Advanced Welding and Deforming 012822049X, 9780128220498

Table of contents :
Front-matter_2021_Advanced-Welding-and-Deforming
Copyright_2021_Advanced-Welding-and-Deforming
Contributors_2021_Advanced-Welding-and-Deforming
Series-Foreword_2021_Advanced-Welding-and-Deforming
Preface_2021_Advanced-Welding-and-Deforming
Chapter-1---Ultrasonic-welding-a-modern-welding-tech_2021_Advanced-Welding-a
Chapter 1 - Ultrasonic welding—a modern welding technology for metals and plastics
1 - Introduction
2 - Ultrasonic welding system and process variation
2.1 - Spot welding
2.2 - Line welding
2.3 - Continuous seam weld
2.4 - Torsion/ring weld
3 - Ultrasonic welding process mechanism and working
4 - Ultrasonic welding process parameters
4.1 - Frequency
4.2 - Amplitude
4.3 - Static clamping force
4.4 - Welding power, time, and energy
4.5 - Material
4.6 - Tooling
5 - Ultrasonic welding of metals and alloys
5.1 - Welding of similar metals and alloys
5.2 - Welding of dissimilar metals and alloys
5.3 - Welding of plastic: similar material
5.4 - Welding of plastic: dissimilar material/hybrid welding
6 - Ultrasonic welding applications
6.1 - Automotive industries
6.2 - Packaging industries
6.3 - Plastic industries
6.4 - Electronic industries
6.5 - Miscellaneous application
7 - Ultrasonic welding: advantages and limitations
7.1 - Advantages
7.2 - Limitations
8 - Summary
9 - Ultrasonic welding: future trends
References
Chapter-2---Fiber-laser-welding-of-Ti-6Al-4V_2021_Advanced-Welding-and-Defor
Chapter 2 - Fiber laser welding of Ti-6Al-4V alloy
1 - Material processing with the laser beam
1.1 - Laser beam generation
1.2 - Optical absorption
2 - Welding process
2.1 - Laser beam welding
2.1.1 - Advantages of LBW
2.1.2 - Limitations of LBW
2.2 - Laser welding modes
2.2.1 - Conduction mode
2.2.2 - Keyhole mode
2.3 - Classification of laser heat sources
2.4 - Fiber laser
2.4.1 - Fiber laser construction
2.4.2 - Laser beam quality
2.4.3 - Advantages of fiber laser
2.5 - LBW process parameters
3 - Weldability of Ti-6Al-4V Alloy
4 - Experimental setup
4.1 - Workpiece fixture
4.2 - Joint configuration
4.3 - Measurement methodology
4.3.1 - Macro and microstructural analysis
4.3.2 - Vickers micro-hardness test
4.3.3 - Tensile test
4.3.4 - Measurement of cooling rate in fusion-zone
4.3.5 - Grain size measurement
5 - Study of different bead features
5.1 - Bead shape
5.2 - Bead surface appearance
5.3 - Penetration depth and fusion zone width
5.4 - Focal position
6 - Microstructural analysis
6.1 - Mechanism of phase transformation
6.2 - HAZ and FZ microstructure
7 - Weld defects and minimization techniques
7.1 - Porosity
8 - Study of mechanical properties
8.1 - Weld bead hardness
8.2 - Tensile properties and fractography
9 - Summary
References
Chapter-3---Advances-in-gas-metal-arc-welding-process--_2021_Advanced-Weldin
Chapter 3 - Advances in gas metal arc welding process: modifications in short-circuiting transfer mode
1 - Introduction to welding process
2 - Gas metal arc welding (GMAW) process
2.1 - Polarities in GMAW
2.2 - Types of metal transferral in gas metal arc welding
2.2.1 - Short-circuit transfer
2.2.2 - Globular transfer
2.2.3 - Spray arc transfer
2.3 - Advantages of GMAW
2.4 - Disadvantages of GMAW
3 - The need for modifications in the shortcircuiting mode of metal transfer
4 - WiseRoot process
5 - Surface Tension Transfer process
6 - Regulated metal deposition process
7 - Cold Arc process
8 - ColdMIG process
9 - Intelligent arc control process
10 - Super-imposition process
11 - Controlled bridge transfer process
12 - Cold metal transfer process
13 - MicroMIG process
14 - Summary
References
Chapter-4---Comprehensive-analysis-of-gas-tungsten-arc_2021_Advanced-Welding
Chapter 4 - Comprehensive analysis of gas tungsten arc welding technique for Ni-base weld overlay
1 - Introduction
2 - GTAW process description
3 - Experimental details and procedure for weld overlay
4 - Results and discussion
4.1 - Heat flow analysis
4.2 - Interfacial weld chemistry analysis
4.3 - Weldment microstructure and micro-hardness
4.4 - X-ray diffraction analysis
5 - Summary and future research directions
References
Chapter-5---Developments-in-laser-welding-of-al_2021_Advanced-Welding-and-De
Chapter 5 - Developments in laser welding of aluminum alloys
1 - Introduction
2 - Aluminum alloys for industrial applications
3 - Basics of laser welding of aluminum alloys
4 - Challenges in laser welding of aluminum alloys
5 - Microstructural and mechanical properties of welded parts
6 - Welding imperfections and their prevention
7 - Conclusions and future prospects
Acknowledgments
References
Chapter-6---Evolution-and-current-practices-in-fric_2021_Advanced-Welding-an
Chapter 6 - Evolution and current practices in friction stir welding tool design
1 - Introduction
2 - FSW process parameters
3 - FSW tool geometry and material
3.1 - Tool shoulder
3.2 - Tool pin profile
3.3 - FSW tool configuration
3.4 - Tool material
4 - Approaches for tool design
5 - Tool design and material mixing
6 - Special purpose FSW tools
6.1 - Friction stir spot welding
6.2 - Retractable pin tool
6.3 - Stationary shoulder tool
6.4 - Cylindrical FSW tool
6.5 - Heat assisted FSW tool
6.6 - Reverse dual rotation FSW tool
7 - Conclusions
References
Chapter-7---Magnetic-pulse-welding_2021_Advanced-Welding-and-Deforming
Chapter 7 - Magnetic pulse welding
1 - Introduction
2 - Comparison of magnetic pulse welding with other welding processes
2.1 - Advantages of MPW over conventional welding processes
2.2 - Comparison with explosive welding
2.3 - Comparison with brazing
2.4 - Comparison of ultrasonic welding with MPW
3 - Process parameters in magnetic pulse welding
4 - Interface structure and joint formation mechanism
5 - Destructive and non-destructive testing of magnetic pulse welded components
6 - Summary
References
Chapter-8---Laser-welding-of-nickel-titanium--NiTi_2021_Advanced-Welding-and
Chapter 8 - Laser welding of nickel-titanium (NiTi) shape memory alloys
1 - Introduction
2 - NiTi shape memory alloys
3 - Laser welding of NiTi alloys
3.1 - Similar laser welding
3.2 - Dissimilar laser welding
4 - Microstructural and metallurgical investigation
5 - Mechanical investigation
6 - Conclusion
References
Chapter-9---Hybrid-welding-technologies_2021_Advanced-Welding-and-Deforming
Chapter 9 - Hybrid welding technologies
Abbreviations
1 - Introduction
2 - Laser-based hybrid welding
2.1 - Laser-TIG hybrid welding
2.1.1 - Relative location of laser beam and TIG arc
2.1.2 - Laser power and arc energy
2.1.3 - Pulsed laser-TIG hybrid welding
2.1.4 - Laser-TIG welding with filler wire
2.2 - Laser-MIG hybrid welding
2.2.1 - Double GMA or twin arc hybrid laser welding process
2.2.2 - Magnetic field assisted laser MIG hybrid welding
2.2.3 - Ultrasonic assisted laser-MIG hybrid welding
2.2.4 - Laser-MIG arc hybrid brazing-fusion welding
2.2.5 - Double sided laser-MIG hybrid welding
2.3 - Laser-assisted plasma arc hybrid welding
2.4 - Laser beam submerged arc hybrid welding
3 - Arc-based hybrid welding
3.1 - TIG-MIG hybrid welding
3.2 - Plasma-MIG hybrid welding
3.3 - Submerged arc welding-GMAW
3.4 - Hot wire arc welding
3.5 - Hybrid multipass arc welding
4 - Solid state hybrid welding
4.1 - Laser friction stir welding (FSW) hybrid welding
4.2 - Ultrasonically assisted FSW/FSSW
4.3 - Electrically assisted FW/FSW
4.4 - Arc assisted FSW/ultrasonic welding
5 - Summary
References
Chapter-10---Modern-optimization-techniques-for-perf_2021_Advanced-Welding-a
Chapter 10 - Modern optimization techniques for performance enhancement in welding
1 - Introduction
2 - Overview of soft computing techniques
2.1 - Fuzzy logic
2.2 - Artificial neural networks
2.3 - Evolutionary computing
2.3.1 - Evolutionary algorithms
2.3.2 - Physics-based algorithms
2.3.3 - Swarm intelligence-based algorithms
2.3.4 - Other bio-inspired algorithms
3 - Performance enhancement in welding
3.1 - Mechanical properties of welds
3.2 - Weld bead geometry
3.3 - Weld microstructure
3.4 - Residual stresses, distortion, and weld defects
3.5 - Arc stability and process monitoring
4 - Conclusions
References
Chapter-11---Laser-cladding-a-modern-joining-t_2021_Advanced-Welding-and-Def
Chapter 11 - Laser cladding—a modern joining technique
1 - Introduction
2 - Laser cladding process and materials
2.1 - Laser cladding/alloying technique
2.2 - Material selection
2.3 - Drawbacks related to laser cladding
3 - Types of laser cladding techniques and their application areas
4 - Alloy production by laser cladding
4.1 - Novel material development
4.2 - Micro-nano laser cladding
4.3 - Engineering microstructures obtained by cladding
4.4 - Modeling, simulation, database, and application-oriented challenge
5 - Laser welding
5.1 - Laser beam features
5.2 - Process control
5.3 - Practical considerations
5.3.1 - Joint constellation and precision
5.3.2 - Safety
5.4 - Developments
6 - Conclusions
References
Chapter-12---A-comprehensive-detail-of-friction-stir-pr_2021_Advanced-Weldin
Chapter 12 - A comprehensive detail of friction stir processing—with a case of fabrication of nanocomposites
1 - Introduction
2 - Friction stir processing working principle and mechanism
2.1 - Microstructure modification during FSP
2.2 - Friction-stir processing (FSP) parameters
2.2.1 - Significance of parameters
2.2.2 - Rotational and traveling speed
2.2.3 - Axial-force of the tool
2.2.4 - Tilt-angle
2.3 - Effects of tool geometry
3 - Techniques for adding reinforcement
3.1 - Smearing
3.2 - Holes
3.3 - Groove
3.4 - Selective laser melting
3.5 - Cold spraying
4 - Manufacturing of nanocomposites by FSP
5 - Summary and scope for future research
References
Chapter-13---Microwave-processing-of-polymer-c_2021_Advanced-Welding-and-Def
Chapter 13 - Microwave processing of polymer composites
1 - Introduction
2 - Microwave-assisted composite fabrication techniques
2.1 - Microwave material processing technology
2.2 - Microwave material interaction
2.2.1 - Microwave transparent materials
2.2.2 - Microwave reflecting materials
2.2.3 - Microwave absorbing materials
2.2.4 - Mixed absorber materials
2.3 - Fabrication of PMC through microwave-assisted heating
2.3.1 - Synthetic fiber-reinforced composites
2.3.2 - Natural fiber-reinforced composites
2.3.3 - CNT reinforced composites
2.3.4 - HA reinforced PCL and PLLA composites
2.3.5 - HA reinforced UHMWPE composites
3 - Properties of various microwave processed composites
4 - Summary and future scope
References
Chapter-14---Equal-channel-angular-processing-a-modern_2021_Advanced-Welding
Chapter 14 - Equal channel angular processing—a modern deforming technique for quality products
1 - Introduction
2 - Working principle and mechanism of ECAP
2.1 - Strain imposed in ECAP
2.2 - Processing routes and their associated slip systems in ECAP
2.3 - Modification of the ECAP process
3 - Variables in ECAP
3.1 - Die design
3.1.1 - Die materials
3.1.2 - Effect of channel angles Ψ and Φ
3.1.3 - Pressing speed
3.2 - ECAP processing temperature
3.3 - ECAP load
4 - Processing routes in ECAP
5 - Temperature measurement during ECAP
6 - Shearing characteristics during ECAP
6.1 - Strain imposed in ECAP
6.2 - Homogeneity in deformation
7 - Microstructural evolution during ECAP
7.1 - Single crystals
7.2 - Polycrystalline materials
7.2.1 - Aluminum (Al) and its alloys
7.2.2 - Magnesium (Mg) and its alloys
7.2.3 - Titanium and its alloys
7.2.4 - Cu and its alloys
7.2.5 - ECAP of steels
8 - Texture behavior
9 - Effect of ECAP on mechanical properties
9.1 - Hardness
9.2 - Tensile behavior
9.2.1 - Stress-strain behavior
9.2.2 - Strain hardening/strain softening
9.2.3 - Superplastic behavior
9.2.4 - Fractography
9.3 - Compression
9.4 - Wear
9.5 - Corrosion behavior
9.6 - Thermal stability of the ECAPed material
10 - Use of finite element methods (FEM) in ECAP
11 - Conclusions
References
Chapter-15---Fundamentals-and-advancements-in-lon_2021_Advanced-Welding-and-
Chapter 15 - Fundamentals and advancements in longitudinal rolling
1 - Introduction to rolling
2 - Working principle and mechanism of rolling
2.1 - Deformation zone and its geometric characteristics
2.1.1 - Strain indicators and their relationship
2.1.2 - Formulas for the deformation zone parameter calculation
2.1.3 - Actual deformation zone during rolling
2.2 - Conditions of metal biting by rolls
2.2.1 - Free biting in a simple rolling process
2.2.2 - Forced biting
2.2.3 - Dynamic biting
2.2.4 - Biting conditions in steady-state rolling process
2.2.5 - Ways to increase the biting ability of the rolls
2.3 - Kinematic conditions of rolling
2.3.1 - Stage of the rolling process
2.3.2 - Ratio of the speed of metal and rolls in the deformation zone
2.3.3 - Advance and lag of strip ends
2.3.4 - Continuous rolling strip speed
2.3.5 - Determination of the average strain rate
2.4 - Stress-strain state and strip deformation
2.4.1 - General description of the metal stress and strain state
2.4.2 - Deformation distribution along the strip height
2.4.3 - Factors affecting broadening
2.4.4 - Determination of the broadening value
2.5 - External friction during rolling
2.5.1 - Physical basics of contact friction
2.5.2 - Determination of the friction factor during rolling
2.5.3 - Influence of rolling factors on the friction factor
2.6 - Rolling process force parameters
2.6.1 - Metal deformation resistance
2.6.2 - Effect of rolling factors on average contact pressure
2.6.3 - Modern methods for calculating the average contact pressure
2.6.4 - Rolling force calculation
2.7 - Rolling torques, work, and power
2.7.1 - Determination of rolling torque by rolling force
2.7.2 - Determination of torque for rolling with tension
2.7.3 - Determination of rolling work and power
2.7.4 - Rolling mill engine power
3 - Advances in longitudinal rolling
4 - Summary
References
Chapter-16---Energy-assisted-forming--theory-an_2021_Advanced-Welding-and-De
Chapter 16 - Energy-assisted forming: theory and applications
1 - Introduction
1.1 - Formability
1.2 - Formability improvement during manufacturing process
1.3 - Fundamentals of plastic deformation
2 - Servo press
2.1 - Mechanism of ductility enhancement due to stress relaxation
3 - Electrical-assisted forming
3.1 - Mechanism for electro-plasticity
3.1.1 - Influence on microstructure and mechanical behavior
4 - Ultrasonic-assisted forming
4.1 - Mechanism
4.1.1 - Stress superposition
4.1.2 - Friction effects
4.1.3 - Acoustic softening
5 - Modeling energy-assisted forming
5.1 - Empirical models
5.2 - Physically based constitutive models
5.2.1 - Extension of dislocation density model for energy-assisted forming
6 - Conclusions and future research
References
Chapter-17---Multi-directional-forging--an-advanced-def_2021_Advanced-Weldin
Chapter 17 - Multi directional forging: an advanced deforming technique for severe plastic deformation
1 - Introduction
2 - Severe plastic deformation
2.1 - Multi directional forging
2.2 - Process parameters of MDF process
2.2.1 - Strain imposed
2.2.2 - Strain rate
2.2.3 - Pressing temperature
2.2.4 - Friction and lubrication
2.3 - Advantages and limitations of MDF
2.3.1 - Advantages of MDF
2.3.2 - Limitations of MDF
3 - Multidirectional forging of different materials
3.1 - Multi directional forging of Al and its alloys
3.2 - Multi directional forging of Mg and its alloy
3.3 - Multi directional forging of Ti and its alloy
3.4 - Multi directional forging of Cu and its alloy
3.5 - MDF/MAF processing of Zn, Ni-Fe, and steel materials
4 - Conclusions
Acknowledgments
References
Chapter-18---Superplastic-forming-analysis-te_2021_Advanced-Welding-and-Defo
Chapter 18 - Superplastic forming analysis techniques
1 - Introduction to superplastic forming (SPF)
2 - Biaxial tests
2.1 - Material selection
2.2 - Clamping and sealing
2.3 - Heat application
2.4 - Height measurement
3 - Theoretical framework
3.1 - Analysis theories in the literature
4 - FEM based analysis
4.1 - Space model
4.2 - Sheet modeling
4.3 - Contact model
5 - Dimensional analysis
5.1 - Normalization
5.2 - Pi-Buckingham
6 - Conclusions
References
Further readings
Chapter-19---Current-technologies-for-aluminum-cast_2021_Advanced-Welding-an
Chapter 19 - Current technologies for aluminum castings and their machinability
1 - Introduction
2 - Importance of casting
3 - Aluminum casting methods and applications
3.1 - Sand casting
3.2 - Permanent mold casting (gravity die casting)
3.3 - Die casting
3.4 - Squeeze casting
4 - Aluminum-based castings alloys and machinability
4.1 - Al-Si alloys
4.2 - Al-Si-Cu and Al-Cu alloys
4.3 - Al-Si-Mg alloys
4.4 - Al-Si-Zn alloys
4.5 - Al-Zn alloys
5 - Conclusions
References
Chapter-20---Processing-and-applications-of-cera_2021_Advanced-Welding-and-D
Chapter 20 - Processing and applications of ceramic microspheres
Nomenclature
1 - Introduction
2 - Processing of ceramic microspheres
2.1 - Hard templating processes
2.2 - Solvothermal process
2.3 - Hydrothermal process
2.4 - Sol-gel process
2.5 - Emulsion process
2.6 - Spray-drying process
2.7 - Self-quenching technology
2.8 - Replication
2.9 - Self-formation phenomenon
2.10 - Post-treatment
2.11 - Zeolitization
2.12 - Selective leaching
2.13 - Breath figures
2.14 - Supercritical fluids
2.15 - Phase separation
2.16 - Bioinspiring process
3 - Conclusion
References
Index_2021_Advanced-Welding-and-Deforming

