Dueling Metrology Labs - Two different labs telling you two different things

Klutz

Registered
#1
What do you do when you have two different labs telling you two different things? I had some samples sent to a metrology lab that I then sent to another lab for verification of the results.

The test was to look at effective case hardness (measure with HV.5 and convert to HRC). Lab #2 measured and reported on Lab #1's imprints and took new readings on areas that failed. The labs are in agreement that the parts are not to specification, but I am getting different values of results.

I understand that if the heat treat was bad, different areas will have varied hardness readings, but the measuring prior indents should be the same, not 7.7 HRC different.

I am at a loss as to what to do next. Any advice would be greatly appreciated.
 
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Big Jim

Trusted Information Resource
#2
What do you do when you have two different labs telling you two different things? I had some samples sent to a metrology lab that I then sent to another lab for verification of the results.

The test was to look at effective case hardness (measure with HV.5 and convert to HRC). Lab #2 measured and reported on Lab #1's imprints and took new readings on areas that failed. The labs are in agreement that the parts are not to specification, but I am getting different values of results.

I understand that if the heat treat was bad, different areas will have varied hardness readings, but the measuring prior indents should be the same, not 7.7 HRC different.

I am at a loss as to what to do next. Any advice would be greatly appreciated.
Get a 3rd opinion.
 

Ron Rompen

Trusted Information Resource
#3
Hardness measurement (particularly when doing Vickers microhardness) is never an exact thing - how much variation did you get between the two labs readings?

Did they both provide the raw data (i.e. the size of the indentation)?

Do they both use the same type of equipment and measurement process, or is one of them an automated measurement?

Did they both use the same conversion factors?

Just a few things to consider.
 

normzone

Trusted Information Resource
#4
Not my area of specialty, but did the second lab attempt measurement in EXACTLY the same area as the first? I'll wager one could not get the same reading twice using that approach.

Oh, and what [Ron Rompen] said. What little experience I have measuring Rockwell hardness showed variation, even using the same sample and me being the only operator.

Do you have another known good piece you could repeat these tests with? If material in spec delivers a similar pattern of readings, then you'd know ....


.... that they were similar patterns of readings. Sorry, I got nothing. Long week. Have a good weekend all. :popcorn:
 

Hershal

Metrologist-Auditor
Staff member
Super Moderator
#6
Based only on the post, it appears you ran an informal ILC. That is your right.

Now, the blocks should first have been calibrated by at least an accredited lab, ideally a higher level lab. Then you have sufficient information for a statistical analysis of the labs to the reference lab.

That would give you the results as to which one to do business with.

Hope this helps.
 
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