EP1757405B1 - Method for machining of workpieces with curved surfaces, in particular for turbine blades, machine tool - Google Patents

Abstract

The method involves moving a wok-piece along an axis (58) and simultaneously rotating the work-piece around another axis (64), where the axis (64) incorporates a finite angle with the axis (58). The work-piece is moved along a third axis (26), where the axis (26) incorporates the finite angle with the axis (58) and the axis (64), and the work-piece is moved in fast oscillating movement along the axis (58) in a direction tangential to the processing of the work-piece. Independent claims are also included for the following: (1) a machine tool for machining a work-piece (2) a programming system for evaluating programming parameters.

Description

The invention relates to a method for machining curved surface workpieces, wherein the workpiece is traversed along a first axis and simultaneously rotated about a second axis that includes a finite angle with the first axis, and a machining tool along a third axis Axis is deliverable, which also includes a finite angle with the first axis and with the second axis.

The invention further relates to a machine tool for machining workpieces having a curved surface, with a tool holder which can be moved along a first axis and at the same time is rotated about a second axis, wherein the second axis includes a finite angle with the first axis, and a machining tool that is deliverable along a third axis that also includes a finite angle with the first axis and with the second axis.

The invention finally relates to a programming system.

A method and a machine tool of the aforementioned type are known from DE 36 25 565 C2 known.

The present invention relates generally to methods and machines for machining workpieces having curved surfaces. By way of example only and not by way of limitation, this will be explained below using the example of turbine blade grinding. In addition, applications in many other workpieces, even with any spatially curved surface (free-form surface) to understand, for example, in artificial joints.

Turbine blades consist of an airfoil and a foot attached to one end of the airfoil and used to secure the blade to the rotor. At the opposite end turbine blades may have a so-called. Platform which is provided with Abdichtprofilen to avoid flow losses.

Turbine vanes, on the other hand, have platforms at the inner and outer ends of the airfoil for attachment and sealing.

Turbine blades usually occupy a circular sector of 6 to 15 °. The platforms have a large radius, which corresponds to the radius of the respective turbine.

In order to grind their contact surfaces, in the prior art the turbine blades were previously mounted on a rotatable, circular workpiece table. its radius corresponded approximately to the radius of curvature of the contact surfaces, wherein the contact surfaces were arranged along the circumference of the workpiece table. Then these contact surfaces could be ground by means of a likewise arranged on the circumference of the workpiece table, stationary grinding tool with the desired radius. However, this approach had the disadvantage that very large grinding machines were created, which were very cumbersome to handle and only allowed a low throughput.

In the course of the development of numerically controlled, multi-axis machine tools, numerous such machines for grinding turbine blades have been proposed later.

In the DE 32 46 168 C2 Such a grinding machine is described in which a workpiece holder is arranged on a carriage which can be moved vertically on a stand, while a grinding spindle can be moved in front of the stator along two horizontal directions which are perpendicular to one another and can additionally be pivoted about a vertical axis. Although this grinding machine can also grind circularly curved contact surfaces of turbine blades, but only under very limited conditions, because the adjustment options of the grinding machine are limited and allow only a small variation. The machine is also not intended for this application.

One from the DE 36 11 103 A1 known, seven-axis grinding machine is designed specifically for grinding turbine blades. The machine has a workpiece holder, which can also be moved in a vertical direction on a stand, but in addition can also be rotated about a horizontal axis and can also be moved together with the stand along a horizontal axis. The grinding spindle in turn is movable against the stand and transversely thereto in the horizontal direction and rotatable about a vertical axis. By means of a suitable CNC path control, the desired contact surfaces can be ground in this way.

Another grinder for this application is in the EP 0 254 526 B1 described. In this known, six-axis machine, the workpiece holder is in turn movable on a stand in the vertical direction and rotatable on the stand about a horizontal axis. The stand as a whole can move around a horizontal axis and be rotated about a vertical axis. The grinding spindle can be moved around two mutually perpendicular, horizontal axes. Also in this machine tool, a CNC path control is provided.

Another similar machine for the same purpose is from the EP 0 666 140 B1 known. This known machine has five axes and allows the alternate machining of two turbine blades, for which two workpiece holders are provided. These workpiece holders can be moved along a first horizontal axis and rotated about a vertical axis. The grinding spindle can be moved along a second, to the first transverse horizontal axis and along a vertical axis and rotated about this vertical axis.

