Consider the bill of materials bom in figure 11.33

Fourth Edition

David G. Ullman

Product Discovery

Project Planning

Conceptual Design

Product Development

Product Support

The Mechanical Design Process

Fourth Edition

U llm

an T

he M echanical D

esign Process

Knowledge about the design process is increasing rapidly. A goal in writing the fourth edition of the Mechanical Design Process was to incorporate this knowledge into a uni� ed structure – one of the strong points of the � rst three editions. Throughout the new edition, topics have been updated and integrated with other best practices in the book. This new edition builds on the earlier editions’ reputation for being concise, direct, and for logically developing the design method with detailed how-to instructions, while remaining easy and enjoyable to read.

What’s New in the Fourth Edition

Improved material to ensure team success

Over 20 templates that can be downloaded from the website to support activities throughout the design process

Improved material on project planning

Improved sections on Design for the Environment and Design for Sustainability

Improved material on making design decisions

A new section on using contradictions to generate ideas

New examples from industry: Irwin Tool, GE Medical, Marin Bicycles, and Jet Propulsion Laboratory are featured.

A book website provides additional resources to instructors and other readers. www.mhhe.com/ullman4e

The fourth edition of The Mechanical Design Process continues to evolve from David Ullman’s years of studying and teaching the design process and his extensive practical experience as a successful designer.

McGraw-Hill EngineeringCS.com

www.McGraw-HillEngineeringCS.com—Your one-stop online shop for all McGraw-Hill Engineering & Computer Science books, supplemental materials, content, & resources! For the student, the professor, and the professional, this site houses it all for your Engineering and CS needs.

Templates are available to both students and faculty for download from the website. These � ll-in-blank forms include:

Product decomposition Team contract Team health inventory Product proposal Pro/con analysis SWOT analysis Plastics part cost calculator Metals part cost calculator Reverse engineering DFAssy FMEA BOM Change order Patent prospects And more M

D D

A L

IM #996887 12/10/08 C

Y A

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Y E

L O

B L

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The Mechanical Design Process

ullman-38162 ull75741_fm December 18, 2008 16:19

McGraw-Hill Series in Mechanical Engineering

Alciatore/Histand Introduction to Mechatronics and Measurement System

Anderson Fundamentals of Aerodynamics

Anderson Introduction to Flight

Anderson Modern Compressible Flow

Barber Intermediate Mechanics of Materials

Beer/Johnston Vector Mechanics for Engineers

Beer/Johnston Mechanics of Materials

Budynas Advanced Strength and Applied Stress Analysis

Budynas/Nisbett Shigley’s Mechanical Engineering Design

Cengel Heat Transfer: A Practical Approach

Cengel Introduction to Thermodynamics & Heat Transfer

Cengel/Boles Thermodynamics: An Engineering Approach

Cengel/Clmbala Fluid Mechanics: Fundamentals and Applications

Cengel/Turner Fundamentals of Thermal-Fluid Sciences

Dieter Engineering Design: A Materials & Processing Approach

Doebelin Measurement Systems: Application & Design

Dorl/Byers Technology Ventures: From Idea to Enterprise

Dunn Measurement & Data Analysis for Engineering and Science

Fianemore/Franzial Fluid Mechanics with Engineering Applications

Hamrock/Schmid/Jacobson Fundamentals of Machine Elements

Heywood Internal Combustion Engine Fundamentals

Holman Experimental Methods for Engineers

Holman Heat Transfer

Hutton Fundamental of Finite Element Analysis

Kays/Crawford/Welgand Convective Heat and Mass Transfer

Meirovioeh Fundamentals of Vibrations

Norton Design of Machinery

Palm System Dynamics

Reddy An Introduction to Finite Element Method

Schey Introduction to Manufacturing Processes

Shames Mechanics of Fluids

Smith/Hashemi Foundations of Materials Science & Engineering

Turns An Introduction to Combustion: Concepts and Applications

Ugural Mechanical Design: An Integrated Approach

Ullman The Mechanical Design Process

White Fluid Mechanics

White Viscous Fluid Flow

Zeid CAD/CAM Theory and Practice

Zeid Mastering CAD/CAM

ullman-38162 ull75741_fm December 18, 2008 16:19

The Mechanical Design Process

Fourth Edition

David G. Ullman Professor Emeritus, Oregon State University

ullman-38162 ull75741_FM December 30, 2008 9:25

THE MECHANICAL DESIGN PROCESS, FOURTH EDITION

Published by McGraw-Hill, a business unit of The McGraw-Hill Companies, Inc., 1221 Avenue of the Americas, New York, NY 10020. Copyright © 2010 by The McGraw-Hill Companies, Inc. All rights reserved. Previous editions © 2003, 1997, and 1992. No part of this publication may be reproduced or distributed in any form or by any means, or stored in a database or retrieval system, without the prior written consent of The McGraw-Hill Companies, Inc., including, but not limited to, in any network or other electronic storage or transmission, or broadcast for distance learning.

Some ancillaries, including electronic and print components, may not be available to customers outside the United States.

This book is printed on acid-free paper.

1 2 3 4 5 6 7 8 9 0 DOC/DOC 0 9

ISBN 978–0–07–297574–1 MHID 0–07–297574–1

Global Publisher: Raghothaman Srinivasan Senior Sponsoring Editor: Bill Stenquist Director of Development: Kristine Tibbetts Senior Marketing Manager: Curt Reynolds Senior Project Manager: Kay J. Brimeyer Senior Production Supervisor: Sherry L. Kane Lead Media Project Manager: Stacy A. Patch Associate Design Coordinator: Brenda A. Rolwes Cover Designer: Studio Montage, St. Louis, Missouri Cover Image: Irwin clamp: © Irwin Industrial Tools; Marin bike: © Marin Bicycles; MER: © NASA/JPL. Senior Photo Research Coordinator: John C. Leland Compositor: S4Carlisle Publishing Services Typeface: 10.5/12 Times Roman Printer: R. R. Donnelley Crawfordsville, IN

Library of Congress Cataloging-in-Publication Data

Ullman, David G., 1944- The mechanical design process / David G. Ullman.—4th ed.

p. cm.—(McGraw-Hill series in mechanical engineering) Includes index. ISBN 978–0–07–297574–1—ISBN 0–07–297574–1 (alk. paper) 1. Machine design. I. Title.

