Process of densification and consolidation of an element by isostatic pressing

Abstract

The invention relates to a method for consolidating and densifying by cold isostatic compression an element (10) preformed from at least one powder. According to the invention, the CIPW method comprises: a bagging step (S2) of the element during which the element is immersed in a pressure-transmitting material (12) within a bag (14), a sealing step (S4) during which the bag is hermetically sealed, a compression step (S6) during which the sealed bag is compressed by isostatic compression. Figure for abstract: Fig. 2

Description

Title of the invention: Method for densifying and consolidating an element by isostatic pressing Technical field

[0001] The present invention generally relates to a method of densifying and consolidating an element.

[0002] More particularly, the method is implemented by isostatic pressing of a preformed element from at least one metal powder.

[0003] The invention finds a particularly advantageous application in the production of objects of complex shape and / or three dimensions, preformed from metal powder or several powders for a multi-material or a metal matrix composite, or "mmc" according to the commonly used acronym. Technological background

[0004] Additive manufacturing is a process for creating three-dimensional elements from a digital file containing a model of the element to be produced. This process consists of the layer-by-layer manufacturing of the element from plastic, metal or ceramic and allows the production of elements with complex shapes.

[0005] This additive manufacturing can be carried out from a bath of powders containing at least one metal. But the element obtained by such a process is extremely fragile. The fragility of the element obtained is all the greater as the shape of the element is complex.

[0006] Consequently, there is a need for methods for consolidating and densifying a complex-shaped element obtained from powder. However, the difficulties inherent in the instability of an object made from powder make the implementation of such methods complex.

[0007] One of the known solutions to this problem consists of carrying out additive manufacturing of the complex-shaped element to be produced not from a powder bath but from metal wires incorporating a polymer matrix. The complex-shaped element produced by this method must, however, then be consolidated and densified. The element must also undergo removal of the polymer matrices and other additives integrated into the metal wires. The consolidation and densification of the complex-shaped element as well as the removal of the polymer matrices are carried out by heat treatment (which leads to the formation of alloys in the case of several metal powders) under vacuum or in a neutral atmosphere to avoid the formation of oxides, which makes such a process complex and expensive. In addition, the removal of the polymer matrix during heat treatment may be imperfect, leading to the presence of carbon residues or even the survival of polymer chains after the heat treatment. Porosity problems may also arise as a result of the removal of the polymer matrix during heat treatment. Finally, this process does not allow the creation of an object from a powder bath containing at least one metal.

[0008] Another known solution, making it possible to avoid the use of a polymer matrix within metal wires, consists of carrying out a laser beam treatment of the element obtained by additive manufacturing from a powder bath containing at least one metal. Exposure to the laser beam of the powder grains constituting the complex-shaped element causes them to fuse and makes it possible to obtain the consolidation and densification of the element. However, the heat treatment induced by exposure of the powder grains to the laser beam leads to the formation of oxides and / or metal alloys on the surface and within the element. To limit the formation of oxides, the treatment by exposure to a laser beam must be carried out in a vacuum or in a neutral atmosphere. However, the formation of alloy cannot be completely avoided during such a consolidation and densification process.Moreover, implementing such a process is costly, complex and time-consuming. Summary of the invention

[0009] The aim of the invention is to propose a solution to these problems and to make it possible to consolidate and densify a preformed element by additive manufacturing from a powder bath without causing the formation of metal oxides and alloys within or on the surface of said element.

[0010] The invention relates more specifically to a method, called CIPW "Cold Isostatic Pressure Welding", for consolidating and densifying a preformed element from at least one powder, the method comprising: a step of bagging the element during which the element is immersed in a pressure-transmitting material within a bag, a sealing step during which the bag is hermetically sealed, a compression step during which the sealed bag is compressed by isostatic compression.

[0011] The proposed consolidation and densification process makes it possible to produce, from at least one powder, elements having sufficient density and solidity without resorting to complex and expensive heat treatment. When the at least one powder is a metal powder, the process also makes it possible to avoid the formation of oxides and alloys, on the surface and within the element.

[0012] This CIPW process allows the consolidation and densification of metal matrix composites comprising a thermo-degradable material because it is produced at low temperature, for example at room temperature or at a temperature close to room temperature.

[0013] This CIPW process leads to the consolidation and densification of multi-materials, of at least two metal powders with very different properties, such as their melting temperatures; thanks to the welding of the grains, initiated by their work hardening.

[0014] This CIPW process allows the adjustment of the densification to obtain a more or less porous element adapted to the intended application.

[0015] This CIPW process makes it possible to avoid the deoxidation treatment of the oxide layer depending on the chemical composition and the size of the grains. Welding is all the more effective due to work hardening inducing significant cracking of this oxide layer.

