*urgent* do i need feeding wire?

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For spot welding, so i need feeding wire?i rent a welder last night, about to get things setup and weld my radiator support now...i was reading spot welding stuff online and found thishttp://www.esabna.com/EUWeb/MIG_handbook/592mig11_1.htmdo i absolutely need the "spot welding cup" for spot welding?and again, do i need feeding wire? (i thought feeding wire is needed say to weld 2 separate piece or if it has groove.)the welder i rent is Lincoln Weld-Pak 100HD, i read the description and i should set it to B-2.5 to weld ~1.6mm metal. (JDM rad support is like 0.5mm, the frame is about 1mm)any input would be much appreciated!This is my first time welding! This forum is my last hope!
Reply:Practice on similar scrap first.  But you techincally aren't "spot welding", which is more correctly known as "resistance spot welding."  You are basically just mimicking the appearance and purpose of a spot weld by concentrating your heat in one location until you get it to burn through and weld with the underlying piece.  Or you can use a small hole in the top piece to get things going, and fill the hole while joining to the bottom piece.  Yes, you will be feeding wire while doing this with a MIG.Are you using soild wire with a shielding gas (easier) or flux-cored wire (difficult on thin material)?You do not need a spot-welding cup.  Those are best used when the machine has timers and such for much more precise mimicking of spot welds.
Reply:no shielding gas, i went and brought some inertshield feeding wire, .35mm or the size indicated on the Lincoln welder. i am gonna try it on my scrapped rad support (the one that i drilled out) with B 1.5 setting as indicated (1-1.6mm metal thickness) and see how it goes.Wish me luck! LOL!Thanks for the reply!!!
Reply:hum... 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.
Reply:It's "Innershield", not inertshield.  Innershield is Lincoln's trademark for a self-shielded flux-cored wire.  It's also .035", more than likely.If you are plug welding (the correct term for this exact procedure) you want to concentrate the heat in the bottom of the hole first, assuming it's not thinner and burns through more easily.  The edges of the hole will melt before a solid surface like the bottom layer, so put less heat there while things are getting started.Take the paint off first whenever possible.