TJ230.U54 2010 621.8′15—dc22 2008049434

www.mhhe.com

http://www.mhhe.com
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ABOUT THE AUTHOR

David G. Ullman is an active product designer who has taught, researched, and written about design for over thirty years. He is president of Robust Decisions, Inc., a supplier of software products and training for product development and decision support. He is Emeritus Professor of Mechanical Design at Oregon State University. He has professionally designed fluid/thermal, control, and transporta- tion systems. He has published over twenty papers focused on understanding the mechanical product design process and the development of tools to support it. He is founder of the American Society Mechanical Engineers (ASME)—Design Theory and Methodology Committee and is a Fellow in the ASME. He holds a Ph.D. in Mechanical Engineering from the Ohio State University.

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CONTENTS

Preface xi

CHAPTER 1 Why Study the Design Process? 1

1.1 Introduction 1 1.2 Measuring the Design Process with Product

Cost, Quality, and Time to Market 3

1.3 The History of the Design Process 8 1.4 The Life of a Product 10 1.5 The Many Solutions for Design

Problems 15

1.6 The Basic Actions of Problem Solving 17 1.7 Knowledge and Learning During Design 19 1.8 Design for Sustainability 20 1.9 Summary 21 1.10 Sources 22 1.11 Exercises 22

CHAPTER 2 Understanding Mechanical Design 25

2.1 Introduction 25 2.2 Importance of Product Function, Behavior,

and Performance 28

2.3 Mechanical Design Languages and Abstraction 30

2.4 Different Types of Mechanical Design Problems 33

2.5 Constraints, Goals, and Design Decisions 40

2.6 Product Decomposition 41 2.7 Summary 44

2.8 Sources 44 2.9 Exercises 45 2.10 On the Web 45

CHAPTER 3 Designers and Design Teams 47

3.1 Introduction 47 3.2 The Individual Designer: A Model of Human

Information Processing 48

3.3 Mental Processes That Occur During Design 56

3.4 Characteristics of Creators 64 3.5 The Structure of Design Teams 66 3.6 Building Design Team Performance 72 3.7 Summary 78 3.8 Sources 78 3.9 Exercises 79 3.10 On the Web 80

CHAPTER 4 The Design Process and Product Discovery 81

4.1 Introduction 81 4.2 Overview of the Design Process 81 4.3 Designing Quality into Products 92 4.4 Product Discovery 95 4.5 Choosing a Project 101 4.6 Summary 109 4.7 Sources 110 4.8 Exercises 110 4.9 On the Web 110

vii

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viii Contents

CHAPTER 5 Planning for Design 111

5.1 Introduction 111 5.2 Types of Project Plans 113 5.3 Planning for Deliverables—

The Development of Information 117

5.4 Building a Plan 126 5.5 Design Plan Examples 134 5.6 Communication During the

Design Process 137

5.7 Summary 141 5.8 Sources 141 5.9 Exercises 142 5.10 On the Web 142

CHAPTER 6 Understanding the Problem and the Development of Engineering Specifications 143

6.1 Introduction 143 6.2 Step 1: Identify the Customers:

Who Are They? 151

6.3 Step 2: Determine the Customers’ Requirements: What Do the Customers Want? 151

6.4 Step 3: Determine Relative Importance of the Requirements: Who Versus What 155

6.5 Step 4: Identify and Evaluate the Competition: How Satisfied Are the Customers Now? 157

6.6 Step 5: Generate Engineering Specifications: How Will the Customers’ Requirement Be Met? 158

6.7 Step 6: Relate Customers’ Requirements to Engineering Specifications: How to Measure What? 163

6.8 Step 7: Set Engineering Specification Targets and Importance: How Much Is Good Enough? 164

6.9 Step 8: Identify Relationships Between Engineering Specifications: How Are the Hows Dependent on Each Other? 166

6.10 Further Comments on QFD 168 6.11 Summary 169 6.12 Sources 169 6.13 Exercises 169 6.14 On the Web 170

CHAPTER 7 Concept Generation 171

7.1 Introduction 171 7.2 Understanding the Function of Existing

Devices 176

7.3 ATechnique for Designing with Function 181 7.4 Basic Methods of Generating Concepts 189 7.5 Patents as a Source of Ideas 194 7.6 Using Contradictions to Generate Ideas 197 7.7 The Theory of Inventive Machines, TRIZ 201 7.8 Building a Morphology 204 7.9 Other Important Concerns During Concept

Generation 208

7.10 Summary 209 7.11 Sources 209 7.12 Exercises 211 7.13 On the Web 211

CHAPTER 8 Concept Evaluation and Selection 213

8.1 Introduction 213 8.2 Concept Evaluation Information 215 8.3 Feasibility Evaluations 218 8.4 Technology Readiness 219 8.5 The Decision Matrix—Pugh’s Method 221 8.6 Product, Project, and Decision Risk 226

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Contents ix

8.7 Robust Decision Making 233 8.8 Summary 239 8.9 Sources 239 8.10 Exercises 240 8.11 On the Web 240

CHAPTER 9 Product Generation 241

9.1 Introduction 241 9.2 BOMs 245 9.3 Form Generation 246 9.4 Materials and Process Selection 264 9.5 Vendor Development 266 9.6 Generating a Suspension Design for the

