Abstract:
The invention relates to a device for green machining bevel gears, including a CNC machining station for gear cutting a wheel blank (K 2 ). The machining station includes a tool spindle which is used to receive a gear cutting tool and a work piece spindle which is used to receive the gear blank (K 2 ). The machining station also relates to a machining station which operates in a vertical manner. The device also comprises a vertical processing station having a tool holder and a work piece spindle which is used to receive a work piece blank (K 1 ). The machining station mechanically forms a functional unit together with the pre-machining station, wherein the work piece blank (K 1 ) undergoes green machining in the pre-machining station, and is transferred as a gear blank (K 2 ) to the first machining station after the first green machining where it is cut into a gear. The machining station and the pre-machining station are linked together in terms of data and control.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of PCT Application No. PCT/EP2005/001478, filed Feb. 14, 2005, the disclosure of which is herein incorporated by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to devices for green machining bevel gears, in particular devices which are designed for dry machining. The present invention also relates to a corresponding method. 
     There are greatly varying machine tools which are used in the manufacture of bevel gears and similar gears. For some time, there has been a wish for automating the manufacture. One solution, which has only been able to succeed in a limited way up to this point, however, is a machining center which is designed so that a large number of manufacturing steps may be executed on the same machine tool. Such machine tools are not only very complex and therefore costly, but rather also require relatively great effort in the preparatory set up (equipping time). On the other hand, such machine tools, which have been developed in regard to high flexibility, are more suitable for producing individual fabrications or extremely small series. 
     A compact machine tool which is designed for turning and hobbing a workpiece is shown and described in European Patent EP 0 832 716 B1, this workpiece not having to be rechucked or transferred. In other words, the workpiece is seated on a main spindle after the chucking and is machined there using various tools. It is seen as a disadvantage of this machine tool that, because of the configuration of the various elements, it is not designed for the purpose of executing dry machining, because the removal of the hot chips is of special significance during dry machining. In addition, the movement clearance is restricted by the lateral configuration of the two carriages having the tools in relation to the workpiece. The machine tool shown is not capable of machining bevel gears, ring gears, or the like, but rather is conceived for machining spur gears. 
     A further machine tool is known from Published Application DE 199 18 289 A1, in which two steps are executed in sequence without having to rechuck the workpiece. The first step executed on this machine tool is rough machining of a spur gear using a hobbing cutter, to give the workpiece a coarse contour and surface. A fine machining method then follows, the workpiece also remaining in the same chucking for this purpose. 
     It is seen as a disadvantage of the machine tools which machine a workpiece in multiple steps without rechucking the workpiece that a large number of different parameters have to be taken into consideration in the design and implementation of the machine tool. A compromise must always be found between greatly varying goals, as is obvious from the following example. Both the roughing and also the fine machining are executed on the machine tool described in the published application cited at the beginning. Roughing is a method in which material is removed from a blank with high metal removing capacity. In contrast, very low feed and higher precision is used in fine machining. This results in different requirements solely in regard to the chucking. However, the type and configuration of the individual tools, as well as their activation, may also vary greatly. If one also wishes to perform a part or all of the cited steps as dry machining, further restrictions in regard to the configuration of the individual axes and tools result because of the special requirements in dry machining for the removal of the hot chips. 
     SUMMARY OF THE INVENTION 
     The present invention is based on the object of simplifying the manufacturing of bevel gears on one hand and accelerating it on the other hand, without having to accept quality losses. 
     A further object of the present invention is to provide a method and a corresponding device which are designed for dry machining. 
