Process for manufacturing a shell mold

Abstract

Method for manufacturing a shell mold The invention relates to a method for manufacturing a shell mold (1) intended for molding a metallic multi-material part comprising a first part portion and a second part portion having different crystalline structures.The method comprises a first operation of manufacturing a first mold part (6) comprising a first contact layer (9) configured to generate a first crystalline solidification during a molding operation and a second operation of manufacturing a second mold part (7) from the first mold part (6) comprising a second contact layer (10) configured to generate a second crystalline solidification during a molding operation, the first mold part (6) comprising at least one component which is not found in the second mold part (7) to generate two different crystalline structures, chosen from a monocrystalline or equiaxed crystalline structure. Figure for abstract: Fig. 2.

Description

Title of the invention: Method for manufacturing a shell mold Technical field

[0001] The invention relates to the general field of aeronautics and more particularly to a method of manufacturing a shell mold intended for the manufacture of turbomachine parts such as bi-material helicopter turbine blades and a shell mold obtained with this method. Prior art

[0002] Rotating aircraft engines must meet demanding criteria of airworthiness, quality and performance. Their performance is generally correlated with the temperatures of the combustion gases circulating at the turbines and in particular their blades. These blades are subjected to very high temperatures, for very long periods, and rotate at very high rotational speeds. Given these stresses, the blades are mainly subjected to fining.

[0003] Turbine blades comprise main sections including a root and a blade. To withstand the aforementioned stresses, achieve mass savings and cost reductions on the parts, the root and the blade can be composed of several alloys having properties adapted to the different thermal stresses. These alloys each have a different crystalline structure including, for example, a first alloy called "monocrystalline" for the blade section (subject to high thermal stresses) and a second alloy called "equiaxed" for the root section (subject to less significant thermal stresses).

[0004] The alloys have specific finishing performances at very high temperatures and can be for example a CMSX-10, a CMSX4+, a TMS-162, a TMS-182 or even a TMS-196 for the blade section. With alloys such as René 41 or Inconel 718 for the root section.

[0005] Document FR3077224B1 describes a turbomachine part comprising a first portion formed from a first alloy and a second portion from a second alloy. The first portion is produced by a first casting step in a first mold. The second portion is produced by a second casting step in a second mold in which the previously obtained first solidified portion is placed. During the second step, the molten material of the second alloy is poured into the mold containing the first solidified portion. The first portion is also used as a seed. The first alloy is denser than the second alloy so as, on the one hand, to avoid complete mixing of the first alloy and the second alloy, and on the other hand to obtain a reduced transition zone as well as controlled. In fact, a portion of the first alloy at the transition zone is remelted when the second alloy is poured.

[0006] However, this manufacturing process requires the use of two molds, which is restrictive.

[0007] Document EP2931458B1 describes another method for manufacturing an aircraft part in which a first alloy is poured into a mold fed from the source by means of a telescopic casting chute. Once the first alloy has solidified, a second alloy is fed from the top of the mold by falling. The telescopic chute makes it possible to choose whether the casting is from the source or by falling for the first alloy.

[0008] However, this manufacturing method requires a telescopic descender which is complicated to use. The other disadvantage is that it is necessary to provide two separate alloy casting paths. Statement of the invention

[0009] The objective of the present invention is to provide a method for manufacturing a shell mold and a shell mold obtained with this method making it possible to simply manufacture, by a foundry operation, a multi-material and more particularly bi-material aircraft part comprising a monocrystalline alloy and an equiaxed alloy.

[0010] The present invention relates to a method for manufacturing a shell mold intended for molding a metallic multi-material part comprising a first part portion and a second part portion having different crystalline structures.

[0011] The manufacturing process comprises: • a first operation of manufacturing a first mold part from first manufacturing components generating a first contact layer on the first mold part configured to form a first crystalline solidification during a molding operation of the first part portion, and • a second operation of manufacturing a second mold part from the first mold part and from second manufacturing components generating a second contact layer on the second mold part configured to form a second crystalline solidification during a molding operation of the second part portion. The first manufacturing components comprising at least one component which is not found in the second manufacturing components so as to obtain two contact layers of different compositions intended to generate two

