FR2949366A1 - Low pressure turbine's fixed or movable blade i.e. nozzle blade, repairing method for aeronautical turbojet engine, involves assembling replacement part on blade by welding/soldering, where part is formed by metal powder injection molding - Google Patents

Abstract

The method involves defining a volume of blade completely encircling a damaged area, and cutting the defined volume. Replacement part formed by a trailing edge (5) of the blade having dimensions similar to the cut volume is formed. The replacement part is assembled on a blade instead of the cut volume by welding or soldering, where the replacement part is formed by metal powder injection molding. Polymer material core is positioned to realize a cavity (6) during the formation of the part, where the cavity has an inner surface provided with asperities forming cooling air flow disruptors (9). An independent claim is also included for a blade of turbine of aeronautical turbomachine, comprising an internal cavity.

Description

The field of the present invention is that of the repair of turbomachine parts and in particular parts of the hot parts of these turbomachines. The hot parts of the turbomachines, such as the distributors or the turbine blades are subjected to very high temperatures and significant thermomechanical stresses. They suffer damage, such as cracks, burns, cracks, impacts, etc., that must be repaired to keep the parts in service. These repairs are essential to be able to use them longer and thus reduce the overall cost of ownership of these turbomachines. Several repair processes have therefore been devised, which generally concern the cutting of the damaged part and its replacement, with welding or brazing, by a new part made especially that is able to take the place of the removed part. Such a process is described in particular in US patent application US 2007/84047. This problem is particularly difficult when it comes to replacing the portion forming the leading edge of a turbine nozzle blade because these parts are traversed by multiple cavities for circulating air to cool the metal. of dawn. These cavities also have internal walls that are not smooth so as to create turbulent flows that improve the heat exchange between the metal and the cooling air. The presence, on the one hand, of these flow disruptors, for which a very precise sizing is imperative and the small size of the parts to be produced, on the other hand, make it very difficult or impossible to manufacture the replacement parts. by foundry. The present invention aims to overcome these disadvantages by proposing a turbine blade repair method that is relatively simple to implement and is economical. To this end, the subject of the invention is a method for repairing a blade, fixed or mobile, of a turbomachine turbine comprising the following steps: a. definition of a volume of dawn encompassing the entire damaged area,

2 b. cutting the volume thus defined, c. making a replacement part having the same dimensions as the cut volume, d. assembly by welding or soldering of the replacement part on the blade instead of the cut volume, characterized in that the replacement part is produced by injection molding of metal powder (MIM process). The use of the preceded MIM makes it possible to make small replacement parts with very precise tolerances, not requiring additional machining. Advantageously, the metal powder has the same composition as the blade to be repaired. This is favorable to the mechanical strength of the part after repair, avoiding differential expansion between the parts constituting the repaired part. Preferably, the replacement part is chosen from a set of parts previously produced. This reduces the number of models of replacement parts, which can be achieved in anticipation; this reduces the time required for repair, avoiding having to make a custom piece 20 for each new repair. Even more preferably, the cut is defined by a selection made from the volumes of the pieces of the game previously produced. In a particular embodiment, the method comprises, in step c), the introduction of a core of polymer material, so as to produce an internal cavity. Preferably, the composition of the polymer material is identical to that of the binder used for the MIM process. The invention also relates to a turbine blade of an aviation turbine engine, repaired using a method as described above. In a particular embodiment, the cut volume comprises an internal cavity. Advantageously, the cavity comprises an internal surface provided with asperities forming disrupters for the flow of the cooling air circulating in said cavity.

Finally, the invention relates to a sector of turbine nozzle blades comprising at least one blade repaired using a method as described above and an aviation turbine engine comprising at least one blade, fixed or movable, as claimed above.

The invention will be better understood, and other objects, details, characteristics and advantages thereof will appear more clearly in the following detailed explanatory description of one or more embodiments of the invention given to As purely illustrative and non-limiting examples, with reference to the attached schematic drawings. In these drawings: FIG. 1 is a front view of a low pressure turbine distributor blade of a turbomachine showing the zone to be repaired; FIG. 2 is a cross-sectional view of a turbine blade showing the portion of its leading edge to be repaired; FIG. 3 is a perspective view of a low pressure turbine nozzle sector showing the leading edge of its cut central blade for a repair according to one embodiment of the invention; FIG. 4 shows a replacement part, according to one embodiment of the invention, for the leading edge of the central blade of the sector shown in FIG. 3; - Figures 5, 6 and 7 show preferred cutting areas to perform a repair according to the invention.

