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Old 03-16-2012, 10:59 PM
Nate Lagler's Avatar
Nate Lagler Nate Lagler is offline
Join Date: Nov 2010
Location: Emmaus, PA
Posts: 298

I'm guessing that the second "scrap" piece was smaller than the pieces for your tank? If so, the smaller piece will come up to temperature much faster than the larger ones. It wouldn't surprise me if you went back and did everything exactly the same, just preheating the parts before welding, and had success. As you heat the panel with a torch, you will notice that it flashes with condensation and then it evaporates off. That is a good temperature indicator, or you can simply lick your finger and give it a quick touch listening for the sizzle. Just don't touch the area you are welding and leave burned on saliva to go into your weld.

Aluminum is more conductive than steel, and the rest of the cold metal (especially in the winter time) will be acting as a heat sink while you are trying to weld and cause you to need more heat from the tig torch. This will cause your tungsten to ball up quicker, and if you are a little off 90 degrees on your torch angle the heat will be reflected, probably towards your filler rod causing it to melt before you even get it to the metal. (Filler rod is small and heats up quickly)

People often challenge this saying it's not necessary. You will notice that by the time you are done welding, the entire piece is probably hotter than your preheat temp. You proabably will also notice that about half way through your weld seem, it suddenly starts to weld much nicer and everything is just flowing together. These two things are related.

I sometimes preheat for tacking as well. You get easier nicer tacks, but the metal is hot when you are handling it. After you get it all tacked, preheat again and then weld. No need to jump around, all the metal is going to be welded. If it is going to shrink, jumping around won't help. You will just loose your preheat by doing that. You are a metal shaper, a little planishing will take care of the shrinkage with no problem.

With following all the proper steps to clean the metal (those should be used reguardless of what metal) and the preheat, I always weld my aluminum sheet metal from one side getting full penetration and fusion on the back side. Then simply grind off the excess metal on the back that you pushed through from the other side (and any profile of the front if necessary) and hammer smooth. If you don't get full penetration and fusion on the back, then it isn't welded yet. Welding both sides is a good way to get crack. Oh yea, practice, practice, practice!!
-Nate Lagler
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Old 04-16-2012, 07:27 PM
SWT Racing SWT Racing is offline
MetalShaper of the Month June 2016
Join Date: Mar 2011
Location: Lake Wylie, South Carolina
Posts: 325

I agree with Ransom that your torch angle may be laid back too far if you are balling up the filler rod.

Sometimes when the tungsten ball up excessively, the arc cone gets pretty wide and makes this a little more problematic. Because the arc cone is not as focused, you throw more pedal to it to melt the joint, and then you start melting the filler rod.

I would do as he suggested and try an angle closer to 90 to the joint. I've also found that using Zirconated (brown color code) tungstens helps with preventing the tungsten from balling up as much. It is usually used on MIL-STD-1595 aluminum radiographic quality welds, and prevents tungsten deposits in the weld. This may also help with cracking when planishing the weld after dressing it out, although this is only a theory.

All I ever use anymore are Lanthanated and Zirconated tungstens.
Andrew Slater
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