I work one of these, made by Sciaky, weld in a vacuum chamber at 7 E-5 torr. Can weld 2" plate or .001" ss to itself or to the 2" plate. Marvelous NC welding machine...
At home I use a Lincoln AC/DC 225 or Snap-on C02/Ar Mig Machine (Century) - not too sophisticated to get a job done...