Methods and Apparatus for Additive Manufacturing of Glass

Abstract

The present invention relates to an additive manufacturing method for producing three-dimensional components made of glass, comprising the steps of continuously feeding a glass filament (160) having a flame-retardant or self-extinguishing protective film (169) applied to its surface from a filament feeding nozzle (120) to a heating source, removing the flame-retardant or self-extinguishing protective film and softening the glass fiber, and applying the softened glass filament to a surface of a substrate (130) or object, wherein the flame-retardant or self-extinguishing protective film is made of a polyimide-based material and has a thickness in the range of 1 micron to 50 microns, and the fed glass filament length is less than 5 millimeters. The present invention also relates to glass filaments and uses thereof.

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 an apparatus for forming three-dimensional components from raw materials made of glass. [Background technology]

[0002] In glass 3D printing, or additive manufacturing, the raw materials can be supplied in either (1) molten form (molten glass), (2) liquid form (liquid resin filled with glass), (3) solid form using glass rods, or (4) glass fibers.

[0003] (1) In US10464305B2 and US10266442B2, a large crucible is used to pour the molten glass onto a 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 lower melting temperatures.

[0004] (2) In US2019 / 0292377A1k, US2020 / 0039868A1, WO2017 / 214179A1, and WO2020 / 118157A1, liquid resins filled with glass nanoparticles are used to build 3D solid objects using, for example, photolithography or inkjet printing techniques. Any organic binders are later burned out, and the porous object is then sintered at high temperatures into a solid glass object. The disadvantages of these techniques are the need for time-consuming post-processing and the limited thickness / dimensions of the printed object (to a few mm). The printing accuracy depends heavily on shrinkage control and homogeneity of the mixture. Defects, i.e. deformations, pores and cracks, are difficult to avoid.

[0005] (3) In WO2018 / 163006A1, US2020 / 0016840A1, continuous rod feeding is used for glass 3D printing. The printing uses glass rods as raw material. The feeding rods are loaded into a rotating cassette and fed through a print head that melts the glass, which is then deposited on the substrate. The continuous feeding is achieved by thermally bonding the rods during the process. This method of melting the glass using a crucible is limited to multi-component silicate glasses, such as soda-lime glass or borosilicate glass, which have a lower melting temperature. This technique also has a risk of nozzle damage due to the corrosive nature of the molten glass.

[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. For silica glass (quartz or fused silica), high temperatures of 1800-2000° C. are required. One method is to provide bare glass filaments, especially for filament sizes that typically have diameters greater than 1 mm.

[0007] However, it is well known in the field of optical fiber manufacturing that bare thin glass fibers are fragile and will break if not properly protected with a thin protective coating or film. Protective coatings or films are used to protect the fiber surface from mechanical interactions (e.g., abrasion) or chemical interactions (e.g., reactions with water or other chemicals) that would rapidly reduce the mechanical strength of the fiber. In the case of communication fibers, the coatings / films also have the function of reducing mechanically induced losses due to microbending.

[0008] For the same reason, when using thin glass fibers for additive manufacturing, a protective coating is necessary to protect the glass filaments during storage and handling. The protective coating may be applied during filament fabrication.

[0009] Prior filament-based glass additive manufacturing requires that protective coatings be removed from the glass filaments prior to printing [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]. Stripping of the coating can be accomplished using mechanical or chemical means (e.g., using sulfuric acid, dichloromethane) prior to feeding the filament into the hot additive fabrication zone.

[0010] Mechanical peeling of the coating may further weaken the mechanical strength of the filament, so this is not an ideal solution 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). 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 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.

[0011] The filament can be brittle without the coating, and delamination of the coating can further weaken the mechanical strength of the filament, posing an additional risk as filament breakage during printing would cause a major interruption to the printing process.

[0012] An alternative method is to burn off the coating, as demonstrated by [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)]. When the hot zone is heated to a very high temperature, the coating is burned off near the hot zone, i.e. the hot zone itself can be used to remove the coating. A problem with said method using commonly used fiber coatings is that they are more likely to leave residues that can result in undesirable combustion by-products and affect the purity of the print, and therefore are not energy efficient. Another problem with this method is the problem of controlling the amount of coating that is burned off, which can occur when the coating ignites and starts to burn the filament for long lengths even after the heat source is turned off.

