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Laser cutting aluminum questions

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REVAN

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I'm working on a tube and gusset design and starting to think about how to make the parts. Can anyone here inform me on dealing with the heat issues of laser cutting gusset parts? I've heard conflicting information depending on the aluminum alloy being used. I'm thinking of using 6061-T6 material in most places. Laser cutting is clean and affordable. If there is a way to accommodate the use of this process, it would be great, as I'm designing to try to keep costs as low as possible. I'd just need to know how to design appropriately so that it can be used without creating structural and fatigue issues. If it's just not possible to use this method, I'd like to know the reasons why.
 

Mad MAC

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In the ideal world don't, but otherwise determine the size of the heat effected zone and remove it with a deburr tool (its not very thick) or weld up the all cut edges. Why, well the heat affected zone is prone to cracking due to high hardness, not dissimulair to how welded 6061-T6 cracks so readily.

there is also this thread which covers this exact question in more detail
 

Jay Kempf

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Cut prototype pieces and load test them. I would not advise using laser cut holes for rivets near edges on highly loaded life dependent parts.

The problem is fatigue. While a well known phenomenon in general it is much harder to nail down analytically. Heat affected edges can just crack when strained. Those cracks can propagate especially in thin heat treated aluminum on a flexible (under load) structure. So the question is will it crack and if it does can you see it and if you can't how many cycles will it last. And if you can't know then it could be a time bomb. Not being dramatic. We started to learn about these things pretty early in the progression of passenger air travel starting with the DeHavilland Comet. Laser cutting didn't exist back then but even mill marks or scratches in finished parts were a problem.
 

pictsidhe

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Fatigue would scare me away from laser cut t6 without heat treating afterwards.
It may not cost too much to have a bag of gussets heat treated. Filing off the HAZ seems like way too much work to me.
 

Jay Kempf

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And how do you know how big the HAZ is without some analysis and testing which isn't really practical. Overdesigning could work. But waterjet is cheaper and in the end requires less material to be removed to get it there with little or no HAZ. Run a drill through the holes on test fit, light deburr sand the edges, Alodine.
 

nestofdragons

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I have a alu project with CNC cut parts. My engineer advised me to use waterjet to keep the strength of the alu not changed by the heat of laser-cutting. Parts were nicely cut. Even the thicker parts for my ultralight glider. No burrs. But i sanded the edges anyway just to be sure.
 

flywheel1935

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Nov 1, 2018
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Downham Market, Norfolk, UK.
I'm working on a tube and gusset design and starting to think about how to make the parts. Can anyone here inform me on dealing with the heat issues of laser cutting gusset parts? I've heard conflicting information depending on the aluminum alloy being used. I'm thinking of using 6061-T6 material in most places. Laser cutting is clean and affordable. If there is a way to accommodate the use of this process, it would be great, as I'm designing to try to keep costs as low as possible. I'd just need to know how to design appropriately so that it can be used without creating structural and fatigue issues. If it's just not possible to use this method, I'd like to know the reasons why.
What, like this ??? (tube and gusset)

20191021_114216 (1).jpg

All gussets cropped on guillotine, then radiused on belt sander, all 300 +
 

Built2Fly

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Feb 21, 2020
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San Diego, California, USA
For the original question, I think laser cut gussets can be done, but with a caviar.

First of all, the concerns is the HAZ. There are two cut edges: the outside profile and the holes. For the outside profile, the HAZ does not matter. It matters around the rivet holes cut.

How wide is the HAZ? I have seen paper stating that it is 0.2~0.4mm on steel (that's about 10 thou). Not sure about aluminum sheets though. You may want to find that out.

This leads to the question: why laser cut? To me, the reason for laser cutting has two main reasons: (1) avoid hand-cutting complex shapes, and (2) avoid measuring dimensions for each hole when in hand-cutting.

So here is how I think it could be done: cut the gusset with all the holes cut small (just a punch). This way you can easily drill out the HAZ and you would need the smooth edge from drilling anyway. And you avoid all the measuring.

Just my 2 cents.
 

flywheel1935

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Nov 1, 2018
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Downham Market, Norfolk, UK.
Looked cool. Looks like it is angles not tubes. What is it?
That is Awesome.... More info please?
Hi Guys its a modified LMA, kit was designed about 35 years ago, and sat in a friends garage , He was the UK/EU Importer for LMA, but as the Florida based Company couldn't supply stress specs the UK CAA/LAA can't allow its design to be 'accepted', but now we have SSDR, so long as its under 300KG AUW we can now build it, Square 6061-T6 tube, 6061-T6 Gussets, 2024-t3 alloy wing ribs etc,
see the build in the Tube and Fabric Forum.
 

REVAN

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Tucson, Arizona USA
...This leads to the question: why laser cut? To me, the reason for laser cutting has two main reasons: (1) avoid hand-cutting complex shapes, and (2) avoid measuring dimensions for each hole when in hand-cutting.

So here is how I think it could be done: cut the gusset with all the holes cut small (just a punch). This way you can easily drill out the HAZ and you would need the smooth edge from drilling anyway. And you avoid all the measuring.

Just my 2 cents.
I was thinking the same thing, just wondering if there was some reason to not consider this. I wasn't sure if the outside edges would be an issue or not. If it is just the holes that are at issue, then maybe this would work okay.

Now, it is a question of what is more cost effective; laser cutting and then re-drilling the holes, or water-jet cutting. Are there any issues with cut-edge roughness on water-jet that would require any hole preparation before riveting, or can I assume the parts will come off the water-jet table ready to install?
 

b7gwap

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Sep 1, 2014
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285
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UT
A router table has to cost less than a laser table. Yeah your kerf is wider but with the correct speeds and feeds, you need not worry about HAZ. At a laser price, you could even look into an NC punch press.
 

b7gwap

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But you said tubes not sheet stock. I still think you’d be better served by traditional machining techniques here.
 

cheapracer

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Australian
There is a scientific research paper available on the Internet comparing water, laser, plasma, mill ect cut rivet holes, and the result was that is just doesn't matter, zilch, nada, zero reason for concern.

The distance from the edges of the hole that the metals were affected by each process, were so insignificant as to not matter. They were going in with electron microscopes too.

I reviewed and shared it a few times in the past, but have since lost the link.


My engineer advised me to use waterjet to keep the strength of the alu not changed by the heat of laser-cutting.
No burrs. But i sanded the edges anyway just to be sure.
Again, no loss of strength with laser cutting, and after 10 years and thousands of parts cut by laser, edge burrs, or not, is completely dependent on the competence of the operator.
 
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