400 AMPS!!! There is nothing on an average car body that cannot be welded with 100 amps. 400amps is just a plain silly thing to be said by your mate. In fact I would be amazed if you could even buy a single phase 400 amp welder. 400 amps is enough to weld mild steel @ around 20mm thick, thickest you'll find on most cars is 3mm for box section chassis, arches will be about 1mm thick.


My personal preference would always be with a TiG welder as I pretty much hate MiG (in most cases it's actually MAG welding rather than MiG) welding, however most people will be better off with a MiG welder, as already said for that type of work avoid arc welders and avoid those stupid little bottles of C02 / C02/Argon mix - they'll cost you a fortune compared with a BOC cylinder.

Go get yourself a MiG welder around the 150amp range, go open an account with BOC and get the smallest cylinder of C02 that they do. I guarantee if anything the problem you'll have when learning will too many amps rather than too few.

I would use 0.6mm wire on those arches too.