Patent Publication Number: US-2021178539-A1

Title: Machine tool and machining method

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application is a continuation of international patent application PCT/EP2019/073258, filed on Aug. 30, 2019 and designating the U.S., which international patent application has been published in German language and claims priority to German patent application 10 2018 121 970.9, filed on Sep. 10, 2018. The entire contents of these priority applications are incorporated herein by reference. 
    
    
     BACKGROUND 
     The present disclosure relates to a machine tool and to a method for processing, for instance machining, at least first workpieces and second workpieces that are different therefrom. In certain embodiments, the present disclosure relates to a machine tool comprising at least one tool spindle and at least one workpiece table, which are movable relative to one another along a vertical axis and two horizontal axes, wherein the three axes are oriented orthogonal to one another, in order to machine a workpiece that is clamped on the workpiece table with a tool that is clamped in the tool spindle. In certain embodiments, the present disclosure relates to a machine tool comprising at least one tool magazine, in which a tool set with tools for machining the workpiece is kept in stock, which tools can be selectively clamped in the tool spindle. 
     DE 102 25 143 A1 discloses a conventional machine tool, the machine tool being arranged as a moving column machine and having a vertical tool spindle, which is arranged to change tools according to the pick-up process with a tool magazine, wherein the tool magazine travels together with the moving column along a horizontal axis of movement, and wherein the tool magazine is mounted so that it can be moved along the other horizontal axis of movement in such a way that it can be moved into the working space with its tool change site for the tool change. 
     Since this tool magazine is arranged to travel with the workpiece, the number of storage locations for tools available therein is limited for dynamic reasons. The conventional machine tool according to DE 102 25 143 A1 is therefore equipped with a background magazine, from which tools can also be exchanged with the tool magazine during the machining of a workpiece parallel to the main processing time. 
     When such a conventional machine tool has to be converted from the machining of first workpieces to the machining of second workpieces that are different therefrom, the tools of the tool magazine and, if necessary, of the background magazine are completely or partially exchanged for new tools, for which the machine tool is shut down. This means that a production downtime occurs during such a changeover. 
     With the conventional machine tool, in addition to the production down-time during changeover, it is also a disadvantage that the traveling tool magazine enables a fast tool change, but negatively influences the dynamics due to the higher weight. All this leads to the fact that the productivity achievable with the conventional machine tool, i.e. the throughput of machined workpieces, is often perceived as insufficient. 
     US 2014/0274627 A1 discloses a machine tool that is arranged as a vertical machining center in gantry form, in which a machine frame in the form of a horizontal U encloses a working space, in which a device for clamping workpieces to be machined is mounted so as to be pivotable about a horizontal axis. The vertical tool spindle is mounted on the side walls of the U-shaped machine frame. 
     A tool magazine in circular form is arranged within the machine frame, at which the tool spindle can change tools in accordance with the pick-up process. 
     Below the tool magazine, an identical tool magazine is provided, in which further tools are kept in stock, which can be reloaded between the two tool magazines with the aid of a reloading device that is arranged at an opening of the machine frame, so that the tools, which can be used directly for machining the workpieces, are respectively located in the upper tool magazine, from which they are interchanged to and from the tool spindle in accordance with the pick-up process. 
     The conventional machining center according to US 2014/0274627 A1 enables the machining of diverse workpieces with a large number of tools, but the total number of available tools is limited to the common storage capacity of the two tool magazines. 
     A further disadvantage is that reloading the tools can require time-consuming indexing, i.e. sharing of both tool magazines, in order to move blanks and tools to be loaded or unloaded to the reloading device. This reduces productivity because, as the case may be, after the end of the machining of a workpiece with a tool, it may be necessary to wait until the reloading process is completed before the old tool can be taken off and a new tool can be taken into the tool spindle. 
     Another disadvantage with the conventional machining center is that when converting from machining first workpieces to machining second workpieces, the tools of both tool magazines have to be completely or partially exchanged for new tools, which leads to a production downtime. 
     In view of this, it is an object of the present disclosure to further refine the machine tool mentioned at the outset to improve performance and productivity. 
     It is a further object of the present disclosure to present a machine tool that requires relatively little design effort and that can be manufactured and operated in a cost-efficient manner. 
     It is a further object of the present disclosure to present a machine tool that is suitable for the manufacture of two different types of workpieces, while reducing non-productive times for the changeover between the different types of workpieces. 
     It is a further object of the present disclosure to present a machine tool and a corresponding machining method that facilitate tool storage and management. 
