EP2483011B1 - Improved lost-wax casting method for manufacturing an annular bladed turbine engine assembly, metal mold, and wax pattern for implementing such a method - Google Patents

Description

TECHNICAL AREA

The present invention relates to the manufacture of a stator bladed annular assembly for a turbomachine, such as an aircraft turbomachine.

The figure 1 represents such a bladed assembly 10, sometimes called distributor or rectifier according to its function within the turbomachine. This bladed assembly 10 typically comprises two coaxial annular structures or ferrules, respectively inner 12 and outer 14, which are connected to one another by a plurality of blades 16.

The invention relates more particularly to the manufacture of a bladed assembly comprising at least one blade 18 incorporating a cavity, of generally elongate shape in the radial direction, intended for example for the measurement of physical parameters, such as the pressure and the temperature of the device. the air flowing along the dawn, possibly via orifices 20 of this dawn.

STATE OF THE PRIOR ART

The stator turbomachine stator sets are generally made by a "lost wax" type casting process, in which a wax model having the shape of the bladed assembly to be manufactured is previously produced, to then allow the manufacture of a cement mold by overmoulding of this model in wax. After removal of the wax, a metal alloy is poured into the cement mold obtained previously to form, after cooling and demolding, the desired bladed assembly.

The preliminary embodiment of the wax model is carried out by means of a metal mold having substantially the shape of the bladed assembly to be manufactured.

In the case of a bladed set of which at least one blade comprises a cavity, an elongated core, as illustrated in FIG. figure 2 , is inserted into the portion of the metal mold which defines the aforementioned blade to form the impression of the cavity. This core 22 is made of ceramic so that it has a thermal resistance sufficient to withstand the high temperatures inherent in the casting of the aforementioned metal alloy, and to allow the subsequent removal of the core by a conventional chemical process.

Wax is then injected under pressure into the metal mold equipped with the core so as to form, while cooling, a model of the bladed assembly to be manufactured, in which the core is coated with the wax and occupies the space corresponding to the aforementioned cavity.

During the injection of the wax, the core is mounted on the metal mold so as to be held firmly in position, to limit as much as possible the risk of deformation of the core under the pressure of the wax, which would degrade the accuracy of the shape of the wax model, and therefore of the bladed assembly obtained at the end of the manufacturing process. The maintenance of the core is generally ensured by two studs 24 and 26 ( figure 2 ) respectively formed at both ends of the core and protruding from the metal mold to allow their gripping by appropriate support means.

The realization of the cement mold is then performed by overmolding the wax model obtained previously and equipped with the core, in such a way that the cement includes the two tenons of this core which protrude out of the wax model. After solidification of this cement and removal of the wax, a cement mold is obtained with the core, which is now maintained by the cement mold itself.

Then, after the casting of the metal alloy in the cement mold obtained previously and after the cooling of this metal alloy, the core is removed, generally by a chemical method, and the metal part obtained is demolded to form an annular assembly. bladed.

The elimination of the core leaves in the inner ferrule of this bladed assembly an orifice 28 formed by the passage of one of the tenons of the core, as shown in FIG. figure 3 . Since the presence of an orifice at this point is not desirable, this orifice is generally filled by brazing or the like.

However, this filling operation increases the manufacturing cost of the bladed annular assemblies.

In addition, the presence of brazed parts in the inner ferrules of these sets induces in these ferrules irregularities of shape and structure likely to reduce the mechanical strength and therefore the life of these ferrules.

In addition, it happens that the core deforms under the pressure of the wax at the time of the injection of the latter, which causes costly scrapping.

STATEMENT OF THE INVENTION

The invention aims in particular to provide a simple, economical and effective solution to these problems.

• la mise en place d'un noyau, destiné à former l'empreinte de ladite cavité, dans une portion dudit moule métallique qui définit l'aube comportant la cavité, le noyau précité ayant une forme générale allongée présentant une extrémité radialement externe montée sur le moule métallique ;
• l'injection d'une cire dans le moule métallique équipé du noyau précité ;
• après refroidissement de la cire, le démoulage du modèle en cire ainsi obtenu, équipé du noyau.