A somewhat different concept is provided in a machine for grinding turbine blades, which in the aforementioned DE 36 25 565 C2 is described. In this known machine, the desired circular path of the point of action of the grinding wheel on the workpiece is not achieved by a CNC path control, but by a superposition of two individual movements, namely a horizontal movement and a pivoting movement of the workpiece carrier. The delivery is achieved by a vertical movement of the grinding spindle.

The known machines described above have in common that the grinding process takes place in the so-called. Tiefschleifverfahren, i. that the entire allowance is removed in a single pass of the grinding wheel. Of course, this does not exclude that, for example, a roughing process and a finishing process take place, each with its own total allowance.

However, the deep grinding has the disadvantage that the contact length of the grinding wheel on the workpiece is also very large because of the large engagement thickness. this leads to high grinding forces and temperatures, high wear on the grinding wheel and a significant deviation in shape. If these quantities are kept within limits by a correspondingly smaller feed, this in turn restricts the achievable chip removal volume.

From the EP 0 981 419 B1 is known as a pendulum grinding machine. This machine is a surface grinding machine in which a flat workpiece is placed on a workpiece carriage which is periodically reciprocable in the direction of a horizontal axis, typically with stroke times of a few seconds. A grinding spindle disposed above the workpiece engages a grinding wheel on the workpiece being moved past. The purpose of this procedure is to divide this total allowance into several passes given a very large overall oversize of a grinding process. Pendulum grinding machines are used, for example, for grinding guide rails.

From the WO 93/15877 a device for grinding workpieces is known. In the known device, the workpiece during the grinding process oscillates in a frequency range of 50 Hz to 40 MHz, referred to as ultrasound. A grinding wheel oscillates on the workpiece with a given stroke. On the one hand, the oscillation amplitude should be equal to half the pendulum stroke, on the other hand it should be 0.023 mm at an oscillation frequency of 1 MHz.

The invention is based on the object of developing a method and a grinding machine of the type mentioned in such a way that the above-mentioned disadvantages of conventional grinding methods or machines are avoided. In particular, it should be possible to grind on a compact machine workpieces with curved surfaces, in particular turbine blades, in high dimensional accuracy with high chip removal rate with low wear of the grinding wheel by the grinding forces and temperatures are reduced.

In a method of the type mentioned above, this object is achieved in that the workpiece is moved along the first axis in a fast oscillating motion, wherein the oscillating movement at a speed of more than 20 m / min, preferably more than 50 m / min, and a reversing acceleration of more than 3 m / s ² , preferably of more than 10 m / s ² , with an adjustable variable stroke length, the stroke length being substantially equal to the distance traveled by the machining tool during the respective oscillating movement in the Workpiece is.

In a machine tool of the type mentioned, this object is achieved according to the invention, the tool holder is connected to a first carriage which moves the workpiece along the first axis in a fast oscillating motion, wherein the oscillating movement at a speed of more than 20 m / min, preferably of more than 50 m / min, and a reversal acceleration of more than 3 m / s ² , preferably of more than 10 m / s ² , is performed with an adjustable variable stroke length, wherein the stroke length is substantially equal to that in the respective oscillating movement of the machining tool traversed path in the workpiece.

The object underlying the invention is completely solved in this way.

According to the invention is achieved by the fast oscillating movement of the workpiece, ie by its rapid lifting movement in a direction substantially tangential to the machining tool direction that the material with significantly shorter contact length and lower machining forces is abgespant, thereby reducing the processing temperature and the shape deviation. In comparison to conventional flat pendulum grinding, there is the advantage of shorter overflow times and thus of a greater removal rate and an overall shorter grinding time.

The values for the oscillatory motion are much higher than comparable values in conventional flat pendulum grinding, have proven to be the best solution to the above-mentioned problem in tests for machining tools available today.

The invention has the advantage that the total grinding time is minimized by the specially set stroke length, because the stroke length is limited to the amount necessary for a complete material removal.

For workpieces of the type of interest here, in particular for turbine blades, as a result of their dimensions, the oscillating movement (ΔX) is carried out with a frequency between 200 and 500 min ^-1 .