Marin 2008 Mount Vision Pro Bicycle 269

9.7 Summary 276 9.8 Sources 276 9.9 Exercises 277 9.10 On the Web 278

CHAPTER 10 Product Evaluation for Performance and the Effects of Variation 279

10.1 Introduction 279 10.2 Monitoring Functional Change 280 10.3 The Goals of Performance Evaluation 281 10.4 Trade-Off Management 284 10.5 Accuracy, Variation, and Noise 286 10.6 Modeling for Performance Evaluation 292 10.7 Tolerance Analysis 296 10.8 Sensitivity Analysis 302 10.9 Robust Design by Analysis 305 10.10 Robust Design Through Testing 308 10.11 Summary 313

10.12 Sources 313 10.13 Exercises 314

CHAPTER 11 Product Evaluation: Design For Cost, Manufacture, Assembly, and Other Measures 315

11.1 Introduction 315 11.2 DFC—Design For Cost 315 11.3 DFV—Design For Value 325 11.4 DFM—Design For Manufacture 328 11.5 DFA—Design-For-Assembly

Evaluation 329

11.6 DFR—Design For Reliability 350 11.7 DFT and DFM—Design For Test and

Maintenance 357

11.8 DFE—Design For the Environment 358 11.9 Summary 360 11.10 Sources 361 11.11 Exercises 361 11.12 On the Web 362

CHAPTER 12 Wrapping Up the Design Process and Supporting the Product 363

12.1 Introduction 363 12.2 Design Documentation and

Communication 366

12.3 Support 368 12.4 Engineering Changes 370 12.5 Patent Applications 371 12.6 Design for End of Life 375 12.7 Sources 378 12.8 On the Web 378

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x Contents

APPENDIX A Properties of 25 Materials Most Commonly Used in Mechanical Design 379

A.1 Introduction 379 A.2 Properties of the Most Commonly Used

Materials 380

A.3 Materials Used in Common Items 393 A.4 Sources 394

APPENDIX B Normal Probability 397

B.1 Introduction 397 B.2 Other Measures 401

APPENDIX C The Factor of Safety as a Design Variable 403

C.1 Introduction 403

C.2 The Classical Rule-of-Thumb Factor of Safety 405

C.3 The Statistical, Reliability-Based, Factor of Safety 406

C.4 Sources 414

APPENDIX D Human Factors in Design 415

D.1 Introduction 415 D.2 The Human in the Workspace 416 D.3 The Human as Source of Power 419 D.4 The Human as Sensor and

Controller 419

D.5 Sources 426

Index 427

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PREFACE

I have been a designer all my life. I have designed bicycles, medical equipment,furniture, and sculpture, both static and dynamic. Designing objects has comeeasy for me. I have been fortunate in having whatever talents are necessary to be a successful designer. However, after a number of years of teaching mechanical design courses, I came to the realization that I didn’t know how to teach what I knew so well. I could show students examples of good-quality design and poor- quality design. I could give them case histories of designers in action. I could suggest design ideas. But I could not tell them what to do to solve a design problem. Additionally, I realized from talking with other mechanical design teachers that I was not alone.

This situation reminded me of an experience I had once had on ice skates. As a novice skater I could stand up and go forward, lamely. A friend (a teacher by trade) could easily skate forward and backward as well. He had been skating since he was a young boy, and it was second nature to him. One day while we were skating together, I asked him to teach me how to skate backward. He said it was easy, told me to watch, and skated off backward. But when I tried to do what he did, I immediately fell down. As he helped me up, I asked him to tell me exactly what to do, not just show me. After a moment’s thought, he concluded that he couldn’t actually describe the feat to me. I still can’t skate backward, and I suppose he still can’t explain the skills involved in skating backward. The frustration that I felt falling down as my friend skated with ease must have been the same emotion felt by my design students when I failed to tell them exactly what to do to solve a design problem.

This realization led me to study the process of mechanical design, and it eventually led to this book. Part has been original research, part studying U.S. in- dustry, part studying foreign design techniques, and part trying different teaching approaches on design classes. I came to four basic conclusions about mechanical design as a result of these studies:

1. The only way to learn about design is to do design. 2. In engineering design, the designer uses three types of knowledge: knowl-

edge to generate ideas, knowledge to evaluate ideas and make decisions, and knowledge to structure the design process. Idea generation comes from ex- perience and natural ability. Idea evaluation comes partially from experience and partially from formal training, and is the focus of most engineering ed- ucation. Generative and evaluative knowledge are forms of domain-specific knowledge. Knowledge about the design process and decision making is largely independent of domain-specific knowledge.

3. A design process that results in a quality product can be learned, provided there is enough ability and experience to generate ideas and enough experi- ence and training to evaluate them.

xi

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xii Preface

4. A design process should be learned in a dual setting: in an academic envi- ronment and, at the same time, in an environment that simulates industrial realities.

I have incorporated these concepts into this book, which is organized so that readers can learn about the design process at the same time they are developing a product. Chaps. 1–3 present background on mechanical design, define the terms that are basic to the study of the design process, and discuss the human element of product design. Chaps. 4–12, the body of the book, present a step-by-step development of a design method that leads the reader from the realization that there is a design problem to a solution ready for manufacture and assembly. This material is presented in a manner independent of the exact problem being solved. The techniques discussed are used in industry, and their names have become buzzwords in mechanical design: quality function deployment, decision-making methods, concurrent engineering, design for assembly, and Taguchi’s method for robust design. These techniques have all been brought together in this book. Although they are presented sequentially as step-by-step methods, the overall process is highly iterative, and the steps are merely a guide to be used when needed.