[0013] Experimental fire spread tests have been performed on a standard telecommunications glass fiber. The glass fiber had a diameter of 125 μm and a standard acrylic coating 62.5 μm thick, for a total diameter of 250 μm. The coating was ignited using a CO2 laser, and when the laser was turned off, fire spread occurred with a flame propagation speed of about 10 mm / s (600 mm / min), which is typically faster than the filament feed rate during glass 3D printing.

[0014] When depositing the first layer on the printing substrate, the filament feed is typically slow to ensure sufficient adhesion to the build plate. Under typical conditions, 3D printing of glass is not done by depositing a single long continuous glass filament at a constant feed rate, but rather the filament is deposited in segments, one layer at a time, depending on the geometry of the object to be printed. Between segments the filament is cut, and during the cut the filament feed rate is zero or even negative (pulling back the filament). The relative position of the feed nozzle is then moved to a new location and continues with a different part of the print. Thus, during printing, there are many different printing conditions, combinations of laser irradiation conditions (temperature of the hot zone), and filament feed rate and feed direction.

[0015] If a protective coating exhibits self-sustaining combustion, there is a risk of fire spreading that could damage the delivery nozzle, destroy extensive filament lengths, and potentially destroy the 3D printer and result in personal injury. Therefore, using a protective coating that exhibits self-sustaining combustion is highly detrimental.

[0016] The coating solutions for 3D printing glass filaments described in [WO2020259898] contain polysaccharides and polyethenes and are generally not flame retardant or self-extinguishing and are not suitable for application to glass filaments in commonly used optical fiber draw towers, but are suitably applied by dip coating or by roller. These coatings typically have decomposition temperatures below 400°C and therefore require longer lengths of extruded filaments, typically greater than 5-20 mm.

[0017] To reduce the spread of the flame, an inert gas such as nitrogen or argon can be used to extinguish the flame, but the problem is that this significantly affects the burning (incinerating) efficiency of the coating, leaving coating residues that become embedded in the printed object. Another option is to use forced convection of air or oxygen gas to reduce the flame spread rate while maintaining efficient decomposition of the coating. The problem with this method is that it may not extinguish the flame, but only reduce the flame propagation rate. Furthermore, the injected gas flow causes significant and uncontrolled temperature fluctuations, and the reduced temperature stability of the hot zone causes poor print quality or print failure. Summary of the Invention [Problem to be solved by the invention]

[0018] The present invention aims to prevent the above-mentioned problems. The main object of the present invention is to provide an improved glass filament for use in forming three-dimensional components.

[0019] Another object of the present invention is to provide an additive manufacturing method for producing three-dimensional components made of glass. [Means for solving the problem]

[0020] According to the invention at least the main object is achieved by means of an additive manufacturing method having the features defined in the independent claims.

[0021] Preferred embodiments of the invention are further defined in the dependent claims.

[0022] According to a first aspect of the invention, there is provided an additive manufacturing method for producing a three-dimensional component / object made of glass, comprising the steps of: a. continuously supplying a glass filament from a filament supply nozzle to a heating source, in particular where the glass filament is made of fused quartz or fused silica and the glass filament has a flame-retardant or self-extinguishing protective film applied to a surface thereof, removing the flame-retardant or self-extinguishing protective film and softening the glass filament; b. applying the softened glass filaments to a surface of a substrate or print / object; and wherein the flame retardant or self-extinguishing protective film is made of a polyimide-based material and has a thickness in the range of 1 μm to 50 μm; c. The provided method comprises providing a glass filament length (L) that is less than 5 millimeters.

[0023] An advantage of this embodiment in fabricating three-dimensional components is that once the heat source is removed or the laser irradiation is turned off, the coating stops burning as it is flame retardant and self-extinguishing. Another advantage is that the burning of the coating does not produce toxic components. Another advantage is that the coating can be easily applied over long lengths of filament during filament fabrication using conventional optical fiber fabrication techniques.

