Multistroke punching method and apparatus therefor

Abstract

To eliminate defects such as burr, rollover, sags, scar, etc. from cut-off surfaces of a workpiece in a turret punch press, for instance, a novel height-different punch formed with a lower front edge, an upper rear edge, and an intermediate edge extending between the two edges is used for the punch press. While feeding the workpiece on a horizontal plane in a predetermined direction, the punch is struck by a striker at a first stroke so that the lower front edge thereof cuts off the workpiece partially in cooperation with a die; at the succeeding strokes so that the intermediate edge thereof cuts off the workpiece mincingly and curls refuse within a recess of the die; and at the last stroke so that the upper rear edge thereof cuts curled refuse away from the workpiece to complete a multistroke punching operation.

What is claimed is: 
     
       1. A method of punching a sheet-like workpiece at multistrokes by a press including a die and a striker, which comprises the following steps of: (a) preparing a height-different punch formed with a lower front edge, an upper rear edge, and an intermediate edge extending between the .[.two edges.]. .Iadd.lower front edge and the upper rear edge.Iaddend.;   (b) feeding the workpiece on a horizontal plane in two predetermined directions step by step;   (c) striking the height-different punch by the striker at a first stroke so that the lower front edge thereof cuts off the workpiece partially in cooperation with the die;   (d) repeatedly striking the height-different punch at succeeding strokes so that the intermediate edge thereof cuts off the workpiece mincingly and curls refuse cut off from the workpiece within a recess of the die at such a stroke that the lower front edge of the punch is repeatedly struck by the striker within a stroke between a height below the workpiece and a height within a thickness of the workpiece; and   (e) striking the height-different punch at a last stroke so that the upper rear edge thereof cuts curled refuse away from the workpiece to complete multistroke punching operation in cooperation with the die.[.;.]..Iadd...Iaddend.   
     
     
       2. An apparatus having a striker for punching a sheet-like workpiece, which comprises: (a) a height-different punch formed with a lower front edge, an upper rear edge, and an intermediate edge extending between .[.two edges.]. .Iadd.the lower front edge and the upper rear edge.Iaddend.;   (b) a die having a recess thereunder and mated with said height-different punch;   (c) means for moving the workpiece on a horizontal plane in predetermined directions;   (d) means for controlling strokes of said height-different punch in such a way that in a first stroke, the lower front edge thereof cuts off the workpiece partially in cooperation with said .[.diee.]. .Iadd.die.Iaddend.; at succeeding strokes, the intermediate edge thereof cuts off the workpiece mincingly and curls refuse of the workpiece within the recess of the die; and at a last stroke, the upper rear edge thereof cuts curled refuse away from the workpiece to complete multistroke punching operation in cooperation with the die.   
     
     
       3. The apparatus as set forth in claim 2, wherein said means for controlling strokes of said height-different punch comprises: (a) a cylinder device for moving a piston provided with a vertically-movable ram for striking said height-different punch;   (b) an encoder disposed for the piston of said cylinder device, for detecting a vertical motion of the piston;   (c) a position detector connected to said encoder, for generating a punch position feedback signal;   (d) a hydraulic circuit having a servovalve for controllably actuating said cylinder device; and   (e) a servovalve controller for controlling said hydraulic circuit on the basis of a vertical punch position feedback signal, target vertical punch position data and vertical punch speed data.   
     
