable units. Due to the very high number of individual parts in many products, the subsequent steps of modularization at individual part level are too labor intensive. Therefore, one does not typically find the level of detail or structure necessary for modularization in the usual product structure documentation.

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Decomposition of the existing, hierarchical products structure Product Component D

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For these reasons, the product family to be modularized must first be broken down into suitable units for further consideration. The term component is used to denote the smallest unit to be considered for modularization. As defined in Sect. 3.2.4, the term component is often used synonymously with the terms single part or assembly [15] but can also describe an assembly. The term is usually not fixed in the product documentation, such as in parts lists. In the context of modularization, on the other hand, components are defined during decomposition of the product structure. They are defined at different levels of detail, depending on the appropriate level of analysis. Defining the components is very important because it is the starting point for rearranging the product structure (see also Sect. 3.2.4). During decomposition, the level of detail of the resulting components should be independent of the currently defined assembly structure. It can be oriented on the complexity of the product under consideration and the planned work capacity of a modularization project. The level of detail of the decomposition may vary considerably in different parts of the product. Suitable components may be based on the assemblies and sub-assemblies of larger products. However, individual parts can also be defined as components if they are of high technical or strategic importance for the respective modularization project. The assembly process also plays an important role in decomposition. If the focus is on reducing the product variety, decomposition should also be oriented towards the variety required by the customer. This leads to components that have a direct influence on a variant product property from the customer’s point of view. In Fig. 5.2, for example, the sensor represents a selection option for the customer or it could be adapted to the customer’s wishes. When modularizing a product family with many variants, it makes sense to define such parts as individual components so that they can be considered in configuration modules later. If the entire drive in Fig. 5.2 can be can be customized to different performance levels, the drive assembly should be defined as a component for the modularization.

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By defining a new decomposition at the beginning of a modularization project, the analysis and regrouping can be carried out detached from existing structures. It is important for the result of a modularization project that the decomposition is regularly checked from different views (life phases) during the procedure and revised if necessary. Step 2 – Analysis of the Components For the later module definition, the individual components are first analyzed according to their suitability for being grouped into modules (see Fig. 5.3). Depending on the objectives of the modularization project, various reasons for the later module definition can be considered. In general, these so-called module drivers can be divided into technical-functional interactions, organizational requirements, aspects of process improvement, and product-­ strategic boundary conditions (see Sects. 4.1 and 4.4). The individual components are then further examined, including their couplings to other components. The reasons for combining different components into different modules are determined. Depending on the objective of the modularization project, different properties and characteristics of the components are examined. If necessary, further requirements, boundary conditions, processes and systems, such as the necessary variety of products or production and assembly processes are then examined in greater detail. During the analysis, it may be necessary to iteratively adjust the decomposition of the components. The identified potential for module definition is used in the following step for the actual process of modularization when defining the new modular product structure. Step 3 – Definition of Modules During the actual modularization, the components are grouped into defined modules based on the previous analysis (see Fig. 5.4). Components that have specific similarities or characteristics dependent on the respective objective of the modularization are grouped together in this step. In some approaches, these groups are appropriately referred to as module candidates [2, 6]. Depending on the objectives of modularization, different reasons for module definition can also lead to contradictions regarding the final module structure. These must be compromised on or otherwise constructively resolved in the following transfer into a modular product structure.

Component A

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Fig. 5.3  Analysis of the components as the second step of modularization

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Fig. 5.5  Definition of a new, modular product structure as the fourth step of modularization

Step 4 – Transfer to a Modular Product Structure The defined module candidates represent a recommendation for the formation of the modules. Technical and economic reasons sometimes make their direct implementation into a new, modular product structure difficult. For this reason, the module candidates must first be converted into a new modular product structure in step four (see Fig. 5.5). This may require redesigning components and redefining new interfaces, with all related documents adapted accordingly. Adaption of corresponding processes is also essential. If, for example, a new assembly module is created to simplify assembly processes, this must be coordinated and implemented accordingly. As an important result, the newly defined modules now form the smallest units that must be handled and communicated within the company from here on. As an example, this could mean that only the newly-defined modules are used for the configuration of product variants, or that the exchange of defective components in the service area is carried out on the basis of these modules. The structuring of the products and the entire documentation and handling of the product structure in all product life phases can thus be significantly simplified.

5.1.2 Definition of Product Structure Strategy The processes of all life phases during the creation and use of the product strongly depend on the product structure. Because of the close integration of the product structures into the overall business strategy, this we speak of a product structure strategy.

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cc Product Structure Strategy  Product structure strategies are policies within a company regarding the execution of product structures to achieve the company’s goals. As a corporate strategy, it is valid across the entire product range and has a medium- to long-­ term orientation, usually covering at least one product generation.  The definition and development of the product structure strategy is a task of the product development department. The product structure is closely linked to the processes of product creation, its use, and its disposal. Many product creation processes are fundamentally dependent on product structuring. The definition of product structure strategy must therefore be closely aligned with corporate strategy. Because subsequent product life phases are dependent on the product structure strategy design, its partial aspects, such as the introduction of a common module, must be coordinated with all departments. The processes of the product life phases depend on the product structures across the entire product range. At the same time, any potential stemming from the joint use of modules and product structures can only be exploited through the coordinated development of the product structures of several product families and product lines. For this reason, the product structure strategy is understood to focus on at least one product family and span up to the entire product range. Frequently, the organizational structures in development are strongly separated by product lines and product families. In order to exploit potentials across the product range, these must be identified and implemented jointly. For many companies this offers great savings effects and competitive advantages.

5.1.3 “Solution Space” of Product Structure Strategies The product structure strategy comprises various measures to create suitable modules in order to better support the processes and requirements of all product life phases. Before the typical product structure strategies are presented in Sect. 5.2, the solution space in which these individual modularization measures can be implemented is first shown here for a better overview. Modular construction kits or platform strategy as “beacons” in the solution space of the product structure strategies are not to be understood as categorical alternatives. The motivations for defining the product structure strategy may be varied (see Sects. 4.1 and 4.4), since advantages can be achieved for all product life phases. These motivations can be summarized in the following groups. –– Reduction of complexity – By creating suitable modules, the internal complexity of product creation is reduced. –– Organization and process strategy – By creating specific modules, organizational units or other resources can be better utilized and process design can be improved. These potentials can be developed for all product life phases. The selected module

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strategy also has a strong influence on batch sizes and economies of scale, which are particularly large in the areas of purchasing, production, and assembly, and directly influence manufacturing costs. –– Product benefits and functionality – The formation of certain modules, such as replacement and maintenance modules, creates significant benefits for product use. –– Product strategy – Strategic requirements leading to the formation of certain modules offer several advantages, such as a future change to a new technology or a supplier strategy. For the sake of clarity, individual measures of product structuring can be described by four basic parameters. These parameters are the level within the product structure, the area of the product structure of the products involved, the scope of the product range involved, the degree of commonality, and the planning interval (see Fig. 5.6). Level Within the Product Structure Measures can be located at different levels within the product structure. Figure 5.7 shows two examples of how modules can be defined at very different product structure levels. For example, load sensors for elevators are often standardized across the entire product range at the individual component level (see Fig.  5.7, left). They can be easily configured, installed, exchanged, or retrofitted as purchased modules with simple interfaces [8]. At a higher level of the product structure, modules are often formed that are designed for use within a product family, such as the platform of a herbicide spraying device for plantations, which comprises a large proportion of the components of all product variants [10] (see Fig. 5.7, right). Several product structuring measures can be combined in one product at the same time at different levels of the product structure. In this way, a common module strategy can be

…

Fig. 5.6  Qualitative classification of key product structure strategies, by Gebhardt et al. [7]

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Product range Product lines

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Fig. 5.7  Examples of product structuring measures at different levels of the product structure, according to Gebhardt et al. [7], Kipp [10]

defined independently of a module or platform strategy at a higher level of the product structure. A product structuring measure does not have to cover the entire product structure, but can often be limited to certain parts of the product structure to reduce effort and achieve success. This is closely linked to the level of the product structure just described, since elements at higher levels of a product structure automatically have a larger share of the product. In parallel, different measures can be combined in different areas of the product structure (i.e. in different assemblies), each of which can have different objectives and designs. Scope of the Product Range If modules are used together across parts of the product range, different sub-areas can be included. This can include only one product up to common modules for the entire product range. Product families and products can be included in individual measures of the product structure strategy regardless of their affiliation to product lines. Figure 5.8 shows an example of a module used for one product only, and one used across almost the entire product range. Floor cleaning robots often have a dust collection container as a removable module (see Fig. 5.8, left). This makes it easier to empty the container without having to lift the entire weight of the robot. It also makes cleaning and maintenance easier. However, as a product structuring measure, the module is limited to the product floor cleaning robot. The second example (see Fig. 5.8, right) shows the product range of a manufacturer of agricultural herbicide spraying devices, in which a rotary nozzle is used as a common module for large parts of the product range [10]. The rotary nozzle shown here enables precise dosage of the spray agent and can be purchased more cheaply due to the increased number of units resulting from multiple use [5].

5.1 Overview of Modular Product Structure Strategies

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Rolling devices

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Module „Rotation nozzle“ as core technology in many product lines of a manufacturer of herbicide sprayers. Tractor attachments

Handsets

Fig. 5.8  Examples of product structuring measures across different scopes of the product range

standardized

individual

Standardized load cells for a product range of elevators Product range Product lines

Individual adaptation of a computer mouse through additive manufactured modules

Fig. 5.9  Examples of product structuring measures with varying degrees of commonality. (Example on the right, courtesy of ROCCAT GmbH)

Degree of Commonality In the case of the multiple use of modules, the question always arises as to how much the solutions used should be reduced to just a few standards, or whether several, differentiated solution variants should be retained (see Fig. 5.9). The cost savings resulting from standardization must be weighed against the differentiated fulfillment of requirements of a higher number of variants. A reduction to a few or only one standard represents a more favorable solution in terms of manufacturing costs, but due to the danger of incorrect dimensioning, it represents a quality risk in some product variants, which may not be offset by the savings effect of the increased number of units. By reducing the number of module variants, however, the complexity costs can usually be significantly reduced. On the other hand, several differentiated solutions offer products that are better adapted to different requirements. This can outweigh the resulting increase in manufacturing costs

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through improved customer benefits. Complexity costs are inevitably increased when deciding on several, differentiated solutions. Their long-term extent is very difficult to estimate (see also Sect. 2.4.2).The influence of the number of different variants of a module on the complexity costs is much more severe than the comparatively well assessable production costs and can quickly be underestimated when deciding between standardization or differentiation of a module and its variants. The load cells in elevator construction already shown in Fig. 5.9, left, are an example of a highly standardized solution for large areas of the product range. Due to the adjustability for different rope diameters and types, one module standard can be used for many elevator sizes. In contrast, the gaming mouse in Fig. 5.9, right, can be individually adapted by the customer either in cooperation with the manufacturer or independently by means of additively manufactured housing parts and operating components. Communality can be understood as going beyond the common use of modules in product variants or across product families and lines. If a single solution cannot be used as a standardized module across different product families and lines due to too different requirements (see Fig. 5.10, left), it must be provided in different variants (see Fig. 5.10, top right). These can, however, be designed in such a way that communality in the processes of all product life phases can be maintained as far as possible (see Fig. 5.10, bottom right). For this purpose, process-relevant features of the modules per product life phase must be designed as communally as possible. These can be, for example, suppliers,

Common module (physical communality)

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documents, processing steps, clamping surfaces, or functionalities. Only absolutely necessary differentiating parameters from the customer’s point of view should by varied between the individual variants of the components (see Sect. 4.6.2). The strategies and procedures of Mass Customization address the production of variant products in large quantities. Mass Personalization integrates the individual adaptation of product characteristics to the wishes of individual customers with the concept of Mass Customization and thus attempts to make mass production more viable for individual products [1] (see Sect. 7.2). Planning Interval Individual measures in the product structure strategy can be planned over different time periods. One can plan to reuse existing solutions or plan multiple uses. In the short term, the product structure can be adapted in order to handle modules particularly well in the organizational structure and the specific competence in the development department. In the medium term, the recurring processes of the product life phases of procurement, production, distribution, use, and recycling are better supported by product structuring measures. Long-term oriented measures support strategic guidelines through product structuring. For example, components that are subject to long-term changes in technology are combined into a module that can be easily separated out, as it becomes necessary to alter the product structure later on.

5.2 Specific Details of the Product Structure Strategy As far as product structuring is concerned, various principles have proven to be useful and have achieved recognition through best practice examples. The most important of these are the platform, modular kit, and common module strategies. Based on various modularization projects, the experience gained makes them particularly suitable for keeping the internal variety of components and processes in the product range low to provide a planned variety of products on the market. However, as shown in Sect. 5.1 above, these product structure strategies do not represent strictly alternative solution strategies for product structuring. In practice, these strategies are rarely used in isolation, but are scaled and combined in different ways. They therefore provide basic ideas for product structuring, whose company-specific combination enables the potential of modularization. In the following, the common module, modular, and platform strategies will be presented as essential product structure strategies.

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5.2.1 Comprehensive Multiple Use of Modules/Common Module Strategy A simple and widespread approach to reduce internal variety is to use modules in different product families and lines – as widely as possible. In the literature, the term common parts or common parts strategy is often used in this context, which “can be used over a wide range of the product spectrum” and which allow for economies of scale due to higher quantities [15]. Due to the obvious reference to individual parts, the term common parts can be easily understood as being reduced to a mere standardization of parts. For this reason, we speak here of a multiple use of modules or a common module strategy and, on the other hand, of standard parts. cc Multiple Use of Modules  Multiple use of modules means the systematic use of identical modules over several parts of the product range in different products. In the case of multiple use, modules are used in different products of the product range or even across the entire product range. The aim is to reduce internal variety by avoiding new developments and to use economies of scale. The feasibility and the savings achieved can be supported by developing a suitable product structure. Possible transfer modules are to be identified, decoupled and developed with regard to their interface and performance features in such a way that they can be used across the entire product range. In order to increase the probability of a takeover, this inevitably leads to smaller module sizes compared to other product structure strategies. The multiple use of modules focuses on average on a medium level of the product structure. In addition to achieving better economies of scale, the advantage is that future development projects can make use of existing modules, thereby reducing development costs and risks. If possible, suitable modules are developed immediately with the aim of simple and later use in new product variants, product families or for the entire product range. Due to the similar functionality, a manufacturer of forklift trucks identified the driver displays of all forklift trucks in the product range as a transfer module and developed a modular concept accordingly (see Fig.  5.11). A complete common module strategy would provide a standardized display module. However, since the requirements across all product lines differ too much for an identical display to be installed in all vehicles, three different display variants were developed. Compared to the development of displays individually for each vehicle, this multiple use offers significant savings in all life cycle phases due to a smaller variety of components and higher quantities. This uniform operating interface across all vehicles facilitates handling and is also an important recognition factor for the products on the market. ◄ In order to develop modules for multiple use, components within the product structures are chosen based on whether they can be used identically across several areas of the product range. Another type of component to be chosen are components that could be used across product ranges in the future by means of an adaptation or new development.

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Forklifts

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Fig. 5.11  Example of multiple use of modules, according to Leichnitz et al. [13]

Depending on the variety of the products, smaller assemblies may be more appropriate, as their functionality and specifications tend to be better reusable across product lines. A product structure strategy characterized by multiple use of modules can usually be realized by a product structure with a larger number of modules, each with a smaller scope. Contrary to the actual definition, the term modular system is often used in practice for simple multiple use of modules across the product range. In actuality, this term refers to the use of different modules to create different product variants through their combination [3, 15]. Modular strategy and multiple use both aim to increase the number of units and the resulting savings through economies of scale. The multiple use of modules achieves this by using the modules as widely as possible across the product range. A modular system, on the other hand, aims at the rapid configuration of different product variants within a product family. cc Standardization  Standardization is the creation of parts and components that are used in the same way, preferably or mandatorily, over significant parts of the product range up to and including industry-wide over a significant period of time.  Standardization involves a comprehensive search for various components from the parts master that have sufficiently similar functions and specifications to be replaced by identical elements. As a rule, this can be done without reference to a specific product. Alternatively, several components can be defined in advance without analyzing the existing parts. The aim is to reduce internal company variety, to avoid additional work through new parts and to use economies of scale. The concept and procedure of standardization can also be applied to procedures and processes. Standardization focuses on parts and components at a low level of the product structure. Due to their smaller scope, these offer greater potential for broad multiple use across the

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product range. Due to the small size of these parts and components, it is not necessary to adjust the product structure. At the same time, potential savings can be achieved with comparatively little effort and risk by standardizing parts and the corresponding processes in procurement, quality assurance, production, and maintenance. Documentation is important for better availability, for example in ERP or PDM systems, as well as a classification and search system, which offers the designer easy access to the existing standard components for a design task. Comparable to the standardization of parts and components are machining features that do not standardize the parts themselves, but do standardize geometries and machining steps. Very closely related to these are industry standards as a repeated application of an identical technical or organizational solution with the aim of a time-limited technical and economic optimization [4]. Standards can exist in the form of a catalogue, an internal company standard, or a national or international standard. Standardization in the true sense of the word is not counted among the product structure strategies here, since it can be implemented mostly independently of product structures. In addition, the cost reduction potential of modular product structure strategies is usually greater for products with a wide external variety.

5.2.2 Size Range Series The development of size range series is a design principle for creating size variants of a product, modules, or components according to different criteria. Other variety, such as in the scope of functions or regarding special designs, cannot be represented by the principle. cc Size Range Series  Size range series comprise a number of components, modules, or products that are identical except for one or a few determining parameters. They thus share the functionality, the design solution and ideally also the manufacturing process. The parameter to be scaled is a size-defining measure, so that the performance of the component can be scaled using the parameter.  The aim of using a size range series is to offer different variants by selecting a size and to achieve lower development costs and high process and solution communality by simply scaling a technical solution, thus achieving savings effects in the product life phases. Risks are an inadequate definition of the number and sizes, which is uneconomical to produce or is not accepted by the customers. The size range series is well suited as a principle for the development of different sized module variants within a modular kit. However, special attention should be paid not to scale the entire module into different size levels at once. First, it should be determined which parts of the module do not necessarily have to vary in sizes and these should be separated into a standard module that is not scaled (Fig. 5.12).

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Fig. 5.12  Principle of the size range series applied to a module (left) and a complete product (right)

The development of size range series calls for the use of so-called “similarity laws”, in which, starting from one or a few basic designs, further stages are scaled in such a way that the design remains valid for them as well. This is achieved by calculating the influence of the size change on stresses and then dimensioning the size steps in such a way that the material stresses remain constant in all steps [15]. An essential aspect of series development is the definition of the number of stages over the intended size range. If the number of stages is set too low, low costs can be generated by high quantities, but if the stages are frequently over-dimensioned, sales might be too low. Conversely, if the number of steps is too high, the advantage in terms of the number of variants is reduced. In addition to mathematical series and standard number series, optimization methods such as cluster analyses and genetic algorithms have also been used for some time now [11] (Fig. 5.13).

5.2.3 Modular Kit Strategy The modular strategy is a fundamental principle for providing high product variety while keeping internal variety as low as possible. Modules with defined interfaces are used to easily configure different product variants. cc Modular Kit Strategy  In the modular strategy, a set of different modules is used to create product variants by combining them. The aim of the strategy is to map the externally required product variants with as few modules as possible within a product family. In addition, modules for other product families can also be used. The modular strategy reduces the number of components and modules used, which in turn enables a significant reduction in company internal complexity. A further benefit are economies of scale within a product family through the common use of the modules.  In the modular strategy, individual, interchangeable modules are formed as independent units that are strongly connected to customer requirements and their variations, in order to enable the configuration of different product variants with a minimum number of modules.

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Fig. 5.13  Example of a size range series of pressure control valves. (Courtesy of Mankenberg GmbH)

Elevator cabins are variant products that are individually tailored to the dimensions of the elevator shaft as well as to the functional and aesthetic requirements of the customer to cover different market segments. In order to avoid having to design and manufacture each car individually within the company, elevator manufacturers are increasingly relying on modular kits to produce any desired car variants by configuration instead of design [8] (see Fig. 5.14). ◄ Depending on the customer’s order, various modules are combined with each other to first build the load-bearing structure adapted to the required dimensions and load capacities. Separated from these primarily load-bearing modules, wall modules are then configured, which allow a choice of colors and materials and can be individually and easily configured by gluing on wall coverings. All interfaces and the non-visible modules remain identical in their design. Finally, further decorative and functional modules are added to equip the cabin. All modules, which are dependent on variant dimensions and positions, are parametrically designed, so that they can be adapted comparatively easily to individual orders. ◄ The main objective of modular strategy is the rapid configuration of product variants through minimal internal variety as well as a broad use of the modules with the resulting potential savings due to economies of scale for higher volumes. The reuse of former development efforts by transferring existing modules into new products is also a major advantage of the modular kit strategy. This means that it usually starts at a higher level in the product structure than a common module strategy. The modules can also be optimized to meet the requirements of all phases of life. A further advantage is possibility to simplify the product documentation. Documentation for quotations, design, supply, production or even operating instructions can be prepared and stored per module and later combined according to application.

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Module kit „floor“

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Fig. 5.14  Example of a modular kit for the configuration of variant elevator cars. (Courtesy of Lutz Aufzüge)

A distinction can be made between closed and open modular kits, depending on whether the range of products that can be configured is fixed or open (see Fig. 5.15). Open modular kits are often found, for example, in production plants or storage systems, where any systems can be put together by adding further modules from the modular kit [15]. Modular kits can also be distinguished according to their visibility to the customer (see Fig. 5.15). Pure manufacturer kits are only used internally in the company to configure product variants. User kits, on the other hand, can be used by the customer when selecting or changing the product. The terms modular kit/module and building set/building block respectively are often used synonymously. What they have in common is the aspect of configuring product variants from elements (modules or building blocks) with different subfunctions. A building set is understood as “a combination system of components and assemblies in general to products with different overall functions” [3]. A building set can thus be seen as an application form of a module strategy.

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Manufacturer modularity

Selection and assembly of individual modules by the customer for a herbicide sprayer

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Fig. 5.15  Examples of open and closed or user and manufacturer modular kits. (Examples courtesy of Lutz Aufzüge & Co KG, Mantis ULV Sprühgeräte GmbH and Jungheinrich AG)

The use of modular construction kits leads to reduced internal variety because a defined number of modules can be used to create many variants. However, a modular strategy does not necessarily have to result in the creation of a complete modular system for the entire product structure. The principle of a modular kit can also be applied to specific areas of the product structure without the need to develop a complete modular system (see Sect. 5.1.3). In addition to the use of modular kits, it is also useful to employ size range series modules within the framework of a module strategy by parametric sizing of certain modules. Product structuring and variant creation using a modular system allows for greater freedom when configuring product variants. The variety of products offered by a modular product structure can be adapted at a later phase after the start of production, although in the best case this should be taken into account in the early development of the modular product structure (see Sect. 7.1). Changes can be particularly challenging if the modules are configurable in many different combinations to form product variants and the effects of changes in all possible combinations must be estimated. The ability to combine individual modules, which is necessary for a modular system, poses special challenges for the interface design. More interfaces are often necessary for better combinability within modular kits. For many products, more interfaces result in additional manufacturing costs and challenges when it comes to quality and installation space requirements. In the case of special lightweight design requirements, the potentially higher number of interfaces poses a particular challenge for the development of a modular product structure strategy (see Sect. 7.4). Furthermore, additional interfaces in electrical

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connections often reduce the safety and reliability of the product. In order to be able to mount different modules on one interface, some of them have to be oversized, for example to bare higher loads. When searching for a suitable compromise in the development of a modular product structure, the departments concerned must cooperate and coordinate their objectives. In the beginning, a modular product structure strategy is more complex than a common module strategy due to the comprehensive planning and design of modules over different life phases. However, the achievable savings in variant-induced complexity costs are significantly higher.

5.2.4 Platform Strategy At first glance, a platform strategy can be seen as a special version of a modular strategy. This involves combining modules that are standardized across all product variants of at least one product family and that can be regarded as stable for the future into one large module, the so-called platform, that is standardized for all variants of the product family. This forms the basis for the configuration of all product variants of a product family and for the future derivation of new variants. This principle is frequently extended, since the term platform can also include the connected processes, knowledge and even persons or organizational structures which can be used over a longer period as the basis for an entire product family [18]. cc Platform  A platform is the overarching, common basis of a product family. For this product family, the platform contains all components that are used for each product variant (see Fig. 5.16). If feasible, other areas may be relevant for the creation of a platform. For example, it can also include additional processes, knowledge, people, and organizational structures. The platform thus forms the basis for all product variants within a product family, which can be efficiently derived and produced with the help of the platform. This ensures that the standardized platform is associated with significant economies of scale.  Product A

Product B

Fig. 5.16  Basic principle of a platform strategy

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On the basis of a platform, different product variants are generated by configuration with the help of additional modules. Ideally, the platform or at least large parts of it can be used over several product generations, so that the life cycle of the platform can be decoupled from that of the derived product variants. The platform comprises the combined share of all product variants of a product family, which in practice is typically 30–60% [12]. Due to this scope, the consistent use within a product family and the medium to long-term orientation of a platform, the core technologies and competencies of the company are usually bundled in the platform. Due to the relatively large share of the platform in the overall product, there is a high degree of specialization for the respective applications, which makes a platform often restricted to one product family. The often considerable savings of a platform strategy are due to the standardized reuse of the platform with identical components and processes, especially in manufacturing. Due to the high proportion of a platform in the product, its broad use and long-term orientation, other product structure strategies are often combined with a platform. A common strategy in this context is a scalable platform, in which different sizes of the platform are provided according to the principle of a size range series in order to generate different performance levels of the product [17, 20]. Based on a platform, the principle of a modular system can be used to create different product variants by combining the platform with further modules. Galleys for passenger aircraft are adapted to the airline’s specific customer order based on different requirements [9]. ◄ In addition to the external dimensions and connections of the galleys for different types of aircraft, the equipment with different numbers and designs of stowage compartments, trolleys, beverage dispensers, or refrigerators is adapted to meet customer requirements. The resulting high degree of company internal variety and the strict approval regulations of the aviation authorities force manufacturers to adopt product structure strategies that can reduce the resulting expenses. Figure 5.17 shows an example of a platform strategy for an aircraft galley, divided into variant and standard parts. Components that can be unified for all variants are combined in the standardized platform. This includes the supporting basic structure with the necessary interfaces. Based on the platform, product variants are derived by configuring different modules that can be combined with each other. Further modules allow the individual consideration of different connections and special requirements. The platform strategy offers the advantage of the highest possible standard share with the corresponding advantages of the same processes in production and design. The verification process can also be significantly simplified. The example also shows the typical combination of a platform strategy with the principle of a modular system for configuring product variants by combining modules based on the platform. ◄

5.2 Specific Details of the Product Structure Strategy

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Fig. 5.17  Example of a platform strategy for a family of aircraft galleys, according to Jonas [9]

A special application of the principle is a platform in the form of a common product architecture, also called standard architecture (1994 ASME Computers In Engineering Conference). The spatial and functional division of the product is unified and maintained. The platform consists primarily of a standardized layout plan of the products, without necessarily standardizing concrete components. This standard architecture can be adopted in the next product generation. Platform development must consider in advance the product variants that will be offered in the medium and long term beyond a certain time horizon and possibly in different market segments with different customer requirements based on the platform. The positioning of the platform concept between standardization and differentiation is one of the greatest challenges in platform development [18]. The development of the platform is associated with increased expenditure and thus, due to the long-term orientation of the platform, a significantly better planning reliability must be achieved. In addition to the current requirements, future changes must also be estimated and considered. At the same time, error effects from platform development are potentially greater, since they cover all variants. However, the one-off development costs can be more than compensated by the long-term benefits [14].

