ROBUSTNESSDEVELOPMENT AND

RELIABILITY GROWTH

VALUE-ADDING STRATEGIES FOR NEWPRODUCTS AND PROCESSES

John P. KingWilliam S. Jewett

PRENTICEHALL

Upper Saddle River, NJ • Boston • Indianapolis • San FranciscoNew York • Toronto • Montreal • London • Munich • Paris • Madrid

Capetown • Sydney • Tokyo • Singapore • Mexico City

Contents

Preface xxi

Acknowledgments xxix

About the Authors xxxi

Section I Critical Drivers of Value

CHAPTER 1 Time, Money, and Risks 3Quality, Costs, and Schedules 4

Product Development 5The Quality Improvement Movement 6

Management of Process Improvements 7Clear and Compelling Call to Action 7Internal Ownership 9Top-Down Enablement 9Bottom-Up Improvement 10Objectives with Substantial Impacts 10Early Measurable Results 11

Soft Causes of Poor Reliability and Durability 12Inadequate Project Management Plans 13Inadequate Development of System Integration and Robustness 13Changing Product Requirements 14Risk Management 16Immature Baseline Technologies 16Lack of Clear Expectations 17Lack of a Disciplined Process 18Inability to Speak Truth to Power 18Failure to Implement Lessons Learned 19Inadequate Development Budgets 19

Key Points 20Discussion Questions 20

CHAPTER 2 Reliability, Durability, and Robustness 21Reliability as an Element of Value to Customers 22Essential Elements of Reliability 23

Designed Quality 24

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viii Contents

Robustness 24Durability 25Manufactured Quality 26

The Taxonomy of a Failure 26The Bathtub Curve 26Early-Life Failures 27Failures during Useful Life 28Wear-out Failures at End of Life 29

Reliability Metrics 29Reliability Is a Probability 31

The Anatomy of Quality Loss 33Reliability as a Subjective Concept 34Performance Variations 34The Concept of Quality Loss 35The Quality Loss Function 36

The Reduction of Performance Variations 39Process of Parameter Design 40Robustness Development 42

Key Points 44Discussion Questions 44

CHAPTER 3 Strategies for Reliability Development 45Are Better Strategies Important? 45

Reliability Growth Plot 46Strategies for Ongoing Processes 48

Voice of the Customer (VOC) 48Competitive Market Situation 49Technology Development 50Information Management - 50

Strategies Specific to Product Development 51System Architecture and Design Concepts 52Reliability Development Strategies 52Reliability Modeling 55Project Management 55Risk Management in Product Development 56

Capabilities of the Organization 57Reliability Growth Rate 57Assessment of Capabilities for Reliability Development 57

Key Points 63Discussion Questions 63

Section II Framework for Reliability Development

CHAPTER 4 A Process Model for Product DevelopmentWhat Is a Product Development Process? 67

Phases and Gates 68

67

Contents in

What's the Problem? 68Why Should Your Organization Have a Standardized

Development Process? 69Published Development Processes 70Process Documentation 71

Integration of Key Development Principles 71DMAIC Six Sigma 71Design for Six Sigma (DFSS) 72Lean Product Development 72Set-Based Design 73Agile Development 73Portfolio Management 75

A Process Model for Product Development 76What Principles Affect the Layout of the Phased Activities? 76

Advanced Product-Planning Process 77Technology Development Process 79

Technology Transfer 80Product Development Process 81

Flexible Phases 82What Questions Are Answered by Major Deliverables? 86Key Principles for Robustness Development and Reliability Growth 87Product Development Plan 87Reliability Development Plan 89The Model for a Product Development Process 89Lessons-Learned Reviews 96

Older versus Better Methods 98Key Points 100Discussion Questions 100

CHAPTER 5 Road Map for Reliability Development 103Build a Compelling Case for Your Reliability Project 103Linking Activities to the Product Development Phases 104Key Initiatives of a Reliability Development Project 104

Defining Realistic Requirements for the Improvementof Reliability and Durability 105

Selecting and Developing a Superior Product Concept 107Identifying Potential Failure Modes and Their Levels of Severity 109Developing Analytical and Empirical Models to Evaluate Designs 110Developing Robustness to Prevent Problems in the Product Designs 111Growing Reliability and Durability with Efficient Problem Solving 113Balancing Performance and Costs through the Optimization of Tolerances 114Improving Manufacturing Process Capabilities 114

The Role of Testing 116Stress Tests 117Reliability Growth Tests 117

Contents

Life Tests 117Reliability Demonstration Tests 118Reliability Development Process Map 118

