Manufacture and use of a lost wax casting refractory core

Abstract

Manufacture and use of a refractory casting core The invention relates to a method for manufacturing a refractory casting core, said method comprising the additive manufacturing of a first and a second element each incorporating a refractory powder, said first and second elements each having one or more channels, the insertion of one or more refractory rods into said channels to connect the first and second elements, and the sintering of the first and second elements. It also relates to the use of the refractory casting core obtained according to this method in a casting process. Figure for abstract: Fig. 1.

Description

Title of the invention: Manufacture and use of a refractory core for lost wax casting Technical field

[0001] The present disclosure relates to the field of foundry, and more particularly to the manufacture of refractory foundry cores, as well as to their use. Prior art

[0002] Climate change is a major concern for many legislative and regulatory bodies around the world. Indeed, various restrictions on carbon emissions have been, are being, or will be adopted by various states. In particular, an ambitious standard applies both to new types of aircraft and those in circulation requiring the implementation of technological solutions in order to make them compliant with current regulations. Civil aviation has been mobilizing for several years now to make a contribution to the fight against climate change.

[0003] Technological research efforts have already made it possible to significantly improve the environmental performance of aircraft. The Applicant takes into consideration the impact factors in all phases of design and development to obtain less energy-intensive, more environmentally friendly aeronautical components and products whose integration and use in civil aviation have moderate environmental consequences with the aim of improving the energy efficiency of aircraft.

[0004] Consequently, the Applicant is constantly working to reduce its negative climate impact by using methods and operating virtuous development and manufacturing processes and minimizing greenhouse gas emissions to the minimum possible in order to reduce the environmental footprint of its activity.

[0005] This sustained research and development work covers new generations of aircraft engines, the lightening of aircraft, particularly through the materials used and lighter on-board equipment, the development of the use of electrical technologies to ensure propulsion, and, as essential complements to technological progress, aeronautical biofuels.

[0006] One way to improve the energy efficiency of gas turbine engines is to increase the combustion gas temperatures. However, this increase in combustion gas temperatures imposes significant thermal stresses on the materials of the gas turbine engine, and in particular on the blades of turbine for extracting mechanical work from the expansion of these combustion gases at very high temperatures. In this context, the term "blades" refers to both stator blades and, above all, rotor blades. To ensure the mechanical strength of these blades in a flow of combustion gases whose temperature can significantly exceed the melting temperature of the metallic material of the blades, it is therefore normally necessary to incorporate increasingly complex cooling circuits inside these blades.

[0007] Turbomachine blades, and in particular those of the hot parts, are typically produced by casting, and in particular by so-called "lost wax" casting techniques, in which the mold is formed around a model of the part to be molded, made of an easily meltable material, such as wax. Once the mold is formed, the model material is removed from the mold to thereby release a molding cavity which will then receive the molten metallic material of the part to be molded.

[0008] In order to form cavities inside the parts thus molded, such as in particular the cavities forming the cooling circuits of turbomachine blades, refractory cores can be integrated inside the models used for their molding. After the evacuation of the material from the model, these cores will therefore remain in the molding cavities to form cavities inside the metallic material of the molded part.

[0009] The increasing complexity of turbomachine blade cooling circuits following the increase in combustion gas temperatures is leading to a reduction in the size of the cores and their multiplication in order to cool the turbomachine blades locally. In order to produce these complex circuits, new processes for manufacturing these cores can therefore be used, such as, for example, additive manufacturing processes. However, even additive manufacturing of cores alone does not allow certain constraints related to the molding of complex parts to be overcome.In particular, the various stages of manufacturing a complex refractory core intended for molding a blade with a fine and complex cooling circuit separated by a metal dome from a larger concavity or tub at the end of the blade can cause significant mechanical stresses within the core and consequently deformations, cracks, or even breakage of the cores.

