Abstract
The issue of determining the accuracy of estimates of the process capability indices Cp and Cpk based on their standard deviations is considered. At the same time, since the capability indices can only be used under conditions of a statistically stable state of the process, which from a practical point of view means the need to maintain appropriate Shewhart control charts, the values Ϭ of the indices of Cp and Cpk should be determined based on k samples (data groups), each volume n and using an estimate of the standard deviation of the process according to the studied quality characteristic Ϭ, found on the basis of intragroup variability. However, in this case, it is necessary to take into account the number of effective degrees of freedom of the estimate Ϭ, since this directly affects the values σ of the standard deviations of the estimates Cp and Cpk.
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