MSA Study Types - How to make an informed decision about a gauge

P

PPAPtastic

#1
I am attempting to determine whether a gauge used in our production facility is acceptable - both for setting up the line and for measuring product during improvement projects.

We have decided to do two studies:

1) Using 'known' prepared and marked (to ensure measurement of sample in same location) samples within a very small range, conduct a basic Gage R&R study to determine gage resolution/accuracy in distinguishing between small product variation.

2) Using 'unknown' unprepared samples (operators will do all normal prep) representing the normal process variation, conduct another basic Gage R&R to determine the usual suspects (repeatability, reproducibility, etc).

Does this sound like a logical start? What other analyses can be done with the gathered data to make an informed decision about the gauge?

Thanks!
 
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Miner

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#2
Option 2) would be the standard approach to determine whether the gauge is acceptable for the current process. This would include whether the resolution is adequate.

Regarding Option 1), the marking of the parts to ensure consistent measurement location would be a good approach for improvement if Option 2) is not acceptable. However, deliberately selecting parts with a narrower range of variation does not really serve a useful purpose unless you expect to reduce the actual process variation to that level and want to verify that the gage will still be useful.
 

bobdoering

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#3
Miner is correct, although I would state that you get your samples per option 2 (you need as wide of a variation to test the ability of the gage - it is not a calibration!), you mark them to ensure you are measuring the same spot as indicated in option 1.(You want to know the variation from the measurement system, not from the part. The variation within the part is not the gage's fault! That is a process capability problem.) You should get the resolution (ndc) and accuracy data you need.

Make sure the operators you use are also the widest variety likely to use the gage. Otherwise, the test will not stand the test of time, and you will fall into the trap of doing them over again when new people show up to use the gage. Gage R&Rs using the widest variety of potential operators should not have to be repeated over time - there is no time function to a gage R&R.

Doing two studies may be academically interesting, but as a rule it will become a burdensome overhead.
 
V

Vicman

#4
I will suggest doing a BIAS and a Linearity study first, this way you will see how accurate is your gage.
An after a R&R study will complete the analysis.
 

bobdoering

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#5
I will suggest doing a BIAS and a Linearity study first, this way you will see how accurate is your gage.
An after a R&R study will complete the analysis.
I agree - in essence, always make sure the gage is calibrated before the Gage R&R study.
 
P

PPAPtastic

#6
Interesting replies -

The gauge is calibrated on a regular basis. No issues there.

The reason for the two studies (at least in my mind :confused:) :

The first study is to ensure that the gauge can decipher between tiny variations in the part as we will be using the gauge during product/process improvement projects which involve modifying the part in small increments. Thus the need to pick parts within a very small tolerance range.

The second study is to bring in the operator variation and see how it affects the overall capability of the gauge.
 
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bobdoering

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#8
If gauge passes in bias & linearity but fails in R&R. What stand to be taken against the evaluation method
:mad:
Well, you can't blame the evaluation method - you need to determine the issues that cause the failure.

It shows that the gage is not suitable for the specific geometry of the actual part, or that there is too much operator influence for that gage to be effective for the dimension.

First, you have to be sure the gage R&R procedure measured the same location of each part - as indicated in the previous post. Then you need to OBSERVE the operators, to see if they are using the gage correctly, or if there is any differences in their usage that can be better controlled with training. Do they run into manipulative, bias, or observational error in their usage? Can it be minimized?

Is the gage influenced by the part? Are there cantilevered loads influencing the gage measurement? Are there corner radii that are influencing the measurement?

If these errors can not be better controlled, then you need to go to another type of gage that does control or eliminate those errors. It is the whole point of the exercise!
 
E

Erik Alburg - 2009

#9
For production option 2 is clearly the best. The Gage R&R is used to determine the components of the "measuring process" not just simply the gauge. The measuring process includes having the operator determine where to measure and which numbers to record. Obvious you want to test parts throughout the range of production.

For you "mini" resolution test, you could use the variation numbers from the repeatability and reproducibility of the production R&R if you make the assumption that the Gage performs the same across the entire range of operation. You are taking a certain amount of risk when doing this, but it could save you some time in performing another Gage R&R. Instead of comparing the %R&R variation to the Spec, compare it to an estimate of the "small" variation that you expect to see.

My :2cents:
 

bobdoering

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#10
The first study is to ensure that the gauge can decipher between tiny variations in the part as we will be using the gauge during product/process improvement projects which involve modifying the part in small increments. Thus the need to pick parts within a very small tolerance range.
I think this would be a good way to determine the issue you are pondering. Keep an eye on the ndc calculation - or your parts by appraiser plots.
 
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