Stereolithographie-System

Abstract

Stereolithography system comprising a mounting block (12) for receiving linear drives (3, 4) movable in the y- and x-axes as a crossed arrangement and for receiving a build vessel (1) with an integrated build platform (2) movable in the z-axis, wherein the crossed arrangement of the linear drives for the y-axis (3) and for the x-axis (4) is arranged vertically above the build vessel (2), wherein a laser source (6) is directed with the beam exiting vertically downwards in the direction of the resin-filled build vessel (1) and is attached to the linear drive for the x-axis (4) via a fastening means (5), wherein a dynamically adjustable focusing optic is integrated on the laser source (6), characterized in that the dynamically adjustable focusing optic is a motor-driven telescope or a driven objective turret.where the dynamically adjustable focusing optics allow the line width of the laser beam to be dynamically adjusted during the construction process while simultaneously modulating the laser power.

Description

[0001] The invention relates to a stereolithography system for the production of three-dimensional components. Description of the invention

[0002] DE 10 2009 009 503 B3 relates to a device and a method for manufacturing a workpiece according to a rapid prototyping process using a laser for generating a laser beam for curing a material and a workpiece carrier that can be directly irradiated by the laser from a predetermined solid angle range. The device consists of a laser for generating a laser beam for curing the material and a workpiece carrier that can be directly irradiated by the laser. Furthermore, the device includes an optical device, in particular a mirror, with which the laser beam is deflected so that the workpiece carrier can also be indirectly irradiated by the laser.

[0003] German patent DE 10 2004 057 527 B4 describes a method for manufacturing an electrode body for electrochemical machining (ECM) of workpieces, wherein the die is produced using stereolithography. In the rapid prototyping (RP) process, the electrode body is built up layer by layer in a liquid polymer bath. For this purpose, the desired cross-section of a layer of the electrode body is created using a laser that is both horizontally movable and height-adjustable. The laser is moved along the horizontal plane according to the desired contour, and a portion of the polymer layer in the liquid polymer is exposed and thus cured by corresponding exposure.

[0004] The invention according to US 2003 001313 A discloses a method and an apparatus for producing ceramic shapes by sintering selected areas of a ceramic material with a laser beam to form the shape. To produce the shape, the liquid suspension or plastic mass is applied layer by layer, and each layer of material is sintered at selected locations with the laser beam. The laser beam is preferably controlled by means of the layer-by-layer design data.The device for producing ceramic molded parts has a support surface, an application unit for depositing layers of a ceramic material, a drying unit for the deposited layers, and a laser unit for generating a laser beam. The laser beam is directed to selected areas of a given layer of the ceramic material to sinter the irradiated material and form the molded part. The laser beam direction control devices are preferably designed as laser scanners, with the laser scanner being controlled by digital design data for the molded part. This allows for the direct production of a prototype from the design data. The laser unit is moved across the surface of the deposited layer by a robotic arm, and the corresponding layer of the molded part to be produced is projected onto the deposited layer.

[0005] US Patent 2002, 185,782 (A1) describes a method for producing a three-dimensional object by stereolithography. Solid reinforcing materials are mixed with the liquid medium such that at least a portion of the solid reinforcing material is located in the layer of liquid medium between the top surface of the last layer formed and the top surface of the liquid medium. An acoustic field is then generated in the liquid medium such that the acoustic field is present in at least a portion of the layer of liquid medium between the top surface of the last layer formed and the top surface of the liquid medium, and the liquid medium is subsequently cured.

[0006] US Patent 2004,094,728 A describes a device for sintering and, optionally, ablating and / or marking, and subsequent reworking of the finished workpiece using focused electromagnetic radiation. The device consists of a machine housing containing a build chamber. A scanner is located in the upper part of the build chamber, into which the beam of a sintering laser is coupled. The lower part of the build chamber contains a height-adjustable workpiece platform and a material feed system that transports powdered, pasty, or liquid sintering material from a storage container into the process area via the workpiece platform.The scanner is movable in the upper part of the build chamber, traveling along one axis, and is mounted on a scanner support bridge that is motor-driven and moves above the workpiece platform. The scanner support bridge moves along a second axis on two parallel supports spaced apart by the width of the build chamber. Motorized drive elements of the scanner support are connected to a control computer, which is responsible for the entire process. During the build process, this control computer manages both the movement of the scanner across the workpiece platform and the movement of the scanner mirror within the scanner housing. In addition to possible movement of the scanner along the x- and y-axes, movement along the z-axis is also possible, allowing the scanner to be moved vertically across the workpiece platform or in adjacent areas.The two parallel supports then bridge onto two vertically arranged supports in the form of linear axes on the right and left walls of the build vessel. The sintering laser beam is directed into the scanner support area parallel to the axes of the scanner support's suspension and, via deflection mirrors, to the scanner's optical input.

