Modified Control Chart for Monitoring the Process Dispersion

• Activity Number: 28 - Computation, Design, and Quality Assurance of Physical Science and Engineering Applications
• Type: Contributed
• Date/Time: Sunday, August 8, 2021 : 1:30 PM to 3:20 PM
• Sponsor: Quality and Productivity Section
• Author(s): Felipe Schoemer Jardim* and Subha Chakraborti and Tiago Landim and Pedro Oprime
• Companies: Fluminense Federal University and The University of Alabama and Federal University of São Carlos and Federal University of São Carlos
• Keywords: Type I and Type II Errors; False Alarm Rate; Average Run Length; Acceptance and Modified Control Chart; S2 Control Chart

Abstract

Control charts are powerful tools used by many industries to monitor the quality of their processes and detect special causes of variation. They are often used to monitor the mean and the variance of some process quality characteristic with the well-known Xbar and S2 Control Charts, respectively. In their original formulation, if the actual process mean (µ) or variance (s2) are different or larger from their specified in-control values (µ0 and s02, respectively), the process is declared out of control. However, in many practical situations, even though the process may be declared out of control, it might be still capable from a practical point of view in terms of the proportion of nonconforming items produced. Thus, it may not be necessary to stop the process and start looking for assignable causes, which can save time and resources. The Modified Control Charts were designed to monitor the process mean in such a capable situation. With this background as motivation, in this paper, we propose the use of the Modified Control Charts for monitoring the process dispersion.