Abstract:
The machine tool comprises a vertical support ( 10 ) with a guide ( 11 ) arranged thereon for vertical movement of a workpiece carrier ( 13 ) holding a workpiece ( 15 ) along an X-axis. Two headstocks ( 24,30 ) are each movable along horizontal guides ( 27,28 ) in the Y-direction. The guides ( 27,28 ) form a frame, with its window ( 23 ) closed by a louver provided with passage openings for the headstocks ( 24,30 ). This arrangement creates a laterally closed machining chamber which comprises vertical walls and does not present any obstacles to falling chippings. Since the chippings need not be washed off, spray cooling may be used for minimum-quantity lubrication. In this manner, the liquid acting on the chippings is reduced.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to a machine tool for the machining of workpieces, particularly a machine tool comprising a tool magazine allowing for an exchange of tools by moving the headstocks in pick-up operation.  
           [0002]    A machine tool according to the preamble of claim  1  is known from DE 32 36 356 C2. This machine tool comprises a vertical support on which a workpiece carrier is arranged for vertical displacement. On a machine base, a spindle head is arranged which is horizontally displaceable and further is movable in the axial direction of the spindle. Also arranged on the machine base is a circulating tool magazine provided with a tool exchange means. The tool exchange means is arranged for the transfer of tools from an exchange position of the tool magazine to the headstock (and vice versa) when the headstock has arrived in a position provided for this purpose. Since the workpiece to be machined and the headstock are oriented horizontally, chippings generated during the machining can drop freely without hitting the workpiece carrier or settling down on the workpiece carrier or the workpiece.  
           [0003]    EP 0 806 998 B1 describes a machine tool comprising two vertically displaceable headstocks each of which can act individually on a workpiece attached to the workpiece carrier, while the other headstock can carry out an exchange of tools on a tool magazine. The tool magazine is configured as a circulating magazine and arranged such that each headstock has its own exchange position on the tool magazine. The machine tool is suited for quick and effective machining of workpieces by use of different tools. A difficulty is caused in that a fast operation on workpieces tends to generate a considerable amount of chippings which are heavily loaded with cooling liquid. These chippings will drop onto the guide track of the workpiece carrier. Although this guide can be provided with a lamellar cover precluding disturbances of the running of the workpiece carrier, the generated chippings will add up to form larger accumulations, resulting in congestion and hindrances of the discharge of the chippings. For the discharge of chippings, oblique walls leading to a chip conveyer are provided below the guide of the workpiece carrier. The cooling liquid is supplied in large quantities and is also used to safeguard the discharge of chippings and to preclude clogging caused by chippings.  
         SUMMARY OF THE INVENTION  
         [0004]    It is an object of the invention to provide a machine tool with workpiece carriers, headstock and tool magazine which is suited for a quick machining of workpieces and is not prone to disturbances caused by chippings generated in fast operation.  
           [0005]    According to the invention, the above object is achieved by the features indicated in claim  1 . Thus, the workpiece carrier, having a horizontal axis of rotation, is mounted on a vertical support, and the (at least one) headstock is guided on a horizontal guide along the horizontally extending first axis of movement. In the machine tool according to the invention, the guide of the workpiece carrier is arranged vertically so that the workpiece extending from the workpiece carrier will project freely into space in a cantilevered manner while the chippings from the workpiece can drop unhindered. The space under the workpiece attached to the workpiece carrier is free from any constructional parts which might obstruct the path of the dropping chips. The chips can descend in free fall to the ground where a chip conveyer or another device for discharge of the chippings is arranged.  
           [0006]    The invention offers the advantage of obviating the need for a cooling agent for washing the chippings away. Thus, the cooling process can be performed through economical supply of a cooling agent, e.g. by means of spray cooling. In spray cooling, the spray liquid is spayed in droplets onto the workpiece. This results in lubricating and cooling characteristics similar to those of a liquid jet while, however, the consumption of cooling liquid is considerably lower. Advantageously, less cooling agent will adhere to the chippings and the removal of cooling agent from the chippings will require less expenditure. Further, the minimum-quantity lubricating which is rendered possible by spray lubrication will lengthen the operational life of the tool and allow for an improved surface quality of the workpiece. Due to the improved discharge of the chippings, the machine tool of the invention is suited to have spray lubrication performed thereon.  
           [0007]    A further advantage resides in that the headstock has direct access to the vertical front strand of the tool magazine so that no tool exchange device is required. Each headstock will be able to fetch the required tool from the front strand of the tool magazine; for this purpose, the headstock is moved into the exchange position where it can take over the tool directly from the tool magazine.  
           [0008]    According to a preferred embodiment of the invention, the guide of the headstock is a component of a rectangular frame which encloses a window in which the headstock is allowed to move. The window is provided with a louver having an opening arranged therein which is capable of adapting to the position of the headstock. In combination with the louver closing the window, the rectangular frame forms a vertical wall, allowing the chippings to fall down therealong.  
