Welding Tips and Tricks

Very new to TIG welding so I need some insight. I do OK with steel, but the Al. is not going well. I am using a Lincoln Percision TIG 225 & foot pedal. Trying to make a lap joint or butt joint on .040 Al. Some times I can half way get a butt joint to weld, but not the lap joint. Every time I get near the cut edge the Al just shrinks back. I can get the puddle started on the one piece but as soon as I get near the cut edge it shrinks back. Have tried starting on the top piece, but the same results. Need insight on how to do this joint. Once I get up to.080 and above material I can weld the joint. I have tried .040 Tungstun up to 3/32 with the same results. Some times if I start the puddle on the lower piece and use 3/32 rod I can get a weld but it is very big and looks bad.
Any insight??

BCZ

Leaning aluminum will be tricky on .040" because you need to manipulate small distances and motions, like a doctor performing a surgery. Leaning on .125" thick aluminum is I think a lot easier for most people, who are not surgeons.

I would go with the .040" tungsten, as long as the tip is not "melting / balling", and try and make your joint fit-up as tight as possible, if you get it close enough you might even be able to get the two parent metals to "fuse" together for a tack weld, without adding any filler. They need to be not only clean (of aluminum oxides), but touching each other right in the spot you are attempting to tack weld, for that to work with aluminum.

Also, are you conscious of your torch angle, and your arc length? Keeping the arc length as small as possible will keep the heat focused more. Also, I would probably aim the torch (torch angle) into the larger flat surface that is not melting back, to direct the heat towards it. Ideally you want a puddle to form on both sides at the same time, in fact it is critical if the pieces aren't touching, and then you'll further have to jab the filler rod right into the middle of the two molten puddles at the proper time, to let the puddles flow together as one. But welding in the middle of a surface needs more heat input than welding on the edge (as with a lap joint) for both to get to melting temperature at the same time. You can direct the heat to one piece or the other by controlling your torch position and torch angle.

Also there are some machine settings you may be able to try - depending on what machine you are using. Using more DCEN% (balance) will also focus the heat input closer to the tip of the tungsten. As will increased AC frequency, or some high speed pulsing. (But if your machine can't control all that, don't worry, there are still plenty of other variables you can play with to hopefully create the desired effect.)

I have trouble dialing my machine in for very thin materials needing very small welding currents, because near the low end of travel of my "current" knob, I find a small adjustment of the knob makes proportionally a very large change in the current setting. If I turn it all the way minimum, it tries to weld with just 1 amp, and will not be able to establish a normal welding arc (won't get past high frequency starting mode.) Then with a knob adjustment, for some reason it likes to try and jump up to 6 amps (a 600% increase.) etc. Wondering if something like that might be causing you problems on the thin material too.

I have no idea if this is the way your supposed to do this because I'm new at TIG also but, I did the same thing as you trying to lap some .040 to 1/8". I ended up using the pulser to get a feeling for how it worked and then I turned it off and went to a/c balanced, a 3/32 thor with about 1/8'' grind and a flat tip about .040 in diameter, #6 cup and about 12 cfh of argon only. I turned the amps up to 130 and put the ground clamp on the piece.

I then used Jody's method of tacking followed by short welds done by pulsing the pedal and watching the .040 metal closely. At times I would back the heat off leaving just enough going to keep some heat in the weld but not really do anything. When I thought the .040 was soild again (a couple of seconds) I'd put the heat back on and the second the puddle formed I dipped the rod and then backed off. I spent more time at full amps when I was on the thicker metal but not so much time as to let the thin stuff melt back. That was just last night and I haven't tried any other ways yet.

On the butt welds with the thin stuff, I imagine that I'd start by dropping down to a 1/16 tungsten a smaller cup or maybe a gas lense and bigger cup to give your self a little more cooling at the outer edges. Not sure on this, I've never tried it. Maybe tonight I've got the same machine.

Thanks for the insight. I have tried a lot of the things and maybe it is just a matter of seat time. Since no one has indicated a major issue I would suspect that the problem is seat time. If I can clamp the pieces tight together they are much easier to get to weld. I will keep trying and repost if I cannot get it to work.

Thanks again,
BCZ

Something I do when trying to get started on the thin stuff is to have the rod there and start the arc on it. Fills the gap and think about welding the puddle with the arc and rod while the puddle moves forward onto the joint.

This may be wrong and bass ackwards but it works even on aluminum cans where if you arc the can, you blow a hole.

no, no major issues. just make sure they're clamped nice and tight and they stay that way thoughout the weld. don't just start at one end and keep running until you get to the other side. sheet aluminum moves a LOT when it's heated.

also, unless you feed a lot of rod (way more than you think you should), you'll cut back the top edge of the lap piece. the toe of the fillet will end up roughly where the bottom edge of the lap piece is.

here's a pic, as my description was clear as mud. with aluminum that thin, you'll almost always penetrate clear through and that sag area is where the rod you're shoving and the bit of metal from the lap piece goes.