Method for manufacturing an element having grooved trunnions and forming method for grooving the trunnions

A method of manufacturing an element having grooved trunnions extending radially from a central axis of the element, said method comprising:

• providing a blank having trunnions extending radially from a central axis of the blank;
• forming grooves in the trunnions of the blank by positioning the blank between two surfaces defining parallel planar guides in a manner in which the blank is slidable relative to the guides, and between punches which are disposed between the guides and have forming edges profiled in correspondence with the grooves to be formed such that the punches occupy respective spaces each defined between the guides and two adjacent ones of the trunnions and such that the forming edges confront the trunnions, respectively,
• moving at least one of the punches relative to the planar guides in a direction toward the central axis of the blank until the respective ones of the forming edges of the at least one of the punches contact the trunnions and slide the blank relative to the guides until the blank is self-positioned in contact with all of the forming edges, and
• subsequently imparting relative movement between all of the punches and the blank under a force sufficient to cause all of the punches to move relative to the blank in a direction toward the central axis of the blank so that the forming edges penetrate the trunnions and form grooves therein respectively complementary to the profile of the forming edges;
• subsequently subjecting the blank to heat treatment that hardens the blank;
• and
• machining at least one surface of each of the trunnions.