Process Capability Evaluation in Skew Distributed Processes Based on SWV Method

Process capability analysis is an important quality tools in 6Sigma management. The calculating methods of standard capability indices in process capability assessment are based on the hypothesis that the distributions of process output are normal or approximate normal. There is a lot of practice cases in which the output isn´t normal. Because the forms of these distributions are unknown, the results of evaluation may be misleading to a judgment about the processes. When the distribution is on the skew, the clements method is used after estimating the form of distribution by a lot of data from process output. With the not truly known distribution, there is big gap in the assessment result. Based on Scaled weighted variance method, some process capability indices formulas, which can be used in skew distribution, are established in the paper. The simulation study was done for comparison between the WV-based and SWV-based PCI.