METHOD OF MANUFACTURING A MOLD FOR CASTING A METAL PART MADE BY LOST WAX CASTING

Abstract

METHOD FOR MANUFACTURING A MOLD FOR CASTING A METAL PART MADE BY LOST WAX CASTING One aspect of the invention relates to a method for manufacturing a mold for casting a cluster of metal parts from a superalloy to be cast in said mold, comprising: determining (1) an optimal set of values ​​() for thermomechanical parameters of the mold, said determination comprising: simulating (14) cooling of an assembly comprising the mold and the superalloy; determining (16), from the simulated cooling, a plurality of risks () of plastic deformation of the assembly; and provided that, for at least one portion, the respective risk of plastic deformation reaches a predefined threshold (), repeating the simulation of the cooling of the assembly and the determination of the plurality of risks of plastic deformation with new thermomechanical parameters for the mold; manufacturing the mold.Figure to be published with the abstract: Figure 3.

Description

Title of the invention: METHOD FOR MANUFACTURING A MOLD FOR CASTING A METAL PART MADE BY LOST WAX CASTING TECHNICAL FIELD OF THE INVENTION

[0001] The technical field of the invention is that of the manufacture of a metal part by lost wax casting and more particularly of the mold allowing the casting to be carried out. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0002] The manufacture of superalloy metal parts, for example a turbine blade, can be carried out using a method known as "lost wax casting". A superalloy is understood to mean a metal alloy which, once solidified, has superior thermomechanical characteristics to a conventional metal alloy. According to this method, originals of the various metal parts, also called "positives", are made with wax. The positives of the parts are assembled together and form a unit called a "cluster of positives" or simply "cluster". Then, a mold, also called a "shell" or "shell mold" or "shell mold", is made around the positive. The wax is then removed from the shell mold which then forms the negative of the cluster of positives.A metallic superalloy is cast into the shell mold (the shell mold is filled with the superalloy) to, after solidification and cooling, form the plurality of final metal parts. The shell mold is then removed to release the parts.

[0003] The shell mold can be made from ceramic materials, offering good mechanical resistance to high temperatures while being easily breakable, to release the metal part. Conventionally, to obtain the shell mold, the cluster of positives is coated with a first layer of ceramic, for example by dipping in a first ceramic suspension, called "slip", providing a surface condition suitable for molding. The slip layer is then coated with a layer of sand (an operation called "stuccoing") and then dried, so as to fix the material deposited in the assembly. The operations of dipping in slips (possibly of different compositions from each other and / or from the first slip), stuccoing and drying are repeated. A shell comprising a plurality of layers (generally between five and ten layers). The cluster of wax positives is finally removed (a step called "waxing").The shell can be heat treated to achieve sintering to provide sufficient mechanical strengthening to withstand high temperature casting of the superalloy. In . In the field of lost wax casting, several solidification techniques are currently distinguished, and therefore several casting techniques, depending on the nature of the superalloy and the expected properties of the metal part resulting from the casting. This may be directed solidification with a columnar structure, directed solidification with a monocrystalline structure or equiaxed solidification.

[0004] During cooling of the superalloy and the shell mold, mechanical stresses may be exerted on the cluster of metal parts. These stresses may, when they exceed a critical threshold, give rise to strong plastic deformation, causing recrystallization or the formation of a crack in the part. Recrystallization of the cluster of parts or the presence of a crack is detrimental to the thermomechanical properties of the metal parts obtained, which therefore cannot be used.

[0005] There is therefore a need to improve existing processes to avoid recrystallization of the produced parts or the formation of cracks in the produced parts.

[0006] The document [“A new experimental and simulation methodology for prediction of recrystallization in Ni-based single crystal superalloys during investment casting” Long & al., Journal of Materials Processing Tech. 306 (2022) 117624] proposes a method for predicting areas at risk of recrystallization based on a simulation of the thermomechanical behavior of a superalloy part during the solidification and cooling phase (i.e. after casting the molten superalloy into the shell mold). This document also suggests optimizing the thermal and mechanical parameters of the part to avoid such recrystallization areas.

[0007] However, tests implementing this method have been carried out and have shown that certain parts still have recrystallization zones.

[0008] There is therefore a need to avoid recrystallization and / or the appearance of cracks during the manufacture of metal parts by lost wax casting. Summary of the invention

[0009] The invention makes it possible to address the aforementioned technical problem by making it possible to optimize a set of values ​​for thermomechanical parameters of the mold so that the optimal set of values ​​makes it possible to manufacture a mold minimizing the risk of recrystallization and / or formation of cracks in the cluster of metal parts. In addition, it also makes it possible to prevent mold fining or the formation of cracks in the mold.

