Foundry core
The lost-wax casting process with ceramic cores and delayed introduction of coated refractory protrusions addresses oxidation issues and machining complexities, enhancing foundry efficiency and reducing scrap rates.
Patent Information
- Authority / Receiving Office
- FR · FR
- Patent Type
- Patents
- Current Assignee / Owner
- SAFRAN SA
- Filing Date
- 2024-06-11
- Publication Date
- 2026-06-12
AI Technical Summary
Existing foundry processes using refractory materials for casting cores face challenges with temperature resistance to oxidation and require complex machining steps, leading to high scrap rates and defects due to electrical discharge machining.
A lost-wax casting process involving ceramic cores with protrusions made of refractory material, where the protrusions are introduced only at the final metal pouring stage, allowing for reduced exposure to oxidation and eliminating the need for complex machining by using coated refractory materials.
Reduces scrap rates and process duration by minimizing coating stress and exposure to multiple atmospheric conditions, ensuring precise cavity formation without complex machining.
Smart Images
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Abstract
Description
Title of the invention: Foundry core technical field
[0001] The present exposition relates to foundry tools for the manufacture of metal parts and more specifically to foundry cores used for the production of hollow parts. Previous technique
[0002] The lost-wax casting process is known from the literature, and allows a metal part to be obtained directly to the desired dimensions by using a wax model of the part to be obtained, forming a mold around the model and removing the wax to obtain in the mold a cavity in the shape of the wax model, and therefore of the desired part.
[0003] When the part is hollow, that is, when it has recesses, it is possible to create these recesses using a casting core shaped like the desired recess. The casting core is positioned in the mold so that the molten metal introduced into the mold cannot occupy the space of the casting core.
[0004] The subsequent removal of the core makes it possible to obtain in the metal part a recess having the shape of the foundry core in place of the foundry core initially present.
[0005] The use of such a foundry core makes it possible to avoid subsequent machining of a massive metal part to create the desired recess, thus making it possible to easily create recesses with complex geometries.
[0006] However, the casting core is in contact with the metal being poured into the mold and must therefore withstand the temperatures involved. Furthermore, it is important that the core be easily removable once the metallic part is obtained, in order to create the desired porosity.
[0007] Known cores can be made of ceramic material. Indeed, these materials exhibit temperature resistance perfectly satisfactory for such an application.
[0008] For the production of thin parts or complex geometry of the core, some processes use portions of core made of molybdenum or molybdenum alloy (sometimes called RMC for the English acronym "Refractory Metal Core").
[0009] However, refractory materials do not exhibit sufficient temperature resistance to oxidation for direct application in foundry processes and are also soluble in nickel-based superalloys. Therefore, it is It is generally recommended to coat them with a protective coating against oxidation before any use in foundry work.
[0010] Such a coating is particularly stressed during foundry processes. Indeed, these processes require, on the one hand, several heating and return-to-ambient-temperature stages and, on the other hand, changes in atmosphere, some stages being carried out in air and others in vacuum.
[0011] Thus, in the current state of lost-wax casting processes using coated refractory materials, it is necessary that the coating protect the refractory material not only from oxidation but also from temperature cycling, while ensuring that it can be easily removed when the process requires it.
[0012] Therefore, although promising, the use of refractory materials for foundry cores is not easy.
[0013] Moreover, it is sometimes preferred to have a complex machining step of the final part obtained after casting in order to obtain the fine and / or complex patterns for which refractory materials would have been indispensable, rather than developing specific foundry cores, requiring the resolution of the problems set out above.
[0014] However, these machining steps are time-consuming and can also lead to a higher scrap rate. Indeed, in the prior art, such a machining step is performed by electrical discharge machining (EDM).
[0015] Although adequate, these methods require significant work and can cause in the part defects due to the local thermal impact of these methods, these defects can lead to the final rejection of the part.
[0016] It is therefore desirable to have processes that make it possible to avoid such complex machining steps in order to obtain metal parts which nevertheless include a cavity. Description of the invention
[0017] The present invention aims to address at least one of the problems described above.
