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 center and variability.

2. How Does the Calculator Work?

The calculator uses the Cpk formula:

Where:

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

Explanation: The formula calculates how many standard deviations the process mean is from the nearest specification limit, providing a measure of process capability.

3. Importance of Cpk Calculation

Details: Cpk is crucial for quality control and process improvement. It helps manufacturers determine if their process is capable of meeting customer requirements and identifies areas for improvement.

4. Using the Calculator

Tips: Enter the upper and lower specification limits, process mean, and standard deviation. All values must be valid (standard deviation > 0).

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 (Six Sigma quality).

Q2: How is Cpk different from Cp?
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 stable processes with normally distributed data and known specification limits.

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

Q5: How is Cpk calculated in JMP software?
A: In JMP, Cpk can be calculated through the Distribution platform or Quality and Process tools using the same mathematical formula shown above.