Furthermore, it is preferred if the first axis, the second axis and the third axis are perpendicular to each other.

This measure has the advantage that conventional controls for three-axis machine tools can be used insofar as the three axes form a Cartesian coordinate system.

A particularly simple control is achieved if the second axis encloses a right angle with the radius of curvature of the surface at an engagement point of the machining tool on the surface.

In embodiments of the method according to the invention, it is taken into account that when machining a concavely curved surface, a residual allowance is removed by means of path control of workpiece and machining tool with reduced web speed.

This measure has the advantage that, for the essential portion of the total allowance, the method according to the invention is used with the already indicated advantages, while only a residual allowance which is unavoidable in the case of concave surfaces is removed in a conventional manner.

In further embodiments of the invention, the workpiece is additionally pivoted during machining about the second axis.

This measure has the advantage that during the stroke of the workpiece, the material is removed along crescent-shaped arches, which in convex surfaces brings about an improvement in dimensional accuracy and a shortening of the processing time.

In this context, if the workpiece oscillating movement is superimposed on a path control between the workpiece and the machining tool, this has the advantage that concave surfaces with the advantages mentioned above can also be machined.

In order to obtain an even higher degree of flexibility in terms of processing and also to be able to process surfaces with higher-order curvatures, further embodiments of the invention provide for the machining tool also to be moved along a fourth axis which preferably runs parallel to the second axis and or to further rotate the machining tool about a fifth axis, which is preferably parallel to the first axis.

In the latter case, two different tools may alternatively be brought into engagement with the workpiece by turning the machining tool about the fifth axis.

With the method according to the invention not only simple curved surfaces, ie cylindrical surfaces, but quite generally arbitrarily in space curved surfaces, so-called free-form surfaces edit.

Although the present invention is applicable to a variety of machining processes, it is preferably used when the workpieces are ground.

The workpieces are preferably turbine blades, the surfaces being, in particular, cylindrical surfaces on a platform of the turbine blade.

In addition, however, the method according to the invention and the grinding machine according to the invention can also be used, as already mentioned, for spatially arbitrarily curved surfaces, the so-called free-form surfaces. As an example, here are artificial joints, such as knee joints, called whose shape to grind along enveloping cuts. A fast oscillating movement also reduces the thermal effect of the grinding wheel on the workpiece. A high machine dynamics shortens the grinding time per enveloping cut and thus the processing time.

In embodiments of the machine tool according to the invention, different drives can be used for carrying out the oscillating stroke movement. It is preferred if the first carriage is coupled with a linear motor, a threaded or spindle drive, or with a crank drive.

In embodiments of the machine tool according to the invention, the first carriage runs on a machine bed along the first axis, and the machining tool runs on a second carriage on a cross member of a machine bed spanning portal along the third axis.

This measure has the advantage that for the fast-moving axes, the lighter components, namely the tool carrier with its rotary drive, run directly on the machine bed, while for the slower moving axes, a heavy and highly stable gantry design is available.

Further advantages will become apparent from the description and the accompanying drawings.

It is understood that the features mentioned above and those yet to be explained below can be used not only in the particular combination given, but also in other combinations or in isolation, without departing from the scope of the present invention.

Figur 1:

eine perspektivische Ansicht eines Ausführungsbeispiels einer erfindungsgemäßen Schleifmaschine;

Figur 2:

eine schematisierte Vorderansicht der Schleifmaschine von Figur 1;

Figur 3:

eine schematisierte Vorderansicht auf einen Werkstückschlitten der Schleifmaschine von Figur 1 und 2;

Figur 4:

eine Draufsicht auf den Werkstückschlitten von Figur 3;

Figur 5:

ein Diagramm zur Veranschaulichung eines Ausführungsbeispiels eines erfindungsgemäßen Verfahrens;

Figur 6 bis 8:

in vergrößerter Darstellung drei Diagramme zur weiteren Erläuterung des in Figur 5 veranschaulichten Verfahrens für die Bearbeitung einer konvex gekrümmten Fläche;

Figur 9 bis 12:

in weiter vergrößerter Darstellung vier Diagramme zur weiteren Erläuterung des in Figur 5 veranschaulichten Verfahrens für die Bearbeitung einer konkav gekrümmten Fläche; und

Figur 13:

eine Darstellung ähnlich Figur 5 zur Erläuterung eines weiteren Verfahrensschritts bei der Bearbeitung einer konkav gekrümmter Oberfläche.

