PROCESS FOR MANUFACTURING RAW PARTS MADE OF CERAMIC AND / OR METALLIC MATERIALS USING ADDITIVE PROCESSES

Abstract

------ METHOD FOR MANUFACTURING RAW PARTS MADE OF CERAMIC AND / OR METALLIC MATERIAL BY THE TECHNIQUE OF ADDITIVE PROCESSES According to the invention, before producing the first layer: the construction platform is covered with a support sheet capable of being urged against it by forming a rigid and fixed surface for receiving the successive layers capable of retaining the successive layers formed thereon; and said support sheet is pressed against said construction platform by suction; the raw part is formed by the technique of additive processes; and once the raw part has been thus formed, the suction is removed in order to detach from said platform said support sheet on which the raw part is located with the part of the photocurable composition which has not been cured; said part of uncured photocurable composition is removed;and said raw part is detached from said support sheet, characterized in that the support sheet is a polymer sheet having a thickness of 0.05 to 5 mm and a flatness of less than 70% of the thickness of a layer, said support sheet being deformable to allow, once the suction is removed, the raw part to be detached therefrom by applying a stress to said sheet so as to deform it in order to release the raw part. Figure to be published with the abstract: Figure 1;

Description

Title of the invention: METHOD FOR MANUFACTURING RAW PARTS MADE OF CERAMIC AND / OR METALLIC MATERIAL USING ADDITIVE PROCESS TECHNIQUE

[0001] The present invention relates to a method of manufacturing, by the technique of additive processes, a raw part made of at least one material chosen from ceramic materials and metallic materials.

[0002] The technique of additive processes, also called stereolithography, generally comprises the following steps, to obtain these raw parts: - a computer model of the part to be manufactured is constructed by computer-aided design, the dimensions of which are slightly larger than those of the part to be manufactured in order to allow for shrinkage of the ceramic or metallic material during the manufacture of the part; and - the part is manufactured using additive processes, a technique according to which: - a first layer of a photocurable composition comprising at least one ceramic or metallic material, at least one photocurable monomer and / or oligomer, at least one photoinitiator and, where appropriate, at least one plasticizer and / or at least one solvent and / or at least one dispersant is formed on a rigid support; - the first layer of the photocurable composition is cured by irradiation (by laser scanning of the free surface of said layer or by diode projection system) according to a pattern defined from the model for said layer, forming a first stage; - a second layer of the photocurable composition is formed on the first stage; - the second layer of the photocurable composition is hardened by irradiation according to a pattern defined for said layer, forming a second stage, this irradiation being carried out as for the first layer; - optionally, the above steps are repeated to obtain the part in its raw state.

[0003] Then, as indicated above, to obtain the finished part, the green part is cleaned to remove the uncured composition; the cleaned green part is debonded; and the cleaned and debonded green part is sintered to obtain the part finished.

[0004] In a pasty manufacturing process, the photocurable composition is in the form of a paste whose viscosity can vary in particular from 1 Pa.s to infinity for a zero shear rate, and the rigid support is a working platform supporting the different layers of the part being constructed as well as the paste and each of the layers is generally formed by lowering the working platform and spreading a predefined thickness of paste. A reserve of paste is stored in tanks which are automatically emptied of a predefined quantity of paste for each layer using a piston. This creates a bead of paste to be spread on the upper layer of the part being manufactured which will have been lowered previously by the working platform.Each layer is usually spread by scraping by a scraper blade which sweeps the working surface of the working platform, for example by advancing in a straight horizontal direction.

[0005] Another manufacturing process using the pasty / creamy route is described in patent application FR3116461 which uses an applicator system with a suspension reserve supplied by an external reservoir, the stacking of layers taking place in a tank which fills with suspension each time a layer is formed.

