Method and apparatus for lithography-based additive manufacturing of three-dimensional bodies

Abstract

A method for lithography-based additive manufacturing of three-dimensional bodies, comprising: a build platform (8) positioned at a distance from a material support (1), the material support (1) being transparent to at least the radiation of a radiation source; the material support (1) being translated between a first position and a second position; several areas of material solidifiable by exposure to said radiation, the material being applied in a defined layer thickness during the movement of the material support (1); from the first position to the second position, the material applied between the build platform (8) and the material support (1) being irradiated position- and / or time-selectively by a radiation source and solidified; and during the movement of the material support (1) from the second position to the first position, the material is removed from the material support (1).

Description

[Technical Field]

[0001] The present invention relates to a method for lithography-based additive manufacturing of three-dimensional bodies, in which a build platform is arranged at a distance from a material support that is transparent to the radiation of a radiation source in at least some areas of a material that is solidifiable by exposure to radiation, the material support being translationally moved between a first position and a second position.

[0002] The invention further relates to an apparatus for carrying out such a method. [Background technology]

[0003] In lithographic or stereolithographic additive manufacturing, a photopolymerizable starting material is molded layer by layer to form a molded object. Layer information is then transferred to the material to be polymerized in a location- and time-selective manner via an optical mask, a projected image area, or a screen via a laser beam. The choice of exposure and structuring methods differs considerably. On the one hand, a (dipping) tank of photopolymerizable material can be exposed from above. The structured object is continuously immersed in the liquid material during production (SLA), or the material reservoir (filled material bath) is exposed from below through a transparent bath bottom, and the object is removed from the material bath above (DLP, laser stereolithography). In the latter case, the object is structured layer by layer by moving up and down, and the respective distance between the object and the bottom of the material bath ensures very precise layer thicknesses. In novel processes, this type of structuring can also occur continuously (without alternating up and down movements), in which case specific requirements must be imposed on the bath bottom. The major advantage of exposure via a material bath, in contrast to the described immersion process (SLA), is, among other things, the significant reduction in the amount of material required to start the process, which is inherently disadvantageous in terms of handling and process costs, since immersion processes require large amounts of reactive consumable materials.

[0004] All of the above process technologies share the same high geometric quality of additively structured products. Especially in the field of plastics technology, surface quality is crucial to compete with current methods such as injection molding. Therefore, lithography-based 3D printing stands out above all other available 3D printing processes in terms of both surface and form quality. The drawback is the high demands placed on the viscosity of the starting material (photopolymer mixture). Therefore, the dynamic viscosity currently required during the processing stage must not exceed 100 Pa.s (Pascal seconds). This constraint on layered processing significantly limits the selection of suitable photopolymers. This is due to the frequently severely limited material properties of the processed plastics, which is the biggest weakness of lithography-based additive layering processes.

[0005] Especially in the field of technical applications and even end-user products, the material quality of the object is important in addition to its geometric quality. In additively processed plastics, known deficiencies are primarily reflected in temperature resistance (strong loss of stiffness / E-modulus with increasing temperature—usually above 40-50°C) and toughness at ambient temperatures (impact strength / resistance to catastrophic fracture or tearing). Currently, stereolithographically processed materials offering a combination of strength, toughness, and efficient heat resistance (e.g., sufficient stiffness up to 80°C) are considered a prerequisite for the successful economic integration of additive stereolithography processes into existing production technologies. However, until now, such materials have either not been available in the desired quality or have only been partially available.

[0006] To develop new photopolymer systems for stereolithography processes, the quoted viscosity requirements of known processes are particularly problematic. A possible remedy is process control at elevated temperatures. Even a slight increase in process temperature above normal room temperature (20°C) significantly reduces the viscosity of most photopolymers. This allows for a significant increase in the number of starting polymer materials to choose from, which can then lead to new 3D printing materials.

