WORKPIECE RECEIPT UNIT FOR A MACHINE TOOL, ESPECIALLY IN A MACHINING CENTER

Description

[0001] The invention relates to a machine tool with a workpiece holding unit, in particular a machining center according to the preamble of the first patent claim.

[0002] Steering knuckles are currently machined on two different types of machines. Horizontal or vertical lathes are used to turn the journal. Milling and drilling operations on these machines are only possible to a very limited extent, if at all. Therefore, further processing of these steering knuckles takes place on machining centers.

[0003] DE 76 08 591 U discloses a double-spindle vertical lathe, which has two tailstocks at the top and two turning spindles at the bottom. The frame consists of two essentially rectangular lateral cheeks, which are connected by an upper part of the same width, thus creating a portal shape. The frame structure used here is suitable for machining fully rotationally symmetrical workpieces, where low forces arise from the imbalance of the workpieces. The narrow lateral cheeks offer only a small surface for a stable connection to the upper part. In the side view of the Fig. 2It can be seen that the tailstock sleeves, which are integrated into the upper part 3, project far from the vertical cheeks over the lathe chuck. In the case of high forces and heat input into the frame, bending of the tailstock sleeves can lead to deviations in the shape of the workpiece. From the publication CH 712 442 A1, a gear machining center with a centering device is known, which is used for machining pre-toothed workpieces. A workpiece carrier in the form of a rotary table or according to Figure 2 a rotating turret. The workpiece carrier is pivotable about a vertical workpiece carrier axis and comprises a counter-support in the form of a superstructure. Two workpiece spindles are arranged on the workpiece carrier, which are diametrically opposite each other with respect to the workpiece carrier axis. Each of the workpiece spindles defines a workpiece spindle axis ( Fig. 3 ).

[0004] The workpiece spindles can be pivoted between a working position and a parking position using the workpiece carrier. In the working position, the respective workpiece spindle is located in a work area. In the parking position, the respective workpiece spindle is located in a handling area. The axis of the swivel table and the axis of the workpiece spindles are therefore not aligned. This allows only small drives and workpiece carriers to be implemented, which are sufficient for high-precision grinding with low process forces. The guide and drive of the counterholder center are apparently not arranged on the same axis. Higher forces, including thermal forces, can lead to inaccuracies in the workpiece.

[0005] DE 43 22 918 C1 describes a machining center that uses a tailstock. Here, the servomotor for adjusting the spindle sleeve is located next to the center point, which does not provide a good flow of force and is also only suitable for absorbing low process forces.

[0006] Powerful drives and a robust frame structure, which are necessary for turning and milling highly unbalanced workpieces, cannot be implemented this way. Furthermore, the off-center force introduction (difference between the swivel axis and the workpiece axis) has a detrimental effect on force introduction and thus on accuracy.

[0007] Another disadvantage is that the pivoting workpiece carrier has to support not only the weight of the workpiece and the weight of the workpiece spindles, but also the weight of the counter-bearing, which means that the bearing and the rotary / swivel motor must be designed accordingly high to realize the swivel movement.

[0008] Such a structure is not suitable for realizing a linear adjustment movement, e.g. as with a feed axis.

[0009] A column extends across the machine bed as a tool carrier, which can be moved horizontally toward the workpiece carrier and supports a vertically movable tool slide with a grinding worm. Turning is therefore not possible on this machine.

[0010] Document EP 1 155 771 A2 discloses a machine tool with a workpiece holding unit. The machine tool comprises a machine bed and a carriage assembly movable in the Z direction on the machine bed, as well as a rotary table mounted on the carriage assembly with a clamping unit for a workpiece. A column extends vertically on the machine bed, on which a machining tool can be moved in a vertical Y direction and a horizontal X direction.

[0011] From the document DE 10 2013 007 670 A1 a rotary table with a lateral counter support for horizontally clamping the workpiece at the second end is known.