     These objects are achieved according to the present invention. One aspect of the invention comprises a device for use in the green machining of bevel gears, having a CNC-controlled machining station for gear cutting a gear blank. The machining station has a tool spindle for receiving a gear-cutting tool and a workpiece spindle for receiving the gear blank. The machining station is a vertically operating machining station, in which, during gear cutting, the workpiece spindle having the gear blank is situated below or above the tool spindle having the gear-cutting tool. The device additionally has at least one vertically operating pre-machining station having a tool holder and a workpiece spindle for receiving a workpiece blank. The machining station forms a mechanical functional unit together with the pre-machining station, in which the workpiece blank experiences green machining in the pre-machining station. Then the blank is transferred after the green machining as a gear blank to the machining station and then is cut into a gear. The machining station and the pre-machining station are linked to one another by control technology. 
     Another aspect of the invention comprises a method for green machining bevel gears, having the following steps:
         (a) chucking a workpiece blank on a first workpiece spindle of a pre-machining station,   (b) performing a first green machining of the workpiece blank using a tool, which is chucked in a first tool spindle of the pre-machining station to generate a gear blank from the workpiece blank,   (c) automated transfer of the gear blank from the pre-machining station to a machining station, the gear blank being transferred from the first workpiece spindle to a second workpiece spindle of the machining station,   (d) performing a second green machining of the gear blank using a tool, which is chucked in a second tool spindle of the machining station to generate teeth on the gear blank,
           the machining station and the pre-machining station being vertically operating stations and the machining station forming a mechanical functional unit together with the pre-machining station.   
               

     Further advantageous embodiments are also disclosed. 
     The method according to the present invention is especially designed for machining tooth flanks before a hardening process, i.e., in the green state. The tools which are used are to be selected accordingly. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of the present invention are described in greater detail in the following with reference to the drawings, in which: 
         FIG. 1  is a schematic, exemplary illustration of the various machining steps in the gear cutting of bevel gears; 
         FIG. 2A  shows a schematic illustration of a first arrangement of a first device for use in the green machining of bevel gears, according to the present invention, while  FIG. 2B  shows a schematic illustration of an alternate arrangement of the first device; 
         FIG. 3A  shows a schematic illustration of a first arrangement of a second device for use in the green machining of bevel gears, according to the present invention, while  FIG. 3B  shows a schematic illustration of an alternate arrangement of the second device. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Terms which are also used in relevant publications and patents are used in connection with the present description. However, it is to be noted that the use of these terms is solely for better understanding. The inventive ideas according to the present invention and the scope of protective of the patent claims are not to be restricted in their interpretation by the specific selection of the terms. The present invention may be transferred without further measures to other term systems and/or professional fields. The terms are to be applied accordingly in other professional fields. 
     The present invention is concerned with the machining of bevel gears. According to the definition, this term also comprises ring gears and bevel pinions. Bevel gears without axial offset and bevel gears with axial offset, i.e., so-called hypoid gears, are also included. 
       FIG. 1  shows a schematic illustration of an exemplary method sequence  10 . The present invention may advantageously be used in the context shown. As noted, this is an example of the machining of a ring gear or bevel pinion. Starting from a workpiece blank (box  101 ), the following green machining steps are performed in the example shown. For example, a (central) hole may be generated by turning (box  102 ). The workpiece blank may then be turned around for further machining (box  103 ). After the turning around, renewed lathe machining may follow (box  104 ). These steps are optional and are referred to in the present context as preform production or pre-machining. Other steps or alternative steps may also be executed in the scope of the preform production. At the end of the preform production, the workpiece is referred to as a gear blank. Step  102  or steps  102 - 104  may be executed in a so-called pre-machining station  40  or  70 . 
     The so-called gear cutting now follows. According to the present invention, preferably (dry) bevel gear cutters (box  105 ) are used to generate teeth on the gear blank. The optional step of deburring (box  106 ) then follows. Step  105  or steps  105 - 106  may be executed in a so-called machining station  30  or  60  according to the present invention. A further machining station may also be used. 
     Typically, heat treatment (box  107 ) to harden the wheel blank, and post machining or fine machining (box  108 ) subsequently follow. The bevel gear is then ready. 
