Sheet metal work

I can weld tubing and flat stock pretty well. It's part of my job.

I tend to screw-up on sheet metal. What's the trick to MIG-welding sheet metal without warping the crap out of it? I've heard of water soaked rags and there was some expensive heat absorbing gel, but what really works? I shaved door handles before and it took forever to massage the warps out of the doors. I've seen S-10 blazers running around with the back windows welded-up and look smooth as OEM. What's the trick?

 

Do a search.

 

The trick with MIG welding is to take your time. Set the welder up to get good penetration. I hope your working with a shielding gas. This is a much cooler weld. Keep your welds small about 1/8" long and work from the centre of the panel out to the corners. Tack the panel about 3/4" apart and just keep working across the panel sides. Hammer and dolly as you go to keep things level and stay away from the water or air. This will cool the metal to quickly and make it draw the weld. I like to "Butt" weld with the MIG so I keep the edges about 1/16" apart, this allows the metal to expand with the heat of the weld and reduces the warpage.

Hope this helps:

The Old Tinbasher

 

I'm an idiot so I only used flux core wire which puts more heat in the metal, but I got away with it because I went VERY slow. Spot here, spot there...wait come back repeat until all filled in. I also didn't go crazy on the settings and kept it just hot enough to get good penetrations on my spot welds.I replaced about 75% of my metal so I guess it worked out ok. Do yourself a favor though and use the gas because everyone who has any sense does lol. Good luck.

 

GO SLOW!!!!!! Do tacks instead of beads, allow to cool, you can do some LIGHT hammer and dolly work but be careful as the mig weld (I'm sure you know this) is a harder weld,and can crack, especially after grinding. Basically the flatter the panel, the slower you go.

T.R.
Steve

 

can't really ad much here. go slow, butt weld with TIGHT tolerances, gas is better than flux core, but either will work, I start at about 1.5 inches between spots and fill from there. oh yeah and go slow--don't be afraid to walk away and let the panel cool for a bit.

 

I first learned, and prefer to still use, a torch w/oxy/acetyl. It does a fine job on old tin.

 

practice on junk pieces of metal before you do any important pieces.Clean the the metal to bare, remove any paints and chemicals that may be on the metal.

 

If everyone was to work this methed first it gives you a good understanding of the metal and what heat can do. I know a older body man that closed all the luvers on a hood with gas and rod it was unreal to watch and with a little hamer and dolley work looked real nice to the point you couldnt tell there was luvers there other then the work itself.

 

Thanks for the replies. To me, flux core is not MIG. I've owned a lot of MIGs over the years, but mostly for bracket, tank, etc fabrication. I guess for shaving door handles, an 1/8" at a time doesn't sound ridiculous. Seems like a quarter panel would take a few days though.

 

If you hav'nt welded alot of sheet metal, get you a couple of flat scrap pieces and get an idea of how to go about this. It does take some time to weld in a big panel, but it is real easy to screw yourself into alot of extra body work. Usually the time you save going fast welding the panel in wil be doubled or tripled in body work if you warp a panel. It's not hard to get it right just have some patients and you'll be fine. Also be careful with the grinder, you can warp a panel just as fast. Good luck.

 

You have a LOT to learn then.

 

Tinbasher nailed it pretty much, (as did others...), follow the advice in his post and you'll do fine. I've welded miles of butt seams, on all different kinds of body steel, using these methods and gotten great results-main thing is, as crackerass54 stated before-don't rush it! Let it cool down between welds-whenever I got in a rush is when it caused problems-would have actually saved me time if I worked more slowly! AND, MAKE SURE YOUR METAL IS CLEAN! Free of rust, scale, grease, old paint, whatever-weld only clean bright metal, and you'll get good results... Good Luck!!

Eric

 

Amen to the comments on going slow and keeping it from getting too hot. In the long run it will take less time (as i can verify from my own impatience on a panel which warped). when in doubt less is better