Key Points 119Discussion Questions 119

CHAPTER 6 Effective Decisions 121Qualities of a Good Decision-Making Process 122

Core Principles Supporting Decisions 123What Is Value? 124Who Makes Which Decisions? 124Rules of Engagement 125Decision Processes 127Standardized Data 128Alternatives for Decisions 128Risk Assessments 130Expectations for the Product Development Core Leadership Team 131

Types of Project Reviews 132Cross-functional Progress Reviews 132Out-of-Bounds Review 133Peer Reviews 133Design Reviews 135Functional Reviews 136Portfolio Reviews 136Gate Reviews 137

Key Points 144Discussion Questions 145

CHAPTER 7 Robustness Development for Product Designs 147Technology and Product Development 147

Technology Development 148Product Development Phases 1-2 149Product Development Phases 3-5 149

Functional Diagram 150Stressful Conditions 151

Expected Consequences of Stresses 152Strategies for Handling Stress 153Develop Methods to Introduce Experimental Stresses 154

Parallel Development of Products and Processes 155Suppliers' Involvement with Product Development Teams 155Product Development Teams' Involvement with Suppliers 155Manufacturing Process Capability 156

Robustness Development 158Traditional Product Development 158Robustness Development 159

Examples of Robustness Development 162

Contents

Scenario 1 162Scenario 2 163Scenario 3 164

Robust Design 165Parameter Design 165Tolerance Design 166

Robustness Development Fixtures 167Key Points 168Discussion Questions 169

CHAPTER 8 Reliability Growth and Testing 171Product Testing 172,

Field Data 172Getting the Most Out of Testing Programs 173

Reliability Growth Testing 174Duane Growth Model 174Dormant Failures 178Reliability Growth Test Considerations 180

Drivers of Reliability Growth Rate 181Accelerated Tests 183

Accelerated Life Testing (ALT) 183Accelerated Stress Testing (AST) 183Highly Accelerated Life Testing (HALT) 183Highly Accelerated Stress Screening (HASS) 184

Understanding Stress versus Strength 185Effect of Increasing Stressful Test Conditions 185The Stress-Strength Distribution 187How High Should Stress Levels Be Set? 189 r

Tools and Systems That Support Testing 190DMAIC Six Sigma Method: A Tool for Efficient Problem SolvingFailure Reporting and Corrective Action System (FRACAS) 192

Overview of Various Types of Tests 196Key Points 197Discussion Questions 197

190

Section III Tools and Methods Supporting Reliability Development

CHAPTER 9 Understanding and Managing Customer-Driven RequirementsObjectives for Product Development 202Types of Requirements 203

Validation versus Verification 203Customer-Driven Requirements 203Externally Driven Requirements 204Internally Driven Requirements 204Requirements for Reliability arid Durability 205Criteria for Good Requirements 205

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xii Contents

How Requirements Affect Project Success 206Incomplete or Incorrect Requirements Can Jeopardize a Project 206It Starts with a Good Idea 207Product Differentiation 209Why Is Differentiation Alone Not Enough? 209Value Drivers 211The Kano Model 211

How Requirements Flow Down 213VOC Activities Vary Throughout the Development Process 214

Level 1 214Level 2 215Level 3 215Level 4 215

The Major Steps in Requirements Gathering 215Planning and Preparation 215Selection of Interviewees 216Customer Engagement 217Customer Interview Guide 218Customer Interview Process 219Ask Better Questions 220

Processing and Analyzing Interview Data 221"KJ" Organization of Requirements 221Validating Results of Requirements KJ with Customers 225

Key Elements of Requirements Management 227Approval of Requirements 227Management of Creep and Gaps in Scope 227Change Control 227Electronic Requirements Management 228

How Can Your Requirements Efforts Fail? 228Bad Attitude 228Failure to Employ a Cross-Functional Team 228Lack of Management Support 228Insufficient or No Budget 228Wrong or Incomplete Requirements 229Requirements That Are Not Sufficiently Differentiated 229Poor or No Process for Disciplined Requirements Management 229

Key Points 229Discussion Questions 230Additional Reading 230Additional Authors Worth Following 230

CHAPTER 10 Quality Function Deployment 231What Is Quality Function Deployment? 231Expected Benefits of QFD 233The Structure of QFD 234

Contents xiii

Project Charter 234Who Are Customers? 235Voice of Your Customers 236Planning Matrix for Customer Needs 237Requirements for Features and Functionality 239Requirements Relationship Matrix 240Correlation of Requirements 242Planning Matrix for Technical Requirements 243

Sequence of Matrices 244The QFD Team 245

Team Members 245Facilitator 246Recorder 246Facility 246

Suggestions to Improve the Facilitation of QFD 246Key Points 247Discussion Questions 248Further Reading 248

CHAPTER 11 Concept Generation and Selection 249Decisions in Product Development 249Concept Generation and Selection 250