Selon l'invention, le noyau précité est réalisé en métal et est positionné de sorte que son extrémité radialement interne soit logée dans la portion du moule définissant l'aube comportant ladite cavité, à distance de l'extrémité radialement interne de cette portion du moule.To this end, it proposes a method of manufacturing an annular wax model with a turbomachine stator blade, intended for the production of a mold of this bladed assembly, the model comprising two coaxial shrouds, radially inner and radially respectively. external, ferrules interconnected by a plurality of blades, at least one of which comprises an internal cavity, said method comprising successively, using a metal mold having substantially a shape to confer on said annular assembly model blurred :

• setting up a core, intended to form the cavity of said cavity, in a portion of said metal mold which defines the blade comprising the cavity, the aforementioned core having a generally elongated shape having a radially outer end mounted on the metal mold;
• injecting a wax into the metal mold equipped with the aforementioned core;
• after cooling the wax, demolding the wax model thus obtained, equipped with the core.

According to the invention, the aforementioned core is made of metal and is positioned so that its radially inner end is housed in the portion of the mold defining the blade comprising said cavity, at a distance from the radially inner end of this portion of the mold. .

The use of a metal core, more rigid than a ceramic core of the type usually used, makes it possible to mount this core on the metal mold only by its radially outer end, while minimizing the risk of deformation of this core. during the injection of the wax. Such mounting of the core on the metal mold is particularly advantageous when the wax model manufactured by this method is used in a method of manufacturing a bladed annular assembly, as will become more clearly apparent in the following.

The improvement of the rigidity of the core makes it possible to increase the injection pressure of the wax, as well as to reduce the rate of defective wax patterns due to kernel deformation.

• la fabrication d'un modèle en cire de l'ensemble annulaire aubagé, par un procédé du type décrit ci-dessus ;
• la réalisation d'un moule en un matériau réfractaire par surmoulage du modèle en cire précité puis élimination de la cire ;
• la coulée d'un alliage métallique en fusion dans le moule en matériau réfractaire équipé du noyau précité pour former ledit ensemble annulaire aubagé ;
• après refroidissement de l'alliage métallique, le démoulage de l'ensemble annulaire aubagé et l'élimination du noyau.

The invention also relates to a method for manufacturing a stator bladed annular assembly turbomachine comprising two coaxial ferrules, respectively radially inner and radially outer, interconnected by a plurality of blades, at least one of which comprises an internal cavity, said method comprising successively:

• manufacturing a wax model of the bladed annular assembly by a method of the type described above;
• the production of a mold made of a refractory material by overmolding the above-mentioned wax model and then removing the wax;
• casting a molten metal alloy into the refractory material mold equipped with the aforementioned core to form said bladed annular assembly;
• after cooling the metal alloy, demolding the bladed annular assembly and removing the core.

This method of manufacturing a bladed annular assembly thus uses the wax model manufacturing method described above, wherein the core is mounted on the metal mold only by its radially outer end.

At the end of the steps of overmolding the wax model and removing the wax, the radially outer end of the core is embedded in the solidified refractory material and thus allows the connection of the core to the mold made in this material, while the radially inner end of the core extends inside this mold, away from the radially inner end of the portion of this mold defining the blade having the aforementioned cavity, and therefore remote from the radially inner shell of the mold.

As a result, the radially inner end of the core does not form an orifice in the inner shell of the bladed annular assembly obtained by this method. It is therefore no longer necessary to provide an orifice filling operation at this inner shroud, which allows a reduction in the manufacturing cost of the turbomachine stator bladed annular assemblies, and an improvement in the service life of these sets.

Preferably, prior to the production of the refractory material mold, the method of manufacturing a turbomachine stator turbomachine annular assembly further comprises extracting said metal core from said wax model and then placing it in the formed cavity. in the wax by said metal core, a core of the same shape made of ceramic.

The core made of ceramic has a better thermal resistance and is therefore better suited to the subsequent casting step of the molten metal alloy. In addition, the ceramic core can be removed, at the end of the process, by a conventional chemical method.

Preferably, the metal core has a tapered section towards its radially inner end.

The tapered shape of the metal core facilitates its removal from the wax model by limiting the risk of damaging this model. The The rigidity of this metal core also makes it possible to limit the risks of kernel breakage during its extraction.

In the case where the metal core is replaced by a ceramic core as described above, the latter has the same shape as the metal core and the tapered nature of this shape facilitates the insertion of this ceramic core into the impression previously formed by the metal core.

