Additive Manufacturing Equipment

Abstract

The present invention relates to an apparatus (100) for additively manufacturing three-dimensional glass bodies, the apparatus comprising: a stage (130) for supporting the glass body; a laser beam source (110) for providing a primary laser beam (150); a printer head (102); and means for relatively moving the printer head (102) and the stage (130), the printer head (102) comprising at least one glass filament delivery nozzle (120) for delivering a glass filament (160) toward a deposition location (140) to form a glass body; and an optical beam path unit configured to direct the laser beam (150) from the laser beam source (110) to the deposition location (140) to heat the glass filament (160). The apparatus is characterized in that the optical beam path unit comprises a beam splitter (145) for splitting a primary laser beam (150) into at least three partial laser beams (150'), the optical beam path unit being 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 comprising means for monitoring a process parameter representative of the temperature of the deposition location (140) and means for controlling the power of the primary laser beam (150) to regulate the temperature of the deposition location (140) to a predetermined level.

Description

[Technical Field]

[0001] The present invention relates generally to the field of additive manufacturing. In particular, the present invention relates to an additive manufacturing apparatus for forming three-dimensional components / objects from glass raw material onto a stage. As used herein, the term "stage" includes any element / object / support onto which a glass body can be printed directly or indirectly.

[0002] The present invention particularly relates to an apparatus for additively manufacturing three-dimensional glass bodies, the apparatus comprising a stage for supporting a printed glass body, a laser beam source for providing a primary laser beam, a printer head, and means for relatively moving the printer head and the stage, the printer head comprising at least one glass filament delivery nozzle for delivering a glass filament to a deposition location to form the glass body, and an optical beam path unit configured to direct a laser beam from the laser beam source to the deposition location to heat / melt the glass filament. [Background technology]

[0003] In three-dimensional printing of glass or additive manufacturing of glass, existing techniques include (1) hot extrusion of glass from a furnace, (2) deposition of glass rods, (3) stereolithography / inkjet with glass-polymer mixed solutions, and (4) deposition of glass filaments.

[0004] Technique (1), as described in US Pat. No. 10,464,305 B2 and US Pat. No. 10,266,442 B2, uses a large crucible and a translation stage to pour liquid glass onto a build plate / stage in a predetermined geometric shape. The drawback of this method is the risk of nozzle damage from 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. The layer thickness is approximately 10 mm, so this technique is only applicable to large-size printing with relatively low resolution. Energy consumption is the highest of all existing techniques.

[0005] Technique (2), US2020 / 0070415A1 and WO2020 / 167470A1, uses a continuous filament feed for 3D printing of glass. This printing uses glass rods with diameters greater than 1 mm as the raw material. The rod feed is fed through a print head and deposited onto a substrate. Glass cannot be printed at temperatures higher than 1700°C, limiting material selection. Problems with this system include the risk of nozzle damage from molten glass, the print volume being limited by the volume of the glass rod, gaps between the rods leading to inconsistent print quality, and the mechanism being considered to be mechanically very complex.

[0006] In technique (3), US2020 / 0039868A1, WO2017 / 214179A1, and WO2020 / 118157A1 disclose a technique in which glass powder is mixed with a liquid polymer. In the printing process, a 3D green body is first fabricated using a polymer 3D printer. The green body then undergoes a debinding process to create a porous mass of pure glass. The porous mass is then sintered to ultimately form a "high-density" glass body. The glass content in the original mixture is low. Therefore, this technique generally can only produce models smaller than 10 mm due to significant volumetric shrinkage. Additionally, the entire process takes several days, and debinding and sintering require energy-intensive furnaces. Print quality is poor due to uneven shrinkage during sintering.

[0007] (4) Laser-based melting of thin glass filaments or optical fibers has also been used for 3D printing of glass. See J.M. Hostetler et al., Fiber-Fed Printing of Free-Form Free-Standing Glass Structures, Solid Freeform Fabrication 2018: Proceedings of the 29th Annual International, pp. 994–1002; and 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). The use of non-contact heating with lasers has been realized, meaning that the glass melt does not come into contact with the walls of the crucible, thereby avoiding corrosion and contamination of the crucible by the glass melt. Here, a silica glass fiber / filament is continuously fed into a deposition location or hot zone with a temperature sufficient to soften the glass. For quartz glass (quartz or fused silica), temperatures in the range of 1800-2000°C are required.

[0008] However, in [JM Hostetler et al.], only one laser beam is used to soften / melt the glass filament. Such asymmetric heating significantly limits directional printing capabilities. Additionally, non-uniform temperature gradients in the molten glass filament can result in high residual stresses within the printed object, potentially leading to material failure and interruptions to the printing process. This technique uses bare glass filament printing, which means that the coating must be removed / stripped from the glass filament before printing / depositing the glass filament. Stripping 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 location. However, such an approach leaves the glass filament unprotected during the final stage of the printing process, i.e., during mechanical feeding of the glass filament into the hot zone. This is not an ideal solution, as stripping the coating can further weaken the mechanical strength of the glass filament, and filament breakage during printing would cause a significant interruption to the printing process. The use of chemical means is also undesirable due to the risks involved when using strong acids (sulfuric acid) or dichloromethane (carcinogenic). The stripping process also limits the total length of printable glass filament: maximum mechanical stripping is less than a few meters, and maximum chemical stripping is typically less than 50 meters, which severely limits the continuity and capacity (volume) of the 3D printing process.

