US20070212977A1

US20070212977A1 - Machine tool

Info

Publication number: US20070212977A1
Application number: US11/716,016
Authority: US
Inventors: Hans-Dieter Braun; Thomas Bader; Tim Kern; Winfried Geiger; Harald Holzer
Original assignee: Individual
Current assignee: Individual
Priority date: 2006-03-10
Filing date: 2007-03-09
Publication date: 2007-09-13
Also published as: EP1832383A3; EP1832383B1; DE102006011551A1; ATE410262T1; ES2314953T3; DE502007000150D1; EP1832383A2

Abstract

A machine tool for machining workpieces (22), comprising three NC-controlled linear axes orthogonal to each other, namely a horizontal X-axis, a horizontal Y-axis and a vertical Z-axis, with a machine base (10), which comprises two vertically upwardly directed side beds (12) that are spaced from each other in the X-axis, with a bridge (28) displaceably guided in the Y-axis on top of the side beds (12), with a Z-slide disposed at the &enter of the bridge (28) in relation to the side beds (12), which slide can be displaced in the Z-axis and carries a tool spindle (46), with an X-guide element (14) disposed on the machine base (10), with a wbrkpiece holder element (16, 18, 20) displaceable on the X-guide unit, and with a tool holder disposed on the tool spindle (46).