However, the process according to the invention can be carried out without performing the above-mentioned step of exchanging cores, in particular when the metal constituting the metal core has a sufficiently high melting point with respect to the melting point of the alloy. metal cast in the mold of refractory material, to allow the metal core to support the casting of this alloy without risk of melting of the core.

The invention also relates to a metal mold intended for the manufacture, by a method of the type described above, of a turbomachine stator turbomachine stator annular wax model comprising two coaxial shrouds, respectively radially inner and radially outer, ferrules interconnected by a plurality of blades, at least one having an internal cavity, the mold comprising, in a portion which defines said blade comprising the cavity, a generally elongated core having a radially external end mounted on the metal mold for forming the cavity of said cavity, characterized in that the core is made of metal and is positioned so that its radially inner end is housed in said portion of the mold defining the blade comprising said cavity, at a distance from the radially inner end of said portion of the mold.

The invention also relates to a wax model for manufacturing, by a method of the type described above, a turbomachine stator turbomachine annular assembly comprising two coaxial ferrules, respectively radially inner and radially outer ferrules connected together. by a plurality of vanes of which at least one has an internal cavity, the model comprising, in a portion which defines said vane comprising the cavity, a generally elongate core having a radially outer end protruding from the model, to form the cavity of said cavity, characterized in that the core is made of metal and is positioned so that its radially inner end is housed in said portion of the model defining the blade comprising said cavity, at a distance from the radially inner end of said portion of the model.

BRIEF DESCRIPTION OF THE DRAWINGS

• la figure 1, déjà décrite, est une vue en perspective d'un ensemble annulaire aubagé de stator de turbomachine d'un type connu ;
• la figure 2, déjà décrite, est une vue en perspective d'un noyau de type connu, destiné à la fabrication de l'ensemble aubagé de la figure 1 ;
• la figure 3 est une vue schématique partielle de la virole interne de l'ensemble annulaire aubagé de la figure 1, avant rebouchage de son orifice formé par le noyau de la figure 2 ;
• la figure 4 est un organigramme illustrant les principales étapes d'un procédé selon l'invention pour fabriquer un ensemble annulaire aubagé de stator de turbomachine ;
• la figure 5 est une vue schématique en perspective d'un noyau destiné à la mise en oeuvre du procédé de la figure 4 ;
• la figure 6 est une vue schématique partielle en perspective, d'un modèle en cire d'ensemble annulaire aubagé, dans lequel est installé le noyau de la figure 5 ;
• la figure 7 est une vue semblable à la figure 6, avec un plan de coupe transversal.

The invention will be better understood, and other details, advantages and characteristics thereof will appear on reading the following description given by way of nonlimiting example and with reference to the accompanying drawings in which:

• the figure 1 , already described, is a perspective view of a turbomachine stator turbomachine annular assembly of a known type;
• the figure 2 , already described, is a perspective view of a known type of core, intended for the manufacture of the bladed assembly of the figure 1 ;
• the figure 3 is a partial schematic view of the inner ferrule of the bladed annular assembly of the figure 1 , before filling its hole formed by the nucleus of the figure 2 ;
• the figure 4 is a flowchart illustrating the main steps of a method according to the invention for manufacturing a turbomachine stator turbomachine annular assembly;
• the figure 5 is a schematic perspective view of a core for implementing the method of the figure 4 ;
• the figure 6 is a partial diagrammatic view in perspective, of a bladed annular wax model, in which is installed the core of the figure 5 ;
• the figure 7 is a view similar to the figure 6 , with a transverse cutting plane.

DETAILED PRESENTATION OF PREFERRED EMBODIMENTS

The organization chart of the figure 4 illustrates a process according to the invention for the manufacture of a turbomachine stator turbomachine annular assembly of the same type as the bladed assembly shown in FIG. figure 1 , and thus comprising two coaxial ferrules, respectively internal 12 and external 14, connected between they by a plurality of blades 16, at least one blade 18 integrates a cavity.

This process comprises four successive main phases, designated by the respective references 30, 32, 34 and 36 on the flow chart of the figure 4 .

The first phase 30 consists in the preparation, in a conventional manner, of a metal mold of the bladed assembly to be manufactured, the second phase 32 consists in the manufacture of a wax model of the bladed assembly by means of this metal mold, the third phase 34 in the production of a cement mold, or more generally of any suitable refractory material, by overmolding the wax model, and the fourth phase 36 in the manufacture of the bladed assembly by means of the cement mold aforesaid.

