suggestions on welding aluminum

[smithworks]

I need to make a pan/tray/5-sided box. I will be using 1 piece of 28" square 1/4" thick plate and 4 pieces of 1/4"X1.5" flat bar. I will be welding the flat bar on edge to the plate around the entire perimeter so that I end up with a 5-sided box that is 28" square by 1.75" high. I need to v-out the weld area so that it may be ground flush after welding to look seamless. So, basically I have 4 lengths of 28" welds plus the 4 corners of 1.5" of weld. My plan is to tig weld it, starting with tacking all the pieces together, making tacks about every 2" then filling in between the tacks in way that most evenly adds heat to the unit as a whole.

Is there a better way to do this? Is this going to warp like crazy? I could probably live with an 1/8" of bow over the whole length but would prefer a 1/16" or better. I do have a 30ton press, if it does bow worse how hard would it be to straighten. I have only ever welded a test scrap of aluminum and have no knowledge of how it acts when fabricating into any said structure.

Any advise is greatly appreciated.

[CurlyGeorge]

I welded aluminum truck tanks for a living and my suggestion would be to weld maybe 6-8 inches. Go to another area and do the same. If you spread the heat like that around the piece being welded, it will give the welds time to cool, a little. Don't try to weld up the whole piece at once or you most likely will get warpage. You should have minimal warpage if you space the welds out like that. Take your time. Hope this helps. :D

[Fosterob]

I would have the four sides bent up the 1 1/2" and just weld the short seams. You will use a lot of gas and rod to make those long welds and it will take some good preheat to be able to even tack it. Good luck.
Rob

[Larry H]

clamp angle iron to both pieces to hold it square and flat, leave it until its cool

[arftist]

FosterRob's solution is the best way. It is so much better in fact, that even if you already cut the peices, you would still be ahead to go that way.

Unfortunately, if you do weld it, the press will not help you much, what you would need to do is learn shrinking.

Assuming you are going to weld it, this method will eliminate most of the need for shrinking;

Take your square piece to your anvil and peen the entire length of all four sides, with light to medium blows.
The goal being to stretch the edge to make up for the shrinkage that will occur as the weld cools.
Try to work as evenly as possible.
Weld following the directions you have been given. You may be fine.

[smithworks]

the outside edges have to be sharp, otherwise I would definitely bend it.

[smithworks]

Why would the press not help? I'm pretty sure I can take a bent flat bar of aluminum and bump it under the press to get it straight just like I do with steel, stainless, brass, copper, and bronze.

[Mainely,Bob]

The warpage will take place because the edge you will be welding will shrink as it cools and it`ll distort both the flat bar and the plate. If you use the press you`ll only be chasing the distortion around the edge. As was stated in the posts above you`ll need to shrink the unwelded edge to match the welded edge in order to straighten it.
Think of the distortion you`d get in a welded rectangular tank made of sheet metal. You can`t press that kind of distortion out,you have to shrink it out.
Proper welding sequence will minimize distortion but the amount of heat you need to crank into aluminum will still cause some,it`s unavoidable that it`ll move as it`s heated and it`ll scare you if you have little experience with it. Experience will tell you how to use one weld to pull back against another and cancel much of that distortion. Chances are there will still be some to shrink out though,especially the way you plan to do it.
If you don`t have any experience then best to find someone who does.Once you find someone with experience then watch what he does and pay close attention to how he shrinks the material to straighten the distortion. That`s why the expression "Experience pays but it`ll also cost ya" was coined.

[smithworks]

my press has 30" square platens, and I have made similar objects in bronze (which definitely expands and contracts more than steel) which I was able to block up where needed and work pretty flat. Could I not do the same with aluminum? I have also made many pieces of angle iron using 2 pieces of cold rolled flat bars (steel) welded up the entire length. Of course they warp a good bit (less if you put a piece of aluminum on the opposite side to suck the heat out and space your welding), but I can put them under a press and straighten them no problem. I know aluminum is a bit unique in its properties for welding/soldering and such but can't you still bend and straighten it like steel, bronze, etc.

[Fosterob]

Welding the piece you want is no problem, I would even say easy. It may warp a bit. My opinion is it is foolish to use the argon$ and filler rod$ to do the job. I think it is better to bend it out of one piece and just weld the corners.
Rob

[BIGGUNDOCTOR]

How big is your TIG? Aluminum takes more power than steel does.

[smithworks]

Again, I cannot bend it because the outside edges have to be sharp. I have a lincoln 255 square wave which maxes out at 315 amps (not sure without looking at it what % duty cycle). Wouldn't this be enough for 1/4" aluminum?

[Mainely,Bob]

My best advice now is to just do it. You seem to be committed to doing it your way.
At the very least you`ll learn why you shouldn`t do it that way again. Good luck to you.

[Fosterob]

Again, I cannot bend it because the outside edges have to be sharp. I have a lincoln 255 square wave which maxes out at 315 amps (not sure without looking at it what % duty cycle). Wouldn't this be enough for 1/4" aluminum?

Since this is the first you said about having to have sharp outside corner welding is your best option, If you said that earlier I must have missed it. Just be sure that your torch is water cooled, that machine should be fine. You should do a practice piece first, the sharp corner you want might melt into the weld and you will end up with a round corner anyway.
Rob

[Old N Rusty]

If you got only a T.I.G. and no Miller M.I.G.spool gun , this would be difficult , but not impossible. If you had a Miller synchrowave with Hi freak T.I.G. and foot pedal it would be EASY.

[Francis Trez Cole]

He is welding 1/4" you could use stick if you are unsure of the tig. I do a lot with with mig. Just have to not over heat. get some scrap and practice.

[jdustu]

Did you ever get around to doing this?

I do quite a bit of aluminum weldments, all kept to pretty strict tolerances. You're always gonna get some movement(especially without a specialized fixture), the trick is to minimize it to where you can straighten without much of a problem. If you can clamp it down, block it up under the center of the plate so that the edges are actually pushed down a bit. "Preload" the plate in the opposite direction, the edges will want to pull up when welded. Then move around like CurlyGeorge said and you should be able to keep it pretty straight.

[SmoothBore]

I would have the four sides bent up the 1 1/2" and just weld the short seams.

Concur.

Brake the edges, and just weld the corners shut.

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