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:

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.

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:

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

1.3 Quality, Customer Satisfaction, and System Effectiveness

For consumer products, quality has been traditionally associated with customer satisfaction or happiness. This interpretation of quality focuses on the total value or the utility that the customer derives from the product. This concept has also been used by the U.S. Department of Defense, focusing on system effectiveness as the overall ability of a product to accomplish its mission under specified operating conditions.

There are various characteristics (e.g., engineering, technological, psychological, cost, and delivery) that impact customer satisfaction. Thus, quality (Q) may be modeled as:

(1.1)

where x_i is the ith characteristic (i = 1, 2, … , n, …).

These qualities will impact the overall value perceived by the customer, as shown in Figure 1.3. In the beginning, we have ideal or target values of the characteristics x₁, x₂, … , x_i, … , x_n, … These values result in some measure of customer satisfaction. With time, changes in these qualities will impact customer satisfaction. Reliability as a “time-oriented” quality impacts customer satisfaction.

The undesirable and uncontrollable factors that cause a functional characteristic to deviate from its target value are called noise factors. Some examples of noise factors are:

• Outer noise: environmental conditions, such as temperature, humidity, dust, and different customer usage conditions.
• Inner noise: changes in the inherent properties of the product, such as deterioration, wear, fatigue, and corrosion—all of which may be a result of the outer noise condition.
• Product noise: piece-to-piece variation due to manufacturing variation and imperfections.

A reliable product must be robust over time, as demonstrated in Figure 1.4.

1.4 Performance, Quality, and Reliability

Performance is usually associated with the functionality of a product—what the product can do and how well it can do it. For example, the functionality of a camera involves taking pictures. How well it can take pictures and the quality of the pictures involves performance parameters such as pixel density, color clarity, contrast, and shutter speed.

Performance is related to the question, “How well does a product work?” For example, for a race car, speed and handling are key performance requirements. The car will not win a race if its speed is not fast enough. Of course, the car must finish the race, and needs sufficiently high reliability to finish the race. After the race, the car can be maintained and even replaced, but winning is everything.⁴

For commercial aircraft, the safe transportation of humans is the primary concern. To achieve the necessary safety, the airplane must be reliable, even if its speed is not the fastest. In fact, other than cost, reliability is the driving force for most commercial aircraft design and maintenance decisions, and is generally more important than performance parameters, which may be sacrificed to achieve the required reliability.

Improving the performance of products usually requires adding technology and complexity. This can make the required reliability more difficult to achieve.

Quality is associated with the workmanship of the product. For example, the quality metrics of a camera might include defects in its appearance or operation, and the camera's ability to meet the specified performance parameters when the customer first receives the product. Quality defects can result in premature failures of the product.

Reliability is associated with the ability of a product to perform as intended (i.e., without failure and within specified performance limits) for a specified time in its life cycle. In the case of the camera, the customer expects the camera to operate properly for some specified period of time beyond its purchase, which usually depends on the purpose and cost of the camera. A low-cost, throwaway camera may be used just to take one set of pictures. A professional camera may be expected to last (be reliable) for decades, if properly maintained.

“To measure quality, we make a judgment about a product today. To measure reliability, we make judgments about what the product will be like in the future” (Condra 2001). Quality in this way of thinking is associated primarily with manufacturing, and reliability is associated mostly with design and product operation. Figure 1.5 shows the role of quality and reliability in product development.

Product quality can impact product reliability. For example, if the material strength of a product is decreased due to defects, the product reliability may also be decreased, because lower than expected life-cycle conditions could cause failures. On the other hand, a high-quality product may not be reliable, even though it conforms to workmanship specifications. For example, a product may be unable to withstand environmental or operational conditions over time due to the poor selection of materials, even though the materials meet workmanship specifications. It is also possible that the workmanship specifications were not properly selected for the usage requirements.

1.5 Reliability and the System Life Cycle

Reliability activities should span the entire life cycle of the system. Figure 1.6 shows the major points of reliability practices and activities for the life cycle of a typical system. The activities presented in Figure 1.6 are briefly explained in the following sections.

