Engineering Methods for Robust Product Design

The practices adopted by companies that are succeeding in the quality competition vary, but two common elements can be found. Careful attention to the customer is absolutely paramount. Products must satisfy a diverse customer base, with features accurately targeted to customer requirements. Technology must serve customer needs and wants, or the latest and greatest widget will languish on the shelf. Also, continuous improvement, applied to both products and business processes, is ubiquitous.

At the Eastman Kodak Company, the authors have been participants in the ongoing effort to improve the equipment development process. The result has been a world-class process for developing products. This process features Quality Function Deployment (QFD) for capturing the voice of the customer, Robust Design (Quality Engineering) to deliver the level of quality demanded by the customer, and a disciplined engineering process for managing the business of product commercialization. Much of the Kodak Equipment Commercialization Process is described in Professor Don Clausing's book Total Quality Development (ASME Press, 1994).

Physics and engineering principles are the basis for beginning a good product design or fixing problems with a design that is already in existence. Any graduate from engineering school knows these fundamental subjects as well. They have been used effectively by many generations of engineers. However, they alone are no longer enough. The current competitive situation requires a disciplined engineering process that ties together the multitude of engineering tools currently being taught and practiced.

The need to further define the process for linking the principles of engineering and physics to commercialization inspired the writing of this book. The authors' experiences in applying Robust Design to mechanical and electrical systems, electrophotographic process optimization, and chemical process optimization at Kodak have demonstrated convincingly that Dr. Taguchi's design optimization techniques are extremely effective in reducing cycle time and rework. Every company that employs Robust Design does so in the context of their own internal culture. Only the books written by Dr. Taguchi follow his views in totality. This book is a reflection of how we have internalized Dr. Taguchi's insights and teachings into our culture at Kodak. In this industrial environment, we have found broad acceptance and a strong willingness to employ Taguchi methods when practiced in an engineering context. This, of course, is exactly how Dr. Taguchi and those who have listened to him over the years approach the topic - as an engineering process. The successes experienced at Kodak and at many other companies we have encountered are derived from Dr. Taguchi's advice T6: "Spend about 80% of your time in engineering analysis and planning and about 20% actually running experiments and evaluating the results."

Recently, engineering process improvement has been introduced into the academic arena. Courses on Robust Design, QFD, Six Sigma, and other quality processes can now be found at an increasing number of schools. Some of the leaders in this new trend include the Massachusetts Institute of Technology, Stanford University, Georgia Institute of Technology, and Michigan Technological University. Rochester Institute of Technology (RIT), where we teach and serve on the Industrial Advisory Board, recently adopted elements of a quality engineering curriculum as mechanical engineering electives. This book is largely based on our experience in teaching the Robust Design course at RIT in an engineering department. This is unique, because much of the academic attention given to Dr. Taguchi's methods has come from the statistics community as a result of Dr. Taguchi's use of empirical statistical techniques, particularly design of experiments. This has led to a misunderstanding of robust design as being statistical in nature. This book takes an entirely fresh look at robust design as an engineering process, where the emphasis is on using engineering analysis to improve product performance.

This book offers simple, yet effective, guidelines on how to practice robust design in the context of a total quality development effort. In these pages, the fundamental metrics of quality engineering are fully developed, and the rationale behind them is explained. Designing low-cost solutions is a given requirement. We discuss the impact of robust design on the cost of a design, as well as how cost and quality can be co-optimized using Dr. Taguchi's Quality Loss Function. The fundamental statistical tools (e.g., design of experiments, analysis of variance, and analysis of interactions) are explained in what we hope will be an intuitive yet mathematically precise way. A healthy balance exists between the statistical sciences and the engineering sciences. In this book, we try to introduce practical insight into the statistical side of Robust Design, while maintaining the hightest priority in basing the experimental approach on sound engineering principles. The most important element of engineering success is clear thinking, planning, analysis, and communication. For this reason, we offer this book primarily as a guide on how to invest your time efficiently in the 80% up-front engineering required, particularly as it pertains to technology development and product commercialization.

