METHOD FOR MANUFACTURED AN INJECTION MOLD FOR A MOLDING CORE AND PRECED BY THE MANUFACTURED CERAMIC MOLDING CORE

Abstract

The invention relates to a method (100) for manufacturing an injection mold (10) for a molding core (1), the method (100) comprising the following steps: - manufacturing (110) a sacrificial mold (15), made of plastic material, having a molding surface (16) and a gripping surface (18), the sacrificial mold (15) being able to be dissolved, - manufacturing (120) a metal mold (20) having an internal surface (21) having a first cavity (22) and a second cavity (24) in which the gripping surface (18) of the sacrificial mold (15) is able to fit, - inserting (130) the sacrificial mold (15) into the second cavity (24) of the metal mold (20) so as to obtain an injection mold (10) comprising the sacrificial mold (15) and the metal mold (20), the sacrificial mold (15) being removable. Figure for the summary: Figure 5

Description

Title of the invention: METHOD FOR MANUFACTURED AN INJECTION MOLD FOR A MOLDING CORE AND METHOD FOR MANUFACTURED A CERAMIC MOLDING CORE Technical field of the invention

[0001] The invention relates to the technical field of manufacturing processes for an injection mold for a molding core. The invention also relates to the technical field of manufacturing processes for a molding core, particularly one made of ceramic.

[0002] Ceramic molding cores are particularly used for manufacturing high-pressure turbine blades in turbomachinery. These high-pressure turbine blades, also called high-pressure turbine distributors, are ventilated by ventilation air during operation. Technical background

[0003] A turbomachine, in particular an aircraft turbomachine, comprises at least one annular duct along a longitudinal axis, in which an aerodynamic airflow, called ventilation air, circulates. This ventilation air passes successively from upstream to downstream through a compressor assembly, a combustion chamber, and a turbine assembly of the turbomachine.

[0004] The terms "upstream" and "downstream" are defined with respect to the direction of gas flow in the turbomachine.

[0005] The compressor assembly comprises one or more compressor stages, and the turbine assembly comprises one or more turbine stages. Each compressor and turbine stage comprises several annular rows of fixed and rotating blades. The fixed blades, known as distributors in a turbine or as rectifiers in a compressor, direct the flow to the rotating blades. The latter transmit the energy of the flow to a rotating shaft coaxial with the longitudinal axis.

[0006] Each blade extends radially between a tip end and a root end and comprises a leading edge upstream and a trailing edge downstream. Between the leading and trailing edges extend opposing intrados and extrados surfaces. The fixed blades extend between two annular walls of the distributor, respectively internal and external. Such a turbine distributor is sectorized and comprises several sectors of distributors arranged circumferentially end to end around the longitudinal axis. A sector generally has several fixed blades.

[0007] In a high-pressure turbine, the stationary blades are subjected to extreme temperatures, typically exceeding 600°C. These blades are therefore hollow along their height and house a cooling system adapted to circulate ventilation air inside each one. Each high-pressure turbine blade thus comprises an internal cavity as well as through holes for ventilation air to pass from the internal cavity to the outside of the blade.

[0008] Currently, high-pressure turbine blades are manufactured using the lost-wax casting process. This process involves pouring metal into a ceramic injection mold that has been previously made around a wax model. The lost-wax casting process uses the fabrication of ceramic molding cores to create the internal cavities of the high-pressure turbine blades with very high precision.

[0009] According to the prior art, turbine blade cores are shaped by a ceramic injection molding process (CIM). The CIM process is commonly used to manufacture ceramic parts of all shapes and sizes because it is generally less expensive than Computer Numerical Control (CNC) or Electrical Discharge Machining (EDM). It is based on the injection of a ceramic powder plasticized by a thermoplastic binder and other additives under high or medium pressure into a closed mold. The raw material cools and solidifies to form the raw body, which is then debound and sintered.Debinding involves removing the thermoplastic binder coating the ceramic powder using a solvent and / or heat, while sintering involves densifying the part to increase its mechanical properties.

[0010] The CIM process makes it possible to obtain mold cores with high repeatability and precision. It allows for the production of parts at a high production rate, making it very economical for parts to be manufactured in large quantities. However, the manufacture of the metal molds used to implement the CIM process is lengthy, approximately 9 months, and can be costly. Furthermore, once the metal mold has been manufactured, it is difficult to make changes to it, and therefore to modify the geometry of the molded parts.

