Method for manufacturing mirrors using 3D printing

Abstract

The invention relates to a method for manufacturing a mirror, the method comprising the steps of: building said mirror by 3D printing using Fused Filament Fabrication (FFF) printing technology on a mold (10) placed on a tray (2) of a 3D printer (1), said mold having a free surface (10a) that corresponds to an optical surface (20) of the mirror (22) to be manufactured, said building comprising depositing successive layers on the mold of a molten polymer filament (4) filled with ceramic powder, said deposition starting from the optical surface (20) of the mirror on said free surface (10a) of the mold; removing the mirror and the mold; degreasing the ceramic powder; and sintering the ceramic powder to solidify the mirror.

Description

Technical Field

[0001] The present invention is from the field of manufacturing mirrors, particularly ceramic such as silicon carbide (SiC), alumina, cordierite, silicon nitride Si3N4, or metal such as aluminum, and proposes a method for manufacturing such mirrors by 3D printing.

Background Art

[0002] In current manufacturing methods of mirrors, particularly ceramic SiC, substrates made by sintering technology are used. These manufacturing methods include powder preparation, production of SiC blocks by applying pressure to the powder, machining and shaping the SiC blocks, and then sintering to weld the particles of the material together or infiltration of a bonding material such as silicon. The resulting substrate is thus shaped, but sufficient accuracy cannot be obtained. Therefore, following grinding of the optical surface and the interface zone, polishing of the optical surface, deposition of the polishing layer, and completion of the polishing are required.

[0003] The polishing steps consist of improving the shape and roughness of the mirror until the surface condition required for optical applications is reached. These steps are long and expensive, and particularly in the case of the aforementioned ceramics, especially silicon carbide, particularly expensive machines and tools suitable for polishing these mirrors are required.

[0004] Every time a new copy of the mirror is desired, all these steps need to be repeated. Particularly when it is difficult to polish the surface, such as in the case of aspherical mirrors or free-form mirrors, the steps are time-consuming and not suitable for mass-producing copies of a single mirror.

Summary of the Invention

Problems to be Solved by the Invention

[0005] With these known solutions, mirrors cannot be replicated, and each mirror produced needs to go through the polishing stage.

[0006] Furthermore, while the manufacture of mirrors by classical additive manufacturing is known, which means starting from a base and finishing with a mirror surface, additive manufacturing still requires polishing because the desired surface condition cannot be achieved during manufacturing.

[0007] Therefore, the problem to be solved is to find an additive manufacturing method that produces parts with the required quality level of surface condition. [Means for solving the problem]

[0008] Taking prior art into consideration, this application proposes a method for producing an optically high-quality surface with sufficient shape and roughness to avoid polishing operations on the resulting surface. To do this, the principle of the present invention is to use a mold having a surface complementary to the optical surface of the mirror, which is created as a molding surface in a 3D printing method.

[0009] More precisely, this application relates to a mirror manufacturing method comprising the step of constructing the mirror by 3D printing on a mold placed on a tray of a 3D printer using a printing technique by deposition of soluble material known as the acronym FFF for fused filament manufacturing, wherein the mold has a free surface complementary to the optical surface of the mirror to be manufactured, and the construction is: - A step of depositing a continuous layer of polymer filaments filled with powder of molten ceramic and / or metallic material onto a mold, wherein the deposition begins from the optical surface of a mirror on the free surface of the mold; - Steps to remove the mirror and mold; - A step of degreasing ceramic and / or metal powder; - A step of sintering ceramic and / or metal powder to solidify the mirror. We propose a mirror manufacturing method that includes [specific details omitted].

[0010] The features disclosed in the following paragraphs may be implemented at will. They may be implemented independently of each other or in combination.

[0011] The ceramics advantageously include silicon carbide (SiC) and / or silicon nitride (Si3N4) and / or alumina and / or cordierite.

[0012] The method of the present invention is particularly well applicable to materials that are hard and difficult to polish, but whose mechanical and thermal properties enable the creation of high-performance materials.

[0013] Metals, especially aluminum, are difficult to polish because they require expensive diamond cutting machines.

