Capability measures for processes with multiple characteristics

TLDR

Process capability indices such as Cp, Ca, and Cpk are widely used to quantify precision, accuracy, and performance for single‑characteristic processes, yet measures for multiple characteristics remain underexplored. This study generalizes Boyles’ yield index S_pk to processes with multiple characteristics. The authors relate the generalized index to process yield and introduce a control chart that displays all characteristic measures simultaneously. The chart enables engineers to monitor and control all process characteristics at once. © 2003 John Wiley & Sons, Ltd.

Abstract

Abstract Process capability indices, such as $C_p$ , $C_a$ , and $C_{pk}$ , have been widely used in the manufacturing industry providing numerical measures on process precision, process accuracy, and process performance. Capability measures for processes with a single characteristic have been investigated extensively. However, capability measures for processes with multiple characteristics are comparatively neglected. In this paper, we consider a generalization of the yield index $S_{pk}$ proposed by Boyles, for processes with multiple characteristics. We establish a relationship between the generalization and the process yield. We also develop a control chart based on the proposed generalization, which displays all the characteristic measures in one single chart. Using the chart, the engineers can effectively monitor and control the performance of all process characteristics simultaneously. Copyright © 2003 John Wiley & Sons, Ltd.