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porosity on tack

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porosity on tack

Postby crimas » Fri Jun 16, 2017 7:08 am

Hi guys, hope someone can help me, i've to weld some exhaust pipe so i'm training with a pipe made fron sheet bended 0.8mm mild steel, i put three tack on it with this settings, welding current 110Amp, 24pps 33% on Time 20% back current, finding this setting very helpful from a fronius tack video, it helps puddle keep moving and can join toghether the piece even ther is a little gap, the tack looks very small, the minimum penetration, the problem came when i weld It togheter, I use this pulse settings, 2pps 60Amp 33% 0n 20% back, all looks greate but when came over the tack, somethimes, a little hole appear on the weld, i think the problem is the tack because the porosity are located Only in this area and on the back of the welded piece I find 3 litte hole like a volcano on the tack zone, so what can i do for elliminate this porosity?
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scrap metal for testing, notice the little hole where i tack the two piece
porosity.jpg (36.16 KiB) Viewed 290 times
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porosity on tack

Postby Coldman » Fri Jun 16, 2017 8:30 am

There are a number of possibilities like gas flow etc., but first I suggest that when you are going over the tacks with pulse you should linger over the tacks a little to fully consume them.


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Re: porosity on tack

Postby zank » Fri Jun 16, 2017 9:09 am

Could also be a crater eye opening up.
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Re: porosity on tack

Postby crimas » Fri Jun 16, 2017 10:36 am

forgot to say that i'm using n°7 gas len with 2,4 thoriated tungsten , 6lt/min gas flow, piece cleaned with nitro diluent (maybe i can try acetone), here a couples of flat piece i welded above a copper plate, the porosity doesn't appear but i can't weld every time with a copper piece on the back of the piece :(
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Re: porosity on tack

Postby AndersK » Fri Jun 16, 2017 10:38 am

I would try tacking with less heat. With that thin material it's easy to pull up scale from the unprotected back side when you melt through.

On edit: you were posting as I wrote above.
The copper can protect the back side from oxidising as well a heat sink so it makes sense with what I wrote above
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Re: porosity on tack

Postby crimas » Fri Jun 16, 2017 12:38 pm

Any tips for tacking ? unfortunately my welder havent the spot function, so i have to switch as fast as i can the torch button , less welding current forces me to wait much time for tack, and the penetration goes deeper, i try nopulse current but sometimes the tack go bad and melt the two pieces with no welding. If i tach the piece with a massive piece of copper or aluminum behind and after welding (without nothing behind the piece) could i resolve this issue?
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Re: porosity on tack

Postby Oscar » Fri Jun 16, 2017 2:51 pm

It might be just too much heat. If the backside ended up "sparkling" because the molten weld puddle went all the way through, that is what might be causing porosity on the backside on the tack. Then when you go over it for the weld, it resumes the "sparkling" all the way up to the top of the puddle, which is really oxidation happening really fast due to heat + oxygen.
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Re: porosity on tack

Postby Poland308 » Fri Jun 16, 2017 4:11 pm

SS,, back purg your parts to avoid sugaring. Oscar gave a good explanation of what's happening.
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Re: porosity on tack

Postby crimas » Fri Jun 16, 2017 5:10 pm

trying with alluminum bar inside the piece but tack penetrete to much, no porosity but very close to have it, so i change my setting to a 33pps, welding current to 70 amp (lower) base current 33% and put a tack, last photo welded with the same settings and without alluminum bar inside.
In the first photo i try different tack settings, the second from right is with settings above, looks no 100% penetration, very satisfied :D
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Re: porosity on tack

Postby AndersK » Fri Jun 16, 2017 5:41 pm

There you go, told ya :mrgreen:
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