What is the meaning of "k" in Cpk and Ppk? And Cpk vs. Ppk

S

Star18

#1
Hi evrybody,

Is someone knows the meaning of "k" in the indexes Cpk and Ppk ?

Thanks in advance.

Rach.:bigwave:
 
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Wes Bucey

Quite Involved in Discussions
#4
Wayne makes an excellent point of citing an authoritative source for information about statistics used in Engineering and Quality.

All our readers should bookmark this excellent FREE handbook published by the National Institute of Standards and Testing. http://www.itl.nist.gov/div898/handbook/

If you are writing a formal paper or document (versus a comment here in the Cove) there is a protocol for making the citation in your footnotes or endnotes:

To reference the Handbook please use a citation of the form:

NIST/SEMATECH e-Handbook of Statistical Methods, http://www.itl.nist.gov/div898/handbook/, date.
(Links to specific pages can also be referenced this way, if suitable.)

Printer friendly versions of each chapter in the e-Handbook can be found
here.

Information on Getting the e-Handbook on CD can be found
here.

Feedback on the Handbook sent to
[email protected] is also much appreciated.
 

Wes Bucey

Quite Involved in Discussions
#7
wmarhel said:
I'm not sure, but the CD used to be free of charge.
Still free PLUS it is copyright-free, which means (and it is encouraged by NIST) you can start with a master copy and make as many additional copies to distribute as you need.

This might make a good free premium to give to employees, customers, or clients (i.e. burn copies of a master CD and give them away.) Having accessed this both by dial-up and high-speed, I can tell you it makes a lot of sense to have a reference copy on disk or hard drive if you don't have high-speed internet access.
 
M

Mr.Nathan

#8
What is the differents between cp and cpk?

Hi Guys,

Does anyone knows " What is the differents between cp and cpk? " As i know that both is use to monitor process capability and the formula is also different but anyway im still not very clear with it.

Cp = ?

Cpk = ?

thanks

Nathan
 

Marc

Hunkered Down for the Duration with a Mask on...
Staff member
Admin
#9
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?
 
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