CarolX said:
Maybe I am wrong here, but this is how I see it
Capability - does the process have the ability to make the part.
Control - what checks are in place to keep the process capable of producing part.
I was thinking specifically about
statistical process control when I was saying "control". As you note, it can also be used to mean the checks that are in place, as in "document control" or "control of non-conforming products".
For "capabilty", I would explicitly add "ability to make the part
to the customer's specifications." It is almost implied that if you are making something, that you are making it to satisfy a particular expectation, but
it never hurts to be overly clear.
jrubio said:
Ppk (Un-stable) Cpk (Stable)
I have a feeling that Cpk and Ppk are among the most abused and confused terms in quality engineering. And I can't say that I am the best authority on the proper use and meaning of the terms.
In my understanding, Ppk and Cpk are two different measures of capability that
tell you two similar but not identical things about a process. Both should only be calculated when the process is reasonably stable and "in control".
Tim F