Reliability Engineering

Kailash C. Kapur, Michael Pecht

• Publisher: Wiley
• Year: 2014
• ISBN:
  9781118841792
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Quality Control in Engineering
• Index: Technology & Engineering

An Integrated Approach to Product Development

Reliability Engineering presents an integrated approach to the design, engineering, and management of reliability activities throughout the life cycle of a product, including concept, research and development, design, manufacturing, assembly, sales, and service. Containing illustrative guides that include worked problems, numerical examples, homework problems, a solutions manual, and class-tested materials, it demonstrates to product development and manufacturing professionals how to distribute key reliability practices throughout an organization.

The authors explain how to integrate reliability methods and techniques in the Six Sigma process and Design for Six Sigma (DFSS). They also discuss relationships between warranty and reliability, as well as legal and liability issues. Other topics covered include:

• Reliability engineering in the 21 st Century
• Probability life distributions for reliability analysis
• Process control and process capability
• Failure modes, mechanisms, and effects analysis
• Health monitoring and prognostics
• Reliability tests and reliability estimation

Reliability Engineering provides a comprehensive list of references on the topics covered in each chapter. It is an invaluable resource for those interested in gaining fundamental knowledge of the practical aspects of reliability in design, manufacturing, and testing. In addition, it is useful for implementation and management of reliability programs.

1
Reliability Engineering in the Twenty-First Century

Institutional and individual customers have increasingly better and broader awareness of products (and services) and are increasingly making smarter choices in their purchases. In fact, because society as a whole continues to become more knowledgeable of product performance, quality, reliability, and cost, these attributes are considered to be market differentiators.

People are responsible for designing, manufacturing, testing, maintaining, and disposing of the products that we use in daily life. Perhaps you may agree with Neville Lewis, who wrote, “Systems do not fail, parts and materials do not fail—people fail!” (Lewis 2003) It is the responsibility of people to have the knowledge and skills to develop products that function in an acceptably reliable manner. These concepts highlight the purpose of this book: to provide the understanding and methodologies to efficiently and cost effectively develop reliable products and to assess and manage the operational availability of complex products, processes, and systems.

This chapter presents the basic definitions of reliability and discusses the rela­tionship between quality, reliability, and performance. Consequences of having an unreliable product are then presented. The chapter concludes with a discussion of supplier–customer reliability objectives and responsibilities.

1.1 What Is Quality?

The word quality comes from the Latin qualis, meaning “how constituted.” Dictionaries define quality as the essential character or nature of something, and as an inherent characteristic or attribute. Thus, a product has certain qualities or characteristics, and a product's overall performance, or its effectiveness, is a function of these qualities.

Juran and Gryna (1980) looked at multiple elements of fitness for use and evaluated various quality characteristics (or “qualities”), such as technological characteristics (strength, weight, and voltage), psychological characteristics (sensory characteristics, aesthetic appeal, and preference), and time-oriented characteristics (reliability and maintainability). Deming (1982) also investigated several facets of quality, focusing on quality from the viewpoint of the customer.

The American Society for Quality (ASQC Glossary and Tables for Statistical Quality Control 1983) defines quality as the “totality of features and characteristics of a product or service that bear on its ability to satisfy a user's given needs.” Shewhart (1931) stated it this way:

The first step of the engineer in trying to satisfy these wants is, therefore, that of translating as nearly as possible these wants into the physical characteristics of the thing manufactured to satisfy these wants. In taking this step, intuition and judgment play an important role, as well as a broad knowledge of the human element involved in the wants of individuals. The second step of the engineer is to set up ways and means of obtaining a product which will differ from the arbitrary set standards for these quality characteristics by no more than may be left to chance.

One of the objectives of quality function deployment (QFD) is to achieve the first step proposed by Shewhart. QFD is a means of translating the “voice of the customer” into substitute quality characteristics, design configurations, design parameters, and technological characteristics that can be deployed (horizontally) through the whole organization: marketing, product planning, design, engineering, purchasing, manufacturing, assembly, sales, and service.

