1. What Are Cp And Cpk?

Cp and Cpk are statistical process control (SPC) indices that measure how well a process can meet specification limits. Cp measures potential capability assuming the process is centered, while Cpk measures actual capability accounting for process centering.

2. How Do The Formulas Work?

The calculator uses these formulas:

Where:

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

Explanation: Cp compares the specification range to the process variation (6σ). Cpk considers both variation and how centered the process is between the specification limits.

3. Importance Of Process Capability Indices

Details: These indices help manufacturers determine if their processes are capable of producing within specifications, identify improvement opportunities, and monitor process performance over time.

4. Using The Calculator

Tips: Enter all values in consistent units. Standard deviation must be greater than zero, and USL must be greater than LSL for valid calculations.

5. Frequently Asked Questions (FAQ)

Q1: What is a good Cp/Cpk value?
A: Generally, Cp/Cpk ≥ 1.33 indicates capable process. Values ≥ 1.67 are excellent. Values < 1.0 indicate process may not meet specifications.

Q2: What's the difference between Cp and Cpk?
A: Cp measures potential capability if centered, while Cpk measures actual capability considering both variation and centering.

Q3: When should I use these indices?
A: Use when process is stable (in statistical control) and data is normally distributed for accurate results.

Q4: What if my data isn't normally distributed?
A: Consider data transformation or use non-normal capability indices for more accurate assessment.

Q5: How can I improve my Cp/Cpk values?
A: Reduce process variation (improve σ) and/or center the process between specification limits.