[0014] This method may include the steps of removing the mirror and mold assembly from the machine and separating the mold and the mirror.

[0015] The degreasing step includes removing polymers that constitute a bond to the ceramic or metallic material, and comprises a step of chemical degreasing and / or a step of heat treatment in a furnace at an appropriate temperature to remove the polymers.

[0016] If the polymer binder contains a polyolefin, the degreasing step may include chemical degreasing by immersing the mirror in an acetone bath, followed by the heat treatment.

[0017] In the case of a concave mirror, the 3D printer can be programmed to deposit filament onto the mold along a series of constant contours, starting from the bottom surface of the mold, whereas in the case of a convex mirror, the 3D printer is programmed to deposit filament along a series of constant contours, starting from the highest point of the mold.

[0018] Prior to constructing the mirror, this method may include a step of positioning the mold, which is done by printing an imprint onto a machine tray in advance to receive the base of the mold, or by using a tool whose position is referenced to the coordinates of the machine.

[0019] Preferably, the deposition step includes at least the step of adhering the first layer of filament onto the mold and heating the mold to a temperature of 30°C to 80°C, which is suitable for reproducing the surface state of the mold by the first layer, prior to the deposition of the first filament layer.

[0020] If the shape or residual roughness / porosity of the sintered material is too large for the intended use, a step may be performed to deposit a finishing layer on the optical surface of the mirror after sintering and then polish it.

[0021] Such finish layers, created by depositing amorphous materials such as glass, are particularly desirable when the sintered material has surface porosity.

[0022] The mold may be reused or not reused, and one or more steps for manufacturing the mold, in order to account for manufacturing chain biases such as shrinkage produced by mirror printing and / or shrinkage produced by mirror sintering, the mold geometry and complementary surface shape may be determined, which may precede the present method.

[0023] This method advantageously includes polishing the mold to achieve a roughness of less than 5 nm RMS.

[0024] The mold may be made from vitroceramic glass, aluminum, ceramic, silicon carbide, cordierite, alumina Si3N4, or any other material that is resistant to the filament deposition temperature and has a roughness of less than 5 nm RMS.

[0025] According to another aspect, a mirror obtained by the method according to the invention is proposed, which comprises an optical surface on a first side and an attachment profile on a second side.

[0026] Other features, details and advantages of the invention will become apparent upon reading the following detailed description and the analysis of the accompanying drawings.

Brief Description of the Drawings

[0027] [Figure 1] It is a diagram showing a preliminary step for the manufacture of a mirror according to the present application related to a 3D printer. [Figure 2] It is a diagram showing a first step for the manufacture of a mirror according to the present application related to a 3D printer. [Figure 3] It is a diagram showing a second step for the manufacture of a mirror according to the present application related to a 3D printer. [Figure 4] It is a diagram showing a third step for the manufacture of a mirror according to the present application related to a 3D printer. [Figure 5] It is a schematic diagram showing the step of separating the mirror and the mold of the present application. [Figure 6] It is a schematic diagram showing the step of degreasing the mirror of the present application. [Figure 7] It is a view of an example of the mirror of the present application seen from above. [Figure 8] It is a sequence diagram showing the method of the present application.

Embodiments for Carrying Out the Invention

[0028] Most of the drawings in the following description contain elements of a clarifying nature. Therefore, they not only help to better understand the invention, but can also contribute to its definition when applicable.

[0029] The mirror manufacturing method of this application aims to replace the conventional steps of manufacturing and polishing a sintered ceramic or metal substrate with a printing operation by using an additive manufacturing machine to replicate a mirror onto a mold from a plastic binder filament having a ceramic or metal.

[0030] To make the idea more concrete, in the case of high-precision mirrors based on sintered substrates, conventional methods involve manufacturing mirror substrates with shape defects of less than 5 μm RMS (RMS is root mean square) and roughness of less than 1 μm RMS.

[0031] To obtain shape defects of less than 100 nm RMS and roughness of less than 5 nm RMS, one or more steps are performed to polish the substrate in a mirror.