[0016] The use of a pressure transmitting material allows for a homogeneous, isotropic transmission of the pressure applied to the bag to the element, which allows for the consolidation and densification of the element without damaging it.

[0017] Other advantageous and non-limiting characteristics of the method according to the invention, taken individually or in all technically possible combinations, are the following: the element is of complex shape. the element is preformed from at least one metal powder. the at least one metal powder used to preform the element comprises one or more different metals, or a metal matrix composite powder or a multi-material powder comprising at least two metals, and is preformed from at least two powders or from a powder resulting from the mixture of the two. the element is preformed by additive manufacturing or by molding or by compression, the method further comprises a removal step during which the pressure-transmitting material covering the element is removed by immersion in a liquid, subjected to ultrasound to accelerate its removal. the liquid used during the cleaning step includes water, the compression step is carried out at room temperature. the hardness of the pressure transmitter material is greater than the hardness of the element, the grain size of the pressure transmitter material is greater than or equal to 10 nm and less than or equal to 10 mm. The pressure transmitting material is sugar or salt.

[0018] The various features, variations and embodiments of the invention may be combined with each other in various combinations to the extent that they are not incompatible or mutually exclusive. Brief description of the figures

[0019] Furthermore, various other characteristics of the invention emerge from the appended description given with reference to the drawings which illustrate non-limiting forms of embodiment of the invention and where:

[0020] [Fig-1] is a functional diagram of a bag 14 containing an element 10 and a pressure transmitting material 12, and to which the CIPW process described in [Fig.2] can be applied.

[0021] [Fig.2] is a summary diagram of a consolidation and densification process of an element 10 according to an embodiment in accordance with the invention. The steps shown in dotted lines are optional.

[0022] It should be noted that in these figures the structural and / or functional elements common to the different variants may have the same references.

[0023] Various other modifications may be made to the invention within the scope of the appended claims. Process

[0024] The invention relates to a CIPW method for consolidating and densifying an element 10 shown in [Fig.l]. The element 10 is preformed from at least one powder, here a single powder. The method, shown in [Fig.2], comprises the following steps: - a bagging step S2 of the element 10 during which the element 10 is immersed in a pressure-transmitting material 12 within a bag 14, - a sealing step S4 during which the bag 14 is hermetically sealed, - a compression step S6 during which the sealed bag 14 is compressed by isostatic compression.

[0025] In the embodiment considered, the element 10 is a part of simple or complex shape. The element 10 may be two-dimensional or three-dimensional. By two-dimensional, it is understood that the element 10 has a third dimension, for example a height, very small compared to the other two dimensions, for example a length and a width. A pellet of small thickness compared to its radius is for example a two-dimensional object.

[0026] By complex shape, it is understood that the element 10 is defined by a large number of parameters, for example greater than 3, such as for example, two radii, a height, an angle and a mathematical equation between the two radii, the height and the angle. For example, a pellet is not an object of complex shape if it does not have surface details, such as for example reliefs, and a three-dimensional grid is a complex shape.

[0027] By preformed, it is understood that the element 10 is produced prior to the bagging step S2 by additive manufacturing or by molding or by compression.

[0028] Preferably, the element 10 is preformed from at least one metal powder.

[0029] By metal powder is meant a pure metal or a metal alloy

[0030] Alternatively, element 10 comprises several metals or is a matrix composite metallic or a multi-material comprising at least two metals, formed from at least two powders or from the powder of the mixture of metals.

[0031] During the bagging step S2, the element 10 is immersed in a pressure-transmitting material 12 within a bag 14. During the bagging step S2, the element 10 is covered by the pressure-transmitting material 12 such that, within the bag 14, the element 10 is not in contact with the inner surface of the bag 14.

[0032] The pressure transmitting material 12 is chosen to conform to the shape of the element 10 and allow for uniform transmission of pressure from the bag 14 to the element 10 when said pressure is applied to the bag 14. The pressure transmitting material 12 is also chosen to be soluble or fusible, abundant or common, natural or environmentally friendly, non-toxic or food grade, and not to induce a chemical reaction between the pressure transmitting material 12 and the material constituting the element 10 and between the pressure transmitting material 12 and the material constituting the interior surfaces of the bag 14. Preferably, the pressure transmitting material 12 is sugar or salt, for example refined sugar or salt flour. By sugar is meant table sugar and by salt is meant sodium chloride.Alternatively, the pressure transmitting material 12 is a naturally occurring inorganic compound, e.g., potassium chloride or magnesium chloride, or a synthetic compound, e.g., potassium chlorate, sodium chlorate, potassium perchlorate, sodium perchlorate, potassium hydroxide, sodium hydroxide, or a naturally occurring organic compound, e.g., corn flour.

