Abstract:
A method includes removing material from a die and thereby changing a location of a cutting edge of the die in a punch entry direction and changing a cutting edge cross-section of the die; and assigning a punch and/or a workpiece thickness to the die based, at least in part, on the change in the cutting edge cross-section of the die.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a divisional of and claims the priority of U.S. Ser. No. 12/579,812, filed Oct. 15, 2009, which claims priority under 35 U.S.C. §119(a) from European Patent Application No. 08 018 279.3, filed Oct. 18, 2008, the entire contents of which are hereby incorporated by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The invention relates to reprocessed dies, and, in particular, to the assignment of a punch or a workpiece thickness to a reprocessed die. 
       BACKGROUND 
       [0003]    U.S. Pat. No. 6,401,056 B1 describes the recording of information about punching tools during the lifetime of a tool. A record is made of regrinding operations performed on dies and of a changing size of a height of the die that is associated with regrinding. The recorded tool data are intended, in particular, to enable the tool user to determine when a punching tool needs to be repaired or replaced. 
         [0004]    The dies normally used in practice are dies having a die orifice whose wall extends at a so-called “relief angle” with respect to the wall of the punch entering the die orifice. The relief angle is intended to ensure that the material which is punched out can reliably leave the die and that the punch can return to its home position without hindrance following penetration of the workpiece to be processed and following associated entry into the die orifice of the die. To obtain the highest possible process reliability during punching, the relief angle on dies would have to be as large as possible. 
         [0005]    Regrinding of dies is typically carried out because of wear to the cutting edge of the die and involves removal of material from the die in the entry direction of the punch. Owing to the relief angle, the removal of material is accompanied by enlargement of the cross-section of the die orifice at the level of the cutting edge of the die (“die cutting edge cross-section”). At the same time, the die cutting edge cross-section is a determining factor for assignment of the die to a punch cooperating therewith (“punch assignment”) and/or for the thickness of the workpiece that can be processed by means of the die and the punch assigned thereto (“workpiece thickness assignment”). For example, in the case of a punching tool set comprising a punch of circular cross-section and a die with a die orifice of circular cross-section, ideally a cutting gap of a width dependent on the thickness of the material to be processed remains between the cutting edge of the die and the punch. If, for example, a circular cut-out of 5 mm diameter is to be made in a metal sheet of 2 mm thickness, there is provided for that purpose a punching tool set comprising a round punch with a diameter of 5 mm and a die with a circular die orifice, the cutting edge of which die has a diameter of 5.2 mm. 
         [0006]    For individual processing tasks, for example for a specific thickness of metal sheet and for a specific punching diameter, users of punching tools keep a stock of punching tool sets specifically designed for the particular processing task. Regrinding of the die of such a punching tool set, for example because of wear to the cutting edge of the die, is envisaged only on a scale such that the enlargement of the die cutting edge cross-section, which is associated with regrinding of the die, does not result in an unduly wide cutting gap being produced between the cutting edge of the die and the assigned punch. 
         [0007]    Owing to the relief angle of the die, however, the die cutting edge cross-section is typically widened, even as a result of a slight regrinding of the die, to a value that should not be exceeded for a given punch if high-quality processing results are to be achieved. In the case of an unduly wide cutting gap, only processing results of an inferior quality would be achievable using the punching tool set. Once the size of the die cutting edge cross-section reaches its limit value, further regrinding is usually abandoned and the die is instead removed from stock and scrapped. 
       SUMMARY 
       [0008]    In general, this invention relates to reprocessed dies, and, in particular, to the assignment of a punch or a workpiece thickness to a reprocessed die. 
         [0009]    One aspect of the invention features a method that includes removing material from a die and thereby changing a location of a cutting edge of the die in a punch entry direction and changing a cutting edge cross-section of the die. The method also includes assigning a punch and/or a workpiece thickness to the die based, at least in part, on the change in the cutting edge cross-section of the die. 
         [0010]    In some embodiments, changing the cutting edge cross-section of the die includes changing a size of the cutting edge cross-section of the die. The punch and/or the workpiece thickness can be assigned based, at least in part, on the change in the size of the cutting edge cross-section. 
         [0011]    In certain embodiments, the die includes a relief angle at which a wall of the die extends in the punch entry direction. The punch and/or the workpiece thickness can be assigned based, at least in part, on the relief angle. 
