Variable Sample Size Control Chart for Monitoring Process Capability Index  
Author Dja-Shin Wang


Co-Author(s) Hau-Yu Yang; Tong-Yuan Koo


Abstract This paper proposed a variable sample size control chart i.e. VSSCpm, to monitoring process capability indices on industry manufacture for improve product quality. It divided the control chart into three regions: central region, warn region and out of control region. We set up the control limits and determined the warning limit on variable sample size control chart, and apply to monitoring process capability index Cpm. This study used average run length, ARL, to evaluate the monitoring performance, and set up the parameter are process shift Δ and sample number n. We compare the monitoring performance of VSSCpm, and fix sample size control chart i.e. FSSCpm, on different sample size and process shift range. A Matlab computer program using the proposed method for finding average run length value, ARL, is developed. The results was that when the process shift between Δ = 0.25 and Δ = 0.5, the ARL value of VSSCpm, is lesser then FSSCpm. It was found that the proposed control chart VSSCpm, are more efficiency to detect small shift then the FSSCpm, it can fast detect and alarm in manufacturing process. We also found that the large ample size range was more efficiency to detect and alarm the process shift on manufacture. A practical example is presented to illustrate the applicability of the proposed method.


Keywords Process capability index, Variable sample size control chart, Quality monitoring performance
    Article #:  22094
Proceedings of the 22nd ISSAT International Conference on Reliability and Quality in Design
August 4-6, 2016 - Los Angeles, California, U.S.A.