Method and apparatus for additive manufacturing of glass objects

Abstract

The present invention relates to an additive manufacturing method and apparatus for forming a glass three-dimensional component / object, the method and apparatus including the steps of feeding a glass filament (160) material in an essentially horizontal direction towards a stage (130); heating the glass filament (160) material such that the glass fiber material melts / softens or remains molten / softened; depositing the molten / softened glass material onto a surface of said stage or object, where the molten / softened glass material is forming said glass three-dimensional component / object, where during at least a portion of the depositing step, the glass three-dimensional component being formed rests on an essentially vertical stage and the molten / softened glass material is deposited layer by layer; and one or more computers that control each layer of molten / softened glass material deposited by controlling a set of actuators that effect movement of the glass filament (160) and / or the stage (130).

Description

[Technical field]

[0001] The present invention relates generally to the field of additive manufacturing. In particular, the present invention relates to a method and apparatus for forming three-dimensional components / objects from glass feedstock. [Background technology]

[0002] In glass 3D printing, or additive manufacturing, existing techniques include (1) hot extrusion from a furnace, (2) deposition of glass rods, (3) stereolithography / inkjet using glass-polymer mixed solutions, and (4) deposition of glass filaments.

[0003] (1) In US10464305B2 and US10266442B2, a large crucible is used to pour the molten glass onto the build plate in a predetermined geometry using a translation stage. The drawback of this method is the risk of nozzle damage by the molten glass, and it is therefore limited to multi-component silicate glasses such as soda-lime glass or borosilicate glass, which have a lower melting temperature. The layer thickness is about 10 mm, and therefore this technique is only applicable to large size printing with a relatively low resolution. The energy consumption is the highest of all existing techniques.

[0004] (2) In US2020 / 0070415A1 and WO2020 / 167470A1, a continuous filament feed is used for glass 3D printing. The printing uses glass rods with a diameter of more than 1 mm as the raw material. The feed rods are fed through a print head and deposited on a substrate. The inability to print glass at temperatures above 1700°C limits the material selection. Problems with this system are the risk of nozzle damage by molten glass, the print volume is limited by the volume of the glass rod, gaps between the fed rods result in non-uniform print quality, and the configuration is considered to be mechanically quite complex.

[0005] (3) In US2020 / 0039868A1, WO2017 / 214179A1, and WO2020 / 118157A1, glass powder is mixed with a liquid polymer. In the printing process, a 3D body is first formed by a polymer 3D printer. The body is then subjected to a debinding process that results in a porous body of pure glass. The porous body is sintered to finally form a "dense" glass print. The glass content in the mixture is low. Therefore, this technique can only produce models that are generally smaller than 10 mm due to the large volumetric shrinkage. The entire process takes several days and requires energy-intensive furnaces for debinding and sintering. Due to the uneven shrinkage during sintering, the print quality is poor.

[0006] (4) Laser-based melting of thin glass filaments or optical fibers [JM Hostetler et al., FIBER-FED PRINTING OF FREE-FORM FREE-STANDING GLASS STRUCTURES, Solid Freeform Fabrication 2018: Proceedings of the 29th Annual International, 994-1002], [T. Grabe et al., Additive Manufacturing of fused silica using coaxial laser glass deposition, experiment, simulation and discussion, Proc. SPIE 11677, Laser 3D Manufacturing VIII, 116770Z (March 8, 2021)] have also been used for glass 3D printing. Using a laser, non-contact heating is realized, and thus the melt is not constantly in contact with the crucible walls, thereby avoiding corrosion of the crucible and contamination of the glass melt. Here, a silica glass fiber / filament is continuously fed into a hot zone with a temperature sufficient to soften the glass. In the case of silica glass (quartz or fused silica), high temperatures of 1800 to 2000°C are required.

[0007] However, in [JM Hostetler et al., FIBER-FED PRINTING OF FREE-FORM FREE-STANDING GLASS STRUCTURES, Solid Freeform Fabrication 2018: Proceedings of the 29th Annual International, 994-1002], only one laser beam is used to soften the glass filament. This asymmetric heating significantly limits the directional printing capability. Non-uniform temperature gradients in the molten glass filament can lead to high residual stresses in the print, with the risk of material fracture and interruption of the printing process. This technique uses bare glass filaments, which means that the coating needs to be removed from the glass filament before printing. However, this approach leaves the fiber unprotected during the last stage, i.e. the mechanical feeding of the fiber into the hot zone. The peeling process also limits the total length of the printable glass filament (i.e. maximum mechanical peeling of less than a few meters, maximum chemical peeling of less than a few tens of meters), which greatly impairs the continuity and capacity (volume) of the 3D printing process.

[0008] [T. Grabe et al., Additive Manufacturing of fused silica using coaxial laser glass deposition, experiment, simulation and discussion, Proc. SPIE 11677, Laser 3D Manufacturing VIII, 116770Z (March 8, 2021)], one laser beam is split into four partial beams. However, the quality of the split beams is poor because it is not a uniform Gaussian laser beam. The problem of non-uniform heating still exists. In this method, a coated glass filament is used. The coating is burned off near the hot zone, i.e. the hot zone itself can be used to remove the coating. The problem with the method with the commonly used fiber coating is that it is more likely to result in undesirable combustion by-products and leave residues that affect the purity of the print. Another problem is that the coating can ignite and start to burn the filament for long lengths even after the heat source is turned off. Therefore, a process gas is needed to suppress the burning of the coating. To burn off the coating, excessive energy is required, which causes enormous glass vaporization during printing.

