Abstract:
A bending tool ( 12 ) for bending workpieces, especially plate and sheet metal blanks includes at least one bending element ( 23 ) positioned on one side of a workpiece as well as a retainer device with clamping elements ( 14, 42 ) on opposite sides of the workpiece. For bending the workpiece, the retainer is moved, together with the workpiece clamped on it, relative to a bending element ( 23 ). In the process, the retainer device with the workpiece and the bending element ( 23 ) move relative to each other in a bending stroke which contains a component in the bending-stroke direction as well as a component in the transverse direction of the bending stroke. The direction of the bending stroke is controlled by at least one control element associated with the bending element ( 23 ) as well as at least one guide element associated with the equal-sided clamping element ( 42 ). The last-mentioned guide element or elements can move in the bending-stroke direction ( 8 ) relative to the first-mentioned control element or elements ( 46 ).

Description:
BACKGROUND OF THE INVENTION 
   This invention relates to a bending tool for bending workpieces, especially plate and sheet metal blanks, along a bending line, with at least one bending element positioned on one side of the workpiece and with at least one retaining device featuring clamping elements on mutually opposite sides in the transverse direction of the workpiece so that a relative movement of the clamping elements on both sides in the transverse direction of the workpiece permits the workpiece to be clamped down on the retaining device, while the retaining device with the clamped-on workpiece and a bending element can be moved toward each other in a bending stroke that bends the workpiece. This bending stroke includes a component in the bending-stroke direction extending in the transverse direction of the workpiece as well as a component in the cross stroke direction that extends transversely relative to the plane bounded by the direction of the bending line and the bending-stroke direction, the directional movement of the bending stroke being controlled by means of a motion control system that encompasses at least one control element associated and moving with a bending element as well as at least one guide element associated with a bending element. This invention also relates to a bending machine that is equipped with at least one such bending tool. 
   A bending tool and a bending machine of the type referred to above have been described in JP 59 033032 A. This earlier bending tool includes an upper tool section positioned above the workpiece to be processed as well as a lower tool section positioned underneath the workpiece to be processed. The upper tool section encompasses a spring-loaded retaining plate which in its home position extends in the transverse direction of the workpiece, and, to the side of that plate, a bending tool. 
   The bending tool can be rotated around a pivot that extends parallel to the bending line along the workpiece that is to be bent and is provided with a control surface that is sloped in the transverse direction of the workpiece. The lower tool section consists essentially of a support block positioned opposite the retaining plate of the upper tool section, as well as a control block positioned to the side of and at a distance from the support block. On its side facing the bending tool of the upper tool section, the control block on its part features a sloped control surface. A metal blank to be processed is placed on the support block of the lower tool section. Next, the upper tool section is lowered toward the lower tool section in the transverse direction of the workpiece. This causes the retaining plate of the upper tool section to make contact with the surface of the metal blank facing it. The blank is thus clamped between the retaining plate of the upper tool section and the support block of the lower tool section. As the downward movement of the upper tool section continues, the retaining plate remains firmly in place. The bending tool of the upper tool section, however, continues to move in the direction of the lower tool section. As a result, the forming edge of the bending tool strikes the rim of the blank laterally protruding between the retaining plate of the upper tool section and the support block of the lower tool section. At the same time the control surface of the bending tool makes contact with the control surface of the control block on the lower tool section. As they come together, the two control surfaces cause the downwardly moving bending tool to rotate around its pivot. The overall result is a bending stroke of the bending punch with a component in the transverse direction of the workpiece and a component parallel to the workpiece. 
   It is the objective of this invention to provide a novel bending tool design that simplifies the prior art construction described above. 
   SUMMARY OF THE INVENTION 
   It has now been found that the foregoing and related object may be readily attained in a bending tool for bending sheet metal and plate workpieces along a bending line, has at least one bending element positioned on one side of the workpiece and at least one retaining device featuring clamping elements on mutually opposite sides in the transverse direction of the workpiece. Relative movement of the clamping elements in the transverse direction of the workpiece permits the workpiece to be clamped to the retaining device while the retaining device with the clamped-down workpiece and a bending element can be moved toward each other in a bending stroke that bends the workpiece. The bending stroke includes a component in a stroke direction extending in a transverse direction of the workpiece as well as a component in the cross stroke direction that extends transversely relative to the plane bounded by the direction of the bending line and the stroke direction. The directional movement of the bending stroke is controlled by a motion control system that includes at least one guide element associated and moving with the retaining device as well as at least one control element associated with a bending element. A guide element associated with the retaining device is provided on the side of the workpiece for contact with a bending element and the guide element is linked to a clamping element positioned on the same side of the workpiece of the retaining device, so that, during a bending stroke, the retaining device with a clamping element and an associated guide element can be moved relative to the bending element and an associated control element in the bending-stroke direction. 
