Process Yield Index and Asymmetric Tolerances

Process yield has been an essential criterion used for manufacturing industries in business management. Quality managers and engineers involved in factories require capability analyses to access process yields, particularly, for processes with a very low fraction of defectives. It is noted that the accuracy of process yield is important; as it is one of major considerations for supplier selections in supply chains. In this paper, we investigate the capability index pk C which is a yield-based index and has gained considerable popularity as well as has been widely used in the manufacturing industry to provide numerical measures on process performance. However, the definition of index pk C is independent of the target T of specification limits. That is, index pk C cannot be used to access process yield for processes with asymmetric tolerances directly. To solve the problem, some investigations proposed modified process capability index based on pk C for processes with asymmetric tolerances. In this paper, we focus on the index  pk C in which the probability density function and cumulative distribution function of index  pk C have been derived. We provide more extensive computations for lower confidence bound for processes with asymmetric tolerances. We also apply the calculation results to determine whether the process with asymmetric tolerance is capable or not for a real-world application. ___________________________________________________________________________