[0006] In liquid manufacturing, the photocurable composition is in the form of a low viscosity suspension. - In a first embodiment by the liquid route, the rigid support is a platform which is lowered into a bath of the photohardenable suspension to cover it with a layer of said suspension, a layer which is then hardened by irradiation as indicated above. On this first layer, each of the other layers is then successively formed by stepwise lowering of the platform into the bath so that the upper level of the part being formed is lowered below the free surface of the photohardenable suspension for the formation of the layer in question, which is then irradiated. - In a second embodiment by the liquid route, the photohardenable suspension is contained in a transparent bottom tank for irradiation, and the part is held on a rigid support which is a platform raised step by step. Thus, we start by curing a base layer, then the platform is raised one step to allow the suspension to constitute a new layer which is then cured, the operation being repeated for each layer. - In a third embodiment by the liquid route, the photocurable suspension is spread in a layer on a transparent film for irradiation, the film being able to unroll horizontally. The part is formed on a rigid platform that descends to come into contact with the layer that is cured by irradiation through the film. A new segment of film coated with a new photocurable layer is then unrolled and the operation is repeated until the part is built.

[0007] It is important that there is a good connection between the construction surface, in other words the rigid working platform (upper face of the working platform in the case of the pasty route and the first embodiment mentioned above in the liquid route, and lower face of the platform in the case of the second and third embodiments mentioned above in the liquid route), and the part which is constructed by stacking the layers.

[0008] A support is therefore placed between the rigid work platform and the part under construction.

[0009] The choice of the support for building the part is crucial both for printing the part and for its recovery. The support must in fact meet several opposing constraints: • adhere sufficiently to the rigid work platform to ensure the stability of the parts; • have sufficient flatness to allow printing of thin layers; • be easily removable from the rigid working platform after printing; and • facilitate the detachment of the raw part so as not to damage them after printing.

[0010] Currently, the printing of ceramic parts by stereolithography takes place on a magnetic support placed on the construction platform and held in place by magnetization. While this system makes it possible to obtain very good adhesion to the working platform, this system does not make it possible to respect the three other constraints stated above for parts with thin walls, typically less than 1 mm, or parts built in thin layers, typically with a thickness of 25 to 30 μm.

[0011] The flatness of the magnetic supports is of the order of 50 pm, which is insufficient for construction in thin layers with a thickness of 25 to 30 pm. In addition, a lack of flatness implies irregular attachments to the support depending on the position of the parts on the platform.

[0012] Furthermore, the rigidity of magnetic supports and their roughness make it difficult to detach the support from the platform and to detach the parts from the support. Thin-walled parts present a high risk of damage during the detachment phase, which makes them unusable.

[0013] The difficulty of detaching thin-walled parts also requires reducing the number of parts that can be printed at the same time on the same printer, which reduces their productivity.

[0014] To solve this problem, the applicant company sought a solution enabling the construction of thin-layer parts as well as thin-walled parts while guaranteeing damage-free detachment of the parts and allowing optimal filling of the construction platform.

[0015] To this end, the present invention relates to a method of manufacturing, by the technique of additive processes, a raw part made of at least one material chosen from ceramic materials and metallic materials,

[0016] method according to which layers based on a photocurable composition comprising said ceramic and metallic material(s) in powder form and an organic part comprising at least one photocurable monomer and / or oligomer and at least one photoinitiator are successively caused to harden by irradiation according to a pattern defined for each layer, the first layer being formed on a construction platform, and each other layer being formed and then caused to harden in contact with the preceding layer,

[0017] method according to which: - before making the first layer: • the construction platform is covered with a support sheet capable of being pressed against it, forming a rigid and fixed surface for receiving the successive layers capable of retaining the successive layers formed thereon; and • said support sheet is pressed against said construction platform by suction; - the raw part is formed using additive processes; and - once the raw piece is thus formed, the suction is removed in order to detach of said platform said support sheet on which is located the green part with the part of the photocurable composition which has not been cured; - said uncured part of photocurable composition is removed; and - said raw part is detached from said support sheet,

[0018] characterized in that the support sheet is a polymer sheet having a thickness of 0.05 to 5 mm and a flatness of less than 70% of the thickness of a layer, preferably less than 40% of the thickness of a layer, said support sheet being deformable to allow, once the suction is removed, the raw part to be detached therefrom by applying a stress to said sheet so as to deform it in order to release the raw part.

