C_pm MPPAC for manufacturing quality control applied to precision voltage reference process

A multiprocess performance analysis chart (MPPAC), based on the process capability index C_pm, called C_pm MPPAC, is developed to analyse the manufacturing quality of a group of processes in a multiple process environment. The C_pm MPPAC conveys critical information about multiple processes regarding the departure of the process and process variability on one single chart. Existing research on MPPAC has been restricted to obtaining quality information from one single sample of each process, ignoring sampling errors. The information provided from the existing MPPAC chart, therefore, is unreliable and misleading, resulting in incorrect decisions. In this paper, the natural estimator of C_pm is considered based on multiple samples. Based on the natural estimator of C_pm, sampling errors are considered by providing an explicit formula with Matlab to obtain the estimation accuracy of the C_pm. The sampling accuracy of C_pm is tablulated for sample size determination so that engineers/practitioners can use it for in-plant applications. An example of multiple PVR processes is presented to illustrate the applicability of C _pm MPPAC for manufacturing quality control.