changes for the worse in quality; techniques exist for identifying and controlling them.

"Chronic" problems, on the other hand, may require scientific breakthrough to achieve higher levels of quality. Chronic problems exist because workers may not accept change and refuse to admit that there may be a better way of doing things. Solving chronic problems requires breakthrough projects, specific targets usually established on a yearly basis, strong and visible senior management support, and the use of quality experts to lead the company-wide quality improvement programs. Unlike Deming, who avoids the use of targets and quotas, Juran's objective is to get management to accept the habit of an annual quality improvement program based upon well-defined targets.

Juran's method for determining the cost of quality, therefore, suggests that the pursuit of quality will pay for itself only up to a certain point, and beyond that point costs may rise significantly.

Crosby argues that the cost of quality includes only the nonconformance costs, whereas Juran includes both conformance and nonconformance costs. Crosby's argument is that the conformance costs of prevention and appraisal are not really the cost of quality but more so the cost of doing business. Therefore, Crosby argues that quality is free, and the only associated costs of quality should be those of nonconformance. Crosby does not emphasize analytical techniques other than measurement methods for nonconformance costs, and he relies heavily upon motivation and the role of senior management.

Table 20-3 compares the approach to quality of the three experts. Although all three emphasize the need for quality and the importance/role of senior management, each goes about it differently.


After World War II the allied forces found that the quality of the Japanese telephone system was extremely poor and totally unsuitable for long-term communication purposes. To

2. Taken from Ranjit Roy, A Primer on the Taguchi Method (Dearborn, MI: Society of Manufacturing Engineers, 1990), Chapter 2. Reproduced by permission.

improve the system, the allied command recommended that Japan establish research facilities similar to the Bell Laboratories in the United States in order to develop a state-of-the-art communication system. The Japanese founded the Electrical Communication Laboratories (ECL) with Dr. Taguchi in charge of improving the R&D productivity and enhancing product quality. He observed that a great deal of time and money was expended in engineering experimentation and testing. Little emphasis was given to the process of creative brainstorming to minimize the expenditure of resources.

Dr. Taguchi started to develop new methods to optimize the process of engineering experimentation. He developed techniques that are now known as the Taguchi Methods. His greatest contribution lies not in the mathematical formulation of the design of experiments, but rather in the accompanying philosophy. His approach is more than a method to lay out experiments. His is a concept that has produced a unique and powerful quality improvement discipline that differs from traditional practices.

These concepts are:

1. Quality should be designed into the product and not inspected into it.

2. Quality is best achieved by minimizing the deviation from a target. The product should be so designed that it is immune to uncontrollable environmental factors.

3. The cost of quality should be measured as a function of deviation from the standard and the losses should be measured system-wide.

Taguchi built on Deming's observation that 85 percent of poor quality is attributable to the manufacturing process and only 15 percent to the worker. Hence, he developed manufacturing systems that were "robust" or insensitive to daily and seasonal variations of environment, machine wear, and other external factors. The three principles were his guides in developing these systems, testing the factors affecting quality production, and specifying product parameters.

Taguchi believed that the better way to improve quality was to design and build it into the product. Quality improvement starts at the very beginning, that is, during the design stages of a product or a process, and continues through the production phase. He proposed an "off-line" strategy for developing quality improvement in place of an attempt to inspect quality into a product on the production line. He observed that poor quality cannot be improved by the process of inspection, screening, and salvaging. No amount of inspection can put quality back into the product; it merely treats a symptom. Therefore, quality concepts should be based upon, and developed around, the philosophy of prevention. The product design must be so robust that it is immune to the influence of uncontrolled environmental factors on the manufacturing processes.

His second concept deals with actual methods of effecting quality. He contended that quality is directly related to deviation of a design parameter from the target value, not to conformance to some fixed specifications. A product may be produced with properties skewed toward one end of an acceptance range yet show shorter life expectancy. However, by specifying a target value for the critical property and developing manufacturing processes to meet the target value with little deviation, the life expectancy may be much improved.

The Taguchi Approach 767

His third concept calls for measuring deviations from a given design parameter in terms of the overall life-cycle costs of the product. These costs would include the cost of scrap, rework, inspection, returns, warranty service calls, and/or product replacement. These costs provide guidance regarding the major parameters to be controlled.

Limitations The most severe limitation of the Taguchi method is the need for timing with respect to product/process development. The technique can only be effective when applied early in the design of the product/process system. After the design variables are determined and their nominal values are specified, experimental design may not be cost-effective. Also, though the method has wide-ranging applications, there are situations in which classical techniques are better suited; in simulation studies involving factors that vary in a continuous manner, such as the torsional strength of a shaft as a function of its diameter, the Taguchi method may not be a proper choice.

Selecting Design Taguchi strives to attain quality by reducing the variation around the

Parameters for target. In an effort to reduce variations, he searched for techniques that

Reduced Variation allow variability to be reduced without necessarily eliminating the causes of variation. Often in an industrial setting, totally removing the causes of variation can be expensive. A no-cost or low-cost solution may be achieved by adjusting the levels and controlling the variation of other factors. This is what Taguchi tries to do through his parameter design approach where there is no cost or low cost in reducing variability. Furthermore, the cost savings realized far exceed the cost of additional experiments needed to reduce variations.

FIGURE 20-4. Factors and levels for a pound cake experiment.
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