A Hypothesis Testing Procedure on Assessing Process Performance for Asymmetric Tolerances

Abstract

The capability index Cpm takes into account the proximity of the process mean to the target and as well as the process variation. However, Cpm index has been shown to be inappropriate for measuring process performance with asymmetric tolerances. Several modifications of Cpm have been proposed to handle asymmetric tolerances, and has been shown to be superior to other existing generalizations. In this article, we implement the theory of hypothesis testing to develop a decision making procedure for assessing process performance based on index with critical values. The behavior of the critical values versus the unknown distribution parameter is also investigated to obtain reliable critical values for testing. To make the proposed procedure practical for in-plant applications, tables of critical values for various parameters are provided and an application example is demonstrated to evaluate the process performance for illustration.