|Title of Invention||
"MACHINE TOOL FOR MACHINING ELONGATED WORKPIECES"
|Abstract||The machine has at least one chuck (22) for a workpiece (23), drivable about a first axis of rotation (A), and at least one tool spindle (18), drivable about a second axis of rotation (C). Displaceable by drives independently of one another on a way (4) are three slides (5, 6, 7) connected by means of guide rods (11, 12, 13) to a unit (17) bearing the tool spindle. By displacement of the slides along the way, the tool (19) is displaceable along an X-axis and a Z-axis and, in addition, sluable within a range. Such a machine has a reduced number of drives, and particularly of ways, as compared with prior art machines of this type, and may easily be produced in a modular design. Moreover, with this machine the masses moved are small as compared with the prior art, thus improving the dynamics of the machine. (Figure 1)|
|Full Text||Machine Tool for Machining Elongated Workpieces
The invention relates to a machine tool for machining elongated workpieces, having at least one chuck for a workpiece, drivable about a first axis of rotation, and at least one tool spindle, drivable about a second axis of rotation lying in the tool axis, which spindle is displaceable along a first axis of translation parallel to the first axis of rotation and along a second axis of translation at right angles to the first axis of rotation and parallel to the second axis of rotation, the chuck being displaceable along a third axis of translation at right angles to the first and second axes of translation, and the tool spindle further being sluable about a swivel axis parallel to the third axis of translation.
For the material-detaching machining of workpieces having surfaces of complex shape, such as turbine blades, for example, numerically controlled machining centers are used almost exclusively at present. The design of such machining centers is based on the concept of enabling differing and complicated workpieces to be machined completely in a single setting. In addition, the centers have at least three axes of translatory motion having a numerical path control, usually supplemented by one or two likewise numerically controlled axes of rotation. The way in which these axes of motion are assigned to the tool or workpiece is determined by the type of construction of the machining center, particularly the structure and mutual arrangement of the different column and table assemblies. The range of parts to be produced determines the technical parameters of a machining center, such as the kind and number of controlled axes, cutting capacity, speed and feeding ranges, and length of the paths of displacement.
Efforts to reduce production costs for the machining of workpieces of the aforementioned type are essentially aimed at two goals. Firstly, it is attempted to reduce the cost of procuring and operating the respective machining centers by simplifying their structure as much as possible and-insofar as this likewise involves a simplification-adapting them to the workpieces they are to machine.
Secondly, many efforts aimed at reducing production costs are aimed at shortening the machining time per workpiece. This can be achieved particularly by increasing the speed of the relative movements between tool and workpiece during the actual machining, but also during delivery and during tool changes. A limiting factor is the attainable acceleration, which is decisively influenced by the masses moved.
International Patent Application Publication No. WO 91/03145 discloses a so-called "Six Axis Machine Tool" having two spaced platforms, one of which may bear a tool and the other a workpiece. The two platforms are joined by six extensible elements, e.g., hydraulic cylinders or threaded spindles, and are movable relative to each other. By controlled varying of the length of the elements, one of the platforms is spatially movable at will with respect to the other within a range.
International Patent Application Publication No. WO 92/17313, entitled "Manipulator," shows a similar machine, but wherein two platforms, one of which may again bear a workpiece, are immovably connected to one another. In this case, the six extensible elements bear the tool and are mounted on the other of the said platforms. By controlled varying of the length of the elements, the tool is spatially movable at will within a range.
One disadvantage of the first of the said machines is that with the movable platform, a relatively great mass must be accelerated, whereby the operating speed of this machine is limited. Common to both machines is that they have at least six controlled drives and a like number of ways just for carrying out the relative movements between tool and workpiece, which is not only very elaborate and expensive, but also difficult to master as regards control technology.
A first object of the present invention is to provide a machine tool for machining elongated workpieces which is of considerably simplified structure as compared with prior art machines of this kind. A second object is to provide a modular design of such a machine, so that particularly its frame can be
assembled simply and quickly according to the required size. A further object of the invention is to propose a machine of the kind initially mentioned wherein the masses moved are small as compared with the prior art. Still another object of the invention is to propose a machine tool in which extensible elements for moving the tool can be dispensed with. Finally, it is also an object of the invention to develop such a machine having a reduced number of drive components, and especially ways, as compared with the prior art.
These objects are achieved by a machine of the type initially mentioned which has the features recited in the characterizing clause of claim 1.
