Abstract:
A method of side-cutting by a turret punch press for improving working efficiency to a large extent. The method comprises a step in which a selected one (5 1 ) of a plurality of punch chips (5 1  to 5 4 ) arranged so as to be selectively hit in a punch assembly (1) provided on the upper turret (2) is used for side-cutting a workpiece (6) and the other step in which one end of a part to be cut into a punching piece with the side cutting is cut off by another punch chip (5 2 ).

Description:
FIELD OF THE INVENTION 
     The present invention relates to a method of side cutting by a turret punch press for punching a plate form work. 
     BACKGROUND OF THE INVENTION 
     A turret punch press is designed to include an upper turret and a lower turret and to punch a plate form workpiece between a punch provided on the upper turret and a die provided on the lower turret. 
     On the other hand, it is possible to perform a side cutting for cutting a workpiece by continuously moving the above-mentioned punch up and down. As the side-cutting method, a method disclosed in Japanese Unexamined Patent Publication No., 63-130228 is known. 
     The side cutting method disclosed in the above-identified publication is that a punch provided with three stage edges, i.e. an upper edge, an intermediate edge and a lower edge, is driven up and down by means of a hydraulic cylinder for performing the side-cutting with the lower and intermediate edges, punching piece retained in a die is cut by means of the upper edge when a predetermined amount of the punching piece is retained, and the side cutting is again performed thereafter. The lower, intermediate and upper edges to be used for cutting are selected by controlling the stroke of the hydraulic cylinder. 
     However, in the above-mentioned side cutting method, since the punch is driven through a substantially small stroke to perform the side cutting with the lower and the intermediate edges, a dimension to be cut in a single stroke is relatively small and such as to require long process period. Furthermore, a saw-tooth like trace is frequently formed along the cutting surface to degrade the product quality. 
     Further, since the punching piece is cut while it is retained in a predetermined position in the die, a drooping can be created on the workpiece to degrade the product quality when the side cutting process is performed along a relatively long dimension. 
     SUMMARY OF THE INVENTION 
     In view of the problems set forth above, it is a primary object of the present invention to provide a side cutting method which utilizes a turret punch press and which permits longer dimension in one stroke of a punch chip so as to significantly improve the processing efficiency. 
     Another object of the invention is to provide a side cutting method which utilizes a turret punch press which can avoid the formation of a residual drooping portion on the cut portion and further reduce the formation of a saw-tooth like trace along a steering surface. 
     In order to accomplish the above-mentioned primary object, there is provided, in accordance with the first aspect of the present invention, a method of side-cutting by a turret punch press comprising the steps of performing a side cutting for a workpiece with predetermined one of a plurality of punch chips which are provided in a punch assembly mounted on an upper turret and adapted to be selectively impacted, and cutting off one end of a portion to be a punching piece by cutting in the side-cutting process by means of another one of punch chips. 
     In order to accomplish above-mentioned various objects, there is provided, in accordance with the second aspect of the invention, a method of side-cutting by a turret punch press comprising the steps of performing a side cutting for a workpiece with predetermined one of a plurality of punch chips which are provided in a punch assembly mounted on an upper turret and adapted to be selectively impacted, cutting off one end of a portion to be a punching piece by cutting in the side-cutting process by means of another one of punch chips, and again performing the side cutting with the one of the punch chips continuing from a remained cut portion, and repeating a cycle consisted of the each steps. 
     The present invention achieves the following advantages. Namely, using one of a plurality of punch chip provided in a punch assembly, the side-cutting process for the workpiece is performed, initially. Then, the punching piece formed by the side-cutting is cut off by means of another punch chip. Repeating the foregoing operation, the side-cutting of the workpiece into the desired configuration is performed. Therefore, the length to be cut in one stroke of the punch chip can be longer than the conventional side-cutting method to significantly improve the working efficiency. Also, upon cutting off of the punching piece, a part of the cut portion is left so that side-cutting is performed subsequently with continuing from the cut portion. By this, it becomes possible to perform side cutting without forming the drooped trace. 
