Title: The development of target-based posterior process capability indices and confidence intervals

Authors: Anintaya Khamkanya; Byung Rae Cho; Paul L. Goethals

Addresses: Department of Industrial Engineering, Thammasat University, Pathumthani, Thailand ' Department of Industrial Engineering, Clemson University, Clemson, SC 29634, USA ' Department of Mathematical Sciences, US Military Academy, West Point, NY 10996, USA

Abstract: One of the most popular quality engineering tools is the process capability index (PCI), which relates the allowable spread of a process defined by engineering specifications to the natural spread of a process. The traditional PCI does not account for the loss in quality when product characteristics fail to achieve their process target value. This research, in contrast, proposes indices, namely posterior PCIs, that consider the underlying result of observations after inspection. Utilising a truncated distribution as the basis for measurement along with a target-based quality loss function for capability analyses, several posterior indices are developed in this paper. A simulation technique is implemented to compare the proposed posterior PCIs with traditional measures. Finally, the confidence interval approximations for the posterior PCIs are derived. Our results suggest using the proposed posterior indices for capability analyses when industrial processes require that non-conforming products be scrapped prior to shipping to the customer.

Keywords: process capability index; PCI; truncated normal distribution; process target; quality loss function.

DOI: 10.1504/IJQET.2017.094313

International Journal of Quality Engineering and Technology, 2017 Vol.6 No.4, pp.269 - 301

Received: 26 Apr 2017
Accepted: 13 Nov 2017
Published online: 29 Aug 2018 *

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