More specifically, the second phase 32 comprises a step 38 of placing, in the metal mold, a core which differs from the conventional core of the figure 2 in that it is made of a metal, for example a steel, and in that it is devoid of tenon at its end intended to be positioned radially inward in the mold.

The figure 5 illustrates a core 40 of this type, and shows in particular its end 42, which is intended to be positioned radially outward in the mold and which is provided with a pin 44 similar to the stud 24 of the core of the figure 2 of conventional type, and its end 46, which is intended to be positioned radially towards the inside in the mold and which is devoid of tenon. This core 40 has a tapered cross section towards its end 46, as shown in FIG. figure 5 , which is made possible in particular by the absence of tenon at this end.

In the aforementioned step 38 ( figure 4 ), the core 40 is installed in the portion of the metal mold defining the blade of the bladed assembly which integrates a cavity, so that the pin 44 of the end 42 of this core projects out of the mold passing through an orifice of the wall of this mold defining the radially outer shell of the bladed assembly, and so that the other end 46 of this core extends inside the mold, at a distance, radially towards the outside, of the wall of this mold defining the radially inner ferrule of the bladed assembly.

The next step 48 of the second phase 32 of the method consists in the pressure injection of a wax into the metal mold equipped with the metal core 40 described above, in a conventional manner, until the mold is filled with wax, the core then being embedded in the wax except for its stud protruding from the metal mold. The rigidity of the metal core allows the latter not to deform during the wax injection despite the pressure exerted on the core by the latter.

After cooling, the hardened wax forms a model 50 of the bladed annular assembly at to manufacture, as illustrated by figures 6 and 7 . This model 50 has substantially the shape of the annular bladed assembly, and therefore comprises two coaxial ferrules, respectively inner 52 and outer 54, and a plurality of blades 56 connecting these two ferrules and comprising a blade 58 intended to define the dawn of the bladed assembly which integrates a cavity, this dawn 58 of the wax model being that which integrates the core 40. figure 7 illustrates in particular the position of the radially inner end 46 of the core 40, which is at a distance, radially outwardly, from the radially inner shell 52 which forms the radially inner end of the blade 58.

In the preferred embodiment of the process according to the invention, the second phase 32 of this process is continued by a step 60 consisting of removing the metal core 40 from the wax model, and replacing it with a core of the same shape. made of ceramic, and thus having a better thermal resistance. The withdrawal of the metal core 40 is achieved by a displacement of this core in substantially rectilinear translation radially outwardly of the model. The tapered, radially inward shape of the metal core 40 makes it possible to reduce at best the risk of damage to the wax during this extraction. The replacement of the metal core 40 by the ceramic core is intended to enable the core to better withstand the subsequent casting of a molten metal alloy, and to facilitate the removal of this core by a conventional chemical method to the end of the manufacturing process, as will become clearer in the following.

The second phase 32 of the method is completed by a step 62 of demolding the wax model 50 incorporating the ceramic core.

The process then continues with the third phase 34, which comprises a step 64 for producing a cement mold, or the like, by overmolding the wax model 50 obtained previously. More specifically, this wax model 50 is coated with cement in such a way that the cement includes the tenon of the ceramic core incorporated in this model.

The third phase 34 ends with a step 66 of removing the wax, in a conventional manner comprising for example the heating of this wax, so as to obtain a cement mold equipped with the aforementioned ceramic core, whose tenon is embedded in the mold so as to ensure a rigid retention of this core.

The fourth phase 36 of the process comprises a step 68 of casting a molten metal alloy in the cement mold obtained previously. The core equipping the mold makes it possible to form the cavity of the corresponding blade 18 of the bladed annular assembly. The following step 70 consists, after cooling of the metal alloy in the mold, in a demolding of the thus obtained bladed assembly and in an elimination of the ceramic core, by a conventional method, preferably of the chemical type.

Because the radially inner end of the core has not protruded out of the bladed assembly during the process described above, the inner ferrule of this set does not include an orifice formed by the core, after the elimination of the latter. The method according to the invention thus makes it possible to save a final step of filling the inner ferrule of the annular bladed assemblies, and makes it possible to improve the regularity of the shape and structure of this ferrule.