[0010] The invention relates more particularly to a method of manufacturing a mold for molding a cluster of metal parts from a superalloy to be cast in said mold, comprising: • determine an optimal set of values ​​of thermomechanical parameters of the mold, said determination comprising: • receive a set of values ​​for the thermomechanical parameters of the mold ; • for the set of values ​​received, simulate cooling of an assembly comprising the mold and the superalloy, the cooling comprising solidification of the superalloy in the mold, so as to obtain thermomechanical behavior of the assembly during cooling; • determine, from the thermomechanical behavior obtained, a plurality of risks of plastic deformation respectively associated with a plurality of portions of the assembly; and • as long as, for at least one portion of the plurality of portions of the assembly, the respective risk of plastic deformation reaches a predefined threshold, repeating the simulation of the cooling of the assembly and the determination of the plurality of risks of plastic deformation with a new set of values ​​for the thermomechanical parameters of the mold; • manufacture the mold from the optimal set of values ​​for the mold's thermomechanical parameters.

[0011] By "metal part" is meant a part formed from a superalloy. By "cluster of metal parts" is meant a metal element resulting from casting which comprises a plurality of metal parts capable of being bonded together.

[0012] By "thermomechanical parameters" is meant parameters which have an impact on the thermal and mechanical behavior of the mold and / or the superalloy. These are, for example, the thermal diffusion coefficient of the mold and / or the superalloy or the thermal expansion coefficient (also called "thermal expansion coefficient") of the mold and / or the superalloy.

[0013] By "optimal set of values" is meant a set of values ​​minimizing a constraint, said constraint being a risk of recrystallization in the super alloy.

[0014] By "simulation of cooling" is meant calculating heat transfers between the assembly and an environment (for example a furnace within which cooling may take place) as a function of time as well as the effect of these heat transfers on the mechanical behavior of the cluster of metal parts and / or the mold. The simulation of the cooling also takes into account the solidification of the superalloy in the mold. Thus, instead of considering simulating only the solidification and cooling of the superalloy in the form of a predetermined cluster, the simulation of the process considers the assembly comprising the mold and the superalloy. melted after it has been poured into the mold.

[0015] By "risk of plastic deformation" is meant a value relating to the probability of plastic deformation of the superalloy. This physical quantity is for example linked to the appearance of recrystallized grain and / or cracks during cooling of the superalloy. This value may be a function of a probability of plastic deformation, or of a parameter relating to plastic deformation.

[0016] By "plurality of portions of the assembly" is meant a virtual discretization of the assembly comprising the superalloy and the mold. This is for example a mesh of the assembly.

[0017] Taking into account the thermomechanical behavior of the mold makes it possible to obtain a more faithful estimate of the mechanical stresses that may be exerted in the superalloy or in the mold during solidification and cooling (and therefore in the cooled superalloy, i.e. the cluster of metal parts). This thermomechanical behavior takes into account, for example, the deformation mismatch that may occur between the superalloy and the mold during their respective thermo-expansion. The relaxation of certain mechanical stresses of the superalloy in the mold (or vice versa) can also be taken into account.

[0018] Contrary to what is taught by the prior art, this method provides for modifying the thermomechanical parameters of the mold to reduce the risk of plastic deformation of the part.

[0019] This method also makes it possible to search, by successive iterations, for the optimal set of values ​​for the thermomechanical parameters for the mold, making it possible to obtain, for a predetermined superalloy, the thermomechanical properties of an ideal shell mold making it possible to manufacture the cluster of metal parts without recrystallization or cracks (and also without rupture of the mold). This allows the manufacture of a shell mold, including in particular the selection of slips and sands, showing the determined thermomechanical properties.

[0020] The initial set of values ​​may be formed by a set of experimental values ​​or a set of values ​​resulting from a previous determination of the optimal values ​​and for which thermomechanical parameters are similar (for example identical geometry and / or identical superalloy). This makes it possible to reduce the number of calculations required or even to provide initial values ​​making it possible to avoid “falling” into a local optimum.

[0021] The use of a risk of plastic deformation makes it possible to take into account several types of plastic deformation of the superalloy, whether it is recrystallization or crack formation, or even other types of deformation (such as sagging or creep). Thus, this method is not limited to the sole reduction of a risk of recrystallization.

[0022] The use of a risk of plastic deformation also makes it possible to take into account several types of deformation of the mold, such as the finishing of the mold.

[0023] Manufacturing the mold from the optimal values ​​makes it possible to manufacture a shell adapted to the thermomechanical needs of the cluster of mechanical parts to be molded.

[0024] Advantageously, the thermomechanical parameters of the mold comprise a coefficient of thermal conductivity and / or a Young's modulus and / or a coefficient of thermo-expansion and / or a coefficient of thermal capacity, preferably mass or molar, and / or a Poisson's ratio.

[0025] Advantageously, the method can comprise a determination of a geometry of the mold from the thermophysical and thermomechanical parameters of the mold and a geometry of the cluster of metal parts, and the simulation of the cooling of the assembly can be carried out from the geometry of the mold.