[0033] In the embodiment considered, the pressure transmitting material 12 has a hardness preferably greater than the hardness of the element 10. Advantageously, this allows good transmission of the pressure applied to the bag 14 to the element 10 and makes it possible to avoid the incrustation of the pressure transmitting material 12 on the surface of the element 10. Advantageously, the greater hardness of the pressure transmitting material 12 compared to that of the element 10 makes it possible to carry out the work hardening of the surface of the element 10 during the compression step S6 described below. Advantageously, this also makes it possible, when the element 10 is made for example of aluminum, to break the layer of aluminum oxide covering on the surface aluminum grains during grain welding during compression step S6.

[0034] Preferably, the grain size of the pressure transmitting material 12 is equal to or greater than 10 nm and less than or equal to 10 mm. Advantageously, the fineness of the grains of the pressure transmitting material 12, adapted to the fineness of the details of the preformed element, allows homogeneous transmission of the pressure applied to the bag 14 to the element 10 and not to damage the element 10.

[0035] The bag 14 is for example made of polymeric material such as polyethylene or of a biodegradable material based on starch.

[0036] During the sealing step S4, the bag 14 is hermetically sealed so that there can be no leakage from the inside to the outside of the bag 14 of the pressure transmitting material 12. During the hermetic sealing of the bag 14, the air can be previously evacuated from the bag 14 to avoid the formation of blisters or porosities within the element 10. The sealing step S4 also makes it possible to prevent liquid from being able to penetrate into the bag 14 during the compression step S6 described below.

[0037] According to the embodiment considered, during the compression step S6, the bag 14 is subjected to an isostatic pressing process. During the isostatic pressing process, the pressure is, for example, equal to or greater than 10 MPa and less than or equal to 600 MPa. The isostatic pressing process is carried out using a liquid compression fluid such as water, oil or a glycol mixture. During the compression step S6, the bag 14 is immersed in the liquid contained in a tank subjected to high pressure. The isostatic pressure applied to the surfaces of the tank is transmitted to the liquid which isostatically transmits the isotropic forces to the bag 14. The isotropic forces applied to the bag 14 are in turn transmitted to the element 10 via the pressure transmitting material 12.

[0038] According to the embodiment considered, the isostatic pressing method used during the compression step S6 is a cold isostatic pressing method. By cold isostatic pressing, it is understood that the isostatic pressing method is carried out at low temperature, preferably at room temperature or at a temperature close to room temperature, for example, at a temperature T such that \ T-Tmnh\ <50 C with Tamb the room temperature.

[0039] Advantageously, the CIPW consolidation and densification process makes it possible to consolidate and densify a part, for example the element 10. At the microscopic level, cold welding of the grains of the element 10 is thus observed, or "cold welding" according to the commonly used English term. Advantageously, the use of the pressure-transmitting material 12 makes it possible to preserve the integrity of the element 10, particularly when the latter is of complex shape, and thus to avoid its destruction during the compression step S6. The process, CIPW "cold isostatic pressure welding" can be carried out as described previously or as a pretreatment prior to heat treatment or before modifying the geometry of the part, for example by removing and / or adding material.

[0040] Advantageously, the CIPW consolidation and densification process makes it possible to produce metallic materials or metal matrix composites or multi-materials of several metals and / or of complex shape, without resorting to heat treatment. The absence of heat treatment makes it possible to eliminate the energy cost linked to the consolidation heat treatment and, consequently, makes it possible to reduce the manufacturing cost linked to the production of parts of complex shape from at least one powder containing at least one metal. Advantageously, carrying out the densification and consolidation process at room temperature or at a temperature close to room temperature makes it possible to avoid the formation of alloys and oxides. In the case of the use of several metals in the production of the element 10, this makes it possible to obtain true composites.Advantageously, carrying out the consolidation and solidification process at room temperature or at a temperature close to room temperature makes it possible to apply the process to composites comprising heat-sensitive materials.

[0041] Advantageously, the CIPW consolidation and densification process is eco-compatible. On the one hand, due to the absence of heat treatment in the consolidation and densification process in the production of the element 10. On the other hand, due to the use of natural or food-grade material, for example sugar, as pressure-transmitting material 12, the consolidation and densification process has a low ecological impact during the elimination S8 of the pressure-transmitting material 12 described below. Due to the use of natural or food-grade material as pressure-transmitting material 12, the consolidation and densification process is also biocompatible. Such a process can therefore be advantageously used in the manufacture of objects intended to be in direct contact, whether brief or prolonged, with the tissues and internal fluids of a living organism.

