Punch for punching sheet metal and apparatus for punching sheet metal having the punch

Abstract

An apparatus 1 for punching sheet metal 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 sheet metal 8 to be subjected to punching is placed; and a die 10 embedded in the lower die 9.

1 . A punch for punching sheet metal comprising: a punch body; and a projection formed in the shape of one of a cone and a pyramid and provided integrally on one end face of said punch body, said projection having a base with an outer edge inscribing an imaginary circle which is concentric with a center of an imaginary circle inscribed by an outer edge of the end face, and which has a smaller diameter than a diameter of that imaginary circle, wherein an angle θ formed by the end face and a tangential line, which intersects an axis passing through the center of the imaginary circle inscribed by the outer edge of the end face, and which touches both a distal end face of said projection and the imaginary circle inscribed by the outer edge of the end face, is not less than 25° and not more than 60°, and a ratio e/L between, on the one hand, a difference e between a radius D 1 / 2  of the imaginary circle inscribed by the outer edge of the end face and a radius d 1 / 2  of the imaginary circle inscribed by the outer edge of the base and, on the other hand, a length L of a circumference of the imaginary circle inscribed by the outer edge of the end face, is a value which is not less than 0.05 and not more than 0.14.  
   
   
       2 . The punch for punching sheet metal according to  claim 1 , wherein the angle θ is less than 30° and not more than 55°, and the ratio e/L is not less than 0.09 and not more than 0.12.  
   
   
       3 . The punch for punching sheet metal according to  claim 1 , wherein the outer edge of the end face is chamfered with a radius of curvature R of not less than 0.3 mm and not more than 3 mm.  
   
   
       4 . The punch for punching sheet metal according to  claim 1 , wherein a diameter D 1  of the imaginary circle inscribed by the outer edge of the end face is not more than 100 mm.  
   
   
       5 . The punch for punching sheet metal according to  claim 1 , wherein a diameter D 1  of the imaginary circle inscribed by the outer edge of the end face is not more than 35 mm.  
   
   
       6 . The punch for punching sheet metal according to  claim 1 , wherein a diameter D 1  of the imaginary circle inscribed by the outer edge of the end face is not more than 30 mm.  
   
   
       7 . The punch for punching sheet metal according to  claim 1 , wherein as a pierced hole is formed in the sheet metal by said projection, and said punch body is further inserted into a hole of a die in a state in which the movement of the sheet metal is restricted by said projection inserted in the pierced hole, the sheet metal is fractured around the end face of said punch body, thereby forming a through hole in the sheet metal, and wherein said punch for punching sheet metal is used for an apparatus for punching sheet metal.  
   
   
       8 . The punch for punching sheet metal according to  claim 7 , wherein the hole of said die is a circular hole.  
   
   
       9 . The punch for punching sheet metal according to  claim 1 , wherein said punch body is formed in the shape of a circular cylinder, and the outer edge of the end face of said punch body is formed in the shape of a circle.  
   
   
       10 . The punch for punching sheet metal according to  claim 1 , wherein said punch body is formed in the shape of a prism including a triangular prism, and the outer edge of the end face of said punch body is formed in the shape of a polygon including a triangle.  
   
   
       11 . The punch for punching sheet metal according to  claim 1 , wherein said punch body is formed in the shape of an elliptic cylinder, and the outer edge of the end face of said punch body is formed in the shape of an ellipse.  
   
   
       12 . The punch for punching sheet metal according to  claim 1 , wherein said projection is formed in the shape of a circular cone, and the outer edge of the base of said projection is formed in the shape of a circle.  
   
   
       13 . The punch for punching sheet metal according to  claim 1 , wherein said projection is formed in the shape of an elliptic cone, and the outer edge of the base of said projection is formed in the shape of an ellipse.  
   
   
       14 . The punch for punching sheet metal according to  claim 1 , wherein said projection is formed in the shape of a pyramid including a triangular pyramid, and the outer edge of the base of said projection is formed in the shape of a polygon including a triangle.  
   
   
       15 . An apparatus for punching sheet metal comprising: said punch for punching sheet metal according to  claim 1;  and said die having the hole into which said punch is inserted, wherein a ratio D 1 /D 2  of a diameter D 2  of an imaginary circle inscribed by an outer edge of the hole of said die with respect to the diameter D 1  of the imaginary circle inscribed by the outer edge of the end face is not less than 0.80, and if the thickness of the sheet metal to be punched is assumed to be t, a difference f between the radius D 1 / 2  of the imaginary circle inscribed by the outer edge of the end face and a radius D 2 / 2  of the imaginary circle inscribed by the outer edge of the hole of said die is not less than 0.15 t.  
   
   
       16 . The apparatus for punching sheet metal according to  claim 15 , wherein the ratio D 1 /D 2  is not less than 0.85.  
   
   
       17 . The apparatus for punching sheet metal according to  claim 15 , wherein the difference f is not more than 2 mm.  
   
   
       18 . The apparatus for punching sheet metal according to  claim 15 , wherein as a pierced hole is formed in the sheet metal by said projection, and said punch body is further inserted into the hole of said die in a state in which the movement of the sheet metal is restricted by said projection inserted in the pierced hole, the sheet metal is fractured around the end face of said punch body, thereby forming a through hole in the sheet metal.  
   
   
       19 . The apparatus for punching sheet metal according to  claim 15 , wherein said die further includes a small hole which is continuous with the hole and has an outer edge inscribing an imaginary circle of a diameter D 3  which is smaller than the diameter D 2  of the imaginary circle inscribed by the outer edge of the hole and is greater than diameter D 1  of the imaginary circle inscribed by the outer edge of the end face.  
   
   
       20 . The apparatus for punching sheet metal according to  claim 15 , wherein at least one of the hole and the small hole is formed in the shape of a circle, a polygon including a triangle, or an ellipse.  
   
   
       21 . A die used for the apparatus for punching sheet metal according to  claim 15 .  
   
   
       22 . A method of forming a through hole in sheet meal by the apparatus for punching sheet metal according to  claim 15 , comprising the steps of: forming a pierced hole in the sheet metal by said projection, and further inserting said punch body into the hole of said die in a state in which the movement of the sheet metal is restricted by said projection inserted in the pierced hole, so as to fracture the sheet metal around the end face of said punch body, thereby forming a through hole in the sheet metal.  
   
   
       23 . A punch unit comprising: a case; a slider fitted to said case vertically slidably; said punch according to  claim 1  fitted in said slider vertically slidably; and returning means disposed in said slider and adapted to return said punch and said slider to their initial positions by upwardly resiliently urging said punch and said slider.  
   
   
       24 . The punch unit according to  claim 23 , further comprising: a slide guiding member provided in said case so as to guide the vertical movement of said punch.  
   
   
       25 . The punch unit according to  claim 23 , wherein said slider has a recess and is adapted to engage at the recess a detent pin secured to said case, so that said slider does not come off said case by the resiliency of said returning means.  
   
   
       26 . The punch unit according to  claim 23 , wherein said returning means has a coil spring.  
   
   
       27 . The punch unit according to  claim 23  which is used for the apparatus for punching sheet metal.