1. Step 1: Need.  The need for reliability must be anticipated from the beginning. A reliability program can then be justified based on specific system requirements in terms of life-cycle costs and other operational requirements, including market competitiveness, customer needs, societal requirements in terms of safety and public health, liability, and statutory needs.
2. Step 2: Goals and Definitions.  Requirements must be specified in terms of well-defined goals. Chapter 2 covers some of the useful ways to quantitatively measure reliability. Additional material given in Chapters 3 and 4 can be used for this. Chapter 3 covers useful life distributions to model time to failure, and Chapter 17 covers topics related to modeling and analysis of system reliability.
3. Step 3: Concept and Program Planning.  Based on reliability and other operational requirements, reliability plans must be developed. Concept and program planning is a very important phase in the life cycle of the system. Figure 1.7 illustrates that 60–70% of the life cycle may be determined by the decisions made at the concept stage. Thus, the nature of the reliability programs will also determine the overall effectiveness of the total program.
4. Step 4: Reliability and Quality Management Activities.  The plans developed in step 3 are implemented, and the total program is continuously monitored in the organization for the life-cycle phases. An organizational chart for the implementation of these plans must exist with well-defined responsibilities. Some guiding principles that can be used for any reliability program and its processes and management include:
   • Customer Focus.  Quality, and reliability as one of its qualities, is defined and evaluated by the customer, and the organization has a constancy of purpose to meet and/or exceed the needs and requirements of the customer.⁵
   • System Focus.  Emphasis is on system integration, synergy, and the interdependence and interactions of all the parts of the system (hardware, software, human, and other elements). All the tools and methodologies of systems engineering and some of the developments in Design for Six Sigma (DFSS) (Chapter 4 in this book) are an integral part of this focus.
   • Process Focus.  Design and management of reliability processes should be well developed and managed using cross-functional teams using the methodology of concurrent design and engineering (Figure 1.8).
   • Structure.  The reliability program must understand the relationships and interdependence of all the components, assemblies, and subsystems. High reliability is not an end in itself but is a means to achieve higher levels of customer satisfaction, market share, and profitability. Thus, we should be able to translate reliability metrics to financial metrics that management and customers can understand and use for decision-making processes.
   • Continuous Improvement and Future Focus.  Continuous, evolutionary, and breakthrough improvement is an integral part of any reliability process. The organization should have a philosophy of never-ending improvement and reliance on long-term thinking.
   • Preventive and Proactive Strategies.  The real purpose of reliability assurance processes is to prevent problems from happening. Throughout the book, we will present many design philosophies and methodologies to achieve this objective.
   • Scientific Approach.  Reliability assurance sciences are based on mathematical and statistical approaches in addition to using all the other sciences (such as the physics, chemistry, and biology of failure). We must understand the causation (cause–effect and means–end relationships), and we should not depend on anecdotal approaches. Data-driven and empirical methods are used for the management of reliability programs.
   • Integration.  Systems thinking includes broader issues related to the culture of the organization. Thus, the reliability program must consider the integration of cultural issues, values, beliefs, and habits in any organization for a quality and productivity improvement framework.
5. Step 5: Design.  Reliability is a design parameter, and it must be incorporated into product development at the design stage. Figure 1.9 illustrates the importance of design in terms of cost to address or fix problems in the future of the life cycle of the product.
6. Step 6: Prototype and Development.  Prototypes are developed based on the design specifications and life-cycle requirements. The reliability of the design is verified through development testing. Concepts, such as the design and development of reliability test plans, including accelerated testing, are used in this step. If the design has deficiencies, they are corrected by understanding the root failure causes and their effect on the design. After the product has achieved the required levels of reliability, the design is released for production.
7. Step 7: Production and Assembly.  The product is manufactured and assembled based on the design specifications. Quality control methodologies, such as statistical process control (SPC), are used. The parts, materials, and processes are controlled based on the quality assurance methodologies covered in Chapter 14 of this book. Product screening and burn-in strategies are also covered in Chapter 15. One of the objectives of quality assurance programs during this phase of the system is to make sure that the product reliability is not degraded and can be sustained in the field.
8. Step 8: Field and Customer Use.  Before the product is actually shipped and used in the field by customers, it is important to develop handling, service, and, if needed, maintenance instructions. If high operational availability is needed, then a combination of reliability and maintainability will be necessary.
9. Step 9: Continuous System Evaluation.  The product in the field is continuously evaluated to determine whether the required reliability goals are actually being sustained. For this purpose, a reliability monitoring program and field data collection program are established. Topics related to warranty analysis and prognostics and system health management are covered in Chapters 18 and 19.
10. Step 10: Continuous Feedback.  There must be continuous feedback among all the steps in the life cycle of the product. A comprehensive data gathering and information system is developed. A proper communication system is also developed and managed for all the groups responsible for the various steps. This way, all field deficiencies can be reported to the appropriate groups. This will result in continuous improvement of the product. Some useful material for this step is also covered in Chapters 13, 18, and 19.

1.6 Consequences of Failure

There is always a risk of a product failing in the field. For some products, the consequences of failure can be minor, while for others, it can be catastrophic. Possible consequences include financial loss, personal injury, and various intangible costs. Under U.S. law, consequences of product failure may also include civil financial penalties levied by the courts and penalties under statutes, such as the Consumer Product Safety Act, building codes, and state laws. These penalties can include personal sanctions such as removal of professional licenses, fines, and jail sentences.

1.7 Suppliers and Customers

The rapid pace of technological developments and the globalization of supply chains have made customers dependent upon worldwide suppliers who provide parts (materials), subassemblies, and final products. When customers have to wait until they receive their parts, subassemblies, or products to assess if they are reliable, this can be an expensive iterative process. An upfront evaluation of suppliers is a beneficial alternative. Measuring the reliability capability of a supplier yields important information about the likelihood that a reliable product can be produced (Tiku et al. 2007). Reliability capability can be defined as follows:

To obtain optimal reliability and mutually beneficial results, suppliers and customers in the supply chain should cooperate. The IEEE Reliability Program Standard 1332 (IEEE Standards Project Editors 1998) identifies three reliability objectives between suppliers and customers:

• The supplier, working with the customer, should determine and understand the customer's requirements and product needs so that a comprehensive design specification can be generated.
• The supplier should structure and follow a series of engineering activities so that the resulting product satisfies the customer's requirements and product needs with regard to product reliability.
• The supplier should include activities that assure the customer that reliability requirements and product needs have been satisfied.

1.8 Summary

Reliability pertains to the ability of a product to perform without failure and within specified performance limits for a specified time in its life-cycle application conditions. Performance and quality are related to reliability. Performance parameters typically describe the functional capabilities of a product. Quality parameters are commonly used to assess the manufacturing goodness and the ability of a product to work when first received by the customer.

Reliability engineering deals with preventing, assessing, and managing failures. The tools of reliability engineers include statistics, probability theory, and many fields of engineering and the sciences related to the problem domain.

Problems