DOI 10.1007/s00170-005-0145-3 ORIGINAL ARTICLE

Abstract Process capability indices Cp, and Cpk have been popularly used in the manufacturing industry for providing measures of process potential and performance. The pre-cision index Cp is used to measure product quality con-sistency, while the yield index Cpk is used to provide measures of percentage of product conforming to manu-facturing specifications. Properties of Cp for processes with a single manufacturing line have been investigated exten-sively. However, research on properties of Cp for processes with multiple manufacturing lines have been neglected. In this paper, we consider the precision index Cp for processes with three manufacturing lines. We develop a practical procedure for process precision testing to determine wheth-er a process meets the precision requirement preset in the factory. An application example is given.