         [0012]    In some embodiments, changing the cutting edge cross-section of the die includes changing a shape of the cutting edge cross-section of the die. The punch and/or the workpiece thickness can assigned based, at least in part, on the change in the shape of the cutting edge cross-section. 
         [0013]    The method can also include arranging the die and an assigned punch in a working state on tool supports of a punching apparatus of a punching machine. 
         [0014]    In certain embodiments, arranging the die and the assigned punch in the working state on the tool supports of the punching apparatus includes arranging the die and an assigned punch on a common tool holder located in a position away from the punching apparatus, and then utilizing the common tool holder to arrange the die and the assigned punch on the tool supports of the punching apparatus. 
         [0015]    In some embodiments, arranging the die and the assigned punch in the working state on the tool supports of the punching apparatus includes positioning the die and the assigned punch relative to each other on the tool supports of the punching apparatus. 
         [0016]    In certain embodiments, arranging the die and the assigned punch in the working state on the tool supports of the punching apparatus includes positioning the die along a stroke axis of the punching apparatus based, at least in part, on a depth of material removed from the die. 
         [0017]    The method can also include performing a punching operation on a workpiece using the punching machine and the die. 
         [0018]    Another aspect of the invention provides a reprocessed die. A height of the reprocessed die, measured in a punch entry direction, differs from a height, in the punch entry direction, of a predecessor die that was reprocessed to produce the reprocessed die. The reprocessed die is provided with a punch assignment and/or a workpiece thickness assignment based, at least in part, on a change in a cutting edge cross-section of the reprocessed die relative to the predecessor die. 
         [0019]    In another aspect, the invention features a punch machine that includes a reprocessed die and a control unit. The control unit is configured to assign a punch or a workpiece thickness to the reprocessed die based, at least in part, on a change in a cutting edge cross-section of the reprocessed die relative to a predecessor die that was reprocessed to produce the reprocessed die. 
         [0020]    The punch machine can also include a plurality of punches. The control unit can be configured to assign one of the plurality of punches to the reprocessed die based, at least in part, on the change in the cutting edge cross-section of the reprocessed die relative to the predecessor die. 
         [0021]    In some embodiments, the punch machine includes a punch assembly including a plurality of punches. The control unit can be configured to assign one of the punches of the punch assembly to the reprocessed die based, at least in part, on the change in the cutting edge cross-section of the reprocessed die relative to the predecessor die. 
         [0022]    In certain embodiments, the punch machine also includes a punch assembly including a plurality of punches, and an adjusting device. The adjusting device is operable to position the punch assembly and the reprocessed die relative to each other based, at least in part, on the punch assignment or the workpiece thickness assignment of the reprocessed die. 
         [0023]    In some embodiments, the adjusting device is in communication with the control unit, and the control unit is configured to position one of the punches and the reprocessed die in a working state via operation of the adjusting device. 
         [0024]    In certain embodiments, the control unit is configured to control relative movement of the punch assembly and the reprocessed die, via the adjusting device, based, at least in part, on the punch assignment or the workpiece thickness assignment of the reprocessed die. 
         [0025]    The punch machine can also include an elevating device operable to position the reprocessed die along a stroke axis of the punch machine. 
         [0026]    In some embodiments, the elevating device is in communication with the control unit, and the control unit is configured to control movement of the reprocessed die along the stroke axis of the punch machine via the elevating device based, at least in part, on a depth of material removed from the predecessor die. 
         [0027]    Another aspect of the invention provides a punch machine that includes a die assembly including a plurality of reprocessed dies, and a control unit. The control unit is configured to assign a corresponding punch and/or a corresponding workpiece thickness to each of the reprocessed dies of the die assembly based, at least in part, on respective changes in cutting edge cross-sections of the reprocessed dies relative to predecessor dies that were reprocessed to produce the reprocessed dies. 
         [0028]    The punch machine can also include a punch assembly including a plurality of punches, and an adjusting device. The adjusting device is operable to position the punch assembly and the die assembly relative to each other based, at least in part, on the punch assignments or the workpiece thickness assignments of the reprocessed dies. 
         [0029]    In certain embodiments, the adjusting device is in communication with the control unit, and the control unit is configured to position one of the punches and one of the reprocessed dies in a working state via operation of the adjusting device. 
         [0030]    In some embodiments, the control unit is configured to control relative movement of the punch assembly and the die assembly, via the adjusting device, based, at least in part, on the punch assignments or the workpiece thickness assignments of the reprocessed dies. 
