how to penetrate both metal sheet without burning a hole?

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i tried to edit my previous thread's title but err... there is no option of edit post or edit thread... my problem:i can penetrate the metal, but i can't penetrate the second one. so i increased the power, i sorta penetrate the second one, but the first one have a hole and they don't stick...how well do i have to clean them? if the second metal sheet have little paint on it, would it matter? since the heat is gonna melt everything including the paint anyway.welder: Lincoln Weld-Pak 100HD, flux core, setting tried B-1.5, C-2, D-2.5on the thin sheet of metal (first one, ~0.80 mm thick), i can penetrate it fine with C-2, and burn a hole with D-2.5the second sheet of metal is about 1mm thick... and penetrate good with C-2 So i tried to use D-2.5 but it just burn through the first metal sheet...how long should i hold the trigger?
Reply:clean, clean, clean.  At the very least it takes heat to burn the stuff away.Could you be more clear about you joint set up?  Is it butt lap or tee?
Reply:Looking at his other posts, he's usnig a mig trying to spot weld with it.Latest Toys Miller 180 Mig and Elite Mask!!Wright Welder 225ACShop OutFitters 20/20 Bending SystemHypertherm 380 Plasma30 Years of Sparking (Electrical & Welding)
Reply:is lap, one on top of the other.first layer ~0.8mmsecond layer (the car frame) ~1.0 - 1.2mmboth layers have paint on them. altho i sort a sand down to the metal on the first later before i tried to spot weld it. i am wondering maybe the electricity didn't pass through to the second layer because of the paint?i am going to clean them both, and both side tomorrow and give it another try. i was able to get a nice, ~5mm circle spot weld (on a single layer). question: 1) is the other side of the spot weld suppose to be smooth? 2) the feeding wire, does it fuse with the metal? or it just vanish as the arc ignite?
Reply:Any metal being welded needs to be cleaned when using a MIG. If your work clamp is on painted material it won't provide and adequate connection. I'm not sure what your other 2 questions mean.John -  fabricator extraordinaire, car nut!-  bleeding Miller blue! http://www.weldfabzone.com
Reply:Well i tested on scrap metal... and the MIG melted a spot. So i was wondering if  the back side of the spot i welded suppose to me smooth?
Reply:As long as it melts into the second layer, you're pretty much done when it comes to sheet metal.  You aren't hanging bridges off of this.If you are using solid wire with a shielding gas, you need CLEAN steel, no paint.
Reply:I think its been said enough.  Clean the metal where your ground goes. Clean the metal where you are going to weld.  As in BARE shiny metal.I have been welding for 30 years and I am still not "good enough" to weld through paint.DavidReal world weldin.  When I grow up I want to be a tig weldor.
Reply:Drill a hole through the top sheet with a flat-faced spot weld cutter and just enough into the underlaying sheet to remove any paint or primer.  I use this type of cutter:  http://buy1.snapon.com/catalog/item....re&dir=catalogPut a clamp or vicegrip near the hole to make sure both panels are tight together.  Then weld around the inside circle of the hole fusing the top metal to the bottom.I've done this type procedure countless times replacing auto door frames, albeit not with flux core wire.WeldingWeb forum--now more sophomoric banter than anything else!
Reply:I cleaned the metal up, to the bare metal, still couldn't get them spot welded.At some point i got them sticked together, but the weld was so weak that i can widget it a few time and then it broke off...I tried to hold the trigger longer so that it can burn through the second metal... but it just make a hole in the first sheet... and then the second... then the first sheet won't stick since it has a hold there... ugh.welding is tougher than i thought lol
Reply:You said before that you are renting this equipment?  I'd go back and also rent the gas shield bottle and get the .023" solid wire, as long as you're going to rent anything at all.Then, you can turn the heat up a little bit for the solid wire, with less chance of blow-through.
Reply:I cleaned the metal up, to the bare metal, still couldn't get them spot welded.At some point i got them sticked together, but the weld was so weak that i can widget it a few time and then it broke off...
Reply:The only advice I can give is to use the higher setting (the one that penetrates the thicker metal,).  Start on the thicker metal, and move very quickly on and off the thin metal and back to the thick.  Make little circles, move slow on the thick side, and do a quick loop onto the thin metal.PatrickLincoln 175HD
Reply:"Spot welding" is a different process.  Spot welding involves heat (from electricity) and pressure (from the tongs that are squeezing the two pieces to be joined together) and when the heat between the two surfaces to be joined is -just- enough to start to melt the surfaces then the pressure holds them together while they fuse together and resolidify.Next, you can't weld paint or rust or dirt.  You can weld metal (sometimes, with the appropriate welding process, parameters, and skill).  So CLEAN THE METAL WELL!!!!!!   Yes, I'm yelling at you.To join two flat pieces of sheet metal together  in the middle when there is no edge or seam to join them, you -make- an edge.  Take your 'top' piece of metal and make a hole in it in the appropriate place and size.  Now when you lay that top piece onto the bottom piece, you have an edge to weld the from the top piece onto the bottom piece.  That's usually called a "plug weld".  Weld the edge of the hole onto the bottom piece.  If you don't need a flat surface, just weld that edge all the way around.  If you do need a flat surface, weld all the way around the edge and then spiral in and fill the hole.There is a procedure where you use a wire-feed welder to do a quasi spot weld, but because there is no pressure squeezing the two pieces together it isn't quite a spot weld and is a wee bit trickier to do.  The plug weld is a better choice IMHO.  And if you make the hole small but appropriately sized, you end up with almost the same result of two piece of sheet metal welded together not at the edges of the sheets.You're working with 20 and 22 gauge sheet metal, that takes a light touch to weld them and not just blow a hole through them.  Practice.And MIG using 0.023/0.025 solid wire and C25 gas (or other argon-CO2 blend gas, C25 is just a very common and useful blend for short-circuit MIG on mild steel) would work better and be easier on that thin sheet metal than trying to use flux-core wire.