[0026] Advantageously, the method may comprise a construction of a geometry of the superalloy from the geometry of the mold, and the simulation of the cooling may further be carried out from the geometry of the superalloy.

[0027] Advantageously, the simulation of the cooling of the assembly may comprise: an estimation of a thermal evolution of the assembly during cooling (including in particular the solidification of the superalloy); and an estimation of mechanical stresses and mechanical deformations in the assembly from the thermal evolution of the assembly, the estimation of the thermal evolution being able to be carried out from a first predetermined mesh of the assembly and the estimation of the mechanical stresses and mechanical deformations being able to be carried out from a second predetermined mesh of the assembly.

[0028] The mold and the superalloy may have a plurality of common interfaces and the first and second meshes may be identical to the common interfaces between the mold and the superalloy. According to one development, the first and second meshes are identical.

[0029] The simulation of the cooling includes the solidification of the superalloy if applicable as well as the cooling as such of the solidified superalloy and the mold in interaction with each other.

[0030] Advantageously, the plurality of portions of the assembly may be based on the second mesh.

[0031] Advantageously, the simulation of the cooling of the assembly can take into account a phase prior to the cooling which includes preheating of the mold alone.

[0032] Advantageously, the simulation of the cooling of the assembly takes into account a solidification of the superalloy during cooling which is modeled as a transition into pasty zone.

[0033] Advantageously, each risk of plastic deformation among the plurality of risks of plastic deformation can be respectively associated with a portion of the superalloy alone.

[0034] Advantageously, the risk of plastic deformation can be a potential energy of plastic deformation.

[0035] Advantageously, the predefined threshold can be determined from a test piece made from an equivalent superalloy. By "equivalent superalloy" is meant a superalloy having thermomechanical parameter values ​​equal to within 20%, or even within 10%, of the thermomechanical parameter values ​​of the superalloy to be cast in the mold.

[0036] Advantageously, the superalloy can be nickel-based.

[0037] The invention further relates to a system comprising a computer and means adapted to execute the steps of the method according to the invention.

[0038] The invention also relates to a computer program comprising instructions which cause the system according to the invention to execute the steps of the method according to the invention.

[0039] The invention also relates to a computer-readable medium, on which the computer program according to the invention is recorded.

[0040] The invention and its various applications will be better understood upon reading the following description and examining the accompanying figures. BRIEF DESCRIPTION OF THE FIGURES

[0041] The figures are presented for information purposes only and in no way limit the invention. Unless otherwise specified, the same element appearing in different figures has a single reference.

[0042] [Fig.l] schematically shows an example of metal parts obtained from casting and a superalloy cast in the mold.

[0043] [Fig.2] schematically shows a mode of implementation of a manufacturing method according to the invention.

[0044] [Fig.3] schematically shows a mode of implementation of a determination step of the method of [Fig.2].

[0045] [Fig.4] shows an example of determining a risk of plastic deformation for two portions belonging to the same superalloy.

[0046] [Fig.5] shows an example of determining a potential energy of plastic deformation in the same portion of a superalloy and for two different molds.

[0047] [Fig.6] schematically shows an embodiment of a system according to the invention.

[0048] [Fig.7] schematically shows an embodiment of a computer for implementing the determination step of [Fig.3]. DETAILED DESCRIPTION

[0049] The invention relates to improving the properties of a shell mold in order to obtain a cluster of metal parts 3 by lost wax casting, as for example illustrated by [Fig.l].

[0050] The lost wax casting method makes it possible to form parts 3 having a particular crystalline arrangement, called “columnar” and / or “monocrystalline”. Such metal parts 3 are known for their mechanical strength under high mechanical and thermal stresses. They are for example advantageously used in an aircraft turbomachine, for example to form turbine blades.

[0051] The parts 3 are obtained by molding from a superalloy 4. The superalloy 4 is, for example, a metal alloy that can also be called a “high-performance” alloy. It can be used at very high temperatures while retaining good thermomechanical properties. The superalloy 4 considered in the invention advantageously makes it possible to carry out crystallization by precipitation. It is, for example, a Ni-based metal superalloy.

[0052] In order to form the metal parts 3, the superalloy 4 in liquid phase (i.e. at a temperature exceeding its melting temperature) is introduced into a mold 2. Then, the assembly 5 formed by the superalloy 4 in liquid phase and the mold 2 is cooled until the superalloy 4 solidifies and forms a cluster 5 of metal parts 3. The cooling of the assembly can implement heat transfers by conduction and / or convection and / or radiation. These heat transfers are advantageously forced, in order to be able to freeze a particular crystalline phase in the cooling superalloy 4. For example, the assembly 5 is placed in contact with a thermal bath (for example a cold plate) or a jet of cold gas is directed towards an external surface of the assembly 5.