         [0031]    The punch machine can also include an elevating device operable to position the die assembly along a stroke axis of the punch machine. 
         [0032]    In certain embodiments, the elevating device is in communication with the control unit, and the control unit is configured to control movement of the die assembly along the stroke axis of the punch machine via the elevating device based, at least in part, on a depth of material removed from the predecessor dies. 
         [0033]    In yet another aspect the invention features a computer readable medium having encoded thereon software for defining punching tool sets. The software includes instructions for assigning a punch or a workpiece thickness to a reprocessed die based, at least in part, on a change in a cutting edge cross-section of the reprocessed die relative to a predecessor die that was reprocessed to produce the reprocessed die. 
         [0034]    The software can also include instructions for receiving information corresponding to a depth of material removed from a predecessor die as a result of the reprocessing of the predecessor die, and determining the change in the cutting edge cross-section of the reprocessed die relative to the predecessor die based on the depth of material removed from the predecessor die and a relief angle associated with the predecessor die. 
         [0035]    In another aspect, the invention features a method for defining a punching tool set for processing workpieces, such as metal sheets, by punching. A punching tool set is assembled from a punch and from a die. The die is produced by reprocessing of a predecessor die. A change in a die cutting edge cross-section associated with the reprocessing is taken into consideration during the assembly the of the punching tool set. Starting with the die cutting edge cross-section of the predecessor die, the die cutting edge cross-section of the die (produced by reprocessing) is obtained by means of the change in the die cutting edge cross-section associated with the reprocessing. The new die cutting edge cross-section (i.e., the cutting edge cross-section of the reprocessed die) forms the basis for a punch assignment and/or a workpiece thickness assignment of the die. It is conceivable that, owing to the reprocessing operation and the associated removal of material, the die may be assigned to a different punch than the predecessor die. In addition or as an alternative, the die may be assigned to a different workpiece thickness than the predecessor die. In each case it is ensured that a reprocessed, e.g., reground, die is used for forming punching tool sets. The reduction or elimination of a rigid association of dies with specific punches and/or specific workpiece thicknesses can help to increase the useful life of the dies. 
         [0036]    In some embodiments, a punching tool can be defined under numerical control. 
         [0037]    In certain embodiments, the method for defining punching tool sets can be integrated in a method for managing punching tool sets for processing workpieces, especially metal sheets, by punching. Such integration can be beneficial in view of the fact that the tool data utilized for defining punching tool sets is also available for managing punching tools. 
         [0038]    In some embodiments, the method for defining punching tool sets can be used when setting up punching apparatuses on punch machines. Thus, when setting up a punching apparatus, a punching tool set, with which the punching apparatus is to be equipped, is defined. 
         [0039]    In some cases, the method for defining punching tool sets and the method for setting up punching apparatuses on punch machines can be integrated in a method for processing workpieces, such as metal sheets, by punching. In the course of such a processing method, punching tools that are to be used for workpiece processing can be determined and installed on a punching apparatus of a punch machine before actual processing of a workpiece can be commenced. 
         [0040]    In some embodiments, a die is provided with a punch assignment and/or a workpiece thickness assignment in dependence on a change in the die cutting edge cross-section associated with reprocessing of the die. Such a die can be used in a punch machine. 
         [0041]    The punch machine can be operated under numerical control. A processing program can be run on a numerical control of the punch machine to control adjusting devices and an elevating device of the punch machine, thereby to control movements of the die and an assigned punch 
         [0042]    A change in a die cutting edge cross-section associated with a processing of a predecessor die may differ in nature. For example, in some cases, reprocessing of the predecessor die results in alteration of a size of the die cutting edge cross-section. Accordingly, a punch assignment and/or a workpiece thickness assignment of the reprocessed die can be carried out in dependence on the change in the size of the die cutting edge cross-section associated with the reprocessing. 
         [0043]    A reason for a change in the size of the die cutting edge cross-section due to reprocessing may be a relief angle at which, on the predecessor die, the wall of the die orifice extends with respect to the wall of the punch entering the die orifice. In that case, the punch assignment and/or the workpiece thickness assignment of the die can be based on the value of the relief angle. Using simple trigonometric functions, the change in size of the die cutting edge cross-section associated with reprocessing can be determined from the relief angle and from the depth of the material removed in the entry direction of the punch during the reprocessing. By reference to the change in size, the size of the die cutting edge cross-section obtained as a result of the reprocessing can be ascertained based on the original size of the die cutting edge cross-section. 
