1. What is Cpk and PPM?

Cpk (Process Capability Index) is a statistical measure of a process's ability to produce output within specification limits. PPM (Parts Per Million) represents the expected number of defective parts per million produced.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( Cpk \) — Process capability index (dimensionless)
• \( \Phi \) — Cumulative standard normal distribution function
• \( PPM \) — Defective parts per million

Explanation: The formula calculates the expected defect rate based on the process capability index, assuming a normal distribution of the process output.

3. Importance of Cpk and PPM

Details: Cpk and PPM are crucial quality metrics in manufacturing and process industries. They help quantify process performance, set quality targets, and monitor improvement initiatives.

4. Using the Calculator

Tips: Enter the Cpk value (must be greater than 0). The calculator will compute the corresponding defect rate in parts per million.

5. Frequently Asked Questions (FAQ)

Q1: What is a good Cpk value?
A: Generally, Cpk ≥ 1.33 is considered capable, Cpk ≥ 1.67 is good, and Cpk ≥ 2.00 is excellent (Six Sigma quality).

Q2: How does Cpk relate to Sigma level?
A: Cpk is directly related to Sigma level. A Cpk of 1.0 corresponds to 3 Sigma, 1.33 to 4 Sigma, 1.67 to 5 Sigma, and 2.0 to 6 Sigma.

Q3: What assumptions does this calculation make?
A: The calculation assumes the process is normally distributed, stable, and centered between specification limits.

Q4: Can I use this for one-sided specifications?
A: This formula is designed for two-sided specifications. For one-sided specifications, different calculations are needed.

Q5: What if my process isn't normally distributed?
A: For non-normal distributions, the relationship between Cpk and PPM may differ, and alternative methods should be used.