[0007] In addition to the high effort required by the arrangement of the three linear axes for two-axis movement or the seven linear axes for three-axis movement and the use of four mirrors, problems arise in the synchronization of the motors of the linear axes, which can lead to the total failure of the stereolithography system.

[0008] The invention according to DE 100 53 741 C1 relates to a device for sintering, ablation and / or marking by means of electromagnetic focused radiation, in particular a laser sintering machine and / or laser surface processing machine with a build chamber housed in a machine casing, in or above which a light guide device, in particular a scanner movable in all directions by means of a cross slide arrangement, in which the beam of a sintering energy source is coupled, a height-adjustable workpiece platform and a material feed device with a coater for feeding sintering material from a storage container into the process area above the workpiece platform are arranged, wherein the workpiece platform can be removed from the build chamber as an interchangeable element, wherein the height-adjustable workpiece platform,The storage container and the coating unit are designed as a single, removable process platform exchange unit from the installation space, and further process platform exchange units of the same or different designs can be inserted into the installation space to carry out the same or different processing processes.

[0009] The cross slide for the scanner, which can move in all directions, is designed as a support bridge movable in the y-direction. A linear drive for the z-axis, along with a laser scanner, is mounted on this bridge. This support bridge runs on two parallel beams, spaced apart by a distance corresponding to the width of the construction vessel, which are movable in the x-axis. The laser beam is guided to the laser scanner via a multitude of mirrors along the beams, the support bridge, and the linear drive for the z-axis. The parallel beams and the support bridge are designed as linear drives.

[0010] As in the invention according to US 2004 094 728 A, in addition to the high costs associated with the arrangement of the four linear drives and the use of five mirrors, problems arise with the synchronization of the linear drive motors, which can lead to a total failure of the stereolithography system. Furthermore, this solution requires the use of high-powered lasers, which are energy-intensive and expensive, to compensate for the energy loss through the mirrors.

[0011] US Patent 2002 171 178 (A1) describes a method for manufacturing a three-dimensional, prosthetic implant with a porous network made of biodegradable polymer. The method uses a stereolithography system, whereby chains of one or more photopolymers and a photoinitiator form a layered, polymeric prosthetic implant using a three-dimensional CAD image. The photocurable, biodegradable polymer is described as a solution of polypropylene fumarate (PPF) and a solvent to adjust the solution's viscosity. During the manufacturing process, the solution is placed in a container within the stereolithography system (a commercially available SLA 250 stereolithography unit).The container contains a z-axis movable build plate to support each of the covalently bonded layers of the polymer prosthetic implant, which are exposed to UV light energy during successive layers of the solution. The UV light energy is generated using a commercially available UV laser, with the laser beam positioned above the container via vector-based scanner mirrors, allowing movement along the x- and y-axes (www.klartext-pr.de / .... / artikel / Die Kultur der Prototypenherstellung.pdf).

[0012] US Patent 45,753,30B1 describes a system with an external laser source, optical beam preparation (expander, shutter, etc.), a laser scanner for beam deflection, and an F-theta lens for compensating for laser focus shifts. The laser beam is guided by two rotating mirrors to cover the entire build area. High resolution requires very precise motors. Furthermore, the focus must be constantly corrected by the F-theta lens, meaning the working distance varies depending on the angle between the laser beam and the surface. An additional disadvantage is that the laser beam penetrates the polymer at a very oblique angle at the edges. The scanner, the F-theta lens, and a sufficiently powerful beam source are very expensive to purchase. Due to the constantly changing angle between the substrate and the laser beam, telephoto optics or interchangeable optics cannot be positioned above the build bath.

[0013] The device for manufacturing an object by stereolithography, as described in US 55 95 703 A, is of a design known per se.

[0014] The invention in DE 100 53 741 C1 relates to a device for sintering, ablation and / or marking by means of electromagnetic focused radiation, in particular a laser sintering machine and / or a laser surface processing machine with a construction space housed in a machine housing, in or above which a light guiding device, in particular a scanner, into which the beam of a sintering energy source is coupled, a height-movable workpiece platform and a material supply device with a coater for supplying sintering material from a storage container into the process area above the workpiece platform are arranged.

