Method of manufacturing crankshaft having weight-reducing forged holes

Abstract

A method of manufacturing a crankshaft having weight-reducing forged holes can achieve lightening and precise forming by additionally including a punching process of using an individual hydraulic press. The method includes steps of: heating a steel bar, performing busting such that the heated steel bar is disposed in a cavity of a mold to be produced as a first intermediate shape of a crankshaft, performing brokering such that the first intermediate shape is produced as a second intermediate shape, performing finishing such that the second intermediate shape is produced as a third intermediate shape, performing trimming such that the third intermediate shape is produced as a complete shape of the crankshaft by cutting portions other than the shape of the crankshaft, and performing punching such that holes are formed in the complete shape of the crankshaft.

What is claimed is: 
     
         1 . A method of manufacturing a crankshaft having weight-reducing forged holes, comprising the steps of:
 heating a steel bar;   performing busting such that the heated steel bar is disposed in a cavity of a mold including an upper mold and a lower mold to be produced as a first intermediate shape of a crankshaft;   performing brokering such that the first intermediate shape is produced as a second intermediate shape;   performing finishing such that the second intermediate shape, after the brokering step, is produced as a third intermediate shape;   performing trimming such that the third intermediate shape, after the finishing step, is produced as a complete shape of the crankshaft by cutting portions other than the shape of the crankshaft; and   performing punching such that holes are formed in the complete shape of the crankshaft after the trimming step.   
     
     
         2 . The method according to  claim 1 , wherein, in the punching step, the holes are formed in both pin web parts in the complete shape of the crankshaft using hydraulic presses. 
     
     
         3 . The method according to  claim 2 , wherein the hydraulic presses are individually applied to the respective pin web parts. 
     
     
         4 . The method according to  claim 3 , wherein the hydraulic presses are simultaneously applied to both web parts of one crankpin and both web parts of another crankpin. 
     
     
         5 . The method according to  claim 4 , wherein the hydraulic presses are diagonally applied to both web parts of each of the crankpins. 
     
     
         6 . The method according to  claim 1 , wherein the holes are formed in the complete shape of the crankshaft in a state in which the complete shape of the crankshaft, after the trimming step, is heated.