Description

The invention relates to a machine tool for machining workpieces with three NC-controlled linear axes orthogonal to each other.
When machining workpieces, particularly when performing fine machining operations in grinding machines, the shape of the workpieces to be machined is taken into account by the number and configuration of the controlled axes. In the cylindrical grinding of rotation-symmetrical workpieces, two linear axes are sufficient, as is true for simple grinding machines, which two axes together with a rotative axis of the workpiece and the rotating tool spindle can produce rotation-symmetrical contours. For machining operations, particularly for grinding workpieces that are not configured rotation-symmetrically to the center line of the workpiece, typically machine tools are used that have three linear axes orthogonal to each other, which position the tool spindle spatially relative to the workpiece, and two rotative axes, which determine the position of the tool, particularly of the grinding tool, at the tool engagement point in two additional angles of attack with respect to the workpiece. In special cases, additionally a third rotative axis is used for producing free-form surfaces so as to reach the machining location with the main axes of the machine tool.
The technical complexity of the design of a machine tool of this type increases with the number of axes interacting with each other during machining. The linear axes must be oriented with utmost precision in their orthogonality to each other and the rotative axes must be oriented with utmost precision in their axial positions with respect to the linear axes. Such precision can be maintained with the necessary tolerances when installing and adjusting the machine tool. It is more difficult, however, to control deviations occurring during the operation of the machine tool. These deviations may be caused thermally as a result of varying levels of heating of individual regions of the machine tool and also by deformations caused by different workpiece weights or machining forces. Such errors can only be compensated for to a certain degree by measurements and corrective action. Consequently, the results improve the fewer the number of axes that are affected by operational factors. In particular, such compensation is possible when always the same workpieces are being machined. As the number of axes increases and as they are used universally for different workpieces, such corrective action is hardly possible.
In known machine tools, typically the workpiece holder and the tool holder are connected to each other on one side and off-center by a machine tool table. Such a stand in principle responds to unilateral heating or loads by becoming deformed. For portal milling machines, such as gantry machines, this situation is more favorable in that the table configuration is provided on both sides of the machining space and symmetrically to an extension of the machine tool. All three linear axes are disposed in a bridge carrying the tool spindle. While this bridge is supported symmetrically on both sides of the machining location, the tool spindle is displaceable in the bridge between the support points, so that this may again create asymmetrical weight and machining forces. Asymmetrical thermal load of the bridge, however, cannot be excluded.
From DE 42 12 175 A1 a lathe is known, wherein a machine base comprises two vertically upwardly directed side beds that are disposed at a distance from each other in the x-axis, on which cheeks a bridge is displaceable in the y-axis. On this bridge, the tool spindle can be displaced in the horizontal x-axis and the vertical z-axis by means of a compound slide. The tool is mounted stationary on the machine base. The weight of the tool spindle and the workpiece as well as machining forces act on the bridge asymmetrically in the Y-direction and their point of attack on the bridge shifts in the X-direction during the machining operation.
It is therefore the object of the invention to create a machine tool for machining workpieces, wherein machining errors as a result of thermal influences and/or weight forces and machining forces are optimized during operation of the machine tool.
This object is achieved according to the invention by a machine tool with the characteristics according to claim 1.
Advantageous embodiments of the invention are disclosed in the dependent claims.
The machine tool according to the invention for the machining of workpieces is preferably configured as a grinding machine.
To minimize deformations due to thermal influences and weight and machining forces, which result in errors, emphasis is placed on the machine tool according to the invention that both the design of the machine tool and the forces occurring during operation are center-symmetric to the extent possible. The tool spindle is provided on a bridge, which is displaceable in the Y-axis. In this bridge, the tool spindle is disposed center-symmetrically in relation to the X-axis. The tool spindle is not displaceable in the X-axis, so that the spindle always remains in this center location in the bridge. The X-axis for machining is configured as a workpiece support axis and provided on the machine base, on which the X-guiding unit for the workpiece holder element is massively supported, so that the workpiece weight and the machining forces acting on the workpiece do not result in deformation.
If the machine tool, in addition to the three orthogonal linear axes, is also provided with rotative axes, as is particularly advantageous for universal grinding machines, these rotative axes are disposed such that their impairment of the entire center symmetry of the machine tool is minimized.
A rotative axis, referred to as the C-axis, is configured to coincide with the vertical Z-axis. The tool spindle can be rotated about this C-axis with the spindle's axis intersecting the Z-axis so as to control and adjust the angle of attack of the tool in relation to the workpiece.
The rotating mount of the C-axis is integrated in the bridge, for which purpose the Z-slide in the bridge is mounted rotatably about this C-axis. It is preferably if the Z-slide is vertically displaceable in the C-axis and for symmetry reasons preferably coaxially in the center of the C-axis. The mass of the rotative C-axis is reduced in that no separate axis housing is required. The mass of the rotative C-axis also does not have to be displaced vertically. The guide and the drive of the Z-slide can be rotated about the C-axis, so that the tool spindle provided on the bottom of the Z-slide always maintains the same relative position to the Z-slide. A coaxially displaceable rotatable spindle is known, for example, from DE 198 58 667 A1.
In an advantageous embodiment, apertures are provided in the side beds of the machine base, through which apertures the X-guide provided on the machine base is guided. This way it is possible to provide a large travel range in the X-axis, for example for workpieces extended in this axis, without having to increase the clearance in the X-direction for the Y-guides carrying the bridge. The support of the bridge and tool spindle masses traveling on top of the side beds is distributed center-symmetrically among four columns, namely the two columns of each side bed remaining on either side of the aperture. With this embodiment, the machine dimensions in the X-axis can be extended in accordance with the respective machining task, without having to change the machine design.
So as not to apply asymmetrical load on the bridge in the Y-travel direction, the Z-slide carrying the tool spindle is preferably disposed in the center of the bridge in relation to this Y-axis. As a result, no moment of tilt occurs on the bridge and the Y-guide thereof, regardless of the weight of the tool spindle and of the machining forces acting on the tool spindle.
To be able to machine workpieces, which are rotation-symmetrical at least to some extent and may be elongated in this rotational axis, a rotative axis, referred to as the A-axis, is preferably configured to coincide with the X-axis. This means that the workpiece in the workpiece chucking device can be rotated about this A-axis coinciding with the linear X-axis. The respective area of the workpiece to be machined can be rotated to face the machining tool by means of the A-axis.
The positioning of the workpiece in the X-axis guarantees that this machining site is always positioned at the center of the machine tool between the side beds.
A third rotative axis can be implemented in that the tool spindle is mounted pivotably about a horizontal axis, referred to as the B-axis, which is provided in a plane orthogonal to the Z-axis.
It is preferable if the tool spindle is disposed in the Z-slide such that a tool chucked in the tool spindle is axially flush with the Z-axis and particularly with the rotative C-axis. As a result, the angle of attack of the tool in the C-axis and optionally in the B-axis can be varied, without causing the machining site, meaning the point of attack of the tool on the workpiece, to migrate from the center position of the machine tool.
It is advantageous to configure the machine base and the side beds as one piece in the form of mineral cast components. This guarantees significantly slower and more even thermal growth and high vibration of the machine base.

