Designing Capable and Reliable Products J.D. potx

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 ? Preface In manufacturing companies the cost of quality can be around 20% of the total turnover. The largest proportion of this is associated with costs due to failure of the product during production or when the product is in service with the customer. Typically, such failure costs are due to rework, scrap, warranty claims, product recall and product liability claims, representing lost pro®t to the company. A lack of understanding of variability in manufacture, assembly and service conditions at the design stage is a major contributor to poor product quality and reliability. Variability is often detected too late in the design and development process, if at all. This can lead to design changes prior to product release, which extend the time to bring the product to market or mean the incursion of high costs due to failure with the customer. To improve customer satisfaction and business competitiveness, companies need to reduce the levels of non-conformance and attendant failure costs associated with poor product design and development. Attention needs to be focused on the quality and reliability of the design as early as possible in the product development process. This can be achieved by understanding the potential for variability in design param- eters and the likely failure consequences in order to reduce the overall risk. The eective use of tools and techniques for designing for quality and reliability can provide this necessary understanding to reduce failure costs. Various well-known tools and techniques for analysing and communicating poten- tial quality and reliability problems exist, for example Quality Function Deployment (QFD), Failure Mode and Eects Analysis (FMEA) and Design of Experiments (DOE). Product manufacturing costs can be estimated using techniques in Design for Assembly (DFA) and Design for Manufacture (DFM). For eective use, these techniques can be arranged in a pattern of concurrent product development, but do not speci®cally question whether component parts and assemblies of a design can be processed capably, or connect design decisions with the likely costs of failure. Quality assurance registration with BS EN ISO 9000 does not necessarily ensure product quality, but gives guidance on the implementation of the systems needed to trace and control quality problems, both within a business and with its suppliers. Chapter 1 of this book starts with a detailed statement of the problem, as outlined above, focusing on the opportunities that exist in product design in order to reduce failure costs. This is followed by a review of the costs of quality in manufacturing 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 [...]... 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, 1989) An important aspect of the designer's work is to understand the tolerances set on the design characteristics, and, more importantly, to assess... 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. .. further developed in Chapter 2 1.3 How and why products fail 1.3.1 Failure mechanisms We have already established that variability, or the lack of control and understanding of variability, is a large determinant of the quality of a product in production and service and, therefore, its success in avoiding failure In addition, understanding the potential failure mechanisms and how these interact with design... design decisions is necessary to develop capable and reliable products (Dasgupta and Pecht, 1991) It is helpful next to investigate the link between the causes and modes of failure and variability throughout the life-cycle of a mechanical product Mechanical failure is any change or any design or manufacturing error that renders a component, assembly or system incapable of performing its intended function... failure costs incurred during production and service would be highly bene®cial to manufacturing industry Conceivably, a number of new issues in product design and development have been discussed in this opening section, but in summary: Understanding and controlling the variability associated with design characteristics is a key element of developing a capable and reliable product Variability can have... systems needed to trace and control quality problems, both within a business and with its suppliers The adoption of quality standards is only the ®rst step in the realization of quality products and also has an ambiguous contribution to the overall reduction in failure costs A more proactive response by many businesses has been to implement and support longterm product design and development strategies... processes, handling and assembly practices Poor quality control Poor workmanship Substandard materials and parts Parts that failed in storage or transit Contamination Human error Improper installation Useful life period ± Stress related failures dominate and occur at random over the total system lifetime ± caused by the application of stresses that exceed the design's 19 20 Introduction to quality and. .. and the bene®ts that can accrue from their usage Chapter 5 discusses the important role of the product development process in driving 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... was based on matching and even bettering the Japanese on the quality of it products Most producers believe in the adage `quality pays' in terms of better reputation and sales, customer loyalty, lower reject rates, service and warranty costs They should also realize that `safety pays' in terms of reducing the legal exposure and the tremendous costs that this can incur, both directly and indirectly, for... improvement A model published recently also combines failure and appraisal costs, two distinct categories (Cather and Nandasa, 1995) Quality managers believe that many of the widely publicised quality±cost models are inaccurate and may even be of the wrong form (Plunkett and Dale, 1988) A valid model that could be used to audit business performance and predict the e€ects of change would be most helpful However, . Variance w Class width z Standard deviation multiplier, Standard Normal variate ( ) Function of È SND Function of the Standard Normal Distribution  Mean  Standard deviation  H Standard deviation estimate. 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. 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.