[0024] In various exemplary embodiments according to this invention, the glass filaments are coated glass fibers having a diameter in the range of 100 to 500 μm.

[0025] An advantage of these embodiments is that filaments of different diameters may be selected depending on the complexity and / or design of the three-dimensional component.

[0026] In various exemplary embodiments of the invention, the heating source is at least one laser source.

[0027] An advantage of these embodiments is that one or more different types of laser sources may be used for heating purposes.

[0028] In another aspect of the invention, there is provided a glass filament for additive manufacturing of three-dimensional components of glass, said glass filament comprising a flame retardant or self-extinguishing protective film applied to a surface thereof, said film being made of a polyimide-based material and having a thickness in the range of 1 μm to 50 μm.

[0029] An advantage of this embodiment is that it provides a raw material for additive manufacturing that is flame retardant or self-extinguishing and does not form any toxic components when used in additive manufacturing.

[0030] In various exemplary embodiments of the invention, the glass filaments are hollow.

[0031] An advantage of these embodiments is that capillary structured filaments can be used to additively print complex structures, e.g., integrated microfluidic structures, i.e. additively manufactured components with hollow features / structures, etc. The volume of the hollow portion may be 10-70% of the volume of the glass content in the glass fiber.

[0032] In another aspect of the invention there is provided the use of glass filaments in an additive manufacturing method for producing three-dimensional components made of glass, said glass filaments being provided with a flame-retardant or self-extinguishing protective film applied to a surface thereof, said film being made of a polyimide-based material and having a thickness in the range of 1 μm to 50 μm.

[0033] Further advantages and features of the present invention will become apparent from the following detailed description.

[0034] 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. [Brief description of the drawings]

[0035] [Figure 1] FIG. 1 is a schematic side view of an exemplary embodiment of an apparatus for manufacturing three-dimensional components made of glass, which can be used to carry out the method according to the invention. [Diagram 2] FIG. 2 is a schematic side view of a glass filament and a filament delivery nozzle. [Diagram 3] 3a-3c show various exemplary embodiments of glass filaments having a protective coating. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0036] The method of the invention relates to a novel additive manufacturing (AM) process where, using a digital model, the geometry of a component is constructed by fusing together multiple glass filaments, free-standing or locally deposited, layer by layer, by locally melting them using an energy source such as a laser beam.

[0037] The present invention relates to a direct manufacturing process by integrating flame retardant and / or self-extinguishing protective films / coatings and their removal from glass filaments within the printing process. This means that the new process can produce fully or nearly fully dense glass components / objects using glass filaments and overcomes all the drawbacks of prior art glass manufacturing methods.

[0038] The new process may enable the direct manufacture of three-dimensional glass components without producing toxic by-products, avoiding health risks.

[0039] The inventors have now identified polyimide-based coatings as suitable filament coatings for laser-based 3D printing. Polyimides are inherently flame-resistant. Polyimides exhibit flame retardant and self-extinguishing properties. Experiments reveal that when combustion is initiated using an open flame or CO2 laser heating, polyimide-coated fused silica and fused quartz fibers with diameters of approximately 200 μm do not ignite or exhibit sustained combustion once the heat source is removed or turned off.

[0040] An additional advantage of polyimide-based coatings is that the coatings can be applied to the glass filaments using techniques commonly used in standard optical fiber draw towers.Typical coating thicknesses for polyimide coatings range from 1 μm to 50 μm, typically 5 μm to 25 μm.

[0041] An added advantage is that the combustion by-products of polyimide burned in an air (or oxygen) atmosphere are generally carbon dioxide, water and nitric oxide, ie, the combustion produces non-toxic fumes.

[0042] Therefore, to protect the delivery nozzle, the filament and filament cassette, the 3D printer, as well as the personal safety of the operator and the environment, it is extremely important that the glass filament film / coating is flame resistant, should be flame retardant, and / or should exhibit self-extinguishing properties.