     It is a further object of the present disclosure to present a machine tool and a corresponding machining method that provide a huge number of tools for immediate use in the machining operation without compromising the dynamic behavior of the machine tool. 
     It is a further object of the present disclosure to present suitable and productive machining methods and processes that make use of respective machine tools. 
     SUMMARY 
     In regard of the machine tool, these and other objects are achieved by a machine tool for machining workpieces, comprising at least one tool spindle, at least one workpiece table, at least one first tool magazine, and at least one second tool magazine, wherein the at least one tool spindle and the at least one workpiece table are movable relative to one another along a vertical axis and two horizontal axes to machine a workpiece that is clamped on the workpiece table with a tool that is clamped in the tool spindle, wherein the vertical axis and the two horizontal axes are orthogonal to one another, wherein in the at least one first tool magazine, a tool set is provided that comprises a plurality of tools for machining, wherein the tools can be selectively clamped in the tool spindle, wherein in the at least one second tool magazine, a tool set is provided that comprises a plurality of tools for machining, wherein the tools can be selectively clamped in the tool spindle, and wherein only one tool magazine of the at least one first tool magazine and the at least one second tool magazine is active at a time, so that exclusively the tool set from the respective active tool magazine is used for machining the clamped workpiece. 
     In certain embodiments, there is provided a machine tool for processing, for instance machining, at least first workpieces and second workpieces that are different therefrom, wherein the machine tool comprises at least one tool spindle and at least one workpiece table, which are movable relative to one another along a vertical axis and two horizontal axes, the three axes running orthogonally to one another, in order to machine a workpiece that is clamped on the workpiece table with a tool that is clamped in the tool spindle, and comprising at least one tool magazine, in which a tool set with tools for machining the workpiece is kept in stock, which tools can be selectively clamped in the tool spindle, wherein at least a second tool magazine is provided, from which tools can optionally be clamped into the tool spindle. In certain embodiments, only one tool magazine is active at a time, in such a way that exclusively the tool set from the active tool magazine is respectively used for machining a clamped workpiece. 
     In certain embodiments, the tools from both tool magazines are available immediately and without delay for machining workpieces without having to transfer tools between the two tool magazines. This may reduce the design effort and increases the throughput because, for example, tools can be removed from one or the other tool magazine as required. By way of example, a tool magazine can provide an empty slot for depositing the last tool used and the other tool magazine can provide the new tool for the next machining operation. When changing tools, it is thus not absolutely necessary to wait until the tool magazine has advanced after a previously used tool has been deposited in order to make the tool to be used next available for removal, which is time-consuming, especially with large tool magazines with many storage locations for tools. 
     In certain embodiments, the time required for the changeover from the machining of first workpieces to the machining of second workpieces is significantly reduced. While the first workpieces are being machined with tools from the active tool magazine, the inactive tool magazine can simultaneously be equipped with a tool set for machining the second workpieces. In certain embodiments, for this purpose, all or only some tools at the non-active tool magazine are exchanged. 
     Immediately after machining the last of the first workpieces with tools from the active tool magazine, machining of the second workpieces with the tools from the previously inactive tool magazine can be started. 
     According to another aspect of the present disclosure, there is presented a method for machining first workpieces and second workpieces that are different from the first workpieces, the method comprising the steps of:
         providing a machine tool, comprising:   at least one tool spindle,   at least one workpiece table,   at least one first tool magazine, and   at least one second tool magazine,   wherein the at least one tool spindle and the at least one workpiece table are movable relative to one another along a vertical axis and two horizontal axes to machine a workpiece that is clamped on the workpiece table with a tool that is clamped in the tool spindle,   wherein the vertical axis and the two horizontal axes are orthogonal to one another,   wherein in the at least one first tool magazine, a tool set is provided that comprises a plurality of tools for machining, wherein the tools can be selectively clamped in the tool spindle,   wherein in the at least one second tool magazine, a tool set is provided that comprises a plurality of tools for machining, wherein the tools can be selectively clamped in the tool spindle, and   wherein only one tool magazine of the at least one first tool magazine and the at least one second tool magazine is active at a time, so that exclusively the tool set from the respective active tool magazine is used for machining the clamped workpiece,   machining the first workpieces with the tool set from the active tool magazine of the at least one first tool magazine and the at least one second tool magazine, and   equipping, at the same time, a non-active tool magazine of the at least one first tool magazine and the at least one second tool magazine with a tool set for machining the second workpieces.       

