But welding sheet metal

[jakeru]

To minimize warping/distortion when TIG welding sheetmetal, use techniques to minimize heat input. That means:
1. strive for as tight of a fit-up as possible (if tight enough so that autogenous welding can work, you can *really* minimize heat input),
2. use pulsing settings on the arc (either low or high speed pulsing can be helpful, but go with "dramatic" pulse settings - low background current/ratio, and low pulse duty cycle, relatively high peak current - to get the most benefit),
3. if back side is accessible have an assistant follow along with a copper spoon tool, (or perhaps rig something up clamped to the back side to suck the heat out,) etc. (A copper spoon tool also works *great* for filling holes!)
4. Use the right set-up for welding thin sheetmetal - adequately small diameter filler rod/wire, adequately small tungsten to crisply start and maintain the low welding current, short arc length, and weld with only as much amps as you need, trying to get a narrow bead width.
5. Do tack welds, stitch weld between the tacks, back step, etc. Don't let the heat affected zone grow too wide (on steel you can judge this by how much of the metal is "glowing".

If while tack welding you find the metal shrunk and pulled out of alignment (e.g., pieces overlapping) and if you have a hammer and dolly and accessible back side, consider hammering "on-dolly" on the tack that shrunk too much, to get it to expand and "undo" the shrinkage. This may not be all that hard to do, although planning to work with some shrinkage (e.g., that a joint will "zipper" and pull together during tack welding) is another OK approach. If you minimize the size of your tacks (make smaller diameter tacks), it will reduce the shrinkage.

It does take time to butt weld a long, thin sheetmetal joint with minimal warping with TIG, but doing it this way, you'll get much better penetration (and a strong weld) than with usual MIG techniques. MIG is another option if the penetration and strength don't matter as much and you prefer to get the job done faster.

Here's a related post:
http://www.everlastgenerators.com/fo...1333#post21333