Taguchi's Robust Design Method
Since 1960, Taguchi's Methods have been used for improving the quality of Japanese products with great success. During the 1980's, many companies finally realized that the old methods for ensuring quality were not competitive with the Japanese methods. The old methods for quality assurance relied heavily upon inspecting products as they rolled off the production line and rejecting those products that did not fall within a certain acceptance range. However, Taguchi was quick to point out that no amount of inspection can improve a product quality must be designed into a product from the start. It is only recently that companies in an effort to improve product quality and design robustness.
What is Robust Design? Robust Design is an "engineering methodology for improving productivity during research and development so that high-quality products can be produced quickly and at low cost" (Phadke, 1989). The idea behind robust design is to improve the quality of a product by minimizing the effects of variation without eliminating the causes (Since they are too difficult or too expensive to control). His method is an off-line quality control method that is instituted at both the product and process design stage to improve product manufacturability and reliability by making products insensitive to environmental conditions and component variations. The end result is a robust design, a design that has minimum sensitivity to variations in uncontrollable factors.
Dr. Genichi Taguchi bases his method on conventional statistical tools together with some guidlines for laying out design experiments and analysing the results of these experiments. Taguchi's approach to quality control applies to the entire process of developing and manufacturing a product from the initial concept, through design and engineering, to manufacturing and production. Taguchi methods are used to specify dimension and feature detail and normally follow DFM activities. In the next section we discuss Taguchi's concept of a quality loss function. This is then followed by a detailed description of Taguchi's approach to parameter design.
Taguchi's Parameter Design Approach
In parameter design, there are two types of factors that affect a product's functional characteristic: control factors and noise factors. Control factors are those factors which can easily be controlled such as material choice, cycle time, or mold temperature in an injection molding process. Noise factors are factors that are difficult or impossible or too expansive to control. There are three types of noise factors: outer noise, inner noise, and between product noise. Noise factors are primarily response for causing a product's performance to deviate from its target value.