The invention will be explained in more detail hereinafter with reference to an exemplary embodiment illustrated in the drawing, wherein:

FIG. 1 is a front view of the machine tool, and

FIG. 2 is a vertically cut side view.

In the exemplary embodiment illustrated in the figures, a machine tool is illustrated, which is configured as a grinding machine.
The machine tool comprises a machine base 10, which extends in the direction of the X-axis. At both ends of the machine base 10, which are spaced from each other in the X-direction, vertically upwardly directly side beds 12 are provided, respectively. The machine base 10 and the side beds 12 are produced as one piece as mineral cast components.
At the top of the machine base 10, an X-guide unit 14 extending horizontally in the X-axis is mounted, which is supported across the entire length by the machine base 10. In the X-guide unit, a workpiece holder element is provided displaceably by NC-control in the X-axis. The workpiece holder element in the illustrated example substantially comprises a workpiece table 16 mounted displaceably on the X-guide element 14, on which table a workpiece chucking element 18 and a tailstock 20 are provided. A workpiece 22 can be chucked in the workpiece chucking element 18 in an axis extending the X-direction and is supported at the opposite end by the tailstock. The workpiece chucking element 18 comprises a rotary drive, which is referred to as the A-axis, by means of which the workpiece 22 can be rotated in an NC-controlled manner about its axis parallel to the X-axis.
The two side beds 12 comprise an aperture 24 in their lower regions connecting to the machine base 10. The apertures 24 are flush with the X-guide element 14 and are configured symmetrically to the X-guide in the horizontal Y-direction perpendicular to the X-axis. The X-guide element may extend through the apertures 24, so that also workpieces 22 elongated in the X-direction can be received in the workpiece holder element and guided through the apertures 24, the linear displacement path of which is larger in the X-direction than the inside clearance of the side cheeks 12.
On the upper horizontal boundary surfaces of the side beds 12 extending in the Y-direction, Y-guides 26 are provided. A bridge 28 that is displaceable in the Y-axis is mounted in these Y-guides 26. The bridge 28 spans the inside of the machine tool between the side beds 12 in the X-direction and then strengthens the side beds 12 at the free upper edges thereof towards each other in the X-direction. The bridge 28 can be displaced by NC-control in the Y-axis by means of a driving motor 32 disposed on a machine back wall 30 and by means of a spindle 34.
At the center of the region, meaning both in relation to the X-direction and in relation to the Y-direction, a Z-slide 36 is provided at the center of the bridge 28. The Z-slide 36 is guided in a sleeve 38 in,the vertical Z-axis. In the sleeve 38, the Z-slide can be displaced vertically by NC-control by means of a driving motor 40 and a spindle 42. The sleeve 38 is not displaceable axially in the bridge 28 and can be rotated about a vertical axis by NC-control. This vertical axis of rotation of the sleeve 38, referred to as the C-axis, coincides with the Z-axis.
On the end of the Z-slide protruding toward the bottom out of the sleeve 38 and the bridge 28, a radially projecting bracket 44 is mounted. On this bracket 44, a tool spindle 46 is pivotably mounted by means of a pivot joint 48. The pivot axis of the pivot joint 48 extends off-center from the Z-axis and/or the C-axis in a horizontal plane orthogonal to the Z-axis. The pivot axis of the pivot joint 48 forms a third rotative axis, referred to as the B-axis.
The tool spindle 46 is driven by a coaxial spindle motor 50 and at the end thereof comprises a tool holder, in which a tool 52, in the illustrated example a grinding tool, can be chucked.
For the grinding operation of the workpiece 22, the workpiece is positioned in the X-axis by means of the workpiece holder device, wherein the respective location of the workpiece 22 to be machined is positioned in the X-axis at the center between the side beds 12. The machining tool 52 is positioned by means of the movement of the bridge 28 in the Y-axis and by means of the movement of the Z-slide 36 in the Z-axis. By rotating the workpiece 22 about the A-axis, the scope of the workpiece 22 to be machined is positioned to face the tool 52. By rotating the sleeve 38 about the C-axis, the axis of the tool spindle 46 and hence that of the tool 52 is positioned in the X-Y plane. By pivoting the tool spindle 46 about the B-axis of the pivot joint 48, furthermore the angle of inclination of the tool spindle 46 and thus that of the tool 52 in relation to the X-Y plane can be adjusted. By disposing the pivot joint 48 and the fastening for the tool spindle 46 outside the Z-axis, the tool 52 and hence the machining location on the workpiece 22 are flush in the Z-axis and/or the C-axis, regardless of the rotation of the tool spindle 46 about the C-axis. The clearance of the side beds 12 in the X-direction allows a rotation of the horizontally disposed tool spindle 46 about the C-axis by 360°.

