Abstract:
A machine tool for separative machining of preferably plate-like workpieces, for example, metal sheets, has a workpiece support and a discharge device on the workpiece support. The discharge device discharges workpiece parts produced as products of the separative machining. The discharge device includes two opening sections are adjustable relative to one another in the horizontal Y direction to form a through-opening for discharge of workpiece parts. The opening sections are adjustable into different positions relative to one another in the horizontal Y direction, to form through-openings of different widths for discharge of workpiece parts.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority under 35 U.S.C. §119(a) to European Patent Application No. 07 012 867.3, filed on Jun. 30, 2007, the entire contents of which are hereby incorporated by reference. 
     TECHNICAL FIELD 
     The invention relates to a machine tool for separative machining of workpieces, for example, metal sheets. 
     BACKGROUND 
     A generic prior art machine tool is known, in which a first opening boundary is arranged in a fixed position in the horizontal direction and a second opening boundary moves in the horizontal direction relative to the first opening boundary and can be positioned in a fixed position. Movement of the second opening boundary to the fixed position causes a through-opening to be formed between the opening boundaries, through which a workpiece part can be discharged downwards. The displacement path of the second opening boundary is here dimensioned so that workpiece parts up to a maximum dimension in the horizontal direction of typically 500 mm can be discharged. 
     SUMMARY 
     In one general aspect, a machine tool for separative machining of workpieces includes a workpiece support; and a discharge device provided on the workpiece support for discharging workpiece parts produced as products of the separative machining. The discharge device includes two opening sections that are adjustable relative to one another in a horizontal Y direction that lies in an X-Y plane with mutual displacement to form a through-opening for discharge of workpiece parts along a vertical direction Z that is perpendicular to the surface of the X-Y plane. The opening sections are adjustable relative to one another in the horizontal Y direction to form through-openings of different widths for discharge of workpiece parts. At least one opening section includes a support that is mounted to widen the through-opening by being pivoted downwardly about a pivot axle that lies in the X-Y plane. 
     Implementations can include one or more of the following features. For example, the machine tool can include a control unit for controlling the position of the opening sections produced during separative machining of the workpiece as a function of a maximum dimension in the horizontal Y direction of the workpiece part. The machine tool can include a movement unit that is configured to continuously move at least one of the opening sections in the horizontal Y direction. The movement unit can include a spindle drive. The machine tool can include a measuring device that determines the distance traveled by the opening sections in the horizontal Y direction. 
     The pivot axle can extend at a right angle to the horizontal Y direction. 
     At least one support can be rotatably mounted to a supporting table that is displaceable in the horizontal Y direction. The supports can be lowerable, under acceleration, with a linear movement in the Z direction. The supports can be lowerable with a linear movement a distance of less than or equal to about 10 mm. 
     At least one opening section can include a supporting table that is displaceable in the horizontal Y direction. At least one end of the supporting table nearest the through opening can be lowerable under acceleration in the direction of gravity. 
     The opening sections can be movable relative to one another in the horizontal Y direction into a closed position in which the opening sections close an opening in the workpiece support. The supports in a downwardly pivoted state can have upper surfaces that lie at least partially adjacent to one another when the opening sections are in the closed position. 
     One of the two opening sections can be in a fixed position in the horizontal Y direction. The machine tool can include a fixing device that fixes the workpiece part in position at the fixed-position opening section during relative movement of the opening sections in the horizontal Y direction. 
     The machine tool can include a rigid chute arranged in the through-opening beneath the opening sections and configured to discharge the workpiece part. 
     In another general aspect, workpiece parts produced on a machine tool as products of the separative machining are discharged using a discharge device. The discharge device includes two opening sections that are adjusted relative to one another in a horizontal Y direction to form a through-opening for discharge of workpiece parts. The opening sections are moved into different positions relative to one another in the horizontal Y direction to form through-openings of different width for discharge of workpiece parts and the through-openings are widened by pivoting downwardly about a pivot axle that lies in the X-Y plane a support of the opening section. 
     Implementations can include one or more of the following features. For example, the position of the opening sections can be controlled as a function of a maximum dimension in the horizontal Y direction of the workpiece part. The opening sections can be moved by continuously displacing at least one of the opening sections with continuous displacement control in the horizontal Y direction. 
     In another general aspect, a machine tool for separative machining of workpieces includes a workpiece support; and a discharge device provided on the workpiece support for discharging workpiece parts produced as products of the separative machining. The discharge device includes two opening sections that are adjustable relative to one another in a horizontal Y direction that lies in an X-Y plane to form a through-opening for discharge of workpiece parts along a vertical direction Z that is perpendicular to the surface of the X-Y plane. The opening sections are adjustable relative to one another in the horizontal Y direction to form through-openings of different widths for discharge of workpiece parts. At least one opening section includes a supporting table that is displaceable in the horizontal Y direction. 
