JP2003508234A - Machine tools with fastening devices - Google Patents

Abstract

(57) [Summary] In a tightening device having a tightening surface adapted to abut on a workpiece, and a drive unit that generates relative movement between a processing unit and the tightening device, the tightening device (3) can be repeatedly reused. A clamping surface (21, 21 '; 22) having at least two clamping claws (15a, 15a'; 15b, 15b ') and formed on the claws (15a, 15a'; 15b, 15b ') of the clamping device (3). , 22 ′) correspond to at least one area of the target shape of the workpiece.

Description

Detailed Description of the Invention

The present invention relates to a machine tool for milling elastically deformable workpieces, particularly metal workpieces such as turbine blades, which is capable of inserting a milling tool and capable of being driven to generate a cutting speed. A clamping device having a clamping surface adapted to receive the workpiece and to come into surface contact with the workpiece during machining; and a drive unit which produces a relative movement between the machining unit and the clamping device. Regarding what you have. The invention also relates to a method suitable for machining elastically deformable workpieces and a clamping device for clamping turbine blades during machining.

[0002] When machining workpieces of complex shape, for example curved multiple times, the problem frequently arises that the way the workpiece is clamped in the machine tool has a very significant influence on the quality of the machining result. . To avoid detrimental bending moments and vibrations of the workpiece during machining, on the one hand, the workpiece is clamped as close as possible to the point to be machined. On the other hand, the points provided for tightening from this point of view are often prefabricated and already have contours which are hardly suitable for conventional tightening. In addition, care must be taken so that the prefabricated part is not damaged by tightening.

This problem arises, for example, in the milling of individual turbine blades, which have been pre-machined for example by precision forging or otherwise, but whose head, base and so-called “snabs” between them have to be milled. Occurs. "Snatsuba" refers to a range of turbine blades used for tightening turbine blades in a turbine. By precision forging, the vane already has a curved surface that is twisted into its plate area. It is therefore advantageous if the blade can be clamped in the plate area.

To make this possible, the so-called “cellobend” method has already been used, in which each blade must be cast individually in the clamping device via a three-point support in the plate range. For the casting process, it is necessary to use casting equipment which is specially designed for this purpose. In this case, the casting material does not bond with the blades and is removed again after processing. The clamping device for machining the blade, together with the blade now contained therein, is clamped and machined on the machine tool.

On the one hand, the position of the blades in this clamping device is not obvious and on the other hand the blades have manufacturing errors in the forging process, so that the partially cast blades must be measured before milling. Only on the basis of this measurement can the relative position of the individual areas of the blade also be ascertained with respect to the target contour and the clamping device. Since the clamping device itself takes a predetermined position on the machine tool, it is possible to determine, based on this measurement, on what path the tool has to move to obtain a particular target contour.

A disadvantage of this tightening device is that the forging material, ie the lead alloy, contains toxic substances and therefore additional safety measures must be taken to protect humans in contact therewith. Performing the work immediately after the casting process is likewise unsatisfactory. Due to the long storage time, the preload holding the blades on the clamping device after cooling of the lead alloy may relax again.

The problem underlying the invention is therefore to provide a tightening device of the type mentioned at the outset that avoids the disadvantages mentioned above.

According to the invention, in the machine tool mentioned at the outset, the clamping device has at least two clamping pawls which can be reused repeatedly and the clamping surface of the clamping device formed at the clamping pawl. Corresponds to at least one area of the target shape of the workpiece. This problem is also solved by the tightening device and method according to claims 8 and 10.

The present invention finds particular use in the processing of turbine blades. However, the field of application naturally also includes the machining of other workpieces, in particular those in which the workpiece has a twisted or other complexly curved surface.

A workpiece, such as a turbine blade, has a small thickness compared to its length and width. Since the blades are also generally made of titanium alloy, they have relatively good elastic deformability.

By suitable placement of the clamping pawls on the machine tool, it is possible to clamp the workpiece and to allow the workpiece to at least approximately assume the target contour due to the deformation in the region of the clamping surface. Therefore, in the clamping device according to the invention, the workpiece is forced into the desired shape as much as possible by conforming to the clamping surface, starting from a position which does not correspond to the target contour. In this context, "target shape" or "target contour" means a workpiece that does not have dimensional, shape or position errors within the achievable manufacturing accuracy.