         [0044]    Alternatively or additionally, the reprocessing of the predecessor die can result in a change in a shape of the die cutting edge cross-section. Accordingly, the punch assignment and/or the workpiece thickness assignment can be carried out in dependence on the change in the shape of the die cutting edge cross-section associated with the reprocessing. 
         [0045]    The punching tool sets defined in the manner described can be arranged on a punching apparatus of a punch machine in such a manner that they are able to perform the desired workpiece processing. A tool holder can be used for that purpose. The die and the punch of a defined punching tool set can be arranged on the tool holder at a location away from the punching apparatus. The punching tool set can then be transferred to the punching apparatus of the punch machine by means of the tool holder. 
         [0046]    In addition or as an alternative, there is the possibility of bringing the die and the punch of a defined punching tool set into a working state on tool supports of the punching apparatus. For example, the die and the punch can be positioned relative to each other on the tool supports of the punching apparatus in such a way as to provide a mutual assignment of die and punch for subsequent workpiece processing. 
         [0047]    When the die is arranged on the punching apparatus of the punch machine, the removal of material from the die, which is associated with the reprocessing of the predecessor die, can be taken into consideration. Owing to the removal of material, the height of the die measured in an entry direction of the punch (i.e., the punch entry direction) is reduced and the location of the cutting edge of the die changes accordingly. The vertical location of the cutting edge of the die on the upper side of the die facing the punch can be significant for workpiece processing in a number of respects. For example, the vertical location of the cutting edge of the die may be necessary to calculate the magnitude of the punch stroke to be carried out by the punch. It may also be necessary to ensure that the upper side of the die does not project above a workpiece support on which the workpiece is supported in the vicinity of the punching apparatus. The aspects mentioned are taken into consideration in setting up the punching apparatus of a punch machine by the die being positioned on the punching apparatus of the punch machine in the entry direction of the assigned punch according to the depth to which material was removed during the reprocessing. 
         [0048]    For relative positioning of the die and punch of a defined punching tool set, appropriate adjusting devices are provided on punch machines according to the invention. 
         [0049]    If the punch assigned to a die forms part of a punch assembly that includes a plurality of punches, the adjusting device serves to position the punch assembly and the die relative to each other in such a manner as to enable the die and the punch of the defined punching tool set to perform the relevant workpiece processing in cooperation with each other. 
         [0050]    If the die is a component part of a die assembly that includes a plurality of dies, the die assembly on the one hand and the punch of the defined punching tool set on the other hand are positioned in such a manner that the die of the defined punching tool set and the assigned punch are operable. 
         [0051]    The height adjustment of the die on the punching apparatus of the punch machine, which is carried out in dependence on the depth of the material removed during the reprocessing, can be implemented by means of an appropriate elevating device of the punch machine. 
         [0052]    Other aspects, features, and advantages will be apparent from the description and drawings, and from the claims. 
     
    
     
       DESCRIPTION OF DRAWINGS 
         [0053]      FIG. 1  is a perspective view of a punch machine. 
           [0054]      FIGS. 2   a ,  2   b , and  2   c  show a die for use on the punch machine of  FIG. 1 . 
           [0055]      FIGS. 3   a  and  3   b  show a die assembly of a first type for use on the punch machine of  FIG. 1 . 
           [0056]      FIGS. 4   a  and  4   b  show a die assembly of a second type for use on the punch machine of  FIG. 1 . 
           [0057]      FIG. 5  illustrates a punch assignment and/or a sheet thickness assignment of dies of the die assembly of  FIGS. 3   a  and  3   b.    
           [0058]      FIG. 6  is a perspective view of a punching tool set. 
           [0059]      FIGS. 7   a  and  7   b  show a punching tool set composed of a punch and a die of the die assembly of  FIGS. 3   a  and  3   b.    
           [0060]      FIG. 8  is a perspective view of a punching tool set composed of a punch of a punch assembly and a die of the die assembly shown in  FIGS. 3   a  and  3   b.    