[0015] The invention in publication EP 1 958 727 A1 relates to a method and a device for processing workpieces using high-energy radiation generated by a radiation source.

[0016] In publication KR 10 2010 0 130 497 A, a stereolithography device is disclosed which has a blue light recording unit to enable the production of a complex structure, since the amount of laser is controlled and thus also the hardened area is controlled.

[0017] A method for fabricating optical elements encapsulated in monolithic matrices is disclosed in US patent US 2005 / 0208431A1. The method is based, at least in one aspect, on the concept of using multiphoton multistep photocuring to fabricate encapsulated optical elements within a body made of a photopolymerizable composition. Image-wise multiphoton polymerization techniques are employed to form the optical element. The body surrounding the optical element is also photocured by planar irradiation and / or thermal curing to support the formation of an encapsulation structure.

[0018] This device mainly comprises a container filled with a liquid photopolymerizable prepolymer, a plateau attached therein which can be moved up and down in the liquid prepolymer by a mechanism not shown, and a laser beam source which can be moved over the surface of the liquid prepolymer according to a certain pattern by a mechanism also not shown.

[0019] A 2D optomechanical laser scanner is a solution in which the laser beam is not controlled by a scanner with rotating mirrors, but rather by several parallel, movable deflecting mirrors (Gandhi, PS et al. Micromech. Microeng., no. 20, pp. 1-11, 2010). By guiding the mirrors at right angles, the laser focus can always be positioned perpendicular to the build area. The decisive disadvantages are the number of deflecting mirrors required. Since the deflecting mirrors are dynamically guided, a high degree of precision is required in each mirror drive as well as in the flatness of the mirrors themselves. Furthermore, a loss of approximately 10% of the laser power is to be expected on each reflective surface. Therefore, a high-power beam source is also required. Both factors—precision at multiple points and laser power—drive up the costs of the system technology.

[0020] A further development for the parallel production of multiple identical components is offered by a design using several parallel optical fibers on an XY plotter. The laser is controlled via shutters and beam guidance optics. A fiber bundle then multiplies the beam source, and the contour is processed line by line or vector by an XY plotter system. This multiplication allows for the parallel production of multiple identical components with perpendicular incidence of the laser radiation. The use of optical fibers to multiply the beam source enables the parallel production of components (K. Ikuta et al., "New Micro Stereo Lithography for freely movable 3D Micro Structure," IEEE, pp. 290-295, 1998). However, the processing speed compared to a scanner optic will hardly increase.Problems arise with the components used to split the laser beam from the beam source (the collimator) and with ensuring a precise, uniform distribution of laser power to the individual fiber strands. If each fiber does not deliver identical parameters, the quality and dimensional accuracy of the components suffer. Furthermore, the use of fibers with UV lasers often leads to fiber aging. Sufficient power must be available to distribute enough light to all fibers. Due to the large number of expensive individual components, such as lasers, collimators, fibers, and drive shafts for the fibers, the system technology is very costly.

[0021] The Colamm process (Maruo, S. et al. Sensors and Actuators, vol A 100, pp. 70-76, 2002) avoids the problems of recoating with a wiper. The resin is exposed to light through a window at the bottom of the vessel. The component is "glued" to the build platform and then lifted layer by layer. It is important that the cured resin does not adhere to the glass window. The laser beam is delivered via scanner or fiber optic cable, and this process also has the disadvantages described above.

[0022] Other technical solutions for stereolithography offer so-called masking processes. These variants are referred to as planar processing. Instead of a laser, a UV lamp is used. Using a switchable LCD mask or pre-made masks, the contours for each layer can be created in a single operation (Ikuta, K. IEEE, pp. 290-295, 1998). This technique is used for processing from above as well as, similar to the Colamm process, from below (Schuster, M. et al. Journal of Polymer Science: Part A: Polymer Chemistry, vol. 47, pp. 7070-7089, 2009).

[0023] Digital Light Processing (DLP) is another modification of stereolithography. Here, the resin is polymerized using visible, non-coherent light. The required pattern is projected directly onto the resin, either by micromirrors or a dynamic LCD mask. The entire layer is cured simultaneously. A disadvantage of this method is that the size of the build area, or the number of pixels, is fixed. The higher the resolution of the structures to be built, the smaller these structures become. Common systems achieve resolutions of 1 to 5 µm within the x-y plane at a layer thickness of 10 µm (Maier, Ch. Diploma Thesis “Production of Biometric Materials with Rapid Prototyping Methods,” University of Vienna, 2005).

