CQI CQI Statistical Process Control 2

Question 1

What does process capability index Cp measure?

Accepted Answer

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

Answer

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

Question 2

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

Accepted Answer

1.33

Answer

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.

Question 3

What does a Cpk value of 1.0 indicate?

Accepted Answer

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

Answer

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

Question 4

What is the key difference between Cp and Cpk?

Accepted Answer

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

Answer

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

Question 5

Process capability studies should only be conducted when:

Accepted Answer

The process is in a state of statistical control

Answer

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

CQI - Certified Quality Inspector Practice Test

CQI - Certified Quality Inspector Practice Test

CQI CQI Statistical Process Control 2