Not sure why you would consider welding unless there was a serious ding, you can't blanket weld a case to add a layer, it is a process for filling holes. Swiss Time Services offer Laser welding along with other more usual servicing and refinishing services. Their work is excellent so as long as you want your watch to look brand new, that is one option, in the UK at least. I would hesitate to do it to an older piece with patina I wanted to respect or retain though since the fixed area will look super tidy and not match the rest any longer.