Owing to the fact that the inventive machine makes possible all movements of the tool spindle in a plane defined by the first and second axes of translation and the swivel movement of the tool spindle by means of a single way, it is simpler, smaller, lighter, and more cost-effective than prior art machines having comparable functions. There is considerably more freedom in the arrangement of the drives of the displaceable slides than with the extensible elements of the prior art. The simplicity of its structure favors a design of the machine in a modular method of construction. The relatively small masses moved result in improved dynamics of the inventive machine as compared with prior art machines.
By means of the method defined in claim 8 for operating a machine according to the invention, the point of contact or working point between tool and workpiece is maintained for all practical purposes during swivelling of the tool spindle, so that only slight linear corrections need take place. This saves unnecessarily long adjusting movements.
The invention is described in detail below with reference to the accompanying drawings, in which:
Figure 1 is an end elevation of an embodiment of the inventive machine,
Figures 2 and 3 are diagrammatic sketches illustrating the kinematics of the machine of Figure 1,
Figures 4 to 7 are diagrammatic sketches of guide-rod arrangements of further embodiments of the inventive machine having three guide rods each, and
Figures 8 to 10 are diagrammatic sketches of guide-rod arrangements of further embodiments of the inventive machine having four guide rods each.
The milling machine shown in Figure 1 is designed especially for producing turbine blades and comprises a bench 1 on which a upper beam 3 is held by means of trusses 2. On the side of the beam 3 facing the bench 1 there is a way 4 extending in the direction of the first axis of translation X with three slides 5, 6, and 7 displaceably mounted thereon independently of one another. Each slide is provided with a drive (not shown) which controlledly moves the slide along the way 4. Each of the slides 5, 6, and 7 comprises a respective joint 8, 9, and 10, to each of which one end of a respective guide rod 11, 12, and 13 is connected. Each of the guide rods is connected at the other end by means of a respective further joint 14, 15, 16 to a milling unit 17 which comprises a tool spindle 18 accommodating a tool, e.g., a milling tool 19, together with its drive. Accommodated on the bench 1 is a table 20 displaceable on a way 21 in the direction of the third axis of translation Y. This table bears a chuck 22 by which a workpiece 23 is held rotatingly about a first axis of rotation A. For supporting the workpiece, there is additionally a tailstock 24 displaceable on the table 20 in the direction of the first axis of translation X.
The kinematics of the machine described above will now be explained with reference to Figures 2 and 3. Figure 2 shows how a movement of the tool 19 by the amount z19 is brought about in the direction of the second axis of translation Z from a starting position, depicted in solid lines, to an end position, depicted in dot-dash lines. For this purpose, the two slides 6 and 7 are moved towards one another by the same amount, x6 = x7, whereby the milling unit 17 is displaced downwards by the desired amount z19. So that the milling unit is not inclined at this time, but is displaced only parallel, the slide 5
must be moved towards the right by the amount x5. A movement of the tool in the direction of the first axis of translation X is obtained by shifting all three slides 5, 6, and 7 by the same amount in the same direction.
Illustrated in Figure 3 is a case in which the axis of the tool spindle, starting from a vertical position shown in solid lines, effects a swivel movement about the axis B through an angle 6 into a position shown in dot-dash lines. Here, the position of the swivel axis is selectable at will within a certain range by appropriate control of the paths of displacement x'5, x'6, and x'7. In the present case, the position of the swivel axis B is so chosen that it lies close to the point of contact of the milling tool 19 with the workpiece 23. This choice has the advantage that the point of contact is substantially maintained upon swivelling of the tool, so that only minimal linear corrections need be made. This saves unnecessarily long adjusting movements.
It will be understood that all combinations of the movements just described are possible, so that by appropriate control of the drives of the slides 5, 6, and 7, the tool can be moved and swivelled as desired in the plane X-Z defined by the first and second axes of translation.
Figures 4 to 10 show guide-rod arrangements of further embodiments of the inventive machine in the form of diagrammatic sketches, identical parts being identified by the same reference numerals. The embodiments of Figures 4 to 7 are each provided with four guide rods. In the embodiment of Figure 4, the arrangement of the joints on the milling unit 17 is substantially the same as in the embodiment described with reference to Figures 1 to 3. Unlike this latter embodiment, however, the joints provided on the slides 5 to 7 are not disposed on an axis parallel to the X-axis but are mutually offset in the Z direction.