     Further details of the present invention are described in the following on the basis of a more precise description of the individual method steps and using two exemplary embodiments, details of the individual embodiments being able to be exchanged or combined with one another. 
     The method according to the present invention for green machining bevel gears comprises the following steps. The reference signs relate to  FIGS. 2 and 3 . A workpiece blank K 1  is chucked on a first workpiece spindle  42 ,  72  of a pre-machining station  40 ,  70 . First green machining of the workpiece blank K 1  is performed using one or more tools  43 ,  73 . 1 - 73 . 5 . The tool  43  or the tools  73 . 1 - 73 . 5  are chucked in a first tool spindle  41 ,  71  of the pre-machining station  40 ,  70 . This first green machining includes one or more of the following machining steps: drilling, turning, milling, etc. The goal of this first green machining is to generate a gear blank K 2  from the workpiece blank K 1 . 
     An automated transfer of the gear blank K 2  from the pre-machining station  40 ,  70  to a machining station  30 ,  60  then occurs. The gear blank K 2  is transferred from the first workpiece spindle  42 ,  72  to a second workpiece spindle  33 ,  63 , which is part of the machining station  30 ,  60 . This transfer may be performed by means which are integrated in the machining station  30 ,  60  and/or pre-machining station  40 ,  70 , as described in connection with  FIG. 3 . External means may also be used for the transfer, however, as described in connection with  FIG. 2 . 
     The gear cutting is now performed in the machining station  30 ,  60 . This occurs as follows. Second green machining of the gear blank K 2  is performed using a tool  32 ,  62 , which is chucked in a second tool spindle  31 ,  61  of the machining station  30 ,  60 . The goal of this second green machining is to generate teeth on the gear blank K 2 . The second green machining preferably comprises the (dry) milling of the bevel gear teeth of the gear blank K 2  using a cutter head  32 ,  62 . 
     To be able to execute these steps in the cited way, the machining station  30 ,  60  and the pre-machining station  40 ,  70  are designed as vertically operating stations and the machining station  30 ,  60  forms a mechanical functional unit together with the pre-machining station  40 ,  70 . 
     All machining steps may preferably be executed dry. In this case, the device  20 ,  50  has to be designed and implemented accordingly. 
     A first device  20  according to the present invention is shown in  FIG. 2 . The device  20  is especially designed for use in the green machining of bevel gears and comprises a CNC-controlled machining station  30  for gear cutting a gear blank K 2 . The machining station  30  has a tool spindle  31  for receiving a gear-cutting tool  32  (such as a dry hobbing cutter) and a workpiece spindle  33  for receiving the gear blank K 2 . 
     According to the present invention, the machining station  30  is a vertically operating machining station, in which, during the gear cutting, either the workpiece spindle  33  having the gear blank K 2  is situated below the tool spindle  31  having the gear-cutting tool  32 , or the workpiece spindle  33  having the gear blank K 2  is seated above the tool spindle  31  having the gear-cutting tool  32 . According to the present invention, the device  20  additionally comprises at least one vertically operating pre-machining station  40  having a tool retainer  41  and having a workpiece spindle  42  for receiving a workpiece blank K 1 . 
     According to the present invention, the machining station  30  forms a mechanical functional unit together with the pre-machining station  40 , in which the workpiece blank K 1  experiences first green machining in the pre-machining station  40 , to then be transferred as the gear blank K 2  to the machining station  30  after the first green machining and be cut into a gear there. The machining station  30  has a CNC controller  34 , which is indicated in  FIG. 2 . The machining station  30  and the pre-machining station  40  are linked to one another by control technology, which is indicated in  FIG. 2  by the arrow  34 . 1 . This linkage may be performed via a bus or a cable connection. Using another type of interface, such as a wireless connection, to link the CNC controller  34  to the pre-machining station  40  is also conceivable. 