[0012] The object of the invention is to develop a machine tool with a workpiece holding unit which is suitable for both asymmetrical workpieces with rotationally symmetrical workpiece contours and for fully rotationally symmetrical workpiece contours, in which workpieces can be machined using the turning manufacturing process and thus to enable process optimizations for complete production lines with one machine system.

[0013] This problem is solved by the characterizing features of the first patent claim.

[0014] Advantageous embodiments arise from the subclaims.

[0015] In this case, a machining center with a machine bed has a workpiece receiving unit in the form of a carriage assembly movable in the Z-direction on the machine bed and a rotary table mounted on the carriage assembly, and wherein a vertically extending column is arranged on the machine bed with a machining tool mounted on the column in a tool holder, which machining tool can be moved on the column in a horizontal X-direction and in a vertical Y-direction (as in the case of the Figure 1 shown prior art), wherein a first receiving surface and a second receiving surface are arranged on the carriage assembly movable in the Z direction in the X direction on both sides of the rotary table and a superstructure is arranged on the first receiving surface and the second receiving surface, which superstructure extends upwards and over the rotary table and has means for fixing the workpiece W.

[0016] The superstructure is supported by a vertically extending first support on the first receiving surface and by a vertically extending second support on the second receiving surface, wherein a cross member is supported or rests on the upper ends of the first and second supports and a centering point that is vertically adjustable by means of a servomotor is arranged centrally in the cross member of the superstructure for additional fixing of the workpiece, wherein the workpiece can be clamped between the clamping unit mounted on the rotary table and the centering point.

[0017] The arrangement of the superstructure with centering point (in the manner of a tailstock) on the slide assembly makes it possible to pick up and machine the workpiece vertically, preferably by turning.

[0018] This also makes it possible to machine asymmetrical workpieces, which sometimes generate a large imbalance, since the superstructure can absorb these forces.

[0019] The cross member rests with its two end undersides on the upper ends of the first and second beams and then extends upwards in a mirror image from each underside at an angle or in an arc.

[0020] The centering point is preferably mounted by means of a sleeve in the middle of the cross member and in particular above the underside of the cross member.

[0021] The centering point is preferably located in its central vertically extended position essentially in the area of ​​the undersides of the cross member or just slightly below the upper ends of the vertical members.

[0022] Advantageously, the respective two-sided receiving surfaces of the slide assembly for receiving the two vertical supports are located essentially above the guides of the slide assembly for its mobility on the machine bed, as this allows the forces to be absorbed better.

[0023] The clamping unit mounted on the rotary table can be, for example, a drive or jaw chuck, particularly one with an integrated, adjustable centering point. A three-jaw chuck with a centering point is preferred.

[0024] The workpiece can be clamped vertically between the center point of the three-jaw chuck and the center point of the tailstock-like superstructure.

[0025] Furthermore, the workpiece can be brought into the machining position with the centering point and fixed in this position.

[0026] Preferably, the centering point is designed in the form of a rotating point and is arranged in a sleeve so that it can be changed.

[0027] The vertical axis of rotation of the clamping unit and the longitudinal axis of the centering tip should be aligned with each other.

[0028] The superstructure is designed to be symmetrical or substantially symmetrical in the X-direction and / or Z-direction with respect to its vertically extending central axis. Advantageously, the superstructure is reduced symmetrically or substantially symmetrically in its length and / or width from bottom to top, thereby reducing weight.

[0029] With the machine tool according to the invention, the turning of workpieces clamped in a vertical direction in the form of pins, steering knuckles or other rotationally symmetrical components and also not completely rotationally symmetrical components can be realized for the first time.

[0030] The subject of the patent application is a yoke-shaped superstructure which is movable with a slide assembly and stationary on the slide assembly and which has a rotating turntable which is equipped with a sleeve arranged opposite the turntable, in particular with a centering point or possibly a conical holder, which enables turning and milling in jaw chucks and between the centering points in driving chucks.