[0032] Finally, an amorphous finish layer is deposited, particularly to compensate for the porosity of the substrate. This layer is then polished so that the finished mirror contains shape defects of less than 10 nm RMS and a roughness of less than 2 nm.

[0033] The present invention aims to simplify the manufacturing of such mirrors and, as described above, eliminate the need for polishing the mirror while simultaneously achieving shape defects of 100 nm RMS or less and a roughness of 5 nm RMS or less.

[0034] To do this, mold 10, shown in Figure 1, is manufactured. This mold includes a top surface representing the complementary shape of the optical surface of the mirror to be created. The complementary surface, with the desired curvature of the mirror, is given the target roughness of the mirror. Furthermore, the shape of the complementary surface of the mold must take into account deviations resulting from this method, particularly shrinkage that occurs during mirror printing and subsequent sintering, which can alter the shape of the optical surface of the mirror.

[0035] The mold may be manufactured from vitro-ceramic glass, aluminum, or any material capable of achieving the desired polishing and roughness specifications, particularly known under the brand Zerodur.

[0036] The mold is preferably a reusable mold for manufacturing a series of mirrors.

[0037] Furthermore, as shown in Figure 1, the mold 10 is placed on the tray of a 3D printer 1 that uses the Fussed Filament Filament (FFF) method. The mold is precisely positioned on the machine because printing must be performed on the mold surface 10a that is complementary to the optical surface of the mirror. Precise positioning of the mold can be achieved by pre-printing an imprint 11 onto the machine's tray 2 to receive and hold the mold base in place, or by using a tool whose position is referenced to the machine's coordinates.

[0038] Printer 1 is a printer that uses polymer filament 4 filled with fine powder of ceramic or metal materials suitable for realizing mirrors, particularly silicon carbide (SiC), silicon nitride (Si3N4), alumina, cordierite, or aluminum. The polymer filament constitutes a binder for the powdered ceramic or metal.

[0039] The filament 4 is melted and deposited by a nozzle 5 driven by an electric device 3 along two horizontal axes to deposit a filament layer, while the tray 2 moves along a vertical axis to achieve a continuous layer of mirrors.

[0040] In the first step shown in Figure 2, the optical surface 20 of the mirror is created on the upper surface 10a of the mold, and then, according to Figures 3 and 4, 3D printing is performed to realize the body 21 of the mirror 22, and then the rear part 23 of the mirror 22 is realized.

[0041] The binder is a thermoplastic material such as PLA (polylactic acid), polyolefin, or polystyrene, as is known in the field, and this binder will be removed after the mirror has been printed.

[0042] In the case of a standard, three-axis 3D machine, the mold surface 10a, which is complementary to the optical surface, is generally not a flat surface but a concave or convex surface; therefore, programming a deposition machine is different from programming a machine that creates parts on a flat tray.

[0043] In fact, the technical problem is that current machines print objects within a range of motion that is assumed to be free of obstacles. Thus, the machine's print head moves freely within the plane of each layer being printed. The shape of the mold 10 becomes an obstacle during the movement of the head, so the presence of the mold necessitates a re-examination of the machine's operation in order to modify the movement of the head 3, which has nozzles 5 for depositing molten filament 4.

[0044] In the context of this invention, the head's movement path takes into account the volume occupied by the mold shape, the volume of the machine's print head, and the kinematics of its movement. Traditional strategies such as layer slicing and the corresponding algorithms for the machine cannot be used, and therefore their programming must be reconsidered.

[0045] To avoid the filament-depositing head coming into contact with the mold zone located above the layer being printed, which needs to be kept at a distance of approximately 0.2 mm to 1 mm from the surface being covered, the machine drive software is configured to move the head along rising contours, starting from the lowest point or surface of the mold, rather than moving along parallel lines of the head. For example, the machine is programmed to deposit filament on concentric circles with gradually decreasing diameter in a mold with a circular convex top surface, or on circles with increasing diameter in a mold with a circular concave top surface.

[0046] For mirrors with more complex shapes, the head always starts from the lowest point or surface of the mold and moves to create a deposit along the contour lines of the appropriate shape.

