Abstract:
A forging machine is described having at least one clamping head ( 6 ) for a work-piece ( 5 ) and having a rotational drive, which is controllable in dependence on the engagement of the forging tools ( 3 ), for the clamping head ( 6 ). To provide advantageous drive conditions, it is proposed that the rotational drive comprise at least one hydraulic motor ( 11 ), which is connected to a pump circuit ( 12 ), and which is connected to a hydraulic circuit ( 17 ), which is connected in parallel to the pump circuit ( 12 ), for the periodic supply and discharge of a predefined quantity of hydraulic medium in dependence on the stroke frequency and/or the stroke location of the forging tools ( 3 ).

Description:
1. FIELD OF THE INVENTION 
       [0001]    The invention relates to a forging machine having at least one clamping head for a workpiece and having a rotational drive, which is controllable in dependence on the engagement of the forging tools, for a spindle of the clamping head. 
         [0002]    2. DESCRIPTION OF THE PRIOR ART 
         [0003]    In round forging, the workpiece, which is held via a clamping head and driven with the aid of a spindle, is fixed in a rotationally-fixed manner by the forging tools during the engagement of the forging tools. To avoid torsion stresses of the workpiece which are thus caused, driving the spindle via a worm gear, the worm of which, which is mounted so it is axially displaceable, is supported axially on a spring mechanism, is known (AT 278 481 B). A rotationally-oscillating drive by the worm gear can thus be superimposed on the continuous rotational drive of the worm, if the worm is axially displaced when the workpiece is fixed by the forging tools. The spring mechanism which is tensioned in this case ensures an axial restoring movement of the worm as soon as the workpiece is released again. With appropriate tuning of the resonant behavior of the spring mechanism to the vibratory drive system, an intermittent drive of the spindle which is synchronous with the drive of the forging tools can therefore be achieved. To adapt the oscillation behavior to different forging conditions, replacing the mechanical spring mechanism with a hydraulic spring having a settable hydraulic volume, into which displacement bodies engaging on an oscillating drive part alternately plunge, is additionally known (AT 396 883 B). 
         [0004]    In addition (EP 1 600 228 A1), providing a rotational drive in the form of a belt drive with a continuously drivable drive wheel and an output wheel connected to the spindle and coupling this rotational drive to a superposition drive, which has a carrier, which is displaceable in a rotationally oscillating manner about the axis of the output wheel, having two deflection rollers for the belt drive, has also been proposed. Due to a rotationally-oscillating drive of the carrier, the belt section alternately lengthens on the feed and discharge sides of the drive wheel, while the belt section on the respective opposing side shortens, so that the rotational movement of the output wheel thus caused is superimposed on the continuous rotational drive by the drive wheel. Notwithstanding the fact that the design expenditure of this known intermittent rotational drive for the clamping heads is substantial, these rotational drives are unsuitable for more recent forging methods, which require higher rotational accelerations and decelerations between the engagements of the forging tools as a result of greater rotational angles. 
       SUMMARY OF THE INVENTION 
       [0005]    The invention is therefore based on the object of embodying a rotational drive for the spindle of a clamping head of a forging machine so that advantageous design conditions result with respect to an intermittent spindle drive and the mass forces to be taken into consideration in this case can be kept comparatively small. 
         [0006]    Proceeding from a forging machine of the type described at the outset, the invention achieves the stated object in that the rotational drive comprises at least one hydraulic motor, which is connected to a pump circuit, and which is connected to a hydraulic circuit, which is connected in parallel to the pump circuit, for the periodic supply and discharge of a predefined quantity of hydraulic medium in dependence on the stroke frequency and/or the stroke location of the forging tools. 
         [0007]    The use of a hydraulic motor, preferably a hydraulic radial piston motor, which develops high torques at low speeds, represents advantageous conditions for a simple, intermittent rotational drive of the spindle of a clamping head, because the mass forces to be taken into consideration can be kept small, on the one hand, and the possibility exists of connecting a separate hydraulic circuit in parallel to the pump circuit having a continuous hydraulic medium flow, on the other hand, via which the hydraulic medium stream impinging the hydraulic motor can be periodically changed in dependence on the stroke frequency or also on the stroke location of the forging tools, in that a predefined quantity of hydraulic medium is supplied to and discharged from the hydraulic medium stream of the pump circuit, with the result that the hydraulic motor is periodically accelerated and decelerated in dependence on the supplied and discharged hydraulic medium quantity, so that with appropriate tuning of the hydraulic medium quantities supplied and discharged via the hydraulic circuit to the hydraulic medium throughput predefined by the pump circuit, the spindle of the clamping head can be driven intermittently. If the hydraulic medium quantity discharged by the hydraulic circuit corresponds to the quantity of hydraulic medium supplied by the pump circuit, the hydraulic motor is thus stationary. During the standstill, the engagement of the forging tools can advantageously occur. However, if the hydraulic motor is first stopped after the tool engagement or accelerated again during the tool engagement, torsion stresses are thus built up in the workpiece, which can be used if needed to influence the crystalline structure of the workpiece. 
