Designing Capable and Reliable Products Episode 1 docx

Designing Capable and Reliable Products Designing Capable and Reliable Products J.D. Booker University of Bristol, UK M. Raines K.G. Swift School of Engineering University of Hull, UK OXFORD AUCKLAND BOSTON JOHANNESBURG MELBOURNE NEW DELHI Butterworth-Heinemann Linacre House, Jordan Hill, Oxford OX2 8DP 225 Wildwood Avenue, Woburn, MA 01801-2041 A division of Reed Educational and Professional Publishing Ltd First published 2001 # J.D. Booker, M. Raines and K.G. Swift 2001 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 W1P 9HE. Applications for the copyright holder's written permission to reproduce any part of this publication should be addressed to the publishers British Library Cataloguing in Publication Data A catalogue record for this book is available from the British Library ISBN 0 7506 5076 1 Library of Congress Cataloging in Publication Data A catalog record for this book is available from the Library of Congress Typeset by Academic & Technical Typesetting, Bristol Printed and bound by MPG Ltd, Bodmin, Cornwall Preface Notation Abbreviations 1 Introduction to quality and reliability engineering 1.1 Statement of the problem 1.2 The costs of quality 1.3 How and why products fail 1.4 Risk as a basis for design 1.5 Designing for quality 1.6 Designing for reliability 1.7 Summary 2 Designing capable components and assemblies 2.1 Manufacturing capability 2.2 Component Manufacturing Variability Risks Analysis 2.3 Assembly capability 2.4 Component Assembly Variablility Risks Analysis 2.5 The effects of non-conformance 2.6 Objectives, application and guidance for an analysis 2.7 Case studies 2.8 Summary 3 Designing capable assembly stacks 3.1 Introduction 3.2 Background 3.3 Tolerance stack models 3.4 A methodology for assembly stack analysis 3.5 Application issues 3.6 Cash study - revisiting the solenoid design 3.7 Summary 4 Designing reliable products 4.1 Deterministic versus probabilistic design 4.2 Statistical methods for probabilistic design 4.3 Variables in probabilistic design 4.4 Stress-strength interface (SSI) analysis 4.5 Elements of stress analysis and failure theory 4.6 Setting reliability targets 4.7 Application issues 4.8 Case studies 4.9 Summary 5 Effective product development 5.1 Introduction 5.2 Product development models 5.3 Tools and techniques in product development 5.4 Supporting issues in effective product development 5.5 Summary Appendix 1 Introductory statistics Statistical representation of data ? Representing data using histograms ? Properties of the Normal distribution ? The Standard Normal distribution ? Appendix 2 Process capability studies ? Process capability concepts ? Process capability index ? Appendix 3 Overview of the key tools and techniques ? A Failure Mode and Effects Analysis (FMEA) ? B Quality Function Deployment (QFD) ? C Design for Assembly/Design for Manufacture (DFA/DFM) ? D Design of Experiments (DOE) ? Appendix 4 Process capability maps ? Index to maps ? Sheet A Casting processes ? Sheet B Casting processes (continued) ? Sheet C Casting processes (continued) ? Sheet D Hot forging processes ? Sheet E Cold forming processes ? Sheet F Cold drawing and rolling processes ? Sheet G Extrusion processes ? Sheet H Sheet metalworking processes ? Sheet I Sheet metalworking processes (continued) ? Sheet K Machining processes ? Sheet L machining processes (continued) ? Sheet M Powder metallurgy processes ? Sheet N Plastic moulding processes ? Sheet P Elastomer and composite moulding processes ? Sheet Q Non-traditional machining processes 6 Sheet R Non-traditional maching processes (continued) ? Appendix 5 Sample case studies used in validation ? Appendix 6 Additional assembly process risk charts ? A Miscellaneous operations ? B Later mechanical deformation ? C Adhesive bonding ? D Brazing and soldering ? E Resistance welding ? F Fusion welding ? Appendix 7 Blank conformability analysis tables ? A Variability risks results table ? B Conformability matrix ? Appendix 8 Assembly problems with two tolerances ? Appendix 9 Properties of continuous distributions ? A Probability Density Functions (PDF) ? B Equivalent mean and standard deviation ? C Cumulative Distribution Functions (CDF) ? Appendix 10 Fitting distributions to data using linear regression ? A Cumulative ranking equations ? B Linear rectification equations and plotting positions C C Distribution parameters from linear regression constants A0 and A1 C Appendix 11 Solving the variance equation ? A Partial derivative method ? B Finite difference method ? C Monte Carlo simulation ? D Sensitivity analysis ? Appendix 12 Simpson’s Rule for numerical integration ? Example 1 ? Example 2 ? Area under a Function ? References ? Bibliography ? Index ? companies, and in particular how failure costs can be related to design decisions and the way products later fail in service. An introduction to risk and risk assessment provides the reader with the underlying concepts of the approaches for designing capable and reliable products. The chapter ends with a review of the key principles in designing for quality and reliability, from both engineering design research and industrial viewpoints. Capable design is part of the Design for Quality (DFQ) concept relating to quality of conformance. Chapter 2 presents a knowledge-based DFQ technique, called Conformability Analysis (CA), for