What is Cp & Cpk? How many types of variation present in a Process? What is special cause variation?

Question

Accepted Answer

Cp & Cpk are statistical tools used to measure process capability. Two types of variation are present in a process: common cause and special cause.

Cp & Cpk are used to determine if a process is capable of producing products within specifications
Cp measures the potential capability of a process, while Cpk measures the actual capability
Common cause variation is inherent in a process and is caused by factors that are always present
Special cause variation is caused by factors that are not always present and can be identified and eliminated
Examples of special cause variation include machine breakdowns, operator errors, and material defects

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