Abstract:
The present disclosure relates to an apparatus as well as to a method for the manufacture or processing of large tooth systems for internal or external teeth or large cogs in small production runs, wherein at least two machining methods are used with the aim of a complete machining of precision-relevant surfaces at these workpieces and while realizing production times which are as short as possible.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority to German Patent Application No. 10 2013 013 276.2, entitled “Machine Tool and Method for the Machining of Workpieces Having at Least Two Separate Machining Units,” filed Aug. 8, 2013, which is hereby incorporated by reference in its entirety for all purposes. 
     TECHNICAL FIELD 
     The present disclosure relates to an apparatus as well as to a method for the manufacture or processing of large tooth systems for internal or external teeth or large cogs in small production runs, wherein at least two machining methods are used with the aim of a complete machining of precision-relevant surfaces at these workpieces and while realizing production times which are as short as possible. 
     BACKGROUND AND SUMMARY 
     Large gear cutting machines are known from the prior art which can currently machine machining diameters of 16,000 mm and more. In this respect they are hobbing and profile milling machines as well as gear planing machines. These machines are also available as gear grinding machines and gear shaping machines for somewhat smaller workpiece diameters. 
     Since the workpieces for the gear cutting process come from a preprocessing such as a forging operation or are assembled from individual segments with very large workpieces, they first have to be subjected to a turning, milling and/or drill machining before a gear cutting machining in order thus to provide the functional surfaces for the use of these gears. The throughput times for these machining operations can take one day up to several days in part, including the set-up times, with workpieces of this order of magnitude. 
     The usual separation of premachining operations and gear cutting operations onto a plurality of individual machines customary in mass production represents a substantial investment cost in a plurality of machines on the manufacture of large teeth and then also has the consequence of a large space requirement for the setting up of the individual machines. Complete production halls then fast become planned for such machines. Machines of this dimension also usually require a huge additional foundation so that these machines cannot be repositioned in the production area without problem. Substantial investment sums result from this which only pay their way when corresponding volumes are also provided. 
     With very large teeth or with inappropriate volumes, a combination machine can be considered which can carry out both the gear cutting operations and also the preparatory cutting operations such as turning, milling or drilling or further additional operations such as plane and/or external circular grinding. 
     There are already different concepts for the machining of large teeth which are frequently oriented on the portal construction of large upright machining centers such as disclosed, e.g., by DE 20 2007 012 450. 
     In the shown upright machining center of the so-called double-column type, the two columns move parallel to the workpiece (Y direction) and thus move the cross-member fastened between these two columns over the workpiece. A support carriage is mounted on the cross-member which can be moved along the transverse carriage at a right angle (X direction) to the direction of travel of the columns. Practically all positions over the workpiece can be traveled to by these movements in the X/Y directions with a sufficient travel path. 
     The delivery of the cutting tool to the workpiece takes place via a lowering movement of the cross-bar (W direction) and a vertical delivery (Z direction, parallel to the W direction) of the RAM configuration with the milling head fastened thereto to bring the tool into engagement with the workpiece. The cross-bar in this configuration has to absorb bending and torsion forces which result from the machining forces and the weight of the machining head. 
     A gear-cutting machine in a vertical construction is described in a similar embodiment in DE 10 2009 008 012 A.1 The two columns having the cross-bar are not moved, but are stationary, with respect to the first-named publication. Instead the machine table moves relative to the workpiece in the direction of the machining head. The moved masses of the machine table are smaller in this embodiment with respect to the above-named embodiment. 
     With large teeth, especially when large modules are milled, very large machining forces arise which nevertheless result in a bending of the cross-bar and of the vertical guide of the ram configuration. These forces in turn have the result of a quality reduction of the gears thus milled independently of whether the gear-cutting process is a hobbing or profile milling process. The assembly arrangement of the gear-cutting milling head at a cross-member with a RAM configuration is considerably inferior to the classical design of a gear-cutting machine in accordance with the prior art with respect to the precision and the force absorption from the gear-cutting milling process. The forces are, however, lower, have a different direction of force effect and can be absorbed more easily by this construction without any great losses in quality for the normal turning, milling or drilling operation carried out at these workpieces. If the second machining is a grinding machining, even lower forces have to be taken up by the second machining head. 