[0043] Decomposition of polyimide occurs above 400°C, typically above 600°C. Such high temperatures are advantageous because the coating is then removed very close to the hot zone, allowing for a shorter distance between the tip of the feed nozzle and the hot zone, thereby allowing for a shorter length of filament extruded from the nozzle. The fed glass filament length L should be less than 5 millimeters. By using a shorter length of filament extruded from the nozzle, the mechanical properties (stiffness) of the filament allow for a significant improvement in printing accuracy and resolution during printing. The preferred length of the extruded filament with a diameter of about 200 μm is typically less than 5 mm, with the polyimide coating typically being removed within 1 mm of the hot zone.

[0044] 1 shows a schematic side view of an exemplary embodiment of an additive manufacturing apparatus 100 according to the present invention configured to manufacture three-dimensional components of glass. 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 in an xy plane relative to the stage 130 such that the filament delivery nozzle 120 covers a predetermined area of ​​the stage 130. The relative movement may be such that the stage 130 is fixed and the filament delivery nozzle 120 moves in xyz directions, or alternatively, the stage 130 may be movable in xy directions while the filament delivery nozzle is fixed. To additively manufacture three-dimensional components and to maintain a constant distance between the filament delivery nozzle and the top surface of the component to which a new layer is applied, one or both of the filament delivery nozzle 120 and / or the stage 130 may be movable in the Z direction, i.e., for each newly applied layer, the stage 130 may be moved downward in the Z direction by a distance corresponding to the thickness of the newly applied layer, or the filament delivery nozzle 120 may be moved upward in the Z direction by a distance corresponding to the thickness of the newly applied layer, or the downward movement of the stage in the Z direction and the upward movement of the filament delivery nozzle in the Z direction may be combined to maintain a constant distance between the filament delivery nozzle and the top surface of the component to which a new layer is applied. The filament 160 may be fed to the filament delivery nozzle 120 via a guide 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, etc. The laser beam 150 may be continuous or pulsed. The laser beam softens or melts the filament in a hot zone 140 adjacent the stage, onto which the softened or molten glass is deposited.

[0045] The filament delivery 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 delivery nozzle with respect to the stage 130. The control unit may also control the laser and laser optics.

[0046] 1, a filament delivery nozzle 120 provides feedstock 160 onto a stage 130 to form a layer of a three-dimensional component. 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. The thickness of the build plate may range from a few tenths of a mm to a few centimeters.

[0047] The first step is the fusion and deposition of the feedstock material onto stage 130. The filament delivery nozzle locally deposits the feedstock material along a predetermined path. The filament delivery nozzle may heat the feedstock material before it exits the nozzle and heads towards stage 130. The nozzle may be adapted to the size and shape of the feedstock material.

[0048] Three-axis kinematics allow the filament delivery nozzle 120 to be positioned within the work envelope of the machine, producing three-dimensional components layer by layer. The raw material 160 is a glass filament. The glass filament 160 has a flame-retardant and / or self-extinguishing protective coating or film 169 applied to its surface.

[0049] 1, only one filament delivery nozzle 120 is shown being used. In various exemplary embodiments, multiple filament delivery nozzles may be used in series or parallel. In various exemplary embodiments, multiple lengths of feedstock 160 may be provided simultaneously on stage 130 to speed up deposition of the feedstock on stage 130.

[0050] One feedstock nozzle may provide the raw material or filament 160 at a first predefined layer area of ​​the three-dimensional component, and two or more nozzles may be used at a second predefined layer area of ​​the three-dimensional component, i.e., the formation of the layer may be varied between one, two, three or more nozzles depending on the shape of the layer to be formed and / or the type of material to be added. In various exemplary embodiments, the multiple nozzles for providing the feedstock / filament on the substrate may have the same diameter or different diameters. The multiple filament delivery nozzles may provide feedstock of different glass materials. In various exemplary embodiments, one feedstock nozzle may include multiple different feedstocks, e.g., multiple fibers of the same material, different materials and / or different diameters.

[0051] In synchronization with the filament extrusion, the tip of the filament 180 is 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 are intended to extend the manufacturing flexibility.

[0052] 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.

[0053] 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.

[0054] To verify and prove process capability, the following aspects may require further testing, such as evaluating achievable manufactured layers, achieving minimum requirements for geometric accuracy, quantifying material shrinkage from nominal design, ensuring achievable layer adhesion and / or defect-free 3D printing, etc.

