it does need to be real clean, like gbadgly said. it doesnt need to be preheated tho. at our shop we dont use just pure argon, we use argon/co2, it works fine, you might get a better weld with pure argon i unno, but its fine with argon/co2. also spool guns are heavy and aqward(sp?) but thats just personal prefference i guess, when you work in an autobody shop, you cant get a spool gun into odd places when welding underneath a car something. you dont need it, it works just as good so thats why i hate them. but its up to you.

 

I MIG weld thin aluminum extrusion at work with pure argon and .8mm wire. We use old Cobramatic wire feeders with motor drive torch and an arc pulsing unit. This combination works excellent on the thin material we weld. The 2-motor feeding system feeds the wire evenly, even through the 20 or so foot long torches we have. I set the drive tension tighter on the torch end than the feeder end and that keeps it from bunching up in the torch. Changing the torch tip often helps the wire feed smooth and consistant. If you have a teflon liner tube in the torch, take it out and check it for worn spots once in a while, sometimes feeding problems are caused by a worn or kinked liner.

Cleanliness of the metal does make a big difference in the weld quality. We do have to weld on painted aluminum often though. The prep guys brush it clean as best they can with a wire wheel, but it still smokes and bubbles up when we weld it. I wear a mask cause I hate breathing the paint smoke. I stitch weld alot of times instead of running a continuous bead to avoid blowing holes due to the contamination making it hard to join the metals. If your metal is less than very clean, turn up the wire speed and the weld time (or power setting, if no pulser is used) and you will be able to weld through the contamination easier, otherwise, move the torch a little slower, but be on the lookout for holes forming and get off it when you see one about to form, pause a second, and start again.

Sometimes we get alot of oil on the aluminum from the hole punching operation that happens before it comes to us for welding. We do fast production welding and don't have time to clean the metal real good, so I just turn up the wire speed and the weld time and that cuts through the oil and helps keep from blowing holes. The smoke can make ya sick after a while though.

On thin aluminum, you don't want to hold the torch at a right angle to the work, it will just poke holes in the weld. I always angle the torch some in the direction of the weld and it works good on aluminum and steel. If the aluminum is thin and you're welding a verticle, point the torch down and the weld will run down the joint nicely without blowing holes.

On welding aluminum, especially thin aluminum, the joint fit-up is important and so is keeping the arc spray aimed evenly over both sides of the joint. Welding over gaps or pointing the torch off to the side will blow holes quickly. If I have a gap to weld accross, I'll go ahead and weld a few short spots spaced evenly along the joint, not too far from eachother, then come back and run over it with the wire speed up and move the torch fast, otherwise I turn it down and stitch weld it. Steel is more forgiving on the joint fit-up, since it doesn't melt away as quickly.

On the thin aluminum we weld, we run the torch fast along the weld joint. Plus, we want to do as much production is as short a time as possible, so fast welding with the machine turned up is a must. On thicker aluminum though, you don't need to weld so fast, you should go a little slower and make sure you get a good weld. It's easy to get excited and go too fast, epsecially if you're afraid of blowing holes. Just watch the spray, put it right over the middle of the joint, keep the torch distance from the work and the angle of the torch uniform over the length of the weld, and move it at a consistent speed and you will be making nice welds in no time .

One thing that really helps to make more uniform welds is to rest the left hand or forearm on a stationary part of the work, or whatever the work is sitting on, and use the left hand under the torch neck like you're guiding a pool cue. Steer the torch with the left hand and drive it with the right, if you're right handed. If you're unsure how a weld might turn out, pre-run it with the torch like you're welding it but with the trigger not held down, so you can see and feel how you want to move the torch along the weld joint. That will help you pick your hand positioning better to guide the torch more evenly and the weld will come out looking nicer.

 

sic inside,
One more tip.

Get your local sheet metal shop to 'form-up' (bend) as much of your box as possible. This will minimize a lot of your welding.

Good luck.