         [0008]    Particularly simple design conditions result if the hydraulic circuit has a piston-cylinder unit, the piston of which is drivable back and forth via a positioning drive, wherein the pressure chambers on both sides of the piston are connected to the hydraulic motor, so that the piston travel in the pressure chambers determines the hydraulic medium quantity of the hydraulic circuit which is supplied on one side and discharged on the other side. The hydraulic medium throughput of the hydraulic motor can therefore be controlled, via the positioning drive for the piston of the piston-cylinder unit of the hydraulic circuit in the meaning of the desired intermittent rotational drive of the spindle of the clamping head, by a comparatively small servo valve. 
         [0009]    To keep the mass forces to be taken into consideration with respect to the spindle drive small, the positioning drive can comprise at least one positioning cylinder, which can be impinged on both sides via a switching valve. However, two positioning cylinders which can be impinged in opposite directions can also be provided for this purpose. Via the control of the positioning drive for the piston of the piston-cylinder unit, the hydraulic motor per se can be activated arbitrarily with respect to the time curve of the rotational angle, which is dependent on the throughput of the hydraulic medium, so that in the case of a control of the positioning drive dependent on the tool engagement, advantageous adaptation possibilities to different forging conditions result. 
         [0010]    Of course, the positioning drive can also be coupled to a spring mechanism to save energy, so that an oscillating system results, which can be excited by the positioning drive in dependence on the stroke frequency of the forging tools. To be able to take different resonant frequencies into consideration in a simple manner, the spring mechanism can be designed as a hydraulic spring mechanism, the resonance behavior of which can be influenced via the definitive volume of the hydraulic medium. 
         [0011]    To be able to exert special tensions inside the workpiece to influence the crystalline structure, on the surface profile during the forging of workpieces which are rectangular or square in cross-section, or on the torsion of a workpiece during the tool engagement, the forging machine can have two clamping heads with rotational drives in the form of hydraulic motors, the hydraulic circuits of which, which are separate from the pump circuits, are controllable in dependence on one another, so that via different rotational angles of the spindles of the clamping heads, different torsion stresses are built up inside the workpiece and can also be maintained during the forging procedure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0012]    The subject matter of the invention is illustrated as an example in the drawing. In the figures: 
           [0013]      FIG. 1  shows a forging machine according to the invention in a schematic side view, 
           [0014]      FIG. 2  shows a rotational drive for the spindle of a clamping head of the forging machine in a simplified block diagram, 
           [0015]      FIG. 3  shows a piston-cylinder unit, which is altered in relation to the embodiment according to  FIG. 2 , for the hydraulic circuit in a block diagram, 
           [0016]      FIG. 4  shows a characteristic curve illustrating a possible time curve of the rotational angle of the radial piston motor, and 
           [0017]      FIG. 5  shows an illustration corresponding to  FIG. 3  of a characteristic curve for a different rotational angle time curve. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0018]    The forging machine has, according to  FIG. 1 , in a conventional manner, a frame  1  having four forging tools  3 , which are opposite to one another in pairs with respect to a forging axis  2 , and which are impinged via positioning drives radially in relation to the forging axis  2  and are equipped with forging hammers  4 . The positioning drives for the forging tools  3  arranged in pairs can be actuated in this case, depending on the selected forging method for the tool pair, simultaneously or in succession at a time interval, so that the workpiece  5  is machined simultaneously or in sections by the forging tools  3  distributed around its circumference. The workpiece  5  is grasped on the end with the aid of at least one clamping head  6  and rotated about the forging axis  2 . The clamping head  6  itself is mounted in a housing  7 , which is movable with the aid of a carriage  8  along a guide  9 . 
         [0019]    The clamping head  6  mounted in the housing  7  is driven via a spindle  10 . The rotational drive provided for this purpose comprises at least one hydraulic motor  11 , which is insensitive to pressure surges, and which can preferably be embodied as a hydraulic radial piston motor, but also as an axial piston motor under certain circumstances. This hydraulic motor  11  is continuously impinged with a hydraulic medium stream via a pump circuit  12  according to  FIG. 2 . The hydraulic pump  13  of the pump circuit  12  is driven by a motor  14 . The drive connection between the hydraulic motor  11  and the spindle  10  is produced in a simple manner via a gearwheel transmission, which comprises a gearwheel  15  seated on the spindle  10  and a pinion  16 , which meshes with the gearwheel  15  and is driven by the hydraulic motor  11 . As can be inferred from  FIG. 2 , the option also exists of driving the gearwheel  15  via two pinions  16 , which are each connected to a hydraulic motor  11 , which enables hydraulic tensioning of the pinions  16 , which mesh with the gearwheel  15 , via the hydraulic motors  11 , which are driven synchronously because they are connected in series and enables a small structural size in comparison to a single drive. 
         [0020]    To be able to drive the spindle  10  for the clamping head  6  intermittently in accordance with the forging conditions, the hydraulic motor  11  is connected, in parallel to the pump circuit  12 , to a separate hydraulic circuit  17 , via which predefined hydraulic medium quantities can be supplied and discharged, so that the continuous hydraulic medium stream predefined by the pump circuit is enlarged or reduced by the hydraulic medium stream of the hydraulic circuit  17  and therefore the hydraulic motor  11  is accordingly accelerated or decelerated. 
