Sheet Metal Welding

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Hello everybodyA little introduction, I've had a welder for about a year and a half now, and in the past 8 months I've been teaching myself to weld. My dad bought a Chicago Electric (HF... not a fan) MIG 151, and I've been using that with .036 flux core, on a dedicated 240 circuit w/ dual 30 amp breakers. Since I started, I've been doing some pretty basic welding projects. Made light mounts, added t shaped stake posts and new fenders, and a new jack all on the same trailer. I've started on a rear bumper for my truck, and already have some mounts made for it. Once I figured out the right settings, I've been able to weld thicker metals that are at the top end of the welder's capacity with no issues.Now my problem is welding sheet metal. In the coming months, I'll be needing to do some body panel repair on my truck. For the life of me, I can't get a weld that doesn't burn through at some point. Even little tack welds burn through. I'm welding at the lowest setting (30 amps) on the welder. I can't figure out what I'm doing wrong, and it's starting to... Annoy me. So any pointers/tips would be appreciated.ThanksJameson
Reply:Flux core burns hotter and gets more penetration. If you want to have a go at doing something as thin as auto body, you're gonna have a much easier time if you reduce the size of the wire or better yet get some gas hooked up to it and run solid.Edit:Hotter compared to solid wire with C25.Last edited by Snuffy; 11-24-2012 at 12:20 AM.
Reply:How small of wire should I use? And the main reason I have been using flux core is because 95% of the welding I do is outside (damn garage is too small for truck or trailer), and up here in the pnw, we get our fair share of wind. I have been looking into getting gas and runnimg solid (or maybe even dual shield..), but I have to source a tank and a location to get it filledThanksJameson
Reply:If you have to use the flux core go with .030. If you can work the gas go .024. Sheet metal that thin is very hard to get right. Once you get to where your not blowing through warpage becomes the next fight. Use a backing plate. This will help with both blow through and warpage. Make very short beads (1" max). Allow the panel to cool between beads.This will minimize distortion but won't eliminate it.Aluminum or copper for the backing plate
Reply:Some other things to consider are mig welds will heat and cool at a different rate than the surrounding metal. If you run a bead across a flat sheet, grind it down, paint it then leave it out in the sun, you will see a faint weld line in the panel as the sun heats it up. There was a discussion that came up the other day about using silicon bronze for body panels. I've got no experience with it and am curious to know if it deals with the above problem.http://weldingweb.com/vbb/showthread.php?t=37770
Reply:use .023 wire with c25 gas. make short tacks and move around. You can also use a piece of copper or al as a heat sink. Just hold the copper tight to the panel behind the weld. This will draw the heat away and prevent major distortion.
Reply:Jameson,what truck are you working on?Lincoln SA 200Esab Caddy 160Thermal Arc 201TSMiller Dialarc HFI don't like making plans for the day because then the word "premeditated" gets thrown around the courtroom....
Reply:Just to make sure, C25 is 75% argon and 25% CO2?Dubl_t: It's a '79 f250. I'm in the middle of a mild restoration Jameson
Reply:Originally Posted by Island BumpkinJust to make sure, C25 is 75% argon and 25% CO2?Dubl_t: It's a '79 f250. I'm in the middle of a mild restoration Jameson