Fabrication method for filled hydraulic piston for hydraulic pump or motor with aluminum insert fitted into central piston blank bore and retained by cold-formed piston material

摘要

A metal piston blank (12) is cold formed into a hollow cylindrical body with one closed end (16), one open end (18) , and a central bore (20). A metal, e.g. aluminum insert (22) fitted into the bore consists of material, which is slightly less dense than the piston body material. The open end of the piston body is cold rolled, to deform the outer end of the central bore for the purpose of reducing the diameter of the outer end section of the bore and partially enclose the outer end of the insert. A partially spherical bearing in the outer end section of the bore is cold formed, and a spherical slide element is fitted into the bearing.