Patent ID: 8087333
Filing Date: 2012-01-03
Classification: B21D,Y10T

Abstract:
1. A punch unit for a press die for punching a hole in sheet metal, comprising: a piercing punch having a piercing punch body, a sharp projection provided on one end of the piercing punch body for first piercing the sheet metal on a piercing die with a hole in a punching operation of the punch unit to form a first pierced hole in the sheet metal, and a flange portion united with another end of the piercing punch body, said piercing punch body having an outer cylindrical surface extending in a punching direction, an end surface provided on said one end thereof opposing the piercing die buried in a lower die, and extending in a direction perpendicular to the punching direction, and a convexly rounded surface disposed between said outer cylindrical surface and an outer periphery of said end surface, said sharp projection projecting in the punching direction from an inner periphery of said end surface, said piercing punch body being adapted to pierce the sheet metal, in which said first pierced hole is already formed by said sharp projection, to form a second pierced hole in the sheet metal in said punching operation of the punch unit, said second pierced hole having substantially the same configuration as that of the hole of the piercing die; a plunger for pressing said piercing punch, said plunger having a plunger body with one end surface which is adapted to be in contact with a plate secured to an upper die, a wall portion integrally provided on another end surface of the plunger body, and a hollow portion provided on the another end surface of the plunger body, said hollow portion being defined by the another end surface of the plunger body and an inner surface of the wall portion, being closed by the another end surface of the plunger body at an upper end portion thereof, and opening at a lower end portion thereof, said piercing punch is partially disposed in the hollow portion, said flange portion is disposed in the hollow portion so as to be brought into contact with the another end surface of said plunger body at an upper surface thereof, a cylinder adapted to be fitted in a pad of the upper die for supporting said piercing punch and said plunger slidably in a punching direction; said cylinder having a larger diameter hole portion in which said plunger is partially disposed, and a smaller diameter hole portion which is communicated with said larger diameter hole portion, and in which said piercing punch is partially disposed, and a step portion disposed between said larger hole portion and said smaller diameter hole portion, and a coil spring disposed between said flange portion of said piercing punch and said step portion of said cylinder for retracting said piercing punch and said plunger, said piercing punch being slidably disposed within said cylinder, and said coil spring, which surrounds said piercing punch, being disposed within said cylinder, and said plunger being partially slidably disposed within said cylinder, said coil spring being in contact with a lower surface of the flange portion at an one end portion thereof, and being in contact with the step portion at an another end portion thereof, said coil spring being disposed between an inner surface of the cylinder and the outer cylinder surface of the piercing punch body, said one end portion of the coil spring being disposed between the inner surface of the wall portion and said outer cylindrical surface of the piercing punch body, said pad and said cylinder each has one end surface, both of the one end surfaces of said pad and said cylinder being coplanar with each other to be brought into contact with the sheet metal thereon during piercing.