     In addition, with this method, since the length of side cutting in one stroke can be made longer, it can reduce the saw-tooth like trace to be formed on the shearing surface. 
     Above-mentioned and other objects of the present invention, aspects and advantages will become clear to those skilled in the art with the following descriptions and associated drawings illustrating preferred embodiment exemplarily shown in consistent with the principle of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be understood more fully from the detailed description given herebelow and from the accompanying drawings of the preferred embodiment of the invention, which, however, should not be taken to be limitative to the invention but are for explanation and understanding only. 
     FIG. 1 is a fragmentary longitudinal section of a major portion of a turret punch press for implementing the preferred method according to the present invention; 
     FIG. 2 is an illustration as viewed along an arrow II in FIG. 1; 
     FIG. 3 is an illustration as viewed along an arrow III in FIG. 1; 
     FIGS. 4 and 5 are illustrations showing operation of the method according to the invention; and 
     FIGS. 6A through 6D, 7 and 8 are illustrations showing operations of other side cutting methods of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A side cutting method according to the present invention will be discussed hereinafter in greater detail with reference to the accompanying drawings. 
     In the drawings, the reference numeral 1 denotes a punch assembly mounted on an upper turret 2 of a turret punch press, 3 denotes a die mounted on a lower turret 4. A side cutting process for a plate form workpiece 6 can be performed between the punch chip 5 and the die 3 of the punch assembly 1. 
     The punch assembly 1 includes a cylindrical punch guide 7, as shown in FIG. 1. The punch chip 5 is disposed within the punch guide 7 for vertical sliding movement. 
     The punch chip 5 comprises a large diameter punch chip 5 1  having a body 5a disposed within the punch guide 7 for vertical sliding movement, and a plurality of, such as three, smaller diameter punch chips 5 2 , 5 3  and 5 4  disposed in a plurality of guide holes 5b formed through the body 5a for vertical sliding movement. The punch chip 5 1  has a rectangular tip end, on which a cutting edge 5c with a lower face tapered in the vertical direction so that the side cutting process for a workpiece 6 can be performed with the cutting edge 5c and a rectangular cutting slot formed in the die 3. 
     The punch chip 5 2  is arranged co-axially with the cutting edge 5c and has a tip end, on which a square cutting edge 5d having the same width to the cutting edge 5c is formed so that punching piece 6a can be cut off by means of the cutting edge 5d. 
     The remaining punch chips 5 3  and 5 4  are arranged at both sides of the punch chip 5 1  as shown in FIG. 2. Circular and triangular cutting edges 5e and 5f are formed on the chip ends of the punch chips 5 3  and 5 4 . 
     On the other hand, the punch chip 5 1  has an upper end portion having smaller diameter. The smaller diameter portion 5g fixedly mounts a punch head 9, center of which is adapted to receive an impact by an striker 14 1  discussed later. Between the punch head 9 and an upper plate 7a provided on the upper end of the punch guide 7, a stripping spring 10 formed of a resilient or an elastic body, such as a rubber, is disposed for urging the punch chip 5 1  upwardly. 
     The upper ends of other punch chips 5 2  to 5 4  are extended around the smaller diameter portion 5g and reach through openings 9a formed through the punch head 9 through through holes 10a defined in the stripping spring 10. The upper ends of the punch chips 5 2  to 5 4  are arranged substantially in flush with the upper surface of the punch head 9. 
     Between spring seats 5h formed at positions slightly above the intermediate portions of respective punch chips 5 2  to 5 4  and the upper surface of the body 5a of the punch chip 5 1 , stripping springs 11 comprising coil springs are disposed. With these stripping springs 11, respective punch chips 5 2  to 5 4  are biased upwardly. 
     On the other hand, at an impacting position of the turret punch press, a ram 14 which is adapted to be driven vertically by means of a not shown drive mechanism. A plurality of strikers 14 1 , 14 2 , 14 3  and 14 4  are provided on the lower surface of the ram 14 for projecting and contracting with respect thereto. 
