When we weld 2 pieces of sheet metal, one of them is perforated and we weld through the holes, we speak about plug welding.
Here i will explain my logic about “how to do this properly”.
Because one of my sheet metals (the body of the car) is not flat, i tight both pieces with pliers around the hole (“it’s not hole, it’s opening” they repeated all the time in the technical school of mechanics). I put them on 45° to have more space for the gun.
Then i push the trigger for less than a second to get the wire out ~15 mm. Before i start, it looks like this:
Then i push the trigger and build a little “mountain” in the middle of the hole. The goal is to make a good penetration to the bottom piece of sheet metal.
Next i start to fill the rest of the hole with rotating motion.
After the hole is full, i stop.
The perfect plug welding should look like this (actually this is my one and only :-)):