[0053] An embodiment of the mold 2 makes it possible to form several metal parts 3 in the form of a cluster 5. The mold 2 comprises, for example, several recesses making it possible to produce the different parts 3. For the description of the invention, a mold 2 is considered for manufacturing a plurality of parts 3. The teachings set out below are, however, transposable to the case of a mold making it possible to manufacture a single part 3.

[0054] [Fig.2] schematically shows a method 7 for manufacturing a mold 2 for molding the cluster of metal parts 3. The method 7 comprises a step of de termination 1 of an optimal set of values ​​7opt for the thermomechanical properties of the mold 2. A mode of implementation of the determination 1 is described with reference to [Fig.3]. The determination 1 is advantageously carried out using the system 6 described with reference to [Fig.6]. The method 7 then comprises a step of manufacturing 73 of the mold 2 from the optimal set of values ​​A>pt obtained. The manufacturing 73 is for example carried out by bubbling and stuccoing, so that the mold is suitable for lost wax casting. The manufacturing step 73 can be followed by a characterization 74 of the mold 2 manufactured in order to determine the concordance between the values ​​ / exp of its thermomechanical parameters and the set of values ​​^opt from which it is manufactured.

[0055] The manufacture 73 of the mold 2 may be preceded by a selection 72 of a slip and a sand for manufacturing the mold 2. The selection 72 is carried out from the set of Jopt values ​​optimal for the thermomechanical properties of the mold 2.

[0056] In order to improve the molding of the cluster, the invention proposes to determine an optimal set of values ​​Apt for thermomechanical parameters of the mold 2. The thermomechanical parameters of the mold 2 can influence the cooling of the assembly 5, since it is generally the mold 2 which is brought into contact with a thermal bath or targeted by a jet of cold air. The thermomechanical parameters of the mold 2 can also influence the mechanical stresses which can form in the assembly 5, that is to say in the superalloy 4, in the mold 2 or at the interface between the superalloy 4 and the mold 2.

[0057] The thermomechanical parameters of the mold 2 comprise, for example, a parameter representative of the rigidity of the mold 2, such as a Young's modulus E. They may also comprise a Poisson's ratio of the mold 2.

[0058] The thermomechanical parameters of the mold 2 may also include a parameter that can have an influence on the heat transfer mechanisms of the mold 2, such as a density P, a thermal conductivity coefficient K or a specific heat Cp (also called specific heat capacity).

[0059] The thermomechanical parameters of the mold 2 may further comprise a parameter representative of the coupling between the thermal behavior of the mold 2 and the mechanical behavior of the mold 2, such as a thermo-expansion coefficient a (also called thermal expansion coefficient).

[0060] Advantageously, the thermomechanical parameters also include geometric parameters of the mold 2, having an impact both on the mechanical behavior of the mold 2 and on the thermal behavior of the mold 2. This is for example a thickness w of the mold 2.

[0061] According to these examples of thermomechanical parameters, a set of values ​​J can be J - {E; p; K; Cp; a; w}.

[0062] The thermomechanical parameters of the mold 2 can be scalar quantities, vector (or tensor), or even functions depending on operating parameters such as the temperature or other thermomechanical parameters of the mold 2. Said functions may for example depend on dimensional characteristics of the mold 2 (for example, the density of the mold P may be greater in one portion of the mold 2 and lower in another).

[0063] [Fig.3] schematically shows a mode of implementation of the determination 1 of an optimal set of values ​​ / opt for thermomechanical parameters of the mold 2 for the molding of the cluster of metal parts 3.

[0064] In a first step, the determination 1 comprises a step 11 of receiving an initial set of values ​​Jo for thermomechanical parameters of the mold 2. Some of these initial values ​​(for example the thickness w of the mold 2) are for example communicated by a user or communicated from a file, while others (for example the thermo-expansion coefficient G) can be communicated from a materials database.

[0065] Determination of the optimal set of values ​​Jopt for the thermometric parameters thermomechanical parameters of the mold 2 is advantageously a function of thermomechanical parameters of the superalloy 4. Indeed, the determination 1 implements the simulation of the thermomechanical behavior of the assembly 5 comprising the mold 2 and the superalloy 4 in the mold 2. The determination 1 then advantageously comprises a step 12 of receiving a set of values ​​for thermomechanical parameters of the superalloy 4. These values ​​(for example the density or the specific heat of the superalloy 4) are for example communicated by a user or communicated from a file or from a materials database. Since the determination 1 aims above all to optimize the parameters of the mold 2, the thermomechanical parameters of the superalloy 4 are not supposed to evolve during the search for the optimal set for the thermomechanical parameters of the mold 2.