     Further details of the device  20  shown in  FIG. 2  are explained in the following. The pre-machining station  40  has a main rotation axis A 1 . The workpiece spindle  42  may rotate around this axis A 1 , as indicated by the double arrow  45 . 1 . Furthermore, the workpiece spindle  42  is seated on a carriage  42 . 1  and may be displaced in various directions, as illustrated by the arrows  45 . 2 ,  45 . 3 , and  45 . 4 . In addition, the tool spindle  41  may have a rotation axis, if a rotation of a tool  43  around its longitudinal axis is desired. In the embodiment shown, the workpiece spindle  41  is seated on a carriage  41 . 1  and may thus be displaced parallel to an axis  44 . 2  together with the tool  43 . Displaceability along the axis  44 . 2  is not absolutely necessary, because the tool  43  may also be engaged by displacing the workpiece spindle  42  parallel to the axis  45 . 2  in the direction of the tool  43 . 
     The machining station  30  has a main rotation axis A 2 . The tool spindle  31  may rotate around this axis A 2 , as indicated by the double arrow  35 . 1 . Furthermore, the tool spindle  31  is seated on a carriage  31 . 1  and may be displaced in various directions, as shown by the arrows  35 . 2 ,  35 . 3 , and  35 . 4 . In addition, the workpiece spindle  33  has a rotation axis B 2  and a pivot axis B 3 . The workpiece spindle  33  may be rotated around this axis B 2 , as indicated by the double arrow  36 . 1 . In addition, the workpiece spindle  33  may be pivoted around the pivot axis B 3 . In the example shown, the workpiece spindle  33  was pivoted counterclockwise together with the gear blank K 2  by an angle W. 
     The configuration of the axes shown in  FIG. 2  is a possible constellation of the axes. The axes of the two machining stations  30 ,  40  may also be implemented in another form. For example, the workpiece spindle  33  may be situated so it is movable parallel to the axis  35 . 3 . In this case, the carriage  31 . 1  does not need to be able to be displaced in this direction. Overall, 6 axes are sufficient in each case for the pre-machining station  40  and also for the machining station  30 . 
     In the embodiment shown, the workpiece spindle  33  may not be displaced translationally together with the gear blank K 2 . Displaceability parallel to the axis  35 . 2  is not absolutely necessary, because the tool  32  may be advanced by displacing the tool spindle  31  parallel to the axis  35 . 2  in the direction of the workpiece K 2 . The workpiece spindle  33  may also be situated on a carriage, however, to obtain further degrees of freedom. 
     The various axes are numerically controlled axes. The individual movements may thus be numerically controlled by the CNC controller  34 . The controller  34  is preferably designed in such a way that all axes are numerically controlled. It is important that individual movement sequences occur in a coordinated way. This coordination is performed by the CNC controller  34 . 
     The device according to the present invention is special and stands out from other known approaches in that the individual machining stations  30 ,  40  are vertically designed. In addition, the position of the various numerically controlled axes has been selected in such a way that there is the largest possible movement clearance for the machining of the workpiece K 1 , K 2 . The following configuration of the individual axes is especially preferred. 
     Pre-machining station  40 : axis A 1  runs parallel to the longitudinal axis of the tool  43 , the two axes being able to be offset in relation to one another by executing a relative movement parallel to the direction  45 . 4 . Thus, for example, a central hole  46  may be worked out in the workpiece blank K 1  using a milling cutter or turning tool  43 . The tool spindle  41 , including carriage  41 . 1 , is situated below the workpiece spindle  42 , including carriage  42 . 1 , and the relative distance to one another may be changed by performing a relative displacement parallel to the axis  45 . 2 . Such a change of the relative distance may be performed in the example shown by a displacement of the carriage  42 . 1  parallel to the axis  45 . 2  and/or by a displacement of the carriage  41 . 1  parallel to the axis  44 . 2 . Preferably, the two axes A 1  and the longitudinal axis of the tool  43  may also be offset to one another in depth (perpendicular to the plane of the drawing). For this purpose, the carriage  42 . 1  may be displaced parallel to the axis  45 . 3 . 