[0009] Glass vaporization is very common and difficult to eliminate during laser-based glass processing. Vaporization forms undesirable fumed silica particles that adhere to surfaces. The presence of fumed silica particles increases the risk of contamination and destruction of optics in the system. Control of vaporization rate and fume direction is critical.

[0010] Additive manufacturing using bare glass filaments has poor mechanical properties and is therefore prone to breakage. Protective coatings are required for mechanical and chemical protection of glass filaments during storage and handling. Protective coatings can be applied during filament fabrication.

[0011] In prior glass additive manufacturing, coatings need to be removed from glass filaments. Stripping of the coating can be done using mechanical or chemical means (e.g., using sulfuric acid, dichloromethane) before feeding the filament into the hot additive manufacturing zone. However, this approach leaves the fiber unprotected during the last stage, i.e., mechanical feeding of the fiber into the hot zone. This is not an ideal solution, since stripping of the coating can further weaken the mechanical strength of the filament, and filament breakage during printing would cause a major interruption to the printing process. The use of chemical means is not preferred due to the risk of problems when using strong acids (sulfuric acid) or dichloromethane (carcinogenic).

[0012] In glass 3D printing, glass filaments are continuously fed into a hot zone at 1800-2200 °C. One common method is to feed pure glass filaments. However, most of the glass filaments are produced with a coating, so the removal of the coating is necessary to produce pure glass filaments before printing. The peeling of the coating can be done using mechanical or chemical means (e.g., using sulfuric acid, dichloromethane). The peeling process limits the total length of printable glass filaments (i.e., maximum mechanical peeling is typically less than 2 m, and maximum chemical peeling is typically less than 50 m), which greatly impairs the continuity and capacity (volume) of the 3D printing process. This poses additional risks, as filaments can be brittle without the coating, and peeling of the coating can further weaken the mechanical strength of the filament, so that filament breakage during printing would cause a major interruption of the printing process.

[0013] An alternative approach is to burn off the coating. If the hot zone is heated to a very high temperature, the coating will start to burn near the hot zone, i.e. the hot zone itself can be used to remove the coating. Problems with said method are that it is more likely to leave residues that may result in print failure, combustion by-products, affecting the purity of the print, and is not energy efficient. Yet another issue is that there is a problem in controlling the amount of coating that is burned off, which may occur when the coating starts to burn over the entire length of the filament.

[0014] In WO2018 / 163006, a continuous filament feed is used for glass 3D printing. The print uses glass rods as feedstock. The feed rods are loaded into a rotating cassette and fed through the print head to be deposited on the substrate. The continuous feed is achieved by thermally bonding the rods during the process. The inability to print glass at higher temperatures limits the material choice. Problems with this system are the risk of nozzle damage by molten glass, the print volume is limited by the cassette volume, the bonding area still results in uneven feeding, resulting in non-uniform print quality, and the setup is considered to be mechanically quite complex. Summary of the Invention [Problem to be solved by the invention]

[0015] The present invention aims to avoid the above mentioned problems.The main object of the present invention is to provide an improved apparatus for forming three-dimensional components of glass.

[0016] Another object of the present invention is to provide an additive manufacturing method for forming three-dimensional components of glass. [Means for solving the problem]

[0017] According to the invention at least the main object is achieved by means of a system having the features defined in the independent claims.

[0018] Preferred embodiments of the invention are further defined in the dependent claims.

[0019] According to a first aspect of the invention there is provided an additive manufacturing method for forming a three-dimensional component / object of glass comprising the steps of: a. feeding a glass filament material toward a stage or object in an essentially horizontal direction; b. heating the glass filament material such that the glass filament material melts / softens or remains molten / softened; c. depositing the molten / softened glass filament material onto a surface of the stage or object, where the molten / softened glass filament material is forming the glass three-dimensional component / object, and during at least a portion of the depositing step, the glass three-dimensional component being formed is placed on an essentially vertical stage and the molten / softened glass filament material is deposited layer by layer; d. controlling deposition of the molten / softened glass filament material using one or more computers and a set of actuators that effect relative movement of the glass filament material and the stage.

[0020] An advantage of this embodiment is that any fumes formed in the hot zone of the additive fabrication of the glass filaments may escape from the hot zone of the additive fabrication without contaminating the laser optics or interfering with the laser beam during melting / softening of the glass filaments.

[0021] In various exemplary embodiments of the invention, the glass filaments are fed essentially perpendicular to the surface of the stage or object.

[0022] An advantage of these embodiments is that the precision of the manufactured details may be increased compared to providing the glass filaments essentially not perpendicular to the substrate.

[0023] In various exemplary embodiments of the invention, at least one laser beam emitted from at least one light source is used to heat the glass filaments.

[0024] An advantage of these embodiments is that one or more laser beams emanating from one or more laser beam sources can be used to heat / melt the glass filaments.

[0025] In various exemplary embodiments of the present invention, the glass filament material is hollow.

