There is alot of good info people are posting up here, and alot of shit. Like off the wall shit.
Let me break it down for everyone here, “GTAW power source basics”, I’ll call it
Your are looking for a tig machine that can weld aluminum and stainless and mild, ect (Non-Ferrous&Ferrous metals)? Right? Right.
Tig machines CONSTANT CURRANT machines, meaning they have a sloping volt/amp curve. In a CC machine, the AMPS are your “HEAT” CC mahicnes can also “Stick” weld.
These machines are sold as DC (direct currant) or AC/DC combo machines (alternating currant/direct currant)
DC: this is what you use to weld mild steel, stainless, titanium, nickel, inconel, other exotics.
AC: this is what you use to weld non-ferrous metals like ALUMINUM or magnesium, ect.
The welding currant can be “distributed” a few different ways (we are talking tig, so i will explian how that is distributed)
You can have DC like this:
-scratch start: you have to strike your tungsten on something (a piece of copper is good) for the arc to start. Usually, you have no amprage control, if the machine is set at 125amps, thats what you get, no remote foot pedal or fingertip control here. This is old school, and alot of REALLY good pipe welders from way back sometimes still use this.
-“touch start” or “Lift-Arc TIG”: This is where you push your foot pedal down to start currant flow, touch your tungsten to what you are gonna weld, and as you lift it up, the arc starts. This is leaps and bounds better than scratch start tig. You can use your remote amp control, and you don’t leave tungsten deposit’s in the finished weld.
-High Freq start: This is the modern, most common way to strike and arc. Hi freq is added to the welding currant to start the arc, once the arc is started, hi freq shuts off. This allows the tungsten not to touch the work at all. Makes life alot easier.
You ALWAYS weld with ELECTRODE NEGATIVE when welding with DC currant, gives you good penetration, and does not put too much heat on your workpiece (tungsten)
Now, here is how your AC currant works:
High freq is ALWAYS used to start the arc.
High freq is ALWAYS used to MAINTAIN the arc on a TRANSFORMER/ RECTIFIER type power source.
AC currant switches between ELCTRODE NEGATIVE and ELECTRODE POSITIVE. The two half cycles of the AC wave (EP&EN) is what enables you to weld aluminum with it.
The ELECTRODE POSITIVE portion of the half cycle gives you the CLEANING action required to break up the oxide coating which forms on aluminum
…Then the opposite side of the half cycle is:
ELECTRODE NEGATIVE. This is where you get your PENETRATION from.
The switching of EN to EP is what gives AC tig welding that distinctive “buzzing” noise.
Now, everytime the currant switches from EN to EP, the arc will go out. That is why high freq is added to the welding currant. It helps maintain the arc when it drops to “0” between half cycles. (It’s real simple, look at an AC sine wave, you’ll see what I mean)
This only holds true with the TRANSFORMER type machines, like a Miller Syncrowave, or a Lincoln Persision TIG.
INVERTER power sources (Like a Miller Dynasty 200/350/700) use “Advanced squarewave technology”, which eliminates the need for CONTINUOUS high freq, due to the differnt shape of the AC waveform. They still use it to start the arc, but not to “carry” the arc. I’m not even going to get into the crazy shit these machines are capable of, but they are THE CAT’s ASS. Period.
Now, you can weld aluminum with Direct Currant, Electrode positive, in a vaccum chamber. You can also weld it with DC, electode negative too. This is total shit, not even worth trying. If you ever think you will want to weld aluminum, you get an AC/DC machine. Don’t cheap out and buy a DC only machine, because they cost half as much. Do it right the first time. There is always some cheap fuck out there that will tell you, you can do this with this and so on, but at the end of the day, it’s all half assed. You need AC to PROPERLY weld aluminum.
What do I recommend for a machine? A Miller Dynasty 200DX TigRunner package. It’s only $5,500.
But, in all seriousness, I would pick up a used Sycnrowave 180SD (later model, not one from the mid 1990’s, one from like 2003 or around there, it’s a better machine) Or buy a new Syncrowave 200. You would be looking for something that puts out around 200amps, unless you plan on welding cylinder heads for top fuel drag cars. The similar offerings form Lincoln are 100% on par with the Millers. Pick what color you like better, blue or red? They both make great products.