[0019] The flatness of the carrier sheet can be defined as the difference in height between the lowest point of the sheet and its highest point, when the sheet is placed on a vertical support.

[0020] For example, in the case of building a part using layers with a thickness of between 25 and 30 pm, the flatness of the support sheet must be less than 17.5 pm, preferably less than 10 pm. It may have, for example, a flatness of 8 pm.

[0021] The support sheet may have a Young's modulus of 2.5 to 80 GPa, preferably 2.5 to 15 GPa.

[0022] The carrier sheet may be a biaxially oriented polyethylene terephthalate sheet, a polyetherimide sheet, a polyamide sheet or a polyolefin sheet.

[0023] A photocurable composition of semi-liquid consistency can be used, which is spread layer by layer on the building platform, the layers being irradiated from above,

[0024] or a suspension photocurable composition can be used,

[0025] the platform being lowered step by step into the suspension to form the successive layers irradiated from above, or

[0026] the platform being arranged at a distance corresponding to the thickness of a layer from the bottom of a photohardenable composition tank with a transparent bottom for irradiation and raised at each layer formation, the layers being irradiated from below each time; or

[0027] the platform coming into contact with each layer formation with a suspension layer applied to a segment of a transparent film which is unrolled horizontally to present a new segment at each layer formation, the layers being irradiated from below each time.

[0028] By photocurable composition of semi-liquid consistency is meant a suspension having a viscosity between 0.5 and 100 Pa.s for a range of shear gradients between 5 and 50 s1.

[0029] It is possible to use, as a construction platform, a perforated or porous flat plate made of a rigid material, such as ceramic, metal or plastic, the free face of which is covered by the support sheet and which is connected, by its opposite face, to a vacuum pump or a vacuum generator, which is put into operation to press the support sheet onto the free face of the platform, forming the rigid and fixed surface for receiving the successive layers of photohardenable composition, and put out of operation to detach said support sheet from said platform.

[0030] In particular, it is possible to use a perforated plate whose perforations are in particular in the form of holes and slots connected to the vacuum pump or to the vacuum generator, arranged to ensure, when the latter is in operation, the plating of the support sheet.

[0031] It is possible to use, as a construction platform, a receptacle, in particular made of metal or plastic, of flat shape, the bottom of which has perforations connected to a vacuum pump and which receives a grid, in particular made of metal, the support sheet being applied to the free edge of the receptacle and to the grid, said vacuum pump being put into operation to press said support sheet onto the free edge of the receptacle and onto the grid, forming the rigid and fixed surface for receiving the successive layers of photohardenable composition, and put out of operation to detach said support sheet from said platform.

[0032] A vacuum of 13.33 Pa - 10 10 Pa (0.133 mbar - 10 12mbar) can be generated.

[0033] The present invention also relates to a manufacturing machine by the technique of additive processes of green parts made of a material chosen from ceramic materials and metallic materials, according to which layers based on a photohardenable composition comprising said ceramic and metallic material(s) in powder form and an organic part comprising at least one photohardenable monomer and / or oligomer and at least one photoinitiator are successively caused to harden by irradiation according to a pattern defined for each layer, the first layer being formed on a construction platform, and each other layer being formed and then caused to harden on the preceding layer,

[0034] the machine comprising means for suctioning against said construction platform a support sheet intended to cover it before the production of the first layer, forming a surface for receiving the successive layers, capable of retaining thereon the successive layers formed, said suction means being capable of being deactivated to detach from said platform said support sheet on which the raw part is located with the part of the photocurable composition which has not been cured,

[0035] the construction platform being a grooved flat plate made of a rigid material, such as ceramic, metal or plastic, the free face of which is covered by the support sheet and which is connected, by its opposite face, to the suction means,

[0036] said machine also comprising means for irradiating successive layers,

[0037] characterized in that the building platform has a roughness Ra of 0.4 to 3.2 pm and a parallelism of 0.002 to 0.1% of the width of the building platform.