[0009] In [T. Grabe et al.], one primary laser beam is split into four sub-laser beams and directed toward the hot zone from different directions. However, because the sub-laser beams are not uniformly Gaussian like the primary laser beam, the quality of the sub-laser beams is poor. This results in uneven heating. This method uses a coated glass filament. The coating burns off from the glass filament near the hot zone, meaning the hot zone itself can be used to remove the coating. A problem with the above method using commonly used fiber coatings is that it can produce undesirable combustion by-products, which are more likely to leave residues that affect the purity of the printed object. Another problem is that the coating can ignite and begin to burn over long areas of the filament even after the heat source is turned off. Therefore, process gas is required to suppress the coating combustion. Excessive energy is required to burn off the coating, which causes extensive glass evaporation during printing.

[0010] Glass evaporation is very common and difficult to remove during laser-based 3D glass printing. It creates undesirable fumed silica particles that adhere to surrounding surfaces, such as the nozzle and mirrors. The presence of fumed silica particles increases the risk of contamination and damage to the optics in the system. Control of the evaporation rate, i.e., the temperature at the deposition location, and control of process fumes are critical.

[0011] Therefore, there remains a great need in the field of additive manufacturing to provide an additive manufacturing method / apparatus for printing glass bodies, where stable / proper temperatures are obtained throughout the deposition location (hot zone) to obtain printed glass bodies without harmful defects, and where the apparatus is not limited to any specific printing orientation with respect to the relative movement of the stage and printer head. Summary of the Invention [Problem to be solved by the invention]

[0012] The present invention aims to obviate the above-mentioned drawbacks and weaknesses of known methods / devices for additively manufacturing three-dimensional glass bodies and to provide an improved device. The main objective of the present invention is to provide an improved device for additively manufacturing three-dimensional glass bodies of the initially defined type, which ensures a stable / proper temperature throughout the deposition location (hot zone) in order to obtain a printed glass body without harmful defects.

[0013] Another object of the present invention is to provide an improved apparatus for additive manufacturing of three-dimensional glass bodies that is not limited to any specific printing orientation with respect to the relative / mutual movement of the stage and printer head. [Means for solving the problem]

[0014] According to the present invention, at least the main object is achieved by a device as defined at the outset, having the features defined in the independent claims. Preferred embodiments of the invention are also further defined in the dependent claims.

[0015] According to the invention, the optical beam path unit comprises a beam splitter for splitting the primary laser beam into at least three partial laser beams, the optical beam path unit being configured to direct each of the at least three partial laser beams from the beam splitter to a deposition location, and a feedback control unit comprising means for monitoring a process parameter indicative of the temperature of the deposition location and means for controlling the power of the primary laser beam to regulate the temperature of the deposition location to a predetermined level.

[0016] Therefore, the present invention is based on the inventors' insight that a stable / proper temperature throughout the deposition location (hot zone) is the single most important factor for being able to obtain a printed glass body without harmful defects. In addition, the present invention is based on the inventors' insight that the stable / proper temperature depends at least on the power of the primary laser beam, the direction of incidence of the laser beam, and the position of the focus of the laser beam relative to the deposition location.

[0017] One immediate advantage of splitting the primary 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 increased heating efficiency.

[0018] According to various embodiments of the present invention, the process parameter representative of the temperature at the deposition location is constituted by the power of the primary laser beam upstream of the beam splitter in the printer head, which facilitates an unambiguous relationship between the measured power of the primary laser beam and the control of the power of the primary laser beam generated in the laser beam source.

[0019] According to various embodiments of the present invention, the means for monitoring the process parameter constituted by the power of the primary laser beam comprises a beam tap configured to split off a predetermined sample of the primary laser beam to a detector / power meter, whereby, using simple mathematics, the power of the non-redirected portion of the primary laser beam is determined, which is proportional to the temperature at the deposition location.

[0020] According to various embodiments of the present invention, the optical beam path unit comprises means for providing circular polarization to the primary laser beam upstream of the beam splitter, whereby the laser beam source used can be essentially cheap and complex, i.e. any negative effects due to unstable polarization that may occur in the laser beam source are reduced / eliminated.

[0021] According to various embodiments of the present invention, the optical beam path unit comprises a pyramid mirror located downstream of the beam splitter to separate the at least three partial laser beams from one another. According to various embodiments, the optical beam path unit comprises, for each partial laser beam, one or more secondary beam steering mirrors configured to direct the partial laser beam toward the deposition location. This allows the length of the beam path to be reduced, thereby reducing / eliminating any negative effects due to possible wavelength instability in the primary laser beam.

[0022] Further advantages and features of the present invention will become apparent from the other dependent claims and the following detailed description of preferred embodiments. A more complete understanding of the above and other features and advantages of the present invention will become apparent from the following detailed description of the preferred embodiments, taken in conjunction with the accompanying drawings. [Brief explanation of the drawings]

[0023] [Figure 1] FIG. 1 is a schematic diagram of a prior art apparatus for additive manufacturing of three-dimensional glass bodies. [Figure 2] FIG. 1 is a schematic diagram of an inventive apparatus for additive manufacturing of three-dimensional glass bodies. [Figure 3] 1 is a schematic perspective side view of an inventive apparatus according to a first exemplary embodiment, showing the inside of a printer head; [Figure 4] 1 is a schematic perspective side view of an inventive apparatus according to a second exemplary embodiment, showing the inside of the printer head; FIG. [Figure 5] 1 is a schematic perspective side view of an inventive device according to a variant of the first exemplary embodiment, showing the inside of the printer head; FIG. [Figure 6] FIG. 10 is a schematic perspective side view of an inventive apparatus according to a third exemplary embodiment, showing the inside of the printer head. [Figure 7] 10 is a schematic perspective side view of an inventive apparatus according to a variant of the third exemplary embodiment, showing the inside of the printer head. FIG. [Figure 8] FIG. 2 is a schematic side view of a glass filament and a filament delivery nozzle. [Figure 9] Figures 9a, 9b, and 9c are schematic diagrams of various exemplary embodiments of glass filaments. DETAILED DESCRIPTION OF THE INVENTION

[0024] Herein, the invention relates to the field of Additive Manufacturing (AM) of three-dimensional glass bodies using digital / computer models, i.e., the geometry of the component / object is built by melting glass filaments / fibers, which are melted layer by layer or in batches of layers using an energy source such as a laser beam, by selective melting or simple scanning of a printed profile after the melting process.

