Abstract:

This paper presents a new approach to rationally allocate means and tolerances in engineering systems at the design stage. Features of second-moment methods and Design for Six Sigma methods are combined. Either point or global variance methods may be invoked to model the uncertainty in the design variables. Shortcomings of Taguchi’s expected loss function and the need to integrate over the failure region in probabilistic methods are obviated. Multiple responses, each with any of the performance metrics including target-is-best, smaller-is-best and larger-is-best, are handled. The novelty of the approach is that cost or quality may serve as an objective with the other serving as a constraint in the optimization process. The impact of the method is that it reinforces quality concepts from Six Sigma design while ensuring that robustness is maximized. Two diverse case studies justify the methodology.