         [0021]    According to  FIG. 2 , a piston-cylinder unit  18  is provided for this purpose in the hydraulic circuit  17 , the piston  19  of which can be driven back-and-forth via a positioning drive  20 . Since the pressure chambers  21  on the two piston sides are connected to the hydraulic motor  11 , a displacement of the piston  19  in one direction causes hydraulic medium to be displaced from one of the two pressure chambers  21  and to be sucked in via the other pressure chamber  21  with the effect that the hydraulic medium quantity from the piston-cylinder unit  18  is supplied and discharged to and from the continuous hydraulic medium stream of the pump circuit  12 . If the hydraulic medium quantity which is supplied and discharged corresponds to the hydraulic medium rate of the pump circuit  12 , the hydraulic motor  11  is thus periodically accelerated and, after a corresponding acceleration, decelerated to a standstill. The positioning drive  20  for the piston  19  is therefore to be activated periodically in dependence on the stroke frequency of the forging tools  3 . In addition, the control can also be made dependent on the stroke location of the forging tools  3 . 
         [0022]    The positioning drive  20  is formed, according to  FIG. 2 , by two positioning cylinders  22  which can be impinged in opposite directions, and which are impinged accordingly via a control valve  23 . The positioning movement of the piston  19  can therefore be adapted to the respective requirements via the activation of the control valve  23 . 
         [0023]    The piston-cylinder unit  18  according to  FIG. 3  differs from that according to  FIG. 2  essentially only in that this piston-cylinder unit  18  is coupled to a hydraulic spring mechanism  24 , so that the piston  19  can be operated in an energy-saving manner as part of an oscillating system. For this purpose, displacement bodies  25  are associated with the divided piston  19 , which engage in boreholes  26  of a housing  28 , which is penetrated by the piston rod  27  between the two partial pistons  19 . These displacement bodies  25 , which are distributed about the piston rod  27 , are supported axially on pressure plates  29 , which are each carried along in one direction by the partial piston  19 . Since the boreholes  26  are connected via a ring chamber  30  to the hydraulic spring mechanism  24 , the back-and-forth piston displacement causes an alternating impingement of the hydraulic spring mechanism  24  by the displacement bodies  25  associated with the two piston sides. 
         [0024]    The time curve of the rotational angle ω of the hydraulic motor  11  is shown in  FIG. 4 . The characteristic curve  31  shows the time curve of the rotational angle ω for the case that the hydraulic circuit  17  is shut down by blocking the control valve  23  and therefore the hydraulic motor  11  is only impinged by the continuous hydraulic medium stream of the pump circuit  12 . With hydraulic pump  13  shut down and an impingement of the hydraulic motor  11  via a piston-cylinder unit  18  according to  FIG. 3 , a sinusoidal curve of the hydraulic medium flow in the hydraulic circuit  17  results, which results in a sinusoidal curve of the rotational angle ω according to the characteristic curve  32  of  FIG. 3 . With a superposition of the hydraulic medium streams of the pump circuit  12  and the hydraulic circuit  17 , a rotational angle curve corresponding to the characteristic curve  33  results for the hydraulic motor  11 . With corresponding adaptation of the hydraulic medium quantities, a periodic standstill of the hydraulic motor  11  can therefore be achieved in a simple manner, as can be inferred from the curve of the rotational angle ω corresponding to the characteristic curve  33 , specifically at the rotational angles ω 1  and ω i+1 . 
         [0025]    The time curve of the rotational angle ω is thus dependent on the size and the speed curve of the hydraulic medium quantity supplied and discharged via the hydraulic circuit  17 . This means that in the case of a linear increase of the supplied and discharged hydraulic medium quantity, a rotational angle curve which changes linearly between a highest value and a lowest value results corresponding to the characteristic curve  34  of  FIG. 4  as a result of impingement of the hydraulic motor  11  solely via the hydraulic circuit  17 . A superposition of the pump circuit  12  with a rotational angle curve corresponding to the characteristic curve  31  and a hydraulic circuit  17  controlled in this manner therefore causes a rotational angle curve according to the characteristic curve  35  having particularly pronounced standstill times at the rotational angles ω 1  and ω i+1 . By way of a corresponding selection of the size and the speed of the hydraulic medium quantity inside the hydraulic circuit  17 , influence may therefore be taken in broad limits on the chronological rotational angle curve of the hydraulic motor  11  and therefore of the clamping head  6  of a forging machine. 
         [0026]    As a result of the control according to the invention of the rotational drive for the clamping head  6 , influence can additionally be taken on the microstructure arising during forging, if the forging machine is equipped with two clamping heads  6  according to the invention, as indicated by the dot-dash lines in  FIG. 1 . Specifically, the workpiece  5  can be subjected to torsion stresses between the clamping heads  6 , which influence the microstructure of the workpiece  5  during forging, as a result of the controllable rotational angle ω of the clamping heads  6 .