Method for repairing and producing integrally bladed rotors for a turbine or turbo engine

[0002] The present invention relates to a method for repairing an integrally bladed rotor for a turbine or turbo engine, in which a plurality of projecting vanes are arranged on the peripheral surface of the carrier, and to a method for manufacturing an integrally bladed rotor for a turbine or turbo engine, in which a plurality of projecting vanes are to be arranged on a peripheral surface of a carrier, each of which is welded to a stub, having a front face, projecting over the peripheral surface.

[0003] Such integrally bladed rotors can be manufactured by milling from the entire unit or by welding the individual vanes to the carrier. U.S. Pat. No. 4,883,216 describes a method of repairing and manufacturing such a rotor in which initially a collar is welded to the stubs projecting over the peripheral surface of the carrier around its entire periphery and subsequently a (replacement) vane is welded to this enlarged bonding surface, made up of stub and collar, which has a considerably widened bonding collar on the vane base. One disadvantage is that the vane cannot be welded in its final/finished form, and a very large amount of subsequent machining is required due to the two collars.

[0004] French Patent Application No. 22 26 241 describes a method for bonding vanes to a rotor carrier. The vanes include a projecting base having a supporting surface for transmitting joining forces. The vanes are welded to the rotor carrier using resistance welding.

[0005] One object of the present invention is to provide a method of repairing a rotor of a turbine or turbo engine in which the replacement vane section can be welded as far as possible in its finished form without many additional machining steps. It is another object of the present invention to provide a method of manufacturing such a rotor, in which the vanes can be welded to the carrier as far as possible in their finished form without many additional machining steps.

[0006] According one embodiment of the present invention, the repairing method includes the following steps: removing a vane section to be replaced leaving a stub section forming a first part of the vane, which has a front face for bonding to a replacement vane section; arranging an inductor around the front face of the stub section; positioning the replacement vane section, corresponding to the removed vane section in shape and size, on the stub section, one surface used as a joining surface of the replacement vane section and the front face of the stub section being essentially aligned with and opposite one another at a small distance; and welding the replacement vane section to the stub section in a protective gas atmosphere by exciting the inductor with high-frequency current and moving the replacement vane section and the stub section together, with the melted front face of the stub section and the surface of the replacement vane section in contact with one another.

[0007] One advantage of the repair method according to the present invention is that the induced high-frequency current is concentrated in the respective joining surfaces and these surfaces are only melted in the area near the surface, so that the replacement vane section and the stub section are pressed together using relatively little force and over an extremely short period of time. For this reason the replacement vane section can be easily held in the blade area.

[0008] Furthermore, particularly thin-walled, mechanically sensitive vanes can be replaced or attached in this way. It is also possible to join cast vanes to forged rotors (disks/rings) in manufacturing new units.

[0009] In one embodiment, the inductor is arranged at a greater distance from the joining surface in the vane front edge and rear edge areas than in the central area of the vane and the stub section, so the induced high-frequency electrical current heats the front face of the stub section and the surface of the replacement vane section as evenly as possible at all points, melting only the areas close to their respective surfaces.

[0010] The surface of the replacement vane section may be positioned at a distance of approximately 2 mm from the front face of the stub section prior to welding, so the front face of the stub section and the surface of the replacement vane section are evenly heated, melting only to a depth of approximately 0.1 mm.

[0011] The replacement vane section may be fitted into a plastic block in a non-slipping manner, so that the replacement vane section can be welded to the carrier in its final form without additional holding or supporting sections. In this manner, expensive machining steps no longer need to be performed on the replacement vane section.

[0012] The welding step may be performed in a maximum of 3 seconds, which guarantees an efficient process and ensures that the stub section and the replacement vane section melt in the areas of their respective surfaces. The replacement vane section and the stub section may be moved together a maximum of for example an additional 1 mm after contact of their surface and front face, so that any contaminants in the melt are pressed out at the sides, but the peripheral thickening of the joint is kept small.

[0013] In another embodiment, the vane blade section to be replaced, which is usually damaged, may be removed along a parting plane extending to the vane tip. In this manner, if only the vane tip area is damaged, only a small section of the vane has to be replaced, and not the entire vane.

[0014] The manufacturing method according to the present invention includes the following steps: arranging an inductor around the front face of the stub; positioning a vane on the stub, one surface of the vane and the front face of the stub being essentially aligned with and opposite one another at a small distance; and welding the vane to the stub in a protective gas atmosphere by exciting the inductor with high-frequency current and moving the vane and the stub together, with the melted front face of the stub and the surface of the vane in contact with one another.

[0015] FIG. 1 shows a perspective view of a rotor having two damaged vanes;

[0016] FIG. 2 shows an enlarged detail from FIG. 1;

[0017] FIG. 3 is a schematic perspective view of a stub section with an inductor, connected to a current source, arranged around the stub section according to one embodiment of the method according to the present invention; and

[0018] FIG. 4 is a perspective view partially in section of a vane blade section held by a (plastic) block.