   Most desirably the clamping element is equal sided, and the bending element and an associated control element are supported on a tool base in the bending-stroke direction. The retaining device with a clamping element and an associated guide element can be moved relative to the bending element and its associated control element, supported on the tool base, in the bending-stroke direction. 
   Preferably, an equal-sided clamping element and an associated guide element are guided on the tool base in the bending-stroke direction. The equal-sided clamping element holds the workpiece in the bending-stroke direction and is movably supported on the tool base in the bending-stroke direction jointly with an associated guide element by a device for generating a restoring force and at least one clamping element of the retaining device bears on the workpiece on its opposite side in the bending-stroke direction. Desirably, the device provided for generating a restoring force is a pneumatic spring. 
   The tool desirably has a unitary assembly of an equal-sided clamping element with an associated guide element, and the support for a bending element and its associated control element is adjustable in its position on the tool base. The support of a bending element and its associated control element on the tool base encompasses a plummer block on which the bending element and its associated control element are seated and which is positionally adjustable in a mount on the tool base. Preferably, the bending element is provided in the form of a swivel lever which, in combination with an associated control element, is supported on the tool base in the bending-stroke direction and which, seated on a swivel mount with a pivot that extends in the direction of the bending line, can be moved transversely relative to the direction of the bending stroke. 
   In the design according to this invention, the control elements for the directional control of the bending stroke between the workpiece being processed and a bending element provided for processing the workpiece are positioned on one and the same side of the workpiece. The result is a structurally compact overall system. This permits the implementation of the novel feature of this invention whereby, in the aforementioned bending stroke, the retaining device holding the workpiece and a control element associated with the retaining device move in the direction of the stroke relative to a bending element and a control element linked to and traveling with it. Thus, according to the invention, the bending stroke is generated in that the travel of the retaining device along one axis is also utilized to clamp the workpiece being processed onto the retaining device. This obviates the need for structural means that move the bending element relative to the workpiece to be processed. 
   The bending tool has a tool base that supports in the direction of the bending stroke at least one bending element and, associated with it, a control element, and an equal-sided clamping element and an associated control element can be moved in the direction of the bending stroke relative to the base. 
   The preferred configuration provides for the automatic, joint resetting of the clamping element and associated control element into their home position following a completed bending stroke. 
   The resetting of the clamping element and associated control element is accomplished by means of a pneumatic spring. According to the invention the use of such a gas-pressure spring makes it possible with a relatively small machine component to strike the workpiece with considerable force in the direction of the clamping element or elements positioned on the opposite side of the workpiece, thus applying a particularly high clamping force on the workpiece. 
   The equal-sided clamping element and an associated control element constitute components of a modular unit. The modular implementation of that clamping element with its associated control element permits easy assembly and disassembly of the bending tool according to the invention. For example, if suitably designed, the clamping element and its associated control element can be jointly detached from the tool base, should it become necessary. The bending element and its control element will thus be accessible with very little effort. 
   In the preferred configuration of the bending tool the support of at least one bending element and its associated control element is positionally adjustable. The adjustability can serve for instance to compensate for assembly and/or manufacturing tolerances on the bending tool. Particularly significant is the adjustability of the bending element in cases where several bending tools in accordance with this invention are juxtapositioned and are operated jointly. An appropriate adjustment allows the bending elements of the individual bending tools to be positioned as needed in relation to one another. 
   In another preferred design concept, a bending element is configured as a swivel lever that is supported on the tool base in the direction of the bending stroke while being movable in the transverse direction of the bending stroke by means of a pivot bearing. 