[0018] To this end, the invention proposes, according to a first aspect, a casting process for a part made of metallic material comprising a cavity, the process comprising at least the following steps: - the arrangement in the cavity of a mold of at least one core made of ceramic material and at least one protrusion made of a first material, the first material being a refractory material, the protrusion made of a first material having a first one end in contact with the core, a protruding body passing through the cavity, and a second free end outside the mold cavity; - the formation of a wax model of the part around the ceramic core obtained by filling the mold cavity with wax; - the removal from the mold of the assembly formed by the wax model, the core and the protuberances in a first material; - the formation of a shell-like mold around the whole formed by the core, the wax model and the protuberances in a first material; - the removal of the wax and protuberances into a first material, to form in the shell mold a cavity, the cavity of the shell mold comprising a main cavity where the wax was and at least one secondary cavity where the protuberances were in a first material; - the partial opening of the shell mold at the end of its secondary cavities; - the insertion into the secondary cavities of the shell mold of at least one protrusion in a second material, the second material being a coated refractory material, the protrusions in a second material being arranged so that their first end is in contact with the core; - the closing of the shell mold around the protuberances in a second material; - the pouring of a metallic material into the main cavity of the shell mold to form the part in metallic material; - the removal of the shell mold around the part made of metallic material; - the removal of protrusions in a second material and of the ceramic core to form a cavity in the part in metallic material.
[0019] The process of the invention makes it possible to solve several problems present in the processes of the prior art.
[0020] On the one hand, it uses cores comprising protuberances in refractory material and therefore offers an alternative to the complex machining steps used in prior art processes.
[0021] In this way, the number of rejects is reduced compared to processes involving final machining and the overall duration of the process is further reduced.
[0022] In addition, it is to the credit of the inventors that they have succeeded in proposing a lost-wax casting process, in which the coated refractory materials are introduced during the process.
[0023] This last characteristic is very advantageous because it ensures that the second material, a coated refractory material, is only exposed to one heating stage, i.e. that during which the metallic material is poured into the shell mold.
[0024] Thus, the characteristics expected for the coating are less demanding because the coating only sees one heating stage and one particular atmosphere.
[0025] Indeed, in prior art processes, the protuberances in refractory material are introduced from the beginning of the process, and the coatings must therefore be able to protect the material throughout the process, which requires more robust coatings.
[0026] In one embodiment, the ceramic core material is chosen from silica, alumina, zirconia, or a mixture of two or more of these materials.
[0027] The ceramic core allows a cavity to be obtained in the final part. Indeed, during the manufacturing process, the metal will be poured around the core before the latter is removed, which will leave a cavity in the resulting part.
[0028] In the present application, the "cavity" or "cavities" comprising the parts made of metallic material are understood as through cavities, that is to say, the interior of the cavities is in fluidic communication with the exterior of the cavities.
[0029] Indeed, it is necessary to be able to eliminate the nucleus in order to form the cavities, and to allow this elimination the cavities must be open-ended.
[0030] The process of obtaining the core is not described here because the latter is obtained by methods known as such, for example additive manufacturing or molding.
[0031] For example, in one embodiment, the core can be produced by ceramic injection (or CIM for the English acronym "Ceramic Injection Molding") or by additive manufacturing.
[0032] It is described that the protuberances have a first end in contact with the nucleus.
[0033] In one embodiment, the protuberances are in contact with the nucleus and further penetrate the latter over a distance greater than or equal to 0.5 mm.
[0034] Such an embodiment ensures that the removal of a protrusion in a first material leaves in the core an imprint of the protrusion, which imprint will allow easy placement of the protrusion in a second material during a subsequent step of the process.
[0035] It is described that the protrusions in a first material have a second end free out of the cavity of the mold.
[0036] In one embodiment, the protrusion passes through the mold, and its second free end is thus outside the mold once the latter is closed.
[0037] In another embodiment, the protrusion does not pass through the mold but fits into a housing provided for this purpose.
[0038] In any event, it shall be said that the second end of the protrusion is outside the cavity provided that it is arranged so that it is not in contact with the wax introduced when the wax is introduced into the cavity of the mold.
[0039] In one embodiment, the process comprises a plurality of protuberances in a first material.
[0040] These protuberances may be of identical or different dimensions.
[0041] In the remainder of the application, a plurality of protuberances is generally described, but it should be understood that this is by no means necessary and that the advantages of the invention are obtained as soon as there is a protuberance.
[0042] In one embodiment, the refractory material of the first and / or second material can be chosen from molybdenum, molybdenum alloys for example molybdenum alloys including rhenium, titanium, titanium and molybdenum and zirconium alloys (also called "TZM" for the English acronym for "titanium-zirconium-molybdenum alloys"), zirconium or a mixture of two or more of these compounds.