Embodiments of the invention are illustrated in the drawings and are explained in more detail in the following description. Show it:

FIG. 1:

a perspective view of an embodiment of a grinding machine according to the invention;

FIG. 2:

a schematic front view of the grinding machine of FIG. 1 ;

FIG. 3:

a schematic front view of a workpiece carriage of the grinding machine of FIG. 1 and 2 ;

FIG. 4:

a plan view of the workpiece carriage of FIG. 3 ;

FIG. 5:

a diagram illustrating an embodiment of a method according to the invention;

FIGS. 6 to 8:

in an enlarged view three diagrams for further explanation of in FIG. 5 illustrated method for processing a convex curved surface;

FIGS. 9 to 12:

in a further enlarged view four diagrams for further explanation of in FIG. 5 illustrated method for machining a concave curved surface; and

FIG. 13:

a representation similar FIG. 5 to explain a further method step in the processing of a concave curved surface.

In FIG. 1 Figure 10 as a whole indicates an embodiment of a machine tool according to the invention, illustrated in the case of a grinding machine suitable for grinding workpieces with curved surfaces. Although the invention is described below with reference to the application example of a grinding process on turbine blades, it is understood that the invention is not limited to this type of machining, nor to this application or this type of workpiece.

The grinding machine 10 has a machine base 12 which carries a machine bed 14. On the front of the grinding machine 10, a chip pan 16 is provided. In the rear area, the machine bed 14 carries a portal 18 with a cross member 20th

On the cross member 20 parallel horizontal guide rails 22 and 24 are arranged, which constitute a first axis 26, the so-called. Z-axis. Along the guide rails 22, 24, a first carriage 30 is movable in the Z direction.

On the first carriage 30 parallel vertical guide rails 32 and 34 are arranged, which constitute a second axis 36, the so-called. Y-axis. Along the guide rails 32, 34, a second carriage 40 is movable.

The second carriage 40 carries a grinding spindle 42. The grinding spindle 42 is on the in FIG. 1 provided on the left side with a first grinding wheel 44. On the right side of the grinding spindle 42 is in FIG. 1 to recognize a stub shaft 46, which may carry a second grinding wheel 48 (see. FIG. 2 ). The grinding spindle is optionally rotatably mounted on the second carriage 40 about a third, horizontal axis 50, the so-called. A-axis.

In the front region of the machine bed 14, a guide 52 is arranged on this, which extends rearwardly into the area below the portal 18. The guide 52 has mutually parallel, horizontal guide rails 54 and 56, which represent a fourth axis 58, the so-called. X-axis.

The fourth axis 58 (X) forms in the illustrated embodiment, together with the first axis 26 (Z) and the second axis 36 (Y) a Cartesian coordinate system.

Along the guide rails 54, 56, a third carriage 60 is movable. The third carriage 60 carries a turntable or turntable 62 which is rotatable about a fifth axis 64, the so-called. B-axis. On the turntable 62 is a workpiece holder 66, in which workpieces are clamped. The third carriage 60 with its components thereon is designed in lightweight construction. The workpiece is thus movable only in the X direction and rotatable about the B axis. This restriction to two axes benefits a high dynamic of the grinding machine 10, as will be explained.

The linear drives of the first carriage 30 and the second carriage 40, as well as the rotary drives for the grinding spindle 42 and the turntable 62 are preferably of conventional design, as used for supports in machine tools. Therefore, they require no further explanation for the expert.

The linear drive of the third carriage 60, however, is of a special design. Besides conventional control, this drive is capable of reciprocating the third carriage 60 together with the tool carrier 66 and the workpiece clamped therein in rapid oscillatory or reciprocating motion along the fourth axis 58 (X).

A "fast" movement is to be understood as speeds of more than 20 m / min, preferably of more than 50 m / min, and reversal accelerations in the range of more than 3 m / s ² , preferably more than 10 m / s ² . In the illustrated embodiment, and in the described workpieces (turbine blades), this as a result of their dimensions to stroke rates between 200 and 500 min ^-1. It is understood that the above values are to be understood as an indication only. It may well be that as a result of new materials, both in the field of moving components as well as in the field of tools (abrasives) or new drive technologies in the future, other, especially higher values of speed and / or acceleration can be achieved. On the other hand, smaller values are possible for very large workpieces, without departing from the scope of the present invention.

