Apparatus for additive manufacturing

Abstract

The invention relates to an apparatus (100) for additive manufacturing of a three-dimensional glass object. The apparatus comprises: a platform (130) for supporting a glass object, a laser beam source (110) for providing a main laser beam (150), a printer head (102) comprising at least one glass filament feed nozzle (120) for feeding a glass filament (160) towards a deposition location (140) in order to form the glass object, and means for relative movement of the printer head (102) and the platform (130); and a beam path unit configured to direct the laser beam (150) from the laser beam source (110) to the deposition location (140) for heating the glass filament (160). The apparatus is characterized in that the beam path unit comprises a beam splitter (145) for splitting the main laser beam (150) into at least three partial laser beams (150 '), where the beam path unit is configured to direct each of the at least three partial laser beams (150') from the beam splitter (145) to the deposition location (140), and a feedback control unit configured to feed back the beam path unit to the deposition location (140), where the beam path unit is configured to direct each of the at least three partial laser beams (150 ') from the beam splitter (145) to the deposition location (140). Comprising means for monitoring a process parameter representative of the temperature at the deposition location (140) and means for controlling the power of the main laser beam (150) in order to adjust the temperature at the deposition location (140) towards a predetermined level.

Description

Technical Field

[0001] The present invention generally relates to the field of additive manufacturing. Specifically, the present invention relates to an apparatus for additive manufacturing, wherein the apparatus is used to form a three-dimensional component / object from a raw material of glass material onto a platform. As used herein, the term "platform" includes any element / body / support onto which a glass object can be directly or indirectly printed.

[0002] The present invention particularly relates to an apparatus for additive manufacturing of three-dimensional glass objects, wherein the apparatus includes a platform for supporting the printed glass object, a laser beam source for providing a primary laser beam, a printer head, and means for relative movement of the printer head and the platform. The printer head includes at least one glass filament feed nozzle for feeding a glass filament toward a deposition location to form the glass object, and a beam path unit configured to direct the laser beam from the laser beam source to the deposition location for heating / melting the glass filament. Background Art

[0003] In glass 3D printing or glass additive manufacturing, existing technologies include (1) extrusion of hot glass from a furnace, (2) glass rod deposition, (3) stereolithography / ink-jetting using a glass-polymer mixed solution, and (4) glass filament deposition.

[0004] Technology (1). In US10464305B2 and US10266442B2, a translation stage is used to pour liquid glass from a large crucible into a predetermined geometry onto a build plate / platform. A disadvantage of this method is the risk of damage to the nozzle by the molten glass, and therefore it is limited to multi-component silicate glasses with lower melting temperatures, such as soda-lime glass or borosilicate glass. The layer thickness is approximately 10 mm, so this technology is only suitable for large-scale printing with relatively poor resolution. Energy consumption is the highest of all existing technologies.

[0005] Technology (2). In US2020 / 0070415A1 and WO2020 / 167470A1, continuous filament feeding is used for glass 3D printing. Printing uses glass rods with a diameter greater than 1 mm as raw material. The feed rods are fed through the print head and deposited on the substrate. It is impossible to print glass at temperatures above 1700°C, which limits the material selection. The problems with this system are the risk of damage to the nozzle by the molten glass, the printing volume is limited by the volume of the glass rods, the gap between the feed rods leads to uneven printing quality, and the setup is considered to have high mechanical complexity.

[0006] Technology (3). In US2020 / 0039868A1, WO2017 / 214179A1 and WO2020 / 118157A1, glass powder is mixed with a liquid polymer. During the printing process, a 3D green body is first created with the aid of a polymer 3D printer. The green body is then subjected to a debind process to produce a porous body of pure glass. The porous body is sintered to ultimately form a "dense" glass object. The glass content in the original mixture is low. Therefore, due to the large volume shrinkage, this technology is generally only able to create models smaller than 10 mm. In addition, 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.

[0007] (4) Laser-based melting of thin glass filaments or optical fibers has also been used for glass 3D printing, see [JM Hostetler et al., FIBER-FED PRINTING OF FREE-FORM FREE-STANDING GLASS STRUCTURES, Solid Freeform Fabrication 2018: Proceedings of the 29th International Annual Conference, 994-1002] and [T. Grabe et al., Additive Manufacturing of fused silica using coaxial laser glass deposition, experiment, simulation and discussion, Proceedings of SPIE 11677, Laser 3D Manufacturing VIII, 116770Z (March 8, 2021)]. Using a laser, non-contact heating is achieved, which means that no glass melt comes into contact with the crucible wall, thereby avoiding crucible corrosion and contamination of the glass melt. Here, silica glass fibers / filaments are continuously fed into a deposition position or hot zone, which has a temperature sufficient to soften the glass. For silica glass (quartz- or fused-silica), temperatures in the range of 1800 to 2000° C. are required.

[0008] However, in the paper by [JM Hostetler et al.], only one laser beam was used to soften / melt the glass filament. Such asymmetric heating significantly limits the ability to directional print. Furthermore, the non-uniform temperature gradients in the molten glass filament can cause high residual stresses in the printed object, which can lead to material failure and interruption of the printing process. This technique uses bare glass filament printing, which means that any coatings need to be removed / stripped from the glass filament before printing / deposition. Stripping the coating can be performed using mechanical or chemical means (e.g., using sulfuric acid, dichloromethane, etc.) before the glass filament is fed into the hot zone / deposition position. However, such methods leave the glass filament unprotected during the final stage of the printing process (i.e., during the mechanical feeding of the glass filament into the hot zone). Stripping the coating can further weaken the mechanical strength of the glass filament, which is not an ideal solution, as filament breakage during printing would cause a serious interruption in the printing process. Due to the risks associated with using strong acids (sulfuric acid) or dichloromethane (carcinogenic), the use of chemical means is not preferred. The stripping process also limits the total length of printable glass filaments, i.e., the maximum mechanical stripping is less than a few meters, and the maximum chemical stripping is typically less than 50 meters, which severely restricts the continuity and capacity (volume) of the 3D printing process.