the prediction of process capability measures in component manufacture and assembly. It introduces the concepts of component manu- facturing capability and the relationships between tolerance, variability and cost. It then presents the Component Manufacturing Variability Risks Analysis, the ®rst stage of the CA methodology from which process capability estimates can be deter- mined at the design stage. The development of the knowledge and indices used in an analysis is discussed within the concept of an `ideal design'. The need for assembly variability determination and the inadequacy of the DFA techniques in this respect is argued, followed by an introduction to assembly sequence diagrams and their use in facilitating an assembly analysis. The Component Assembly Variability Risks Analysis is then presented, which is the second stage of the CA methodology. Finally explored in this chapter is a method for linking the variability measures in manufac- turing and assembly with design acceptability and the likely costs of failure in service through linkage with FMEA. The use of CA has proved to be bene®cial for companies introducing a new pro- duct, when an opportunity exists to use new processes/technologies or when design rules are not widely known. Design conformance problems can be systematically addressed, with potential bene®ts, including reduced failure costs, shorter product development times and improved supplier dialogue. A number of detailed case studies are used to demonstrate its application at many dierent levels. Chapter 3 reports on a methodology for the allocation of capable component tolerances within assembly stack problems. There is probably no other design eort that can yield greater bene®ts for less cost than the careful analysis and assign- ment of tolerances. However, the proper assignment of tolerances is one of the least understood activities in product engineering. The complex nature of the problem is addressed, with background information on the various tolerance models commonly used, optimization routines and capability implications, at both component manufac- turing and assembly level. Here we introduce a knowledge-based statistical approach to tolerance allocation, where a systematic analysis for estimating process capability levels at the design stage is used in conjunction with methods for the optimization of tolerances in assembly stacks. The method takes into account failure severity through linkage with FMEA for the setting of realistic capability targets. The application of the method is fully illustrated using a case study from the automotive industry. Product life-time prediction, cost and weight optimization have enormous implica- tions on the business of engineering manufacture. Using large Factors of Safety in a deterministic design approach fails to provide the necessary understanding of the nature of manufacture, material properties, in-service loading and their variability. Probabilistic approaches oer much potential in this connection, but have yet to be taken up widely by manufacturing industry. In Chapter 4, a probabilistic design x Preface methodology is presented providing reliability estimates for product designs with knowledge of the important product variables. Emphasis will be placed on an analysis for static loading conditions. Methods for the prediction of process capability indices for given design geometry, material and processing route, and for estimating material property and loading stress variation are presented to augment probabilistic design formulations. The techniques are used in conjunction with FMEA to facilitate the setting of reliability targets and sensitivity analysis for redesign purposes. Finally, a number of fully worked case studies are included to demonstrate the application of the methods and the bene®ts that can accrue from their usage. Chapter 5 discusses the important role of the product development process in driv- ing the creation of capable and reliable products. Guidance on the implementation problems and integrated use of the main tools and techniques seen as bene®cial is a key consideration. The connection of the techniques presented in the book with those mentioned earlier will be explored, together with their eective positioning within the product development process. Also touched on are issues such as design reviews, supplier development and Total Quality Management (TQM) within the context of producing capable and reliable products. The book provides eective methods for analysing mechanical designs with respect to their capability and reliability for the novice or expert practitioner. The methods use physically signi®cant data to quantify the engineering risks at the design stage to obtain more realistic measures of design performance to reduce failure costs. All core topics such as process capability indices and statistical modelling are covered in separate sections for easy reference making it a self-contained work, and detailed case studies and examples are used to augment the approaches. The book is primarily aimed at use by design sta for `building-in' quality and reliability into products with application of the methods in a wide range of engineering businesses. However, the text covers many aspects of quality, reliability and product development of relevance to those studying, or with an interest in, engineering design, manufacturing or management. Further, it is hoped that the text will be useful to researchers in the ®eld of designing for quality and reliability. The authors are very grateful to Mr Stan Field (formerly Quality Director at British Aerospace Military Aircraft & Aerostructures Ltd) and to Mr Richard Batchelor of TRW for their invaluable support and collaboration on this work. Thanks are also extended to Mr Bob Swain of the School of Engineering for his help with the prepara- tion of many drawings. The Engineering & Physical Sciences Research Council, UK (Grant Nos GR/J97922 and GR/L62313), has funded the work presented in this book. J.D. Booker, M. Raines, K.G. Swift School of Engineering, University of Hull, UK May 2000 Preface xi [...]