[0011] New high-pressure turbine blade geometries, equipped with complex internal cooling systems, raise design problems. Indeed, increased complexity of the internal cooling systems is inevitable to improve blade cooling efficiency. The new geometries The blades feature both thin and long sections, reversals, multi-cavities, and other geometric complexities. These geometries are therefore very complex to demold.

[0012] However, the creation of internal cavities requires the demolding capability of the molding cores, which is not always possible with the CIM process. "Demolding capability" refers to the ability of an object, for example a molding core, to be extracted from the metal mold used during the molding step. Thus, manufacturing certain molding cores with complex geometries using CIM requires several separate injected parts. A mold must therefore be used for each part geometry, which implies the use of several molds to manufacture a single molding core resulting from the assembly of these parts. In some cases, a core may result from the assembly of as many as six parts.

[0013] Internal cavities are therefore very difficult, or even impossible, to obtain (non-demoldable geometry) with the current CIM manufacturing process, which remains a real obstacle to innovation and makes production increasingly time-consuming while preventing rapid prototyping of small series.

[0014] The invention aims to overcome at least some of the aforementioned problems and proposes in this regard a method for manufacturing an injection mold for a molding core which is simpler and faster to implement than the methods implemented so far. Summary of the invention

[0015] The invention proposes for this purpose a method for manufacturing an injection mold for a molding core, the method comprising the following steps: - to manufacture a sacrificial mold, made of plastic, comprising a molding surface and a gripping surface, the sacrificial mold being capable of being dissolved, - to manufacture a metal mold comprising an internal surface having a first cavity and a second cavity into which the gripping surface of the sacrificial mold is capable of fitting, - insert the sacrificial mold into the second cavity of the metal mold so as to obtain an injection mold comprising the sacrificial mold and the metal mold, the sacrificial mold being removable.

[0016] The method for manufacturing an injection mold according to the invention is simpler and faster to implement than the manufacturing methods known in the prior art. Indeed, to produce molding cores of complex shapes, it is no longer necessary to make a separate mold for each part of the final injection mold to be manufactured, so that the injection mold obtained can then be used to make a core single-piece molding. The injection mold results from the assembly of two molds: the sacrificial mold made of plastic and the metal mold.

[0017] As mentioned in the preamble to this description, metal molds are very difficult to adapt to complex shapes. This is not the case with the two-material injection mold obtained using the process according to the invention. This mold comprises a sacrificial mold made of plastic, and is therefore simpler and faster to manufacture than a metal mold, and better suited for molding cores with very complex shapes. The complex and non-removable parts of the molding core to be manufactured can thus be produced using the molding surface of the sacrificial mold, while the simple and removable parts can be produced using the first and second cavities of the metal mold.

[0018] Since the sacrificial mold is removable, during the demolding operation of an intermediate molding core, both the demoldable and non-demoldable parts of the intermediate molding core can be extracted from the metal mold. Indeed, the non-demoldable parts are not demolded directly but indirectly via the sacrificial mold, which can be removed from the second cavity during demolding because it is removable. Subsequently, since the sacrificial mold is capable of being dissolved, the complex and non-demoldable parts of the intermediate molding core are released following the dissolution of the sacrificial mold.

[0019] Furthermore, the injection mold obtained by the process according to the invention is also very easily modified after manufacturing, unlike a conventional metal mold. Indeed, since the injection mold is made of two materials, comprising both a sacrificial plastic mold and a metal mold, post-manufacturing adaptations of the injection mold can be implemented using the sacrificial mold, which is faster and simpler to produce. The lead times for modifying injection molds produced by the process according to the invention are therefore much shorter than those previously known. The impact of a modification, a defect, or damage is much more limited on production, both in terms of production line downtime and costs.