The front view in FIG. 2 shows that at the two ends of the grinding spindle 42 two different grinding wheels 44 and 48 can be arranged to grind the workpiece shown, namely a turbine blade 68, in particular their so-called platforms 69a and 69b. It can be seen in the dot-dashed representation that the grinding spindle 42 can be brought into engagement with the left platform 69a of the turbine blade 68 while maintaining its rotational position (A-axis 50) with the first grinding wheel 44 '. In contrast, when the grinding spindle 42 is rotated by 180 ° about the A-axis 50 and correspondingly moved in the Z-direction and possibly also in the Y-direction, the second grinding wheel 48 'can now machine the right-hand platform 69b.

In FIG. 1 Finally, on the right side of the grinding machine 10 is still a magazine 70 to recognize, in the different grinding wheels and / or workpieces and / or dressing tools are included to be switched on and replaced as needed. The exchangers and conveyors required for this purpose are likewise known to the person skilled in the art and are therefore not shown.

Also not shown are the necessary means for dressing the grinding wheels 44 and 48. These devices are preferably rotary dressing spindles with diamond dressing rollers. They can be permanently installed on the machine bed 14 so that the moving masses do not increase in the selected machine concept

The FIGS. 3 and 4 show in two views more details of the third carriage 60th

It can be seen that the third carriage 60 can be driven via a first drive 72 along the guide 52 in the X direction. The first drive 72 is preferably a linear motor, but may also be a crank mechanism or the like. Importantly, the first drive 72 is capable of rapidly moving the entire third carriage 60 with jigs and clamped workpiece with high stroke rate and registration along the fourth axis 58 (X-axis).

On the first carriage 60 is seated a second drive 74, namely a rotary drive, for the fifth axis (B-axis). The second drive 74 rotates the turntable 62 by predetermined angle or angle increments. The rotation of the workpiece 68 on the turntable 62 can be performed by a rotary table of known type, as in FIG. 2 indicated, or - as an alternative in the FIGS. 3 and 4 represented - by a pivoting device.

The turntable 62 is in FIG. 3 guided and supported in an indicated there arcuate rotary guide 78. The second drive 74 can perform a slow rotational or pivotal movement, in embodiments of the invention but also a fast oscillatory movement, preferably superimposed on the slow rotational movement. In both cases, so-called direct drives are advantageously used, which consist of electromotive rotors and stators, require no further mechanical transmission parts and allow high angular acceleration.

The machine concept according to the invention is thus characterized overall by the following distribution of the machine axes X, Y, Z and B required for the path grinding and the pivot axis A required for positioning the grinding spindle 42:

The workpiece 68 is clamped in the workpiece holder 66 on the turntable 62 (B-axis), which in turn is arranged on the X-carriage 60. The grinding spindle 42 is optionally arranged on a pivoting device (A-axis) and on a cross slide 22,24, 26, 30, 32, 34, 36, 40 in the Y and Z directions movable.

The web feed tangential to the workpiece surface, which is to be particularly fast, is performed by the relatively light X-carriage 60, which is equipped with strong drive elements and rigidly supported against the massive machine bed 14. The X-carriage 60 carries only the turntable 62 (B-axis) with the workpiece holder 66th

The velocity and acceleration vectors of the other slide units may be smaller by about a factor of 3 to 10, for example. These sled units are associated with the massive components. The grinding spindle 42 is movable on the cross slide 22, 24, 26, 30, 32, 34, 36, 40 in Y and Z directions. The elements of the cross slide 22,24, 26, 30, 32, 34, 36, 40, the grinding spindle 42, and an optionally installed pivoting device (A-axis) are usually considerably heavier than the workpiece holder 66 and the associated turntable 62nd In addition, their dynamics are limited by the generally larger projection. The numerous supply and control lines that lead to the grinding spindle and mitzuschleppen in their movements, further limit their acceleration capacity.

The concept developed in the context of the present invention thus represents a particularly advantageous arrangement of the machine axes. No other axle sequence would offer comparable favorable conditions for high web speeds and path accelerations as well as fast oscillation strokes.