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5.3 Development of a Product Structure Strategy For the development of a suitable product structure strategy, the product structure strategies of multiple use (in the sense of a common module strategy), modular kit or platform strategy do not form mutually exclusive decision alternatives. Rather, they are to be seen as individual “pillars” in the solution space of product structure strategies and can be understood and combined with each other as basic principles of modular product structuring. When developing a product structure strategy, it is helpful to understand these basic strategies and apply their principles to a product range to derive the company- and product-­ specific product structure strategy. This strategy is usually a combination of the basic strategies. –– When combining various product structuring measures, it is essential that these are differentiated according to the parameters presented in Sect. 5.1.3. Different product structuring measures can be applied to different levels within the product structure and do not have to cover the entire product structure. The scope can be set at different levels of the product structure. –– The parts of the product range involved in a product structuring measure may comprise only one product, one or more product families or lines, or even the entire product range. –– The time schedule used to plan the strategies and their individual measures can be a short-term reuse of existing modules or a long-term pre-planned strategy. –– The degree of commonality describes how much the solutions used are reduced to a few standards, or whether several differentiated solutions should be retained. It is helpful to consider the granularity of modularization and its suitability for different product structure strategies when classifying various product structuring measures (see Fig. 5.18). In general, modules with a smaller scope are better suited for broad use in different products across the product range. They include a smaller scope of functions and proportion of the products. Modules with a large scope are less suitable for use in other product families and product lines, since their large scope means that they are more likely to be restricted to one application area. As the standard basis for all variants of a product family, a platform forms the limit of the module size. A product structure strategy with intense multiple use of modules exhibits a repertoire of modules of small to medium size, which should be reused as often as possible across the entire product range. A module or platform strategy, on the other hand, usually focuses on the simple provision of a wide range of products. A platform is particularly characterized by the bundling of the standard share of the product variants of a product family over a longer time horizon. Platform development is closely related to modularization, since the creation of modules for variant configuration based on the platform is particularly useful.

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 Great potential as standard or platform of the product family  Easily optimized for one product family  Few interfaces  Hardly any synergies possible over the whole product range

Fig. 5.18  Overview of the typical product structure strategy according to the granularity of modularization

Literature 1. Baumberger GC (2007) Methoden zur kundenspezifischen Produktdefinition bei individualisierten Produkten. Verlag Dr. Hut, München 2. Blees C (2011) Eine Methode zur Entwicklung modularer Produktfamilien. Dissertation, Technische Universität Hamburg-Harburg 3. Ehrlenspiel K, Meerkamm H (2013) Integrierte Produktentwicklung  – Denkabläufe, Methodeneinsatz, Zusammenarbeit. Hanser-Verlag, München 4. Ehrlenspiel K, Kiewert A, Lindemann U, Mörtl M (2014) Kostengünstig Entwickeln und Konstruieren – Kostenmanagement bei der integrierten Produktentwicklung. Springer, Berlin 5. Eilmus S, Krause D (2010) Experimentelle Ansätze zur Optimierung von Rotationszerstäubern. In: Gutheil E, Fritsching U (Hrsg) Spray 2010, 9. Workshop über Sprays, Techniken der Fluidzerstäubung und Untersuchungen von Sprühvorgängen, Heidelberg 6. Erixon G (1998) Modular function deployment  – a method for product modularisation. Dissertation, The Royal Institute of Technology, Stockholm 7. Gebhardt N, Kruse M, Krause D (2015) Gleichteile-, Modul- und Plattformstrategie. In: Lindemann U (ed) Handbuch Produktentwicklung. Hanser-Verlag, München, pp 111–149 8. Gebhardt N, Beckmann G, Lüsebrink S, Fischer N, Lutz H-M, Krause D (2016) Projekt ModSupport  – Methodische Entwicklung eines innovativen Modulbaukastens für Aufzugsanlagen. In: Krause D, Paetzold K, Wartzack S (Hrsg) Design for X. Beiträge zum 27. DfX-Symposium Oktober 2016. Hamburg, pp 3–14 9. Jonas H (2014) Eine Methode zur strategischen Planung modularer Produktprogramme. Dissertation, Technische Universität Hamburg-Harburg

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10. Kipp T (2008) Methodische Unterstützung der variantengerechten Produktgestaltung. Dissertation, Technische Universität Hamburg-Harburg 11. Kipp T, Krause D (2009) Computer aided size range development – data mining vs. optimization. In: Proceedings of the ICED09: 17th international conference on engineering design society, Stanford University, California, pp 179–190 12. Kraus PK (2005) Plattformstrategien. Dissertation, Friedrich-Alexander Universität Erlangen Nürnberg 13. Leichnitz, Julia, Eilmus S (2013) Methoden für die Entwicklung modularer Produkte bei der Jungheinrich AG. In: Krause D, Paetzold K, Wartzack S (Hrsg) Design for X. Beiträge zum 24. DfX-Symposium, Oktober 2013, Hamburg 14. Meyer M (1997) Revitalize your product lines through continuous platform renewal. Res Technol Manag 40:17–28 15. Pahl G, Beitz W, Feldhusen J, Grote K-H (2007) Konstruktionslehre – Grundlagen erfolgreicher Produktentwicklung; Methoden und Anwendung. Springer, Berlin/Heidelberg 16. Pine BJ (1994) Maßgeschneiderte Massenfertigung  – Neue Dimensionen im Wettbewerb. Wirtschaftsverlag Überreuter, Wien 17. Pirmoradi Z, Wang GG (2012) Recent advancements in product family design and platform-­ based product development: a literature review. In: Proceedings of the ASME international design engineering technical conferences and computers and information in engineering conference, Washington, 28–31 August 2011, pp 1041–1055 18. Robertson D, Ulrich K (1998) Planning for product platforms. Sloan Manag Rev 39:19–32 19. Schuh G (2005) Produktkomplexität managen – Strategien – Methoden – Tools. Hanser-Verlag, München, Wien 20. Simpson TW, Siddique Z, Jiao JR (eds) (2006) Product platform and product family design. Springer, Boston 21. Ulrich KT, Tung K, Sloan School of Management (1991) Fundamentals of product modularity. Sloan School of Management, Massachusetts Institute of Technology, Cambridge

6

Methods for the Development of Modular Product Families

A large number of processes, methods and tools have been developed for the development and implementation of new product structures. These provide guidelines in various forms for solving specific problems. Some of them support implementation directly, for example in the form of examples, templates, or software tools. However, the various processes, methods, and tools available differ in many ways. On the one hand, they are intended for different starting situations and goals. In some cases, they only address the implementation of specific product structure strategies or are limited to individual product types, industries, or company strategies. To make matters worse, the understanding of the terms can vary widely among the many methods and tools offered in the literature. For this reason, this chapter provides a systematic overview of selected methods and tools for product structuring from a scientific perspective. This is done based on the views of modularity and product structure strategies presented in Sect. 4.1, which were described in Chap. 5. For a better understanding, basic terms for the classification of methods and tools are presented in Sect. 6.1. Afterwards, the task areas of program planning are presented in Sect. 6.2 and the development of variety-oriented product families in Sect. 6.3. The different approaches to modularization usually follow a common basic procedure, which is described in Sect. 6.4. Afterwards, selected methods for modularization are presented in Sect. 6.4. The evaluation of modular product structure concepts represents a particular methodological challenge. Corresponding evaluation methods are presented in Sect. 6.5. In order to provide tailor-made methods and tools especially for the task of developing modular product families, the Institute of Product Development and Mechanical Engineering Design at Hamburg University of Technology has developed and is developing the Integrated PKT Approach for the Development of Modular Product Families. This approach is presented in Sect. 6.6.

© Springer-Verlag GmbH Germany, part of Springer Nature 2023 D. Krause, N. Gebhardt, Methodical Development of Modular Product Families, https://doi.org/10.1007/978-3-662-65680-8_6

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6.1 Terms of Processes, Methods and Tools The important terms for the overview and classification of product development activities, such as process, method or partly also methodology and tools are often used differently in the literature and are therefore defined in the following for the context of this book. cc Process, Method, Methodology and Tools  A process is a planned, closed, logical and chronological sequence of work steps intended to achieve a specific goal. The work steps are usually described by name, goal, responsibility, necessary resources, and inputs as well as outputs (see Fig. 6.1 above). A method is a description of a planned approach to obtaining knowledge or results (see Fig. 6.1 below). In product development, a method formally describes an operational procedure and supports the development, design and production of products. Methods support the penetration of even complex problems by breaking them down into manageable subproblems, pointing out conflicting goals and defining focal points for action. Methods should have a cleavr objective, help overcome barriers to thinking, and promote creativity. Methods often include the application of other methods. For such combinations of several methods the term methodology is often used. Due to the combinability of many methods, they are also referred to as method modules or, in the case of extensive and versatile method collections, as a method kit.

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Fig. 6.1   Systematics of processes (top) and methods (bottom)

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Tools are supporting aids for the execution of methods or individual work steps within the methods and range from checklists, forms or templates to visualizations and extensive software tools. Tools have a great influence on the success of a method and represent a resource of the method application. They are the technical instruments to support the methods with their work steps.

Classification of the Presented Methods As described at the beginning, the literature offers a variety of different methods for the development of modular and variant product families, which differ in many ways. On the one hand, they are directed at different objectives and in some cases only address the implementation of a very specific product structure strategy. On the other hand, some of them only provide specific work procedures or even work tools for the application, and the uses of terms may differ among the many methods available. In order to give a rough overview in this method landscape, a selection of product development methods is presented in this chapter. Following the development cycle, methods for planning product programs that have a high variety of products are first listed in Sect. 6.2. Methods for the development of product families with many variants with the objective of minimizing internal company variety are presented in Sect. 6.3. Methods of modularization are dealt with in Sect. 6.4, where their common basic procedure is presented. The methods themselves are presented grouped according to the different views on the topic of modularity described in Sect. 6.4. Evaluation procedures for modular product structure alternatives must meet the demanding task of being able to estimate and evaluate the savings potentials over all product life phases and the entire product life cycle as explained in Sect. 5.4. Special procedures for this are shown in Sect. 6.5. Common key figures are also covered in all subject areas in relation to the methods. The different methods are presented below and for each method a short overview is given with the most important information, such as the addressed initial situation, the desired goals, the required inputs and the procedures. Since 2006, the Institute for Product Development and Mechanical Engineering Design of the authors at the Hamburg University of Technology has been developing the so-called Integrated PKT Approach for the Development of Modular Product Families, which is presented as a methodical toolbox in Sect. 6.6.

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6.2 Methods for Program Planning This section was created under the co-authorship of Dr. Henry Jonas. This section explains a selection of methods for the systematic planning of product programs. The term portfolio planning can be used synonymously in some cases. In the context of the development of modular product families, a major motivation is the orientation of the modules towards easy configurability of the necessary product variety and the associated reduction of internal company complexity while at the same time offering a wide range of products. Therefore, compared to single product development, systematic foresight, segmentation of individual markets, and applications in product program planning are particularly important steps. The methods presented in the following can significantly improve the initial situation by a better anticipated product program for planned product development projects. Methods of future planning, such as scenario techniques or road mapping, are helpful additions. With the help of general methods of market analysis, the activities of product program planning can be meaningfully supported. In Product Program Planning, the components of the product range that will be offered in the future are defined and it is avoided that the planning of product structure strategies is not based on an obsolete product range. It should be noted that common potential between different product families must be recognized and measures must be planned for the long term. The use of modules across product families or even product lines usually requires earlier planning.

6.2.1 Forward Planning Some methods of advance planning look many years ahead and examine global trends that interact with the product portfolio. They are less focused on the technical details of the

External perspective Strategic level Qualitative and long-term Tactical level Qualitative and medium-term Operational level Quantitative and short-term

Internal perspective

Scenarios

Visions (=internal scenario)

Trends

Roadmaps

Forecasts

Planning (=internal forecasts)

Szenario planning  Interaction scenarios  Narrative scenarios  Market analysis

 SWOT analysis  Trend research

 Expert surveys  Delphi technique

 Strategy options  Mission statements  Partizipative vision finding

 Balanced Scorecard  Technology and strategy roadmapping

 Program planning  Business cases  Risk management

Fig. 6.2   Different methods of forward planning (methods presented here in bold), according to Fink and Siebe [22], Jonas [40]

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147

product. Figure 6.2 shows an overview of the most common methods in this field, some of which are presented below. Scenario Technique The Gausemeier Scenario Technique attempts to investigate the future, take into account global trends and produce a comprehensive analysis of the relevant dimensions (see Fig. 6.3). In the first step, the so-called scenario preparation, both the project goals and the so-called design fields are defined. The design fields describe, among other things, companies, products, industries, and technologies. In the scenario field analysis phase, key factors are prepared by defining and analyzing the actual situation, while the scenario forecasting phase provides the actual view into the future. In a three-step procedure, this phase shows several development possibilities for each key factor. Scenario building is finally a summary of future projections that fit together. The central criterion for this summary is consistency, that is, the consistency of individual key factor scenarios. There is exactly one projection per scenario for each key factor. Finally, the task of scenario transfer is to use the scenarios as a basis for strategic management. The scenario technique has a comparatively long-term time horizon and considers environmental conditions on a global level. This makes it possible to investigate far-­ reaching future developments with methodical support. Due to the global perspective, direct effects on the product program are not directly deduced. Roadmapping Roadmaps present linked objects in their chronological order (see Fig. 6.4) and serve to visualize strategic planning. These objects are usually products, technologies, or projects. Roadmaps serve to bundle expert knowledge and to predict and plan future developments in a field of action. Scenario preparation

 Determine objectives  Analyse design possibilities

1 Scenario field analysis

Project goals  Determine areas of influence and influencing factors  Impact analysis  Relevance analysis

Key factors

2 Scenario prognosis

3 Scenario building

4 Scenario transfer

5

 Determine possible developments for each key factor  Create projection catalog  Pairwise consistency evaluation of projections  Determine projection bundle  Cluster similar bundles

Future projections

Future scenarios

 Analyze scenarios  Evaluate probabilities and impacts

Strategic measures

Fig. 6.3   Procedure of the scenario technique according to Gausemeier et al. [25]

6  Methods for the Development of Modular Product Families

Development projects

Product range

148

Fig. 6.4   Principle of a roadmap for planning the product program and development projects

In a two-dimensional search field, consisting of a time axis and an object axis, the current objects and development projects are shown in a creative, sometimes intuitive process. Tools available for the creation of technology roadmaps include exploration as a retrospective projection of the scenario technique. By initially investigating technologies (technology push) and products (market pull) separately and then transferring them to a joint roadmap, consistent recommendations for action can be derived. Roadmaps are a visualization tool. To develop a roadmap, the user is always dependent on suitable and proved creation methods. The time horizon of roadmaps is usually long term, especially when building on the results of the scenario technique. Roadmaps are generally well suited to provide an overview of the development of the product program. However, with a large number of products and possible developments of the product program, the limits of clarity are quickly reached. Delphi Technique In the Delphi Technique, iterative rounds of expert interviews are used to create a forecast. In this respect, new knowledge is not generated by an external analysis, but existing knowledge is brought together and consolidated by consistency considerations. In a multi-stage process, groups of experts are interviewed about technical development trends and their possible course over time. The results are then fed back to the expert groups anonymously. The iterative process is intended to improve the quality of the results and bring them closer to a consensus. Several repetitions can be carried out, in which not only the content but also the consensus reached so far is detailed more and more. Advantages of the Delphi technique are the triggering of cognitive processes, the multi-­ stage procedure and the avoidance of group dynamic problems. The Delphi technique can therefore also be classified as a creative method. However, a comparatively high time requirement must be accepted, which is why the Delphi method is preferably used for analyses with a longer time horizon.

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149

SWOT Analysis With the help of a SWOT matrix comprising four fields (strengths/weaknesses versus opportunities/threats), the factors determined from the environmental and corporate analysis can be compared with each other (see Fig. 6.5). The company analysis reflects the internal strengths and weaknesses, while the environmental analysis represents the external opportunities and risks. The SWOT method compares all four factors and helps to derive concrete strategy recommendations. The best case is the strength/opportunity combination in which a competitive advantage meets a positive environmental impulse. This constellation should be stabilized and strengthened. If a chance meets a weakness, the weakness should be eliminated as quickly as possible. The other possible combinations must be considered in a more differentiated way as risk situations. Strengths can be used to avoid risk situations or to turn them into opportunities. The SWOT method can be used for analysis or to create field-specific forecasts. Preliminary analyses are necessary to apply the method. As a starting point, these contribute strengths and weaknesses as well as opportunities and risks.

Strengths

III Strenghts meets threat

I Strength meets opportunity

→ overcoming threats!

→ stabilize and strenghten!

Weaknesses

Trend Analysis Trends are future developments that have a certain probability of occurrence and influence the company’s activities. The knowledge of these trends can be used as a foresight to identify and derive fields of action. Trend analyses are mostly intuitive and individual approaches. To classify trends, they can be differentiated in terms of their scope into megatrends, which cause global changes, consumer trends, which affect marketing and product concepts, and industry trends, which influence industries and technologies. Based on trend research, which analyses and describes future developments, trend portfolios can be set up and recommendations for action derived from them [25]. Due to their intuitive approach, trend analyses are also suitable for smaller projects. A pragmatic forecast can be created with relatively few resources and without special tools.

IV Weakness meets threat

II Weakness meets opportunity

→ act differentiated!

→ work on weaknesses!

Threats

Opportunities

Fig. 6.5   Principle of SWOT analysis as a comparison of strengths and weaknesses versus opportunities and risks

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This can be used to derive recommendations for action. However, the possible risks of trend analyses lie in the timely and accurate identification of the relevance of trends with regard to one’s own business objectives as well as in difficult consistency checks.

6.2.2 Market Analysis Market analyses create transparency about the sometimes complicated competitive situation. They can also show the economic characteristics of the product portfolio. Stakeholder Analysis The aim of the stakeholder analysis is to analyze interest groups with their attitudes and possibilities of influence. Stakeholders can be groups or individuals who influence the company or are influenced by it. A graphical representation is called a stakeholder map. Here, a network diagram is used to create an overview of the stakeholders analyzed. Following a stakeholder analysis, corresponding fields of action are derived. First, the stakeholders and their members must be identified. It has proven as a good practice to select different groups of “radii”, starting centrally from one’s own area and moving on to global stakeholder groups. Then the stakeholders are evaluated, for example, according to the degree of influence and degree of support. Finally, measures per stakeholder are derived, which have a positive influence on the success of a project. The stakeholder analysis is suitable for deriving fields of action based on the stakeholder groups to the company. These can serve abstractly as a vision for the entire company, but can also be integrated into the operative business in the form of functional models in the form of instructions for action. Competitor Analysis Companies are in more or less pronounced competition. A competitor analysis can provide knowledge about the competition and its competitiveness as well as critical information for fields of action. Based on the analysis of the competitive situation, the company can derive suitable measures to improve its own situation and to make use of advantages over the competition. First, the market shares of relevant competitors are determined for each business segment. Using the resulting prioritization, individual competitors are selected and analyzed in more detail. The fact that the prioritization resulting from the market shares does not necessarily coincide with the actual relevance of the competitor may prove to be a disadvantage. Therefore, the resulting prioritization should only be seen as an indication for subsequent analyses. A model developed by Porter [67] offers an extended view of this. A response profile for competitors can be created using four perspectives: goals, current strategy, assumptions, and capabilities. Compared to market share-based analyses, this approach is future-oriented and, above all, allows a preview to be created for each competitor so that future steps can be forecasted, and countermeasures developed.

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The market share-based analysis of the competition is an intuitive procedure and requires a careful prioritization of the analysis objects. The competitor analysis according to Porter enables the creation of simple forecasts. The relatively simple method is suitable for use in small project teams. Market Performance–Market Segment Matrix The method involves an analysis of the product portfolio by comparing market performance and market segments (sales markets/customer groups) [25]. The market segments can be classified, for example, according to the three criteria of customer type, distribution channels, and geographical customer locations. An occupied matrix field, referred to as a business area, can be characterized by economic indicators, sales volume, earnings before taxes, and sales growth. Depending on the intended goals of the analysis, other key figures can also be used. The market performance can therefore include product groups and service packages. Three criteria of “Independent market performance”, “Share of company earnings”, and “Relative independence of strategic decisions”, can determine the main business areas. Finally, segmentation gaps are identified as market segments that are only insufficiently covered by current products. The method creates an overview of the entire product portfolio and presents the products, customers/markets, and economic parameters. It is also possible to compare different scenarios. Fields of action are determined separately. Market Share – Market Growth Portfolio The well-known portfolio representation, named after the Boston Consulting Group, relates the products with their market share and market growth (see Fig. 6.6) [49]. The diameter of the circle represents the respective turnover. The portfolio is divided into the four fields “Poor Dogs”, “Question Marks”, “Stars”, and “Cash Cows”. Lombriser and Abplanalp summarize standard strategies for portfolio development for the four product types [56]. The ideal development of a product is assumed to be a transition Fig. 6.6   Example of a market share – market growth portfolio, according to Kotler et al. [49]

Market growth Question Marks

Stars

Poor Dogs

Cash Cows Market share

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from “question marks” to “stars” and finally to “cash cows”. Stars are to be developed at comparatively high investments in order to finally convert them into cash cows at relatively low investments. Poor dogs should be liquidated or, if strategically sensible, maintained at low investments. Question marks require further examination as to whether they warrant heavy investment to possibly generate stars, or whether liquidation makes more sense. The market share/market growth portfolio provides a quick overview of the product range. The standardization strategies provide indications of possible directions of thrust, albeit at a very rough level.

6.2.3 Program Planning Product program planning methods combine the external view of trends and markets with the internal view of the technical properties of your own products. Design Driven Portfolio Management The model described by Petersen is intended to support portfolio project management on the basis of so-called design aspects, whereby the program hierarchy is plotted against the two parameters of execution risk and market risk [64]. In addition, the estimated turnover, the current development phase and an estimate of the necessary investment, so-called design quality criteria, are also provided as further variables. The first step is to create a graphical visualization of the current situation. In parallel, critical Design Quality Criteria are determined, which represent potential dangers in development, such as budget overruns or quality problems. On the one hand, this is intended to support product developers in achieving the required design philosophy while, on the other hand, drawing the attention of management to these aspects of portfolio controlling. The analysis model combines new product planning and product program planning. The visualization is particularly suitable for small and medium product programs. For larger product programs, this method has its limits in both the analytical and visual part. Product Program Strategies On the basis of Köster, Schuh builds up four strategic goals, which divide the product program into the categories active standard, legacy and customer-specific individual solutions [48, 76]. Scenario 1  – Customer-specific engineering  – here a growing product program is assumed, whereby customer-specific individual productions are included in the program and a reduction in variety is not necessarily planned. This strategy quickly leads to extensive product programs.

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Scenario 2 – Release engineering – the range of the program remains constant, with new customer requirements leading to new products while eliminating existing products from the program. Scenario 3 – Variant maintenance – the program is characterized by low volatility and an almost constant range of offers, with individual optimizations taking place at the product variety. This strategy is often used in conservative markets. Scenario 4  – Basic type engineering  – regular new developments and a high degree of innovation characterize the program. Complexity is characterized more by market dynamics than by product variety. This strategy is mainly used in new technology markets. There are four steps to help reduce the complexity of a product range: prevention (decisions on the program on the basis of forecasts), avoidance (through a variety-oriented product structure), mastery (measures at the part level), and reduction (redesign to plan and cost data). To avoid variety, the tree of variety is recommended as a tool for the representation of the variant components and the assembly sequence. At the core of this method are four basic scenarios, which help with making decisions on the development of the product range. The decision directions are aimed at questions concerning the elimination of products or variants.

6.3 Product Variety Management and Design-for-Variety The objective of Product Variety Management is, on the one hand, to increase the demand by improved product variety and usability and, on the other hand, to control and reduce the internal costs of product variety caused by the increased complexity of components and processes in the company. According to Wildemann, the disciplines of Product Variety Management are the generation, avoidance, control, and reduction of variety (see Fig. 6.7).

Variety generation Variety reduction Variety governance Variety avoidance

Fig. 6.7   Tasks of Product Variety Management along the product cycle, according to Wildemann [87], Heina [33]

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The variety of products offered usually results in an increase in the number of components and processes and thus in complexity in the company. Product Variety Management can be seen as a sub-discipline of complexity management, which addresses the part of complexity that is influenced by product variety. One speaks accordingly of variety-­ induced complexity. The areas of Product Variety Management are demand variety, product variety, and the internal variety of components and processes [33]. An essential success factor of Product Variety Management is its anchoring in the consciousness not only of the employees in the variant-implementing product life phases, but above all in the variety-generating product life phases, i.e. primarily in sales and product planning. As described in Sect. 2.1.2, the structures of performance evaluation and incentives as well as cost accounting systems often do not adequately reflect the necessity of Product Variety Management. Rather, this must be regarded and implemented as a crosssectional function analogous to that of quality management if the increasing variety of demand is not to lead to a sharp increase in company internal complexity. Generation of Variants The tasks of Complexity or Product Variety Management are often seen as limited to avoidance, control and reduction. Heina usefully extends the scope of tasks to the targeted generation of variants, since the product variety should not be avoided in the literal sense, but rather aligned as well as possible to the variety of demand [33]. Through the targeted generation of variants, company internal variety and thus the later complexity costs can be significantly reduced or preemptively avoided when determining the future variety of the product range. In addition to precise advance planning of the required product variety and the development of modular, variety-optimized product structure strategies, particular attention must be paid to the awareness of all those involved in order to avoid the negative effects of product variety. Variety generation is of great importance, especially in the context of modular product family development, since a large part of the complexity for the company, which only arises in the medium and long term, can be avoided at this stage. Variety Avoidance If product variety is not seen and rewarded from the customer’s point of view, product variants should be avoided. Variants must also be avoided if, instead of generating additional sales, only a shift of existing customers away from their accustomed solutions and towards buying the new variants takes place. Starting from a defined range of products, the generation of an excessive internal variety of components and processes must be avoided in development. To achieve this, the design-for-variety of the product families must be optimally implemented and the possibilities of production technologies, planning and control must be fully exploited. With a variety-appropriate product design, product development can improve the ratio of external to internal variety and thus enable a significant reduction of variety-induced complexity. This can also improve the conditions for mass production in the case of variant products [71]. The product structure strategies described in Sect. 6.5, such as modular product structures or product platforms, offer excellent principles for this purpose.