[0026] An advantage of these embodiments is that the hollow structure of the filaments can be constructed into the final three-dimensional component, such as a microfluidic structure.

[0027] In various exemplary embodiments of the invention, the glass filament material has a protective film made of polyimide having a thickness in the range of 1 to 50 μm.

[0028] An advantage of these embodiments is that as this protective film is automatically removed during use in additive manufacturing, the filament is protected prior to use and exhibits little, if any, contamination of the produced material and its laser beam guidance optics.

[0029] In various exemplary embodiments of the invention, the glass filament is heated by at least three laser beams having a wavelength greater than 2 μm.

[0030] An advantage of these embodiments is that multiple laser beams provided symmetrically with respect to the glass filaments can speed up the melting / softening time. Another advantage is that the wavelength and / or number of laser beams can be selected to have customized heating efficiency.

[0031] In various exemplary embodiments of the invention, the glass filaments are coated glass fibers having a diameter in the range of 100 to 500 μm.

[0032] An advantage of these embodiments is that various diameters of glass filaments may be used to maximize precision or manufacturing speed.A further advantage of the present invention is that optical fiber may be used as the raw material.

[0033] In various exemplary embodiments of the invention, the stage is a glass plate having a thickness within the range of 80% to 300% of the diameter of the glass filaments, which may range from a few tenths of a millimeter to a few centimeters.

[0034] An advantage of these embodiments is that the manufacturing method is compatible with very thin substrates.

[0035] In various exemplary embodiments of the invention, the method further includes pre-heating the glass filaments prior to heating with the at least one laser beam.

[0036] An advantage of these embodiments is that lower laser power may be required to reach the desired melting / softening temperature of the glass filament. Preheating may be accomplished by resistive heating within the filament delivery nozzle.

[0037] In various exemplary embodiments of the invention, the distance between a filament delivery nozzle and the point where the glass filament intersects the laser beam is less than 5 mm. The angle of the laser beam relative to the surface of a stage or object to which the glass filament is applied may be in the range of 30° to 60°. Multiple laser beams may be configured to intersect at the glass filament essentially symmetrically with respect to the glass filament.

[0038] The advantage of these embodiments is that the short distance increases the precision of the manufacture of three-dimensional components. The short distance can be adopted because the protective film on the glass filament is self-extinguishing. The impingement angle of the laser beam is selected such that the hot zone is applied to the glass filament and to the stage for efficient fusion of the stage and the glass filament. The stage may further be heated from behind using an independent heating source, for example at least one other laser beam impinging from the opposite side to where the glass filament is applied on the stage.

[0039] In various exemplary embodiments of the invention, the glass filaments are made of at least two different materials and a protective film.

[0040] An advantage of these embodiments is that functional optical waveguides, such as optical circuits for use in communications, sensing or biomedical applications, can be fabricated.

[0041] In another aspect of the invention, there is provided an apparatus for additive manufacturing of glass components / objects, comprising: a. Stage and; b. one or more heating elements for heating the glass filament material such that it melts / softens or remains molten / softened; c. a filament delivery nozzle for delivering the glass filament in an essentially horizontal direction towards a stage to form the glass component / object disposed on the stage; d. one or more computers for controlling the production such that the molten / softened glass material is deposited layer by layer and for controlling the relative movement of the glass filament material and the stage, wherein the stage is essentially vertical.

[0042] Further advantages and features of the present invention will become apparent from the following detailed description. [Brief description of the drawings]

[0043] [Figure 1a] FIG. 1 is a schematic side view of a first exemplary embodiment of an apparatus for manufacturing three-dimensional components of glass according to the invention. [Figure 1b] FIG. 2 is a schematic side view of a second exemplary embodiment of an apparatus for manufacturing three-dimensional components of glass according to the invention. [Diagram 2] FIG. 2 shows a schematic side view of a glass filament and a filament delivery nozzle. [Diagram 3] 3a-3c show various exemplary embodiments of glass filaments. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0044] A more complete understanding of the above-discussed and other features and advantages of the present invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings.

[0045] The method of the present invention relates to a new additive manufacturing (AM) process whereby using a digital model, the geometry of a component is constructed by either simple scanning or selective melting of a printed contour using an energy source such as a laser beam, fusing molten filaments / fibers, either layer by layer or as a batch of layers, followed by a fusion process.

[0046] The present invention relates to a direct manufacturing process by integrating the removal of the protective film of the filaments into the printing process. This means that the new process is able to manufacture fully or almost fully dense glass components using glass filaments and overcomes all the drawbacks of prior art glass manufacturing methods.

[0047] The new process allows for the direct production of glass components without any of the safety precautions and / or health risks associated with the use of prior art glass filaments.

