Method for manufacturing constant velocity drive shaft

Abstract

A constant velocity drive shaft manufacturing method capable of manufacturing a constant velocity drive shaft among drive shafts with high efficiency and with stable and high accuracy. A method for manufacturing a constant velocity drive shaft by full enclosed die cold forging including a metal mold pair including an upper metal mold and a lower metal mold includes an annealing step of partially annealing a molding material at positions where a first large-diameter part and a second large-diameter part included in the constant velocity drive shaft are respectively molded, a cooling step of cooling the molding material partially annealed in the first step, and a molding step of molding in one step a first large-diameter part, a second large-diameter part, and a third large-diameter part in the molding material cooled in the second step by pressing with the metal mold pair and pressing from both directions of the molding material.

What is claimed is: 
     
         1 . A method for manufacturing a constant velocity drive shaft by full enclosed die cold forging including a metal mold pair including an upper metal mold and a lower metal mold, the method comprising:
 an annealing step of partially annealing a molding material at positions where a first large-diameter part and a second large-diameter part included in the constant velocity drive shaft are respectively molded;   a cooling step of cooling the molding material partially annealed in the first step; and   a molding step of molding in one step a first large-diameter part, a second large-diameter part, and a third large-diameter part in the molding material cooled in the second step by pressing with the metal mold pair and pressing from both directions of the molding material.   
     
     
         2 . A method for manufacturing a constant velocity drive shaft by full enclosed die cold forging including a metal mold pair including an upper metal mold and a lower metal mold, the method comprising:
 a heating step of subjecting a molding material to heat treatment at positions where a first large-diameter part and a second large-diameter part included in the constant velocity drive shaft are respectively molded; and   a molding step of molding in one step a first large-diameter part, a second large-diameter part, and a third large-diameter part in the molding material subjected to the heat treatment in the first step by pressing with the metal mold pair and pressing from both directions of the molding material.   
     
     
         3 . The method for manufacturing the constant velocity drive shaft according to  claim 1 , wherein the constant velocity drive shaft includes a shaft part and the first large-diameter part, the second large-diameter part, and the third large-diameter part respectively having larger diameters than the diameter of the shaft part toward both end portions from the center of the shaft part. 
     
     
         4 . The method for manufacturing the constant velocity drive shaft according to  claim 1 , wherein the metal mold pair includes a first cavity for molding the first large-diameter part, a second cavity for molding the second large-diameter part, and a third cavity for molding the third large-diameter part. 
     
     
         5 . The method for manufacturing the constant velocity drive shaft according to  claim 1 , wherein the annealing step includes subjecting a first position where the first large-diameter part is molded and a second position where the second large-diameter part is molded of the molding material to annealing treatment while holding the positions, respectively, at substantially the same temperatures for a predetermined time period. 
     
     
         6 . The method for manufacturing the constant velocity drive shaft according to  claim 5 , wherein respective timings at which cooling is started at the first position and the second position are simultaneous in the cooling step, but one of the positions is cooled for a longer cooling time period than the other position while being repeatedly cooled and heated. 
     
     
         7 . The method for manufacturing the constant velocity drive shaft according to  claim 2 , wherein temperatures at which a first position where the first large-diameter part is molded and a second position where the second large-diameter part is molded of the molding material are respectively heated differ from each other in the heating step. 
     
     
         8 . The method for manufacturing the constant velocity drive shaft according to  claim 2 , wherein the constant velocity drive shaft includes a shaft part and the first large-diameter part, the second large-diameter part, and the third large-diameter part respectively having larger diameters than the diameter of the shaft part toward both end portions from the center of the shaft part. 
     
     
         9 . The method for manufacturing the constant velocity drive shaft according to  claim 2 , wherein the metal mold pair includes a first cavity for molding the first large-diameter part, a second cavity for molding the second large-diameter part, and a third cavity for molding the third large-diameter part.