A method of including material variation in capability studies

Process capability studies are of great use to the quality practitioner, but quite often, processes with excellent capability indices have a high percentage of nonconformance. One of the major reasons for this is that the studies do not take the variation in the raw materials into account. For this study, we propose a method that allows for variations in material properties to be considered as a part of the capability study. Unlike long‐term capability studies, this method requires only a short period of time. This method has been successfully applied to an injection molding process at Cascade Engineering, Inc. in Grand Rapids, Michigan.