What Are Your Cp and Cpk Values?

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Posted by: Larry Seibel
Posted on: Monday, 7th May 2001, 12:00 AM.

The general rule of thumb states that if a Cpk value of a process is less than 1.33, then the process is incapable of producing a repeatable part. Most of our injection molding processes yield a Cpk value of around 1.0. That means that I, as a black belt, have a great deal of work to do to make the processes predictable, then I can proceed with DOE's and find the optimal preocess settings. Also, remember this, there is a difference between Cpk and long term process capability. That difference is long term is typically a 1.5 sigma shift for the worse, accounting for white noise (common cause variation. Cpk is basically a snap shot of what you have going on right now, unless of course you have the time to take data ofer a long period of time and are considering ALL variation (Common and Special Cause). Hope this helps!

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 Message Thread:

What Are Your Cp and Cpk Values? by Tom on Sunday, 6th May 2001

Re: What Are Your Cp and Cpk Values? by Ken Myers on Sunday, 6th May 2001

Re: What Are Your Cp and Cpk Values? by Grant Blair on Monday, 7th May 2001

Re: What Are Your Cp and Cpk Values? by Harvey C. Smith on Thursday, 6th May 2004

Re: What Are Your Cp and Cpk Values? by Andy Brody on Monday, 7th May 2001

Re: What Are Your Cp and Cpk Values? by Joy on Monday, 7th May 2001

Re: What Are Your Cp and Cpk Values? by jilly on Thursday, 25th July 2002

Re: What Are Your Cp and Cpk Values? by anonymous on Monday, 7th May 2001

Re: What Are Your Cp and Cpk Values? by Larry Seibel on Monday, 7th May 2001

Re: What Are Your Cp and Cpk Values? by Carlos Díaz on Wednesday, 30th April 2003

Re: What Are Your Cp and Cpk Values? by Gabriel on Wednesday, 30th April 2003

Re: What Are Your Cp and Cpk Values? by Venkat Rao Kesana on Thursday, 10th March 2005

Re: What Are Your Cp and Cpk Values? by Sam on Wednesday, 1st November 2006

Re: What Are Your Cp and Cpk Values? by Joe Perito on Thursday, 10th May 2001

Re: What Are Your Cp and Cpk Values? by James on Wednesday, 24th July 2002

Re: What Are Your Cp and Cpk Values? by Gabriel on Thursday, 25th July 2002

Re: What Are Your Cp and Cpk Values? by James A on Thursday, 25th July 2002

Re: What Are Your Cp and Cpk Values? by Mike Carnell on Thursday, 25th July 2002

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