EP3544754B1 - Cluster model and shell for obtaining an accessory for the independent handling of formed parts, and associated method - Google Patents

Description

TECHNICAL AREA

The present invention relates to the field of cluster manufacturing of elements, in particular bladed elements, of turbomachines by the lost-wax casting technique. Each element is preferably an individual blade such as a compressor or turbine impeller blade.

The invention relates to all types of land or aeronautical turbomachines, and in particular aircraft turbomachines such as turbojets and turboprops.

More specifically, the invention relates to the design of the model in the form of a cluster and that of the shell intended to be formed around this model partially in wax, shell in which the metal is intended to be cast to obtain the elements of turbomachinery.

The invention thus proposes a model in the form of a cluster and a shell for obtaining at least an accessory for handling the cluster independent of the formed turbomachine elements, as well as an associated manufacturing method by lost-wax casting of a plurality of turbomachine elements.

PRIOR ART

The lost-wax casting technique for simultaneously manufacturing several bladed elements of an aircraft turbomachine, such as moving blades, is well known in the prior art. Such a technique is for example described in the French patent application FR 2 985 924 A1 .

As a reminder, lost-wax precision casting consists of producing in wax, by injecting into tools, a model of each of the desired bladed elements. The assembly of these models on a wax distributor makes it possible to constitute a model in the shape of a cluster which is then immersed in different substances in order to form around it a ceramic shell of substantially uniform thickness. The cluster-shaped model is also commonly referred to as a "replica", "cluster-assembly" or even "wax tree", although not all of its components are necessarily made of wax or other sacrificial material.

The process is continued by melting the wax, which then leaves its exact imprint in the ceramic shell, into which the molten metal is poured, via a pouring cup assembled on the metal distributor. After the metal has cooled, the shell is destroyed and the metal parts are separated and finished.

This technique offers the advantage of dimensional precision, making it possible to reduce or even eliminate certain machining operations. In addition, it offers a very good surface appearance.

In the field of lost-wax casting, the principle of drop casting, or gravity, of the molten metal is known, which consists of casting the metal from above into the cavities of the shell intended to form the turbomachine parts. According to this principle, the molten metal is poured into the bucket and then generally reaches an annular system for supplying the plurality of cavities intended to form the turbomachine parts, as described for example in the French patent application FR 2 985 924 A1 .

Advantageously, such a supply system can also be used as a handling crown for the cluster at different stages of the manufacturing process, in particular at the exit from the furnace, during shake-out, that is to say during the destruction of the shell, or even during cutting to obtain metal turbomachine parts.

Furthermore, in the field of lost-wax casting, the principle of source casting of the molten metal is also known, which consists on the contrary of casting the metal from below into the cavities of the shell intended to form the parts of turbomachinery. Most often, the molten metal is poured into the cup then specific conduits connected to the cup then allow the injection of the metal from the lower part of the cavities.

In the context of source casting, the kinetic energy stored before entering the cavities is greater so that the speed is higher. The metal supply means therefore promote pressure drops and have, for example, a bend to reduce the speed.

In addition, as a general rule, the cluster for which the source casting principle is applied is provided with a supply system forming a ring for handling the cluster as described previously in connection with the drop casting principle.

This handling crown is typically in direct connection with the parts to be formed. So, if the mass of the crown is equivalent to that of the parts, there is a strong risk that the crown will interact mechanically with the parts during solidification and/or during cooling, which can lead to the parts, when the efforts are sufficient, to defects of the crack or core offset type, but also in the case of single-crystal solidification to the generation of recrystallized grains due to the internal stresses generated in the parts.

There is therefore a need to optimize the current technique of lost-wax casting, and in particular within the framework of the principle of source casting with a model in the form of a cluster provided with handling accessories, to avoid the appearance of defects. mentioned above typically generated by harmful interactions between the parts to be formed and handling accessories of the cluster, such as a handling ring formed by a drop casting feed system.

In particular, there is a need to make it possible both to benefit from the advantages of gravity casting at source without degrading the metallurgical health of the turbomachine parts, and to ensure the casting of handling accessories, such as a handling of the cluster without further degrading the metallurgical health of the turbomachine parts.

The documents FR3026973A1 , CN105290333A , FR2990370A , US7231955B1 and WO2015/080854A1 also represent the state of the prior art.