[0010] However, thickening the bonds in the core between a part intended to form the cooling circuit and another part intended to form the tub in order to reduce these mechanical stresses results in larger channels through said metal dome in the blade resulting from this molding. However, current filling technologies normally only allow the filling of holes of limited diameter. Thus, filling by laser metal deposition (in English: Laser Metal Deposition (LMD) is possible on holes with a maximum cross-section of about 0.79 mm2, corresponding to approximately 1 mm in diameter), while brazing normally requires a large contact surface. Furthermore, the increasing complexity and finesse of cooling circuits also tends to reduce the size of the ducts and cavities that form them, which in turn can also prevent thickening of the connections with the corresponding part of the core. Disclosure of the invention

[0011] The present disclosure aims to present a method for manufacturing a refractory molding core making it possible to form at least two separate cavities while limiting the subsequent operations of filling orifices between these two cavities. For this, according to a first aspect of the present disclosure, the method comprises the additive manufacturing of a first and a second element each incorporating a refractory powder, said first and second elements each having one or more channels, the insertion of one or more refractory rods into said channels to connect the first and second elements, and the sintering of the first and second elements.These refractory rods may in particular be mainly made of ceramic, and in particular of alumina, although they may also be coated with one or more agents, for example adhesives, possibly loaded with refractory particles, for example ceramics, in the form of a colloidal suspension, in particular to play the role of a sealing agent.

[0012] Thus, the channels formed in the first and second elements make it possible to connect them by inserting, into these channels, thin refractory rods having a diameter typically between 0.4 mm and 1.5 mm, which will consequently leave only a reduced and easily refilled imprint in the molded part.

[0013] In particular, in order to limit as much as possible the refilling operations on the molded part, the first and second elements may be manufactured separately. In this case, in order to ensure the accuracy of the relative positioning of the first and second elements, the method may also comprise the additive manufacturing of one or more connecting elements, and the refractory rods may be incorporated into the connecting elements before inserting the connecting elements, with the refractory rods, between the first and second elements.

[0014] Alternatively, however, the first and second elements may be manufactured in a single-piece blank. In this case, after insertion of the refractory rods, it is possible to remove at least part of the remaining material connecting the first and second elements so as to limit the cross-section of the connections between the first and second elements and therefore that of the passages to be possibly filled between the cavities formed by these elements in the molded part.

[0015] Said channels may comprise at least one groove on the first and / or second elements, open perpendicular to a main direction of the refractory rod inserted into the groove. By "main direction" of the rod, is meant, in the context of the present application, that of the greatest length of the rod. Thus, the insertion of the refractory rod into this channel, to connect the first and second elements, may be done laterally. In this case it is possible to cover at least a portion of the rod received in the groove after insertion.

[0016] Alternatively or additionally, said channels may however comprise at least one orifice in the first and / or second elements, open in a main direction of the refractory rod inserted into the orifice.

[0017] In this case, said orifice may have a shoulder against which one end of the refractory rod inserted into the orifice comes to bear, and an evacuation conduit, opposite the refractory rod inserted into the orifice, connecting said shoulder to the outside so as to be able to evacuate from the orifice a fluid material when the rod is inserted therein, for example still liquid remains of a masterbatch used in the additive manufacturing step and / or a coating of the rod.

[0018] Alternatively, however, said orifice may connect to the outside a reservoir inside said first or second element, so that the fluid material remaining in the orifice can be pushed therein by the rod, or said orifice may be a blind orifice. In the latter case, the clearance between the rod and the blind orifice may be sufficient to allow the expulsion of the fluid material from the orifice when the rod is inserted therein.

[0019] The manufacturing method may further comprise a step of cleaning the first and / or second elements before sintering, in particular to remove still liquid remains of a masterbatch used in the additive manufacturing step.

[0020] In this case, said insertion of one or more refractory rods may in particular be carried out before said cleaning of the first and / or second elements, for example so that these masterbatch remnants fill the interstices between the refractory rods and the channels in which they are received. Alternatively, however, it could be carried out after cleaning, so as to facilitate the insertion of the rods.

