Control charts for process capability monitoring based on the probability distribution parameters of the quality characteristics

Process capability indices are widely used in different industries for quality assurance purposes. An appropriate analysis of the process capability index can result in improving quality level and satisfying customer requirements. Recently, some control charts have been developed for continuous evaluation of process capability in producing conforming products. However, these charts are designed to monitor a single index and cannot directly show the relation between parameters of the quality characteristic distribution and the process capability index. In fact, average and dispersion of a process are combined into an index and control charts monitor this individual index. In this research, control charts are developed for monitoring the capability of a process in producing conforming products. In these charts, the capability of a process in producing conforming products is monitored in terms of the average and dispersion of the process. Therefore, interaction between these measures can also be considered into account. Control charts are developed for Normal, Lognormal and Weibull distributions and their performances are evaluated through simulation and Average Run Length (ARL) and Standard Deviation of Run Length (SDRL) measures. The results show that the proposed control charts can lead to an appropriate monitoring of the process capability.