Tig / Mig / Aluminum / Stainless help

[jwmorris]

I don't think it's a question on if you should go with a MIG or TIG, you really want both. Same goes or Oxy/Act or plasma, to do anything all you need is one of everything.

Craigslist will find you and older liquid cooled Miller TIG for around $1000 and you will likely get some extras with it. Pass on the Chinese stuff.

 

[Mark @ Everlast]

Square wave TIG machines have been around for quite a while. I used to have a Lincoln Square Wave TIG 255 with the digital control panel. On a transformer rectifier machine you still need continuous high frequency on the AC output, even if it's square wave, when welding aluminum but on DC you can just use it for the start. On inverter based machines like a Miller Dynasty, which is also square wave, you don't need continuous high frequency for aluminum but do need it at the start. The reason you don't need continuous HF on an inverter is because inverters themselfs work on the high frequency principle. Transformer machines operate at 60 cycles where inverter machines operate over 1000 cycles. I've tried finding out the frequency inverters use but couldn't get an exact number except it can be over a 1000 cycles. That would explain why continuous HF isn't required. As far as changing polarity, the high end machines allow you adjust the balance/time between the - and + of the AC cycle. The electrode positive side does provide cleaning action but without the HF to cut through the aluminum oxide, that melts at a higher temp. than the base metal, you wouldn't get a sound weld. A tombstone is a very basic machine and doesn't have square wave. You can buy HF controls but they will cost more than the tombstone. I think a Miller 251 HF is about $800.

Arc Weld,
there's plenty of information on inverter frequencies out there. Ours cycle (depending upon the unit) from 40khz to 120 khz. Miller's is somewhere between 80-10khz, if not a little higher.

 

[Arc weld]

Did you mean 80 to 100 khz on a Miller? I looked a while ago and even asked a Miller rep. who didn't know. Wow:shocked: That is pretty high frequency at over 100,000 cycles! Thanks Mark:thumbsup:

 

[Mark @ Everlast]

Yeah. Miller discusses the frequencies in some of their "informational" literature on inverters.

Here's one such place: http://www.millerwelds.com/resource...-amplitude-balance-waveform-controls-inverter
and another: http://www.millerwelds.com/resources/articles/index.php?page=articles31.html

 

[Arc weld]

Those articles give a really good explanation. Although basic, at least my explanation was pretty close.

 

[bikerdib]

You could try this old trick, I've never tried it, but have all the confidence in the world it will work! This was posted on another site by a member who passed away couple years ago. Rest in peace Ken!
I respected and admired this gentleman immensely! He was a weldor and engineer.

Dropper resistor trick for CC constant current machines only!
You need to use a dropper resistor made from a piece of 3/32" or 1/8" filler rod, depending on the amount of amps you want to drop.
Attach the 1/8" filler rod to the welding bench with a vise-grip and let it hang vertical then attach the ground clamp to the other end of the filler rod.
As the arc is established the filler rod (dropper resistor) will begin to heat thus lowering out-put amps at the torch / stinger.
CAUTION as the filler rod can become cherry red depending on the amount of amps being dropped.
To adjust for the correct amount of amps required of the weldment, one could trim the filler rod to different lengths or change the diameter although I've never found this to be necessary.

It will work and give some control and you don't have to trim the electrode, you simply move the ground clamp on the rod. More distance between the table and ground clamp = more resistance and thus more amperage drop. Less distance between = less resistance and less amperage drop. This gives some fine tuning but requires a LOT of trial and error. You just have to make sure the ground clamp doesn't touch the rod anywhere below where it is clamped. Anything hanging below the clamp will have zero effect on the resistance. But of course you could make up a variety of different lengths and keep them sorted so you know about how much drop each provides.

 

[CNC Dan]

Square wave TIG machines have been around for quite a while. I used to have a Lincoln Square Wave TIG 255 with the digital control panel. On a transformer rectifier machine you still need continuous high frequency on the AC output, even if it's square wave,...

I think on the older transformer square wave machines the waveform wasn't all that square. Thus the need for the HF.

when welding aluminum but on DC you can just use it for the start. On inverter based machines like a Miller Dynasty, which is also square wave, you don't need continuous high frequency for aluminum but do need it at the start. The reason you don't need continuous HF on an inverter is because inverters themselfs work on the high frequency principle.

