Howdy,

The design of my footpedal current-controlled DC TIG welder is coming along
smoothly, but it has brought me to a crossroads.

It has come to my attention that welding aluminum with DC is best to be
avoided (I am guessing due to the need to get through the oxide layer), and
so far I am only designing a provision for foot control of DC current (the
current control is via a thyristor bridge after the AC transformer).

Here's my question: this project will have a (low current) HF/HV arc
starting module. If I leave this on while welding with DC, will that,
superimposed on top of the DC current, be of any significant help with
welding aluminum?

Thanks for any insight into this issue,

Jon

Howdy,

The design of my footpedal current-controlled DC TIG welder is coming along
smoothly, but it has brought me to a crossroads.

It has come to my attention that welding aluminum with DC is best to be
avoided (I am guessing due to the need to get through the oxide layer), and
so far I am only designing a provision for foot control of DC current (the
current control is via a thyristor bridge after the AC transformer).

Here's my question: this project will have a (low current) HF/HV arc
starting module. If I leave this on while welding with DC, will that,
superimposed on top of the DC current, be of any significant help with
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.

"Mechanical Magic" wrote:

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.

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?

"Mechanical Magic" wrote:

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.

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

Square wave AC with variable duty cycle is best. More negative cleans

On Sun, 4 May 2008 21:04:24 -0700, "Jon Danniken" wrote

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

Square wave AC with variable duty cycle is best. More negative cleans
better, more positive penetrates better, from what I remember.

Here's my question: this project will have a (low current) HF/HV arc
starting module. If I leave this on while welding with DC, will that,
superimposed on top of the DC current, be of any significant help with
welding aluminum?

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.

Jon Danniken wrote:

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?


I would say 20-200 Hz

"Ignoramus11115":> Jon Danniken wrote:

Here's my question: this project will have a (low current) HF/HV arc
starting module. If I leave this on while welding with DC, will that,
superimposed on top of the DC current, be of any significant help with
welding aluminum?

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, Iggy, I appreciate it.

Jon


Greetings Jon,

"Ignoramus11115":> Jon Danniken wrote:

Here's my question: this project will have a (low current) HF/HV arc
starting module. If I leave this on while welding with DC, will that,
superimposed on top of the DC current, be of any significant help with
welding aluminum?

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, Iggy, I appreciate it.

Jon

Most full function tig welders have this AC as an ajustable

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

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

Square wave AC with variable duty cycle is best. More negative cleans
better, more positive penetrates better, from what I remember.

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
The commercial inverter welders I 've seen use a transistor H bridge between

clare at snyder dot ontario dot canada> wrote:

On Sun, 4 May 2008 21:04:24 -0700, "Jon Danniken" wrote

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

Square wave AC with variable duty cycle is best. More negative cleans
better, more positive penetrates better, from what I remember.

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

"Jon Danniken" wrote:

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
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.

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