Citation preview

Handbooks in Advanced Manufacturing

Advanced Welding and Deforming Series Editors-in-Chief

J. PAULO DAVIM AND KAPIL GUPTA

Edited by

KAPIL GUPTA University of Johannesburg, South Africa

J. PAULO DAVIM University of Aveiro, Portugal

Elsevier Radarweg 29, PO Box 211, 1000 AE Amsterdam, Netherlands The Boulevard, Langford Lane, Kidlington, Oxford OX5 1GB, United Kingdom 50 Hampshire Street, 5th Floor, Cambridge, MA 02139, United States Copyright © 2021 Elsevier Inc. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Details on how to seek permission, further information about the Publisher’s permissions policies and our arrangements with organizations such as the Copyright Clearance Center and the Copyright Licensing Agency, can be found at our website: www.elsevier.com/permissions. This book and the individual contributions contained in it are protected under copyright by the Publisher (other than as may be noted herein). Notices Knowledge and best practice in this field are constantly changing. As new research and experience broaden our understanding, changes in research methods, professional practices, or medical treatment may become necessary. Practitioners and researchers must always rely on their own experience and knowledge in evaluating and using any information, methods, compounds, or experiments described herein. In using such information or methods they should be mindful of their own safety and the safety of others, including parties for whom they have a professional responsibility. To the fullest extent of the law, neither the Publisher nor the authors, contributors, or editors, assume any liability for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions, or ideas contained in the material herein. Library of Congress Cataloging-in-Publication Data A catalog record for this book is available from the Library of Congress British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library ISBN: 978-0-12-822049-8 For information on all Elsevier publications visit our website at https://www.elsevier.com/books-and-journals

Publisher: Matthew Deans Acquisitions Editor: Brian Guerin Editorial Project Manager: John Leonard Production Project Manager: Sojan P. Pazhayattil Designer: Victoria Pearson Esser Typeset by Thomson Digital

Contributors Kumar Abhishek Department of Mechanical Engineering, Institute of Infrastructure Technology Research and Management (IITRAM), Ahmedabad, Gujarat, India Bappa Acherjee Production Engineering Department, Birla Institute of Technology, Mesra, Ranchi, Jharkhand, India Şenol Bayraktar Recep Tayyip Erdogan University, Faculty of Engineering and Architecture, Department of Mechanical Engineering, Rize, Turkey Udaya Bhat K Department of Metallurgical & Materials Engineering, NITK Surathkal, Srinivasnagar, Karnataka, India Devadas Bhat Panemangalore Department of Metallurgical & Materials Engineering, NITK Surathkal, Srinivasnagar, Karnataka, India Suma Bhat Department of Mechanical Engineering, SJEC,Vamanjuru, Mangaluru, Karnataka, India K.S Bindra Laser design and industrial applications division, Raja Ramanna Center for Advanced Technology, Indore, Madhya Pradesh; Homi Bhabha National Institute, BARC Training School Complex, Mumbai, Maharashtra, India Pierpaolo Carlone Department of Industrial Engineering, University of Salerno, Salerno, Italy Somnath Chattopadhyaya Department of Mechanical Engineering, Indian Institute of Technology (ISM) Dhanbad, Dhanbad, Jharkhand, India R. Comesaña CINTECX, Universidade de Vigo, LaserON Research group, School of Engineering,Vigo; Universidade de Vigo, Materials Engineering, Applied Mechanics and Construction Dpt., University of Vigo, Vigo, Spain Arash Darafsheh Department of Radiation Oncology, Washington University School of Medicine, St. Louis, MO, United States xvii

xviii

Contributors

Manas Das Department of Mechanical Engineering, Indian Institute of Technology, Guwahati, Assam, India Amir Dehghanghadikolaei School of Mechanical, Industrial and Manufacturing Engineering, Oregon State University, Corvallis, OR, United States Dinbandhu Department of Mechanical Engineering, Institute of Infrastructure Technology Research and Management (IITRAM), Ahmedabad, Gujarat, India A.J. Gámez Department of Mechanical Engineering and Industrial Design, School of Engineering, University of Cadiz. Av. Universidad de Cádiz, Puerto Real, Cádiz, Spain L. García-Barrachina Department of Mechanical Engineering and Industrial Design, School of Engineering, University of Cadiz. Av. Universidad de Cádiz, Puerto Real, Cádiz, Spain Gozde Gecim Department of Chemical Engineering, Faculty of Engineering and Natural Sciences, Bursa Technical University, Bursa, Turkey Annamaria Gisario Department of Mechanical and Aerospace Engineering, Sapienza University of Rome, Rome, Italy S.M. Gorbatyuk National University of Science and Technology «MISIS», Moscow, Russia Ali Pas¸a Hekimog˘lu Recep Tayyip Erdogan University, Faculty of Engineering and Architecture, Department of Mechanical Engineering, Rize, Turkey N. Rajesh Jesudoss Hynes Department of Mechanical Engineering, Mepco Schlenk Engineering College (Autonomous), Sivakasi, Tamil Nadu, India Ayse Kalemtas Department of Metallurgical and Materials Engineering, Faculty of Engineering and Natural Sciences, Bursa Technical University, Bursa, Turkey Hariharan Krishnaswamy Department of Mechanical Engineering, Indian Institute of Technology Madras, Chennai, Tamil Nadu, India

Contributors

xix

Manoj Kumar Singh Composite Design and Manufacturing Lab, School of Engineering, Indian Institute of Technology Mandi, Mandi, Himachal Pradesh, India Chandan Kumar Department of Mechanical Engineering, Indian Institute of Technology, Guwahati, Assam, India R. Kumar Faculty of Mechanical Engineering, Eritrea Institute of Technology, Eritea Rajeev Kumar Composite Design and Manufacturing Lab, School of Engineering, Indian Institute of Technology Mandi, Mandi, Himachal Pradesh, India Hossein Lavvafi Department of Radiation Oncology, William Kahlert Cancer Center, Westminster, MD, United States F. Lusquiños CINTECX, Universidade de Vigo, LaserON Research group, School of Engineering, Vigo, Spain G. Madhusudhan Reddy Defence Metallurgical Research Laboratory, Kanchanbagh, Hyderabad, Telangana, India P. Mastanaiah Defence Research and Development Laboratory, Kanchanbagh, Hyderabad,Telangana, India Mehrshad Mehrpouya Faculty of Engineering Technology, University of Twente, Enschede, The Netherlands Kush P. Mehta Department of Mechanical Engineering, School of Technology, Pandit Deendayal Petroleum University, Gandhinagar, Gujarat, India; Advanced Manufacturing and Materials Research Group, Department of Mechanical Engineering, School of Engineering, Aalto University, Espoo, Finland N.A. Chichenev National University of Science and Technology «MISIS», Moscow, Russia Maria Ntsoaki Mathabathe Council of Scientific Industrial Research, Materials Science and Manufacturing, Manufacturing cluster, Advanced Materials Engineering, Pretoria, South Africa Sharath P C Department of Metallurgical Engineering, Jain University, Bengaluru, Karnataka, India

xx

Contributors

Amogelang Sylvester Bolokang Council of Scientific Industrial Research, Materials Science and Manufacturing, Manufacturing cluster, Advanced Materials Engineering, Pretoria, South Africa Himanshu Pathak Composite Design and Manufacturing Lab, School of Engineering, Indian Institute of Technology Mandi, Mandi, Himachal Pradesh, India C.P. Paul Laser design and industrial applications division, Raja Ramanna Center for Advanced Technology, Indore, Madhya Pradesh, India; Homi Bhabha National Institute, BARC Training School Complex, Mumbai, Maharashtra, India J. Pou CINTECX, Universidade de Vigo, LaserON Research group, School of Engineering,Vigo, Spain Vishalkumar Prajapati Department of Mechanical Engineering, Institute of Infrastructure Technology Research and Management (IITRAM), Ahmedabad, Gujarat, India Dinesh W. Rathod Department of Mechanical Engineering, Thapar Institute of Engineering and Technology, Thapar Technology Campus, Patiala, Punjab, India A. Riveiro CINTECX, Universidade de Vigo, LaserON Research group, School of Engineering,Vigo; Universidade de Vigo, Materials Engineering, Applied Mechanics and Construction Dpt., University of Vigo,Vigo, Spain Pankaj Sahlot Department of Mechanical Engineering, School of Technology, Pandit Deendayal Petroleum University, Gandhinagar, Gujarat, India R. Sankaranarayanan Department of Mechanical Engineering, Mepco Schlenk Engineering College (Autonomous), Sivakasi, Tamil Nadu, India Sachindra Shankar Department of Mechanical Engineering, Indian Institute of Technology (ISM) Dhanbad, Dhanbad, Jharkhand, India Abhay Sharma KU Leuven, Faculty of Engineering Technology, Department of Materials Engineering, Campus De Nayer, Jan Pieter de Nayerlaan, Sint-Katelijne-Waver, Belgium

Contributors

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Shivraman Thapliyal Mechanical Engineering Department, National Institute of Technology,Warangal,Telangana, India J. del Val CINTECX, Universidade de Vigo, LaserON Research group, School of Engineering,Vigo; Centro Universitario de la Defensa, Escuela Naval Militar, Marín, Spain P. Shenbaga Velu Department of Mechanical Engineering, PSR Engineering College, Sivakasi, Tamil Nadu, India Nishant Verma Composite Design and Manufacturing Lab, School of Engineering, Indian Institute of Technology Mandi, Mandi, Himachal Pradesh, India Pedro Vilaça Advanced Manufacturing and Materials Research Group, Department of Mechanical Engineering, School of Engineering, Aalto University, Espoo, Finland Jay J. Vora Department of Mechanical Engineering, School of Technology (SOT), Pandit Deendayal Petroleum University (PDPU), Gandhinagar, Gujarat, India D. Wallerstein CINTECX, Universidade de Vigo, LaserON Research group, School of Engineering, Vigo, Spain Sunny Zafar Composite Design and Manufacturing Lab, School of Engineering, Indian Institute of Technology Mandi, Mandi, Himachal Pradesh, India

Series Foreword Dear Readers, This series of handbooks on advanced manufacturing covers four major areas, namely, advanced machining and finishing, advanced welding and deforming, additive manufacturing, and sustainable manufacturing. The series aims to not only present the advancements in various manufacturing technologies, but also provides a fundamental and detailed understanding about them. It encompasses a wide range of manufacturing technologies with their mechanisms, working principles, salient features, applications, and research, development, and innovations in there. Fundamental research, latest developments, and case studies conducted by international experienced researchers, engineers, managers, and professors are mainly presented. Handbook 1 on advanced machining and finishing majorly covers advanced machining of difficult-to-machine materials; hybrid, high speed, and micromachining; and burnishing, laser surface texturing, and advanced thermal energy-based finishing processes. Handbook 2 on advanced welding and deforming covers ultrasonic welding, laser welding, and hybrid welding type advanced joining processes and also describes advanced forming techniques such as microwave processing, equal channel angular pressing, and energy assisted forming, etc. Handbook 3 additive manufacturing sheds light on 3D and 4D printing, rapid prototyping, laser-based additive manufacturing, advanced materials and post-processing in additive manufacturing. Handbook 4 on sustainable manufacturing presents advancements, results of experimental research, and case studies on sustainability interventions in production and industrial technologies. We hope that this series of handbooks would be a good source of knowledge and encourage researchers and scientists to conduct research, developments, and innovations to establish these fields further. J. Paulo Davim and Kapil Gupta