     Within this arrangement, too, the length of the cross-member has a considerable influence on its bending and torsion properties or a shorter cross-member of the same construction has much better properties with respect to its bending and torsion. 
     The present disclosure now combines the positive properties of a gear-cutting machine with the positive properties of an upright machining center for turning/milling operations in a two-column embodiment and in so doing simultaneously increases the stability of the total machine. This is achieved by a machine tool having a correspondingly smaller space requirement being required instead of a plurality of individual machines. 
     From the aspect of the basic design, a gear-cutting machine for large machines in accordance with the prior art is combined with a vertical turning/milling device having two columns. With respect to the prior art, however, this machine differs at least in that the transverse portal does not extend over the total machine width and in this respect has to be very long and thus flexible. In the machine in accordance with the present disclosure, the second column is located in the middle of the machine table, where the self-supporting length can be almost halved and the cross-beam becomes a lot stiffer or can be configured with a smaller cross-section with the same bending stiffness. 
     To load the workpieces onto the machine table, the cross-member/portal carrier in the machine in accordance with the present disclosure is configured as outwardly pivotable. In addition, the column in the middle of the machine in the table can be lowered so that the workpieces can be conveyed more easily onto the table. 
     The outward pivotability of the cross-member/portal carrier furthermore offers still a further advantage. Further machining units and/or tool holders can thus be supported within the machine housing at defined preparation spaces. These spaces can be moved to under NC control by the machining head via the portal carrier. A change of the machining heads and/or a tool change can take place there via an automatic interface in dependence on the design of the selected interface or in accordance with the selected machining operation. 
     In a further embodiment of the portal carrier, it can be lowered together with the middle column and the outer column so that the linear axles of the RAM configuration do not project so far outwardly during machining, which produces a much more stable axle, which in turn produces a better machining result or makes much higher cutting performances possible. 
     A movability of the transverse portal over the workpiece is not necessary since rotationally symmetrical workpieces may be machined using this machine. All required work positions can be traveled to by a combination of the rotational movement of the table with a linear travelability of the second machining unit radially to the table. 
     Further details of the present disclosure will be described in the drawing with reference to schematically shown embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  shows a gear-cutting machine, in particular for large teeth, in accordance with the prior art. 
         FIG. 2  shows a machine tool having a machining head for outer teeth in accordance with an embodiment of the present disclosure. 
         FIG. 3  shows a machine tool having a machining head for inner teeth in accordance with an embodiment of the present disclosure. 
         FIG. 4  shows a machine tool having an inwardly pivoted portal in accordance with an embodiment of the present disclosure. 
         FIG. 5  shows a machine tool having an inwardly pivoted portal and the second machining head in its work position in accordance with an embodiment of the present disclosure. 
         FIG. 6  shows a machine tool having an inwardly pivoted portal and the second machining head in its work position in accordance with an embodiment of the present disclosure. 
         FIG. 7  shows a section through a machine tool in accordance with an embodiment of the present disclosure. The figures are drawn approximately to scale and thus illustrate example relative dimensions and positioning with respect to each other, although other relative dimensions and positioning may be used, if desired. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a perspective view of a gear-cutting machine  1  for machining inner teeth in accordance with the prior art for machining large teeth. The gear-cutting machine in this respect has the degrees of freedom required for the machining and can in particular carry out the drawn movements A 1 , B 1 , C 1 , X 1  and Z 1 . In detail, X 1  describes the radial movement of the column carriage, Z 1  the axial movement of the tool, B 1  the rotary movement of the tool, C 1  the rotary movement of the workpiece and A 1  the pivot movement of the tool. Workpieces which are fastened to the machine table  30  can be machined at their inner diameters with the machining head shown for inner teeth  75 . For this purpose, the machining head for inner teeth  75  is moved by the machine column  10  to the machining site with the X 1  axle and dips during the machining by a linear movement of the Z 1  axle into the workpiece and in so doing generates the teeth, with the tool rotating about its B 1  axis for this purpose. This is controlled by an NC control with an operating unit  95 . The further machining heads  70 ,  80  can be replaced as required with the machining head for inner teeth  75  if, e.g., outer teeth are to be machined. In this case, the machining head for outer teeth  70  is mounted instead of the machining head for inner teeth  75 . 