     In another general aspect, a machine tool for separative machining of workpieces includes a workpiece support, a discharge device on the workpiece support and configured for discharging workpiece parts produced as products of the separative machining, and a fixing device that fixes the workpiece part in position at the fixed-position opening section during relative movement of the opening sections in the horizontal Y direction. The discharge device includes two opening sections that are adjustable relative to one another in a horizontal Y direction that lies in an X-Y plane to form a through-opening for discharge of workpiece parts along a vertical Z direction that is perpendicular to the surface of the X-Y plane, the opening sections are adjustable relative to one another in the horizontal Y direction, to form through-openings of different widths for discharge of workpiece parts. 
     Implementations can include one or more of the following features. For example, fixing device can include a punch apparatus having a resilient element and a punch. 
     A machine tool and a method for discharging workpiece parts are designed to more rapidly discharge the workpiece parts and hence the idle time of the machine tool during discharge can be reduced. 
     The opening sections are adjustable into different positions relative to one another with mutual displacement in the horizontal direction, to form through-openings of different widths for discharge of workpiece parts. 
     At least two different positions are provided, in which the opening boundaries can be positioned during the relative movement in the horizontal direction and which, by virtue of the relative movement, each form a through-opening, through which a workpiece part can be discharged. For that purpose, the opening sections can be positioned, for example, at a plurality of different fixed positions each spaced from the other. 
     In some embodiments, the machine tool has a control unit for controlling the position of the opening sections as a function of a maximum dimension in the horizontal direction of the workpiece part produced during separative machining of the workpiece. In this way, it is possible to select the position in which discharge through the through-opening is only just possible for a workpiece part to be discharged at any one time, thus ensuring that the opening sections do not have to be moved further in the horizontal direction than is necessary to discharge the workpiece part produced at any one time. The path of movement of the opening sections for discharge of workpiece parts is thereby minimized or reduced, with the result that the speed during discharge is increased and hence the idle time of the machine tool during discharge can be reduced. Information about the maximum dimension of the workpiece part to be discharged each time is already available in the control unit of the machine tool, since this is needed for controlling the separative machining of the workpiece. 
     In some embodiments, the machine tool includes a movement unit for displacement-controlled, continuous movement of at least one of the opening sections. In that case, the different positions are continuously selectable over the travel of the opening section, thus enabling the position to be exactly matched to the dimension of the workpiece part in the horizontal direction. 
     In some implementations, the movement unit includes a spindle drive for continuous movement of at least one of the opening sections in the direction of the opening movement. Such a spindle drive typically includes a gear spindle, which is driven via an electric motor and allows a linear movement of the opening sections that is both rapid and precise. 
     In some implementations, the machine tool also includes a measuring device for determining the distance covered by the opening sections in the horizontal direction. The path of movement covered can thereby be monitored and, if need be, corrected. 
     In other implementations, at least one opening section includes a support, which is mounted so as to pivot downwardly about a pivot axle running preferably at right angles to the direction of the opening movement. Normally, during movement of the opening sections, the workpiece part lies on the upper surface of the support until the particular position for discharge of the workpiece is reached. The support is then pivoted and the workpiece part can be brought to a removal position below the support or the opening section. Alternatively, a superimposed movement is possible, in which the support is already being pivoted during the movement of the opening sections. By providing pivotable supports at the opening sections, the path of movement of the opening sections can be reduced, since the through-opening can be widened by pivoting the supports. 
     In a preferred refinement, at least one opening section includes a supporting table displaceable in the horizontal direction, on which the support is rotatably mounted. The opening section can here be adjusted to a position in which the workpiece part lies only on the support and not on the supporting table. The support is then pivoted, and the workpiece part can be removed downwards through the through-opening. If supports are provided at both opening sections, by synchronous pivoting of the supports the workpiece part can be discharged under the effect of gravity in the direction of gravity through the through-opening, without the workpiece part at the same time performing a rotary movement. If the supports in the supporting regions where the workpiece part is supported on their upper surfaces are moved downwards during pivoting with an acceleration that is greater than that of the workpiece part, then the workpiece part lifts away from the supports and can free fall to a removal position situated below the supports. 