Referring to Figure 1, we see a blade 1 of low pressure turbine distributor of an aeronautical turbojet. This blade is located in the center of a distributor sector consisting of three blades cast simultaneously and is shown following a section of this sector between two consecutive blades. The sector comprises two platforms that join the blades, an upper platform 2 and a lower platform 3. Between these two platforms the dawn 1 extends into the gas bed, which flows from an edge 4 to a trailing edge 5. The leading edge 4 is assumed to be damaged over a substantial part of its height and a zone to be removed and replaced has been defined, which is represented by a dotted line in FIG. .

4 In Figure 2 we see the same blade in section along a plane substantially parallel to the planes of the platforms. It comprises three cavities for the circulation of cooling air, a cavity 6 leading edge, a cavity 7 for the central part and a cavity 8 trailing edge. The part to be removed and replaced for repairing the blade corresponds to the leading edge cavity 6 and the half thickness of the partition separating the leading edge cavity 6 from that of the central portion 7. Figure 3 shows a sector of three low pressure turbine valve vanes, with their common upper 2 and lower 3 platforms. The central blade 1 is cut at its leading edge 4 over most of its height and is intended to receive a replacement part of its leading edge. Such a replacement part 5 is shown in FIG. 4. It has a shape complementary to that of the recess formed in the leading edge 4 of the blade 1, that is to say that of a cylinder whose guidelines are parallel to the largest dimension of the dawn and whose generatrix has the shape of the section of the leading edge by a plane substantially parallel to the platforms of the dawn. It is limited to the rear by a plane perpendicular to the median surface of the dawn. This replacement part 5 has a cavity 6 identical to that of the leading edge of the blade to resume the function of circulation of the cooling air along the leading edge 4. Inside this cavity appear disturbers 9 which have the form of asperities extending from the front tip of the cavity 6 and which are evenly distributed along the height of the blade. These disrupters have the function of generating a turbulent flow in the cavity and thus increasing the heat exchange between the metal constituting the leading edge and the cooling air. It is therefore extremely important for the holding of the dawn that these disturbers are reproduced faithfully on the replacement part. Referring now to Figures 5, 6 and 7 there are various possibilities for making a cut of the blade 1, depending on the severity of the damage found. The cut can be made in the middle of a cavity or in the thickness of an inter-cavity partition. It can even, as seen in Figure 7, be performed on a non-cooled blade and having no internal cavity. It is preferable to limit the number of possibilities for cutting the blades to a few predefined cutting planes and to remove on a damaged blade a corresponding zone, in the predefined cuts, to that having a volume immediately greater than that required. In this way we limit the number of types of replacement parts that must be made; then simply choose the replacement part that corresponds to the volume of metal removed, without having to make a custom part for each repair. The cutting planes are defined so as to repair either a leading edge 4 or a trailing edge 5, or even the upper or lower surfaces of the blade 1. Complete replacement of the blade can also be realized. The method of repairing a turbine blade element according to one embodiment of the invention will now be described, taking for example the replacement of the entire cavity of a leading edge. Beforehand a set of replacement parts 5 for damaged parts of a turbine distributor blade has been defined, as indicated above. This is characterized by a series of pieces each having a height along the blade and / or a length along the rope of the dawn 1 different. An example of a set of replacement parts is given in FIGS. 5 to 7, without this list being limiting. In preparation for blade repair operations 1 such replacement parts are produced by the technique of metal powder injection molding, known as MIM, which is commonly used for the manufacture of parts of relatively small dimensions and geometry that can be complex. This technique consists of preparing a homogeneous mixture from fine metal alloy powders and thermoplastic binder. The mixture is heated to a temperature sufficient to melt the binder and allow the metal particles to be coated with the binder. After being heated to a suitable temperature, the mixture is of fluid to pasty consistency. It is maintained at this temperature and introduced by injection, at a predetermined pressure, into a mold whose footprint corresponds to the shape of the part to be manufactured. he

It should be noted that the shape of the impression takes into account the deformations that the part undergoes during the following steps of the process, in particular sintering. The rheological and injection pressure parameters are chosen so that the molding cavity is suitably filled with the material. A so-called green blank is obtained which is extracted from the mold after cooling and solidification of the thermoplastic binder. The next step is to debond the blank. The purpose of this operation is to extract at first a part of the components of the binder of the blank without deforming the latter.

The removal of a portion of the binder leads to the production of a porous structure formed of the metal particles bound by residual binder. The porous structure allows both the evacuation of the binder and the balancing of internal pressures ensuring the stability of the shape of the blank part. Debinding, according to the materials used for the binder, can be chemical, with the use of appropriate solvents, or thermal. The remainder of the binder is removed in a second step, which is generally combined with the following sintering operation, to avoid any stress likely to affect the cohesion. For this reason this second time is usually done thermally.

