MSA on a Hardness Tester to satisfy a Customer who is requiring Hardness Cpk

S

sc00by

#11
On our MSA Study, the standard value is shown as 87.2 min & 89.2 max.
The standard is marked 88.2 +/- 1.0
OK

I have ordered new USA made & certified test block statndards for HRC & HR15n scales. When the new HR15n standard arrives i will mark 10 distinct areas on it & perform a new MSA.
New master will most likely not improve the result gradually. In our site we have a number of hardness testers and we send them on a yearly basis to the manufacturer for re-callibration, they strip them down, clean and calibrate the transducer so it conforms to their (much tighter) tolerances then certify it to the standard. Do you have such at your place if yes then when was the last calibration of this kit?

You mention a V interesting point. The parts are small threaded insert nuts & are V difficult to measure. Also, after heat treating, the parts are plated & then thermally trated for hydrogen embrittlement. Any valid testing resluts would only be obtainable from 'test' samples of the actual raw bar stock used to make the part. We use the samples to verify the lot but the customer tests the final parts.
Can you use collar of the nut, typically there is some reasonable flat surface for such.
Typically such testing requirements are described in PPAP spec sent by the customer and so if they test it for hardness then you should have common methodology but if PPAP does not show any method then I would suggest to agree with the customer such common procedure so there is no discrepancy between what you measure and what they measure.
If they agree to test samples then it would be the best situation.

The parts are .625" dia x .312" thick. the production run is roughly 2000 parts. they take up V little room in the contractors oven.
Do not just automatically assume that if volume is small then all parts comming out of it are uniform, there is alot to heat treatment that affects final spec, position of the part inside the chamber matters but also the way the part is presented also matters, existence of cold/hot spots.
Is it case hardening or through? If you do case hardening then you may test for stability of the process through the depth of hard case.

The cusotmer will not modify their specification.
Customer requires part hardness spec of such and such, but they don't specify to you exact heat treatment process, do they?

Not likely. As long as material cert is provided our plant manager will always insist purchasing order based on the best price.
He will have to consider this option if client will be close to say "good bye".
What raw material do you use?
Typically you can buy pre-conditioned material so that it's hardness spec is much tighter i.e. you can get EN24 but also you can get EN24T which is hardened and tempered condition.
 
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W

WKHANNA

#12
So, after a few months, I thought I would report back on how all this turned out.

Just to bring everyone up to speed on the topic??

For years my previous PPAP submissions to our customer for parts where the hardness after heat treating was listed as critical characteristic had been accepted with the explanation that the process by its very nature could never be at a normal condition; therefore an arbitrary minimum Cpk requirement was meaningless. Furthermore, each and every shipment was & is accompanied by a certified test report by the subcontractor who performs the heat treating process exactly to the customer?s specification along with a hardness test report we conduct at our facility prior the parts being received to our inventory.

When a new order for over 80 different parts that had previously been produced in-house by the customer was placed I brought up the topic of the Cpk requirement listed on a handful of the part drawings and stated that we would not be supplying statistical data that would produce a Cpk of 1.66 or better for a specified hardness value of 86 to 89 HR15n with a specified case depth of .015 min. We never received a response indicating this would be a problem and after one of the PPAPs? was accepted we later were informed that the acceptance been reversed and we would be required to provide data that met the 1.66 min Cpk requirement.

The ensuing ?negotiation? was intense at times to say the least. Over the course of the following months I was constantly reminded by the customer?s Supplier Quality engr that they had data from their in-house production runs that met the 1.66 min requirement and therefore we were required to do the same. [Interestingly, to this very day my request to actually see their data was never fulfilled.] We eventually agreed to a plan of action that involved testing at the customer?s site, the heat treater?s site and by our (me) QC dept.

We first started by performing an MSA on our individual hardness test machines (all of which had third party certified calibration certificates issued within past six months) using the same two certified test block standards that we passed onto each other. The standards were marked with zones and we all took our data from the same regions on the standards. None of the three sites were able produce data that met the customer requirement of total gage R&R variation of less than 30%.

Next, we produced 30 test slugs made from the same material lot as the original parts. Each slug was marked numerically from 1 -30 and their position in the oven mapped. All three sites then performed measurements on the parts. None of the data was able to produce Cpk values within the customer?s requirement of 1.66 or higher.

Still, the customer resisted revising the tolerance range of the hardness insisting that statistical capability calculations intended for dimensional measurements of machined parts can be applied to heat treat measurement with the same level of confidence & validity. Meanwhile, we still had 12,000 finished parts that we could not ship.

A few weeks ago I received another request from our customer for another complete set of 30 test slugs from the same material lot. The entire test process was repeated however I never received any results from the customer?s measurements. To this day I have not seen any supporting data from the customer supporting their claim that they routinely achieved Cpk results within their required range.

Last week we received an order for the parts with expedited delivery. When asked about not having PPAP approval we were informed there was new part revision that we would receive soon. It turns out the new rev no longer calls out the hardness as a critical characteristic. When I called the engr responsible for the part, he informed me that the reason the critical status was originally applied to the part in first place many years ago was as a corrective action for a production run they made that missed their heat treat operation.

Amazing how a rubber stamp can get used, isn?t it?
 
W

WKHANNA

#16
You should have charged them for the whole trouble.
Unfortunately, when dealing with a major international corporation, things like this are simply considered part of the 'cost of doing business'.:(

bobdoering said:
Physical testing is a horrible thing to attempt to do capability and MSA on.
I guess that is what they finally realized. And I never said it can not be done. But in the 'real' world, necessary precautions do not always demand such measures be taken.

Golfman25 said:
So how much hair did you loose on this one?
Not nearly as much as everyone else. I have been doing hardness testing long enough to be able to predict what the outcome of all this would be.

This entire issue had been one I have been contesting for years with this particular customer. My boss (our plant manager) felt this was a total waste of time & resources. I countered that it would be to our advantage to work with them. I volunteered to coordinate, manage & track the entire process. All the costs from machining the sample slugs, heat treating, purchasing of the certified test block standards, shipping, et. al. was covered by us. The customer's Quality Engr. was standing firm, & I knew this would be our only chance as this event would set precedent for all future orders. To me it was worth the time & cost because I was confident they would never be able to repeatably produce a capability of the process to within the unrealistic range they were asking for.
 
S

supreecha

#18
Type 1 Gage Study for Hardness

- Capability
Cg = 0.11

Cgk =-0.10 (Non Process Capability)

:agree:
- Bias
- 0.375
T = 7.7943
P-Value =0.000 (Significant)
(Test Bias = 0)
 

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