[0043] In one embodiment, the protuberances have a cylindrical shape of revolution.
[0044] In one embodiment, the protuberances have an elliptical shape.
[0045] This embodiment is all the more advantageous as such protrusion shapes are inaccessible for current manufacturing processes and in particular via electro-erosion sinking processes.
[0046] In one embodiment, the refractory material of the first and second materials is identical.
[0047] In one embodiment, the refractory material of the first and second materials is different.
[0048] In one embodiment, the coating of the refractory material to form the second material can be chosen from alumina, silica, zirconia or any other material used for foundry cores.
[0049] In one embodiment, the coating of the second material is chosen from alumina, silica, zirconia or a mixture of two or more of these compounds.
[0050] These coatings ensure excellent resistance of the refractory material underlying the cast alloy during the casting stage.
[0051] In one embodiment, the shell mold can be obtained by one or more cycles of steps including a slip-soaking step, a drying step, a firing step and optionally a sandblasting step.
[0052] In particular, these steps may include dipping the assembly formed of the core, the wax and the protuberances, in a slip comprising a ceramic powder.
[0053] In one embodiment, the process may include a step of cooking the shell mold, for example carried out at a temperature between 1100°C and 1200°C.
[0054] In one embodiment, the wax removal step can be carried out by exposing the assembly to a temperature greater than or equal to 150°C, for example under a humid atmosphere.
[0055] In addition, the removal of the wax can be carried out via orifices made in the shell mold according to practices known in the field of lost-wax casting.
[0056] Such particular orifices, which may be reused for casting the alloy if necessary, will not be described in further detail and should not be considered in the same way as the openings which will be made in the shell mold during a step subsequent to the removal of the wax.
[0057] In one embodiment, the partial opening of the mold is achieved by means of a file, a milling cutter, a rotary tool or any other cutting object.
[0058] The partial opening of the mold is made at the end of the secondary cavity, that is to say at the place where the second end of the protuberance was located in a first material.
[0059] Partial opening of the shell mold is understood as the opening of the end of the secondary cavities only, as opposed to a complete unbuckling of the shell mold which will take place later in the process.
[0060] This allows the introduction of the protuberances in a second material, without risking deformation of the main cavity of the shell mold.
[0061] This ensures that the desired shape of the main cavity is maintained.
[0062] In one embodiment, the removal of protrusions in a first material is carried out by heat treatment under air at a temperature greater than or equal to 600°C.
[0063] Furthermore, the introduction of the protrusions in a second material at this advanced stage of the process ensures that these protrusions, and in particular their coatings, are only stressed at the time of the casting of the metallic material, and not at all the stages already carried out.
[0064] It is to the credit of the inventors that they have proposed all the preceding steps which make it possible to carry out a lost-wax process with a core of the desired shape, but whose coated protuberances are introduced only at the last moment before the pouring of the metallic material.
[0065] In one embodiment, the protrusions in a second material have dimensions similar to those of the first protrusions, for example, which do not differ in any dimension by more than 5% of the dimensions of the first protrusions.
[0066] In one embodiment, when the protrusions are cylindrical, the diameter of the second protrusions does not differ by more than 5% from the diameter of the corresponding first protrusion.
[0067] In one embodiment, when the protrusions are cylindrical, the length of the protrusions in a second material does not differ by more than 5% from the length of the corresponding protrusion in a first material.
[0068] The expression "the corresponding protuberance in a first material" refers to the protuberance in a first material which formed the secondary cavity which the protuberance in a second material comes to occupy.
[0069] Once the protuberance(s) in a second material have been introduced, the mold is closed around these protuberances.
[0070] In one embodiment, the step of closing the shell mold around the protuberances includes the same steps of dipping in a slip, heating, sandblasting as the first step of forming the shell mold.
[0071] Preferably, a slip identical or not to that used for obtaining the shell mold can be applied specifically to the places where the mold is to be closed.
[0072] In one embodiment, the slip for closing the openings can be supplemented with sand.
[0073] In one embodiment, the slip used to close the openings can be applied with a brush.
[0074] Thanks to the closure of the mold at the end which allowed their introduction, the protuberances in a second material are fixed in the mold.
