The design six sigma is a measure of the design quality: how the design meets it intended specifications, regardless of the manufacturing steps necessary to produce the product or system. It is determined by the variability of the components specified in the design versus the overall design performance to its specifications.
The application of the six sigma design is based on the selection of components for the design. In order to obtain a proper estimate of the design quality, the components’ specifications must be known, and the design has to be modeled to obtain a distribution of the performance based on its components, tolerance distribution.
In many cases, the distribution of the components’ characteristic values is not known, though the worst-case conditions are readily available. This has led to worst-case analysis, in which the design performance is evaluated when the components’ characteristics are assumed at their specification limits. When using six sigma design, the span of the components, specifications to the nominal value is considered to be 6 a, and the nominal becomes the component average value μ