   The tool holders in the machine base of a conventional bending press accommodate at least one bending tool. One of the tool holders is provided with at least one bending element, at least one equal-sided clamping element and at least one control element associated with the bending element and the equal-sided clamping element. The tool holder on the opposite side of the workpiece holds at least one clamping element of the retaining device. The relative movement of the workpiece necessary for the processing of the workpiece and, respectively, of at least one bending element is generated by the usual relative motion of the tool holders on the bending press. As an alternative to the preferred bending tools made according to the invention, conventional bending tools can be interchangeably mounted in the tool holders of the machine base, thus permitting variable utilization of the machine base. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The following will explain this invention in more detail with the aid of schematic illustrations of a design example in which: 
       FIG. 1  is a diagrammatic illustration of a bending machine with a processing station composed of several bending tools; 
       FIGS. 2 and 3  are sectional views of the bending tool of  FIG. 1  in various workpiece processing stages; 
       FIGS. 4 to 6  are side elevational views of the bending tool of  FIGS. 1 to 3  in various workpiece processing stages; 
       FIG. 7  is a perspective view of a bending tool of  FIGS. 1 and 4 ; and 
       FIG. 8  shows the bending element, in the form of a swivel lever, for the bending tool of  FIGS. 1 to 7 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   As shown in  FIG. 1 , a bending machine  1  employs as a machine base  2  the machine base of a conventional bending press and is additionally equipped with a processing station  3 . In traditional fashion, the machine base  2  encompasses a machine frame  4  as well as a crosshead beam  5 . The machine frame  4  forms a support table  6  with a lower tool holder  7 . The crosshead beam  5  is movably guided on the machine frame  4  in a bending-stroke direction  8  and a return-stroke direction  9 . The crosshead beam  5  is driven by hydraulic piston-cylinder units  10 . On its side facing the support table  6 , the crosshead beam  5  is provided with an upper tool holder  11 . 
   The lower tool holder  7  and the upper tool holder  11  will accept the conventional lower and upper tools of bending presses. In the example illustrated, however, the tool holders  7 ,  11  of the bending machine  1  provide the processing station  3  which, as shown in  FIG. 1 , is composed of a total of four bending tools  12 . Along a bending line  13 , indicated in  FIG. 1  by a dot-dash line, the bending tools  12  are lined up in contiguous fashion. By adding or removing one or several of the bending tools  12 , it is possible to vary the overall width of the processing station  3  and thus the maximum bending length. 
   Each of the bending tools  12  includes an upper tool in the form of a hold-down  14  as well as a lower tool  15  which includes a tool base  16  and an upper section  17 . The hold-downs  14  of the bending tools  12  are seated in the upper tool holder  11  of the crosshead beam  5 , and the lower tools  15  are seated in the lower tool holder  7  of the support table  6 . 
   Alternatively, if the tool holders are suitably designed, the hold-downs  14  of the bending tools  12  can be mounted in the lower tool holder  14  and the lower tools  15 , now serving as upper tools, can be mounted in the upper tool holder  11 . 
   The specific structural configuration of the bending tools  12  will be evident especially from  FIGS. 2 and 3 . 
   As shown, the hold-down  14  of a bending tool  12  extends with a projection relative to the vertical line. At its end facing away from the lower tool  15 , the hold-down  14  is provided with a mounting flange  18  by means of which it is retained in the upper tool holder  11  on the crosshead beam  5  of the bending machine  1 . At its end on the side of the lower tool, the hold-down  14  is provided with a contact surface  19 . At the bend  20 , the contact surface  19  transitions into a horizontal surface of the hold-down  14 . 
   The lower tool  15  of each bending tool  12  rests with its tool base  16  on the support table  6  of the machine frame  4  of the bending machine  1 . A lug  21  on the tool base  16  engages in the lower tool holder  7  of the support table  6 . At the same time a protruding catch  22  on the tool base  16  extends around the side of the support table  6 . The lug  21  locks the tool base  16  in the lower tool holder  7 . 
   In the bending stroke direction  8  and return-stroke direction  9 , the tool base  16  supports a bending element in the form of a swivel lever  23 . The support seat for the swivel lever  23  is a plummer block  24  on which the swivel lever  23  is mounted in a manner permitting its rotation around a fulcrum pin  26  in the form of a journal  25 . The plummer block  24  is mounted on the tool base  16  and is capable of rotating around a pivot  27 . For the rotary movement of the plummer block  24  around the pivot  27 , the position of the plummer block  24  can be adjusted by means of a set screw  28 . A lock screw  29  secures the plummer block  24  in the selected position. 
   Apart from the receptacle  30  for the plummer block  24 , and facing toward the upper section  17 , the tool base  16  is provided with seats  31 ,  32  for accepting the guide posts  33 ,  34  as well as a seat  35  for the pneumatic spring  36 . 