       
    
    
     DETAILED DESCRIPTION 
       [0061]    As shown in  FIG. 1 , a punch machine  1 , for processing workpieces in the form of metal sheets  2  by punching, has a C-shaped machine frame  3  with an upper frame member  4  and a lower frame member  5 . A conventional coordinate guide  7  is accommodated in a throat  6  of the machine frame  3 . As is customary, the coordinate guide  7  comprises a transverse rail guide  8  and a transverse rail  9  guided thereon. The transverse rail guide  8  is displaceable together with the transverse rail  9  in the direction of a horizontal y axis by means of a drive motor. The transverse rail  9  can be moved in the direction of a horizontal x-axis, which at the same time is perpendicular to the y-axis, by means of a drive motor. 
         [0062]    Clamps  10  of a conventional type are provided on the transverse rail  9  for holding a workpiece (e.g., metal sheet  2 ). The metal sheet  2  is supported on a workpiece support  34  of the punch machine  1 . In addition, the transverse rail  9  serves as a tool magazine. For that purpose, tool holders  11  are detachably mounted on the transverse rail  9 . A tool holder  11  is illustrated in detail in  FIG. 7 . 
         [0063]    At the free ends of the upper frame member  4  and the lower frame member  5 , there is a punching apparatus configured as a punching station  12 . The punching station  12  is a mono-punching head. Accordingly, the punching station  12  includes tool supports in the form of an upper tool receiver  13  on the upper frame member  4  and in the form of a lower tool receiver  14  on the lower frame member  5 . 
         [0064]    In the example illustrated, a punch  15  is loaded into the upper tool receiver  13  and a die  16  is loaded into the lower tool receiver  14 . The punch  15  and the die  16  form together a punching tool set  17 . The die  16  is illustrated in detail in  FIGS. 2   a ,  2   b ,  2   c .  FIG. 7  shows the die  16  in combination with the punch  15 . 
         [0065]    An electric rotary/stroke drive  18  of the punch machine  1  comprises an upper electric rotary/stroke drive unit  19  and a lower electric rotary/stroke drive unit  20 . By means of the upper rotary/stroke drive unit  19 , the punching tool loaded into the upper tool receiver  13 , in this case the punch  15 , is raised and lowered along a stroke axis  21  extending in the direction of a vertical z-axis and, in addition, is rotated about the stroke axis  21  in a rotation direction  22  illustrated by a double-headed arrow. Correspondingly, the punching tool loaded into the lower tool receiver  14 , the die  16  here, can be translated along the stroke axis  21  and rotated about the stroke axis  21  in the rotation direction  22  by means of the lower rotary/stroke drive unit  20 . 
         [0066]    In some cases, all of the major functions of the punch machine  1  can be numerically controlled. A CNC control  23  indicated in  FIG. 1  is provided for that purpose. 
         [0067]    As shown in  FIGS. 2   a ,  2   b , the die  16  is of a conventional type. It has a cutting edge  24 , which is circular in the case illustrated and which in turn delimits a die orifice  25  of circular cross-section. In the installed position on the punch machine  1 , the die orifice  25  extends in the direction of the stroke axis  21 . The punch  15  enters the die orifice  25  along the stroke axis  21  during processing of a metal sheet. An arrow  26  in 
         [0068]      FIG. 2   b  represents the entry direction. In the conventional manner, during processing of a metal sheet by punching, the cutting edge  24  of the die  16  and a corresponding circular cutting edge of the punch cooperate with each other to process the relevant metal sheet  2  by punching. 
         [0069]    Starting at the level of the cutting edge  24  of the die, the die orifice  25  becomes wider in the entry direction  26  to form a relief angle α, which is highly exaggerated in the drawing. Accordingly, the die orifice  25  has a frustoconical shape. The relief angle α is intended to ensure that pieces cut out of a processed metal sheet  2  by means of the cutting edge  24  of the die reliably exit from the die  16  in a downward direction. 
         [0070]    In  FIG. 2   c , the magnitude of the diameter of the die orifice  25  at the level of the cutting edge  24  of the die and hence the size of the die cutting edge cross-section is denoted by “d” and the height of the die  16  measured along the stroke axis  21  is denoted by “h”. 
         [0071]    As indicated by a dashed line in  FIG. 2   c , the die  16  has been produced by reprocessing a predecessor die  16 ′ of height h 0 . In the course of that reprocessing, the die  16 ′ was reground owing to wear to the cutting edge of the die. In that operation, material having a removal depth of Δh was removed from the predecessor die  16 ′ in the entry direction  26 . Owing to the relief angle α, the removal of material was accompanied by enlargement of the die cutting edge cross-section or the die cutting edge diameter from d 0  to d. The increase in diameter can be determined using simple trigonometric functions. 
