Patent Application
20120121427
This application claims the priority of German Patent Document No. 10 2010 045 331.5, filed Sep. 14, 2010, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a joining element and a method for the production of such a joining element.
Various production methods are known for producing a BLISK or a BLING (blade-integrated disc or blade-integrated ring) for jet engines such as aircraft engines. In one method, for example, the BLISK is produced in one piece from a disc by shaping its outer contour using a chip removal process in order to form blade profiles. In another method, the rotor blades are produced separately from the disc and connected to the outer circumference of the rotor disc by linear friction welding.
In order to increase the durability of turbine blades and compressor blades, it is increasingly common to use blades with a monocrystalline structure because such blades have virtually no crystal boundaries or other structural defects. However, when connecting the monocrystalline rotor blades to a polycrystalline rotor disc by friction welding, it is important to note that, depending on the crystallographic orientation of the monocrystalline material structure, another load may be necessary in order to bring the monocrystalline material structure into a plasticizable condition. Applied to the friction welding method, this means that the welding method for the monocrystalline material changes as a function of the crystallographic orientation of the monocrystalline material relative to the oscillation and pressure direction. In the least favorable case, the load required for friction welding may be so high due to the crystallographic orientation of the monocrystalline material that the machine tool or tool head is damaged.
In order to solve this problem, WO 2007/144557 A1 proposes that a monocrystalline component be orientated for linear friction welding in such a way that a primary gliding plane of the monocrystal is oriented to a plane that contains the oscillation direction as well as the pressure direction and such that a primary gliding plane of the monocrystal extends within a certain angle range relative to the oscillation direction. Although this method does allow the direct welding of a rotor blade to a rotor disc, the method is limited to oblong geometries. In addition, this method does not solve general problems of linear friction welding such as a thin, extremely smooth, and sometimes brittle diffusion zone as well as rapid crack propagation.
Therefore, MTU's German patent DE 10 2008 039 113 B3 proposes that a polycrystalline adapter, which is initially connected to the rotor blade by rotational friction welding, be disposed between a monocrystalline rotor blade and a polycrystalline rotor disc. After the production of the blade-adapter arrangement, the adapter is connected to the rotor disc by a fusion welding method or the like.
However, the adapter is subjected to high temperatures and chemical damage, particularly in the connective region on the side of the blade, such that a monocrystalline material structure is preferred, at least on the side of the blade.
The object of the present invention is to create a joining element, in particular for welding to a fusion weldable body segment of an element to be welded, that eliminates the disadvantages discussed above and has a joining surface that is fusion weldable independently of its base material, a method for producing a joining element of this type, as well as an integrally bladed rotor of a jet engine, in particular of an aircraft engine.
A joining element according to the invention, in particular for welding with an element to be welded, comprises a base body and a joining surface. According to the invention, the joining surface is formed by a fusion weldable coating made of a compressed powder that is connected in a positive fit to a contour of the base body. The joining element is thus fusion weldable in the region of its joining surface independently of the material of its base body. Thus, the contour achieves a mechanical, intensive compression of the coating to the base body, such that the coating is connected to the base body in a resilient manner. In addition, the coating, which may be a few centimeters thick, achieves a gradual expansion of the diffusion zone and therefore a gradual, soft transition of the elastic and fracture mechanical properties. Moreover, the coating prevents the propagation of cracks into the joining surface or into the joining region, because such cracks are only able to propagate up to the contour of the base body.
The greater the area of the contour, the more fundamentally stable the compression of the coating to the base body. In one exemplary embodiment, therefore, it is preferred for the contour to extend over a large area of a surface of the base body.
The coating preferably has a thickness that corresponds to a height of the contour. This allows the contour to penetrate the coating over its entire cross section such that the coating is prevented from shearing off in the case of a transverse load.
A particularly intensive mechanical compression may be achieved by designing the contour as a fractal structure. In a preferred exemplary embodiment, the contour is designed as a Koch curve, for example, according to the second iteration.
In one exemplary embodiment, the joining element is designed as an adapter for connecting a monocrystalline rotor blade to a polycrystalline rotor disc, with the base body being composed of a monocrystalline material and the coating being composed of a polycrystalline material corresponding to the material of the rotor disc.
In another exemplary embodiment, the joining element is designed as a monocrystalline rotor blade for attachment to a polycrystalline rotor disc, with the base body forming the rotor blade and the coating being applied to the blade. This allows a direct, fusion welding-based connection of the rotor blade to the rotor disc, whereby a BLISK or BLING of this type is made particularly resilient.
