When the factory mass production, will be based on previous historical data to assess the Cpk value of the process. Afterwards, the quality engineer will need to monitor the Cpk value of the measured value and maintain it at a fixed high level. If there is an abnormal decrease in the subsequent Cpk value, it means that the process conditions (equipment, consumables, manufacturing parameters, or human error) have changed, and the cause must be followed and improved to prevent the occurrence of out-of-spec product and cause significant losses to the factory.
Perhaps it can be said that Cpk Control is a kind of "prevention" quantitative engineering.
Ca represents the "Accuracy" of the measured value of the product, Cp represents the "Precision" of the measured value of the product, and Cpk is the combined value of the above two indexes.
CPK = 1.67, which is 0.57 per million defective items; that is, the passing rate is 99.99995%