Cp and Cpk - Definitions

The Cp index is used to summarize a system’s ability to meet two-sided specification limits (upper and lower). Cp uses estimated sigma and shows the system’s potential to meet the specifications. However, it ignores the process average and focuses on the spread. If the system is not centered within the specifications, Cp alone may be misleading.

Cp = Process Capability. A simple and straightforward indicator of process capability.
Cpk = Process Capability Index. Adjustment of Cp for the effect of non-centered distribution.
Pp = Process Performance. A simple and straightforward indicator of process performance.
Ppk = Process Performance Index. Adjustment of Pp for the effect of non-centered distribution.

To demonstrate that a process is stable. Is it valid to compare that these parameters have not changed?

To demonstrate that a process is stable. Is it(he) valid to compare that these parameters have not changed?

Cp = Process Capability = (USL-LSL) / 6σ

CpK= Process Capability Index - (USL-µ)/3σ & (µ - LSL)/3σ

where: USL = upper specification limit
LSL = lower specification limit
σ = standard deviation
µ = mean

when should the PPk be used?

should each parameter in validation process be evaluated using cpk?

This I would also like to ask…

I want to know this too :slight_smile:

Can someone post a sample spreadsheet on computation of cpk. Thank you