PPAP - What are the Gage R&R Requirements?

[CarolX]

PPAP and R&R

Hello Fellow Covers,

I am in need of some help...

I wasn't real sure where to post this…..but I thought this would be the right spot.

We have a customer who is implementing PPAP for all new parts (non-automotive). Here is what they say about Gage R & R:


"All equipment used for inspection as listed on the control plan must have an associated Gage R&R or measurement study (except where visual inspection is used.) Equipment without Gage R&R should then have calibration records provided."

Ok….so I have 2 questions

1. "All equipment used for inspection as listed on the control plan" Does this mean that I am to do a R&R on ALL of my calipers? Or is doing one set sufficient?
2. "Equipment without Gage R&R should then have calibration records provided." Is this a standard "out" for PPAPs? My preference would be to just submit my cal records.

The document package from our customer looks like a "canned" package.

Any input is greatly appreciate.

Regards,
CarolX

 

[Atul Khandekar]

My understanding is that calibration cannot be a substitute to R&R. R&R is not just about gages. R&R study really establishes if the measurement system as a whole - appraisers, methods, environment, fixtures and gages etc - is suitable for the measurement in question and whether any of the components of the measurement system introduce any variationin in the measurements. I believe there is a 'requirement' that R&R studies should be conducted for all the instruments referenced in the control plan.

Apparantly, there is also a way of doing R&R for a 'family' of gages - kind of a representative R&R study. You must be able to prove that the gages, fixtures, environment and process variation/tolerances on the parts measured - are similar. (That still leaves the question of Operators and how they handle the the gages - appraiser variation - open to question.)

Whether R&R is required for ALL your calipers - IMO, this question would be best answered by your customer. That would depend on what concessions the customer is willing to make.

 

[howste]

I've done R&Rs for "families" of gages before, but only if they were the same make & model. As far as calibration goes, it's only an alternative if you can't reasonably be expected to do an R&R. An example would be a tensile tester that does destructive testing. You can't measure the same sample multiple times, but you can calibrate the load cell. Of course like Atul mentioned, the key is to find out what your customer will accept.

 

[db]

R&R is not just about gages. R&R study really establishes if the measurement system as a whole - appraisers, methods, environment, fixtures and gages etc

Precisely!

 

[CarolX]

thanks

As usual, you guys are the best! Thanks you very much for your replies.

When performing R&R, is it customary to test "everything"?

For example....We have about 30 calipers and at least as many people that use them to perform some type of inspection (1st piece, in-process checks, final inspection). Does the gage R&R encompass all?

Just trying to learn more....enough to be dangerous....LOL.

CarolX

 

[Al Dyer]

Carol.

In your spare time

Run an R&R on all the calipers (various appraisors) and plot the results on a variables chart. It is a good visual for an overview of gage and appraisor error. With whichever system (Cp, CpK, etc...) you can show gage capability and appraisor.

We used this process as a training tool in our gage class and really opened peoples eyes!

Good Luck, Al...

 

[howste]

I would do R&R studies with a "representative sample" of gages and a "representative sample" of operators. I've never seen an R&R done with 30 people, though I'm sure it can be done. Your studies should take into consideration the range of tolerances that are required.

 

[Al Dyer]

Howste,

Sorry I was unclear

I meant to do GR/R on the 30 sets of calipers with 3 random appraisors chosen for each set.

Although I think 30 appraisors "could" do an R&R I believe it would lead to highly increased appraisor error.

Hmmmmmmmmmmmmmm, I might try it!!!

Al...

 

[Atul Khandekar]

Re: thanks

Originally posted by CarolX
For example....We have about 30 calipers and at least as many people that use them to perform some type of inspection (1st piece, in-process checks, final inspection). Does the gage R&R encompass all?

This is probably one of the reasons MSA is considered to be a big pain!
How many apparaisers use each of these calipers? I would agree with Al here. IMO, if you plan out the frequency / timetable for studies, and assign proper responsibilities, it should not be very difficult to get them done. Use a good software to take the drudgery out of complex calculations.

 

[tomvehoski]

I see R&R for a gage system built around a single part/assembly as a valuable tool. For example, if you have a gage dedicated to checking a single part (or feature) for a continuous process. It would make sense to perform a gage R&R using the part measured, and the operators that typically do the measurement.

When you get to a situation where a gage may be used for hundreds of parts/features, R&R becomes less valuable or more time consuming to do properly. We used to do them in our receiving inspection department where a micrometer might check dozens of parts. It was not practical to do a R&R on every part, but we did some experiments and found that variation did change based on the part. Using a micrometer in a stand gave less variation than holding it. Of course this was not convenient for most parts, so the R&R was about the only inspection ever done with the stand. I set up the % variation calculation somewhat backwards. On each R&R sheet there were multiple sample tolerances. We could do a quick check and find that a caliper was OK for a .010 tolerance, but too much variation for a .004. Again we normally based this on a common or easy to measure part, so there is no telling how accurate these measurements were for EVERY part.

Now if you have 30 appraisers using calipers, I think the only true correct method would be to have all of them participate in the study. If 3 out of 30 do not know how to use the gage, you have 10% of you inspections suspect. Not many places have the time to do this detailed of a study.

The MSA manual does allow for some common sense approaces to gage R&R. Also look at tolerances and how critical the part is.

Tom