[0025] Referring first to FIG. 1, FIG. 1 depicts a prior art apparatus for additively manufacturing three-dimensional glass bodies. The apparatus includes a stage 130, a laser beam source 110 providing a laser beam 150, and a glass filament delivery nozzle 120 providing a glass filament 160 having a coating 169 to a deposition location 140, where the filament delivery nozzle 120 is part of or comprises a printer head. The glass filament delivery nozzle 120 and the stage 130 are configured to move relative to / with respect to each other to deposit a layer / strand of glass material onto the glass body at the deposition location 140, also referred to as a hot zone. The glass filament 160 can be delivered to the glass filament delivery nozzle 120 via a tube 170, which is also applicable to the present invention.

[0026] Referring now to FIG. 2, FIG. 2 depicts a schematic diagram of an inventive apparatus for additively manufacturing three-dimensional glass bodies, generally designated 100. Apparatus 100 comprises a stage 130 for supporting a glass body, a laser beam source 110 for providing a primary laser beam 150, and a printer head 102. As used herein, the term stage 130 includes any element / object / support onto which a glass body can be printed, directly or indirectly, for example, via a build plate / object connected to stage 130. Thus, a build plate / object can be connected to stage 130, and the glass body is printed on the build plate / object and is still considered to be supported by stage 130. The build plate / stage can be made of any material, for example, the same material as the final three-dimensional glass component / object, a ceramic material, or any other metallic material different from the material of said three-dimensional glass body / component. Hereinafter, use of the term stage 130 shall be understood to include build plates, components, objects, etc., unless otherwise stated.

[0027] The printer head 102 and / or stage 130 may be mounted on a robot, such as an articulated robot with one or more rotary joints, a Cartesian robot with linear axes, a cylindrical robot with one rotary axis and two linear axes, or a combination thereof. Accordingly, the apparatus 100 includes means for moving the printer head 102 and stage 130 relative to each other, i.e., motorized supports. Thus, in order to additively manufacture a three-dimensional glass component / object and to maintain a constant distance between the printer head 102 and the top surface of the stage or component / object to which a new layer is to be attached, one or both of the printer head 102 and the stage 130 may be displaceable in a direction perpendicular to the surface of the stage 130 or a predetermined geometric plane, i.e., for every newly applied layer, the stage 130 may be moved backward (away from the printer head 102) by a distance corresponding to the thickness of the newly applied layer, or the printer head 102 may be moved away from the stage 130 by a distance corresponding to the thickness of the newly applied layer, or a combination of movements of the stage 130 and the printer head 102 may be used to maintain a constant distance between the printer head 102 and the top surface of the stage or component / object to which a new layer is to be attached.

[0028] A control unit can control the relative movement of the printer head 102 with respect to the stage 130. The printer head 102 can be configured to move in a plane essentially parallel to the stage 130 so that the printer head 102 covers a predetermined area of ​​the stage 130. The stage can be positioned vertically or in any other direction. The relative movement can be such that the stage 130 is fixed and the printer head 102 moves in the plane. In an alternative embodiment, the stage 130 moves while the printer head 102 is fixed to cover the entire stage 130. In a further alternative embodiment, both the stage 130 and the printer head 102 are movable in the plane, allowing the printer head 102 to cover the entire area of ​​the stage 130. The printer head 102 and / or stage 130 are also preferably tiltable with respect to each other, allowing new layers to be printed that are not necessarily parallel to other layers.

[0029] The laser beam source 110 can be directly attached to the printer head 102, i.e., connected as a single 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 for directing the primary laser beam 150, i.e., the raw laser beam, from the laser beam source 110 to the printer head 102, or can include opto-mechanical directing means, i.e., the unexposed laser beam, or can include glass fiber / laser guide directing means, i.e., flexible fiber, or a combination thereof. The printer head 102 can print in any orientation, i.e., vertical, horizontal, from above, from below, at any angle of inclination, etc., and the stage 130 can be oriented in any direction.

[0030] Referring now to FIG. 3, FIG. 3 depicts a first exemplary embodiment of an inventive apparatus 100 for additively manufacturing three-dimensional glass bodies. The housing of the printer head 102 has been removed. The printer head 102 includes a glass filament delivery nozzle 120 configured to deliver and guide a glass filament 160 toward a deposition location 140, also known as a hot zone. The glass filament 160 can be delivered to the filament delivery nozzle 120 via a flexible tube 170. The laser beam source 110 can be a CO laser, CO laser, Nd:YAG laser, fiber laser, excimer laser, nitrogen laser, or the like. The laser beam 150 can be continuous wave or pulsed wave, or a combination thereof. The laser beam 150 softens or melts the glass filament 160 at the deposition location 140 adjacent to the stage 130 or a component / object to which the glass filament 160 is to be attached.

