1. What Is The Cpk?

The Process Capability Index (Cpk) is a statistical measure that indicates how well a process can produce output within specified limits. It compares the process variability to the specification limits, providing insight into process performance and capability.

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: The formula calculates how centered the process is between the specification limits and how much variability exists in the process relative to those limits.

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 reducing variation and improving quality.

4. Using The Calculator

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

5. Frequently Asked Questions (FAQ)

Q1: What is a good Cpk value?
A: Generally, a Cpk ≥ 1.33 indicates a capable process. A Cpk ≥ 2.0 is considered excellent and represents Six Sigma quality level.

Q2: How is Cpk different from Cp?
A: Cp measures process potential without considering centering, while Cpk considers both variability and how centered the process is within specifications.

Q3: Can Cpk be negative?
A: Yes, a negative Cpk indicates that the process mean is outside the specification limits.

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 conditions.

Q5: How often should Cpk be calculated?
A: Cpk should be monitored regularly as part of ongoing process control, typically calculated from recent production data to reflect current process capability.