January 24, 2010

Big Aluminum Boxes

I recently had the opportunity to make some large display cases from 1/4" aluminum to house some of the Dead Sea Scrolls for an upcoming exhibit at the Science Museum of Minnesota. Aluminum tends to warp and move around a lot from the heat of welding, and the idea of welding all the corners and having it come out perfectly made me pretty nervous. But it all worked out better than I feared. There was certainly warpage to straighten out, but it wasn't so bad that a few whacks with a dead blow hammer couldn't correct it.

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clamping the bottom frame

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The underside seam here isn't seen, so it only had to be tacked.

I found that welding into a fairly shallow 45° bevel (at about half the plate thickness) was sufficient to join the corners without causing a lot of warpage. Since this had to be more flat and square than strong, it seemed like a good risk to take. The joint was strong enough that I could hammer a sample to about 30° before it would start to break. Keeping the bevel away from the corner kept the corner from melting back.

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Mig welding aluminum isn't always pretty. But with my fancy Lincoln PowerMig and its push-pull gun and "pulse on pulse", it worked great. It's at least 5 times faster than Tig welding and it heats up the aluminum far less. Maybe not quite as pretty, but it didn't matter here, as it was all being ground and routed.

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I used a 1/8" roundover (climb cut, for a good finish) and 100 grit orbital to even it out.

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Gap for the gasket

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2 of the finished cases

Posted by Hal Eckhart at January 24, 2010 11:05 PM
Comments

nice project! Have you ever used a spool gun for aluminum? If so how does the push/pull gun compare? Does the pulse make a big difference?

Posted by: backsix at January 29, 2010 03:17 PM

I know people who swear by a spool gun, but I'm not crazy about them. The push-pull gun is pretty heavy though, so that's not a big concern. The big deal is that it's a lot cleaner. Prettier weld and less spatter. The pulse on pulse process seems to give me a stronger, less porous and brittle weld than a conventional mig. Not as much heat distortion as tig, and it's insanely fast. I was plug welding some 3/16" alum. plate a while back. It took a good half minute at 300 amps to do it with a tig. The mig was about 2 seconds.

Posted by: Hal at January 29, 2010 04:14 PM
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