Statistical process control

Statistical Process Control

For Susan, Jane and Robert

Statistical Process Control
Sixth Edition
John S. Oakland
PhD, CChem, MRSC, FCQI, FSS, MASQ, FloD

Executive Chairman of Oakland Consulting plc Emeritus Professor of Business Excellence and Quality Management, University of Leeds Business School

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Butterworth-Heinemann is an imprint of Elsevier

Butterworth-Heinemann is an imprint of Elsevier Linacre House, Jordan Hill, Oxford OX2 8DP, UK 30 Corporate Drive, Suite 400, Burlington, MA 01803, USA First edition 1986 Reprinted 1986, 1987, 1989 Second edition 1990 Reprinted 1992, 1994, 1995 Third edition 1996 Fourth edition (paperback) 1999 Fifthedition 2003 Reprinted 2005 Sixth edition 2008 © 1986, 1996, 1999, 2003, 2008 John S. Oakland. All rights reserved. © 1990 John S. Oakland and Roy R. Followell. All rights reserved. The right of John S. Oakland to be identified as the author of this work has been asserted in accordance with the Copyright, Designs and Patents Act 1988 No part of this publication may be reproduced, stored in aretrieval system or transmitted in any form or by any means electronic, mechanical, photocopying, recording or otherwise without the prior written permission of the publisher Permissions may be sought directly from Elsevier’s Science & Technology Rights Deparment in Oxford, UK: phone ( 44) (0) 1865 843830; fax ( 44) (0) 1865 853333; email: permissions@elsevier.com. Alternatively you can submit yourrequest online by visiting the Elsevier website at http://elsevier.com/locate/permissions, and selecting Obtaining permission to use Elsevier material Notice No responsibility is assumed by the publisher 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 containedin the material herein. British Library Cataloguing in Publication Data A catalogue record for this book is available from the British Library Library of Congress Cataloging-in-Publication Data A catalog record for this book is available from the Library of Congress ISBN–13: 978-0-7506-6962-7 For information on all Butterworth-Heinemann publications visit our website at books.elsevier.com Printedand bound in Great Britain 07 08 09 10 10 9 8 7 6 5 4 3 2 1

Contents

Preface

xi

Part 1 Process Understanding
1 Quality, processes and control Objectives 1.1 The basic concepts 1.2 Design, conformance and costs 1.3 Quality, processes, systems, teams, tools and SPC 1.4 Some basic tools Chapter highlights References and further reading Discussion questions Understanding the processObjectives 2.1 Improving customer satisfaction through process management 2.2 Information about the process 2.3 Process mapping and flowcharting 2.4 Process analysis 2.5 Statistical process control and process understanding Chapter highlights References and further reading Discussion questions Process data collection and presentation Objectives 3.1 The systematic approach 3.2 Data collection 3.3 Barcharts and histograms 3.4 Graphs, run charts and other pictures 3.5 Conclusions Chapter highlights References and further reading Discussion questions 3 3 3 8 14 18 20 21 21 23 23 23 26 30 35 37 40 41 41 42 42 42 44 47 54 57 58 58 59

2

3

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Contents

Part 2 Process Variability
4 Variation: understanding and decision making Objectives 4.1 How some managers look at data 4.2Interpretation of data 4.3 Causes of variation 4.4 Accuracy and precision 4.5 Variation and management Chapter highlights References and further reading Discussion questions Variables and process variation Objectives 5.1 Measures of accuracy or centring 5.2 Measures of precision or spread 5.3 The normal distribution 5.4 Sampling and averages Chapter highlights References and further reading Discussion...