Stock material flaw?
Stock material flaw?
(OP)
Hi,
I've had a some turned parts come in the from a supplier, made from Aluminium 6082-T6. These parts provide a seal in an oil filled vessel. On assembly some oil was noticed leaking from a tiny witness line, and curiosity led to putting the part in a press and this happened... See pictures
http:/ /files.eng ineering.c om/getfile .aspx?fold er=3e943f2 3-512e-450 8-8830-f98 4dc392af8& amp;file=Q Cpics1.JPG
http:/ /files.eng ineering.c om/getfile .aspx?fold er=cd33df2 9-74b5-487 b-95c6-36f 29b01cfd0& amp;file=Q Cpics2.JPG
http:/ /files.eng ineering.c om/getfile .aspx?fold er=b5a35a7 3-501a-40f 8-8612-582 8dffc1090& amp;file=Q Cpics3.JPG
The profile between the two parts in slightly tapered, and slightly oval. Can anyone shed some light on this for me please? My thoughts are that this is a flaw in the stock material, where the material has not bonded during cooling, but having been drawn it is forced together. Would our supplier notice this flaw in the material during machining or inspection?
Thanks,
Steve
I've had a some turned parts come in the from a supplier, made from Aluminium 6082-T6. These parts provide a seal in an oil filled vessel. On assembly some oil was noticed leaking from a tiny witness line, and curiosity led to putting the part in a press and this happened... See pictures
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The profile between the two parts in slightly tapered, and slightly oval. Can anyone shed some light on this for me please? My thoughts are that this is a flaw in the stock material, where the material has not bonded during cooling, but having been drawn it is forced together. Would our supplier notice this flaw in the material during machining or inspection?
Thanks,
Steve





RE: Stock material flaw?
Or is it that the fit tolerance isn't what it's supposed to be?
TTFN
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RE: Stock material flaw?
I _have_ seen similar parts made from a piece of plate and a piece of bar to save machining time (or if the bigger bar was unavailable), but tapering the joint is unusual, and most vendors will ask before doing something like that.
Mike Halloran
Pembroke Pines, FL, USA
RE: Stock material flaw?
If I understand you correctly, there was a seam in your raw material that should not have been there? I would get back to the shop that made the parts and ask if it was made from extruded round. I am not that familar with 6082, what forms is it available in? A wild guess is that it was extruded along the axis and the seam is an extrusion artifact. See if the shop has any more of the material and even have them get back to their material supplier to check out if the seam runs thru the whole bar. I would say this is sure looks like flawed material. Another remote possibility is the shop pressed together two pieces to make your one part but this seems to be a lot of extra work unless the material is real difficult to get.
My 2 cents worth,
Timelord
RE: Stock material flaw?
I have seen flaws that ran lengthwise but none that formed a ring like this. Probably the result of a circular inclusion that got extruded the length of the bar in the rolling or extruding process. I would have expected the machine shop would have seen unusual rings peeling off as they cut into the flaw. It would be worth asking them.
Ted
RE: Stock material flaw?
KENAT, probably the least qualified checker you'll ever meet...
RE: Stock material flaw?
Yes, it should be one part, but under light pressure in the press the flange came away, but the fault line does not follow the hub/flange change in cross section, it's a little wider, and on other parts it is within the hub.
I think the stock material is extruded or drawn bar along the axis of the parts. And this is a possible inclusion.
Our stores has no batch identification number, so we cannot be sure which supplier they came from. I've spoken with both of them, but they are both a bit cagey and suprised.
I'd like to find more information about whether this flaw, if it is that, is noticeable in stock material or during machining. As I'm wondering if we have been supplied with questionable parts before, and we have missed it and it has made it to the customer.
Cheers
RE: Stock material flaw?
RE: Stock material flaw?
Ted
RE: Stock material flaw?
RE: Stock material flaw?
From here It sure looks like they pressed/shrunk/loctited pieces together
RE: Stock material flaw?
1) Size. We shrink fit die inserts into cases all the time with similar OD/ID shoulder configurations. The application is different though (it's common in my field). Take the hub diameter. If it was a shrink fit, figure a .001" per inch of hub OD. See if the ring ID of the flange correlates to this.
2) Use a 7X + power eye loupe and look for evidence of grind lines or some other remnanat machining.
3) Look for any discoloration (blueing or gold) in the ID of the flange that might indicate the flange was heated.
Having an ovular hole is not uncommon when you pull apart thinner flanges that have been shrunk fit to a hub. If they put the flange on with a press fit, you might have a difficult time seeing any machining lines if you scored the flange pressing out the hub.
RE: Stock material flaw?
Just what are the odds of something like a circular flaw occuring in normal stock?
Have you measured the concentricity of the "flaw?"
If it's within machining tolerances, you've got the perfect scholarly article candidate for the "Journal of Irreproducible Results."
TTFN
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RE: Stock material flaw?
Regards,
Cory
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RE: Stock material flaw?
I can't see anything I would recognise as a machining mark on the broken surfaces, but there are marks I am not familiar with. I've done a lot root cause failure analysis work and seen all manner of sheared parts and fatigue cracks and have not seen surfaces like this. As you can see in the photo there is almost a grain to the surface like on wood.
I am still wondering if the supplier fitted a bar and hollow bar together somehow, but next step I'll contact some extruders and see if they can shed any light on it.
Thanks.
RE: Stock material flaw?
Not that there is necessarily anything wrong with this but you might want to get them to share the exact procedure. You may find some problems associated with how they made the fit, coeff of thermal expansion, stress from press fit, material strength, etc... Modulus of elasticity for aluminum is about 1/3 that of steel, tells you something right there.
My opinion, this is not a material issue, that would be the least probable cause for this failure. I just can't picture aluminum being a good candidate for a press fit assembly.
RE: Stock material flaw?
Please look closer at the pictures. The break does NOT follow the change in cross section between flange and hub. And one of the components a huge chunk fell out of the hub itself? I'll post another picture on Monday of that one.
There is something wrong with thermally pres fitting two parts together if it is not to my drawing. With all the info I have I still wouldn't dare draw a conclusion - I'm an engineer and have to use good science. I just thought somebody here may have seen it before. Next step I'll ask stock material suppliers.
RE: Stock material flaw?
Ted
RE: Stock material flaw?
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Ted, I will get a metalurgical examination done as well.
RE: Stock material flaw?
Regards,
Mike