Volume 40, Issue 4 (July 2012)
Implementation of Evaluating Process Capability Index Cpk for Processes with Multiple Characteristics
Process yield has been the most common criterion used in the manufacturing industry for measuring process performance. In many industrial applications, processes often have multiple characteristics with various specifications. The generated yield index CpkT establishes the relationship between the manufacturing specifications and the actual process performance, which provides a lower bound on process yield. In this paper, the explicated formula of the lower confidence bound is derived, and then the lower confidence bound for various values of α-risk, capability requirements, and sample sizes are calculated via the use of R programs. The lower confidence bound is essential to product reliability assurance and is important in the hypothesis testing of process capability. We not only provide some reliable lower confidence bound tables but also develop a simple and practical procedure for engineers. The practitioners can use the proposed procedure to determine whether their process meets the preset capability requirement and to make reliable decisions.