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[0018] different crystal structures, chosen from a monocrystalline crystal structure or an equiaxed crystal structure. The invention thus provides a method for manufacturing a shell mold and a shell mold obtained with this method making it possible to simply manufacture, by a foundry operation, a multi-material and more particularly bi-material aircraft part comprising a monocrystalline alloy and an equiaxed alloy. The shell mold comprises two different contact layers, allowing two distinct microstructures to be obtained later by casting in the same metal part. The shell mold allows the complex crystalline structure of bi-material blades, for example, to be properly controlled. This type of blade results in a weight saving in aircraft. Alternatively, the first and second manufacturing operations are steps in a lost wax casting process. This technique is particularly well suited to obtaining shell molds comprising two different contact layers. Alternatively, the method comprises: • a step of manufacturing a wax model comprising at least one part model, • a step of dipping a first portion of the wax model into a first contact slip to form the first part of the mold, • a sandblasting step of the first portion soaked with a first contact stucco, • a drying stage of the first sanded portion, • a step of dipping at least a second portion of the wax model into a second contact slip to form the second mold part, the second contact slip having a composition different from that of the first contact slip, • at least one step of dipping the first and second portions in a reinforcing slip, • at least one step of sandblasting the first and second portions soaked with a reinforcing stucco, • at least one drying step of the first and second sanded portions, • a wax removal step to remove the wax model and obtain a mold raw shell, and • a step of heat treatment of the raw shell mold to obtain the shell mold comprising the first mold part and the second mold part. This sequence of steps is optimal for providing a shell mold having two different contact surfaces suitable for the manufacture of a bi-material part comprising two different crystalline structures.

[0019] Alternatively, the first and second contact slips are different and chosen from an equiaxed contact slip and a monocrystalline contact slip.

[0020] The term "equiaxed contact slip" means that the slip generates a contact surface having an equiaxed crystalline structure. The term "monocrystalline contact slip" means that the slip generates a contact surface having a monocrystalline crystalline structure.

[0021] Alternatively, the equiaxed contact slip comprises at least one germinating agent.

[0022] The germinating agent makes it possible to obtain an equiaxed crystalline structure with a controlled grain size.

[0023] Alternatively, several shell molds are manufactured simultaneously. The wax model is in the form of a wax cluster comprising several part models.

[0024] This makes it possible to reduce manufacturing times.

[0025] Alternatively, during the step of dipping the first portion of the wax model into an equiaxial contact slip, the dipping is carried out up to a transition zone intended to form a junction zone between the first portion of the part and the second portion of the part during a step of molding the multi-material part.

[0026] This transition zone makes it possible to obtain a junction zone between the two alloys of the bi-material part which will be manufactured later.

[0027] Alternatively, during the dipping step, the wax model is fully dipped into the second contact slip.

[0028] This makes it possible to simplify the manufacturing process.

[0029] The present invention also relates to a shell mold obtained by the manufacturing method, as defined above and intended for molding a multi-material part comprising a first part portion and a second part portion having different crystalline structures, chosen from a monocrystalline or equiaxed crystalline structure.

[0030] Alternatively, the shell mold comprises a first mold part comprising a first contact layer configured to generate equiaxed crystalline solidification during a molding operation of the first part portion and a second mold part comprising a second contact layer configured to generate monocrystalline crystalline solidification during a molding operation of the second part portion.

[0031] The invention thus provides a shell mold making it possible to manufacture in a simple manner, by a foundry operation, a multi-material aircraft part and more par- particularly bi-materials comprising a monocrystalline alloy and an equiaxed alloy.

[0032] The invention makes it possible to control and monitor the crystal growth of the two distinct zones of the part, equiaxed and monocrystalline. Brief description of the drawings

[0033] The invention and its advantages will be better understood on reading the detailed description given below of different embodiments of the invention given as non-limiting examples. This description refers to the appended figures, in which:

[0034] [Fig-1] [Fig.l] schematically represents a longitudinal sectional view of a cluster-shaped wax model after a step of dipping a first portion of the wax model into a first contact slip, according to a first embodiment of the invention,

[0035] [Fig.2] [Fig.2] schematically represents a longitudinal sectional view of the wax model of [Fig.l] after a step of dipping the entire wax model into a second contact slip,

[0036] [Fig.3] [Fig.3] schematically represents a diagram illustrating a method of manufacturing a shell mold, according to an embodiment of the invention. Description of the embodiments

[0037] The invention relates to a method for manufacturing a shell mold (1) intended for molding a multi-material and more particularly bi-material metal part comprising a first part portion and a second part portion having different crystalline structures.