[0038] To better illustrate the object of the present invention, a particular embodiment will be described below, for informational and non-limiting purposes, with reference to the attached drawing.

[0039] In this drawing:

[0040] [Fig. 1] is a perspective view of the building platform and sheet support equipping a stereolithography machine.

[0041] [Fig.2] is a schematic view of the steps of introducing a detachment aid sheet between the construction platform and the support sheet.

[0042] The stereolithography machine is a conventional machine of the state of the art, of which only the platform will be described in more detail below. [Fig.l] shows the construction platform 1 which is used in the present invention. A conventional laser irradiation means 2 is used for the irradiation of the successive layers.

[0043] This platform 1 has a plurality of grooves 3. A support sheet 4 is placed, said support sheet being a sheet of biaxially oriented polyethylene terephthalate.

[0044] The support sheet 4 has a thickness of 190 pm with a flatness of 8 pm, as well as a Young's modulus of 4.5 GPa.

[0045] It is possible to construct a plurality of parts 5 on the support sheet 4.

[0046] Before the construction of the parts, the support sheet 4 is arranged on the construction platform 1 and the air between the platform 1 and the support sheet 4 is sucked through the grooves 3 using a closed-loop venturi vacuum generation system. Thus, during the construction of the parts 5, the support sheet 4 is firmly held on the platform 1, which ensures the stability of the parts 5.

[0047] Once the parts 5 are built, the vacuum is stopped, which allows the support sheet 4 to be easily peeled off the platform 1.

[0048] In the case of building a part in a so-called top-down system, where the parts under construction are illuminated from above and the building platform is submerged as the parts are built, it is possible to use a detachment aid sheet in order to further facilitate the detachment of the support sheet from the building platform. This is illustrated in [Fig.2].

[0049] A detachment aid sheet 6 is provided which is a poly(vinyl chloride) sheet and which has a Young's modulus of 4.2 GPa and a thickness of 4 mm greater than that of the support sheet 3.

[0050] Firstly, after stopping the vacuum, the detachment aid sheet 6 is placed near the construction platform 1 on which the support sheet 4 is placed and on which the parts 5 have been constructed.

[0051] We start by slightly peeling off the support sheet 4 from the construction platform 1 in order to place the edge of the detachment aid sheet 6 between the platform 1 and the support sheet 4. We then gradually slide the detachment aid sheet 6 between the support sheet 4 and the construction platform 1 as shown in the central drawing of [Fig.2].

[0052] Once the unhooking aid sheet 6 is fully inserted between the support sheet 4 and the construction platform 1, the assembly can be lifted consisting of the parts 5, the support sheet 3 and the detaching aid sheet 6.

[0053] It is thus easier to detach the support sheet 4 from the platform 1. The greater thickness of the detaching aid sheet 6 also makes it easier to handle the assembly formed by the constructed parts 5, the support sheet 4 and the detaching aid sheet 6 in order to remove the parts 5 more easily.

Claims

1. Claims - Method for manufacturing, by the technique of additive processes, a green part made of at least one material chosen from ceramic materials and metallic materials, method according to which layers based on a photohardenable composition comprising said ceramic and metallic material(s) in powder form and an organic part comprising at least one photohardened monomer and / or oligomer and at least one photoinitiator are successively caused to harden by irradiation according to a pattern defined for each layer, the first layer being formed on a construction platform, and each other layer being formed and then caused to harden in contact with the preceding layer, method according to which: - before making the first layer: • the construction platform is covered with a support sheet capable of being pressed against it, forming a rigid and fixed surface for receiving the successive layers capable of retaining the successive layers formed thereon; and • said support sheet is pressed against said construction platform by suction; - the raw part is formed using additive processes; and - once the raw part has been thus formed, the suction is removed in order to detach from said platform said support sheet on which the raw part is located with the part of the photocurable composition which has not been cured; - said uncured portion of photocurable composition is removed; and - said raw part is removed from said support sheet, characterized in that the support sheet is a polymer sheet having a thickness of 0.05 to 5 mm and a flatness of less than 70% of the thickness of a layer, preferably less than 40% of the thickness of a layer, said support sheet being deformable to allow, once the suction is removed, the raw part to be detached from this by applying a constraint on said sheet so as to deform it in order to release the raw part.