     In some implementations, the supports are lowerable, under acceleration, with a linear movement in the direction of gravity, the linear movement preferably being effected over a distance of at most 10 mm, in particular of at most 8 mm. In that case, the lowering movement is preferably effected with an acceleration greater than the acceleration due to gravity, so that the workpiece part lifts away from the supports. 
     In other implementations, at least one opening section includes a horizontally displaceable supporting table, which preferably at least at one end nearest the through-opening is lowerable, under acceleration, with a linear movement in the direction of gravity, the linear movement preferably being effected over a distance of at most 10 mm, in particular of at most 8 mm. In particular, when the opening sections do not have pivotable supports, it is advantageous to implement a linear lowering movement at the supporting table itself. The linear movement can here be effected by a parallel displacement of the supporting table in the direction of gravity or the supporting table can preferably be rotatably mounted at the end remote from the through-opening, so that in the case of a supporting table that has an adequate length in the horizontal direction (normally more than 1000 mm, preferably more than 1500 mm), at the end nearest the through-opening a virtually linear movement in the direction of gravity is achieved over the comparatively small distance to be covered in the vertical direction. The supporting table may also be non-rotatably mounted at the end remote from the through-opening and consist of a flexible material. If, to generate the lowering movement, the supporting table is in that case supported only at its end remote from the through-opening, with a suitable choice of the resilient properties of the material and the length and the width of the supporting table, a virtually linear lowering movement at the end nearest the through-opening is achieved. It will be understood that here in each case the mounting of the support table at the end nearest the through-opening can be effected by an axle controllable in the vertical direction. 
     In other implementations, the opening sections are movable relative to one another in the horizontal direction into a closed position, in which the opening sections completely or nearly completely close an opening in the workpiece support and in which preferably the supports in the downwardly pivoted state lie adjacent to one another at least partially with their upper surfaces. The closed position can be assumed when the supports are to be protected or an opening in the workpiece support is to be completely closed. This may be the case, for example, when the machine tool has more than one machining station, that is, when, for example, in addition to a laser cutting station a punching station is provided. If the opening sections are mounted at the laser cutting station, and if the laser processing is complete, the closed position is assumed before the punching station commences processing of the workpiece part. The two opening sections can also assume a closed position, in which an opening in the workpiece support is completely closed, independently of the provision according to the invention of different-width through-openings. 
     In another embodiment, one of the two opening sections is arranged in a fixed position in the horizontal direction. This fixed-position opening section can be located at a machining position of the machine tool and serves there to support the workpiece during machining, for example, when cutting a workpiece part free from a workpiece at a laser cutting station, in order to prevent the workpiece part sagging as it is cut free. Workpiece separation in this case can be effected either before or after setting the opening sections to the position provided in each case for discharge. 
     In another embodiment, the machine tool includes a fixing device for fixing the workpiece part in position at the fixed-position opening section during relative movement of the opening sections in the horizontal direction. This can be needed where appropriate when the workpiece part is displaced too far in the horizontal direction as it is slid along the upper face of the movable opening section, or when the workpiece part is supported on the upper face of the opening sections using guide rollers. In particular, the fixing device can be formed by the punch apparatus, at which the fixed-position opening section is used as a die block for a punch of the punch apparatus. The punch apparatus can be include a spring, for example, of Eladur™, arranged on sides of the punch, and the spring fixes the workpiece part in position when the punch remains inserted into the die block during the movement in the horizontal direction. 
     In another embodiment, a rigid chute for discharging the workpiece part is arranged in the through-opening beneath the opening sections. The workpiece part falls through the through-opening onto the rigid chute and slides along this in order to be removed from the machine tool in this way. 
     The invention is also implemented in a method of the kind described initially, in which the opening sections are adjusted relative to one another in the horizontal direction with mutual displacement to form a through-opening for discharge of workpiece parts. Advantageous variants of this method are specified in the claims. Reference can be made to the above description relating to the machine tool in respect of the advantages connected with these variants. 