[0021] The manufacturing method may further comprise a step of at least partially removing binders in the first and / or second elements before sintering.

[0022] In this case, to facilitate the insertion of one or more refractory rods, this insertion can be carried out after said at least partial removal of binders in the first and / or second elements, but before sintering, or even after sintering.

[0023] Said additive manufacturing of the first and second elements can in particular be carried out by a ceramic manufacturing process based on lithography (in English: Lithography-based Ceramic Manufacturing or LCM), although other additive manufacturing processes may be possible.

[0024] A second aspect of the present disclosure relates to a molding method comprising manufacturing a refractory molding core according to the first aspect, introducing the refractory core into an injection mold, injecting a non-refractory material into the injection mold to create a pattern, forming a refractory mold around the pattern, removing said non-refractory material to empty a molding cavity within the refractory mold, filling the molding cavity with a molten metallic material, solidifying the metallic material in the refractory mold, and demolding the solidified metallic material from the refractory mold.

[0025] This molding method may in particular be intended to produce a turbomachine blade in which the first element corresponds at least partially to a cooling circuit of the turbomachine blade, and the second element corresponds at least partially to a tub formed in an end platform of the turbomachine blade, said cooling circuit and tub being separated by a metal dome from the turbomachine blade. Brief description of the drawings

[0026] The invention will be better understood and its advantages will appear better, on reading the detailed description which follows, of embodiments shown as non-limiting examples. The description refers to the appended drawings in which:

[0027] [Fig. 1] [Fig. 1] represents a green or debound or sintered body, for the manufacture of a foundry refractory core according to a first embodiment, comprising a single monobloc part produced by additive manufacturing, with two separate elements connected by refractory rods inserted into the part.

[0028] [Fig.2] [Fig.2] represents a green or debinded or sintered body, for the manufacture of a foundry refractory core according to a second embodiment, comprising two separate parts produced by additive manufacturing, connected by refractory rods inserted into the parts.

[0029] [Fig.3] [Fig.3] represents a green or debinded or sintered body, for the manufacture of a foundry refractory core according to a third embodiment, comprising two separate parts produced by additive manufacturing, connected by a fastening part and refractory rods inserted into the parts.

[0030] [Fig.4] [Fig.4] represents a groove receiving a refractory rod in a body green or debinded or sintered produced by additive manufacturing.

[0031] [Fig.5] [Fig.5] represents an orifice receiving a refractory rod in a body green or debinded or sintered produced by additive manufacturing, the orifice having a conduit evacuation.

[0032] [Fig.6] [Fig.6] represents an orifice receiving a refractory rod in a green or debinded or sintered body produced by additive manufacturing, the orifice connecting to the outside a reservoir inside the green sintering body.

[0033] [Fig.7] [Fig.7] represents a blind orifice receiving a refractory rod in a green or debinded or sintered body produced by additive manufacturing.

[0034] [Fig.8] [Fig.8] shows a turbomachine blade produced by casting with a foundry core manufactured by a method according to any one of the first to third embodiments. Description of the embodiments

[0035] In a first step of a method for manufacturing a refractory molding core according to a first embodiment, a blank 1, or “green body”, can be produced by additive manufacturing, and more particularly by a lithography-based ceramic manufacturing method (LCM). This additive manufacturing method can use a liquid masterbatch comprising a photosensitive resin comprising monomers and / or oligomers and loaded with ceramic particles, typically of the order of a micrometer in size, as well as various additives, for example dispersants, solvents, or photoinitiators, to form a part by selective polymerization of the monomers and / or oligomers of the photosensitive resin in successive layers. To form each layer, a thickness of this masterbatch, typically between 25 μm and 100 μm, can be spread on the bottom of a tank.A projector then selectively illuminates the surface of the masterbatch so as to selectively polymerize the photosensitive resin over this thickness by trapping ceramic particles in the newly formed polymer layer. Once this layer is formed, the bottom of the tank can descend by a step corresponding to the thickness of each layer, before repeating the same steps to form a new layer. These steps can be repeated as many times as the number of layers required to form the blank 1. The precision of this additive manufacturing process can be in the order of several tens of micrometers, which allows the creation of high-precision geometry and channels.