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155

Control of Variants The aim is to efficiently manage the variety that is desired or unavoidable, so that the resulting complexity in the company is kept to a minimum. The existing variety must be handled as efficiently as possible throughout the entire product creation process. These activities are strongly dependent on the results of the preceding phases being as variety-­ optimized as possible. Reduction of Variants Variety reduction includes the elimination of unnecessary variants and the simplification of processes. Existing product variants should be regularly checked for their necessity and, if necessary, removed from the product range. Changing market requirements or other external factors, such as standards or regulations, can be the trigger for product variants to become obsolete. Regular and comprehensive checking is important, as unnecessary product variants can quickly become obsolete. In most cases, an ABC analysis is used to select the product variants according to their cumulative sales contribution, while the C variants, with their very low to almost zero sales figures, are selected as candidates for a phase out [63]. However, it should be noted that these variants do not necessarily have to make a significant contribution to the complexity of the company. It is therefore not necessarily a lever for complexity reduction. Also, the strong remanence of the complexity costs built up by the product variety should be considered when calculating this measure (see Sect. 2.3). In addition to turnover, other variables such as profit or customer turnover can also be examined.

6.3.1 Design-for-Variety Both the external range of products and the internal variety of products, components and processes as well as the relationship between external and internal product variety are decisive for a variety-oriented product design. For this reason, various methods have been developed that address external or internal variety or deal with both simultaneously. These methods are described below. The methods that are geared towards external product variety are described first, followed by an explanation of the methods that address both external and internal variety. Finally, the methods that address the internal variety are presented. Radical Simplification Via Design This method was developed more recently at the Technical University of Denmark [60]. It is based on various theories and models, such as the Theory of Technical Systems [37] or the Chromosome Model (Andreasen) and combines them in a single approach for reducing internal variety in the company. The approach includes an analysis of the current sales markets, the products with their product structure and variety, the production processes and the order fulfillment process. The recording and analysis of this information is visually depicted on a poster wall. This method makes it easier to discover weak points, seek

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Fig. 6.8   Example of visualizations used in the Radical Simplification via Design [60]

out technical solutions, and align the products, while keeping the focus on general objectives. An initial situation and performance analysis includes the examination of the existing product range, including its sales figures, production, order processing, and its complexity or cost structure. For each of these areas, different visualizations are used, which are usually summarized on a poster wall (see Fig. 6.8). The objective for variety reduction is set in the second step. In the third step, the planned changes to the product architecture are described, developed, and evaluated, and the implementation of this new product architecture is planned and initiated in the fourth and final step. Here, 12 principles are offered for the development of the product architecture changes, such as “integration of suppliers” or “isolation of variety “. This approach offers a compact and transparent guide for the analysis and visualization of product variety and the definition of improvement measures. Integrated Framework for Product Family Design The Integrated Framework for Product Family Design according to Simpson et al. is an overarching procedure for the development of product families [78]. It is divided into three phases: product planning, differentiation planning and commonality planning, each of which uses a tool of the same name (see Fig. 6.9). The procedure is based on the Product Family Planning Framework of Robertson and Ulrich and uses the workflow proposed there, according to which the differentiation and commonality plan are processed in parallel [73]. The differentiation plan uses the Generational Variety Index (GVI) to show the extent to which components are affected by changing customer requirements. The additionally created Design Structure Matrix (DSM) evaluates the chance of change propagation of a component when customer requirements change. A low GVI indicates the need of using the component as a platform component and a high GVI indicates an flexible embedding of the component.

6.3 Product Variety Management and Design-for-Variety

Variant 2

Variant 3

User Requirements Product plan

Segments

Identification of the product variety and market entries

Positioning of the products in the market segments Variant 1

157

Market segmentation grid

time

Communality plan

Differentiation plan Generational Variety Index (GVI) Design Structure Matrix (DSM) Multi-Objective Optimization

Generational Variety Index (GVI) Multi-Objective Optimization

Planning of common use of modules across the different products Part

Variant 1

Variante2

Variant 3

Communality specifications

Fig. 6.9   Procedure of the Integrated Framework for Product Family Design with the visualizations product, differentiation and commonality plan as working tools, according to Simpson et al. [78]

In the following steps, algorithms that allow optimization with respect to several target variables are used to define the optimal parameters for variant components and platform components. The optimization is performed based on customer requirements in the niches of the Market Segmentation Grid. Simpson et al. recommend the Product Family Penalty Function (PFPF), an optimization method that considers individual design parameters. PFPF evaluates the commonality of a product variant, the extent to which the individual product variants with their design parameters vary from the mean value of the design parameters of all product variants. A high degree of commonality requires a low PFPF. The results of the different concepts are compared and evaluated in visualizations. VMEA for the Elimination of Offer Variants The Variety Mode and Effects Analysis (VMEA) is based on the basic procedure of the Failure Mode and Effects Analysis (FMEA) [11]. It aims at the cost-oriented design for mass-production. It supports the determination of the appropriate range of products and the design of the variety of parts and assemblies (see Fig. 6.10). In a “variety tree”, the internal variety and the assembly process are analyzed and parts, assemblies, and product variety are forecast. Using the variety tree, the four process steps of analysis of the variety, a prioritization of problematic parts and assemblies, an improvement of product design, and the variety-oriented evaluation of the result are iteraded. The variety tree provides a visual aid for the variety in the assembly process. A late variant formation is recognizable by a slim variety tree. Various measures are offered to achieve this. Examples of such measures include the restriction of the influence of specification features to a scope, or the integration of installed part variants in scopes with the same specification features. The design of a product family that is as variety-oriented as possible is supported from the assembly viewpoint. Clues are also given for the optimization of external variety.

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Current state

According to: time, quantity, variety and cost variables Variant analysis

Design elements, specifications and measures Prioritization

iterative process of design optimization

Variety-oriented design Evaluation

Target state Selection

Based on technical-economic key figures and significant product parameters

Fig. 6.10   Procedure diagram of Variety Mode and Effects Analysis (VMEA) and the variant tree as the main tool of the procedure, according to Caesar [11]

Variety-Optimized Design The Variety-optimized product design according to Franke, developed at the Technische Universität Braunschweig, is a method for the development of variant products [24]. Firchau [23] extended the method. A method catalogue ensures its usability. Figure 6.11 gives an overview of the procedure. In the analysis, relevant product groups and their assemblies to be considered are identified. These are then structured and optimized according to their variety by means of product synthesis, whereby the Strength diagram according to Franke or the Modular Function Deployment according to Erixon (see Sect. 6.4.4, [21]) can be used as support. An ongoing cost-benefit analysis accompanies the procedure. To avoid the effort of an activity-based costing (ABC), a process cost estimation according to Jeschke is pursued [39]. Two principles are followed to ensure that the product family is redesigned in a variety-­ oriented matter. On the one hand, this is the independent combinability of features and functions by realizing variant features and functions in single modules, and on the other hand, the configurability of the product variants from standard and variant modules, whereby the proportion of standard modules should be as high as possible. Variant modules should have a lower frequency of use and a lower value compared to standard modules. In addition, guidelines are given for variety-oriented product design, such as symmetrical design or targeted oversizing.

6.3 Product Variety Management and Design-for-Variety

159

Product analysis

Product synthesis

Transfer

Product group selection

Creation of variant-oriented product structures

Visualisation of the variant optimization

Product planning

Improvement of functionrelatedness

Evaluation

Variant characteristic analysis of the product group

Differentiation between variant and standard modules

Selection of the considered assemblies or structural level Variant characteristic analysis of the assembly

Evaluation

Variant-optimizing design Standardization of individual design elements Design of compatible interfaces

Optimization of the assembly sequence

Evaluation

Tools (examples)     

     

Market analysis Sales volume analysis Competition analysis Table of characteristics Assembly bill of materials for product structuring with characteristic values and variant assignment Key figures for assessing the degree of standardization Strength diagram Similarity analysis Classification according to characteristics Assembly sequences Variant catalogs

Fig. 6.11  Overview of the Variety-optimized design method, according to Firchau [23], Franke [24]

Design-for-Variety The method developed at Stanford University supports the development of product platforms which should be as stable as possible against future product changes [58]. The necessary internal variety of a product family, which results from product variety across generations, should be avoided. The procedure is based on the GVI and Coupling Index (CI) (see Sect. 6.3.2). The GVI shows the probability and extent to which changes to components can be expected in the future. The strength of the coupling between the components of a product is assessed with the CI. If the coupling is strong, the probability increases that a change in one component will result in necessary changes in other components. The first step of the procedure is to calculate the described indices. The components are then sorted according to the values and priorities for their redesign are determined. The actual development of the product platform takes place in the last step, with the goal of minimizing the GVI and CI of the relevant components. The following two measures are proposed for this purpose. The assignment between functions and components should be changed. For example, functions for which future changes are expected are shifted away from relevant components. Specifications should be frozen so that single features do not need to be changed over the life of the platform. In order to minimize the sensitivity of components to changes, it is recommended to reduce the internal couplings by using differential instead of integral design and to avoid the necessity of later changes by oversized components. Design Rules for Variant Product Families The methods presented in this chapter support the development of variety-oriented product family concepts. Design principles can be used efficiently to design these concepts and

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to avoid new product variety during the detailed design phase of the components in the course of the design process. Kipp and Krause summarized 16 such principles based on a literature search and product example analysis (see Figs. 6.12–6.14) [45]. These principles support the design engineer and ensure the implementation of an optimized product family concept. For example, the oversizing of components can help to provide them as standard components that can be installed in different product variants. A symmetrical interface design makes it easier to configure product variants by means of different orientations of the same component during assembly. Furthermore, care must be taken to vary only the necessary geometries and to realize this by simple designs and as late in production as possible.

6.3.2 Key Figures for Variety-Optimized Product Design A product family’s variety-optimized design can be described as the relationship between the external variety of offers and the internal variety of components and processes intended for their realization. Indicators that help to estimate the variety-optimized design of a product family or a product concept must therefore cover factors of external and internal product variety and be able to put them in relation to each other (see [9]). Key Figures for Product Variety The number and difference of variants are the main determinants of variety [75]. For the mathematical expression of difference, differentiating parameters of the variants must be used, whose extreme and mean values, distances, or distribution coefficients can provide information about the variety. Buchholz gives an overview of different parameters [9]. The flexibility of variants Evar expresses the dependence of the external product variety on internal component variety [14, 21]. It can be determined, for example, from the number of product variants in relation to the number of module variants used for their configuration. This is intended to identify the highest possible reuse share of modules and processes. Evar =

N var N mtot

(6.1)

with Nvar: number of variants in the entire product program Nmtot: number of modules in the entire product program For each component, the degree of reuse reflects the average number of product variants in which it is installed. The reuse frequency of a component variant is the number of times it appears in a particular product variant [70].

6.3 Product Variety Management and Design-for-Variety Guide line

Guide line

Poor solution

Poor solution

161 Good solution

Good solution

use common parts to generate product variants

reduce the amount of variant characteristics (materials, geometries, ...)

common use of components by over sizing

use symmetrical parts to generate product variants

variety in software instead hardware

compatible interface design

variable valve characteristics by variant spring length

variable valve characteristics by variant spring diameters

variant valve body height and shape

variant valve body height only

variant battery sizes

standard battery sizes

simple geometry

higher geometry for more variability

interfaces for different languages

standard interface with choice of language

Fig. 6.12   Collection of helpful design guidelines for the variety-optimized design of product families, according to Kipp and Krause [45])

162 Guide line

6  Methods for the Development of Modular Product Families Poor solution

Good solution

configuration by serial an parallel connection of standard components

separation of standard geometries of variant components

cut-to-fit modularity for the configuration of variety

additional components for size range construction

development of new product variants as separated entities

variant battery sizes

standard battery sizes

h f d d different designs off shaft drive ends

separation of variant drive ends

rollers in different lengths

pipe sections cut to lengths and standard bearing flanges

rollers in different lengths

standard bearing flanges, standard section and optional extension

prefer the development of complete new versions of a variant over an additional variant

Fig. 6.13   Collection of helpful design guidelines. (Continued Fig. 6.12)

6.3 Product Variety Management and Design-for-Variety Guide line

Poor solution

163 Good solution

postponement of variety generation along the production and assembly process

communality of process steps for variant products

Fig. 6.14   Collection of helpful design guidelines. (Continued Fig. 6.13)

Interdependence is the ratio of the real possible combinability to the mathematically maximum combinability of the components and thus gives an indication of the extent of the mutual dependence of the components [70]. Degree of the Interdependence the Components l  1 

K real K real  1 (6.2) k K max  i 1K VAi

with l:interdependence of the components Kreal: real combinability of the components Kmax: maximum combinability of the components KVAi:number of variants of component i k: number of components of the product variant The degree of integration indicates the degree to which the functionality is combined in the components. If the degree of integration is zero, no component would be dependent on more than one product characteristic. Absolute degree of integration a variant IG abs 

E real E  1  mreal E min  i 1n i

(6.3)

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with IGabs: absolute degree of integration of the product variant Ereal:real number of component variants Emin:minimum number of component variants ni: number of values of characteristic i m:number of characteristics of the product variant The product variants are created by combining a minimum total number of components. If each component variant is only dependent on one characteristic, the degree of integration takes on a value of zero. However, there are only a few cases in which this can be achieved. Key Figures of Variety-Optimized Product Design The number of components required for the configuration of product variants  – determined, for example, by the number of articles – and the proportion of standard components among these provide a much simpler way of checking whether a product family is well designed in terms of variety. Standard components are components that are installed in each product variant of the product families in unchanged form. As a part of methodological support for variant-optimized product design (see Sect. 6.6.4), Kipp provides a number of additional key figures to describe variant-oriented design [44]. These are based on an ideal concept of variant-oriented product family structures (see Sect. 4.6), which comprises four characteristics (clear differentiation between standard and variant components, reduction of variant components to absolutely necessary variety, oneto-one relationship between variant components and differentiating product characteristics from the customer’s point of view, and decoupling of variant components) [44]. Ideally, each variant component configures exactly one differentiating product characteristic from the customer’s point of view. The intensity of the deviation from this ideal state can be determined by the key figures KUnt and KComp. A value of zero indicates the ideal situation in which each variant component is sufficient to configure exactly one differentiating product property from the customer’s point of view. KUnt specifies the average number of additional components that are variant for the configuration of one differentiating product property from the customer’s perspective. K Unt 

N Assignments Number of Assignments 1  1 N Dis Number of Distinguishing Properties

(6.4)

KComp is the average number of additional product properties that cause the variety of a component. K Komp 

N Assignments Number of Assignments 1  1 N varComp Number of variants Components

(6.5)

6.3 Product Variety Management and Design-for-Variety

165

Platform Commonality Index The ratios according to Siddique and Rosen give a rough assessment of carry-over effects in the product range [77]. The proportion of communal components or interfaces is used.



CC =

Number of shared Components Number of all Components

(6.6)

Number of shared Interfaces Number of all Interfaces

(6.7)

CN =

Commonality Index The Commonality Index (CI) according to Martin and Ishii is a measure of the quality of a product concept with regard to the utilization of the variety of parts for variety generation [12, 57]. It describes the ratio of different parts of an assembly to the sum of the parts used in all variants. A high value indicates a low number of components for configuring the product variety. CI 

u



vn

p

, 0  CI  1

(6.8)

j 1 j

with u: number of part numbers pj: number of parts in variant j vn: number of product variants The Degree of Commonality Index (DCI) according to Collier determines the reuse of components in a product platform [12]. The more often a component is reused, the higher the DCI value.



 DCI 

id

j

j  i 1

d



(6.9)

with Φj: number of direct parent components of component j d: number of distinguishable components i: number of product variants As there are no limits for the DCI due to the lack of mathematical norming, Wacker and Treleven have extended the approach by standardizing the value range between 0 and 1

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[86]. This Total Constant Commonality Index (TCCI) can be interpreted as the ratio of the number of multiple components in a product family to the number of all components in the product family. TCCI  1 

d 1



id

j  1

(6.10)

j  i 1

6.4 Modularization Targeted modular product structuring is an essential measure for reducing complexity in all product life phases and also forms an important basis for further measures in the product life cycle (see also effects of product variety in Sect. 6.2 and potentials of modular product structures in Sect. 4.4). A large number of different frameworks and methodical approaches have emerged for the implementation of a modularization project (Ripperda and Krause 2013). Since the (modular) structuring of products has an influence on all product life phases and, conversely, can also enable the use of different potentials for all product life phases, the methods differ greatly in their orientation, the potentials or product life phases considered and the tools used. However, they all have a basic procedural scheme, which is explained in Sect. 6.4.1. For the presentation of a selection of modularization methods in this section, the different views on modularity, as presented in Sect. 4.1, are used as a classification system for the methods. Not all methods can be clearly assigned to one of the views here, but it provides an initial classification aid. The views used here are briefly explained below: • the technical-functional view (Sect. 6.4.2), for modularization of the product according to technical functionality or according to functions and their properties, • the organizational and process view (Sect. 6.4.3), for methods that align modularization with the organizational structure of the company or the resources of the processes in the product life phases, and • the strategic view (Sect. 6.4.4), for methods that support the medium and long-term strategies of the company and the individual product life phases by means of targeted module definition.Due to the different potentials of modular product structures for all product life phases, integrative methods exist that are dedicated to the combination and harmonization of the requirements for modularization from different perspectives. These are also presented in Sect. 6.4.4. Finally, Sect. 6.4.5 lists various key figures that can be used to quantify certain, fundamental aspects of the modularity of a product family.

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6.4.1 Basic Procedure of Modularization A common procedural scheme of the methods for modularization is given by the objective of these approaches that an existing product structure is to be recorded, analyzed and restructured into modules according to individual objectives. These basic steps can be found in all approaches, but with different objectives, emphases, designs and working tools, as well as additional work steps. Often, however, the transfer of the new module structure into the process and IT landscape of the company after the execution of a modularization project is not explicitly described in methods from the literature. The generic procedure for modularization with the steps for the decomposition of the existing product structure, analysis of the components, modularization and transfer to a modular product structure is described in detail in Sect. 5.1.1. An essential step for a modularization project is the breaking up of the existing product structure and the definition of the smallest units to be considered (see Fig. 6.15). In addition, contradictory objectives of modularization must be resolved. The result of modularization is a modular product structure with modules that are reintegrated into the company’s process and IT landscape. This reduces complexity within the company, as the modules can be used as the smallest organizational unit of the product structures for better communication across departments.

6.4.2 Modularization According to Technical-Functional Aspects Modularization methods according to technical-functional aspects focus on the definition of modules to improve the technical functionality of a product. In addition, some of these methods also focus on functions for the implementation of further and more indirect advantages. For example, it can be assumed that a product, modularized according to product functions, can be better developed by independent teams who are specialized in specific functions (see also Sect. 4.4.2). However, since such effects are only addressed as indirect advantages in the technical-functional oriented methods and there is no explicit orientation of the module structure to these aspects, they must be separated from the organizational and process-oriented modularization methods presented in Sect. 6.4.3. 11.

2 2.

3 3.

Module 1

9

Product

3 8

4 5

Components

1 Module 3 Module 2

Fig. 6.15   Basic procedure for modularization (see also Sect. 5.1.1)

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Modules Heuristics in the Modular Design Methodology The Theory of Modular Design according to Stone comprises the Modular Design Methodology, a methodical procedure in the development of modular products [82]. Several approaches are integrated, such as Quality Function Deployment (QFD) [1], and a special approach is given with the definition of modules from a technical-functional point of view. This approach was published for the first time within the framework of Modular Design Methodology and therefore briefly presented here. The modularization is based on three heuristics, which are applied to a sales-oriented functional structure of the product. In the first step the heuristic Dominant Flow is used. For this purpose, the customer requirements are first mathematically weighted (see Fig. 6.16, left). The flows between functions are evaluated according to their importance for the fulfillment of customer requirements and their weighting. The flow with the highest priority is called the dominant flow and the functions through which it flows are combined into a module (see Fig. 6.16, middle and right). The second heuristic Branching Flow combines functions that together form a chain starting from a branching point (see Fig. 6.17, left). The third heuristic, Conversion Transmission, combines functions that convert a flow with the functions that follow along a flow (see Fig. 6.17, right). After the application of the three heuristics, the proposed modules are combined into an overall solution. Contradictions are identified in the following concept development and conflicts are resolved in the final evaluation of the concepts. Customer request Gewicht Weight Kundenwunsch

A (3) B (1) C (1)

…

∑

Material

Energy

A Output Ausbringung

3

Material Stoff

B Mileage Laufleistung

1

Energie Energy

4 1

C Mass Gewicht

1

Signal Signal

1

…

…

…

…

Modul„Material Stofffluss Module flow“

Interaction Interface

Fig. 6.16   Module definition by the heuristic Dominant Flow, according to Stone [82]) Modules Module Branching flow 1

Modules Transformation

Module Branching flow 2

Transformation-Transmission Module Branching flow 3 Interfaces Transformation-Transmission-chain

Fig. 6.17   Module definition by the heuristics Branching Flow (left) and Conversion Transmission (right), according to [82])

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The Theory of Modular Design according to Stone works with clear heuristics that make the application easier. In addition, it offers a function-oriented approach that can also be implemented without product design. However, the purely technical-functional optimization of the module structure has the disadvantage that it hides other module drivers. Furthermore, module recommendations are sometimes technically contradictory and the analytical approach cannot always be communicated transparently. Although only indirectly described within the method, the heuristics can also be applied to components with their connecting flows or couplings, such as in the life-phase modularization (see Sect. 6.6.4). Extensions of the Modular Design Methodology The approach for the development of product families developed by Stone was extended by Zamirowski and Otto [88]. In contrast to the approach of the Modular Design Methodology, no function structure is formed for a product, but all products of the family are combined in a function structure. The purely functional heuristics developed by Stone are largely adopted, whereby the following variant-related heuristics are also used. The heuristic Isolation of Variety leads to an isolation of variant functions in modules. The heuristic Function structure modification for variety reduction intends to standardize variant. functions in order to increase the commonality of the product family. Dahmus et al. [38] supplement this approach with a modularity matrix in which the functions occurring in the product family are compared with the product variants. The function values are entered into the fields of the matrix. The respective modules are identified by a colored background of the corresponding fields. The range of application is wider than the original Modular Design Methodology according to Stone, but without further product strategic requirements. Development of Modular Products According to Kusiak et al The procedure of the Development of Modular Products according to Kusiak, Szczerbicki and Huang is based on the use of coupling graphs to represent the components of the product and their connections [36]. These are included in corresponding adjacency matrices, which are used for the computer-aided application of clustering algorithms. The connections between the components are weighted according to the number of product variants in which the connections exist. The product concept is presented with components and their connections as a coupling graph (Fig. 6.18, left). The connections between the components are also shown as a coupling matrix, and are counted several times, depending on the number of product variants in which this connection exists (Fig.6.18, middle). Connections between product components that are not desired are also listed in a compatibility matrix (Fig. 6.18, right). The matrix is clustered under different parameters by an algorithm with computer support. The results are differently clustered matrices, which can be transferred as suggestions into possible module concepts.