... likely that about 15 billion was wasted in defects and failures A 10 % improvement in failure costs would have released an estimated 1. 5 billion into the economy IBM, the computer manufacturer, estimated that they were losing about $5.6 billion in 19 86 owing to costs of non-conformance and its failure to meet quality standards set for its products and The costs of quality Figure 1. 8 The optimization... external, with around 50% being the average (Crosby, 19 69; Russell and Taylor, 19 95; Smith, 19 93) A survey of UK manufacturing companies in 19 94 found that failure under the various categories was responsible for 40% of the total cost of quality, followed by appraisal at 25%, and then prevention costs at 18 % This is shown in Figure 1. 6 Of the companies surveyed, 17 % were unsure where their quality costs originated,... is the driving force behind designing capable and reliable products, lessens the need for inspection and can reduce the costs associated with product failure Variability must become the responsibility of the designer in order to achieve these goals (Bjùrke, 19 89) An important aspect of the designer's work is to understand the tolerances set on the design characteristics, and, more importantly, to assess... sales turnover and product liability history It is not easy to make a satisfactory estimate of the product liability costs associated with quality of non-conformance, and 11 12 Introduction to quality and reliability engineering Figure 1. 9 US tort cost escalation compared with GNP growth (Sturgis, 19 92) losses due to safety critical failures in particular are subject to wide variation (Abbot, 19 93) It is... probable severe injury and/ or loss of life, a business could well face the need for cover in excess of 10 million Less safety critical business sectors and lower severity ratings reduce the exposure considerably, but losses beyond 1 million have still been recorded (Abbot, 19 93) The relationship between safety critical failures and potential cost is summarized in Figure 1. 11 It is evident that as... of the performance in service (Kotz and Lovelace, 19 98) Ideally, designers like tight tolerances to assure ®t and function of their designs All manufacturers prefer loose tolerances which make parts easier and less expensive to make (Chase and Parkinson, 19 91) Tolerances alone simply do not contain enough information for the ecient manufacture of a design concept and the designer must use process capability... component characteristics (Harry and Stewart, 19 88; Vasseur et al., 19 92) Process capability analysis has proven to be a valuable tool in this respect, and is most useful when used from the very beginning of the product development process (Kotz and Lovelace, 19 98) If the product is not capable, the only options available are to either: manufacture some bad product, and sort it out by inspection; rework... Tolerance to process risk Variance Class width Standard deviation multiplier, Standard Normal variate Function of Function of the Standard Normal Distribution Mean Standard deviation Standard deviation estimate for a shifted distribution Sum of Ultimate shear strength Shear yield strength 2 Introduction to quality and reliability engineering Figure 1. 1 Effect of quality loss on the pro®tability of a... department too much if I have to modify the design 7 The costs of quality Unsure 17 % Failure costs 40% Prevention costs 18 % Appraisal costs 25% Figure 1. 6 The costs of quality in UK industry (Booker, 19 94) (Dale, 19 94; Kehoe, 19 96; Maylor, 19 96) This ®gure can be as high as 40% in the service industry! (Bendell et al., 19 93) In general, the overall cost of quality in a business can be divided into the... and assurance, design reviews, tools and techniques, and training Appraisal costs ± Costs which include inspection and the checking of goods and materials on arrival Whilst an element of inspection and testing is necessary and justi®ed, it should be kept to a minimum as it does not add any value to the project Failure costs ± Internal failure costs are essentially the cost of failures identi®ed and . 1. 3 How and why products fail 1. 4 Risk as a basis for design 1. 5 Designing for quality 1. 6 Designing for reliability 1. 7 Summary 2 Designing capable components and assemblies 2 .1 Manufacturing. Designing Capable and Reliable Products Designing Capable and Reliable Products J.D. Booker University of Bristol, UK M. Raines K.G (Kotz and Lovelace, 19 98; Vasseur et al., 19 92). Making the product robust to variation is the driving force behind designing capable and reliable products, lessens the need for inspection and can