     Further advantages of the invention are apparent from the description and the drawing. The above-mentioned features and also those listed hereafter can be used alone or severally in any combination. The embodiments described and shown are not to be understood as an exclusive enumeration, but are merely of an exemplary nature for the description of the invention. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a machine tool; 
         FIGS. 2   a - 2   d  are cross-sectional views of a workpiece part and a workpiece support showing a process for discharging the workpiece part through a through-opening; 
         FIGS. 3   a  and  3   b  are perspective partial cutaway views of the machine tool of  FIG. 1  with two opening sections and two supports before and after pivoting; 
         FIGS. 4   a  and  4   b  are side and opposite cross-sectional views of a movement unit and a guide for moving the supports; 
         FIG. 5  is a perspective partial view of the machine tool of  FIG. 1  with the two opening sections in a closed position; 
         FIG. 6   a  is a perspective view of an implementation of a supporting table of the machine tool of  FIG. 1 ; 
         FIGS. 6   b  and  6   c  are side views of an implementation of a supporting table of the machine tool of  FIG. 1 ; and 
         FIGS. 7   a  and  7   b  are side and partial cutaway views of an implementation of a punch apparatus of the machine tool of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a machine tool  1  in the form of laser punch press, which includes a conventional punch apparatus  3  and a laser machining head  4  that are used as tools for machining a workpiece  2  such as a metal sheet. The workpiece  2  to be machined is supported during machining of the workpiece on a workpiece support  5  in the form of a machining table. By means of a conventional holding device  6 , which includes clamps  7  for holding the workpiece  2 , the workpiece  2  can be displaced with respect to the punch  3  and the laser machining head  4  in the X direction of the sheet plane (that is, the X-Y plane of an XYZ co-ordinate system). The workpiece  2  can be moved in the Y direction of the sheet plane by displacing the workpiece support  5 , together with the holding device  6 , by means of a conventional guide (not shown) relative to a base  8 , on which the workpiece support  5  is supported. 
     The workpiece  2  can thus be displaced in the X and Y directions with respect to the punch apparatus  3  and the laser machining head  4 , so that the region of the workpiece  2  that one plans to process or machine can be brought into a machining region  9  of the punch apparatus  3 , which is fixed in position, or into a machining region  11  of the laser machining head  4 , which is defined by a substantially circular suction opening  10  in the workpiece support  5 . The subregion of the workpiece support  5  in the X direction, on which the machining regions  9 ,  11  are formed, is stationary, and is not displaced in the Y direction relative to the base  8 . The punch apparatus  3  can be movable in a Z direction and the laser machining head  4  can be movable in the X and Y directions within the area of the suction opening  10 . 
     Once a region of the workpiece  2  has been brought into the machining region  11  of the laser machining head  4 , as described above, the laser machining head  4  is activated to cut, for example, a rectangular workpiece part  12  completely free from the workpiece  2 . After being cut free, the workpiece part  12  rests in the plane of the sheet (which is parallel with the X-Y plane) on a supporting table  16  and on two supports  13   a ,  13   b  adjoined to one another and positioned parallel with the plane of the sheet, the supports  13   a ,  13   b  being in the form of flaps. The first support  13   a  is arranged directly below the laser machining head  4  and has the suction opening  10  defining the machining region  11 . 
     To bring the workpiece part  12  out of the plane of the sheet into a removal position (not shown in  FIG. 1 ) located beneath the plane of the sheet and beneath the workpiece, the supports  13   a ,  13   b  may be pivoted at opposite sides  14   a ,  14   b  around two parallel pivot axles  15   a ,  15   b . The pivot axles  15   a ,  15   b  are arranged at a distance apart that corresponds to twice the width ( 2   b ) of each of the two supports  13   a ,  13   b  in the Y direction. When the supports  13   a ,  13   b  are positioned as shown in  FIG. 1 , the workpiece part  12 , the dimension of which in the Y direction is larger than the width  2   b , cannot be brought into the removal position without being rotated about its own axis (which extends along the Z direction), which would result in a slow discharge of the workpiece part  12 . 
     In order to be able to discharge the workpiece part  12  without producing a rotary movement about the Z direction, the second support  13   b  is secured to the supporting table  16  and can be displaced jointly with the supporting table  16  in the Y direction, i.e., horizontally, in the plane of the sheet. The distance between the two pivot axles  15   a ,  15   b  is thereby enlarged in the Y direction and between the two supports  13   a ,  13   b  a through-opening (not shown in  FIG. 1 ) forms in the workpiece support  5 . The supporting table  16  is displaced until the workpiece part  12  rests only at its opposite ends on the upper surfaces of the two supports  13   a ,  13   b  and no longer lies on the supporting table  16 . 
     The process of discharging the workpiece part  12  out of the position W 1  shown in  FIG. 1  in which the workpiece part  12  is located in the plane of the workpiece support  5 , into a removal position W 2  located beneath the position W 1 , is explained in detail with reference to  FIGS. 2   a - d . In  FIG. 2   a , the workpiece part  12  is supported both on the upper surface of the first support  13   a , which together with a stationary part of the workpiece support  5   a  form a first opening section  17   a , and on the upper surface of the second support  13   b  and on the supporting table  16 , which together form a second opening section  17   b . The two opening sections  17   a ,  17   b  form two parts of a discharge device  17  for discharging the workpiece part  12 . 
