TIG welding aluminum

Jon, For ultra thin materials, DC/HF may work, reverse polarity IIRC.

But for sheet metal on up, nope.

There is a VERY significant swirl on the puddle caused by the AC, that moves crap to the edge. On many settings, it is almost invisible, depending on the machine.

Dave

No. The point of AC is that the reverse polarity cleans the aluminum oxide layer, thus achieving a good bond. HF would not help with it.

Thanks, Dave, I appreciate that. Didn't know that about the puddle, either, so I'll watch for that.

Alrighty then, so a squarewave would be the easiest waveform to make, would that be a sufficient enough selection of waveforms, and what frequency range would be most useful?

Jon

I would say 20-200 Hz

Square wave AC with variable duty cycle is best. More negative cleans better, more positive penetrates better, from what I remember. Almost needs to be an inverter unit to do this.

** Posted from **

Thanks, Clare, I appreciate it. A duty cycle control shouldn't be too hard to put in there, if I'm feeding them anyway.

Brings up another issue though, I'm guessing the waveform will need to swing from positive to negative, and not just dance around above the work potential. Hmmm, I'll have to think about that one.

Jon

Thanks, Iggy, I appreciate it.

Jon

Thanks for that, Iggy. That's a nice approachable range. I'm smelling a

555 chip in this thing.

Jon

Greetings Jon, Years ago I was taught how to weld aluminum with DC tig. The material was .25 wall thickness 6061 channel. I had to clean the aluminum with a cleaner that had hydrofluoric acid in it. Anyway, the parts were milled first with a 45 degeree angle on each edge about 2/3 of the material thickness. The resulting groove at the butt joint was then about 5/16 wide. I used helium, not argon, because helium welds hotter. I filled the groove in one pass using 1/8 rod with the welder in the 125-300 amp range. Lots of black residue was left on the weld but since the tops of the weld were ground off this didn't matter. Ac is really much better and the cleaning action is remarkable. ERS

Most full function tig welders have this AC as an ajustable feature...more bias one one for cleaning, the other way for more penetration.

Personally I use more penetration by about 60/40 over cleaning most fo the time, at about 60 hz, though I do have the option of going from

1pps to about 300.

Many plain tig welders get by just fine at 60 hz

Gunner, Dauber at Large.

Political Correctness is a doctrine fostered by a delusional, illogical liberal minority, and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a turd by the clean end.

The commercial inverter welders I 've seen use a transistor H bridge between the DC output and the work piece to get the AC output. The technology is the same as a VFD but single-phase only. A microprocessor would seem to make it fairly easy to vary both freq. and pulse width as needed.

Randal

Thanks, Randall, I appreciate that. When I was looking at inverters the other night (from Clare's suggestion), I was contemplating a two-mosfet jobby, such as this:

Since I haven't built an inverter of any type before, what would be the advantage of going with an H bridge?

Thanks,

Jon

Thanks, Gunner, I appreciate knowing your experience in this matter. BTW, in your usage, do you tend to find having a foot control an important part of TIGging aluminum?

Thanks,

Jon

Not sure if it will help but I posted the schematic of my Hitachi inverter TIG to the dropbox a couple of years ago

and .

Could you get the best of both worlds if the bias was changed back and forth at a few hertz? Spend a portion of a second 'more negative' then 'more positive' etc etc.

Dave

Sounds like a center tap output with the center driven from one rail, to the other or between by a control pot shifting the waveform to be all + or all - or any area within.

Mart> clare at snyder dot >> On Sun, 4 May 2008 21:04:24 -0700, "Jon Danniken" wrote

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If you have a center tapped power transformer, you can get polarity reversal and DC shift rather than just pulsing out of two switches. Without the center tap, you need to swap the work and the electrode polarities with 4 switches (H).

Not related to this conversation, but here is a pointer to a guy who built a TIG machine from a buzz box I think:

Good Luck, BobH

Gotcha, thanks Bob. I was wondering about how I was going to get the polarity shifts, didn't think about swapping it out between the two leads.

Thanks for that tip! [NPI] :)

Jon

An inverter welder is really a switching power supply with an unusual control loop and a strange load. Even the H bridge is pushing into that area. There are a number of good books on switching power supply design. My favorites are by a guy named Marty Brown, "Practical Switching Power Supply Design" and "Power Supply Cookbook". He talks about switching section design as H bridge or half bridge and thermal aspects and lots of good stuff. Powells Technical books in Portland, OR is where I got my copies.

Also, I did not want to speak for Gunner, but your question about TIG'ing aluminum and footpedals - I think you need the footpedal even more for aluminum than steel, and I would hate to weld steel without one!

Good Luck, BobH