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Where did "breakpoint" analysis come from? AIAG MSA book

M

mwohlg

#1
Hi all,

I've done some searching in the forums for information about the RPN breakpoint calculations, the section of the (somewhat common) GR&R form that evaluates whether the gage system is acceptable for use when the R&R is between 10% & 30%. I'm asking because no calculation like this is in the AIAG MSA book, it only says "may be acceptable based upon importance of application, cost of measurement device, cost of repair, etc." (page 77 MSA 3rd edition). So far I've only found one poster who attributed the breakpoint calculations to Delphi. Does anyone know anything else about this?

If you're curious, I've got a caliper being used for some part quality inspections with a GR&R of 11.73% and a breakpoint of 9.39, well below the cutoff of 37.8, but my customer won't accept without an improvement plan for the gage.

Thanks,
Mike
 
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Stijloor

Staff member
Super Moderator
#2
Hi all,

I've done some searching in the forums for information about the RPN breakpoint calculations, the section of the (somewhat common) GR&R form that evaluates whether the gage system is acceptable for use when the R&R is between 10% & 30%. I'm asking because no calculation like this is in the AIAG MSA book, it only says "may be acceptable based upon importance of application, cost of measurement device, cost of repair, etc." (page 77 MSA 3rd edition). So far I've only found one poster who attributed the breakpoint calculations to Delphi. Does anyone know anything else about this?

If you're curious, I've got a caliper being used for some part quality inspections with a GR&R of 11.73% and a breakpoint of 9.39, well below the cutoff of 37.8, but my customer won't accept without an improvement plan for the gage.

Thanks,
Mike
Can anybody help?

Thank you!
 
Last edited:

Jim Wynne

Staff member
Admin
#3
Hi all,

I've done some searching in the forums for information about the RPN breakpoint calculations, the section of the (somewhat common) GR&R form that evaluates whether the gage system is acceptable for use when the R&R is between 10% & 30%. I'm asking because no calculation like this is in the AIAG MSA book, it only says "may be acceptable based upon importance of application, cost of measurement device, cost of repair, etc." (page 77 MSA 3rd edition). So far I've only found one poster who attributed the breakpoint calculations to Delphi. Does anyone know anything else about this?

If you're curious, I've got a caliper being used for some part quality inspections with a GR&R of 11.73% and a breakpoint of 9.39, well below the cutoff of 37.8, but my customer won't accept without an improvement plan for the gage.

Thanks,
Mike
What is the "breakpoint" you're referring to? What do the 9.39 and 37.8 numbers mean?
 
M

mwohlg

#4
In one of the Gage R&R forms that seems to be pretty commonly used here in the Cove, there is a section that calculates a "breakpoint". If the GR&R is more than 10% but less than 30%, the gage would be considered acceptable if the breakpoint is less than 37.8. The breakpoint is the RPN (from the PFMEA) for the characteristic in question times the GRR.

In my situation our GRR is 0.1173 (11.73%) and the RPN is 80, so the breakpoint is 9.39, well below the limit of 37.8.
 

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Jim Wynne

Staff member
Admin
#5
In one of the Gage R&R forms that seems to be pretty commonly used here in the Cove, there is a section that calculates a "breakpoint". If the GR&R is more than 10% but less than 30%, the gage would be considered acceptable if the breakpoint is less than 37.8. The breakpoint is the RPN (from the PFMEA) for the characteristic in question times the GRR.

In my situation our GRR is 0.1173 (11.73%) and the RPN is 80, so the breakpoint is 9.39, well below the limit of 37.8.
I've never seen that breakpoint thing being used, and using the RPN from the PFMEA as a multiplier doesn't make much sense to me. It's a misguided attempt to quantify something that probably can't be quantified in a meaningful way. Unfortunately, there are customers who believe that the AIAG acceptability breakdown is inviolable scripture when in fact it's mostly arbitrary and of uncertain provenance. The best thing you can do is rationally explain to the customer that whatever risk there is in using the gage/measurement system is made negligible in terms of what would be required to improve it.
 

Miner

Forum Moderator
Staff member
Admin
#6
I remember seeing it once here in the forums, but had never seen it used then or later. I also am very suspicious of a method based on RPN numbers because the RPN numbers depend on the scales used, the interpretation of each scale by the users etc. The absolute value of an RPN is not important. It is only used to rank and prioritize improvement efforts.
 
E

equesnel

#7
Agreed..I would suggest sticking to a know standard and accepted approach to assessing the GR&R of your gauge.

The AIAG-Manual is very good at giving required forumulas and techniques.

I would use RPN for PFMEAs only and would wonder why there is a need to complicate an already approved and accepted method for GR&R calculation???

Just my 2 Cents worth.
Eric
 
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