1. What is Cpk?

Cpk (Process Capability Index) is a statistical measure that indicates how well a process can produce output within specified limits. It compares the process variation to the specification limits and indicates how centered the process is within those limits.

2. How Does the Calculator Work?

The calculator uses the Cpk formula:

Where:

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

Explanation: The formula calculates two capability indices (one for each specification limit) and returns the minimum value, representing the worst-case scenario for the process capability.

3. Importance of Cpk Calculation

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

4. Using the Calculator

Tips: Enter all values in consistent units. Standard deviation must be greater than zero. The calculator will compute Cpk based on the input parameters.

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

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

Q4: What if my process has only one specification limit?
A: For one-sided specifications, use the appropriate numerator (USL-μ or μ-LSL) with 3σ in the denominator.

Q5: How often should Cpk be calculated?
A: Regular monitoring is recommended - typically calculated periodically (weekly, monthly) or when process changes occur.