         [0072]    For example, the increase in the die cutting edge diameter is given by 
         [0000]      Δ d=d−d   0 =2*tan α*Δ h,  where Δ h=h   0   −h.  
 
         [0073]    A corresponding enlargement of the diameter of the cutting edge  24  of the die will be obtained when the die  16  is reground again by the amount Δh starting from its dimensions shown in  FIGS. 2   a ,  2   b , and  2   c.    
         [0074]    The same effect is obtained with the removal of material from cutting plates in the form of die assemblies  27 ,  28  shown in  FIGS. 3   a ,  3   b  and  4   a ,  4   b .  FIGS. 3   a ,  4   a  show the die assemblies  27 ,  28  in section along the lines of sections indicated in  FIGS. 3   b ,  4   b.    
         [0075]    Integrated into each of the die assemblies  27 ,  28 , are ten dies  27 / 1  . . .  27 / 10  and  28 / 1  . . .  28 / 10 , respectively. Each of those dies has a die orifice  25  with a cutting edge  24  of the kind described with reference to  FIGS. 2   a ,  2   b ,  2   c . The die orifice  25  of each die  27 / 1  . . .  27 / 10 ,  28 / 1  . . .  28 / 10  forms a relief angle α. The die assemblies  27 ,  28  are otherwise identical in construction to a large extent. The only structural difference resides in a greater height of the die assembly  28  as compared with the die assembly  27 . The die assembly  28  thereby offers a greater regrinding reserve. 
         [0076]    The orientation of the stroke axis  21 , which at the same time forms a rotation axis, is indicated in  FIGS. 3   a ,  3   b  and  4   a ,  4   b . The die orifices  25  of the dies  27 / 1  . . .  27 / 10 ,  28 / 1  . . .  28 / 10  are arranged with their centre points on a circular arc about the stroke/rotation axis  21 . 
         [0077]    In dependence on the size of the die cutting edge cross-section or diameter d, the die  16  shown in  FIGS. 2   a ,  2   b ,  2   c  and the dies  27 / 1  . . .  27 / 10  and  28 / 1  . . .  28 / 10  shown in  FIGS. 3   a ,  3   b  and  4   a ,  4   b  are assigned to a specific punch (“punch assignment”) and/or to a specific workpiece thickness (“workpiece thickness assignment”)—in the present case to a specific thickness of metal sheet (“sheet thickness assignment”). 
         [0078]    A determining factor for the punch assignment and for the sheet thickness assignment of the die  16 ,  27 / 1  . . .  27 / 10 ,  28 / 1  . . .  28 / 10  is the processing task that is to be accomplished. 
         [0079]    If, for example, circular cut-outs are to be made in metal sheets, the punch assignment and/or the workpiece thickness assignment of a die is carried out in dependence on the diameter of the cut-out to be made and, in addition, in dependence on the thickness of the metal sheet that is be processed by punching. The diameter of the cut-out that is to be made dictates the corresponding punch diameter of the punch that is to be used. The thickness of the metal sheet to be processed is a determining factor in the respect that, with a view to achieving reliable workpiece processing, the die cutting edge diameter can exceed the punch diameter of the punch to be combined with the die by an amount dependent on the thickness of the metal sheet to be processed. 
         [0080]    In view of those relationships, a change in the die cutting edge diameter, as occurs as a result of regrinding dies having a relief angle, may require a change to the punch assignment and/or the sheet thickness assignment of the corresponding die. 
         [0081]      FIG. 5  illustrates the die assembly  27  and the die assembly  28 , which in this view is identical to the die assembly  27 . Near the die orifices  25  of the dies  27 / 1  . . .  27 / 10 ,  28 / 1  . . .  28 / 10  the respective die cutting edge diameter before and after a regrinding operation is indicated. The die cutting edge diameter of the individual dies  27 / 1  . . .  27 / 10 ,  28 / 1  . . .  28 / 10  has accordingly been enlarged by  0 . 2  mm in each case owing to the removal of material associated with regrinding. 
         [0082]    If the punch assignment of the dies  27 / 1  . . .  27 / 10 ,  28 / 1  . . .  28 / 10  remained the same regardless of the regrinding operation, only the sheet thickness assignment of the dies  27 / 1  . . .  27 / 10 ,  28 / 1  . . .  28 / 10  may have to be changed. If a round punch having a nominal diameter of 4 mm were used, sheet thicknesses of 3 mm, 4 mm . . . 12 mm could be processed with the dies  27 / 1  . . .  27 / 10 ,  28 / 1  . . .  28 / 10  following regrinding instead of sheet thicknesses 1 mm, 2 mm . . . 10 mm before regrinding. 