     In certain aspects, the present disclosure also relates to a method for machining at least first workpieces and second workpieces, which are different therefrom, on a machine tool, in which first workpieces are machined with the tool set from an active tool magazine, while at the same time a non-active tool magazine is equipped with a tool set for machining second workpieces. In certain embodiments, the method utilizes a machine tool in accordance with at least one embodiment described herein. 
     In certain embodiments, the tool magazines are arranged side by side. In certain embodiments, the tool magazines are arranged one above the other. 
     In certain embodiments, the arrangement of the tool magazines depends on the space available. In certain embodiments, a terraced arrangement of the tool magazines one above the other offers time advantages during tool changes and increases productivity when tools are selectively removed from one or the other tool magazine. 
     In certain embodiments, the terraced arrangement also offers design advantages when equipping the tool magazines, because automated setup can be performed with a common loading device on both tool magazines. 
     In certain embodiments, each tool magazine has a tool change site, and that either the tool spindle changes tools at the tool change site of the active tool magazine using the pick-up process, or that a tool changer is provided, which changes tools between the tool spindle and the tool change site of the active tool magazine. 
     In certain embodiments, tool changing in accordance with the pick-up process is advantageous from a design point of view, because it does not require a tool changer. However, with the pick-up method, either the tool change site must protrude or be moved into the working space, or the tool spindle must move out of the working space. 
     In certain embodiments, a cover is provided for the tool change site of at least one tool magazine, which cover is closed at least when the respective tool magazine is not active. 
     In certain embodiments, this has the effect that chips or drilling coolant cannot get into the other tool magazine during the tool change at one tool magazine. This means that the tool change sites of the two tool magazines can be arranged, in terms of design, in such a way that fast tool changes are possible, which increases productivity. 
     In certain embodiments, each tool magazine has a tool fitting site, at which tools are exchanged in order to equip the inactive tool magazine completely or partially with new tools for machining a workpiece. In certain embodiments, a loading device is assigned to each tool magazine, by means of which tools can be removed from an inactive tool magazine and/or tools are inserted into an inactive tool magazine at the tool fitting site. In certain embodiments, a common loading device is provided for all tool magazines so that tools can be removed from an inactive tool magazine and/or tools are inserted into an inactive tool magazine at the tool fitting site. 
     In certain embodiments, the currently inactive tool magazine can be equipped with one or more new tools without having to interrupt the machining of workpieces, since these can be machined simultaneously with the tools from the active tool magazine. In this way, the limited storage capacity of the tool magazines can be taken into account. That is, in practice any number of tools are available because each tool magazine can be provided with new tools without any loss of machining time. 
     In certain embodiments, the inactive tool magazine can be provided with a new tool set for machining second workpieces, while at the same time first workpieces are being machined with the tool set from the active tool magazine. This means that there is no interruption in production during the changeover from the machining of first workpieces to the machining of second workpieces, which consequently increases productivity. 
     In certain embodiments, a cover is provided for the tool fitting site of at least one tool magazine, which is closed at least when the tool magazine in question is active. 
     In certain embodiments, during setup at a non-active tool magazine, chips or drilling coolant cannot get out of the active tool magazine and into the non-active tool magazine or contaminate or injure operators. This means that the tool fitting sites of the two tool magazines can be arranged, terms of design, for example in terraces one above the other, so that fast set-up is possible, which may be advantageous from a design point of view and may increase productivity. 
     At least some objects can be achieved in accordance with the present disclosure with machine tools of the different types, for instance involving machines having a moving column and portal-type machines. The present disclosure is does not necessarily limited to a certain specific type of machine tool. In certain embodiments, the tool spindle is arranged on a moving column, on which it is movably mounted along the vertical axis. In certain embodiments, the moving column is movable along at least one of the two horizontal axes, or on a portal beam, on which it is movably mounted along the vertical axis and optionally along one of the two horizontal axes extending parallel to the portal beam. 
     The portal beam can be moved along the other of the two horizontal axes. When, however, the portal beam cannot be moved, the workpiece table can be moved instead along the other of the two horizontal axes. 
     In certain embodiments, during machining of workpieces with tools from an active tool magazine, the cover of the tool change site of the or each non-active tool magazine is closed, wherein the cover of the tool fitting site of the active tool magazine is closed, at least in certain embodiments. 
     In certain embodiments in accordance with the present disclosure, the productivity of the machine tool is increased in a structurally simple manner. 
