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  Statistical Techniques and 6 Sigma
  SPC all the time

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Author Topic:   SPC all the time
Wavie Davie
posted 20 March 2001 06:15 PM           Edit/Delete Message   Reply w/Quote
Am I correct in thinking that QS9000 states that some kind of statistical control must be conducted on all processes? If you can prove capability over time, can you gauge check ect?

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Al Dyer
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Posts: 622
From:Lapeer, MI USA
Registered: Oct 2000

posted 21 March 2001 01:40 PM     Click Here to See the Profile for Al Dyer   Click Here to Email Al Dyer     Edit/Delete Message   Reply w/Quote

The requirement is to determine "applicable" statistical techniques during the APQP process. If determined that they are needed they are to be included in the control plan (4.20)

Applicable? This is defined by by the end user. The end users are both internal and external customers. (ie op 200 is the customer of op 100)

Although the words SPC are not directly addressed by a shall statement (alluded to in 4.9.1) I would be hard pressed to explain to an auditor by we wouldn't use some type of statistical control.

When determining what statistical techniques are needed to control the system, don't limit yourself to the usual X-R type charts. Any type of methodology or report that tracks some type of numerical value or trend is a statistical technique.

Possible Statistical Techniques:

Expedited freight cost graph
Late delivery graph
Prioritized reduction list for FMEA RPN's
Machine uptime graphs
Cost of quality trends
PPM reports
In-process scrap reports


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Wavie Davie
posted 02 April 2001 01:58 PM           Edit/Delete Message   Reply w/Quote
OK. I think i get that.! We do all that stuff, monitoring systems and so on, but maybe this example may explain my problem beter.

I have a process, a moulding machine, now we conduct SPC on a certain dimension, the dimension that showed the lowest cpk at PPAP stage. Since then, we have conducted spc and recalulated cpk regularly. The cpk has alway been maintained or betered, currently appro 12!!

So, i decide we are probably monitoring the wrong dimension, but a full cap study on several dims only shows a higher cpk that 12. Can we use gauges only, along with attribute checks, or is it down to the customer. It seems that we may be wasting valuable time.

Thanks for the help.


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Al Dyer
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Posts: 622
From:Lapeer, MI USA
Registered: Oct 2000

posted 02 April 2001 05:33 PM     Click Here to See the Profile for Al Dyer   Click Here to Email Al Dyer     Edit/Delete Message   Reply w/Quote
In this situation I would go by 4.9.2 in the QS-9000 manual, and revise the control plan accordingly.

Then follow the PPAP manual (table 1.3.1 #9) and contact your SQA (or whatever approval authority) for further directions. Take a pro-active approach and tell them what you are proposing, i.e. frequencies, gage types, the capability of the proposed process change, and let them prove you wrong, the worst they can do is say no!

You might be asked to submit a new warrant and control plan. Just make sure you have the backup data to prove your point and bring to the attention of any future auditors (if requested). Sounds like a good situation where you could document some continuous improvement.

Don't forget to review the FMEA!


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