The Shewhart F control chart for monitoring processes with finite number of inspections

Processes with a finite number of scheduled inspections are very common in industry. Frequent setup changeovers in mass production aimed at switching from one product code to another and the growing need to manufacture small lots of customized products are challenging issues for quality engineers who want to perform statistical process monitoring. In this paper, we propose a Shewhart control chart plotting a statistic defined as the ratio F of the between-sample variability over the within-sample variability. The F control chart is able to monitor the stability of the location for a normally distributed quality parameter. Being the F statistics autocorrelated, the statistical performance has been evaluated by means of simulation. The numerical analysis shows that the F control chart outperforms the available t control chart for monitoring finite production horizon processes.