         [0083]    If the sheet thickness assignment of the dies  27 / 1  . . .  27 / 10 ,  28 / 1  . . .  28 / 10  is retained despite regrinding of the die assemblies  27 ,  28 , then the punch assignment of the dies  27 / 1  . . .  27 / 10 ,  28 / 1  . . .  28 / 10  may have to be changed. If sheet thicknesses of 1 mm, 2 mm  . . . 10 mm are to be processed also following the reprocessing, then following reprocessing the dies  27 / 1  . . .  27 / 10 ,  28 / 1  . . .  28 / 10  have to be assigned to a punch having a punch diameter of 4.2 mm. 
         [0084]    In addition to changes to the workpiece thickness assignment alone or to the punch assignment alone, changes to both the workpiece thickness assignment and the punch assignment are conceivable. A large number of assignment changes are possible. 
         [0085]    A punch assignment and/or a sheet thickness assignment of the dies  16 ,  27 / 1  . . .  27 / 10 ,  28 / 1  . . .  28 / 10  can be carried using computer-assisted tool management. The essential data of the tools kept in stock by a user of the punch machine  1  is stored in a data memory of a numerical tool management system  32  ( FIG. 1 ). The data stored comprises, in particular, identification numbers (“ID numbers”) assigned to the individual tools, dimensions of the respective tool in new condition and a regrinding length of the individual tools, i.e., the amount in millimeters that has been removed from the respective tool starting from the new condition, especially owing to wear. 
         [0086]    The data inventory of the tool management system  32  can be altered. For example, additional tools may be included in the tool management or tools included may be removed from the inventory. In the case where tools are reprocessed, the grinding length in respect of the relevant tool can be entered and placed in the data memory of the tool management system  32 . The regrinding length, for example of dies, can be limited for structural reasons. Once a maximum regrinding length is reached, the tool in question is no longer reprocessed but is removed from the inventory when reprocessing would actually be necessary. In the case of dies having a relief angle, a computer of the tool management system  32  determines the new diameter of the die orifice obtained as a result of the reprocessing by reference to the regrinding length entered and by reference to the value of the relief angle stored in the tool management system  32 . 
         [0087]    A numerical processing program, e.g., an NC program  33  ( FIG. 1 ), can be created for processing a metal sheet  2  on the punch machine  1 . The NC program  33  can then be implemented by means of the CNC control  23  of the punch machine  1 . A tool requirements list can also be created. The tool requirements list can include a listing of all the tools required for implementing the NC program  33 . To create the tool requirements list, reference is made to the tool data stored in the tool management system  32 . If a circular cut-out of diameter d is to be made in a metal sheet  2  of thickness s, a round punch having the nominal diameter d is selected from the tool inventory entered into the tool management system  32 . A die having a circular die orifice whose nominal diameter is greater than the nominal diameter d of the punch by s/10 is assigned to that punch from the tool inventory of the tool management system  32 . The die selected may be a punching tool in new condition but may also be a reprocessed punching tool whose die orifice has acquired the required nominal diameter only as a result of the removal of material which has occurred during reprocessing. 
         [0088]    In the tool requirements list of the NC program  33  the selected punching tools appear with their identification numbers. By reference to those identification numbers, the user of the punch machine  1  is able to assemble the punching tool set defined by means of the data of the tool management system  32  in order to set up the punching apparatus  12 . For that purpose, the user takes the punching tools from a stock of tools held, for example, in a tool cabinet. 
         [0089]    In the manner shown in  FIG. 6 , the user arranges the selected punching tool set  17  on a tool holder  11 . As shown in  FIG. 6 , in addition to the punch  15  and the die  16 , a stripper  29  is fixed to the tool holder  11 . The tool holder  11  together with the punch  15 , the die  16  and the stripper  29  is then mounted on the transverse rail  9  of the punch machine  1 . The transverse rail  9  is used as a tool magazine. Correspondingly, the remaining magazine stations on the transverse rail  9  are loaded with tool holders  11  and punching tool sets arranged thereon. The distribution of the individual tool holders  11  with the respective punching tool sets among the magazine stations on the transverse rail  9  is defined in the set-up procedure for the punch machine  1 . 
