We have used a special tip for the MIG welder torch with some success. It has been a while, but as I remember it is a carbon rod that makes electrical contact with the warped metal heating it up in a localized area, acting a bit like a soft gas welder flame. Maybe your MIG welder could be set up with that. Check with the welder supplier. Ours is a Lincoln Idealarc about 25 years old. It took a little practice but it works.
Mar-Ktech