     The opening sections  17   a ,  17   b  in  FIG. 2   a  are located in a position in which the two supports  13   a ,  13   b  are near or close to each other. The workpiece part  12  lies on the supporting table  16  and without being moved along the plane of the sheet cannot be discharged vertically (along the Z direction) downwards. To discharge the workpiece part  12 , the second opening section  17   b  is therefore moved horizontally along the arrow shown in  FIG. 2   a  by moving the supporting table  16  in the Y direction until the second opening section  17   b  has reached a position at which the edge of the second support  13   b  is at position A 1 , and in this position, the workpiece part  12  no longer lies on the supporting table  16 , as shown in  FIG. 2   b . After movement in the Y direction, a through-opening D 1  forms between the two supports  13   a ,  13   b , through which the workpiece part  12  can be discharged downwards, by pivoting the supports  13   a ,  13   b  downwards about the respective pivot axles  15   a ,  15   b  and thereby enlarging the through-opening D 1  substantially by twice the amount  2   b  of the width of the supports  13   a ,  13   b.    
     The position A 1  of the second opening section  17   b  depends both on the position of the workpiece part  12  relative to the supports  13   a ,  13   b  and on the maximum dimension (that is, a length) L 1  of the workpiece part  12  in the horizontal Y direction. Since the position of the end of the workpiece part  12  that lies on the stationary opening section  17   a  corresponds, after the cutting has finished, to the position of the machining region  10 , the discharge position A 1  is determined substantially by the length L 1  of the workpiece part  12  in the horizontal Y direction and is selected so that the workpiece part  12  can only just be discharged through the through-opening D 1  widened by twice the amount  2   b  of the width of the supports  13   a ,  13   b.    
     In  FIG. 2   b , a further position A 2  of the second opening section  17   b  is shown by a dot-dash line, in which a further through-opening D 2  is formed, the width of which is larger than the through-opening D 1 . A workpiece part  12  having a larger maximum dimension (that is, a length) L 2  can be discharged through the through-opening D 2  widened by twice the amount  2   b  of the width of the supports  13   a ,  13   b . The travel of the opening sections  17   a ,  17   b  is calculated as a function of the lengths L 1  and L 2  of the workpiece part  12  by the numerical control (NC) of the machine tool  1  and the supporting table  16  is correspondingly moved under control. 
     In another implementation, as an alternative to moving the opening sections  17   a ,  17   b  shown in  FIGS. 2   a, b  after cutting the workpiece part  12  free from the workpiece  2 , the positions A 1 , A 2  can also be assumed by moving the opening sections  17   a ,  17   b  before the workpiece part  12  is cut free from the workpiece  2 . 
     To bring the workpiece part  12  in free fall through the through-opening D 1  to the removal position W 2 , the two supports  13   a ,  13   b  are accelerated linearly downwards in the negative Z direction (to a position shown in  FIG. 2   c ) out of their horizontal position in the plane of the sheet (shown in  FIG. 2   a ) with an acceleration that corresponds, for example, to three times the acceleration due to gravity acting on the workpiece part  12 . Through the linear movement of the supports  13   a ,  13   b  downwards for a distance d of about 3 mm, the workpiece part  12  is lifted off the supports  13   a ,  13   b  as shown in  FIG. 2   c . The two supports  13   a ,  13   b  are then pivoted about their respective pivot axles  15   a ,  15   b  as indicated by the arrows in  FIG. 2   c , and thus brought into an opening position situated outside a path of movement  18  of the workpiece part  12 , as shown in  FIG. 2   d . In this way, the workpiece part  12  is able to reach its removal position W 2  in free fall and unimpeded by the supports  13   a ,  13   b  after the supports are accelerated linearly in the negative Z direction to the position shown in  FIG. 2   c , from which the workpiece part  12  can subsequently be discharged from the machine tool  1 . Thus, the time required to move the supports  13   a ,  13   b  from the position shown in  FIG. 2   b  to the position shown in  FIG. 2   d  is less than the time during which the workpiece part  12  falls through the distance d such that the workpiece part  12  does not touch the supports  13   a ,  13   b  after the supports  13   a ,  13   b  have been moved. The movement of the supports  13   a ,  13   b  after the position of  FIG. 2   b  is a combination of a linear movement (along the negative Z direction) and a pivoting movement about the respective axles  15   a ,  15   b.    