DISCLOSURE OF THE INVENTION

The object of the invention is to remedy at least partially the needs mentioned above and the drawbacks relating to the embodiments of the prior art.

• une réplique, par exemple en cire, d'un godet de coulée apte à permettre l'injection de métal en fusion dans la carapace,
• une réplique, par exemple en métal, d'un descendant (ou support) central s'étendant selon l'axe longitudinal, apte à être en communication fluidique avec le godet de coulée pour recevoir le métal en fusion,
• une pluralité de répliques, par exemple en cire, d'éléments, notamment aubagés, de carapace chacun destiné à l'obtention de l'un des éléments de turbomachine, chaque élément de carapace comprenant une première partie d'extrémité basse et une deuxième partie d'extrémité haute,

caractérisé en ce qu'il comporte en outre :

• une pluralité de répliques, par exemple en cire, de conduits d'alimentation en source des éléments de carapace, aptes à être en communication fluidique avec le descendant central et les deuxièmes parties d'extrémité basse des éléments de carapace pour permettre une coulée en source des éléments de carapace,
• une réplique, par exemple en cire, d'une carapace d'accessoire de manutention, indépendante de la pluralité d'éléments de carapace et de leur circuit d'alimentation en métal de sorte à être sans communication fluidique avec les éléments de carapace, la carapace d'accessoire de manutention étant apte à être en communication fluidique avec le descendant central pour permettre une coulée en chute de la carapace d'accessoire de manutention.

The object of the invention is thus, according to one of its aspects, a model in the form of a cluster, around which a shell is intended to be formed for the manufacture by lost-wax casting of a plurality of elements, in particular bladed elements, of a turbomachine, said model having a longitudinal axis and comprising:

• a replica, for example in wax, of a casting cup capable of allowing the injection of molten metal into the shell,
• a replica, for example in metal, of a central descender (or support) extending along the longitudinal axis, able to be in fluid communication with the pouring cup to receive the molten metal,
• a plurality of replicas, for example in wax, of shell elements, in particular bladed, each intended to obtain one of the turbomachine elements, each shell element comprising a first lower end part and a second part high end,

characterized in that it further comprises:

• a plurality of replicas, for example in wax, of source supply conduits of the shell elements, capable of being in fluid communication with the central descender and the second lower end portions of the shell elements to allow source casting carapace elements,
• a replica, for example in wax, of a handling accessory shell, independent of the plurality of shell elements and of their metal supply circuit so as to be without fluid communication with the shell elements, the handling accessory shell being adapted to be in fluid communication with the central descender to allow falling casting of the handling accessory shell.

• un godet de coulée apte à permettre l'injection de métal en fusion dans la carapace,
• un descendant central s'étendant selon l'axe longitudinal de la carapace, en communication fluidique avec le godet de coulée pour recevoir le métal en fusion,
• une pluralité d'éléments, notamment aubagés, de carapace chacun destiné à l'obtention de l'un des éléments de turbomachine, chaque élément de carapace comprenant une première partie d'extrémité basse et une deuxième partie d'extrémité haute,

caractérisée en ce qu'elle comporte en outre :

• une pluralité de conduits d'alimentation en source des éléments de carapace, en communication fluidique avec le descendant central et les deuxièmes parties d'extrémité basse des éléments de carapace pour permettre une coulée en source des éléments de carapace,
• une carapace d'accessoire de manutention, indépendante de la pluralité d'éléments de carapace et de leur circuit d'alimentation en métal de sorte à être sans communication fluidique avec les éléments de carapace, la carapace d'accessoire de manutention étant en communication fluidique avec le descendant central pour permettre une coulée en chute de la carapace d'accessoire de manutention.

Another subject of the invention, according to another of its aspects, is a shell for the manufacture by lost-wax casting of a plurality of elements, in particular bladed elements, of a turbomachine, said cluster-shaped shell having an axis longitudinal and comprising:

• a casting bucket capable of allowing the injection of molten metal into the shell,
• a central descender extending along the longitudinal axis of the shell, in fluid communication with the pouring bucket to receive the molten metal,
• a plurality of shell elements, in particular bladed, each intended to obtain one of the turbomachine elements, each shell element comprising a first lower end part and a second upper end part,

characterized in that it further comprises:

• a plurality of shell element source supply ducts in fluid communication with the central descender and the second bottom end portions of the shell elements to allow source casting of the shell elements,
• a handling accessory shell, independent of the plurality of shell elements and their metal supply circuit so as to be without fluid communication with the shell elements, the handling accessory shell being in fluid communication with the central descender to allow falling casting of the handling accessory shell.