[0009] In [T. Grabe et al.], one main laser beam is split into four sub-laser beams directed to the hot zone from different directions. However, the quality of the sub-laser beams is poor because they are not uniform Gaussian laser beams like the main laser beam. Therefore, the problem of uneven heating still exists. According to this method, coated glass filaments are used. The coating is burned off from the glass filament near the hot zone, that is, the hot zone itself can be used to remove the coating. The problem with the method using conventional fiber coatings is that it may cause undesirable combustion by-products, making it more likely to leave residues that affect the purity of the printed object. Another problem is that even after the heat source is turned off, the coating may ignite and start burning long lengths of the filament. Therefore, process gas is required to suppress the burning of the coating. In order to burn off the coating, excessive energy is required, which causes a large amount of glass to vaporize during printing.

[0010] During laser-based 3D glass printing, glass vaporization is common and difficult to eliminate. Vaporization creates undesirable fumed silica particles that attach to surrounding surfaces, such as nozzles and mirrors. The presence of fumed silica particles increases the risk of contamination and damage to the system's optics. Controlling the vaporization rate (i.e., the temperature at the deposition location) and the process fumes are crucial.

[0011] Therefore, there remains a great need in the field of additive manufacturing to provide an additive manufacturing method / apparatus for printing glass objects, wherein a stable / correct temperature is achieved throughout the deposition location (hot zone) to obtain the printed glass object without detrimental defects, and wherein the apparatus is not limited to any particular printing orientation with respect to the relative movement of the platform and the printer head.

[0012] Purpose of the Invention

[0013] The present invention aims to eliminate the above-mentioned drawbacks and disadvantages of previously known methods / devices for additive manufacturing of three-dimensional glass objects and to provide an improved device. The main object of the present invention is to provide an improved device for additive manufacturing of three-dimensional glass objects of the initially defined type, which device ensures a stable / correct temperature throughout the deposition location (hot zone) in order to obtain a printed glass object without harmful defects.

[0014] Another object of the present invention is to provide an improved apparatus for additive manufacturing of three-dimensional glass objects that is not restricted to any particular printing direction with respect to the relative / mutual movement of the platform and printer head. Summary of the Invention

[0015] According to the present invention, at least the primary object is achieved by means of the initially defined device having the features defined in the independent claim. Preferred embodiments of the invention are further defined in the dependent claims.

[0016] According to the invention, the beam path unit comprises a beam splitter for splitting a main laser beam into at least three partial laser beams, wherein the beam path unit is configured to direct each of the at least three partial laser beams from the beam splitter to a deposition location, and comprises a feedback control unit comprising means for monitoring a process parameter representative for a temperature at the deposition location and means for controlling the power of the main laser beam in order to regulate the temperature at the deposition location towards a predetermined level.

[0017] The present invention is therefore based on the insight of the inventors that a stable / correct temperature throughout the deposition location (hot zone) is the single most important factor for obtaining printed glass objects without harmful defects. Furthermore, the present invention is based on the insight of the inventors that a stable / correct temperature depends at least on the power of the main laser beam, the direction of incidence of the laser beam, and the position of the laser beam focus relative to the deposition location.

[0018] An immediate advantage of splitting the main laser beam into at least three partial laser beams is that multiple laser beams can be provided symmetrically around the glass filament (deposition location), which provides uniform temperature, reduced melting / softening time and improved heating efficiency.

[0019] According to various embodiments of the present invention, the process parameter representing the temperature at the deposition location is constituted by the power of the main laser beam upstream of the beam splitter in the printer head. This facilitates a clear relationship between the measured power of the main laser beam and the control of the main laser beam power generated in the laser beam source.

[0020] According to various embodiments of the present invention, the means for monitoring a process parameter consisting of the power of the main laser beam includes a beam tap configured to split a predetermined sample of the main laser beam toward a detector / power meter. Thus, the power of the unredirected portion of the main laser beam is determined using a simple mathematical calculation, where the power of the main laser beam is proportional to the temperature at the deposition location.

[0021] According to various embodiments of the present invention, the beam path unit includes means for providing circular polarization to the main laser beam upstream of the beam splitter. As a result, the laser beam source used can be of a less expensive and less complex nature, i.e. any negative effects originating from possible unstable polarization of the laser beam source are reduced / eliminated.

[0022] According to various embodiments of the present invention, the beam path unit includes a pyramid mirror located downstream of the beam splitter to diverge the at least three partial laser beams from one another. According to various embodiments, the beam path unit includes one or more secondary beam steering mirrors for each partial laser beam, the one or more secondary beam steering mirrors being configured to direct the partial laser beam toward the deposition location. This reduces the length of the beam path and, consequently, reduces / eliminates any negative effects of possible unstable wavelengths of the primary laser beam.

[0023] Further advantages and features of the invention will be apparent from the other dependent claims and from the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] A more complete understanding of the above and other features and advantages of the present invention will be apparent from the following detailed description taken in conjunction with the accompanying drawings, in which:

[0025] FIG1 is a schematic diagram of a prior art apparatus for additive manufacturing of three-dimensional glass objects,

[0026] Figure 2 is a schematic diagram of an apparatus according to the present invention for additive manufacturing of three-dimensional glass objects.

[0027] Figure 3 is a schematic perspective side view of the apparatus of the present invention disclosing the interior of a printer head according to a first exemplary embodiment.

[0028] Figure 4 is a schematic perspective side view of the apparatus of the present invention disclosing the interior of a printer head according to a second exemplary embodiment.

[0029] Figure 5 is a schematic perspective side view of the device of the invention disclosing the interior of a printer head according to a variant of the first exemplary embodiment.

