Aluminium extrusion bending

[Ghuuuu]

Hello all, we are an aluminium extrusion company. However we have a problem where our profiles are bending, I measure a bending of about 5-10mm in a length of 3.5m. Keep in mind that this is measured with a profile which has already been from the oven and powder coated. Can those process cause the bending? Does anyone know how resolve this issue or point me where to check. Thank you!

 

[EdStainless]

Have you checked them before powder coat?
It is possible that some combination of aging, stress relief, or non-uniform heating/cooling are making this situation worse.
I suggest that you check samples at each step in the process.

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P.E. Metallurgy, Plymouth Tube

 

[Stick.]

In my experience, straightness issues in extrusions sometimes aren't the easiest to diagnose.

What processes are involved in making this profile and what order are they done in (is there a heat treat cycle, any cold working/straightening operations, any aging operations, what's the temperature in the oven that you mention, etc)? Are you using a single or multi-hole die? What stage in the process are you first finding the straightness to be out of tolerance? Are you allowed to provide any info on what the profile is (cross sectional shape, rough size)?

Also, just because I'm a fan of checking the simple stuff, how are you measuring the straightness?

 

[Ghuuuu]

Hey Ed, thanks for the reply. I just got in this problem recently, and I haven't checked it on every step of the process. Thanks for the input, I will check it now after each process. Thank you.

 

[Ghuuuu]

Hey Stick, I will try to answer your questions as best I can.

The extrusion process is done normally, it gets pulled just as it comes out, and laid out to cool down on the side track/rail. It then gets cut to lengths of 6m, and then joins the queue to the heat trestment for aging. I don't know the temp, I will check and let you know. It then goes to the powder coating line, where it gets coated and then ovened again.

The profile is a complicated shape for aluminium sliding doors, 40x100mm on a 4" dies.

The way I measure it is simple enough, I don't know how else to measure it. I put two profiles side by side and put them together, and I can see the bending very obviously. I measured from there.

Sorry I'm not an engineer so I don't know much. I will have to talk to my people about details. Thank you.

 

[Sparweb]

The profile is a complicated shape for aluminium sliding doors, 40x100mm on a 4" dies.

Like a "W" shape, then?
Can you take a photo of the cross-section and post it here?
Which way is it bending?
How is it being pulled out of the die?
It is straight as it passes between heat-treat and powder coat?

No one believes the theory except the one who developed it. Everyone believes the experiment except the one who ran it.
STF

 

[Ghuuuu]

It's more of a H shape. Here is the picture. If you put the 100mm face down, and put two side by side and look from above, you can see the bending.

It's being pulled out of the extrusion hoizontally.

 

[Sparweb]

Thank you for the cross-section image.

The only way to get to the bottom of the problem is for you to investigate, in great detail.
Sometimes it's hard to appreciate how small details matter.

"How is is being pulled?"
...implying many possibilities...
...but until you tell us what...
...we can make up some guesses...
Does a guy clap on to it with pliers and haul like he's leading a horse?
Or does a mechanical actuator with a custom fit grip and articulated head clamp it?

I am absolutely certain that you don't do either one of these extremes, but actually do something in between. Either share with us how it is actually done in your plant for us to consider, or examine it in detail yourself, looking for any way that the process could induce a bend in your material. Your own investigation is the essential step.

And then, more questions:
Is is straight when it first comes out?
Is is straight when it is fed into the heat-treatment oven?
Does it run out on rollers?
How cold are the rollers?
Are there other distortions in the profile?

Again, where between the two extremes of brutality and delicate control does your process fall?

Observe the entire process, and at every single step, put your own mind into the mode of asking questions about everything.

No one believes the theory except the one who developed it. Everyone believes the experiment except the one who ran it.
STF