What do Cp and Cpk measure in a capability study?

What do Cp and Cpk measure in a capability study?

• A. They measure only the product yield.
• B. They quantify inventory levels and throughput.
• C. They assess supplier on-time delivery performance.
• D. They quantify potential and actual process capability and centering.

Answer: (D)

Cp and Cpk are indicators used in capability studies to quantify how well a process can meet its specification limits. Cp measures potential capability by looking at the spread of the process relative to the tolerance window, assuming the process is perfectly centered. It is calculated as (USL minus LSL) divided by six times the process standard deviation. A higher Cp means more of the tolerance range could be covered by the natural variation if the process were centered. Cpk adds the reality of where the process actually sits relative to the limits. It accounts for centering by taking the smaller of two values: how far the mean is from the upper limit divided by three times the standard deviation, and how far the mean is from the lower limit divided by three times the standard deviation. This reflects both spread and alignment of the process with the target; a high Cpk means the process is both tight and well-centered, while a low Cpk signals either excessive spread or a shift from center. These measures focus on process capability relative to specifications, not on product yield, inventory levels, throughput, or supplier delivery performance.

Cp and Cpk are indicators used in capability studies to quantify how well a process can meet its specification limits. Cp measures potential capability by looking at the spread of the process relative to the tolerance window, assuming the process is perfectly centered. It is calculated as (USL minus LSL) divided by six times the process standard deviation. A higher Cp means more of the tolerance range could be covered by the natural variation if the process were centered.

Cpk adds the reality of where the process actually sits relative to the limits. It accounts for centering by taking the smaller of two values: how far the mean is from the upper limit divided by three times the standard deviation, and how far the mean is from the lower limit divided by three times the standard deviation. This reflects both spread and alignment of the process with the target; a high Cpk means the process is both tight and well-centered, while a low Cpk signals either excessive spread or a shift from center.

These measures focus on process capability relative to specifications, not on product yield, inventory levels, throughput, or supplier delivery performance.