Ok, bit of a bragging moment here: my grandpa, with two other gentlemen, created the process for machining seamless cans that is described here. Before them, cans had a lead seam in them. They discovered that you could draw down the aluminum and stretch it to form cans in one piece. He also invented the process for creating the bottom of soda cans, and his friend invented the modern tab on the top of soda cans.
Aren't these both part of the same process? Whatever is being done to force that piece of aluminum into the correct shape, it involves the same piece of metal.