As mentioned earlier, domain knowledge is somewhat distinct from process knowledge. Because of this independence, a successful product can result from the design process regardless of the knowledge of the designer or the type of design problem. Even students at the freshman level could take a course using this text and learn most of the process. However, to produce any reasonably realistic design, substantial domain knowledge is required, and it is assumed throughout the book that the reader has a background in basic engineering science, material science, manufacturing processes, and engineering economics. Thus, this book is intended for upper-level undergraduate students, graduate students, and professional engineers who have never had a formal course in the mechanical design process.

ADDITIONS TO THE FOURTH EDITION

Knowledge about the design process is increasing rapidly. A goal in writing the fourth edition was to incorporate this knowledge into the unified structure—one of the strong points of the first three editions. Throughout the new edition, topics have been updated and integrated with other best practices in the book. Some specific additions to the new edition include:

1. Improved material to ensure team success. 2. Over twenty blank templates are available for download from the book’s web-

site (www.mhhe.com/ullman4e) to support activities throughout the design process. The text includes many of them filled out for student reference.

3. Improved material on project planning.

http://www.mhhe.com/ullman4e
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Preface xiii

4. Improved sections on Design for the Environment and Design for Sustainability.

5. Improved material on making design decisions. 6. A new section on using contradictions to generate ideas. 7. New examples from the industry, with new photos and diagrams to illustrate

the examples throughout.

Beyond these, many small changes have been made to keep the book current and useful.

ELECTRONIC TEXTBOOK

CourseSmart is a new way for faculty to find and review eTextbooks. It’s also a great option for students who are interested in accessing their course materials digitally and saving money. CourseSmart offers thousands of the most commonly adopted textbooks across hundreds of courses from a wide variety of higher education publishers. It is the only place for faculty to review and compare the full text of a textbook online, providing immediate access without the environmental impact of requesting a print exam copy. At CourseSmart, students can save up to 50% off the cost of a print book, reduce their impact on the environment, and gain access to powerful Web tools for learning including full text search, notes and highlighting, and email tools for sharing notes between classmates. www.CourseSmart.com

ACKNOWLEDGMENTS

I would like to thank these reviewers for their helpful comments:

Patricia Brackin, Rose-Hulman Institute of Technology William Callen, Georgia Institute of Technology Xiaoping Du, University of Missouri-Rolla Ian Grosse, University of Massachusetts–Amherst Karl-Heinrich Grote, Otto-von-Guericke University, Magdeburg, Germany Mica Grujicic, Clemson University John Halloran, University of Michigan Peter Jones, Auburn University Mary Kasarda, Virginia Technical College Jesa Kreiner, California State University–Fullerton Yuyi Lin, University of Missouri–Columbia Ron Lumia, University of New Mexico Spencer Magleby, Brigham Young University Lorin Maletsky, University of Kansas

http://www.CourseSmart.com
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xiv Preface

Make McDermott, Texas A&M University Joel Ness, University of North Dakota Charles Pezeshki, Washington State University John Renaud, University of Notre Dame Keith Rouch, University of Kentucky Ali Sadegh, The City College of The City University of New York Shin-Min Song, Northern Illinois University Mark Steiner, Rensselaer Polytechnic Institute Joshua Summers, Clemson University Meenakshi Sundaram, Tennessee Technical University Shih-Hsi Tong, University of California–Los Angeles Kristin Wood, University of Texas

Additionally, I would like to thank Bill Stenquist, senior sponsoring editor for mechanical engineering of McGraw-Hill, Robin Reed, developmental editor, Kay Brimeyer, project manager, and Lynn Steines, project editor, for their interest and encouragement in this project. Also, thanks to the following who helped with examples in the book:

Wayne Collier, UGS Jason Faircloth, Marin Bicycles Marci Lackovic, Autodesk Samir Mesihovic, Volvo Trucks Professor Bob Paasch, Oregon State University Matt Popik, Irwin Tools Cary Rogers, GE Medical Professor Tim Simpson, Penn State University Ralf Strauss, Irwin Tools Christopher Voorhees, Jet Propulsion Laboratory Professor Joe Zaworski, Oregon State University

Last and most important my thanks to my wife, Adele, for her never ques- tioning confidence that I could finish this project.

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1C H A P T E R Why Study the Design Process?

KEY QUESTIONS ■ What can be done to design quality mechanical products on time and within

budget? ■ What are the ten key features of design best practice that will lead to better

products? ■ What are the phases of a product’s life cycle? ■ How are design problems different from analysis problems? ■ Why is it during design, the more you know, the less design freedom you

have? ■ What are the Hanover Principles?

1.1 INTRODUCTION Beginning with the simple potter’s wheel and evolving to complex consumer products and transportation systems, humans have been designing mechanical objects for nearly five thousand years. Each of these objects is the end result of a long and often difficult design process. This book is about that process. Regardless of whether we are designing gearboxes, heat exchangers, satellites, or doorknobs, there are certain techniques that can be used during the design process to help ensure successful results. Since this book is about the process of mechanical design, it focuses not on the design of any one type of object but on techniques that apply to the design of all types of mechanical objects.

If people have been designing for five thousand years and there are literally millions of mechanical objects that work and work well, why study the design process? The answer, simply put, is that there is a continuous need for new, cost-effective, high-quality products. Today’s products have become so complex that most require a team of people from diverse areas of expertise to develop an idea into hardware. The more people involved in a project, the greater is the need for assistance in communication and structure to ensure nothing important

1

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2 CHAPTER 1 Why Study the Design Process?

is overlooked and customers will be satisfied. In addition, the global marketplace has fostered the need to develop new products at a very rapid and accelerating pace. To compete in this market, a company must be very efficient in the design of its products. It is the process that will be studied here that determines the efficiency of new product development. Finally, it has been estimated that 85% of the problems with new products not working as they should, taking too long to bring to market, or costing too much are the result of a poor design process.