Advantageously, the handling accessory, in particular in the form of a handling ring, has in the invention a single purpose of handling the bunch, in particular at the exit of the oven, on shakeout and during cutting, and no longer a sighting of molten metal supply as according to the drop casting principle described above. Preferably, the handling accessory has sufficient mechanical properties not to yield under its own weight during handling and mainly not to fracture during cooling.

The cluster-shaped model and the shell according to the invention may also include one or more of the following characteristics taken separately or in any possible technical combination.

The handling accessory shell may comprise radial arms fluidically connecting a handling ring shell, centered on the longitudinal axis, to the central descender.

Furthermore, the handling accessory shell may comprise a central element with a central axis coinciding with the longitudinal axis of the shell, fixed to the central descender or to the casting bucket, the radial arms fluidically connecting the shell of the handling crown and the central element.

In addition, the shell elements can advantageously be arranged around the longitudinal axis, being circumferentially spaced from each other, and defining an interior space centered on the longitudinal axis in which the central descendant is located.

According to a first variant, each shell element can be in fluid communication, at its second upper end part, with a single wax discharge conduit connected to the casting cup.

According to a second variant, each shell element can be in fluid communication, at its second upper end part, with a single wax evacuation duct. The shell may comprise at least a first set and a second set of a plurality of wax evacuation ducts respectively interconnected by at least a first lateral duct and a second lateral duct, said at least one first lateral duct and a second lateral conduit being respectively fluidically connected with the pouring cup by means of at least a first and a second main wax evacuation conduits extending respectively between the pouring cup and the said at least one first and one second conduits side.

The carapace turbomachine elements can for example be bladed carapace elements, each designed to obtain a single moving blade.

Another subject of the invention, according to another of its aspects, is a process for the manufacture by lost-wax casting of a plurality of elements, in particular bladed elements, of a turbomachine, characterized in that it is placed implemented using a shell as defined previously and/or using a model in the form of a cluster as defined above, the method comprising a step of pouring the metal into the shell.

BRIEF DESCRIPTION OF DRAWINGS

• la figure 1 représente une vue en perspective partielle d'un premier exemple de réalisation d'une carapace conforme à l'invention, pour la fabrication par moulage à cire perdue d'une pluralité d'éléments de turbomachine, et
• la figure 2 représente une vue en perspective partielle d'un deuxième exemple de réalisation d'une carapace conforme à l'invention, pour la fabrication par moulage à cire perdue d'une pluralité d'éléments de turbomachine, formant une variante de réalisation de la figure 1.

The invention can be better understood on reading the detailed description which follows, of non-limiting examples of implementation thereof, as well as on examining the figures, schematic and partial, of the appended drawing, on which :

• the figure 1 shows a partial perspective view of a first embodiment of a shell in accordance with the invention, for the manufacture by investment casting of a plurality of turbomachine elements, and
• the picture 2 shows a partial perspective view of a second embodiment of a shell according to the invention, for the manufacture by lost-wax casting of a plurality of turbomachine elements, forming a variant embodiment of the figure 1 .

In all of these figures, identical references can designate identical or similar elements.

In addition, the various parts shown in the figures are not necessarily shown on a uniform scale, to make the figures more readable.

DETAILED DISCUSSION OF PARTICULAR EMBODIMENTS

It is noted that, throughout the description, the possible terms “top”, “bottom”, “above” and “below” are understood according to the orientation of the views in the figures.

In addition, it is noted that the invention makes it possible to manufacture turbomachine elements, which may for example be moving compressor or turbine blades, or even compressor or turbine stator blades, produced individually or in sectors comprising several blades.

It is also noted that if the characteristics mentioned below are described in relation to shell 1, it should be understood that they apply manner analogous to the cluster-shaped model, around which this shell 1 is intended to be formed.

We have represented with reference to the figure 1 a first embodiment of a shell 1 according to the invention, for the manufacture by investment casting of a plurality of turbomachine elements, in particular bladed elements.