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Preface Joining and forming are two major groups of manufacturing processes. Limitations of traditional processes have been overcome by technological advancements that derived advanced welding and deforming processes to attain the special requirements related to quality, cost, and sustainability. This handbook covers such technological advancements in a wide range of welding and deforming processes. Basic to advanced level knowledge along with the latest research in this area as well as possible avenues of future research are also highlighted to encourage the researchers. The handbook consists of a total of 20 selected chapters on advances in welding and deforming processes. It starts with Chapter 1 where joining of metals and plastics using ultrasonic welding, is discussed. Laser welding is introduced in Chapter 2 along with a special focus on fiber laser welding of titanium alloys. Chapter 3 discusses advancements in gas metal arc welding process via modifications in short circuiting transfer mode. A comprehensive analysis of gas tungsten arc welding with a case of nickel alloys is presented in Chapter 4. Recent developments in laser welding of aluminum alloys are highlighted in Chapter 5. Friction stir welding tool design for joining lightweight materials is given in Chapter 6. Chapter 7 sheds light on magnetic pulse welding. Chapter 8 provides insights on laser welding of NiTi shape memory alloys. Aspects of hybrid welding technologies are presented in Chapter 9. A wide range of optimization techniques and their implementation and effectiveness for enhancement of weldability in case of various welding processes are discussed in Chapter 10. Chapter 11 presents joining by laser cladding. Chapter 12 introduces friction stir processing and a case of fabrication of nanocomposites. A unique microwaveassisted polymer composite fabrication process is detailed in Chapter 13. Chapter 14 presents equal channel angular pressing as a modern deforming technique. Fundamental and advances in longitudinal rolling are described in Chapter 15. Energy assisted forming and its applications are focused on Chapter 16. Chapter 17 discusses multi directional forging as an advanced deforming technique for severe plastic deformation. Analysis of superplastic forming process is presented in Chapter 18. Casting techniques for aluminum and machinability analysis of cast parts are covered in Chapter 19. Chapter 20 sheds light on forming of ceramic microspheres for various specialized applications. xxv

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We hope that this handbook would be a good source of knowledge and information for researchers, engineers, technical experts, and specialists working in the area of welding and deforming processes. We sincerely acknowledge Elsevier for this opportunity and their professional support. Finally, we would like to thank all contributors for their time and efforts. Kapil Gupta and J. Paulo Davim January 2021

CHAPTER 1

Ultrasonic welding—a modern welding technology for metals and plastics Shivraman Thapliyal Mechanical Engineering Department, National Institute of Technology, Warangal, Telangana, India

1 Introduction Ultrasonic welding (USW) is the solid-state welding process in which joint between metals, metal-plastic, and plastics is developed by high-frequency ultrasonic vibrations [1–3]. The faying surfaces are clamped under the application of the static force and subjected to ultrasonic vibration. The highfrequency vibration causes the relative motion between the surfaces, which causes disruption of asperities by simultaneous plastic deformation. The frictional heating, along with the heat generated during plastic deformation, is sufficient to produce the joint between the surfaces. Initially, ultrasonic vibrations were applied to the resistance spot welds to improve the grain structure of the welds. Later, it was realized that weld was developed between faying surfaces with the sole application of ultrasonic vibrations only. The first report on the implementation of ultrasonic vibration as the welding source was published in 1950 [1]. Initially, this process was restricted to thin sheets, foil bonding, and tube sealing [2]. However, the current demands and advancement in the process made it feasible for the welding of thick sheet [3]. The USW has extensively been used in microelectronics, automotive, medical, and aerospace industries [4,5]. This welding used to join various alloys of copper, aluminum, steel, and nickel. The ultrasonic welding process can also be used for the joining of different dissimilar metals, plastics, and metal-plastic combinations.

2  Ultrasonic welding system and process variation USW system consists of an electronic power supply that converts line power into high frequency and high voltage power for the transducer. The transducer converts the electrical energy into high-frequency mechanical Advanced Welding and Deforming http://dx.doi.org/10.1016/B978-0-12-822049-8.00001-3

Copyright © 2021 Elsevier Inc. All rights reserved.

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vibration ranging from 15 to 300 kHz [6]. These high-frequency vibrations are transferred to the workpiece by the sonotrode. The workpiece is held firmly between the sonotrode tip and anvil that provides the necessary clamping force, and the anvil act as the supporting system for the workpiece. The lateral drive system and wedge reed system are the two types of USW systems. The wedge reed system was designed and patented in 1960, which uses a vertical vibrating member termed as a reed to which vibrations are supplied from a coupler transducer assembly perpendicular to the reed. The clamping forces are applied on the weld plates through the reed. The vibrations produce a shear motion at the interface region, as the vibration directions are parallel to the weld interface. However, in the lateral drive system, the vibrations are transferred directly to the welding horn from the booster-transducer-sonotrode assembly. The booster that is mounting the total stack of the tooling system directly applies the downward force (Fig. 1.1A,B). Nowadays, fully programmable USW systems are available, in which the process parameters are controlled by the microprocessors. USW uses a closed-loop feedback system, which regulates a process variable to the desired value with the help of the feedback system. An example of 3 kW and with a frequency of 20 kHz wedge is shown in Fig. 1.2.These USW systems have different variants that can produce different types of weld joints, that is, spot, line, ring, and continuous.

2.1  Spot welding The joint between two overlapping material is developed at a small spot by the introduction of vibratory energy into the workpiece held between sonotrode and the anvil. The vibrations are applied parallel to the joint line or weld interface. The welding can be achieved in less than 1.5 s, but the weld time is dependent on the material type, thickness, and power unit.

2.2  Line welding This welding is a variation of spot welding in which a continuous line weld is achieved by the help of linear sonotrode tip vibrating parallel to the weld interface. A weld of length nearly equal 6 in. can be obtained in a single weld cycle.

2.3  Continuous seam weld These welds are obtained when a rotating disked shaped ultrasonic horn is rotated and traversed over the workpiece supported on the anvil. This setup can be used to join foils up to 0.15 mm thickness.

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Figure 1.1  Schematic of (A) wedge reed and (B) lateral drive ultrasonic welding system.

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Figure 1.2  Photograph of (A) wedge reed ultrasonic metal welder with (B) sonotrode tip, (C) weld tip [7]. (With kind permission from Elsevier).

2.4  Torsion/ring weld The torsion/ring welds are produced by imparting twisting or torsional motion to the horn. This system uses two transducers vibrating longitudinally which are 180 degrees out of phase with each other and thus providing torsional motion at the weld interface. This system is used for sealing of the container carrying liquid and powder propellant with the thin foil sheets. Ring weld of diameter 50 mm has been successfully produced for aluminum and copper foils.

3  Ultrasonic welding process mechanism and working In USW, when two surfaces are brought in contact by static clamping force, immediately, the asperities present on the surface come in contact (Fig. 1.3A) [2]. When the ultrasonic vibrations are applied on the top part which in contact with sonotrode tends to vibrate in the direction of applied vibration resulting in sliding, deformation of the asperities along with the disruption of metal oxides present at faying surfaces, which increases the area of contact and coefficient of friction (Fig. 1.3B) [5,7].This increase in the area causes direct metal-to-metal contact, and the formation of micro welds due to deformation. Increasing the duration of ultrasonic vibration causes significant heat generation due to friction and plastic deformation, which causes material softening and ease the material flow near the

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Figure 1.3  Schematic depicting the working operations of the ultrasonic welding process.

joint line (Fig. 1.3C). Additionally, the acoustic vibrations are absorbed in the dislocation, which also increases the material flow. As the welding cycle terminates, the contact area and adjacent area are completely deformed with recrystallized grains. The metallic bonding in the weld zone under the sonotrode tip is visible (Fig. 1.3D). The metallic bonding achieved due to welding is a solid-state, which implies no melting and fusion of the workpiece. The temperature measurement studies on USW suggested that the temperature rises rapidly in the initial stage of welding, and then it remains stable for the remaining cycle. Although a significant rise in the temperature is observed initially, it remains below the melting point of the metals/alloys [8].

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In USW, the different phenomenon occurs, that is, (1) surface film disruption, (2) plastic deformation, (3) recrystallization, and (4) diffusion across the interface. However, the diffusion and recrystallization phenomenon were ruled out after investigating the low-frequency USW of aluminum and copper alloys [9–11]. Therefore, the dominant phenomenon for the solid-state joining of material in USW is slip and plastic deformation [12]. The weld interface is subjected to non-uniform deformation throughout the structure. Visually a weld zone exhibits shear bands and swirls, and thermomechanically affect zone (TMAZ) consists of the convoluted wavelike pattern. This convoluted bonding line appears in the weld region also when the energy input increases beyond the optimum range due to the combined action of shear and normal force.

4  Ultrasonic welding process parameters The quality of the ultrasonic weld depends on the system and material parameters (Fig. 1.4). The system parameters will dominate the weld quality of the joint. However, the material parameters govern the weldability of materials. The various parameters affecting the USW process are explained briefly in this section [6,13].

Figure 1.4  Ultrasonic welding process parameters.

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Table 1.1  Showing operating range of USW frequency for various material systems. Frequency range (kHz)

Material system

15–20 20–60 120–300

Plastic Metal Electronic micro bonding system

4.1 Frequency In USW, the transducer operates at different ranges of frequencies varying from 15 to 300 kHz. The selection of frequencies is based on the material to be joined (Table 1.1). The high-frequency equipment offers lesser noise, better part protection, and small tooling size, but it comprises the power capability. During welding of different material classes, the system operates at fixed frequencies. Hence, the role of frequency in the weld quality is not considered.

4.2 Amplitude The welding amplitude is the critical parameter that governs the soundness of the weld joint.The amplitude during welding is small, ranging from 10 to 50 µm at the weld region. The amplitude controlling can be related to the power input, and sometimes it can be controlled by the separate feedback system depending upon the welding systems. The selection of the optimum amplitude for the welding of the material is based on other factors like power, welding time, and clamping force.

4.3  Static clamping force It is the force applied on the workpiece by the welding tip and sonotrode to hold the part firmly together and develop the intimate contact between the parts to be joined. It is one of the critical factors, which depends upon the material, thickness of the material, and weld size. It ranges from 10 to 103 N, and there exists an optimum range of clamping force for a set of parameters that defines the strength of the weld.

4.4  Welding power, time, and energy The welding power (P), time (t), and energy (U) are not independent variables [Eq. (1.1)]. The weld can be obtained for peak power after a substantial amount of time (s) or weld cycle. The weld energy will be the area under the power v/s time curve (Fig. 1.5). The power transmitted to the

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Figure 1.5  Power curve for ultrasonic welding.

transducer from the electrical systems is transferred to the weld in terms of ultrasonic power.

U =P× t

(1.1)

The actual power obtained at the weld zone will depend upon (1) the efficiency of the electro-mechanical conversion system, (2) losses in the bulk material, and at the interfaces of the transducer-booster-sonotrode system, and (3) energy dissipated by the weld to surroundings, that is, workpiece and anvil.

4.5 Material The properties of materials like hardness, ductility, and oxide formation tendency to govern the weld quality of the ultrasonic weld. The hard materials exhibit poor weldability due to their higher resistance to the plastic deformation during welding.The ductile materials support smooth material flow during welding and hence are easier to weld. Oxide layer formation on the metal surface causes entrapment of oxides in the form of a thin layer near the weld interface due to which the weld quality compromises.

4.6 Tooling The tooling refers to sonotrode tip and anvil that contact the top and bottom portion of the weld, respectively. The tooling serves the purpose of

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transmission of ultrasonic vibration to the weld interface and supports the workpiece firmly. The primary design modifications are performed on the sonotrode, but the anvil face is kept flat most of the time. The tool tips are specially designed and treated to improve gripping and wear resistance.

5  Ultrasonic welding of metals and alloys USW is used for the joining of various similar and dissimilar metal, plastic, and metal-plastic systems. The bond formed in between these combinations exhibits various features, which explain the joining mechanism and mechanical properties of the weld. This section will elaborate on the welding metallurgy, and weldability aspect of various material systems joined by USW.

5.1  Welding of similar metals and alloys USW is one of the most preferred joining techniques for the aluminum alloys because in conventional fusion welding of aluminum alloys, the melting and solidification of weld results in the hot cracking, liquation cracking, and welding defects which compromise with the mechanical properties. However, these defects were not encountered in the solid-state welding (USW) process because it does not involve melting. An ultrasonically welded (USWed) aluminum joints consist of three zones (1) weld zone, (2) weld affected zone, and (3) compression zone. The weld affected zone and compression zone exhibits deformed and elongated grains. However, the grains in the weld zone are refined and difficult to resolve, suggesting the dynamic recrystallization [14]. Haddadi and colleagues [15] categorized the different deformation zone as (1) forging zone near contact point of sonotrode tip and sheet, (2) shear zone at the mid-section of the upper sheet, (3) ultrafine grain structure near the weld interface, (4) shear bands and swirl, and (5) convoluted wave-like pattern in TMAZ of Al 6111-T4 ultrasonic weldments (Fig. 1.6A,B). The fine grain structure in the USWed is attributed to severe plastic deformation and dynamic recrystallization [16–19]. The formation of shear bands, swirl, and convoluted patterns depends upon the welding parameters, specifically welding energy. At low energies or shorter weld time, the presence of these features is rare due to non-uniform contact pressure. However, increasing the weld energies or weld time results in a significant amount of plastic deformation and frictional heating, which causes the formation of swirls and convoluted wave-like patterns [20,21]. Additionally, the extreme

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Figure 1.6  Optical macro images of ultrasonically welded Al 6111 developed with a pressure of 40MPa and weld energies and time of (A) 150 J/0.06 s and (B) 750 J/0.3 s [21]. (With kind permission from Elsevier).

deformation causes the rotation of the micro bond region due to cyclic strain within the local regions at the interface, which also plays an essential role in swirl development. The microstructure of dissimilar aluminum alloys, that is, Al 6022 and Al 7075 weld, revealed that grain refinement in the top plate and grain coarsening in the bottom plates with significant diffusion of Zn in the aluminum.The refine grain structure is attributed to severe plastic deformation and frictional heating, and the grain coarsening in the bottom plate is due to limited plastic deformation [22]. Therefore, it can be concluded that the alloying elements play an essential role in controlling the grain size in the weld zone. The ultrasonic welded pure copper exhibited fine grain structure as compared to the base metal. However, increasing the welding energy causes grain coarsening in the bonded region (dotted region) (Fig. 1.7A,B) owing to excessive strain and heat accumulation at the bond zone [23]. Ward and colleagues [24] also observed the grain coarsening and second phase precipitation at the weld zone of Cu foils at higher weld time owing to significant frictional heating. The presence of nano-particles interlayer between the Cu–Cu joints improves the joint quality owing to enhanced frictional coefficient and

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Figure 1.7  EBSD orientation maps at the center of weld zone of welded Cu plates with weld energy of (A) 800 J and (B) 2400 J [23].

friction heating and better area of contact between the plates [25]. Additionally, the easier softening of nanoparticles due to lower melting point results in a better flow, which helps in the closure of the voids (Fig. 1.8). Similarly, the preheating of the Cu plates before welding is beneficial because it improves the material flow and inter-diffusion of atoms and hence enhances the mechanical interlocking during lower energy input. However, the effect of preheating at high-energy input is not significant in terms of bonding and mechanical performance of the weldments [26]. The ultrasonic spot welding of the magnesium alloy performed at different energy inputs revealed that increasing the power input causes recrystallization and grain coarsening [27,28]. The grain coarsening is attributed to increased temperature at the interface due to the higher strain rate at higher energy input.The increase in the temperature causes partial recrystallization of the deformed grain and coarsening of the equiaxed grains of the base metal [29]. The plastic deformation during USW also develops a sharp texture that weakens with an increase in welding energy [27].

