Method for manufacturing disk member

Abstract

“MEANS TO SOLVE” A burring area Wb is axially compressed from above and from below between an upper die 5 and a lower die 6 to undergo a plastic deformation, thereby forming a cylindrical boss 1 B. A pressing surface of the lower die 6 is formed with an annular recess 6 A, whereby the burring area Wb is less susceptible to move radially outward in the process of plastic deformation. Accordingly, a base (a bottom portion) of the burring area Wb fills the annular recess 6 A without leaving any space. “EFFECT” A cylindrical boss 1 B having no hiatus in its axial end can be formed.

1 . A method of manufacturing a disk member comprising a piercing step of forming a through-opening centrally in a plate-shaped raw material, a burring step of causing the margin of the through-opening in the plate-shaped raw material to rise to its feet to one side of the plate-shaped raw material to form a substantially cylindrical burring area, and a forging step of causing the burring area to undergo a plastic deformation to form a cylindrical boss and a disk-shaped body which is located on the outside of the boss; 
 in which at least one end of the cylindrical boss is caused to project beyond an end face of the body which is disposed on the opposite side from the direction in which the burring area is caused to rise to its feet.    
   
   
       2 . A method of manufacturing a disk member according to  claim 1  in which the burring area is caused to undergo a plastic deformation by being compressed axially by a pressing surface of a first die and a pressing surface of a second die while the burring area is supported on the inside by a punch, thereby causing a base of the burring area to be filled into an annular recess formed in the pressing surface of the second die and thus forming the boss and the body.  
   
   
       3 . A method of manufacturing a disk member according to  claim 2  in which the pressing surface of the first die is formed with an annular projection which bulges toward the second die and the first die is moved toward the second die to bring the annular projection on the first die into abutment against the distal end of the burring area, thereby forming the boss by axially compressing the burring area between the pressing surface of the first die and the pressing surface of the second die.  
   
   
       4 . A method of manufacturing a disk member according to  claim 3  in which the boss is formed to have a wall thickness which is greater than the wall thickness of the body and the end of the boss which is disposed on the same side as the direction in which the burring area is caused to rise to its feet is formed so as to be recessed below the end face of the body which is located adjacent to and outward of the boss.  
   
   
       5 . A method of manufacturing a disk member according to  claim 3  in which the boss is formed to have a wall thickness which is greater than the wall thickness of the body and the end of the boss which is disposed on the same side as the direction in which the burring area is caused to rise to its feet is formed to be coplanar with the end face of the body which is located adjacent to and outward of the boss.  
   
   
       6 . A method of manufacturing a disk member according to  claim 3  in which the boss is formed to have a wall thickness which is greater than the wall thickness of the body and the end of the boss which is disposed on the same side as the direction in which the burring area is caused to rise to its feet is formed to project beyond the end face of the body which is located adjacent to and outward of the boss.