controlling undercut

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What exactly causes undercutting with MIG/fluxcore ? I notice it sometimes when I am doing T-joints.Is it caused by pointing the gun at the vertical part of the joint at too much of an angle (perpedicular) or not enough ? I typically do a zig-zag or C's . Any help to cure this would be great !Thanks,Rich
Reply:torch angle could have a little to do with your results.Also you would want to pause a little on each side of your Z ro CKinda like you would do on vert up.
Reply:Concentrating too much heat on the vertical leg of the t-joint while advancing the torch too fast is a sure recipe for undercut along the upper toe line.   Slow down your hand or pause on the vertical leg to fill it in.   If you have too much heat and are trying to do too big a weld at once and can't control the puddle, then turn it down and do multiple passes instead.   Run straight stringers and stack them bottom to top untill you fill the joint, cleaning between each pass.MM350P/Python/Q300MM175/Q300DialarcHFHTP MIG200PowCon300SMHypertherm380ThermalArc185Purox oaF350CrewCab4x4LoadNGo utilitybedBobcat250XMT304/Optima/SpoolmaticSuitcase12RC/Q300Suitcase8RC/Q400Passport/Q300Smith op
Reply:I notice sometimes if the gun isn't below 45 that there is less metal laid against the vertical part - and I theorize the vertical part, because it dead ends against the flat has nowhere for the heat to go, except up- overheats and can get undercut. So letting the torch sit at 35 to 40 allows the puddle to wash up and at the same time have a bit more metal to sink the heat into. I'm with DesertRider on minimizing weaves, and doing multi passes.Last edited by maarty; 08-25-2009 at 10:41 PM.
Reply:Suppose I'm getting too much into non manipulation.Watching the puddle fill, and slow travel, generally solves the problem.Any considerable weave takes the electrode out of the hot zone from what I'm starting to see.  With flux core,  I imagine that allows for the oppurtunity for slag to be trapped in the weld.  Not sure.Now here's something for consideration...............Know it's not a stick thread, but..........The gospel is drag, or slight weave with LO HY electrodes.  OK,  I got that.  NO problem.HOW COME A WEAVE IS ACCEPTABLE FOR VERTICAL UP WELDING???????The heat is dissipated to a great degree.  And the puddle has time to cool before the next weave across the face of the shelf.  Curious huh?LIncoln approves these procedures with their consumables, and even says to pause at the toes to burn out residual slag.  Now isn't that funny?Methinks I smell a rat.I'm gonna find a good lab or whatever, dunno how this stuff works..........to do some pics (x ray) of verts, pure drag welds, and the old way I was doing thingsThe old way I did it was not a conventional whip.  The rod never left the puddle.  No circular motion.  Always was in the puddle, and keeping the heat up.  More of an oval shaped side to side weave.I have absolutely no intention of going back to that, because I feel that root penetration suffered.  But I'd be curious about the pics.Just thinking here."Any day above ground is a good day"http://www.farmersamm.com/
Reply:IMHO Undercut is misnamed, I think it should be called under fill at the toe. As that is what it is, most of the time. One has applied the arc and progressed, before allowing the filler to fill the area that the arc has eroded away. Slow down, or turn the heat down. As to weaving, anything over 1-1/2  times the diameter of the electrode/filler would be weaving. Anything less is just puddle manipulation.
Reply:Samm, when you're weaving vert up with your 7018 or others, the slag is falling down instead of running ahead of the puddle.  Wait untill it fills at each toe line and when you see the slag run around the side of the puddle and down, move.No whipping out of the puddle with fluxcore wire.  That is a recipe for slag inclusion.  Run it like a 7018 and you will be fine.MM350P/Python/Q300MM175/Q300DialarcHFHTP MIG200PowCon300SMHypertherm380ThermalArc185Purox oaF350CrewCab4x4LoadNGo utilitybedBobcat250XMT304/Optima/SpoolmaticSuitcase12RC/Q300Suitcase8RC/Q400Passport/Q300Smith op
Reply:Getting sort of esoterical here, but how about the arc force in a tight weave?You definitely know when the puddle is starting to outrun the electrode.  You see it.Changing the angle of the electrode can force the puddle back upstream.  Dropping the angle too much, and you face spatter issues.FB nailed it.  At what point do you pass beyond puddle manipulation to a slag including movement?Leaving the puddle for any length of time, and going into uncut metal, is definitely a disaster.  Puddle cools, and any further movement back into it would probably bury cooled slag.You can see the dark line between the molten puddle, and the cooling slag.  It's pretty definite.If any movement is still within the bright part of the bead, IE the puddle, are we talking manipulation?The slag cooks to the surface at the right temp.  The question is how long can that temp fall, and is it brought up again by the next weave enough to cook any possible slag out again?"Any day above ground is a good day"http://www.farmersamm.com/
Reply:In all the weave caps I have made on pipe I would never had called them verticals, I always thought of them as a series of short horizontals stacked on one another.