[0020] According to various features of the invention which may be taken together or separately: • the sacrificial mold is manufactured using a 3D printing process; • The sacrificial mold is manufactured using a 3D printing process based on photopolymerization of a thermosetting resin; • The sacrificial mold is manufactured by digital light processing (DLP), stereolithography (in English Stereolithography apparatus (SLA)) or by a process "of the liquid crystal display type" (in English Liquid Crystal Display (LCD)); • the second impression is a female shape made in the internal surface, the attachment surface of the sacrificial mold being a male shape able to fit, without play, into the female shape; • the second impression is formed within the first impression; • the sacrificial mold has a third impression, of female shape, made in the molding surface, the third impression having a plurality of segments forming a pattern; • the first imprint has a zero Gaussian curvature while the third imprint has a non-zero Gaussian curvature; • The sacrificial mold is made of a thermoplastic material preferably chosen from polyvinyl alcohol (PVA), polypropylene (PP), polyethylene (PE), polystyrene (PS), polycarbonate (PC), acrylonitrile butadiene styrene (ABS), nylon (PA), poly(ethylene terephthalate (PET), polyoxymethylene (PGM) and polyurethane (PU).

[0021] The invention further relates to a method for manufacturing a ceramic molding core, the method comprising the following steps: - provide an injection mold obtained by the process as previously described, - inject a ceramic paste into the injection mold until the first cavity and the sacrificial mold are filled, - Allow the ceramic paste to cool until an intermediate molding core is formed, this intermediate core being embedded in the sacrificial mold, - extract the intermediate core and the sacrificial mold from the injection mold, and dissolve the sacrificial mold, - cook the intermediate core to obtain the molding core.

[0022] The manufacturing process for a molding core according to the invention is particularly well-suited to molding cores with complex shapes. Indeed, it is no longer necessary to extract the complex, non-removable parts of the molding core in several stages, each corresponding to the geometric shape to be demolded for each individual part. On the contrary, the intermediate molding core, still embedded in the sacrificial mold, can be demolded and then separated from the sacrificial mold by dissolving the latter. This manufacturing process for a molding core is therefore simple and quick to implement, while also being reliable because it preserves the integrity of the molded shapes.

[0023] According to various features of the invention which may be taken together or separately: • the sacrificial mold is dissolved in a liquid chosen from water, acetone or an alkaline solution; • the dissolution of the sacrificial mold is achieved thermally; • The molding core is a ceramic core of turbomachine blades. Brief description of the figures

[0024] Other objects, features and advantages of the invention will become more apparent in the following description, made with reference to the accompanying figures, in which:

[0025] - Fig. 1 is a schematic view illustrating the different stages of a process of manufacturing an injection mold according to an embodiment of the invention,

[0026] - [Fig. 2] is a schematic view illustrating the different stages of a process of manufacturing a molding core according to an embodiment of the invention,

[0027] - [Fig. 3] is a schematic cross-sectional view of a metal mold used in the injection mold obtained by the manufacturing process according to an embodiment of the invention,

[0028] - [Fig. 4] is a schematic cross-sectional view of a sacrificial mold used in the injection mold obtained by the manufacturing process according to an embodiment of the invention,

[0029] - [Fig. 5] is a schematic cross-sectional view of an injection mold obtained by the manufacturing process according to an embodiment of the invention,

[0030] - [Fig. 6] is a schematic cross-sectional view of an injection mold obtained by the manufacturing process according to an embodiment of the invention after filling the mold with a ceramic paste and before demolding an intermediate molding core,

[0031] - [Fig. 7] is a side view of an intermediate molding core nested in a sacrificial mold,

[0032] - [Fig. 8] is a lateral view of the intermediate nucleus of [Fig. 7] after dissolution of the sacrificial mold;

[0033] - [Fig. 9a] is a 2D view of an internal surface of a sacrificial mold according to a first variant of implementation;

[0034] - [Fig. 9b] is a 2D view of an internal surface of a sacrificial mold according to a second variant of implementation;

[0035] - [Fig. 9c] is a 2D view of an internal surface of a sacrificial mold according to a third variant of implementation. Detailed description of the invention

[0036] The invention relates to a method 100 for manufacturing an injection mold 10 for a molding core 1.

[0037] The molding core 1 is typically a ceramic molding core 1 for making aircraft parts, in particular fixed high-pressure turbine blades.

[0038] As already mentioned in the preamble to the description, the fixed high-pressure turbine blades are hollow parts incorporating an internal cavity and a cooling system adapted to circulate ventilation air inside each of them. The geometry of these blades is constantly evolving and becoming increasingly complex in order to adapt to the structural changes in the cooling systems.

[0039] The molding core 1 is produced in the injection mold 10 suitable for implementing a ceramic injection molding (CIM) process. However, the CIM process is not a limiting factor within the scope of the present invention. We will return to this point later.