In an embodiment of a method according to the invention for the production of a joining element, first a base body is provided. The base body is then provided with a contour. Then the base body is framed in the region of the contour for the purpose of forming a powder basin. Then the power basin is filled with a polycrystalline powder, which is poured into the powder basin until the contour is completely covered by the powder. The powder is subsequently compressed under pressure and temperature in order to form a coating that is connected to the contour in a positive fit. After compression, the base body or contour is removed from the mold and, if necessary, the joining element is finished. The method according to the invention allows the production of a joining element made of two different materials that together form a body section that is connectable to a connecting element, the materials being securely connected to one another by mechanical compression. The mechanical compression is of such intensity that the joining element is able to be connected to another element to be welded in the region of its base body and its coating by a welding and soldering method.
In a method that is simple from a manufacturing standpoint, the base body is a cast, forged, or sintered metal body into which the contour is mechanically placed by partially lowering a surface of the base body. This may occur, for example, by a chip removal process such as milling, grinding, boring, and the like.
In another exemplary embodiment, the contour is placed into a surface of the base body thermally, for example, by wire erosion and/or electrochemical machining (ECM or PECM).
In a preferred exemplary embodiment, a surface of the base body is not lowered by segments, but rather provided with elevations by segments. To this end, the base body is produced with an integral contour in a generative fashion or by a generative production method such as selective laser sintering. This allows the contour to have virtually any geometric shape desired, such that even highly complex fractal structures can be reproduced as contours. In addition, no additional strains or changes to the material are introduced into the base body in the course of forming the contour.
In a method, the powder is connected to the base body by hot isostatic pressing, whereby the coating receives isotropic properties and a particularly highly compacted and thus intensive compression of the coating onto the contour results.
An integrally bladed rotor according to the invention of a jet engine, in particular an aircraft engine, has a plurality of rotating blades that are each connected to the outer circumference of the rotor by a joining element according to the invention, with the base body being disposed on the side of the rotating blades and the coating being disposed on the side of the rotor. A rotor of this type is particularly highly resilient because of the excellent connection of the rotating blades to the rotor resulting from the joining element.
Other advantageous exemplary embodiments of the invention may be found in the disclosure.
A preferred exemplary embodiment of the invention shall be described in greater detail in the following with reference to the schematic drawings.
As shown in
The base body 4 is composed of a monocrystalline metal material and serves to connect the adapter 2 to the rotor blade, for example, by a rotational welding method, in the region of an outer surface 8 facing away from the coating 6. It has an integral contour 10 with a fractal structure for the purpose of forming a positive fit with the coating 6.
According to
The coating 6 is composed of a compressed powder 24 (see
In a preferred method for the production of the adapter 2, according to
Then, in a second step, the base body 4 is surrounded in the region of its contour 10 by a frame 28 that defines a powder basin 30 for accommodating a polycrystalline powder 24. Then the powder 24 is poured into the powder basin 30, such that free spaces or remaining volumes 32a, 32b, 32c, 32d of the contour 10 are filled between the projections 14, 16, 18 and between the projections 16, 18 and the lateral frame 28. The powder basin 30 is filled with the powder 24 in such a way that the contour 10 or its highest projection 14 viewed in the vertical direction z is covered with the powder 24 such that, after a compression of the powder 24 and final finishing of the adapter 2, the joining surface 26 is disposed at a distance from the surface 12 that corresponds to the height of the highest projection 14, thus corresponding to the height h of the contour (see
Then, in a third step according to
Then, in a fourth step according to
Finally, in a fifth step, the adapter 2 is unmolded and the adapter 2 is finished to its target dimensions. After finishing, the adapter 2 comprises a monocrystalline base body 4 having a polycrystalline coating 6 that defines a fusion weldable joining surface 26. The thickness d of the coating 6 corresponds to the height h of the contour 10. The adapter 2 can now be joined to a rotor blade, for example, by a rotation friction fusion welding method, and then be joined as a blade-adapter arrangement in the region of the joining surface 26 to a polycrystalline rotor disc by a fusion welding method.
Disclosed is a joining element, for example, an adapter, for connecting a rotor blade to a rotor disc or a rotor ring, or a rotor blade per se of an aircraft engine, having a base body and a joining surface, with the joining surface being formed by a fusion weldable coating made of a compressed powder that is connected in a positive fit to a contour of the base body, a method for the production of such a joining element, as well as an integrally bladed rotor.
The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2010 045 331.5 | Sep 2010 | DE | national |