     It is to be understood that the previously mentioned features and the features mentioned in the following may not only be used in a certain combination, but also in other combinations or as isolated features without leaving the spirit and scope of the present disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further features and advantages of the disclosure are disclosed by the following description of a plurality of exemplary embodiments, with reference to the drawings, wherein: 
         FIG. 1  is a schematic side view showing a simplified illustration of a first exemplary embodiment of a machine tool; 
         FIG. 2  is a schematic front view showing a simplified illustration of the machine tool of  FIG. 1 ; 
         FIG. 3  is a schematic front view showing a simplified illustration of a second exemplary embodiment of a machine tool having tool magazines that are arranged side by side; 
         FIG. 4  is a schematic side view showing a simplified illustration of an embodiment of a machine tool based on the arrangement of  FIG. 2 , the machine tool provided with tool magazines that are arranged one above the other; and 
         FIG. 5  is a schematic top view of an embodiment of a machine tool based on the arrangement of  FIG. 3 , the machine tool comprising a tool changer and a loading device for each of the tool magazines. 
     
    
    
     EMBODIMENTS 
       FIG. 1  shows a schematic side view, not drawn to scale, of a machine tool that is designated in its entirety by the reference numeral  10 . 
     The machine tool  10  has a moving column  12 , which is arranged on a cross member  16  via a first slide guide  14 . The moving column  12  can be moved by means of the first slide guide  14  on the cross member  16  in the direction of an axis, which is usually referred to as the y-axis and is symbolically shown here by an arrow  18 . It is understood that the moving column  12  is moved on the first slide guide  14  by means of a motor, wherein a corresponding drive unit is not shown here for clarity reasons. 
     The cross member  16  is mounted on a machine frame  22  via a second slide guide  20 . The second slide guide  20  enables movement of the cross member  16  along a second axis, which is shown here at reference numeral  24 . The reference numeral  24  designates the so-called X-axis. It is understood that the movement of the cross member  16  on the second slide guide  20  is also performed with the aid of a suitable drive unit, which is not shown here for clarity reasons. 
     A spindle head  25  having a tool spindle  26 , which is rotatably mounted therein, is suspended vertically on the moving column  12 . At its lower end, the tool spindle  26  comprises a spindle holder  28 , in which a tool holder  29  having a tool  30  attached thereto can be clamped in a generally known manner. Typically, the tool holder is standardized and of the steep taper (SK) or hollow shank taper (HSK) type. The tool spindle  26  is configured to rotate the tool  30  about its spindle axis  32 , which is shown by an arrow  34 . Typically, the tool spindle  26  is capable of rotating the machining tool  30  at several thousand revolutions per minute, for instance for drilling and milling workpieces made from metal material. 
     The tool spindle  26  can be moved on the moving column  12  along the direction of an arrow  36 , i.e. here in the vertical direction, by means of a drive unit, which is also not shown herein, and which can be arranged as a ball screw or linear direct drive. Accordingly, the tool spindle  26  is mounted on the moving column  12  via a third slide guide  38 . The movement of the tool spindle  26  in the direction of the arrow  36  is typically referred to as the Z-axis. Typically, the three slide guides  14 ,  20  and  38  for the three axes of movement  18 ,  24 ,  36  are orthogonal to each other. 
     Reference numeral  40  designates a workpiece table that is mounted on the machine frame, on which a workpiece  42  to be machined is clamped. Reference numeral  44  designates a housing which encloses the components of the machine tool  10  described hereinbefore. Further, the reference numeral  46  designates a machine control, by means of which any movement of the machine tool  10  as well as auxiliary units (coolant supply, compressed air, and the tool magazine described below) are controlled. 
     Hence, that machine tool  10  is a moving column machine having a vertical tool spindle  26 , in which all three axes of movement  18 ,  24 ,  36  are implemented in the tool  30 . It is also possible to relocate one or both of the horizontal axes of motion  18 ,  24  in the workpiece table  40  in the machine tool of  FIG. 1 . In addition, instead of a vertically aligned tool spindle  26 , the machine tool  10  can also have a horizontally aligned tool spindle. 
     During the machining of the workpiece  42 , different tools  30  are used, which are kept in stock as a tool set  49  in a first tool magazine  50  shown only rather schematically in  FIG. 1 . 
