1. What is the Cpk Formula?

The Cpk (Process Capability Index) formula measures how well a process can produce output within specification limits. It considers both the centering of the process and its spread relative to the specification limits.

2. How Does the Calculator Work?

The calculator uses the Cpk formula:

Where:

• \( USL \) — Upper Specification Limit (units vary)
• \( LSL \) — Lower Specification Limit (units vary)
• \( \mu \) — Process Mean (units vary)
• \( \sigma \) — Process Standard Deviation (units vary)

Explanation: The formula calculates the minimum distance between the process mean and either specification limit, normalized by three standard deviations.

3. Importance of Cpk Calculation

Details: Cpk is crucial for assessing process capability, ensuring quality control, and determining if a process can consistently produce within specification limits.

4. Using the Calculator

Tips: Enter all values in consistent units. Standard deviation must be greater than zero. The result 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.

Q2: How is Cpk different from Cp?
A: Cp measures potential capability assuming the process is centered, while Cpk considers both centering and spread.

Q3: What if Cpk is negative?
A: A negative Cpk indicates the process mean is outside the specification limits.

Q4: What are the limitations of Cpk?
A: Cpk assumes normal distribution and may not be accurate for non-normal processes.

Q5: How often should Cpk be calculated?
A: Regular monitoring is recommended, typically as part of ongoing quality control processes.