[0024] Since no laser source is used in these two methods, these methods do not directly relate to the invention.

[0025] All stereolithography devices described in the prior art include optical beam preparation equipment such as expanders and shutters, beam deflection devices such as laser scanners, rotating or parallel-movable deflecting mirrors, beam misalignment compensation devices such as F-theta lenses, or beam guidance devices such as optical fibers. This makes stereolithography systems, especially micro-stereolithography systems, expensive and limits the applications of stereolithography. Furthermore, the losses incurred during beam preparation necessitate the use of high-powered lasers, which are also very expensive.

[0026] All known solutions for mounting laser scanners vertically above the build vessel are also complex, as the mounting is either in the form of a linear drive movable along the z-axis on a support bridge or directly on this support bridge, which in turn runs on two parallel supports. Furthermore, these solutions are used to enlarge the build area, since the scanners can only illuminate a limited area of ​​the build field. For this reason, the build field in these solutions is divided into squares, with the scanner being moved to the next square by means of a cross slide after illuminating one square and irradiating that square. Despite the scanner's vertical positioning above the build field, the problems described above persist in these solutions.

[0027] Furthermore, these solutions can cause significant problems with the synchronization of the linear axis motors, especially during longer run times, which can then lead to the failure of the stereolithography systems.

[0028] The object of the invention is to create a new suspension of the radiation source for stereolithography systems as well as a significantly simplified beam shaping and guidance, whereby significant cost savings are to be achieved through the reduction of components and sensitive parts while simultaneously increasing the processing possibilities and quality as well as the reliability, even during longer operating times, of the stereolithography systems, in particular the micro-stereolithography systems.

[0029] According to the invention, the problem is solved by a stereolithography system consisting of a mounting block (12) for linear drives (3, 4) movable in the y- and x-axes in a crossed arrangement and for a build vessel (1) with an integrated build platform (2) movable in the z-axis, wherein the crossed arrangement of the linear drives for the y-axis (3) and for the x-axis (4) is arranged vertically above the build vessel (2). A laser source (6), with its beam exiting vertically downwards towards the resin-filled build vessel (1), is attached to the linear drive for the x-axis (4) via a mounting means (5). Directly adjacent to the laser source (6) is the holder with the integrated focusing optics (7), which focuses the exiting laser light (8) directly onto the required plane. The component (9) is thus built up layer by layer either by line-by-line or vector-by-vector movement of the laser head.During the process, the laser cures the liquid photopolymer. A practical arrangement of the electrical connections (11) of the laser source (6) allows for easy power supply via trailing cables. In a further embodiment of the invention, the focusing optics (7) can be designed as interchangeable focusing optics (7). This makes it possible to generate different line widths during photopolymerization and to optimize the resolution and processing speed. In the case of static optics, only one resolution is fixed per build job. However, it is also possible to replace these static optics with a motor-driven telescope or a driven objective turret, thus dynamically adjusting the line width of the laser beam during the build process while simultaneously modulating the laser power. This significantly increases the processing speed.

[0030] The invention will now be explained in more detail using an exemplary embodiment, wherein the Fig. 1 represents a schematic diagram of the stereolithography system, with List of symbols 1 building vessel 2 building platforms 3 Linear drives for the y-axis 4 Linear drives for the x-axis 5 Mounting element for the laser head 6 Laser source 7 focusing optics 8 Laser beam 9 component 10 Harz 11 electrical connections 12 Recording block

