Sheet metal punching apparatus and method thereof

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 secured to the pressing pad 5 by means of a bolt 6 and the like and constructed as a punch unit; a lower die 9 on which a sheet metal 8 to be subjected to punching is placed; and a die 11 embedded in the lower die 9 and having a though hole 10 of an oval shape conforming to the shape of a through hole to be punched in the sheet metal 8.

1 . A sheet metal punching apparatus comprising: a die having a through hole of a configuration conforming to a configuration of a through hole to be formed in a sheet metal; and a punch means including a punch body means having an outer configuration dissimilar to a configuration of an outer edge of the through hole of said die and adapted to form a through hole in the sheet metal in cooperation with said die and a pierced hole forming means which is integrally provided on one end face of said punch body means facing the through hole of said die and is adapted to form a pierced hole in the sheet metal, wherein the pierced hole is formed in the sheet metal by said pierced hole forming means, and in a state in which the movement of the sheet metal is restricted by said pierced hole forming means inserted in the pierced hole, said punch body means is inserted into the through hole of said die, whereby the sheet metal is subjected to tensile fracture at the outer edge of the through hole of said die through cooperation between said die and said punch body means, to thereby form the through hole in the sheet metal. 
     
     
         2 . The sheet metal punching apparatus according to  claim 1 , wherein said punch body means has at least one punch body having an outer configuration dissimilar to the configuration of the outer edge of the through hole of said die, and said pierced hole forming means has a conical or pyramidal projection provided integrally on the one end face of said at least one punch body facing the through hole of said die. 
     
     
         3 . The sheet metal punching apparatus according to  claim 1 , wherein the through hole of said die has a polygonal shape including a triangular shape, an elliptical shape, an oval shape, or a closed curve shape, and said punch body means has at least one punch body having an outer configuration of a circular or quadrangular shape. 
     
     
         4 . A method of forming a through hole in a sheet metal by the sheet metal punching apparatus according to  claim 1 , comprising the steps of: forming the pierced hole in the sheet metal by said pierced hole forming means; inserting said punch body means into the through hole of said die in a state in which the movement of the sheet metal is restricted by said pierced hole forming means inserted in the pierced hole; subjecting the sheet metal to tensile fracture at the outer edge of the through hole of said die through cooperation between said die and said punch body means, to thereby form the through hole in the sheet metal.