1. What is Unilateral Cpk?

Unilateral Cpk (Process Capability Index) measures how well a process meets a single specification limit. It indicates the capability of a process to produce output within specified limits, considering only one side of the distribution.

2. How Does the Calculator Work?

The calculator uses the unilateral Cpk formula:

Where:

• \( Limit \) — Specification limit (units vary)
• \( Mean \) — Process mean (units vary)
• \( SD \) — Standard deviation (units vary)

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

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 customer requirements and identifies areas for process optimization.

4. Using the Calculator

Tips: Enter the specification limit, process mean, and standard deviation. All values must use consistent units, and standard deviation must be greater than zero.

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

Q3: When should unilateral Cpk be used?
A: Use unilateral Cpk when you have only one specification limit (either upper or lower limit but not both).

Q4: 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 conditions.

Q5: 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.