Incorporating process capability index and quality loss function into analyzing the process capability for qualitative data

Abstract

Process capability analysis (PCA) is frequently em- ployed to evaluate a product or a process if it can meet the cus- tomer's requirement. In general, process capability analysis can be represented by using the process capability index (PCI). Until now, the PCI was frequently used for processes with quantitative characteristics. However, for process quality with the qualitative characteristic, the data's type and single specification caused lim- itations of using the PCI. When the product can not meet the target, even if it lies in the specified range, it should lead to the corresponding quality loss. Taguchi developed a quadratic qual- ity loss function (QLF) to address such issues. In this study, we intend to construct a measurable index which incorporates the PCI philosophy and QLF concept to analyze the process ca- pability with the consideration of the qualitative response data. The manufacturers can not only employ the proposed index to self-assess the process capability, but they also can make com- parisons with the other competitors.