     
       4. The apparatus as set forth in claim 2, wherein said means for controlling strokes of said height-different punch comprises: (a) a first hydraulic device including a first cylinder for determining a vertical position of said height-different punch whenever said punch is repeatedly struck by the striker at the succeeding strokes so that the intermediate edge thereof cuts off the workpiece mincingly and curls refuse of the workpiece within the recess Of the die; and   (b) a second hydraulic device including a second cylinder provided with a spacer intervened between the striker and said punch, for determining a vertical position of said height-different punch when said punch is struck by the striker at the last stroke so that the upper rear edge thereof cuts curled refuse away from the workpiece. .Iadd.5. A punch tool for a press for punching a sheet-like workpiece by cutting a predetermined length of curl of a curled refuse away from the workpiece, comprising:   a punch guide adapted to be mounted on a punch tool support means of the punch press, the punch guide being formed with a through hole having a longitudinal axis;   a punch fitted in the through hole of the punch guide, said punch being movable in the direction of the longitudinal axis of the through hole, between a rest position in which a tip section of the punch is located within the punch guide, and a working position in which the tip section protrudes from the punch guide for performing a multiple stroke punching operation:   a punch head provided on the punch, the punch being moved toward the working position by a strike of a ram of the punch press against the punch head:   a spring provided between the punch head and the punch guide for urging the punch toward the rest position;   said tip section of the punch having a shape of a rectangle in cross-section; the tip section being formed with a high edge section at one side of the rectangle in the transverse direction thereof, a low edge section formed at and extending along the opposite side of the rectangle, and a curved intermediate edge section extending between said high and tow edge sections; wherein, in the process of the punching operation, at a first stroke the low edge section is adapted to break through the workpiece to form a break therein, at repeated second strokes the intermediate edge section is adapted to widen the break, thereby forming a curled refuse and at a last stroke the high edge section is adapted to cut off the refuse from the rest of the workpiece to complete a punching   
     
     
        operation. .Iaddend. .Iadd.6.  The punch tool claim 5, wherein a curve of the curved intermediate edge section comprises a first curved section of a radius R1 and a second curved section of a radius R2. .Iaddend. .Iadd.7. The punch tool of claim 5, wherein the through hole of the punch guide and a body of the punch have a cylindrical shape, and the punch is provided with a key for preventing the punch from rotating in the through hole. 
     
     
        .Iaddend. .Iadd.8.  The punch tool of claim 5, wherein the length of the curl is larger than the width of the tip section of the punch. .Iaddend. 
     
     
        .Iadd.9.  A punch tool as in claim 5, wherein the transverse dimension of the tip section is larger than the diameter of the curled shape of the 
     
     
        workpiece refuse formed by multiple punchings. .Iaddend. .Iadd.10.  An apparatus having a punch tool for punching a sheet-like workpiece by cutting a predetermined length of curl of a curled refuse away from the workpiece, which comprises: (a) a punch tool for a punch press, including:   (i) a punch guide adapted to be mounted on a punch tool support means of the punch press, the punch guide being formed with a through hole having a longitudinal axis;   (ii) a punch fitted in the through hole of the punch guide, said punch being movable in the direction of the longitudinal axis of the through hole, between a rest position in which a tip section of the punch is located within the punch guide, and a working position in which the tip section protrudes from the punch guide for performing a punching operation;   (iii) a punch head provided on the punch, the punch being moved toward the working position by a strike of a ram of the punch press against the punch head;   (iv) a spring provided between the punch head and the punch guide for urging the punch toward the rest position;   (v) said tip section of the punch being formed with a high edge section, a low edge section, and a curved intermediate edge section extending between said high and low edge sections; wherein, in the process of the punching operation, the low edge section breaks the workpiece to form a break therein at a first step, the intermediate edge section widens the break at a second step, and the high edge section cuts off a refuse of the workpiece from the rest of the workpiece at a third step to complete a punching operation;   (b) a die having a recess thereunder and mated with said punch tool;   (c) means for moving the workpiece on a horizontal plane in predetermined directions;   (d) means for controlling strokes of said punch tool in such a way that in a first stroke, the low edge section thereof cuts off the workpiece partially in cooperation with said die; at succeeding strokes, the intermediate edge section thereof cuts off the workpiece mincingly and curls refuse of the workpiece within the recess of the die; and at a last stroke, the high edge section curls refuse away from the workpiece to complete a multistroke punching operation in cooperation with the die. .Iaddend.