CQI Statistical Process Control Flashcards

What does process capability index Cp measure?

Answer: The spread of the process relative to the specification width, without regard to centering

Cp measures the ratio of the specification width to the process spread (6σ), indicating potential capability without considering how well the process is centered.

What is the minimum acceptable Cpk value for most manufacturing processes?

Answer: 1.33

A Cpk of 1.33 is the generally accepted minimum for a capable process, providing approximately 99.994% conformance and is required by many automotive standards.

What does a Cpk value of 1.0 indicate?

Answer: The nearest specification limit is exactly 3 standard deviations from the process mean

A Cpk of 1.0 means the process mean is exactly 3 standard deviations from the nearest specification limit, yielding approximately 0.27% nonconformance.

What is the key difference between Cp and Cpk?

Answer: Cp ignores centering while Cpk accounts for how well the process is centered within specifications

Cp measures potential capability (spread only), while Cpk measures actual capability by accounting for both the process spread and its centering within the specification.

Process capability studies should only be conducted when:

Answer: The process is in a state of statistical control

Capability indices are only meaningful when the process is stable (in statistical control), because special cause variation invalidates capability calculations.

What does DPMO stand for in quality measurement?

Answer: Defects Per Million Opportunities

DPMO (Defects Per Million Opportunities) is a quality metric used in Six Sigma that normalizes defect rates by accounting for the complexity of a product or process.