1. What is Cpk?

Cpk (Process Capability Index) is a statistical measure of a process's ability to produce output within specification limits. It indicates how well a process meets specifications, considering both the process mean and variability.

2. How Does the Calculator Work?

The calculator uses the Cpk formula:

Where:

• \( USL \) — Upper Specification Limit
• \( Mean \) — Process mean value
• \( StDev \) — Process standard deviation
• \( LSL \) — Lower Specification Limit

Explanation: Cpk measures how close the process is to the specification limits and how consistent the process is around the average performance.

3. Importance of Cpk Calculation

Details: Cpk is crucial for quality control and process improvement. It helps determine if a process is capable of meeting customer requirements and identifies opportunities for process optimization.

4. Using the Calculator

Tips: Enter USL, Mean, Standard Deviation, and LSL values. All values must be valid (Standard Deviation > 0). The calculator will compute the Cpk value, which is dimensionless.

5. Frequently Asked Questions (FAQ)

Q1: What is a good Cpk value?
A: Generally, Cpk ≥ 1.33 indicates a capable process. Cpk ≥ 2.0 is considered excellent. Values below 1.0 indicate the process may not meet specifications.

Q2: What's the difference between Cp and Cpk?
A: Cp measures potential capability assuming the process is centered, while Cpk measures actual capability considering both centering and spread.

Q3: When should Cpk be used?
A: Cpk should be used when you have specification limits and want to assess how well your process meets those limits while considering process centering.

Q4: What are the limitations of Cpk?
A: Cpk assumes normal distribution of data and may not be accurate for non-normal processes. It also requires stable process data.

Q5: How is Cpk interpreted in Minitab?
A: In Minitab, Cpk is calculated using the same formula and is typically reported alongside other capability indices in process capability analysis.