[0075] Once the mold is closed, it only includes the main cavity, i.e. the space occupied by the wax earlier in the process.
[0076] Indeed, the secondary cavities were filled by the protuberances with a second material.
[0077] The process then includes a step of introducing a metallic material into the main cavity of the mold.
[0078] In one embodiment, this step is carried out between 1400°C and 1600°C, such temperatures allowing the metallic material to be kept in a liquid state.
[0079] This step allows the part to be formed in metallic material as such.
[0080] In one embodiment, the metallic material may be a superalloy of nickel.
[0081] Such a metallic material is particularly interesting when the part is a part of aeronautical interest.
[0082] In one embodiment of the process, the steps between the introduction of the protuberances into a second material and until the end of the casting of the metallic material are carried out under vacuum.
[0083] In this way, the protrusions in a second material are not exposed to an oxidizing atmosphere during the process, which reduces the coating requirements for a material that is particularly resistant to oxidation. This allows, on the one hand, the use of less specific and therefore less expensive coatings, and on the other hand, it guarantees the integrity of the coating during the process, thus reducing the risk of scrap.
[0084] In one embodiment, the metallic material part can be a turbomachine part, for example selected from a turbomachine blade, for example a high or low pressure blade or a portion of a distributor.
[0085] Indeed, such parts require internal cavities to form cooling circuits, some portions of which have dimensions too small to be accessible only with ceramic cores, and the methods of the invention simplifying the use of cores in refractory materials are therefore advantageous.
[0086] The method of the invention makes it possible to avoid precise and complex drilling in the trailing edges of turbomachine blades recommended in prior art methods.
[0087] Once the metallic material has been introduced and then cooled, the shell mold is removed.
[0088] Such a step, classically called mold removal, can be carried out by chemical dissolution or mechanical attack of the mold, it being understood that the removal must not compromise the integrity of the part obtained.
[0089] In particular, it is desirable that the de-sewing step should not have any influence on the microstructure of the metal part obtained.
[0090] Finally, the protuberances are removed from a second material and the ceramic core is removed to form a cavity in the metallic material part.
[0091] The specific parameters of this step are chosen with regard to the nature of the ceramic core and the second material.
[0092] For example, the step of removing protrusions into a second material can be carried out by chemical dissolution, for example by means of an acid bath, for example of a mixture of nitric acid and sulfuric acid.
[0093] In one embodiment, the step of removing the ceramic core can also be carried out by chemical dissolution, for example by means of a basic bath, for example of soda, in an autoclave under a pressure of 10 to 20 bars, and at a temperature between 100°C and 200°C. Brief description of the drawings
[0094] [Fig.1] Fig.1 schematically represents a step in a process.
[0095] [Fig.2] Fig.2 represents another step in a process, this step being carried out after the one carried out on the [Fig.l].
[0096] [Fig.3] [Fig.3] represents another step in a process, this step being carried out after the one carried out in [Fig.2].
[0097] [Fig.4] [Fig.4] represents another step in a process, this step being carried out after the one carried out in [Fig.3].
[0098] [Fig.5] [Fig.5] represents another step in a process, this step being carried out after the one carried out in [Fig.4].
[0099] [Fig.6] [Fig.6] represents another step in a process, this step being carried out after the one carried out in [Fig.5].
[0100] [Fig.7] [Fig.7] represents another step in a process, this step being carried out after the one carried out in [Fig.6].
[0101] [Fig.8] [Fig.8] represents another step in a process, this step being carried out after the one carried out in [Fig.7].
[0102] [Fig.9] [Fig.9] represents another step in a process, this step being carried out after the one carried out in [Fig.8].
[0103] [Fig. 10] The [Fig. 10] represents another step in a process, this step being carried out after the one carried out in the [Fig.9]. Description of the implementation methods
[0104] The invention is now described by means of figures, which are provided for descriptive purposes to illustrate certain embodiments of the invention and which should not be interpreted as limiting the latter.
[0105] In particular, several protuberances are used in the described embodiments.
[0106] However, this is by no means necessary, and the benefits are obtained as soon as a protrusion is present.
[0107] In addition, the process only includes a wax model of the part to be obtained.
[0108] Nevertheless, it is by no means excluded that a plurality of models may be used and clustered together to produce several parts in a metal casting, according to known specificities of the foundry processes.