[0038] The multi-material part may be a turbomachine rotor part subjected to high thermomechanical and / or environmental constraints. The rotor part may, for example, be a helicopter turbine blade.

[0039] Of course, the multi-material part can still be used in other fields where the thermomechanical constraints it undergoes are significant. The multi-material part makes it possible, on the one hand, to obtain a weight saving and, on the other hand, to obtain different material properties for the two parts constituting the final part. In particular, the multi-material part makes it possible to improve its performance thanks to materials having reinforced physicochemical and thermomechanical characteristics.

[0040] The first part portion is made of a first metallic material and the second part portion is made of a second metallic material. A junction zone is located between the first part portion and the second part portion.

[0041] The first metallic material and the second metallic material are different. More specifically, the first metallic material and the second metallic material have different crystalline structures. The first and second portions of the part may optionally have different shapes and / or different physicochemical compositions and / or different densities. The choice of alloys depends on the intended application, the desired mass gain and the desired thermomechanical performance.

[0042] The first metallic material and / or the second metallic material may comprise a pure metal or an alloy. In the case of an alloy, the first metallic material and / or the second metallic material is / are a nickel-based alloy (or superalloy).

[0043] In order to improve the resistance of the parts to mechanical and thermal stresses, the first metallic material and / or the second metallic material has(have) a specific crystalline structure such as an equiaxed or monocrystalline structure.

[0044] For example, the structure of the first metallic material is monocrystalline and the structure of the second metallic material is an equiaxed structure.

[0045] In the case of a monocrystalline structure, the superalloys have a low concentration of tantalum, titanium, aluminum, chromium, and / or cobalt (less than 10% of the total mass of the alloy, for example).

[0046] Advantageously, the first metallic material and / or the second metallic material are chosen from the group comprising CMSX4®, CMSX4® (SLS), AMI, AM3, René N6, René N5, TMS 75, Inconel® 100, and Inconel® 718.

[0047] The bi-material part is obtained by a foundry process in which two different molten alloys are poured into a shell mold 1. The densest alloy is poured first.

[0048] The invention relates to a method for manufacturing the shell mold 1 comprising a first operation for manufacturing a first mold part 6 from first manufacturing components generating a first contact layer 9 on the first mold part 6. The first contact layer 9 is configured to form a first crystalline solidification during a molding operation of the first part portion.

[0049] The manufacturing method also comprises a second operation of manufacturing a second mold part 7 from the first mold part 6 and from second manufacturing components generating a second contact layer 10 on the second mold part 7. The second contact layer 10 is configured to form a second crystalline solidification during a molding operation of the second part portion.

[0050] The first manufacturing components comprise at least one component which does not is not found in the second manufacturing components so as to obtain two contact layers of different compositions, generating different crystalline structures, chosen from a monocrystalline or equiaxed crystalline structure.

[0051] For example, the first contact layer 9 may be configured to generate equiaxed solidification and the second contact layer 10 may be configured to generate monocrystalline solidification. The first contact layer 9 then has an equiaxed crystalline structure and the second contact layer 10 has a monocrystalline crystalline structure.

[0052] The first manufacturing components comprise at least one germinating agent which is not found in the second manufacturing components.

[0053] Thus, the first mold part 6 comprises at least one component which is not found in the second mold part 7.

[0054] The shell mold 1 thus comprises two mold parts 6, 7 each comprising a contact layer capable of generating monocrystalline or equiaxial solidification during a molding operation.

[0055] The first mold part 6 and the second mold part 7 are separated by a transition zone 5. The transition zone 5 can be more or less extensive. The transition zone 5 is extended if it is desired to obtain a zone mixed by the two alloys, for example.

[0056] Preferably, the first and second manufacturing operations are steps of a lost wax casting process in which two different contact slips are used. One of the contact slips is an equiaxed contact slip and the other contact slip is a single crystal contact slip comprising at least one germinating agent.

[0057] Lost wax casting is a metal forming process that involves building a ceramic mold layer by layer around a wax model that is then removed. This mold is then sintered and heated to a high temperature before the metal is cast.

