Press forming method

Abstract

A press forming method includes a forming step of pressing an intermediate formed body including an intermediate ridge line portion with a large edge radius, into a target formed body. An upper die includes an upper die step portion at a boundary portion between a product portion and a discarded portion. The discarded portion of the intermediate formed body includes a separation portion which is spaced apart from the upper die at an initial stage of the forming step, to provide an elongation allowance for the discarded portion, and a first contact portion and a second contact portion which are brought into contact with the upper die at the initial stage of the forming step, to prevent occurrence of wrinkles.

What is claimed is: 
     
         1 . A press forming method for forming a plate material into a target formed body, the plate material including a product portion and a discarded portion located on an outer periphery of the product portion, the discarded portion being to be separated from the product portion after forming, the target formed body including a ridge line portion in the product portion, the press forming method comprising:
 forming an intermediate formed body including an intermediate ridge line portion with an edge radius larger than an edge radius of the ridge line portion; and   forming the target formed body from the intermediate formed body,   wherein the product portion of the intermediate formed body includes: an inner portion deviated inward in an edge radial direction of the ridge line portion from the target formed body; and a slack portion deviated outward in the edge radial direction from the target formed body, and   the discarded portion of the intermediate formed body includes: a separation portion which is spaced apart from an upper die at an initial stage of the forming of the target formed body to provide an elongation allowance for the discarded portion; and a contact portion configured to come into contact with the upper die to prevent movement of the plate material at the initial stage of the forming of the target formed body.   
     
     
         2 . The press forming method according to  claim 1 , wherein:
 a forming die used in the forming of the target formed body includes the upper die having a shape of the target formed body, a lower die facing the upper die, and a blank holder disposed on an outer peripheral side of the lower die and configured to hold the discarded portion of the intermediate formed body between the blank holder and the upper die,   the forming of the target formed body includes:   holding the discarded portion between the blank holder and the upper die; and   pressing the intermediate formed body with the upper die and the lower die to form the intermediate formed body into the target formed body,   the upper die includes an upper die step portion at a boundary portion between the product portion and the discarded portion, and   the separation portion of the intermediate formed body is disposed at a position facing the upper die step portion.   
     
     
         3 . The press forming method according to  claim 2 , wherein the intermediate formed body includes an adjustment bead at a position between the blank holder and the upper die, the adjustment bead being spaced apart from the upper die to provide the elongation allowance. 
     
     
         4 . The press forming method according to  claim 3 , wherein the blank holder includes an adjustment recess configured to accommodate the adjustment bead to thereby space the intermediate formed body apart from the upper die. 
     
     
         5 . The press forming method according to  claim 3 , wherein the contact portion includes: a first contact portion configured to be in line contact with the upper die at an inner end portion of the adjustment bead; and a second contact portion configured to be in line contact with the upper die step portion, and
 the separation portion is located between the first contact portion and the second contact portion.   
     
     
         6 . The press forming method according to  claim 5 , wherein in the pressing of the intermediate formed body, the separation portion and the adjustment bead of the intermediate formed body elongate to thereby deform the discarded portion into a shape that causes the discarded portion to be in close contact with the upper die.