1. What is Cpk in APQR?

The Process Capability Index (Cpk) is a statistical measure used in Annual Product Quality Review (APQR) to assess how well a process meets specification limits. It indicates the capability of a process to produce output within specification 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
• \( \sigma \) — Process Standard Deviation

Explanation: The formula calculates how many standard deviations the process mean is from the nearest specification limit, providing a measure of process capability.

3. Importance of Cpk Calculation

Details: Cpk is crucial in APQR for evaluating process performance, identifying areas for improvement, and ensuring consistent product quality that meets regulatory requirements.

4. Using the Calculator

Tips: Enter all specification limits, process mean, and standard deviation. Ensure standard deviation is greater than zero for valid calculation.

5. Frequently Asked Questions (FAQ)

Q1: What is a good Cpk value?
A: Generally, Cpk ≥ 1.33 indicates a capable process. Cpk ≥ 1.67 is considered excellent, while Cpk < 1.0 may indicate process improvement is needed.

Q2: How does Cpk differ from Cp?
A: Cp measures potential capability assuming the process is centered, while Cpk measures actual capability accounting for process centering.

Q3: When should Cpk be calculated in APQR?
A: Cpk should be calculated annually as part of the product quality review to monitor process stability and capability over time.

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 to improve Cpk value?
A: Improve Cpk by reducing process variation (lower σ) or centering the process mean between specification limits.