[0040] With reference to [Fig.1], the process 100 for manufacturing the injection mold includes a step 110 for manufacturing a sacrificial mold 15, made of plastic, having a molding surface 16 and a gripping surface 18.

[0041] The mold 15 is called a "sacrificial" mold because it is intended to be dissolved at the end of the process 200 for manufacturing a molding core, which will be described in more detail in the description relating to [Fig. 2]. Thus, the sacrificial mold 15 is capable of being dissolved, that is to say, it is soluble. Since a sacrificial mold 15 can only be used for the manufacture of a single molding core 1, each sacrificial mold 15 is therefore for single use only.

[0042] Preferably, the sacrificial mold 15 is made of a thermoplastic material, which makes it recyclable. Indeed, when the sacrificial mold 15 is made of such a plastic material, it can be dissolved thermally, and thus melted, and then used to manufacture a new sacrificial mold 15. This melting and recycling process can be repeated many times, which makes the use of a sacrificial mold 15 particularly inexpensive, in addition to the reduced cost of the material and manufacturing processes of such a plastic mold compared to a metal mold.

[0043] Even more preferably, the sacrificial mold 15 is made of a thermoplastic material preferably selected from polyvinyl alcohol (PVA), polypropylene (PP), polyethylene (PE), polystyrene (PS), polycarbonate (PC), acrylonitrile butadiene styrene (ABS), nylon (PA), polyethylene terephthalate (PET), polyoxymethylene (POM), and polyurethane (PU). These thermoplastic materials are easy to process and retain their properties when melted and recycled repeatedly. The mold sacrificial 15 can also be made from a mixture of thermoplastic materials, and therefore may not be recyclable.

[0044] The sacrificial mold 15 can be made from other materials, for example a mixture of organic substances.

[0045] In this regard, the sacrificial mold 15 can be manufactured by conventional processes such as injection molding, compression molding, thermoforming, blow molding or rotomolding.

[0046] That being said, advantageously the sacrificial mold 15 is manufactured by a 3D printing process. Manufacturing the sacrificial mold 15 by 3D printing offers a fast and inexpensive alternative to manufacturing metal molds. In this respect, 3D printing the sacrificial mold 15 used in process 100 according to the invention, carried out by indirect additive manufacturing (IAM), is particularly advantageous. Indeed, it reduces manufacturing time and cost compared to the aforementioned conventional processes, and a fortiori compared to the CIM process.

[0047] Indeed, although a sacrificial mold 15 produced by 3D printing, particularly by FAI, can only be used to produce a few dozen parts, compared to the several hundred to several thousand parts that can be manufactured using a metal mold, its manufacturing time is only a few days, whereas it takes several months (typically around 9 months) to manufacture a metal mold. Furthermore, the cost of a sacrificial mold 15 produced by 3D printing is less than ten euros, while that of a metal mold ranges from ten thousand to one hundred thousand euros. In addition, producing a sacrificial mold 15 by 3D printing requires only a few basic skills in computer-aided design and 3D printing, whereas producing a metal mold requires the services of a specialized mold manufacturer.Finally, and importantly, the fabrication of a sacrificial mold 15 using 3D printing overcomes the geometric limitations imposed by the CIM process and allows the production of parts with complex internal circuits. In the case of turbine blades, this ultimately results in improved cooling. Process temperatures can therefore be increased, making aircraft turbomachinery manufactured with such blades more efficient.

[0048] Even more advantageously, the 3D printing of the sacrificial mold is based on the photopolymerization of a thermosetting resin. For example, 3D printing can be implemented by Direct Light Processing (DLP), stereolithography (SLA), or liquid crystal display (LCD). These printing methods, based on the use of UV light to solidify a liquid resin layer by layer, offer the highest resolution available for 3D printing. and are therefore intended for high-precision applications. Preferably, 3D printing is performed using DLP or LCD. Indeed, these printing methods, which allow for the polymerization of an entire layer at a time, are faster than stereolithography. Furthermore, it improves the dimensional accuracy and surface quality of the printed sacrificial molds 15, and makes it possible to obtain sacrificial molds 15 with sufficient mechanical properties to withstand the real-world conditions (high temperature and high pressure) of a process such as injection molding, as preferred in this application for producing the molding core 1.