[0030] Figure 6 is a schematic perspective side view of the apparatus of the present invention disclosing the interior of a printer head according to a third exemplary embodiment.

[0031] Figure 7 is a schematic perspective side view of the device of the invention disclosing the interior of a printer head according to a variant of the third exemplary embodiment.

[0032] Figure 8 is a schematic side view of a glass filament and a filament feed nozzle, and

[0033] Figure 9a-9c are schematic diagrams of various example embodiments of glass filaments. DETAILED DESCRIPTION

[0034] The present invention relates to the field of additive manufacturing (AM) of three-dimensional glass objects using digital / computer models, i.e. the component / object geometry is built up by fusing glass filaments / fibers which are melted layer by layer or in batches using an energy source such as a laser beam, either by simple scanning or selective melting of the printed contour after the fusing process.

[0035] Reference is first made to FIG. 1 , which discloses a prior art apparatus for additive manufacturing of three-dimensional glass objects. The apparatus includes a platform 130, a laser beam source 110 that provides a laser beam 150, and a glass filament feed nozzle 120 that provides a glass filament 160 having a coating 169 to a deposition location 140. The glass filament feed nozzle 120 is part of a printer head or constitutes the printer head. The glass filament feed nozzle 120 and the platform 130 are configured to move relative to each other to apply a layer or strand of glass material to the glass object at the deposition location 140 (also referred to as the hot zone). The glass filament 160 can be fed to the glass filament feed nozzle 120 via a conduit 170. This also applies to the present invention.

[0036] Now Figure 2Reference is made to FIG. 1 , which discloses a schematic diagram of an inventive apparatus for additive manufacturing of three-dimensional glass objects, wherein the apparatus is generally designated 100. Apparatus 100 includes a platform 130 for supporting the glass object, a laser beam source 110 for providing a primary laser beam 150, and a printer head 102. As used herein, the term platform 130 includes any element / body / support on which a glass object can be printed, either directly or indirectly (e.g., via a build plate / object connected to platform 130). Thus, a build plate / object can be connected to platform 130, with the glass object printed on the build plate / object, and still be considered supported by platform 130. The build plate / platform can be made of any material, such as the same material as the final three-dimensional glass component / object, a ceramic material, or any other metallic material different from the material of the three-dimensional glass object / component. Hereinafter, unless otherwise mentioned, the use of the term platform 130 should be understood to also include build plates, components, objects, etc.

[0037] The printer head 102 and / or the platform 130 can be mounted on a robot, such as an articulated robot having one or more rotary joints, a Cartesian robot having linear axes, a cylindrical robot having one rotary axis and two linear axes, or a combination thereof. Therefore, the apparatus 100 includes components for relative / mutual movement of the printer head 102 and the platform 130, namely, motorized supports. Thus, one or both of the printer head 102 and / or the platform 130 can be displaced in a direction perpendicular to the surface of the platform 130 or a predetermined geometric plane so as to allow additive manufacturing of three-dimensional glass components / objects and to allow the distance between the printer head 102 and the top surface of the platform or component / object to which a new layer is to be attached to be maintained at a constant distance, i.e., for each newly applied layer, the platform 130 can be moved back (away from the printer head 102) a distance corresponding to the thickness of the newly applied layer, or the printer head 102 can be moved away from the platform 130 a distance corresponding to the thickness of the newly applied layer, or a combination of movements of the platform 130 and the printer head 102 so as to maintain a constant distance between the printer head 102 and the top surface of the platform or component / object to which the new layer is to be attached.

[0038] The control unit can control the relative movement of the printer head 102 with respect to the platform 130. The printer head 102 can be configured to move in a plane substantially parallel to the platform 130 and relative to the platform 130 so that the printer head 102 covers a predetermined area of ​​the platform 130. The platform can be arranged in a vertical direction or any other direction. The relative movement can be such that the platform 130 is fixed and the printer head 102 moves in the plane. In an alternative embodiment, the platform 130 is moving and the printer head 102 is fixed so as to cover the entire platform 130. In another alternative embodiment, both the platform 130 and the printer head 102 can move in the plane to allow the printer head 102 to cover the entire area of ​​the platform 130. The printer head 102 and / or the platform 130 can also preferably be tilted relative to each other so as to be able to print new layers that are not necessarily parallel to other layers.

[0039] The laser beam source 110 can be mounted directly to the printer head 102, i.e., connected as a unit, or can be separate from the printer head 102. According to various embodiments in which the laser beam source 110 is separate from the printer head 102, the apparatus 100 can include free-space optics to direct the primary laser beam 150 from the laser beam source 110 to the printer head 102 (i.e., a bare laser beam), or can include optomechanical directing components (i.e., an unexposed laser beam), or can include fiberglass / laser guide directing components (i.e., a flexible fiber), or a combination thereof. The printer head 102 can print in any orientation (i.e., vertical, horizontal, from above, from below, tilted at any degree, etc.), and the platform 130 can be oriented in any orientation.

[0040] Now Figure 3 Reference is made to the figure which discloses a first exemplary embodiment of the inventive apparatus 100 for additive manufacturing of three-dimensional glass objects. The outer housing of the printer head 102 is removed. The printer head 102 includes a glass filament feed nozzle 120 configured to feed and direct a glass filament 160 toward a deposition location 140 (also referred to as a hot zone). The glass filament 160 can be fed to the filament feed nozzle 120 via a flexible tube 170. The laser beam source 110 can be a CO2 laser, a CO laser, an Nd:YAG laser, a fiber laser, an excimer laser, a nitrogen laser, or the like. The laser beam 150 can be continuous or pulsed, or a combination thereof. The laser beam 150 softens or melts the glass filament 160 at the deposition location 140, which is near the component / object or platform 130 to which the glass filament 160 is to be attached.