Figure 1.8  SEM images of cross-section of (A) Cu/Cu joint without Cu NPs interlayer and (B) Cu/Cu joint with Cu NPs interlayer at the optimal welding amplitude [25]. (With kind permission from Elsevier).

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5.2  Welding of dissimilar metals and alloys Dissimilar metal welding enables the development of lightweight and highperformance structures in the automobile, aerospace, and marine industries [30].The dissimilar welding helps in the utilization of different properties of materials joints to achieve the required performance. The difference in the physical and mechanical properties offers difficulties like high residual stress and porosity during fusion welding. Additionally, the formation of brittle intermetallic compounds (IMC) degrades the mechanical property of the joint. Therefore, USW is a solid-state welding process that is implemented for the joining of dissimilar materials successfully by controlling the development of the intermetallic layer in the weld interface. The formation of the intermetallic layer in USW is a diffusion-governed phenomenon. The diffusion occurs due to (1) increase in the temperature rise as a result of friction and plastic deformation and (2) increase in the dislocation density and grain boundaries due to plastic deformation [31]. The IMC development during the welding cycle follows three sequences, first during the initial stage, IMC is discontinuous and formed on the different sites in the weld zone. In the second stage, the IMC, a continuous thin layer (0.4–0.6 µm), tends to grow along the joint line. In the terminal stage or third stage, this IMC tend to grow in both the metals [32].The growth of IMC is quantified in terms of the thickness of IMC in the weld zone, which usually increases with weld time and enters into the metals matrix (Fig. 1.9).

Figure 1.9  Backscatter electron SEM image of the interfacial reaction between aluminum and DC04 bare steel for different welding time of (A) 0.25, (B) 1.5, (C) 3.0 s and (D) higher magnification SEM image of a thin sample produced by Focused Ion Beam (FIB) for a 0.4 s welds [33]. (With kind permission from Elsevier).

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However, the aluminum and titanium joint developed by USW exhibited no intermetallic compound later. The absence of the IMC layer is attributed to the low welding energy, which is required for the nucleation of the IMC layer below the activation energy [34–36]. It should be worth mentioning here that during the USW of dissimilar alloy systems, localized melting is encountered in some cases, which can be confirmed by the formation of eutectic structure [31,33,37,38]. During the USW of material with significant strength difference, the higher strength material showed no change in the grain size, but the lower strength material exhibited a fine grain structure near the weld interface. Additionally, the occurrence of adhesive wear for a shorter welding time process was observed due to the adherence of softer material to the surface of the harder material due to friction and sliding of faying surfaces [39].

5.3  Welding of plastic: similar material Welding of plastic is one of the most distinctive features of USW, and the equipment utilized for the welding is similar to that of setup used for metals [40]. However, based on the location of ultrasonic horn from the joint interface, this process is categorized as (1) near field, that is, the distance between the ultrasonic horn and joint interface is less than 6 mm and (2) far-field, in which distance between the ultrasonic horn and joint interface is more than 6 mm [41]. Additionally, the other categorization of ultrasonic welding of plastic is the plunge and continuous plastic welding. In plunge welding, the ultrasonic horn is plunged against part held against a fixture, whereas in continuous welding, a horn is pressed against the continuously moving part or vice-versa [42]. The process can be used for the joining of amorphous, semi crystallite, and crystallite thermoplastics. In the case of amorphous and semi crystallite thermoplastic joints, weld formation occurs as the temperature reaches glass transition temperature. However, crystallite thermoplastic forms a bond above the melting point [43]. The USW of thermoplastics follows various sequences. First, the contact of sonotrode and application of force up to a certain level on the weldments is achieved. The second sequence involves the introduction of vibration during USW increases the temperature at the interface, which changes the physical state of the thermoplastics at the interface [44]. Subsequently, heat generation and entanglement of the polymeric chain take place due to friction and viscoelastic heating at the interface. During the initial stage, the heat generation occurs due to surface friction, and as the glass transition temperature is achieved during welding, the heat generation occurs due to viscoplastic

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heating. This dominating viscoelastic heating increases the diffusive mobility of the polymeric chain and promotes the chain entanglement across the interface [45]. The viscoelastic heating depends on applied frequency, the square of the amplitude, and the loss of the material modulus [46]. Finally, the consolidation phase in which a sufficient amount of force is applied until the temperature reaches below the glass transition temperature. In the consolidation phase, applied force and time duration are a vital parameter for the weld quality [47]. Unlike metal, the heat generation in thermoplastic polymers during welding is complicated because of their poor thermal properties as compared to the metals. Therefore, the welding between the thermoplastic polymers can be performed by concentrating heat at the interface region with the help of the energy director (ED) [48].The EDs provide better strength for amorphous thermoplastic as compared to the semi crystallite thermoplastics [40]. The EDs are the protrusion provided on the surface of the polymer by premolding, and these protrusion acts as asperities at the faying surface and assist the heat generation. The ED produces good bonding without excessive flash formation by ensuring the melting of a specific amount of material during welding.The EDs come in different shapes, that is, triangular, rectangular, and semicircular, as it governs the heat generation [49]. The triangular ED is found to have better heat generation and results showed better mechanical properties [46,47]. It should be worth mentioning here that for reinforced thermoplastic composite fabricating ED increases the manufacturing steps and complexities. Therefore, flat EDs are generally preferred for reinforced thermoplastic owing to its easy manufacturing. However, the thickness of the flat ED must be considered while fabrication as it governs the heat generation and cyclic strain during welding [50]. Recently, due to the complexity in the manufacturing and designing of the ED, the feasibility of USW without the ED is investigated [51,52].

5.4  Welding of plastic: dissimilar material/hybrid welding The increased efficiency and reduced carbon emission by the use of lightweight structural components in the automotive and aerospace industries increase the demand for hybrid joints of lightweight material in these industries.The multi-material/hybrid joining is well established for the metal, but the multimaterial joining in the case of plastic/polymer is less explored. Recently, the advances in USW techniques provided a window for the development of hybrid joints of thermoplastic with thermoset, thermoplastic with metals, and thermosets with metals. Although this process of joining is at a nascent stage but it is still gaining interest from the last 5 years.

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The joining of thermoset and thermoplastic by USW uses a thermoplastic interlayer at the joint interface. The joining is performed by the placement of a thermoplastic interlayer at the joint interface [53]. The interlayer is bonded with the thermoset composite by curing and physical/chemical treatment method [53,54]. Afterward, the thermoset with an embedded interlayer is bonded with the thermoplastic welding. This method produces a hybrid joint without degradation of the thermoset polymer, as compared to the other welding methods [55]. The joining between metal and thermoplastic polymer can be performed by both ultrasonic metal welding and ultrasonic plastic welding setup [35]. The two welding setup can be differentiated by the direction of ultrasonic vibration with respect to the joint interface. In plastic welding set up, the direction of vibration are perpendicular to the joint interface, whereas in metal welding setup, the vibration is parallel to the joint interface. However, the ultrasonic metal welding setup provided better results owing to the direct contact between fiber and metal surface due to high plasticization and displacement of the polymer matrix after melting [56,57]. The possible mechanism in the joining of metal and reinforced thermoplastic is plastic deformation, which results in intermolecular contact and mechanical interlocking between the fiber and bulk material [9]. The surface condition of the metal counterpart also plays a vital role in the quality of the hybrid joint between thermoplastic and metals [58]. In the case of thermoset and metal combination, the joints are developed by using a thermoplastic interlayer in the joint interface. During the joining, the interlayer will melt and displaced due to heating encountered and results in the interlocking between fiber and metal matrix. However, very few groups of researchers explore metalthermoset welding, and it is at a preliminary stage [59,60].

6  Ultrasonic welding applications The earlier discussion establishes that USW can be used for the joining of metal and plastic, and this feature of the USW makes it suitable for various unique applications that are discussed further [6,40,61].

6.1  Automotive industries The automotive industries are using USW for the fabrication of parcel shelves, spoilers, light units, and dashboard instruments. Additionally, it has been used for the staking purpose of assembling metal electrical contact on the plastic parts. It is used for the connection of battery tabs in an electric vehicle.

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6.2  Packaging industries USW is used for the sealing of cups and food packets to develop leak-proof packaging and for the bonding of label holders. It is utilized for the joining of injection-molded parts with good reproducibility. USW can perform the sealing of thermoplastic-coated boxes and cartons.

6.3  Plastic industries The industry involved in the development of plastic-based products uses USW for the joining of plastic toys and the joining of frame components.

6.4  Electronic industries The electronic industries utilize this process for the assembly of the semiconductor, capacitors, and electronic couplers, and wiring purposes.

6.5  Miscellaneous application Apart from the direct application USW, its variants are used in the various other industrial applications, for example, textile industries use it for cutting of fabrics and labels. Additionally, in medical industries for joining of medical adapters and cutting of filters make use of the USW process.

7  Ultrasonic welding: advantages and limitations 7.1 Advantages 1. USW being a solid-state process is free from the microstructural defects, that is, pores, solidification cracking, and segregation of alloying elements observed in the fusion welding process. The severe plastic deformation encountered during welding results in fine equiaxed grain structure with better mechanical properties. 2. This process is utilized for the joining of difficult to weld material like aluminum and copper, which generally offers difficulty during fusion welding. This process is utilized for the joining of the materials like metal and plastic which are nearly impossible to weld by other welding techniques. 3. The sliding friction involved during the initial stage during the process provides cleaning of oxide and contaminants and hence, provides a weld-free of oxide and contaminants. 4. The process enables to produce weld in short of time with high reproducibility. The use of high-end microcontroller and process provide excellent automation.

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5. The absence of filler and fume gases makes this process environmentfriendly. Additionally, the low energy inputs during the process provide energy savings.

7.2 Limitations 1. This process is limited for the development of the lap joint with limited thickness joining. 2. This process induces the deformation on the top and bottom surfaces due to sonotrode and anvil surface. An increase in the welding energy/ force results in the impression of the sonotrode tip on the top surface, which compromises, with mechanical properties of the weld. 3. This process offers high tooling costs for the fixture. The tool design for different materials is complicated and requires a significant amount of process optimization.

8 SUMMARY The USW for the joining of different materials has shown significant development and now consists of a significant amount of details and knowledge. The implementation of this knowledge resulted in improved efficiency, diversity in the application, and new developments. This chapter has provided a brief review of the mechanism and problem encountered during the USW of metals and plastic. The mechanical performance of the joints depends on the process parameters, that is, welding energy and weld time. The effect of process parameters on the material flow, grain size, and heat generation has been comprehensively discussed. The microstructural studies of the weld joints help to predict the joining mechanism and mechanical performance of the joints. The joining mechanism for plastics and metals has also been differentiated. Additionally, the recent research on the hybrid joint developed by USW has been discussed with a hope that it will encourage the researchers and engineers for further research, development, and innovations.

9  Ultrasonic welding: future trends USW exhibited an excellent possibility for the joining of various alloys and material systems. Its industrial application in terms of automation and shorter welding time has displayed the process of significant benefits. How-

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ever, to overcome the limitation and challenges of the process, the following avenues can be explored: • Development of advance/hybrid welding system The current system is available for the USW which encounter challenges like joint thickness and material welding limitation. Therefore, in the near future, the focus should be on the development of dedicated indigenous setup with higher power output. Past researches have shown that a system having bidirectional vibration provision resulted in weld with better mechanical properties [62]. Therefore, more research should be focused on the development of such hybrid systems. • Online process monitoring Developing an online process monitoring system for USW will help in process of weld defect detection and rectification. Additionally, an online monitoring system will also be helpful for the understanding of the welding mechanism in a better way. • Joint types Currently, USW is restricted to lap welding configuration. Therefore there is a need to develop a system and fixture, which may aid in developing weld of different joint configurations. The development of this type of fixture and system will broaden the application horizon of the USW process. • Reducing the process steps This problem is typically encountered during the joining of plastic and metal-plastic combination. A methodology is needed to be developed to reduce the number of process steps such as (1) fabrication of energy director and (2) application of interlayer to reduce the manufacturing time of the joints. • Corrosion studies The corrosion behavior affects the weld performance, and lack of corrosion behavior studies of the dissimilar material weld is major roadblock into the industrial applications. Hence, it is essential to study the corrosion behavior of the dissimilar material joints developed by USW. Additionally, other important properties like fatigue performance of the joints need to be investigated.

References [1] H. Willrich, Applications of ultrasonic waves, Welding 18 (1950) 61–66. [2] E.A. Neppiras, Ultrasonic welding of metals, Ultrasonics 3 (1965) 128–135 doi:https:// doi.org/10.1016/S0041-624X(65)80003-8.

