NEED HELP Aluminum Extrusion Failure

[Hill05]

Hello,
We had a part fail in an odd way. The part is 6061 aluminum. The same company cast, Hot extrudes and machines. During our process a center core plug of the aluminum popped out. Being this was extruded from a billet, this is not supposed to happen. The company that makes the part has run a ground so to say, and does not understand how this happend.

Anyone have any expierene to this type of aluminum failure that can help?

 

[3DDave]

Assuming you mean there was a discontinuous piece of aluminum, I'd guess a layer of aluminum oxide got folded in during the casting process, though I'm surprised it was aligned in a way to cause that problems instead of simply failing across the section.

The usual way to trace this down is to see who was involved at each step and ask them if they noticed anything.

The key is to get buy-in from the factory management that anything other than deliberate sabotage will not get any mark-down or other reprimand because it is far more important to understand what happened in order to avoid it again, even if the action was against some rule.

If that isn't done then the workers will all clam up and you won't find anything from them.

I've had a similar event happen - it was caused by a technician trying to fix a problem and made it 100X worse. Out of that we got a second data point and clue as to how to improve the situation. Lesson - punishing people for making errors or acting without official authorization doesn't stop them - it just makes it tougher to figure out what happened.

 

[Hill05]

3dDAve,
Thank you. Below are some picture of the failed part. The first image is what it is supposed to be. The second image is the plug out. The aluminum part is supposed to be one solid piece But as you see the core plug easily came out.

 

[3DDave]

If you can figure out how to do that reliably there must be someone willing to pay to fit a requirement they've had for a long time.

That is more uniform than I expected.

Have the alloy of the two parts checked.

Also, what does the die look like, particularly the support for the center hole and keyway?

 

[Hill05]

Hardness is in spec for 6061. Hardness between both pieces match. Surface structure match. We tried to recreate with another part on our shear tester. Our molding machine maxes out at 9kn, the shear test was done at 90kn damaged our tooling and did not press out.

We are of the mind that this happened at the extruder. The extruder is baffled, never seeing this before.

Not sure if this started at the casting since of the billet since it is just melted aluminum.

 

[Stick.]

Can you give a ballpark sense of how easily that plug actually came out?

 

[Hill05]

Stick,
I can push it out with my fingers.

 

[EdStainless]

Are the billets worked before extrusion?
Have they changed extrusion dies?
Have they changed extrusion ratio? Temperature? speed?
these should all be well documented so that they can be reviewed.
In fact they should all have control limits and charts to go with them.
These are friendly questions, you are just trying to understand the process better.
And I hope that you have your hands on all of the pieces that came out of that extrusion, as this likely effects all of them to some extent.

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P.E. Metallurgy, consulting work welcomed

 

[Hill05]

EdSTainless,
Thank you for your inquires. See below

Per the the extruder-
Are the billets worked before extrusion?-NO
Have they changed extrusion dies?- No
Have they changed extrusion ratio? -NO
Temperature? -NO
speed?-NO

 

[EdStainless]

No tells you almost nothing. You want to see what the natural variations in the process are.
Since you know that the variability cannot be zero.
They should be very concerned about this.
If they aren't it tells me that either they know what happened but don't really care to fix it it, or they really don't care about what they ship to you.

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P.E. Metallurgy, consulting work welcomed

 

[Hill05]

EdStainlessn,
This is our concern. Agreed that a "no" answer tells us nothing about the process nor helps to find rootcause. Sadly if we dropped our inquires then they would not proceed with investigation. This is the reason i have turned to forums for help. We have a team member flying to this factory at the moment.

Any other thoughts are certainly welcome!

 

[Stick.]

Could you push it out with your fingers the first time it came out? That would make me consider if the plug was something that happened after extruding (like somebody machined the plug and pressed it in the outer piece for some reason). I've seen situations where two separate pieces of aluminum went into the extrusion press and came out "welded" together fairly solidly (the bond only came apart during machining or a tension test), so that makes me question if this actually happened in or before the press. However, I've also never worked with hollow extrusions and wasn't too heavily involved with the actual extrusion process, so I could be way off base there.

Make sure that everything the supplier tells you is backed up with documentation. It's one thing for the supplier to say they didn't switch dies, it's another for them to send you the QA documents that actually shows which dies were used for this lot. The same goes for every other process parameter you ask about. I'd also request all QA documents for the billets that were used for this lot to see if there's any issues there.

I'll second EdStainless's comments that the supplier should be extremely concerned about this. When I've seen defects of a similar level to this, the supplier was willing to dedicate two employees to inspect 100% the entire lot before it left the facility (at least for a while before root cause was found, fixes implemented, process control was established, etc.).

 

[3DDave]

Just one? This oddity deserves more.

 

[Hill05]

One was found. Because of this the entire lot (5k pcs) have been quarantined. Those have not been gone through.

 

[3DDave]

I meant, you are sending only one person?

 

[kingnero]

Even if the dies have not changed, they often manually adjust them in production in order to have uniform flow through the different openings. Here it appears that the extrusion weld (bonding after going through the die) failed. A common causes of this is different flow speeds. This is, if the failure happened at such a bond. But I couldn't understand how/where else such a disconnecting failure could appear.

 

[Hill05]

Is there a possibility there was a problem with the billet before extruding?

 

[EdStainless]

It almost feels like they greatly slowed or even interrupted the extrusion and that allowed surface oxides to form preventing the fusion of the separate elements.

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P.E. Metallurgy, consulting work welcomed

 

[Hill05]

EdStainless, since this is cast billet, can it be that the butt weld could have got surface oxide < say from moisture from air line> and did not weld correctly?

Even with that said, i have reviewed their process documents and the butt weld is supposed to be removed and scrapped.

 

[EdStainless]

Everyone misses one from time to time. But I sort of doubt that it would generate this kind of defect.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed