Gage R&R - Destructive Test - Tensile Tester

D

Denise

#1
Good Afternoon to All,

We are a company that produces flat rolled strip steel. Does anyone know if it is absolutely a must to do R&Rs on Tensile Testers (on final product)? The test destroys the piece.

In the past (prior company), we performed R&Rs by taking the sample tests on pieces from the same strip of steel.

On some of our other measurement devices we have exempted R&Rs. I would like to do this with the tensile tester.

Is it simply our choice to exempt certain devices? Is there any logical reasoning behind it.

We plan to be certified to TS16949:2002 by the end of the year. I can't find anything in the TS spec or the MSA book to give me an answer.

Thanks,

Denise:bigwave: :bigwave:
 
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howste

Thaumaturge
Super Moderator
#2
In the past (on many occasions) I have submitted calibration certificates for tensile testers instead of R&R studies in PPAPs. I have never had a customer reject one. What do your customers say?
 
D

Denise

#3
Howste,

Thanks for the reply. I checked and we do the same. No, none of our customers have ever rejected it.

Is your company certified to QS, ISO, or TS?

Denise
 
N

noboxwine

#4
Absolutely impossible

to do an R & R on destructive equipment. I have always done the same as our friend howste--just submit the calibration certificate. Have a day !:smokin:
 
D

Denise

#5
I should edit my reply.

Is you company tier 1 or 2 to one of the Big 3?

Is your company certified to QS, ISO, or TS?

Do you do verifications on the tensile tester? If so, what frequency?

Denise:bigwave: :bigwave:
 

howste

Thaumaturge
Super Moderator
#7
Originally posted by Denise
I should edit my reply.

Is you company tier 1 or 2 to one of the Big 3?

Is your company certified to QS, ISO, or TS?

Do you do verifications on the tensile tester? If so, what frequency?

Denise:bigwave: :bigwave:
I worked for two different companies. One was tier 1, the other was tier 2. Both were certified to QS-9000. In one company the only verification was an annual calibration by an outside lab. The other company verified the tester on a more frequent basis internally, backed up by an annual outside calibration.
 
D

Denise

#8
Atul,

I want the exemption because I feel that not being able to test the same sample really defeats the purpose of the R&R. It seems like wasted effort just to satisfy a standard.

Now, I can guess what you are going to say.:) :)......

"Is the device reliable? Do the calibrations come back passing every time? What are the results of the R&R? If the results are not good then perhaps I should be checking into that further."

According to the Lab supervisor, there has never been an issue with the tensile machine readings. In his opinion, the device is reliable. It is calibrated regularly. But, the R&R results are questionable. I haven't personally seen the R&R results.

I just don't have any faith in R&Rs for devices that destroy the sample and neither does the Lab supervisor. I am not an MSA guru. So, I've only researched this just recently. It just doesn't seem logical to do the test on different samples. I can't seem to find a satisfactory answer to the destructive test issue. Can you help me out?



Denise
 

Atul Khandekar

Quite Involved in Discussions
#9
No, I am not going to deliver any sermon on why R&R should be done or how it is different from calibration.

You are quite right. There is an issue with destructive measurement systems because parts cannot be tested repeatedly. The MSA manual also is rather ambiguous, esp. if you try to read the section IV of the third edition. However, there are accepted methods of calculating GR&R for such systems. As with any R&R study, it is very important that parts for the study are selected carefully. With certain assumptions about 'homogeneity' of sample parts, Nested ANOVA is usually recommended. Due to the nature of the test, some of the part-to-part variation is always confounded with other components of variation and there is no way you can avoid it. This risk can be minimzed (but not completely eliminated) with proper selection of parts. The basic purpose is to find out if there are any 'undesirable' errors creeping into the measurement due to factors such as appraisers and methods etc - apart from the equipment used. You can then make an attempt to minimize these errors and the risk associated with a fauly measurement system. A carefully done R&R study may well "throw up a surprise or two" and may provide opportunities for improvement. To that extent, it is a waste of efforts.

That said, here are two thoughts that may be worth discussing:

1. Have there been instances when the prduct you okayed was rejected by the customer based on the same test/measurement? Is there a chance of obtaining a fauly measurement even when using a well calibrated equipment? In such case what is the risk that you or your customer can accept? If the measurement system is such that the opertors, the method used or the setup required for testing do not influence the measurement, you can probably argue that calibration is enough. However, you will have to prove that there is no appraiser variation in the system by conducting at least a sample R&R study. Thereafter you can use the Stability Study to monitor the staus of the measurement system.

2. If your process has been stable, highly capable and centered over a long period of time (seen from historical SPC data/charts), then, according to AIAG, there may be no need to study your measurement error from a purely "acceptability" viewpoint. Many times it not economical to try to improve the measurement system beyond a certain point. You can use this measurement system for the purpose of monitoring the process - status quo - only. You will also have to ascertain the ability of the measurement system to detect any special cause of variation in the process.

The bottom line, as usual, is: discuss with your customer. There is no question of faith in the holy book, the standard. IMHO, you can try it out - there's nothing to lose.

One good reference is: "Evaluating the Measurement Process" by Donald J. Wheeler.

You may also try to investigate Shainin's ISOPlot method which some people recommend for destructive Testing (Sorry, I do not know much about it).
 
#10
I work for a tier 2 stainless steel mill. We are going to be certified to the TS standard in October. So far we have no intent on performing R&R studies on our tensile tester and have not had any issues with customers about doing this. All we are ever asked for is a certificate of calibration and SPC. We pull 3 samples / day. These samples come from a single coil and we just have created a boatload of them. Usually last us about 2-3 years before we have to create new ones. We put these results into the computer and the lab techs monitor any trends. They report any unusual points to the lab supervisor and he determines if any action is necessary. Hope this helps.;)
 
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