welding 3/8" aluminum question

thelbz · Fri Apr 10, 2015 4:18 pm

I have some 3/8" bar stock that needs butt welded, the joint is prepped to 60° and I'm using a old Hobart cyber tig.

When I get my puddle going I have this large crater or void directly in front of the puddle. It seems like the force of the arc is pushing the puddle away from the area where the arc is focused. What can I do to prevent this or is it normal?

Fri Apr 10, 2015 6:42 pm

60* total? 30* per side?

Are you beveled to a land, or a knife edge? How much gap?

How much current are you welding with? How much argon (100% argon, right?) You're on AC?

The devil is in the details...

Steve S

thelbz · Fri Apr 10, 2015 7:03 pm

Beveled to about 3/16 land, yes using argon no need for any helium, couldn't tell you the amperage but the machine has more than enough (no digital readout).
Running 60Hz ,1/8 Tungsten ,#6 cup and 30cfh.

Fri Apr 10, 2015 7:16 pm

thelbz wrote:Beveled to about 3/16 land, yes using argon no need for any helium, couldn't tell you the amperage but the machine has more than enough (no digital readout).
Running 60Hz ,1/8 Tungsten ,#6 cup and 30cfh.

You need control over the amperage to do aluminum with any success. Do you have a foot pedal or hand control on the machine?
(You can also to it with a 2T switch, an on-off on the torch)

Steve S

thelbz · Fri Apr 10, 2015 7:30 pm

Yes a foot pedal, I have been doing 1/8" all week with no issues but this 3/8 is giving me problems.

This is a basic transformer machine pre and post flow, amperage and 10-100Hz frequency. I have a max amperage of 300.

Fri Apr 10, 2015 7:41 pm

It's typical for aluminum to have a huge crater at 60*. I can only suggest backing off the power, or beveling to 75*. I'm sure you're using pure tungsten on this, and a wider bevel will allow you to focus a bit more to the bottom. Are you using the smallest tungsten for the job? I would suppose this to be 3/32 for the root pass, but you may need larger for fill passes.

Steve S

thelbz · Fri Apr 10, 2015 8:09 pm

I'm using 1/8" Tungsten and 3/32 filler on the root. I can try a wider weld prep on Monday. I may just end up using the spool gun but I was just wondering why I am having trouble on this thickness. I did a few joints on some 1/4 no problem but I am not very experienced with tig but I'm sure a new inverter would make things way easier than using a 36 year old machine.

Fri Apr 10, 2015 8:52 pm

That 36 YO machine can stack dimes...

It's a technique or prep or tungsten issue.

A wider bevel and a smaller tungsten for the root may be your solution.

It's tough to say, without looking over your shoulder.

Steve S

Bill Beauregard · Fri Apr 10, 2015 9:54 pm

Are you near perpendicular with the plane of the material? Focusing a short arc on the leading edge of the puddle? I don't know if you can do a single pass on something this thick. Try getting down into the root, filling that, then fill on the second pass.

AKweldshop · Sat Apr 11, 2015 1:53 am

30 cfh seems high, might bump it down to 15-20.

IMO, FWIW.

thelbz · Sat Apr 11, 2015 9:22 am

I'm running multiple passes I don't see how I could possibly do it in one pass.

And the gas is up that high due to a longer stick out to get to the root and avoid contamination from not enough gas coverage, plus I don't pay for gas when I use my machine to make my boss money.
It's most likely just user error on my part but I don't have anyone in the shop to get any guidance from.

thelbz · Sat Apr 11, 2015 9:32 am

This is my current level of ability, this is after about a hour of messing around and the first real time I have tiged aluminum

Bill Beauregard · Sat Apr 11, 2015 10:27 am

More questions; Are you using gas lens? What cup size? Do you have balance control?

I want to be clear, Are you talking about a keyhole blowing ahead of your puddle at the joint in metal?

aeroplain · Sat Apr 11, 2015 10:44 am

1/8th inch filler may help.

thelbz · Sat Apr 11, 2015 10:48 am

Bill Beauregard wrote:More questions; Are you using gas lens? What cup size? Do you have balance control?

I want to be clear, Are you talking about a keyhole blowing ahead of your puddle at the joint in metal?

No gas lens just a #8 cup, and no ac balance just frequency 10-100Hz.

On the root it does keyhole but not a big deal it's on the cover passes where there is material below the weld I tend to get a large crater where the arc is focused.

It's almost like the heat is being pulled away from the puddle rapidly and as soon as I start to taper off on the puddle to fill in the crater the bead cools and causes a very defined crater. I thought possibly that I may not be feeding the filler fast enough but not sure if it would make much of a difference.

AndersK · Sat Apr 11, 2015 4:38 pm

Try and taper off slower and add some extra filler. The more metal you have in the puddle the more it will shrink.

Have you watched where they pour metal in a foundry? You would be amazed how much metal they need to put in extra when the gate starts to cool off.

Bill Beauregard · Sat Apr 11, 2015 4:45 pm

I think you need to be more thorough with cleaning, or turn up EP share of AC. The crater you speak of, is it only at the end of a weld? I've practiced quite a bit, and have to watch pretty careful to avoid. A little extra dab at the end with filler, a swirl motion as you finish, and a gradual taper holding heat at the end longer will control crater.

If it's a crater under the second bead as you progress, you need to move forward with your arc, step harder on the pedal, and wait to dab until the puddle flows to fill the bottom of the joint. This may require you to back away with the arc far enough to avoid fouling tungsten. Remember the sense of accomplishment when you mastered using a clutch, in a truck? It's a lot like that. It'll seem awkward at first.

thelbz · Sat Apr 11, 2015 11:22 pm

Thanks for the input, I will try what has been suggested.

I may not have much seat time next week because I think the job needs to be completed and delivered by Friday.