2. - Method according to claim 1, characterized in that the support sheet has a Young's modulus of 2.5 to 80 GPa, preferably of 2.5 to 15 GPa.

3. - A method according to claim 1, characterized in that the support sheet is a biaxially oriented polyethylene terephthalate sheet, a polyetherimide sheet, a polyamide sheet or a polyolefin sheet.

4. - Method according to one of claims 1 to 3, characterized in that a photocurable composition of semi-liquid consistency is used, which is spread layer by layer on the construction platform, the layers being irradiated from above, or a photocurable composition in suspension is used, the platform being lowered step by step into the suspension to form the successive layers irradiated from above, or the platform being arranged at a distance corresponding to the thickness of a layer from the bottom of a photocurable composition tank with a transparent bottom for irradiation and raised at each layer formation, the layers being irradiated from below each time;or the platform coming into contact with a suspension layer applied to a segment of a transparent film which is unrolled horizontally at each layer formation, the layers being irradiated from below each time;

5. - Method according to one of claims 1 to 4, characterized in that the construction platform is a perforated or porous flat plate made of a rigid material, such as ceramic, metal or plastic, the free face of which is covered by the support sheet and which is connected, by its opposite face, to a vacuum pump or a vacuum generator, which is put into operation to press the support sheet onto the free face of the platform, forming the rigid and fixed surface for receiving the successive layers of photohardenable composition, and put out of operation to detach said support sheet from said platform.

6. - Method according to claim 5, characterized in that a perforated plate is used, the perforations of which are in the form of holes and slots connected to the vacuum pump or vacuum generator, arranged to ensure the support sheet is pressed when it is in operation.

7. - Method according to one of claims 1 to 6, characterized in that the construction platform uses a receptacle, in particular made of metal or plastic, of flat shape, the bottom of which has perforations connected to a vacuum pump and which receives a grid, in particular made of metal, the support sheet being applied to the free edge of the receptacle and to the grid, said vacuum pump being put into operation to press said support sheet onto the free edge of the receptacle and onto the grid, forming the rigid and fixed surface for receiving the successive layers of photohardenable composition, and put out of operation to detach said support sheet from said platform.

8. - Method according to one of claims 1 to 7, characterized in that a vacuum of 13.33 Pa - 10 10 Pa (0.133 mbar-10 12mbar) is generated.

9. - Machine for manufacturing by additive process technique raw parts made of a material chosen from ceramic materials and metallic materials, according to which layers based on a photocurable composition comprising said ceramic and metallic material(s) in powder form and an organic part comprising at least one photocurable monomer and / or oligomer and at least one photoinitiator are successively caused to harden by irradiation according to a pattern defined for each layer, the first layer being formed on a construction platform, and each other layer being formed and then caused to harden on the previous layer, the machine comprising means for suctioning against said construction platform a support sheet intended to cover it before the production of the first layer, forming a surface for receiving the successive layers,capable of retaining thereon the successive layers formed, said suction means being capable of being deactivated to detach from said platform said support sheet on which the raw part is located with the part of the photocurable composition which has not been cured, the construction platform being a grooved flat plate made of a rigid material, such as ceramic, metal or plastic, the free face of which is covered by the support sheet and which is connected, by its opposite face, to the suction means, said machine also comprising means for irradiating successive layers, characterized by the fact that the build platform has a roughness Ra of 0.4 to 3.2 pm and a parallelism of 0.002 to 0.1% of the width of the build platform.

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