An ewma-cuscore quality control procedure for process variability

Combined Shewhart-cumulative score (cuscore) quality control schemes are available for controlling the mean of a continuous production process. In many industrial applications, it is important to control the process variability as well. The proposed exponentially weighted moving average combined Shewhart-cumulative score ewma-cuscore quality control procedure for detecting shifts in process variability uses the procedures developed by Ncube and Woodall [1] to monitor shifts in the process mean of continuous production processes. It is shown, in the one-sided case, by Average Run Length (ARL) comparisons, that the proposed scheme performs significantly and uniformly better than comparative standard cuscore procedures for shifts in the process standard deviation values considered.