Random Mig porosity issues - ideas?

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Hey guys, I have a Hobart Handler 210 mig running .035 Hobart wire (3 different spools), C25 (3 different bottles) that we've been using for some roll cage work. The welder generally welds beautifully and I've been very happy with it for virtually any job I've done with it 99% of the time. However, on occasion we'll be welding a tube junction (1.75" x .120 wall DOM tubing, notched with a JD2 notcher and beveled at the end) and part way through a section of the weld will just bubble up and get porous. It doesn't seem to matter if it's a tight fitting joint or if it has a gap (it's acted up on both). I thought it might be air getting to the back side of the joint, but even a tight joint can have this issue. Gas flow has been tried from 18-32 cfh with no change (again, it's a rare event, but it's a pain to have to clean it up and grind it out). We clean the tubing with a flap disc and a grinder and wipe with acetone. The mill scale has been removed from the surfaces to be welded (and the surrounding area).Any suggestions of what I'm missing?KevinHobart Handler 210Tweco Fabricator 181iLincoln Squarewave Tig 175
Reply:Does this happen when you are making the last weld on a tube, making the tube 'air tight'? If you are bottling up pressure inside a tube that is being sealed on both ends, the air inside will heat and expand, blowing out the last little bit of your weld. A vent hole drilled in the tube wall will prevent this.
Reply:Cleaning the inside of the tube back at least a few inches-and/or swabbingthe entire length gets rid of any residual oil. When the tube gets warm to hot,you'd be surprised how much hidden oil and how quickly it will find its way tothe weld in process.Blackbird
Reply:Originally Posted by welds4dDoes this happen when you are making the last weld on a tube, making the tube 'air tight'? If you are bottling up pressure inside a tube that is being sealed on both ends, the air inside will heat and expand, blowing out the last little bit of your weld. A vent hole drilled in the tube wall will prevent this.
Reply:if its not contaminates getting pulled from the backside of the weld, could your solenoid be closing on you?  Or maybe a specific torch position is restricting your gas flow.XMT 350 MPa, w/D52-DTA 185 TSWHarris of
Reply:Originally Posted by dave powelsonCleaning the inside of the tube back at least a few inches-and/or swabbingthe entire length gets rid of any residual oil. When the tube gets warm to hot,you'd be surprised how much hidden oil and how quickly it will find its way tothe weld in process.
Reply:In addition to inside oil contamination, there can be residual paint spray from the tube ID coloring that will cause porosity.The first step is to clean the tube ID's.Contamination is the biggest single offender-by far.(An oil film can literally run for inches, quickly--right towards a weld in progress, if you haven't noticed.)You don't say if this is angled joint, perpendicular 'T' or what....makesa difference in torch attitude, stickout, etc. --as others have said.Nozzle and tip:-the nozzle size, taper counts-the relationship of the end of the contact tip relative to the faceof the nozzle opening can make big time difference in porosity,flush, recessed or tip sticking out.Blowout or blowback from the tube final sealing--you don't indicate if thisis a final seal weld.Too much or too little gas flow causes porosity--but setting contact tip flushto slightly recessed, relative to nozzle face is first thing, before fiddling with gas flow. Gas flow can create porosity dependent on torch attitude and the joint.Taking a little more studied approach to solving this problem would help you,before changing gas bottles, blaming the wire or machine--especially since it'sonly on occasion. Lots of variables to eliminate; or you may have combinations of variables.Blackbird
Reply:Originally Posted by dave powelsonYou don't say if this is angled joint, perpendicular 'T' or what....makes a difference in torch attitude, stickout, etc. --as others have said.
Reply:We used to have problems like this at work....Be welding normal, and then out of the blue get porosity in the middle of a weld. Check the nozzle, check gas flow, they're clean and no problems there. Couldn't predict when it would happen either, it was random.The culprit? Where I work, we use large industrial pneumatic grinders. The exhaust ports put out a pretty strong stream of air when you run them. If another guy 15 - 25 feet away was using a grinder, and it was pointed the right (wrong) way, it would mess with our shielding gas.... Doesn't take much breeze to blow away your gas, might be your problem. Or it might not Give me fuel, give me fire, give me that which I desire.
Reply:I recently had problems with MIG porosity on patinaed A46 steel plate. The problems went away when I cleaned the pieces correctly. My guess is either you're getting random local breezes or it's workpiece contamination.
Reply:My friend (who has my machine right now, but we've done cage work together and been fighting this issue) switched from my Hobart wire to a spool of wire from Washington Alloys that was on my cart and had no more issues. I still can't believe that was truly the cause, so I'll keep you posted when the trouble reappears.KevinHobart Handler 210Tweco Fabricator 181iLincoln Squarewave Tig 175
Reply:Originally Posted by trackbirdMy friend (who has my machine right now, but we've done cage work together and been fighting this issue) switched from my Hobart wire to a spool of wire from Washington Alloys that was on my cart and had no more issues. I still can't believe that was truly the cause, so I'll keep you posted when the trouble reappears.
Reply:I still haven't truly fixed this problem, but the wire change seems to have helped. The last time I had issues I was welding a roll cage hoop to the floor plate and had done 3/4 of the joint before having to move position. Once I got in position I had issues and in that case I believe the heat allowed some preservative to run down the inside of the tube. I ground it out, cleaned it up and it was ok.KevinHobart Handler 210Tweco Fabricator 181iLincoln Squarewave Tig 175
Reply:My welding knowledge is not all that it needs to be, but isn't TIG the recomended process for roll cages, considering the forces at play in a crash or rollover? MIG creates welds that are more brittle than the TIG process and under stress is more likely to cause failures. The TIG process creates welds cooler in temp with deeper penetration. If MIG is the process that you want to use, would back purging be apropriate here to insure weld integrity, kinda like TIGing stainless? Otherwise, is your fill wire appropriate for this application? Perhaps torch angle, amperage and technique (push or pull) need to be experimented with a bit more. Straight Co2 should also allow for a hotter weld with deeper penetration. Interesting dilema, no doubt.  When a welder tells you to "stick it", what do they really mean?"In a time of universal deceit, telling the truth is a revolutionary act." - George Orwell
Reply:Originally Posted by bearstonMy welding knowledge is not all that it needs to be, but isn't TIG the recomended process for roll cages, considering the forces at play in a crash or rollover? MIG creates welds that are more brittle than the TIG process and under stress is more likely to cause failures. The TIG process creates welds cooler in temp with deeper penetration. If MIG is the process that you want to use, would back purging be apropriate here to insure weld integrity, kinda like TIGing stainless? Otherwise, is your fill wire appropriate for this application? Perhaps torch angle, amperage and technique (push or pull) need to be experimented with a bit more. Straight Co2 should also allow for a hotter weld with deeper penetration. Interesting dilema, no doubt.