REFERENCE LIST


10	machine base
12	side beds
14	X-guide unit
16	workpiece table
18	workpiece chucking element
20	tailstock
22	workpiece
24	aperture
26	Y-guide
28	bridge
30	machine back wall
32	driving motor
34	spindle
36	Z-slide
38	sleeve
40	driving motor
42	spindle
44	bracket
46	tool spindle
48	pivot joint
50	spindle motor
52	tool.

Claims

1. A machine tool for machining workpieces (22), comprising three NC-controlled linear axes orthogonal to each other, namely a horizontal X-axis, a horizontal Y-axis and a vertical Z-axis, with a machine base (10), which comprises two vertically upwardly directed side beds (12) that are spaced from each other in the X-axis, with a bridge (28) displaceably guided in the Y-axis on top of the side beds (12), with a Z-slide disposed at the center of the bridge (28) in relation to the side beds (12), which slide can be displaced in the Z-axis and carries a tool spindle (46), with an X-guide element (14) disposed on the machine base (10), with a workpiece holder element (16, 18, 20) displaceable on the X-guide unit, and with a tool holder disposed on the tool spindle (46),

characterized in that the axis of the tool spindle (46) intersects the Z-axis and that the tool spindle (46) can be rotated by NC-control about an axis (C-axis) coinciding with the Z-axis, for which purpose the Z-slide (36) is mounted in the bridge (28) rotatably about this C-axis.

2. The machine tool according to claim 1, characterized in that the side beds (12) each comprise an aperture (24), through which the X-guide element (14) is guided.

3. The machine tool according to claim 1, characterized in that the Z-slide is disposed in the center of the bridge (28) also in relation to the Y-axis.

4. A machine tool according to claim 1, characterized in that the workpiece (22) can be rotated about an A-axis coinciding with the X-axis by NC-control in the workpiece holder device (16, 18, 20).

5. A machine tool according to claim 1, characterized in that the tool spindle (46) is mounted pivotably about a horizontal B-axis, which is located in a plane orthogonal to the Z-axis.

6. A machine tool according to claim 1, characterized in that a tool (52) chucked in the tool holder of the tool spindle (46) is located substantially in the Z-axis.

7. The machine tool according to claim 6, characterized in that the clearance of the side beds (12) in the X-direction allows a rotation of the tool spindle about the C-axis by 360°.

8. A machine tool according to claim 1, characterized in that a machine base (10) and the side beds (12) form a single-piece mineral cast component.

9. A machine tool according to claim 1, characterized in that the machine tool is configured as a grinding machine.