[0036] According to this first embodiment, the blank 1 can be formed, in this additive manufacturing step, as a single-piece blank with two separate elements 2, 3, as illustrated in [Fig. 1]. These first and second elements 2, 3 can be connected by supports 4 also included in the blank 1 formed by additive manufacturing. Channels 5 can also be formed, in the first and second elements 2, 3, to receive refractory rods 6 connecting the first and second elements 2, 3. These refractory rods 6 can in particular be principally ceramic payment, and in particular alumina, although they can also be coated with one or more agents, for example adhesives, possibly loaded with refractory particles, for example ceramic, in the form of a colloidal suspension, in particular to act as a sealing agent. It is also possible to use the same masterbatch used for additive manufacturing. They can have, for example, a round cross-section, and a diameter between 0.4 mm and 1.5 mm, although other cross-sections are possible.

[0037] At least one of the channels 5 may take the form of a groove, open perpendicular to a main direction L of the refractory rod 6 which is inserted therein, as illustrated in [Fig.4]. As illustrated, in the transverse plane XY, orthogonal to an axis Z parallel to the main direction L of the refractory rod 6, this groove may have a funnel-shaped cross-section, with converging walls 5a, 5b, in order to facilitate the insertion of the refractory rod 6 into the groove. After the insertion of the refractory rod 6 into the groove, it is also possible to cover at least a portion of the refractory rod 6 received in the groove, for example with a sealing agent and / or masterbatch such as those with which the refractory rod 6 may be coated.Furthermore, to facilitate their adhesion, the depth and / or the cross-section of the groove can be variable along the length of the groove following the main direction of the refractory rod 6.

[0038] Alternatively or in addition to the preceding form, at least one of the channels 5 may take the form of an orifice open in the main direction L of the refractory rod 6 inserted in the orifice, as illustrated in each of FIGS. 5 to 7. As in [Fig. 5], this orifice may have a shoulder 5c against which one end of the refractory rod 6 inserted in the orifice comes to bear, and an evacuation conduit 5d, of cross-section substantially smaller than the refractory rod 6 inserted in the orifice and opposite it, and connecting said shoulder 5c to the outside so as to be able to evacuate from the orifice a fluid material when the refractory rod 6 is inserted therein, for example still liquid remains of the masterbatch used in the additive manufacturing step and / or the coating of the refractory rod 6. Alternatively, as in [Fig.6], this orifice can connect to the outside a reservoir 5e inside said first or second element 2,3, so that the fluid material remaining in the orifice can be pushed back into the reservoir 5e by the refractory rod 6. In yet another alternative, illustrated in [Fig.7], this orifice can simply be a blind orifice. In the latter case, a clearance of the order of a tenth of a millimeter between the refractory rod and the interior surfaces of the blind orifice can be sufficient to allow the expulsion of the fluid material from the blind orifice when the refractory rod 6 is inserted therein.

[0039] After the additive manufacturing step, the blank 1 can still be covered with a excess unpolymerized masterbatch. Consequently, the method for manufacturing the refractory core may then comprise a step of cleaning the blank 1 in which this remaining masterbatch is removed at least in part. In a first variant of this first embodiment, the insertion of at least one of the refractory rods 6 into the corresponding channel 5 could be carried out after this cleaning step, rather than directly after the additive manufacturing of the blank 1.

