FR2897550A1 - Automatic repair or recuperation of high pressure turbine components by means of a recharging tool controlled by determination of a numerical image of the component and the defects to be recharged - Google Patents

Abstract

The repair of a metal turbine component with at least one defect using a recharging tool operated by a control system comprises the following steps: (A) the acquisition of a numerical image of the shape of the component and its spatial position by an opto-electrical device with a resolution allowing the detection of the defect; (B) the determination of the position of the defect; (C) the determination of the recharging parameters for the recharging tool; (D) the transfer of the parameters to the tool control system to effect the repair.

Description

The present invention relates to the field of turbomachines and

  metal parts, including the blades, which compose them. It concerns the repair or the recovery of the latter.

  Nickel or cobalt-based superalloy parts with monocrystalline structure or directed solidification are manufactured to enable them to withstand the high temperatures and thermomechanical stresses to which they are subjected during the operation of the engine on which they are mounted. In particular, the HP turbine blades are mounted with a clearance as low as possible relative to the stator ring to ensure a good seal. Frictions are inevitable and lead to wear of their top which can also generate randomly distributed cracks. Cracks or other defects may also appear on dispenser elements.

  When the damage reaches a certain threshold it is necessary to replace these parts; however, given their manufacturing cost, we then try to repair them.

  The problem also arises in manufacturing. For new parts, inclusions of ceramic material or structural defects, randomly distributed, may remain after manufacture. Such defects normally involve scrapping the part. It would also be desirable to be able to recover them.

  Repair or recovery of these parts when they present defects of the crack type, punctual defect, mobile blade tip wear is currently carried out according to various processes including that known under the acronym SWET which is an acronym in English of the terms superalloys welded at elevated temperature for high temperature welded alloy. The method consists in preheating the room, totally by quartz lamps or locally by induction and then recharging it. The reloading is generally done manually by conventional TIG welding or by mini plasma with metal supply in the form of rod. This operation involves working in an argon box to avoid the risk of oxidation. Success depends heavily on the skill of the operator and retouching rates are sometimes important.

  According to another technique, high energy processes such as laser or plasma are used.

  The reloading metal can be supplied in the form of wire or powder. When it comes to a wire, its guidance often generates geometrical defects and does not allow to follow a fine trajectory. It is not possible to use very fine threads, with a diameter of less than 0.76 m in particular, without the drive systems becoming complex and with reliability not ensured industrially. This requires the formation of a minimum width of cord does not allow total control of the energy provided to the room or optimize machining time. In addition, the flexibility of the wire does not allow to consider reloading cracks.

  The technique using laser heating with the addition of powdered material (laser cladding) makes it possible to obtain thin and localized cords. For example, the applicant has filed a patent application FR 04 51 934 on a method of reloading a monocrystalline metal part or directed solidification, less than 2 mm thick, in which a laser beam and a flux of metal powder on the part whose beam power and its speed of movement along the part are maintained in a determined ratio. However, there is currently no repair or recovery system that would allow for a complete cycle including the reloading of cracks, open defects or simply cleaned, and the top of a blade.

  The subject of the invention is therefore an automatic method for recharging cracks-like defects, peak wear and point defects of the vanes and high-pressure turbine distributors, in particular nickel-base alloys.

  In the remainder of this application the following terms are used as follows: The term repair includes the recovery of new parts. The term "reloading" refers to the deposition of molten material with the formation of successive layers when it comes to repairing open cracks, point defects or reconstructing the top of the blades. This term also refers in the case of non-machined cracks, low opening, to the realization of a melting line of the material by applying energy through a welding source, and with or without input of material . The energy source can be a laser beam or a mini plasma (Pta for plasma transferred arc).

  The term defect designates at least one of the following defects: a crack on the part, a lack of material at the top of the blade, on the trailing edge or in another zone, a punctual defect due to an inclusion of ceramic Manufacturing.

