I never had any awareness of the amount of metal work, dent removal, and ding repairs needed to fix brass band instruments, but it's pretty similar to hot rod work... even using bodywork hammers and an english wheel

I started reading hot rod magazines about 30 years ago, I don't mean looking through them in grade school, but actually reading them, and Ron Covell had an article in one, or more, of them at the time. He's one of the best, and dent removal was one specific article I recall. 

This video shows several methods of dent removal, even the rebound method. I think the magnet and ball for the inside curve is dam clever. 

he even uses a slide hammer when necessary https://youtu.be/EYe9jh4_94s