[0040] The material of the blank 1 may still contain, after its cleaning, agents such as for example solvents and / or binders. Consequently, the method for manufacturing the refractory core may still comprise, after the additive manufacturing or the cleaning of the blank 1, steps of pre-conditioning and / or debinding of the blank 1, in which these agents are at least partially removed. Thus, for example, the blank 1 could first be pre-conditioned by drying and partial evaporation of said agents, and then debinded by substantially completely removing these agents. In a second variant of this first embodiment, the insertion of at least one of the refractory rods 6 into the corresponding channel 5 could be carried out after or between these pre-conditioning and / or debinding steps, rather than directly after the additive manufacturing or the cleaning of the blank 1.

[0041] Finally, the blank 1 can be consolidated by sintering in a high temperature and / or pressure furnace, typically but not restricted to sintering in air at ambient pressure with a temperature between 1000°C and 1800°C. In a third variant of this first embodiment, the insertion of at least one of the refractory rods 6 into the corresponding channel 5 could even be carried out after this sintering. In each of the variants of this first embodiment, the supports 4 can be removed at least partially, for example by machining, for example manually with a file, after the insertion of these refractory rods 6 into the channels 5, in order to reduce the cross-section of the connections between the first and second elements 2, 3.

[0042] Although in this first embodiment the blank 1 may be formed as a single-piece blank incorporating the first and second elements 2, 3, as illustrated in [Fig. 1], it is also conceivable to manufacture these first and second elements 2, 3 separately, and then connect them with the refractory rods 6. Thus, in a second embodiment, illustrated in [Fig. 2], the first and second elements 2, 3 may be assembled using the refractory rods 6 and a jig to ensure their correct relative positioning. Temporary supports 4 may also be formed with the first and / or second element 2, 3 to assist in this positioning. As in each of the variants of the first embodiment, these supports 4 can be removed at least partially, for example by machining, after inserting these refractory rods 6 into the channels 5, in order to reduce the cross-section of the connections between the first and second elements 2, 3.

[0043] In a third embodiment, the blank 1 may further comprise, apart from the first and second elements 2, 3, one or more connecting elements 7 manufactured separately. The connecting elements 7 may also be manufactured by additive manufacturing, in particular with the same additive manufacturing method as the first and second elements 2, 3. The refractory rods 6 may, in the assembly according to this third embodiment, be incorporated into the connecting elements 7 before inserting the connecting elements 7, with the refractory rods 6, between the first and second elements 2, 3. In order to ensure stable and precise positioning of the first and second elements 2, 3, their assembly with the connecting elements 7 may be ensured by complementary shapes, for example dovetails.

[0044] Apart from manufacturing the blank 1 in several separate parts rather than in a single monobloc piece, the methods according to the second and third embodiments can be analogous to that of any of the variants of the first embodiment, and thus comprise the same steps and use the same alternatives for the channels.

[0045] The refractory molding core obtained by the manufacturing method according to any one of these three embodiments and their variants can be used in a molding process. In this molding method, after the refractory core has been manufactured, it can be introduced into an injection mold, and a non-refractory material can be injected, into the injection mold, around the refractory core to create a model overmolded on the refractory core. After demolding the model, a refractory mold, which can for example be a shell mold, can then be formed around this model or even a cluster of models produced in the same way. The non-refractory material can then be removed, for example by melt evacuation, to empty a molding cavity inside the refractory mold.This molding cavity can then be filled with molten metallic material, then solidified in the refractory mold, and finally demolded from the refractory mold.

[0046] This molding method can in particular be used to produce a turbomachine blade 10, as illustrated in [Fig. 8], in which the first element 2 corresponds at least partially to a cooling circuit (not illustrated) of the blade 10, and the second element 3 corresponds at least partially to a tub 11 formed in an end platform of the blade 10, said cooling circuit and tub 11 being separated by a metal tub bottom crossed only by orifices 12 of small diameter corresponding to the imprint of the rods refractories 6 in the metallic material of the blade 10. Thus, thanks to the manufacturing process of the refractory core used in the molding of the blade 10, it is possible to reduce the size of these passages between adjacent cavities of the blade 10 after its molding, and thus facilitate their subsequent filling.