The gantry design of the grinding machine 10 according to FIG. 1 represents an advantageous embodiment of the machine dynamics embodiment. However, it is not the only conceivable design, because in the context of the present invention also alternatives are possible.

An embodiment of the method according to the invention, as it on the grinding machine according to the FIGS. 1 to 4 is executable, should now be based on the FIGS. 5 to 8 be explained.

In FIG. 5 is drawn through a (here any) workpiece 79 shown in a first position. The workpiece 80 has a convexly shaped surface 80 in certain areas. 81 denotes an engagement point of the grinding wheel 44 on the convex surface 80, where a radius of curvature at R _{K is also} drawn. When the convex curved surface is a cylindrical surface, the radius of curvature has R _{K is} a constant size and includes a right angle with the fifth axis 64 (B-axis). For a conically shaped surface, this angle is finite, and for a surface with a higher order curvature, the angle is finite and dependent on the point of engagement.

To grind the convex surface 80, the workpiece 79 is rapidly oscillated and moved at a predetermined stroke along the fourth axis 58 (X-axis). This lifting movement is in FIG. 5 indicated by a double arrow and the symbol ΔX. The end positions of the workpiece within the lifting movement are represented by reference numerals 79 (solid line) and 79 '(dashed lines).

One recognizes FIG. 5 clearly that the oscillating movement of the workpiece 79, 79 'is effected such that the workpiece 79, 79' and the grinding wheel 44 are guided past each other substantially tangentially. The material of the workpiece 79, 79 'is thus removed in strip-shaped areas. As an alternative, the workpiece 79, 79 'additionally oscillated about the fifth axis (B-axis) can be pivoted, as indicated by a double arrow 82. Then there is a material removal in crescent-shaped areas, which is closer to the convex shape of the surface 80, 80 'and allows longer stroke lengths ΔX.

Simultaneously, the grinding wheel 44 is delivered along the first axis 26 (Z-axis) as indicated by the symbol ΔZ. This sets the desired partial allowance for each stroke, but also determines the shape of the machined surface 80, 80 'because at the same time the workpiece 79, 79' is slowly rotated about the fifth axis 64, 64 'as shown by an arrow B. The shape of the surface 80, 80 ', in the representation of FIG. 5 is generated from left to right, thus results from a superposition of the delivery (Z) and the slow rotational movement (B).

The FIGS. 6 to 8 illustrate on the basis of machining a turbine blade 68 a way to optimize the stroke length .DELTA.X. One recognizes there on an enlarged scale the convexly curved surface 80 in the region of the platform 69a and the desired total allowance 83 to be removed in a predetermined number of strokes.

In the presentation of FIG. 6 is the turbine blade 68 in a first rotational position in which a center line 84 of the turbine blade 68 is rotated by an angle B ₁ in a clockwise direction with respect to a vertical. In this first rotational position, the grinding wheel 44 can only ablate a material region from a first engagement point 85a to a second engagement point 85b. Therefore, a stroke length Δ ₁ X is set which corresponds to just the distance between the two engagement points 85a and 85b, to avoid an additional idle stroke that would take time.

FIG. 7 shows a second rotational position in which the turbine blade 68 'has been rotated by the angle B ₁ in the counterclockwise direction, so that now the center line 84' coincides with the vertical. The grinding wheel can now be guided over the entire width of the platform 69a, ie from a third engagement point 85c to a fourth engagement point 85d. The distance between these two engagement points 85c, 85d now also determines the stroke length Δ ₂ X.

In FIG. 8 a third rotational position is shown in which the turbine blade against the second rotational position by an angle B _{2 has been} further rotated counterclockwise. The possible distance of the material removal between a fifth engagement point 85e and a sixth engagement point 85f is now limited by the reaching of the limit of the total allowance 83, and accordingly also the length of the now to be set stroke Δ ₃ X.

A the FIGS. 6 to 8 corresponding representation is, again in a slightly enlarged scale, the FIGS. 9 to 12 in the case of a concavely curved surface 86 on the opposite platform 69b of the turbine blade 68 to be removed with a total allowance 88.

