Too bad. Roll forming is a very tricky thing when you depart from a few standard shapes, as we've discussed. Ram-forming or some kind of mandrel-stretching probably would be the way to go if you were making a lot of them, but I can see the tooling costing $100,000 or more because of all the constraints that would be required to prevent twisting and wrinkling.
Conceptually, it could be spun, but it would require an enormous specialized lathe (probably a custom-built VTL) and I've never heard of such a thing, except, in photos only, some machines built for the rocket-engine business. Even there, I have no idea if they could handle making a bell-type expansion in 15 mm stainless. The superalloys used in some rocket parts really aren't that much different in terms of properties, at room temperatures, than some grades of stainless. They're generally high-nickel, high-temperature "superalloys." And I don't know where those machines would be today. Pratt & Whitney Aircraft probably would know.
Can you tell us what the application is, or is it a secret?
-- Ed Huntress