you won't draw more than 20-25 amps on 1/8" aluminum depending on your machine. check the welder, and somewhere it should the max amps it will draw.
I know it's not up to code, but I've run my lincoln 175 MIG off of 2 seperate 20 amp breakers (which adds up to 40 amps and 230 V) and didn't have a problem. the only thing that might go wrong w/ that is if one breaker trips and the other doesn't, you could fry your welder. but my welder doesn't draw more than 25 amps, so I was well within the 40 amp range.