     The strikers 14 1  to 14 4  are arranged at corresponding positions to a plurality of punch chips 5 1  to 5 4  provided in the punch assembly 1. By driving the ram 14 vertically with selectively projecting the strikers 14 1  to 14 4 , the punch chips 5 1  to 5 4  corresponding to these strikers 14 1  to 14 4  can be impacted. 
     By impact given by the strikers 14 1  to 14 4 , one of the chips 5 1  to 5 4  is driven downwardly to extend the cutting edges 5c. 5d, 5e and 5f provided at the tip ends thereof downward from the holes 15 1  to 15 4  of a stripper plate 15 provided on the lower end of the punch guide 7. Thus, as shown in FIG. 3, the cutting edge 5c, 5d, 5e and 5f can perform punching of the workpiece with the cutting slots 3a, 3b and 3c formed in the die 3 at corresponding positions thereto. 
     It should be noted that, in the drawings, the reference numeral 20 denotes a positioning key for positioning the punch chip 5 relative to the punch guide 7, 21 denotes a positioning key for performing positioning of the punch assembly 1 relative to the upper turret 2. 
     Next, discussion will be given for a process for side cutting of the workpiece 6 using a die apparatus composed of the punch assembly 1 and the die 3, with reference to FIGS. 4 to 8. 
     During side cutting of the workpiece 6, the workpiece 6 is initially moved by a clamp 22 for setting the side cutting start position of the workpiece 6 at a punch position. The clamp 22 is designed to clamp the workpiece 6 and move the latter relative to the punch assembly in per se known manner. Then, the side cutting process is initiated by projecting the striker 14 1  from the lower end of the ram 14 for impacting the punch chip 15 1 . 
     By downward motion of the ram 14, the striker 14 1  impacts the punch head 9 corresponding to punch chip 15 1 . Thus, the punch chip 15 1  is moved downwardly against the stripping spring 10 to extend the cutting edge 5c at the lower end of the punch chip 5 1  from the hole 15 1  of the stripper plate 15. Thus, the workpiece 6 is cut in the length l 1  between the cutting edge 5c and the die 3. 
     Subsequently, according to upward motion of the of the punch chip 5 1 , the striker 14 1  is retracted. Then, the striker 14 2  necessary for the next operation is projected and the punch chip 5 2  is impacted from the above by downward movement of the ram 14, as shown in FIG. 5. 
     By this, the punch chip 5 2  is moved downwardly to cut off the punching piece 6a cut by the punch chip 5 1  m between the cutting edge 5d of the punch chip 5 2  and the die 3. Thus, a rectangular hole of the length l 2  is formed in the workpiece 6. 
     In this case, by making the vertical stroke of the ram 14 variable and thus making the vertical stroke of the punch chip 5 1  variable, the length l 2  of the hole can be differentiated within a predetermined range. 
     It should be appreciated that although the punch chip 5 2  is used in the foregoing process for cutting off the slug, the punch chip 5 3  or 5 4  may be used in place of the punch chip 5 2 . 
     The foregoing is an example, in which the length l 1  is initially cut by the punch chip 5 1  and subsequently, the punching piece 6a is cut off by the punch chip 5 2  for forming the rectangular hole 6b in the length of l 2 . Conversely, an example shown in FIG. 7 is adapted to initially cut a length l 3  by making the vertical stroke of the ram 14 variable, and then, as shown in FIG. 8, a length l 4  of the punching piece 6a is cut off by the punch chip 5 2  with leaving the cut portion in the length l 5 . Subsequently, the side cutting is continued following to the cut portion. With this process, it becomes possible to perform a side cutting process without leaving a drooping portion while reducing the saw-tooth like trace along the shearing surface, as shown in FIGS. 6A to 6D. 
     Although the invention has been illustrated and described with respect to exemplary embodiment thereof, it should be understood by those skilled in the art that the foregoing and various other changes, omissions and additions may be made therein and thereto, without departing from the spirit and scope of the present invention. Therefore, the present invention should not be understood as limited to the specific embodiment set out above but to include all possible embodiments which can be embodies within a scope encompassed and equivalents thereof with respect to the feature set out in the appended claims.