| For holes up to about ¼” in diameter, MIG welding is an effective method.
For holes larger than this, a sheetmetal plug butt fit and welded in is most efficient.
To minimize warpage, the following technique works very well:
1. Weld the hole closed in short blips using enough amperage to get good penetration. Too low of amperage will result in fill that can crack on the edge of the hole. You don’t want the weld to be sitting on top; it should be melting in well and on the verge of burning through.
2. After each short weld burst, wait for the weld to cool to just past the red color stage, then cool it with a blow gun. I hold the blow gun in my left hand and weld with the right.