The Effect of Gauge Measurement Capability and Dependency Measure of Process Variables on the MCp

It has been proved that process capability indices provide very efficient measures of the capability of processes from many different perspectives. These indices have been widely used in the manufacturing industry for measuring process reproduction capability according to manufacturing specifications. In the past few years, univariate capability indices have been introduced and used to characterize process performance, but are comparatively neglected for multivariate processes where multiple dependent characteristics are involved in quality measurement. Also, most of researches related to process capability indices have assumed no gauge measurement errors. Unfortunately, such an assumption does not reflect real situations accurately even with highly sophisticated advanced measuring instruments. Conclusions drawn from process capability analysis are hence unreliable. In this paper, we consider the effect of process variables correlation coefficient on the multivariate process capability index (MCp) for different gauge measurement capabilities. Also, with respect to correlation coefficient and measurement capability we investigate the statistical properties of the estimated MCp. The results indicate that gauge measurement capability has an important role in determining process capability. This factor would increase the effect of correlation coefficient on estimating the process capability, such that for different gauge measurement capabilities, correlation coefficients will change the results of estimating and testing the process capability.