Patent ID: 7171837
Filing Date: 2007-02-06
Classification: B21C,B21J,B21K

Abstract:
1. A method of forming a hollow stepped shaft, comprising: holding an upper axial part and a lower axial part of a solid rod-like blank with an upper and a lower die, respectively, which define a stepped recess of large diameter in a region where the upper and lower dies are opposed to each other; compressing the blank from axially opposite sides thereof with an upper punch and a lower punch, respectively, each of which is smaller in diameter than the blank and at least one of which is moving during the compressing, thereby extruding the blank such that an axial hollow is formed in each of said upper and lower parts about an axis of the blank, with a solid plug-like portion left in between the axial hollows, such that a portion of the blank opposed to said stepped recess of large diameter expands in diameter and deforms into said recess, and such that the blank expands axially to become longer while said portion of the blank deforms into said recess; and thereafter moving one of said punches to shear said solid plug-like portion away from the blank and to force it out of the blank, wherein, as a result, said blank is formed with a stepped portion of large diameter by the radial expansion and deformation, with a long axial portion, and with a continuous axial hollow about the axis of the blank, such that a hollow stepped shaft is formed.