Functional process capability analysis in mechanical systems

Functional quality in the mechanical products is governed mainly by the degree of satisfaction of the design requirements, which itself depends on the variations in the effective variables. The functional parameters cannot be easily measured in mass production, and thus, are not usually considered as a direct inspection objective. Process capability indices are useful tools for evaluating the ability of a process to produce the dependent variables of a product that meet certain specifications. In this paper, the conventional process capability concept is extended to develop a computational tool for analysis of the functional quality of a mechanical product. Through defining new proper indices called functional process capability indices (FPCp, FPCpk, FPCpm, and FPCpmk ), a statistics-based process capability analysis method is used to estimate the ability of a manufacturing process for meeting the functional requirements of a mechanical system. Using this approach for statistical design of a mechanical product, the effects of variations in manufacturer's dimensions on the functional requirements of a product can be evaluated. A parameter is introduced which quantifies the contribution of variables that reduce the functional process capability. The applications of the proposed method are demonstrated through implementing it on two case studies and the results are discussed.