Identifying Selection Requirements 252Weighting of Selection Requirements 253Generation of Alternative Concepts 253The Selection Process 254Exception for Requirements Weighting and Concept Scoring 256

Process Guidance 256Teamwork 259Key Points 260Discussion Questions 260

CHAPTER 12 Axiomatic Design 261Axiomatic Design 262

Design Axioms 262Domains 264Constraints (CONs) 266Design Hierarchies 267Zigzagging 267Design Matrix 268Populate the Design Matrix 270Example 272

Improvement of Design Concepts 272Decouple the Design 272

System Decomposition 274Set Expectations for the Decomposition Process 275

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Define the Strategy for High-Level Decomposition 276Develop a First-Pass Constraints Domain 276Work with Derived Constraints 276Decompose Functional Requirements and Map Them to

Design Parameters 277Ensure Conformance to the Rules of Decomposition 277Consequences for Development Teams 278

A Familiar Example 279Remove Coupling in a Design 279

Key Points 282Discussion Questions 282

CHAPTER 13 Tools to Reduce Risks 285Project Team Meetings for Risk Reduction 285Useful Tools Provide Valuable Benefits 286

Risk Analyses 287Matrix Analyses 287Flowcharts 288Tree Analyses 289

Risk Analyses 289Failure Modes, Effects, and Criticality Analysis (FMECA) 289

Matrix Analyses 294Customer-Oriented Product Concepting (COPC) 294Goals, Objectives, Strategies, Plans, and Actions (GOSPA) 295

Flowcharts 296Precedence Diagramming Method 296Functional Analysis System Technique (FAST) Diagram 298Reliability Functional Block Diagram 299

Tree Analyses 301Cause-and-Effect Diagram 301Event Tree Analysis 303Fault Tree Analysis (FTA) 305

Key Points 307Discussion Questions 307Further Reading 307

CHAPTER 14 Descriptive Statistics 309Why Do You Need Statistics? 309Graph the Data First 310

Graphical Display Tools 311Scatter Plot 312Matrix Plot 312Box Plot 314Individual Value Plot 314Time Series Plot 315Histogram 317

Contents

Dot Plot 319Probability Plot 319Control Chart 321

Descriptive Statistics 322Measures of Location and Spread 322

The Normal Distribution 325Properties of the Normal Distribution 325

Key Points 329Discussion Questions 329

CHAPTER 15 Inferential Statistics 331Questions You Need Statistics to Help Answer 331Population versus Samples 332

What Is Random and What Is Not? 333The Power of Averaging 333Making Comparisons and Assessing Progress 335

Useful Distributions for Making Comparisons 335Normality of Data 336Statistical Inferences about Means 336

Hypothesis Testing, Confidence Intervals, and p-Values 339Making Comparisons 339Confidence Intervals for the Mean 340Steps in Hypothesis Testing Using the One-Sample t-Test 343How to Interpret p-Values 345Sometimes You Will Be Wrong 346Comparing Population Mean to a Standard—One-Sample t-Test 350Statistical Inferences about Variances 353Comparing Two Population Means 357Comparing Proportions 363

Equivalence Testing 364Equivalence Test versus Difference Test 364

Some Concerns with Significance Tests 368Interval Estimates or p-Values? 369

Key Points 369Discussion Questions 370

CHAPTER 16 Building Models Using ANOVA and Regression 371Uncovering Relationships and Proving Cause and Effect 371

The Difficulties of Using Historical Data 371Identifying Cause-and-Effect Relationships 373

Empirical Models 375ANOVA 376

Understanding the Importance of Factors 376 --Model Building Using Regression 380

Linear Regression 380How Do You Build Regression Models? 381

xvi Contents

Is the Model "Good"? 383Summary 391Key Points 392Discussion Questions 393

CHAPTER 17 Building Empirical Models Using DOE 395Overview of DOE 395

Some History 396What Do You Need to Know? 396Why Empirical Models Using Designed Experiments? 397Screening, Modeling, and Robustness 397Advantages of Designed Experiments 398Ways of Experimenting 399

Important Questions to Answer before an Experiment 400Important Questions to Answer after Running the Experiment 404Some Important Considerations 406

Purpose of an Experiment 406Type of Model Required 407Principle of Parsimony 407Aliasing 408Resolution Required for Modeling 408Orthogonality 409 -

Types of Experiments 409Factorial Experiments 409Response Surface Methods (RSM) 410Computer-Generated Optimal Experiments 411

Sequential Approach to Experimentation 412A Simple Example 412Key Points 414Discussion Questions 415

CHAPTER 18 Developing System Robustness Using DOE 417Using System Models and Noise to Improve Robustness 417