[0031] The Fig.Figure 1 shows a schematic representation of the essential components for the stereolithography process according to the invention. Directly above the build vessel (1), with its integrated, lowerable build platform (2), a linear axis system is mounted on a granite mounting block (12). The laser source (6) is mounted on the crossed arrangement of the y-axis (3) and the x-axis (4) via a suitable mounting element (5) such that the laser beam exits vertically downwards onto the build vessel (1) filled with resin (10). A diode laser is used as the laser source (6). The holder with the integrated focusing optics (7), which focuses the exiting laser light (8) directly onto the required plane, is attached directly to the laser source (6). The component (9) can thus be built up layer by layer either by line-by-line or vector-by-vector movement of the laser source (6). During the process, the laser beam cures the liquid photopolymer.A practical arrangement of the electrical connections (11) of the laser source allows for easy power supply via trailing cables. Liquid photopolymer is cured by a laser beam in thin layers with a standard layer thickness in the range of 0.05–0.25 mm, and down to 1 µm in microstereolithography. The process takes place in the build vessel (1), which is filled with the photopolymer, in this example, epoxy resin. In the build vessel (1), the build platform (2), which is movable along the z-axis, is immersed in the epoxy resin by moving the build platform (2) along the z-axis. It is then raised along the z-axis by the amount of the layer thickness, and the epoxy resin is applied with a wiper. After the epoxy resin has been applied, the laser source (6) is moved over the build platform (2) using the x- and y-axes (4, 3), and the epoxy resin is cured by the laser beam.The laser source (6) is moved line by line across the build area and its position is modulated via its digital input.

[0032] After each step, the workpiece is lowered a few millimeters into the liquid and returned to a position one layer thickness below the previous one. The epoxy resin on top of the component is then evenly distributed by a wiper. Next, the laser source (6), controlled by a computer via a crossed x- and y-axis arrangement (4, 3), moves across the new layer over the surfaces to be cured. After curing, the next step is carried out, gradually creating a three-dimensional part.

[0033] In stereolithography, support structures are typically built during the manufacturing process because the laser-cured resin is still relatively soft, and certain features (e.g., overhangs) need to be securely fixed during the build process. After the build process, the build platform (2) with the part(s) is removed from the build vessel (1). After the uncured resin has drained off, the model is removed from the build platform, the support structures are removed, it is washed with solvents, and then fully cured in a cabinet under UV light.

[0034] In the stereolithography system according to the invention, the laser source (6) and the focusing optics (7) are moved directly above the build vessel (1) and thus across the entire build area by means of linear axes, whereby the beam exit and thus the laser beam always remains perpendicular above the build vessel. Compared to laser-based stereolithography systems described in the prior art, the system according to the invention does not require any deflecting mirrors, optical fibers, or similar beam-modifying components. With otherwise comparable performance, the stereolithography system according to the invention is therefore significantly simpler and requires laser sources with considerably lower power (diode lasers). This results in a considerable cost advantage compared to all previous laser-based stereolithography systems.Furthermore, the use of only two linear drives, which are also operated independently of each other, eliminates problems with the synchronization of the motors for the linear drives and significantly reduces the susceptibility to interference of the stereolithography system.

[0035] Further advantages of the stereolithography system according to the invention include reduced laser power losses in the optical system due to component reduction and the consistently perpendicular arrangement of the laser source and the perpendicular exit of the laser beam relative to the build vessel. The perpendicular angle of incidence of the laser radiation avoids the non-perpendicular angle of incidence in the edge region of the build area that is typical in laser scanning processes, thus ensuring consistently high manufacturing precision across the entire build area. Furthermore, no aging occurs in functional components (e.g., optical fibers), and the system is highly maintainable, as a replaced laser does not need to be aligned with the optical system.

[0036] The stereolithography system is further characterized by low energy consumption and therefore lower operating costs.

[0037] The system according to the invention can also be used in laser sintering and laser cutting and marking using laser sources.

Claims

Stereolithography system comprising a mounting block (12) for receiving linear drives (3, 4) movable in the y- and x-axes as a crossed arrangement and for receiving a build vessel (1) with an integrated build platform (2) movable in the z-axis, wherein the crossed arrangement of the linear drives for the y-axis (3) and for the x-axis (4) is arranged vertically above the build vessel (2), wherein a laser source (6) is directed with the beam exiting vertically downwards in the direction of the resin-filled build vessel (1) and is attached to the linear drive for the x-axis (4) via a fastening means (5), wherein a dynamically adjustable focusing optic is integrated on the laser source (6), characterized in that the dynamically adjustable focusing optic is a motor-driven telescope or a driven objective turret.where the dynamically adjustable focusing optics allow the line width of the laser beam to be dynamically adjusted during the construction process while simultaneously modulating the laser power. Stereolithography system according to claim 1, characterized in that the focusing optics (7) are designed to be interchangeable. Stereolithography system according to claim 1, characterized in that the laser source (6) is electrically supplied via trailing cables. Stereolithography system according to claim 1, characterized in that a diode laser is used as the laser source (6).

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