Development of a New Process Incapability Index with an Application to the Evaluation of Manufacturing Risk

Abstract

Process capability indices have been widely used in industry today since they provide quantitative measures of process performance. Instead of using process capability index, the process incapability index C _pp introduced by Greenwich and Jahr-Schaffrath ( 1995 Greenwich , M. , Jahr-Schaffrath , B. L. ( 1995 ). A process incapability index . Int. J. Quality Reliab. Manage. 12 : 58 – 71 . [Crossref] [Google Scholar] ) has an advantage of separating the information of process accuracy and precision for a symmetric tolerance. Using C _pp process incapability index, the process performance and its risk level can easily be understood by quality practitioners. Another process incapability index proposed by Chen ( 1998 Chen , K. S. ( 1998 ). Incapability index with asymmetric tolerances . Statistica Sinica 8 ( 1 ): 253 – 262 . [Google Scholar] ) is to measure the process performance for an asymmetric tolerance. However, it can't correctly reflect the true manufacturing risk. In order to accurately measure the process performance for both symmetric and asymmetric tolerances, a new process incapability index using desirability function is proposed in this article. The relationship between various new process incapability indices and their associated nonconforming rates has also been explored. Finally, two numerical examples show that our new process incapability index can be used in the evaluation of manufacturing risk.