[0041] Through Figure 3Providing the platform 130 in a vertical orientation, as disclosed in

[15] , ensures that any fumes (such as silica particles generated by overheating) from, for example, combustion byproducts of the coating material or vaporized / molten glass, are moved upward rather than toward the interior of the printer head 102. This is beneficial because such fumes could otherwise damage the optics of the printer head 102 and the glass fiber feeder nozzle 120, requiring frequent cleaning or part replacement. Furthermore, by arranging the platform 130 vertically, relative movement of the printer head 102 and the platform 130 can be performed such that any fumes and gaseous matter exiting the hot zone are positioned outside the optical path of the laser beam, thereby improving the performance of the additive manufacturing apparatus 100. The present invention is not limited to a vertical orientation of the platform 130.

[0042] During additive manufacturing, glass filaments (i.e., feed material) are melted / deposited onto a platform 130 or object. The filament feed nozzle 120 deposits the glass filaments locally along a predetermined path provided from a slice computer model. The filament feed nozzle 120 may preheat the glass filaments before the glass filaments exit the nozzle 120 on their way to the platform 130. The filament feed nozzle 120 may adapt to the size and shape of the glass filaments, but may also be configured to be able to feed different glass filaments having different sizes / diameters. Therefore, there may be gaps between the glass filaments 160 and the glass filament feed nozzle 120, wherein the fumed silica particles must not enter such gaps. In Figure 3 In FIG, only one glass filament 160 is fed to the platform 130, but according to various example embodiments, a plurality of glass filaments 160 having the same or different shapes and / or material compositions / colors may be sequentially fed through a single filament feeding nozzle 120 in order to perform multi-material deposition. Figure 3 In the embodiment shown, only one filament feed nozzle 120 is used, but according to various exemplary embodiments, multiple filament feed nozzles can be used, which are positioned adjacent to each other and oriented more or less parallel to each other so as to direct the glass filaments 160 to the same deposition location 140. According to various exemplary embodiments, multiple strands of glass filaments 160 can be simultaneously provided to the platform 130 to provide three-dimensional glass components of different materials / colors. Different layers of the three-dimensional component can include different materials, and / or different locations within a single layer can include different materials, i.e., multi-material deposition can be made within a layer and / or in different layers.

[0043] Figure 3A schematic side view of an exemplary embodiment of an additive manufacturing apparatus 100 configured to manufacture three-dimensional glass objects according to the present invention is disclosed. The apparatus 100 includes a platform 130, a laser beam source 110, and a printer head 102 having a filament feed nozzle 120. Furthermore, the printer head 102 includes a beam path unit configured to direct a laser beam 150 from the laser beam source 110 to a deposition location (hot zone) 140 for heating a glass filament 160, and to an area of ​​the object or platform 130 to which the glass filament 160 is to be attached / adhered. The beam path unit can be based on a technology using reflective and / or transmissive optics.

[0044] The beam path unit comprises a beam splitter 145 for splitting the main laser beam 150 into at least three partial laser beams 150 ′. The beam path unit is configured to direct each of the at least three partial laser beams 150 ′ from the beam splitter 145 to the deposition position 140 . Figure 3 The use of four partial laser beams 150' is disclosed. By directing the at least three partial laser beams 150' onto the deposition location 140, the at least three partial laser beams 150' are used to heat the glass filament 160 at the deposition location 140. The laser beam source 110 can operate in a wavelength region where the glass filament 160 has high light absorption, which causes the glass filament 160 to melt / soften when irradiated by the laser beam 150.

[0045] Therefore, independent of the direction of relative movement of the printer head 102 and the platform 130 , the beam splitter 145 is used to enable the plurality of partial laser beams 150 ′ to be directed towards the deposition location 140 from different directions, thereby obtaining a uniform temperature throughout the deposition location (hot zone) 140 .

[0046] The glass filament feed nozzle 120 is configured to feed the glass filament 160 in a direction perpendicular to a geometric plane, wherein the geometric plane is preferably the plane on which the layer is being printed, wherein each of the at least three partial laser beams 150' has an angle of incidence in the range of 30-60 degrees (preferably in the range of 40-50 degrees, and most preferably about 45 degrees) with respect to the geometric plane. The beam path unit is configured to direct the partial laser beams 150' toward the deposition position 140. The geometric plane is generally parallel to the platform 130. The geometric plane can be a spherical surface or a non-planar surface.

[0047] Silica and silica-based glass filaments have strong absorption at wavelengths above 2.2 μm. Irradiating glass filament 160 with a CO 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 absorption of radiation, leading to subsequent heating of glass filament 160. A CO laser operating at a wavelength of 10.6 μm can be used. At this wavelength, silica glass is opaque, resulting in efficient heating. The absorption depth is approximately 2 μm to 40 μm and is effective for heating glass filaments 160 having diameters in the 100-300 μm range. For larger glass filaments, the shallow penetration depth at 10.6 μm makes it difficult to heat rapidly without causing significant vaporization. Using a CO laser operating at 5.5 μm is more suitable for glass filaments larger than approximately 0.5 mm. The penetration depth at 5.5 μm is much greater (100 μm), resulting in more efficient energy deposition into glass filament 160.

[0048] The beam path unit also includes a feedback control unit that includes components for monitoring a process parameter representative of the temperature at the deposition location 140, and components for controlling the power of the main laser beam 150 in order to adjust the temperature at the deposition location 140 toward a predetermined level. The temperature at the deposition location 140 determines the viscosity of the deposited glass material and has a significant impact on the printing result. For long-duration printing, the temperature must be well controlled over time in order to provide high-quality printed glass objects.

