Materials for Automobile Bodies Materials for Automobile Bodies Geoff Davies F.I.M., M.Sc. (Oxon) AMSTERDAM BOSTON HEIDELBERG LONDON NEW YORK OXFORD PARIS SAN DIEGO SAN FRANCISCO SINGAPORE SYDNEY TOKYO Butterworth-Heinemann An imprint of Elsevier Linacre House, Jordan Hill, Oxford OX2 8DP 200 Wheeler Road, Burlington MA 01803 First published 2003 Copyright © 2003, Elsevier Ltd. All rights reserved No part of this publication may be reproduced in any material form (including photocopying or storing in any medium by electronic means and whether or not transiently or incidentally to some other use of this publication) without the written permission of the copyright holder except in accordance with the provisions of the Copyright, Designs and Patents Act 1988 or under the terms of a licence issued by the Copyright Licensing Agency Ltd, 90 Tottenham Court Road, London, England W1T 4LP. Applications for the copyright holder’s written permission to reproduce any part of this publication should be addressed to the publisher Permissions may be sought directly from Elsevier’s Science and Technology Rights Department in Oxford, UK: phone: (+44) (0) 1865 843830; fax: (+44) (0) 1865 853333; e-mail: [email protected]. You may also complete your request on-line via the Elsevier homepage (http://www.elsevier.com), by selecting ‘Customer Support’ and then ‘Obtaining Permissions’ British Library Cataloguing in Publication Data A catalogue record for this book is available from the British Library Library of Congress Cataloguing in Publication Data A catalogue record for this book is available from the Library of Congress ISBN 0 7506 5692 1 For information on all Butterworth-Heinemann publications visit our website at www.bh.com Typeset by Replika Press Pvt Ltd, India Printed and bound in Great Britain Contents Preface vii Acknowledgements ix About the author xi Disclaimer xiii 1 Introduction 1 1.1 Overview of content 1 1.2 Materials overview 1 1.3 General format of presentation 5 1.4 Introduction to body architecture and terminology 7 2 Design and material utilization 10 2.1 Introduction 10 2.2 Historical perspective and evolving materials technology 11 2.3 Finite element analysis 18 2.4 One manufacturer’s approach to current design 22 2.5 Panel dent resistance and stiffness testing 29 2.6 Fatigue 32 2.7 Alternative body architecture 35 2.8 Integration of materials into designs 45 2.9 Engineering requirements for plastic and composite components 55 2.10 Cost analysis 56 2.11 Learning points from Chapter 2 59 3 Materials for consideration and use in automotive body structures 61 3.1 Introduction 61 3.2 Material candidates and selection criteria 65 3.3 Aluminium 87 3.4 Magnesium 91 3.5 Polymers and composites 92 3.6 Learning points from Chapter 3 97 4 The role of demonstration, concept and competition cars 99 4.1 Introduction 99 4.2 The BL Energy Conservation Vehicle (ECV 3) and aluminium structured vehicle technology (ASVT) 100 4.3 ULSAB and ULSAB 40 105 4.4 Concept cars 108 4.5 Competition cars 111 4.6 Key learning points from Chapter 4 128 5 Component manufacture 130 5.1 Steel formability 130 5.2 Aluminium formability 146 5.3 Manufacture of components in magnesium 158 5.4 Production of polymer parts 158 5.5 Learning points from Chapter 5 166 6 Component assembly: materials joining technology 170 6.1 Introduction 170 6.2 Welding 170 vi Contents 6.3 Adhesive bonding 183 6.4 Mechanical fastening 185 6.5 Learning points from Chapter 6 186 7 Corrosion and protection of the automotive structure 189 7.1 Introduction 189 7.2 Relevant corrosion processes 190 7.3 Effective design principles 194 7.4 Materials used for protection of the body structure 196 7.5 Empirical vehicle and laboratory comparisons 209 7.6 An introduction to electrochemical methods 210 7.7 Learning points from Chapter 7 216 8 Environmental considerations 220 8.1 Introduction 220 8.2 Effect of body mass and emissions control 221 8.3 Life cycle analysis (LCA) 224 8.4 Recycling and ELV considerations 228 8.5 Hygiene 237 8.6 BIW design for safety 239 8.7 Learning points from Chapter 8 249 9 Future trends in automotive body materials 252 9.1 Introduction 252 9.2 Factors influencing material change in the future – trends and requirements 253 9.3 Combined effect of above factors on materials utilization within ‘expected’ and ‘accelerated’ timescales 262 9.4 Learning points from Chapter 9 268 Index 271 Preface The field of materials used for automotive body construction has become increasingly complex over the last 10 years or so, whilst time available for the understanding of the various technologies involved has diminished. As well as body specialists the current volume will be additionally useful to those in peripheral areas of automotive engineering and associated manufacturing and purchasing functions, aware of much of the terminology used but who now wish to understand specific elements of materials technology in greater breadth and depth. This would include processing aspects such as hydroforming, laser welding, tailor welded blanks and polymeric materials, as well as steel and aluminium, and hopefully this will assist them in their decision making where choices in design or sourcing have to be made. Those in the automotive supply industry should also find it instructive in understanding the objectives and requirements of design engineers, and the