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 centering of the process and its spread 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
• \( Cpu \) — Upper capability index
• \( Cpl \) — Lower capability index

Explanation: Cpk is the minimum value between Cpu and Cpl, representing the worst-case scenario of the process capability.

3. Importance of Cpk Calculation

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

4. Using the Calculator

Tips: Enter all four required values (USL, LSL, mean, and standard deviation). Standard deviation must be greater than zero.

5. Frequently Asked Questions (FAQ)

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

Q2: How is Cpk different from Cp?
A: Cp only considers the spread of the process, while Cpk considers both spread and centering.

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

Q4: What if my Cpu and Cpl are very different?
A: This indicates your process is not centered between the specification limits.

Q5: How can I improve my Cpk?
A: Either reduce process variation (σ) or center the process mean between the limits.