1. What is Cpk?

Cpk (Process Capability Index) is a statistical measure of a process's ability to produce output within specification limits. It indicates how well a process meets specifications, considering both the process mean and variability.

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 the capability of the process by comparing the distance from the process mean to the nearest specification limit relative to the process spread (3 standard deviations).

3. Importance of Cpk Calculation

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

4. Using the Calculator

Tips: Enter the upper and lower specification limits, process mean, and standard deviation. All values must be valid (standard deviation > 0). The calculator will compute the Cpk value.

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 and represents Six Sigma quality level.

Q2: What's the difference between Cp and Cpk?
A: Cp measures process potential capability without considering centering, while Cpk measures actual capability considering both variability and centering.

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

Q4: How often should Cpk be calculated?
A: Cpk should be monitored regularly as part of ongoing process control, typically with each significant process change or at regular intervals.

Q5: 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.