Welded Box Tube

[tenfour]

Our team is making an assembly that consists of welded Aluminum box tube. The box tube is 1.5 outside wall 1/16” thick wall square. This frame will have several 45-degree joints.

My question was regarding how to weld an assembly like this. We are taking it to the shop at our local college. They do questionable work some of the time and I was wondering if any of you had any tips on what to tell them or any ideas on making it stronger.

[ajlapp]

we weld this type of frame all the time.......

using the 45 degree angles is a good idea.....if you have the time making a jig and standarizing sections really saves time and makes things more uniform.

if you can design the frame around a few uniform sections then there will be less variation in your final dimensions.

do carefully consider your tolerances though. don't count on your dimensions being exact, welding can produce lots of variant, especially when welding aluminum, and especially when your welder doesn't know the deisgn and doesn't take their time.

good luck and take a look at wildstang's robot from last year, they used a square tube frame very effectively.

[NateBot16]

If you need to make it stronger afterwards, you could always grind the welds down, so the surfaces are flush, cut some sheet metal that goes with the shape of the two welded peices, and use pop rivets.

[Gui Cavalcanti]

You use 1/16" wall? After seeing the beating our summer robot Phoenix took at the Maryland State Fair (it was built out of a combination of 1.5x1.5 and .75x1.5, 1/8" wall) I'm beginning to doubt 1/8" wall. To each their own, but I know 1/16" wall is much harder to weld.

Aluminum joints are strongest if they're end-to-end instead of mitered. For instance, if you plan on doing this: (excuse the ASCII)

-------| <---- end piece
/ |
/ |
---| |
| |

This would actually produce a stronger weld:

-------- |
|
|
-------- |
| |
| |

If you do need to make mitered welds, I suggest welding the small angled end piece first instead of the base of the tube, because that end piece has a tendency to flex outward if you weld the base first.

Good luck!

[tenfour]

I would think that a miter joint is stronger than a butt joint as a result of more weld engagement. Am I wrong?

[Dick Linn]

First, make sure whoever welds it is experienced in welding thin Aluminum! Second, make sure that you know which alloy is being used for the tubes, and use the proper filler metal for that alloy. Some alloys are virtually unweldable, some depend highly on the exact filler alloy and others are not too finicky. Check out the sites of the major welder manufacturers like Licoln (do a Google search on Aluminum welding - Licoln should pop up to the top).

Is there any way you can use gusset or reinforcing plates and rivet/pop-rivet/screw the sections together? You will note that aircraft and monocoque racing cars are typically held together this way, not welded. For that matter, steel buildings are often bolted/riveted together. This year, our chassis is 1" x 1" square tube held together with #10-32 alloy allen-head screws and gusset plates/angle brackets.

If you are using heat-treated or work-hardened Aluminum, welding will soften it and you will lose structural strength. You can, with difficulty, heat treat some alloys (have a 1000 degree oven?). You cannot work-harden a complicated construction (unless it bends and you beat it back in shape.)

There are some interesting new techniques like "friction stir welding" that may show up in future aircraft but I'd stick with something simple, like riveting, if at all possible. That, or weld, then reinforce as necessary.