Developing a variables repetitive group sampling plan based on process capability index C_pk with unknown mean and variance

Abstract

In this paper, variables repetitive group sampling plans are developed based on the process capability index C _pk when the quality characteristic follows a normal distribution with unknown mean and variance. The sampling plan parameters such as the sample size and the acceptance constant are determined to minimize the average sample number. Symmetric and asymmetric cases, in percent defectives due to two specification limits, are dealt with for specified combinations of acceptable quality level and limiting quality level. Tables are provided and examples are given to use proposed plans in practice.

Keywords:

• repetitive group sampling
• process capability index
• upper and lower specifications limits
• operating characteristics curve

Acknowledgements

The authors are deeply thankful to the editor and the reviewers for their several valuable comments to improve the quality of the manuscript. The work by Chi-Hyuck Jun was financially supported by Korea Ministry of Environment (MOE) as ‘Ecodesign Human resource development Project’.