An approach to controlling process variability for short production runs

A Shewhart R control chart is developed to monitor the process variance for large production runs. It is not appropriate to monitor the process varian ce using the Shewhart R control chart for short production runs. In this pa per, we propose the design of the R central chart for short production runs . For various combinations of the number of samples and the size of each sa mple, control coefficients of the R control chart are calculated by numeric al methods. Using these results, the R control chart for short production r uns is developed to monitor the process variance correctly. Finally, the de sign procedure of the R control chart for short production runs and the res ults of misusing the Shewhart R control chart are illustrated by an example .