Economic design of moving average control chart for non-normal data using variable sampling intervals

In this article, we propose an economic design of moving average (X) over bar control chart for non-normal quality characteristics using variable sampling intervals (VSI) policy. An expression for expected loss cost function is derived for continued and ceased process designs. The performance of two operational modes is compared numerically and the comparison between fixed sampling interval (FSI) and VSI control schemes is carried out. The VSI scheme is found to be superior to FSI scheme. As the number of sampling intervals increases, percentage saving in cost with respect to FSI design increases. The ceased VSI production process shows more saving with respect to continuous VSI production process. Percentage saving due to ceasing increases with increasing shift in the process. Also, the sample size increases with the decreasing values of shift. Overall, the ceased VSI moving average process design seems to be economically superior to other process designs.