[0049] The predetermined temperature level can vary across a single layer of the glass object, can vary for different layers of the glass object, or a combination of both. The predetermined temperature level can depend, for example, on the printing speed, the glass filament feed speed, the material type at the deposition location (i.e., platform, build plate, glass object, etc.), the width and / or thickness of the previous layer(s) of the object, the glass filament cutoff, etc. Thus, if the process parameters indicate that the temperature stage is too low, the power of the main laser beam 150 is increased by controlling the laser beam source 110, and vice versa. The temperature at the deposition location 140 is proportional to the power of the main laser beam 150.

[0050] The means for monitoring a process parameter representative of the temperature at the deposition location 140 may be comprised of equipment configured to monitor blackbody radiation at the deposition location 140, i.e., temperature measurement at or near the deposition location 140 using a camera, a thermal imager, a pyrometer, spectrum / intensity measurement of the radiation, etc. (i.e., other forms of in-situ non-contact temperature monitoring / measurement at the deposition location 140).

[0051] The device for monitoring a process parameter representative of the temperature at the deposition location 140 may be comprised of equipment having laser / interferometry-based temperature measurement technology, i.e., temperature measurement at or near the deposition location 140 using the wire itself as a Fabry-Perot, Mach-Zehnder interferometer, etc. (i.e., other forms of in-situ non-contact temperature monitoring / measurement at the deposition location 140).

[0052] The means for monitoring the process parameter representative of the temperature at the deposition location 140 may consist of equipment configured to separate a small sample from the laser beam to a detector / power meter and evaluate the sample, i.e., measure the power of the sample, thereby enabling determination of the total power of the main laser beam, which is proportional to the temperature at the deposition location 140. This separation of the small sample from the laser beam may be performed upstream or downstream of the beam splitter 145. Examples of such means will be described in more detail below.

[0053] The means for monitoring the process parameter representing the temperature at deposition location 140 may be comprised of equipment based on geometric imaging technology. That is, the shape of the glass object and / or the shape of the glass filament at and / or near deposition location 140 will differ depending on the temperature at deposition location 140. Too high a temperature (i.e., too low a viscosity of the glass material) will result in poor adhesion, while too low a temperature (i.e., too high a viscosity of the glass material) will result in breakage of the glass filament. Therefore, this technology is based on the actual viscosity of the glass at deposition location 140, which is proportional to the temperature at deposition location 140.

[0054] The beam path unit may include one or more primary beam steering mirrors 115 located between the laser beam source 110 and the beam splitter 145 and configured to direct the primary laser beam 150 from the laser beam source 110 to the beam splitter 145 .

[0055] The beam path unit may include a focusing lens 135 located upstream of the beam splitter 145 in order to focus the main laser beam 150, i.e., to control the diameter of the main laser beam 150 and thereby the size of the hot zone, in order to accommodate glass filaments 160 of varying diameters and to compensate for beam pointing instabilities of the laser beam source 110. The focusing lens 135 may be fixed relative to the beam splitter 145 or may be displaceable back and forth relative to the beam splitter 145 in order to adjust the focus of the main laser beam 150, i.e., to adjust the diameter of the main laser beam 150 and the diameters of the at least three partial laser beams 150′, and thereby to adjust the size and intensity of the hot zone, in order to modify the heating dynamics of the device 100. The focusing lens 135 may be mounted on a computer-controlled motorized translation stage.

[0056] According to various embodiments, the device 100 may include a focusing lens for each partial laser beam 150 ′, i.e. downstream of the beam splitter 145 , in order to be able to compensate for any instabilities of the beam splitter 145 , such as wavelength instabilities of the laser beam and beam pointing instabilities of the laser beam source 110 .

[0057] When one or more focusing lenses 135 are used in the beam path unit, the power of the main laser beam 150 can be varied, as the focusing lens can be used to adjust / control the laser intensity at the deposition location in order to achieve a suitable temperature at the deposition location.

[0058] The beam path unit may include components for providing circular polarization to the main laser beam 150 upstream of the beam splitter 145 in order to obtain a stable circularly polarized main laser beam 150. A quarter wave plate 125 may be used to generate the circularly polarized main laser beam 150 (and preferably a linear polarization unit 126 ( Figure 7 The circularly polarized main laser beam 150 may be polarized using a reflective phase retarder 129 (disclosed in FIG. 1 ). Figure 4 ) instead of the quarter wave plate 125 (eg, replacing one of the main beam steering mirrors 115). When the reflective phase retarder 129 is used, the direction of the linear polarization of the main laser beam 150 must be tilted 45 degrees to the incident plane.

[0059] According to various embodiments, the beam splitter 145 is configured to provide a uniform partial laser beam 150 ′ having a circular / near-circular polarization in order to obtain a uniform and stable temperature throughout the deposition location 140 .

[0060] Circular / near-circular polarization of the laser light is preferred because it is preferred to have identical partial laser beams 150' downstream of the beam splitter 145. If the laser beam is not circularly polarized, different partial laser beams 150' will acquire different polarizations depending on the angle / direction of incidence, and different partial laser beams 150' will have different heating efficiencies, resulting in non-uniform temperatures at the deposition location.

[0061] The beam splitter 145 may be formed by a diffractive optical element (DOE) configured to split the main laser beam 150 into at least three (but preferably four) partial laser beams 150', wherein each partial laser beam 150' is identical, i.e., has the same characteristics as the main laser beam 150. Using a circularly polarized main laser beam 150 ensures that the partial laser beams 150' are identical / identical, as the DOE 145 may have polarization dependence, thereby achieving a uniform and stable temperature at the deposition location.

[0062] The beam path unit includes one or more secondary beam steering mirrors 165 for each partial laser beam 150' to direct each partial laser beam 150' from the beam splitter 145 to the deposition location 140, wherein all partial laser beams 150' impinge on the glass filament 160 from different directions. Each of the partial laser beams 150' should have the same beam path length to achieve a uniform temperature at the deposition location 140.