[0058] A particular embodiment of the invention will be described in the remainder of the description with reference to Figures 1 to 3.

[0059] As illustrated in the diagram of [Fig.3], the manufacturing process comprises: • a manufacturing step A of a wax model 2 comprising at least one part model 8, • a step B of dipping a first portion 3 of the wax model 2 into a first contact slip to form the first mold part 6, as illustrated in [Fig.l], • a sandblasting step C of the first portion 3 hardened by a first contact stucco, • a drying step D of the first sanded portion 3, • a step E of dipping at least a second portion 4 of the wax model 2 into a second contact slip to form the second mold part 7, as illustrated in [Fig.2], the second contact slip having a composition different from that of the first contact slip, • a sandblasting step F of the second portion 4 hardened by a second contact stucco, • a drying step G of the second sanded portion 4, • at least one step of soaking H of the first and second portions 3, 4 in a reinforcing slip, • at least one sandblasting step I of the first and second portions 3, 4 hardened with a reinforcing stucco, • at least one drying step J of the first and second shortbreaded portions 3, 4, • a dewaxing step K to remove the wax model 2 and obtain a raw shell mold, and • a heat treatment step L of the raw shell mold to obtain the shell mold 1 comprising the first mold part 6 and the second mold part 7.

[0060] Preferably, several shell molds 1 are manufactured simultaneously. The wax model 2 is then in the form of a wax cluster comprising several part models 8, as illustrated in [Fig.l] showing two part models 8, by way of example.

[0061] The first portion 3 therefore corresponds to the first portion 3 of the wax cluster and the second portion 4 corresponds to the second portion 4 of the wax cluster.

[0062] The wax model 2 is a counterform of the shell mold 1 which will be manufactured during the molding process. The wax model 2 comprises a crown model 19 connected to a cup model 20. The cup of the shell mold 1 is intended to feed the crown of the shell mold 1. The crown model 19 is connected to an upper part 12 of each part model 8 by an annular element 11. The wax model 2 also comprises grain selector models 14, each connected to a lower part 13 of one of the part models 8. The wax model 2 comprises a central tube 16 connected to the cup model 20. Tubular structural elements 17 connect the central tube 16 to the grain selector models 14.

[0063] The wax model 2 can be obtained by casting wax in an elastomer mold or by injection into a metal mold, for example.

[0064] Alternatively, the wax model 2 can be obtained by additive manufacturing where the Wax models are made from a digital file and a 3D wax printing machine.

[0065] The example of Figures 1 to 3 is given with a first contact slip which is an equiaxed contact slip and a second contact slip which is a monocrystalline contact slip.

[0066] During the step B of dipping the first portion 3 of the wax model 2 into the equiaxial contact slip, the dipping is carried out up to a transition zone 5 intended to form the junction zone between the first portion of the part and the second portion of the part during a step of molding the multi-material part 2.

[0067] In the example of Figures 1 and 2, the transition zone 5 is positioned substantially halfway between the first and second ends 12, 13 of the part models 8.

[0068] The transition zone 5 is positioned substantially midway between the crown 9 and a lower end 18 of each grain selector 14.

[0069] Alternatively, the transition zone 5 may be positioned differently, closer to the second end 13, for example, to obtain a first portion of part of greater length than the length of the second portion of part.

[0070] Slips are a mixture of water, binder, ceramic flours and organic additives. Equiaxed and monocrystalline contact slips are composed of chemically inert refractory ceramic materials, such as mullite, zirconia, yttrium or alumina, for example, and a colloidal binder such as silica, yttrium, zirconia or alumina, for example.

[0071] What can differentiate a contact slip suitable for equiaxial solidification from one intended for single-crystal casting is the addition of at least one germinating agent. The equiaxial contact slip comprises at least one germinating agent which promotes homogeneous germination of the grains in the microstructure during solidification of the alloy. The germinating agents can be oxides, aluminates, nickel, cobalt, for example.

[0072] The first portion 3 is sandblasted with a first contact stucco during the sandblasting step C.

[0073] The first contact stucco and the second contact stucco comprise refractory sand to form the two contact layers based on alumina, silica, mullite, yttrium, zircon, zirconia sand, for example, called "stucco".

[0074] The first contact stucco and the second contact stucco may be the same or different.

[0075] The first sanded portion 3 is then dried during drying step D.