[0031] As disclosed in FIG. 3 , providing the stage 130 in a vertical orientation ensures that any fumes (fumed silica particles due to overheating), for example from combustion by-products of the coating material or evaporated / melted glass, move 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 filament delivery nozzle 120, requiring frequent cleaning or part replacement. Also, the vertical arrangement of the stage 130 allows for relative movement of the printer head 102 and the stage 130 to be configured to move any fumes and gaseous materials emanating from the hot zone out of the laser beam's optical path, thereby improving the performance of the additive manufacturing apparatus 100. The present invention is not limited to a vertical orientation of the stage 130.

[0032] During additive manufacturing, a glass filament, i.e., raw material, is melted and / or deposited onto a stage 130 or object. A filament delivery nozzle 120 locally deposits the glass filament along a predefined path provided by a sliced ​​computer model. The filament delivery nozzle 120 can preheat the glass filament before it leaves the nozzle 120 on its way to the stage 130. The filament delivery nozzle 120 can be adapted to the size and shape of the glass filament, but can also be configured to deliver different glass filaments with different dimensions / diameters. Thus, a gap may exist between the glass filament 160 and the glass filament delivery nozzle 120, preventing fumed silica particles from entering such a gap. While FIG. 3 shows only one glass filament 160 being delivered to the stage 130, according to various exemplary embodiments, multiple glass filaments 160 having the same or different shapes and / or material compositions / colors can be sequentially delivered through a single filament delivery nozzle 120 to perform the deposition of multiple materials. 3, only one filament delivery nozzle 120 is used, but according to various exemplary embodiments, multiple filament delivery nozzles positioned alongside one another and oriented more or less parallel to one another can be used, so that glass filaments 160 are directed to the same deposition location 140. According to various exemplary embodiments, multiple rows of glass filaments 160 can be simultaneously delivered to the stage 130 to provide a three-dimensional glass component of different materials / colors. Different layers of the three-dimensional component can include different materials and / or different locations within a single layer, and can include different materials, i.e., deposition of multiple materials within one layer and / or different layers can occur.

[0033] 3 discloses a schematic side view of an exemplary embodiment of an additive manufacturing apparatus 100 according to the present invention configured to produce a three-dimensional glass body. The apparatus 100 comprises a stage 130, a laser source 110, and a printer head 102 having a filament delivery nozzle 120. In addition, the printer head 102 comprises an optical beam path unit configured to direct a laser beam 150 from the laser beam source 110 to a deposition location (hot zone) 140 to heat a glass filament 160 and the region of the stage 130 or object where the glass filament 160 is attached / adhered. The optical beam path unit can be based on techniques using reflective and / or transmissive optics.

[0034] The optical beam path unit includes a beam splitter 145 for splitting the primary laser beam 150 into at least three partial laser beams 150′. The optical 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. FIG. 3 discloses the use of four partial laser beams 150′. The at least three partial laser beams 150′ are used to heat the glass filament 160 at the deposition location 140 by directing the at least three partial laser beams 150′ to the deposition location 140. The laser beam source 110 can operate within a wavelength region in which the glass filament 160 has high optical absorption, resulting in melting / softening of the glass filament 160 when irradiated by the laser beam 150.

[0035] Therefore, the use of the beam splitter 145 makes it possible to direct multiple partial laser beams 150' towards the deposition location 140 from different directions, thereby obtaining a uniform temperature across the deposition location (hot zone) 140 regardless of the direction of relative movement of the printer head 102 and the stage 130.

[0036] The glass filament delivery nozzle 120 is configured to deliver the glass filament 160 in a direction perpendicular to a geometric plane, which is preferably the plane on which the layer will be printed, and each of the at least three partial laser beams 150' has an incident angle relative to the geometric plane within a range of 30 to 60 degrees, preferably within a range of 40 to 50 degrees, and most preferably approximately 45 degrees. The optical beam path unit is configured to direct the partial laser beams 150' toward the deposition position 140. The geometric plane is typically parallel to the stage 130. The geometric plane may be spherical or non-flat.

[0037] Quartz and silica-based glass filaments have strong absorption at wavelengths above 2.2 μm. Irradiating a glass filament 160 with a CO laser (typically operating in the 9.2–10.6 μm wavelength range) or a CO laser (operating in the 5.5 μm wavelength range) results in strong radiation absorption, which then heats the glass filament 160. CO lasers operating at a wavelength of 10.6 μm can be used. At this wavelength, quartz glass is opaque, resulting in efficient heating. The absorption depth is approximately 2–40 μm, which is efficient for heating glass filaments 160 with diameters in the 100–300 μm range. For larger glass filaments, the shallow penetration depth of 10.6 μm makes it difficult to heat them rapidly without causing significant evaporation. For glass filaments larger than approximately 0.5 mm, it is more suitable to use a CO laser operating at 5.5 μm. The penetration depth of 5.5 μm is much larger (several hundred μm), resulting in more efficient energy deposition into the glass filament 160 .

[0038] The optical beam path unit also includes a feedback control unit that includes means for monitoring a process parameter indicative of the temperature of the deposition location 140 and means for controlling the power of the primary laser beam 150 to regulate the temperature of the deposition location 140 to a predetermined level. The temperature of the deposition location 140 determines the viscosity of the deposited glass material and has a significant impact on the printing result. For long printing periods, the temperature must be well controlled over time to provide a high-quality printed glass body.

