Performance evaluation of continuous production process by trapezoidal fuzzy process capability indices

Process capability indices (PCIs) can be viewed as the effective and excellent means of measuring product quality and process performance. They are very useful statistical analysis tools to summarise process dispersion and location by using process capability analysis (PCA). However, they have some limitations which prevent a deep and flexible analysis because of the crisp measurements and specification limits (SLs). Fuzzy set theory can be used to add more flexibility to process capability analyses. In this study, the fuzzy X and MRX control charts are used to analyse the process of continuous production in terms of trapezoidal fuzzy numbers (TrFN). Also, fuzzy PCIs are produced when SLs and measurements are presented as trapezoidal fuzzy numbers. For this aim, a computer program is coded in MATLAB software. The fuzzy control charts are utilised in Yazd Fiber Production Plant. The results show that in continuous production processes, fuzzy measurements can yield a more accurate analysis. Furthermore, relying on the fuzzy capability indices, one can have a flexible analysis of the process performance.