[0076] Alternatively, several steps of dipping B in the first slip, sandblasting by a first contact stucco and drying can be applied to form a first mold part 6 with several equiaxed contact layers.

[0077] At least the second portion 4 of the wax model 2 undergoes a dipping step E in the second contact slip to form the second mold part 7.

[0078] According to a variant, during the dipping step E, the wax model 2 is entirely dipped in the second monocrystalline contact slip, as illustrated in [Fig. 2]. The first contact layer 9 of the first portion 3 of the wax model 2 is covered by the second contact layer 10. The second portion 4 of the wax model 2 comprises only the second contact layer 10.

[0079] The second hardened portion 4 then undergoes the sandblasting step F with the second contact stucco described previously and the drying step G of the second sandblasted portion 4.

[0080] According to a variant, the sandblasting step F and the drying step G can be carried out several times to form a second portion 4 comprising several monocrystalline contact layers.

[0081] The soaking step H is then carried out on the first and second portions 3, 4 in the reinforcing slip, in other words on the entire cluster.

[0082] The sandblasting step I is carried out on the first and second hardened portions 3, 4, i.e. on the entire cluster, by the reinforcing stucco.

[0083] A drying step J is then carried out on the first and second sanded portions 3, 4.

[0084] Alternatively, the sandblasting step I with the reinforcing stucco and the drying step J are carried out several times so as to cover the equiaxed and monocrystalline contact layers with several reinforcing layers.

[0085] The reinforcing layers provide mechanical strength to the shell mold 1. The reinforcing slip is commonly composed of refractory ceramics such as alumina, mullite, silica and zircon, for example, as well as colloidal binders such as alumina, silica or zirconia, for example.

[0086] Several layers of reinforcement are deposited in order to obtain a shell mold thickness 1 sufficient to provide correct mechanical strength.

[0087] The waxing step H makes it possible to eliminate the wax model 2 and to obtain a raw shell mold.

[0088] The raw shell mold is sintered during the heat treatment step in order to obtain a shell mold 1 ready to be used for the manufacture of bi-material parts.

[0089] Thus a first molten alloy can be poured into the cup of the shell mold 1 and cast into the second mold parts 7 up to the transition zone 5 to obtain several second portions of part of monocrystalline structure thanks to the contact surface of the second mold parts 7 having a crystalline structure monocrystalline.

[0090] Once the first alloy has solidified, a second molten alloy is poured into the cup of the shell mold 1 and cast into the first mold parts 6 from the transition zone 5 to obtain several first portions of part with an equiaxed crystalline structure thanks to the contact surface of the first mold parts 6 having an equiaxed crystalline structure.

[0091] After demolding, several shell molds 1 are obtained, each comprising a first portion of a part with an equiaxed crystalline structure and a second portion of a part with a monocrystalline structure separated by a junction zone coinciding with the transition zone 5 of the shell mold 1.

[0092] Alternatively, the first contact slip is a single-crystal contact slip and the second contact slip is an equiaxed contact slip.

[0093] A dipping step is then carried out on the first portion 3 of the wax model 2 in a first contact slip which is in this case a monocrystalline contact slip to form the first mold part 6.

[0094] A dipping step is carried out on at least the second portion 4 of the wax model 2 in a second contact slip which is then an equiaxed contact slip to form the second mold part 7.

[0095] The other steps of the manufacturing process are identical to the steps previously described.

[0096] Thus a first molten alloy can be poured into the cup of the shell mold 1 and cast into the second mold parts 7 up to the transition zone 5 to obtain several second portions of part of equiaxed structure thanks to the contact surface of the second mold parts 7 having an equiaxed crystalline structure.

[0097] Once the first alloy has solidified, a second molten alloy is poured into the cup of the shell mold 1 and cast into the first mold parts 6 from the transition zone 5 to obtain several first portions of part with a monocrystalline crystalline structure thanks to the contact surface of the first mold parts 6 having a monocrystalline crystalline structure.

[0098] After demolding, several bi-material parts are obtained, each comprising a first portion of a part with a monocrystalline structure and a second portion of a part with an equiaxed crystalline structure separated by a junction zone coinciding with the transition zone 5 of the shell mold 1.

[0099] Alternatively, the shell mold 1 can be produced by direct or indirect additive manufacturing. The stereolithography process or the LCM (Liquid Composite Molding) process can be used, for example.

