Press-forming die

Abstract

A press-forming die ( 1 ) includes a die ( 2 ) having a die corner ( 21 ), which follows along an inward-facing corner ( 41 ) of a blank sheet ( 4 ), and a punch ( 3 ) having a punch corner ( 31 ). A corner groove ( 6 ) extends along a portion of the punch corner at which leading surfaces ( 33 ) and a side surface ( 34 ) intersect in a relative stroke direction (X) of the punch. The corner groove is shaped such that its groove width (W) decreases in the stroke direction and converges at a punch corner center (C 1 ). A shoulder radius (Rps) of punch shoulders ( 3 S), which are portions along which the corner groove and the leading surfaces intersect with the side surface, a sheet thickness (t) of the blank sheet ( 4 ), and a flange length (Ls) at both ends of the inward-facing corner preferably satisfy the relationship t≦Rps≦Ls.

We claim: 
     
         1 . A press-forming die configured to press-form at least a region around an inward-facing corner of a blank sheet to form, on the blank sheet, a curved corner flange that rises from an inner edge of the inward-facing corner, and first and second side flanges that respectively extend from opposite sides of the corner flange, the press-forming die comprising:
 a die having a curved die corner shaped to form the curved corner flange and first and second die sides configured to respectively form the first and second side flanges; and   a punch having a curved punch corner and first and second punch sides that are configured to respectively cooperate with the curved die corner and the first and second die sides;   wherein a corner groove is defined in the curved punch corner and extends along a portion of the punch at which leading surfaces and a side surface of the punch intersect in a stroke direction of the punch; and   the corner groove is shaped such that its groove width decreases in a direction moving away from the leading surfaces in the stroke direction and converges at a punch corner center on the side surface of the punch.   
     
     
         2 . The press-forming die according to  claim 1 , wherein:
 groove shoulders extend along intersections of the corner groove and the leading surfaces, the groove shoulders having a shoulder radius Rgs,   punch shoulders extend along an intersection of the corner groove and the side surface and along intersections of the leading surfaces and the side surface, the punch shoulders having a shoulder radius Rps, and   the relationships Rps≦Rgs and Rgs≦30 mm are satisfied.   
     
     
         3 . The press-forming die according to  claim 2 , wherein intersections of the punch shoulders and the groove shoulders on the leading surfaces are at or outside of boundaries of the punch corner with the first and second punch sides on the side surface of the punch. 
     
     
         4 . The press-forming die according to  claim 3 , wherein a ratio D/W of a groove depth D of the corner groove in the stroke direction to a groove width W of the corner groove at the leading surfaces is larger than 0.25. 
     
     
         5 . The press-forming die according to  claim 4 , wherein the corner groove is formed by first and second inclined surfaces that respectively extend from the leading surfaces and converge along a diagonal line intersecting a center point of the punch corner. 
     
     
         6 . The press-forming die according to  claim 1 , wherein the die has four of said die corner, and the punch has four of said punch corner. 
     
     
         7 . The press-forming die according to  claim 1 , wherein a ratio D/W of a groove depth D of the corner groove in the stroke direction to a groove width W of the corner groove at the leading surfaces is larger than 0.25. 
     
     
         8 . The press-forming die according to  claim 1 , wherein the corner groove is formed by first and second inclined surfaces that respectively extend from the leading surfaces and converge along a diagonal line intersecting a center point of the punch corner. 
     
     
         9 . The press-forming die according to  claim 8 , wherein the first and second inclined surfaces respectively extend from the leading surfaces at an angle within the range of 30°-60°. 
     
     
         10 . The press-forming die according to  claim 1 , wherein the corner groove is V-shaped. 
     
     
         11 . A method for forming, on a blank sheet having an inward-facing corner, a curved corner flange that rises from an inner edge of the inward-facing corner, and first and second side flanges that respectively extend from opposite sides of the corner flange, the method comprising:
 placing the blank sheet between a die and a punch of a press-forming die; and   advancing the punch relative to the die and thereby bending the curved corner flange and the first and second side flanges,   wherein:   the die has a curved die corner and first and second die sides,   the punch has a curved punch corner and first and second punch sides,   the curved die corner and curved punch corner form the curved corner flange on the blank sheet,   the first and second die sides and the first and second punch sides respectively form the first and second side flanges on the blank sheet,   a corner groove is defined in the curved punch corner and extends along a portion of the punch at which leading surfaces and a side surface of the punch intersect in a stroke direction of the punch, and   the corner groove is shaped such that its groove width decreases in a direction moving away from the leading surfaces in the stroke direction and converges at a punch corner center on the side surface of the punch.   
     
     
         12 . The method according to  claim 11 , wherein, as the punch advances relative to the die, the corner groove causes the first and second side flanges to be bent before the curved corner flange is bent. 
     
     
         13 . The method according to  claim 12 , wherein, as the punch advances relative to the die, the corner groove causes outer edges of the curved corner flange to be bent before a center portion of the curved corner flange is bent. 
     
     
         14 . The method according to  claim 13 , wherein:
 punch shoulders extend along an intersection of the corner groove and the side surface and along intersections of the leading surfaces and the side surface, the punch shoulders having a shoulder radius Rps,   the blank sheet has a sheet thickness t,   the blank sheet has a flange length Ls at both ends of the inward-facing corner, and   the relationship t≦Rps≦Ls is satisfied.   
     
     
         15 . The method according to  claim 14 , wherein:
 groove shoulders extend along intersections of the corner groove and the leading surfaces, the groove shoulders having a shoulder radius Rgs, and   the relationships Rps≦Rgs and Rgs≦30 mm are satisfied.   
     
     
         16 . The method according to  claim 15 , wherein intersections of the punch shoulders and the groove shoulders on the leading surfaces are at or outside of boundaries of the punch corner with the first and second punch sides on the side surface of the punch. 
     
     
         17 . The method according to  claim 16 , wherein a ratio D/W of a groove depth D of the corner groove in the stroke direction to a groove width W of the corner groove at the leading surfaces is larger than 0.25. 
     
     
         18 . The method according to  claim 17 , wherein the corner groove is formed by first and second inclined surfaces that respectively extend from the leading surfaces and converge along a diagonal line intersecting a center point of the side surface of the punch corner. 
     
     
         19 . The method according to  claim 18 , wherein the first and second inclined surfaces respectively extend from the leading surfaces at an angle within the range of 30°-60°. 
     
     
         20 . The method according to  claim 19 , wherein the blank sheet is composed of an aluminum alloy.