Abstract:
Device for punching blanks from a planar part ( 10 ), having a punching blade ( 20 ) attached in a support plate ( 22 ) and projecting from the latter as a blade or cutting line, and profile strips which flank the punching blade ( 20 ), are made of a material that is flexible to a limited extent and are each inserted into a channel profile ( 50 ) in a positive-locking manner with a region of their cross section, wherein both the channel profile ( 50 ) and the profile strip, as insert profile ( 70 ), are formed from a material that is elastic to a limited extent.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The invention relates to a device for punching blanks from a planar part, in particular package blanks of cardboard or corrugated board, having a punching blade, attached in a support plate and projecting from the latter as a blade or cutting line, and profile strips which flank said punching blade, are made of a material that is flexible to a limited extent and are each inserted into a channel profile in a positive-locking manner with a region of their cross section. 
         [0002]    A device of this type can be seen from EP 1 567 309 B1. A strip steel blade is accompanied by lateral profile strips made of rubber or flexible plastic. The channel profiles made of a rigid material are adhesively bonded in a planar manner to the support plate made of plywood. 
         [0003]    Owing to this device, package blanks can be cut out in groups from a cardboard or corrugated board sheet. The automatic punching machine processes the “printed sheets” cyclically; the cutting contours and scoring lines are mainly produced in its punching section. 
         [0004]    To transport the punched sheet further, “holding points” are required which hold the packages—also called copies—together. When the cutting lines penetrate into the sheet material, very high wedge forces develop, which attempt to destroy the holding points. By the attachment of the abovementioned channel profiles running on both sides of the punching blade, together with the elastic profile strips clipped in place, the elastic pressure emanating from said profile strips produces a high frictional resistance between the underside of the punched sheet and the surface, and said frictional resistance prevents the holding points from rupturing. The cross section of the elastic profile strip is in this case to be selected in such a way that forces additionally act toward the blade. 
       SUMMARY OF THE INVENTION 
       [0005]    In the knowledge of these conditions, the aim of the inventor is to simplify the device, facilitate the manipulation of the machine parts and improve production. 
         [0006]    The teaching of the present disclosure leads to the achievement of this object as well as additional favorable developments. In addition, all the combinations of at least two of the features disclosed herein come within the scope of the invention. When designation ranges are specified, values lying within said limits are also intended to be disclosed, and to be capable of being used in any desired manner, as limit values. 
         [0007]    According to the invention, both the channel profile and the profile strip, as insert profile, are formed from a material that is elastic to a limited extent; both the channel profile and the insert profile are preferably made of the material that is elastic to a limited extent, with a molded strip connecting the two. Said material may be an elastomer, a caoutchouc or preferably a rubber material of 60 Shore to 90 Shore. 
         [0008]    According to the invention, one channel leg of the channel profile is to have an inner rib which projects toward its channel space and from which an inner contour, in the shape of a circle segment in cross section, of the channel space starts, that is to say an undercut lateral region of the latter. Apart from that, an inner rib of the other channel leg—likewise as a retaining member for the insert profile—is opposite this inner rib of the channel leg; these inner ribs jointly define an undercut region of the channel space in the channel profile. 
         [0009]    The side faces of the insert profile preferably run at an angle to the center line of the cross section and are provided at one end with a respective side rib. 
         [0010]    It is also important that the base surface, assigned to the two side ribs, of the insert profile is to be assigned to the inner surface of the channel profile, with the molded strip being bent. In addition, it has proved to be favorable to arrange the two side ribs of the insert profile at a distance from the inner contour of the channel profile fitted into said insert profile. 
         [0011]    It has also proved to be favorable to form the unit comprising the channel profile, the molded strip and the insert profile from said molding material by extrusion, that is to say in a single molding operation. 
         [0012]    It is also within the scope of the invention that the molded strip of small thickness is integrally formed with its marginal regions on opposite side faces of the channel profile on the one hand and of the insert profile on the other hand. In addition, that side face of a channel leg of the channel profile which faces the molded strip has two inclined surfaces which run at an angle—preferably about 130° to 140°—to one another and which form a type of projecting construction line between them. The molded strip connecting the channel profile and the insert profile is preferably integrally formed on the inclined surface close to the free end of the channel leg. The molded strip is preferably integrally formed on that side face of the insert profile which is adjacent to the channel profile; the side faces are to run at a slight angle to the center line of the insert profile cross section and are provided at one end with a respective side rib. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    Further advantages, features and details of the invention follow from the description below of preferred exemplary embodiments and with reference to the drawing, in which: 
           [0014]      FIG. 1  shows a plan view of a punching die of an automatic punching machine with folding box blanks resting thereon; 
           [0015]      FIGS. 2 ,  4  show details of a punching operation, on an enlarged scale compared with  FIG. 1 , in the cross section of a tool which contains, according to the prior art, two rubber strips engaging in channel profiles; 
           [0016]      FIG. 3  shows part of a blade in an oblique view; 
           [0017]      FIGS. 5 to 6  show a front view of a tool according to the invention in the dismantled state and assembled state, respectively. 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    For punching packages from cardboard or corrugated board, a sheet  10  made of this material is fed, for example, to a flat bed automatic punching machine; the sheet  10  exhibits the contours of eight adjoining blanks  12  for folding boxes; these blanks  12  result in cyclic punching operations and have scoring lines  14 —predetermining the subsequent folding operation—and cutting lines  16 , defining the outside, as punching contours; adjacent cutting lines  16  are connected by pairs of “holding points”  18 ; the latter are required for transporting the punched sheet  10  further to a punching tool  20 . 