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Components

Components

Number of connections in the product family

Compatibility matrix

Legend Structural connections Energy flow

variant components standard components

a

Components suitable for a common module

o

Components not suitable for a common module

Fig. 6.18   Coupling graph, coupling matrix and compatibility matrix using the example of a desk lamp, according to Kusiak and Chun-Che Huang [53]

The process offers a good approach for module definition based on the technical couplings between the components, especially for small to medium size products. Together with approaches such as the Integration Analysis Methodology according to Pimmler and Eppinger [65], the method is one of the first approaches to technical modularization using matrices. Integration Analysis Methodology The Integration Analysis Methodology according to Pimmler and Eppinger examines the couplings between components of a product and transfers these into concepts for the modularization of the product and the distribution of the modules to development teams [65]. As couplings, connections are distinguished into four types: spatial arrangement, energy, information, and material. The Design Structure Matrix (DSM) according to [81] is used as the main tool for recording the connections and their analysis. The method first differentiates according to the current status in the development project. Then the method can be applied to functional units of the product if their implementation in components during development is not yet sufficiently clarified, or concrete components can be considered. The authors recommend using functions and concrete components at the same time, depending on the status of development. In any case, however, these should be on a more detailed level in the product structure than the module concept aimed at as a result. Using a DSM, all elements are examined in pairs with regard to their couplings. The four coupling types of spatial arrangement, energy, information, and material are each

Component 6

Component 5

Component 4

Component 3

Component 2

171

Component 1

6.4 Modularization

Component 1

Component 2 Component 3

Component 4 Component 5

Coupling types

Component 6

Spatial Information

S E I M

Energye Material

Fig. 6.19   Example of a Design Structure Matrix (DSM)

evaluated on a scale of −2 (harmful relationships) to +2 (essential relationship). The result is a symmetrical DSM with four entries per element (one per coupling type, see Fig. 6.19). Similar to the Development of Modular Products according to Kusiak, the DSM can be clustered with the help of computers. Since each type of coupling is considered separately, four clustered block DSMs are created, which, as suggestions for modularization, must then be transferred into an overall technical concept. The application of DSM is clearly structured and can be carried out with computer support, so that even large problems can be dealt with. However, the purely computer-aided evaluation can make the result difficult to implement, which can weaken acceptance and feasibility. Special software tools are available, such as Loomeo, but tools like Matlab, Maple, and Mathematica can also be used. Modular Development Pahl and Beitz use function structures for the development of modular sets [62], in which the overall function of a product is divided into basic functions, special functions, auxiliary functions, and fitting functions. By means of a modular set, product variants with different overall functions can be configured by combining blocks (modules) with different performance parameters or functions. The overall function of different products or product variants should be fulfilled by combining as few and simple modules as possible. Standard modules are mandatory modules that are installed in all product variants. Variant

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6  Methods for the Development of Modular Product Families

modules configure product variants that are rarely required. These are special additions to the standard modules. In addition, auxiliary modules with connection functions can be provided as well as adaptation modules for adaptation to surrounding systems. Due to size steps of modules, modular sets often also contain size ranges. By combining a modular system with order-specific extensions, so-called mixed systems are created. The advantage of a modular set lies in the large number of product variants that can be created with a limited number of building blocks. In contrast, the modular system is described in a comprehensive way, which consistently exploits the potential of using modules across the entire product range. Size Range Development A size range consists of several technical systems that perform the same function with the same solution in different sizes with as far as possible the same processes in product development [15, 62] (see also Sect. 5.2.2). By means of different size steps, size ranges allow the variance of a product in a few parameters, such as different performance values. The principle of a size range can be applied to products, assemblies or modules or even components. Typically, a basic design is drawn up and validated as the starting point for size range development. Based on this design stage, different size variants of the basic design can now be derived in order to realize different performance levels of the product or component. By using the basic design, development efforts can be reduced when deriving the size steps. A major challenge in the development of a size range is the determination of the number and size of the steps. On the one hand, the number of sizes should be as small as possible in order to reduce internal variety and increase batch sizes, while on the other hand a higher number of steps can better meet customer requirements and application situations [16]. The concrete increments must cover the variety in market demand in the best possible way in order to keep the oversizing of the size increments within acceptable limits. The interpretation of the basic design can be transferred to the further size levels by means of physical similarity laws. For this purpose, the Cauchy number must be constant, that is, there must be constant speeds at comparable component positions of the size range variants for the same material. If, for example, a size step is increased by the factor 2 compared to the basic design, the permissible angular velocity is reduced by the factor 2−1 = 0, 5  , an increase of the forces and power by factor 22  =  4, masses and torques by factor 23 = 8. This way, strains and stresses remain constant and the design is therefore feasible. An equidistant graduation (linear arithmetic) of the size range is the simplest way to define the size graduations. However, a size graduation based on a geometric size range is usually preferred. Various standard number size ranges are recommended for determining the individual size steps, for example according to (DIN 323). The geometric size range is characterized by a constant percentage increase of the step increments. Since the incorrect

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dimensioning of the individual size steps is also percentage-based in most cases and less often absolute, the geometric series usually offers the advantage of less oversizing. Oversizing by a fixed value is perceived by the customer as less critical for a larger step. In addition, a geometric series generally aligns the series with physical laws. Often the desired geometric similarity cannot be achieved because technological limitations or such requirements as ergonomics or multiple use of standard modules, limit scalability and non-stepped modules must be integrated into the size-stepped product variants. This is referred to as semi-similar size range [62]. In addition to mathematical size range and standard numbers, optimization methods such as cluster analysis and genetic algorithms have been used for some time now, as presented in [46]. These define the size grading by evaluating acceptable oversizing, existing sales figures or market studies in such a way that the customer requirements are met with as few but appropriate step changes as possible. Especially when more than two parameters are taken into account in a size range development, it is hardly possible to find a solution manually without such algorithms [46].

6.4.3 Modularization According to Organizational and Process Aspects From the point of view of the different product life phases, modules can form beneficial product structure units that significantly simplify the processes along the product creation and use phases, as already explained in Sect. 4.4. Complicated product families and systems in particular can be structured and handled more easily through modularization. For the development process, for example, large products can first be broken down into smaller module developments. Production and assembly tasks benefit significantly from modules that have been defined to match the work steps and assembly systems. This process- and resource-oriented strategy of modular product structuring makes it easier to organize the processes of the entire product development and production process. The clear decoupling of the modules offers an essential prerequisite for the easy execution of tasks. It is important to note that not only physical couplings are considered. A module here is a physical and/or conceptual grouping of components with certain commonalities, which are treated as a logical unit (Krause and Paetzold 2010). The modules interact with the organizational units and resources of all product life phases, such as in development tasks, procurement, assembly steps or use and maintenance. Essential for an organizational and process-related orientation of modularization is the coordination of the modules, the interactions and the respective organizational units and resources in the life phases, so that the resource load and the coordination efforts are reduced [3, 21]; Ripperda and Krause 2013; [6].

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VDI Guideline 2221 (Structuring in Modules) The VDI Guideline 2221 Systematic approach to the development and design of technical systems and products provides a general procedure and, as the fourth of seven work sections, integrates the structuring into feasible modules. The aim of this step is to divide the previously developed, basic solution into modules in order to identify development priorities and to achieve an efficient division of the later design work. It is generally recommended that the division into modules be based on various criteria, such as the formation of design modules according to pragmatic engineering work aspects in product development, assembly modules, maintenance modules for a maintenance-­ friendly product structure, recycling modules as well as basic and variant modules for the configuration of product variants. The four sub-steps “Selecting design-relevant requirements”, “Check sector-specific procedure”, “Create preliminary product structure” and “Create work plan for the design phase” are mentioned. In addition, the use of further methods such as creativity techniques, morphology, design guidelines, methods of modular and size range development is recommended. The result is a modular structure which, in contrast to the functional or effective structure, already shows the division of the solution into groups and elements essential for its realization, including their interfaces [85]. The VDI Guideline 2221 shows the great importance of modularization for product development. However, the guideline lacks a concrete methodical procedure for the development of modular product structures (see also Sect. 7.1.1). Methodological Support for System Formation The Methodical support of system formation according to Göpfert aims at a common modularization of product and organizational structure [30]. Technical modularization is intended to create functionally and physically independent products, whereby functional independence is guaranteed when a module fulfils a function independently of other modules. Physical independence exists if the modules can be easily separated from each other due to the design of the interfaces. Technical modularization is intended to create new products by combining existing modules according to the modular principle. This is also a method of creating new product variants or product families with relatively little development effort, provided that they differ in functionality (see Fig. 6.20). The goal of organizational modularization is to create self-contained task scopes that can be processed as independently as possible. Technical and organizational modularization are directly related, since each interface of technical modules causes a coordination effort between responsible organizational units. The modular product structure, which reflects the organizational structure, reduces this effort. The graphic shown in Fig. 6.20 visualizes the common modularization of product and organizational structure, which is organized according to product functions. The procedure of the method consists of the following five steps:

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175

Organizational units Component

Function Product idea

Functional structure

Module

Product

Product structure

Fig. 6.20  Presentation of product architecture (functional and building structure) and project organization in the Methodical Support of System Formation [30]

1. Definition of boundary conditions  – determination of the requirements, specified interfaces and assemblies and whether the previous organizational structure must be questioned. 2. Creation of technical design alternatives – development of various product architectures, consisting of functional and building structure. 3. Evaluation and selection of a design alternative – selection of an alternative based on a value analysis. Further use of the alternative as a basis for the development of the organizational structure. 4. Creation of organizational design alternatives – development of alternative organizational structures by combining different product architectures according to the scope of activities. 5. Evaluation and selection of overall solution  – selection of the overall solution by means of value analysis based on technical and organizational evaluation criteria. To ensure a coherent development of product and organizational structures, the steps are carried out iteratively. The aim is to create functionally and physically autonomous modules that also reduce internal variety and organizational complexity. The aim of the method is to create modules that are as functionally and physically independent as possible, which reduces the interconnections in internal variety and avoids organizational complexity. It focuses on the coordinated design of the modular product structures with the organizational structuring of the development. The method focuses the modularization by function according to the organizational structure of the development department.

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6.4.4 Product Strategic and Integrative Modularization Methods The product strategy is designed for the medium to long term and includes the successful positioning of the product variants on the market, product innovation, the market life cycle and the further development of new product versions and generations. Modularization methods offer excellent opportunities to align and prepare product structures for the strategic planning of the company and its departments. For example, the integration of a new technology can be simplified in the future by implementing affected components in a well-decoupled module. The simple configuration of variants by modules or the multiple use of modules in different product families or lines are essential strategic potentials. As shown in the previous sections, there are several different motivations for modularization. In practical implementation, this represents a major challenge due to the necessary integration of these objectives and their correspondingly different module requirements into the modular product structure. Integrative methods are dedicated to this consolidation and harmonization of the requirements for modularization from different views and product life phases. Many of these methods also support the inclusion of individual views and the derivation of a modular product structure before the views are merged and harmonized. Modular Function Deployment (MFD) The Modular Function Deployment (MFD) of Erixon borrows its title from the Quality Function Deployment (QFD), which is also used as one step within the method [21]. The method is based on the model of module drivers (see Sect. 4.4.9), which is a collection of reasons for creating modules. The module drivers used in the MFD are based on several company studies, conducted by means of questionnaires. In contrast to technical-­functional modularization methods, they mainly comprise the objectives from the different product life phases and are thus oriented from a product strategy point of view. Examples are the transfer of modules into other products or product generations, modules for production and assembly or modules for maintenance, which allow a quick exchange during operation. As a first step, customer requirements are checked and converted into suitable technical requirements, for which the QFD is proposed. The QFD uses a matrix template to check which technical specifications contribute to which customer requirements. Modularity is entered as a technical feature of the product structure to show the contribution of modularity to the fulfillment of customer requirements. In the second step, the product is broken down into functions and subfunctions and their technical solutions. To support the decomposition of the functions and technical solutions, the Design Matrix according to Suh [83] and the Functions-Means-Tree according to Buur [10] are proposed as working tools. When assigning technical solutions to the functions, it may be necessary to select several alternatives, which is supported by the use of a so-called Pugh Selection Matrix [68] as a simple point evaluation. The result of this step is a hierarchical function structure of the product alongside possible technical solutions.

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The actual module determination is carried out based on the product strategic module drivers of the product life phases, listed in Table 6.1. These represent reasons for creating individual modules within the product structure (see also Sect. 4.4.9). The above list represents a generic collection of module drivers that must be adapted and, if necessary, supplemented in the application of the MFD in a company for the specific product. Special attention must be paid to supplementing aspects of the corporate strategy. In the so-called Modular Indication Matrix (MIM), the sub-functions are evaluated together with defined technical solutions to determine how strongly the respective module driver applies to the sub-function (see Fig. 6.21). An energy storage device in the form of a rechargeable battery, for example, could be replaced for maintenance purposes and therefore be an important module for servicing (service/maintenance module driver). The evaluations should be carried out by a team consisting of representatives of the respective company departments and supported by a questionnaire on the individual module drivers. Table 6.1   Generic module drivers after Modular Function Deployment [21] 1. Product life phase 2. Module driver Product Carry-over development and design Technological evolution/ technology push Planned design changes/ product planning Sales/ Technical configuration specification Styling Production

Quality Procurement After sales

Common unit

Process and/or organisation re-use Separate testing of functions Black box engineering Service/ maintenance Upgrading Recycling

3. Explanation Use of a module over several product generations and/ or product families (long-term) Likely technology changes due to new developments or significantly changed customer requirements Probable or planned product maintenance measures during the product life Generation of product variants through decoupled modules Essential styling modules for later changes in product design Multiple use or reuse of modules in the product range, which, compared to the “carry-over” driver, is aimed at short-term effects and higher quantities and should ideally be combined with them Similar or identical process steps in production, appropriate scope of work for an organizational unit Earlier and simpler functional testing of modules in the production process before assembly Purchase of a module, reduction of the number of suppliers and procurement processes Replacement of defective modules instead of repair with major operational disruption Modules for changing or extending the functions of the product in the use phase Simplified recycling by combining the same or similar materials and harmful substances in individual modules

6  Methods for the Development of Modular Product Families

Sub-function (technical solution)

Module driver

Carry-Over Technology Push Planned Design Changes Technical Specification Styling Common Unit Process / Organisation Separate Testing Black-Box-Engineering Service / Maintenance Upgrading Recycling Module driver sum

Shut-off vale Axle Battery Outrigger (shield) Flow control glas Nozzle holder Filter Handle Height adjuster Charging socket Solenoid valve Pump Wheel Wheel frame Frame Switch Shield widths adjustment Fuse box Spray shield Spray shield end piece Ständer Tank Teleskopic rod Shaft Atomizer nozzle Atomizer nozzle motor

178

  

 

 





      

 









   



                                            18 12 45 18 18 9 18 9 10 10 42 46 18 12 12 22 9 10 18 19 18 10 9 22 45 46

Legend  Weak driver (value 1)

 Medium driver (value 3)

 Strong driver (value 9)

Fig. 6.21  Completed Module Indication Matrix (MIM) of the Modular Function Deployment, according to Erixon [21])

The evaluation sums and evaluation profiles of the subfunctions are used to create modules. On the basis of production characteristics, Erixon derives a “rule of thumb”: that the square root of the number of average assembly steps represents a reasonable number of modules for a product. This number of the highest rated subfunctions are therefore called module candidates. Other subfunctions with similar evaluation profiles but significantly lower evaluation sums are assigned to these module candidates, unless there are clear contradictions, such as in the case of carry-over and technology push. Subfunctions with a comparatively unique evaluation profile should be implemented in an independent module if possible (see Fig. 6.22). Based on the module recommendations of the MIM, alternative product concepts are developed and evaluated. For these steps, the MFD refers to common methods of product development and design as well as the methods of Design-for-X (DfX). As an aid, the MFD provides an evaluation matrix for interfaces, which gives hints for a reasonable design principle of the product structure. Furthermore, various design guidelines and key figures for the evaluation of interfaces and individually for the module drivers are listed. This is the basis for the evaluation of concept alternatives. A so-called Modularity Evaluation Chart (MEC) is provided for this purpose. Finally, the planned modules are revised and a so-called Module Specification Sheet is created for documentation purposes in order to pass on the essential information of a planned module and notes on its design to the design department.

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Sub-funcon (technical soluon)

Module driver Carry-Over Technology Push Planned Design Changes Technical Specificaon Styling Common Unit Process / Organisaon Separate Tesng Black-Box-Engineering Service / Maintenance Upgrading Recycling Module driver sum

Baery Sha Solenoid vale Nozzle holder Handle Telescopic rod Wheel Switch Charging socke Backup Stand Shield width adjustment Spray shield Spray shield end piece Tank Shut-off valce Flow control glas Filter Outrigger (shield) Wheel frame Frame Axis Height adjuster Atomizer nozzle motor Atomizer nozzle Pump

Module recommendaons

      

 

  

    

    

                                               45 22 42 9 9 9 18 22 10 10 18 9 18 19 10 18 18 18 18 12 12 12 10 46 45 46

Legend  Weak driver (value 1)

 Medium driver (value 3)

 Strong driver (value 9)

Fig. 6.22  Reordered Module Indication Matrix (MIM) for module formation in Modular Function Deployment, according to Erixon [21]), compare Fig. 6.21

The Modular Function Deployment offers a comprehensible and broadly applicable procedure for modularization according to product strategy aspects. The use of module drivers is simplified by questionnaires. The module drivers enable comprehensive consideration. However, evaluation according to a simple point scheme at a high level of abstraction can lead to modules whose physical combination is technically impossible. Merging of Design Structure Matrix (DSM) and Modular Indication Matrix (MIM) A common representation for the DSM and Module Indication Matrix (MIM) is provided by Lanner/Malmquist [54]. The developed matrix is a DSM in which the previously free diagonal elements are filled with evaluations from the MIM. For this purpose, the module drivers are assigned letters from A to L and are arranged accordingly on the diagonal of the matrix (see Fig. 6.23). Analogous to the application of DSM, the matrix is converted into a block form by permutation of the rows and columns, whereby this restructuring only takes place for one

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6  Methods for the Development of Modular Product Families

Component 1

Component 2

Component 3

Component 4

Component 5

Component 6

Legend Nondiagonal elements

Spaal

R

E

Energy

Informaon

I

M

Material

Diagonal elements

ABCDE FGH I J KL

Fig. 6.23   Example of the merging of Design Structure Matrix and Modular Indication Matrix, according to Lanner and Malmqvist [54]

prioritized relationship type. Other relationships are only used in the subsequent analysis of the module distribution. Although technical-functional and product-strategic aspects are taken into account in the developed matrix, an application is difficult to handle if the products under consideration become larger or more varied due to the manifold solutions and the types of relationships to be considered. Structural Complexity Management Compared to the Integration Analysis Methodology, Structural Complexity Management according to Lindemann represents an extension of the application of coupling matrices beyond the technical connections of product components [55]. The method is primarily

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intended for the (partly multi-criteria) development of the product structure and thereby integrates the domains necessary for the structural analysis of products, product development processes and the persons and organizations involved. These can be, for example, functions, persons, production constraints, documents or test efforts. The method can therefore be used in a very wide range of applications. Not only technical products, but also all kinds of systems can be considered for analysis and structuring. The method analyses the relationships between different system elements from different domains. In an initial system definition, the system boundaries and the domains essential for the task are determined. For a modularization, the components are selected and, depending on the objectives of the respective modularization project, additional domains, such as functions, customer-relevant differentiating product properties or production constraints are added. For better clarity and analysis, the structures are displayed simultaneously in a matrix and weighted multigraphs (see Fig. 6.24). In addition to the relationships between all elements, indirect relationships are also included as soon as two elements are connected by another element between them. For example, two components can be indirectly related if they perform the same function. For identification purposes, additional matrices are set up which map the derived indirect couplings. The matrices are clustered to form modules. Since functional relationships between components are considered crucial for module definition, cluster analysis is applied to the DSM of functional relationships. In order to consider not only functional but also geometric couplings as well as couplings via features, the corresponding matrices are permuted to the functionally coupled matrix and overlaid with it. Finally, the results of the analysis are transferred to the product design. At this point, design changes to the product are also targeted, for example to resolve unfavorable geometric dependences between components. The principles underlying the Structural Complexity Management are also the basis for further work in the field of modular and variant product structures (see e.g., [4, 43, 47]). This method offers the advantage of a very broad applicability wherein the products, with their components and other domains, such as persons, documents, or functions, are

Fig. 6.24   Example of different matrices and graphs for the structural analysis of technical systems in the Structural Complexity Management, from Lindemann et al. [55]

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considered in the interest of the analysis and structuring of large technical systems. The method focuses on the relationships between the various system elements and the elements from the other domains. However, the identification of structures takes place within the domain to simplify the analysis and interpretation. Computer-aided analysis allows even very complex systems to be analyzed. However, computer-aided analysis bears the risk that, given the large amount of data, errors are difficult to detect and that the user can only understand the resulting module definition with difficulty. The result can therefore be difficult to communicate in some cases. Also, strategic aspects would first have to be formulated in matrix form in order to be integrated.

6.4.5 Key Figures for Modularity Methods for evaluating modular product structures can provide valuable aids in the selection of concepts, particularly in the development phase, since an examination of the manufacturing costs alone is not sufficient to achieve the desired results (see also Sect. 6.5). Accordingly, there are many key figures for mudularity, but their significance, certainty, and suitability for evaluation vary. In principle, single key figures cannot be evaluated with sufficient accuracy. In order to increase the informative value of key figures, several key figures can be combined to form a key figure system. Cluster Independence The basic property of modules is their strong internal couplings compared to their external couplings to other modules or components. The Cluster Independence (CI) after Newcomb et al. measures this property [61]. For this purpose, the number of relationships within the modules in the product is related to the total number of relationships.

I=

Number of relations within modules Total number of relations

(6.11)

A theoretical value of 1 would result in modules that are completely decoupled from each other. A value of 0 means that all couplings between the components are evenly distributed and no modules are visible. The CI is a simple and applicable measure for the evaluation of the physical decoupling in the product and a good indication for the modularity. However, it does not represent any other aspects of modularity, such as the common use of modules or the fulfillment of product strategic drivers by the modules. Coupling Index The effort required to adapt a product concept to future, variety-causing requirements depends on the linkage of product components and can be described by the CI according to Martin and Ishii [58]. This index reflects the coupling of single product components with regard to the necessity of having to adapt the design of other components if certain

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parameters of a component are changed. To calculate the CI, all mutual influences are determined for the components. The sensitivity of the affected component to changes in these influences is then evaluated with points from 0 to 9 and summed up. Interface Complexity According to [7], interfaces should make the handling and joining processes as simple as possible. The key figure interface complexity is the quotient of the summed up assembly time of the module interfaces and the optimal assembly time [21]. The latter is empirically determined by Boothroyd and Dewhurst and is fixed at a value of three seconds per assembly step.



 Interface complexity at 

N m 1

TBDIi

i 01

3



(6.12)

with Nm: number of modules in one product variant TBDIi : installation time for one interface i Product Range Complexity A product range that is structured as simply as possible offers several advantages, including reduced product costs and faster satisfaction of customer requirements. Following Pugh [69], the key figure Range complexity is therefore used to describe the complexity of the product range.

Range complexity = 3 N m N mtot N c

(6.13)

with Nm:number of modules in an average product variant Nmtot: number of module variants in the entire product family Nc: number of contact areas between the modules of a product According to the key figure, the complexity of a product program increases with the number of modules required to configure an average product variant, the number of module variants required in the entire product program and the number of interfaces between the modules. Product Family and Product Line-Crossing Share In order to assess the size of the potential in a product program to use components across its product families, the Method for the strategic planning of modular product programs

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developed by Jonas compares the technical specifications of the components and thus identifies possible common components (see Sect. 6.6.4) [40]. The Product Family Crossing Share (CS) key figure is the ratio of the number of components used across the product range to the total number of components. CS 

Number of components used across the product range 100% Total number of coponents

(6.14)

As a Product Line Crossing Share (CSPL), Eilmus applies this key figure to a product line instead of a product family [17]. Module Coupling Independence and Module Driver Independence To evaluate modular product structures Blees uses the key figures Module Coupling Independence (MCI), based on [61], and Module Driver Independence (MDI) [6]. MCI indicates the extent to which a high number of internal couplings is achieved with a low number of external couplings.

MCI =

Number of interfaces within the modules Total number of interfaces

(6.15)

The key fig. MDI indicates to what extent modules correspond to the module drivers defined within a modularization project. Thus, this indicator is only applicable if the module drivers have been defined consistently (see Sects. 4.4.9 and 6.6.4). Ideally, all components that have been evaluated by a module driver are combined in one module.



MDI 



n i 1

C Call i  Ci n



(6.16)

with Ci: number of components with reference to the module driver characteristic i Call i: number of components in modules with reference to the module driver characteristic i C∞i: number of component relationships in modules with reference to the module driver characteristic i to modules with reference to other module driver characteristics n: number of module driver characteristics The two key figures serve to evaluate the extent to which a modular product family meets the modularization goals formulated in the module driver concept in terms of technology and product strategy. For this purpose, for example, corresponding module drivers and their characteristics must be created in accordance with the Life cycle modularization according to Blees [6] or the MFD according to Erixon [21].

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185

Carry-Over and Specification Variety The key figures regarding Carry-over and Specification variety according to Hölttä-Otto and Otto aim at an evaluation of the savings achieved by modules used across the range for specific functions [35]. The key figures are standardized on a scale up to a value of 10. The key figure Carry-over Ycarry expresses how many functions could be directly transferred to other products. Ycarry  10 



Number of transferable functions Number of functions

(6.17)

The key figure Specification Variety Ydiff examines how many functions exist that have variant specifications. For example, a variant specification could describe different performance values of the product.

Ydiff 

Number of functions with different specifications 100 Total number of functions

(6.18)

In another key figure, which is not described in detail here, it is also described with how much modification effort the modules of individual functions can be transferred to another product. The key figures enable a simple comparison of the potential for the adoption of modules within a product range.

6.5 Evaluation Procedures This chapter has been written with the assistance of Dr.-Ing. Sebastian Ripperda. As described in Sect. 2.4.2, a large part of the cost effects caused by high product variety has to do with complexity costs. The modular structuring of product families is one of the essential measures for easy handling of high product variety. Accordingly, it is aimed at reducing these indirect, distributed, and long-term costs. Evaluation procedures for modular product structure strategies are thus faced with the challenge of estimating these indirect effects with sufficient accuracy and thus support decision making on alternative product structure concepts. The cost accounting methods commonly used in practice as overhead calculation on a full cost basis usually only take into account direct costs, i.e. mainly material and labor costs. Other cost effects are added to the material costs and labor costs as overhead costs on the product variants as a tracing factor, and are thus assigned indirectly. Using conventional methods of cost accounting, overhead costs cannot usually be assigned to product variants according to their cause. Particularly disadvantageous with this generalization are the use of a simplified tracing factor and the assumption of volume proportionality from quantity to costs. Here, equal jumps in the number of variants in the lower value range are usually associated with higher cost effects in reality. Standard variants are therefore

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calculated as too expensive and special variants as too cheap [76]. The equally common concept of contribution margins exacerbates this problem, since contributions of new product variants are suggested to cover fixed costs that are incurred anyway. New and initially low-­sales product variants are thus given a preferential evaluation [79]. This creates the danger that cost-driving product variants are not identified and that the costs of creating and especially managing the variants are higher than the later profit. The difficulties in cost accounting of negative effects of high product variety ensure that the positive effects of a reduced variety through modular product structuring cannot be predicted either. Measures for variety reduction are therefore rarely, and at most only to a limited extent, quantifiable in advance [79]. Activity-based costing methods (ABC) aim to calculate costs as accurately, source-­ related, and transparently as possible based on the required activities and processes. Indirect costs do not have to be allocated on a general basis by means of overhead surcharges. As a resource-oriented ABC, this can be carried out with a focus on the variant-­ dependent enterprise areas and activities. These also take into account the creation of components and therefore the direct costs. However, such procedures are often extensive, detailed and time-consuming to apply, so that they are not usually used in small and medium-sized companies due to the effort involved.

6.5.1 Material Number Cost Methods (Average Cost Methods) The effects of different product family concepts on complexity costs are very difficult to determine due to their indirect and decoupled occurrence in terms of time and company departments. A simple way to evaluate at least parts of the cost effect is to use part number costs. These comprise the average costs incurred for a single part number [34]. In development and design, as well as in production, assembly, marketing, sales, service and administration, a part number can result in total costs of up to several thousand euros per year. Administrative components costs of up to 12,000€ per year have been reported [59] – however, orders of magnitude of between 1500€ and 2000€ for purchased components and between 3000€ and 3500€ for components manufactured in-house are common [16]. It is practically impossible to calculate the exact costs, as many of the cost are fixed costs and occur indirectly and with a time delay. In different cases, these costs depend mainly on the similarity of the variant to other part numbers, their quantities, and other factors. Nevertheless, a comparatively good and stable estimate can be made of the annual part number costs and thus the first portions of the complexity costs can be included in a cost evaluation [19]. For alternative product concepts, the approximate total costs can be plotted over a range of part number costs. For this purpose, the direct material and production costs are determined from historical data, quotations or expert estimates, the forecast component quantities are determined, and the production costs of alternative product family concepts are calculated from these values. The straight-line gradients are determined by the number of components per concept (see Fig. 6.25). The diagram shows the total costs of alternative

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187

Total costs

FH201X

1,30,000 €

TCi =mi * CC + PCi

Concept A

1,10,000 €

Concept B Concept C

90,000 €

70,000 €

50,000 €

0- €

1,000 €

2,000 €

3,000 €

4,000 €

Part number costs per year Fig. 6.25  Example of a part number cost calculation, see text for explanation, according to Eilmus et al. [19])

concepts as a function of possible part number costs. If these exceed a value of approximately 1500€, as in the example shown, concept C should be chosen, while concept B is more economical below this value. Estimating the impact on complexity costs using the typical part number costs of a company represents a significantly simplified procedure with corresponding uncertainties in the results. Essentially, a reduction in the number of different part numbers is favored and the resulting cost savings are roughly calculated. However, the assessability of alternative product family concepts is significantly improved, thus providing assistance in the selection of concepts. It is necessary to consider which cost factors from which product life phases are to be integrated into the process with which accuracy. The procedure can be improved by using different part number categories for classification according to different part number costs.