[0109] Figures 1 to 10 describe the successive steps in an embodiment of a process.
[0110] The [Fig. 1] describes a first step of a process.
[0111] A core made of ceramic material is disposed in the cavity 1100 of a mold 1000.
[0112] Figure 1 illustrates that the prominences 200 are arranged in contact with the nucleus at ceramic material 100 and have a first portion in contact with the core, a protrusion body through the cavity 1100 and a second end free out of the mold cavity.
[0113] The process for obtaining the core 100 in ceramic material is not described here, because any embodiment allowing such a core 100 to be obtained could be suitable for the invention.
[0114] In particular, the core 100 can be obtained with the protuberances 200 in a first material or alternatively, the protuberances 200 can be added after obtaining the core 100.
[0115] In one embodiment, which is that of the figure, the protuberances 200 penetrate the core over a short distance, for example less than or equal to 0.5 mm, in a notch 110 of the core provided for this purpose.
[0116] In [Fig. 1], the cavity 1100 of the mold is shown already filled with wax 300.
[0117] The protuberances 200 are further arranged so that they comprise a body passing through the cavity 1100 and that their end which is not in contact with the core 100 is disposed in the mold 1000 but outside the cavity 1100.
[0118] In another unshown embodiment, the protuberances may protrude from the mold 1000.
[0119] It is important that the end of the protuberances 200 be outside the cavity 1100 because this ensures that the protuberances pass through the entire wax model 300 which will ensure at the end of the process that the opening obtained by removing the protuberances 200 connects the outside of the part and the cavity obtained by removing the core 100.
[0120] Fig. 2 represents another step of a described process, this step being carried out after the one carried out in Fig. 1.
[0121] In the stage shown, the mold 1000 is opened and we then have an assembly comprising a wax model 300 formed around the core 100, and protuberances 200.
[0122] This step can be carried out at room temperature.
[0123] Fig. 3 represents another step of a described process, this step being carried out after the one carried out in Fig. 2.
[0124] During the step shown in [Fig.3], a carapace mold 400 is formed around the assembly obtained in the previous step, the assembly comprising a wax model 300 formed around the core 100, and protuberances 200.
[0125] Such a shell mold can be formed in a manner known as such, particularly in the field of lost-wax processes.
[0126] For example, such a mold can be obtained by carrying out one or more cycles of dipping in a slip, sandblasting and then drying.
[0127] The mold formation must enable it to conform to the shape of the assembly comprising the wax model 300 formed around the core 100 and the protrusions 200, and retain this shape during the subsequent steps of the process.
[0128] In the process, and since the shell mold 400 is formed around the assembly described above comprising a wax model 300 formed around the core 100, and the protuberances 200, it is important to note that the protuberances 200 are completely covered by the shell mold 400.
[0129] Fig. 3 illustrates the part of the mold 410 corresponding to the covering of the ends of the protuberances which were not in contact with the core 100.
[0130] Fig. 4 represents another step of a described process, this step being carried out after the one carried out in Fig. 3.
[0131] The step corresponds to the step usually called dewaxing during which the wax mold 300 is removed.
[0132] In addition, the protrusions 200 in a first material are also removed.
[0133] In a conventional manner in the field, the removal of the wax and the protrusions can be carried out through openings provided for this purpose in the shell mold 300.
[0134] For example, the dewaxing step is carried out at a temperature between 170°C and 200°C.
[0135] In addition, the dewaxing step can allow the removal of protrusions in a first material 200.
[0136] Otherwise, a step of removing protrusions into a first material is carried out.
[0137] The mold shown in [Fig. 4] describes what is obtained after the dewaxing step. It can be seen that the wax model 300 and the protrusions 200 have disappeared, leaving a cavity 500, but the ceramic core 100 and the mold 400 remain.
[0138] Although not shown in the figure, core retaining elements, according to a conventional embodiment in the field, ensure that the core cannot move within the mold.
[0139] Fig. 4 also allows us to understand what is meant by the main cavity 510, which is obtained at the location where the wax model was initially present, and the secondary cavities 520 which are obtained at the locations where the protuberances 200 were in a first material.
[0140] After the dewaxing step, a mold baking step can be carried out, not shown in a figure.
[0141] In one embodiment and for dewaxing, it is possible to carry out the subsequent steps under vacuum.
