Steel TIG welding problems

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I need some help to figure out what's going on. I am still learning to TIG weld but do have some experience and some successful small hobby projects.Today I'm welding in a sensor bung into the oil pan of my car and experiencing a problem I haven't experienced before.It starts up fine but then suddenly the puddle explodes, jumps to the tungsten and leaves a crater... I'm attaching a picture of what it looks like.My setup:- Miller Dynasty 200- DC at 80A- 3/32 2% tungsten- Flowrate set at around 15Does anyone have any ideas why this might be happening?Can the oil pan be porous and have oil trapped that explodes under temperature and ruin my weld?
Reply:Why don't we start by asking:  exactly how well did you clean this oil pan?  I have welded on two steel oil pans and have not encountered this problem, and both had nearly a decade of being in service---but I did clean them very very very well. 1st on WeldingWeb to have a scrolling sig! HTP Invertig 400HTP Invertig 221HTP ProPulse 300HTP ProPulse 200 x2HTP ProPulse 220MTSHTP Inverarc 200TLP HTP Microcut 875SC
Reply:I'm with Oscar I weld bungs and drain fittings in oil pans very frequently....my guess is contamination. Old oil pan or pans that have been used need extensive cleaning or any oil will come out of the pores in the metal.Wipe it all down with Acetone, let it dry well and try again. You could get away with a little less amps as well just make sure you don't put too much heat in the bung and distort the threads.Last edited by Rick_H; 03-23-2014 at 04:20 PM.
Reply:Is the bung steel? It looks aluminum in the pic...
Reply:Wow, thanks guys for quick replies. I did spend some cleaning effort before I started. I wiped it with Acetone as well, I'll do some more wire brushing and try again. As far as amperage, I'm using foot pedal and I'm not flooring it actually, I'm monitoring the puddle to make sure I don't have too much amps.Anything else I can do to clean it?And the bung is definitely mild steel Can it be bad ground? I think I'm OK, but the pan is painted so I had to ground it to the inside of the pan using an additional piece of steel between the pan and the ground clamp. Ohm-meter test shows good ground.
Reply:Seems like contamination to me also, try cleaning it with acetone again after grinding away the weld
Reply:The pan might aswell be considered stamped tin, not the best for weld quality. You have too wide of bead to start with, keep the arc mostly on the bung and wash the weld onto the pan with a quick dip of filler rod. Tack the bung in with 4 tacks before you start, but something still does not look right in your picture. What machine are you using and what shielding gas do you have?
Reply:Originally Posted by Flug540Wow, thanks guys for quick replies. I did spend some cleaning effort before I started. I wiped it with Acetone as well, I'll do some more wire brushing and try again. As far as amperage, I'm using foot pedal and I'm not flooring it actually, I'm monitoring the puddle to make sure I don't have too much amps.Anything else I can do to clean it?And the bung is definitely mild steel Can it be bad ground? I think I'm OK, but the pan is painted so I had to ground it to the inside of the pan using an additional piece of steel between the pan and the ground clamp. Ohm-meter test shows good ground.
Reply:.....and after you manage to make a seal tight weld around that bung,be prepared to chase the threads with the correct tap; since the mannerof that weld joint you're attempting can easily shrink the thread ID's.Blackbird
Reply:Originally Posted by kkustomzThe pan might as well be considered stamped tin, not the best for weld quality. You have too wide of bead to start with, keep the arc mostly on the bung and wash the weld onto the pan with a quick dip of filler rod. Tack the bung in with 4 tacks before you start, but something still does not look right in your picture. What machine are you using and what shielding gas do you have?
Reply:Looks like it turned out well!Hobart 210 MVPHobart Stickmate AC/DCMiller 180Miller 211 MVPMiller Spectrum 625 PlasmaOxy TorchMisc Benders / PressesLots of Duct Tape