processing expectations of technologists involved with component manufacture (‘the process chain’ or ‘AMC’, the automotive process chain). Above all, it is hoped that students and future generations of automotive design and related engineers should benefit from an introduction to all topics relevant for the understanding of automotive body materials technology, now gathered for once in a single digestible volume. It is intended that the format, starting with the initial specification of the material and concluding with the issues involved in the final vehicle disposal, is straightforward and presents the facts he/she ‘needs to know’, with the presentation of detail only when it may be justified. However, should additional information be required, authoritative references are provided. As well as conveying the properties relevant to the selection and use of body materials, together with essential features of their preparation, two recurrent themes are emphasized. The first is the need for material consistency which is a major factor in achieving maximum utilization in production and the second is the need for thorough rehearsal of any new aspect of materials technology before implementation is even considered. The evolutionary principle whereby new technology is gradually assessed and introduced in low volume applications, before introduction to high production models is a major feature of all successful European and Japanese marques. The urge to release innovatory technology too early – however attractive potentially – can often cause pain, in the form of delayed launch time and wasted resources. With the advent of computer aided design procedures it has become increasingly incumbent on the structural engineer himself to make a material choice from a number of predetermined choices programmed into his particular system. The opportunity may not nowadays always exist to consult a materials engineer who used to be steeped in many decades of experience in evolving designs and appreciated the many hidden issues that can arise during processing and service. The ‘obvious’ choice may not be too obvious and involve indirect costs and consequences which may unexpectedly occur at a future date. The need exists therefore for easily digested explanations of materials ‘pros and cons’ to help him in his choice and assess implications of associated treatments which again may not be immediately apparent to the non-specialist. Likewise it may also assist the purchasing agent in understanding price extras applying to many apparently similar materials options, and treatments, viii Preface plus other specialists and suppliers involved in the ‘automotive process chain’ seeking to anticipate the effects of changing specifications on their processes. Even to the more experienced design engineer it will be obvious that the field of associated body materials technology has become increasingly complex over the past twenty years and a reference to the 1970s will quickly show that the selection of materials was then limited to a simple selection of 4–5 sheet forming grades. Processing technology has changed significantly and the introduction of a comparatively small number of changes in steel and aluminium grades and choice of several coating types have served to generate a surprising level of confusion. Thus for even the seasoned engineering specialist the need also exists to augment existing knowledge and it is hoped that this volume will fulfil this need or at least provide a pointer as to where that data can be found. Wherever possible examples of production bodies have been used to illustrate the development of the various design technologies and the experience of key manufacturers such as BMW (body design/ environmental aspects) and Volvo (safety engineering) employed to illustrate the synergies achieved by the use of newer materials. This experience is augmented by the massive resources that have been utilized within the ULSAB programmes by the steel industry and also draws on the ASV(Alcan) and ASF(Audi) technology to demonstrate the potential of aluminium. Geoff Davies Acknowledgements The author would like to acknowledge the contributions made by a host of colleagues in the automotive materials and associated supply fields, and academia. Particular thanks are due to Dr Richard Holliday for his initial encouragement and authoritative chapter on ‘Joining’, together with background preparation for other chapters including the polymer content. Many thanks are due to Dr John Sykes, University of Oxford, and Dr David Worsley of the University of Swansea for their help in preparing the chapter on ‘Corrosion’. Also to Brian Simonds for inserting the original artwork and Mike Boyles and his team at Corus for proof reading sections on the various aspects of steel technology. Similar thanks are due to Roy Woodward for his helpful guidance with respect to the latest aluminium technology. The contribution of Brian O’Rourke on Formula 1 and competition body materials was invaluable, and because of its comprehensive yet concise insight into the complex and wider issues surrounding the choice of F1 composite materials his contribution, originally made to a companion volume, has been updated and reproduced in its entirety. Finally, special thanks are due to the author’s family for their patience and encouragement over many months.