Patent ID: 7278286

Claim:
A rolling die for forming a rod member having a ball portion, comprising: a first die member; and a second die member facing the first die member, each of the first die member and the second die member having a process surface, the process surface having: a start forming portion having a process tooth configured to bite a rod member and an arc surface portion proximate the process tooth, the process tooth in the start forming portion having an inverse V-shaped cross-section for biting into the rod member and producing an excess portion in the rod member; an intermediate forming portion having the process tooth and a curved surface proximate the process tooth, the curved surfaced being configured to press the rod member to form an arched shape; and a finish forming portion having the process tooth and a hemispheric groove configured to press the rod member into the arched shape to form the ball portion, the hemispheric groove being configured to move the excess portion in axial and radial directions of the rod member, and wherein a height and a width of the process tooth in the start forming portion increase towards the intermediate forming portion.