For the sintering operation, the blank is heated in an oven to a temperature close to but less than the melting temperature of the metallic material. The temperature, the duration of the treatment and the atmosphere in the oven are controlled so that the metal particles bind to each other by diffusion. The pores of the structure are gradually reduced and the room becomes denser during this stage. Densification generally leads to a shrinkage of the part which can be of the order of 10 to 20%. The shrinkage value depends on the initial void fraction before sintering and the ratio of the volume of metal material to that of the binder in the green part. It also depends on the rate of densification made. The MIM technique has many advantages, in terms of mechanical properties that are comparable to those of products from forging, in terms of costs by producing series of manufacture. It is also characterized by excellent surface finish and fine tolerances, allowing direct use as a part

7 replacement to repair a damaged part of a turbine blade. This technique is particularly suited to the manufacture of mass-produced parts, and more particularly to that of low mass parts. It is, a priori, not well suited to the production of complex parts, such as those used in aeronautics, and especially those with internal cavities with disrupters. In fact the cavity parts are generally made by very complex mold systems, such as drawer molds, which can not be considered here given the geometry of the cavities and the presence of the disturbers. A person skilled in the art will therefore not be encouraged to use this method to produce replacement parts for turbine valve vanes 1 that are to be repaired.

According to the invention, the manufacture of the replacement part 5 is carried out by injection of a powder having the same composition as the part to be repaired (that is to say in general a nickel base superalloy) which is agglomerated by a conventional binder. The shape of the cavity and disrupters 9 therein is given by a core previously introduced into the injection mold. This core is generally made of a polymer, the composition of which may or may not be identical to that of the binder, but which must be eliminated naturally during the subsequent debinding operation. This preliminary step of making a set of damaged parts being performed, the operator can begin the repair operation of the damaged dispenser vane 1. To do this, he analyzes the extent of the damaged area and selects from the set of spare parts at his disposal the smallest of those whose volume includes that of the damaged part. It cuts the damaged part, according to conventional techniques, giving the cut the exact shape of the replacement part 5 which was chosen in the game at its disposal. The replacement part chosen, having been made by the MIM process, has dimensional characteristics that make it fit exactly to the cut made. The operator then assembles the replacement part 5 to the blade 1 by brazing or welding, with a supply of soldering powder, possibly pre-densified by sintering, and performs brazing or welding in a known manner. The part obtained is then ready for a return to service, after possibly undergoing a slight surface machining.

The use of the MIM process has the advantage of obtaining parts substantially at the final dimensions, even for small parts such as replacement parts for turbine valve blades. By way of example, a replacement part for a turbine distributor leading edge has dimensions of the order of 45 mm × 4 mm × 7 mm. The corresponding tolerances to be respected are +/- 0.1 mm for the part and especially +/- 0.05 mm for the disturbers. The method also allows a substantial saving in terms of the material used and practically eliminates machining operations.

The invention has been described with the introduction into the injection mold of a polymer core which is evacuated during the debinding operation. It is obvious that it can also be made with a core of any other material, provided that the core can be destroyed by a process, whether mechanical or chemical, after the injection and solidification operation of roughing. Although the invention has been described in connection with a particular embodiment, it is obvious that it includes all the technical equivalents of the means described and their combinations if they fall within the scope of the invention.

Claims (11)

REVENDICATIONS1. A method of repairing a blade, stationary or movable, of a turbomachine turbine comprising the steps of: a. defining a volume of dawn (1) encompassing the entire damaged area, b. cutting the volume thus defined, c. producing a replacement part (5) having the same dimensions as the cut volume, d. assembly by welding or soldering of the replacement part (5) on the vane (1) in place of the cut volume, characterized in that the replacement part (5) is produced by injection molding of metal powder (process MIM). 15 2. The repair method according to claim 1 wherein the metal powder has the same composition as the blade (1) to be repaired. 3. The repair method according to one of claims 1 or 2 wherein the replacement part (5) is selected from a set of previously made parts. 20 4. The repair method according to claim 3 wherein the cut is defined by a selection made from the volumes of the parts of the game previously performed. 5. Repair method according to one of claims 1 to 4 comprising in step c) the establishment of a core of polymer material, so as to achieve an internal cavity (6). 6. The method of claim 5 wherein the composition of the polymeric material is identical to that of the binder used for the MIM process. 7. A turbine blade of an aircraft turbine engine, repaired using a method according to one of the preceding claims. 8. turbine blade according to claim 7 wherein the cut volume comprises an internal cavity (6). 9. A turbine blade according to claim 8 wherein the cavity (6) has an inner surface provided with disturbing asperities (9) of the flow of cooling air flowing in said cavity. A turbine nozzle blade sector having at least one blade (1) repaired by a method according to one of claims 1 to 6. 11. Aeronautical turbomachine having at least one blade, fixed or movable, according to one of claims 7 to 9.