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[3] J. Tsujino, K. Hidai, A. Hasegawa, R. Kanai, H. Matsuura, K. Matsushima, et al. Ultrasonic butt welding of aluminum, aluminum alloy and stainless steel plate specimens, Ultrasonics 40 (2002) 371–374 doi:https://doi.org/10.1016/S0041-624X(02)00124-5. [4] J. Markham, H. Ulrich, Direct integration of feedthrough to implantable medical device housing with ultrasonic welding. U.S. Patent No. 9,504,841. 29 Nov. 2016. [5] G. Harman, J. Albers, The ultrasonic welding mechanism as applied to aluminum-and gold-wire bonding in microelectronics, IEEE Trans. Parts Hybrids Packag. 13 (1977) 406–412. [6] K. Graff, Ultrasonic metal welding, in: N. Ahmed, (Ed.), New Developments in Advanced Welding, in: Woodhead Publishing Series in Welding and Other Joining Technologies, Woodhead Publishing, 2005, pp. 241–269. doi:https://doi. org/10.1533/9781845690892.241. [7] K.C. Joshi, The formation of ultrasonic bonds between metals, Weld. J. 50 (1971) 840– 848. [8] M.P. Matheny, K.F. Graff, Ultrasonic welding of metals, in: J.A., Gallego-Juárez, K.F. Graff, (Eds.), Power Ultrasonics Applications of High-Intensity Ultrasound, Woodhead Publishing, Oxford, 2015, pp. 259–293, doi:https://doi.org/10.1016/B978-1-78242028-6.00011-9. [9] F. Balle, G. Wagner, D. Eifler, Ultrasonic metal welding of aluminium sheets to carbon fibre reinforced thermoplastic composites, Adv. Eng. Mater. 11 (2009) 35–39. [10] J.L. Harthoorn, Ultrasonic Metal Welding, Technische Hogeschool Eindhoven, Eindhoven, 1978. https://doi.org/10.6100/IR161561. [11] E. Heymann, G. Pusch, Contribution to the study of the role of recrystallisation in the formation of the joint in ultrasonic welding, Schweisstechnik 19(12) (1969) 542–545. [12] J.M. Gibert, D.T. McCullough, G.M. Fadel, G.K.M. Martin, E.M. Austin, Stick-slip dynamics in ultrasonic consolidation, in: ASME 2009 International Design Engineering Technical Conferences & Computers and Information in Engineering Conference, American Society of Mechanical Engineers Digital Collection, 2009, pp. 307–317. [13] E. De Vries, Mechanics and mechanisms of ultrasonic metal welding, Dissertion, Ohio State University, Columbus, 2004. [14] S.M. Allameh, C. Mercer, D. Popoola, W.O. Soboyejo, Microstructural characterization of ultrasonically welded aluminum, J. Eng. Mater. Technol. Trans. ASME 127 (2005) 65–74 doi:10.1115/1.1836792. [15] F. Haddadi, D. Tsivoulas, Grain structure, texture and mechanical property evolution of automotive aluminium sheet during high power ultrasonic welding, Mater. Charact. 118 (2016) 340–351 doi:10.1016/j.matchar.2016.06.004. [16] F.A. Mirza, A. Macwan, S.D. Bhole, D.L. Chen, Microstructure and fatigue properties of ultrasonic spot welded joints of aluminum 5754 alloy, JOM 68 (2016) 1465–1475 doi:10.1007/s11837-015-1796-7. [17] Y. Lu, H. Song, G.A. Taber, D.R. Foster, G.S. Daehn, W. Zhang, In-situ measurement of relative motion during ultrasonic spot welding of aluminum alloy using Photonic Doppler Velocimetry, J. Mater. Process. Technol. 231 (2016) 431–440 doi:https://doi. org/10.1016/j.jmatprotec.2016.01.006. [18] H. Ji, J. Wang, M. Li, Evolution of the bulk microstructure in 1100 aluminum builds fabricated by ultrasonic metal welding, J. Mater. Process. Technol. 214 (2014) 175–182 doi:https://doi.org/10.1016/j.jmatprotec.2013.09.005. [19] J. Xie,Y. Zhu, F. Bian, C. Liu, Dynamic recovery and recrystallization mechanisms during ultrasonic spot welding of Al-Cu-Mg alloy, Mater. Charact. 132 (2017) 145–155 doi:https://doi.org/10.1016/j.matchar.2017.06.018. [20] R. Jahn, R. Cooper, D. Wilkosz, The effect of anvil geometry and welding energy on microstructures in ultrasonic spot welds of AA6111-T4, Metall. Mater. Trans. A 38 (2007) 570–583 doi:10.1007/s11661-006-9087-0.

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[21] D. Bakavos, P.B. Prangnell, Mechanisms of joint and microstructure formation in high power ultrasonic spot welding 6111 aluminium automotive sheet, Mater. Sci. Eng. A 527 (2010) 6320–6334 doi:10.1016/j.msea.2010.06.038. [22] T. Wang, S. Sinha, M. Komarasamy, S. Shukla, S. Williams, R.S. Mishra, Ultrasonic spot welding of dissimilar Al 6022 and Al 7075 alloys, J. Mater. Process. Technol. 278 (2020) 116460 doi:https://doi.org/10.1016/j.jmatprotec.2019.116460. [23] J. Yang, B. Cao, Q. Lu, The effect of welding energy on the microstructural and mechanical properties of ultrasonic-welded copper joints, Materials (Basel) 10 (2017) 193 doi:10.3390/ma10020193. [24] A.A. Ward, M.R. French, D.N. Leonard, Z.C. Cordero, Grain growth during ultrasonic welding of nanocrystalline alloys, J. Mater. Process. Technol. 254 (2018) 373–382 doi:10.1016/j.jmatprotec.2017.11.049. [25] Z.L. Ni, X.X.Wang, S. Li, F.X.Ye, Mechanical strength enhancement of ultrasonic metal welded Cu/Cu joint by Cu nanoparticles interlayer, J. Manuf. Process 38 (2019) 88–92 doi:10.1016/j.jmapro.2019.01.014. [26] Y. Luo, H. Chung,W. Cai,T. Rinker, S.J. Hu, E. Kannatey-Asibu, et al. Joint formation in multilayered ultrasonic welding of Ni-coated Cu and the effect of preheating, J. Manuf. Sci. Eng. Trans. ASME 140 (2018) doi:10.1115/1.4040878. [27] V.K. Patel, S.D. Bhole, D.L. Chen, Ultrasonic spot welded AZ31 magnesium alloy: Microstructure, texture, and lap shear strength, Mater. Sci. Eng. A 569 (2013) 78–85 doi:10.1016/j.msea.2013.01.042. [28] V.K. Patel, S.D. Bhole, D.L. Chen, Influence of ultrasonic spot welding on microstructure in a magnesium alloy, Scr. Mater. 65 (10) (2011) 911–914, doi: 10.1016/j.scriptamat.2011.08.009. [29] A. Macwan, D.L. Chen, Ultrasonic spot welding of a rare-earth containing ZEK100 magnesium alloy: effect of welding energy, Metall. Mater.Trans. A 47 (2016) 1686–1697 doi:10.1007/s11661-016-3355-4. [30] K. Martinsen, S.J. Hu, B.E. Carlson, Joining of dissimilar materials, CIRP Ann. Manuf. Technol. 64 (2015) 679–699 doi:10.1016/j.cirp.2015.05.006. [31] J.W.Yang, B. Cao, X.C. He, H.S. Luo, Microstructure evolution and mechanical properties of Cu-Al joints by ultrasonic welding, Sci. Technol. Weld. Join. 19 (2014) 500–504 doi:10.1179/1362171814Y. 0000000218. [32] L. Xu, L. Wang, Y.C. Chen, J.D. Robson, P.B. Prangnell, Effect of interfacial reaction on the mechanical performance of steel to aluminum dissimilar ultrasonic spot welds, Metall. Mater. Trans. A Phys. Metall. Mater. Sci. 47 (2016) 334–346 doi:10.1007/ s11661-015-3179-7. [33] F. Haddadi, Rapid intermetallic growth under high strain rate deformation during high power ultrasonic spot welding of aluminium to steel, Mater. Des. 66 (2015) 459–472 doi:10.1016/j.matdes.2014.07.001. [34] C.Q. Zhang, J.D. Robson, O. Ciuca, P.B. Prangnell, Microstructural characterization and mechanical properties of high power ultrasonic spot welded aluminum alloy AA6111–TiAl6V4 dissimilar joints, Mater. Charact. 97 (2014) 83–91 doi:https://doi. org/10.1016/j.matchar.2014.09.001. [35] J. Magin, F. Balle, Solid state joining of aluminum, titanium and their hybrids by ultrasonic torsion welding: Fügen von Aluminium, Titan und deren Mischverbunde durch Ultraschalltorsionsschweißen, Materwiss. Werksttech. 45 (2014) 1072–1083. [36] C.Q. Zhang, J.D. Robson, P.B. Prangnell, Dissimilar ultrasonic spot welding of aerospace aluminum alloy AA2139 to titanium alloy TiAl6V4, J. Mater. Process Technol. 231 (2016) 382–388 doi:10.1016/j.jmatprotec.2016.01.008. [37] A. Panteli,Y.C. Chen, D. Strong, X. Zhang, P.B. Prangnell, Optimization of aluminiumto-magnesium ultrasonic spot welding, JOM 64 (2012) 414–420 doi:10.1007/s11837012-0268-6.

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[38] F. Haddadi, D. Strong, P.B. Prangnell, Effect of zinc coatings on joint properties and interfacial reactions in aluminum to steel ultrasonic spot welding, JOM 64 (2012) 407– 413 doi:10.1007/s11837-012-0265-9. [39] J.Y. Lin, S. Nambu, T. Koseki, Evolution of bonding interface during ultrasonic welding between steel and aluminium alloy, Sci. Technol. Weld. Join. 24 (2019) 83–91 doi:10.10 80/13621718.2018.1491376. [40] M.J. Troughton, Ultrasonic welding, in: M.J. Troughton (Ed.), Handbook of Plastics Joining, second ed., William Andrew Publishing, Boston, 2009, pp. 15–35, doi:https:// doi.org/10.1016/B978-0-8155-1581-4.50004-4. [41] D. Ensminger, Ultrasonics: Fundamentals, Technology, Applications, Revised and Expanded, CRC Press, (1988). [42] A. Benatar, Ultrasonic welding of plastics and polymeric composites, in: J.A., GallegoJuárez, K.F. Graff (Eds.), Power Ultrasonics, Woodhead Publishing, Oxford, 2015, pp. 295–312. doi:https://doi.org/10.1016/B978-1-78242-028-6.00012-0. [43] A. Yousefpour, M. Hojjati, J.P. Immarigeon, Fusion bonding/welding of thermoplastic composites, J. Thermoplast. Compos. Mater. 17 (2004) 303–341 doi:10.1177/0892705704045187. [44] M.N. Tolunay, P.R. Dawson, K.K. Wang, Heating and bonding mechanisms in ultrasonic welding of thermoplastics, Polym. Eng. Sci. 23 (1983) 726–733 doi:10.1002/ pen.760231307. [45] I.F. Villegas, Ultrasonic welding of thermoplastic composites, Front. Mater. 6 (2019) 1–10 doi:10.3389/fmats.2019.00291. [46] K.S. Suresh, M.R. Rani, K. Prakasan, R. Rudramoorthy, Modeling of temperature distribution in ultrasonic welding of thermoplastics for various joint designs, J. Mater. Process. Technol. 186 (2007) 138–146 doi:https://doi.org/10.1016/j.jmatprotec.2006.12.028. [47] S.F. Raza, S.A. Khan, M.P. Mughal, Optimizing the weld factors affecting ultrasonic welding of thermoplastics, Int. J. Adv. Manuf. Technol. 103 (2019) 2053–2067 doi:10.1007/s00170-019-03681-7. [48] I. Fernandez, D. Stavrov, H.E.N. Bersee, Ultrasonic welding of advanced thermoplastic composites: An investigation on energy directing surfaces, ICCM Seventeenth International Conference on Composite Materials, Edinburgh, United Kingdom, 2009. [49] Y.K. Chuah, L.-H. Chien, B.C. Chang, S.-J. Liu, Effects of the shape of the energy director on far-field ultrasonic welding of thermoplastics, Polym. Eng. Sci. 40 (2000) 157–167 doi:10.1002/pen.11149. [50] G. Palardy, I.F. Villegas, On the effect of flat energy directors thickness on heat generation during ultrasonic welding of thermoplastic composites, Compos. Interfaces 24 (2017) 203–214 doi:10.1080/09276440.2016.1199149. [51] Y. Luo, Z. Zhang, X.Wang,Y. Zheng, Ultrasonic bonding for thermoplastic microfluidic devices without energy director, Microelectron. Eng. 87 (2010) 2429–2436. [52] Y.-H. Gao, Q. Zhi, L. Lu, Z.-X. Liu, P.-C. Wang, Ultrasonic welding of carbon fiber reinforced nylon 66 composite without energy director, J. Manuf. Sci. Eng. 140 (2018). [53] I.F. Villegas, R. van Moorleghem, Ultrasonic welding of carbon/epoxy and carbon/ PEEK composites through a PEI thermoplastic coupling layer, Compos. Part A Appl. Sci. Manuf. 109 (2018) 75–83. [54] M.T. Heitzmann, M. Hou, M. Veidt, L.J. Vandi, R. Paton, Morphology of an interface between polyetherimide and epoxy prepreg, in: Advanced Material Research, Trans Tech Publications, 2012, pp. 184–188. [55] F. Lionetto, M.N. Morillas, S. Pappadà, G. Buccoliero, I.F.Villegas, A. Maffezzoli, Hybrid welding of carbon-fiber reinforced epoxy based composites, Compos. Part A Appl. Sci. Manuf. 104 (2018) 32–40.

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[56] H. Kuckert, C. Born, G. Wagner, D. Eifler, Residual stress distributions in glass/metaljoints produced by ultrasonic torsion welding, Mater. Und Werkstofftechnik Entwicklung, Fert. Prüfung, Eig. Und Anwendungen Tech. Werkstoffe. 34 (2003) 30–33. [57] H. Kuckert, C. Born, G. Wagner, D. Eifler, Helium-tight sealing of glass with metal by ultraasonic welding, Adv. Eng. Mater. 3 (2001) 903–905. [58] G. Wagner, F. Balle, D. Eifler, Ultrasonic welding of aluminum alloys to fiber reinforced polymers, Adv. Eng. Mater. 15 (2013) 792–803 doi:10.1002/adem.201300043. [59] F. Lionetto, C. Mele, P. Leo, S. D’Ostuni, F. Balle, A. Maffezzoli, Ultrasonic spot welding of carbon fiber reinforced epoxy composites to aluminum: mechanical and electrochemical characterization, Compos. Part B Eng. 144 (2018) 134–142 doi:10.1016/j. compositesb.2018.02.026. [60] F. Lionetto, F. Balle, A. Maffezzoli, Hybrid ultrasonic spot welding of aluminum to carbon fiber reinforced epoxy composites, J. Mater. Process. Technol. 247 (2017) 289–295 doi:10.1016/j.jmatprotec.2017.05.002. [61] Cheersonic-fabric, Ultrasonic horns. Available from: https://www.cheersonic-fabric. com/portfolio-items/ultrasonic-horns/. Accessed 01.01.2020 [62] M.P. Satpathy, S.B. Mishra, S.K. Sahoo, Ultrasonic spot welding of aluminum-copper dissimilar metals: A study on joint strength by experimentation and machine learning techniques, J. Manuf. Process 33 (2018) 96–110 doi:https://doi.org/10.1016/j. jmapro.2018.04.020.

CHAPTER 2

Fiber laser welding of Ti-6Al-4V alloy Chandan Kumara, C.P. Paulb,c, Manas Dasa,∗, K.S Bindrab,c

Department of Mechanical Engineering, Indian Institute of Technology, Guwahati, Assam, India Laser design and industrial applications division, Raja Ramanna Center for Advanced Technology, Indore, Madhya Pradesh, India c Homi Bhabha National Institute, BARC Training School Complex, Mumbai, Maharashtra, India ∗Corresponding author. a

b

1  Material processing with the laser beam Light is a form of electromagnetic radiation of energy having different kinds of wavelengths and frequencies. Based on the wave-particle duality concept, it is considered as an energy wave with distinct quantized energy levels. The laser beam is also a light source, and from 1960 onward, it has been extensively utilized as a heat source for material processing. The full form of laser is “Light Amplification by Stimulated Emission of Radiation.” The laser beam was initially demonstrated by Schawlow and Townes [1,2]. The laser delivers a parallel beam and their properties are significantly different than the regular light source. The most attractive laser properties which are essential in material processing are high energy density, monochromatic and low divergence beam, directional and coherent beam. The term “monochromatic” describes the wave having a single wavelength. The monochromatic characteristic of beam energy is essential to focus the beam on a tiny area that provides maximum power density. The coherence characteristic of the beam describes the constant phase relationship between the two waves. In laser beam, photons are in phase and are aligned parallel and it slightly diverges from the beam source.These properties of laser light are utilized in many fields such as welding, cutting, and drilling in a wide range of metals or non-metals. One of the most critical features of the laser beam is its high energy density due to which it is widely used in the welding of materials having a high melting point [3,4]. There is no requirement of filler materials in laser beam welding (LBW) and a faster cooling rate promotes the development of fine microstructure in the fusion zone (FZ) which enhances material’s strength without undergoing further heat treatment. The high welding speed contributes to high solidification and Advanced Welding and Deforming http://dx.doi.org/10.1016/B978-0-12-822049-8.00002-5

Copyright © 2021 Elsevier Inc. All rights reserved.