[0007] The application of heated process systems is already widely known. Another option for handling high-viscosity systems lies in the process control itself, for example, when replacing existing immersion systems (material baths with a fill level height of several millimeters or centimeters) with other material supply methods (such as coating systems). Increasing the process temperature can also bring important advantages with these approaches, but the temperature sensitivity of the processed photopolymer must always be taken into account. Complex heating of individual process elements or the entire process chamber is an alternative, but often involves considerable mechatronic expenditure and, if implemented incorrectly, can seriously jeopardize the process stability by reducing the long-term stability of the photopolymer mixture. Summary of the Invention [Problem to be solved by the invention]

[0008] It is therefore an object of the present invention to provide process control for high viscosity resins that combines the benefits of selective heating of individual process steps with the benefits of delivering defined materials to each process zone, while still providing a stable, long-term production system. [Means for solving the problem]

[0009] To solve this object, the invention essentially provides that in a method of the initially defined type, material is applied in a defined layer thickness during movement of the material support from a first position to a second position, after which the build platform and the material support are position- and / or time-selectively irradiated and solidified by a radiation source, and after which material is removed from said material during movement of the material support from the second position to the first position.

[0010] The present invention includes a coating and circulation process that can deliver a photosensitive material to an exposure zone in the form of a thin layer. This process uses a translatable material support, designed, for example, as a material reservoir, which primarily functions as a carrier plate for the thin layer of photosensitive material involved in the process. The photopolymerizable material is delivered onto the movable carrier plate. The material may comprise a pure photosensitive monomer or oligomer compound, or a compound containing a photoinitiator component. Furthermore, such compounds may comprise organic or inorganic fillers and / or further organic or inorganic additives or other substances, colorants, absorber materials, or functional or non-functional components. Furthermore, other photopolymerizable materials can also be used, provided that lithographic interaction with this material is possible in the wavelength range between 150 nm and 950 nm.

[0011] The material is preferably applied or removed by a static material introduction device, which is further in a fixed process position relative to the movable material support.

[0012] Preferably, the material is applied or removed by first and second doctor blades.

[0013] The first doctor blade preferably moves away from the material support perpendicular to the direction of movement of the material support before or during the movement of the material support from the second position to the first position, and preferably moves toward the material support to adjust the defined layer thickness during or before the movement of the material support from the first position to the second position. The first doctor blade is designed so that its height can be variably adjusted in the z-direction (a direction perpendicular to the x-direction in which the material support moves), and the height adjustment is performed by an active process mechanism (e.g., a doctor blade motor) and a passive process mechanism. The first doctor blade can preferably be adjusted in height so that no doctor blade gap is allowed between the first doctor blade and its lowest material support, or a height gap of several micrometers to a maximum of several millimeters in the raised position, so that the material introduction device is completely closed.

[0014] The second doctor blade forms a removal mechanism and its feed height (z-direction) can be passively or actively adjusted. Preferably, the second doctor blade is held adjacent to the material support by a return device, e.g., a spring. Thus, the material introduction device is at least partially sealed against the photosensitive material contained therein at all times.

[0015] Furthermore, it is preferred that a material reservoir be formed between the first doctor blade and the second doctor blade. A particularly preferred method provides that, while the material support moves from the second position to the first position, the material removed from the material support is at least partially returned to the material reservoir. In this regard, it is particularly preferred that, while the material support moves from the first position to the second position, the material is applied from the material reservoir through a gap defined between the first doctor blade and the material support with a layer thickness defined by the translational speed of the material support and the gap.

[0016] The method according to the invention in this case provides for linear movement of the material support under the material introduction device, i.e., under the first and second doctor blades. During the fourth movement of the material support (i.e., from the first position to the second position), a defined thin layer of photopolymerizable material is applied to the material support at least partially and in part of the material support, and during the return movement of the material support (i.e., from the second position to the first position), the remaining photosensitive material film is at least partially detached or removed in part of the material support, so that, on the one hand, the material support is composed of a clean or at least partially cleaned surface in the detached part, and, on the other hand, the previously remaining photosensitive material is at least partially returned to the material reservoir.

[0017] The thin layer of photosensitive material applied during the fourth movement of the material support is transported to an exposure zone, where position- and time-selective exposure information is applied to the material support from the opposite side of the material. In a preferred embodiment, this is achieved, for example, from below, and the exposure information must pass through the material support. For this reason, the material support is designed to be transparent or at least partially transparent to the optical information used. After the photopolymerizable material is exposed and selectively cured, the processed material is pulled away from the material support, leaving unpolymerized residues of the photosensitive material in the form of discontinuous thin layers or material accumulations, forming material islands or other layer patterns. During the return movement of the material support, this material is again supplied to the material reservoir. To facilitate this, the first doctor blade can be actively or passively raised during the return movement of the material support to facilitate the passage of unpolymerized material residues under the first doctor blade. After the return movement of the material support is complete, the first doctor blade can be immediately lowered, either actively or passively, to prevent the photopolymerizable material from flowing out of the material reservoir. During the return movement of the material support, the photosensitive material is peeled off from the bottom of the material support by the second doctor blade and can therefore remain, at least temporarily, in the material reservoir.