Reply:So the heat from the next "pass",  I don't know a better word, is sufficient to cook the slag to the surface?Because my feeling is, despite what's been said, that not all of the slag runs down off of the shelf.  There has to be some left.  You stop the weld, let it cool, and there's slag at the top of the weld.  It's minimal compared to what's dripped down the face of the weld, but it's there.Wasting bandwidth, but trying to get a better understanding of that little world at the front of the electrode"Any day above ground is a good day"http://www.farmersamm.com/
Reply:Originally Posted by farmersammSo the heat from the next "pass",  I don't know a better word, is sufficient to cook the slag to the surface?Because my feeling is, despite what's been said, that not all of the slag runs down off of the shelf.  There has to be some left.  You stop the weld, let it cool, and there's slag at the top of the weld.  It's minimal compared to what's dripped down the face of the weld, but it's there.Wasting bandwidth, but trying to get a better understanding of that little world at the front of the electrode
Reply:Do you think that the slight pause on the toes of the fillet is sufficient to get rid of the slag?"Any day above ground is a good day"http://www.farmersamm.com/
Reply:LOst my connection trying to post a "quick reply". didn't get to make the next post to fill out my thoughtsThanks to some good instruction, I sh11tcanned the wide weld.Small focused beads probably no more than 2x the electrode size.I'm seeing a uniformly hot puddle below the electrode.I look at a lot of out of position welds and see a HUGE side to side movement."Any day above ground is a good day"http://www.farmersamm.com/
Reply:Originally Posted by farmersammDo you think that the slight pause on the toes of the fillet is sufficient to get rid of the slag?
Reply:I'm good to go then.Thanks for fleshing it out.I can refine what I've been taughtHelps to think about what's actually going on.  Bad habit I have, but it's MY HABIT"Any day above ground is a good day"http://www.farmersamm.com/
Reply:Samm you should have taken up a career in engineering you got the inquisitive mind for it.MM350P/Python/Q300MM175/Q300DialarcHFHTP MIG200PowCon300SMHypertherm380ThermalArc185Purox oaF350CrewCab4x4LoadNGo utilitybedBobcat250XMT304/Optima/SpoolmaticSuitcase12RC/Q300Suitcase8RC/Q400Passport/Q300Smith op
Reply:ok , back to my MIG question . Should I spend more time on the vertical surface so the puddle fills ? less time ? slow down ? speed up ? anything I missed ?!
Reply:Now I gotta take the puter to the shop so I can try to follow this logic while the welder is on.A butterfly without wings, is just an ugly bug
Reply:When you're doing your zig-zag or C, hang more at the upper toe line to let it fill.   Turn the machine down a little if it's too hot and the puddle is getting too big and out of control.  If you're going to weave, you're going to have to run a tad cooler than if you're running a straight push (or drag for fluxcore) stringer with no manipulation.   Torch to work angle at 45* for fillets is good.   If you want the weld to climb the wall more, lower the torch angle.  If you want it to lay down on the flat more, raise the torch angle.MM350P/Python/Q300MM175/Q300DialarcHFHTP MIG200PowCon300SMHypertherm380ThermalArc185Purox oaF350CrewCab4x4LoadNGo utilitybedBobcat250XMT304/Optima/SpoolmaticSuitcase12RC/Q300Suitcase8RC/Q400Passport/Q300Smith op