The goal of this book is to give you the tools to develop an efficient design process regardless of the product being developed. In this chapter the important features of design problems and the processes for solving them will be introduced. These features apply to any type of design problem, whether for mechanical, elec- trical, software, or construction projects. Subsequent chapters will focus more on mechanical design, but even these can be applied to a broader range of problems.

Consider the important factors that determine the success or failure of a product (Fig. 1.1). These factors are organized into three ovals representing those factors important to product design, business, and production.

Product design factors focus on the product’s function, which is a description of what the object does. The importance of function to the designer is a major topic of this book. Related to the function are the product’s form, materials, and manufacturing processes. Form includes the product’s architecture, its shape, its color, its texture, and other factors relating to its structure. Of equal importance to form are the materials and manufacturing processes used to produce the product. These four variables—function, form, materials, and manufacturing processes—

Business

Production

Product design

Product form Price

Promotion

Distribution coverage

Sales forecast

Target market

Manufacturing processes

Production planning/ sourcing

Production system

Cost/risk

Facilities

Materials

Product function

Figure 1.1 Controllable variables in product development.

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1.2 Measuring the Design Process with Product Cost, Quality, and Time to Market 3

are of major concern to the designer. This product design oval is further refined in Fig. 9.3.

The product form and function is also important to the business because the customers in the target market judge a product primarily on what it does (its function) and how it looks (its form). The target market is one factor important to the business, as shown in Fig. 1.1. The goal of a business is to make money— to meet its sales forecasts. Sales are also affected by the company’s ability to promote the product, distribute the product, and price the product, as shown in Fig. 1.1.

The business is dependent not only on the product form and function, but also on the company’s ability to produce the product. As shown in the production oval in Fig. 1.1, the production system is the central factor. Notice how product design and production are both concerned with manufacturing processes. The choice of form and materials that give the product function affects the manufacturing processes that can be used. These processes, in turn, affect the cost and hence the price of the product. This is just one example of how intertwined product design, production, and businesses truly are. In this book we focus on the product design oval. But, we will also pay much attention to the business and production variables that are related to design.As shown in the upcoming sections, the design process has a great effect on product cost, quality, and time to market.

1.2 MEASURING THE DESIGN PROCESS WITH PRODUCT COST, QUALITY, AND TIME TO MARKET

The three measures of the effectiveness of the design process are product cost, quality, and time to market. Regardless of the product being designed—whether it is an entire system, some small subpart of a larger product, or just a small change in an existing product—the customer and management always want it cheaper (lower cost), better (higher quality), and faster (less time).

The actual cost of designing a product is usually a small part of the manufac- turing cost of a product, as can be seen in Fig. 1.2, which is based on data from Ford Motor Company. The data show that only 5% of the manufacturing cost of a car (the cost to produce the car but not to distribute or sell it) is for design activities that were needed to develop it. This number varies with industry and product, but for most products the cost of design is a small part of the manufacturing cost.

However, the effect of the quality of the design on the manufacturing cost is much greater than 5%. This is most accurately shown from the results of a detailed study of 18 different automatic coffeemakers. Each coffeemaker had the same function—to make coffee. The results of this study are shown in Fig. 1.3. Here the effects of changes in manufacturing efficiency, such as material cost, labor wages, and cost of equipment, have been separated from the effects of the design process. Note that manufacturing efficiency and design have about the same influence on the cost of manufacturing a product. The figure shows that

ullman-38162 ull75741_01 December 17, 2008 11:15

4 CHAPTER 1 Why Study the Design Process?

15% Design Labor

Material

5%

50%

30% Overhead

Figure 1.2 Design cost as fraction of manufacturing cost.

$4.98 Good design

Efficient manufacturing

$9.72 Good design

Inefficient manufacturing

$8.17 Average design

Average manufacturing

$8.06 Poor design

Efficient manufacturing

$14.34 Poor design

Inefficient manufacturing

Figure 1.3 The effect of design on manufacturing cost. (Source: Data reduced from “Assessing the Importance of Design through Product Archaeology,” Management Science, Vol. 44, No. 3, pp. 352–369, March 1998, by K. Ulrich and S. A. Pearson.)

Designers cost little, their impact on product cost, great.

good design, regardless of manufacturing efficiency, cuts the cost by about 35%. In some industries this effect is as high as 75%.

Thus, comparing Fig. 1.2 to Fig. 1.3, we can conclude that the decisions made during the design process have a great effect on the cost of a product but cost very little. Design decisions directly determine the materials used, the goods

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1.2 Measuring the Design Process with Product Cost, Quality, and Time to Market 5

Product cost is committed early in the design process and spent late in the process.

purchased, the parts, the shape of those parts, the product sold, the price of the product, and the sales.

Another example of the relationship of the design process to cost comes from Xerox. In the 1960s and early 1970s, Xerox controlled the copier market. However, by 1980 there were over 40 different manufacturers of copiers in the marketplace and Xerox’s share of the market had fallen significantly. Part of the problem was the cost of Xerox’s products. In fact, in 1980 Xerox realized that some producers were able to sell a copier for less than Xerox was able to manu- facture one of similar functionality. In one study of the problem, Xerox focused on the cost of individual parts. Comparing plastic parts from their machines and ones that performed a similar function in Japanese and European machines, they found that Japanese firms could produce a part for 50% less than American or European firms. Xerox attributed the cost difference to three factors: materials costs were 10% less in Japan, tooling and processing costs were 15% less, and the remaining 25% (half of the difference) was attributable to how the parts were designed.