[0049] Still with reference to [Fig.1], the process 100 of manufacturing the injection mold includes a step 120 of manufacturing a metal mold 20 having an internal surface 21 having a first impression 22 and a second impression 24 in which the gripping surface 18 of the sacrificial mold 15 is able to fit together.

[0050] Step 120 of manufacturing the metal mold 20 can be carried out before, after or concurrently with step 110 of manufacturing the sacrificial mold 15. That being said, it is preferable to carry out these two steps concurrently in order to reduce the manufacturing time of the injection mold 10.

[0051] The metal mold 20 can be manufactured by conventional processes such as die casting, lost-wax casting, sand casting, forging, etc. The metal mold 20 can be made of a metal selected from steels or aluminum alloys, the choice of metal depending on the part to be manufactured. Preferably, the metal mold 20 is made of steel, which gives said metal mold 20 increased resistance to the pressure and temperature conditions used during the subsequent process 200 of manufacturing the molding core 1.

[0052] The internal surface 21 of the metal mold 20 is the surface used for molding the parts. As indicated above, the internal surface 21 has the first cavity 22 and the second cavity 24.

[0053] The first cavity 22 may be distinct from the second cavity 24, that is to say that the first cavity 22 is separate from the second cavity 24 or, in other words, that the first cavity 22 does not overlap with the second cavity 24. In this configuration, a separate extraction must be carried out for each of the parts of the molded part contained in said first 22 and second 24 cavities, the molded part being the assembly formed by the molding core 1 and the sacrificial mold 15. This configuration is therefore of limited interest.

[0054] Alternatively, the first cavity 22 and the second cavity 24 can be formed as a single unit, that is, the internal surface 21 is uninterrupted between the first cavity 22 and the second cavity 24, or, in other words, the first cavity 22 and the second cavity 24 are contiguous. In this configuration, the molded part can be extracted in a single operation.

[0055] Again with reference to [Fig.1], the process 100 of manufacturing the injection mold includes a step 130 of inserting the sacrificial mold 15 into the second cavity 24 of the metal mold 20 so as to obtain an injection mold 10 comprising the sacrificial mold 15 and the metal mold 20, the sacrificial mold 15 being removable.

[0056] Step 130 can only be carried out if manufacturing steps 110 and 120, respectively, of the sacrificial mold 15 and the metal mold 20, have been completed beforehand. This step of the manufacturing process 100 for the injection mold 10 therefore follows steps 110 and 120.

[0057] The second cavity 24 allows the sacrificial mold 15 to be housed and positioned within the injection mold 10. Indeed, once the sacrificial mold 15 has been inserted into the metal mold 20, there is no play between the sacrificial mold 15 and the second cavity 24 because the sacrificial mold 15 is nested in the second cavity 24 by means of its gripping surface 18. In this respect, the second cavity 24 is advantageously a female form made in the internal surface 21, while the gripping surface 18 is a male form suitable for fitting, without play, into the female form of the second cavity 24. Incidentally, as the second cavity 24 and the gripping surface 18 have complementary shapes, the sacrificial mold 15 cannot move involuntarily from its position, and therefore from the second cavity 24, although it is removable, and therefore demoldable.Once the sacrificial mold 15 has been inserted into the metal mold 20, it is fixed to the metal mold 20, such that the sacrificial mold 15 and the metal mold 20 have a common movement. In other words, the sacrificial mold 15 cannot be extracted from the injection mold 10 without a deliberate action by an operator, for example by exerting appropriate pressure or using an extraction tool, once the insertion step 130 has been carried out.

[0058] The method 100 for manufacturing the injection mold 10 according to the invention is therefore simpler and faster to implement than the injection mold manufacturing methods known in the prior art, this in particular for injection molds intended for molding cores 1 of complex shapes.

[0059] Indeed, to produce molding cores of complex shapes, it is no longer necessary to adapt the number of parts of the injection mold according to the complexity of the shape to be molded, thereby increasing the number of parts constituting the injection mold as the shape to be produced becomes more complex. The injection mold 10 used in the context of the invention comprises two molds, namely the metal mold 20 and the sacrificial mold 15. The complex-shaped parts to be produced, which are impossible to demold, can easily be produced using the sacrificial mold 15, which is made of plastic, via the molding surface 16. While the simple, easily demolded, one-piece parts, i.e., "drafted," can be produced using the metal mold 20, via the first 22 and second 24 cavities. This overcomes the difficulty related to the limited adaptability, i.e., transformability, of the metal molds 20.

