1. What is the Cpk Calculation Formula?

The Cpk (Process Capability Index) formula measures how well a process meets specification limits. It compares the process spread to the specification range while considering how centered the process is within that range.

2. How Does the Calculator Work?

The calculator uses the Cpk formula:

Where:

• \( USL \) — Upper Specification Limit
• \( LSL \) — Lower Specification Limit
• \( \mu \) — Process Mean
• \( \sigma \) — Process 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 process capability.

3. Importance of Cpk Calculation

Details: Cpk is crucial for quality control and process improvement. It helps determine if a process is capable of producing within specification limits and identifies opportunities 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: How is Cpk different from Cp?
A: Cp measures process potential without considering centering, while Cpk accounts for how centered the process is within specifications.

Q3: What does Cpk < 1 mean?
A: Cpk < 1 indicates the process spread exceeds specification limits, meaning some output will be out of specification.

Q4: Can Cpk be negative?
A: Yes, negative Cpk values indicate the process mean is outside the specification limits.

Q5: 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 data.