         [0019]    During its processing, the cardboard or corrugated board sheet  10  rests below a support plate  22 , of thickness a, of the punching tool  20  according to  FIG. 2  of a punching plate  24 . The support plate  22  consists of a multi-layer plywood plate in which laser cuts  26  have been made, in an arrangement corresponding to the contours of the intended packages, for accommodating punching blades as “blade or cutting lines”  30 ; a plurality of packages—up to fifty or sixty—are often arranged in groups on such a cardboard or corrugated board sheet  10 . 
         [0020]    As  FIG. 3  shows, the punching blade  30 , which as stated is designated as blade or cutting line and which has, for example, a thickness b of 0.7 mm, a height e of 24 mm here and a length f of about 60 mm, is provided at its cutting edge  28  with notches or interruptions  29  which are arranged at a distance i from one another, have a length n of, for example, 1 mm and determine said holding points  18  in a cutting line  16  produced in the sheet  10 . 
         [0021]    That section of the punching blade  30  which projects from the plywood plate  22  is flanked on both sides by channel profiles  34  formed from metal, in particular light metal, plastic or ceramic and having a height c of about 2 mm. The width q of the channel profiles  34  measures about 12 mm here. The channel legs  35  of the channel profile  34 , adhesively bonded to the plywood plate  22  by an adhesive layer  33 , define a channel space  36  and are curved on the inside in cross section in  FIGS. 2 ,  4 —with a respective lateral undercut region being formed—in order to provide a clamping hold for the ridge region  38 , correspondingly formed in cross section, of a rubber profile  40  of virtually rectangular cross section of free height h. The profile side faces  42 , in cross section, are curved slightly away from the ridge region  38  toward the profile center line M and are curved further downwards and outwards, such that a type of foot bead  43  is produced on both sides close to the profile base surface  44 . 
         [0022]    During the punching operation, the base surfaces  44 , directed in pressure direction x, of the rubber profiles  40  come to rest on the sheet  10  on both sides of the corresponding punching contour  16 —with the profile cross section being changed ( FIG. 4 ). Huge wedge forces which destroy the holding points  18  are produced when the cutting lines  30  penetrate into the sheet material. Due to the insertion of the rubber profiles  40  on both sides of the punching blade  30 , the pressure of said rubber profiles  40  produces a high frictional resistance between the underside of the sheet  10  and the surface of the punching board  24 , said frictional resistance preventing the holding points  18  from rupturing. In this case, the cross section of the rubber profiles  40  is selected in such a way that additional forces act toward the punching blade  30 . 
         [0023]    The rubber profiles  40  sitting in the channel profiles  34  adhesively bonded in place can be easily removed from and returned to said channel profiles  34 . A quick change to other, i.e. softer, rubber materials is also possible. 
         [0024]    A channel profile  50  according to the invention which is formed from elastomer, caoutchouc or a rubber material of a Shore hardness according to DIN 53 505 of between 60 and 90 and has a width g of about 10 mm and the two channel legs  54 ,  58  of which, projecting from a base plate  52 , have a free height k of about 3.5 mm is sketched in  FIG. 5 . The left-hand channel leg  54  therein forms a side face  53 , at right angles to the base plate  52 , of the channel profile  50  and has an inner contour  53   a  which is in the shape of a circle segment and forms an inner rib  56  with an end region  55 , likewise in the shape of a circle segment, of the channel leg  54 . The other channel leg  58  adjoins said base surface  52  by means of an outer inclined surface  57  and likewise has, toward the channel space  62 , an inner contour  57   a  which is in the shape of a circle segment and which likewise merges into an inner rib  64 . With the inner contours  53   a  and  57   a  in the shape of a circle segment, which respectively adjoin them, the inner ribs  56 ,  64  define an undercut region  63  of the channel space  62  ( FIG. 6 ). 
         [0025]    In cross section, the abovementioned inclined surface  57  adjoins, at one end, the outer surface  51  of said base plate  52  and, at the other end, an end inclined surface  59  which encloses with the outer inclined surface  57  an angle w of about 135° and merges into an end region  55   a  in the shape of a circle segment. 
         [0026]    At a distance from the channel profile  50 , an insert profile  70  of virtually rectangular cross section is assigned to said channel profile  50  in  FIG. 5  and is connected to it by a molded strip  60  of small thickness b 1 ; the latter is integrally formed on the one side on the end inclined surface  59  of the channel profile  50  and on the other side on a side face  68  of the insert profile  70  of height k 1 . This side face  68 , which starts from the ridge surface  72  of the insert profile  70 , and the other side face  69  of the insert profile  70  run inward at an angle t of about 10° to the profile center line Q and merge into a respective side rib  74  or  76 , respectively, of the insert profile  70 . The one side rib  74  is formed by an approximately equilateral triangular cross section and the other side rib  76  is formed by a triangular cross section of non-equilateral shape. Both adjoin a base surface  72   t , parallel to the ridge surface  72 , of the insert profile  70 . 
         [0027]    The above-described unit consisting of channel profile  50 , molded strip  60  and insert profile  70  is jointly formed from the abovementioned material, for example by extrusion, and can then be installed according to  FIG. 6 . In this connection, it may be pointed out that the channel profile  50  is within the scope of the invention even without connection to the insert profile  70 . 
         [0028]    The insert profile  70  is fed to the channel space  62  of the channel profile  50  in such a way that the two side ribs  74 ,  76  come into the channel space  62  and engage behind the inner rib  56 ,  64  there, wherein the base surface  72   t  of the insert profile  70  abuts against the inner surface  51   t  of the base plate  52  of the channel profile  50 .