[0047] Other trajectories are also possible, depending on the shape of the optical surface of the mold and the geometry required for the mirror.

[0048] It should be noted that the kinematics of the machine are not final. In particular, there is a machine that allows for the movement of a nozzle along three axes, which can be used within the scope of this invention.

[0049] In particular, if the curvature of the mirror is such that the head may come into contact with the mold wall due to the dimensions of the head, a machine is used in which the head is fixed to a robotic arm having at least 5 axes, or a numerically controlled machine having at least 5 axes.

[0050] Therefore, this method covers the kinematics of various filament placements, particularly the realization of system inclination for nozzle displacement to maintain perpendicularity to the surface.

[0051] In current 3DFFF machines, the material is deposited on a tray designed to facilitate the adhesion of the first layer deposited on the tray, primarily by using a heated tray or an adhesion promoter. During printing to the mold, adhesion must be maintained so that the deposited mirror replicates the surface condition of the mold.

[0052] To enable the adhesion of the first layer on the mold, the mold is brought to an appropriate temperature so that the paste-like filament coming out of the nozzle does not cool too quickly.

[0053] With this in mind, the mold is preheated to a temperature appropriate for the filament material, ranging from approximately 30°C to a maximum of 80°C, depending on the filament being used. This temperature can be maintained throughout the deposit to ensure uniformity.

[0054] Once the mirror is created by depositing material on the mold, the mold and mirror are removed from the machine together.

[0055] In the next step, the mirror is separated from the mold without damaging the optical surface in contact with the mold. To do this, methods such as ultrasonic methods, for example, by placing the mirror in an ultrasonic generator bath 30 as shown in Figure 5, or thermal methods can be particularly used.

[0056] Next, the realization of the mirror involves an operation called degreasing, which removes the polymer.

[0057] This degreasing can be carried out by combining, for example, a chemical step using an acetone bath with a heat treatment in a furnace 40 schematically shown in Figure 6, which is equipped with a suitable heating device 41.

[0058] For reference, in the case of polyolefin / alumina filaments, a furnace 40 suitable for gradually producing temperatures of approximately 500°C is used, with a mirror placed on the hearth or a bed of refractory material 42. Depending on the material of the filament used, other temperatures and heating profiles may be used.

[0059] Depending on the binder, degreasing, which may cause sublimation, evaporation, or thermal decomposition of the binder, can likely be done directly, perhaps thermally, according to the recommendations of the binder and filament manufacturers.

[0060] Once degreasing is performed, the method includes sintering the material in furnace 40, or in another furnace, according to a thermal cycle suitable for the material, for example, raising the temperature from 20°C to 1550°C over 15 hours and holding for 4 hours, if the required temperature is suitable.

[0061] An example of the finished mirror 22 is shown in Figure 7, where the bottom of the optical surface 20, which is concave or convex, the body of the mirror 21, and the mounting feet 22a, which have wings 23 with holes for attachment to a transport device, are visible from top to bottom.

[0062] To ensure the geometry of the printed object corresponds to the desired final shape, and due to shrinkage phenomena during printing and heat treatment of the printed object, this method must include a behavioral model of the part during manufacturing and the inverse calculation from this model to determine the shape the mold should have so that the mirror has the correct geometry at the end of the method.

[0063] Figure 8 schematically shows the steps of the method starting from mold manufacturing 100, and this method is: - Step 110 involves the step of placing the mold on the printer, - Step 120 involves the step of printing a mirror, - Step 130 is a step of removing the mold and mirror and separating the mold and mirror; the mold may be readjusted in step 180 for reuse, - Step 140 involves a step of chemically and / or thermally degreasing the mirror, - Step 150 involves the step of sintering the mirror, and then, - The process is completed when the mirror has reached the desired surface condition and optical properties, step 170 involves depositing and polishing a finishing layer if a revised version of the mirror is required, and the process is completed. Includes.

[0064] The mirror is not limited to the examples shown, and in particular, while remaining entirely within the scope of the present invention, the mold may be concave and the mirror convex.

