AC TIG: balance control vs. differential current adjustment

[mjc79]

I started a new job back in February, and I use a Dynasty 350. I weld mosty stainless, but I get quite a bit of aluminum as well, and I have been having trouble getting heavier aluminum to weld decently. (I weld alot of 1/2" aluminum, and some thicker.) I have been experimenting with settings quite a bit, but I would really appreciate some knowledgeable guidance.

I have a question about AC current settings for TIG welding aluminum when using an advanced power source like the Dynasty 350. I am not quite sure how to word this, but what is the difference between increasing the balance control (for more penetration and less cleaning) and changing the ratio of EP and EN current (increasing the EN and decreasing the EP, for more penetration and less cleaning)? I undertand that the differential current control affects the actual amperage each of "side" of the AC wave, and that the balance controls the proportion of time that the arc spends on each side regardless of current the current setting. But do these two approaches simply achieve the same thing in different ways, or is there a difference in the arc? I hope that question makes sense.

It seems to me that achieving the more penetration/less cleaning condition by turning up the EN and/or dropping the EP gives more of a sharp, biting, and harsh arc, while leaving the EP a little higher and turning the balance up gives a focused but smoother arc with a more fluid puddle, maybe? Has anyone else made observations like this? (My observations may not be very accurate because I have the bad habit of trying to make too many adjustments at once.)

I have been trying to get the most heat I can out of the machine for welding thick aluminum, and I tend to dislike the arc characteristics I get when I have the settings really cranked up. (I am sure there are some technique issues involved as well.)

I would appreciate any info, observations, or advice anyone might have on this. Thanks much!


-mjc

[ASKANDY]

mjc,

You are correct in saying they do somewhat have the same effect. By lowering the EP, the cleaning zone does decrease and so does the average amperage. while changing balance, the cleaning changes but the average amps do not.
When running less EP, the amp swing from EP to EN is less severe and is less destructive on tungsten. If you are looking for increased power at the weld, you can turn the EP down, EN up and increase the main amperage to suit your material thickness. Try a 2/3 EP ratio at first and go as high as 1/2 if less cleaning can be used. Example: 2/3 ratio would be 200 Amp EP, 300 Amp EN, and a 1/2 ratio would be 150 A EP and 300 A EN. If you get too low on your EP you will not get enough cleaning and your welds will grey up and look bad especially at the toes.
The frequency focuses the arc. Higher the number, tighter the arc will be. The freq setting will be determined by joint design. If you have an outside corner joint, the freq should be less to tie in the toe edges. If the joint is an included angle where you have to weld in a tight spot, turn the freq much higher to get in the tighter, deeper joint.
Turning the freq up will also put more heat in a tighter area which will also give deeper penetration.

Hope this helps.
A-

[Broccoli1]

http://www.millerwelds.com/resources...rticles46.html

[SundownIII]

mjc79,

Can't make things any clearer than Andy has already done.

I would make one additional suggestion on something to try. If you're using the advanced squarewave (AC Waveform) try shifting to the "soft squarewave". That may take some of the harshness you're experiencing out.

You didn't define "thicker aluminum" in your comments, but assuming you're pushing the machine limits, you may wish to try adding a little (10-25% helium) to your gas mix. Will result in a much hotter arc.

[ASKANDY]

Good point on the Helium.

A-

[H80N]

Guys
this is just one example of the types of questions that would be addressed by the Dynasty Textbook/Handbook
tnx
Heiti

[HAWK]

Have you considered running DC GTAW with UHP+ helium? It is a completely different process and your customer may not accept it. If interested, do a thread search. Penetration results may surprise you. You can use a lower amperage with smaller tungsten and not out the max out your machine. It does take practice. I have several posts regarding this process as do a few others. I know NASA has specs for certain aluminum alloys using this process. Good luck.

[H80N]

Wes
Great to see you back!!!!!

Heiti

[SundownIII]

Hawk,

Pangea (works for NASA) and BC on the Hobart board are big fans of DC and "lab grade" helium for heavy aluminum weldments.

I've used DC/straight Helium quite extensively in the past, but for many years now, I've found I can get my work done with AC and the addition of about 25% helium.

DC welding with Helium definitely has it's place, but when you factor in the cost of the Helium along with the higher flow rates required, your covering gas ends up costing you about 7 times as much as using Argon.

Sometimes you just got no other options though.

[con_fuse9]

mjc,

If you get too low on your EP you will not get enough cleaning and your welds will grey up and look bad especially at the toes.

A-

I have not experiment much with the setting. Right now 3/4 ratio.

Question:
As long as I see the cleaning area around the weld bead and no graying (even at the toes) can I assume that I have enough cleaning?

Slightly different question:
Which is a better indicator of enough cleaning, the color of the bead, or the size of the cleaning zone around the bead?