[0142] This makes it possible in particular to lower the melting temperature of the wax which limits its expansion at the time of dewaxing, so that the mold is not too constrained during this step.
[0143] This step aims to ensure the properties of the carapace mold 400 for the rest of the process.
[0144] In one embodiment, the cooking step can be carried out under air.
[0145] In one embodiment, the cooking step can be carried out at a temperature between 1100°C and 1200°C.
[0146] In one embodiment, the cooking step can be carried out for a period greater than or equal to 1 hour, for example between 1 hour and 3 hours.
[0147] [Fig.5] represents another step of a described process, this step being carried out after that carried out in [Fig.4].
[0148] Figure 5 illustrates the opening of the secondary cavities 520 of the mold by removing the portion of the shell mold 410 formed around the end of the protuberances in a first material.
[0149] This step makes it possible to create an opening 420 at the ends of the secondary cavities 520, without affecting the integrity of the rest of the carapace mold 400, and in particular without modifying the shape of the main cavity 510 of the carapace mold 400.
[0150] Fig. 6 represents another step of a described process, this step being carried out after the one carried out in Fig. 5.
[0151] During this step, protuberances in a second material 600 are introduced into the secondary cavities.
[0152] The protuberances in a second material 600 have a first end in contact with the nucleus 100.
[0153] In an embodiment which is the one shown, the protuberances in a second material 600 are inserted up to the notches 110 left vacant in the core 100 by the elimination of the protuberances in a first material 200 during a previous step.
[0154] The second material 600 is a coated refractory material, the refractory material being selected from molybdenum, molybdenum alloys for example molybdenum alloys comprising rhenium, titanium, titanium and molybdenum and zirconium alloys (also known as "TZM" for the English acronym for "titanium-zirconium-molybdenum alloys"), zirconium or a mixture of two or more of these compounds.
[0155] The protrusions in a second material 600 must have dimensions corresponding to those of the desired openings in the final part.
[0156] In the embodiment shown, the protuberances in a second material 600 have the same dimensions as those of the protuberances in a first material 200.
[0157] Preferably, the dimensions of the protuberances in a first material 200 and the protuberances in a second material 600 do not vary by more than 5%, or even by more than 3%, or even vary by less than 1%.
[0158] This ensures minimal play between the shell mold 400 and the protuberances in a second material 600 when the latter are introduced into the secondary cavities 520, with dimensions of the protuberances in a first material 200.
[0159] Fig. 7 represents another step in a described process, this step being carried out after the one carried out in Fig. 6.
[0160] During this step, the openings 420 made in the shell mold 400 for the insertion of the protuberances in a second material 600 are plugged to form a new portion of shell mold 430 around the protuberances in a second material 600.
[0161] The closing of the mold by these new portions 430 ensures the retention in place of the protuberances in a second material 600.
[0162] In one embodiment, the new portions 430 can be obtained in the same way as the shell mold 400 was obtained.
[0163] Alternatively, a slip identical or not to that used for obtaining the shell mold 400 can be applied specifically to the places where new portions 430 are desired.
[0164] For example, slip mixed with sand allows the shell to be reconstructed locally and the whole thing is then dried.
[0165] Alternatively, ceramic adhesive materials, for example composed of mixtures of silica and zirconia, can be used.
[0166] Fig. 8 represents another step in a described process, this step being carried out after the one carried out in Fig. 7.
[0167] Fig. 8 illustrates the casting step of the metal part 700 into the main cavity 510 of the shell mold 400.
[0168] This step can be carried out under argon and / or under vacuum.
[0169] This step can be carried out at a temperature greater than or equal to 1400°C, for example between 1500°C and 1600°C.
[0170] Once the metal 700 has been poured into the main cavity 510 of the shell mold 400, the shell mold 400 and everything in it is cooled to allow the metal 700 to solidify.
[0171] Fig. 9 represents another step in a described process, this step being carried out after the one carried out in Fig. 8.
[0172] The step shown in [Fig.9] corresponds to the removal of the carapace mold 400, also called demolding in lost-wax casting processes.
[0173] This step makes it possible to obtain the metal part 700, as well as the protrusions in a second material 600 and the ceramic core 100.
[0174] Mold removal can be carried out mechanically or chemically, or even by a combination of both methods.
[0175] Figure 10 represents another step in a described process, this step being carried out after the one carried out on the [Fig.9].