[0039] The predetermined temperature level can vary along a single layer of the glass body, can vary for different layers of the glass body, or can be a combination of these. The predetermined temperature level depends, for example, on the printing speed, the glass filament feed rate, the deposition location (i.e., stage, build plate, glass body, etc.) material type, the width and / or thickness of the previous layer(s) of the object, the breaking of the glass filament, etc. Thus, if the process parameters indicate that the temperature is too low, the power of the primary 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 primary laser beam 150.

[0040] The means for monitoring a process parameter indicative of the temperature of the deposition location 140 may consist of equipment configured to monitor the blackbody radiation of the deposition location 140, i.e., temperature measurement at or near the deposition location 140 using a camera, thermal imager, pyrometer, spectrum / intensity measurement of radiation, etc., or other forms of in-situ non-contact temperature monitoring / measurement at the deposition location 140.

[0041] The means for monitoring the process parameter indicative of the temperature at the deposition location 140 can consist of equipment having laser-based / interferometric temperature measurement techniques, i.e., temperature measurement of the filament itself at or near the deposition location 140 using Fabry-Perot type, Mach-Zehnder type interferometers, etc., or other forms of in-situ non-contact temperature monitoring / measurement at the deposition location 140.

[0042] The means for monitoring the process parameter indicative of the temperature of the deposition location 140 may consist of an instrument configured to split off 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 making it possible to determine the total power of the primary laser beam, which is proportional to the temperature of the deposition location 140. Such splitting off of the small sample from the laser beam may be performed upstream or downstream of the beam splitter 145. Examples of such means are described in more detail below.

[0043] The means for monitoring the process parameter representing the temperature of the deposition location 140 can be constituted by an instrument based on a geometric imaging technique, i.e., the shape of the glass body and / or the shape of the glass filaments at and / or near the deposition location 140 varies depending on the temperature of the deposition location 140. If the temperature is too high, i.e., if the viscosity of the glass material is too low, adhesion will be insufficient, and if the temperature is too low, i.e., if the viscosity of the glass material is too high, the glass filaments will break. This technique is therefore based on the actual viscosity of the glass at the deposition location 140, which is proportional to the temperature of the deposition location 140.

[0044] The optical beam path unit may include one or more primary beam steering mirrors 115 positioned 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.

[0045] The optical beam path unit may include a focusing lens 135 located upstream of the beam splitter 145 to focus the primary laser beam 150, i.e., to control the diameter of the primary laser beam 150, thereby controlling the size of the hot zone, adapting to different diameters of the glass filament 160, and compensating 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 to adjust the focus of the primary laser beam 150, i.e., to adjust the diameter of the primary laser beam 150, adjust the diameters of the at least three partial laser beams 150′, and thereby adjust the size and intensity of the hot zone, and modify the heating dynamics of the apparatus 100. The focusing lens 135 may be mounted on a computer-controlled motorized translation stage.

[0046] According to various embodiments, the device 100 may comprise a focusing lens for each partial laser beam 150′, i.e., downstream of the beam splitter 145, to enable compensation for any instabilities in the beam splitter 145, such as instabilities in the wavelength of the laser beam and instabilities in the beam pointing of the laser beam source 110.

[0047] When one or more focusing lenses 135 are used in the light beam path unit, the power of the primary laser beam 150 can be varied, as the focusing lenses can be used to adjust / control the laser intensity at the deposition location to achieve a suitable temperature at the deposition location.

[0048] The optical beam path unit may comprise a means for providing circular polarization to the primary laser beam 150 upstream of the beam splitter 145 to obtain a stable circularly polarized primary laser beam 150. A quarter-wave plate 125 may be used to generate the circularly polarized primary laser beam 150, and preferably a linear polarization unit 126 (disclosed in FIG. 7) is located between the laser beam source 110 and the quarter-wave plate 125 to obtain the best output from the quarter-wave plate 125 regardless of the polarization stability of the laser beam source 110. The circularly polarized primary laser beam 150 may also be obtained using a reflective retarder 129 (disclosed in FIG. 4) instead of the quarter-wave plate 125, for example instead of one of the primary beam steering mirrors 115. When using a reflective retarder 129, the direction of linear polarization of the primary laser beam 150 must be tilted 45 degrees with respect to the plane of incidence.

[0049] According to various embodiments, the beam splitter 145 is configured to provide a uniform partial laser beam 150' with circular / near-circular polarization to obtain a uniform and stable temperature across the deposition location 140.

[0050] Circular / near-circular polarization of the laser is preferred, since it is preferable to have identical partial laser beams 150' downstream of the beam splitter 145. If the laser beam is not circularly polarized, depending on the incident angle / direction, different partial laser beams 150' will acquire different polarizations and different partial laser beams 150' will have different heating efficiencies, which will result in non-uniform temperatures at the deposition location.

[0051] The beam splitter 145 may be constituted by a diffractive optical element (DOE) configured to split the primary laser beam 150 into at least three, but preferably four, partial laser beams 150′, each of which is uniform, i.e. has the same properties as the primary laser beam 150. The use of a circularly polarized primary laser beam 150 ensures that the partial laser beams 150′ are identical / uniform, since the DOE 145 may be polarization dependent, thereby achieving a uniform and stable temperature at the deposition location.

[0052] The optical 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, so that the partial laser beams 150′ all impinge on the glass filament 160 from different directions. To obtain a uniform temperature at the deposition location 140, each of the partial laser beams 150′ should have the same beam path length.

[0053] The inventors have realized / discovered the importance of eliminating wavelength instability / fluctuations of the primary laser beam 150, since wavelength instability / fluctuations provide for beam alignment changes, thereby providing for hot zone position changes and non-uniform temperatures at the deposition location 140. The inventors have also realized / discovered that the diffraction angle, i.e. the angle between the incoming primary laser beam 150 and the outgoing partial laser beam 150′ at the beam splitter 145, must be as small as possible in order to minimize the negative impact on the position of the focus of the partial laser beam 150′ resulting from an unstable / fluctuation wavelength.