In FIG. 9 is, analogous to FIG. 6 , a first rotational position of the turbine blade 68 is shown. Here, too, we initially have only a relatively short distance between a first and a second engagement point 89a, 89b, which determines the stroke Δ ₁ X in this rotational position.

In FIG. 10 is, analogous to FIG. 7 , A second rotational position shown in which a third and a fourth engagement point 89c, 89d lie at the edges of the platform 69b and thus define a maximum distance or a maximum stroke Δ ₂ X.

The removal of material can now be continued with in each case maximum stroke, which increases slightly due to the widening in the Z direction form of the platform 69b to a value Δ ₃ X until the limit of the total allowance 88 is reached, as FIG. 11 shows.

FIG. 12 shows that the described approach reaches its limits on concave mold elements of the workpiece 68 ", if the dynamics of the linear axes are not sufficient to follow tight bends at the desired high speed Such crescent-shaped sections 90 can be finished with reduced web speed and correspondingly reduced removal rate This movement is in FIG. 12 indicated by an arrow 91.

Alternatively, at such concave portions, a higher line speed can be achieved when the workpiece performs an additional pivoting movement, as in FIG FIG. 13 in one too FIG. 5 sketched analogous manner for the general workpiece 79. From an initial rotational position, the workpiece 79 (drawn in a solid line) is rotated in the clockwise direction about the fifth axis 64 (B-axis) by an angle ΔB and at the same time along the fourth axis 58 (X-axis) by a distance ΔX to the left, until it assumes a rotational position 79 "(shown by dashed lines) The grinding wheel 44 is simultaneously moved downwards along the first axis 26 (Z-axis) by a distance ΔZ until it assumes the position 44". Through these superimposed movements, the engagement point 89 travels along the concave surface 86, 86 "to 89". It is off FIG. 13 It can be seen that the point of contact between the grinding wheel 44 and the workpiece 79 moves 89 ° to 89 ° with the rotation of the workpiece 79 at the angle ΔB, while at the same time the fast fourth axis 58 (X-axis) is the distance ΔX and the first axis 26 (Z-axis) have to travel the much smaller distance ΔZ.

To optimize the web speed, the component "rotation" must be adapted to the workpiece curvature, the grinding wheel diameter and the acceleration capacity of the linear axes. It is favorable for the grinding process from the viewpoint of accuracy, if the engagement point 89, 89 'relative to the grinding wheel coordinates shifts only slightly, as in FIG. 13 entered as ΔU.

Claims (27)