This has the advantage that the clamping surface or any one or more predetermined points of the clamping surface can be used as a reference for the next machining direction. Since the path of travel of the tool is now related to the position of the clamping surfaces and the corresponding areas of the workpiece at these clamping surfaces assume the target contours or positions, significant systematic errors that reduce manufacturing accuracy are eliminated. Apart from other possible influences, in the ideal case, the tool can now produce a contour on the workpiece which corresponds to the target contour, for which purpose no workpiece measurement is required in advance. The processing time of the turbine blades on the milling machine is reduced by about 10-15% to avoid the measurement.

Another advantage is that the fade-in location, ie the transition between the non-milled and milled areas of the workpiece, can be formed qualitatively, at a low cost. . That is, a workpiece having a movement path based on the target contour actually engages the target contour and not a toleranced contour.

In a particularly advantageous embodiment, the tightening of the tightening device is produced on the same machine tool on which the actual workpiece is also machined. This can reduce manufacturing tolerances.

In a further advantageous configuration, the clamping device according to the invention has a body which is clamped to the machine tool. One or more insert pieces are insertable into the body and a clamping surface is formed on these insert pieces for clamping the workpiece. This has the advantage that the main part of the clamping device can be used for different workpieces. If another workpiece is to be machined, the insert pieces need only be replaced. Therefore, since the important parts of the clamping device are designed to be replaceable, the costs required for the production of different workpieces with respect to the clamping device can be reduced.

[0016]   Further preferred configurations of the invention can be seen from the claims.

[0017]   The invention is explained in greater detail on the basis of the exemplary embodiment shown schematically in the drawings.

The milling machine 1, a part of which is shown in FIG. 1, has a circular station 2 with a head 2 a and a base 2 b. The head 2a can be provided with a clamping device 3 which is considered for receiving the workpiece. The circular station 2 has an X direction and a Z direction.
It is on a carriage 4 movable in a direction (right angle to the plane of the drawing). The circular station 2 is further provided with a rotational axis 5 which is driven, by means of which the clamping device 3
Are rotatable about axis 5. The machine tool or the tightening device and the workpiece form a workpiece manufacturing system described later.

The milling machine further has a tool carrier 6 as a processing unit, and a milling tool 7 is provided on this tool carrier and can be driven. Tool carrier 6 is in X direction and Y
It is movable in the direction, and can be swiveled around the tool tip 7a within a range of about ± 80 °.
Thus, in the region of the tool tip, the machining axis of the tool intersects the swivel axis of the tool carrier. The basic structure and operation mode of such a machine tool are described in the European application No. 93120 of the applicant.
198.2, the contents of which are fully incorporated by reference.

Two clamping devices 3 can be held in each circular station 2,
The clamping device is considered for receiving the workpiece. In FIG. 1, the workpiece is a turbine blade 8 that has been pre-machined by precision forging, the plate of which already has a contour that is within tolerance limits. Due to the material of the turbine blades, i.e. the titanium alloy material, and due to the ratio of blade length and width to thickness, this blade is elastically deformable over a relatively wide range.

As can be seen from the magnified partial view of FIG. 2, the clamping device 3 has a body 10 which is constructed rotationally symmetrical about the axis 5. The body can be received in the circular station 2 shown in FIG. In the circular station 2, its driven rotation axis 5 is aligned with the axis of symmetry of the tightening device 3. At the end of the body 10 opposite the centering pin 11, the body is bifurcated. Two facing claws can be provided on each leg 14a, 14b of the bifurcation 14.

Each of the two leg sides 14a, 14b shown in FIG. 2 has a receiving portion, and the fastening claws 15a,
One insert piece, which is configured as 15b, can be inserted into this receiving part. The clamping pawls 15a and 15b are shown in FIG. Two separate clamping pawls 15a ', 15b' each rest on the surface of the turbine blade 8 on the side facing the clamping pawls 15a, 15b. As a result, the clamping pawls 15a and 15a 'directly face each other on the one hand, and the clamping pawls 15b and 15b' directly face each other on the other hand, the turbine blades being respectively provided between these clamping pawls. Each of the clamping pair pawls 15a ', 15a' and 15b, 15b 'thus formed can be secured to each other by suitable means, not shown, such as screws, so that the clamping surface of the clamping pawls is of a given nature. To face each other. The clamping surfaces 21, 21 ′ and 22, 22 ′ form respectively one laterally opening volume or cavity between them, the shape and the mutual position of which being of the desired shape of the turbine blade. It corresponds precisely to the area. Unlike FIG. 3, FIG. 2 shows only one clamping pawl 15a ', 15b' of each clamping unit.