[0042] Preferably, the compression step S6 is followed by an elimination step S8. During the elimination step S8, the bag 14 is opened and then the element 10 covered with the pressure-transmitting material 12 is removed from the bag 14 and immersed in a liquid, for example water, subjected to ultrasound. Advantageously, the elimination of the pressure-transmitting material 12 from the surface of the element 10 by immersion in a liquid subjected to ultrasound makes it possible to accelerate its elimination S8. Preferably, the elimination step S8 is carried out at room temperature or a temperature close to room temperature.

[0043] Advantageously, the use of salt, for example table salt or sugar, for example table sugar, as pressure transmitting material 12 facilitates the removal of the pressure transmitting material 12 by its dissolution during the removal step S8, which makes it possible to avoid the element 10 being damaged during the removal step S8 and makes it possible to avoid the presence of residues on the surface of the element 10 after the removal step S8.

[0044] Advantageously, the use of water for the elimination of the pressure transmitting material 12 during the elimination step S8 reinforces the eco-compatible dimension of the consolidation and densification process.

[0045] The invention also provides a computer program product comprising one or more sequences of instructions which are accessible to a processor and which, when executed by said processor, cause said processor to implement a method according to one of the possible embodiments, for example, a method as described above with reference to [Fig.2].

[0046] The invention also proposes a non-transitory information storage medium, in which one or more sequences of instructions accessible to a processor are stored and which, when executed by said processor, cause said processor to implement a method according to one of the possible embodiments.

[0047] It should be noted that all or part of the operations of the various methods in which the above embodiments can be understood by those skilled in the art can be accomplished by giving instructions to the relevant hardware through the computer program, and the computer program can be stored in the computer-readable storage medium, which can include, but is not limited to: a read-only memory (ROM), a random access memory (RAM), a disk, a CD or a memory unit having a similar function.

[0048] Of course, the various features, variants and embodiments of the invention may be combined with each other in various combinations to the extent that they are not incompatible or mutually exclusive. Variants

[0049] The present invention is in no way limited to the embodiment described and shown, but those skilled in the art will be able to provide any variant in accordance with the invention.

[0050] In a variant of the invention, the element 10 is a multi-material comprising a metal and another non-metallic material.

[0051] In a variant of the invention, the element 10 is a metal matrix composite comprising a metal and another non-metallic material.

[0052] In another variant of the invention, the compression step S6 is carried out with a gaseous compression fluid. The gas used is, for example, argon.

[0053] In another variant of the invention, the liquid used during the removal step S8 comprises an organic solvent, for example ethanol, benzene, acetone, dimethyl sulfoxide or ether.

[0054] In another variant of the invention, the removal step S8 is carried out at a temperature above ambient temperature, for example by heating the liquid in which the element 10 is immersed. Advantageously, carrying out the removal step S8 at a temperature above ambient temperature makes it possible to increase the solubility of the pressure-transmitting material 12 and, consequently, facilitates its removal from the surface of the element 10.

Claims

Claims

1. Method for consolidating and densifying by cold isostatic compression an element (10) preformed from at least one powder, the method comprising: - a bagging step (S2) of the element (10) during which the element (10) is immersed in a pressure-transmitting material (12) within a bag (14), - a sealing step (S4) during which the bag (14) is hermetically sealed, - a compression step (S6) during which the sealed bag (14) is compressed by isostatic compression.

2. A consolidation and densification method according to claim 1, wherein the shape of the element (10) is defined by a number of geometric parameters greater than 3.

3. A consolidation and densification method according to claim 1 or 2, wherein the element (10) is preformed from at least one metal powder.

4. A consolidation and densification method according to claim 3, wherein the element (10) comprises several metals or is a metal matrix composite or a multi-material comprising at least two metals, and is preformed from at least two powders or from a powder resulting from the mixture of the two.

5. Consolidation and densification method according to one of claims 1 to 4, in which the element (10) is preformed by additive manufacturing or by molding or by compression.

6. A consolidation and densification method according to one of claims 1 to 5, further comprising a removal step (S8) during which the pressure-transmitting material (12) covering the element (10) is removed by immersion in a liquid, subjected to ultrasound to accelerate its removal.

7. A consolidation and densification method according to claim 6, wherein the liquid used during the cleaning step (S8) comprises water.

8. Consolidation and densification method according to one of claims 1 to 7, during which the compression step (S6) is carried out at room temperature.

9. A consolidation and densification method according to one of claims 1 to 8, wherein the hardness of the pressure transmitting material (12) is greater than the hardness of the element (10).

10. Consolidation and densification method according to one of claims 1 to 9, in which the particle size of the pressure transmitting material (12) is greater than or equal to 10 nm and less than or equal to 10 mm.

11. A consolidation and densification method according to one of claims 1 to 10, wherein the pressure transmitting material (12) is sugar or salt.

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