     For the tool change, the moving column moves to the rear in the y-direction  18 , i.e. in  FIG. 1  to the right. The tool spindle  26  is now above the tool magazine  50 , in which a blank slot is provided, into which the tool spindle  26  now places the tool holder  29  with the tool  30  that was previously in use by movement along the vertical movement axis  36 . Then the tool magazine  50  advances and moves an equipped magazine slot into the transfer position below the tool spindle  26 , in which a tool holder  29  with a tool  30  now intended for use is located. 
     In the alternative, after depositing the “old” tool  30 , the moving column  12  can also approach an equipped magazine slot of the first tool magazine  50 , in which the tool holder  29  with the tool  30  now intended for use is located. 
     In both cases, the tool spindle  12  then picks up a new tool  30  by moving again along the vertical axis of motion  36 . This type of tool change is referred to as pick-up process. 
     Different tools  30  can thus be moved one after the other into a working space that is designated by  48  in order to machine a variety of first workpieces  42  there, one after the other, with the tools  30  from the first tool set  49 . 
     When second workpieces  42  that are different from the first workpieces  42  are to be machined on the machine tool  10 , tools  30  are generally required for this purpose, which are at least partially different from the tools  30  with which the first workpieces  42  were machined. 
     With conventional machine tools, then all or some of the tools  30  in the tool set  49  are replaced, resulting in extended production downtime on conventional machine tools as they are converted from machining first workpieces  42  to machining second workpieces  42 . 
     The machine tool  10  of  FIG. 1  is therefore equipped with a second tool magazine  52 , in which a second tool set  53  is kept in stock, the tools  30  of which are used to machine the second workpieces  42 , as can be seen in the schematic and sectional front view of the machine tool  10  in  FIG. 2 . 
     Consequently, as soon as the machining of the first workpieces  42  is completed, the machining of the second workpieces  42  can be started immediately because the second tool magazine  52  is already ready with a second tool set  53 . 
     The loading or equipping of the second tool magazine  52  with the second tool set  53  takes place during the period, in which the first workpieces  42  are being machined with the first tool set  49  from the first tool magazine  50 , which is active during this period. 
     While the second workpieces are now being machined with the tools  30  from the second, now active tool magazine  52 , the first tool set  49  in the first, no longer active tool magazine  50  can be renewed. On the one hand, this may involve that all tools  30  of the first tool set  49  are replaced, or that only some tools  30  are replaced. 
     In this way, the downtimes of the machine tool  10  are reduced to a considerable extent, because the setting-up of the respective non-active tool magazine  50 ,  52  can already take place during the machining of workpieces  42  with tools  30  from the active tool magazine  50 ,  52 . 
     Of course, it is possible to provide more than two tool magazines  50 ,  52  in the machine tool  10 . 
     If more tools  30  are needed to machine a workpiece  40  than can be stored in a tool magazine  50 ,  52 , the tools from both tool magazines  50 ,  52  can also be accessed. 
       FIG. 3  shows another exemplary embodiment of the machine tool, which is designated by the reference number  100  and is arranged as a portal machine. The reference signs from  FIGS. 1 and 2  are used for identical components. 
     The machine tool  100  of  FIG. 3  comprises a portal beam  55  that is arranged on two cheeks  56  and that extends along the direction of the second axis of motion  24 . The portal beam  55  is either fixedly mounted on the cheeks  56  or is mounted for movement on the cheeks  56  along the direction of the first axis of movement  18 . If the portal beam  55  is fixedly mounted on the cheeks  56 , the first axis of movement  18  is implemented in the workpiece table  40 . 
     The spindle head  25  is mounted on the portal beam  55  for movement along the direction of the vertical axis of movement  36 . The spindle head  25  is further movable along the portal beam  55  along the direction of the second axis of movement  24  so that the tool  30  received in the tool spindle  26  and the workpiece  42  can be moved relative to each other angle all three orthogonal spatial axes  18 ,  24 ,  36 , commonly referred to as X, Y and Z axes. 
     Below the portal beam  55 , the first tool magazine  50  with the first tool set  49  and the second tool magazine  52  with the second tool set  53  are arranged in the working space  48 . 
     As with the machine tool  10  from  FIGS. 1 and 2 , the tool change is also carried out here in accordance with the pick-up method. 
     While the first tool magazine  50  is active, and first workpieces  52  are being machined with the first tool set  49  kept in stock therein, the second tool set  53  can again be renewed in the second tool magazine  52 . 
     While  FIGS. 1 to 3  show the tool magazines  50 ,  52  arranged side by side,  FIG. 4  shows the machine tool  100  of  FIG. 3  in an embodiment with tool magazines  50 ,  52  that are arranged one above the other. 
