On the performance of median-based Tukey and Tukey-EWMA charts under rational subgrouping

Control Chart (CC) is used to monitor specic problems and causes that arise during a process. These causes constantly change the process parameters until they are identied and removed. To this end, the techniques that present a true representation of the entire process should be used. Rational subgrouping is an essential concept in Statistical Process Control (SPC), which is usually overlooked by the practitioner. Hence, most of the manufacturing, engineering, and production processes give out output products in the form of batches over smaller time intervals. The aim of this study is to provide a median-based design for Tukey and Tukey-EWMA control charts under subgrouping. This study uses the idea of boxplot to monitor the process behavior. This study provided a brief discussion about selecting and forming subgroups from the process data. The performance of the median-based Tukey and Tukey-EWMA charts was evaluated using average, median, and standard deviation of run length as performance measures. This study considered subgroup sizes of m = 1:5 and 10 at pre-specied ARL0 equal to 370. Real-life applications of the median-based Tukey designs were given to demonstrate their proper implementation in food manufacturing and hard-bake processes.