Place the welding tip wire at the gap and tack weld several small spots spacing them evenly apart.
How to mig weld automotive sheet metal.
When welding a long bead on sheet metal you ll put excessive heat into the panel and run the risk of the puddle falling through the panel.
A better technique is to move around the weld seam doing short quick stitch welds that you eventually connect all together.
Tack in a few places apart from each other and wait until the panel is cool to the touch.
The main reason to use a smaller diameter wire is that it takes less heat for melting and hence the metal around the weld is not heated to a very great extent.
The best two electrodes for welding auto body sheet metal is either ceriated tungsten or thoriated tungsten.
While replacing body panels overheating and warping thin sheet metal is common.
Ditch a 1 8 inch tungsten electrode for something much smaller like 1 16 inch tungsten.
Sheet metal warps easily and also can burn through easily.
Then tack between the two previous tacks.
I keep blowing through my thin sheet.
For mig welding sheet metal it is often recommended to use an electrode wire of the smallest diameter to prevent burn through and warping.
Because it will have you a lot more control over the whole process and it is more forgiving in case you do anything wrong.