[0060] Since the sacrificial mold 15 is removable, i.e., demoldable, the non-demoldable parts of the molded part using the injection mold 10 are not demolded directly but indirectly via the sacrificial mold 15. Indeed, the sacrificial mold 15 can be extracted from the second cavity 24 during demolding. Subsequently, since the sacrificial mold 15 is capable of being dissolved, the complex and non-demoldable parts of the intermediate molding core are exposed following the dissolution of the sacrificial mold 15.

[0061] Furthermore, the injection mold 10 is very easily modified after its manufacture, unlike a conventional metal mold. Indeed, post-manufacturing adaptations of the injection mold 10 can be implemented by modifying the sacrificial mold 15, which is faster, simpler, and less expensive to produce than a metal mold.

[0062] According to a particular embodiment illustrated in [Fig. 3], the second cavity 24 can advantageously be formed within the first cavity 22. Once the part is molded in the injection mold 10, this facilitates its extraction from the injection mold 10, even though it is still embedded in the sacrificial mold 15. Indeed, since the molded part and the sacrificial mold 15 are joined, they can be extracted by a single movement. As previously stated, the invention is by no means limited to such a configuration, although it is advantageous.

[0063] According to a particular embodiment illustrated in Figures 4, 5, 6, and 7, the sacrificial mold 15 comprises a third cavity 17, of female shape, formed in the molding surface 16. The third cavity 17 comprises a plurality of segments 17b forming a pattern 17a. More specifically, the third cavity 17 allows for the molding of complex shapes. In the embodiment illustrated in [Fig. 4], the third cavity 17 has a generally hollow tubular shape intended to receive a molding paste. In the illustrated example, the pattern 17a is in the form of a U comprising three segments 17b. Two of the segments 17b correspond to longitudinal arms of the U, one of the longitudinal arms being cut, and one of the segments 17b to a transverse arm of the U. The shape of the pattern 17a would make the molded part impossible to demold because it has an undercut.Indeed, motif 17a produces a cavity on the molded part, specifically at the U-shaped feature, which prevents direct demolding of the molded part. This is what is called an undercut.

[0064] In this regard, undercuts are not the only complex shapes that could hinder demolding.

[0065] Figures 9b and 9c, which are described below, show a side view of the sacrificial mold 15. In these configurations, the removal of the intermediate core 1' from the sacrificial mold 15 is upwards. As explained below, the intermediate cores made from these motifs 17 are not demoldable.

[0066] In [Fig. 9b], at least one of the segments 17b has a dimension an order of magnitude larger than the corresponding dimension of the first impression 22. In this case, the shape produced by the third impression 17 is much elongated compared to that produced by the first impression 22. If the ceramic paste were injected into an all-metal mold, as described in the prior art, the operator would be limited by the metal separating the motifs 17b when withdrawing the intermediate core (upwards). In this case, the intermediate core 1' is said to be non-removable from the mold.

[0067] In the example illustrated in [Fig. 9c], the motif 17a produces a cavity on the molded part which prevents direct demolding of the molded part. This cavity is formed by the transverse bar extending from one of the segments 17b, in particular the segment 17b located at the top in [Fig. 9c].

[0068] In the example of [Fig. 9a], although the shape produced by the third impression 17 is very fine compared to that produced by the first impression 22, the intermediate core made from motifs 17a, 17b is simple and can be demolded. Indeed, a difference in dimensions alone does not constitute complexity.

[0069] According to one embodiment, the first indentation 22 has zero Gaussian curvature, while the third indentation 17 has non-zero Gaussian curvature. An indentation with zero Gaussian curvature is an indentation whose surface is developable, so that it can be represented without shrinking or enlarging on a 2D plane. This is the case, for example, for cylinders, cones, etc. An indentation with non-zero Gaussian curvature is an indentation whose surface is not developable. In this case, the indentation cannot be represented without shrinking or enlarging at least one of its parts on a 2D plane. This is the case, for example, for truncated spheroids and other shapes exhibiting double curvatures and / or asymmetrical curvatures.In the aforementioned configuration, the fact that the third cavity 17 has a non-zero Gaussian curvature makes the demolding of the molded part very complex since the molded part cannot be extracted without being damaged.

[0070] Of course, a complex form may include different combinations of the aforementioned examples, these being by no means limiting.