[0066] The determination 1 may also comprise a step of receiving the geometry of the mold 2. By geometry, we mean a representation, in two or three dimensions, of the surfaces or volumes of the mold 2. Alternatively, the geometry of the mold 2 may be a mesh of the mold 2. By mesh, we mean a discretization of the mold 2 into a plurality of polygons, which may also be called “vertexes”. During the step of receiving the geometry of the mold 2, said geometry may be communicated by a user or communicated from a file or a database.

[0067] Alternatively to receiving the geometry of the mold 2, the determination 1 may comprise a step 131 of constructing a geometry of the mold 2. This construction 131 may be carried out from a geometry of the cluster of parts 3 to be molded and / or from the thermomechanical parameters previously received. For example, when the thermomechanical parameters of the mold 2 include a thickness of the mold 2, the geometry of the mold 2 can be constructed by carrying out an extrusion of the external surfaces of the geometry of the cluster of parts 3, the extrusion being for example carried out perpendicular to the external surfaces of the geometry of the cluster of parts 3 and according to the thickness w of the thermomechanical parameters of the mold 2.

[0068] The interest of the method for constructing 131 the geometry of the mold 2 from the thermomechanical parameters of the mold 2, rather than upon receipt, is to enable the geometry of the mold 2 to be optimized automatically in parallel with the optimization of the values ​​of the thermomechanical parameters of the mold 2.

[0069] Determination 1 then comprises a simulation step 14 of cooling of the assembly 5 (comprising the mold 2 and the superalloy 4) so ​​as to obtain a thermomechanical behavior of the assembly 5 during cooling.

[0070] The simulation of the cooling is carried out from a model of the assembly 5. This is more particularly a model of the mold 2 and a model of the superalloy 4 contained in the mold 2. The model of the mold 2 comprises for example the geometry of the mold 2 as well as its thermomechanical properties. In the same way, the model of the superalloy 4 comprises for example thermomechanical parameters of the superalloy 4 (which may be received in a previous step or predetermined). The model of the superalloy 4 may comprise a geometry of the superalloy, which corresponds to a geometry of the cluster of metal parts 3.

[0071] It is preferable that the determination 1 comprises a step 132 of constructing the geometry of the superalloy 4. This step 132 of constructing is particular in that it is carried out from the geometry of the mold 2 rather than from the geometry of the cluster of metal parts 3. The geometry of the superalloy 4 is for example defined by internal surfaces of the geometry of the mold 2. This way of doing things is preferable because the superalloy 4 can be introduced into the mold 2 after the latter has been preheated. If the preheating induces a thermo-expansion of the mold 2, then the shape defined by the internal surfaces of the mold 2 can be different from the geometry of the cluster of parts 3 when the superalloy 4 is poured into the mold. Constructing the geometry of the superalloy 4 from the geometry of the mold 2 therefore makes it possible to improve the simulation of the thermomechanical behavior of the model of the assembly 5.

[0072] The geometry of the superalloy 4 may also comprise a complementary surface corresponding to a free surface of the superalloy 4 when it is poured into the mold 2.

[0073] Cooling corresponds to a duration during which heat transfers issue in the assembly 5 and between the assembly 5 and an environment external to the assembly 5 (such as the interior of a furnace) make it possible to reduce the temperature of the assembly 5. Cooling therefore begins as soon as the superalloy 4 is poured into the mold 2 (this operation can also be called "casting"). It ends at a later time, for example when the entire superalloy 4 is in a solid phase. Cooling can therefore end as soon as the entire superalloy 4 has a temperature below a so-called "critical" temperature, corresponding to the liquid / solid transition of the superalloy 4. When the superalloy 4 can adopt several solid phases, for example characterized by different transition temperatures, cooling ends as soon as the entire superalloy 4 has a temperature below a transition temperature of a targeted phase.

[0074] It is however advantageous to consider that the cooling ends when the assembly 5 reaches thermal equilibrium with a thermal bath with which it is thermally coupled (for example a cold plate or an external environment). Indeed, thermo-expansion stresses in the assembly 5 can vary until the assembly 5 is at thermal equilibrium. The thermo-expansion stresses accumulated after complete solidification of the superalloy 4 can also represent a substantial part of the stresses which can lead to plastic deformation of the superalloy 4.

[0075] The model of the assembly 5 advantageously comprises the equations governing its thermomechanical behavior and more particularly the thermomechanical behavior of the model of the mold 2 and of the model of the superalloy 4 in the mold 2. These equations comprise for example a heat transfer equation and a mechanical deformation equation.

[0076] The model of superalloy 4 may comprise a set of equations governing the solidification of superalloy 4 upon cooling. The solidification of superalloy 4 is, for example, modeled as a transition into a pasty zone.

[0077] The model of the assembly 5 may also include boundary conditions making it possible to model the interaction of the assembly 5 with its external environment. The boundary conditions model, for example, mechanical clamping of the mold 2 or thermal contact of the mold 2 with a thermal bath.

