Die set and processing method using die set

Abstract

A die set capable of suppressing breakage or wrinkling of the workpiece during bending and a processing method using the die set. A die set used for bending a plate-like workpiece includes a lower die on which the workpiece is placed, and an upper die having a pressing surface formed to press the workpiece against the lower die. The lower die includes a lower movable part slidable in the same direction as a moving direction of the upper die, a reaction force generating member configured to elastically support the lower movable part from beneath, and receiving members located on both sides of the lower movable part. The pressing surface has an arc-shaped cross-section protruding toward the lower die and extends in a longitudinal direction of the workpiece. The maximum push-in position of the lower end portion of the pressing surface is deeper than a position lowered by a finished inner diameter dimension of the workpiece from an upper surface of the lower die.

1 . A die set used for bending a plate-like workpiece, the die set comprising:
 a lower die on which the workpiece is placed; and   an upper die having a pressing surface formed to press the workpiece against the lower die,   wherein the lower die comprises:
 a lower movable part slidable in the same direction as a moving direction of the upper die; 
 a reaction force generating member configured to elastically support the lower movable part from beneath; and 
 receiving members located on both sides of the lower movable part, 
   wherein the pressing surface has an arc-shaped cross-section protruding toward the lower die and extends in a longitudinal direction of the workpiece, and   wherein the maximum push-in position of the lower end portion of the pressing surface is deeper than a position lowered by a finished inner diameter dimension of the workpiece from an upper surface of the lower die.   
     
     
         2 . The die set according to  claim 1 , wherein the reaction force generating member is a gas spring. 
     
     
         3 . The die set according to  claim 1 , wherein a plurality of reaction force generating members are arranged in a longitudinal direction of the lower die. 
     
     
         4 . The die set according to  claim 1 , wherein the reaction force generating member is configured such that a magnitude of a reaction force is adjustable. 
     
     
         5 . The die set according to  claim 1 , wherein the lower die includes a pressing force receiving surface having an inwardly recessed curved shape, and a difference between a diameter dimension of the pressing force receiving surface and a diameter dimension of the pressing surface of the upper die is smaller than a thickness dimension of the workpiece. 
     
     
         6 . The die set according to  claim 1 , wherein the pressing surface of the upper die is formed by a cylindrical mandrel member extending in a longitudinal direction of the lower die. 
     
     
         7 . The die set according to  claim 1 , wherein the lower movable part is accommodated inward of the receiving members, and a movable range of the lower movable part is equal to the maximum stroke distance of the reaction force generating member. 
     
     
         8 . The die set according to  claim 1 , wherein an inner edge portion of each receiving member has a rounded shape having a radius smaller than a radius of the pressing surface. 
     
     
         9 . The die set according to  claim 1 , wherein a hard chrome plating layer is formed on a surface of the lower movable part and surfaces of edge portions of the receiving members. 
     
     
         10 . A processing method using the die set as claimed in  claim 1 , the method comprising:
 a setting process in which the workpiece is placed on the lower die;   a pressing process in which the workpiece is pressed by the upper die; and   an advancing process in which the lower movable part and the upper die are moved downward while the reaction force generating member urges the workpiece by a reaction force thereof in a direction opposite to the moving direction of the upper die.   
     
     
         11 . A processing method using the die set as claimed in  claim 1 , the method comprising:
 a setting process in which the workpiece protected by a protective sheet is placed on the lower die;   a pressing process in which the workpiece is pressed by the upper die; and   an advancing process in which the lower movable part and the upper die are moved downward while the reaction force generating member urges the workpiece by a reaction force thereof in a direction opposite to the moving direction of the upper die.   
     
     
         12 . A processing method comprising a process of further bending a U-shaped member having been processed using the die set as claimed in  claim 1  into an O-shape to finish the U-shaped member into a pipe member.