Monitoring Dispersion in the Compressive Strength of Parts Using Group Runs Control Chart

Given the limited sensitivity of Shewhart-type control charts in detecting small shifts in the process mean, synthetic control charts have been proposed as a more effective alternative for enhancing detection performance. Group Runs (GR) control chart is a further extension of synthetic chart, which performs better than the synthetic chart. This study proposes a GR control chart based on the range, referred to as the GR-R chart, for monitoring process dispersion in normally distributed processes. With the help of extensive simulation, the proposed GR control chart (GR-R) is compared with synthetic R chart using run length characteristics. The proposed chart is found to be superior to the synthetic chart in detecting shifts in process standard deviation. An illustrative example is provided to demonstrate the application of proposed GR-R chart.