     In  FIG. 2 , a perspective representation of an embodiment of the machine in accordance with the present disclosure is shown. In turn, the machining head for outer teeth  70  is mounted at the machine column  10 . The portal carrier  50  with the second machining head  60  mounted thereat is located in an outwardly pivoted position. This position is reached in that the portal carrier is pivoted about the C 3  axis on the outer support column  45 . The support column  40  is here shown in the middle of the machine table  30  in its lowered position. 
     The second machining head  60  in this embodiment has a vertical guide  65  via which a machining unit  85  can be supplied by the Z 5  axle in the direction toward the workpiece  25  and is there brought into engagement with the workpiece. The workpiece  25  is in this respect clamped on the apparatus  35  and on the machine table  30 . 
     In the outwardly pivoted position of the portal carrier, a change of the machining units  85  or of the tool for a machining unit can take place. The machining head  60  is for this purpose moved via the Y 1  axle along the portal carrier  50  for so long until an empty preparation space  90  is located beneath the machining head  60 . Subsequently, the machining unit  85  is lowered via the linear unit in the Z 5  axial direction and the no longer required machining unit  85  or the tool is placed down in this space in that the automatic interface is opened after reaching the placing down position. The linear unit  65  is again moved upwardly and the machining head  60  travels over the position with the new tool or the new machining unit. The linear unit  65  there travels downwardly until its automated interface travels onto the next tool or the next machining head. The interface closes and the linear unit  65  again travels back together with the tool or machining unit  85  into the working position by a Y 1  axial movement and an inward pivoting of the portal carrier about the C 3  axis. 
     For reasons of safety, the working space is closed during the machining in that the two sliding doors  100  are moved together. 
       FIG. 3  now shows a perspective representation of the machine in accordance with the present disclosure in which the middle support column is raised. The portal carrier can now be moved into its working position by pivoting the portal carrier about the C 3  axis. For this purpose, the front end of the carrier is coupled via coupler elements suitable for this purpose with the support column in the table middle  40  as is shown in  FIG. 4 . For the machining, the second machining head  60  can now be moved along the Y 1  axis in the direction toward the table middle into its working position. This situation is shown in  FIG. 5 . The machining unit  85  is in this respect located in engagement with the workpiece  25  and machines its surface. 
       FIG. 6  shows the machine in accordance with the present disclosure in an embodiment in which the two columns  40 ,  45  were lowered together with the portal carrier to bring the tool into engagement. The outward projection of the linear unit is hereby considerably reduced. Higher cutting performances can hereby be processed or the quality of the machined surface is improved due to a lower sag of the linear unit. 
     A section through an embodiment of the machine in accordance with the present disclosure is shown in  FIG. 7 . The support column  40  is shown in the middle of the machine table  30  in its lowered position. The column is supported in its support position  55  which allows a movement of the support column in the direction of the Z 4  axis. A workpiece  25  with the apparatus  35  is mounted on the machine table  30 . For machining this workpiece  25 , the machining head  70  is delivered with the column  10  along the X 1  axis on the column bed  20  in the direction toward the workpiece  25 . The carriage  15  serves to adjust the height of the machining head  70  in the Z 1  direction or to move the machining head  70  in the axial direction of the workpiece  25 , while the tool generates or machines the teeth.