Aluminium orbital Welding with Reverse polarity

By Lawrence (*****)

Date 03-16-2012 13:52

Hey 46

I've done limited DCEP welding of aluminum, however I have done many thousands of magnesium welds with DCEP and GTAW.

You are doing orbital yes?

Comparatively thin base metal?

I've never seen this done with orbital, but I would imagine that parameters would be very tight and very difficult to put sequence.

Say more about your project.

By 46.00

Date 03-16-2012 20:02

Hi Lawence,

We are welding 1½" to 6" OD Aluminium pipe which is 3 to 4mm thick. These welds are performed with DC-(negative) pulsed orbital GTAW sets.

Like I stated, never come across this method before and just wondered if anyone on here had experience of this technique?

By Lawrence (*****)

Date 03-17-2012 01:51

Ok I see why I was confused

You said "DC-(reverse polarity)?"

Maybe a language thing..

DC- is also known as DCEN, DC electrode negative and DC Straight polarity

DC+ is also known as DCEP, DC electrode positive and DC Reverse polarity

DCEN is fairly commonly used with helium gas on thick sections of aluminum.. I'm sorry that I don't have experience with this specific process and orbital units.... I know you will spend quite a bit of effort on process control and surface prep... Especially if your orbital employs AVC.

By MMyers

Date 03-19-2012 21:20

I've seen a procedure that used pulsed DCEN with helium for orbital aluminum. I would say I've run it, but that would be lying because I have only run the 1G section of it for development purposes, but it wasn't a bad weld by any stretch of the imagination.

By Tommyjoking (****)

Date 03-19-2012 22:29

Not trying to hijack but just adding a question to the subject. You can get a lot more heat input with DCEN and helium per a given power supply and equal amperage settings right? Ran into that problem recently on a field weld, just did not have enough AC output (had to use a torch to help out) and I considered getting a small bottle of helium to run it DC straight. Never have tried it.

By MMyers

Date 03-20-2012 14:21

"heat input" as defined with the variables of volts, amps, and travel speed. So according to the definition, no, changing the gas does not change "heat input".

Now according to the arc physics, the plasma temperature will be higher, which combined with some other things typically makes the material flow better. I've welded some materials where helium additions didn't make a whole lot of difference, I've welded other materials where you needed every bit of helium you could get. It all depends.

I'd suggest trying it just to say you've run it, but try it on something you don't care about before you try it on something that counts. DCEN helium on aluminum is an entirely different animal than AC aluminum. Oh, and prep, as Lawrence mentioned above, is everything.

By Lawrence (*****)

Date 03-20-2012 14:30 Edited 03-20-2012 14:39

Ok... To double hijack the thread..

MMyers... I think it's a matter of perspective..

A change to helium gas almost automatically is going to allow for an increase travel speed... (especially in an orbital setting) Which is a direct componant in figuring heat input :)

By MMyers

Date 03-20-2012 15:52 Edited 03-20-2012 15:56

As is ionization potential which changes voltage (for a given arc length), and don't forget that going from AC to DC will change a few things too :)

As my previous post says "it all depends". Heat input is still only amps, volts and travel speed, so all other things equal, change gas does not change heat input. What you choose to mess with after changing gas is a different story and obviously will change heat input.

Now for the application in Tommy's post, if I were having trouble getting a good puddle, I don't think speeding up would be on my list of things to do after changing shielding gas.