[0054] More precisely, each DOE 145 has a predetermined grating frequency / density, and the higher the value of the grating frequency / density, the more rapidly the diffraction angle varies with a particular variation in the laser beam wavelength. The increased variation in the diffraction angle entails instability / axial movement of the focal spot, and thus temperature instability at the deposition location 140.

[0055] The primary laser beam 150 inherently has a varying wavelength when generated. In addition, changes in the power of the laser beam source 110 affect the structure of the laser beam source 110 to obtain a different preset / predetermined temperature at the deposition location 140 or due to feedback information confirming that the temperature at the deposition location 140 is incorrect. Therefore, changes in the equilibrium temperature of the laser beam source 110 entail changes in the dimensions of the laser cavity within the laser beam source 110, thereby varying the wavelength of the primary laser beam 150.

[0056] 3-7, the glass filament delivery nozzle 120 is positioned so as to be surrounded by the beam path of the partial laser beam 150′, i.e., so as to be surrounded by the secondary beam steering mirrors 165. To obtain an incident angle in the range of 30-60 degrees and at the same time have space for the glass filament delivery nozzle 120 between the secondary beam steering mirrors 165, and additionally have a small diffraction angle, the beam path length of the partial laser beam 150′ must be relatively long (see FIG. 5). The longer the beam path, the greater the displacement of the focal point due to wavelength fluctuations of the primary laser beam 150.

[0057] Therefore, in the embodiment disclosed in FIG. 5, the DOE 145 may be selected to produce a small diffraction angle of 15 degrees or less, preferably 10 degrees or less, and most preferably 5 degrees or less, in order to make the variation / movement in the position of the focal spot small / acceptable.

[0058] According to various embodiments, and with reference to the schematic exemplary embodiments of Figures 6 and 7, the optical beam path unit can include a pyramid mirror 155 located downstream of the beam splitter 145 to diverge / redirect the at least three partial laser beams 150' from one another more rapidly than in the embodiment of Figure 5. A secondary beam steering mirror 165 is located downstream of the pyramid mirror 155. The pyramid mirror 155 significantly reduces the beam path of the partial laser beams 150', i.e., the design of the printer head 102 becomes much more compact compared to a setup without the pyramid mirror 155. Therefore, the use of the pyramid mirror 155 downstream of the beam splitter 145 shortens the beam path of the partial laser beams 150', thereby increasing the stability of the position of the focal point.

[0059] Therefore, in the embodiments disclosed in Figures 6 and 7, the DOE 145 can be selected to produce larger diffraction angles, i.e., diffraction angles of 45 degrees or less, preferably 30 degrees or less, and most preferably 20 degrees or less, while still resulting in small / acceptable fluctuations / movements in the position of the focal point.

[0060] It should be pointed out that when using a laser beam source 110 with advanced wavelength stabilization means, such as the embodiment disclosed in Figures 3 and 4, the DOE 145 can be selected to produce a diffraction angle of 80 degrees or less, thereby eliminating the need for the use of a pyramidal mirror.

[0061] An example of a process parameter monitoring means of a feedback control unit based on separation of a small sample from the laser beam will now be described in more detail with reference to FIGS.

[0062] The process parameter monitoring means may include a beam tap 127 located upstream of the beam splitter / DOE 145. The beam tap 127 separates a predetermined sample of the primary laser beam 150, for example, within a range of 1-10%. The beam tap 127 directs the separated sample to a detector 128, such as a power meter, and a control unit compares the measured power of the primary laser beam 150 with a reference value. Any deviation is used to adjust / control the power of the primary laser beam 150 originating from the laser beam source 110. The beam tap 127 may be polarization-dependent, with different polarizations being removed by different amounts, resulting in power reading errors. That is, depending on the polarization stability of the primary laser beam 150, primary laser beams 150 with the same total power may result in different power readings. According to various embodiments of the apparatus 100 having a quarter-wave plate 125 in combination with a linear polarization means (see FIG. 7), the beam tap 127 can be located upstream of the quarter-wave plate 125 and downstream of the linear polarization means 126. According to embodiments of the apparatus 100 having a phase delay mirror 129 (FIG. 4) or a quarter-wave plate 125 (FIGS. 3 and 5-7), 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 using the quarter-wave plate 125 or the phase delay mirror 129 to obtain a circularly polarized laser beam, blocking of laser reflections directed back into the laser beam source 110 from downstream of the quarter-wave plate 125 or the phase delay mirror 129 may also be achieved. A shutter (not shown) may be used to turn the primary laser beam 150 on and off adjacent the entrance to the printer head 102. When OFF (closed), the entire primary laser beam 150 is directed to a beam dump, which can then be used as a detector / power meter. When ON (open), the entire primary laser beam 150 enters the printer head 102.

[0063] It should be pointed out that, alternatively, separation of the sample from the laser beam can be performed downstream of the beam splitter / DOE 145, i.e., a sample of the laser beam originating from the beam splitter / DOE 145 is directed to a detector / power meter.

[0064] According to various embodiments of the apparatus 100, the printer head 102 includes a gas purging device configured to remove deposits, i.e., fumed silica particles and combustion by-products, from an area including the deposition location 140 and the glass filament delivery nozzle 120. The gas purging device is configured to generate a gas / air flow in the area of ​​the glass filament delivery nozzle 120. According to one exemplary embodiment, to obtain overpressure within the housing of the printer head 102, the gas / air flow is supplied therein, and then the gas / air flow leaves the housing of the printer head 102 around the filament delivery nozzle 120.

