1. What is Cpk Value?

Cpk (Process Capability Index) is a statistical measure of a process's ability to produce output within specification limits. It indicates how well a process meets specifications by comparing the spread of the process to the width of 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: The formula calculates the capability of a process by determining how close the process mean is to the specification limit and comparing it to the natural variation of the process.

3. Importance of Cpk Calculation

Details: Cpk is crucial for quality control and process improvement. It helps manufacturers determine if their process is capable of meeting customer requirements and identifies areas for process 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). The units must be consistent across all inputs.

5. Frequently Asked Questions (FAQ)

Q1: What is a good Cpk value?
A: Generally, a Cpk value of 1.33 or higher is considered acceptable, while 2.0 or higher indicates excellent process capability.

Q2: What's the difference between Cp and Cpk?
A: Cp measures process potential without considering centering, while Cpk considers both process variation and centering relative to specification limits.

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

Q4: What are the limitations of Cpk?
A: Cpk assumes normal distribution of data and may not be accurate for non-normal processes. It also requires stable process conditions.

Q5: How often should Cpk be calculated?
A: Cpk should be calculated regularly as part of ongoing process monitoring, especially after process changes or improvements.