In FIG. 3, for the sake of clarity, the clamping pawls are shown separated from the turbine impeller. Tightening surfaces 21, 21 '; 22 of the fastening claws of the same fastening unit
, 22 'are aligned on the same line 20. Thereby, each one projection plane along the line 20 of the opposite clamping surfaces on different sides of the turbine blade is
Same or congruent.

Accordingly, the turbine blade 8 is held between two clamping claws which face each other at two points. Both clamping points are in the plate area of the turbine blade, a first clamping point is provided in the area of the plate end 16 and a second clamping point is provided behind the base area 17 of the turbine blade 8. Thus, when the turbine blade 8 is clamped with its longitudinal axis 18 approximately at right angles to the axis of rotation 5, a so-called "snubber" 19 lies between both clamping units. This snubber, like the legs, is used to fasten the blades to the turbine.

Therefore, due to the machining of the turbine blades 8, the plate edge 16, the snubber 19 and the base area 17 are accessible to the milling tool. Due to the possible relative movements of the workpiece and the tool along the three linear axes X, Y and Z, the axis of rotation 5, the pivot axis of the tool carrier 6,
And due to the good accessibility of the work piece provided by the structural design of the clamping device, all milling operations can be performed particularly advantageously with only one clamping.

In a clamping position, not shown, the clamping pawls 15 a, 15 a ′; 15 b, 15 b ′ are moved in parallel along the line 20 and come into surface contact with the turbine blade. In FIG. 4, the turbine blade before tightening is indicated by reference numeral 8. The contour of the turbine blade, which results from elastic deformation during tightening, is indicated by the dashed line 8 '. The turbine blade base 17 is shown without deformation. Because this base takes on the role of a reference point,
This is because it is not manufactured until after tightening.

All clamping jaws 15a, 15a '; 15b, 15b' have clamping surfaces 21, 21 '; 22, 22' which correspond to the negative contour of the respective area of the turbine blade. The clamping surfaces 21, 21 '; 22, 22' can therefore be produced on the machine shown in FIG. 1 on the basis of the geometrical data of the target contour of the turbine blade type to be clamped. Using the same data, which is also used for the production of the forging dies by milling, a particularly simple and inexpensive production of the clamping jaws takes place. Since the clamping pawls are milled on the same machine that also processes the turbine blades, very good manufacturing accuracy can be obtained on the turbine blades.

In the clamping device, both clamping pawls face each other, so that one clamping pawl abuts one side of the turbine blade and the other clamping pawl abuts the opposite side. Since the plate range is already completed after forging and matches the target contour or target value within normal tolerances in contour accuracy, deflection and twist, the plate range is set within the elastic deformation range by the tightening unit. Alternatively, it is only necessary to force the target shape. In order for the turbine blades to assume the correct position in the X-direction shown in FIG. 1, at least one clamping pawl can be provided with at least one stop, against which the plate edge abuts. The correct position of the turbine blade in the Z direction or the longitudinal axis of the turbine blade, and the correct position of the turbine blade in the Y direction or the length of the snapper, is generally obtained by itself due to the matching of the plate contour and the clamping surface contour. To be

After the completion of the turbine blade and the removal of the turbine blade from the clamping device, the blade is loosened again. As a result, inaccuracies are regenerated by the values that had been present before tightening due to the forging process but were already within the permissible limits. The vane contours that occur during tightening (high finishing accuracy is assumed during milling) are therefore likewise within acceptable limits.

[Brief description of drawings]

1 shows in a front view a part of a machine tool provided with a clamping device for holding a workpiece.

[Fig. 2]   2 shows a plan view of the tightening device of FIG. 1 according to the invention.

FIG. 3 shows a perspective view of a turbine blade to be clamped by the clamping device according to the invention, in which two clamping pawls of different clamping units are shown spaced from the blade.

FIG. 4 shows the turbine blade of FIG. 3 in two different states, the broken line showing the deformation of the blade in the clamping device.