[0065] This is to ensure that any fumes from the combustion by-products of the coating material 169 or vaporized / molten glass (fumed silica particles due to overheating) do not move toward the glass filament delivery nozzle 120 or other parts / optics of the printer head 102, or remain / remain at the deposition location 140. Otherwise, such fumes could damage the printer head optics and filament delivery nozzle 120, necessitating frequent cleaning or replacement of parts, and potentially negatively impacting the printed glass body. In FIG. 3 , printing is performed with the glass filament delivered horizontally toward the stage 130. This is beneficial because fumes automatically leave the area of ​​the glass filament delivery nozzle 120 and deposition location 140. However, with the use of a suitable gas purge, the printer head 102 can also be positioned in any orientation (e.g., facing up, down, sideways, etc.).

[0066] Please refer now to Figures 8 and 9a-9c. 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. Protective coatings can be applied during filament fabrication, for example, using a fiber draw tower, which is used to fabricate optical fiber. A furnace heats the preform (a larger version of the filament in both shape and composition). The softened glass is then pulled using a capstan in combination with a diameter gauge for the correct filament size. While the filament is being pulled, the preform is further fed into the furnace. Typically, a coating resin is introduced into a coating cup through which the filament passes. The coating is then later cured, either thermally or using, for example, a UV lamp, before the filament can be wound onto a spool for storage and transportation. Curing temperatures for polyimide coatings on optical fiber typically range from about 100 to 400 °C.

[0067] Polyimide-coated optical fibers can withstand operating temperatures of approximately 300°C and are commonly used in higher temperature (sensing) applications, where coating thicknesses of 10-15 μm are typically used. Thicker coatings can also be applied by repeating the coating procedure, adding multiple layers of coating while still obtaining only one coating.

[0068] For glass filaments, the coating thickness should be as thin as possible while still providing adequate mechanical and chemical protection for the fiber. We have found that a single layer polyimide coating thickness of approximately 5 μm on a filament gives good results.

[0069] The preferred outer diameter of the glass filament is in the range of 100 μm to 500 μm. This diameter significantly affects the mechanical properties of the filament; increasing the diameter results in a stiffer filament. The translation of the printer head and glass filament relative to the object / stage being printed during printing exerts lateral forces on the filament. Filament misalignment depends on the viscosity and surface tension of the liquid glass in the hot zone and the printing speed. A schematic diagram of the delivery nozzle 120 and the delivered glass filament 160 is shown in Figure 6. Using a stiffer filament allows for an increased distance between the filament delivery nozzle 120 and the stage 130. L is the distance between the glass filament delivery nozzle 120 and the stage 130. Therefore, the diameter of the glass filament, the design of the filament delivery nozzle 120, and the distance between the glass filament delivery nozzle 120 and the stage 130 significantly affect printing accuracy / quality. A larger diameter of the glass filament 160 and a shorter distance between the glass filament delivery nozzle 120 and the stage 130 reduce sagging / misalignment of the glass filament during printing. If the distance L is too short, the temperature of the hot zone may damage the filament delivery nozzle 120. Theoretically, under the same processing conditions, a glass filament having a diameter of approximately 200 μm will deflect only one-fourth the amount of a glass filament having a diameter of approximately 125 μm. By using a glass filament having a diameter of 200 μm and a distance L of 5 mm or less, the deflection / misalignment will be a fraction of a μm, which can be considered negligible.

[0070] In glass 3D printing, when printing fused silica / fused quartz glass, glass filaments are continuously fed into a hot zone with temperatures ranging from 1800 to 2200 °C. Other types of glass, such as soft glass, require much lower temperatures. One common method is to feed pure glass filaments. However, because most glass filaments are fabricated with a coating, fabricating pure glass filaments requires the removal of the coating before printing / deposition. Stripping the coating can be performed using mechanical or chemical means (e.g., using sulfuric acid or dichloromethane). This creates additional risks, as glass filaments can become brittle without the coating, and stripping the coating can further weaken the filament's mechanical strength, resulting in a significant interruption of the printing process if the filament breaks during printing.

[0071] Another approach is to directly feed coated glass filaments from the glass filament delivery nozzle 120. A protective coating 169 extends the printable filament length to several kilometers. However, because glass filaments 160 are typically coated using flammable polymers, such as acrylic, this approach can potentially cause open flames in the filament due to high printing temperatures, leading to print failures and often the destruction of the 3D printer. Additionally, standard coatings have a thickness of approximately 50 μm, which is considered excessively "thick" for glass 3D printing. Directly burning such "thick" coatings is not an ideal solution because it can produce more combustion byproducts, is more likely to leave residue that affects print purity, and is not energy-efficient.

[0072] Our approach is to fabricate glass filaments with a thin, flame-retardant, self-extinguishing coating. The thin coating has a thickness in the range of 1 to 50 μm. When a hot zone is heated to a very high temperature using a CO₂ laser beam, the coating begins to burn near the hot zone, meaning that the hot zone itself can be used to remove the coating. When the coating is flame-retardant, the risk of an open flame is eliminated. After the laser beam source 110 and the glass filament supply are turned off, the coating stops burning. The thin coating can easily burn off. In addition to increasing efficiency and reducing environmental impact, a thin coating also reduces the generation of combustion by-products. An ideal coating would have a non-toxic chemical composition to further reduce toxic fumes generated during combustion, and should not contain halogens, for example.