6.5.2 Time Driven Activity-Based Costing With Activity-Based Costing (ABC) the production sites are included. The actual costs are assigned to the processes and finally the cost rate of the process steps is determined. The ABC thus focuses on the utilization per process. Time-Driven Activity-Based Costing (TDABC) is a further improvement of ABC. In this procedure, the different use of time is estimated. Alternative product concepts or product variants can be estimated by comparing their different use of time resources. The time-based approach estimates the required resources of a company department by a simple comparison. Above all, special processes and work steps often show a higher time load of the resources which can be estimated [42].

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6.5.3 Complexity Cost Prognosis and Complexity Cost Evaluation for Modular Product Family Concepts The evaluation of measures and alternatives of product structuring to reduce internal product variety can be extended and supported by an estimation of variety-induced complexity costs. Even if these cannot be calculated concretely, an estimation of these costs can significantly sharpen the understanding of the effects of product structuring and design on complexity within the company and improve the quality of decision-making. In order to integrate product variety-induced complexity into the evaluations, complexity costs can be considered as a second criterion of economic value in addition to manufacturing costs. The complexity cost assessment method supports the selection of suitable product structure concepts within the framework of the modularization of variant-rich product families. The procedure is divided into the three phases: cost forecasting, cost evaluation, and cost reduction (see Fig.  6.26). The focus of the method is on the cost forecasting phase, which is based on time-driven ABC. The monetary effects of changes in the modularization are forecasted on the product structure and the related changes in the process structure. The monetary effects can then be linked to further qualitative target figures in a semi-quantitative evaluation. In the final step, further cost reduction measures can be derived by linking the forecasted costs to a generic cost impact model. In addition to the selection of alternative product structure concepts, further application scenarios are possible. For example, a pure survey of the current cost structure of the product family, a pure cost forecast of existing concepts, a combined cost forecast and evaluation, a combined cost forecast and reduction, and a collection of suitable measures for the development of a modular product structure can be carried out. The complexity cost method is particularly suitable for comparing different product structure concepts in order

Concept

Product family structure concept

Cost forecast

2

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Cost reduction

Results

6

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Decision

Goals 1. Product-familystructure concepts and goals

2. Analysis of product structure, process and cost 3. Determination of the cost driving processes

6. Semi-quantitative evaluation of the product strucure concepts

7. Derive measures for cost reductions

8.Product structure concept decision supported by cost data

4. Identification of changes in product, process and cost 5.Cost forecast

Fig. 6.26   Procedure for cost-based selection of modular product structures (Ripperda 2015)

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189

to make a decision not only based on the usual production costs, but also on an additional evaluation of the complexity costs. The evaluation method is based on newly developed product structure concepts and the respective objectives of a modularization project. In the first phase of the cost forecast, the product, process, and cost structure of the product family under consideration are recorded in the company, the cost-driving processes are determined, the changes in the product, process and cost structure in relation to the various newly developed modular product structure concepts are identified, and the costs are forecast (see Fig. 6.27). Both material and process costs are considered in the forecast. The procedure focuses on the essential processes that drive costs and are affected by product variety, and estimates their changes in the respective concepts using TBABC. Thus, despite uncertainties in the estimation, the total costs of the alternative product structure concepts can be predicted and compared relative to each other. In the Fig. 6.28, three fictitious concept alternatives (A, B and C) have been compared as examples. The cost forecast is followed by a cost assessment, which carries out a semi-­quantitative evaluation of the developed product structure concepts. In the third phase of cost reduction, measures for further cost reduction are derived, which finally allows a cost-supported product structure concept decision to be made. The complexity cost-based evaluation method according to Ripperda supports the selection of alternative module concepts based on a forecast of the expected costs

Product structure

K3

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I.2 determination of the cost driving processes

I.3 Identification of product, process and cost changes

P1.1.3

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Concept

Process structure

Cost structure

Current product line

I.1 Acquisition

K1

… New process structure

Legend Kn Components

Pn

Processes

equal

omitted

Fig. 6.27   Overview of the cost forecast, for explanation see text (Ripperda 2015)

new/changed

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6  Methods for the Development of Modular Product Families Product structure

Process structure

Cost structure Design Procurement

Stock Suppliers Production After Sales Material

Cost forecast Kostenprognose A B C

Design

Procurement

102,5% 103,6% 104,8%

91,0% 73,9% 72,7%

Number of After Production Material suppliers Sales 95,9% 117,2% 90,4% 101,4% 98,6% 89,6% 198,5% 88,9% 80,0% 97,8% 87,8% 221,5% 74,8% 82,2% 95,4% Stock

Total 98,4% 97,2% 94,8%

Fig. 6.28  Predicted costs using the example of a product family of floor cleaning robots (Ripperda 2015)

depending on the internal variety. The monetary effects of modularization strategies on product, process, and cost structure are shown.

6.6 The Integrated PKT Approach for the Development of Modular Product Families As shown in the previous sections of this chapter, there is a wide number of methods and tools with different orientations and suitability for the development of modular product families. Modular product structures offer great potential for reducing the internal complexity within a company for all product life phases, which results in the necessity to integrate all affected departments in the development of the modular product structure. Thus, a comprehensive and methodically structured approach is indispensable. Applicable methods that can be adapted to boundary conditions and goals are of particular importance. The large number and variety of existing methods, their frequent specialization in certain fields of application and conditions, as well as an often highly analytical approach, make it difficult to use different methods alone as a continuous support for product development. The Institute of Product Development and Mechanical Engineering Design (PKT) at the Hamburg University of Technology (TUHH) has developed and is continuously improving the Integrated PKT Approach for the Development of Modular Product Families, which is presented in this chapter.

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191

6.6.1 Motivation and Objectives of the Integrated PKT Approach The Integrated PKT Approach for the Development of Modular Product Families, or Integrated PKT Approach in short, was developed as a holistic approach at the Institute of Product Development and Mechanical Engineering Design (PKT) under the direction of Prof. Dieter Krause. This approach summarizes the results of research and method development at PKT since 2006. As a concept of an adaptive methodical toolbox, the approach is in continuous development. The effectiveness of the methods is ensured by numerous applications in industry. The approach is geared towards the requirements of product developers (see Sect. 6.6.5). The motivation and objective of this approach is to reduce the internal variety of components and processes as much as possible through a modular product structure strategy, while still being able to serve the customer’s demand of product variety without restrictions (see Fig. 6.29). The strategy of a modular product structure is by far the greatest lever for product development in this challenge (see Sects. 1.4 and 4.4). Through the targeted and consistent reduction of component variety, product development can significantly reduce variety-induced complexity for all product life phases in the company. The approach does not focus on specific industries or products. By applying basic strategies and ideal models, the methods can be applied to manufacturing companies in

Technology convergence

Individualization

Standards

Globalization laws

...

New consumation patterns

Variety of demand

...

Product planning/sales Product variety

Product development Component variety / Process variety methodical deficits Unsuitable evaluation and communication systems

...

...

Lack of communication

Fig. 6.29  Internal component variety should only be aligned with the variety of customer demand

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different industries, be it mechanical engineering, plant engineering, or aircraft design. The approach has proven to be particularly successful for small and medium volume production.

6.6.2 Basic Strategy of the Approach A number of basic directives are envisioned for the integrated PKT approach as an overarching methodical toolbox. These support the achievement of the approach’s objectives and its strategic embedding in business processes. They can be divided into strategic principles and helpful operational measures, which are presented below. Strategic Directives of the Integrated PKT Approach Thorough variety orientation – Internal complexity is largely due to the variety of market demand and the correspondingly increased product range (see Sect. 2.1.1). Product variety, which is perceived by the customer and contributes to the satisfaction of individual needs, generally has a positive effect on sales. The modular structure of product families in the integrated PKT approach is therefore geared solely to external demand variety, as outlined in Fig. 6.29. The aim is to enable the simple configuration of the product variants required by the customers by a small number of modules, thus significantly and sustainably reducing internal complexity. The alignment of the internal variety exclusively with the variety of products perceived and rewarded by the customer avoids unnecessary variety within the company. Reduction of internal variety before reduction of the variety of offers  – Many approaches see the elimination of low-sales product variants as a central measure to reduce internal variety. However, the decline in sales resulting from a reduction in the variety of the product range as well as a possible damage to the company’s image is often underestimated (see Sect. 2.5.1). In addition, low-sales product variants do not necessarily always cause much additional complexity in the processes. Moreover, the costs incurred by the increased product variety are largely remanent and cannot be released again by simply removing them from the product range. The key to reducing internal company complexity lies rather in a product design that is appropriate to the variety and in a modularization of the product structures that is geared to the planned variety of products. The focus here is not only on the assignment of modules to product functions, since this does not allow the effect of reusing modules to be achieved in a targeted manner. Rather, the focus of the development of modular structures is on their alignment with the product variety required on the market and to be covered by the company (see Fig. 6.30). Methodical development of a suitable product structure strategy mix instead of spontaneous or blanket decisions – Certain modular product structure strategies, such as platform or a modular design, are strongly present in practice and in the technical literature. It is therefore all the more important to ensure that modular product structuring is not seen as an early or even product line-wide commitment to one of these strategies. Rather,

6.6 The Integrated PKT Approach for the Development of Modular Product Families Fig. 6.30  Increased complexity should be reduced by reducing internal variety first before the variety of offered products on the market is reduced

193

Variety of offers Not immediatelyy / Not alone

interne Vielfalt Internal variety

the principles of modular product structuring can be applied individually and scaled according to the requirements of the product families, thus developing a uniquely attuned product structure strategy (see Sect. 6.5). Furthermore, the aim of product modularization is not to maximize modularity, but to optimize the modular product structure to the different objectives of all product life phases [62]. Integration of all stakeholders along the product life phases (module process) – The modularization of product structures has an impact on the processes of all product life phases and can also enable a significant reduction in complexity with different objectives for all life phases (see Sect. 4.4). A direct consequence of this is the need to integrate all product life phases into the process of modularization. Only if all stakeholders are involved in the process, can the result be implemented in the long term. A modular product structure should therefore be seen as a compromise formation. There is no “optimal modular product structure” that unites all off the different objectives. Rather, modularization must pursue the integration of the different goals of all product life phases in order to skillfully coordinate and harmonize them for the modular structures. In the final analysis, this can mean that not only one modular structure exists in the company, but that several life-­ phase-­specific views, some with different module definitions, must be possible, as shown in Fig. 6.31 (using a Module Process Chart, see also Sect. 6.6.4). It is important that all participants communicate and agree to these different views and modules, so that a clear understanding of the module can be realized company wide. Moderated alignment of the product life phases instead of mathematical optimization – The development of modular product structures spanning all life phases is practically impossible to model due to different objectives with partially contradictory sub-objectives. It therefore cannot be optimized mathematically. In addition, the often uncertain initial situation and planning, the dynamics of the requirements, and the strategic expert knowledge, which cannot easily be modeled for mathematical optimization, are also important. Rather, the systematic analysis of product variety as well as moderated workshops with the various stakeholders are the appropriate means for the development and company-wide implementation of modular product structures (see Fig. 6.32).

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6  Methods for the Development of Modular Product Families

Produkt- Procurement Development Einkauf entwicklung

Tank Tank[€€] Filter Filter[€] Absperrventil [€€] Shut-off valve Pumpe Pump [€€€] Akku [€€€] Battery Ladebuchse [€] Charging socket Sicherung [€] Fuse Hauptschalter Main switch [€] Taster [€] Push button Laufrad [€€€]

Production Produktion

Sales Vertrieb Ta

Ta

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F

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Präperatfluss Übernahme/ Präperatfluss

Spritzguss

AV P

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Spanende B.

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variant

Übernahme Tiefenentlad.

Polungstest Elektronik

T

T

LR

MK

Sel. Sprühen Sel. Sprühen

module

Fig. 6.31   Example of a modular process over the product life phases as seen in an herbicide sprayer product family (see Fig. 4.16)

Fig. 6.32  The moderated integration of stakeholders from all product life phases and expert knowledge as an essential success factor for modularization

Variety-oriented product design and modularization as an overarching task across departments – The monitoring and improvement of modular product structures should not be limited to activities in product development projects, nor should it be restricted to product family managers. The tasks include the ongoing analysis of product structures, the streamlining of internal variety, the early identification of product variants that will be

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195

required in the future, and the appropriate alignment of modules with the least possible internal variety. These must be carried out continuously and across the product range in order to identify and implement possible potential. Comparable to today’s embedding of quality management in companies, variant and complexity management must be able to act comprehensively and with its own budget. Development of the Integrated PKT Approach as a methodical toolbox – Projects and measures for modular product structuring differ in their initial situation, objectives, scope and other parameters. In order to be broadly applicable, the approach is structured as a methodical toolbox, which allows a company-specific and scaled composition of method blocks for the respective project. This methodical tool box integrates existing and newly developed methods and tools. Consistent support for redesign and new design – In order to enable the fast and sustainable implementation of modularization and a significant reduction of internal variety, the mere definition of module boundaries, specifications, and interfaces is not sufficient. Rather, the Integrated PKT Approach methodically supports the concrete redesign and, if necessary, new design of components and modules. The method units include the necessary design work steps to reduce internal variety, so that methodical support is not limited to conceptual planning. Operational Directives of the Integrated PKT Approach Workshop-based approach  – The necessary integration of all stakeholders along the product life phases described above requires a suitable, interdisciplinary working format, which is ensured in the method units of the Integrated PKT Approach through systematic, well prepared and moderated workshops. These enable the necessary compromises to be made and facilitate the communication and implementation of the results. Phases of information gathering and analysis therefore alternate with phases of workshop preparation, implementation and follow-up. The implementation of the modularization therefore requires both the appropriate moderation skills and a moderator who is positioned as neutrally as possible within the project team and amongst the stakeholders. Establishment of product architects – The overall identification and implementation of modular product structuring measures as an overarching cross-sectional task is ideally not limited to execution in product development projects, but is better assigned to an appropriately-qualified person or group of product architects. These architects can carry out the ongoing activities of maintaining and further developing modular product structures in coordination with sales/marketing and technology and contribute the necessary methodical skills and moderation tasks for product development projects. Simplified mapping of external and internal complexity (analysis model)  – An almost complete mapping of complexity from reality into models with subsequent analysis and solution development in order to reduce internal complexity with the help of modular product structures is not practicable to implement. Therefore, in the integrated PKT approach, the necessary information for a specific problem is collected separately and only this information is analyzed. Comparable to the analysis models of computer-aided

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Fig. 6.33  Examples of analysis models used in the integrated PKT approach [52]

Input

Work step

Output

Goals

Method modules

Required methodical knowledge Tools, models, visualizations

Fig. 6.34   Use of special visual aids in the method modules of the integrated PKT approach [26]

development, specific models are thus derived in order to reduce complexity [27]. This also makes software implementation easier and more comprehensible (see Fig. 6.33). Use of special visual aids as analysis models – For the described integration of the stakeholders of all product life phases, information from different data domains and departments must be collected and understood quickly and correctly by all participants in the workshops. The best way to implement the above-mentioned analysis models for the development of modular product structures is therefore to use specially adapted visualizations that have been developed in the Integrated PKT Approach for the individual work steps and workshops (see Fig. 6.34). When correctly designed and used, these offer the advantage of interdisciplinary comprehensibility of the contents and visualization of critical variance. As a common work tool, visualizations promote teamwork and act as a crystallization point for new solution ideas. In this way, specific knowledge and the creativity of experts from different company departments can be brought into the development process.

6.6.3 Overview of the Method Units of the Approach In the following, an overview of the method units of the Integrated PKT Approach is given. The Integrated PKT Approach provides various method units that are used as a supplementary procedure in the product development process (see Fig. 6.35, middle). The

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Red u

co

Reducon of

Des n of p ig r Mod n for S ocess c u Ram ularisa pply C omple p-up on- hain xity orie for-As Requ thro nted ug se ire prod mbly ments h uct des ign

internal varie ty through Product prog ram planning Developmen t of modular product prog Desig ra

ms

n-for-Variety

Life phase

modulariza on

Legend Methodological modules of the integrated PKT approach

Reduction of internal product variety as an objective

Fig. 6.35   Objective of the Integrated PKT Approach for the development of modular product families as a reduction of internal variety for the provision of external product variety [50]

potentials of modular product structures extend over all product life phases, which processes can also be simplified through joint modification and coordination with the product structures. The modular structure specifies requirements for the product development processes, just as the existing and adapted processes generate requirements for the products to be developed. For this reason, method units are offered to reduce the variety on the product side as well as on the process side (see Fig. 6.35, above). Against the background of research in the field of modular structures for aviation, the third block in the Integrated PKT Approach is the modular lightweight design. It is precisely here that the contradiction between light weight with few interfaces and a modular structure with many interfaces represents a methodical challenge that should not be underestimated. This methodical challenge of modular lightweight design is not dealt with in depth in this book but is briefly listed with the approaches developed in Chap. 7. Central Method Units for the Development of Modular Product Structures The Integrated PKT Approach provides four basic method units for the development of modular product families. The method unit Product Program Planning [40] initially looks at the structure of the product program from a strategic perspective. If necessary, a product program structure is derived and the basic potential of modular structures in the

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product program is identified. Based on this, the method unit for the Development of Product Programs with a high Degree of Commonality [17] identifies possible module candidates across product families and lines supports their development. In order to be able to reduce the necessary internal variety without restricting the range of products on offer, product families must be designed in a variety-oriented manner and structured in modules. The Integrated PKT Approach therefore provides the method units Design-for-­ Variety [44] and Life-Phases-Modularization [6]. Design-for-Variety enables a simple mapping of the relevant, differentiating product properties from the customer’s perspective to the components of the product family. In the process, variant components that depend on several product properties and are thus responsible for an above-average internal component variety are identified. Concepts are systematically developed to eliminate this deficit. Using this product family concept, which is designed in a variety-oriented way, as a new starting point, separate modular structures are developed for each life phase with the help of Life-Phases-Modularization. Contradictions between these views of the modular structure will be identified, visualized, discussed in workshops with all stakeholders of the product life phases and transformed into a harmonized modular structure that is consistent throughout all life phases. This results in a modular concept of the product family that has a minimized internal variety and at the same time opens up further potential for the respective product life phases. Method Units for Process Design of Modular Product Structures The method unit Design for Value Chain [8] identifies strategic fields of action for variety-­ induced complexity reduction along the value chain and feeds these back into the further development of the product families. In order to improve the transition of new module structures in production during the start of mass production, the method for Assessment of Ramp-up Risks in Product Development identifies and evaluates possible risks with a wide range of influencing factors [20]. Modular product structures can provide a better overview of the processes in all product life phases and thus lead to significant savings in complexity costs. For this reason, Life-Phases-Modularization integrates the views of all company- and product-specific product life phases. Modular structures are developed for each life phase and then coordinated together. The development of the modular structures of a product life phase can be methodically supported and coordinated with the respective process design of the life phase. The method unit of Modular Design for Assembly [32], for example, identifies relevant target parameters of the assembly processes and systematically integrates them into the modular structure of the assembly phase. For this purpose, information on the product structure and the assembly process is brought together and visualized, and the effects of various modularization measures on both the product structure and the assembly process are directly shown and evaluated.

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Method Units for the Development of Modular Lightweight Structures In many industries, product development is facing a trend towards ever lighter products. The requirements from the viewpoints of lightweight design and modularization often contradict each other due to additional interfaces and the risk of oversizing. The implementation of modular product structure strategies in the case of lightweight products therefore represents a major challenge, which is briefly outlined in Chap. 7. For the lightweight design of modular product families, a system model is being created in the method unit Modular Lightweight Design [31] and the modularization is being revised with a focus on lightweight design. Adjusting the dimensions of the modules and other lightweight design measures help to reduce the overall weight of the modular product family. The method unit of System Analysis and Synthesis of Variant Lightweight Structures [66] supports lightweight design with a simulation-based prediction of the vibration behavior for a high number of product variants by coupling several dynamic substructures according to a modular product structure.

6.6.4 Presentation of Selected Method Units of the Integrated PKT Approach The method units of the Integrated PKT Approach presented here comprise the essential steps for developing more modular product families. They form the core of the approach, but can also be applied individually or in various combinations in projects, depending on the objectives. The other method units of the Integrated PKT Approach represent optional extensions of this approach. Strategic Planning of Modular Product Ranges The method for product program planning according to Jonas supports the initial planning and revision of the product program with the aim of identifying and designing possible technical carry-over components to simplify the component portfolio [40]. The method is divided into scenario development and program structuring (see Fig. 6.36) [40]. By using key figures, it is then determined to what extent the identified candidates for common components enable synergy effects within product families or across product families. For the structural and economic analysis of the existing product range, the Program Structuring Model (PSM) is used as a tool (see Fig. 6.37) to visualize the products, their hierarchy, and economic parameters of the product range. In a further analysis, trends influencing the future development of the product range are identified from an internal and external perspective and scenarios for the future structure of the product range are developed. A modified SWOT analysis is used for this purpose [41]. The results are trends at product family level, which are combined to form overall scenarios.

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6  Methods for the Development of Modular Product Families

Phases of the method

Tools

Steps of the method

A. Program Structuring Model PSM (last business periode) B. Module Interface Graph MIG (existing product families)

1.1 Current state analysis

C. Tree of external variety TEV (existing product range)

D. Analysis of internal / external trend factors

Phase 1 Scenario development

1.2 Strategy workshop

E. Extended SWOT analysis (product families)

1.3 Derivation of program scenarios

F. Program Structuring Model PSM (Szenarios of the future product program structure)

2.1 Conception of takeover candidates

G. Inverted Tree of variety (product range) H. Carryover Assignment Plan CAP (products and components)

Phase 2 Program structuring

I. Module Interface Graphs MIG (developed program concept)

2.2 Derivation of program concepts

J. Tree of external variety TEV (developed program concept) K. Key figure evaluation (developed program concept)

Fig. 6.36   Process steps of the method for Strategic Planning of Modular Product Programs, according to Jonas [40])

Products Product families

Product lines

Production program Product range

Legend Profit margin

≤0

>0

Fig. 6.37  The Program Structuring Model (PSM) as one of the central visual tools of the method unit for the Strategic Planning of Modular Product Programs according to Jonas [40])

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For program structuring with the aim of potential common components for the product program, a feature comparison of all components is carried out, whereby a distinction is made between primary and secondary features. Primary characteristics must necessarily match to form a carry-over candidate, while secondary characteristics can be harmonized by design measures if necessary. The overall presentation of the carry-over concepts is carried out in a Carry-over Assignment Plan (CAP), a graphical listing of all products and components with color-coded carry-over concepts. In the last step, the designed product range is summarized and evaluated. The method offers continuous and transparent support in the strategic planning of modular product programs. By thinking in scenarios, uncertainties regarding future development can be analyzed. The program-wide conception of carry-over candidates supports the reduction of complexity at program level.

Fig. 6.38   Process steps of the Development of Product Programs with high Commonality, according to Eilmus [17])

1. Visualization of the product range 2. Analysis of potential to increase the communality 3. Development of a product structure strategy 4. Development of common module concepts 4.1 Current state analysis 4.2 Design-for-Variety 4.3 Life phase communality 4.4 Evaluation of common concepts Suitbable communality in the product range

Coordination with the development of modular product families

Development of Product Programs with a High Degree of Commonality The aim of the method is to reduce internal company variety by taking a product-program-­ wide view [17]. For this, the development of modular product programs is accompanied by the development of possible transfer components within a product family that can also be used in other product families or even in the entire product program (Fig. 6.38). For the development of components used across product families, various driving forces from the different product life phases are analyzed. These are arguments for a design of a component in more or less different variants. The sometimes contradictory requirements of different company departments are thus analyzed and determined for further design.

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Legend Generic modules 1 Hydraulic power unit 2 Electrical system 3 Traction drive 4 Brake

5 Steering

No carryover Carryover Carryover with … strong modular coupling

Fig. 6.39   Extract from a Carry-over Chart as the central tool of the method unit, according to Eilmus [17])

The product range is first visualized with its product lines and families as well as its components in tabular form in a so-called Carry-over -Chart (see Fig. 6.39). This shows which components are already in common use in which product families and variants. On this basis, further potentials for common use of components are identified by comparing the differentiating technical properties of the components in terms of identification and classification. Depending on how high the potential for the common use of components in the product family is, the use of a platform strategy, a modular set strategy or the development of modular product families is recommended. In order to coordinate this strategy definition, further reasons are discussed with various stakeholders in the company to either emphasize the commonality across product families more strongly or to allow greater differentiation across the product range [17]. The development and design according to the decided strategy is carried out with the help of the method units Design-for-Variety according to Kipp and Life-Phases-­ Modularization according to Blees [6, 44] (see following sections). The implementation of the cross-product family use of components is specifically supported. The final evaluation and selection of the developed concepts is supplemented by an assessment of the common modules with their achievable cost advantages. Design-for-Variety With the help of the method unit Design-for-Variety, the internal variety of components of a product family can be significantly reduced. The aim is to reduce the number of components in a product family while at the same time retaining the external variety of the product range [44]. An ideal concept of a variety-oriented product family structure (see Sect. 4.6) serves as the target picture, and the so-called Variety Allocation Model (VAM) is the central tool for bringing a product family closer to this target.

