Process capability evaluation for the process of product families

Process capability analysis is a highly effective means of assessing the process ability of manufacturing product that meets specifications. A larger process capability index (PCI) implies a higher process yield, and lower expected process loss. Many PCIs have been effectively and widely used to determine whether the quality of a process meets preset targets. However, those existing PCI cannot be applied to evaluate the process capability of a process producing a product family. This work presents a novel PCI (C-pm(T)) which takes into account all family members and obtains the probability density function for the PCI for a product family. The relationship between the PCI and process yield is described. An example is provided to demonstrate the methodology for practical application.