[0071] The invention further relates to the method 200 of manufacturing the molding core 1 using the injection mold 10 obtained by the manufacturing method 100.

[0072] With reference to [Fig. 2] and according to a first aspect, the process 200 comprises a first step 210 of supplying an injection mold 10 obtained by the process 100 as previously described. Thus, the description relating to the characteristics of the injection mold 10 is repeated in its entirety here. As mentioned previously, the injection mold 10 comprises both a metal mold 20 and a sacrificial mold 15 nested within the metal mold 20 by means of the second cavity 24 and its gripping surface 18.

[0073] According to a second aspect, the process 200 comprises a step 220 of injecting a paste into the injection mold 10 until the first cavity 22 and the sacrificial mold 15 are filled. The paste is advantageously a ceramic paste when the molding core 1 to be manufactured is a ceramic core 1. Injection is a conventional step in the CIM process and is not described exhaustively in this description. However, it should be noted that in the CIM process implemented, a ceramic powder plasticized by a thermoplastic binder and, optionally, other additives, is injected into the closed injection mold 10 under high or medium pressure. This makes it possible to obtain a component with the desired shape by replicating the shape of the cavity in the injection mold 10.

[0074] The process 200 includes a third, also conventional, step 230 of cooling the paste until an intermediate molding core 1' is obtained. This intermediate core 1' is embedded in the sacrificial mold 15 and is made of an insoluble material by the process of dissolving the sacrificial mold 15. During this step, the paste cools and solidifies to give a raw intermediate core 1', as exemplified in [Fig. 8]. If the ceramic powder is plasticized with a thermoplastic binder, debinding and sintering steps can be carried out.

[0075] The process 200 includes a fourth step 240 of extracting the intermediate core 1' and the sacrificial mold 15 from the injection mold 10, then a fifth step 250 of dissolving the sacrificial mold 15.

[0076] During extraction 240, everything that is not metallic can be extracted. Thus, the intermediate core 1' and the sacrificial mold 15 remain together since they are not made of metallic material.

[0077] Furthermore, the extraction 240 of the intermediate core 1' and the sacrificial mold 15 is facilitated by using the injection mold 10 obtained by the process 100 according to the invention. Indeed, the internal surface 21 of the injection mold 10 comprises, on the one hand, the first cavity 22 which allows for the creation of simple draft shapes, and on the other hand, the second cavity 24 which accommodates the sacrificial mold 15, itself made of a plastic material which facilitates the creation of complex shapes, for example in undercuts.

[0078] During extraction 240, complex and therefore "fragile" shapes of the molded part are protected by the sacrificial mold 15. Furthermore, it should be noted that the molding surface 16 of the sacrificial mold 15 is not necessarily used to create complex shapes, as it can also be used to create simple shapes. That being said, in this case, the benefit of having a sacrificial mold 15 is more limited.

[0079] According to the invention, the sacrificial mold 15 is dissolved during a dissolution step 250. Dissolution 250 removes the plastic material from the sacrificial mold 15 located around the intermediate core 1', thereby revealing the shapes obtained by the third cavity 17. The sacrificial mold 15 is thus destroyed once the safe extraction 240 has been carried out, resulting in an intact intermediate core 1' with increased shaping accuracy.

[0080] Dissolution 250 can advantageously be carried out in a liquid chosen from water, acetone, or an alkaline solution, which is practical, quick to implement, and economical. Indeed, dissolution 250 can be carried out by immersion in a bath of appropriate composition depending on the plastic material from which the sacrificial mold 15 is made. However, certain solvents can alter the volume of the sacrificial mold 15 depending on the plastic used. The sacrificial mold 15 may, for example, swell or expand, which can generate stresses on the intermediate core 1' and potentially cause damage to the molding core 1 to be manufactured.

[0081] Dissolution 250 can also be carried out thermally. Although it is longer and requires a furnace, thermal dissolution or decomposition can be advantageous when the use of solvents is unsuitable or in the case of a sacrificial mold 15 made of thermoplastic. Indeed, as mentioned earlier in the description, thermoplastics can be melted and recycled, some as many times as desired, without compromising their resistance to pressure and temperature during the CIM process. This is particularly advantageous as it allows for the recycling of the plastic material. In this regard, while the sacrificial mold 15 can be made from a mixture of plastics, it is advantageous for it to be made of a single material.