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cooling rates and it results in a narrow FZ and heat-affected zone (HAZ). Due to low heat input, the deformation of parts is minimal and at the same time, there is no direct contact between workpiece and energy source. Besides, there is a short interaction time between laser light and workpiece surface due to less start and stop time. Both precision and speed of welding can be significantly enhanced by delivering laser beam through fiber optics. However, a small spot diameter is essential for precise part fit-up. Misalignment of workpieces is a critical issue during LBW process.The laser welding equipment is highly expensive than traditional fusion welding systems. Whenever there is a necessity for highquality weldments, LBW is an attractive and cost-effective way of welding technique [5,6]. Nowadays, the newly developed solid-state fiber laser is extensively used in many fields of material processing. The most frequently used laser heat source adopted by industries are carbon dioxide (CO2) laser followed neodymium-doped yttrium aluminum garnet (YAG; Nd: YAG) laser, ytterbium-doped YAG (Yb:YAG) laser, excimer laser, and diode laser.

1.1  Laser beam generation The generation of a laser beam is a three-step process. All three steps cooccur, that is, atomic excitation, spontaneous and stimulated emission, and population inversion. The laser consists of three components as followed: • Lasing medium or “gain medium”—It can be a solid (crystal, glass, etc.), liquid (organic materials), gas (He, CO2, etc.). • Energy source or “pump”—It can be a high voltage discharge, chemical reaction, flash lamp, or other laser sources. • Optical cavity—It is made of a cavity which contains the lasing medium. Also, the two parallel mirrors are placed on each side of the cavity. One mirror is enormously reflective, and the second mirror is partially reflective. It allows some part of the light to exit from the cavity to produce the laser beam. When a sufficient amount of energy is delivered to the lasing medium, the atoms or electrons of the lasing medium may elevate temporarily from the low-energy state, also known as ground state, to high-energy states by the energy absorption process. The electrons cannot stay indefinitely at this excited state. Some of the electrons drop down to the ground state. While returning to a low energy state, it releases energy by emitting a photon. This phenomenon is known as spontaneous emission, and released photons are the seed for laser production. The collisions of the emitted photon with one of the mirrors in the resonating cavity occur. After the collision, the photon

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again reflected back into the lasing cavity and it further collides with some of the already excited atoms. If an excited atom is struck, it can be stimulated to decay back to the ground state, releasing two photons that are in the same phase, identical wavelength, and moving in the same direction. This phenomenon is known as stimulated emission. Photons are emitted in multidirections. However, some of the photons moving along the lasing medium strike with resonator and further reflected back in the cavity. The resonator mirrors provide the direction for amplification of stimulated emission [2,7].

1.2  Optical absorption When a light beam interacts with the material, a portion of the beam is reflected by the material, absorbed, or transmitted through the material. The following parameters strongly influence metal’s absorptivity to incident laser irradiation. • Wavelength—At a shorter wavelength, highly excited photons are absorbed by a large number of bound electrons. Hence, for a lower value of wavelength, the reflectivity of the beam decreases, and absorptivity with the workpiece surface increases. Generally, laser energy is highly absorbed by metals for shorter wavelengths. • Temperature—As the workpiece surface temperature of the material increases, the photons density is also increased.Therefore, a large number of phonon-electron energy exchange occurs. Hence, the electrons interact with the surface of the material rather than vibrate and re-radiate. Thus, the reflectivity of the beam decreases, and absorptivity increases with increased workpiece surface temperature. • Surface roughness—Absorption of the beam energy is profoundly affected by the surface roughness of the workpiece due to multiple reflections with undulations present on the material surface. When the roughness values are lower than the beam wavelength, the incident beam does not suffer from this phenomenon. When a laser light falls on a workpiece surface, a portion of the energy is absorbed by the material. The laser light intensity can be modeled by BeerLambert law. It states that the intensity of light decreases exponentially with the depth in the material which is expressed as

I = I0 exp  

− 4πα d  λ 

(2.1)

where, I = laser intensity at any depth (d), I0 = intensity of light on workpiece surface, λ = beam wavelength, and α = extinction coefficient.

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2  Welding process In general, welding is a procedure of joining two separate materials to make an integrated one where the entire structural continuity exists. It can also be described as the joining of two or more metallic pieces by coalescence produced with or without application of external heat source/pressure [4,8]. The welding can also be used to join other non-metals like thermoplastics. Welding can join various kinds of materials using different welding techniques in which heat energy is provided in different ways like electric energy, frictional force, electron beam, or gas flame, etc. This coalescence is achieved by melting two parts simultaneously as in case of fusion welding or heating up to the plastic state to form a metallic bond across the boundary in case of solid-state welding.The welding process applies to the manufacturing of numerous products used in many industries. Joining of metallic components is required whenever the required components cannot be produced by simple manufacturing processes like casting, forging, rolling, extrusion, etc. Joining of components by using nut and bolt is commonly used in industries. However, it increases the weight of an assembly unlike in the welding process. Following points are considered while designing a joint [8]: • Workpiece material properties to be joined • Joint efficiency • The environmental condition where the joint is to be placed • Overhauling and maintenance of the joint • Load condition on the joint Different energy sources are employed for welding, for example, gas flame, arc produced by an electric circuit, laser source, electron beam, friction, and ultrasound. In industry, welding is carried out in various types of environmental conditions such as open atmosphere, beneath the water surface, etc.Welding is a highly harmful process, and it requires protections to escape from burning, electric shock, retina injury, the breathing of toxic gases, smokes, and exposure to ultraviolet rays.Welding processes are categorized as presented in Fig. 2.1.

Figure 2.1  Different kinds of welding processes [9]. (With kind permission from Springer).

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2.1  Laser beam welding The experimental studies on laser beam are initiated in 1962. However, in 1971, first CO2 laser heat source was employed for welding [10]. Since then, the usage of laser beams in welding purposes had multiplied in manufacturing industries. Various kinds of either similar and dissimilar metals or non-metals can be joined utilizing a laser heat source [3]. Various kinds of intricate shapes, weld design and structures can be made with high quality in case of LBW. Nowadays, different types of laser are established for microwelding in electronic circuit and in other specific applications where traditional techniques fail to make a consistently high-quality joint. Nowadays, the demand for joining of engineering materials are continuously increasing using laser heat source due to their various attractive advantages like capable of joining very thin to thick plates, producing very narrow HAZ and FZ, minimal residual stress, and minimal weld defects [5,11]. LBW is one of the non-conventional and advanced welding techniques for welding various kinds of materials. LBW has many benefits as compared to traditional fusion welding techniques. The primary features of the LBW process are its high efficiency, excellent controllability, and its ability to focus on a tiny area which yields a high intensity of beam energy on the workpiece surface [12]. The LBW process is completed in three main consecutive processes, namely, energy absorption, melting, and solidification. In the beginning, the laser beam strikes the workpiece. A large percentage of the beam energy is reflected back from the material surface depending on the absorptivity of the material. A specific portion of the beam energy is absorbed to heat the surface of the workpiece.The laser beam absorption by the workpiece material is increased with the increase of surface temperature and it forms a weld pool. Further, the melt pool transforms into solid-state due to rapid cooling [13,14]. The laser radiation on the workpiece material is often interrupted due to the formation of hot gases on the irradiated material. At certain conditions, the hot gases may convert into plasma via metal vaporization, and it attenuates the beam energy due to beam absorption and beam scattering. Consequently, the shallow bead depth is achieved in the base material. To eliminate the plasma, the shielding gas is applied. The laser beam can easily weld various kinds of metals and plastics from very thin sheets as low as 0.01 mm to very thick sheets as high as 50 mm under inert gas atmosphere. Its popularity in material processing is growing because of its high performance, high speed, operational flexibility, and lower distortion in the weldments. This process can be robotized and can be made fully automated

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which reduces workforce requirement [15,16]. The LBW process can be carried out either in pulsed mode or in continuous wave (CW) mode. Knowledge regarding material properties, the capability of the laser system, influencing parameters for penetration depth, weld defects and mechanical properties of weldments are required to decide the mode of operation. 2.1.1  Advantages of LBW The significant advantages of LBW are manifolds: • The laser beam has a high energy density. Hence, it provides a high welding speed. • Unlike the electron beam welding (EBW) process, LBW does not require a vacuum chamber.Therefore, it is mostly carried out in the atmospheric condition. • Magnetic materials can also be welded by the LBW process, which is not possible in the EBW process. • Being a non-contact type process, the welded workpiece does not require further cleaning, unlike submerged arc welding (SMAW) or tungsten inert gas (TIG) welding. • Inaccessible areas can be welded by passing the laser beam through an optical fiber. • The laser beam is having high power density, high heating, and cooling rate helps to reduce HAZ size. • LBW can be carried out at higher operating temperatures than other welding processes. • The energy density of the laser beam is comparable to the electron beam and is higher than arc or plasma heat sources. • LBW can be carried out at higher welding speed than arc and plasma welding processes. • LBW joint possesses higher reliability than other welding processes. • LBW can be executed autogenously having accurate control over penetration and weld bead with excellent repeatability. 2.1.2  Limitations of LBW The limitations associated with LBW process are listed as follows [17,18]: • Laser welding equipment is expensive, and the initial investment and maintenance costs of the LBW equipment are higher than traditional welding processes. • Due to smaller spot diameter and narrower weld bead, high precision of joining edges of samples is required. Hence, the tolerance available for the joint fit-up and workpiece alignment is very less.

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• Laser weld conversion efficiency is generally very low, typically 5%~30%. • In some cases, undercut and underfill weld defects are observed. • High reflectivity and high conductivity of some materials may reduce laser weldability. • Maximum joint thickness is limited in the case of the LBW process as compared to EBW.

2.2  Laser welding modes Based on energy density, two kinds of LBW processes are described by researchers [19], that is, conduction mode and keyhole mode of welding, as presented in Fig. 2.2A,B, respectively. Both the welding modes are performed autogenously, that is, filler material is not used during welding. 2.2.1  Conduction mode The energy density in conduction mode is between 103 and 105 W/cm2. Therefore, it is known as a low energy density process. The workpiece surfaces absorb the beam energy and it is dispersed by conduction mode of heat transfer. The balance between convective and conductive modes of heat transfer affects the weld pool shape. In conduction mode, the aspect ratio of the weld bead is lower than the keyhole mode of welding. The geometrical profile of the weld bead is shallow and is bowl-shaped, as shown in Fig. 2.2A. In conduction mode, most of the energy is reflected away. Hence, the conduction mode has a lower efficiency than the keyhole mode. Low penetration depth, lower aspect ratio, poor coupling efficiency, very smooth and highly aesthetic weld bead, and large HAZ are associated with conduction mode of welding as compared to keyhole mode [15]. Less

Figure 2.2  Pictorial description of (A) conduction and (B) keyhole mode of welding [20]. (With kind permission from Springer).

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distortion in the weldments and very less quantity of the loss of alloying elements are the main features of the conduction mode. It is well suited for welding of thin plates due to the requirement of lesser power density which is comparable to lower thickness of workpiece material. 2.2.2  Keyhole mode During welding in keyhole mode (Fig. 2.2B), the power density is higher (105−108 W/cm2). The laser beam deeply penetrates into the workpiece. Due to high energy density, the metal evaporates from the workpiece surface forming a cavity in the base plate, which is called a keyhole. The driving force for the keyhole establishment is recoil pressure and it pushes down the molten material toward the weld pool. Besides the laser-induced recoil force, other forces such as hydrodynamic force, hydrostatic force, and Marangoni shear force are also collectively involved in the formation of the keyhole. Vapor pressure holds surrounding molten material and keeps the keyhole open during the process. The metal vapor also re-radiates beam energy into the molten material through the keyhole sidewall. A series of multiple reflection and absorption processes occur inside the keyhole. The keyhole helps to transfer the beam energy to deeper inside the melt pool and yield a larger penetration depth. Therefore, the energy is transferred through the entire depth of the keyhole and a high-aspect-ratio hole is generated.The energy is absorbed by inverse bremsstrahlung and by Fresnel absorption with reflections on the walls of the keyhole. Keyhole modes of welding process have higher efficiency than conduction mode [21,22]. A higher bead depth to width ratio is obtained in the keyhole mode. The small size of keyhole yields narrower FZ and HAZ. Keyhole mode of welding is applied for joining intricate and thick materials, automobile bodies, and aerospace parts. Deep penetration, larger aspect ratio, high coupling efficiency, smooth and highly aesthetic bead appearance, and smaller size of HAZ are the critical characteristics of keyhole mode of welding [23].

2.3  Classification of laser heat sources Different laser heat sources employed in various welding processes are as follows: • Gas laser: CO2 laser, helium-neon laser, argon laser, and nitrogen laser, etc. • Solid-state laser: Nd:YAG, fiber laser, Er:YAG laser, etc. • Diode laser • Disk laser

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Table 2.1  Comparison between different laser heat sources. Laser type

Wavelength (µm)

Avgerage power (kW)

Beam quality

CO2 Nd:YAG Diode Disk Fiber

10.6 1.06 0.98 1.03 1.08

50 (maximum) 10–15 10–15 16 100

Good Poor Poor Good Good

The comparison between different laser heat sources in terms of wavelength and beam quality are presented in Table 2.1 [24].