           [0009]    Preferably, the support in combination with the guide of the headstock forms an L-shaped structure in plan view which together with complementary walls and doors, respectively, encloses a machining chamber on the lateral sides. In this manner, there is obtained a laterally continuously enclosed machining chamber with exclusively vertical walls and without inner fittings which would impair the fall of the drillings.  
           [0010]    The machine tool of the invention is preferably used as a two-spindle machine wherein respectively one headstock performs the machining while the other headstock can carry out an exchange of tools. Both spindles are adapted for movement along horizontal guides arranged with a vertical distance from each other. Each of the guides is arranged relative to the tool magazine in such a manner that the headstock can perform the exchange of tools in pick-up operation. In the process, the headstock will be moved behind the tool holder—placed in its exchange position—of the tool magazine while the tool fastened to the headstock is transferred to the tool holder directly and without the use of a tool exchanger. In a similar manner, the headstock fetches the tool from the tool magazine by direct access along the Z-axis.  
           [0011]    If a lower guide is provided, with its upper side designed for movement of the headstock therealong, the guide is suitably joined in a downward direction by a skirt connected to a collecting means for chippings. The skirt constitutes a component of the vertical wall provided for the discharge of chippings exclusively through gravitational force. This collecting means is preferably provided as a chip conveyer.  
           [0012]    With the invention, it is further possible to provide two tool magazines in a common vertical plane, notably on both ends of the guide for the headstock.  
           [0013]    According to a further alternative embodiment of the invention, two workpiece carriers are provided to engage the workpiece under treatment from two opposite sides. For this purpose, two vertical supports can be provided, each of them comprising a vertical guide for a workpiece carrier. The vertical guides are covered by a lamellar louver or a similar vertical cover means, thus precluding the intrusion of chippings. This also applies for the tool magazine. Projecting into the machining chamber are only those parts of the tool magazine which are required for an exchange of tools. All other parts are located behind the respective limiting wall of the machining chamber, and the passages of the tool magazine through this partitioning wall are closed by a chip sealing. 
       
    
    
       [0014]    Embodiments of the invention will be explained in greater detail hereunder with reference to the drawings.  
       BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    [0015]FIG. 1 is a schematic perspective view of a first embodiment of the machine tool.  
         [0016]    [0016]FIG. 2 is a plan view of the machine according to FIG. 1.  
         [0017]    [0017]FIG. 3 is a lateral view of the machine according to FIG. 1, partially sectioned along the line III-III of FIG. 1.  
         [0018]    [0018]FIG. 4 is a view illustrating the configuration of the machine tool with two tool magazines.  
         [0019]    [0019]FIG. 5 is a view of the machine tool with two workpiece carriers to be moved in synchronism.  
         [0020]    [0020]FIG. 6 is a view of a modification of the machine tool according to FIG. 5. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0021]    The machine tool as illustrated in FIGS.  1 - 3  comprises a vertical support  10  provided with a vertical guide  11  arranged to have a carriage  12  vertically moved thereon in a controlled manner. On carriage  12 , a workpiece carrier  13  is supported for controlled rotation about a horizontal rotational axis  14 . The workpiece  15  to be machined will be fastened to workpiece carrier  13 . The movement of the carriage  12  along the vertical X-axis is performed by a spindle drive provided internally of support  10  and comprising a spindle  16 , a spindle nut  17  connected to carriage  12 , and a motor  18  rotating the spindle  16 . Motor  18  is a NC drive (NC=numerically controlled) allowing for a highly accurate height adjustment of workpiece carrier  13 . Mounted to carriage  12  is a further NC drive (not shown) for rotating workpiece carrier  13 .  
         [0022]    A lower beam  19  and an upper beam  20  extend horizontally from support  10 . The beams are arranged at a mutual distance and together with the support  10  and a vertical post  21  form a rectangular frame  22  enclosing a rectangular window  23 . Arranged in window  23  is a first headstock  24  comprising a rotatably driven spindle  25  with a tool  26  fastened thereto. Headstock  24  is arranged to be moved on a carriage  34  in the direction of an axis of movement Z 1  extending axially to spindle  25 . Carriage  34  is movable in a horizontal guide  27  along a first axis of movement Y 1  extending at a right angle to the axial direction of spindle  25 , while traveling in the lengthwise direction of guide  27 . The movements along the axes Y 1  and Z 1  are carried out by headstock  24 . The movement along the X-axis and the rotation about rotational axis  14  are carried out by workpiece  15 . The mounting surface of the workpiece carrier has a normal line which coincides with the rotational axis  14  and extends parallel to the first axis Y 1 .  
         [0023]    The upper side of beam  19  is provided with a horizontal guide  28  for a carriage  29  having a second headstock  30  arranged thereon. Headstock  30  comprises a spindle  31  with a tool  32  fastened thereto. Headstock  30  is movable on guide  28  along the first axis of movement Y 2  and further along a second axis of movement Z 2  extending axially to spindle  31 . The movement along axis of movement Z 2  is generated by a linear drive  33 .  