[0082] Thus, the use of a more efficient process according to the invention is also advantageous for reducing the applicant's environmental footprint. Indeed, it makes it possible to increase and optimize manufacturing, production, and / or repair capacity and, consequently, to significantly reduce associated greenhouse gas emissions. This optimization also makes it possible to decrease raw material consumption. It makes it possible to significantly decrease the number of discarded molds that may be difficult to recycle. Furthermore, the solution It also has the advantage of reducing its energy input (water, electricity, ...) and / or the use of any chemicals contrary to environmental standards and regulations in force.

[0083] Furthermore, dissolution 250 does not affect the intermediate core 1' because it is made of a stable material, that is to say, one whose integrity is not altered by the aforementioned dissolution 250. In this case, the intermediate core 1' is indeed made of a ceramic material.

[0084] Once the sacrificial mold 15 has dissolved, the manufacturing process 200 also includes a baking step 260 of the intermediate core 1' in order to obtain a molding core 1 with the desired functional and mechanical properties. In the figures shown, the molding core 1 is typically suitable for high-pressure turbine blades.

[0085] The configurations shown in the cited figures are only possible examples, by no means limiting, of the invention which on the contrary encompasses the variants of designs within the reach of the person skilled in the art.

Claims

Demands

1. A method (100) for manufacturing an injection mold (10) for a molding core (1), the method (100) comprising the following steps: - manufacturing (110) a sacrificial mold (15), made of plastic, having a molding surface (16) and a gripping surface (18), the sacrificial mold (15) being able to be dissolved, - manufacturing (120) a metal mold (20) having an internal surface (21) having a first cavity (22) and a second cavity (24) in which the gripping surface (18) of the sacrificial mold (15) is able to fit, - inserting (130) the sacrificial mold (15) into the second cavity (24) of the metal mold (20) so as to obtain an injection mold (10) comprising the sacrificial mold (15) and the metal mold (20), the sacrificial mold (15) being removable.

2. A manufacturing method (100) according to claim 1, wherein the sacrificial mold (15) is manufactured by a 3D printing process, preferably based on a photopolymerization of a thermosetting resin.

3. Method (100) of manufacturing according to any one of claims 1 or 2, wherein the second cavity (24) is a female form made in the internal surface (21), the gripping surface (18) of the sacrificial mold being a male form capable of fitting, without play, into the female form.

4. Method (100) of manufacturing according to any one of claims 1 to 3, wherein the second cavity (24) is formed in the first cavity (22).

5. A manufacturing method (100) according to any one of claims 1 to 4, wherein the sacrificial mold (15) has a third cavity (17), of female shape, made in the molding surface (16), the third cavity (17) having a plurality of segments (17b) forming a pattern (17a).

6. Method (100) of manufacturing according to claim 5, wherein the first impression (22) has a zero Gaussian curvature while the third impression (17) has a non-zero Gaussian curvature.

7. A method (100) of manufacturing according to any one of claims 1 to 6, wherein the sacrificial mold (15) is made of a preferably selected thermoplastic material among polyvinyl alcohol (PVA), polypropylene (PP), polyethylene (PE), polystyrene (PS), polycarbonate (PC), acrylonitrile butadiene styrene (ABS), nylon (PA), poly(ethylene terephthalate (PET), polyoxymethylene (POM) and polyurethane (PU).

8. A method (200) for manufacturing a ceramic molding core (1), the method (200) comprising the following steps: - providing (210) an injection mold (10) obtained by the method (100) according to any one of the preceding claims, - injecting (220) a ceramic paste into the injection mold (10) until the first cavity (22) and the sacrificial mold (15) are filled, - allowing the ceramic paste to cool (230) until an intermediate molding core (1') is obtained, this intermediate core (1') being embedded in the sacrificial mold (15), and - extracting (240) the intermediate core (1') and the sacrificial mold (15) from the injection mold (10), and dissolving (250) the sacrificial mold (15), - firing (260) the intermediate core (1') so as to obtain the molding core (1).

9. A method (200) according to claim 8, wherein the dissolution (250) of the sacrificial mold (15) is carried out in a liquid selected from water, acetone or an alkaline solution, and / or by thermal means.

10. Method (200) according to any one of claims 8 to 9, wherein the molding core (1) is a ceramic core for the manufacture of turbomachine blades.

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