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TIG Advice
RPS - 12/6/06 at 06:32 PM

Just a little guidance needed, if anyone can help.

I sometimes get a few pin prick holes in the weld when I use the TIG. This seems to be from the molten metal 'bubbling'.

Is this caused by impurities on the parent metal i.e. I need to clean the joint more thoroughly? Or is there some other explanation?

Thanks in advance,

RPS

mark chandler - 12/6/06 at 06:43 PM

assuming the gas is clean etc then yes, impurites.

The longer you dwell on an area the more impurities will bubble to the top (like a miniture melten pot), try more current and use the filler rod to cool the weld, this will make you work faster and lessen the effect.

Regards Mark

Triton - 12/6/06 at 07:02 PM

Clean with thinners especially oil on new steel also the tungsten needs to be kept sharp...touch down and it needs sharpening again.....this gets a ballache when you are learning how to tig weld but once sussed it's really satisfying and better than getting a belt when you touch down

James - 12/6/06 at 07:03 PM

I wonder if it might also be that you're sealing a tube?

I had some issues when TIGing the upper wishbones to the threaded bar. Because I was sealing a tube the hot air inside was expanding and bubbling up through the weld.

I was a bit unsure about it but my instructor confirmed this to be a possibility.

In the end I drilled a small hole for the air elsewhere on the tube. I did the TIG welding then a blob of MIG over the hole.

May not be the cause of your problem though!

Cheers,
James

joneh - 12/6/06 at 07:05 PM

Sorry to hijack the thread but whats the best welding method to use when doing the chassis?

Triton - 12/6/06 at 07:13 PM

Easiest has to be mig but I prefer TIG but welding a chassis can take a tad longer than using a mig set

Simon - 12/6/06 at 07:16 PM

Agree with Triton - I did my whole chassis in TIG as that's all that was available.

I've since spent a tidy sum on a decent MIG, and can't believe how quick I can weld with it.

Just need to keep finding things to weld

ATB

Simon

RPS - 12/6/06 at 07:17 PM

TIG for me, tried to use MMA and couldn't get the standards, never did like MIG too much. And TIG is much more fun to do!

As with the bubbling, I have had it bubble up when sealing a tube, but that usually leaves larger holes not the pin pricks holes I was talking about.

I guess I will have to take more care with the cleaning and will try the more amps and faster technique.

Thanks,

RPS

JB - 12/6/06 at 07:41 PM

Check your rods. I was using the wrong rod and the correct ones that were a little dirty.

Lack of gas can also cause the problem.

John

Simon - 12/6/06 at 07:46 PM

Could also be the wrong gas - what are you using?

ATB

Simon

JohnN - 12/6/06 at 08:08 PM

Welding mild steel by TIG requires the use of high purity steel filler rod. I had the same problem as you when I tried using some old gas welding filler rods with my TIG. TIG certified rods from my local stockist solved the aero bar problem

907 - 12/6/06 at 08:32 PM

You could be "boiling" the metal. If you have a soft start or slope in, then use it.

Failing that, start with a lower tungsten angle and get the first blob of filler in quickly.
Turn the amps down a bit and go slower.
As already said, the filler is double deoxidized so better quality than the base metal.

Paul G

Triton - 12/6/06 at 09:07 PM

Top Tip:
Use mig wire rather than expensive filler rods unless you are welding something more exotic than mild steel.

NS Dev - 12/6/06 at 09:46 PM

Noooooo!!

As was said further up the thread, you need TIG specific rod, gas rod or mig wire will usually result in bubbling (in my experience which is limited, but also follows the advice of my local welding supplier, who gave that advice despite having gas rod on the shelf and having run out of tig rod.

Decent tig rod is not copper coated (as is also the case with decent MIG wire) as the copper can also contaminate the weld slightly.

Basically check the base metal is clean (also cheap steel sheet from the far east will frequently contain inclusions which will bubble welds as well) then use TIG grade rod and if you still have probs its probably down to boiling the weld.

kaizokuace - 12/6/06 at 11:22 PM

how does wire feed speed affect the weld? i want to see how i can control the weld with the feed. cuz i tried it at a higher rate and it makes a mess and i dont know how well it penetrates and slow speed seems to get me more blowing holes thru the tube.

Peteff - 12/6/06 at 11:28 PM

What does this mean? It sounds like the gas is not shielding the weld and you are carbonising the metal.

NS Dev - 13/6/06 at 05:57 PM

quote:
Originally posted by kaizokuace
how does wire feed speed affect the weld? i want to see how i can control the weld with the feed. cuz i tried it at a higher rate and it makes a mess and i dont know how well it penetrates and slow speed seems to get me more blowing holes thru the tube.


that's mig not tig, if you do a search on here for mig welder setup you should find lots of info.

907 - 13/6/06 at 07:37 PM

quote:
Originally posted by Peteff
"You could be boiling the metal"
What does this mean? It sounds like the gas is not shielding the weld and you are carbonising the metal.



Hi Pete,

I'm not good at explaining things but I'll have a go.

Steel melts at 1450 C (ish)
The Tig arc can be as high as 5000 C
The sudden ZAP of the arc can "boil" the metal before heat starts to dissipate through conduction.
Careful observation will show minute gaseous bubbles rising to the surface of the molten pool and bursting,
just like watching water boil.
Some of the bubbles get trapped as the metal solidifies and this we call porosity.
It is inevitable that the odd bubble will freeze just as it bursts, and this we will see in the weld surface as a pore or pin hole.

Other metals do this. Brass is a fine example, only with this alloy it's the zinc that boils if over heated.

The cure? No more heat than necessary, soft start, and get the filler rod in quickly.
Don't puddle the weld pool without adding nice pure filler.

HTH

Paul G

[Edited on 13/6/06 by 907]

John Bonnett - 15/6/06 at 04:23 PM

Hi, The problem with the bubbling is the rod. To TIG weld mild steel you must use triple deoxidised welding rods. The rods you are using are fine for oxy acetylene but absolutely not for TIG. If you have trouble sourcing them please let me know.

Hope this helps

Cheers

John

RPS - 15/6/06 at 06:42 PM

Thanks for all the advice.

The rods I am using have the following written on then end of the tube:

Dia. 1.6mm
SIFSTEEL
No.11

Are these right or wrong?

Cheers,

Richard

Peteff - 15/6/06 at 07:06 PM

Got that Paul, I see what you mean.

John Bonnett - 17/6/06 at 10:31 AM

When TIG welding mild steel, you must use triple deoxidised welding rods. Standard rods are fine for oxy-acetylene but absolutely not for TIG. The bubbling as has been corectly pointed out is due to oxide and this is coming from the rod and no amount of cleaning will solve the problem.

John

John Bonnett - 4/7/06 at 10:50 AM

Sorry this has taken so long. The rods you need for TIG welding mild steel are SIFSTEEL A15.

Cheers

John