Is Gage R&R required on a 100% Dimensional Layout?

B

bchapman

#1
I have been asked the following question and am looking for answers. Since our 100% dimensional measurements (performed on the CMM) are on the control plan, do we need to perform a GRR for these? Thanks!
 
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Bev D

Heretical Statistician
Staff member
Super Moderator
#2
are you - or someone - thinking that because you measure each part (instead of a sample of parts) that a GRR is not needed? If so, the sample size of the inspection is not relevant to the applicability of a GRR

Or are you asking about using about using the 'family' of similar characteristics for the GRR so that you don't have to perform a GRR on each individual characteristic?

If so, families of characteristics can be utilized, however, you need to be cautious about how you group them. CMM's are sensitive to the type of characteristic (geometry), the access/touch off path (Spatial), the fixturing method, any within part dimensional differences that can be confounded with other factors, the type of material and the resolution as well as the size of the feature...I have seen two very similar parts (same shape and features just a different size) have completely different GRRs due to some of the factors I listed
 

AMIT BALLAL

Trusted Information Resource
#3
I have been asked the following question and am looking for answers. Since our 100% dimensional measurements (performed on the CMM) are on the control plan, do we need to perform a GRR for these? Thanks!

As per ISO/TS16949:2009, if any measurement technique is specified in control plan, you should do MSA study of that Measurement system.

MSA study of all dimensions won't be required (Don't know whether this is one of your questions, still clarifying).

:2cents:

Regards,
Amit
 
Last edited:
B

bchapman

#4
You say that MSA is not required on all of the 100% dimensional requirements. Let me see if my thinking here is correct. MSA (GRR) needs to be performed on all measurement systems that we end up doing a capability study or SPC charts on. Since we do not do capability or SPC charts for the CMM we do not need to do GRR. Is this correct? Additionally, since the 100% Dimensional does not specifically call out a measurement system per say, we do not need GRR on the dimensionals?
 

Ron Rompen

Trusted Information Resource
#5
bchapman, it appears you have misunderstood some of the previous replies. Whether or not you do SPC or capability on any of the features measured with the CMM doesn't matter - the measurement method is shown on the control plan, therefor you must do MSA on the equipment used for that measurement method.
If you choose NOT to show the CMM on the control plan, that is fine - but then you need to be prepared to define the method you DID use for measurement, and have supporting evidence (MSA studies) for the alternative method(s) used.
Long story short - yes, you need to do an MSA study on the different types of characteristics measured. Bev D raised a very valid point cautioning you about lumping features together without proper consideration .
 
B

bchapman

#6
Okay. Thanks all for the valuable input. My final question is this... I need an MSA study for the CMM machine, but do we need to perform a GRR for every single separate part (automotive reflectors, etc.), every separate PPAP? Or do we just need to have one GRR study on hand for the CMM?
 

Bev D

Heretical Statistician
Staff member
Super Moderator
#7
for clarity (now that you raised the capability/SPC aspect): GRR is to determine if your measurement system is capable of distinguishing passing parts from failing parts - this applies to capability studies AS WELL as and even more importantly for your inspection testing that accepts or rejects parts as conforming to the specifications. GRR also helps you understand if your system can distinguish between parts well enough to detect true process changes for SPC.

as for your final question: I and others have addressed this by discussing the 'family' question. So I'm wondering what your real confusion is on this point? (it is NOT sufficient to perform a single GRR on 'the CMM')

From my earlier post: "families of characteristics can be utilized, however, you need to be cautious about how you group them. CMM's are sensitive to the type of characteristic (geometry), the access/touch off path (Spatial), the fixturing method, any within part dimensional differences that can be confounded with other factors, the type of material and the resolution as well as the size of the feature...I have seen two very similar parts (same shape and features just a slightly different size) have completely different GRRs due to some of the factors I listed "
 
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