Process Capability: Formulas & Implementation

Juran Knowledge

How do you find process capability?

  1. Identify the process subjects for measurement.
  2. Establish units of measure, sensors, and upper and lower specification limits for the selected subjects.
  3. Operate the process through a number of cycles. (A minimum of 40 observations without any assignable causes are usually needed.)
  4. Identify and remove any observations that are out of control as the result of assignable causes.
  5. Construct a histogram of the remaining observations for each subject.
  6. Evaluate the process capability visually.
  7. Calculate the Cpk index for each process subject. CPK Index Formula
    The index must, at a minimum, equal 1. 0. Most processes should have a minimum index of 1.33.
  8. If the process is not capable, identify and eliminate the root causes for excessive variability.

Process Capability Formula Example

Author: Juran

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