2.4  Fiber laser The solid-state lasers working at wavelength very near to 1 µm (micron) have a benefit that the laser beam can be transferred through an optical fiber, and it makes the laser setup highly flexible.The high-power solid-state lasers (like Nd:YAG laser) have comparatively poor beam quality and lesser electrical efficiency. One of the main workhorses of laser material processing is a fiber laser. It operates at near-infrared wavelength region (just outside the visible wavelength region). Currently, the fiber laser has improved significantly in terms of beam quality and electrical efficiency [25].The fiber laser can be employed in a variety of metals and their alloys. Fiber laser possesses a smaller wavelength between 1.06 and 1.08 µm which is absorbed by almost all the known materials and their alloys.The use of fiber laser in the material processing area was started in the year 2000 with 100 W laser power and later in 2005 maximum 17 kW fiber laser was fabricated. It is a favorable alternative to the traditional solid-state lasers. Although fiber lasers are relatively new, they started competing for applications with many other types of lasers having active materials such as solid rods, gases, or semiconductors. However, the applications of fiber lasers are still in a state of rapid development having become important in material processing, communications, spectroscopy, medicine, and military applications. Nowadays, the fiber laser is preferred in commercial industries during thick plates welding with high welding speed where traditional welding processes are not suitable [26,27]. 2.4.1  Fiber laser construction Optical fiber is used as an active gain medium in a fiber laser system. The gain medium is also doped with either erbium, neodymium, dysprosium, ytterbium, etc. It is excited by a diode laser. The fiber laser system is

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Figure 2.3  Double-clad fiber laser source [27]. (With kind permission from Elsevier).

depicted in Fig. 2.3.The unique feature of fiber laser is that the lasing media is contained within an optical fiber. Broad area multimode pump diodes surrounding the fiber are then used to invoke the doped fiber to produce photons. To prevent the uncontrolled escape of photons in the fiber ends, Bragg gratings are created in the fiber. These gratings are created by intense ultraviolet light that writes a periodic change in the refractive properties of the affected area. The Bragg gratings act as high-efficiency mirrors in the fiber and can be modified for a specific desired wavelength, which allows fiber laser beams to be created with a range of wavelengths [27]. The outer casing is enclosed with glass or maybe with the polymeric substance of lesser refraction coefficient to inhibit signal attenuation. The initial equipment expenses of the fiber laser system are moreover its life cycle as it requires almost no maintenance, no additional requirement of cooling. Also, it has the highest wall-plug efficiency (between 25% and 30%), among other laser beam systems. Also, the resulting beam experiences less divergence than other comparable laser beams.The significant difficulty with fiber laser technology is that it is patented proprietary knowledge and it uses fiber optics in the creation of the laser beam and further to convey to the laser head [27,28]. 2.4.2  Laser beam quality In the case of material processing, the ability of the laser beam to focus on a well-defined area is a critical issue. The focusing ability describes the capability of the laser heat source to focus on a tiny spot. The focusing ability of a laser beam is generally defined by beam quality, which is very important in laser welding and cutting process [27]. In the area of laser technology, a parameter is introduced, that is, M2 value, which defines the laser beam quality. It is defined as the ratio of divergence angle of the beam to the beam

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divergence angle of the Gaussian mode beam with the identical aperture which is positioned at the same location.The value of M2 is unity for a perfect Gaussian-shaped beam. However, the value of M2 is greater than “one” if the beam shape deviates from the ideal Gaussian shape. Also, due to the presence of high order modes in the beam, the M2 value is larger than “one.” In fiber-optics communications, the laser beam must have M2 value near to unity to get it combined with single-mode optical fiber. In laser material processing, the lower value of M2 is essential for yielding a tiny beam spot over a small region. This is the remarkable benefits of fiber laser over various kinds of existing lasers. Fiber laser working at relatively low beam power possesses a lower value of M2 (M2  0.6–0.8. Due to the relative increase in value of hav, the effect of friction forces on the middle (in height) metal layers weakens; these layers are deformed most intensively. At the same time, zones of difficult deformation are formed in the near-contact layers. The strip lateral edges become clearly convex (Fig. 15.16B). This type of the strip cross-section is sometimes called a “single barrel.” 4. Thin strip rolling—ld/hav > 3–4. In this case, the contact arc length is several times greater than the average strip thickness in the deformation zone. The supporting effect of the friction forces extends to the entire strip thickness, and therefore the deformation extends approximately uniformly along the strip height.The strip lateral edges after rolling have a very low convexity (Fig. 15.16A). It should be borne in mind that this classification is somewhat arbitrary, because the strip shape change depends not only on ld/hav and the ratio b0/h0, but also on other rolling factors.

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2.4.3  Factors affecting broadening The broadening during longitudinal rolling depends on many factors. Considering these factors, it should be borne in mind that the movement of metal in width and in the longitudinal direction obeys the law of least resistance, according to which the greatest deformation occurs in the direction in which most moving metal particles meet the least resistance to their movement. Thus, the ratio between transverse and longitudinal deformation obeys the volume constancy condition Eq. (15.9).

η ⋅ξ ⋅ λ = 1

or

λ=

1 . η ⋅ξ

Let us analyze the effect of individual rolling factors on broadening. Compression. With increasing compression, broadening increases (Fig. 15.17). This is because the displaced metal volume increases both in the longitudinal and transverse directions. In addition, in accordance with formula Eq. (15.24), the deformation zone length increases, and, therefore, the sum of the longitudinal friction forces increases, which complicates the reduction and promotes the increase in broadening. Roll diameter. With the same compression, and the constancy of other factors, with an increase in the diameter of the rolls, broadening increases (Fig. 15.18). This is also explained by the increase in the deformation zone length and the corresponding increase in the sum of the longitudinal friction forces.

Figure 15.17  Broadening dependence on absolute compression [4]. (With kind permission from Izdatel’skii Dom NITU «MISiS»).

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Figure 15.18  Broadening dependence on roll diameter [4]. (With kind permission from Izdatel’skii Dom NITU «MISiS»).

Strip width. The wider the rolled strip, the greater the sum of the transverse supporting friction forces on the contact surface. Consequently, broadening decreases with increasing strip width (Fig. 15.19). It is well known from practice that when rolling wide strips and sheets, broadening is insignificant. Strip tension. If tensile forces are applied to the strip ends, they facilitate the longitudinal metal flow, that is, contribute to the reduction. Therefore, the tension of the strip ends should reduce broadening. This kind of

Figure 15.19  Broadening dependence on strip width [4]. (With kind permission from Izdatel’skii Dom NITU «MISiS»).

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Figure 15.20  The back (q0) and front (q1) tension effect on the broadening [4]. (With kind permission from Izdatel’skii Dom NITU «MISiS»).

dependency is clearly observed in practice (Fig. 15.20). It is important to note that back tension affects broadening much stronger than the front one. Friction factor. With increasing friction factor, both longitudinal and transverse friction forces increase. However, it should be borne in mind that the metal flows mainly in the longitudinal direction (to the reduction). The increase in the inhibitory effect of the friction forces in the longitudinal direction affects the deformation distribution more significantly than the increase in the transverse friction forces. As a result, with an increase in the friction factor, the reduction decreases, and the broadening increases. 2.4.4  Determination of the broadening value Reducing the strip height during rolling leads to an increase in the strip length and width. The strip width b1 at the exit of the rolls is usually always slightly larger than the initial width b0, and their difference is called absolute broadening: ∆b = b1 − b0 . From the well-known empirical formulas for determining broadening, we can use a rather simple Siebel formula [2,6,10] ∆b = C ⋅

∆h ⋅ R ⋅ ∆h, h0

(15.20)

where C—factor depending on the rolled metal temperature and chemical composition.

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Given the temperature range of rolled steels and their chemical composition, it is possible to approximately take C = 0.4.Then formula Eq. (15.20) will be as follows: ∆b =

0.4 ⋅ ∆h ⋅ ld = 0.4 ⋅ ε ⋅ ld . h0

In practice, the use of this formula in the broadening determination gives satisfactory results, which are quite applicable for calculating various rolling parameters. To quantify the broadening, relative parameters are also used: C b = ∆b/∆h

ξ = b0 /b1

− broadening, − broadening factor.

2.5  External friction during rolling The presence of friction forces and their values determine the biting ability of the rolls, and with the steady-state rolling process, the ratio between the reduction, the broadening, and the advance of the metal during rolling. The external friction forces, requiring additional work to overcome them, cause an increase in resistance and strain energy. External friction affects the heating, wear, and durability of the rolls, dimensional accuracy, surface roughness, and other characteristics of the rolled product quality.

2.5.1  Physical basics of contact friction By the nature of the slip between the metal and the rolls, three types of friction can be distinguished: dry, liquid, and adsorption (boundary). Dry friction—friction between clean metal surfaces, observed only in a deep vacuum metal forming. G. Amonton first formulated the famous empirical law of the linear dependence of friction force on load: F f = f FN , where f—friction factor, FN—load normal to the friction plane. Coulomb generalized this law, showing that the friction force Ff during the mutual displacement of the contacting surfaces consists of two components: mechanical Fmec and molecular Fmol F f = Fmec + Fmol .

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In most practical cases, Fmec ≫ Fmol, and therefore the forces of molecular interaction can be neglected, and when analyzing the rolling process, the ratio (66), which is called the Amonton-Coulomb law, can be used. Liquid friction is observed in cases where both friction surfaces are completely separated by a continuous layer of lubricant, and the friction resistance is reduced to shear resistance in the layers of the lubricant, this requires the lubricant to adhere to the tool and the processed metal and hold well on contact surfaces at given pressure without squeezing out. The founder of the hydrodynamic lubrication theory is N.P. Petrov [12], who described the behavior of hydrodynamic lubricant by an equation obtained on the basis of the famous I. Newton’s law: f =η⋅

v sl , δ

where vc—relative sliding speed between rubbing surfaces, m/s; δ—lubricant layer thickness, m; η—lubricant dynamic viscosity factor. Adsorption (boundary) friction is a friction with a separating film that does not have the liquid properties. Boundary friction can also occur with liquid lubrication at high pressures, when the lubricant layer does not thin and behaves like a viscoplastic body. The boundary layer behavior is described by the equation of A.A. Ilyushin [13] f = η ⋅ v sl . 2.5.2  Determination of the friction factor during rolling When rolling, it is necessary to distinguish between two types of friction factors, significantly different from each other under the same conditions of metal contact with the rolls: (1) when metal is bitten by rolls fbit; (2) during the steady-state rolling process fest, when the metal sliding on the roll surface occurs in the directions opposite to the neutral plane. It was shown earlier that at the moment of the strip biting by rolls, the bite angle is equal to the friction angle, and its tangent is equal to the friction factor: f bit = tgα bit . When hot rolling steel with a rolling speed above 5 m/s, calculations can be performed according to the Ekelund-Bakhtinov formula [1,4–7,10]. f = k1 ⋅ k2 ⋅ k3 ⋅ (1.05 − 0.0005 ⋅ T ),

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Figure 15.21  The value of the factor К2, taking into account the influence of the metal rolling speed [4]. (With kind permission from Izdatel’skii Dom NITU «MISiS»).

where κ1, κ2, κ3—factors taking into account the roll material, rolling speed, and chemical composition of the rolled metal; T—metal temperature, degree Celsius (°C). For cast iron rolls with a hardened surface κ1 = 0.8, for steel rolls—κ1 =1.0. Fig. 15.21 shows the dependence of the factor κ2 on the rolling speed VR: with an increase in the rolling speed from 5 to 25 m/s, the factor κ2 decreases from 0.72 to 0.40. The resulting dependence is described by the following ratios: k2 =

1.16 − 0.001 ⋅ v R at 5 ≤ v R ≤ 16 M/C; ln v R

k2 = 0.4

at v R > 16 M/C.

Table 15.3 shows the values of the factor κ3, which takes into account the influence of the rolled metal chemical composition [4].

Table 15.3 Factor к3, taking into account the rolled metal chemical composition. Class of steel

к3

Carbon Low alloyed Austenitic Austenitic with the inclusion of ferrite Ferritic Ferritic and martensitic High alloyed

1.00 1.30 1.40 1.47 1.50 1.55 1.65

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In case of cold rolling of a strip to determine the contact friction factor, the A.P. Grudev formula [2,7] obtained experimentally by rolling metal with various lubricants is widely used:  0.1 ⋅ v 2  , f = klub ⋅  0.07 −  2 ⋅ (1 + v ) + 3 ⋅ v 2  where κlub—factor taking into account the effect of lubricant; for dry rolls κlub =1.55; machine oil κlub =1.55; water κlub =1.00; palm oil κlub = 0.85. 2.5.3  Influence of rolling factors on the friction factor The friction factor value depends on many rolling factors (conditions), the main of which are given later [4]. Roll material. Rolling is carried out in steel or cast-iron rolls. Numerous data indicate that when rolling strips on steel rolls, the friction factor is higher than when rolling on cast iron rolls. The difference averages 15%– 20%. This is explained by the fact that components (ledeburite, cementite, graphite), which have a relatively low tendency to adhesive interaction (setting) with the actual metal phases (ferrite, austenite) of the strip material, occupy a large place in the cast iron structure. It is well known from practice that deformed metal sticks much less to cast iron rolls than to steel ones. This is especially true for chilled cast iron rolls. Roll surface condition. Considering the influence of this factor, two circumstances must be taken into account: surface roughness (microrelief) and the presence of adhering metal particles and scale on the surface. The surface roughness of the rolls strongly affects the friction factor value, and it increases with increasing roughness (Fig. 15.22).

Figure 15.22  Friction factor dependence on roughness [4]. (With kind permission from Izdatel’skii Dom NITU «MISiS»).

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The experimental data indicate that when the surface roughness of the rolls changes from class 6-7 to class 2-3, the friction factors fbit and fest increase by approx. 1.5–2 times. In cases where the biting conditions limit the possible compression, resort to roughening the roll surface in various ways, for example, to rolling the roll surface with a gear (corrugated) roller. The adhesion of deformed metal particles on the rolls also strongly affects the friction factor. During hot rolling, scale particles and roll wear products (chipping of individual particles from the surface) are added to them. Once in the friction zone, such particles enhance the mechanical engagement of the surfaces. Metal chemical composition. When rolling carbon steels, it was found that the friction factor decreases slightly with increasing carbon content in the metal (Fig. 15.23). This is due to a decrease in the forces of adhesive interaction in the area of the metal contact with the rolls. Those metals that have a pronounced tendency to set and stick, have an increased friction factor. Rolling temperature. With increasing rolled metal temperature, the friction factor first increases, and then decreases (Fig. 15.24). This pattern is observed when rolling various steels and some other metals, such as copper.

Figure 15.23  Friction factor dependence on the carbon content in steel at different rolling temperatures [4]. (With kind permission from Izdatel’skii Dom NITU «MISiS»).

Figure 15.24  Typical friction factor dependence on the hot rolling temperature [4]. (With kind permission from Izdatel’skii Dom NITU «MISiS»).

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Depending on the steel chemical composition and heating conditions, the maximum on the curve can shift in one or another direction, but most often it is within the range of 700°C–1000°C. Rolling speed. Numerous studies indicate that with an increase in rolling speed, the friction factor decreases (Fig. 15.25). The data were obtained when rolling low-carbon steel at 1200°C–1250°C. The direct cause of the friction factor drop is an increase in the amount of lubricant drawn into the deformation zone. Process lubricants. The process lubricant main purpose is to reduce friction forces on contact surfaces in the deformation zone and reduce roll wear. With an increase in viscosity, the contact surface lubricant layer thickness increases, which leads to decrease in the friction factor (Fig. 15.26). Mineral oils are almost free of surfactants and have a lower lubricating efficiency than vegetable oils. This can be seen from a comparison of curves 1 and 2.

Figure 15.25  Friction factor dependence on the rolling speed. 1, grooved rolls; 2, plain rolls [4]. (With kind permission from Izdatel’skii Dom NITU «MISiS»).

Figure 15.26  Friction factor dependence on the lubricant viscosity and type. 1, mineral oils; 2 -vegetable oils [4]. (With kind permission from Izdatel’skii Dom NITU «MISiS»).

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2.6  Rolling process force parameters During rolling, the forces arising from the strip strain are taken by the mill rolls. Exact formula for the rolling force is given as follows: l

F = ∫ p ⋅ b ⋅ dx, 0

where: p—contact pressure; b—strip width at a given point of the contact arc. However, this formula is practically not used for calculation, since in the general case integration is very difficult. Therefore, most often the rolling force (metal pressure on the rolls) is calculated by the formula:

F = pav ⋅ AK ,

(15.21)

where pav—average contact pressure in the deformation zone; Ak—horizontal projection of the contact surface, calculated by the formula Eq. (15.1). 2.6.1  Metal deformation resistance In the metal forming theory, the term “deformation resistance” means the stress of internal forces. Recently, the point of view according to which the deformation resistance σs is identified with the true yield strength σT is becoming more widespread. Temperature effect. With increasing temperature, all the metal strength characteristics, including deformation resistance, monotonically decrease. Fig. 15.27 shows dependence of carbon steel σB on temperature [4]. In the interval of phase transformations, the dependence monotonicity is violated. This is because the volume change during phase transformations does not occur simultaneously in all grains, additional stresses arise between the grains, causing an increase in σB. Influence of strain rate and deformation degree. In cold rolling, the decisive factor affecting the rolled metal deformation resistance is the total relative compression value (deformation degree). With an increase in the deformation degree, the deformation resistance increases, the metal hardens, and rivets. As an example, Fig. 15.28 shows the dependences for low-carbon steel. For cold rolling of thin strips, the value of deformation resistance can be determined by the Zyuzin-Tretyakov formula [1,4,8,12–14].

