EWMA Control Chart in Detecting and Diagnosing a Persistent Shift in a Process Mean

Statistical Quality Control(SQC)is a statistical technique used to monitor and control the production of goods and services in order to have good quality. Statistical Process Control (SPC) mainly involves control charts, which are used to detect the occurrence of a shift in a process mean in a production area. The Exponentially Weighted Moving Average (EWMA) control chart is one of the control charts used to detect the occurrence of a shift in a process mean compared to widely used Shewhart control chart. In this paper, two data sets collected respectively from a production process of small electronic devices designed to emit timing signal of 200 milliseconds (ms) duration and from a production line of forged piston rings, are analyzed. The two processes are sampled periodically with five samples per time and the mean is calculated. The EWMA and Shewhart control charts are constructed based on 15 mean values and used to indicate whether the process is in control or out of control. The results show more sensitive behavior by EWMA control chart to the mean shift in comparison to Shewart control chart.