[0048] FIG. 1a shows a schematic side view of a first exemplary embodiment of an additive manufacturing apparatus 100 according to the present invention configured to manufacture a glass three-dimensional component / object. The additive manufacturing apparatus 100 comprises a stage / substrate 130, a laser source 110 and a filament delivery nozzle 120. The filament delivery nozzle 120 may be configured to move relative to the stage 130 in essentially parallel planes such that the filament delivery nozzle 120 covers a predefined area of ​​the stage 130. The stages are arranged in a vertical direction. The relative movement may be such that the stage 130 is fixed and the filament delivery nozzle 120 moves in the plane, or such that the stage is moving while the filament delivery nozzle 120 is fixed, such that the entire stage 130 is covered. In a further alternative embodiment, both the stage 130 and the filament delivery nozzle 120 are in the plane, allowing the filament delivery nozzle 120 to cover the entire area of ​​the stage. Providing the stage 130 in a vertical orientation ensures that any fumes, for example from the combustion products of the coating material or vaporized / molten glass (due to overheating), move upwards and not towards the print head. This is beneficial because otherwise fumes could damage the optics and filament delivery nozzle of the print head, requiring frequent cleaning or part replacement. Also, due to the vertical arrangement of the stage 130, the relative movement of the filament delivery nozzle 120 and the stage 130 can be configured such that any fumes and gaseous materials exiting the hot zone are out of the optical path of the laser beam, thereby improving the performance of the additive manufacturing device.To additively manufacture a three-dimensional component / object and maintain a constant distance between the filament delivery nozzle 120 and the top surface of the stage or component / object to which the new layer is applied, one or both of the filament delivery nozzle 120 and / or the stage 130 may be movable in a direction perpendicular to the surface of the stage, i.e., for each new applied layer, the stage 130 may be moved backwards (away from the print nozzle) a distance corresponding to the thickness of the new applied layer, or the filament delivery nozzle 120 may be moved away from the stage a distance corresponding to the thickness of the new applied layer, or the backward movement of the stage and the forward movement of the filament delivery nozzle 120 may be combined to maintain a constant distance between the filament delivery nozzle 120 and the top surface of the stage or component / object to which the new layer is applied. The filament 160 may be fed to the filament delivery nozzle 120 via a flexible tube 170. The laser source 110 may be a CO2 laser, a CO laser, a Nd:YAG laser, a fiber laser, an excimer laser, a nitrogen laser, or the like. The laser beam 150, which may be continuous or pulsed, softens or melts the filament in a hot zone 140 adjacent the stage onto which the softened or molten glass is deposited.

[0049] The filament-feeding nozzle 120 and / or the stage 130 may be disposed on at least one motorized support. A control unit may control the relative movement of the filament-feeding nozzle 120 with respect to the stage 130. The control unit may also control the print head optics and laser.

[0050] 1a, a filament delivery nozzle 120 provides source material 160 onto a stage 130 to form a layer of a glass three-dimensional component / object. A build plate may be provided on the stage 130 on which the three-dimensional component is formed. The build plate may be made of any material, for example the same material as the final three-dimensional component, a ceramic material, or any other metallic material different from the material in the three-dimensional component.

[0051] The first step is the fusion and deposition of the raw material on the stage 130. The filament delivery nozzle 120 locally deposits the raw material along a predetermined path. The filament delivery nozzle 120 may heat the raw material before it leaves the nozzle 120 and heads towards the stage 130. The filament delivery nozzle 120 may be adapted to the size and shape of the raw material. Three-axis kinematics may position the filament delivery nozzle 120 within the work envelope of the machine to produce three-dimensional components made of glass layer by layer. The raw material 160 is a glass filament. In FIG. 1a, only one glass filament 160 is delivered to the stage. In various exemplary embodiments, multiple glass filaments 160 of various shapes and material compositions may be delivered in series through a single filament delivery nozzle 120 to perform multi-material deposition. In FIG. 1a, only one filament delivery nozzle 120 is used. In various exemplary embodiments, multiple filament delivery nozzles may be used in series or parallel. In various exemplary embodiments, multiple pieces of feedstock 160 may be provided simultaneously on stage 130 to provide three-dimensional components of different materials. Different layers of the three-dimensional component may include different materials and / or different locations within a single layer may include different materials, i.e., deposition of two materials may occur in one layer and / or in different layers.

[0052] FIG. 1b shows a schematic side view of a second exemplary embodiment of an additive manufacturing apparatus 100 according to the present invention configured to manufacture three-dimensional components of glass. The apparatus 100 also comprises a vertical stage 130, a laser source 110 and a filament delivery nozzle 120. Furthermore, the embodiment may comprise a first beam steering mirror 115, a wave plate 125, a lens 135, a diffractive optical element (DOE) 145, a pyramidal mirror 155, and at least three second beam steering mirrors 165. At least three laser beams may be used to heat the glass filament 160. The laser emission may operate within a wavelength range in which the glass filament has high optical absorption and heats the filament 160 when irradiated with the laser beam 150. Silica and silica-based glass filaments have strong absorption at wavelengths above 2.2 μm. Irradiation of the glass filament 160 with a CO2 laser (typically operating in the 9.2-10.6 μm wavelength region) or a CO laser (operating in the 5.5 μm wavelength region) results in strong radiation absorption and subsequent heating of the glass filament 160.

[0053] A CO2 laser operating at a wavelength of 10.6 μm may be used. At this wavelength, silica glass is opaque and efficient heating is obtained. The absorption depth is about 2 μm to 40 μm, which is efficient for heating glass filaments on the order of several hundred μm in diameter. For larger glass filaments, the shallow penetration depth at 10.6 μm makes them difficult to heat quickly. For glass filaments larger than about 0.5 mm, a CO2 laser operating at 5.5 μm is more suitable. The penetration depth at 5.5 μm is much larger (several hundred μm), which results in more efficient energy deposition into the glass filament 160.