[0031] The workpiece holding unit is designed so that the sleeve is symmetrically integrated into the frame structure. This prevents any deviation in the workpiece's shape due to slight bending, as is the case with designs with lateral guidance of the sleeve (see, for example, the aforementioned utility model DE 76 08 591 U). Thermal influences lead to symmetrically uniform expansion and thus do not cause deviations in the workpiece's shape.

[0032] The symmetrically stable frame construction is also suitable for absorbing high forces, which occur, for example, during the turning of asymmetrical workpieces with rotationally symmetrical geometric components, such as steering knuckles.

[0033] Rotationally symmetrical workpieces with forged, cast or machined center holes can be accommodated between two center points via the stroke of up to 160 mm of the quill of the superstructure and thus of the centering point.

[0034] One center point is located in the clamping unit on the rotary table, the other on the superstructure which acts like a tailstock.

[0035] The workpieces are held at the bottom in a self-centering or jaw chuck. Centering of the workpiece is achieved in the jaw chuck by the uniform closing of the jaws, or in the self-centering chuck by an adjustable centering point integrated into the chuck.

[0036] The workpiece is brought into the machining position using the live center located at the top of the quill. Different workpiece lengths can be compensated for, for example, using a position measuring system in the quill. The live center in the quill is preferably replaceable.

[0037] During machining, the workpieces are additionally clamped radially (drive chuck) or with center-alignment (jaw chuck). The position of the workpiece's rotational axis is determined by the two centers. Radial alignment in drive chucks is achieved via a fixed stop in the chuck.

[0038] The power transmission for the turning process takes place via the fixed system in the driving chuck or the compensating tension in the jaw chuck.

[0039] For example, a spindle flange with a short taper 11, according to DIN ISO 702-I A2, with integrated media transfer for air and hydraulics serves to mount the chuck. During machining, coolant nozzles located in the superstructure in the form of the counterholder with the appropriately directed coolant outlet serve for process cooling and lubrication and for chip removal.

[0040] The loading and unloading of the workpieces can be done manually, using an articulated arm robot or via a loading / unloading unit.

[0041] During the machining process, the machine's control system, via the safety technology in the yoke-shaped superstructure, prevents the clamping mechanism from opening and the associated ejection of workpieces. This ensures safe workpiece clamping.

[0042] All process steps can be performed on a single machine system. Both turning and milling operations can be performed in a single machining line on virtually identical machines.

[0043] The roughing and finishing of the flange surfaces on the steering knuckle is now carried out by the new workpiece holding unit, preferably by roller milling.

[0044] This avoids the time-consuming rough turning of the flange surfaces by turning, especially in the case of interrupted cuts, which often have a high tendency to chatter or vibration and the associated tool wear. Alternatively, finishing can be performed with turning tools.

[0045] Advantageously, a change of the tool cutting edges during machining is possible by using sister tools, provided there is a sufficient tool magazine.

[0046] By using machining centers for turning, the often limited tool magazine or tool turret on lathes can be replaced with magazines containing multiple sister tools. Machining lines can thus operate autonomously for longer, without operator intervention.

[0047] By exchanging used tools from the tool magazine during machining, the machining center provides the prerequisites for fully automated tool supply during ongoing machining. Using a well-established wear monitoring system, used tools can be replaced automatically during machining.

[0048] With the existing yoke-shaped superstructure, the turning of the journal of, for example, steering knuckles or other rotationally symmetrical components that can be clamped between the centers is possible on a machining center.

[0049] By using the workpiece holding unit with a superstructure in the form of a tailstock in a complete machining line with almost identical machines, advantages such as the same loading and unloading, control, operating elements, automation, accessories such as chip conveyors, coolant systems, extraction systems and much more can be utilized.

[0050] The component is positioned vertically during transport and at the start of processing, thus offering advantages for automation and the transport of workpieces within a processing line. Loading and unloading of the machines takes place via identical loading hatches. The machine concept, with the almost identical machines, enables a compact system layout.

