1. What Are Cp and Cpk?

Cp and Cpk are statistical measures of process capability. Cp measures the potential capability of a process assuming it's centered, while Cpk measures the actual capability considering how centered the process is within the specification limits.

2. How Does the Calculator Work?

The calculator uses the following formulas:

Where:

• \( USL \) — Upper Specification Limit
• \( LSL \) — Lower Specification Limit
• \( \sigma \) — Standard Deviation of the process
• \( \mu \) — Process Mean

Explanation: Cp compares the process spread to the specification range, while Cpk considers both the spread and centering of the process.

3. Importance of Process Capability Indices

Details: These indices are crucial in quality control and Six Sigma methodologies to determine if a process can consistently produce output within specification limits. Higher values indicate better process capability.

4. Using the Calculator

Tips: Enter all values in consistent units. Standard deviation must be greater than zero. The calculator will compute both Cp and Cpk indices.

5. Frequently Asked Questions (FAQ)

Q1: What is a good Cp/Cpk value?
A: Generally, values above 1.33 are considered capable, with 1.0 being the minimum acceptable for most processes. Six Sigma processes aim for 2.0.

Q2: What's the difference between Cp and Cpk?
A: Cp measures potential capability if the process is centered, while Cpk measures actual capability considering how centered the process is.

Q3: When should I use Cp vs Cpk?
A: Use Cp when you want to know the potential capability, and Cpk when you want to know the actual capability considering process centering.

Q4: Can Cp be higher than Cpk?
A: Yes, this indicates the process is not centered between the specification limits, reducing its actual capability.

Q5: What if my Cpk is negative?
A: A negative Cpk indicates the process mean is outside the specification limits, meaning the process is producing non-conforming output.