[0054] A DOE 145 may be used to split the original laser beam 150 into at least three uniform laser beams 150'. Several second beam steering mirrors 165 may be used to direct the split laser beams 150' to the hot zone 140. A first optional beam steering mirror 115 may be used to make the laser beam path more compact and facilitate beam alignment. At least three second beam steering mirrors 165 deflect the at least three laser beams to the hot zone 140 where the at least three laser beams impinge on the glass filament 160. A quarter wave plate 125 may be used to control the polarization of the laser beam. Since the DOE 145 may have some polarization dependence, the use of a circularly polarized beam ensures that the split laser beams 150' are identical. A circularly polarized beam may also be achieved using a reflective retarder as the (first or second) beam steering mirror 115. A focusing lens 135 may be used to change the focal spot size at the hot zone 140 to allow for altered heating dynamics. The focusing lens 135 may be mounted on a computer-controlled motorized translation stage. The DOE shown is a 2×2 DOE, i.e. splitting the single laser beam 150 into four laser beams 150′. A pyramidal mirror 155 may be used to deflect the beam 150′ from the DOE 145. The use of the pyramidal mirror 155 shown in FIG. 1b may allow for a much more compact design of the optical path of the laser beams 150, 150′ compared to a configuration without said pyramidal mirror. Said pyramidal mirror 155 may also increase the stability of the laser beam at the hot zone 140 against wavelength variations of the laser source 110. The diffraction angle from the DOE 145 is wavelength dependent. As the wavelength of the laser varies, so does the diffraction angle. The larger the diffraction angle, the greater the effect. Thus, by using a DOE with a small diffraction angle, the print head is less sensitive to wavelength variations. A large shift in the diffraction angle will change the location of the hot zone, resulting in print instability.To allow for a compact design, a pyramidal mirror 155 is used to increase the deflection angle of the laser beam 150'. After the pyramidal mirror 155, the four laser beams 150' are directed to intersect at the same place on the filament 160, labeled as hot zone 140, using the second beam steering mirror 165, one mirror 165 for each laser beam 150'. The beam steering mirrors are configured to deflect the laser beam 150' in any direction. Here, the second beam steering mirror 165 is configured to deflect the four laser beams 150' to one same hot zone 140 on the glass filament 160. The laser beams 150' impinge on the glass filament 160 from different directions but at essentially the same distance from the exit of the filament delivery nozzle 120 or the top surface of a substrate disposed on the stage 130. Due to the open structure with four beams 150', the filament delivery system 170 and nozzle 120 are easily added below the pyramidal mirror 155 and between the laser beams 150'. The distance L between the hot zone 140 and the exit of the filament delivery nozzle 120 may be more than 10 mm, and in various exemplary embodiments, the distance L may be less than 5 mm. The thickness of the substrate 130 may be a few tenths of a mm to a few centimeters. The glass filament 160 and the laser beam impinging on the substrate 130 may have an angle of 45° with respect to the surface of the substrate. In various exemplary embodiments, the angle with respect to the surface of the substrate may be in the range of 30° to 60°.

[0055] The laser and beam steering may be equipped with a beam tap, which taps off a few percent of the laser beam power, monitored using a reference power meter. The input from the reference power meter is used as a feedback signal to stabilize the laser power, for example using a closed loop feedback system. A shutter may be used to turn the laser beam on and off the print head. When off (closed), the beam is directed to a beam dump, which may also be an additional power meter. When on (open), the beam enters the print head. In Figures 1a and 1b, printing is performed with a filament that impinges horizontally on the stage 130. This is to ensure that any fumes, for example from combustion products of the coating material, or vaporized / molten glass (due to overheating), travel upwards without heading towards the print head. This is beneficial, because otherwise the fumes could damage the optics and filament delivery nozzle of the print head, requiring frequent cleaning or part replacement. However, with a suitable gas purge, the print head can be installed in any orientation (up, down or sideways).

[0056] One or several filament supplies may be used to add raw material during printing. The printing stage may be a three-axis (xyz), four-axis or five-axis translation system that preserves the contour of the substrate or print. When using silicate glass filaments (e.g. borosilicate or soda-lime glass), the build volume may also include a heating chamber. For fused silica or fused quartz glass filaments, this may be relatively unproblematic (due to their extremely low thermal expansion coefficients) and printing can be done without additional heating. To improve bonding to the substrate, a separate laser beam may be employed to illuminate below the point where the softened glass filament is deposited. As both CO2 and CO lasers operate in the infrared wavelength spectrum, a laser operating at visible wavelengths is used for beam alignment. The accuracy of the alignment may be crucial to achieve uniform heating of the filament. The alignment technique is based on using the filament as a miniature interferometer.

[0057] For example, a He-Ne laser (wavelength 632.8 nm) is focused on the filament at a designated location (corresponding to the hot zone) where the four laser beams intersect. The light from the red laser can be reflected at two interfaces of the glass fiber. The circular glass fiber can form a concentric cavity interferometer (CCI). The two reflected beams of the CCI can interfere with each other to form interference fringes. If the temperature increases at the location of the focused He-Ne laser, the interference fringes move outward, whereas if the temperature decreases, they move inward. The procedure for alignment of CO2 or CO laser beams is then straightforward: each beam is precisely aligned by simply maximizing the interference fringe shift (increasing the temperature).

