Tolerance design bridges design and manufacturing. Concurrent design of tolerances and manufacturing processes may ensure the manufacturability, reduce the manufacturing and other related costs, decrease the number of fraction nonconforming (or defective rate), and shorten the production lead time. Since process capability indices relate tolerance specifications to manufacturing process capabilities, it is quite natural to apply them to concurrent design of tolerances and processes. As process shifts often exist in a manufacturing process, using C_p does not yield a good estimation of fraction nonconforming. Index C_(pk) does not precisely measure process shift either, but C_(pm) does. Therefore, this research compares the applications of C_p, C_(pk) and C_(pm) based on a numerical example of non-linear mechanical tolerance synthesis. In addition, the Taguchi quality loss function is used together with the manufacturing cost as the objective function.
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