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6.6.4.1 System Analysis Initially, it is analyzed which variety-induced problems exist in the company with regard to the product family under consideration and which are to be improved. Typical goals of Design-for-Variety are, for example, the acceleration of order fulfillment processes, the reduction of set-up times, or simplified warehousing. Particularly in the case of larger product families, it is worthwhile first analyzing the components of the product family with their variety and their influence on the defined target variables. In this way, relevant parts of the product structure can be focused on in advance and further work can be reduced. This analysis can be done in portfolio diagrams (see Fig. 6.40). 6.6.4.2 Analysis of the External Variety In order to align the product structure with the external variety of offers, this is first of all visualized in the form of a Tree of external Variety (TeV), as shown in Fig. 6.41 as an example using a product family of herbicide sprayers as an example. In the TeV, the differentiating product properties are arranged according to the average customer relevance in a purchase decision, so that the process of buyers’ decision making is reflected. The formulation of the product properties from the customer’s point of view is essential here. For example, the formulation of a battery capacity of “3000 mAh”, which is often found in product catalogues, is not very helpful from the customer’s point of view, whereas the runtime of the device would be much more relevant (see also systematics of properties and features in Sect. 3.2.1). Each branch of the TeV corresponds to a product variant with its respective differentiating properties relevant to the customer, from a customer’s point of view. In order to reflect the variety of requirements that is really relevant Time to deliviery

long

medium

Legend

short

none

medium

high

Variety of components

Components

Fig. 6.40   An example of a portfolio diagram of the components of a product family with their variety and the effects on variety-induced problems in a company, according to Kipp [44]

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6  Methods for the Development of Modular Product Families Tree of external Variety (TeV)

Variant product properties from the customer‘s point of view

Product property

Number of spray lanes

Arrangement of the spray lanes

Spray width

Arrangement of the spray lanes

20-45 cm

off center

30-50 cm

MANKAR Roll

middle

Number of spray lanes

1

P 45 L

2

P 45 L+R

1

P 30-50 FLEX

1

P 50

50 cm

middle

60-80 cm

middle

1

70-110 cm

middle

1

Spray width

2

P 50 L+R

P 60-80 P 70-110

Fig. 6.41   Tree of external Variety of an exemplary product family of herbicide sprayers for visualizing and planning the variety of the product family, according to Kipp [44]

to the customer and thus promotes sales, the variant product properties are recorded from the customer’s point of view, including their required combinations (see Fig. 6.41). The analysis of the external variety of the product range in the form of the TeV facilitates the definition of the product family, its alignment with the customers’ view and the coordination of the project results with product planning and sales.

6.6.4.3 Analysis of the Internal Variety The variety of functions is recorded by adding the aspect of variety to a flow-oriented function structure (see Sect. 3.2.2). For this purpose, the functions are divided into standard and variant functions. The latter can have different values, optionalities, and number of variants, as well as any combination of these three types of variety (see Fig.  6.42). Different variants of functions exist if their input and/or output states differ so greatly between different product variants that the same function carriers cannot be used or can only be used with considerable over-dimensioning. In addition to the variety of the functions, attention is paid to the variety of the working principles and geometries. A distinction is made as to whether an entire working principle is a variant – that is, whether variant physical effects are used – or whether only elements of the working principle are variant, such as active surfaces or materials. At component level, the variety of the components of the product family is recorded and displayed in the form of a Module Interface Graph (MIG, see Fig. 6.43). This shows the arrangement and rough form of the components of a product family as well as the flows and interfaces between them (see Fig. 6.43). As in the case of functional variety, a distinction is made between variant, optional and standard components.

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Product Family Function Structure (PFS) Energie

electrical vor energy Düse(n)

Düse nozzle

convert electrical Energieinto rotational umwandeln energy

Präparat herbizide vor Düse

Energie rotational vor energy Düsenrad

Sprüh-for setting spray sektor sectors eingestellt

B

B

Spray zerstäuben

produce spray

serbizide Sprühspray nebel

Spray Spray im in Sprühspray sector sektor

Spray

Spray nicht not im in spray Sprühsector sektor

Sprühspray width breite setting eingestellt

Präparat return spray rückführen

Legende Material flow Energy flow Information flow

Präparat herbizide onBoden floor auf

lead spary Spray richten

P Prätarat nicht im spray Sprühsektor

Spray schützen

protect spary

Standard function

state

Optional function Variant function Variant number

Fig. 6.42   Identification of variant functions in a Product Family Function Structure (PFS), here as a section of the herbicide sprayer product family shown above using the rotation atomizer, according to Kipp [44]

6.6.4.4 Analysis of the Variety-Orientation The variety of the product family at the levels of external product variety and internal variety of functions, working principles, and components is transferred into a so-called Variety Allocation Modell (VAM) and jointly visualized (see Fig. 6.44). This serves as the central working visualization of the method and also depicts the causal relationships between the external and internal product variety. It compares the external product variety, as an sales-promoting variety of offers, with the cost side of the product variety within the company. As an alternative procedure, a simplified structure of the VAM can be used, which can be applied specifically to projects that aim for redesigning a product family with a lower level of innovation [28]. This replaces the middle levels of the VAM of variant functions

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6  Methods for the Development of Modular Product Families

Input

Flow

Variants of the product family

Structure Electrics Herbizide

P 45 L P 45 L+R P 30-50 GP 30-50

Components

Data sources • • • •

standard variant optional variant number

PDM CAD BOMs etc.

Fig. 6.43   Module Interface Graph (MIG) using the herbicide sprayer product family as an example for the visualization of component variety [29] based on [6]

Variety Allocation Model (VAM) Variant product properties

Number of spray lanes

Spray width

Arrangement of the spray lanes

Benefits of variety Cost effect of variety

Variant functions

Variant operating principles and geometries

VolumenGenerate strom volume flow erzeugen

AxialkolbenAxial piston pumpe pump

Position Hub

Store information

mech. structure

Düse Düse Protect spray

Nr. of shields

Pump

Düse Düse Straghten spray

angle

Schirm Shield

Düse Düse Atomize spray

mech. separate trennen

mech. leiten rotate

Düse nozzle

Variant components

Legend standard

optional

variant

variant quantity

Fig. 6.44   Section of a Variety Allocation Model (VAM) as the central analysis and working tool for Design-for-Variety, using the example of herbicide sprayers, according to Kipp [44]

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Simplified Variety Allocation Model (VAM) variant product properties

Number of spray lanes

Spray width

Arrangement of the spray lanes

Benefits of variety Cost effect of variety

variant technical characteristics

Number of Pumpvolumen volume flows

Pump volume

Flexible connection

Schirm shield

Pump

Spray angle

Shield width

nozzle

Düse nozzle

variant components

Legend standard

optional

variant

variant quantity

Fig. 6.45   Section of a simplified Variety Allocation Model (VAM) with technical characteristics as an alternative to the description of internal product variety (see Fig. 6.44)

and working principles/geometries with a description with variant technical characteristics, such as variant dimensions or materials (see Fig.  6.45). Such a simplified VAM reduces the effort for training and creation, but cannot sufficiently resolve the functional details in an extensive new product development. Deviations of the product family structure from the ideal picture of variety-optimal product structures (see Sect. 4.6) can be easily identified in the VAM (see Fig. 6.46). Thus, the VAM is used to analyze the existing product family structure for problem areas as well as in the following search for and evaluation of improvement possibilities.

6.6.4.5 Improving the Design-for-Variety For the improvement of variety-oriented product design, the method offers a series of procedures and design guidelines with which the weak points of a variety-oriented product family design identified in the VAM can be improved. This provides support for different degrees of innovation – from an adaptation design to a completely new development(see Fig. 6.47). A comparatively simple design adaption (Step 1 in Fig. 6.47) can already significantly improve the Design-for-Variety by means of the following design principles.

208

6  Methods for the Development of Modular Product Families Variant product properties ! Düse

Variant functions

Düse

Variante operating principles and geometries !

Variant components

Schirm

Schirm

Legend standard !

optional

variant

variant quantity

Contradiction to the ideal variety-oriented product family structure

Fig. 6.46   Schematic representation of the actual state (left) and ideal image (right) of a variety-­ oriented product family structure in the VAM, according to Kipp [44]

variant product properties

Change in the variety of offers

variant functions

variant operating principles and geometries variant components

Redesign

Fig. 6.47   Recommended procedure in the VAM with increasing degree of novelty for the improvement of a Design-for-Variety project, according to Kipp [44]

• Technical variety of components that does not relate to the product variety perceived by the customer can often be eliminated without limiting the external variety of products. • Components that are variant from the customer’s point of view due to several variant product properties should be divided into several separate components, each of which is only dependent on one customer-relevant property.

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• The design of the variant components should be limited as far as possible to the geometries that are absolutely necessary for configuring the customer-relevant variant product property. All other parts and geometries of the components should either be separated into a new standard component or integrated into another, already standardized component. • Different variants of a component can be standardized by oversizing. • If several components are variant view because of the same customer-relevant product properties, they can often be integrated with each other in a single component, thus reducing the amount of part numbers. Concepts with a higher degree of novelty make use of additional solution approaches that have been developed in the search for solutions at the levels of working principles and functions (Step 2 in Fig. 6.47). They usually open up greater potential for improvement, but are associated with greater development costs and risks. If the components of the product families are not only redesigned, but changes can also be made to the way they work and function, further solution principles can be applied in a helpful way. Reducing the variety in the working principles and geometries reduces the number of component variants. If different working principles are currently provided in the product family to implement a function, there is great potential for reducing internal variety. These might be limited to one of these working principles or a single new one. For this purpose, an alternative working principle must be found with which the necessary variety can only be created by means of variant operating elements or geometries. A frequently applicable and effective strategy is the realization of the necessary product variety by software. To achieve this, digital and mechatronic working principles which can represent the variety within a part of the software must be provided. If looking at the flows through the functions of the product family and the variety of the functions included in the PFS, indications can be identified for improving Design-for-­ Variety by applying simple design rules (Step 3  in Fig.  6.47). This involves checking which function chains are variants in the PFS, whether the starting point of a variant function chain can be moved back along the chain, or whether a variant function chain can be standardized earlier in its sales (see Fig. 6.48). Furthermore, variant functional chains should not interact with standardized functional chains if possible, or at least not be the cause for further variant functional chains.

6.6.4.6 Evaluation The method aims at the development of alternative solution concepts. These alternative concepts are evaluated by a value analysis, taking into account the defined goals of the Design-for-Variety project (Fig. 6.49). The method unit offers a structured analysis of the variety of a product family and thus enables the generation of solution approaches. The latter are actively supported by

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6  Methods for the Development of Modular Product Families

Standardize inputs

Minimize interactions

Variant input variables should be standardized within the function structure directly at the input

Interactions and reactions from variant areas must be avoided. Functional chain

Functional chain

!

!

better

Postpone variants formation The formation of variety should be postpone along a functional chain to the last possible function. Functional chain

!

Variant function Standard function

Fig. 6.48   General solution approaches by analyzing the flow-oriented Product Family Function Structure (PFS) on the basis of the variety of the functions, according to Kipp [44] Number of spray lanes (1/2)

Buying Decision by the customer

Aarrangement (central, lateral)

Spray lane width

Selective spraying (yes/no)

Off-road capability (yes/no)

Pre-assembled standard module Delivered modules

or or

or

Legend

screwing

variant optional

screwing & wiring

or

assembly

screwing

36 p possible product p variants

F

F F

standard

Assembly of the variant by the customer

Fig. 6.49   Example of a variant-oriented product family concept for herbicide sprayers with simple modules for configuring the range of products, according to Kipp [44]

procedural recommendations and design guidelines. The design rules presented in Sect. 6.3.1 also help in the implementation of variant-optimized product design. Life Phase Modularization The development of modular product families according to Blees is referred to as Life-­ Phases-­Modularization, since a modular product structure should be aligned and coordinated with all product life phases involved [6].

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The method uses the so-called Module Interface Graph (MIG) as a central working tool to show the arrangement and rough form of the components of a product family as well as their flows and interfaces, and the Module Process Chart (MPC) to visualize and harmonize the module definition over the product life phases. The aim of the Life-Phases-Modularization is to include the requirements of all life phases of a product family with regard to modular structuring. For this purpose, following the Modular Function Deployment (MFD) according to Erixon [21], the module drivers of all life phases are included and integrated into the development of the modular product structure (see Sects. 4.4.9 and 6.4.4). For the modularization of variant products, it is recommended to first ensure a variant-oriented design (see previous section) of the relevant product family, as described in [44], for example. In addition to the module drivers, their characteristics(module driver characteristics), must be included in the Life-Phases-Modularization. These apply the generic module drivers to a product family in order to obtain specific suggestions for module formation (see the following procedure description). In addition to the module drivers, technical-functional modularization must also be included [51]. Modularization according to the modified heuristics of Stone [82] (see Sect. 6.4.2) provides results that are directly incorporated into the life phase of product development. In the Module Process Chart, the modularizations of the life phases are summarized and aligned. It is not necessary for all life phases to work with the same modularization; they must only be compatible with each other.

6.6.4.7 Technical-Functional Modularization With the help of the adapted module heuristics according to Stone (see Sect. 6.4.2), a technical-functional module structure is developed based on the components of the product families. Here, Stone’s method is not applied to flows between functions, but the flows between the components are analyzed. This can be, for example, an electrical current, a flow of a hydraulic liquid or a structural force flow between the components. The flows can be easily recognized and understood by the MIG (see Fig. 6.50). The MIG offers an easy-­ to-­understand and thus interdisciplinary representation of all variants of a product family and their internal variety in a visualization as well as a suitable level of abstraction for the tasks of modularization. With the help of the module heuristics according to Stone and the MIG, the results of the technical-functional modularization are adopted as a modularization concept and serve as a starting point for the next steps. 6.6.4.8 Strategic Product Modularization In order to integrate the modularization requirements of all product life phases, a “desired” modularization concept is first developed separately for each product life phase. For these respective modularization concepts, module drivers are individually compiled for each life phase on the basis of a generic list and used to determine which of the components of the product family can be combined into a module from the point of view of the respective life phase (see Table 6.2). The technical-functional modularization developed in Step 1 is used as the starting point.

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6  Methods for the Development of Modular Product Families T HG

Module „Dominant flow (herbicide)“

Module „conversion and transmission (electrical to mechanical power)“

A

SA

AL SH

Module „Branching flow (electrical line)“

S LR

DH EM

ZD

A

Fig. 6.50   Module heuristics for technical-functional modularization according to Stone applied to the components of a product family using the Module Interface Graph (MIG) [6, 29] Table 6.2   List of generic module drivers [6] based on Erixon [21] Product development Temporal variety The design or technical specification of the module is subject to a planned change or will be affected by a change in technology. Carry-over parts The module is to be taken over from the previous product generation or retained in the subsequent product generation. Procurement Modular sourcing The module should be purchased externally for business, technical or strategic reasons. Production Process The module is subject to special manufacturing or assembly processes. Organization The module offers a suitable scope of work for an organizational unit. Separate testing The module should be tested separately before final assembly. Distribution Variant product The module configures a variant property of the product family from the property customer’s point of view. Use Adaptation/ To adapt or extend the product, the module must be interchangeable for the extension user. Maintenance The module must be removable for maintenance, repair or inspection purposes. Recycling/disposal Product recycling The module is to be transferred to a new stage of use while retaining its shape. Material recycling The module is to be returned to a new production process. Thermal utilization The module is to be thermally recycled. Disposal The module shall be disposed of.

6.6 The Integrated PKT Approach for the Development of Modular Product Families Product planning & sales

Product development

Production

Procurement

213

Application & After Sales

Procurement Module drivers

Product development Module drivers

Module driver specifications

Module driver specifications

Component

Injection moulding supplier I

Tank

Components

Module

Shut-off valve Product strategic module driver Carry-over

!

Module conflict

Tank

Machining module I

Filter Carry-over Pump

Pump

Herbizide Flow Module

Flow control

Module electronics

Atomizer nozzle Switch

Technical-functional module …

battery

Fig. 6.51  Use of network graphs and MIG for the development of life phase specific modularization concepts, here for the life phase of product development, according to [6]

For the application of the module drivers, a network graph per product life phase is created as a working tool, which visually records the selected module drivers and their allocation to the components. The technical-functional modularization from step 1 is first entered on the right-hand side of the graph (see Fig. 6.51). In the example shown in Fig. 6.51, a key objective of modularization for the product development life phase is the strategic option of a simple transfer of certain modules to other products. Here, the necessary module driver characteristics are created for the corresponding module driver “carry-over parts”, − in this case the “strategically planned carry-overs”. In the example shown, only the pump component is a candidate for transfer to other product families. Ideally, the network graph shows that modules from a strategy point of view match the technical-functional modules exactly. If this is not the case – as in Fig. 6.51 – a compromise must be found for the desired modularization of the life phase. By splitting the technical-­functional module in the example, it is possible to ensure that only the components directly affected can be transferred to other product families. However, the newly created interface between the newly formed modules must also be taken into account.

6.6.4.9 Consolidation of the Technical-Functional and Product-Strategic Modular Concepts The modular product structures for the different product life phases, which were developed in Step 2, reflect the requirements of the different phases in the best possible way. However, to derive a continuous process from the modular structures, they must be coordinated with each other, whereby contradictions between the different life phases are identified and resolved. For the development of a modular product structure, this is the core work step, in which the modules are coordinated across the company departments and defined with their module process over all product life phases.

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Product development

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Fremdbezug Elektronik

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Fig. 6.52   Extract from a Module Process Chart (MPC) for the coordination of life-phase-specific modularization concepts, according to Blees [6]

Fig. 6.53   Identification and handling of conflicts in module definition along the product life phases, after [6])

For this purpose, the desired modularizations per product life phase are visualized with the help of the MPC (see Fig. 6.52) and compared, so that any contradictions in the different modularizations of the life phases can be identified and possible solutions presented (see Fig. 6.53). Through comparison and conflict identification and -solution, a continuous process of the module structure through the product life phases is derived and a final modular structure is developed.

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6.6.4.10 Concept Evaluation and Selection Technical-functional and product-strategic criteria are taken into account for evaluation and selection. The evaluation of the concepts relative to each other or to an actual state is supported by key figures for the modularity and the correspondence of the final modules with the module driver characteristics (see Sect. 6.4.5). The technical-functional view evaluation is thereby supported by the Module Coupling Independence (MCI), which gives an indication for the decoupling of the modules. The Module Driver Independence (MDI) is used for the evaluation of the compliance of the developed modularization with the product life phases module drivers. 6.6.4.11 Derivation of the Modular Product Structure Finally, the modular product structure and the modules are defined company wide, so that a design implementation of the modules can follow. Special attention should be paid to the definition and the simplest possible design of the module interfaces in order to facilitate the exchangeability of modules. In the same way, the requirements for the modules from the various product life phases must be observed and implemented. The Life-Phases-Modularization takes into account and integrates technical-functional, organizational, process-related, and strategic aspects from all departments involved in the product development process and attempts to compensate for the disadvantages of other, integrative methods in practical application. Under these partially contradictory boundary conditions, modularization is not an optimization task, but includes all aspects of all life phases, which leads to a harmonized modular product structure. Modular Design for Assembly In order to develop modular assembly-oriented product structures, the method unit focuses on the interactions between the assembly processes and the product structure of variant product families [32]. There are numerous guidelines for assembly-oriented product design to be found in the literature to help improve the assembly-orientation in product development. Design-for-Assembly is also dedicated to this task. The method unit of Modular Design for Assembly complements the development of assembly-oriented modularization and additionally integrates the consideration of product variety. The method represents a product life-phase-specific modularization from the point of view of assembly and can be integrated as an optional extension in the Life-Phase Modularization presented above. It enables a detailed view of assembly as a life phase and supports the transfer of assembly-relevant aspects into product structuring. The so-called integral Product and Assembly Structure (iPAS) is used as the central working tool for this as a visualization model. On the basis of a current state analysis of the existing or planned assembly system, the weighted objectives of the assembly, such as a reduction in lead times or the optimization of the use of resources, are recorded and suitable assembly strategies such as postponement, commonality, or parallelization are selected from a catalog. The current assembly

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A.1 ZMT OG

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Fig. 6.54   Coordinated module formation for assembly process and product structure using the integral Product and Assembly Structure (iPAS), here using the example of a computer mouse [32]

process and the product structure are visualized with the help of the iPAS (see Fig. 6.54) and the assembly-relevant effects of the product structure are analyzed. The selected assembly strategies can be applied with the help of iPAS and coordinated with the modular product structure. For this purpose, the above-mentioned catalogue offers more detailed action cards, which facilitate the application of the strategies by means of characteristic patterns of assembly steps and sequences. For a final evaluation, a system of key figures is used, which includes key figures for the initial definition of objectives as well as so-called measures for the degree of fulfillment of a specific measure.

6.6.5 Application Studies on the Approach The Integrated PKT Approach for the Development of Modular Product Families has been used in numerous industrial development projects to reduce the internal complexity of existing product families or to develop new modular product families [5]. At the same time, these application projects provide valuable information on the need for improvement and expansion of the method units, so that the Integrated PKT Approach is constantly being expanded. Due to the overarching negative impact of increased product variety in all product life phases on the one hand, and the manifold potentials for reducing the complexity of modular product structures on the other, the objectives of modularization projects can be motivated in very different ways. Against this background, a comprehensive comparison of application projects and an evaluation of the applicability and effectiveness of corresponding methods for modularization are only possible using simplified key figures. Since the Integrated PKT Approach is generally aimed at reducing internal company complexity caused by increased product variety, the main options are to reduce the number of

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Sum of all components

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Fig. 6.55   Results of a comparative study of seven use cases of the integrated PKT Approach for the Development of modular Product Families in industry [18]

components, for example, through the number of parts, and the proportion of standard components (see Sect. 6.3.2). In a comparative case study, seven projects that were carried out using the Design-for-Variety and Life-Phases-Modularization methods were evaluated using such simplified key figs [18]. The seven case studies were conducted in four different companies from different industries. The significant reduction in the number of components in all projects clearly illustrates the great potential that the strategy of modular product structuring offers for reducing and mastering complexity (see Fig. 6.55) and as it is also frequently shown in other studies (e.g., [74, 84]). Due to the significantly reduced number of components required to provide the variety of products, the processes of all product life phases can be simplified. The increase in the proportion of standard components significantly strengthens this effect, as it greatly increases the probability of being able to standardize larger proportions of the processes as well.

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7

Effects on Product Development Processes and Future Trends

As a concluding consideration, this chapter examines the effects of modular product structures on the development processes in the company, and goes on to illustrate how current trends in society and research will continue to shape and change this topic in the near future. Modularization as product structure development is not just a single step in the product development process: it keeps the development team and decision makers constantly on their toes during product development. The design of the modular product structure has an impact on all life phases, so that overall coordination and close alignment of the affected company departments are necessary. Modularization thus places special demands on the product developer. Section 7.1 describes how these tasks are embedded in development. As explained at the beginning in Chap. 1, a decisive future trend is the increasing individualization of products, which leads more and more to an orientation towards individual requirements and wishes and finally ends in a batch size of 1. The topic of Industry 4.0 describes this from a production technology perspective. For product development, this can best be mastered with modular product architectures. In addition to the configuration of individual products, adaptation may also be necessary during the usage phase. Changing conditions can be addressed by exchanging modules. Such adaptations must be planned for when designing the product architecture and are presented in Sects. 7.2 and 7.3. New cyber-physical systems (CPS) will further promote the potential adaptability of a product, as products will be able to decide on adaptations independently. Software updates are already a good example of automatic adaptations, which can be extended into the area of hardware and individual adaptability. The linking of products and services, the so-called Product-­ Service-­Systems (PPS), also open up new possibilities for and through modular product structures. If the service of the product is more decisive than the ownership, the high adaptability of a product through modular structures also gains new significance in this business model.

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Another trend with major implications for modularization is lightweight design. Due to rising cost pressure, material consumption and weight are becoming an increasingly important factor for many mobile products. The dilemma lies in the mostly contradictory requirements of lightweight design and modularization, which means their integration into a modular product architecture poses special challenges. Possible solutions are 7.4 in Sect. 7.4.

7.1 Classification of Modularization in the Processes of Product Development Modularization as a development of product structure is not a single work step that can be inserted into a product development process in isolation. Rather, modularization keeps the development team and decision-makers constantly busy during product development. The task of modularizing the product structure is best performed across, in parallel with, or at least coordinated between the existing organizational units of product development in order to identify overarching potential. In addition, defining the product structure has an impact on all phases of the product’s life cycle. The product structure can therefore only be determined in close coordination with the affected company departments and is characterized by strong interdisciplinary cooperation. Defining product structures is therefore a task that places special demands on the product developer. The necessary orientation of a company towards the provision of a high product variety by means of modular product structures includes aspects on the organizational, process and personnel level. The process-related aspects are examined in more detail below. There is a large number of concepts and suggestions for product development processes described in literature (see, e.g., [7]). Different industries shape their respective adaptations of these processes with special focuses, orientations and also different obligations in the individual work steps. In order to be able to clearly classify different tasks in the development of modular product families despite this diversity of processes, we need a reference process that –– provides for the development of a modular product structure and is not focused on a single product, but includes the development of a product family with its necessary external and internal variety, and –– considers the development of product structure strategies across product families and lines to enable synergies across the boundaries of product families or lines. Most of the process descriptions of product development from the literature are primarily focused on the general development of individual products. The special challenges of developing a product family with many product variants while at the same time keeping

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the internal variety of components and processes as low as possible are only addressed indirectly at most. Some approaches recommend that the corresponding data and information are made available in multiple sets for all the individual variants and processed sequentially. However, there are no hints of how these can be used to generate synergies across individual products and thus develop a product family.

