Process for manufacturing hollow plastic objects

A process for the manufacture of synthetic resin objects comprising the steps of producing at least one hollow core by casting a plurality of metal half shells in a casting mold comprising a pair of opposed mold halves which close on opposite sides of a center plate, and after casting said cast metal half shells, the center plate is withdrawn from between the mold halves and said cast metal half shells are assembled and joined together by reclosing the mold halves such that said cast metal half shells are pressed in contact with each other to form said at least one core such that said cast metal half shells enclose a hollow interior cavity, placing the produced at least one hollow core in a mold of an injection molding machine, injecting synthetic resin material around said at least one core in said mold of the injection molding machine so that the at least one core is enclosed in the synthetic resin material, said synthetic resin material having a melting temperature which is higher than the melting point of the core, and thereafter heating said at least one core enclosed in synthetic resin material to a temperature at which said at least one core melts, and removing the molten material from the mold of the injection molding machine.