Monitoring and Diagnosing Process Loss Using a Weighted-Loss Control Chart

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 (X) over bar and S-2 charts and the VSI Average Loss chart in detecting out-of-control process loss. Thus, the proposed VSI WL chart is recommended. Copyright (C) 2014 John Wiley & Sons, Ltd.