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 process variability and how centered the process is between the specification limits.

2. How Does the Calculator Work?

The calculator uses the Cpk formula:

Where:

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

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 for quality control and process improvement. It helps determine if a process is capable of meeting specifications and identifies opportunities for improvement.

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 indicates a capable process. Cpk ≥ 2.0 is considered excellent.

Q2: How is Cpk different from Cp?
A: Cp measures potential capability assuming the process is centered, while Cpk measures actual capability considering both variability and centering.

Q3: What if my process has only one specification limit?
A: For one-sided specifications, use the appropriate part of the formula (either USL or LSL calculation).

Q4: What are common Cpk interpretation guidelines?
A: Cpk < 1.0: process not capable; Cpk = 1.0-1.33: marginally capable; Cpk > 1.33: capable process.

Q5: How often should Cpk be calculated?
A: Regular monitoring is recommended - typically calculated periodically (daily, weekly, or monthly) depending on process criticality.