Not only is much of the product cost committed during the design process, it is committed early in the design process. As shown in Fig. 1.4, about 75% of the manufacturing cost of a typical product is committed by the end of the conceptual phase process. This means that decisions made after this time can influence only 25% of the product’s manufacturing cost. Also shown in the figure is the amount of cost incurred, which is the amount of money spent on the design of the product.

100

80

60

40

20

Sp ec

if ic

at io

n de

ve lo

pm en

t

C on

ce pt

ua l

de si

gn

Pr od

uc t

de si

gn

Cost com mitted

Cost incurred

Time

Pe rc

en ta

ge o

f pr

od uc

t c os

t c om

m itt

ed

0

Figure 1.4 Manufacturing cost commitment during design.

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6 CHAPTER 1 Why Study the Design Process?

Table 1.1 What determines quality

1989 2002

Works as it should 4.99 (1) 4.58 (1) Lasts a long time 4.75 (2) 3.93 (5) Is easy to maintain 4.65 (3) 3.29 (5) Looks attractive 2.95 (4–5) 3.58 (3–4) Incorporates latest technology/features 2.95 (4–5) 3.58 (3–4)

Scale: 5 = very important, 1 = not important at all, brackets denote rank. Sources: Based on a survey of consumers published in Time, Nov. 13, 1989, and a survey based on quality professional, R. Sebastianelli and N. Tamimi, “How Product Quality Dimensions Relate to Defining Quality,” International Journal of Quality and Reliability Management, Vol. 19, No. 4, pp. 442–453, 2002.

It is not until money is committed for production that large amounts of capital are spent.

The results of the design process also have a great effect on product quality. In a survey taken in 1989, American consumers were asked, “What determines quality?” Their responses, shown in Table 1.1, indicate that “quality” is a compos- ite of factors that are the responsibility of the design engineer. In a 2002 survey of engineers responsible for quality, what is important to “quality” is little changed. Although the surveys were of different groups, it is interesting to note that in the thirteen years between surveys, the importance of being easy to maintain has dropped, but the main measures of quality have remained unchanged.

Note that the most important quality measure is “works as it should.” This, and “incorporates latest technology/features,” are both measures of product function. “Lasts a long time” and most of the other quality measures are dependent on the form designed and on the materials and the manufacturing process selected. What is evident is that the decisions made during the design process determine the product’s quality.

Besides affecting cost and quality, the design process also affects the time it takes to produce a new product. Consider Fig. 1.5, which shows the num- ber of design changes made by two automobile companies with different design philosophies. The data points for Company B are actual for a U.S. automobile manufacturer, and the dashed line for Company A is what is typical for Toyota. Iteration, or change, is an essential part of the design process. However, changes occurring late in the design process are more expensive than those occurring ear- lier, as prior work is scrapped. The curve for Company B shows that the company was still making changes after the design had been released for production. In fact, over 35% of the cost of the product occurred after it was in production. In essence, Company B was still designing the automobile as it was being sold as a product. This causes tooling and assembly-line changes during production and the possibility of recalling cars for retrofit, both of which would necessitate significant expense, to say nothing about the loss of customer confidence. Com- pany A, on the other hand, made many changes early in the design process and finished the design of the car before it went into production. Early design changes require more engineering time and effort but do not require changes in hardware or documentation. A change that would cost $1000 in engineering time if made

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1.2 Measuring the Design Process with Product Cost, Quality, and Time to Market 7

C ha

ng es

Time

St ar

t p ro

du ct

io n Company B

Actual project hours

Company A Ideal effort

Figure 1.5 Engineering changes during automobile development. (Source: Data from Tom Judd, Cognition Corp., “Taking DFSS to the Next Level,” WCBF, Design for Six Sigma Conference, Las Vegas, June 2005.)

Fail early; fail often.

early in the design process may cost $10,000 later during product refinement and $1,000,000 or more in tooling, sales, and goodwill expenses if made after production has begun.

Figure 1.5 also indicates that Company A took less time to design the auto- mobile than Company B. This is due to differences in the design philosophies of the companies. Company A assigns a large engineering staff to the project early in product development and encourages these engineers to utilize the latest in design techniques and to explore all the options early to preclude the need for changes later on. Company B, on the other hand, assigns a small staff and pres- sures them for quick results, in the form of hardware, discouraging the engineers from exploring all options (the region in the oval in the figure). The design ax- iom, fail early, fail often, applies to this example. Changes are required in order to find a good design, and early changes are easier and less expensive than changes made later. The engineers in Company B spend much time “firefighting” after the product is in production. In fact, many engineers spend as much as 50% of their time firefighting for companies similar to Company B.

An additional way that the design process affects product development time is in how long it takes to bring a product to market. Prior to the 1980s there was little emphasis on the length of time to develop new products, Since then competition has forced new products to be introduced at a faster and faster rate. During the 1990s development time in most industries was cut by half. This trend

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8 CHAPTER 1 Why Study the Design Process?

has continued into the twenty-first century. More on how the design process has played a major role in this reduction is in Chap. 4.

Finally, for many years it was believed that there was a trade-off between high-quality products and low costs or time—namely, that it costs more and takes more time to develop and produce high-quality products. However, recent experience has shown that increasing quality and lowering costs and time can go hand in hand. Some of the examples we have discussed and ones throughout the rest of the book reinforce this point.

1.3 THE HISTORY OF THE DESIGN PROCESS During design activities, ideas are developed into hardware that is usable as a product. Whether this piece of hardware is a bookshelf or a space station, it is the result of a process that combines people and their knowledge, tools, and skills to develop a new creation. This task requires their time and costs money, and if the people are good at what they do and the environment they work in is well structured, they can do it efficiently. Further, if they are skilled, the final product will be well liked by those who use it and work with it—the customers will see it as a quality product. The design process, then, is the organization and management of people and the information they develop in the evolution of a product.

