Effect of AC Balance control on aluminum
When the tig welding process was first developed, it used pure DC current to weld with. Early models of it were designed primarily to weld and repair the magnesium and aluminum products found on airplanes and related equipment. The original name Heli-arc came from the helium originally used in the DC aluminum welding process. It was a name brand at the time but the name became synonomous with the TIG welding process. Many older welders still refer to TIG welding as "Heli-Arc", though that name is now owned by ESAB.
Reverse polarity (DCEP) allows electrons to flow from the base metal to the electrode tip. Since aluminum rapidly forms an oxide layer which has a melting point much higher than the aluminum itself, the DCEP provides the force necessary to break up the oxide layer to allow the molten aluminum underneath to be welded. Since applications of aluminum welding were primarily in the aviation industry, the shallow penetration allowed by the use of DCEP wasn't a problem for welding on thin sheets of aircraft grade aluminum.
DCEN soon came around but it was only suitable for steel and other metals that don't rapidly form such oxide layers. In fact, it was superior in all respects except aluminum and magnesium. The problem faced when welding in with DCEP is that the tungsten is rapidly contaminated by particles flying toward the electrode tip by force of the electrons. It also causes the tungsten to get quite hot and ball up very quickly, destabilizing the arc.
After a while, AC machines with a high frequency overlay of current came on the scene which allowed both AC and DC type welding. The advantage of AC was clear. It was much more adept at welding aluminum. The AC positive to negative cycle proved to be the best of both worlds: cleaning and penetration.
As inverters were developed, the technology became available to adjust the previous 50/50 positive, negative balance that the older transformer machines only afforded. The newer technology allowed adjustment in the "balance" of positive and negative parts of the Altenating Current cycle. It was noticed that a 50/50 balance wasn't needed for the majority of aluminum welding tasks. In fact, a setting of 30% DCEP is often recommended by various professionals. Although this is not a steadfast rule, 30% DCEP seem to be the most efficient setting for most people. As you notice, there is a wide range of adjustment in the Balance control of many welders. This is fine. It will allow you to find your own comfort level when welding aluminum.
