1. What is Cpk?

Cpk (Process Capability Index) is a statistical measure of process capability that indicates how well a process can produce output within specification limits. It considers both the centering and the spread of the process.

2. How Does the Calculator Work?

The calculator uses the Cpk formula:

Where:

• \( USL \) — Upper Specification Limit
• \( \mu \) — Process Mean
• \( \sigma \) — 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 specifications and identifies opportunities for process optimization.

4. Using the Calculator

Tips: Enter all four required values: USL, mean, standard deviation, and LSL. Standard deviation must be greater than zero for valid calculation.

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.

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: Can Cpk be negative?
A: Yes, negative Cpk indicates the process mean is outside the specification limits.

Q4: How often should Cpk be calculated?
A: Regular monitoring is recommended, typically as part of ongoing statistical process control activities.

Q5: What are the limitations of Cpk?
A: Cpk assumes normal distribution and may not be appropriate for non-normal processes. It also requires stable process conditions.