[0051] Maintaining machines of the same type is easier and more cost-effective. Stocking spare parts is only necessary for one machine type. Service and preventive maintenance only need to be scheduled for one machine system from one manufacturer.

[0052] The safety and control technology is the same at all processing stations in complete production lines. Digital transformations, as well as process control and optimization, can be carried out on a unified system. Training requirements for the entire system and individual machines are reduced to a minimum. The consistent machine system from a single manufacturer limits the training requirements for operating, programming, maintenance, and repair personnel to a single system.

[0053] The invention is explained in more detail below using an exemplary embodiment with reference to the drawings. They show: Figure 1 shows a basic structure of a machine tool or a section of a machining center according to the state of the art, Figure 2 shows the slide assembly with workpiece in 3D view, Figure 3 shows the slide assembly without workpiece and without three-jaw chuck in 3D view, Figure 4 shows the front view according to Figure 2 , Figure 5the side view according to Figure 2 , Figure 6Representation according to Figure 2 , but without the servomotor cover, Figure 7 the individual representation of the tailstock / superstructure with uncovered counterholder, Figure 8 the individual representation of the slide assembly with rotary table, Figure 9 the schematic representation of a machine tool with the slide assembly 2 with superstructure 10 mounted on the bed 1.

[0054] Figure 1shows the basic structure of part of a prior art machine tool / machining center. This includes a machine bed 1, a carriage assembly 2 movable in the Z direction on the machine bed 1, a rotary table 3 mounted on the carriage 2, a column 4, and a rotating machining tool 5.1 rotatably mounted on the column 4 along a vertical axis 5. This rotating machining tool 5.1 is in this case a milling tool that can be moved on the column 4 in a horizontal X direction and in a vertical Y direction. A pallet 3.1 is mounted on the rotary table 3 and serves to clamp the workpiece (not shown) to be machined. A tool magazine 6 and a tool changer 7 are also provided.

[0055] The insertion and removal of a workpiece is realized by changing the pallet 3.1 with a workpiece changer 8.

[0056] For turning the outer contour of a workpiece, a non-rotating tool is required. Typically, the workpiece is held between two centers and rotated, which is not provided for in the current state-of-the-art machining center.

[0057] For the realization of a vertical turning machining of a workpiece W in a machining center, a workpiece holding unit according to the invention is provided, which is Figures 2 to 8 in various representation variants (partly without workpiece W).

[0058] Stand, tool and machine bed are in the Figures 2 to 8 not shown.

[0059] On the rotary table 3 of the machining center, a clamping unit 9 is provided for a first end of a workpiece W (see Figures 2 , 4 , 5 ).In particular, the workpiece W is held at the bottom of the rotary table 3 in a driving or jaw chuck, e.g. a three-jaw chuck 9 (preferably with a centering point).

[0060] Furthermore, on the Z-direction on the machine bed 1 (only in Figure 9 A vertically extending superstructure 10 with vertically extending and mutually aligned supports 10.1a and 10.1b is arranged on both sides of the rotary table 3 above the two guides 2.1 of the slide assembly 2 (shown). For this purpose, a first receiving surface 2a and a second receiving surface 2b are arranged on the slide assembly 2 on both sides of the rotary table 3.

[0061] The receiving surfaces 2a and 2b extend in the direction of the guides 2.1 and thus in the Z direction.

[0062] Here, the superstructure 10 is arranged on the first receiving surface 2a and the second receiving surface 2b, which extends upwards and over the rotary table 3 and has means for fixing the workpiece W. A carrier 10.1a of the superstructure 10 is supported on the first receiving surface 2a and a second carrier 10.1b is supported on the second receiving surface 2b of the carriage assembly 2.

[0063] A cross member 10.2 rests on the upper end of the two beams 10.1a and 10.1b. A vertically adjustable centering point 11 is located in a sleeve 11.1 in the center of the cross member 10.2 of the superstructure 10. A servomotor 12 is incorporated into the cross member 10.2 to implement this adjustment movement.

