Vickers hardness testing - Gage R&R Study for Hardness m/c

Hi folks,

Can anyone help with a method to conduct a R&R study on a Vickers hardness testing m/c?

(We manufacture small rivets)

Thanks in advance.

Geoff

The first rule for performing an R&R study is that the test be repeatable. Any device that is essentially a destruct test such as force gages and hardness testers cannot repeat. Therefore they fall beyond the scope of the R&R study.
Reliability may however, be obtained by applying statistical techniques to show capability of the gage itself. Repeated test that track the results with : Xbar & R charts, and a histogram to show the dispersal of the readings and figuring the Cp, Cpk will provide confidence in the readings. Unforunately, trying to determine how much of the variability in the process is attributable to the device itself is virtually impossible. Comparisons to the calibration standards shown in a graphical format is about the best you will be able to achieve. Luck to ya.

We have a Ford auditor who is demanding gage R & R's on hardness testers. Is there someone out there who has performed one and can help me?

This question has been asked before, but it has been awhile. You may want to do a search in the old forum. Also, EOMs for destructive testing are not unusual. You have to make some assumptions, but it can be done. Some of the texts mentioned in the Bibliography of the MSA manual contain information on destructive testing - one by Donald Wheeler, for instance. In fact, Wheeler's text book (reference 27) should have something in it.

Looking for Details

Anyone have any recent info / comments on R&R in hardness testing?

I would imagine it is possible to use a calibration block for your study. If you knew what hardness value(s) you needed to measure and obtained a certified calibration block for that value, then the Gauge R&R could be performed on that.

I say this because I assume it is calibrated somehow and that the calibration isn't a destructive calibration.

Hardness Tester Calibration

Supposing it is nearly impossible to find an accredited lab to do hardness tester calibration and supposing we perform verification with hardness blocks every time we use the tester which is quite often. The hardness blocks are ground and come with a cert traceable to NIST. We used to get them re-ground but dont anymore because they lose their accuracy. Are we legal if we stop external calibration?

Hardness Tester Calibration

Supposing it is nearly impossible to find an accredited lab to do hardness tester calibration and supposing we perform verification with hardness blocks every time we use the tester which is quite often. The hardness blocks are ground and come with a cert traceable to NIST. We used to get them re-ground but dont anymore because they lose their accuracy. Are we legal if we stop external calibration?

Re: Hardness Tester Calibration

Originally posted by Dawn
Supposing it is nearly impossible to find an accredited lab to do hardness tester calibration and supposing we perform verification with hardness blocks every time we use the tester which is quite often. The hardness blocks are ground and come with a cert traceable to NIST. We used to get them re-ground but dont anymore because they lose their accuracy. Are we legal if we stop external calibration?

Click to expand...

What quality system(s) do you comply with currently?

If you are using hardness blocks that verify the bottom, middle, and top of the range in which you use the tester, you have established range and linearity of the machine. It's been a while, but I also remember checking the indicator separately on the old Wilson gages, as the gear teeth do tend to wear in the range that it is most often used (this would only be done periodically though). The main thing is to write a procedure outlining what you are doing. You have the components of "external calibration" already in place. You state that your hardness blocks are traceable to NIST, and when you use those, you are transferring that traceability to the machine, which is not only legal, it is what your outside vendor is doing!

Ryan

you can perform an internal calibration using hardness standard test block. in our company, we use vickers test block. it is a destruct test but you can make several destruct tests (hence the R&R ) as it has an area of around 15 x 15 mm compared to the very minute indentation made by the hardness tester.

well, there's my 2 cents.

oh, and this is my first post so hooray to me!