7.1.1 Process Models of Product Development VDI 2221 Methodology for Developing and Designing Technical Systems and Products A basic process description for product development, which is common in Germany, is given in the guideline VDI 2221 Methodology for Developing and Designing technical Systems and Products [30]. The VDI guideline provides for a general procedure with seven work stages. In the fourth section, Structuring into realizable modules, the previously developed basic solutions are divided into modules in order to identify development priorities and to achieve an efficient division of the later design work. The starting point includes the requirements, an initial outline of functional modules (without any concrete reference to components), and principal solutions in the form of schematics, circuit diagrams or concept descriptions. For the module definition, it is recommended to focus on pragmatic aspects of product development and thus to form development modules. Assembly modules, maintenance modules for a maintenance-friendly product structure, recycling modules, as well as basic and variation modules for the creation of product variants are also recommended. The result is a modular structure that, in contrast to the functional or effective structure, already shows solutions for the assemblies and components essential for its realization, including their interfaces [30]. The VDI recommends the development of modular product structures as an overarching development procedure and lists several motives for this, which can serve as reference points in product development. More detailed work instructions or methodical procedures are not mentioned. A possibility for further adaptation or supplementation of the procedure of the VDI guideline is shown in Fig. 7.1. In order to be able to relate the development to an entire product family from the beginning and to methodically support the elaboration of a modular product structure in the later course of a development project, selected methods of the Integrated PKT Approach (see Sect. 6.6.4) are integrated into the procedure diagram of VDI 2221. In the first section, the planned external variety of the product family is included along with the requirements, in order to be able to get an initial overview of the necessary product variety. In the second stage, the functional structure should not only be developed for a basic variant, from which the other product variants are later derived, but rather a functional structure for the entire product family. In this way, it is possible to prepare early on in the development of the product family if individual product variants can only be realized with great effort in their later design. Similarly, simple solution principles for realizing the necessary variety must

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Product program planning

Essential results for the development of modular product families Planning of variety of offers Variant-oriented function structure Variant-oriented solution princliples Variant-oriented product family concept

Life-phases modularization Module, interface and system development

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Designed modules Modular system Product documentation Optional methods

Fig. 7.1  Classification of the essential work steps of a product family development using the integrated PKT approach in the workflow of VDI 2221

be considered when working out the working principles. In the fourth section, the product architecture is developed with the definition of the modules. Here the essential methods for modularization are to be applied, in Fig. 7.1 exemplary the life phase modularization. In the design phase (Chaps. 5 and 6), special attention should be paid to the module interfaces, which should be as simple and standardized as possible. In addition, the lowest possible internal variety in the design of the components should be achieved by methodical Design-for-Variety. Product Generation Development The integrated Product Engineering Model (iPEM) takes over the problem-solving activities of VDI 2221 and allows for better applicability through a phase model and a target, operational and functional system according to Ropohl [25] and Meboldt [20] (see Fig. 7.2). It is therefore integrated into the new edition of VDI 2221 [6]. As with the procedure of VDI 2221, iPEM does not have a concrete orientation towards the concurrent development of several product variants in a combined product family or the identification of modular product structure strategies across the product range. However, a significant contribution to the development of modular product structures is made by the concept of Product Generation Development. The essential starting point here is the consideration that in the practice of product development, a real new development without a previous solution status on which to build upon is very rare. Instead,

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Fig. 7.2  Process model of the integrated Product Engineering Model (iPEM) with the activities of VDI 2221 (left) [1]

existing product generations, reference products or at least competing products or solution ideas are usually used as a basis. Also aspects from other domains, such as existing production systems and the knowledge of the product developers ensure that a complete new development situation rarely occurs. The development of modular product structures can be aligned across several product generations through long-term potentials, such as modular systems or a platform strategy, so that the model of PGD provides a helpful basis. V-Model for the Development of Mechatronic Systems The development of mechatronic systems requires the interaction of the disciplines mechanical engineering, electrical engineering, and information technology. VDI 2206 was created to promote this interdisciplinary cooperation. As a generic model, the V-Modell describes the macro cycle in the development of mechatronic systems (see Fig. 7.3). Originally coming from software development, the V-Modell was adapted to the requirements of mechatronics. In practical application, the time and logical sequence of the steps may differ [31]. Based on defined requirements, the overall function is broken down into essential sub-­ functions during the system design phase, and working principles or solution elements are assigned to these sub-functions. In the next step, these are concretized within the individual domains. In the system integration phase, the results of the domain-specific concepts are integrated into a higher-level system. A product is often the result of several runs of the V-model. Along the right branch of the V-Model (see Fig. 7.3), the design states must be continuously checked against specific solution concepts and requirements (left branch). The V-Model offers a good basis for the development of a modular product by the procedure of structuring into functional scopes, the development in separate domains as well

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Product

Requirements

Development in the disciplines

Mechanical engineering Electrical engineering Information technology Modelling and analysis

Fig. 7.3  V-model for the development of mechatronic systems, according to VDI Guideline 2206 [31]

as the reintegration of partial solutions and system validation. The product variety and its lean representation by a few components is not directly supported by the V-Modell. Model of Architecting Steps Otto et al. developed the Model of Architecting Steps as a reference process description, which specifically addresses the development of variant and modular products as a generic procedure [22] (see Fig. 7.4). The model was developed on the basis of common process descriptions from the literature and by studying the product development processes of several well-known companies. In the procedure, the necessary steps for development and product variety are concentrated. Many general development steps are therefore underrepresented in the model, so that even if the model is easy to understand, it remains difficult to relate to product development processes in practice. Verified by means of best practice processes from industry, the reference model does, however, provide a good illustration of the overarching importance of activities for the development of modular product structures in all phases of product development processes. Different Procurement Strategies A key point of reference for the development of modular product families and the embedding of the necessary activities in the product development processes is the type of business production strategy used in the company (see Fig. 7.5).

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Step 1: Define Market Segments

Step 2: Market Attack Plan Step 3: Customer Needs Gathering Step 4: System Requirements Definition Step 5: Functional Requirements Definition

Step 6: Generic System Platform Architecture Definition Step 7: Component Alternatives

function-based or componentbased approach possible

Step 8: Module Boundary Definition Step 9: Architecture Roadmap and Future Uncertainty Management

Step 10: Commonality Assignment Step 11: Architectural Module Sizing

Legend

standard

Step12: Architecture Concept Layout

optional

Step 13: Architecture Downselection

Fig. 7.4 The Model of Architecting Steps as a reference process for the development of modular product families according to Otto et al. [22]

Depending on the strategy, the customer orders flow into the product creation process either sooner or later, dividing it into a customer order-neutral part and a customer-specific part. From this point on, the necessary information for configuring the ordered product variant out of various modules is established. The development of modular product structures must be geared to the different requirements set by the product life phases in the product creation process. The approach of defining the business production strategies by decoupling point of customer orders can be further extended. The increasingly present linking of products and services, the so-called Product Service Systems (PPS), open up new possibilities. The customer decoupling point can thus be shifted immediately before or into the product use phase (see Fig. 7.6). If the service is more decisive than the ownership of the product, the high adaptability of modular product structures also gains new significance in this business model.

230 Engineerto-Order

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Distribution

Developm.

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Recycling

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Customer order-neutral procuct life cycle phases

Customer order-specific product life cycle phases

Fig. 7.5  Overview of different business production strategies by decoupling point of the customer orders (compare Fig. 4.14), according to Beckmann [5]

Make-toStock

Distribution

Development Procurement

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Provide-inDemand

Recycling

Customer order-specific product life cycle phases

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Fig. 7.6  Business production strategy for extended services (extended according to [5])

7.1.2 Necessary Activities for the Sustainability of Modular and Variant Products This section was co-authored by Tammo Bahns. After the market launch of a modular product family, the ongoing development of modular structures remains vital: it reduces the unnecessary creation of new variety and at the

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same time adapts the product family to ever-changing requirements. These changes can be divided into planned or unplanned at the time of the initial development of the product family. Planned Changes Planned changes must be closely linked to the launch strategy and the planning of further product variants to be launched on the market at a later date. On the one hand, an attempt can be made to bring as many product variants as possible to market as quickly as possible, although the development time until their joint market launch is longer, with correspondingly higher risks. On the other hand, synergies between the individual product variants can be better exploited in development, since they are developed in close cooperation with each other. In the sense of an incremental launch strategy, a few product variants of the product family can be offered first with a comparatively fast market launch, and the product family’s range can then be expanded step by step. By means of an already pre-­planned modular product structure strategy, effort and risk per variant can be reduced by successively developing individual modules. Facelifts are another well-known option for the planned product maintenance measures, as known from the automotive industry, for example. In this case, the product variants of a product family are usually revised visually and sometimes also in their functions. Unplanned Changes Unplanned changes after market entry can be seen as part of change management. Therefore, they can be divided into the corresponding categories of application, decision, coordination, and implementation [19]. –– The application identifies the need for changes during the market phase, such as new customer requirements, changes in legislation, or technical developments, and initiates the corresponding changes [8]. –– The decision analyzes the change requirements and chooses between a modification or an extension of the product family and rejection or postponement of the change. In addition, ongoing change processes must be monitored and corrected if necessary [12]. –– The coordination is supported by preparation, coordination, moderation, and documentation. These tasks should be organized as independently of the project as possible. Changes can quickly have an impact on other product families and -lines, for example, through the common use of modules in other product variants [13], which must also be anticipated and coordinated. –– The implementation is responsible for the operational tasks of change, including goal setting, solution finding, elaboration and implementation [2]. Depending on the solution, new versions or variants of components or modules are created. The implementation should be clearly separated from the decision.

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The ongoing development and maintenance of a modular product structure after market entry requires similar competencies as its initial development. For the tasks described, a good understanding of modular product structures as an overall system and, in particular, of the dependencies arising from multiple use of the modules across the entire product range is essential. The use of modules across several product families must be able to be supervised and analyzed in decision-making and coordination. In addition, knowledge of product and process control and reduction of complexity is required. This competence profile has great similarities with the role of the system architect described by Haberfellner [11]. Exemplary Process Landscape for Modular Product Families in SMEs  In the context of the small and medium-sized enterprise (SME) innovation project ModSupport, a process landscape was developed for the development and maintenance of modular products across the product range in SMEs, an example of which is presented below [3]. This is oriented on a Configure-to-Order strategy (see Fig. 7.5), in which product variants are put together order-specifically by configuring modules and module variants. For this purpose, the modules require a clear assignment to the variant product properties from the customer’s point of view, according to which the product variants are configured, and must have clearly defined and easily combinable interfaces. If necessary, they can be parameterized for this purpose [3].  In order processing, the modular system is used as the basis for handling orders (see Fig. 7.7). Since for many SMEs the fulfilment of special requests is decisive for the competitive strategy, an adaptation and even special design can be included as fixed process alternatives in the processes of order processing for the use of the modules. This can already be planned into order placement by the sales department. Should it be determined during order processing that individual modules cannot be used appropriately for the order, this is an essential indicator for a possibly necessary adaptation or extension of the modular system. Furthermore, errors such as poor assembly or problems in meeting customer requirements, can occur in all phases of order

Order fulfillment Design order

Sales and project planning

Engineer to order

Procurement

Production

Assembly

Delivery

Configure to order

Errror management process

Modular kit

Adaptation of the modular kit

Fig. 7.7  Process landscape for modular product families in SMEs, according to Bahns et al. [3]

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Adaptation of the modular kit

Modular kit

Need for change

Identification of the affected modules

Analysis of the effects

Evaluation & dicision

Implementation

Adapted modular kit

discard / hold back / revalue

Fig. 7.8  Maintenance process for modular system (see Fig. 7.7), according to Bahns et al. [3]

processing. These must first be solved in an order-specific error management system and then passed on to the person in charge o the modular system for checking and rectification. The adaptation of the modular kit (see Fig. 7.8) begins with the collection, analysis, and filtering of change requirements. These change triggers, suggestions for improvement, and problems are analyzed with regard to the necessary changes to the module kit and their effect on the modules. Further change triggers can be a newly planned variant, new technologies, or changes in legislation. Members of the product management and planning department should therefore be involved in this process step in addition to those responsible for the modular system. For further processing of change requirements, various stages of the product family sustainability process shown in Fig. 7.8 should be taken into account. These steps may differ according to the scope of the change, the allocated responsibilities or resources. Setting up a process with several process levels makes it possible to proceed smaller changes quickly and easily, while the costs and risks of more extensive changes with potentially greater effects on many modules of the modular system can be better mitigated with appropriate measures. The sustainability process for the modular system is triggered at regular intervals and additionally by special demand situations. The activities in the process should be under the aegis of a dedicated development team with interdisciplinary skills. It is also important to budget independently of specific customer orders, as the modular system is implemented across the product range.

7.2 Product Individualization and Personalization This section was co-authored by Johanna Spallek. In variant series production, the aim is to identify the customer’s requirements and to develop a predefined product variety based on these, with the result that the product variants are anonymously pre-developed for the customer. The risk here is that any predefined variants may not optimally identify and satisfy individual customer needs. Similarly, variant series production entails the risk of high up-front expenditures for the complete development of the product spectrum in the event of uncertain demand. It would therefore be expedient to supplement variant series production by adapting the product’s properties to the preferences of the individual customer, which is where the main motivation for product individualization and personalization lies.

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cc Product Individualization  Product individualization is a product provision adapted to customer-specific requirements with the aim of enabling a high differentiation advantage over competitors [24]. The individual customer benefit is increased by designing the product for use by a specific individual [4]. The product is characterized by its high adaptability and reconfigurability [14]. Customers do not choose from predefined variants, but rather co-create with the developer to a certain extent in individual product development [15].  The term mass customization describes the mass production of customized products to meet individual customer requirements. However, the term is sometimes also used for highly variant mass production, so that the term mass personalization is coined in English to emphasize the customer-specific product design once again. The term “personalization” is often used in the field of individualization of communication with the customer, so that the term product individualization is preferred for customer-specific product design. This includes product adaptation to individual customer requirements, such as the design of a product according to individual human body dimensions in medical technology. It is essential that very different forms of customer integration into the product adaptation process can be realized. The individualization of products according to the preference of a customer significantly increases the product benefit. However, increasing the variety of the product range also means increasing the internal variety of components and processes. It is therefore crucial to be able to offer individualization at a manageable additional cost by developing suitable product structures and processes [24]. Individual product customization and the resulting added value for the customer must outweigh the process complexity required for its realization in all product life phases. Modularization and Product Individualization Modular product structure strategies offer a very suitable basis for the development of customizable products. Modular product families are characterized by their structure of decoupled modules with defined interfaces. The individual product variants are configured by combining standard modules with variants and optional modules. For product individualization, additionally customizable modules can be provided as a further module type and used to individualize the product variants [27]. This strategy limits the customer-specific adaptation of product variants to the individualizable modules. Analogous to the variant modules, they should also be as decoupled from other components as possible so that no adaptations to other modules are necessary (see Sect. 4.6.1). Product Development Processes for Individualized Serial Products The development of a product family that can be individualized requires that the product characteristics which can be variably designed are identified at an early stage. In the development of the modular product structure, customizable modules are pre-planned and decoupled as much as possible. These modules can be used during the market phase for

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order-related adaptation. The customizable module is order-specific in both design and production. The pre-planned combination of standard, variant, and option modules of the product family meant to configure customer-specific product variants means that good economies of scale can continue to be used for most processes in terms of mass customization. It is important that these process components are not affected by the individualization of the products in day-to-day business, so that their standardization is retained. For the ongoing process of order-related product customization, different degrees of customization can be distinguished, depending on the extent to which the customizable modules are predefined. The size of the parameter space that is permitted for individualization is also decisive. This results in different product development processes [27]. Frequently, the product features that can be individualized and their expected characteristics are already sufficiently known, such as the specific adaptation of a prosthesis worn by a person. With such predictability, it is expedient to strongly pre-define the customizable module and to strongly standardize the process of individualization in the series production. The customer data is recorded and used to generate adapted production data for the individualized modules. After completion or adaptation, these are combined with further modules and the individualized product variant is assembled. This process offers good opportunities for automation, so that an individualized product is possible with low internal variety. When predicting individual product feature characteristics is difficult, there needs to be greater flexibility in the individualization process. Based on an assessment of the individual requirements, larger design services require extensive planning in order to carry out the individualization. In contrast to the standardized process of individualization described above, it is much more difficult to evaluate the permissible scope for individualization in advance. Additive Manufacturing (AM) for Product Individualization Individualization of products in series production increases the demands on the flexibility. AM technologies with their recent leaps in development can become key players and offer new solutions to this. The various AM processes, in which a component is created by adding material element by element or layer by layer, have been increasingly used in recent years to produce tool molds, final components, and prototypes [28]. Individualized modules and components can thus be produced flexibly in a standardized process step. Tool-­ less manufacturing directly from digital production data allows a high degree of geometric freedom. This creates a high potential for future product individualization – even if manufacturing costs and times are not yet competitive with conventional manufacturing processes. Providing individualized products ideally entails the use of modular product structures, in which a few customizable modules with flexible AM processes can be produced according to individual customer data and combined with other modules. The advantages of conventional and AM processes can thus be cleverly combined for optimal results.

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7.3 Demographic Change and the Development of Ageing-Appropriate Products This section was co-authored by Olga Sankowski. Declining birth rates, increasing ageing, and shrinking populations are key aspects of demographic change. The proportion of people over 65 years of age in Germany is one of the largest in the world at around 33% [29]. The effects are increasingly being felt in all areas of social life. From the point of view of product development, demographic change holds various opportunities and risks. Companies are feeling the effects both from within, due to ageing employees, and from outside – due to ageing customer groups [16]. Internally, changed work processes and environments as well as enhanced human resource and knowledge management methods are required to transfer experience from older to younger employees. Externally, new and growing markets are emerging for the customer group of senior citizens. Growing markets include medical products, rehabilitation, and nursing care for the elderly as well as products in the fields of household appliances and leisure. A major challenge for product development is to ensure that product innovations are accepted by the older target group. Reliable and appropriate products are often not sufficient [26]. A more critical attitude towards the handling and costs of new purchases as well as negative associations of age, illness, and infirmity in society must be considered. Medical products and products intended for older people often meet with rejection, especially from the intended customers, as they are reluctant to be regarded as old and frail. At the same time, the development of such products is cost-intensive. The requirements are particularly diverse due to different life situations and physical restrictions of potential customers. The so-called “competence model” is now used in methodical product development. According to this model, with increasing age, there is not only a marked loss of skills and senses, but also a shift of competencies. Knowledge, experience, and quality awareness often increase, while strength and endurance decrease [32]. These changes are very individual and cannot be determined by the age of a person. Preferences, wishes and requirements must also be considered when defining user groups. Modern approaches to product development sometimes integrate the user earlier and more intensively into the product development process, for example, in mixed development groups of users and developers [9, 21]. A universal product that meets different needs is essential. What is easy to use for a severely restricted user is extremely convenient for a less restricted user. The integration of users to ascertain requirements is increasingly finding its way into product development. Especially in medicine, sports, and rehabilitation, user integration is used to create individually adapted products. Methods of AM and modular product structures make it easier to control the age-based adaptation of products (see previous section). A modular product structure also makes it easier to adapt products to changing requirements during use by customers. The customer, manufacturer, or a third-party provider can do this by replacing or adapting modules [17].

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Research efforts to develop products suitable for the ageing are being intensified not merely as a response to the ongoing demographic change, but also because of the huge resulting potential. The major challenges facing the methodology of product development include how users can be effectively integrated into the development process and how products can be adapted to the user and at the same time offered at low cost.

7.4 Modular Lightweight Design Products Modular product structures usually mean a higher number of interfaces and the danger of the over-dimensioning of modules. These aspects majorly contradict the requirements of lightweight design, which generally aims to minimize the energy consumption of a product through an optimum ratio of payload to weight. In the field of traffic engineering, the driving forces of lightweight design are the increase in payload and speed, and the reduction of inertia of acceleration or rolling resistance, which then lead to a reduction of energy costs and emissions. In commercial aviation development projects, for example, an increase in weight with the same functionality is virtually not acceptable. Here, lightweight design methods such as material, structural or system lightweight design are used in combination with special manufacturing processes to achieve the lightest possible design. Many industries with high demands on the lightweight design of products also make high demands on verification calculations and approval tests as soon as humans are directly involved in the use of the products [18]. At the same time, however, these industries are also facing the trend towards ever more individualized customer requirements and are increasingly attempting to cover the required product variance with a reduced internal variety of components and processes through product configuration. In aircraft design, for example, this applies to the cabin area, which is equipped with different layouts and designs while offering the same functionality for the airline. Against the background of this variety of demand, modular product structure strategies offer great potential – but the apparent contradiction between lightweight construction and modularization does not necessarily mean that this product structure strategy is completely excluded for lightweight products. Despite the contradictions between modular construction and lightweight construction, the goal for variant lightweight products must be to cleverly combine both modes of design (see Fig. 7.9). This innovation in development methodology is characterized by the term modular lightweight design. Modular designs can provide a number of benefits to reduce and master internal variety and reduce complexity within the organization, thus reducing the resulting complexity costs. Above a certain product variety required by the market, a modular product architecture is of great advantage for the entirety of a product family. Economies of scale through the reuse of modules can reduce the testing effort by making it easier to design and test self-contained modules with clear and simple interfaces.

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Fig. 7.9  Field of tension in the development of modular lightweight products [18]

The main disadvantages of modular design are, on the one hand, additionally required interfaces and, on the other hand, the oversizing that is usually necessary when modules are used several times. Additional module interfaces may become necessary when new modules are created to configure customer-relevant properties. From the point of view of lightweight design, these interfaces represent an unnecessary increase in weight. On the other hand, however, they simplify the configuration of product variants and can significantly reduce the process variety in all product life phases. The multiple use of modules in different product variants or families usually leads to an extension of the requirement ranges for these modules. The correspondingly necessary over-dimensioning of the module also leads to an increased weight of the individual product variants. The overall goal of modularization for lightweight products must be not only to find the optimum weight for each individual product variant, but also to focus on the entire product family weight – that is, the total weight of all possible product variants or of the modules intended for the product families. Sales estimates for each variant can also be included in the analysis, so that the fleet weight can be optimized. In the product family of a modular aircraft galley shown in Fig. 7.10, the modules are used in different product variants. Each product variant places different demands on the modules, for example, due to different equipment features. These different equipment features result in different mechanical loads in relation to the individual modules. For use in several product variants, certain modules must therefore be oversized, which in turn increases their weight. ◄

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Fig. 7.10  Using the modules of a product family of aircraft galleys to configure the product variants (compare Fig. 5.17) [10]

In order to optimize this oversizing with respect to the entire product family and not to the individual product variant, the oversizing of the individual modules in each planned product variant must be determined and the effect on the product variants iteratively analyzed. In this way, the potential for weight reduction of the modules in relation to the product family can be determined [10, 18]. For the use of modular product structure strategies in the lightweight design of product families, dynamic loads must also be taken into account [23]. The modular product structure must be broken down into into a dynamic sub-structure that is necessary for FEM modeling. The module interfaces must be specified so that all necessary information is available for the FEM simulation. In contrast to the usual descriptions of modular product structures, the design must be significantly more detailed. For individual modules, the frequency response functions are determined either by FEM simulations or by tests. In an overall model, the information is configured from the modules or substructures depending on the desired product variant. Although a series of module simulations or tests are initially required to determine the data, these can then be reused for other product variants (see Fig. 7.11). New modules can easily be added in the same way without having to perform a large number of necessary overall tests of new product variants [18].

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Connecting element

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Fig. 7.11  Principle of the “test pyramid” of material, structural and component tests and the reduction of the number of necessary tests in a product family [18]

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11. Haberfellner R (2012) Systems Engineering – Grundlagen und Anwendung. Orell Füssli, Zürich 12. Hiller F (1997) Ein Konzept zur Gestaltung von Änderungsprozessen in der Produktentwicklung. Dissertation, Universität Kaiserslautern 13. Jarratt TA, Eckert CM, Caldwell NH, Clarkson J (2011) Engineering change: an overview and perspective on the literature. Res Eng Des 22:103–124 14. Jiao RJ (2012) Prospect of design for mass customization and personalization. In: Proceedings of the ASME international design engineering technical conferences and computers and information in engineering conference, Washington, 28–31 August 2011. pp 625–632 15. Ko H, Moon SK, Otto KN (2015) Design knowledge representation to support personalised additive manufacturing. Virtual and Physical Prototyping 10:217–226 16. Kohlbacher F, Herstatt C, Schweisfurth T (2010) Produktentwicklung in Zeiten des demografischen WandelsWissenschaftsmanagment, pp 30–36 17. Koren Y, Hu SJ, Gu P, Shpitalni M (2013) Open architecture products. CIRP Ann Manuf Technol 62:719–729 18. Krause D, Seemann R, Oltmann J, Rasmussen O (2016) Produktvalidierung von Leichtbaustrukturen für die Flugzeugkabine. 65. Deutsche Luft- und Raumfahrtkongress (DLRK) der DGLR, Braunschweig 19. Langer S (2015) Änderungsmanagement. In: Lindemann U (ed) Handbuch Produktentwicklung. Hanser-Verlag, München, pp 513–539 20. Meboldt M (2008) Mentale und formale Modellbildung in der Produktentstehung – Als Beitrag zum integrierten Produktentstehungs-Modell (iPeM). Dissertation, Universität Karlsruhe 21. Ministerium für Soziales und Integration (2016) Soziale Teilhabe durch technikgestützte Kommunikation – Projekt Sonia. maschenta design. Seitingen-Oberflacht, Stuttgart 22. Otto K, Hölttä-Otto K, Simpson TW, Krause D, Ripperda S, Ki Moon S (2016) Global views on modular design research  – linking alternative methods to support modular product family concept development. J Mech Des 138:71101 23. Plaumann B (2015) Systemanalyse und -synthese für die Auslegung varianter Leichtbaustrukturen unter dynamischen Lasten. Dissertation, Technische Universität Hamburg-Harburg 24. Reichwald R, Piller F (2009) Interaktive Wertschöpfung. Gabler Verlag, Wiesbaden 25. Ropohl G (2009) Allgemeine Technologie  – Eine Systemtheorie der Technik. KIT Scientific Publishings, Karlsruhe 26. Sankowski O, Wollesen B, Köhler B, Krause D, Mattes K (2016) Avoiding fall related injuries in older adults  – an interdisciplinary design approach. In: Boks C (Hrsg) Proceedings of NordDesign 2016, Trondheim, August 10–12 2016 27. Spallek J, Sabkowski O, Krause D (2016) Influences of additive manufacturing on design processes for customised products. In: Marjanović D, Storga M et  al. (Hrsg) Proceedings of the design 2016 14th international design conference, Dubrovnik, pp 513–522 28. Thompson MK, Moroni G, Vaneker T, Fadel G, Campbell RI, Gibson I, Bernard A, Schulz J, Graf P, Ahuja B, Martina F (2016) Design for additive manufacturing – trends, opportunities, considerations, and constraints. CIRP Ann Manuf Technol 65:737–760 29. United Nations (2015) World population prospects  – the 2015 revision, key findings and advance tables. https://esa.un.org/unpd/wpp/publications/files/key_findings_wpp_2015.pdf, Zugegruffen: 13.1.2017 30. Verein Deutscher Ingenieure (1993) VDI-Richtlinie 2221  – Methodik zum Entwickeln und Konstruieren technischer Systeme und Produkte. Beuth Verlag, Berlin 31. Verein Deutscher Ingenieure (2004) VDI-Richtlinie 2206 Entwicklungsmethodik für mechatronische Systeme. Beuth -erlag, Berlin 32. Williger B, Lang F (2012) Senioren als Zielgruppe der Produktentwicklung. In: Leitfaden für die alternsgerechte Produktentwicklung. Fraunhofer-Verlag, Stuttgart, pp 13–25

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Alternative Alternatives are different technical systems with identical requirements, which are developed in parallel as different (partial) solutions within the scope of product development – but from which only one alternative is ultimately pursued. Alternatives are different solutions to a task. They meet the same requirements but are different in concept or design. They are developed in parallel to each other as different (partial) solutions within the scope of product development and are subsequently reduced to a final solution in an evaluation and selection process. An alternative is chosen or the contents and findings from several alternatives are merged into a new alternative concept to be further developed. Alternatives can be turned into variants by changing the task definition. Assembly Assemblies are units of a technical entity’s or system’s product structure. They typically comprise components and individual parts that form a unit from the point of view of assembly, functionality, production or transport. An assembly is typically referred to when the purpose of the grouping is to define a scope of assembling the product [8]. Building Block The term building block describes an element of a modular building set. Function blocks are defined from the point of view of fulfilling technical functions that they can perform either individually or in combination with other blocks. Production blocks, on the other hand, are defined according to technical production aspects. see also [18, 23].