For the manufacture of the shell, a cluster-shaped model (not shown) is first made around which the shell 1, preferably made of ceramic, is intended to be formed. This cluster-shaped model is essentially composed of sacrificial elements made of wax, but not exclusively. However, for the sake of simplicity, it is referred to as a "wax pattern".

The implementation of the step of producing the ceramic shell 1 is carried out in known manner by dipping the wax model in successive baths (not shown).

After its drying, the shell 1 obtained has the general shape of a cluster, and comprises shell elements which will be described below, with the shell 1 represented on the figure 1 in a position as adopted afterwards when it is filled with molten metal.

The shell 1 firstly comprises a pouring cup 2 of metal, which can be completely or partially covered with the shell 1. This pouring cup 2 is in fluid communication with a central descender 3 extending along the longitudinal axis X of the shell 1. This central descendant 3 preferably takes the form of a hollow cylinder of axis X which extends from the bottom of the casting cup 2 to the level of the lower ends 4a of the bladed shell elements 4.

The central descender 3 advantageously communicates, in a manner known per se, with source supply conduits 5, visible on the picture 2 described below, bladed shell elements 4 intended to form the metal parts in the form of bladed elements. In other words, the molten metal is injected into the casting cup 2, then passes through the central descender 3 and is injected, in the lower part, into the source supply ducts 5 so as to allow the bladed shell elements to be filled. 4 from below, that is to say from bottom to top.

The bladed shell elements 4 are said to be bladed because after removal of the wax replica, they each internally form a cavity corresponding to a blade. These bladed shell elements 4 extend upwards, being arranged around the axis X, and also around the central descender 3 extending along this same axis, downwards from the bottom of the casting bucket 2 The bladed shell elements 4 form the peripheral wall of the shell 1, of longitudinal axis X. They are circumferentially spaced from each other, and define an interior space centered on this axis X, space in which is therefore located central 3.

Furthermore, in accordance with the invention, the shell 1 comprises a handling accessory shell 6 which is completely independent of the bladed elements of the shell 4 and of their molten metal supply circuit.

This handling accessory shell 6 comprises for example a central element 7 of revolutionary shape, cylindrical or conical, with a central axis coinciding with the central axis X of the shell 1, oriented vertically.

This central element 7 is fixed to the central descender 3, or even to the casting cup 2 directly. Radial arms 8, more visible on the picture 2 , connect the central element 7 to a handling ring shell 9 centered on the axis X. The radial arms 8 and the handling ring shell 9 are for example arranged just below the casting bucket 2.

Advantageously, the radial arms 8 and the central element 7 are in fluidic communication with the central descender 3, itself in fluidic communication with the casting cup 2, in order to allow the metal construction of the handling accessory . In accordance with the invention, a drop casting is carried out in order to obtain this handling accessory. Thus, the invention implements both casting at the source to allow the formation of the bladed elements of the turbomachine and casting at the drop to allow the formation of the handling accessory, the bladed elements and the handling accessory being thus produced completely independently in order to avoid the appearance of manufacturing defects as explained above.

Furthermore, in this embodiment of the figure 1 , each bladed shell element 4 is in fluid communication, at its upper end 4b, with a single wax evacuation duct 10, also called a wax-puller or even dewaxing vents 10. These wax evacuation ducts 10 are oriented substantially vertically in the position of the shell 1 shown schematically on the figure 1 .

Furthermore, the figure 1 also shows that, to reinforce the holding of the shell of the handling crown 9, several ceramic holding reinforcements 11 may be provided connecting the shell of the crown 9 to the casting cup 2.

In the embodiment of the picture 2 , the choice was made not to link the wax pullers to a part formed by a bladed shell element 4, in other words not to associate a wax puller with each bladed shell element 4. Thus, in this example, a first 12a, a second 12b, a third 12c and a fourth 12d sets of four wax evacuation ducts 10 respectively associated with four bladed shell elements 4 are each fluidly connected to each other by respectively first 14a, second 14b, third 14c and fourth 14c side ducts.

The wax discharge ducts 10 are therefore partly connected to each other in order to make them integral. In this way, it is possible to avoid having excessive vibrations during the shake-out step in particular. Indeed, these vibrations could be very detrimental by causing recrystallization, and therefore the appearance of recrystallized grains on the formed parts.