1. Method for machining of workpieces (68; 79) with a curved surface (80, 86), in which the workpiece (68; 79) is moved along a first axis (58; X) and at the same time is rotated about a second axis (64; B) which encloses a finite angle with the first axis (58; X), and in which a machining tool can be advanced along a third axis (26; Z) which likewise encloses a finite angle with the first axis (58; X) and with the second axis (64; B), characterized in that the workpiece (68; 79) is moved along the first axis (58; X) in a rapidly oscillating movement (ΔX), the oscillating movement (ΔX) being executed at a speed of more than 20 m/min, preferably of more than 50 m/min, and a reverse acceleration of more than 3 m/s², preferably of more than 10 m/s², with an adjustable, variable stroke length (Δ₁X, Δ₂X, Δ₃X), the stroke length (Δ₁X, Δ₂X, Δ₃X) being substantially identical to the path traversed in the workpiece (68; 79) by the machining tool during the respective oscillating movement (ΔX).
2. Method according to Claim 1, characterized in that the oscillating movement (ΔX) is executed at a frequency of between 200 and 500 min^-1.
3. Method according to Claim 1 or 2, characterized in that the first axis (58; X), the second axis (64; B) and the third axis (26; Z) are each perpendicular to one another.
4. Method according to one or more of Claims 1 to 3, characterized in that the second axis (64; B) encloses a right angle with the radius of curvature (R_K) of the surface (80; 86) in an engagement point (81; 89) of the machining tool on the surface (80; 86).
5. Method according to one or more of Claims 1 to 4, characterized in that, during the machining of a concavely curved surface (86), a residual oversize (90) is removed at a reduced path speed by means of continuous-path control of the workpiece (68) and machining tool.
6. Method according to one or more of Claims 1 to 5, characterized in that, during the machining, the workpiece (68; 79) is additionally pivoted in an oscillating manner about the second axis (64; B).
7. Method according to one or more of Claims 1 to 6, characterized in that a continuous-path control between the workpiece (68, 79) and machining tool is superimposed on the oscillating movement (ΔX) of the workpiece (68, 79).
8. Method according to one or more of Claims 1 to 7, characterized in that the machining tool is furthermore moved along a fourth axis (36; Y) which preferably runs parallel to the second axis (64; B).
9. Method according to one or more of Claims 1 to 8, characterized in that the machining tool is furthermore rotated about a fifth axis (50; A) which preferably runs parallel to the first axis (58; X).
10. Method according to Claim 9, characterized in that, by rotation of the machining tool about the fifth axis (50; A), two different tools are alternatively brought into engagement with the workpiece (68).
11. Method according to one or more of Claims 1 to 10, characterized in that surfaces having any curvature on the workpieces (68; 79) are machined.
12. Method according to one or more of Claims 1 to 11, characterized in that the workpieces (68; 79) are ground.
13. Method according to one or more of Claims 1 to 12, characterized in that the workpieces are turbine blades (68).
14. Method according to Claim 13, characterized in that the surfaces (80, 86) are cylindrical surfaces on a platform of the turbine blades (68).
15. Machine tool for machining of workpieces (68; 79) with a curved surface (80, 86), with a tool holder (66) which is movable along a first axis (58; X) and at the same time is rotatable about a second axis (64; B), wherein the second axis (64; B) encloses a finite angle with the first axis (58; X), and with a machining tool which can be advanced along a third axis (26; Z) which likewise encloses a finite angle with the first axis (58; X) and with the second axis (64; B), characterized in that the tool holder (66) is connected to a first slide (30) which moves the workpiece (68; 79) along the first axis (58; X) in a rapidly oscillating movement (ΔX), the oscillating movement (ΔX) being executed at a speed of more than 20 m/min, preferably of more than 50 m/min, and a reverse acceleration of more than 3 m/s², preferably of more than 10 m/s², with an adjustable, variable stroke length (Δ₁X, Δ₂X, Δ₃X), the stroke length (Δ₁X, Δ₂X, Δ₃X) being substantially identical to the path traversed in the workpiece (68; 79) by the machining tool during the respective oscillating movement (ΔX).
16. Machine tool according to Claim 15, characterized in that it executes an oscillating movement (ΔX) at a frequency of between 200 and 500 min^-1.
17. Machine tool according to Claim 15 or 16, characterized in that the first slide (30) is coupled to a linear motor (72).
18. Machine tool according to one or more of Claims 15 to 17, characterized in that the first slide is coupled to a crank drive.
19. Machine tool according to one or more of Claims 15 to 18, characterized in that the first axis (58; X), the second axis (64; B) and the third axis (26; Z) are each perpendicular to one another.
20. Machine tool according to one or more of Claims 15 to 19, characterized in that the second axis (64; B) encloses a right angle with the radius of curvature (R_K) of the surface (80; 86) in an engagement point (81; 89) of the machining tool on the surface (80; 86).
21. Machine tool according to one or more of Claims 15 to 20, characterized in that the tool holder (66) is provided with a rotary drive (76) which can be operated continuously or in an oscillating manner selectively.
22. Machine tool according to one or more of Claims 15 to 21, characterized in that the machining tool can furthermore be moved along a fourth axis (36; Y) which preferably runs parallel to the second axis (64; B).
23. Machine tool according to one or more of Claims 15 to 22, characterized in that the machining tool can furthermore be rotated about a fifth axis (50; A) which preferably runs parallel to the first axis (58; X).
24. Machine tool according to one or more of Claims 15 to 23, characterized in that the first slide (60) runs along the first axis (58; X) on a machine bed (14), and in that the machining tool runs along the third axis (26; Z) on a second slide (30) on a transverse support (20) of a portal (18) spanning the machine bed (14).
25. Machine tool according to one or more of Claims 15 to 24, characterized in that the machining tool is at least one grinding wheel (44, 48) with which the workpieces (68; 79) are ground.
26. Machine tool according to one or more of Claims 15 to 25, characterized in that the workpieces are turbine blades (68).
27. Machine tool according to Claim 26, characterized in that the surfaces (80; 86) are substantially cylindrical surfaces on a platform of the turbine blades (68).

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