[0073] 9a-9c disclose three different types of glass filaments 160 with one protective coating 169 that can be used within the additive manufacturing apparatus 100. Figure 9a shows a single composition (rod / fiber filament), and the composition (type of glass) can be high-purity fused silica glass, such as fused silica or fused quartz (used for printing high-purity transparent glass). These materials have a low thermal expansion coefficient, meaning they do not require a heated printing plate, and subsequent thermal annealing is not always necessary. The fused silica filament can be co-doped with GeO2, Al2O3, BO3, or F, or a combination thereof. Multifilament printing (with fused silica filaments) can be used to create 3D prints with designed shapes and refractive index structures. Examples include the fabrication of optical fiber preforms or different optical components. The fused silica is doped with rare-earth oxides, such as Er, Yb, or Er / Yb, in combination with additional dopants (e.g., GeO2, Al2O3, BO3, or F). These filaments can be used to create 3D prints of active laser materials. Silicates, borosilicates, aminoborosilicates, and soda-lime glasses represent standard types of lower-cost materials. Due to their higher thermal expansion coefficients, they may require heated printing plates and subsequent thermal annealing to relieve stress.

[0074] FIG. 9b discloses a glass filament 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. When pressure control is applied to the interior of the capillary filament, active contraction / expansion of the filament during printing is possible. The volume of the air hole 162 can be 10-70% of the volume of the glass inclusion within the glass filament 160. The air hole 162 can be centrally or non-centrally located within the glass filament 160. In various exemplary embodiments, the glass filament 160 can have multiple air holes.

[0075] FIG. 9c discloses glass filaments 160 made of a silica-based composition containing a central core structure 160' of refractive index-modifying dopants, e.g., GeO2, Al2O3, BO3, F. These core / clad filaments function as optical waveguides and can be used to print optical circuits on different types of glass substrates for use in telecommunications, sensing, or biomedical applications. In addition to glass-based, other core materials include semiconductors and alloys, e.g., silicon, germanium, etc.

[0076] 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 explanation and illustration. This patent application is intended to cover all adaptations and modifications of the preferred embodiments described herein, and the present invention is therefore defined by the language of the appended claims and their equivalents. Thus, the device can be modified in any manner within the scope of the appended claims.

[0077] 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. Apparatus (100) for additive manufacturing of a three-dimensional glass body, - A stage (130) for supporting the glass body, - A laser beam source (110) for providing a primary laser beam (150), - Printer head (102), - Means for moving the printer head (102) and the stage (130) relative to each other Equipped with, The aforementioned printer head (102) - To form the glass body, at least one glass filament supply nozzle (120) for supplying glass filaments (160) toward the deposition position (140), - A light beam path unit configured to guide the laser beam (150) from the laser beam source (110) to the deposition location (140) in order to heat the glass filament (160), the light beam path unit comprising a feedback control unit having means for monitoring process parameters representing the temperature of the deposition location (140), and means for controlling the power of the primary laser beam (150) to adjust the temperature of the deposition location (140) to a predetermined level. In an apparatus (100) comprising, The aforementioned optical beam path unit, - Apparatus (100) further comprising a beam splitter (145) for splitting the primary laser beam (150) into at least three partial laser beams (150'), wherein the optical beam path unit is configured to guide each of the at least three partial laser beams (150') from the beam splitter (145) to the deposition position (140), and the optical beam path unit comprises a pyramidal mirror (155) located downstream of the beam splitter (145) for branching the at least three partial laser beams (150') away from one another.

2. The apparatus (100) according to claim 1, wherein the process parameter is determined by the power of the primary laser beam (150) upstream of the beam splitter (145) in the printer head (102).

3. The apparatus (100) according to claim 2, wherein the means for monitoring the process parameters, which are determined by the power of the primary laser beam (150), comprises a beam tap (127) configured to separate a predetermined sample of the primary laser beam (150) toward a detector (128).

4. An apparatus (100) according to any one of claims 1 to 3, wherein the optical beam path unit comprises means for providing circular polarization to the primary laser beam (150) upstream of the beam splitter (145).

5. An apparatus (100) according to any one of claims 1 to 3, wherein the optical beam path unit comprises one or more secondary beam steering mirrors (165) configured to guide each partial laser beam (150') toward the deposition position (140).

6. The apparatus (100) according to claim 5, wherein the glass filament supply nozzle (120) is positioned so as to be surrounded by the secondary beam steering mirror (165).

7. The apparatus (100) according to any one of claims 1 to 3, wherein the glass filament supply nozzle (120) is configured to supply the glass filament (160) in a direction perpendicular to the geometric plane, and each of the at least three partial laser beams (150') has an incident angle equal to 30 to 60 degrees with respect to the geometric plane.

8. An apparatus (100) according to any one of claims 1 to 3, wherein the optical beam path unit comprises a focusing lens (135) located upstream of the beam splitter (145) for adjusting the primary laser beam (150).

9. The apparatus according to claim 8, wherein the focusing lens (135) is displaceable forward and backward relative to the beam splitter (145) in order to adjust the diameter of the primary laser beam (150).

10. The apparatus (100) according to any one of claims 1 to 3, wherein the printer head (102) is equipped with a gas purging device configured to remove deposits from an area including the deposit position (140) and the glass filament supply nozzle (120).

11. The apparatus (100) according to claim 1, wherein the process parameter is determined by the temperature of the deposition position (140).

12. The apparatus (100) according to claim 11, wherein means for monitoring the process parameters, which are determined by the temperature of the deposition location (140), include a thermal imager / camera.

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