[0058] One feedstock nozzle 120 may provide the raw material 160 at a first predetermined layer area of ​​the three-dimensional component, and two or more nozzles may be used at a second predetermined layer area of ​​the three-dimensional component, i.e., the layer formation may vary between one, two, three or more nozzles depending on the shape of the layer being formed and / or the type of material being added. In various exemplary embodiments, the multiple nozzles for providing the raw material on the substrate may have the same diameter or different diameters. The multiple filament delivery nozzles may provide raw material of different glass materials.

[0059] In synchronization with the filament extrusion, the functional points (hot zones) are positioned according to a predefined path, which is obtained by slicing the workpiece geometry into layers and calculating a time-efficient trajectory for the extrusion of the filament 160. The positioning can be performed by a 3-axis positioning unit. To further position the workpiece with respect to the Earth's gravitational field, 5-axis kinematics is intended to extend the manufacturing flexibility.

[0060] The first option is simultaneous processing with a moving laser beam, in close proximity to the deposition of the filaments, to subsequently sinter / melt the deposited glass filaments 160.

[0061] An alternative is sintering / melting a thin layer of glass filaments with a high power laser beam, by selective laser scanning of the just printed layer. This process may require controlled heat input and timing. To ensure geometric accuracy, in situ measurements may be made that allow direct compensation of process variations. Material defects may require quality inspection of the sintered / melted glass layer. In situ quality control to ensure geometric accuracy may require appropriate temperature, gas content and pressure in the printing environment.

[0062] One or more laser beams may be used simultaneously to melt / soften the glass filaments.

[0063] Bare glass filaments have poor mechanical properties and are therefore prone to breakage. Protective coatings are necessary for mechanical and chemical protection of glass filaments during storage and handling. Protective coatings may be applied during filament fabrication, for example using a fiber draw tower used to produce optical fiber. A furnace heats the preform (which is like an enlarged filament in both shape and composition). The softened glass is then drawn to the correct filament dimensions using a capstan combined with a diameter gauge. As the filament is drawn, the preform is fed further into the furnace. Typically, a coating resin may be introduced into a coating cup through which the filament passes. The coating may then be subsequently cured, either thermally or using, for example, a UV lamp, before the filament is wound onto a spool for storage and transport. Curing temperatures for polyimide coatings on optical fiber may typically be within a temperature range of about 100-400°C.

[0064] Polyimide-coated optical fibers can withstand operating temperatures of about 300 °C and are commonly used for higher temperature (sensing) applications, where coating thicknesses of 10-15 μm are typically used. Thicker coatings can be applied by repeating the coating procedure to add multiple coating layers.

[0065] For glass filaments, the coating thickness should be as thin as possible while still ensuring adequate mechanical and chemical protection of the fiber. Filaments evaluated as giving good results have a single layer polyimide coating thickness of about 5 μm.

[0066] The preferred outer diameter of the glass filament is in the range of 100 μm to 500 μm. The diameter greatly influences the mechanical properties of the filament, with an increased diameter resulting in a stiffer filament. Translation of the nozzle and filament relative to the printing structure during printing results in lateral forces on the filament. The misalignment of the filament depends on the viscosity and surface tension of the liquid glass in the hot zone, as well as the printing speed. A schematic of the printing nozzle and the extruded filament is shown in the figure below. For stiffer filaments, the distance between the filament delivery nozzle and the hot zone may be increased. Thus, the filament diameter, nozzle design, and distance to the hot zone greatly influence the printing accuracy / quality. A large filament diameter and a short length of the extruded filament reduce the misalignment of the filament during printing. As the filament diameter increases, the printer resolution decreases. If the length of the extruded filament is too short, the filament delivery nozzle may be damaged by the hot zone.

[0067] The total deflection / displacement δ is given by the following formula:

[0068]

number

[0069] In glass 3D printing, glass filaments are continuously fed into a high-temperature zone at 1800-2200 °C. One common method is to feed pure glass filaments. However, most of the glass filaments were produced with a coating, so the removal of the coating is necessary to produce pure glass filaments before printing. The peeling of the coating can be done using mechanical or chemical means (e.g., using sulfuric acid, dichloromethane). The peeling process limits the total length of printable glass filaments (i.e., maximum mechanical peeling of less than a few meters, maximum chemical peeling of less than a few tens of meters), which greatly impairs the continuity and capacity (volume) of the 3D printing process. The filament can be brittle without the coating, and the peeling of the coating can further weaken the mechanical strength of the filament, thus posing an additional risk since filament breakage during printing would cause a major interruption of the printing process. The use of chemical means is not preferred due to the risk of problems when using strong acids (sulfuric acid) or dichloromethane (carcinogenic).

[0070] Another approach is to directly feed coated filaments. With protective coatings, printable filament lengths are extended to the kilometer range. However, because filaments are generally coated with flammable polymers, such as acrylic resins, this approach can cause open flames in the filaments due to high printing temperatures, resulting in print failure and destruction of the 3D printer. Furthermore, standard coatings have a thickness of about 50 μm, which is considered too "thick" for glass 3D printing. Direct incineration of "thick" coatings is not an ideal solution, as it can generate more combustion by-products, is more likely to leave residues that affect the purity of the print, and is not energy efficient.

