Method for manufacturing a piston rod unit and a hollow shaft

A piston rod unit comprising:

• a piston rod with a rod shank, wherein the rod shank comprises a bore extending in a longitudinal direction from a piston rod head to a mounted piston;
• wherein the bore is closed at a rod end of the rod shank by a forging process whereby a cavity of the piston rod is sealed at the rod end of the bore by a material excess left at the rod end during forming of the bore;
• wherein the piston rod is form-fittingly connected with the mounted piston exclusively via an external connection, and wherein there is no weld inside the piston rod;
• wherein the bore is formed by deep-hole drilling the rod shank;
• and
• during the forging process, the material excess left at the rod end of the piston rod by the drilling is used to close an opening of the bore at the rod end, thereby sealing the cavity of the piston rod;
• wherein the rod end of the piston rod having the material excess has a greater thickness on either side of the bore than an immediately adjacent section of the piston rod, and wherein an outer diameter of a length of the piston rod extending from the piston rod head to the mounted piston is constant.