I can't think of any reason to do a flange weld except on an original flange. A flange weld cannot be metal finished to require minimum filler because the back side isn't flat. The double layer of metal may show when the car sits in the sun or after driving causes stress to show at the overlap and cause ripples. The extra thickness of filler needed gives you more chance of shrinkage. Repairs should be metal worked as close to the original shape as practical.