At each of the four side ducts 14a-14d is fluidically connected a main wax discharge duct 13a, 13b, 13c or 13d, or wax puller 13a-13d, itself fluidically connected to the pouring cup 2.

In other words, the evacuation of the wax, in this example, takes place in the pouring cup 2 by means of first 13a, second 13b, third 13c and fourth 13d main wax evacuation ducts, each being fluidly connected to a plurality of bladed shell elements 4.

Advantageously, such an embodiment according to the example of figure 2 can improve molding and safety aspects. This can also make it possible to reduce or further increase the stresses in the blade during the solidification phase and a finer evacuation of the wax. In this way, it may therefore be possible to optimize the dewaxing system.

After obtaining shell 1 and eliminating most of the cluster model enclosed in it, shell 1 is preheated to high temperature in a dedicated furnace, for example between 1000 and 1200°C, in order to promote the fluidity of the metal in the shell 1 during casting.

On leaving the preheating of the shell 1, metal coming out of a melting furnace is poured into the bladed shell elements 4 via the casting bucket 2, with the shell 1 in the position as shown in the picture 1 or 2 , that is to say with the pouring bucket 2 open upwards and the X axis still oriented vertically.

The molten metal therefore successively borrows the casting cup 2, then the central descender 3, the central element 7, the radial arms 8 and the crown shell 9 to form the handling accessory in falling casting, and almost simultaneously the central downcomer 3, the source supply ducts 5 and the shell bladed elements 4 to form the turbomachine bladed elements by source casting.

After the metal has cooled following casting, the shell 1 is destroyed, then the moving blades are extracted from the cluster for any machining and finishing and inspection operations.

Advantageously, stiffeners can be added to each radial arm 8 of the handling crown to stiffen the cluster and prevent it from collapsing under its own weight.

In addition, the production of a handling ring, and more generally of a handling accessory, totally independent of the bladed elements makes it possible to reduce the dimensioning of the handling ring compared to that formed by the supply system in a drop casting solution as previously described in the part relating to the prior art. This reduction in size can then lead to a reduction in the metal mass, in particular greater than 50%. In addition, such a handling accessory, and in particular such a handling ring, can be made other than in metal, and in particular in ceramic, because it is only used for handling and no longer for supplying the bladed shell elements 4. As a result, the metal mass can even be reduced to zero if a material other than metal is used. This reduction in size and metal mass of the handling accessory can be done while maintaining sufficient mechanical properties.

Furthermore, casting the cluster at source can make it possible to preserve the metallurgical health of the parts formed. It is thus possible to reduce the risks of offset and core breakage because the attack speeds of the metal are very low, typically between 0.2 and 0.6 m/s. Furthermore, it is possible to reduce the metallurgical defects such as those of inclusion, oxidation, recrystallized grains, parasites, among others, as described above in connection with the state of the prior art.

In general, the invention makes it possible to obtain ventilation of the cluster and an increase in its rigidity with better resistance to molding and finishing. The principle in accordance with the invention aimed at isolating the handling ring from the bladed elements allows a reduction in the stresses and plastic deformations during solidification and cooling.

The invention in fact seeks to limit the thermomechanical stresses due to thermal gradients in the direction of directed solidification. The risks of recrystallized grains and cold cracks are reduced with the solution of the invention. As this is a directed solidification process, the mold cools heterogeneously, with the bottom cooling first, causing cold metal to pull hot metal. By controlling the temperature at the bottom of the mould, it is possible to control the temperature gradient along the direction of solidification. A balance of the metal masses of the upper part with respect to the lower part is established, and the stresses on all the manufactured parts are reduced and better distributed.

In addition, it should be noted that a numerical validation of the solution of the invention by estimation of the plasticity criterion of the von Mises criterion type at the end of solidification shows that the significantly reduced stresses of the order of 45 to 50% when the cluster is directly connected to the casting cup 2, as according to the examples of figures 1 and 2 according to the invention, rather than being connected to a system supply in the form of a crown as in the classic solution of the prior art in drop casting. Then, the probability of forming metallurgical defects, in particular of the recrystallized grain type, is less.

Advantageously, the principle of the invention described previously can be applied to any type of cluster configuration.