In simpler times, one person could design and manufacture an entire product. Even for a large project such as the design of a ship or a bridge, one person had sufficient knowledge of the physics, materials, and manufacturing processes to manage all aspects of the design and construction of the project.

By the middle of the twentieth century, products and manufacturing processes had become so complex that one person no longer had sufficient knowledge or time to focus on all the aspects of the evolving product. Different groups of people became responsible for marketing, design, manufacturing, and overall management. This evolution led to what is commonly known as the “over-the- wall” design process (Fig. 1.6).

In the structure shown in Fig. 1.6, the engineering design process is walled off from the other product development functions. Basically, people in market- ing communicate a perceived market need to engineering either as a simple, written request or, in many instances, orally. This is effectively a one-way com- munication and is thus represented as information that is “thrown over the wall.”

Customers Marketing Engineering design

Production

Figure 1.6 The over-the-wall design method.

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1.3 The History of the Design Process 9

Engineering interprets the request, develops concepts, and refines the best concept into manufacturing specifications (i.e., drawings, bills of materials, and assembly instructions). These manufacturing specifications are thrown over the wall to be produced. Manufacturing then interprets the information passed to it and builds what it thinks engineering wanted.

Unfortunately, often what is manufactured by a company using the over-the- wall process is not what the customer had in mind. This is because of the many weaknesses in this product development process. First, marketing may not be able to communicate to engineering a clear picture of what the customers want. Since the design engineers have no contact with the customers and limited communi- cation with marketing, there is much room for poor understanding of the design problem. Second, design engineers do not know as much about the manufacturing processes as manufacturing specialists, and therefore some parts may not be able to be manufactured as drawn or manufactured on existing equipment. Further, manufacturing experts may know less-expensive methods to produce the prod- uct. Thus, this single-direction over-the-wall approach is inefficient and costly and may result in poor-quality products. Although many companies still use this method, most are realizing its weaknesses and are moving away from its use.

In the late 1970s and early 1980s, the concept of simultaneous engineering began to break down the walls. This philosophy emphasized the simultaneous development of the manufacturing process with the evolution of the product. Simultaneous engineering was accomplished by assigning manufacturing repre- sentatives to be members of design teams so that they could interact with the design engineers throughout the design process. The goal was the simultaneous development of the product and the manufacturing process.

In the 1980s the simultaneous design philosophy was broadened and called concurrent engineering, which, in the 1990s, became Integrated Product and Process Design (IPPD). Although the terms simultaneous, concurrent, and inte- grated are basically synonymous, the change in terms implies a greater refinement in thought about what it takes to efficiently develop a product. Throughout the rest of this text, the term concurrent engineering will be used to express this refinement.

In the 1990s the concepts of Lean and Six Sigma became popular in manu- facturing and began to have an influence on design. Lean manufacturing concepts were based on studies of the Toyota manufacturing system and introduced in the United States in the early 1990s. Lean manufacturing seeks to eliminate waste in all parts of the system, principally through teamwork. This means eliminating products nobody wants, unneeded steps, many different materials, and people waiting downstream because upstream activities haven’t been delivered on time. In design and manufacturing, the term “lean” has become synonymous with min- imizing the time to do a task and the material to make a product. The Lean philosophy will be refined in later chapters.

Where Lean focuses on time, Six Sigma focuses on quality. Six Sigma, some- times written as (6σ) was developed at Motorola in the 1980s and popularized in the 1990s as a way to help ensure that products were manufactured to the highest

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10 CHAPTER 1 Why Study the Design Process?

Table 1.2 The ten key features of design best practice

1. Focus on the entire product life (Chap. 1) 2. Use and support of design teams (Chap. 3) 3. Realization that the processes are as important as the product (Chaps. 1 and 4) 4. Attention to planning for information-centered tasks (Chap. 4) 5. Careful product requirements development (Chap. 5) 6. Encouragement of multiple concept generation and evaluation (Chaps. 6 and 7) 7. Awareness of the decision-making process (Chap. 8) 8. Attention to designing in quality during every phase of the design process (throughout) 9. Concurrent development of product and manufacturing process (Chaps. 9–12)

10. Emphasis on communication of the right information to the right people at the right time (throughout and in Section 1.4.)

standards of quality. Six Sigma uses statistical methods to account for and manage product manufacturing uncertainty and variation. Key to Six Sigma methodology is the five-step DMAIC process (Define, Measure, Analyze, Improve, and Con- trol). Six Sigma brought improved quality to manufactured products. However, quality begins in the design of products, and processes, not in their manufacture. Recognizing this, the Six Sigma community began to emphasize quality earlier in the product development cycle, evolving DFSS (Design for Six Sigma) in the late 1990s.

Essentially DFSS is a collection of design best practices similar to those introduced in this book. DFSS is still an emerging discipline.

Beyond these formal methodologies, during the 1980s and 1990s many de- sign process techniques were introduced and became popular. They are essential building blocks of the design philosophy introduced throughout the book.

All of these methodologies and best practices are built around a concern for the ten key features listed in Table 1.2. These ten features are covered in the chapters shown and are integrated into the philosophy covered in this book. The primary focus is on the integration of teams of people, design tools and techniques, and in- formation about the product and the processes used to develop and manufacture it.

The use of teams, including all the “stakeholders” (people who have a concern for the product), eliminates many of the problems with the over-the-wall method. During each phase in the development of a product, different people will be important and will be included in the product development team. This mix of people with different views will also help the team address the entire life cycle of the product.

Tools and techniques connect the teams with the information.Although many of the tools are computer-based, much design work is still done with pencil and paper. Thus, the emphasis in this book is not on computer-aided design but on the techniques that affect the culture of design and the tools used to support them.