[0071] Our approach is to produce glass filaments with a thin, flame-retardant and self-extinguishing coating. When the hot zone is heated to an extremely high temperature using a CO2 laser beam, the coating starts to burn off near the hot zone, i.e. the hot zone itself can be used to remove the coating. If the coating is flame-retardant, the risk of an open flame is eliminated. When the laser and filament supply are turned off, the coating stops burning. Thin coatings are easily burned off. In addition to increasing efficiency and reducing environmental impact, it also reduces the production of combustion by-products. An ideal coating may have a non-toxic chemical composition and should not contain halogens, for example, to further reduce the toxic smoke produced during combustion.

[0072] The filaments of the invention for additive manufacturing offer the possibility of applying a thin coating layer to the glass filaments while still providing mechanical and chemical protection of the filaments during (temporary) storage and handling. The coating can be easily removed by thermal means (heating / plasma / laser irradiation). The coating may not contain toxic components or produce harmful combustion products when incinerated. The coating may be flame retardant and self-extinguishing.

[0073] The additive manufacturing method according to the invention may be used to generate three-dimensional components of glass. The method comprises the steps of feeding a glass filament having a protective film thereon to a heating source, removing the protective film and softening the glass filament, and applying the softened glass filament to a surface of a substrate, the protective film being made of polyimide and having a thickness in the range of 1 μm to 50 μm. The feeding of the glass filament may be continuous or discontinuous.

[0074] FIG. 2 shows a side view of a filament delivery nozzle 120. Extending from the filament delivery nozzle 120 is a glass filament 160 having a protective film or coating 169. The length of the filament from the exit of the filament delivery nozzle 120 to a hot zone 140 where at least one laser beam impinges on the glass filament 160 is indicated as L. In various exemplary embodiments, L may be greater than 10 mm or less than 5 mm. In various exemplary embodiments, the length L is less than 5 mm. A longer L may increase filament misalignment, which is the distance between a non-misaligned central portion of a tip 180 of the filament 160 and a misaligned central portion of the same tip 180. Any such misalignment may result in misalignment of the filament relative to its intended location on the surface of the substrate or print / object, which may result in a defective three-dimensional article and / or reduce the accuracy of additive manufacturing. Because the protective coating is flame retardant and / or self-extinguishing, a portion of the protective coating 169 remains on the filament outside the exit of the filament delivery nozzle 120 during additive manufacturing. The length of the remaining protective coating portion during manufacturing can be at least a few tenths of a millimeter.

[0075] Figure 3a-c shows three different types of glass filaments 160 with protective coating 169 that can be used in additive manufacturing processes. Figure 3a shows a single composition (rod / fiber filament), the composition (type of glass) can be high purity silica glass, e.g. fused silica, fused quartz (used for printing high purity transparent glass). These materials have low thermal expansion coefficients, i.e. do not require heated printing plates and thermal annealing post-treatment is not necessarily required. Silica glass filaments with GeO2, Al2O3, B2O3, or F co-doping or combinations thereof. Multifilament printing (with silica glass filaments) can be used to form 3D printed objects with structures of designed shapes and refractive index. An example of this could be the fabrication of optical fiber preforms or different optical components. Silica glass doped with rare earth oxides such as Er, Yb, Er / Yb in combination with additional dopants (e.g. GeO2, Al2O3, B2O3, F). These filaments can be used to form 3D printed objects of active laser materials. Silicates, borosilicates, aluminoborosilicates and soda-lime glasses represent standard(er) low cost materials. Due to their higher thermal expansion coefficients, they may require heated printing plates and post-thermal annealing to relieve stress.

[0076] FIG. 3b shows a glass filament 160 with a central air hole 162, i.e., a capillary structure. These capillary filaments can be used to print different kinds of glass / air structures. If pressure control is applied to the inner part of the capillary filament, active contraction / expansion of the filament during printing is possible. The volume of the air hole 162 may be 10-70% of the volume of the glass content in the glass filament 160. The air hole 162 may be in the center of the glass filament 160 or not. In various exemplary embodiments, the glass filament 160 may include multiple air holes.

[0077] FIG. 3c shows that glass filaments 160 made of silica-based composition contain a central core structure 160' of refractive index modifying dopants, e.g., GeO2, Al2O3, B2O3, F. These core / cladding filaments acting as optical waveguides can be used to print optical circuits on different types of glass substrates for use in communication, sensing or biomedical applications. Other core materials besides glass-based include semiconductors and alloys, e.g., silicon, germanium, etc.

[0078] The filaments may be continuously fed towards the substrate while hot zones formed by single or multiple laser beams bond them together, with the relative motion between the substrate and the filament under computer control to define the print shape.

[0079] Simple structures such as microspheres, micropillars, microlines, microcircles and nanotapers were printed with a single deposition. Printing of free-standing models / arrays was also demonstrated. Multilayer printing with complex geometries was realized. Both hollow (vase-shaped) and dense models (100% filled) were printed using glass filaments. In conclusion, glass filaments are applicable for all the above mentioned glass 3D printing tests and their performance is similar to plastic filaments in FDM systems.