  According to the invention, the method for repairing a turbomachine metal part having at least one defect, by means of a reloading tool, the tool being implemented by a control means, is characterized by the fact that it comprises the following steps: acquisition of a digitized image of the shape of the part as well as its position in space, by an optoelectronic measuring means, such as photogrammetry or triangulation, the resolution of said measuring means allowing detecting the presence of said defect, Determining the position of the defect on the part, Determining the parameters for reloading the defect by the tool, Transferring the data concerning the parameters by means of command of the reloading tool to perform the reloading. The determination of the parameters includes, without limitation, the calculation of the trajectory of the tool, the power of the beam as well as its speed of advance. For a machined defect, they are determined from including the depth of the defect, its opening and if necessary the thickness of the wall and the presence or absence of stiffeners of the latter. Other features are reported in the following description of a non-limiting embodiment of the method of the invention with reference to the accompanying drawings, in which: FIG. 1 shows a moving blade on which a few types of defects have been shown in FIG. to fix ; Figure 2 shows a two-way dispenser also having defects to be repaired; FIG. 3 shows a dawn in perspective with machined cracks. FIG. 4 shows an equipment for acquiring a digitized image of the part; Figure 5 shows the contour of the part, in a section plane 35 along the Z axis; Figure 6 shows an example of laser charging head with powder supply. Figure 7 shows a portion of a blade which has been repaired by the method. FIG. 1 shows a turbine blade 10 for a high pressure stage. It comprises a blade 12, a platform 13, a foot 14 for its mounting on the rim of a turbine disk, and sealing walls 15 delimiting a tub forming zone at its top which cooperate with a turbine ring so that the engine gases do not circumnavigate the blade. Orifices 16 for the passage of cooling air are provided near the leading edge of the blade and the trailing edge. In operation, the blades undergo high thermomechanical stresses. The damage that is found towards the top after many hours of engine operation is a wear 15a of the walls 15, radial cracks 15b on the intrados or extrados or cracks 15c on the bottom wall of the engine. bathtub. Cracks 12a are also found parallel to the direction of the gas flow in particular on the intrados face.

  In FIG. 2 showing a two-valve distributor element 20, cracks 22a are seen parallel to the direction of the gas flow on the intrados face of one of the blades 22. There is also a lack of material 22f along the blade 22 trailing edge 22. Spot defects 12p or 22p may also exist on blades 12 or 22. These defects are present on new parts whose manufacturing process leads to the presence of ceramic inclusions.

  As part of the preparation of the part to be repaired, after cleaning, sandblasting and dealuminization in acid baths to remove the surface coating, the cracks are machined so as to allow a satisfactory deposit of the reloading metal. . After manual machining by means of a ball mill, for example, or automatic by EDM, so-called open cracks are obtained. Figure 3 shows a turbine blade whose cracks have been machined. There are three open creeks 12u1, 12u2, 12u3 near the top of the dawn. These creeks in addition to their position relative to the geometry of the room, are characterized by their width D and their depth. It is observed that the summit has been prepared equally; the walls forming the bath were machined with equalization of the level. The walls are characterized by their thickness E. The invention also relates to the repair of closed, open, non-machined cracks. The preparation in this case consists of a chemical or thermochemical cleaning. The first phase of the repair is to create a digital image of the part. According to the exemplary apparatus 40 of FIG. 4 using a laser beam, the piece to be digitized A is placed on a support 41, which can be adjusted along the two main directions in the reference plane (x, y) of the table on which it is mounted, and in rotation about itself around the perpendicular axis (z). A laser sensor 42 is mounted on a bracket 44. It comprises a laser beam transmitter and a receiver. The beam is projected onto the surface of the room and the reflected beam picked up by the receiver. We proceed by triangulation. The profile of the part and its position in space are calculated from this information and are stored in an appropriate memory. The system resolution shall be sufficient to identify impact or cracks of a size that may be less than 50 m. Indeed, we see that this resolution is sufficient for such an application.

  Other modes of digitizing the form are also suitable. It can be done by digital photogrammetry which gives a three-dimensional envelope of the room from which sections are extracted along the main axis of the room. Once the shape of the piece has been digitized, appropriate calculation means ensure the geometric extraction of the defects. The system identifies machined shapes in the workpiece, distinguishing a machining or drilling inherent in the design of the part from a functional wear defect. After the position in the defect space and their dimensions have been calculated, a path for the tool or the reloading head is determined. From the geometry of the defects, the software calculates the trajectories of the tool or robot supporting the tool via an algorithm and the trajectory is transmitted to the robot.

  For example, for a machined crack, the parameters of the trajectory are determined from the defects found on the successive cuts parallel to the reference plane (x, y) along the axis (z). For each defect 51 or 52 on each section plane, as illustrated in FIG. 5, a mean point is determined from the depth P of the defect and its opening D. The set of average points thus calculated forms a curve from which the trajectory of the reloading tool is determined. The wall thickness is also involved. 40 The other parameters necessary for reloading are determined. This is to ensure a homogeneity of the reloading as large as possible for each crack configuration.