         [0024]    Each of the two spindles  25 , 31  is rotatably driven by a motor  35  and  36 , respectively, of the respective headstock.  
         [0025]    On support  10 , a tool magazine  37  is mounted which is provided with a circulating continuous endless conveyer  38  equipped with tool carriers  39  projecting therefrom to the outside. Each tool carrier  39  comprises two fingers configured for clamping the shaft of a tool  40  therebetween. The tool magazine  37  is arranged in a vertical plane extending parallel to the movement axes Y 1  and Y 2 . The vertical front strand  41  of the tool magazine projects out of support  10  and comprises two exchange positions, respectively one for each headstock  24  and  30 . A tool  40  arranged in an exchange position can be gripped and taken over by the spindle of the respective headstock  24  or  30 . On the other hand, each headstock  24 , 30  can hand over a tool  26 , 32  attached to its spindle  25 , 31  to that workpiece holder  39  of tool magazine  37  which is arranged in the exchange position. The drive of continuous conveyer  38  is controlled by a motor  42 .  
         [0026]    As evident from FIG. 2, the vertical support  10  together with the horizontal beams  19  and  20  in plan view forms an L-shaped structure enclosing a machining chamber  43 . Machining chamber  43  is further delimited by a side wall  44  and a front wall  45  or door, thus being completely enclosed on the sides. The window  23  surrounded by frame  22  is closed by a louver  46  which is not shown in FIG. 1. The louver is a lamellar louver comprising two longitudinal slots, one for each headstock  24 , 30 . The slots are closed by lamellae configured to adapt to the respective position of headstock  24 , 30  in the direction of the axis of movement Y 1  or Y 2  and allowing only the headstock  24 , 30  to pass while the rest of the window  23  will remain closed. The front wall of beam  19  is formed by a vertical skirt  47 . Thus, the machining chamber  43  is delimited exclusively by vertical walls. Arranged on the lower end of machining chamber  43  is a chip conveyer  48  which can be provided e.g. as a belt or chain conveyer but also as a screw conveyer. The conveyer is sized to occupy the whole width of machining chamber  43  and will remove the dropped chippings from the machine tool.  
         [0027]    The embodiment according to FIG. 4 is different from the first embodiment only in that, apart from the tool magazine  37  on support  10 , a further similar tool magazine  37   a  is arranged on the post  21 . Both tool magazines are arranged at the same height and delimit the moving path of the headstocks  24 , 30  in the horizontal direction, wherein each headstock  24 , 30  can access each of the tool magazines  37 , 37   a  arranged in a common vertical plane.  
         [0028]    In both tool magazines  37 , 37   a,  the rear or outer strand  50  is arranged externally of support  10  and post  21  and thus will be accessible from the outside for manual exchange of tools.  
         [0029]    In the embodiment according to FIG. 5, a further support  10   a  is provided in addition to support  10 , replacing post  21 . Support  10   a  comprises a second workpiece carrier  13   a  arranged for controlled movement along a vertical guide and for rotation about its horizontal longitudinal axis. The workpiece  15  can by each of its ends be clamped into a workpiece carrier  13  and  13   a,  respectively. The workpiece carriers  13  and  13   a  are moved in synchronism with each other in the vertical direction and are also rotated in synchronism. This two-sided clamping attachment of the workpiece provides for a highly precise positioning even of bulky or heavy workpieces.  
         [0030]    On the other hand, an option exists to fasten e.g. an auxiliary bar to one workpiece carrier  13   a;  the bar will be attached to the workpiece and support the same on the respective side.  
         [0031]    In the embodiment shown in FIG. 6, which largely corresponds to that according to FIG. 5, the two workpiece carriers  13 , 13   a  hold a U-shaped holder  55  clamped between them which has its legs  56  attached to the workpiece carriers by axes  57 . The base  58  of holder  55  carries a rotary table  59  for attachment of the workpiece  60  thereon. By pivoting the holder  55  about the axes  57 , the workpiece  60  can be brought into an oblique position so that, using the tool fastened to the respective headstock  24 , 30 , an angular machining process can be carried out. The pivotable holder  55  allows for a quick repositioning of workpiece  60  for performing machining processes on different sites or in different directions.  
         [0032]    In each of the embodiments according to FIGS.  4 - 6 , a laterally closed machining chamber  43  is provided; in these Figures, the walls  44  and  45  have been omitted for easier survey. In any case, chippings will fall down along vertical walls onto a collecting means  48  for chips, e.g. a chip conveyer, without being hindered by fittings.  
         [0033]    In each of the embodiments, all functions of the machine tool are controlled numerically according to predetermined programs so that the machining of workpieces and the exchanging of tools can be performed fully automatically. Also the control of the tool magazine  37 , 37   a  is fully automated, wherein the respectively required tool  40  is brought into the exchange position. Likewise, the exchange of workpieces  15  and their delivery and removal are performed in a controlled manner.