They do. But that's before the output stage. The output frequancy is often adjustable on inverters. And even on 60 HZ output you don't need HF. I have a miller dynasty and can change the output to a sine wave. Next time I'm welding something I'll try using that waveform an see how it goes.

Transformer machines operate at 60 cycles where inverter machines operate over 1000 cycles. I've tried finding out the frequency inverters use but couldn't get an exact number except it can be over a 1000 cycles....

I've heard 10KHZ to 20KHZ. But again, that's before the output stage. The output AC is generated after the 10KHZ to 20KHZ is rectified and filtered to DC. I think the inverters super quick change from pos. to neg. is the reason HF isn't needed.

....
That would explain why continuous HF isn't required. As far as changing polarity, the high end machines allow you adjust the balance/time between the - and + of the AC cycle. The electrode positive side does provide cleaning action but without the HF to cut through the aluminum oxide, that melts at a higher temp. than the base metal, you wouldn't get a sound weld.

So how does DC tig handle the aluminum oxide? Helium? Super clean prep?

A tombstone is a very basic machine and doesn't have square wave. You can buy HF controls but they will cost more than the tombstone. I think a Miller 251 HF is about $800.

I agree with that. If I only had a AC/DC transformer machine and needed to weld aluminum, I'd try DC with helium.

 

[Arc weld]

I'm not an electrical engineer so don't have all the answers but on the sq. wave 255 transformer machine I had, you could adjust the AC balance. The sq. wave TIG 355 had all kinds of adjustability. You don't have to have any HF when welding steel or stainless. On the start it helps so you don't accidentally contaminate the tungsten. DC TIG on aluminum is extremely rare and from what I've read is very difficult to find the sweet spot. Even if the high khz of an inverter machine are reduced after being rectified, there still has to be a significant increase in hz at the arc to allow to not need continuous HF at around the same amps as a transformer machine. Inverter machines also have a much finer arc and you use a pointed tungsten on AC. If the super high hz of an inverter made no difference at the arc, there wouldn't be much sense in making them other than to save power. I found an XMT 304 inverter to be extremely smooth burning 7018 and you almost didn't even need to strike an arc. However on MIG, I think it was too smooth and much preferred the MIG arc of a Dimension 452 transformer machine.

"I think the inverters super quick change from pos. to neg. is the reason HF isn't needed." That's the same thing I was saying when I said inverters work on the HF principle. hz refers to how fast the AC switches from - to +.

 

[Mark @ Everlast]

It's not the Hertz that stabilizes the arc with HF. It's the switching speed of the IGBT's that speed it through the 0 point so the arc virtually never goes out. Arc Weld, when you say high frequency, it's referring to inverter speed, not an overlaying HF with continuous high voltage/high frequency for transformer welders. Two completely different animals.

There's a lot of reasons to make an inverter. The power can be diced and sliced exactly as it is needed. It can be made to weld CC or CV for different processes with relatively minimal effort. It's also much more compact.

Some tranformer units, the top end ones, have a limited AC adjustment for balance, but not near as much as most inverters offer. The real kicker is the AC frequency adjustment...which is not typically found on standard transfomer welders.

 

[CNC Dan]

I'm not an electrical engineer so don't have all the answers but on the sq. wave 255 transformer machine I had, you could adjust the AC balance. The sq. wave TIG 355 had all kinds of adjustability. You don't have to have any HF when welding steel or stainless. On the start it helps so you don't accidentally contaminate the tungsten. DC TIG on aluminum is extremely rare and from what I've read is very difficult to find the sweet spot. Even if the high khz of an inverter machine are reduced after being rectified, there still has to be a significant increase in hz at the arc to allow to not need continuous HF at around the same amps as a transformer machine. Inverter machines also have a much finer arc and you use a pointed tungsten on AC. If the super high hz of an inverter made no difference at the arc, there wouldn't be much sense in making them other than to save power. I found an XMT 304 inverter to be extremely smooth burning 7018 and you almost didn't even need to strike an arc. However on MIG, I think it was too smooth and much preferred the MIG arc of a Dimension 452 transformer machine.

"I think the inverters super quick change from pos. to neg. is the reason HF isn't needed." That's the same thing I was saying when I said inverters work on the HF principle. hz refers to how fast the AC switches from - to +.

Sorry thats not what i ment when i said "how fast it changes from pos. to neg.". I was refering to the waveform( square vs. sine) and not the frequency( how many times per second).