What is the Formula for CPK (Process Capability Index) in Sigma?

Learn the formula for CPK in sigma, a key metric showing process capability by comparing specification limits, mean, and standard deviation.

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CPK (Process Capability Index) is calculated using the formula: CPK = min[(USL - μ) / 3σ, (μ - LSL) / 3σ], where USL is the Upper Specification Limit, LSL is the Lower Specification Limit, μ (mu) is the process mean, and σ (sigma) is the standard deviation. This metric helps determine how well a process can produce output within specified limits, thus indicating the capability of a process in relation to its specifications.

FAQs & Answers

  1. What does CPK stand for in quality control? CPK stands for Process Capability Index, a statistical measure that assesses how well a process produces output within specified limits.
  2. How is the CPK calculated using sigma? CPK is calculated as the minimum of [(USL - mean) / 3 sigma] and [(mean - LSL) / 3 sigma], where USL and LSL are specification limits, mean is the process average, and sigma is the standard deviation.
  3. Why is CPK important in Six Sigma? CPK indicates the capability of a process relative to specification limits and helps identify if a process is consistently producing quality outputs, which is vital in Six Sigma methodology.

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