After watching several videos on youtube about mig welding a patch in a auto body panel, one thing is worth mentioning...
In most of the videos I have seen, they start out with a nice clean patch that fits perfectly. All signs of paint are gone and all you see is virgin metal. then care is taken for a great fitup by using vise grip clamps.
Everything is still looking ok at this point. Next small tacks are made with the mig gun. Everything is still ok. But before long, the mig guns lack of precise placement of metal rears its ugly head and very soon you see what appears to be pigeon crap that will have to be sanded off.
If all you have is a mig welder, then here are a few pointers to help you do a better job:
1. use a small welder with .023 wire and 75/25 argon/co2 gas
2. take great pains to get a good ground. I have a neat trick for a good ground using old copper welding leads...see it here. tip for a better ground clamp 3. use a hammer and dolly to peen the short tack welds to prevent distortion.
But if you have a tig welder..., well if you have a tig welder and are watching this video , you know exactly what i am talking about. I could do that weld in half the time it is taking this guy to skip around with a mig gun.
And to prevent distortion, I could just skip around just like the guy in the welding video is doing. Get in. Get out. let cool...or speed cool with air nozzle.
then lightly tap with hammer and dolly. and a whole lot less sanding in the end. It almost hurts my feelings to see this mig welding video. Because it shows the mig welder messing up such a nice clean patch job.
The setup for tig welding this patch in is something like this:
1. 1/16" electrode sharpened like a freakin needle
2. Use a #7 gas lens cup with about 15-20 fh argon
3. about 40-65 amps on the machine amperage knob and fine tune with food pedal
4. use e70s2 tig wire - 1/16" diameter or .045"
---or--- just strip off some .035 e70s6 mig wire