[0176] During the stage shown, the ceramic core 100 and the protuberances in a second material 600 are eliminated.
[0177] This step thus enables the creation of the cavity in the metal part 700.
[0178] Furthermore, the use of the 600 protrusions in a second material ensures that the opening between the cavity of the part and the outside can be as thin as desired, unlike the processes of the prior art.
[0179] As has just been illustrated in the embodiment described via Figures 1 to 10, it is to the credit of the inventors that they have succeeded in proposing a process in which the protuberances in a second material 600 and in particular their coatings do not have to withstand all the steps of the process.
[0180] In particular, the steps of firing the ceramic core 100, dewaxing, and firing the shell mold 400 can, in prior art processes, weaken refractory materials, even coated ones.
[0181] On the contrary, the process of the invention only subjects the protuberances to a second refractory material at the metal casting stage.
[0182] The material undergoes only one temperature rise stage. Furthermore, this stage is generally carried out under a protective atmosphere, for example under argon, to protect the alloy.
[0183] Thus, the protective coating of the refractory material in the second material does not necessarily have to protect the refractory material from oxidation, since the latter does not see a stage with an oxidizing atmosphere.
[0184] The coatings of the protrusions are then less stressed, and this results in a greater choice of suitable coatings, and therefore a lower cost, and on the other hand a smaller number of rejected parts at the end of the process than when prior art processes are used.
Claims
1. Demands A casting process for a part made of metallic material (700) comprising a cavity, the process comprising at least the following steps: - the arrangement in the cavity (1100) of a mold (1000) of at least one core of ceramic material (100) and at least one protrusion of a first material (200), the first material being a refractory material, the protrusion of a first material having a first end in contact with the core, a body of protrusion passing through the cavity, and a second end free outside the cavity of the mold; - the formation of a wax model (300) of the part around the ceramic material core obtained by filling the mold cavity with wax; - the removal from the mold of the assembly formed by the wax model (300), the core (100) and the protuberances in a first material (200); - the formation of a shell mold (400) around the assembly formed by the core, the wax model and the protuberances in a first material; - the removal of the wax and protuberances into a first material, to form in the shell mold a cavity (500), the cavity of the shell mold comprising a main cavity (510) where the wax was and at least one secondary cavity (520) where the protuberances were in a first material; - the partial opening of the shell mold at the end of its secondary cavities; - the insertion into the secondary cavities of the shell mold of at least one protrusion in a second material, the second material being a coated refractory material, the protrusions in a second material being arranged so that their first end is in contact with the core; - the closing of the shell mold around the protuberances in a second material; - the pouring of a metallic material (700) into the main cavity of the shell mold to form the part in metallic material; - the removal of the shell mold around the part made of metallic material; - the removal of protrusions in a second material and of the ceramic core to form a cavity in the part in metallic material.
2. A casting process according to claim 1, wherein the ceramic core material (100) is selected from silica, alumina, zirconia, or a mixture of two or more of these materials.
3. A casting method according to claim 1 or 2, wherein the protrusions in a first material (200) in contact with the core penetrate into the core over a distance greater than or equal to 0.5 mm.
4. A casting process according to any one of claims 1 to 3, wherein the refractory material of the first material and / or the second material can be selected from molybdenum, molybdenum alloys for example molybdenum alloys comprising rhenium, titanium, titanium and molybdenum and zirconium alloys (also known as "TZM" for the English acronym for "titanium-zirconium-molybdenum alloys"), zirconium or a mixture of two or more of these compounds.
5. A casting process according to any one of claims 1 to 4, wherein the coating of the second material is selected from alumina, silica, zirconia or a mixture of two or more of these compounds.
6. A casting process according to any one of claims 1 to 5, wherein the metallic material is a nickel superalloy.
7. A casting process according to any one of claims 1 to 6, wherein the steps between the introduction of the protrusions into a second material and until the end of the casting of the metallic material are carried out under vacuum.
8. A casting process according to any one of claims 1 to 7, wherein the removal of protrusions in a first material (200) is carried out by heat treatment under air at a temperature greater than or equal to 600°C.
9. A casting process according to any one of claims 1 to 8, wherein the removal of protrusions into a second material (600) is carried out by chemical dissolution.
10. A casting method according to any one of claims 1 to 9, wherein the part is selected from a turbomachine blade, for example a high or low pressure vane or a portion of a distributor.