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  Statistical Techniques and 6 Sigma
  Cpk Sigma and PPM

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Author Topic:   Cpk Sigma and PPM
Marc Smith
Cheech Wizard

Posts: 4119
From:West Chester, OH, USA
Registered:

posted 05 February 2000 07:30 PM     Click Here to See the Profile for Marc Smith   Click Here to Email Marc Smith     Edit/Delete Message   Reply w/Quote
From: aschlo3307@cs.comABC123 (ASchlo3307)
Newsgroups: misc.industry.quality
Subject: Re: Cpk Sigma and PPM

Date: 03 Feb 2000 00:41:42 GMT

Organization: CompuServe (http://www.compuserve.com/)

Brett and Tracey Kimmel wrote:

>I'm wondering if anyone can help. I am working on target goals for a
>production floor that has no experience with capability studies, and process
>capability. I'm trying to make a simple target in PPMs. I know that 1.33 Cpk
>at 6 sigma is approximately 64 PPM. what would that be if I used 4 sigma
>instead. I would appreciate the math formula too.

Step No. 1 - run a Capability Study on the process. I prefer using a standard Xbar & R chart as a format with five-sample subgroups for 20 subgroups. Reading will be taken on consecutive pieces (100% inspection). The Capability Study will tell you two important things. First, is the process variation random? Assuming it is, is the process capable of meeting the print tolerance (what is the Cp, CpK, CpU --- whatever capability index you choose to use)?

Step No. 2 - Assuming your process is varying randomly (read: predictable) and capable of meeting the spec, run a control chart over time. For example, sample five consecutive pieces with a frequency of 1 hour. You can use the control limits from your capability study and plot points as you go. Assuming the operator has adjustment control over the process, he/she can use this "real time" control chart to make adjustment decisions.

Personal note: All of the quality buzzwords are nothing more than a way to make consulatnts money. Every single statistically based quality program owes its roots to Deming. Save yourself many thousands of dollars and a lot of frustration (consulants have to make you feel "stupid" for the first few sessions to justify their full fee) by going to the library and reading some of Deming's books. His students wrote some, too and they are worth reading.

You'll learn that sigma is a measure of variation about it's mean and that it's value is not a constant; it changes with each process and can be calculated quite simply.

You'll learn that your own fear of the unknown is the biggest roadblock to quality improvement --- not lack of knowing a formula to calculate PPM based on some fictitious sigma value.

Finally, you'll learn that there is no rocket science involved here (no matter WHAT the thousands or "quality consulants," statistical guru's and black belts would have you believe).

--------------snippo------------

Comments, folks?

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Sam
Forum Contributor

Posts: 244
From:
Registered: Sep 1999

posted 07 February 2000 08:53 AM     Click Here to See the Profile for Sam   Click Here to Email Sam     Edit/Delete Message   Reply w/Quote
"Every single Statistically based . . . . to Deming"
Try "Shewhart" Deming and Juran were students, as well as many others.

"Consultants make you feel stupid"
Only our own lack of self worth can do that.

Some consultants may be overbearing/overzealous in there actions, but I have not met one yet that is not committed to there job.

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Brian Dowsett
Forum Contributor

Posts: 35
From:Waterford, Ireland
Registered: Nov 1999

posted 07 February 2000 12:10 PM     Click Here to See the Profile for Brian Dowsett   Click Here to Email Brian Dowsett     Edit/Delete Message   Reply w/Quote
Well thanks a bunch to whoever wrote this. As a "blackbelt" I feel quite insulted by these comments. I don't think there is any need to make blanket assumptions about people based on what training course they attended.

[This message has been edited by Brian Dowsett (edited 08 February 2000).]

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Marc Smith
Cheech Wizard

Posts: 4119
From:West Chester, OH, USA
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posted 07 February 2000 01:41 PM     Click Here to See the Profile for Marc Smith   Click Here to Email Marc Smith     Edit/Delete Message   Reply w/Quote
Brian: None of this is personal. The beginning post was from:
From: aschlo3307@cs.com (ASchlo3307)
Newsgroups: misc.industry.quality

I re-posted this as an excerpt from a news group. I, being a consultant, are to some degree 'insulted' as well - which is in part why I posted it. Personally I have a fair amount of respect for someone who goes thru the Black Belt program - I would like to have the opportunity some time. But let's not get into that here. Rather have comments such as agree or not, with what and why.

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BRoyal
Forum Contributor

Posts: 22
From:Charlotte, NC
Registered: Nov 98

posted 07 February 2000 07:34 PM     Click Here to See the Profile for BRoyal   Click Here to Email BRoyal     Edit/Delete Message   Reply w/Quote
Speaking of Six Sigma, found out today that my company is shipping me off to "Master Black Belt" Training.

Has anyone been there? What should I expect? There will be four week-long sessions, spaced a month apart.

As for consultants, the ones I have worked with, without exception, have been very earnest and bright men and women, who freely shared their knowledge and experience. The problem was the usual lack of upper management involvement.

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Brian Dowsett
Forum Contributor

Posts: 35
From:Waterford, Ireland
Registered: Nov 1999

posted 08 February 2000 03:21 AM     Click Here to See the Profile for Brian Dowsett   Click Here to Email Brian Dowsett     Edit/Delete Message   Reply w/Quote
To Mark,
Please accept my apologies for attributing the orignal text to your good self, I've edited out any references to "you"!

With regard to the next message from BRoyal, I'd say that your company is almost certainly sending you on blackbelt training, based on the course duration (exactly the same as my own). Master blackbelts are those who train blackbelts, I couldn't see you being sent to learn this without doing the blackbelt first.
The training will be to learn quality improvement tools, both "soft" and statistical, and will involve you applying these tools to a real project in between the sessions. (The first day back is spent presenting your work to date to the group).

Hope this helps and sorry for jumping to a wrong conclusion with Mark.

Cheers

Brian

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