     Machining station  30 : axis A 2  runs parallel to the axis B 2  (if W equal 0°), but an angle W, which is preferably between 0° and ±90°, may also be set between the axes A 2  and B 2  by pivoting the workpiece spindle  33 . The tool spindle  31 , including carriage  31 . 1 , is situated above the workpiece spindle  33  in the embodiment shown and the relative distance to one another may be changed by performing a relative displacement parallel to the axis  35 . 2 . Such a change of the relative distance may be performed in the example shown by a displacement of the carriage  31 . 1  parallel to the axis  35 . 2 . Preferably, the two axes A 2 , B 2  may be shifted toward one another laterally (in the plane of the drawing). For this purpose, the carriage  31 . 1  may be displaced parallel to the axis  35 . 4 . Preferably, the two axes A 2 , B 2  may also be moved toward one another in depth (perpendicular to the plane of the drawing). For this purpose, the carriage  31 . 1  may be displaced parallel to the axis  35 . 3 . 
     According to one embodiment of the present invention, the workpiece spindle  33  for receiving the gear blank K 2  has clamping or gripping means to be able to chuck the gear blank K 2 . An embodiment in which the clamping or gripping means are designed for automatically chucking the gear blank K 2  is especially preferred. 
     The device  20  may comprise a feed apparatus, which executes the transfer of the gear blank K 2  from the pre-machining station  40  to the machining station  30 . The feed apparatus may, for example, comprise a horizontal conveyor which accepts the gear blank K 2  in the pre-machining station  40  and transports it to the machining station  30 . Such a feed apparatus is preferably designed for completely automatic operation, so that the workpiece spindle  42  releases the gear blank K 2 , for example, by opening clamping or gripping jaws, and the gear blank K 2  is moved horizontally along a conveyor line of the horizontal conveyor. The clamping or gripping means of the workpiece spindle  33  grip the gear blank K 2  in the area of the machining station  30 . 
     The tool retainer  41  of the pre-machining station  40  may preferably be equipped with a revolver head, which may receive multiple tools, as described on the basis of the second embodiment (compare  FIG. 3 ). An embodiment in which at least one of the tools which is located on the revolver head may be driven individually is especially preferred. 
     The pre-machining station  40  may be used for turning, milling, boring, etc. Pre-machining station  40  may also have means for turning over the workpiece blank K 1 . 
     A second embodiment of the present invention is shown in  FIG. 3 . The device  50  is especially designed for use in the green machining of bevel gears and comprises a CNC-controlled machining station  60  for gear cutting of a gear blank K 2 . The machining station  60  has a tool spindle  61  for receiving a gear-cutting tool  62  and a workpiece spindle  63  for receiving the gear blank K 2 . 
     According to the present invention, the machining station  60  is a vertically operating machining station in which the workpiece spindle  63  having the gear blank K 2  is situated below the tool spindle  61  having the gear-cutting tool  62  during the gear cutting. The tool spindle  61  having the gear-cutting tool  62  may also be situated below the workpiece spindle  63  having the gear blank K 2 , however. According to the present invention, the device  50  additionally comprises at least one vertically operating pre-machining station  70  having a tool holder  71  and having a workpiece spindle  72  for receiving a workpiece blank K 1 . 
     According to the present invention, the machining station  60  forms a mechanical functional unit together with the pre-machining station  70 , in which the workpiece blank K 1  experiences first green machining in the pre-machining station  70 , to then be transferred as the gear blank K 2  to the machining station  60  after the first green machining and be cut into a gear therein. The machining station  60  has a CNC controller  64  which is indicated in  FIG. 3 . The machining station  60  and the pre-machining station  70  are linked to one another by control technology, as indicated in  FIG. 3  by the arrow  64 . 1 . This linkage is implemented identically or similarly to the linkage which was described in connection with  FIG. 2 . 