─────────────────────────────────────────────────── ─── Continued front page    (81) Designated countries EP (AT, BE, CH, CY, DE, DK, ES, FI, FR, GB, GR, IE, I T, LU, MC, NL, PT, SE), OA (BF, BJ , CF, CG, CI, CM, GA, GN, GW, ML, MR, NE, SN, TD, TG), AP (GH, GM, K E, LS, MW, MZ, SD, SL, SZ, TZ, UG , ZW), EA (AM, AZ, BY, KG, KZ, MD, RU, TJ, TM), AE, AG, AL, AM, AT, AU, AZ, BA, BB, BG, BR, BY, BZ, C A, CH, CN, CR, CU, CZ, DE, DK, DM , DZ, EE, ES, FI, GB, GD, GE, GH, GM, HR, HU, ID, IL, IN, IS, JP, K E, KG, KP, KR, KZ, LC, LK, LR, LS , LT, LU, LV, MA, MD, MG, MK, MN, MW, MX, MZ, NO, NZ, PL, PT, RO, R U, SD, SE, SG, SI, SK, SL, TJ, TM , TR, TT, TZ, UA, UG, US, UZ, VN, YU, ZA, ZW

Claims (12)

[Claims] 1. A machine tool for milling elastically deformable, especially metal workpieces such as turbine blades, which is insertable with a milling tool and is drivable to produce a cutting speed. Including a clamping device having a clamping surface adapted to receive the workpiece and to come into surface contact with the workpiece, and a drive unit which produces a relative movement between the working unit and the clamping device. At least two clamping pawls (15a, 15a,
15a '; 15b, 15b') and tightening claws (15a, 15a '; 15b,
15b ') tightening surfaces (21, 21'; 22) of the tightening device (3) formed at 15b ')
, 22 ') corresponds to at least one area of the target shape of the workpiece. 2. Clamping pawls (15a, 15b) are provided on the clamping device, whereby the geometry of the workpiece is deformed by clamping faces (21, 21 '; 22, 2).
Machine tool according to claim 1, characterized in that it is fitted to the contour of 2 '). 3. The tightening surfaces (21, 21 '; 22, 22') are turbine blades (
The machine tool according to claim 2, wherein the machine tool is adapted to the target shape of 8). 4. A clamping device (3) with a turbine blade (8) is provided on a circular station (2), the longitudinal axis (18) of the turbine blade being substantially relative to the axis of rotation (5) of the circular station. Machine tool according to claim 3, characterized in that it is oriented at a right angle to the. 5. At least two clamping pawls (15a, 15a '; 15b, 1)
Machine tool according to one or more of the preceding claims, characterized by 5b '). 6. The tightening surfaces (21, 21 '; 22, 22') of the tightening device are
Machine tool according to claim 5, characterized in that it corresponds to the target-shaped areas of the turbine blade (8), respectively, with a snub (19) between these areas. 7. A body (10) having at least one receiving part, to which a replaceable insert piece configured as a clamping pawl can be provided, the insert piece having a clamping surface (21, 21 '). Machine tool according to one or more of the preceding claims, characterized in that: 22, 22 ') are provided. 8. A clamping device for positioning and holding turbine blades during machining of the turbine blades, the clamping surfaces (21, 21) being formed on the clamping pawls.
';22,22') with their clamping surfaces abutting the opposite surface areas of the turbine blade, at least two clamping pawls (15a, 15a,
15a '; 15b, 15b') are reusable and the clamping surfaces (21, 21 ';
Clamping device, characterized in that the geometry of 22, 22 ') corresponds to at least one area of the target geometry of the turbine blade. 9. A tightening device according to claim 8 having one or more features of the tightening device according to claims 2-7. 10. A method of machining an elastically deformable workpiece, such as a turbine blade, in which a clamping device is first created and a plurality of workpieces of the same type are present in a machine tool and are structurally invariant. Workpieces are sequentially installed and processed by various tightening devices.
Between the clamping surfaces of the clamping pawls of the clamping device, the clamping surfaces (21, 21) being held in at least one surface area different from the flat surface of the workpiece.
';22,22') each have a contour corresponding to the area of the target contour of the workpiece, and the workpiece is elastically deformed during clamping, so that during clamping the shape of the workpiece approaches at least the target shape. A processing method characterized by being processed. 11. Clamping device (3) for holding a work piece is a circular station (2).
A turbine blade in which the circular station during machining rotates the clamping device about the axis of rotation (5) of the circular station, if necessary, and the workpiece is oriented at right angles to the axis of rotation. The method according to claim 8, characterized by: 12. Clamping surface (21 ,; 22) of the clamping device (3) is formed on the same machine tool that also processes a workpiece, 1 according to claim 8 and 9.
The method described in one or both.