Claims

1. A mirror manufacturing method, characterized by comprising a step (120) of constructing the mirror by 3D printing on a mold (10) placed on a tray (2) of a 3D printer (1) using a printing technique by depositing a soluble material, wherein the mold comprises a free surface (10a) complementary to the optical surface (20) of the mirror (22) to be manufactured, and the construction is A step of depositing a continuous layer of polymer filaments (4) filled with molten ceramic and / or metal material powder onto a mold, wherein the deposition begins from the optical surface (20) of a mirror on the free surface (10a) of the mold, Step (130) to remove the mirror and mold, Step (140) of degreasing ceramic and / or metal powder, Step (150) of sintering ceramic and / or metal powder to solidify the mirror and Includes, The machine control software is configured to move the head along rising contours, starting from the lowest point or surface of the mold. The machine is programmed to deposit filament on concentric circles with gradually decreasing diameters for molds with a circular convex top surface, or on circles with increasing diameters for molds with a circular concave top surface. For concave mirrors, the 3D printer is programmed to deposit filament on the mold along a series of constant contours, starting from the bottom surface of the mold. For convex mirrors, the 3D printer is programmed to deposit filament along a series of constant contours, starting from the highest point of the mold. Mirror manufacturing method.

2. The ceramic is silicon carbide (SiC) and / or silicon nitride (Si). ３ N ４ The method for manufacturing a mirror according to claim 1, comprising and / or alumina and / or cordierite.

3. The method for manufacturing a mirror according to claim 1 or 2, wherein the metal is aluminum.

4. A method for manufacturing a mirror according to claim 1 or 2, comprising the steps of removing the assembly of the mirror (22) and the mold (10) from the machine (130), and separating the mold and the mirror (30).

5. A mirror manufacturing method according to any one of claims 1 to 4, wherein the degreasing step (140) removes polymers constituting a bond to a ceramic and / or metallic material, and the degreasing step includes a step of chemical degreasing and / or a step of heat treatment in a furnace at a suitable temperature for removing polymers.

6. The method for producing a mirror according to claim 5, wherein the polymer binder comprises a polyolefin, and the degreasing step (140) may include chemical degreasing by immersing the mirror in an acetone bath, followed by a heat treatment.

7. A method for manufacturing a mirror according to any one of claims 1 to 6, comprising the step of positioning a mold, which is done by printing an imprint on a machine tray in advance to receive the base of the mold, or by using a tool whose position is referenced to the coordinates of the machine, prior to the construction of the mirror.

8. A mirror manufacturing method according to any one of claims 1 to 7, wherein the deposition step includes, at least, a step of heating the mold to a temperature of 30°C to 80°C, which is suitable for adhering a first layer of filament onto the mold and for reproducing the surface state of the mold by the first layer, prior to the deposition of the first filament layer.

9. A method for manufacturing a mirror according to any one of claims 1 to 8, comprising the step of depositing a finishing layer on the optical surface of the mirror after sintering and polishing it.

10. A method for manufacturing a mirror according to any one of claims 1 to 9, characterized in that a mold (10) which may or may not be reused, is preceded by one or more steps (100) for manufacturing a mold (10) in which the geometry of the mold and the shape of a complementary surface are determined in order to account for biases in the manufacturing chain such as shrinkage produced by printing the mirror and / or shrinkage produced by sintering the mirror.

11. The method according to claim 10, comprising polishing the mold to achieve a roughness of less than 5 nm RMS.

12. The mold is made of vitroceramic glass, aluminum, ceramic, silicon carbide, cordierite, and alumina. ３ N ４ The method according to claim 10, or made of any other material that is resistant to the filament deposition temperature and has a roughness of less than 5 nm RMS.

13. A mirror (22) made of a ceramic filament comprising silicon carbide SiC and / or silicon nitride Si3N4 and / or alumina and / or cordierite, wherein the first side comprises a polished optical surface (20) formed by depositing the ceramic filament on concentric circles whose diameter gradually decreases on a surface with a circular concave top surface, or on circles whose diameter increases on a surface with a circular convex top surface, and the second side comprises a mounting profile (23) providing mounting feet.

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