Process capability monitoring and change-point analysis for S-type quality characteristic

Abstract

Among various quality assurance activities, process capability indices (PCIs) are recognized as the most effective tools to quantify and evaluate process performance. The one-sided capability index (Formula presented.) can adequately measure the process capability for processes with a smaller-is-better (S-type) quality characteristic. While focusing on the index (Formula presented.), this study constructs a capability control chart to monitor the short-term capability based on the exponentially weighted moving average (EWMA). Simulations have shown that the EWMA capability control chart is adaptive regarding average run length. Further, this study applies change-point analysis to determine whether and when the short-term capability-level changes. Using these two proposed methods, engineers can realize a variety of short-term process capabilities in good time and implement control measures efficiently against a poor long-term process capability.