New to Metrology and told to complete Gage R&R with AIAG compliant software

Miner

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#11
Re: New to Metrology and told to complete Gage R&R

The key I mentioned above is making sure those 10 parts represent the full range of your spec, or you may fail because you don't have much part-to-part variation in the analysis. If your spec is "5.0mm +/- 0.5mm", try to include a part around 5.5mm and a part around 4.5mm in your 10-part trial.
While the rest of the advice was fine, this may be bad advice depending on the metric in which you are interested.

If you are using the measurement device for part inspection and are using %Tolerance as you metric this is acceptable. However, if you are using the device for process control, the parts should represent actual process variation. They should never be hand selected to increase that variation just to pass %Study Variation or ndc. In fact, the best approach is to use the results from a capability study and use %Process Variation in lieu of %SV.
 
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Miner

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#12
Re: New to Metrology and told to complete Gage R&R

Parts... 10 parts, 3 trials by 3 operators. But with regards to the parts do we measure all features relating to drawing/ customer requirements but using the lowest tolerance and then randomly choose the dimensions to input into the GRR template? Do they have to be the same part? .
At the worst case, with an unreasonable auditor, you any need to do those dimensions listed on your control plan. However, you should be able group similar dimensions measured by the same device. See my blog on creating gauge families, specifically:
If gauges are used for inspection, state the smallest tolerance at which an acceptable % Tolerance may still be achieved

Validation of the software. This was one of our non conformance's from the audit. I have read through Miner's blog and tried to understand the Ford validation but to validate the software is it as simple as input the data from the Ford document into the GRR template? Or do I have to provide some form of reasoning and method as to how I came to the conclusion that the template is AIAG compliant? Miner's template has the readings from the manual and shows results.
For standard ISO/TS audits, showing that the template provides correct results using the Ford data set should be sufficient. I cannot speak for any special requirements in the medical industry.
 
G

Grimaskr

#13
Re: New to Metrology and told to complete Gage R&R

However, if you are using the device for process control, the parts should represent actual process variation. They should never be hand selected to increase that variation just to pass %Study Variation or ndc. In fact, the best approach is to use the results from a capability study and use %Process Variation in lieu of %SV.
The reasoning behind my advice is two-fold:
1) In my experience, AIAG and automotive industry auditors/customers tend to focus on a "good" measurement system being <10% Study Variation. I see people exceed 10% Study Variation by simply not having enough part-to-part variation in their process and MSA.

If my spec is is +/- 0.5mm, but my process tends to run +/- 0.1mm... the 10 production parts I grab may lead to an ugly %SV on a measurement system that is perfectly capable of discriminating +/- 0.5mm.

I assume where you are coming from is that accurate SPC on your process variation within that tighter +/- 0.1mm process range might be poor and that's a very good point, if that's a concern.

However, a measurement system that can tell good parts from bad parts is often more of a concern to customers/auditors than a measurement system that can accurately accurately control-chart a process that runs well-within the spec limits.

2) From a practical standpoint, measurement error out at your specs should also be of interest to you and your customer. I like to have at least 85% of spec range covered to predict linearity of my measurement system through the entire range of my spec limits.

Anyway, there are a lot of nuances when you start getting deeper into all of this. I just wanted to warn Brackish about an issue I see very often: you grab ten parts from production, they don't vary hardly at all because they are grabbed at the same time from the same batch, your part-to-part variation is tiny, and next thing you know... your %SV is >70% and your auditors/customers are freaking out.
 

Miner

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#14
Re: New to Metrology and told to complete Gage R&R

Grimaskr,

You appear to be coming from a parts inspection perspective. That's fine and your advice is legitimate if your only interest is in % Tolerance. PERIOD.

As I stated previously, measurement devices may also be used for SPC, or only for SPC, in which case the appropriate metric is one of %SV, %PV or ndc. In these cases, your advice would be incorrect. It would wrongly inflate the study variation making these metrics appear better that they actually were. Deliberately doing this with full understanding of the implications would also be unethical.

My issue with your post was that you were offering blanket advice, which really applies to a very specific scenario.
 
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B

Brackish

#15
Re: New to Metrology and told to complete Gage R&R

View attachment MSA 4th Ed with ANOVA Vernier 0-150mm Actual.xlsx Afternoon!

Ok I have conducted the GRR on a digital vernier caliper and was wondering if some one could breakdown the numbers for me?

*I have changed some of the decimel places so it displays the results as per the manual. (Had to show an additional method of validation to my manager to try and play safe).

The way i see it is that we have issues with the operators and that the parts are showing to be closer to the USL rather than the nominal?

I really can not thank you enough for all the help provided! Also, Miner, your template and blog has been fantastic but once this is all done, pass or fail I will continue to learn the GRR MSA as a side project at work so I can learn to help control and address issues.

Thank You,

Brackish

Ps. Looking at the Curve graph... it is pretty bad.
 
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Miner

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#16
Re: New to Metrology and told to complete Gage R&R

It looks like you have problems in both repeatability and reproducibility, but the issue is greater with repeatability (EV). This is the harder if the two to address. Part of this may be with the measurement device itself, part with the procedure, and part may be due to the variation within a single part.

Let's use internal diameter as an example and assume that the ID is not a perfect cylinder but is actually elliptical in cross section. A random ID check might pick up the major diameter one time, the minor diameter the next, etc. All of this variation will appear in repeatability.

The reproducibility problem may usually be addressed by a well documented procedure and training to that procedure. Operator issues will be easier to diagnose after you address the repeatability issues.
 
B

Brackish

#17
Re: New to Metrology and told to complete Gage R&R

Thank you for the clarification Miner.

I looked at the part (a nylon washer used to bond to carbon fibre) and the ID has poor circularity which explains the results.

Our production parts are carbon fibre which are classed as hand made parts. Trimmed partly by hand and partly by CNC depending on the project and some parts are measured by vernier or micrometer but majority are measured using the CMM portable arm. The last person to try and conduct the GRR used spheres on a chassis and used say the X value but that did not fall in with the 10-3-3 guideline. Now I have me as the only competent CMM arm user.

I will try the vernier GRR in the morning with a stem (?) pressed metal bracket and a newer vernier to compare the results to what I have gotten today.

Ps: I fell asleep at my computer reading the 4th edition manual...:lol:
 
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