[0100] After the additive manufacturing operation, several bi-material parts are obtained. each comprising a first portion of monocrystalline structure part and a second portion of equiaxed crystalline structure part separated by a junction zone coinciding with the transition zone 5 of the shell mold 1.

[0101] Although the present invention has been described with reference to specific exemplary embodiments, it is obvious that modifications and changes may be made to these examples without departing from the general scope of the invention as defined by the claims. In particular, individual features of the various illustrated / mentioned embodiments may be combined in additional embodiments. Therefore, the description and drawings should be considered in an illustrative rather than restrictive sense.

[0102] It is also obvious that all the characteristics described with reference to a method are transposable, alone or in combination, to a device, and conversely, all the characteristics described with reference to a device are transposable, alone or in combination, to a method.

Claims

Claims

1. Method for manufacturing a shell mold (1) intended for molding a metallic multi-material part comprising a first part portion and a second part portion having different crystalline structures, characterized in that the method comprises: • a first operation of manufacturing a first mold part (6) from first manufacturing components generating a first contact layer (9) on the first mold part (6) configured to form a first crystalline solidification during a molding operation of the first part portion,and • a second operation of manufacturing a second mold part (7) from the first mold part (6) and from second manufacturing components generating a second contact layer (10) on the second mold part (7) configured to form a second crystalline solidification during a molding operation of the second part portion, the first manufacturing components comprising at least one component which is not found in the second manufacturing components so as to obtain two contact layers of different compositions intended to generate two different crystalline structures, chosen from a monocrystalline crystalline structure or an equiaxed crystalline structure.,

2. Manufacturing method according to claim 1, characterized in that the first and second manufacturing operations are steps of a lost wax casting process.

3. Manufacturing method according to claim 2, characterized in that the method comprises: • a step of manufacturing (A) a wax model (2) comprising at least one part model (8), • a step of dipping (B) a first portion (3) of the wax model (2) in a first contact slip to form the first mold part (6), • a sandblasting step (C) of the first portion (3) hardened with a first contact stucco, • a drying step (D) of the first sandblasted portion (3), • a dipping step (E) of at least a second portion (4) of the wax model (2) in a second contact slip to form the second mold part (7), the second contact slip having a composition different from that of the first contact slip, • at least one dipping step (H) of the first and second portions (3, 4) in a reinforcing slip, • at least one sandblasting step (I) of the first and second portions (3, 4) hardened with a reinforcing stucco, • at least one drying step (J) of the first and second sandblasted portions (3, 4), • a wax removal step (K) to remove the wax model (2) and obtain a raw shell mold,and • a heat treatment step (L) of the raw shell mold to obtain the shell mold (1) comprising the first mold part (6) and the second mold part (7).,

4. Manufacturing method according to claim 3, characterized in that the first and second contact slips are different and chosen from an equiaxed contact slip and a monocrystalline contact slip.

5. Manufacturing method according to claim 4, characterized in that the equiaxial contact slip comprises at least one germinating agent.

6. Manufacturing method according to any one of claims 3 to 5, characterized in that several shell molds (1) are manufactured simultaneously, the wax model (2) being in the form of a wax cluster comprising several part models (8).

7. Manufacturing method according to any one of claims 3 to 6, characterized in that during the step of dipping (B) the first portion (3) of the wax model (2) in an equiaxial contact slip, the dipping is carried out up to a transition zone (5) intended to form a junction zone between the first portion of the part and the second portion of the part during a step of molding the multi-material part (2).

8. Manufacturing method according to any one of claims 3 to 7, characterized in that during the dipping step (E), the wax model (2) is entirely dipped in the second contact slip.

9. Shell mold (1) intended for molding a multi-material part comprising a first part portion and a second part portion having different crystalline structures, chosen from a monocrystalline crystalline structure or an equiaxed crystalline structure, characterized in that it is obtained by the manufacturing method as defined according to any one of claims 1 to 8.

10. Shell mold (1) according to claim 9, characterized in that it comprises a first mold part (6) comprising a first contact layer 9 configured to generate equiaxed crystalline solidification during a molding operation of the first portion of the part and a second mold part (7) comprising a second contact layer (10) configured to generate monocrystalline crystalline solidification during a molding operation of the second portion of the part.

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