1. What Is Cpk For Attributes?

Cpk (Process Capability Index) for attributes is a statistical measure that quantifies how well a process can produce output within specified limits. It compares the spread of the process variation 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 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, a Cpk value of 1.33 or higher is considered acceptable, with values of 1.67 or higher indicating excellent process capability.

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

Q3: When should Cpk be used?
A: Cpk should be used when evaluating process capability for normally distributed data with two-sided specification limits.

Q4: What are the limitations of Cpk?
A: Cpk assumes normal distribution and may not be appropriate for non-normal data or processes with one-sided specifications.

Q5: How can I improve my Cpk value?
A: Improving Cpk typically involves reducing process variation, centering the process mean, or both through process optimization.