Hollow stepped shaft and method of forming the same

Abstract

A hollow stepped article is formed from a solid blank to reduce the material cost, and cracking is prevented in a stepped portion of large diameter when a portion of the blank is de-formed by its radial expansion. A hollow, stepped shaft is formed by holding an upper and a lower part axially of a solid rod-like blank with an upper and a lower die, respectively, which have a stepped recess of large diameter in a region where they are op-posed to each other; compressing the blank from both its axially opposite sides with an upper and a lower punch each of which is smaller in diameter than the blank, thereby extruding the blank so that an axial hollow is formed therein about its axis in each of its upper and lower parts and that a portion of the blank op-posed to the stepped recess of large diameter expands in diameter and deforms into that recess while leaving a solid plug-like portion between the punches; and thereafter further compressively moving one of the punches to shear the solid plug-like portion and force it out of the blank, whereby the blank is formed with a stepped portion of large diameter by radially expanding deformation in a region intermediate between its op-posed ends or at one of these ends and with a continuous axial hollow about its axis.

1 . A method of forming a hollow stepped shaft, comprising:
 supporting a solid rod blank at a first end with a bearer while an outer periphery of the blank is bound, and extruding the blank about an axis from a second end with a first punch so as to form an axial hollow therein about the axis; and   extruding the hollow blank forwards and backwards with a second and a third punch so as to form the hollow blank with a stepped portion enlarged in both diameter and thickness in a region of the blank that is one of: (i) intermediate between the first and second ends and (ii) at one of the first and second ends, while simultaneously making the blank longer.   
   
   
       2 . A method of forming a hollow stepped shaft as set forth in  claim 1 , wherein the blank is extruded about the axis with the first punch to form the axial hollow while the bearer supporting the blank at the first end is resiliently supported by one of a hydraulic device and a pneumatic device. 
   
   
       3 . A method of forming a hollow stepped shaft as set forth in  claim 1 , wherein the blank is extruded about the axis to form the axial hollow by rapidly advancing the first punch while the bearer supporting the blank at the first end is allowed to move back slowly by a servo mechanism. 
   
   
       4 . A method of forming a hollow stepped shaft as set forth in  claim 1 , wherein the solid rod blank is made of carbon steel and is hollowed at a rate of reduction in area of 25%,
 wherein a depth of the axial hollow in the blank is at least 5 times larger than an inner diameter of the axial hollow, which is a criterion of stable working in a cold forging,   and wherein a boring region is heated at a temperature ranging between room temperature and 700 C.   
   
   
       5 . A method of forming a hollow stepped shaft as set forth in  claim 2 , wherein the solid rod blank is made of carbon steel and is hollowed at a rate of reduction in area of 25%,
 wherein a depth of the axial hollow in the blank is at least 5 times larger than an inner diameter of the axial hollow, which is a criterion of stable working in a cold forging, and   wherein a boring region is heated at a temperature ranging between room temperature and 700 C.   
   
   
       6 . A method of forming a hollow stepped shaft as set forth in  claim 3 , wherein the solid rod blank is made of carbon steel and is hollowed at a rate of reduction in area of 25%,
 wherein a depth of the axial hollow in the blank is at least 5 times larger than an inner diameter of the axial hollow, which is a criterion of stable working in a cold forging, and   wherein a boring region is heated at a temperature ranging between room temperature and 700° C.   
   
   
       7 . A method of forming a hollow stepped shaft as set forth in  claim 1 , wherein the hollow stepped shaft has regions at axial end portions thereof where serrations are formed which have a tooth form applied thereto by one of fitting and press-and-shrink fitting, and said regions are at least one of further drawn and made smaller in diameter by multistage pressure forming with upper punches and lower dies. 
   
   
       8 . A method of forming a hollow stepped shaft as set forth in  claim 2 , wherein the hollow stepped shaft has regions at axial end portions thereof where serrations are formed which have a tooth form applied thereto by one of fitting and press-and-shrink fitting, and said regions are at least one of further drawn and made smaller in diameter by multistage pressure forming with upper punches and lower dies. 
   
   
       9 . A method of forming a hollow stepped shaft as set forth in  claim 3 , wherein the hollow stepped shaft has regions at axial end portions thereof where serrations are formed which have a tooth form applied thereto by one of fitting and press-and-shrink fitting, and said regions are at least one of further drawn and made smaller in diameter by multistage pressure forming with upper punches and lower dies. 
   
   
       10 . A hollow stepped shaft formed by a method as set forth in  claim 1 .