[0064] The cross member 10.2 rests with its two undersides 10.2.1 on the upper ends of the supports 10.1a and 10.1b and then extends upwards at an angle a, mirror-inverted from each underside 10.2.1. As a result, the fastening / bearing in the form of the sleeve 11.1 of the centering point 11 is located centrally in the cross member 10.2 and above the undersides 10.2.1 of the cross member 10.2. In its central, vertically extended position, the centering point 11 is located essentially in the area of ​​the undersides 10.2.1 of the cross member 10.2, or just slightly below the upper ends of the vertical supports 10.1a and 10.1b.

[0065] Due to the upwardly "curved" or centrally upwardly extending supporting structure of the cross member 10.2 of the superstructure 10, higher axial forces can be absorbed than with a straight extension.

[0066] The unmarked dimensions within the superstructure 10, in particular the (unmarked) height between the centering point 11 and the clamping unit 9, depend largely on the dimensions, in particular the height of the workpiece W to be machined.

[0067] In the Figures 2 to 6 the superstructure 10 is shown with a cover 13 of the actuator 12, which is attached to the cross member 10.2 and conceals the actuator 12 in these representations.

[0068] In the Figures 6 and 7 The cover 13 of the actuator 12 is not shown and it is evident that it extends upwards centrally over the cross member 10.2. Figure 6 the entire workpiece holding unit and Figure 7 only the superstructure 10.

[0069] In Figure 4It was indicated that the vertical axis of rotation of the clamping unit A1 (e.g. a three-jaw chuck with centering point) and a longitudinal axis A2 of the centering point 11 as well as the longitudinal axis AW of the workpiece W are aligned with each other.

[0070] The superstructure 10 is symmetrical in the X-direction with respect to its vertically extending axis AY, with which the rotational axis of the clamping unit A1 and the longitudinal axis of the centering point A2 are also aligned (see Figure 4 ) and in Z-direction (see Figure 5 ) executed.

[0071] For example, Figure 6 It can be seen that the opening (working space) formed by the inner sides of the vertical supports 10.1a, 10.1b has a width which decreases upwards towards the underside 10.2.1 of the cross member 10.2 to a smaller width.

[0072] It can be seen that the superstructure 10 has a length L1 in the lower area of ​​the vertical supports 10.1a, 10.1b and it is evident that the length of the superstructure 10 is reduced towards the top, namely to a length L2 in the area of ​​the contact surfaces between the vertical supports 10.1a and 10.1b and the cross member 10.2 and that the cross member 10.2 is reduced to a length L3 in the direction of the receiving area of ​​the sleeve 11.1.

[0073] The width b1 of the vertical supports 10.1a, 10.1b is increased by an inward-facing projection / bevel 10.1.2 to a width b2 in the area of ​​the support surfaces or underside 10.2.1 of the cross member 10.2. This gives the cross member 10.2 a large support surface.

[0074] The cross member 10.2 extends upwards in a substantially prismatic shape, with regions 10.2.2 angled obliquely upwards from the outside to the inside being present on both sides and an upper central and horizontally extending region 10.2.3 of the cross member 10.2 being arranged between them for receiving the sleeve 11.1 for receiving the centering tip 11.

[0075] The superstructure 10 has according to Figure 6 a height H and the working space for clamping and machining the workpiece (not shown here) is located in the central free space of the superstructure 10 above the rotary table 3 and within the vertical supports 10.1a and 10.1b and the cross support 10.2.

[0076] In Figure 8 The slide assembly 2 is shown with the rotary table 3. The slide assembly 2 is mounted on the machine bed 1 via guides 2.1 (see Figure 9 ) movable in the Z-direction.

[0077] The workpiece holding unit with the rotary table 3 and the superstructure 10 is thus mounted on the machine bed 1 ( Figure 9 ) arranged adjustable in the Z direction via the slide assembly 2.

[0078] The carriage assembly 2 has mutually parallel support surfaces 2a, 2b on both sides of the turntable 3, which serve to receive the superstructure 10, which is positioned thereon with the lower surfaces 10.1.1 of the supports 10.1a and 10.1b.

