1. What is Cpk?

Cpk (Process Capability Index) is a statistical measure of a process's ability to produce output within specification limits. It considers both the variability of the process and its centering relative to the 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: Cpk is the minimum value between the upper capability index (Cpu) and lower capability index (Cpl), representing the worst-case scenario for process capability.

3. Importance of Cpk Calculation

Details: Cpk is crucial for quality control, helping manufacturers determine if their process can consistently produce products within specifications. Higher Cpk values indicate better process capability.

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).

5. Frequently Asked Questions (FAQ)

Q1: What is a good Cpk value?
A: Generally, Cpk ≥ 1.33 is considered acceptable, ≥ 1.67 is good, and ≥ 2.00 is excellent.

Q2: How is Cpk different from Cp?
A: Cp measures potential capability without considering centering, while Cpk considers both variability and centering.

Q3: What does a negative Cpk mean?
A: Negative Cpk indicates the process mean is outside the specification limits.

Q4: When should Cpk be used?
A: Use Cpk when you need to assess both process variability and centering relative to two-sided specification limits.

Q5: What are limitations of Cpk?
A: Cpk assumes normal distribution and may not be accurate for non-normal processes. It also requires stable, controlled processes.