The Structure of This Book

The rest of the book is presented in three major parts. The first is an introduction to Quality Engineering Metrics. It consists of Chapters 2 through 6. Robust Design is a data driven process. Chapter 2 goes through Introductory Data Analysis for Robust Design and is presented to establish a context for how data will be treated throughout the rest of the book. Chapter 3 presents the theory and derivation of the various forms of the Quality Loss Function. An application of the quality loss function to tolerance design is also included. Chapter 4 presents the fundamental knowledge behind the Signal-to-Noise Ratio. The static and dynamic signal-to-noise ratios are fully discussed with numerous examples in Chapters 5 and 6, respectively.

The second part delves into the details of the parameter design process with a special emphasis on achieving additivity.1 Additivity is a property of a design that reduces harmful interactions,1 thus simplifying the optimization process. Chapter 7 is a practical Introduction to Designed Experiments. Without the use of designed experiments, the process of optimizing a product becomes a time consuming endeavor laced with rework and unwanted surprises due to interactions. Chapter 8 is focused on a thorough discussion concerning the Selection of the Quality Characteristics. Few choices in the process of quality engineering are as critical as the selection of the physical responses to be measured during the designed experiments. Chapter 9 provides a sound basis for the Selection and Testing of Noise Factors to stress the design during the development of robustness. Constructing viable noise factor experiments is an indispensable step in preparing for credible and realistic optimization experiments. Chapter 10 completes the discuss

William Y. Fowlkes, winner of the prestigious Taguchi Award for his work at Eastman Kodak, is experienced both in using Taguchi methods as well as teaching them. He teaches a course on robust design at the Rochester Institute of Technology, has created a video tape and tele-course on the subject that is used at General Motors, and was instrumental in creating the training materials on robust design that continue to be used at Eastman Kodak.

Clyde "Skip" Creveling is the president and founder of Product Development Systems & Solutions Inc. (PDSS) (http://www.pdssinc.com). Since PDSS' founding in 2002, Mr. Creveling has led Design for Six Sigma (DFSS) initiatives at Motorola, Carrier Corporation, StorageTek, Cummins Engine, BD, Mine Safety Appliances, Callaway Golf, and a major pharmaceutical company. Prior to founding PDSS, Mr. Creveling was an independent consultant, DFSS Product Manager, and DFSS Project Manager with Sigma Breakthrough Technologies Inc. (SBTI). During his tenure at SBTI he served as the DFSS Project Manager for 3M, Samsung SDI, Sequa Corp., and Universal Instruments.

Mr. Creveling was employed by Eastman Kodak for 17 years as a product development engineer within the Office Imaging Division. He also spent 18 months as a systems engineer for Heidelberg Digital as a member of the System Engineering Group. During his career at Kodak and Heidelberg he worked in R&D, Product Development/Design/System Engineering, and Manufacturing. Mr. Creveling has five U.S. patents.

He was an assistant professor at Rochester Institute of Technology for four years, developing and teaching undergraduate and graduate courses in mechanical engineering design, product and production system development, concept design, robust design, and tolerance design. Mr. Creveling is also a certified expert in Taguchi Methods.

He has lectured, conducted training, and consulted on product development process improvement, design for Six Sigma methods, technology development for Six Sigma, critical parameter management, robust design, and tolerance design theory and applications in numerous U.S, European, and Asian locations. He has been a guest lecturer at MIT, where he assisted in the development of a graduate course in robust design for the System Design and Management program.

Mr. Creveling is the author or coauthor of several books, including Six Sigma for Technical Processes, Six Sigma for Marketing Processes, Design for Six Sigma in Technology and Product Development, Tolerance Design, and Engineering Methods for Robust Product Design. He is the editorial advisor for Prentice Hall's Six Sigma for Innovation and Growth Series.

Mr. Creveling holds a B.S. in mechanical engineering technology and an M.S. from Rochester Institute of Technology.

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