     As alternative to the above-described movement of the supports  13   a ,  13   b , the same result can also be achieved by merely pivoting the supports  13   a ,  13   b . But in this case, the acceleration that is required to lift the workpiece part  12  from the supports  13   a ,  13   b , without this sliding along the supports  13   a ,  13   b , depends on the distance of the workpiece part from the respective pivot axles  15   a ,  15   b . The smaller is the distance of the workpiece part  12  from the pivot axles  15   a ,  15   b , the greater must the acceleration during the pivoting be selected to be. 
     As another alternative to the movement sequence described in connection with  FIGS. 2   c - d , the workpiece part  12 , supported initially on the upper surface of the supports  13   a ,  13   b , can be moved by means of a linear movement by a distance of, for example, a few millimeters, into a position located beneath the plane of the sheet, in order to avoid the workpiece part getting caught on the remainder of the workpiece (not shown). The above-described sequence of movements shown in  FIGS. 2   b - 2   d ) can then be effected from this lowered position. As an alternative to pivoting the supports  13   a ,  13   b , the supports  13   a ,  13   b  can be moved out of the path of movement  18  of the workpiece part  12  in some other way, for example, in a linear movement at right angles to the direction of gravity (along one or more of the X and Y directions), for example, by displacing the supporting table  16  horizontally, whereby the through-opening D 1  is likewise widened. 
     With reference to  FIGS. 3   a, b , which each show a perspective detail view of the bottom part of the machine tool  1  of  FIG. 1 , there follows an explanation of how the movement sequence described in  FIGS. 2   a - d  can be implemented in terms of structural engineering. In order to move the opening sections  17   a ,  17   b  to the position A 1  shown in  FIG. 2   b , the supporting table  16  is in connection with a spindle drive shown in  FIG. 3   a  as a movement unit, and the spindle drive includes an electric motor  19  and a threaded spindle  20  that extends in the direction of the opening movement (Y direction). The threaded spindle  20  and the electric motor  19  are arranged beneath the plane of the sheet, are offset in the X direction with respect to the supporting table  16 , and are adjacent to the supporting table  16 . A spindle nut  21  secured to the supporting table  16  is guided on and by the threaded spindle  20  and serves for continuous movement of the supporting table  16  in the horizontal Y direction. 
     The path of movement of the spindle nut  21  along the Y direction is controlled by way of a control unit  22  (shown in  FIG. 1 ) of the machine tool  1 . The control unit  22  is used additionally to control the movement of the workpiece  2  and the punch apparatus  3  and the laser machining head  4  during implementation of a machining program for cutting the workpiece part  12  free from the workpiece  2 . The control unit  22  is also used for controlling the displacement of the supporting table  16 , by controlling the flow of current through the electric motor  19  as a function of the maximum dimension L 1 , L 2  of the workpiece part  12 . The discharge position, for example, A 1  or A 2  along the horizontal direction Y is continuously controllable by the threaded spindle  20 . 
     From the horizontal position shown in  FIG. 3   a  (which corresponds to the position depicted in  FIG. 2   b ), the supports  13   a ,  13   b  are brought into a downwardly pivoted position shown in  FIG. 3   b  (which corresponds to the position depicted in  FIG. 2   d ), in order to discharge the workpiece part  12  as shown in  FIGS. 2   a - d . For this, a second movement unit shown in  FIGS. 4   a  and  b  is provided. The second movement unit includes a second electric motor as drive  23 , which is coupled in respect of movement via a toothed belt  24  to a vertically extending threaded spindle  26  guided in an overload-protected bearing  25 . The vertical threaded spindle  26  of the second movement unit includes a spindle nut  27 , which can be moved in and against the direction of gravity (negative Z direction). The spindle nut  27  is secured to a guide plate  28 , which in turn is linearly slidably guided in a plate  29  extending along the Y-Z plane in and against the direction of gravity. 
     As shown in  FIG. 4   b , the guide plate  28  has a guide rail  30  extending horizontally along the Y direction, in which two connection pieces  31   a ,  31   b  are linearly slidably guided. The connection pieces  31   a ,  31   b  act on the respective supports  13   a ,  13   b  eccentrically with respect to the pivot axles  15   a ,  15   b  and are rotatably mounted thereon, whereas they are guided non-rotatably along the guide rail  30 . The connection pieces  31   a ,  31   b  are rotatably coupled to the supports  13   a ,  13   b  by holes  310   b ,  310   a  that receive the respective axles  15   a ,  15   b . If the spindle nut  27  is moved downwards by means of the drive  23 , the guide plate  28  is lowered and the connection pieces  31   a ,  31   b  guided on the guide rail  30  are carried with it. During this movement, the connection pieces  32   a ,  31   b  are displaced horizontally along the guide rail  30  owing to the non-rotatable mounting. During this movement, the supports  13   a ,  13   b  are pivoted downwards out of their horizontal position by the connection pieces  31   a ,  31   b  acting eccentrically with respect to the pivot axles  15   a ,  15   b . The length of the guide rail  30  is such that, during the movement of the second opening section  17   b  in the horizontal direction (by moving the support  13   b ), the second connection piece  31   b  is able to be carried along into the position along the Y axis shown in  FIGS. 3   a, b.    
