Patent ID: 8172692
Filing Date: 2012-05-08
Classification: B21K,C21D,F16B

Abstract:
1. A method for forming a thread forming screw which is configured to cold form threads in a workpiece having a surface hardness which exceeds HRC 23, said method comprising: providing a wire made of steel; drawing the wire at a cold heading machine to form a head and a shank extending from the head to a free end; forming threads on the shank to form a screw, wherein the formed threads comprise full threads proximate to the head and lead threads between the full threads and the free end; performing a heat treating process on the screw, by first carbon enriching the screw to provide that a surface hardness of the screw is at a Rockwell C33 to 39 hardness and to provide that the surface hardness of the screw does not exceed a core hardness of the screw by more than 3 Rockwell C points, and by second induction hardening the lead threads and at least three of the full threads of the screw that are provided closest to the lead threads, such that the induction hardened threads have a surface hardness of at least HRC 56.