[0063] The inventors have recognized / discovered the importance of removing instabilities / variations in the wavelength of the main laser beam 150, as such instabilities / variations in wavelength will provide changes in beam alignment, thereby providing changes in hot zone positioning and non-uniform temperatures at the deposition location 140. The inventors have also recognized / discovered that the diffraction angle (i.e., the angle between the incoming main laser beam 150 and the outgoing partial laser beam 150' at the beam splitter 145) should be as small as possible in order to have as little negative effect on the focal position of the partial laser beam 150' as possible from the unstable / varying wavelength.

[0064] More specifically, each DOE 145 has a predetermined grating frequency / density, and the greater the grating frequency / density value, the faster the diffraction angle variation will increase for a given change in laser beam wavelength. Increased diffraction angle variation requires unstable focus position / axial travel, and thus temperature instability at deposition location 140.

[0065] The primary laser beam 150 naturally has a varying wavelength when generated. Furthermore, changes in the power of the laser beam source 110, either to achieve a different preset / predetermined temperature at the deposition location 140 or due to feedback information confirming an incorrect temperature at the deposition location 140, will have an impact on the configuration of the laser beam source 110. Therefore, changing the equilibrium temperature of the laser beam source 110 requires that the size of the laser cavity in the laser beam source 110 be changed, thereby causing the wavelength of the primary laser beam 150 to vary.

[0066] According to various embodiments, see Figures 3 to 7 In the exemplary embodiment of the present invention, the glass fiber feed nozzle 120 is surrounded by the beam path of the partial laser beam 150 ′, i.e., by the secondary beam deflection mirrors 165. In order to be able to achieve an angle of incidence in the range of 30 to 60 degrees while having space for the glass fiber feed nozzle 120 between the secondary beam deflection mirrors 165 and also to have a small diffraction angle, the beam path length of the partial laser beam 150 ′ must be relatively long (see Figure 5 ). Since the wavelength of the main laser beam 150 varies, the longer the beam path, the greater the shift of the focus.

[0067] Therefore, in Figure 5In such embodiments disclosed in , DOE 145 can be selected to generate a small diffraction angle equal to or less than 15 degrees (preferably equal to or less than 10 degrees, and most preferably equal to or less than 5 degrees) in order to have a small / acceptable variation / travel in the focus position.

[0068] According to various embodiments, see Figure 6 and Figure 7 In an exemplary embodiment of the present invention, the beam path unit may include a pyramid mirror 155 located downstream of the beam splitter 145 so as to Figure 5 In an embodiment, the at least three partial laser beams 150' are diverged / redirected more quickly from one another. The secondary beam steering mirror 165 is located downstream of the pyramid mirror 155. Due to the pyramid mirror 155, the beam paths of the partial laser beams 150' are significantly reduced, i.e., a more compact design of the printer head 102 is achieved compared to an arrangement without the pyramid mirror 155. Therefore, the use of the pyramid mirror 155 downstream of the beam splitter 145 improves the stability of the focus position due to the shortened beam paths of the partial laser beams 150'.

[0069] Therefore, in Figure 6 and Figure 7 In such embodiments disclosed in , DOE 145 can be selected to generate larger diffraction angles (i.e., equal to or less than 45 degrees, preferably equal to or less than 30 degrees, and most preferably equal to or less than 20 degrees) and still have small / acceptable variations / travels in the focal position.

[0070] It should be noted that when using a laser beam source 110 comprising complex wavelength stabilization components (such as Figure 3 and Figure 4 ), DOE 145 can be selected to generate a diffraction angle equal to or less than 80 degrees, thereby making the use of a prism unnecessary.

[0071] We will now refer to the Figure 3-7 Examples of components for process parameter monitoring of a feedback control unit based on a small sample of a split laser beam are described.

[0072] Components for process parameter monitoring may include a beam tap 127 located upstream of the beam splitter / DOE 145. The beam tap 127 separates a predetermined sample, for example in the range of 1-10% of the main laser beam 150. The beam tap 127 directs the separated sample to a detector 128 (such as a power meter), where a control unit compares the measured power of the main laser beam 150 with a reference value. Any deviation is used to adjust / control the power of the main laser beam 150 originating from the laser beam source 110. The beam tap 127 may be polarization dependent and different polarizations will be tapped by different amounts, which will result in power reading errors, i.e., the same main laser beam 150 total power will produce different power readings depending on the stability of the main laser beam 150 polarization. According to the embodiment of the present invention, the beam tap 127 has a quarter wave plate 125 combined with a linear polarization component (see Figure 7 ), the beam tap 127 may be located upstream of the quarter wave plate 125 and downstream of the linear polarization component 126. Figure 4 ) or quarter wave plate 125 ( Figure 3 and Figure 5-Figure 7 ), the beam tap 127 is located downstream of the phase delay mirror 129 / quarter wave plate 125 and upstream of the beam splitter / DOE 145. When the quarter wave plate 125 or the phase delay mirror 129 is used to obtain a circularly polarized laser beam, this will also block laser reflections directed back into the laser beam source 110 from downstream of the quarter wave plate 125 or the phase delay mirror 129. A shutter (not disclosed) can be used to open / close the main laser beam 150 near the entrance of the printer head 102. When OFF, the entire main laser beam 150 is directed to a beam dump that can then be used as a detector / power meter. When ON, the entire main laser beam 150 enters the printer head 102.

[0073] It should be noted that splitting the laser beam sample may alternatively be performed downstream of the beam splitter / DOE 145, ie, the laser beam sample originating from the beam splitter / DOE 145 is directed to a detector / power meter.