[0079] The support surfaces 2a, 2b of the carriage assembly 2 are essentially located above the guides 2.1 and are aligned in the Z direction.

[0080] The workpiece W is clamped between the three-jaw chuck 9 and the centering point 11 (see Figures 2 and 4 ).

[0081] The machining space is formed between the sides of the supports 10.1a and 10.1b and the cross support 10.2 facing towards the workpiece W.

[0082] In Figure 9 a machine tool in the form of a milling machining center is shown.

[0083] This has a machine bed 1, which supports a slide assembly 2 that can be moved in the Z direction. The superstructure 10 is arranged on the receiving surfaces 2a, 2b of the slide assembly 2 and extends upwards and over the rotary table 3 like a bridge. The sleeve and the centering point of the superstructure 10 are not visible here. A column 4 is arranged fixed to the frame on the machine bed 1. The column 4 has a rotating machining tool 5.1, in this case a milling tool, which, as in the prior art, can be moved on the column 4 in a horizontal X direction and in a vertical Y direction. A pallet (not shown) is usually held on the rotary table 3, which is used to clamp the workpiece (not shown) to be machined, or the workpiece is clamped in a three-jaw chuck (also not shown here) held on the rotary table 3.A tool magazine 6 and a tool changer 7 are also provided.

[0084] The insertion and removal of a workpiece is carried out by a handling device (not shown) located outside the machine.

[0085] For machining a workpiece (in Figure 9 (not shown) the superstructure 10 is positioned in front of the column 4, and the machining tool 5.1, which can be moved in X and Y directions on the column 4, engages in the machining space for machining the workpiece. The tool (a turning tool / turning chisel for turning) does not rotate, but rather the workpiece is set in a rotary motion by means of the rotary table 3.

[0086] Due to the vertical alignment of the workpiece between the clamping on the rotary table 3 and the centering point 11, it is possible to subject it to turning on a milling machining center if a turning tool is used as the tool.

[0087] When using a milling tool as a machining tool 5.1, as in Figure 1 As shown, milling of the workpiece is of course also possible, preferably in the same clamping setup.

[0088] The feed movement of the workpiece W in the direction of the machining tool 5.1 is carried out via a movement of the slide assembly 2 with the workpiece holder (rotary table 3, clamping unit 9 and superstructure 10) in the Z direction - ie in the direction of the column 4.

[0089] The centering point 11 acts with a counterforce in the direction of the clamping unit 9 on the rotary table 3 to securely clamp the workpiece W.

[0090] To reduce weight, the vertical supports 10.1a and 10.1b have unmarked recesses.

[0091] Furthermore, it is advantageous that the length and width of the superstructure 10 are reduced from bottom to top symmetrically or essentially symmetrically from a length L1 to a length L3 and from a width B1 to a width B2.

[0092] A significant advantage of the solution according to the invention in the form of the workpiece carrier or the workpiece holding unit is that it is constructed completely axially symmetrically, ie from the workpiece table / rotary table 3 via the sleeve 11.1 with centering point 11, to the guide and the drive of the sleeve 11.1, everything is in one axis. List of reference symbols

[0093] 1Machine bed 2Slide assembly 2.1Guides 2aFirst mounting surface 2bSecond mounting surface 3Rotary table 3.1Pallet 4Stand 5Axis 5.1Machining tool 6Tool magazine 7Tool changer 8Workpiece changer 9Clamping unit / three-jaw chuck (preferably with centering center) 10Superstructure 10.1aFirst support 10.1bSecond support 10.1.1Lower surface 10.1.2Slopes 10.2Cross member 10.2.1Underside of the cross member 10.2.2Sloped areas of the cross member 10.2.3Horizontal area of ​​the cross member 11Centering center 11.1Quill 12Servo motor 13Cover aAngle on the cross member A1Rotational axis of the clamping unit A2Longitudinal axis of the centering center AYAxis of the superstructure AW Longitudinal axis of the workpiece b1Width of the vertical supports at the bottom b2Width of the vertical supports at the top B1Width of the superstructure B2Width of the cross member at the top HHeight of the superstructure L1Length of the supports at the bottom L2Length of the supports at the top L3Length of the cross member in the area of ​​the quill WWorkpiece