Claims (9)

1. Cluster model, about which is intended to be formed a shell (1) for the production, by lost wax casting, of a plurality of turbomachine elements, said model having a longitudinal axis (X) and comprising:

   - a replica of a casting cup (2) suitable for the injection of molten metal into the shell (1),

   - a replica of a central sprue (3) extending along the longitudinal axis (X), suitable for being fluidically connected to the casting cup (2) for receiving the molten metal,

   - a plurality of replicas of shell elements (4) each intended for obtaining one of the turbomachine elements, each shell element (4) including a first bottom end portion (4a) and a second top end portion (4b),

   characterised in that it further comprises:

   - a plurality of replicas of bottom feed conduits (5) for the shell elements (4), suitable for being fluidically connected to the central sprue (3) and the second bottom end portions (4a) of the shell elements (4) so as to allow bottom-pour casting of the shell elements (4),

   - a replica of a handling accessory shell (6) that is independent of the plurality of shell elements (4) and of the metal supply circuit thereof, such that there is no direct fluidic connection to the shell elements (4), the handling accessory shell (6) being suitable for being fluidically connected to the central sprue (3) so as to allow top-pour casting of the handling accessory shell (6).
2. Shell (1) for the production, by lost wax casting, of a plurality of turbomachine elements, said cluster shell having a longitudinal axis (X) and comprising:

   - a casting cup (2) suitable for the injection of molten metal into the shell (1),

   - a central sprue (3) extending along the longitudinal axis (X), of the shell (1) that is fluidically connected to the casting cup (2) for receiving the molten metal,

   - a plurality of shell elements (4) each intended for obtaining one of the turbomachine elements, each shell element (4) including a first bottom end portion (4a) and a second top end portion (4b),

   characterised in that it further comprises:

   - a plurality of bottom feed conduits (5) for the shell elements (4) that are fluidically connected to the central sprue (3) and the second bottom end portions (4a) of the shell elements (4) so as to allow bottom-pour casting of the shell elements (4),

   - a handling accessory shell (6) that is independent of the plurality of shell elements (4) and of the metal supply circuit thereof, such that there is no direct fluidic connection to the shell elements (4), the handling accessory shell (6) being fluidically connected to the central sprue (3) so as to allow top-pour casting of the handling accessory shell (6).
3. Shell according to claim 2, characterised in that the handling accessory shell (6) comprises radial arms (8) fluidically connecting a handling ring shell (9), centred about the longitudinal axis (X), to the central sprue (3).
4. Shell according to claim 3, characterised in that the handling accessory shell (6) comprises a central element (7) of central axis coinciding with the longitudinal axis (X) of the shell (1), attached to the central sprue (3) or to the casting cup (3), the radial arms (8) fluidically connecting the handling ring shell (9) to the central element (7).
5. Shell according to any one of claims 2 to 4, characterised in that the shell elements (4) arranged about the longitudinal axis (X), being spaced circumferentially apart from one another, and defining an inner space centred about the longitudinal axis (X) wherein the central sprue (3) is located.
6. Shell according to any one of claims 2 to 5, characterised in that each shell element (4) is fluidically connected, at the level of the second top end portion (4b) thereof, to a single wax discharge conduit (10) connected to the casting cup (2).
7. Shell according to any one of claims 2 to 5, characterised in that each shell element (4) is fluidically connected, at the level of the second top end portion (4b) thereof, to a single wax discharge conduit (10), and in that the shell (1) comprises at least one first assembly (12a) and one second assembly (12b) of a plurality of wax discharge conduits (10) respectively connected to one another by at least one first lateral conduit (14a) and one second lateral conduit (14b), said at least one first lateral conduit (14a) and one second lateral conduit (14b) being respectively fluidically connected to the casting cup (2) via at least one first (13a) and one second (13b) main wax discharge conduits extending respectively between the casting cup (2) and said at least one first (14a) and one second (14b) lateral conduits.
8. Shell according to any one of claims 2 to 7, characterised in that the shell turbomachine elements (4) are shell bladed elements (4), each designed for obtaining a single moveable blade.
9. Method for producing, by lost wax casting, a plurality of turbomachine elements, characterised in that it is implemented using a shell (1) according to any one of claims 2 to 8 and/or using a cluster model according to claim 1, the method comprising a step for casting the metal in the shell (1) for forming at least the turbomachine elements.

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