Laser Processing in Manufacturing PDF
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Laser Processing in Manufacturing Engineering Aspects of Lasers Series Series editor Dr T.A. Hall, Reader in Physics, University of Essex In the late 1960s and early 1970s the laser was still something of a scientific curi osity with only a limited practical use. The extent of the four volumes in this series shows the enormous change that has happened since that time. The laser is now an indispensable addition to the toolbox of the engineer and scientist. The progress from the time when the laser was often dubbed 'a solution in search of a problem' to today, when engineers of all disciplines frequently use lasers as a matter of course, is a remarkable transformation. Even so, the use of lasers in engineering and other walks of life is still in its infancy and has been held back partly by their relatively high cost and in some cases by their inconvenience in use. The cost of many laser systems has been falling for several years, they are becoming much more convenient to use and no longer need trained personnel to operate them. As these problems are overcome, lasers will find wider and wider application and there is an ever increasing need for engineers and scientists, who perhaps have little interest in lasers themselves, to have access to an authoritative source which not only acts as an introduction but also takes the reader up to the latest developments in laser applications. The four books of the series 'Engineering Aspects of Lasers' arose from a series of laser workshop courses which have been held each year at the University of Essex since 1979. These courses have evolved very considerably since their inception but aspects of their organization have not changed - the contents of the courses have always been co-ordinated by the recognized international authority in each subject area and the lectures given by experts in the particular field from industry, government laboratories or universities. When the idea of publishing a series of books based upon the contents of these courses was first suggested the course co ordinators at that time quite naturally became the editors of each volume and the lecturers were asked to contribute. The workshops are self-supporting courses which originally formed part of the MSc degree in Lasers and their Applications. There are many people who have contributed much to these courses over the years and have made them the success that they are. I would like to express my gratitude to them all. The courses and the MSc were the brainchild of T.P. Hughes who was then Reader in Physics at Essex University. Without his foresight, hard work and determination in setting up the courses, this series of books would not have been written. Other titles in this series Optical Methods in Engineering Metrology Edited by D.C. Williams Nonlinear Optics in Signal Processing Edited by R.W. Eason and A. Miller Advances in Optical Communications Edited by N. Doran and I. Garrett Laser Processing in Manufacturing Edited by R.C. Crafer Partner Abington Consultants and P.J. Oakley Consultant 1a111 Springer-Science+Business Media, B.V. First edition 1993 © 1993 Springer Seienee+Business Media Dordreeht Originally published by Chapman & Hall in 1993. Typeset in 10/12 pt Times by Graphieraft Typesetters Ltd, Hong Kong ISBN 978-94-010-4685-5 ISBN 978-94-011-1570-4 (eBook) DOI 10.1007/978-94-011-1570-4 Apart from any fair dealing for the purposes of research or private study, or criticism or review, as permitted under the UK Copyright Designs and Patents Act, 1988, this publication may not be reprodueed, stored, or transmitted, in any form or by any means, without the prior permission in writing of the publishers, or in the ease of reprographie reproduction only in aceordance with the terms of the lieences issued by the Copyright Lieensing Ageney in the UK, or in aceordanee with the terms of lieences issued by the appropriate Reproduetion Rights Organization outside the UK. Enquiries coneerning reproduction outside the terms stated here should be sent to the publishers at the London address printed on this page. The publisher makes no representation, express or implied, with regard to the accuraey of the information contained in this book and eannot accept any legal responsibility or liability for any errors or omissions that may be made. A catalogue re cord for this book is available from the British Library Library of Congress Cataloging-in-Publication data available. Contents Contributors vii Preface ix 1 Introduction to lasers 1 R.C. Crafer 2 Background to laser processing 19 R. C. Crafer and P.J. Oakley 3 Beam transmission systems 45 D.E. Greening 4 Pulsed Nd:YAG lasers in manufacturing applications 67 T.M.W. Weedon 5 Continuous wave and Q-switched Nd:YAG lasers 91 A.B. May 6 C0 gas lasers: engineering and operation 115 2 M.J. Adams 7 C0 industrial laser systems and applications 141 2 C. Williams 8 Excimer lasers: principles of operation and equipment 163 M.C. Gower 9 Excimer lasers: current and future applications in industry and medicine 189 M.C. Gower 10 Practical aspects of laser processing 273 P.J. Oakley Index 285 Contributors M. Adams A. May Partner, Beech House Associates Laser Lines Limited (formerly Technical Director, Banbury Electrox Limited) Oxfordshire R.C. Crafer P.J. Oakley Partner, Abington Consultants Consultant (formerly, The Laser Centre, TWI) (formerly, The Laser Centre, TWI) T.M.W. Weedon M.C. Gower Lumonics Limited Exitech Limited Rugby Long Hanborough Warwickshire Oxford C. Williams D. Greening Sales Engineer V &S Scientific (London) Limited Laser Ecosse Limited Potters Bar Dundee Hertfordshire Angus Preface Laser processing of material, to effect a change in shape or form, has been available for thirty years. The use of lasers was not widespread initially, but did fire the imagination of the popular press and the general public. More recently, the situation has reversed, with laser processing being used as part of the production route for many items, usually without the pur chaser realizing it. This lower profile and wider use has allowed the laser to become 'just another machine tool' to many production engineers. However, because of the uniqueness of the laser's capabilities and process ing route, increased usage does require the education and training of staff at different levels in order to build up the necessary infrastructure in industry. This is where our book is targeted, and hopefully it will play its part in this education and training process. The origins of the book lie in the Laser Technology MSc course run at Essex University each year from the late 1970s until 1990. In the spring term of the course, a series of one-week laser applications workshops were organized by people active in the respective fields, and were open to in dustrial delegates as well as the MSc students. The 'Applications of Lasers in Welding, Cutting, and Surface Treatment' was one of these intensive workshops, which called on a range of experts from the UK laser fraternity to impart their knowledge in both formal and informal sessions. The book is based on the formal presentations made by contributors to the course. The MSc has been superseded by more specific courses. However, at the time of writing the 'Applications of Lasers in Welding, Cutting, and Surface Treatment' workshop is continuing as a stand-alone event for industrial delegates. The book is based on refined versions of the formal presentations made as part of the course. Both carbon dioxide and solid-state lasers have been part of the course since its inception, and principles, engineering, and usage are covered. Excimer laser engineering and applications were in troduced more recently to the course as a result of their growing signifi cance to laser materials processing. The excimer laser and its actual and potential applications form an extensive part of the book, because we x Preface believe many people are totally unfamiliar with this area of our subject. With such a range of authors, some repetition was unavoidable. This has been eliminated where it was a major concern, but left where the overlap was minor, or the authors brought a different perspective to the topic of discussion. Similarly, rather than impose a uniform writing style on the authors, the range of styles has been left largely as originated. In preparing this book, the editors would like to acknowledge and thank several groups of people. Firstly there are the staff of the Physics De partment of Essex University, who started and continue to run the course on which the book is based. Particular mention must be made of Carol Snape and David Lovett, who have ensured the smooth running of the course despite gales and snowstorms. Secondly, we must thank the au thors, not only for their book chapters, but also for their continuing contributions to the course. Lastly, we would also like to thank the MSc students and industrial participants of the courses who, generally after a quiet start to the week, have soon overcome their reserve and played their part in making the courses lively, stimulating events, often challenging the speakers with inventive questioning. Roger Crafer Peter Oakley 1 An introduction to lasers R.C. Crafer 1.1 DEFINITION The internationally recognized term LASER is an acronym standing for Light Amplification by Stimulated Emission of Radiation. The word laser can be either a noun or an adjective. As a noun it represents an item of equipment utilizing the principle above to produce a light beam having remarkable properties. In this usage it is often preceded by the name of the principal substance involved in its operation, for example Neodymium: YAG, Carbon Dioxide, Excimer, etc. As an adjective it generally describes the use to which a laser (noun) can be put. Examples here would include materials processing (e.g. welding), ophthalmology, range finding, commun ications, etc. This chapter introduces the physical ideas involved and some of the concepts and jargon to be encountered in later chapters. 1.2 BRIEF HISTORY The laser as an identifiable item of equipment made its first appearance with the work of Maiman (1960). However a number of key advances during the preceding century contributed to its development. Some famil iarity with these will be helpful in understanding the laser and its remark able properties. In the mid-nineteenth century the behaviour of light was quite successfully explained by the laws of Ampere, Gauss and Lenz, which are better known today in combined form as Maxwell's Equations (see Chapter 2, section 2.10.1). These were, and still are, highly successful in explaining large-scale or macroscopic behaviour, but fail to explain interactions on an atomic scale. In particular, these equations predicted the occurrence of a so-called ultraviolet catastrophe which fortunately was not observed in practice. This anomaly between theory and experiment was eventually resolved by the German physicist Planck, who postulated a particulate or quantum Laser Processing in 1\lanufacturing. Edited by R.e. Crafer and P.l. Oakley. Published in 1993 by Chapman & Hall, London. ISBN 978-94-010-4685-5
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