Cp and Cpk Print E-mail

Cp’s and Cpk’s are much alike, however they are different. Cp tells you the capability of a process while Cpk tells you where the process really is.

When to use

In different stages in the product/process development. In the α-phase, β-phase as well as the  mass production phase Cp and Cpk are determined. This tool is not only a development tool but also a tool that can be used in production.

Cp’s and Cpk’s are used:

  • if new production machines are installed
  • when changes have been made to the production process
  • when monitoring production

Description

Cp is the difference between the Upper Specification Limit (USL) and the Lower Specification Limit (LSL) divided by 6x the standard deviation (σ). A good value is minimal 3.

Cpk is minimal difference between the average and the USL or the LSL divided by 6x the standard deviation. A good Cpk value is at least 1.33, the higher the better.