Press forming method

Abstract

In a press forming method including pressing a plate material to form an intermediate formed body including an intermediate ridge line portion with an edge radius larger than an edge radius of a ridge line portion of a target formed body, and pressing the intermediate formed body to form the target formed body including the ridge line portion, in a cross section of the intermediate formed body along a direction orthogonal to an extending direction of the ridge line portion, the intermediate formed body includes first and second slack portions on both sides of an included-angle center line, the first and second slack portions bulging more outward in a direction of the edge radius than the target formed body, the included-angle center line bisecting an angle between first and second sides that are located on both sides of the ridge line portion of the target formed body.

What is claimed is: 
     
         1 . A press forming method comprising:
 pressing a plate material to form an intermediate formed body including an intermediate ridge line portion with an edge radius larger than an edge radius of a ridge line portion of a target formed body; and   pressing the intermediate formed body to form the target formed body including the ridge line portion,   wherein, in a cross section of the intermediate formed body along a direction orthogonal to an extending direction of the ridge line portion, the intermediate formed body includes a first slack portion and a second slack portion on both sides of an included-angle center line, the first slack portion and the second slack portion bulging more outward in a direction of the edge radius than the target formed body, the included-angle center line bisecting an angle between a first side and a second side that are located on both sides of the ridge line portion of the target formed body.   
     
     
         2 . The press forming method according to  claim 1 , wherein the intermediate formed body includes an inner region at a portion around the included-angle center line, the inner region deviating more inward in the direction of the edge radius than the target formed body, and a first maximum deviation in a press stroke direction between the intermediate formed body and the target formed body in the inner region is larger than a second maximum deviation in the press stroke direction between the intermediate formed body and the target formed body in each of the first slack portion and the second slack portion. 
     
     
         3 . The press forming method according to  claim 2 , further comprising determining a shape of the intermediate formed body, wherein the determining of the shape includes:
 drawing the included-angle center line at a position bisecting the angle between the first side and the second side that are located on the both sides of the ridge line portion of the target formed body;   drawing an imaginary upper-die profile line obtained by shifting the target formed body upward in the press stroke direction by the first maximum deviation;   drawing a first tangent line tangent to a portion of the imaginary upper-die profile line that lies on a first direction side, and a second tangent line tangent to a portion of the imaginary upper-die profile line that lies on a second direction side, from an intersection point of the included-angle center line, the first side, and the second side;   drawing an imaginary line orthogonal to the included-angle center line at a position located, by the first maximum deviation, downward in the press stroke direction from the intersection point;   determining a first circular arc inscribed in the first tangent line and the imaginary line, and a second circular arc inscribed in the imaginary line and the second tangent line;   determining a third circular arc connecting an end portion of the first circular arc on the first direction side and a matching region on the first direction side that matches a shape of the target formed body; and   determining a fourth circular arc connecting an end portion of the second circular arc on the second direction side and a matching region on the second direction side that matches the shape of the target formed body.   
     
     
         4 . The press forming method according to  claim 3 , wherein the intermediate formed body includes a discarded portion held between a blank holder and an upper die, and when the intermediate formed body is held between the blank holder and the upper die, a separation distance in the press stroke direction between the matching region and the upper die is equal to the first maximum deviation. 
     
     
         5 . The press forming method according to  claim 1 , wherein a maximum inclination angle of the intermediate ridge line portion of the intermediate formed body is smaller than a maximum inclination angle of the target formed body.