[0047] Although the present invention has been described with reference to specific embodiments and variations by way of example, it is obvious that various modifications and changes may be made to these examples without departing from the general scope of the invention as defined by the claims. Furthermore, individual features of the various embodiments discussed may be combined in additional embodiments. Therefore, the description and drawings are to be considered in an illustrative rather than restrictive sense.

Claims

Claims

1. A method of manufacturing a refractory casting core, said method comprising the following steps: additive manufacturing of first and second elements (2, 3) each incorporating a refractory powder, said first and second elements (2, 3) each having one or more channels (5), inserting one or more refractory rods (6) into said channels (5) to connect the first and second elements (2, 3), and sintering the first and second elements.

2. A manufacturing method according to claim 1, wherein the first and second elements (2, 3) are manufactured separately.

3. A manufacturing method according to claim 2, further comprising additively manufacturing one or more connecting elements (7), and wherein the refractory rods (6) are incorporated into the connecting elements (7) before inserting the connecting elements (7), with the refractory rods (6), between the first and second elements (6).

4. A manufacturing method according to claim 1, wherein the first and second elements (2, 3) are manufactured in a single-piece blank.

5. Manufacturing method according to any one of claims 1 to 4, wherein said channels (5) comprise at least one groove on the first and / or second elements (2, 3), open perpendicular to a main direction of the refractory rod (6) inserted in the groove.

6. Manufacturing method according to any one of claims 1 to 5, wherein said channels (5) comprise at least one orifice in the first and / or second elements (2, 3), open in a main direction of the refractory rod (6) inserted in the orifice.

7. A manufacturing method according to claim 6, wherein said orifice has a shoulder (5c) against which one end of the refractory rod (6) inserted into the orifice presses, and an evacuation conduit (5d), opposite the refractory rod (6) inserted into the orifice, connecting said shoulder (5c) to the outside.

8. A manufacturing method according to claim 6, wherein said orifice connects to the outside a reservoir (5e) inside said first or second element (2, 3).

9. A manufacturing method according to claim 6, wherein said orifice is a blind orifice.

10. A manufacturing method according to any one of claims 1 to 9, further comprising a step of cleaning the first and / or second elements (2, 3) before sintering.

11. A manufacturing method according to claim 10, wherein said insertion of one or more refractory rods (6) is carried out before said cleaning of the first and / or second elements (2, 3).

12. A manufacturing method according to any one of claims 1 to 10, further comprising a step of at least partially removing binders in the first and / or second elements (2, 3) before sintering.

13. A manufacturing method according to claim 12, wherein said insertion of one or more refractory rods (6) is carried out after said at least partial removal of binders in the first and / or second elements (2, 3), but before sintering.

14. A manufacturing method according to any one of claims 1 to 10 or 12, wherein said insertion of one or more refractory rods (6) is carried out after sintering.

15. A manufacturing method according to any one of claims 1 to 14, wherein said additive manufacturing of the first and second elements (2, 3) is carried out by a lithography-based ceramic manufacturing method.

16. A molding method comprising the steps of: manufacturing a refractory molding core according to any one of claims 1 to 15, introducing the refractory core into an injection mold, injecting a non-refractory material into the injection mold to create a pattern, forming a refractory mold around the pattern, removing said non-refractory material to empty a molding cavity inside the refractory mold, filling the molding cavity with a molten metallic material, solidifying the metallic material in the refractory mold, and demolding the solidified metallic material from the refractory mold.

17. A molding method according to claim 16 for producing a turbomachine blade in which the first element corresponds at least partially to a cooling circuit of the turbomachine blade, and the second element corresponds at least partially to a tub formed in an end platform of the turbomachine blade, said cooling circuit and tub being separated by a metal dome of the turbomachine blade.

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