MSA using tolerances - Page 116 of the AIAG MSA manual

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Miner

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#11
CREED said:
DOES ANY ONE KNOW WHAT THE RECOMMENDATION FOR PV% SHOULD BE. ACCORDING TO THE MSA MANUAL, GRR% SHOULD BE UNDER 10% GOOD, 10%- 30% MAY BE ACCEPTABLE, OVER 30% NOT ACCEPTABLE. ndc SHOULD BE GREATER THAN 5. BUT IT DOES NOT GIVE ANY GUIDE LINES FOR PV%.
The guidelines are the same: 10% good, 10%-30% may be acceptable, over 30% not acceptable.

The difference between the metrics is %GRR is the acceptability of the gage for process control (or statistical/capability studies) and P/V is the acceptability of the gage for product acceptance (inspection).

See the following threads for more detail:
http://elsmar.com/Forums/showthread.php?p=124339#post124339
http://elsmar.com/Forums/showthread.php?p=125257#post125257
 
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Chris Willis

#12
Well, this has just caught me out, we have been evaluating a variety of MSA forms that we use worldwide in out organisation.

Using three of the forms and the test data from MSA 3, we chose our form from the German side of the business (it had been adjusted for the new constant values). However when we input data from and old MSA 2 study into the MSA 3 form we found that we had a brilliant GRR.

At this point we were surprised, and almost framed the results. This new form was brilliant, GRR less than 1% of the overall tolerance, I'll have some of that please.

Then the old quality questions triggered in the brain, WHY has this happened. What is different. A line by line reading of the formulae reveals we have an MSA 2.5 form, the constants K1, K2 and K3 have been adjusted to MSA 3, the tolerence calculation has remained at MSA 2. The result, when based on a tolerance calulation we are out by a factor of SIX!

Why is this possible to miss, alas as the MSA manuals only show test data and results based on Total Variation and not Tolerance. So all of our testing showed that all of our calculations were correct and the error slipped through undetected.

Ooops,

Chris
 
A

Atul Khandekar

#13
Re: Msa Manual Third Edition

DOES ANY ONE KNOW WHAT THE RECOMMENDATION FOR PV% SHOULD BE. ACCORDING TO THE MSA MANUAL, GRR% SHOULD BE UNDER 10% GOOD, 10%- 30% MAY BE ACCEPTABLE, OVER 30% NOT ACCEPTABLE. ndc SHOULD BE GREATER THAN 5. BUT IT DOES NOT GIVE ANY GUIDE LINES FOR PV%.
The measurement system is supposed to be able to detect variation in parts (PV). Most of the observed study variation should be contributed by PV. This ability is reduced by the presence of GRR error. The standard acceptance criteria (%GRR/TV) are based on ratios of standard deviations. You should also consider the Variance Contribution (ratio of squares of standard deviations: Adds up to 100%). The worst case 30% GRR is roughly equal to 10% contribution which means 90% contribution by PV. A 10% GRR would mean variance contribution of 1% by GRR error and 99% PV.
 
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khowell

#14
We are preparing gage R&R for Percent Tolerance, and have converted from MSA v2 to MSA v3. I have specifically referenced this forum to our customer for the changes between the versions.

I have received back a question that when using the v3 K1, K2 & K3 constants as they are found in the book, doesn't that provide a 1-sigma result and you still need to multiply by 6 to get to 6-sigma.

This is one of the last things holding up their acceptance of our results.
Any clarification would be greatly appreciated!
:confused:
 
K

khowell

#18
Thank you! I am not quite sure of the results columns and which would be the 6-sigma %GRR that would typically be reviewed as the 0-10%, 20-30% and over 30%.
Thanks you,
-Kerry:confused:
 

Miner

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#19
I have attached my spreadsheet analysis below. Your worksheet is close, but the appraiser variation is slightly high. Nothing major.

You are correct that the revised k constants give a 1 sigma result, but the formulae where these are used also removed the 6 from the equations, so that the result is the same. This was done to simplify the equations.
 

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