     In addition to the pivoting movement (which is shown in  FIG. 2   d ), to implement also the linear movement in the first part of the movement sequence shown in  FIG. 2   c , it is necessary to move the pivot axles  15   a ,  15   b  in or against the direction of gravity. This is achieved by moving the connection pieces  31   a ,  31   b  further upwards than would be necessary for the horizontal alignment of the supports  13   a ,  13   b . The supports  13   a ,  13   b  are here pressed against a stop (not shown), which prevents the supports  13   a ,  13   b  from pivoting upwards out of the horizontal position. A force is exerted on the supports  13   a ,  13   b  and hence also on the bearings of the pivot axles  15   a ,  15   b.    
     As shown in  FIG. 3   a , the pivot axle  15   a  is rotatably mounted on a support plate  32  that is vertical, i.e., running in the direction of gravity such that the axle  15   a  can rotate as shown in  FIG. 2   d . The support plate  32  is coupled to the connection pieces  31   a ,  31   b  via the supports  13   a ,  13   b . The support plate  32  is guided on a further plate  33 , likewise running in the direction of gravity, of a cross-frame (not shown) and by applying a force (along the Z direction) against the direction of gravity, can be biased by means of a stop unit  34 , which includes a spring unit (not shown) as a shock-absorber and also a hydraulic piston (not shown). The force applied by the connection pieces  31   a ,  31   b  against the direction of gravity presses the support plate  32  (which is coupled to the connection pieces  31   a ,  31   b  via the supports  13   a ,  13   b ) and hence the bearing of the pivot axle  15   a  upwards, against the spring and hydraulic force of the stop unit  34  acting in the direction of gravity, typically by a stroke of about 3-5 mm. The mounting of the second support  13   b  on the supporting table  16  is of corresponding construction. 
     If the connection pieces  31   a ,  31   b  in the position shown in  FIG. 4   a, b  are moved downwards by the drive  23 , the pivot axles  15   a ,  15   b  also move synchronously downwards on account of the mechanical bias of the spring and hydraulic forces of the stop unit  34  acting in the direction of gravity, so that the supports  13   a ,  13   b  move for the extent of the bias in a linear movement parallel to the plane of the sheet, that is, perpendicular to the X-Y plane. As soon as the connection pieces  31   a ,  31   b  are moved further downwards, the above-described pivoting of the supports  13   a ,  13   b  immediately follows the linear movement. The speed of pivoting is here matched to the preceding linear movement in such a way that after being lifted or separated from the supports  13   a ,  13   b , the workpiece part  12  does not come into contact with the supports  13   a ,  13   b .  FIG. 3   b  shows the supports  13   a ,  13   b  after completion of the above movement in an open position, in which they have been fully pivoted and are at an angle of about 80° to 90° relative to the plane of the sheet (the X-Y plane). 
     In order to remove a workpiece part  12  after its free-falling movement, shown in  FIGS. 2   c - d , from the working region of the machine tool  1 , a chute  35  is mounted on the first connection piece  31   a . The chute  35  is carried downwards by the parallel displacement of the connection piece  31   a  and in the open position of the supports  13   a ,  13   b  projects into the path of movement (not shown) of the workpiece part  12 . In the open position of the supports  13   a ,  13   b , a fixed chute  36  immediately adjoins the chute  35  mounted on the connection piece  31   a . At its removal position, the free-falling workpiece part  12  thus meets either the fixed chute  36  or the chute  35  secured to the first connection piece  31   a  and referred to hereafter as the movable chute, and can be removed from the working region of the machine tool  1  in a sliding movement. 
     The movable chute  35  provided in addition to the fixed chute  36  is needed to cover a suction pipe  37  shown in  FIG. 3   a . The suction pipe  37 , in the horizontal position of the first support  13   a  shown in  FIG. 3   a , is connected to the suction opening  10  of the first support  13   a . The suction pipe  37  is secured to the spindle nut  27  shown in  FIG. 3   b  and on displacement of the spindle nut  27  is carried downwards with it in the direction of gravity. An end piece  38  of the suction pipe  37  is mounted on the first support  13   a  and is pivoted with this, as shown in  FIG. 3   b . A beam stop (not shown) is provided in the suction pipe  37  at the lower end thereof, in order to intercept the laser beam that passes through the suction opening  10  during laser operation. 