Claims

1. Machine tool, in particular a machining center, having a workpiece receiving unit, wherein the machine tool has a machine bed (1) and a carriage assembly (2) that can be moved in the Z-direction on the machine bed (1), and a rotary table (3) that is accommodated on the carriage assembly (2) and has a clamping unit (9) for a workpiece (W), and having a vertically extending stand (4) on the machine bed (1) and a machining tool (5.1) mounted on the stand (4), which tool can be moved on the stand (4) in a vertical Y-direction and in a horizontal X-direction, characterized in that a first receiving surface (2a) and a second receiving surface (2b) are arranged on the carriage assembly (2), which can be moved in the Z-direction, on both sides relative to the turntable (3), and in that a superstructure is arranged on the first receiving surface (2a) and the second receiving surface (2b), which extends upwards and over the turntable (3) and has means for fixing the workpiece (W).

2. Machine tool according to claim 1, characterized in that the superstructure (10) is supported by a vertically extending first beam (10.1a) on the first receiving surface (2a) and by a vertically extending second beam (10.1b) on the second receiving surface (2b), wherein a crossbeam (10.2) is supported on the upper ends of the first and second beams (10.1a, 10.1b) and a centering tip (11) that is vertically adjustable by means of a servomotor (12) is arranged in the center of the crossbeam (10.2) of the superstructure (10) for the additional fixing of the workpiece (W), wherein the workpiece (W) can be clamped between the clamping unit (9) received on the turntable (3) and the centering tip (11).

3. Machine tool according to claim 2, characterized in that the crossbeam (10.2) rests with its two lower sides (10.2.1) on the upper ends of the beams (10.1a, 10.1b) and then extends in a mirror-inverted manner upwardly at an angle (a) from each lower side (10.2.1).

4. Machine tool according to one of the preceding claims, characterized in that the carriage assembly (2) is mounted on the machine bed (1) via guides in the Z-direction and the first bearing surface (2.a) and the second bearing surface (2b) of the carriage assembly (2) for accommodating the beams (10.1a and 10.1b) are arranged essentially above the guides (2.1) of the carriage assembly (2).

5. Machine tool according to one of the preceding claims 2-4, characterized in that the clamping unit is a drive or jaw chuck with an alignable centering tip integrated in the chuck, in particular a three-jaw chuck (9) with a centering tip, and in that the workpiece (W) can be clamped between the centering tip of the three-jaw chuck and the centering tip (11) of the superstructure (10).

6. Machine tool according to one of the preceding claims 2-5, characterized in that the workpiece (W) can be brought into the machining position by means of the centering tip (11).

7. Machine tool according to one of the claims 2-6, characterized in that the centering tip (11) is designed in the form of a revolving center and is exchangeably arranged in a sleeve (11.1).

8. Machine tool according to one of the preceding claims, characterized in that a vertical axis of rotation (A1) of the clamping unit and of the rotary table (3), a longitudinal axis (A2) of the centering tip (11) and a longitudinal workpiece axis (WA) of the workpiece (W) are aligned with one another.

9. Machine tool according to one of the preceding claims, characterized in that the superstructure (10) is designed symmetrically or substantially symmetrically in the Y-direction and / or in the Z-direction with respect to its vertically extending axis (AY).

10. Machine tool according to one of the preceding claims, characterized in that the superstructure (10) is reduced in its length and / or width from bottom to top symmetrically or substantially symmetrically.

11. Machine tool according to one of the preceding claims, characterized in that it can be used to carry out turning operations on workpieces in the form of journals, steering knuckles or other rotationally symmetrical components, which are clamped in the vertical direction, on the machining center.