Process for manufacturing hollow one-piece metal elements

Claim 1

A process for manufacturing hollow, one-piece metal elements comprising the following steps: placing cylindrical pipe of given length and having opposite ends between two dies designed, when closed in mutually contacting manner, to define a cavity having the same profile as said finished element; applying a given hydraulic pressure directly inside said pipe; applying axial pressure simultaneously with said hydraulic pressure on said opposite ends of said pipe, so as to permanently deform and radially widen the same, said axial pressure being applied by means of a pair of opposed pistons sealing in fluidtight manner, and resting on, said opposite ends of said pipe; said pistons being thrust towards each other at such a pressure as to permanently shorten said pipe, gradually widening said pipe to the size and shape of said hollow element via a first series of gradually increasing deformations for forming on said pipe a gradually increasing radial annular convex portion, by selectively placing between said dies, inserts having a curved radial profile of given shape and gradually increasing size molding said pipe against said inserts by the application of said internal hydraulic pressure and said axial pressure for producing a blank of gradually decreasing length; and finally deforming said blank to the size and shape of said hollow element by inserting it directly, without said inserts, between said dies, and by deforming it against said dies by applying only said internal hydraulic pressure, the axial pressure exerted on said pistons being sufficient solely for balancing said internal hydraulic pressure.