     In the case of the machine tool  1  shown in  FIG. 1 , machining of the workpiece  2  with the laser machining head  4  at the machining position  11  can be followed by machining of the workpiece  2  at the adjacent machining position  9  of the punch apparatus  3 . For that purpose, the opening sections  17   a ,  17   b  can be moved out of the position shown in  FIG. 3   b  into a closed position, which is shown in  FIG. 5 . In the closed position, the opening sections  17   a ,  17   b  completely close an opening in the workpiece support  5  and the supports  13   a ,  13   b  lie in their downwardly pivoted position with their upper surfaces adjacent. The supports  13   a ,  13   b  are thus protected against debris (for example, chips etc.) produced during machining of the workpiece  2  at the machining position  9  of the punch apparatus  3 . A subregion  16   a  of the supporting table  16 , the width of which subregion corresponds approximately to the width  2   b  of the supports  13   a ,  13   b , completely covers the region that in  FIG. 1  was occupied by the supports  13   a ,  13   b.    
     The above-described movement sequence can be used not only to discharge workpiece parts from the machining region  11  of the laser machining head  4 , but also to discharge workpiece parts from the machining region  9  of the punch apparatus  3 . 
     It shall be understood that a discharge can advantageously be carried out in the above-described manner also on other machine tools, for example, on the punch apparatus and on bending machines, in which, after being cut free, the workpiece parts are subjected to further machining by bending before they are discharged from the machine tool. The discharge can also be accelerated in this case by the variable positions of the opening sections as a function of the individual dimensions of the particular workpiece part to be discharged, and thus idle times during machining can be reduced. 
     In other implementations, the opening sections may have supports  13   a ,  13   b  that are not pivotable, and the supporting table  16  can be linearly lowered, as shown in  FIG. 6   a . The linear movement of the supporting table  16  can here be effected by a parallel displacement of the supporting table  16  in the direction of gravity (Z direction) or the supporting table  16  can be rotatably mounted at the end remote from the through-opening (see  FIG. 6   b ), so that in the case of a supporting table  16  that has an adequate length in the horizontal Y direction (for example, more than 1000 mm, or more than 1500 mm), at the end nearest the through-opening a virtually linear movement in the direction of gravity is achieved over the comparatively small distance to be covered in the vertical Z direction. As shown in  FIG. 6   c , the supporting table  16  can also be non-rotatably mounted at the end remote from the through-opening and consist of a flexible material. If, to generate the lowering movement, the supporting table  16  is in that case supported only at its end remote from the through-opening, with a suitable choice of the resilient properties of the material and the length and the width of the supporting table, a virtually linear lowering movement at the end nearest the through-opening is achieved. The mounting of the support table at the end nearest the through-opening can be effected by an axle-controllable in the vertical direction. 
     In other implementations, the machine tool can include a measuring device that determines a distance traveled by the opening sections  17   a ,  17   b  in the horizontal Y direction. The measuring device can be a position sensor or any other suitable position measuring device. 
     Referring also to  FIGS. 7   a  and  7   b , the punch apparatus  3  can additionally serve as a fixing unit for a workpiece part  12  during movement of the second opening section  17   b . During the opening movement of the second opening section  17   b , a punch  73  of the punch apparatus  3  remains engaged in a die block (the opening section  17   a ) and to the workpiece  2  mounted at the machining region  9  on the workpiece support  5 , and at the same time presses the workpiece part  12  to be discharged, for example, by means of a resilient element  70  that can be made of, for example, Eladur™, towards the workpiece support  5 . The two parts of the resilient element  70  are arranged to the left and to the right of the portion of the punch  73 , which is inserted into the opening section  17   a . The resilient element  70  can be made of an appropriate kind of elastically deformable material, in particular, of a synthetic material such as Eladur™. During the relative movement between the opening sections  17   a ,  17   b , the resilient element  70  (and not the portion of the punch  73  that is inserted into the opening section  17   a ) presses the workpiece  2  and the workpiece part  12  against the opening section  17   a , as shown in  FIG. 7   b , to prevent movement of the workpiece part  12  relative to the workpiece  2 . In this way, the punch apparatus  3  (and in particular, the punch  73 ) and the resilient element  70  act as a fixing device to fix the workpiece part  12  in position at the fixed-position opening section  17   a  during relative movement of the opening sections  17   a ,  17   b  in the horizontal Y direction.