Things that will make your arc spread out wider in A/C mode (and give you a wider, less penetrating bead):
* more EP% (more "cleaning") AC Balance setting
* rounder tungsten shape (think more "balled", not as "sharp")
* longer arc length
* lower AC frequency
Usually, the only applications where I will sometimes purposely want the arc to be spread out wide is for some build-up operations. Then for example you can build up without penetrating and "mixing" very deeply into the parent metals. Usually for joining two pieces together, I will want a more narrow, deeper penetrating arc.
If your weld puddle is slumping it's because you have over penetrated on the the back side, and gravity is taking over on that large molten puddle. With a small enough puddle, surface tension "wins" over the force of gravity (and you can even weld upside-down, for example.) With a large enough puddle, gravity will eventually win over and pull the puddle downwards. You may be overheating the piece of metal you are welding on if the puddle is growing too big. If that is the case, you need to let it cool down, then weld "hotter and faster". Or, there is nothing wrong with doign some welding, then stopping for a few seconds or maybe even longer, to let the workpiece cool down some, before finishing off the bead. Sometimes that is necessary to maintain puddle control approaching an edge to prevent the puddle from spreading out way too wide.
You could put a piece of copper backing plate tight against the back side of the weld if you wanted to "cheat" a little bit. You could certainly penetrate better while keeping the back side from sagging.
Don't expect to be able to fully penetrate on aluminum with a well-fused backside, while welding from one side only with the A/C TIG welding process. Aluminum just doesn't work that way, usually. If you liquify the material through to the back side, oxides will form on the hot back side, that the A/C arc will not break down. As a result, the puddle will not "wet out" on the back side. If you penetrate through about 90% of the material depth, you can build the bead raised up on the front side a little bit to make up for the lack of penetration, and still achieve decent strength through the weld (notwithstanding loss of heat treatment and cold working from the annealing of the metal.) Welding on both the front and the back sides is best if you don't want any discontinuities on the back side, for A/C TIG welding.
Aluminum certainly doesn't weld like steel does.
'13 Everlast 255EXT
'07 Everlast Super200P
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