   With their longitudinal sections positioned outside the seats  31 ,  32 , the guide posts  33 ,  34  engage in recesses  37 ,  38  in the upper section  17  of the lower tool  15 . The upper section  17  of the lower tool  15  is provided with a recess that accepts the pneumatic spring  36 . 
   The recess  39  for the pneumatic spring  36  is located on the upper section  17  of the lower tool  15  underneath a groove  40 . The groove  40  accepts a support element  41  of a workpiece support  42  of the upper section  17 . Manually operated fasteners  43  retain the support element  41  in the groove  40 . 
   The swivel lever  23  extends through the upper section  17  of the lower tool  15  in the bore  44 . Within that bore  44 , the swivel lever  23  can be rotated around the fulcrum pin  26  within a limited angle of rotation, thus permitting movement in the transverse direction of the bending stroke, i.e. perpendicular to the plane established by the direction of the bending line  13  and the bending-stroke direction  8  or return-stroke direction  9 . Protruding from the swivel lever  23  is a control element in the form of a cam gate  46 . Associated with the cam gate  46  on the swivel lever  23  in the upper section  17  of the lower tool  15  is a cam-gate guide which, on its part, serves as a control element and consists of a guide roller  47  and a guide pin  50 . 
   The guide roller  47 , which is rotatable around a pivot  48 , is supported by a base  49  on the upper section  17 . The base  49  also holds the guide pin  50  that engages in a guide slot  51  on the swivel lever  23 .  FIG. 8  shows in an enlarged view the physical details of the swivel lever  23 . 
   The progression of the processing of a strip of sheet metal  52  by means of a bending tool  12  is shown in  FIGS. 2 to 7 . 
   Before the processing of the workpiece is started, the crosshead beam  5  is raised relative to the support table  6  of the bending machine  1  so as to create a space between the free end of the hold-down  14  on the crosshead beam  5  and the upper section  17  of the lower tool  15  or, more specifically, the workpiece support  42 . The flat metal strip  52  is inserted in that space. The depth to which it is inserted determines the ultimate location of the bend. The flat metal strip  52  rests on the workpiece support  42 . 
   When the hydraulic piston-cylinder system  10  lowers the crosshead beam  5  of the bending machine  1 , the hold-down  14  of the bending tool  12  makes contact with the upper surface of the metal strip  52  facing it, creating the operating state condition illustrated in  FIGS. 2 ,  4  and  7 . In that operating state, the upper section  17  of the lower tool  15  is in its home position relative to the tool base  16  in the stroke direction  8  and return-stroke direction  9 . In that direction the upper section  17  is positioned at a distance from the tool base  16 . The upper section  17  is supported on the tool base  16  under the action of the pneumatic spring  36 . The swivel lever  23  is aligned in an essentially vertical position. The metal strip  52  is clamped under low pressure between the hold-down  14  and the workpiece support  42  on the upper section  17  of the lower tool  15   
   When, through an appropriate movement of the crosshead beam  5  of the bending machine  1 , the hold-down  14  is lowered further in the bending-stroke direction  8 , the pneumatic spring  36  will exert a relatively high counterpressure. This counterpressure reinforces the clamping of the metal strip  52  between the hold-down  14  and the workpiece support  42  of the upper section  17  of the lower tool  15  which is lowered in unison with the hold-down  14 . The hold-down  14  and the workpiece support  42  thus perform the function of clamping elements for locking the metal strip  52  in place. The holding power acting on the metal strip  52  is further increased by a friction-enhancing coating on the support element  41  of the workpiece support  42  on which rests the metal strip  52 . 
   Structurally interacting with the workpiece support  42 , the guide roller  47  and the guide pin  50  on the upper section  17  of the lower tool  15  descend in the bending-stroke direction  8 . The support pressure on the swivel lever  23  on the tool base  16  exerted in the bending-stroke direction  8  causes a relative movement between the guide roller  47  and guide pin  50  combination and the cam gate  46  provided on the swivel lever  23 . Given the shape of the cam gate  46  chosen for the example described, the swivel lever  23  will not initially change its nearly vertical starting position. Instead, there will initially be an approximately straight-line vertical movement between the swivel lever  23  and the metal strip  52 . As the swivel-lever tip strikes the bottom side of the metal strip  52 , the rim of the metal strip  52  which laterally protrudes at the hold-down  14  and the workpiece support  42  is bent upwardly as seen in  FIG. 5 . 
