Die for punching sheet metal and sheet metal punching apparatus having the die

Abstract

A sheet metal punching apparatus 1 includes an upper die holder 2 which is raised and lowered by a hydraulic ram and the like; a pressing plate 3 secured to the upper die holder 2 ; a pressing pad 5 suspended from the upper die holder 2 through a resilient member 4 ; a punch holder 7 constructed as a punch unit secured to the pressing pad 5 by means of a bolt 6 and the like; a lower die 9 on which thin sheet metal 8 to be subjected to punching is placed; and a die 10 embedded in the lower die 9.

1 . A die for punching sheet metal comprising:
 an end face opposing sheet metal to be punched; a through hole which is open at said end face and into which a punch is inserted through an opening in said end face; and an inner peripheral surface defining said through hole, wherein said end face and said inner peripheral surface are contiguously connected to each other with an acute angle θ at the opening of said through hole in said end face.   
   
   
       2 . The die for punching sheet metal according to  claim 1 , wherein said end face extends in such a manner as to be inclined with respect to an axis of said punch, and said inner peripheral surface extends in parallel to the axis of said punch, and wherein said end face extending in the inclined manner and said inner peripheral surface extending in parallel are contiguously connected to each other with an acute angle θ at the opening of said through hole in said end face. 
   
   
       3 . The die for punching sheet metal according to  claim 1 , wherein said end face extends perpendicularly to the axis of said punch, and said inner peripheral surface extends in such a manner as to be inclined with respect to the axis of said punch, and wherein said end face extending perpendicularly and said inner peripheral surface extending in the inclined manner are contiguously connected to each other with an acute angle θ at the opening of said through hole in said end face. 
   
   
       4 . The die for punching sheet metal according to  claim 1 , wherein the acute angle θ is 45° to 87°. 
   
   
       5 . The die for punching sheet metal according to  claim 1 , wherein the acute angle θ is 65° to 85°. 
   
   
       6 . The die for punching sheet metal according to  claim 1 , wherein the acute angle θ is 75° to 83°. 
   
   
       7 . The die for punching sheet metal according to  claim 1 , wherein the opening is formed in the shape of a circle, an ellipse, an elongated circle, a triangle, a rectangle, or a polygon. 
   
   
       8 . A sheet metal punching apparatus comprising: the die for punching sheet metal according to  claim 1 ; and said punch which is inserted into said through hole of said die, wherein said punch includes a columnar punch body having a tubular surface extending in parallel to the axis and a projection provided integrally on one end face of said punch body on a side of insertion into said through hole of said die, said one end face of said punch body provided with said projection including an annular surface surrounding a bottom plane of said projection and extending perpendicularly to the axis and a curved surface extending from an annular outer edge of said annular surface to an annular edge of said tubular surface, whereby the sheet metal is punched in cooperation with said end face and said inner peripheral surface of said die which are contiguously connected to each other with the acute angle θ on the one hand, and said curved surface of said punch body on the other hand.