What to Do about Noises 419How Noises Affect Responses and What Can Be Done about It 420Minimizing Error Transmission to Improve Robustness 420

Robustness Optimization of the Machining Process 421Augmenting the Model for the Machining Example 421Using the System Model to Optimize Robustness 423

Additional Options for Optimization 426 --Special-Purpose Optimization Programs 426What Should You Optimize? 429

Key Points 429Discussion Questions 429

CHAPTER 19 Robustness Optimization Using Taguchi's Methods 431Taguchi's Contributions to Robust Design 431Building a Detailed Model versus Improving System Robustness 433

Contents xvii

Interactions 433Additivity 434Inner and Outer Arrays and Compound Noise Factors 434Compound Control Factors 435Orthogonal Arrays 436Importance of Confirmation Experiments 437

Signal-to-Noise Ratio (S/N) 437Types of S/N 438

Example Problem 440Orthogonal Array Experiment 442Response Surface Experiment 445Stochastic Optimization Using the RSM Model 448Conclusions 450

Key Points 452Discussion Questions 454

CHAPTER 20 Tolerance Optimization 455The Tolerance Design Problem 455

What Is a Design Tolerance? 456Truth in Tolerance Design: The Need for Communication and

Trust 457Controlling Variability 458How Do Tolerances Affect Product Performance? 459

Things Customers See 459Not Seen by Customers, but Important to Your Business 460

Steps for Tolerance Design 462Error Transmission 463The Effect of Error Transmission on Tolerances 463

Tolerances and the Cost of Quality 464Quality Loss and Manufacturing Cost 464Cost of Quality and Optimal Tolerances for a Simple Case 464

Analysis of Tolerance Stacks 466Types of Tolerance Design Problems 466Analysis of Tolerance Stacks: Simple Cases versus the

Not-So-Simple 467Optimization of Functional Responses 474

Natural Tolerances 475Accommodate Looser Tolerances with Assembly Adjustments 476 ^Let's Fix It in Software 476Tolerances and Repeatable, High-Precision Positioning 476

Key Points 477Discussion Questions 477

CHAPTER 21 Reliability Functions and Life Distributions 479Fundamental Reliability Functions 479

Modeling Reliability 480

xviii Contents

Fundamental Reliability Functions and Relationships among Them 480Useful Life Distributions 483Key Points 493Discussion Questions 494

CHAPTER 22 Life Data and Their Implications 495Sources of Life Data 495

Life Testing 495Field Data 496

Competing Failure Modes, Mixtures of Life Distributions, and the Importanceof Failure Analysis 496

Mixtures of Distributions and the Bathtub Curve 498Preventive Maintenance of Repairable Systems 499

Components Failing from Random Events 499Components Failing from Wear-out 500

Fitting a Life Distribution to a Data Set 501Complete Data 501Censored Data 502Competing Failure Modes and Mixtures of Distributions 503

Accelerated Life Testing (ALT) 506Accelerated Life Models 506Fitting a Model and Distribution to ALT Data 507

Mixed Failures from Time and Actuations 510Key Points 512Discussion Questions 512

Section IV Integration of Framework and Methods

CHAPTER 23 Critical Parameter Management 515CPM and the Domains of Product Development 515

What Is a Critical Parameter? 515Categories of Critical Parameters 516External Noise Factors 518Durability and Deterioration 518

Linking Customer Satisfaction and Critical Parameters 519Soft Failures: Performance That Is Out of Specification 519Hard Failures: Things That Break 519How Do You Decide What Is Critical? 520

Assessing Difficulty 522Qualitative Factors to Consider 522Quantitative Measures of Difficulty 523

Assessing Importance 525Quality Loss—A Measure of Importance 527

Critical Parameters and Risk 528Risk Assessment 528

Contents xix

Using the Kano Model to Evaluate Risks 529Critical Parameter Measurement 531

The Importance of Good Data 531Measurement System Analysis 531

CPM: A Process for Creating, Using, and Maintaining Information 532Key Points 532Discussion Questions 533

CHAPTER 24 An Illustration of Process Methods and Tools 535Advanced Product Planning 536

Product Concept Proposal 536Product Development 538

Voice of the Customer 538Competitive Assessment 542System Requirements 542Functional System Analysis 544Concept Generation and Selection 546Baseline Design Description 553Robustness Development 554

Epilogue 559

CHAPTER 25 Balancing Schedules, Budgets, and Business Risks 561Ongoing Attention to Product Development Capabilities 563

Lean Product Development 565Flexible Product Development 567Set-Based Design 568Agile Development 569Realistic Project Planning and Management 570

Be a Student of the Process 572

GLOSSARY 573

BIBLIOGRAPHY 585

INDEX 593