  Other reloading parameters for a laser tool include: laser power, focal length, shielding gas, feedrate, distance between two successive z-axis cutting planes, incrementation speed z-axis passes, laser fiber size, powder flow, etc. This data set is then transmitted to the control means of the tool, that is to say to the control of the robot with which the loading is to be performed. According to an advantageous embodiment, a database relating to the welding parameters makes it possible to associate with each class of defects the appropriate parameters. The transmission of the parameters to the robot is carried out with the passage of the path of the fault and its position. The database is enriched from the results of tests and also by experience in production.

  Preferably, reload sequences are predefined in a database that integrates the geometry of the crest or machined point defect.

  The reloading can be done either from the top or from the side of the piece. Preferably start from the bottom of the machined cavity, in successive passes until complete filling.

  Once the reloading is complete, the method of the invention, by implementing again the part shape detection system, makes it possible to carry out a check of the reloaded geometry, to make sure of its conformity, and to define the machining sequence to be performed with respect to a standard.

  FIG. 6 shows a laser beam recharging head 60 with a reloading powder spraying nozzle. This comprises a frustoconical end portion 62, comprising a central bore 63 and a series of antistatic channels 64 extending into the generating wall of its frustoconical end 62. The channels are fed with powder 65, while The rectilinear laser beam 66 propagates within the central bore. The nozzle is of the nozzle type described in DE 3935009, to which reference may be made for further details.

  The laser beam 66 is produced by a laser source called YAG. It emits a continuous beam of energy. The optical fiber for guiding the beam is, for example, of diameter 0.3 or 0.6 mm, depending on the geometry of the wall to be recharged. For example, a 0.6 mm diameter fiber can recharge walls whose thickness is between 0.5 and 2 mm. The YAG laser allows a very good interaction between the laser beam 6 and the material, and allows greater maneuverability of the projection head, because of the maneuverability of its optical fiber.

  The nozzle 61 is connected to one or more distributors of alloy powder. The powder 65 is driven by Argon, to ensure its protection. The laser beam 66 propagates coaxially with the powder 65.

  FIG. 7 shows the upper part of a turbine blade which has been repaired according to the method of the invention. This piece was previously prepared by machining the crack 12u4 and removing the bath wall. After recognition of the shape, the device calculated the trajectory of the welding head by laser beam and then controlled the robot supporting the welding head. The milled creek 12u4 was filled from the bottom by successive layers which we see the separation lines 25 in the photo. Then the tool moved along parallel paths and along the periphery of the bottom of the tub to the prescribed wall height.

  In the case of unmachined cracks, the reloading consists of the realization of a melting line of the material along the defect. The welding head is preferably arranged so as to form a right angle with the workpiece relative to its direction of advance or the support table. This angle can vary between 45 and 135. The melting line is simple or with powder in the case of a non-machined but larger defect. This is done for example from the bottom of the crack or from the widest zone of the opening of the crack.

  Laser charging has been described. The invention is also applicable to welding by means of a plasma torch. The parameters of this medium are arc height and intensity.

Claims (12)

claims   1. A method for repairing a turbomachine metal part having at least one defect, by means of a reloading tool, said tool being implemented by a control means, characterized in that it comprises the following steps: acquiring a digitized image of the shape of the part as well as its position in space, by an optoelectronic measuring means (42), the resolution of said measuring means for detecting the presence of said defect, the determination of the position of the defect on the part, the determination of the parameters of reloading of the defect by the tool (60), the transfer of the parameters by means of command of the reloading tool to carry out the repair.   2. Method according to claim 1, the determination of the parameters includes, without limitation, the calculation of the path of the tool, the beam power and its speed of advance.   3. Method according to claim 1, the acquisition of the form is performed by digital photogrammetry.   4. The method of claim 1, the acquisition of the form is performed by laser triangulation.   5. Method according to claim 1, the shape acquisition of which comprises the extraction of sections along the main axis of the part, the determination of the defect on each section.   6. Method according to the preceding claim comprising the determination of a mean point forming a point of the trajectory to calculate.   7. Method according to the preceding claim, the average point is determined from the depth of the crack, its width and the thickness of the wall.   8. Method according to one of the preceding claims, the defect is a machined crack, a non-machined through crack, a blade crown wall or a point defect.   9. Method according to one of the preceding claims, the reloading is carried out by powder spraying and heating by means of a high energy source.   10.Procédé according to the preceding claim whose charging tool is laser type.   11.Procédé according to claim 5 whose reloading tool is a plasma torch. 2897550 io   12.Procédé according to one of the preceding claims comprising a control repair by acquisition of the shape of the repaired part.