   As the hold-down  14  and upper section  17  of the lower tool  15  are lowered further in the bending-stroke direction  8 , the cam gate  46  on the swivel lever  23  interacts with the guide roller  47  and guide pin  50  on the upper section  17  and causes the swivel lever  23  to rotate in a direction which, in the illustrations, is counterclockwise. The swivel-lever tip shifts accordingly, with the rim of the metal strip  52  impacted by it, in the transverse stroke direction toward the hold-down  14 . In the process the swivel lever  23  passes through a swivel position in which the bent rim of the metal strip  52  points straight up as seen in  FIG. 6 . By the end of the downward movement of the hold-down  14  and the upper section  17  of the lower tool  15 , the rim of the metal strip  52  will have been bent by the swivel-lever tip past its vertical position and toward the hold-down  14  as seen in  FIG. 3 . The bottom side of the lower tool  15  now rests on the top side of the tool base  16 . This completes the bending stroke and the processing operation resulting in the bending of the metal strip  52 . 
   When the crosshead beam  5  and the hold-down  14  are moved in the return-stroke direction  9 , the upper section  17  of the lower tool  15  will initially follow that movement due to the pressure of the prestressed pneumatic spring  36 . In this return movement, the guide posts  33 ,  34  guide the upper section  17  on the tool base  16  of the lower tool  15 . 
   Once the pneumatic spring  36  is fully extended, the continued movement of the crosshead beam  5  and hold-down  14  in the return-stroke direction  9  will cause the hold-down  14  to lift off the bent metal strip  52 . The metal strip  52  can now be taken out of the bending tool  12 . 
   Synchronously with the return-stroke movement of the hold-down  14 , the guide roller  47  and guide pin  50  on the upper section  17  will lift from the swivel lever  23  and its cam gate  46 . As a result, the swivel lever  23  will rotate counterclockwise out of the position shown in  FIG. 3  and into its starting position as seen in  FIGS. 2 ,  4  and  7 . 
   The position of the support of the swivel lever  23  on the tool base  16  can be modified to permit compensation for assembly and/or manufacturing tolerances, variation of the travel path of the swivel-lever tip as well as the mutual adjustment of the swivel levers  23  of juxtapositioned bending tools  12 . For that purpose, the first step is to loosen the lock screw  29  on the plummer block  24 . Next, turning the setscrew  28  allows the adjustment of the rotary position of the plummer block  24  relative to the pivot  27  and thus of the position of the fulcrum pin  26  of the swivel lever  23 . The repositioned plummer block  24  is then secured again using the lock screw  29 . As can be seen especially in  FIGS. 4 to 7 , the adjustment mechanism for the plummer block  24  on the bending tool  12  is accessible when the upper section  17  of the lower tool  15  is installed. 
   However, detaching the upper section  17  takes just a few steps. The first step is to loosen the fasteners  43  by means of which the support element  41  of the workpiece support  42  is held in the groove  40 . Next, the support element  41  is removed from the groove  40 , permitting access to the mounting of the pneumatic spring  36  in the upper section  17 . After that mounting is removed, the upper section  17  can be removed from the tool base  16  as a single structural unit. The guide pin  50  in the upper section  17  can be removed from the guide slot  51  of the swivel lever  23  through the downward opening in the direction of disassembly. 
   Mounting the upper section  17  on the tool base  16  of the lower tool  15  is just as easy. When the upper section  17  is removed, it is possible to replace the existing swivel lever  23  with its cam gate  46  with another swivel lever and cam gate combination. Changing the cam gate geometry will change the maximum bending angle attainable with the swivel lever concerned. Moreover, using a cam gate with a different gate geometry permits adaptation of the bending tool  12  to different sheet-metal thicknesses and workpiece materials. 
   Another possibility is to replace the swivel lever  23  shown in the illustrations with a swivel lever that offers a wider swivel-lever tip in the direction of the bending line  13 . In particular, it may be desirable to use, instead of the swivel lever  23  illustrated, a swivel lever whose swivel lever tip is flush on its sides with the side walls of the lower tool  15 . If several bending tools  12 , equipped with such a swivel lever, are lined up in contiguous fashion in the direction of the bending line  13 , the result on the lower tools  15  of the bending tools  12  will be a continuous bend in the direction of the bending line  13 . 
   Thus, it can be seen from the foregoing detailed specification and attached drawings that the bending machine of the present invention provides a novel and highly effective bending action.