[0074] According to various embodiments of the apparatus 100, the printer head 102 includes a gas purge arrangement configured to remove deposits, namely, fumed silica particles and combustion byproducts, from an area including the deposition location 140 and the glass filament feed nozzle 120. The gas purge arrangement is configured to generate a gas / air flow in the area of ​​the glass filament feed nozzle 120. According to one exemplary embodiment, the gas / air flow is fed into the printer head 102 housing to achieve an overpressure therein, wherein the gas / air flow then exits the printer head 102 housing around the filament feed nozzle 120.

[0075] This is to ensure that any fumes (soot silica particles due to overheating) from the combustion byproducts of the coating material 169 or vaporized / molten glass do not migrate toward the glass filament feed nozzle 120 or optics / other components of the printer head 102, or remain / reside at the deposition location 140. Otherwise, such fumes could damage the printer head optics and filament feed nozzle 120, requiring frequent cleaning or parts replacement, and have a negative effect on the printed glass object. Figure 3 In the embodiment, printing is performed using glass filaments fed in a horizontal direction toward the platform 130. This is beneficial because the fumes will automatically leave the area of ​​the glass filament feed nozzle 120 and the deposition location 140. However, using appropriate gas purge, the printer head 102 can be placed in any orientation (upward, downward, sideways, etc.).

[0076] Now Figure 8 and Figure 9a-9c Make a reference.

[0077] Bare glass filaments have poor mechanical properties and are therefore susceptible to breakage. In order to mechanically and chemically protect the glass filaments during storage and handling, a protective coating is required. The protective coating can be applied during filament production, for example using a fiber draw tower for producing optical fiber. A furnace heats a preform (a large version of the filament in shape and composition). The softened glass is then pulled using a capstan in conjunction with a diameter gauge to obtain the correct filament size. While the filament is being pulled, the preform is fed further into the furnace. Typically, a coating resin can be introduced into a coating cup that the filament is passing through. The coating can then be cured by heat or using, for example, a UV lamp before the filament is wound onto a storage and transport spool. The curing temperature for polyimide coatings on optical fibers is typically performed in a temperature range of about 100 to 400°C.

[0078] Polyimide-coated optical fibers can survive operating temperatures of approximately 300°C and are often used in higher temperature (sensing) applications. Coating thicknesses of 10 to 15 μm are typically used here. Thicker coatings can be applied by repeating the coating process (adding multiple layers but still obtaining only one layer of coating).

[0079] For glass filaments, the coating thickness should be as thin as possible while ensuring adequate mechanical and chemical protection of the fiber. Fibers that we have evaluated that gave good results had a single layer polyimide coating thickness of approximately 5 μm.

[0080] Suitable outer diameters for glass filaments range from 100 μm to 500 μm. The diameter has a significant impact on the filament's mechanical properties, with increased diameter producing stiffer filaments. During printing, translation of the printer head and filament relative to the object / platform being printed generates lateral forces on the filament. Deviations in filament positioning depend on the viscosity and surface tension of the liquid glass in the hot zone, as well as the printing speed. Figure 6 A schematic feed nozzle 120 and feed glass filament 160 are shown in FIG. Using stiffer filaments, the distance between the filament feed nozzle 120 and the platform 130 can be increased. L represents the distance between the glass filament feed nozzle 120 and the platform 130. Therefore, the glass filament diameter, the filament feed nozzle 120 design, and the distance between the glass filament feed nozzle 120 and the platform 130 have a significant impact on printing accuracy and quality. A large glass filament 160 diameter and a short distance between the glass filament feed nozzle 120 and the platform 130 reduce glass filament deflection during printing. If the distance L is too short, the filament feed nozzle 120 may be damaged by the temperatures in the hot zone. Theoretically, under the same processing conditions, a glass filament with a diameter of approximately 200 μm will deflect only one-quarter of that of a glass filament with a diameter of approximately 125 μm. Using a glass filament with a diameter of 200 μm and a distance L equal to or less than 5 mm, the deflection will be a fraction of μm and can be considered negligible.

[0081] When printing fused silica / fused quartz glass, in glass 3D printing, the glass filament is continuously fed into a hot zone with a temperature in the range of 1800 to 2200°C. Other types of glass, such as soft glass, require much lower temperatures. A commonly used method is to feed pure glass filament. However, since most glass filaments are produced with a coating, the coating must be removed before printing / deposition to produce pure glass filament. Stripping the coating can be performed using mechanical or chemical means (e.g., using sulfuric acid, dichloromethane). Since the glass filament may become brittle in the absence of a coating, and stripping the coating may further weaken the mechanical strength of the filament, this carries an additional risk, as filament breakage during printing will cause a serious interruption to the printing process.

[0082] Another method is to feed the coated glass filament directly from the glass filament feed nozzle 120. Using the protective coating 169, the printable filament length can be extended to several kilometers. However, since flammable polymers (such as acrylic resins) are usually used to coat the glass filament 160, this method may cause open flames on the filament due to the high printing temperature, resulting in printing failure and possible damage to the 3D printer. In addition, the standard coating has a thickness of about 50 μm, which is considered too "thick" for glass 3D printing. Direct combustion of such a "thick" coating is not an ideal solution because it may produce more combustion byproducts, is more likely to leave residues that affect the purity of the print, and is not energy-efficient.

[0083] Our method produces glass filaments with a thin, flame-retardant, and self-extinguishing single coating. The thin coating has a thickness in the range of 1 to 50 μm. When the hot zone is heated to a very high temperature using a CO2 laser beam, the coating will begin to burn near the hot zone, i.e., the hot zone itself can be used to remove the coating. Although the coating is flame-retardant, the risk of open flames is eliminated. Once the laser beam source 110 and the glass filament feed are turned off, the burning of the coating will cease. The thin coating will burn off easily. In addition to improving efficiency and reducing environmental impact, it will also reduce the production of combustion by-products. The ideal coating would have a non-toxic chemical composition to further reduce the toxic fumes produced during combustion, for example, it should not contain halogens.