[0055] One or more laser beams may be used simultaneously to melt / soften the glass filaments.

[0056] The present invention relates to glass filaments for use in laser-based glass 3D printers. Bare glass filaments have poor mechanical properties and are therefore prone to breakage. Protective coatings are required for mechanical and chemical protection of glass filaments during storage and handling. To increase safety during mechanical operation, the coating needs to be flame-retardant and self-extinguishing to avoid self-sustained open flame propagation. Flame-retardant and self-extinguishing protective coatings can be applied during filament fabrication, for example, using fiber draw towers used to produce optical fibers. A furnace heats the preform (which is like an expanded filament in both shape and composition). The softened glass is then drawn to the correct filament dimensions using a capstan in combination with a diameter gauge and a tensiometer. As the filament is drawn, the preform is further fed into the furnace. Typically, a coating resin can be introduced into the coating cup through which the filament passes. The coating can then be cured thermally or, for example, using a UV lamp before the filament is wound onto a spool for storage and transportation. Polyimides are inherently flame-resistant. Polyimides exhibit flame retardant and self-extinguishing properties. The curing temperature of polyimide-based coatings on optical fibers may typically be carried out within a temperature range of about 100-400°C.

[0057] Polyimide-based coatings on optical fibers can withstand operating temperatures of about 300 °C and are commonly used for higher temperature (sensing) applications. Here, coating thicknesses of 10-15 μm are typically used. Thicker coatings can be applied by repeating the coating procedure to add multiple coating layers.

[0058] 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.

[0059] The preferred outer diameter of the glass filament is in the range of 100 μm to 500 μm. The diameter greatly affects 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 140, as well as the printing speed. A schematic of the printing nozzle and the extruded filament is shown in Figure 2. For stiffer filaments, the distance between the filament delivery nozzle and the hot zone 140 may be increased. Thus, the filament diameter, nozzle design, and distance to the hot zone 140 greatly affect the resolution, accuracy, and quality of the print. 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 resolution of the printer decreases. If the length of the extruded filament is too short, the filament delivery nozzle may be damaged by the hot zone, which can reach temperatures of over 2000 °C.

[0060] The total deflection / displacement δ of the filament is given by:

[0061]

number

[0062] During glass 3D printing, the glass filament is continuously fed into a high temperature zone at 1800-2200 °C. One common method is to feed it using uncoated glass optical fiber. However, most optical fibers are produced with a coating, so removal of the coating 169 is necessary to produce a pure glass filament before printing. Peeling of the coating 169 can be done using mechanical or chemical means (e.g., using sulfuric acid, dichloromethane). The peeling process limits the total length of the printable glass filament (i.e., maximum mechanical peeling of a few meters, maximum chemical peeling of 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 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).

[0063] Another approach is to directly feed coated filaments. With a protective coating, the printable filament length is extended to the kilometer range. However, since the 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, filament destruction and damage to the 3D printer. Furthermore, standard coatings have a thickness of about 62.5 μm, which is significantly 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.

[0064] Our approach is to produce glass filaments 160 with a thin flame-retardant and self-extinguishing coating 169. When the hot zone 140 is heated to an extremely high temperature, for example using a CO2 laser beam, the coating starts to burn off near the hot zone 140, i.e. the hot zone 140 itself can be used to remove the protective coating 169. If the protective coating 169 is flame-retardant and self-extinguishing, the risk of an open flame is eliminated. When the laser and filament supply are turned off, the coating combustion process stops. The thin coating is easily incinerated. 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.

[0065] The filament 160 of the invention for additive manufacturing offers the possibility of applying a thin flame-retardant and self-extinguishing protective coating layer 169 to the glass filament, while still providing mechanical and chemical protection of the filament during (temporary) storage and handling. The protective coating 169 can be easily removed by thermal means (heating / plasma / laser irradiation). The protective coating 169 may be one that does not contain toxic components or produce harmful combustion products when incinerated. The protective coating 169 may not have the property of self-sustaining combustion.

