Topic: Welding Help, welding thin metal to thick metal

I've got a Millermatic 141 (MIG with gas) and have low double-digit hours using it. I can weld thin metal to other thin metal, I just have to keep the power down and be smooth. Thick metal to other thick metal is easy, but thin metal to thick metal is giving me a hard time.

I end up keeping the power low to keep from burning holes in the thin metal, and laying down a few beads on the thin metal until I've got some mass of metal built up so I can turn up the power and weld the built-up bead to the thick metal. This appears to work, but looks nothing like what good welders do when they weld thick to thin. I was thinking that I could turn up the power and re-flow the whole thing, but is that necessary or even a good idea?

What am I missing here (other than skill, knowledge, talent, etc)?


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Re: Welding Help, welding thin metal to thick metal

This is all about how you point the gun and the amount of time spent pointed at each of the pieces.  Angle the gun so that it dramatically faces the thick metal and spend 80% of the time the arc is struck pointed at the thick metal, then just flick the gun onto the thin metal and then back to the thick.  This keeps enough heat in the thick stuff for good penetration and spends as little time on the thin stuff as possible to join it up well without burning through.  Keep the heat moderate, as hot as you can go without making a mess of the thin stuff.   This has been learned for me over several cages now, especially on the thin floors on a Honda.

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Re: Welding Help, welding thin metal to thick metal

Thanks so much, that was it. I was focusing on the seam before and blowing through the thin metal while not penetrating the thick metal. I just went out and welded an 1/8" plate to some Honda sheet metal and it went really smoothly and quickly with no burn throughs.  I'm using less power than I would for 1/8", but way more than I was using before and taking much less time and using less wire. It also looks about a million times better than it did before. I pried it apart just to see how well it was getting through the sheet metal, and the metal surrounding the weld tears, but the weld holds. This just made my day.

Thanks again.

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4 (edited by TheEngineer 2017-07-18 09:45 AM)

Re: Welding Help, welding thin metal to thick metal

Yup, welding is very much about heat management. With thickness discrepancies it's easy to get a junk weld for a few reasons. If you turn the power down too low, you don't actually penetrate the thick metal, so it's a weak joint.

I use lap joints of equal thickness metal when I teach this to beginners. You have them focus all of the heat in the base piece, and then quickly walk the puddle onto the edge of the top piece. It easily demonstrates how you need more heat in the base than you do on the edge of the top piece. When welding in spreaders it's the same idea. Focus it all on the spreader plate, and then briefly walk the puddle over to melt into the car's metal.

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Re: Welding Help, welding thin metal to thick metal

Some machine you can switch + - of the machine this will let  the weld puddle up a bit,  I do do short burns let it cool a second and repeat .
Bob Ma