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GRR for a tolerance that has changed

#1
Hi Everyone,

We performed a GRR for a part for a tolerance +/- 0.5 and passed. Now we changed the tolerance to +/-0.6mm. Should I redo or can I keep with the same result of GRR?

All comments are really important.

Cheers,

Luci
 
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Welshwizard

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#4
Hi Lucienne,

Assuming that the tolerance change didn't also involve any change to the manufacturing process or the behaviour of approaching the new tolerance then widening the tolerance width will impact the % tolerance in a positive way if you measure your success by pass or fail.

You can, bearing all the above in mind and for the sake of completeness recompute the numbers with your new tolerance band if you wish but you shouldn't need to redo the test again.
 

Sebastian

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#6
Very good question. Answer relies on your organizational MSA strategy.
Strategy, which can be presented in one of documents required by IATF 16949 - laboratory scope.
In section 7.1.5.3.1 we read, that in this document, we shall identify our capabilities to perform required inspection activities.

So we have measurement systems, that need to be verified using analytical methods, e.g. presented in MSA manual as required by 7.1.5.1.1
Every measurement system has variables.
Let's say, there are at least three variables - equipment, inspected characteristic and characteristic specification or process variation.
This is a basic example.

In your case measurement system consisted of unidentified measuring gauge, unidentified characteristic and characteristic specification +/- 0,5 mm.
MSA result was satisfactory and you can transfer it to your laboratory scope descriptively stating, that "Measuring system consisting of "this" gauge, "this" characteristic and characteristic specification >= +/- 0,5 mm is capable to deliver valid inspection results." Or you can present it in form of table, with following columns: "Equipment", "Characteristic", "Specification".
Then every new/changed measuring system, that meets these criteria is automatically capable and does not require further verification.
Next steps can be searching for this particular measuring system boundaries, asking "What if specification is +/- 0,4 mm? Does a system is still capable?"

You can add another variables (column to above table), as e.g. material part is made of. There is significant difference between measuring with a caliper, internal diameter of part made, one from steel and another one from rubber, where specification for both is +/- 0,15 mm.
Another one could be part weight.
 

Ron Rompen

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#7
I agree with Welshwizard, and have done the same in the past. If the tolerance is changed (either larger or smaller) just rerun the study using your original measured values, and the new tolerance. As long as nothing else has changed (measurement method, manufacturing method, etc) then this should be sufficient.
 
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