A new capability index for dynamic process analysis

Abstract

Nowadays, the trend to produce with reduced specification limits width and at a low defectives rate seems to be irreversible. In such conditions, reliable evaluation of the process capability level represents a crucial activity to assess the quality related performance of a production process. By adopting the classical approach, such evaluation is performed by verifying the process in-control condition and by evaluating suitable capability indices. However, considering the natural dynamic behavior of production processes, i.e. the process variability over the time domain, the in-control condition characterizes only a part of the production process functioning cycle, the one with the lowest defectives rate. Therefore, by adopting such classical approach an underestimation of the process defectives rate is achieved. In order to overcome the previously described limitation, the present paper proposes a new capability index, suitable to perform dynamic process capability analysis, i.e. which considers also effects of the process variability over the time domain.