Product and service quality and productivity loss are all crucial competitive factors of companies in numerous industries. The loss function is a popular method for measuring the loss caused by variations in product or service quality. This study proposes a weighted-loss (WL) control chart to monitor the loss variation among manufacturing or service processes. Because loss is caused by a quality variable deviating from its target value, we set up two corresponding control charts to diagnose the sources of out-of-control loss and implement processes to correct these losses. We further present a WL chart using optimal variable sampling intervals (VSIs) in order to detect out-of-control losses faster compared with a WL chart using a fixed sampling interval (FSI). An example then demonstrates and evaluates the ability of the proposed VSI WL control chart to monitor and diagnose out-of-control process loss. Numerical analyses indicate that the optimal VSI WL chart outperforms the FSI WL chart, the joint inline image and S2 charts and the VSI Average Loss chart in detecting out-of-control process loss. Thus, the proposed VSI WL chart is recommended.
Quality and Reliability Engineering International, Vol.30, No.7, pp.951-959