Gage R&R Anova Report

pmwong

Involved - Posts
#1
Maybe someone will be able to shed some light on this report (pls refer attachment). We receive this format from our customer that we need to submit to them, as our understanding, based on the data, there is no much variation, but the ANOVA Report shows that the total variation is more than 90% and our gage system needs improvement.

Is there something wrong to this format that they have send us? Maybe some expert out there can advise.

regards
 

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martin elliott

#2
I have punched the data into my GRR pack and come up with very simular values. As I have noted with all the different anova packs some very minor discrepencies can occur I suggest someone with MINTAB checks it.

I will bow to those with greater knowledge, but on the face of it, the parts are too good with virtually no significant difference part to part. Thus the error within an operator, and within part, measurements becomes dominant.

Did these parts really represent the full range actually seen in manufacture? The selection of parts is critical to get any sense from this type of study.

The other issue is 200mm caliper, the results are better than I would get on a single part with some of my operators using such an instrument and a 3 digit micrometer might give more sensible readings.

However if the range is really as reported, then it is basically saying your instrument is inadequate for detecting change for the control of SPC features.
 

Miner

Forum Moderator
Staff member
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#3
I agree with Martin. This gage is acceptable for Pass/Fail inspection, but not for process control (SPC) use because it cannot distinguish one part from the next. The logical question posed by Martin is: does the part variation truly reflect the variation of the process? If this is the true process variation, you need a better gage for process control. If it does not reflect the process variation, you need to collect more samples that do reflect it and repeat your study.
 

pmwong

Involved - Posts
#4
Thanks for the feedback guys, but the question here is when we send them the ppap package which includes the gage GRR (in this case is the caliper), they have rejected the ppap package bcos the ANOVA report shows our caliper needs improvement, but in reality its not based on the data given.

So, now I am assuming that they just look at the report and not the data.

Is there any other ANOVA Method packs that I can use as you have mentioned different anova packs have some discrepencies.

Any other advise to convince to our customer that the gage is good condition and not improvement in needed.

regards
 

Ron Rompen

Trusted Information Resource
#5
What your R&R report shows is that the gauge selected may not be able to properly tell the difference between a good and bad part; they ARE looking at the report and the data.

A caliper is a good instrument for 'large' tolerances, but is not (in my experience) suitable for precision measurement and SPC analysis.

I would recommend investigating another measurement method (you didn't indicate what the characteristic being measured was) that is more appropriate.
 

Miner

Forum Moderator
Staff member
Admin
#6
pmwong said:
Thanks for the feedback guys, but the question here is when we send them the ppap package which includes the gage GRR (in this case is the caliper), they have rejected the ppap package bcos the ANOVA report shows our caliper needs improvement, but in reality its not based on the data given.

So, now I am assuming that they just look at the report and not the data.

Is there any other ANOVA Method packs that I can use as you have mentioned different anova packs have some discrepencies.

Any other advise to convince to our customer that the gage is good condition and not improvement in needed.

regards
You need to explain what you mean by "... but in reality its not based on the data given."

At this point, I agree with Ron's comments. If I were in the customer's position, I would make the same decision. It sounds like you have an acceptable alternative in the mic. Why do you not want to use it?
 
M

martin elliott

#7
pmwong said:
Thanks for the feedback guys, but the question here is when we send them the ppap package which includes the gage GRR (in this case is the caliper), they have rejected the ppap package bcos the ANOVA report shows our caliper needs improvement, but in reality its not based on the data given.

So, now I am assuming that they just look at the report and not the data.

Is there any other ANOVA Method packs that I can use as you have mentioned different anova packs have some discrepencies.

Any other advise to convince to our customer that the gage is good condition and not improvement in needed.

regards

MINITAB is a recognised package used for all Gage R&R etc which is why I suggested someone else try your data, but I don't think it will significantly alter the position here.

I would agree with Ron and Milner and also REJECT the study if it was for SPC control.

Like them I don't understand your comment regard the data origin. For SPC control the selected parts MUST represent the true range seen in a production process and YOU MUST NOT select your test parts to have minimum variation from one to annother. If you do not select correctly, you are serously wasting your time.:nope:

If these parts do represent the true spread, then the measuring instrument needs to be more accurate and with a greater resolution to see any differences. A 200mm caliper is conventionally plus minus 0.02 and you are not seeing even that variation in the parts. As a good start you will need a resolution one tenth of the variation
 
A

Atul Khandekar

#8
A related question

Calculations are correct. I just ran the data throgh our software.

Just to add to what martin, Miner and Ron have said:

Your parts range is 0.04 against tolerance of 0.26 (about 15%). This probably means parts have not been selected to cover the entire range of tolerance. On the other hand it is possible that you cannot select parts spanning the tolerance range because your process capability is so high (low process variation) that there is not much difference in the parts even if you cover the entire 'process range'. If this is the case, your GRR will be high. The results tell us that this measurement system is no good for the purpose of process control and that it cannot adequately detect part-to-part variation. My question is: is it your topmost priority to improve the measurement system if you do have a high Cp ?

Also see:
http://elsmar.com/Forums/showthread.php?t=12113
http://elsmar.com/Forums/showthread.php?t=5104
 
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