[0080] A flame retardant and / or self-extinguishing protective film 169 is applied to the surface of the glass filaments 160 . Possible modifications of the present invention The present invention is not limited to the embodiments described above and shown in the drawings, which are primarily for the purpose of illustration and example. This patent application is intended to cover all modifications and variations of the preferred embodiments described herein, and therefore the present invention is defined by the words of the appended claims and their equivalents. Thus, the device may be modified in any manner within the scope of the appended claims.

[0081] Throughout this specification and the claims that follow, unless the context requires otherwise, the term "comprise" and variations such as "comprises" or "comprising" are understood to imply the inclusion of stated integers or steps, or group of integers or steps, but not the exclusion of any other integers or steps or group of integers or steps.

Claims

1. An additive manufacturing method for forming three-dimensional glass components / objects, a. feeding a glass filament (160) material towards a stage (130) or object in an essentially horizontal direction; b. heating the glass filament (160) material such that the glass filament material melts / softens or remains melted / softened; c) depositing the molten / softened glass filament (160) material onto a surface of the stage (130) or object, the molten / softened glass filament material forming the glass three-dimensional component / object, and during at least a portion of the depositing step, the glass three-dimensional component being formed is placed on an essentially vertical stage and the molten / softened glass filament material is deposited layer by layer; and d. controlling the deposition of the molten / softened glass filament material using one or more computers and a set of actuators for relative movement of the glass filament material and the stage (130).

2. 2. The additive manufacturing method of claim 1, wherein the glass filament material is fed essentially perpendicular to the stage (130) or the surface of the object.

3. 3. The additive manufacturing method of claim 1 or 2, wherein at least one laser beam (150) emanating from at least one laser source (110) is used to heat the glass filament (160) material.

4. 4. The additive manufacturing method of claim 3, wherein the glass filament (160) material is heated by at least three laser beams (150) having a wavelength greater than 2 μm.

5. 4. The additive manufacturing method of claim 3, wherein a distance between a filament delivery nozzle (120) and a point where the glass filament (160) material intersects with the at least one laser beam (150) is less than 5 millimeters.

6. 6. The additive manufacturing method of claim 5, wherein the multiple laser beams intersecting on the glass filament material have an angle in the range of 30° to 60° with respect to the surface of the stage or object on which the glass filament material is provided.

7. 7. The additive manufacturing method of claim 6, wherein multiple laser beams are configured to intersect at the glass filament material essentially symmetrically with respect to the glass filament material.

8. 3. The additive manufacturing method of claim 1 or 2, wherein the glass filament material has a protective film made of polyimide having a thickness in the range of 1 to 50 μm.

9. 3. The additive manufacturing method of claim 1 or 2, wherein the glass filament material is a glass fiber having a diameter in the range of 100 to 500 μm.

10. 3. The method of claim 1 or 2, wherein the glass filament material is made of at least two different materials and a protective film.

11. 3. The additive manufacturing method of claim 1 or 2, wherein the glass filament material is hollow.

12. 3. The additive manufacturing method of claim 1 or 2, wherein the stage is a glass plate having a thickness within a range of 80% to 300% of a diameter of the glass filament material.

13. 4. The additive manufacturing method of claim 3, further comprising pre-heating the glass filament material prior to heating the glass filament material with the at least one laser beam.

14. 1. An additive manufacturing apparatus for glass components / objects, comprising: a. a stage (130); b. one or more heating elements for heating the glass filament (160) material such that said glass filament material melts / softens or remains melted / softened; c. a filament delivery nozzle (120) for delivering the glass filament (160) in an essentially horizontal direction towards the stage (130) to form the glass component / object disposed on the stage; d. one or more computers for controlling the production of the molten / softened glass material as it is deposited layer by layer, and for controlling the relative movement of the glass filament (160) material and the stage (130), wherein the stage is essentially vertical.

15. The apparatus of claim 14 , wherein the glass filament material is fed essentially perpendicular to the stage.

16. 16. Apparatus according to claim 14 or 15, wherein the one or more heating elements are at least one laser beam.

17. 17. The apparatus of claim 16, wherein the multiple laser beams originate from one and the same laser beam source.

18. 20. The apparatus of claim 17, further comprising a diffractive optical element for splitting a single laser beam into multiple laser beams, a pyramidal mirror configured to deflect the split laser beams, and a plurality of beam steering mirrors configured to direct the deflected laser beams across the glass filament material.

19. 20. The apparatus of claim 18, wherein the at least three laser beams intersecting on the glass filament material have an angle in the range of 30-60 degrees with respect to the surface of the stage or object on which the glass filament (160) material is provided.

20. 20. The apparatus of claim 18, wherein the laser beams are configured to intersect at the glass filament material essentially symmetrically with respect to the glass filament material at essentially the same distance from the stage (130).

21. 16. The apparatus of claim 14 or 15, further comprising at least one preheater configured to preheat the glass filaments prior to when the heating element is heating the glass filaments.

22. 16. Apparatus according to claim 14 or 15, further comprising at least one heating means for heating the stage.

23. 23. The apparatus of claim 22, wherein at least one laser beam heats the stage from behind.

24. 16. Apparatus according to claim 14 or 15, wherein the stage is provided in a build chamber having an inert atmosphere and / or a dry atmosphere with a dew point below -20°C.

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