[0018] The described operation can be repeated as many times as necessary, thus constantly applying a freshly applied layer of photopolymerizable material to the material support and continuously supplying the applied material to the exposure zone. The height or thickness of this applied photosensitive material layer can be continuously adjusted by adjusting the height of the first doctor blade and the linear movement speed of the material support. The height adjustment options for the photosensitive layer range, for example, from a few micrometers to several millimeters. Furthermore, the final achievable layer thickness of the photosensitive material is a function of the viscosity of the photosensitive material and its flow properties, which are largely temperature-dependent. To illustrate this aspect, it is preferred that the material be heated within the material introduction device. In a preferred embodiment, all related process components, such as the first and / or second doctor blades and / or the material support, can further be designed to be heatable in a selective and / or individually adaptable manner.

[0019] The build platform used in a suitable stereolithography printing process is designed to be preferably heatable, to mechanically adjust (along the z-axis) the layer gap used for polymerization, and to reliably detach the selectively polymerized material layer from the linearly movable material support after polymerization.

[0020] During the described process, photosensitive stock material is preferably constantly present in the material reservoir. Alternating linear motion of the material support below the material reservoir causes periodic movement of the photosensitive stock material in the material reservoir in the form of a moving or circulating material wave or material sweep of the photosensitive material. To optimize process control, it is advantageous to actively or passively detect the material level of the photosensitive stock material continuously or at defined intervals, which can be achieved in exemplary embodiments according to the present invention by using ultrasonic, optical, or touch sensors. Other unspecified feedback systems, such as switches, buttons, or fill level probes, can also be used to measure the fill level of the photosensitive stock material. To maintain a desired fill level of the photosensitive stock material, it is preferable for material to be introduced into the material reservoir by a conveying device. For example, it may be possible to continuously or at desired time intervals to supply new photosensitive material to the material reservoir. The conveying device may be designed to be selectively and individually heatable.

[0021] Furthermore, the linearly movable material support can actively or passively assist a desired release process of the selectively solidified photosensitive material from the material support in the exposure zone, and the linear movement of the material support in the exposure zone can be combined with an active or passive tilting movement of the overall process setup relative to the build platform, or with an active or passive tilting movement of the build platform itself relative to the process setup, to lead to a predefined or undefined multi-axis removal process of the solidified photosensitive material, such as a combined removal movement that approaches as close as possible to an ideal release process. Therefore, it is preferred that the build platform tilt during movement of the material support from the second position to the first position. In a preferred configuration, this release process of the selectively cured photosensitive material layer is determined by the linear lift (z-direction) of the build platform, passive or active rotation of the build platform about a pivot point carried by the support platform, and active or passive linear translation of the material support, all in combination to enable a multi-axis release process. To aid in this peeling process, the material support may be provided with a special anti-stick coating and / or may consist of a stack of different materials that are transparent or at least partially transparent to the operating wavelengths used in the photopolymerization exposure process.

[0022] The described process control according to the present invention enables precise processing of highly viscous photosensitive starting materials that have high molecular weights and can exist as non-fluids or even solids at room temperature. Furthermore, the described refill system ensures high process safety, since only the amount of photosensitive material required for a stable pressure process needs to be available in the process zone. Additional photosensitive stock material can be kept away from the process zone until use, significantly preventing potential long-term adverse effects from process temperature and other environmental influences. Furthermore, supplying the photosensitive material to the exposure zone in a defined thin layer on the material support allows for control of air that may be entrapped in the solidified photopolymer layer. It is also possible to influence the sweep of the periodically rotating material in the material reservoir via the linear travel speed of the material support, the fill level of the photosensitive material in the material reservoir, and the travel height of the doctor blade to optimize the mixing of fresh photosensitive material with photosensitive material already removed from the material support and minimize the introduction of unwanted air bubbles into the stock material in the material reservoir.