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Building Set A building set is a collection of different building blocks that can be used to create products with different functions (or only with different parameter values) by combining building blocks. Different blocks typically perform different functions or have different function values. For example, by different sizes of blocks a building set can include size ranges. In the case of building sets, variants are created by combining building blocks of different function and design with uniform interfaces. A very large number of product variants can be created with a limited number of blocks by using a modular system. The advantages for the manufacturer include large batch sizes in production, cost-effective storage, and short delivery times. The term pairs building set/building block and modular set/module are often used synonymously. Building Structure A building structure is created by combining several components. The components can be individual parts or assemblies. Assemblies can, in turn, consist of individual parts or sub-­ assemblies. The physical building structure specifies the technical-physical assembly through which these functions are fulfilled. In contrast, the function structure shows in detail which functions the product should fullfill. see also [23]. Characteristic, Technical The technical characteristics of a product are the variables that can be directly influenced or defined by the designer. They describe the structure, shape, dimensions, materials, and surfaces of parts. The set of characteristics of a product constitutes its properties, that is, the behavior of the product (for example it’s function, weight, safety, or it’s producibility, testability, or costs), which are perceived by the customer. The systematic differentiation between characteristics and properties is found in the Characteristics-Properties Modelling (CPM) according to Weber or in Axiomatic Design according to Suh [35]. Combinability Combinability describes the possibility to create different product variants by configuring existing (configuration) modules. The combinability of modules is one key parameter of modularity. According to Salvador, the combinability of modules is ensured if they are sufficiently decoupled and if functional binding and standardized interfaces are given. see also ([28]). Common Part Common parts are components that are used identically in different products across several parts of the product range. Ehrlenspiel already describes as “common parts” those which are reused in the same product and uses the term “repeated parts” when used across

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different products. Other sources use the term only when parts are used together across series, product lines and even brands. see also [9, 29]. Commonality Commonality refers to “similarity”, “mutuality” or “sharing of common features” and stands for the utilization of similarities of variant products to reduce the internal variance of the products and the associated complexity in the company. The commonality of modules is a key parameter of modularity as well as a gradual and relative property of variant products. The term is often further specified and used for example for [14, 28]. –– –– –– ––

functional commonality as similarity of requirements and solution principles, component commonality or technical commonality as physical similarity, structural commonality as similarity of product structures or process commonality as similarity of processes.

Common Parts Strategy In a common parts strategy, components are used across areas of the product range or even across the entire product range (standardization). The aim is to reduce variety through multiple uses at the component level and smaller assemblies. The feasibility of a common parts strategy can be supported by developing a suitable product structure. Possible transfer components are to be identified, decoupled and developed with regard to their interface and performance characteristics in such a way that they can be used comprehensively. Complexity Complexity is composed of the number, diversity and relationships of the system elements as well as their states and variability. A system is complex if it is non-deterministic, uncertain and dynamic. If the aspect of temporal variability is missing, we speak of complicacy. This distinction is widely used in the literature but is not often used in practice, since an increase in complicacy also increases complexity in its subjective perception. On the one hand, complexity can be measured in its objective partial aspects, but on the other hand, its perception is subjectively dependent on the frame and point of view as well as the context of the observation. It has a negative effects through increased expenditure and information needs in the company, but can also have positive effects, such as serving as a barrier to market entry. The effects of complexity are often underestimated, as they occur long after their cause and in completely different areas of the company. In the topic of modular product families, variety is a key aspect and a major cause of complexity. see also [31, 34].

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Complexity Costs Product variety-induced complexity costs result from the internal diversity of the product range in the company. Variety-related costs are a significant part of the complexity costs. Complicacy The complicacy of a system is determined by the number, variety and relationships between the system elements and their possible states. It is a subset of the complexity, but in contrast to this, it describes deterministic, safe and static systems. A complicated system has comparatively many elements and relationships, but also a deterministic behavior. Component The term component is often used synonymously to the term single part [23] but can also describe an assembly. The term is usually not used as a fixed term in product documentation, such as in bills of materials. In the context of modularization, on the other hand, components are defined by decomposition of the product structure. The project-related use of the term offers the advantages of being able to define a suitable view with different levels of detail and to be able to break down and optimize the existing product structure more easily. This definition of components is very important for the successful development of a modular product structure, as it is the starting point for reconfiguring product structure. Configuration Product variants can be configured by combining (configuration) modules. Configuration describes the process of creating specific product variants depending on their requested properties by selecting and assembling modules instead of having to design them individually. This configuration offers the potential to enable the greatest possible variety of products to be offered by a small number of configuration modules without specific design effort, thus reducing development times, delivery times and stock volumes. A modular configuration kit can be used to facilitate the configuration of product variants. The approach of design for variety aims at the development of product families that are as easy to configure as possible. see also [29]. Coupling A coupling between components of a product exists if any change to one component would make it necessary to change another component. In addition to structural dependencies, this can also include information flows, or heat, or magnetism, for example. A basic distinction is made between information flow couplings, material or energy exchange couplings, and structural connection couplings. (see also decoupling)

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Cyber-Physical System The physical world and the virtual world merge into so-called Cyber-Physical Systems (CPS), which represent physical products which exist on the Internet or the Internet of Things. Computers or processors embedded in the products (embedded systems) realize intelligence and networking and enable independent communication, monitoring and control on the Internet, as well as triggering actions in the product or the environment. The terms Product Service System, Cognitive Systems and CPS cannot be clearly distinguished from each other. In production, CPS comprises intelligent machines, storage systems and operating equipment that carry on an independent exchange of information, trigger actions and control each other independently. They are interlinked throughout, from inbound logistics, to production, to marketing, to outbound logistics, to service – all using intelligent communication technology. see also [5, 19]. Decomposition (see component) Decoupling The decoupling of components of a product is a key principle of modularization and design for variety. It describes product structure divided into components that are very little dependent on each other. The dependency can come from structural connections, but also the exchange of information, materials or energy. The constructive process of decoupling a component or module from the rest of the product structure can also be called decoupling. The decoupling of modules is a key aspect of modularity. Modules are based on decoupling since modules are only created by concentrating couplings within a module and decoupling it from the rest of the product structure. In terms of design for variety, the components of a product family are ideally strongly decoupled from one another. Changes to one component to create a new variant do not result in changes to other components. This is supported by a minimized number of standardized and permanently stable interfaces. Differential Design/Integral Design The integral design method describes the design principle of building components or even entire products from as few individual parts as possible. The aim is often to combine several functions on one component. Reasons for an integral design are, for example, the reduction of part numbers, weight reduction, the improvement of stiffness, or the saving of interfaces or assembly steps and production tools. In many cases, product optimization often aims at a cost-effective transfer of several functions to one part. It is often used for mass products.

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The differential design method, on the other hand, describes the design principle of dividing components or even entire products into several individual parts. Drivers for differential design can be: easier handling of smaller components in production and transport, or reusing existing parts, or greater freedom in material selection and component design. They are more likely to be used for single parts or small batch sizes. Dividing into several smaller parts also aims to increase part lot sizes, as they can be used several times. see also [23]. Economies of Scale Economies of scale describe the dependence of costs on the lot size or frequency of repetition of an activity. For example, unit costs are reduced significantly with increasing batch size by reducing allocation of one-off costs, automation and, above all, greater efficiency of larger production plants. Economies of scale are thus a fundamental motivation for mass production. In addition to demand, the decisive factor for the utilization of scale effects in a specific case is the exact cost effect in relation to batch size, since positive economies of scale cannot always be expected. see also [24]. External Diversity (see the Variety of Offers) Function A function is an intentional connection between the input and output of a technical (sub) system to fulfil a task. Functions, like requirements, are formulated as solution-neutral as possible in order not to anticipate technical solution possibilities when defining and solving design tasks. They are described by subject and verb (e.g. “increase pressure”, “direct torque” or “reduce speed”) and classified according to energy, material and information flows in a task-specific manner. As far as possible, this information should be supplemented or specified by the physical quantities involved. see also [23, 34]. Function Binding Function binding is a characteristic of product architecture and a key aspect of modularity. If individual modules of the product architecture always fulfill exactly one function or a defined set of several functions completely, function binding is achieved. It describes the one-to-one assignment between functions and modules. Function binding reduces development effort, since system understanding is facilitated and development tasks can be better parallelized. However, this process requires more effort to be allocated to interface design. Function binding also supports new or variant overall functions by configuring (function) modules. see also [23, 34].

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Function Structure Functions of a product and their interaction can be represented by a function structure. This is usually done either through hierarchical function structures, which show the main functions, functions, subfunctions and auxiliary functions, or through flow-oriented function structures, which show the connection between the functions according to energy, material and information flows in the manner of a block diagram. Functions are described by subject and verb, such as “increase pressure”, “direct torque”, “reduce speed”, and are derived from energy, material and information flows in a task-specific manner. As far as possible, this information should be supplemented or specified by the physical quantities involved. Integral Construction (see differential design) Interface An interface is an area or point of interaction between two (sub)systems, for example between components or between modules of a product. The interaction can be a structural connection or the exchange of energy, material or information. If an interface is used more frequently in its design or is used for exchange or multiple use of modules, it is useful to design it accordingly and, above all, to document it. There are options of an open interface, which allows the connection with third-party products, or a proprietary interface. Human-machine interfaces play a special role. Internal Variety Internal variety describes the variety of components, assemblies, products, and processes that occur in order processing. It is essentially accepted as a cost driver for external product variety and should therefore be avoided or reduced – to the extent that it is no longer needed in order to provide the external variety of products. It increases the complexity within the company, reduces the transparency of company processes and thus increases overheads and production costs. Avoiding internal diversity is the goal of design-for-variety methods and a core task of product development. see also [11, 16]. Mass-Customization The strategy of Mass-Customization (also customer-specific mass production) pursues the goal of combining the mass production economies of scale with the individual design of certain customer-relevant features. As such, the strategy combines cost leadership and differentiation strategy and attempts to achieve commodity-like price levels, and to form long-term and individual relationships to manufacturers and customers. see also [2, 12].

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Method, Methodology A method is a rule-based and planned approach to obtaining knowledge or results. It formally describes an operational procedure and supports the development and design of products. Methods support the understanding of even complex problems by breaking them down into manageable sub-problems, pointing out conflicting goals and defining focal points for action. Methods can help to overcome barriers to thinking and promote creativity. Methods often include the application of other methods. For such combinations of several methods, the term methodology is often used. Because many methods can be combined, they are also referred to as “method modules”. see also [18, 23]. Methodical Tool Tools are supporting aids for methods and range from checklists, forms or templates to visualizations and complex software tools. Tools have a great influence on the success of a method and provide a resource for the application of a method. They are the technical instruments intended to support the multiple steps that comprise a method. see also [18]. Module Modules of a product show strongly pronounced relations between their elements compared to other elements or modules of the product (decoupling). The definition of modules in the product structure can bring many advantages in all phases of the product life cycle. The term is relative, as no clear line can be drawn as to when a module can be considered a module. What is important is how consciously and skilfully module boundaries have been set in order to take advantage of the benefits in the product life cycle phases. The decoupling of modules is used to enable the configuration of product variants, economies of scale through common use, and other advantages for all product life phases. Module interface standardization is a prerequisite for this, and function binding is a helpful design principle, which allows the modules to fulfill exactly one function or a defined set of functions. Modular Product Families The variants of a product family can be configured by combining modules with defined interfaces. A modular structure is therefore particularly well suited to achieve a high level of product family variety with a low internal variety of components. Design for variety is essential to keep the number of modules required for configuration low. Ideally, one module should realize exactly one variant product property that is relevant and differentiating from the customer’s point of view.

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Modularization Modularization is the goal-oriented development of the modularity of the product structure with the concrete definition of modules and their interfaces. For this purpose, the product structure is broken down into suitable components (decomposition) depending on the respective scope, objectives and boundary conditions. The components are then analyzed and grouped into new modules according to technical-functional and/or product-­ strategic aspects. On this basis, the new modular product structure is developed and designed, including the necessary interfaces. The terms modularization and product structuring can be understood synonymously since in modularization the product structure is fundamentally designed. It is essential to understand that the goal of modularization is not necessarily to achieve the highest possible modularity of the product structure, but rather a strategic, companyand product-specific optimal modular product structure that brings advantages in all product life phases. Modularity Modularity is a gradual characteristic of the product structure. The term is defined very differently in different fields. Common to the various definitions, however, is the concentration of couplings of system elements within the modules. These have stronger couplings between their elements than to other elements or modules. A product’s modularity is specifically designed to meet the requirements of all of its life phases. The following criteria are particularly noteworthy: –– commonality (modules are used in different products to allow savings through economies of scale), and –– combinability (combining modules enables the configuration of different product variants.) The standardization of the module interfaces is a prerequisite for modular Products. Function binding is a helpful design principle, which allows the modules to fulfil exactly one function or a defined set of functions. see also ([28]) Modular Design/Modular Kit Modular design – also known as modular kit – is a product structure strategy in which different modules are combined to create product variants, to achieve savings through increased commonality or to achieve further technical-functional and/or product-strategic advantages for all product life phases. The creation of different product variants through the combination of modules is essential. Modules consist of one or more components that are strongly coupled to each other compared to their coupling to other components.

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Module Driver Module drivers are technical or product-strategic reasons for creating modules within the product structure. Examples are “outsourcing of development”, “special production processes”, “ product variant configuration” or “simple maintenance”. These are individually specified within a concrete modularization project in so-called module driver specifications, for example, “purchase A”, “leak test” or “short maintenance interval”. Multiplication Effects Multiplication effects occur when several influencing factors act synergistically on a system through their combination and lead to a number of system states equal to the product of their manifestations. Multiplication effects often occur in the context of modular product families. For example, to provide product variants that differ in two variant properties with three values each, in the worst case 3 × 3 = 9 component variants have to be developed and produced. By using a modular product structure designed for variety, it is often possible to limit the effects of the variant properties, even up to one module each, so that only 3 + 3 = 6 variants are necessary. Multiple Use Multiple use of modules means the systematic use of identical modules in different products of several parts of the product range. In the case of multiple use, modules are used across areas of the product range or even across the entire product range. The aim is to reduce internal variety by avoiding new development efforts and by using economies of scale. The feasibility and the savings achieved can be supported by developing a suitable product structure. Possible transfer modules are to be identified, decoupled and developed with regard to their interface and performance features in such a way that they can be used across the product range. In order to increase the probability of a takeover, this inevitably leads to smaller module sizes compared to other product structure strategies. Option Options are a type of decision alternative provided to the customer in the course of a purchase decision. In contrast to obligatory choices, the customer sees options as separate properties or functions of the product that can be selected or not. see also [20] Oversizing Oversizing describes the fulfillment of requirements of different application variants by a component or a product with the aim of increasing lot sizes and resulting economies of scale. Oversizing is one principle of design for variety.

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Examples of this is the design of components’ dimensions for their use in the most heavily loaded product variant. Also the preventing and optional allowance of product functions in the control software is seen as over-dimensioning. Packaging Packaging pursues the goal of reducing internal complexity. Product packages are formed from property values within a product family which are only offered together. The aim is to limit the possible combinations so that complicated combinations of configuration modules within the company can be avoided. At the same time, packaging can help to increase sales volumes of otherwise low-running functions by offering them as a package with strong sales numbers. Packages are not a product structure in the strict sense, but rather a structuring of the offered product range. see also [25]. Platform A platform is the common basis of a product family. It comprises all components that are present in all variants of the product family. Platforms are the basis for product variants, and help to efficiently derive and produce these variants. Depending on the industry and company, different areas can be relevant for the creation of a platform. These can include processes, knowledge, people and relationships. see also [22, 26]. Postponement Postponement is understood to be a process strategy that postpones the differentiation of product variants to the last possible process step and, if necessary, to the customer. The advantages are low process variety and shorter reaction and delivery times. As with most process strategies for product creation, this is best closely coordinated with the product structure strategy. Process A process is a closed, logical and temporal sequence of work steps to achieve a specific goal. The work steps are usually described by name, goal, responsibility, necessary resources and inputs and outputs. Process Commonality The term process commonality describes the use of common production (sub-)processes for different component or product variants. The advantage lies in lower process variety. As with most process strategies, this is best coordinated with the product structure strategy and product design.

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Procurement Strategies (see X-to-Order strategies) Product Architecture The product architecture summarizes the product structure as the physical structure and the functional structure as the functional description of a product, and relates their elements to each other. Product architecture is the totality of the functional and physical descriptions of a product. see also [10, 23, 33]. Product Family A product family refers to a set of product variants that have similar functional principles, technologies and the same application areas or production processes. A product family comprises all variants in which a product is offered. Product variants differ from one another in at least one property or element but have the same basic functionality. see also [22, 27]. Product Generation A product generation is described as an entirety of products at one stage of development and characterized by a certain conception and design, which is offered on the market over a longer period of time. It typically comprises a product family or line, has a market cycle of several years, and is technically based on the previous product generation. Particularly in the large-scale production industry, the development of new product generations is one of the main activities of product development compared to new development, adaptation design, or variant design. This is due to the high development costs and comparatively long product life cycles on the market – nevertheless, it is often carried out as part of a new development process. The aim is to develop a product that is as innovative as possible and at the same time to develop only few subsystems from scratch. This can be achieved by planning appropriate modules of the product structure for the new product generation to be developed. see also [4]. Product Life Cycle The product life cycle is seen as the chronological development of various aspects of products on the market. The following key aspects apply: [27]. –– the “business product life cycle” as the duration of the market presence of a concrete product with parameters such as sales and profit, –– the “technological product lifecycle” as the chronological course of the implementation of technological advancement –– the “intrinsic product life cycle” describes the “CV” of a single product from development, production, sale and use to disposal.

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Product Life Phase A product life cycle phase represents a corporate function along with product development or a significant phase of use. In companies, behind each product life cycle phase, there is a department that strives to implement its requirements for the product structure. Blees provides a generic overview of the life cycle phases with product development, procurement, manufacturing, sales, use, and recycling/disposal (Blees 2011). However, these are to be adapted to the specific needs of the company – taken in the order above, they are only suitable for a make-to-stock strategy type. In contrast to this, the term “product life cycle” is also frequently used to describe the typical sales process of a product from market launch to phasing out and is sometimes seen as including development. Product Line The product line represents a set of products that have similar areas of application, functions or production processes, and whose combination makes sense from a business and organizational point of view. Product Range The product range is the totality of the products offered by a company [27]. It is composed of the company’s own production program and the purchased products, which are offered on the market as merchandise without substantial changes, and services. The production program is usually further subdivided into product lines and product families. Product Strategic Modularization A product-strategic modularization refers to the definition of the module structure of a product and its interfaces with a focus on product-strategic module drivers – that is, those that are not technically and functionally motivated. The latter are addressed in technical-­ functional modularization. Typically, however, both types of module drivers are integrated into a modularization project. It makes sense to first carry out a technical-functional modularization and then a product-strategic modularization (see also the method of life-phase modularization). Product Structure The product structure describes the physical, hierarchical composition of a product, its components, and their physical relationships. Within the product structure, assemblies form structural entities by grouping together individual components and other (sub-) assemblies at a lower level of the product structure. The product structure is of crucial importance for creating variants. see also [23].

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Product Structure Strategy Product structure strategies are company guidelines regarding the definition of product structures to achieve the company’s goals. As a corporate strategy, it is valid across the product range and has a medium- to long-term orientation, usually covering at least one product generation. Property Properties describe the behaviour of a product (for example function, weight, safety and reliability, aesthetic properties, manufacturability, testability, costs). They are perceived by the customer but usually cannot be influenced by the designer directly. For example, the reliability of a product is determined by several of its technical characteristics and only those can be directly influenced by the designer (dimensions, materials, surfaces etc.). The systematic differentiation between properties and characteristics is found in CharacteristicsProperties Modeling (CPM) according to Weber or in the Axiomatic Design according to Suh. see also [30, 35]. Requirement A requirement is a specified, presupposed, and mandatory demand regarding a characteristic of a product. They are either needed or desired by a stakeholder. Requirements are typically recorded and documented during the definition of a development project on the basis of a requirements list, quantified as concretely as possible and divided into fixed requirements and wishes. Requirements concern the market and the customer’s product use, but also different areas of the company or legal requirements. The formulation of requirements from the customer’s perspective and in a solution-neutral form is of particular importance. This is the only way to ensure that customer requirements are met and innovative technical solutions are not prematurely ruled out. All tasks of recording and managing requirements are summarized under the term requirements management and engineering. see also DIN EN ISO 9000:2015-11 [13, 18]. Requirements List The requirements list is created from the target specification and serves as a basis for product development. It has a controlling effect on all subsequent design steps by providing the target properties of the product, which are compared in all decision phases with the properties that can be realized by individual solution alternatives. Objectives and conditions are entered, which are then structured and prioritized according to requirements and wishes. Size Range A size range comprise a number of components or products that are identical except for one or a few determining spatial parameters. They thus share functionality, design solution

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and ideally also the manufacturing process. The parameter can be a size-determining measure or the material, so that the performance of the component can be scaled by altering the parameter. The aim in using a size range is to be able to offer different product variants by selecting a gradation and to achieve high commonality and thus savings effects in the product life phases by simply scaling a technical solution. see also [17]. Standard A standard designates parts, components, or modules as well as procedures and processes and, in a broader sense, also technical solutions, technical features and specifications that are intended to be used preferentially or compulsorily. The Standard can be applicable within the company over significant parts of the product range up to industry-wide, and over a significant time period. The term standard can also be used to indicate the repeated application of an identical technical or organizational solution with the aim of technical and economic optimization for a limited period of time. see also [9]. Standardization Standardization is the creation or identification of parts and components that are used in the same way, preferably or mandatorily, over significant parts of the product range up to and including industry-wide over a significant period of time. Standardization involves a comprehensive search for various components that have sufficiently similar functions and specifications to be replaced by identical elements. Usually, this can be done without reference to a certain product. Alternatively, components can be defined as “standard” in advance without analyzing the existing parts. The aim is to reduce internal variety, to avoid additional work through new part development and to use economies of scale. The term and procedure can be applied similarly to procedures and processes. Standard Component Standard components are identically used in all product variants of a product families. Ideally, they make up a high proportion of the product. They offer the potential to be integrated into a platform for the product family. The variant components used to configure the product variants of a product family are distinguished from the standard components. Standard components are an essential term in the context of design-for-variety methods, in which their share of the product family is systematically increased in order to simplify the configuration of product variants and reduce internal complexity. see also [11].

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Technical-Functional Modularisation Technical-functional modularization refers to the definition of the modular structure of a product and its interfaces with the focus on technical and functional module drivers – that is, those that are not motivated by product strategy. The latter are addressed in product-­ strategic modularization. For technical-functional modularization, the product is broken down into suitably detailed components or functions. These are evaluated with their technical and functional interactions. Based on this, suitable modules are defined and combined. Typically, a modularization project combines a technical-functional modularization with a product-strategic modularization. It makes sense to first carry out a technical-­ functional modularization and then a product-strategic modularization (see also Life Cycle Modularization Method). Variant Variants are simultaneously implemented technical systems with similar functions and structure, typically with a high proportion of identical components that differ in at least one relationship or property. The specific values of these sales-relevant properties or technically relevant features differentiate the variants. A further distinction is made between product variants and process variants. In common parlance, the term “version” is also often used incorrectly for a variant, but it refers to successive, mutually alternating revisions of the same element. see also [1, 11]. Variant Component In contrast to standard components, variant components serve to configure the product variants of a product family. Ideally, the variant components realize exactly one product property that differentiates the products significantly from the customer’s point of view. They have a small share in the product family, are inexpensive to produce, easy to procure and can be stocked with little effort. Variant components are an essential concept within design-for-variety methods, in which they are systematically developed and designed in order to simplify the configuration of product variants and reduce internal complexity. Variant Costs New product variants always lead to increased costs. In addition to the development efforts, process variants are often required in order fulfillment. These expenses are called variant costs. They are difficult to calculate and are therefore usually underestimated, with the result that order-specific variants are often charged with too low indirect costs to the detriment of standard variants. Variant-related costs are a significant portion of the complexity costs. see also [11].

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259

Variant Management Variant management is concerned with the tasks of designing, steering, and controlling the diversity of variants. it represents a cross-sectional function in the company that covers all phases of order processing. The objectives are to avoid, control, and reduce the internal variety in products and processes, which is associated with costs, as well as to optimise the external diversity of products and processes, which leads to customer benefit. see also [11; Quantity 2001]. Variety of Offers The offer variety describes the variation of products offered to the customer. In order for it to have an effect on sales and contribute to the fulfilment of customer wishes, it must be recognisable to the customer and at least include the essential selection criteria in the purchase decision. It must therefore be a significant subset of the demand variety. On the other hand, it must be possible to communicate the variety of products on offer to the customer clearly and concisely, so as to keep the selection of a product variant sufficiently simple. Even though the term “external diversity” can encompass more than offer variety, these two terms are often used synonymously. Variety The term variety describes the number and diversity of variants of a component, an assembly, a product, or even a process/process step. see also [11]. Version A version is a precisely defined temporal state of an object within the scope of its life cycle. It determines the current release of the object. Versions of an object are released one after the other. A version is created at a defined point in time and is linked to its predecessor and successor in a chronological sequence. This means that only one version of an object exists at any one time, but there may be several variants. In general usage, the terms variant or execution are often used incorrectly, but they also denote valid, similar elements. see also [11, 29]. X-to-Order Strategies X-to-order strategies differentiate the product creation process according to the point at which component or product variants are created. This is in some cases flexible, but four approaches are specifically named in this spectrum. –– Make To Stock (MTS), products are produced according to fixed specifications, stored, and sold on order request.

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–– Customize-To-Order (CTO), products are produced and stored. Products then are customized and delivered according to an order and specifications. –– Make-To-Order (MTO), products are produced for the respective customer order and delivered within defined selection parameters. –– Engineer-To-Order (ETO), products are developed, produced, and delivered according to customer specifications. The Configure-To-Order and Assembly-To-Order strategies are understood here as Customize To Order strategies in the context of product variety. The definition of the order decoupling point and the product structure as well as the product variety must be coordinated. see also [2].

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