Thread: Bubble at end of TIG weld

Sounds like a crater. As things cool too quickly you can get a crater. One tip I got from TAFE teachers is to back off the pedal slowly and just swirl the arc around to keep some heat on the last bead for a second or two.

On advanced wave machines you can set the downslope control to back off the current slowly after the pedal or button is released.

http://www.millerwelds.com/resources...-guide-graphic

Could be a crater yes. Unfortunately my TIG is a pretty basic unit so it's either on or off, but I may be able to vary my technique to reduce the amount of heat at the end by going backwards or similar just as I stop. Being at the edge of the material there would be less "heat sinking" of the weld so I can certainly imagine the heat would increase right at that point.

I hadn't used the machine all that much as a TIG until recently so don't have much practice at it. I've never been that keen on welding (basically because I'm crap at it) but must admit I really enjoy the TIG. Nice and quiet, smoke free and actually quite therapeutic to be quite honest. I'm actually rethinking a lot of projects along the lines of "eww I can WELD that, yay!" This machine will probably do me for a while but at least if I ever upgrade it I'll have a better idea next time of what features I may like to go for.

Ah. No controls. Possibly you can use a bit of scrap to have a run off area rather than stopping at the edge. That's where a crack can occur.

Hmm, no don't thing scrap would work very well in this instance. The SHS has a radius on it and so you could never really get them to butt up together properly, also wouldn't really help with the heat sinking effect. But that's ok, if it's possibly due to much heat, there's certainly other things I can try to alleviate that. Maybe even bringing the weld in from either end rather than just doing it in one run. Maybe get a bit creative, more than one way to skin a cat

Pete

Originally Posted by Pete F

The areas seemed to be quite clean yet it looks like gas bubbling out of the weld at the end.

G'day Grahame, yeah as you may have suspect I was thinking along the same lines initially too. But I can't see where this contamination is coming from, with this last lot I really did try to get the joint really clean. Unfortunately I'm basically finished all the welding I need to do on this job, just a touch up where I could only see one side of the weld properly (weird angle) so had to wing it. Too much heat on one side and blew a hole which I filled in as soon as I saw it but it looks a bit ugly. I'll grind that one out and do a quick pass to make it look "nice"

Is a stainless wire brush ok to use on normal mild steel? I brushed the steel back to bare metal but believe on aluminium you should reserve a brush just for that purpose to prevent cross contamination. The filler rods are good quality copper coated (can't recall brand, something Italian) and straight out of the tube.

Pete

Originally Posted by Pete F

In one instance the bubble even came up to touch the tungsten which was a pain.

HI PETE,
The above is the dead give away.

What made the bubble raise up to nearly touch the the tungsten ?

The answer is that that there is contamination in the metal-what ever it is ,it is reacting with the heat to form a gas in the molten metal.The gas forms and expands from the heat and that is why the bubble raised.

Metal can absorb contaminant is the form of oil ,grease paints and and many others.

In extreme cases I have soaked work in solvents for a few days to rid the metal of the unwanted materials,not always with success.

Hope this helps

Grahame

A stainless brush is ok for steel.
the same brush is no longer good for use on Ali though.

I use a separate S/S brush with ali only written all over it.
Also try a heating to red heat and let cool to burn the crap out of the pores,then brush.

cheers
Grahame