The method according to the invention may, alternatively, be implemented without performing the step 60 of removing the metal core and replacing this core with a ceramic core. In this case, the whole process is carried out using the same metal core. The metal core then has a sufficiently high melting point relative to that of the cast metal alloy to withstand the high temperatures inherent in the casting of the molten metal alloy during step 68.

In general, the method according to the invention can be used for the manufacture of integral bladed annular assemblies such as the assembly described above, or for the manufacture of assemblies formed of a plurality circumferentially mounted sectors end-to-end, in which case each of the sectors comprising a blade provided with an internal cavity can be realized by means of this method.

Claims (7)

1. A method of manufacture of a wax model (50) of an annular bladed turbomachine stator assembly (10), intended for manufacture of a mould of this bladed assembly, where the model (50) includes two coaxial shrouds, respectively radially internal (52) and radially external (54), which shrouds are connected to one another by multiple blades (56), at least one of which (58) includes an internal cavity, where the said method includes, in succession, using a metal mould having roughly a shape to be given to the said model (50) of an annular bladed assembly:

   - positioning (38) of a core (40), intended to form the impression of the said cavity, in a portion of the said metal mould which defines the blade (58) including the said cavity, where the abovementioned core (40) has a generally lengthened shape having a radially external end (42) assembled on the said metal mould;

   - injection (48) of a wax in the said metal mould fitted with the said core (40);

   - after the said wax has cooled, removal (62) of the resulting wax model (50), fitted with the said core (40), from the mould;

   characterised in that the said core (40) is manufactured in metal, and is positioned such that its radially internal end (46) is housed in the said portion of the mould defining the blade (58) including the said cavity, away from the radially internal end of this portion of the mould.
2. A method according to claim 1, characterised in that the said metal core (40) has a transverse section which tapers in the direction of its radially internal end (46).
3. A method of manufacture of an annular bladed turbomachine stator assembly (10) including two coaxial shrouds, which are respectively radially internal (12) and radially external (14), connected to one another by multiple blades (16) at least one of which (18) includes an internal cavity, where the said method includes, in succession:

   - a step (32) of manufacture of a wax model (50) of the said bladed annular assembly (10), by a method according to claim 1 or 2;

   - a step (34) of manufacture of a mould in a refractory material by duplicate moulding (64) of the said wax model (50), followed by elimination (66) of the wax;

   - a step (68) of casting of a molten metal alloy in the said mould made from a refractory material fitted with the said core (40) to form the said bladed annular assembly (10);

   - after the said metal alloy has cooled, a step (70) of removal of the said bladed annular assembly (10) and of elimination of the said core (40).
4. A method according to claim 3, characterised in that before the step (34) of manufacture of the mould in a refractory material, the method also includes a step (60) of extraction of the said metal core (40) out of the said wax model (50), followed by positioning in the impression formed in the wax by the said metal core (40) of a core of the same shape manufactured in a ceramic material.
5. A method according to claim 4, characterised in that the said refractory material is a cement.
6. A metal mould intended for manufacture, by a method according to claim 1 or 2, of a wax model (50) of an annular bladed turbomachine stator assembly including two coaxial shrouds, respectively radially internal (52) and radially external (54), which shrouds are connected to one another by multiple blades (56), at least one of which (58) includes an internal cavity, where the mould includes, in a portion which defines the said blade (58) including the said cavity, a core (40) of a generally lengthened shape having a radially external end (42) assembled on the said metal mould to form the impression of the said cavity, characterised in that the said core (40) is manufactured in metal, and is positioned such that its radially internal end (46) is housed in the said portion of the mould defining the said blade (58) including the said cavity, away from the radially internal end of the said portion of the mould.
7. A wax model (50) intended for manufacture, by any method according to claims 3 to 5, of an annular bladed turbomachine stator assembly (10) including two coaxial shrouds, respectively radially internal (12) and radially external (14), which shrouds are connected to one another by multiple blades (16), at least one of which (18) includes an internal cavity, where the model (50) includes, in a portion (58) which defines the said blade (18) including the said cavity, a core (40) of a generally lengthened shape having a radially external end (42) protruding from the said model (50), to form the impression of the said cavity, characterised in that the said core (40) is manufactured in metal, and is positioned such that its radially internal end (46) is housed in the said portion (58) of the model (50) defining the said blade (18) including the said cavity, away from the radially internal end (52) of the said portion (58) of the model (50).

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