         [0090]    After setting-up the tool magazine on the transverse rail  9  of the punch machine  1 , the first punching tool set  17  to be used in the processing operation to be carried out on the metal sheet is loaded at the punching station  12  of the punch machine  1 . The transverse rail  9  travels under numerical control to the punching station  12  where the punch  15  and the die  16  of the first punching tool set  17  are transferred to the upper tool receiver  13  and to the lower tool receiver  14 . The stripper  29  is also installed at the punching station  12 . 
         [0091]    The transverse rail  9  then travels with the then empty tool holder  11  to a position in which the metal sheet  2  to be processed can be gripped by means of the clamps  10  also provided on the transverse rail  9 . The situation shown in  FIG. 1  is thus obtained. As a result of being loaded into the upper tool receiver  13  and into the lower tool receiver  14 , the punch  15  and the die  16  are arranged in a working state. Before processing of the metal sheet is commenced the height of the die  16  can be adjusted. Such a height adjustment may be necessary, such as when the die  16  in question is a reprocessed die and the lower tool receiver  14  is still adjusted to a predecessor die as regards its height setting. In that case, the lower tool receiver  14  can be raised by means of the lower rotary/stroke drive unit  20 , acting as an elevating device, by the extent of the material removed in the reprocessing of the predecessor to the die  16 . Alternatively, it is possible for a shim for the die  16  to be inserted into the lower tool receiver  14  before the die  16  is loaded, which shim compensates for the material removed. 
         [0092]    After the punch  15  and the die  16  have been arranged in a working state, the metal sheet  2  is positioned by means of the coordinate guide  7  and then processed by the punch  15  with one or more working strokes. 
         [0093]    Instead of using the punching tool set  17  shown in  FIG. 6 , consisting of the punch  15  and the die  16 , it is also possible for a punching tool set  17  of the kind shown in  FIGS. 7   a  and  7   b  to be employed. That punching tool set  17  comprises one of the dies  27 / 1  . . .  27 / 10  of the die assembly  27  shown in  FIGS. 3   a  and  3   b  and an eccentric punch  30 . For clarity, only five of the total of ten dies  27 / 1  . . .  27 / 10  on the die assembly  27  are shown in  FIGS. 7   a ,  7   b.    
         [0094]    When defining the punching tool sets  17  composed of the dies  27 / 1  . . .  27 / 10  and the eccentric punch  30 , reference is made to the tool data of the tool management system  32  available to the punch machine  1 . Reprocessing of the die assembly  27  is taken into consideration in the punch assignment and/or in the sheet thickness assignment of the dies  27 / 1  . . .  27 / 10  where applicable. 
         [0095]    In the manner described above with reference to  FIG. 6 , the die assembly  27  and the eccentric punch  30  are placed on a tool holder  11  and fixed to the transverse rail  9  of the punch machine  1  by means of the tool holder  11 . On movement of the transverse rail  9 , the eccentric punch  30  is loaded into the upper tool receiver  13  and the die assembly  27  is loaded into the lower tool receiver  14  of the punching station  12 . The vertical position of the die assembly  27  is adjusted, if necessary, by means of the lower rotary/stroke drive unit  20 . 
         [0096]    After tool loading, the punching tool set shown in  FIGS. 7   a  and  7   b  is arranged in a working state by relative movement of the die assembly  27  on the one hand and of the eccentric punch  30  on the other hand. That relative movement involves a relative rotational movement about the stroke axis  21 . In the example shown, the relative rotational movement is performed by means of the upper rotary/stroke drive unit  19 . The latter is able to move the eccentric punch  30  about the stroke axis  21  to rotational positions in which the eccentric punch  30  is able to cooperate with each of the dies  27 / 1  . . .  27 / 10  to process the metal sheet. 
         [0097]    As shown in  FIG. 8 , the eccentric punch  30  forms part of a punch assembly  31  that cooperates with the die assembly  27 . In punching operation, only one of the punches of the punch assembly  31  is activated and assigned to one of the dies  27 / 1  . . .  27 / 10  for processing of the workpiece. In the case of the arrangement shown in  FIG. 8  also, the punching tool set  17  used for processing of the workpiece is arranged in a working state by relative rotational movement of upper tool (punch  30  of the punch assembly  31 ) and lower tool (one of the dies  27 / 1  . . .  27 / 10  of the die assembly  27 ). 
         [0098]    Other embodiments are within the scope of the following claims.