[0084] Figure 9a-9c Three different types of glass filaments 160 having a protective coating 169 are disclosed that may be used in the additive manufacturing apparatus 100 .

[0085] Figure 9a A single component (rod / filament) is disclosed, where the component (type of glass) can be high-purity silica glass, such as fused silica, fused quartz (for printing high-purity transparent glass). These materials have a low coefficient of thermal expansion, meaning a heated printing plate is not required, and post-thermal annealing is not always necessary. The silica glass filaments can be co-doped with GeO2, Al2O3, B2O3, or F, or combinations of these. Multi-filament printing (with silica glass filaments) can be used to create 3D prints with designed shapes and refractive index structures. Examples can be the fabrication of optical fiber preforms or various optical components. Silica glass can be doped with rare earth oxides (e.g., Er, Yb, Er / Yb) in combination with other dopants (e.g., GeO2, Al2O3, B2O3, F). These filaments can be used to create 3D prints of active laser materials. Silicate, borosilicate, aluminoborosilicate, and soda-lime glasses are standard low-cost materials. Due to the higher coefficient of thermal expansion, these may require a heated print plate and post thermal annealing to relieve stress.

[0086] Figure 9b Disclosed are glass filaments 160 having a central air hole 162 (i.e., a capillary structure). These capillary filaments can be used to print different types of glass / air structures. If pressure control is applied to the inner portion of the capillary filament, active contraction / expansion of the filament during printing is possible. The volume of the air hole 162 can be between 10-70% of the volume of the glass content in the glass filament 160. The air hole 162 can be located in the center or non-center of the glass filament 160. In various exemplary embodiments, the glass filament 160 can be provided with a plurality of air holes.

[0087] Figure 9c Disclosed are glass filaments 160 composed of a silica-based composition, including a central core structure 160' containing a refractive index-modifying dopant (e.g., GeO2, Al2O3, B2O3, F). These core / cladding filaments, acting as optical waveguides, can be used to print optical paths on various glass substrates for use in telecommunications, sensing, or biomedical applications. In addition to glass-based materials, other core materials include semiconductors and alloys such as silicon and germanium.

[0088] Possible modifications of the present invention

[0089] The present invention is not limited to the embodiments described above and shown in the accompanying drawings, which are intended primarily for purposes of illustration and description. This patent application is intended to cover all modifications and variations of the preferred embodiments described herein, and the invention is therefore defined by the wording of the appended claims and their equivalents. Therefore, the device may be modified in various ways within the scope of the appended claims.

[0090] Throughout this specification and the claims that follow, unless the context requires otherwise, the word "comprise" and variations such as "comprises" or "comprising" will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

Claims

1. An apparatus (100) for additive manufacturing of three-dimensional glass objects, comprising: - a platform (130) for supporting the glass object, - a laser beam source (110) for providing a main laser beam (150), - a printer head (102), and - a member for relative movement of the printer head (102) and the platform (130), Wherein, the printer head (102) comprises: - at least one glass filament feeding nozzle (120) for feeding glass filament (160) towards a deposition position (140) for forming said glass object, and a beam path unit configured to direct the laser beam (150) from the laser beam source (110) to the deposition position (140) for heating the glass filament (160), Characterized in that, the beam path unit comprises: a beam splitter (145) for splitting the main laser beam (150) into at least three partial laser beams (150'), wherein the beam path unit is configured to direct each of the at least three partial laser beams (150') from the beam splitter (145) to the deposition position (140), and - a feedback control unit comprising means for monitoring a process parameter representative of the temperature at the deposition location (140), and means for controlling the power of the main laser beam (150) in order to regulate the temperature at the deposition location (140) towards a predetermined level.

2. The device (100) according to claim 1, wherein The process parameter consists of the power of the main laser beam (150) upstream of the beam splitter (145) in the printer head (102).

3. The apparatus (100) of claim 2, wherein the means for monitoring the process parameter constituted by the power of the main laser beam (150) comprises a beam tap (127) configured to separate a predetermined sample of the main laser beam (150) towards a detector (128).

4. The device (100) according to any of the preceding claims, wherein the beam path unit comprises means for providing circular polarization to the main laser beam (150) upstream of the beam splitter (145).

5. The device (100) according to claim 1, wherein the beam path unit comprises a pyramid mirror (155) downstream of the beam splitter (145) in order to diverge the at least three partial laser beams (150') from one another.

6. The device (100) according to any of the preceding claims, wherein the beam path unit comprises one or more secondary beam steering mirrors (165) for each partial laser beam (150'), which are configured to direct the partial laser beam (150') towards the deposition position (140).

7. The device (100) according to claim 6, wherein the glass fiber feed nozzle (120) is surrounded by the secondary beam deflecting mirror (165).

8. The device (100) according to any of the preceding claims, wherein the glass filament feed nozzle (120) is configured to feed the glass filament (160) in a direction perpendicular to a geometric plane, wherein each of the at least three partial laser beams (150') has an angle of incidence equal to 30-60 degrees with respect to the geometric plane.

9. The device (100) according to any of the preceding claims, wherein the beam path unit comprises a focusing lens (135) upstream of the beam splitter (145) in order to condition the main laser beam (150).

10. The device according to claim 9, wherein the focusing lens (135) is displaceable back and forth with respect to the beam splitter (145) in order to adjust the diameter of the main laser beam (150).

11. The apparatus (100) of any one of the preceding claims, wherein the printer head (102) comprises a gas purge arrangement configured to remove deposits from an area comprising the deposition location (140) and the glass filament feed nozzle (120).

12. The apparatus (100) of claim 1, wherein the process parameter consists of the temperature at the deposition location (140).

13. The apparatus (100) of claim 12, wherein the means for monitoring the process parameter consisting of the temperature at the deposition location (140) comprises a thermal imager / camera.

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