[0078] The simulation 14 of the thermomechanical behavior of the assembly 5 can be carried out in two stages. In a first stage, the simulation 14 of the cooling comprises an estimation 141 of the temperature T^t) of the assembly 5 during cooling at different points i and for all times l. In a second stage, the simulation 14 of the cooling comprises an estimation 142 of the mechanical stresses oj) and of the deformation Tj) induced at different points j in the set 5 and from the temperature evolution t ) previously obtained.

[0079] The estimation 141 of the temperature T^t) of the model of the set 5 may comprise a step of constructing a first mesh from the geometry of the set 5 (and more particularly from the geometries of the mold 2 and of the superalloy 4 in the mold 2). The first mesh makes it possible to obtain a plurality of points / at which the temperature T^t) of the set 5 is estimated. The first mesh makes it possible, for example, to carry out the estimation 141 of the temperature T^t) by means of a finite element calculation.

[0080] The estimation 142 of the induced mechanical stresses and deformation may also comprise a step of constructing a second mesh from the geometry of the assembly 5. The second mesh makes it possible to obtain a plurality of points j at which the mechanical stresses cr / Ty) and the mechanical deformations are estimated. The second mesh may also make it possible to carry out the estimation 142 of the mechanical stresses and the deformations by means of a finite element calculation.

[0081] When the first and second meshes are different, the estimation of the mechanical stresses and deformations at points j can take into account an interpolation of the temperature Tj at points j.

[0082] When the first and second meshes are identical, it is not necessary to perform an interpolation of the temperature between the two meshes. The calculation accuracy is therefore improved. On the other hand, this solution can be detrimental in terms of calculation time or simulation fidelity. Indeed, a mesh can be characterized by a fineness, which will be understood as being an average of a quantity inversely proportional to a dimension of the vertices forming the mesh. Certain types of calculations, such as the estimation of the temperature T^t)^ may require a low fineness while other types of calculations, such as the estimation of mechanical stresses cr / Tj) and mechanical deformations may require a high fineness.Using the same mesh, with the same fineness, can therefore lengthen the estimation time of the temperature Tt(t) and / or reduce the fidelity of the estimation of the mechanical constraints. It is therefore advantageous to use different first and second meshes, with different finenesses. The first mesh, for example, has a low fineness while the second mesh has a high fineness.

[0083] The richness of the simulated physical phenomena can especially intervene at the level of the interfaces between the mold 2 and the superalloy 4. It can therefore be advantageous to consider first and second meshes having finenesses equal to + / - 20% in the vicinity of the mold / superalloy interfaces. For the same reason, it is advantageous not to perform interpolation at the mold / superalloy interfaces. Thus, points i, j of the first and second meshes at the mold / superalloy interface are advantageously identical.

[0084] The estimation 141 of the temperature T, is for example carried out with the software “ProCAST”. The estimation 142 of the mechanical stresses and mechanical deformations s / T,) is for example carried out with the software “ABAQUS”. The first and second meshes can be determined with the software “ANSA”.

[0085] Determination 1 comprises a step 15 of determining a plurality of risks Rk of plastic deformation of the assembly 5. The risks Rk are determined from the thermomechanical behavior of the model of the assembly 5 obtained from the simulation 14 of the cooling.

[0086] The plurality of risks Rk is determined 15 for a plurality of portions Pk of the geometry of the set 5. Each risk Rk is respectively associated with a portion Pk of the geometry. The portions Pk correspond for example to the mesh of the set 5 used to carry out the estimation of the mechanical stresses and mechanical deformations. Depending on the nature of the data taken into account to determine the risk Rk, each portion Pk then corresponds to a vertex of the mesh or to a point of this vertex. The risk Rk of plastic deformation can then be calculated from the mechanical stresses (T^T^ and / or the temperature variation Tk of each portion Pk during cooling.

[0087] The risk Rk, for example, accounts for the probability of the appearance of plastic deformation in the superalloy 4 during cooling. Plastic deformations include, for example, recrystallization, the formation of cracks or fissures, or even sagging.

[0088] [Fig.4] shows an example of determining the risk Rk for two portions P\, Pz belonging to the superalloy 4. In this example, the risk Rk of plastic deformation is proportional, or even equal, to a potential energy of plastic deformation determined for each portion P\, Pz. [Fig.4] shows in particular the variation of the potential energy of plastic deformation Vk as a function of the temperature Tk in each portion P\, P2 of the superalloy 4. As the assembly 5 cools, that is to say, as the temperature Tk of the two portions Py, P2 decreases, the potential energy Vk of each portion Py, P2 increases. At the end of the cooling, one of the two portions P^ has a higher potential energy, exceeding a threshold G (discussed below).