Products have several characteristics, and the “ideal” state or value of these characteristics is called the target value (Figure 1.1). QFD (Figure 1.2) is a methodology to develop target values for substitute quality characteristics that satisfy the requirements of the customer. Mizuno and Akao (Shewhart 1931) have developed the necessary philosophy, system, and methodology to achieve this step.

Figure 1.1 The relationship of quality, customer satisfaction, and target values.

Figure 1.2 Illustration of the steps in QFD.

1.2 What Is Reliability?

Although there is a consensus that reliability is an important attribute of a product, there is no universally accepted definition of reliability. Dictionaries define reliability (noun) as the state of being reliable, and reliable (adjective) as something that can be relied upon or is dependable.

When we talk about reliability, we are talking about the future performance or behavior of the product. Will the product be dependable in the future? Thus, reliability has been considered a time-oriented quality (Kapur 1986; O'Conner 2000). Some other definitions for reliability that have been used in the past include:

• Reduction of things gone wrong (Johnson and Nilsson 2003).
• An attribute of a product that describes whether the product does what the user wants it to do, when the user wants it to do so (Condra 2001).
• The capability of a product to meet customer expectations of product performance over time (Stracener 1997).
• The probability that a device, product, or system will not fail for a given period of time under specified operating conditions (Shishko 1995).

As evident from the listing, various interpretations of the term reliability exist and usually depend on the context of the discussion. However, in any profession, we need an operational definition for reliability, because for improvement and management purposes, reliability must be precisely defined, measured, evaluated, computed, tested, verified, controlled, and sustained in the field.

Since there is always uncertainty about the future performance of a product, the future performance of a product is a random variable, and the mathematical theory of probability can be used to qualify the uncertainty about the future performance of a product. Probability can be estimated using statistics, and thus reliability needs both probability and statistics. Phrases such as “perform satisfactorily” and “function normally” suggest that a product must function within certain performance limits in order to be reliable. Phrases such as “under specified operating conditions” and “when used according to specified conditions” imply that reliability is dependent upon the environmental and application conditions in which a product is used. Finally, the terms “given period of time” and “expected lifetime” suggest that a product must properly function for a certain period of time.

In this book, reliability is defined as follows:

Reliability is the ability of a product or system to perform as intended (i.e., without failure and within specified performance limits) for a specified time, in its life cycle conditions.

This definition encompasses the key concepts necessary for designing, assessing, and managing product reliability. This definition will now be analyzed and discussed further.

1.2.1 The Ability to Perform as Intended

When a product is purchased, there is an expectation that it will perform as intended. The intention is usually stated by the manufacturer of the product in the form of product specifications, datasheets, and operations documents. For example, the product specifications for a cellular phone inform the user that the cell phone will be able to place a call so long as the user follows the instructions and uses the product within the stated s...

Table of contents

• Cover
• Table of Contents
• Wiley Series in Systems Engineering and Management
• Title page
• Copyright page
• Preface
• 1: Reliability Engineering in the Twenty-First Century
• 2: Reliability Concepts
• 3: Probability and Life Distributions for Reliability Analysis
• 4: Design for Six Sigma
• 5: Product Development
• 6: Product Requirements and Constraints
• 7: Life-Cycle Conditions
• 8: Reliability Capability
• 9: Parts Selection and Management
• 10: Failure Modes, Mechanisms, and Effects Analysis
• 11: Probabilistic Design for Reliability and the Factor of Safety
• 12: Derating and Uprating
• 13: Reliability Estimation Techniques
• 14: Process Control and Process Capability
• 15: Product Screening and Burn-In Strategies
• 16: Analyzing Product Failures and Root Causes
• 17: System Reliability Modeling
• 18: Health Monitoring and Prognostics
• 19: Warranty Analysis
• Appendix A: Some Useful Integrals
• Appendix B: Table for Gamma Function
• Appendix C: Table for Cumulative Standard Normal Distribution
• Appendix D: Values for the Percentage Points tα,ν of the t-Distribution
• Appendix E: Percentage Points X2α,ν of the Chi-Square Distribution
• Appendix F: Percentage Points for the F-Distribution
• Bibliography
• Index
• End User License Agreement