     Further details of the device  50  shown in  FIG. 3  are explained in the following. The pre-machining station  70  has a main rotation axis A 1 . The workpiece spindle  72  may rotate around this axis A 1 . In addition, the tool carrier  73  has a pivot axis C 2 , which is perpendicular to the plane of the drawing. The tool carrier  73  may be rotated around this axis C 2 , as indicated by the double arrow  74 . 1 . In the embodiment shown, the tool carrier  73  is seated on a carriage  71  and may be displaced together with the tools  73 . 1 - 73 . 5  parallel to the axes  75 . 1  and  75 . 2 . Separate displaceability of the workpiece spindle  72  parallel to the axes  75 . 1  and  75 . 2  is not absolutely necessary, but may be provided in an alternative embodiment (see  FIG. 2 , for example). 
     In the following, further special features of the device  50  are described. These features may also be used in connection with the device  20  shown in  FIG. 2 . 
     The device  50  has an integrated feed apparatus, which executes the transfer of the gear blank K 2  from the pre-machining station  70  to the machining station  60 . The tool carrier  73  has special clamping or gripping jaws in an area identified by the number 1. After the workpiece blank K 1  has been finish machined in the pre-machining station  70 , it is transferred to the machining station  60 . The finish-machined workpiece blank K 1  is also referred to here as the gear blank K 2 , to be able to differentiate it from the workpiece blank K 1 . In a first step, the tool carrier  73  is moved by the carriage  71  parallel to the axis  75 . 2  toward the gear blank K 2  (i.e., the relative distance is reduced), which is still chucked on the workpiece spindle  72  at this moment. For the removal and transfer, the gear blank K 2  is accepted by the clamping or gripping jaws identified by 1 in that these clamping or gripping jaws engage in a (central) hole  76 . 1  of the gear blank K 2 . Before this occurs, the clamping or gripping jaws are moved from the “3 o&#39;clock position” (in  FIG. 3 ) into a “12 o&#39;clock position”. As soon as the clamping or gripping jaws have grasped the gear blank K 2 , the gear blank K 2  is released by the workpiece spindle  72 . The tool carrier  73  now rotates (preferably clockwise) from the “12 o&#39;clock position” into the “3 o&#39;clock position” shown in  FIG. 3  and the carriage  71  moves, as far as necessary, in the direction of the workpiece spindle  63 . This position of the tool carrier  73  is schematically indicated at the position marked by 2 in  FIG. 3 . 
     In the following step, the workpiece spindle  63  is rotated into a “9 o&#39;clock position”. The embodiment shown is preferred, in which no displaceability parallel to the axis  75 . 1  is provided for the workpiece spindle  63 , but rather in which the transfer occurs in that the carriage  71  may be displaced to the right and left parallel to the axis  75 . 1 . 
     The clamping or gripping jaws of the workpiece spindle  63  now engage from the rear in a (central) hole  76 . 2  of the gear blank K 2 . In this transfer position, the gear blank is identified by K 2 ′ and the workpiece spindle by  63 ′. As soon as the clamping or gripping jaws of the workpiece spindle  63 ′ close, the gear blank K 2 ′ is released by the clamping or gripping jaws  1  of the tool spindle  73 . The workpiece spindle  63  may now be rotated back from the transfer position into a machining position (for example, by the angle 90°-W), and the machining using the gear-cutting tool  62  may begin. 
     Optionally, the device  50  may have means for turning over the workpiece blank K 1 . These means are schematically indicated in  FIG. 3  and are identified by the reference sign  3 . So as not to interfere with the overall illustration in  FIG. 3 , the means  3  together with the chucked workpiece blank K 1  are shown in a smaller scale. It is indicated by a double arrow that the workpiece blank K 1  may be turned over by the means  3 . It is important that the means  3  are situated and executed in such a way that they allow the workpiece blank K 1  to be turned over together with (in interplay with) the workpiece spindle  72 . 
