Cp vs. Cpk - What is the difference - A visual animation
The thread started with
Cpk vs.
Ppk which I don't think was directly answered in this thread yet, but for the Cp vs. Cpk post above:
Take a look at the visual animation here:
Cp vs. Cpk visual animation
The essential difference is Cpk addresses centering on the specification spread / center point. Cp only addresses the tightness of the process (machine) its self.
k = a constant.
I did notice in the 'Similar Threads' listing at the bottom of the page. This is a very common question. I think a page with good links to major threads here in the forums is
What is the difference between Cp, Cpk and Ppk?.
- Cmk – Machine capability
- Cpk – Process capability index
- Cpm – Targeted capability index
- Ppk – Performance capability index
- Ppk – Preliminary process capability index (had to use it for Ford in
the start up of new projects)
Are Cpk & Ppk acronyms? If so, what do they actually mean or represent?
From a link:
Since their introduction, there has been a lot of speculation as to meaning.
Cp has always been know as capability of the process since I became aware of it and it has been around for some time. My connection with Cpk came through the Ford "Continuous Process Control and Process Capability Improvement Manual" probably more than 20 years ago. In the Ford manual, a k value was used to represent the number of standard deviations between the Target and the x double bar. I would assume that the Cpk came literally from Cp with a k factor adjustment. In reference to the Pp and Ppk, the reference from the beginning has been to Process Performance as opposed to Process Capability.
Can anyone summarize when to use Cpk vs. Ppk - And why?