[0019] FIG. 1 is a perspective view of the rotor for a turbine or turbo engine which has a carrier 1 designed as a disk, on whose peripheral surface 2 a plurality of vanes 3 are integrally arranged projecting outward. Vanes 3 are generally arranged equidistant on periphery 2 of carrier 1. In addition to a plurality of undamaged vanes 3, two vanes 4 and 5 are damaged in the area of their front edge 6.

[0020] As can be seen more clearly in the detail of FIG. 2, damage on vanes 4 and 5 appear on their front edge 6, while the opposite rear edge 7 is basically undamaged. The damage on vane 4 appears in an area near a vane tip 8, so that in one embodiment of the repair method according to the present invention, a vane blade section 4′ is removed along a parting plane 9 and a stub section 10 forming a part of vane 4, i.e., of the vane blade, and having front face 11, is left unremoved. For damages such as the damage on vane 4, it is not necessary to separate and almost fully remove vane 4 or its blade.

[0021] The damage on vane 5 appeared in the direction of the stack axis in the central area between vane tip 8 and peripheral surface 2 of carrier 1. In such a case, according to another embodiment of the repair method according to the present invention, a vane section 5′ of damaged vane 5 is almost fully removed along a parting plane 12, so that a stub 13 projecting approximately 2 to 3 mm over peripheral surface 2 of carrier 1 and having a front face 14 remains. While parting plane 9 of vane 4 extends obliquely to a cross-section surface up to vane tip 8, parting plane 12 of vane 5 extends substantially parallel to a cross-section surface of vane 5. Front faces 11 and 14 of vanes 4 and 5, respectively, need not necessarily be flat, but may have a curvature depending on the application.

[0022] According to the next step of the repair method according to the present invention, an inductor 16 is arranged in the area of front face 14 of stub 13 around its periphery 15; The inductor is electrically connected to power source 17. As can be seen from the top view illustrated in FIG. 3, the distance between inductor 16 and stub 13 is greater in the area of front edge 6 and rear edge 7 of the vane than in central area 18 in order to achieve even heating of the joint formed by front face 14 of stub 13 during the subsequent welding step. The geometry of section 19 in which inductor 16 is located should be selected depending on the application, so that the material melts or softens only at the joint, i.e., front face 14 of stub 13, in order to allow quick welding and avoiding subsequent machining of the joint after welding.

[0023] FIG. 4 shows the next step of the repair method according to the present invention as a perspective drawing in which inductor 16 is arranged with its section 19 around periphery 15 of front face 14 of stub 13 which projects over peripheral surface 2 of carrier 1. A replacement vane 20 having surface 21 is securely held in a two-part cassette 22 in a plastic block 23. Cassette 22 is secured in a machine slide. Surface 21 of replacement vane 20 corresponds in shape and curvature to front face 14 of stub 13. In order to position replacement vane 20 for the subsequent welding step, the machine slide is moved so that surface 21 of replacement vane 20 is exactly aligned with and opposite front face 14 of stub 13. Before testing, replacement vane 20 may be moved to such front face 14 with its surface 21, then moving them at part again to a distance of approximately 2 mm from one another before the welding step that follows.

[0024] The subsequent welding takes place in a protective gas atmosphere. A high-frequency current is applied to inductor 16 for approximately 1 second. The application of the high-frequency current and thus heating is held as short as possible depending on the material used so that the material of stub 13 and of replacement vane 20 melts or becomes softened only in the area of the joint formed by front face 14 of stub 13 and surface 21 of replacement vane 20. After heating, surface 21 of replacement vane 20 is brought together with front face 14 of stub 13 to contact with one another, an upsetting course of approximately 1 mm being obtained as a result of the distance control. As an alternative, the parts may also be brought together using pressure control.

[0025] FIG. 4 shows a replacement vane 20′, which is bonded to a stub 13′ by high-frequency welding. In the area of joint 24 a slight thickening can be seen. The extent of this thickening depends, in addition to the upsetting course, on the material of stub 13, 13′ and of replacement vane 20, 20′ and it may require removal in a subsequent machining step. In many cases, the thickening at joint 24 is so small that it can be tolerated from the aerodynamic point of view, so that no subsequent machining is required.

[0026] If a vane section 4′ is removed along a parting line 9 as illustrated in FIG. 2 in a repair procedure and the respective joint 24 is located in the area of the blade, subsequent machining of the blade surface may be required for aerodynamic reasons. Also the use of high-frequency current may be advantageous, because it is concentrated at front face 11 of stub section 10 and on the respective surface of replacement vane section 20, only melting the areas near the surface.

[0027] The manufacturing method differs from the above-described repair method only in that no damaged vane section need be initially removed, and stub 13 has the shape and size according to parting plane 12 illustrated in FIG. 2 instead.