[0089] The potential energy of plastic deformation Vk is determined, for each portion Pk, as a function of the thermomechanical behavior of the assembly 5 obtained thanks to the simulation of cooling. It is obtained from the mechanical constraints a^Tk) estimated previously. It can also take into account the mechanical deformations s / Tj) of the assembly 5 when the latter undergoes relaxation.

[0090] In one embodiment, the plurality of risks is only associated with a plurality of portions / d of the superalloy 4. It may be advantageous to also determine the risks Rk relating to the mold 2 in which case the plurality of risks Rk is associated with a plurality of portions of the superalloy 4 and a plurality of portions p| of the superalloy 2.

[0091] The determination 1 then comprises a comparison 16 of the risk Rk of plastic deformation for each portion with a predefined threshold G. At the end of this comparison 16, if the risk Rk of plastic deformation of at least one portion P^ of the assembly 5 is greater than the predefined threshold G, then the determination 1 then comprises a reiteration of the simulation 14 of the cooling of the model of the assembly 5 and a reiteration of the determination 15 of the plurality of risks Rk of plastic deformation for the plurality of portions P^. However, unlike the previous iterations of these steps, the simulation 14 and the determination 15 are carried out with a new set of values ​​Jn for the thermomechanical parameters (for example E, (\ K , ) of the mold model 2. Providing a new set of values ​​Jn for the thermomechanical parameters of the mold 2 amounts to considering a new mold 2 (for example harder or thicker) at each iteration.

[0092] The new set of values ​​J„ can be communicated directly as input to the simulation step 14 so that the model of the set 5 takes into account the new set Jn. It may however be preferable to provide this new set Jn at an earlier step of the determination 1, for example to reiterate the construction 131 of the geometry of the mold 2 from the new set of values ​​Jn. This construction 131 may depend on the values ​​Jn of the thermomechanical parameters of the molded, such as its thickness w. The new set Jn is for example communicated at the reception step 11, in place of the initial set of values ​​Jo.

[0093] Determination 1 provides that the aforementioned steps are repeated with a new set of values ​​J n as long as at least one portion P^ of the assembly presents a risk Rk of plastic deformation greater than the predefined threshold G. Since no portion P^ of the assembly presents a risk Rk greater than the threshold G, then the last set of values ​​J„ considered is the optimal set of values ​​Jopt of the mold 2.

[0094] [Fig.5] shows an example of determination of the potential energy of plastic deformation (corresponds to a risk Rk of plastic deformation) determined for the same portion P{ of the superalloy 4 but for two different molds 2', 2” (i.e. for a mold model 2 comprising two different sets of values). [Fig.5] shows that the set of values ​​Jn associated with the first mold 2' is not optimal since the potential energy Vk exceeds the threshold G. Conversely, the set of values ​​Jn associated with the second mold 2” is optimal because the potential energy Vl of the portion p^" remains below the threshold G throughout the cooling.

[0095] The determination 1 may comprise a step 17 of providing the new set of values ​​J n at each reiteration of the aforementioned steps (where the index n corresponds for example to the number of reiterations). Each new set of values ​​Jn may be provided according to an inverse problem solving approach, for example, on the basis of a sequential search algorithm for an optimum, such as a dichotomy search algorithm. It may also be a search algorithm based on a gradient depending on the plurality of risks Rk.

[0096] The fidelity of the simulation 14 can be improved by also taking into account a phase prior to the cooling of the assembly 5 in which the mold 2 is preheated to a preheating temperature. The effect of the preheating is to induce a thermo-expansion of the mold 2 which can have an effect on the accumulation of stresses in the superalloy 4 and / or the mold 2 and modify the results of the determination of the plurality of risks Rk.

[0097] [Fig. 6] schematically shows a system 6 comprising means 61 adapted to execute the different steps of the manufacturing method 7 and in particular of the determination 1 as described previously. The system 6 comprises for example a computer 61, as illustrated by [Fig. 7], and configured to execute the different determination steps 1 described.

[0098] The computer 61 comprises a memory 611 for storing instructions allowing the implementation of the determination 1, an initial set of values, and temporary data for carrying out the different steps of the determination 1 described previously.

[0099] The computer 61 further comprises a circuit 612. This circuit may be, for example, a processor capable of interpreting instructions in the form of a computer program, an electronic card whose steps of the method of the invention are described in the silicon, or even a programmable electronic chip such as an FPGA chip (for “Field-Programmable Gate Array” in English).

[0100] The computer 61 comprises an input interface 613, for example, for receiving an initial set of values ​​or a geometry of the cluster of parts (or of the part alone) or a geometry of the mold, and an output interface 614 for providing the optimal set of values. Finally, the computer 61 may comprise, to allow easy interaction with a user, a screen 615 and a keyboard 616. Of course, the keyboard is optional, in particular in the context of a computer having the form of a touchscreen tablet, for example.

