Process capability analysis of a product family of larger-the-better type

Process Capability Indices (PCIs) have proliferated in both use and variety during the last decade. They can provide the manufacturers with a means to monitor the quality levels of the procedures in process. However, most of the studies associated with analyzing the quality and efficiency of a process is limited to discussing one single quality characteristic of a process capability. In general, quality characteristics can be categorized into three types, the nominal-the-best, the smaller-the-better, and the larger-the-better types. Typical quality characteristics of the larger-the-better type include the hardness, the tensile and the compressive strengths. In manufacturing practices, a process usually contains several models, which result in different specifications. However, it seems that there is still no academic report published for evaluating the process capability of a product family of the larger-the-better type with several models. The objective of this paper is thus aimed at proposing a process capability index for evaluating a product family of the larger-the-better type. The relationship between the index and the yield as well as some statistical features of the index will also be discussed in this paper. Finally a set of simple procedure for evaluation purpose will also be provided to the industry for reference.