     As a further modification compared to the exemplary embodiment of  FIG. 3 , the workpiece table  40  is arranged here as a swivel table, which can be swiveled about a direction oriented parallel to the second axis of movement  24 . Furthermore, in a generally known manner, it is also further possible to rotate or move the workpiece  42  about a vertical axis, which is parallel to the vertical axis of movement  36 . 
     The workpiece change also takes place in the two tool magazines  50 ,  52 , which are arranged in terraces one above the other, using the pick-up process. The first tool magazine  50 , which is located at the bottom, protrudes with its tool change site  58  at the bottom beyond the upper tool magazine  52 , so that the tool spindle  26  can deposit tools  30  in and remove them from both the first and the second tool magazines  50 ,  52 . 
     In order to protect the tools  30  in the inactive first tool magazine  50  from the entry of contaminants, a cover  59  is provided at its tool change site  58 , which can be opened or closed automatically. 
     In the illustrated embodiment, the second tool magazine  52  is active, so that the cover  62  is open at its tool change site  61  so that the tool spindle  25  can exchange tools  30  with the second tool magazine  52 , which is currently active. The cover  62  can remain open while the workpieces  42  are being machined, or it can be closed again after each tool change. 
     The tool magazines  50 ,  52  are equipped, i.e. the tool magazines  50 ,  52  are loaded with a new tool set  49 ,  53 , at the rear side of the tool magazines  50 ,  52 , where they each have a tool fitting site  65 ,  63  with a cover  66 ,  64 . 
     The tool change sites  58 ,  61  and the tool fitting site  63 ,  65  are formed by openings in housings of the tool magazines  50 ,  52 , which are closed by the covers  59 ,  62 ,  64 ,  66  and are released when required. 
     While the tool fitting site  65  is closed by the cover  66  in the case of the active tool magazine  52 , the tool fitting site  63  is open in the case of the non-active tool magazine  50 , and the cover  64  has been pushed aside so that the tool set  49  can be renewed. 
     The lower tool magazine  50  also projects beyond the upper tool magazine  52  at the tool fitting site  63  at the bottom. Nevertheless, the arrangement is such that both tool magazines  50 ,  52  can store up to eighty tools  30  in a tool set  49 ,  53 . In general, eighty tools  30  are sufficient to machine the workpieces  42 . 
     A loading device  67  is provided behind the terraced tool magazines  50 ,  52 , which exchanges tools  30  between the inactive tool magazine  50  and a background magazine  71 , which is only shown schematically, by means of a tool gripper  68 , which can be moved both horizontally and vertically on a column  69 . 
     From the background magazine  71 , the tool set  49 ,  53  of the respective non-active tool magazine  50 ,  52  can in this way be completely or partially renewed by means of the loading device  67 , while the tool set  49 ,  53  of the active tool magazine  50 ,  52  is used to machine workpieces  42 . 
     While a common loading device  67  is provided for both tool magazines  50 ,  52  in  FIG. 4 , a separate loading device  67  may also be provided for each tool magazine  50 ,  52 , as illustrated in  FIG. 5 , which shows a schematic top view of the machine tool  100  of  FIG. 3 . 
     Incidentally, the tool magazines  50 ,  52  are chain magazines with tools  30  that are circulating in a loop, which is schematically indicated in  FIG. 5 . 
     In deviation from  FIG. 3 , the tool change to the tool spindle  26  is also performed here via tool changer  72 , wherein a tool changer  72  is provided for each tool magazine  50 ,  52 . The tool changer  72  is shown only schematically. Like the loading device  67 , it may comprise a tool gripper, which moves via a suitable mechanism between the tool change site  58 ,  61  on the respective tool magazine  50 ,  52  and a changing position, in which it offers a received tool  30  to the tool spindle  26  or receives a used tool  30  therefrom in order to deposit it in the tool magazine  50 ,  52 . 
     In the machining state shown in  FIG. 5 , the tool magazine  50  is active, the tool fitting site  63  is closed and the tool change site  58  is open. In the case of the inactive tool magazine  52 , the tool change site  61  is closed and the tool fitting site  65  is open. 
     While in the tool magazines  50 ,  52  of  FIG. 4 , the tool change takes place from above, i.e. the covers  59 ,  62 ,  64 ,  66  rest on top of the housing of the tool magazines  50 ,  52 , the tool change according to  FIG. 5  takes place via the front sides of the housings.