DCEN Voltage for different materials, GTAW

[Capntom]

Hello:
I seem to recall a chart of recommended voltages when GTAW steels. I can not seem to find it anywhere, anybody have a link to it?
Typically 300 SS was around 9.0 DCEN. The specific reason is that we are Welding Inconel 718 and are getting a 50%fallout from X-Ray. Inclusions mainly. I believe our welders are "boiling" the puddle. The Voltages are at 12.5 VDC up to 13.5 VDC. He is weaving a 1/2" wide bead on plate material that is .125 thick. I am unable to locate the original WPS, not sure one was even generated.
Someone suggested using Argon-Hydrogen at 2.5% ??
Thanks for your advise in this matter.

 

[pipewelder1999]

For the GTAW process that is manual, the voltage would be governed by the machine and the amperage.

The amperage is what I would check. The nickel alloys can get a little sluggish and weaving has not worked well for me when welding by hand.

I have no experience with 718 so it may be a different creature.

Gerald Austin
Iuka, Mississippi

http://www.weldingdata.com

 

[Mr168]

I will second that. The nickel alloys do indeed have a sluggish puddle, and when not experienced in welding them, can lead the operator to increase the amperage in an attempt to get it to "wet out" more. The fact that he's trying to create a 1/2" weave on 1/8" sheet would lead me to believe that the welder is striving for appearance more than anything, and may not be suitably skilled for this job.

 

[stanweld]

Capntom
Constant current power supplies are used with GTAW. Arc voltage is a function of tungsten tip to work disatnce, amperage and shielding gas type. Without Automatic Voltage Control(available on automatic equipment), the arc voltage will fluctuate as the welder manipulates the electrode and it would be highly improbable for a welder to maintain 9V without sticking the tungsten, resulting in a tungsten inclusion.

The flaws defined are workmanship flaws, which can be mitigated with increased training, changing shielding gas to Argon-Hydrogen or Argon-Helium mixes, decreasing weave, shape of tungsten tip, and quality of shield gas.

 

[gtaw]

I agree with most of what has been said.

Arc length will determine the arc voltage and it will vary as the welder either lengthens or shortens the distance between the end of the tungsten and weld puddle.

Voltage will also vary if the shielding gas is changed.

A small percentage of hydrogen (5%) may be added to the Argon to increase penetration, but it will not do much for the fluidity of the puddle. Nickel is like toothpaste in the puddle. It doesn't wet out like carbon steel and simply increasing the amperage does little to help.

This is where stringer beads will result improve the appearance of the bead. Be sure to clean between each weld pass. Wire brushing is not aggressive enough. You will need to use a carbide rotary file (burr) or grinding disk. Don't bear down hard, just enough to abrade the surface to break up the surface oxides. Wire brushing will "shine" the bead, but it will not break up the oxides. If the oxides are not removed between passes, it will build up with each successive bead and the weld will wet in less and less.

Good luck.

Best regards - Al

 

[pipewelder1999]

I second the interpass cleaning. I didn't mention it because of the thickness. The interpass temperature and amount of interpass cleaning can really make a difference on hoe the oxides build up. I have only used Ar and never on the mentioned alloy but on other Nickel and Copper/Nickel alloys I have noticed that reducing the interpass temperature decreases the buildup of oxides on the surface.



Gerald Austin
Iuka, Mississippi

http://www.weldingdata.com

 

[strider6]

try this source of data from Miller

http://www.millerwelds.com/resources/calculators/tig_amperage_calculator.php

http://www.millerwelds.com/resources/TIGhandbook/

hope this help

S


Corrosion Prevention & Corrosion Control

 

[Capntom]

Is there any test for residual oxides left on the surface? I found a knotted rotary SS wire brush that works great in a pneumatic tool. The alloy really flows nicely after brushing.
I am looking for a more pro-active test to confirm successful brushing.
We changed to stringer beads and they are helping with his consistency of the arc gap and subsequent voltage.