     The machining station  60  may, for example, have the following axial constellation having a total of 6 axes: pivot axis (A 2 )  65 . 3 , two linear axes  65 . 1  and  65 . 2 , as well as a workpiece pivot axis (B 2 )  65 . 5 , swivel axis (B 3 )  65 . 6 , and a linear axis  65 . 4  (perpendicular to the plane of the drawing). It is obvious that there are also other axial constellations having a total of 6 axes which are suitable. 
     In the embodiment shown, the tool carrier  73  has multiple tool holders. Five tool holders are equipped with tools  73 . 1 - 73 . 5  in the example shown. The workpiece carrier  73  is preferably implemented in such a way that at least one of the tool holders is provided with a spindle head, to be able to drive the corresponding tool individually. The tools  73 . 1  may, for example, be a drill or a milling head, which may be put into rotation around its longitudinal axis. The tools  73 . 2  and  73 . 3  may be cutter heads or turning tools, for example, which are each chucked permanently in a tool holder of the tool carrier  73 . The tools  73 . 3  and  73 . 5  may be deburring heads or the like. 
     Both embodiments may be modified and adapted appropriately to the framework conditions. 
     Thus, for example, the device  20  or  50  may also be used for deburring. There are two different approaches. Either the deburring is executed after the pre-machining, for example, after step  104  in  FIG. 1 . In this case, the deburring occurs in the pre-machining station  70 . 
     Or the deburring is executed after the bevel gear milling, for example, after step  106 . In the latter case, the workpiece spindle  63  is rotated counterclockwise around the axis B 3  to allow machining of the gear blank K 2  using a deburring tool on the tool carrier  73 . In this case, the deburring occurs through interaction of the pre-machining station  70  and the machining station  60 . 
     A device which is distinguished in that the machining station comprises a CNC controller which is designed in such a way that the machining station is operable either autonomously or as a functional unit together with the pre-machining station is especially preferred. This makes it possible to operate the machining station alone and to expand it as needed by adding the pre-machining station and/or further stations. The advantage of the fact that there is only one CNC controller, which is located in the machining station, or which is designed for operation with the machining station, is seen in that the pre-machining station may thus be implemented more cost-effectively. This cost savings results primarily because the pre-machining station does not require its own CNC controller. In addition, the linkage of the two stations is much simpler and the coordination of the individual movement sequences of the device is simpler. 
     To be able to operate machining station and pre-machining station jointly, as provided in the present invention, the pre-machining station is connectable mechanically and by control technology to the machining station using add-on connections. It is made possible by the control technology connection for the CNC controller of the machining station to numerically control axes of the pre-machining station and to coordinate the individual movement sequences. A precise transfer from the pre-machining station to the machining station using a horizontal conveyor, or by the integrated feed apparatus shown in  FIG. 3 , is made possible by the mechanical connection of the two stations. The collection devices F 1 , F 2  for chips may also be combined with one another by the mechanical connections of the two stations in such a way that the chips may be removed rapidly and without problems to the rear. 
     Preferably, the pre-machining station comprises its own drives, which are all controllable by the CNC controller. Thus, the pre-machining station and the machining station may be used synchronously. This allows at least partially synchronous green machining of a workpiece blank K 1  in the pre-machining station and gear cutting of a gear blank K 2  in the machining station. 
     An embodiment in which the machining station is designed for dry milling a bevel gear is especially preferred. 
     According to the present invention, tools made of high-performance steel, hard metal, ceramic, or cermet (combination of metal and ceramic), each having a suitable hard material coating, are used for machining the bevel gear teeth. 
     It is seen as an advantage of the present invention that more than one workpiece may always be machined in the machine tool. It is thus more or less a very compact manufacturing line, which may be implemented in an extremely small space and made available for reasonable prices by special measures, however. 
     Such a compact manufacturing line has higher throughput than the machine tool of the prior art cited at the beginning, for example (compare EP 0 832 716 B1).