σ s = σ 0 + a ⋅ ε b.

(15.22)

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Figure 15.27  Dependence of carbon steel temporary resistance sВ with 0.15%–0.55% С on temperature; figures on the curves—carbon content, % [4]. (With kind permission from Izdatel’skii Dom NITU «MISiS»).

Figure 15.28  Dependence of the low-carbon steel (0.15%С, 0.08%Mn) deformation resistance on compression at different temperatures and strain rates [4]. (With kind permission from Izdatel’skii Dom NITU «MISiS»).

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where σ0, a, b—experimentally determined factors that characterize the group of steel and alloy grades [1,4,7]; ε—relative strip compression, percentage (%). For hot strip rolling, the deformation resistance depends on three factors: strip temperature, relative compression, and strain rate. Therefore, the formula for determining the steel deformation resistance during hot rolling has the following form [1,4,12,14,15].

σ s = A ⋅ ε B ⋅ uC ⋅ e − D⋅T , (15.23) where A, B, C, D—factors depending on the grade of steel [1,4]; ε—relative compression; u—strain rate, c−1; T—metal temperature, °C. 2.6.2  Effect of rolling factors on average contact pressure The decisive value and consideration of rolling forces both in the design and operation of rolling mills necessitated the calculation of the average contact pressure pav under various rolling conditions. The meaning of this quantity is quite simple: this is the pressure that corresponds to the condition of its uniform distribution over the contact surface. Contact pressure under various rolling conditions can be determined by the general dependence [1,4,5,8,16,17]. pav = nξ ⋅ nσ ⋅ σ s , where nξ—stress state coefficient, taking into account the influence of contact friction forces and the shape of the deformation zone, independent of the rolled metal nature, and temperature-speed strain conditions; nσ—stress factor taking into account the influence of non-contact zones of the strip and external axial forces (supporting, tension, etc.); σs—metal deformation resistance, which depends on the metal nature and the deformation conditions. Let us discuss the average contact pressure dependence on individual specific rolling factors. Strip thickness. The smaller the strip thickness, the stronger the inhibitory effect of friction forces in the deformation zone is manifested, therefore, with a decrease in the strip thickness, the average contact pressure increases. However, this is true only for relatively thin strips. For thick strips, the discussed dependence is the opposite: pressure increases with increasing strip thickness (Fig. 15.29). This is explained by the fact that friction forces do not have a noticeable effect on pressure during rolling of thick strips, and

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Figure 15.29  Principal view of the average contact pressure dependence on the rolled strip thickness [4]. (With kind permission from Izdatel’skii Dom NITU «MISiS»).

the main role in the stress state formation is played by external zones, the influence of which increases with increasing strip thickness. Compression. With an increase in compression, the deformation zone length grows, which means that the sum of the longitudinal supporting friction forces also increases. The metal movement along the contact surface is hindered, as a result of which the average contact pressure increases (Fig. 15.30A). Roll diameter. It should be borne in mind that with an increase in the roll diameter, other things equal, the deformation zone length increases and, therefore, the supporting effect of friction forces increases. This causes an increase in the average contact pressure (Fig. 15.30B). The noted dependence allows us to make an important practical conclusion: in those cases of rolling, when the pressure limits the possible compression, it is advisable to use small diameter rolls.

Figure 15.30  Diagrams of pressure distribution along the contact arc (A) when rolling with various compression; (B) when rolling with various roll diameters; (C) at various friction factors [4]. (With kind permission from Izdatel’skii Dom NITU «MISiS»).

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Figure 15.31  Typical diagrams of pressure distribution along the contact arc when rolling thick (A), medium (B), and thin (C) strips [4]. (With kind permission from Izdatel’skii Dom NITU «MISiS»).

Friction factor. With an increase in the friction factor, the pressure on the rolls increases, since the supporting friction forces on the contact surface increase (Fig. 15.30C). Shape factor ld/hav effect. At small values of ld/hav (below 0.8), the pressure has a maximum value near the entry plane (Fig. 15.31A). This is explained by the supporting effect of the rear hard end of the strip [4]. In the interval ld/hav=0.8–1.5, the pressures are distributed approximately uniformly along the contact arc (Fig. 15.31B). In this case, the influence of external zones on the deformation zone becomes insignificant, and the friction forces at the point of the strip contact with the rolls do not yet have a noticeable supporting effect, since the strip thickness remains relatively large. At higher values of the parameter ld/hav, especially when ld/hav>3–4 (thin strips), a distinct peak appears in the pressure diagrams located in the neutral plane area (Fig. 15.31C). This nature of the pressure distribution along the contact arc is due to the effect of friction forces. Along with the movement from the deformation zone boundaries to the neutral plane, the sum of the longitudinal supporting friction forces grows—contact pressures increase accordingly. The maximum friction force support is created in a neutral plane, therefore, the pressure in this area is maximum. Fig. 15.32 shows experimental data obtained when rolling thick sheets on various mills. Contact pressures are presented depending on the deformation zone shape factor. The curves are saddle-shaped in nature, the right branch of which at ld/hav > 1 is determined by the influence of contact friction forces, and the left branch at ld/hav< 1 is determined by the influence of non-contact strip forces. Strip end tension. The tension forces facilitate the longitudinal metal flow and, therefore, contribute to a decrease in the average contact pressure.

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Figure 15.32  Contact pressures during sheet rolling on plate mills depending on the deformation zone shape factor at various temperatures [4]. (With kind permission from Izdatel’skii Dom NITU «MISiS»).

Figure 15.33  The effect of back and front tension on the average contact pressure: (A) back; (B) front; (C) front and back [4]. (With kind permission from Izdatel’skii Dom NITU «MISiS»).

The rear strip end tension affects the pressure to a greater extent than the front end tension (Fig. 15.33), since it affects the lag zone, which makes up the main part of the deformation zone [4]. 2.6.3  Modern methods for calculating the average contact pressure The calculation of pav, which is necessary to determine the rolling force, is performed differently for rolling thick and thin strips. Given that the transverse metal flow intensity depends on the parameter b0/h0.V.S. Smirnov proposed a formula for calculating nξ for a three-dimensional diagram of the metal stress state during rolling: nξ = 1 +

f ⋅b 3⋅h

if

0
h f

and

nξ = 1.155.

When rolling blooms, slabs, billets, and thick sheets, as well as thin strips at low deformation degrees, when the shape factor ld/hav   1, when the influence of external zones is noticeably weakening, and the influence of contact friction forces increases, the value of the stress state factor nσ is calculated by the formula:

Figure 15.34  The influence of the shape factor ld/hav on the stress state factor due to the effect of non-contact strip forces during rolling. At blooming mill 1 and on plate mills 2 [5]. (With kind permission from Izd-vo MGTU im. N.ZE. Baumana).

Fundamentals and advancements in longitudinal rolling

nσ = 0.75 + 0.252 ⋅

469

ld . hav

If the strip hot rolling is carried out with tension, when the shape factor ld/hav> 1, the influence of the strip end tension on the contact pressure can be taken into account additionally using the formula:  σ +σ  pav = pav/ ⋅  1 − 0 / 1  , 2 ⋅ pav   where σ0 and σ1—back and front strip tension; p’av—average contact pressure excluding tension. When rolling a thin strip (cold rolling), the pressure required for plastic deformation of the extreme sections is equal to the strip yield strength during plane deformation at the entry and exit of the deformation zone (Fig. 15.35). If the front σ1 and back σ0 tensions are applied to the strip, it is possible to obtain the metal pressure values at the entrance to the rolls and the exit from the deformation zone from the plasticity condition:

Figure 15.35  Determination of stresses affecting the rolled strip [4]. (With kind permission from Izdatel’skii Dom NITU «MISiS»).

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p0= 2K0 - σ0—at the entrance to the deformation zone, p1= 2K1 - σ1—at the exit from the deformation zone. Here 2K0= 1.155 σs0 and 2K1= 1.155 σs1—metal yield strengths in a plane-deformed state, respectively, at the entry and exit. As the discussed section moves away from the metal entry or exit from the rolls, the pressure increases.The pressure curves built from the two edges of the deformation zone intersect in a neutral plane, forming a hill-like diagram of the metal pressure on the roll. The average metal pressure on the roll pav is determined as the average integral value of the specific values of p(x): 1 pav = ⋅ ∫ p( x ) ⋅ dx. l The simplest expression for determining the average specific pressure was proposed by A.I. Tselikov under the assumption that the yield strengths are constant from the deformation zone entry and exit to the neutral plane, and the contact arc is replaced with a chord: 1  2 ⋅ ξ0 ⋅ K 0 ⋅ h0 pav = ⋅ δ −2 ∆h  

 h  δ − 2  2 ⋅ ξ ⋅ K ⋅ h  h  δ + 2   γ 1 1 1 ⋅   − 1  . ⋅  0  − 1 + δ +2  h1     h1   

(15.24) The values of hγ, δ, ξ0, ξ1 , 2K0, 2K1 are calculated based on formula Eq. (15.19). As the practice of using Eq. (15.24) shows, as well as specially conducted studies, the obtained accuracy is sufficient for most cases of a thin strip rolling. 2.6.4  Rolling force calculation The rolling force means the resultant of all elementary forces of normal pressure and friction applied to the metal from the rolls (Fig. 15.36). The same, but oppositely directed force acts from the metal on the rolls. With the steady-state rolling process, the resultant F, regardless of its value, is directed perpendicular to the strip axis. Otherwise, the force F would give a longitudinal component that would cause either braking or acceleration of the strip. The latter circumstance contradicts the condition for the strip ends to move at a constant speed, that is, condition for the very existence of a steady-state rolling process.

Fundamentals and advancements in longitudinal rolling

471

Figure 15.36  Diagram of forces affecting the metal in the deformation zone during rolling.

Therefore, the force on the rolls transmitted through the compression screws is equal to the sum of the vertical components of the radial force and the resulting friction force: Fy = Fr ⋅ cos ϕ + f av ⋅ Fr ⋅ sin ϕ . In applied calculations usually take: Fy = Fr = pav ⋅ AK . When rolling between plain rolls, the rolling force is: F = pav ⋅ AK , (15.25) where pav—average specific or contact pressure; AK—area of metal contact with roll equal to AK= ld b. Under the force effect, the roll is somewhat flattened (Fig. 15.37) and therefore the actual radius of the roll Rc will be greater than the initial radius R0, that is, RF> R0.

Figure 15.37  Diagram for contact arc length determination, taking into account the elastic roll flattening.

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Advanced Welding and Deforming

To determine the “flattened” radius RF, a solution to the problem of cylinder contact deformation due to the elliptically distributed load is normally used. As applied to the flat rolling conditions, the solution to this problem has the form

F , RF = R0 ⋅  1 +  ∆h ⋅ B ⋅ m 

(15.26)

where m = πE/[16 (1 - µ2)]—roll contact stiffness modulus; E—modulus of elasticity of the roll material; µ—Poisson’s ratio of the roll material. The value of m depends only on the mechanical properties of the roll material: E = 2.06105 MPa; µ = 0.3—for steel rolls E = 1.26105 MPa; µ = 0.25—for chilled cast iron rolls E = 6.51105 MPa; µ = 0.3—for tungsten carbide rolls When using Eq. (15.26) to determine a flattened contact arc, a difficulty arises because the rolling force F is determined through pav, which in turn depends on ld and cannot be determined independent of the deformation conditions. However, when the roll deformation is small, it can be assumed that pav= 1.155σs. Then the length of the “flattened” contact arc will be equal to lF ≈

1.155 ⋅ σ s ⋅ R 0 + ∆h ⋅ R 0 . 2 ⋅m

Substituting this formula into the expression for calculating the contact area Ak, we obtain  1.155 ⋅ σ s ⋅ R 0  AK =  + ∆h ⋅ R 0  ⋅ b.   2 ⋅m This formula is applicable to all rolling cases when it can be assumed that b0 ≈ b1. In compression stands and blooming, when the broadening is significant, the formula for calculating Ak is as follows:  1.155 ⋅ σ s ⋅ R 0  b +b  AK =  + ∆h ⋅ R 0  ⋅  0 1  .    2  2 ⋅m Since (b0+ b1)/2 ≈ bav, then  1.155 ⋅ σ s ⋅ R 0  AK =  + ∆h ⋅ R 0  ⋅ bav .   2 ⋅m

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Table 15.4  Reference rolling forces [4]. Mill type

Rolling force, MN

Blooming Slabbing Heavy section and rail and structural steel Medium section Light section Hot-rolled and cold-rolled broad-strip Plate

5.0–15.0 6.0–18.0 1.5–7.0 0.50–2.0 0.15–0.6 10.0–25.0 30–100

With kind permission from Izdatel’skii Dom NITU «MISiS».

Thus, in order to calculate the rolling force, it is necessary to determine the strip deformation resistance, the area of its contact with the roll and the average specific pressure, and then use the formula Eq. (15.25) to calculate the rolling force. Table 15.4 shows reference rolling forces for various mill types [4].

2.7  Rolling torques, work, and power The rolling torque MR is the torque necessary to overcome the deformation resistance of the rolled metal and the resulting forces of the metal friction on the roll surface. Torque values for industrial mills are given in Table 15.5 [4].

Table 15.5  Rolling torques in various mills [4]. Mill type

Rolling torque, MN·m

Blooming Slabbing Plate 3000-5000 Hot-rolled broad-strip Cold-rolled thin-sheet Rail and structural steel Heavy section Medium section Light section Rod

3.0–5.5 4.0–4.5 2.0–6.0 0.20–2.5 0.05–0.2 1.0–1.5 0.4–1.0 0.1–0.3 0.08 0.04

With kind permission from Izdatel’skii Dom NITU «MISiS».

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Advanced Welding and Deforming

Figure 15.38  To the derivation of the formula for torque by rolling force.

2.7.1  Determination of rolling torque by rolling force Let us determine the amount of torque that must be applied to the rolls in order to ensure their rotation during the rolling process. With the steadystate free rolling process, the resultant of all the forces applied to the roll in the deformation zone is the vertically directed force F (Fig. 15.38). The torque created by the force F is equal to M R = F ⋅ aF , where aF—arm of the resultant of forces on the contact surface, that is, of force F, against the line of the roll centers. The arm aF is usually determined in fractions of the deformation zone length, that is, aF = ψ ⋅ ld . Where ψ is called the rolling torque arm factor. Thus, for one roll, we have M R = F ⋅ψ ⋅ ld = F ⋅ψ ⋅ ∆h ⋅ R . (15.27) With a uniform pressure distribution, the point of application of the force F is in the middle of the contact arc, and therefore ψ = 0.5. Any asymmetry in the pressure distribution leads to a deviation of ψ from a value of 0.5.When rolling thick strips, ψ > 0.5, since in this case the maximum pressure is shifted to the entry plane (see Fig. 15.31A). On the contrary, when rolling thin strips, ψ