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Integrated parameter and tolerance design is a cost-effective method to multiresponse quality improvement. However, previous methods usually ignore model parameter uncertainty, dispersion effect, or correlation among responses. This may lead to the obtained optimal solutions far from the true optimal values of parameters and tolerances. To address the problem, a novel integrated parameter and tolerance design method is proposed to solve correlated multiple response problems under consideration of model parameter uncertainty, the location and dispersion effects of the quality loss, and the tolerance costs simultaneously. As there usually exists uncertainty in the quality loss and tolerance costs, multiobjective optimization is adopted to seek for the robust optimal solutions. The effectiveness and robustness of the proposed method are illustrated with a practical example and a random simulation example. The results show that the proposed method provides more reasonable results in quality improvement and cost reduction than those of the existing methods. KEYWORDSlocation and dispersion effects, model parameter uncertainty, multiresponse, quality loss, tolerance design | INTRODUCTIONIn today's economy, improving quality and reducing cost are essential for the business enterprise to survive. However, this cannot be achieved without effective quality or process design. An efficient and cost-effective engineering approach of product or process design is advocated by Taguchi, 1 which includes system design, parameter design, and tolerance design. Parameter design is used to reduce variation in quality characteristic first, followed by tolerance design if the variability could not be satisfactorily. For more details on robust parameter design, please see Myers et al. 2 The design factors that are allowed to vary within certain tolerance ranges due to the manufacturing error, and the design factor is supposed to follow a normal distribution in tolerance design. Conventionally, Taguchi's product design approach is known as a sequential method in which the tolerance design is performed after parameter design. Li and Wu 3 and Kim and Cho 4 argued that the sequential design method may obtain a suboptimal solution, and they proposed an integrated parameter and tolerance design (IPTD) approach to optimal parameter and tolerance design simultaneously. The advantage of IPTD is that it can reduce time-to-market, improve quality, and reduce costs by considering manufacturing processes in the early stage of product design.

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