[0101] In a variant, the method 7 may also comprise a step of determining the predefined threshold G. The threshold G may be entered by a user or provided by a database. It may also be determined experimentally, from a test piece. By test piece, we mean a sample manufactured from a test superalloy and having a predefined shape. This test piece makes it possible, for example, to carry out tensile or compression tests making it possible to determine the thresholds of certain mechanical or thermomechanical properties of the test superalloy, such as a plastic deformation threshold.

[0102] The predefined threshold G can therefore be determined experimentally, by carrying out compression and / or tensile tests on a test specimen made from a test superalloy having thermomechanical parameters substantially equivalent to those of the targeted superalloy 4. By “substantially equivalent”, we mean that the thermomechanical parameters are equal to within + / - 20%, or even + / - 10%.

[0103] The system 6 may also comprise a memory 62 in which a database is stored linking thermomechanical parameters to a slip and / or a sand. This database thus makes it possible to select 72 the slip and the sand to be used to manufacture 73 the mold 2.

[0104] The system 6 may also comprise a stucco bench 63 for manufacturing the mold 2, for example from the selected slip and sand.

[0105] The system 6 can also comprise a bench 64 for characterizing the thermomechanical parameters Jexp of the mold 2.

[0106] In the event of an experimental determination of the threshold G, the system 6 may also comprise a means 65 configured to carry out the experimental determination of the threshold G from a test piece. This is for example a bench for mechanical characterization of test pieces.

Claims

Claims

1. Method (7) for manufacturing a mold (2) for molding a cluster of metal parts (3) from a superalloy (4) to be cast in said mold (2), comprising: - determining (1) an optimal set of values ​​(Jopt) for thermomechanical parameters of the mold (2), said determination comprising: • receiving (11) a set of values ​​(Jo) for the thermomechanical parameters of the mold (2); • for the received set of values, simulating (14) a cooling of an assembly (5) comprising the mold (2) and the superalloy (4), the cooling of the assembly comprising the solidification of the superalloy in the mold, so as to obtain a thermomechanical behavior of the assembly (5) during cooling; • determine (16), from the thermomechanical behavior obtained, a plurality of risks (Rj) of plastic deformation respectively associated with a plurality of portions (Pi) of the assembly (5);and • as long as, for at least one portion (P^) of the plurality of portions of the assembly, the respective risk (¾) of plastic deformation reaches a predefined threshold (G), repeat the simulation of the cooling of the assembly (5) and the determination of the plurality of risks of plastic deformation with a new set of values ​​(Jn) for the thermomechanical parameters of the mold (2); - manufacture (73) the mold (2) from the optimal set of values ​​( ■^opt) for the thermomechanical parameters of the mold (2).;

2. Method (1) according to the preceding claim, comprising a determination (131) of a geometry of the mold (2) from the thermomechanical parameters of the mold (2) and a geometry of the cluster of metal parts (3), the simulation (14) of the cooling being carried out from the geometry of the mold (2).

3. Method (1) according to the preceding claim, comprising a construction (132) of a geometry of the superalloy (4) from the geometry of the mold (2), the simulation (14) of the cooling being further carried out from the geometry of the superalloy (4).

4. Method (1) according to one of the preceding claims, according to which the simulation (14) of the cooling of the assembly (5) comprises: an estimation (141) of a thermal evolution of the assembly (5) during cooling; and an estimation (142) of mechanical stresses and mechanical deformations in the assembly (5) from the thermal evolution of the assembly (5), the estimation of the thermal evolution being carried out from a first predetermined mesh of the assembly (5) and the estimation of the mechanical stresses and mechanical deformations being carried out from a second predetermined mesh of the assembly (5).

5. Method (1) according to the preceding claim, according to which the plurality of portions (Pi) of the set (5) is based on the second mesh.

6. Method (1) according to one of the preceding claims, according to which the simulation (14) of the cooling of the assembly (5) takes into account a phase prior to the cooling which comprises preheating of the mold (2) alone.

7. Method (1) according to one of the preceding claims, according to which the simulation (14) of the cooling of the assembly (5) takes into account a solidification of the superalloy (4) during cooling which is modeled as a transition into a pasty zone.

8. Method (1) according to one of the preceding claims, according to which each risk (R,) of plastic deformation among the plurality of risks (Ri) of plastic deformation is respectively associated with a portion (Pi) of the superalloy (4) alone.

9. Method (1) according to one of the preceding claims, according to which the risk (Ri) of plastic deformation is a potential energy (V^) of plastic deformation.

10. Method (1) according to one of the preceding claims, according to which the superalloy is based on Nickel.

11. System (6) comprising a computer (61) and means adapted to carry out the steps of the method (1) according to one of claims 1 to 1H.

12. 1U. Computer program comprising instructions which drive the system according to the preceding claim to carry out the steps of the method (1) according to one of claims 1 to 10.

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