1. What is Cpk Capacity?

Cpk (Process Capability Index) measures how well a process meets specification limits, considering both the process variation and centering. It indicates the capability of a process to produce output within specification limits.

2. How Does the Calculator Work?

The calculator uses the Cpk formula:

Where:

• \( USL \) — Upper Specification Limit
• \( \mu \) — Process mean
• \( LSL \) — Lower Specification Limit
• \( \sigma \) — Standard deviation

Explanation: Cpk considers both the process variation (σ) and how centered the process is between the specification limits.

3. Importance of Cpk Calculation

Details: Cpk is crucial for quality control, helping determine if a process is capable of meeting specifications and identifying opportunities for process improvement.

4. Using the Calculator

Tips: Enter all four values (USL, mean, LSL, and standard deviation). Standard deviation must be greater than zero.

5. Frequently Asked Questions (FAQ)

Q1: What is a good Cpk value?
A: Generally, Cpk ≥ 1.33 indicates capable process. Cpk ≥ 2.0 is considered excellent. Cpk < 1.0 indicates process may not meet specifications.

Q2: How is Cpk different from Cp?
A: Cp only considers process variation, while Cpk considers both variation and centering. Cp ≥ Cpk always.

Q3: What if my process has only one specification limit?
A: For one-sided specifications, use either (USL-μ)/3σ or (μ-LSL)/3σ as appropriate.

Q4: How many data points should I use?
A: For reliable Cpk calculation, use at least 25-30 data points to estimate σ accurately.

Q5: What if my data isn't normally distributed?
A: Cpk assumes normal distribution. For non-normal data, consider transformations or non-parametric methods.