[0066] The additive manufacturing method according to the invention may be used to generate three-dimensional components made of glass. The method comprises the steps of continuously feeding a glass filament having a flame-retardant and / or self-extinguishing protective film applied to its surface from a filament feeding nozzle to a heating source, removing the flame-retardant and self-extinguishing protective coating and softening the glass fiber, and applying the softened glass fiber to a surface of a substrate or print / object, wherein the flame-retardant and self-extinguishing protective coating is made of a polyimide-based material and has a thickness in the range of 1 μm to 50 μm, and the fed glass filament length L is less than 5 millimeters. The feeding of the glass filament may be continuous or discontinuous.

[0067] FIG. 2 shows a side view of a filament delivery nozzle 120. Extending from the filament delivery nozzle 120 is a filament 160. The length of the filament from the exit of the filament delivery nozzle 120 to the surface of the substrate 130 where at least one laser beam impinges on the filament is indicated as L. It should be understood that the delivered glass filament length L is the distance between the filament delivery nozzle 120 and the surface to which the glass filament 160 is applied, either the surface of the substrate 130 or the surface of the printed item / object. In various exemplary embodiments, the delivered glass filament length L may be greater than 10 mm, but may be less than 5 mm according to the present invention. An L longer than 5 mm increases filament misalignment, as shown by the dashed filament in FIG. 2. Any filament misalignment, which may be the distance between the non-misaligned central portion of the tip 180 of the filament 160 and the misaligned central portion of the same tip 180, results in misalignment of the filament with respect to its intended location on the surface of the substrate or printed item / 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 filament delivery nozzle outlet during additive manufacturing. The length of the remaining protective coating portion during manufacturing can be at least a few tenths of a millimeter.

[0068] 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 and fused quartz glass (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 designed shapes and refractive index structures. 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, B3O3, 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.

[0069] FIG. 3b shows a glass filament 160 with a central air hole 162, i.e., a capillary or hollow structure. These capillary / hollow 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.

[0070] 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, B3O3, F. These core / cladding filaments acting as optical waveguides can be used to print optical circuits onto 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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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. 1. An additive manufacturing method for producing three-dimensional components / objects made of glass, comprising: a. continuously feeding a single glass filament (160) from a filament feeding nozzle (120), the glass filament (120) having a single flame-retardant or self-extinguishing protective film (169) applied to a surface thereof, removing the single flame-retardant or self-extinguishing protective film (169) and feeding the glass filament (160) to a heat source to soften it; b. applying the softened glass filaments (160) to a surface of a substrate (130) or object, wherein the flame-retardant or self-extinguishing single protective film (169) is made of a polyimide-based material and has a thickness in the range of 1 μm to 50 μm; c) the length (L) of the delivered glass filament is the distance between the filament delivery nozzle (120) and the surface of the substrate (130) or object and is less than 5 millimeters.

2. The method of claim 1, wherein the glass filaments are glass fibers having a diameter in the range of 100 to 500 μm.

3. The method of claim 1 or 2, wherein the heating source is at least one laser source.

4. 3. The method of claim 1 or 2, wherein the glass filament (160) is hollow, the method further comprising providing a gas pressure to an interior of the hollow filament to produce a three-dimensional component having the hollow feature.

5. 1. A single glass filament (160) for additive manufacturing of three-dimensional components of glass, the single glass filament (160) having a single flame-retardant or self-extinguishing protective film (169) applied to a surface thereof, the film (169) being made of a polyimide-based material and having a thickness in the range of 1 μm to 50 μm.

6. The glass filament of claim 5, wherein the glass filament (160) is a glass fiber having a diameter in the range of 100 to 500 μm.

7. The glass filament of claim 6, wherein the glass filament (160) is an optical fiber.

8. The glass filament according to claim 6 or 7, wherein the glass filament (160) is hollow.

9. The glass filament of claim 8, wherein the volume of the hollow portion is 10-70% of the volume of the glass content in the glass filament (160).

10. 1. Use of a single glass filament (160) in an additive manufacturing method for producing a three-dimensional component made of glass, said single glass filament (160) having a single flame-retardant or self-extinguishing protective film (169) applied to a surface thereof, said film (169) being made of a polyimide-based material and having a thickness in the range of 1 μm to 50 μm.

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