Hey Guys,
What is the best way to minimize raised spots of weld metal at the end of a DC TIG weld? It is like the opposite of a crater in an aluminum weld. It seems no matter how slow I lift off the pedal and how much I move my tungsten around at the end of my weld I get the sharp raised spot of weld metal. Wondering if this is the result of welding too cold? Any help is appreciated. I'm using 309L TIG rod for this particular application.
Thanks!
Great question. I get this sometimes too and I don't really understand it but I have some hunches. It seems to happen to me more frequently on my cheaper 2 phase machine than on the decent machines I use at work. When tapering off, the arc seems to swirl around this little spot which raises up and up. It also seems to happen more if the material is very hot, or oxidised, or if my gas coverage isn't optimal.
I don't actually think it's solved by tapering down the current more slowly. I say that because at work on DC I weld on 4T (without a foot pedal) and with zero down slope time, so there is no tapering off, and I don't have problems with raised spots or with craters. The machine just drops instantly to about 10% of the main welding current and then the arc goes out when I release the on/off switch. In fact, I have experienced that if I taper down slowly when doing autogenous pulsed welds (DC) I get a raised spot. They come out way better if you reduce the current abruptly.
So these are really just my thoughts, no idea if they'll be helpful, but I'd be asking the questions:
- is your material clean and oxide free
- are your welds getting very glowing hot by the time you finish up
- are you using a high quality machine with a stable arc, if not can you try one out for comparison
- is your gas coverage good
- might a more rapid current taper-off help
Cheers
I agree with Josef. The puddle wants to follow the arc. When you taper slowly in one spot the diameter of the puddle shrinks and the remaining molten metal raises up to "follow the arc". I actually used this phenomenon to my advantage on an art piece to put little buds on a vine by tapering very slowly while pulling the torch back ever so slightly to exaggerate the effect.
One common technique to avoid craters and points is to drag backward or continue forward as you taper off. It leaves a "comet tail" shape.
Very cool Brian! Those buds and the curvature of the vine have a really lifelike look which I don't see often on metal art. Nice one
Josef and Brian, thank you for the replies and information. Initially it appeared to me the faster I came off the pedal the higher the puddle jumped to follow the arc (I'll have to retest), so right now what I do is come off slow and keep the tungsten moving forward (comet tail shape) and I still get a little "pin point" at the end of the puddle but it is not standing up like it was before. I need to do some testing on cleaner material to see how it behaves vs. the material I'm welding which is relatively dirty by the nature of it's manufacture. I'm welding medium carbon steel using 309L rod (it is art type stuff, not structural or strength critical). I also need to try the drag backward technique as well and see how that works.
My welder is a Dynasty 280, Jazzy 10 w/gas lens, 20 CFH (ball gauge), 3/32 2% Lanth Tungsten, reasonable stick out for the Jazzy 10, and a good ground so I don't think it is my equipment or my gas coverage but I'll do more testing to see if I can better understand cause and effect and levers I can pull to minimize or eliminate it. I'm a relatively new welder and switching back and forth between aluminum and steel it takes me a bit to get re-acclimated to the different material as well.
Again, thanks for taking the time to reply, sharing your knowledge, and the tips! DZ
I forgot to mention that if the metal is dirty or has scale the oxidizers in the filler will grab it and float it to the top of the puddle. That little bugger will try its hardest to jump up to your electrode. When you trail off it will be at the last place to solidify making that point more pronounced.
Copy that, I think you are on to it Brian. I just don’t recall it ever being this pronounced (the puddle jumping to the electrode that is) but it’s something I’ll have to deal with in this case. I can definitely see a lot of stuff dancing around in the puddle and I have to use a slow travel speed and a really tight arc to keep that puddle where I want it and ahead of the tungsten. It’s been a good learning experience.
Yup. That dancing puddle is dirty weld stuff. When it gets crazy stop and hit it with a wire brush or wire wheel. When you start back up it will run clean until it builds back up. If you restart without cleaning it, it will get dragged along as if nothing happened.