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Design for Six Sigma, also called Robust Design, designs quality into a product. By assessing the variations that a product experiences during manufacture and use, it is possible to make a product that performs its intended function regardless of these variations; such a product is “robust.”
Design for Six Sigma (DFSS) is an analysis technique to determine the extent to which uncertainties in the model affect the results of an analysis. Based on a probabilistic characterization, Design for Six Sigma enables users to quantify the quality of product, addressing issues such as minimizing warranty costs and quantifying the reliability. Design for Six Sigma goes one step further than a probabilistic characterization by allowing users to optimize design variables to achieve a particular probabilistic level, such as Six Sigma*, which is 3.4 failures in one million parts!
Six Sigma initiatives try to optimize the manufacturing process so it automatically produces parts conforming to six sigma quality. In contrast, DFSS optimizes the design itself so the part conforms to six sigma quality even with variations in manufacturing. For Design for Six Sigma and Robust Design, quality is an explicit goal of the optimization.
*A probability of 3.4 out of 1 million is achieved when the performance target is 4.5 standard deviations away from the mean value. The additional 1.5 standard deviations leading to a total of 6 standard deviations are used as a safety margin to allow for "drift of the mean value" in the properties and environment which the product can see over its lifetime.