The reason why two guide rods intersect in the embodiments described heretofore resides in the optimizing of the forces transferred by the guide rods. For the guide rod that controls the inclination of the milling unit 17 should
form as small an angle as possible with the X-axis, whereas the guide rods effecting the movement of the milling unit in the Z direction should form as large an angle as possible with the X axis. This arrangement has the drawback, however, that because of the guide rod 11 running obliquely outwards, the way 4 must be made longer. Figure 5 shows an example in which this drawback is eliminated in that the joint 14 for the guide rod 11 on the milling unit 17 is laterally offset with respect to the axis C, so that the guide rod 11 can be disposed relatively obliquely even without crossing over the guide rod 12. It is thereby possible to make the way 4 somewhat shorter than in the examples described previously. The embodiment of Figure 6 illustrates that the joints 15 and 16 of the guide rods 12 and 13 on the milling unit 17 need not be spaced from one another in the X direction as shown previously, but may lie on the same axis. In all of the embodiments described previously, there exists the drawback that the slides 5 and 6 may mutually hinder one another in their movements on the common way 4. This can be remedied in an embodiment according to Figure 7, where provision is made, parallel to the way 4, for a further way 4a on which one of the slides runs. Thus, the slides 5 and 6 may cross for moving the milling unit 17.
Figures 8 to 10 are diagrammatic sketches of guide-rod arrangements of further embodiments of the inventive machine, each having four guide rods. Although such guide-rod arrangements are statically indeterminate, the drives of the slides can readily be governed by means of appropriate controls. The embodiment of Figure 8 corresponds in principle to the one shown in Figure 6, except that it has a further guide rod 11 a with an associated slide 5a. In the example shown in Figure 9, the positions of the slides 5, 5a, 6, and 7 on the way 4 are interchanged as compared with Figure 8, so that the guide rods 11/12,11 a/13 cross. Finally, Figure 10 shows that embodiments are also conceivable in which two each of the joints disposed on the milling unit are respectively situated on a common axis, which axes lie on a line parallel to the X-axis.
In the embodiments described above, especially that of Figure 1, the way 4 is disposed above the first axis of rotation A. Such a configuration is not compulsory, however. Insstead, the way might occupy any other desired position, e.g., laterally beside the first axis of rotation A.
1. A machine tool for machining elongated workpieces (23), having at
least one chuck (22) for a workpiece, drivable about a first axis of rotation (A),
and at least one tool spindle (18), drivable about a second axis of rotation (C)
lying in the tool axis, which spindle is displaceable along a first axis of
translation (X) parallel to the first axis of rotation (A) and along a second axis of
translation (Z) at right angles to the first axis of rotation (A) and parallel to the
second axis of rotation (C), the chuck being displaceable along a third axis of
translation (Y) at right angles to the first (X) and second (Z) axes of translation,
and the tool spindle (18) further being sluable about a swivel axis (B)
parallel to the third axis of translation (Y), characterized in that spaced from the
first axis of rotation (A), a way (4) running in the direction of the first axis of
translation (X) is disposed, along which way slides (5, 6, 7) are displaceable
independently of one another, that each of the slides (5, 6, 7) is connected by
means of a joint (8, 9, 10) to one end of a guide rod (11, 12, 13), and the other
end of each guide rod is connected by means of a joint (14, 15, 16) to a unit
(17) bearing the tool spindle.
2. A machine tool according to claim 1, characterized in that it has three
guide rods (11, 12, 13).
3. A machine tool according to one of the preceding claims,
characterized in that the joints (14, 15, 16) disposed on the unit (17) bearing
the tool spindle are spaced from one another.
4. A machine tool according to one of the preceding claims,
characterized in that it has four guide rods (11, 11a, 12, 13).
5. A machine tool according to one of the preceding claims,
characterized in that two of the joints disposed on the unit (17) bearing the tool
spindle are disposed on a common axis.
6. A machine tool according to one of the preceding claims,
characterized in that running parallel to the way (4), it comprises a further way
(4a) on which at least one of the slides is disposed.
7. A machine according to one of the preceding claims, characterized in
that it has a beam (3) held spaced by trusses (2) over a bench (1), on which
beam the way (4) running in the direction of the first axis of translation (X) is
situated, that a table (20) displaceable in the direction of the third axis of
translation (Y) is mounted on the bench, and that the chuck (22) for a orkpiece
(23) is situated on the table.
4. A method of operating a machine according to one of the preceding claims, characterized in that the three slides (5, 6, 7) are controlled to move in such a way that the tool spindle (18) is swivelled about a swivel axis (B) stuated at the point of contact of the tool with the workpiece.
5. A machine tool for machining elongated workpieces substantially as herein described with reference to the accompanying drawings.
|Indian Patent Application Number||1267/DEL/1998|
|PG Journal Number||31/2009|
|Date of Filing||13-May-1998|
|Name of Patentee||LIECHTI ENGINEERING AG.|
|Applicant Address||KANALWEG 4, 3550 LANGNAU, SWETZERLAND.|
|PCT International Classification Number||B23Q 1/48|
|PCT International Application Number||N/A|
|PCT International Filing date|