Measuring process capability using indices — some new considerations

摘要

AbstractProcess capability indices are key measures in the context of never‐ending improvement in quality. The capability of a process and the effectiveness of control charts are directly related. For samples of size 2 or greater, a Cpk value of 2 ensures that the control chart gives an immediate warning of the potential danger of producing material outside the specification following a shift in the process mean. Capability studies usually result in single point estimates for Cp and Cpk. This ignores sampling variation. More useful estimates can be obtained by constructing confidence intervals for Cp and Cpk. Evaluation of process capbility is relatively easy when a single variable describes the process. However, most processes are multivariate in nature and this makes it difficult to assess the overall capability of the proces