1.4 THE LIFE OF A PRODUCT Regardless of the design process followed, every product has a life history, as described in Fig. 1.7. Here, each box represents a phase in the product’s life.

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1.4 The Life of a Product 11

. . .

Use Operate in sequence 1

Operate in sequence N

Clean

Maintain Diagnose

Test Repair

Use

Manufacture

Assemble

Distribute

Install

Production and delivery

Identify need

Plan for the design process

Develop engineering specifications

Develop concepts

Develop product

Product development

Retire

Disassemble

Reuse or recycle

End of life

Figure 1.7 The life of a product.

These phases are grouped into four broad areas. The first area concerns the development of the product, the focus of this book. The second group of phases includes the production and delivery of the product. The third group contains all the considerations important to the product’s use. And the final group focuses on what happens to the product after it is no longer useful. Each phase will be introduced in this section, and all are detailed later in the book. Note that design- ers, responsible for the first five phases, must fully understand all the subsequent phases if they are to develop a quality product.

The design phases are:

Identify need. Design projects are initiated either by a market requirement, the development of a new technology, or the desire to improve an existing product.

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12 CHAPTER 1 Why Study the Design Process?

The design process not only gives birth to a product but is also responsible for its life and death.

Plan for the design process. Efficient product development requires plan- ning for the process to be followed. Planning for the design process is the topic of Chap. 4. Develop engineering requirements. The importance of developing a good set of specifications has become one of the key points in concurrent engi- neering. It has recently been realized that the time spent evolving complete specifications prior to developing concepts saves time and money and im- proves quality. A technique to help in developing specifications is covered in Chap. 6. Develop concepts. Chapters 7 and 8 focus on techniques for generating and evaluating new concepts. This is an important phase in the development of a product, as decisions made here affect all the downstream phases. Develop product. Turning a concept into a manufacturable product is a ma- jor engineering challenge. Chapters 9–12 present techniques to make this a more reliable process. This phase ends with manufacturing specifications and release to production.

These first five phases all must take into account what will happen to the product in the remainder of its lifetime. When the design work is completed, the product is released for production, and except for engineering changes, the design engineers will have no further involvement with it.

The production and delivery phases include:

Manufacture. Some products are just assemblies of existing components. For most products, unique components need to be formed from raw materials and thus require some manufacturing. In the over-the-wall design philoso- phy, design engineers sometimes consider manufacturing issues, but since they are not experts, they sometimes do not make good decisions. Concur- rent engineering encourages having manufacturing experts on the design team to ensure that the product can be produced and can meet cost require- ments. The specific consideration of design for manufacturing and product cost estimation is covered in Chap. 11. Assemble. How a product is to be assembled is a major consideration dur- ing the product design phase. Part of Chap. 11. is devoted to a technique called design for assembly, which focuses on making a product easy to assemble. Distribute. Although distribution may not seem like a concern for the design engineer, each product must be delivered to the customer in a safe and cost- effective manner. Design requirements may include the need for the product to be shipped in a prespecified container or on a standard pallet. Thus, the

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1.4 The Life of a Product 13

design engineers may need to alter their product just to satisfy distribution needs. Install. Some products require installation before the customer can use them. This is especially true for manufacturing equipment and building industry products. Additionally, concern for installation can also mean concern for how customers will react to the statement, “Some assembly required.”

The goal of product development, production, and delivery is the use of the product. The “Use” phases are:

Operate. Most design requirements are aimed at specifying the use of the product. Products may have many different operating sequences that describe their use. Consider as an example a common hammer that can be used to put in nails or take them out. Each use involves a different sequence of operations, and both must be considered during the design of a hammer. Clean. Another aspect of a product’s use is keeping it clean. This can range from frequent need (e.g., public bathroom fixtures) to never. Every consumer has experienced the frustration of not being able to clean a product. This inability is seldom designed into the product on purpose; rather, it is usually simply the result of poor design. Maintain. As shown in Fig. 1.7, to maintain a product requires that problems must be diagnosed, the diagnosis may require tests, and the product must be repaired.

Finally, every product has a finite life. End-of-life concerns have become increasingly important.

Retire. The final phase in a product’s life is its retirement. In past years de- signers did not worry about a product beyond its use. However, during the 1980s increased concern for the environment forced designers to begin con- sidering the entire life of their products. In the 1990s the European Union enacted legislation that makes the original manufacturer responsible for col- lecting and reusing or recycling its products when their usefulness is finished. This topic will be further discussed in Section 12.8. Disassemble. Before the 1970s, consumer products could be easily disas- sembled for repair, but now we live in a “throwaway” society, where disas- sembly of consumer goods is difficult and often impossible. However, due to legislation requiring us to recycle or reuse products, the need to design for disassembling a product is returning. Reuse or recycle. After a product has been disassembled, its parts can either be reused in other products or recycled—reduced to a more basic form and used again (e.g., metals can be melted, paper reduced to pulp again).

This emphasis on the life of a product has resulted in the concept of Prod- uct Life-cycle Management (PLM). The term PLM was coined in the fall of 2001 as a blanket term for computer systems that support both the definition or authoring of product information from cradle to grave. PLM enables management

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14 CHAPTER 1 Why Study the Design Process?

of this information in forms and languages understandable by each constituency in the product life cycle—namely, the words and representations that the engineers understand are not the same as what manufacturing or service people understand.

Apredecessor to PLM was Product Data Management (PDM), which evolved in the 1980s to help control and share the product data. The change from “data” in PDM to life cycle in PLM reflects the realization that there is more to a prod- uct than the description of its geometry and function—the processes are also important.

As shown in Fig. 1.8, PLM integrates six different major types of information. In the past these were separate, and communications between the communities