[0023] According to a further aspect of the present invention, there is provided an apparatus for lithography-based additive manufacturing of three-dimensional bodies, comprising a source of electromagnetic radiation, a material support that is at least partially transparent to the radiation of the source in an area for a material that can be solidified by exposure to said radiation, and a build platform held at a distance from the material support, wherein the material support is translatable between a first position and a second position, and wherein a material introduction device is provided that is designed to apply a defined layer thickness of material during movement of the material support from the first position to the second position and to remove material from the material support during movement of the material support from the second position to the first position.

[0024] Preferably, it is provided that the material introduction device comprises at least first and second doctor blades, the first doctor blade being height adjustable, preferably perpendicular to the direction of movement of the material support.

[0025] Furthermore, the second doctor blade preferably cooperates with a return element (for example a spring).

[0026] In a preferred configuration, it is provided that the build platform is tiltably arranged.

[0027] The material introduction device preferably includes a heating device for heating the material.

[0028] Furthermore, a material reservoir is preferably formed between the first and second doctor blades, which are preferably arranged parallel to each other.

[0029] Preferably, it is provided that the material reservoir is connected to a conveying device to enable material to be introduced into the material reservoir. [Brief explanation of the drawings]

[0030] [Figure 1] FIG. 1 shows a material support. [Figure 2]FIG. 2 shows the stage after solidification of the material layer is complete. DETAILED DESCRIPTION OF THE INVENTION

[0031] In the following, the invention will be explained in more detail by means of exemplary embodiments shown diagrammatically in the drawings, in which Figures 1 and 2 show schematic cross-sectional views of an apparatus according to the invention in successive stages of the process cycle.

[0032] In Figure 1, the material support is designated 1, on which a material layer 11 is arranged. At a distance from the material support 1, a build platform 8 is arranged, which is height adjustable in the z direction and tiltably mounted about an axis 4. Several material layers 11 have already been built between the build platform 8 and the material support 1. The material support 1 is translatable along the x direction, which is perpendicular to the z direction.

[0033] Further provided is a material introduction device 3 comprising a first doctor blade 5 and a second doctor blade 6. The first doctor blade 5 is height adjustable in the z-direction by a doctor blade motor 10, and the second doctor blade 6 comprises a spring 7 that holds the second doctor blade 6 in contact with the material support 1 in the z-direction. Between the two doctor blades 5, 6 is formed a material reservoir 2 into which material can be supplied by a conveying device.

[0034] 1, the material support 1 is in a second position. When the build platform 8 is lowered towards the material support 1, a radiation source (not shown) can selectively irradiate and solidify the material layer 11 on the material support 1 to form a new material layer 11. During the movement of the material support 1 to the second position, the material layer 11 has been applied by a first doctor blade 5.

[0035] FIG. 2 shows the stage after the solidification of the material layer 11 is completed. The material support 1 moves in the direction of arrow 12 from the second position toward the first position. At the same time, the build platform 8 rises slightly in the z direction. The combination of the lifting action of the build platform 8 and the movement of the material support 1 in the direction of arrow 12 causes the build platform 8 to tilt about axis 4, facilitating the multiaxial separation of the completed material layer 11 from the material support 1 in the manner of a peeling process. For this purpose, the position of axis 4 on the build platform 8 can also be located on the opposite side of the build platform 8 in the x direction, if this further facilitates the peeling process. While the material support 1 moves from the second position to the first position, the material 11 remaining on the material support 1 is peeled off by the second doctor blade 6 and recollected in the material reservoir 2, which is optionally replenished with new material by a conveying device to ensure sufficient material is always available.

[0036] After the material layer 11 has been peeled off by the second doctor blade 6 and the material support 1 has reached the first position, a material layer 11 is again applied from the material reservoir 2 by the first doctor blade 5 by moving the material support towards the second position relative to the direction of the arrow 12 until it reaches the second position depicted in Figure 1. After this, the build platform and the structure formed by the already solidified layer 11 are each lowered into the material layer to adjust the thickness of the layer to be solidified, after which further exposure and solidification of the material layer 11 can take place.

Claims

1. 1. A method for lithography-based additive manufacturing of a three-dimensional body, comprising: a build platform (8) arranged at a distance from a material support (1), the material support (1) being transparent to radiation of a radiation source in at least some areas for a material that can be solidified by exposure to radiation, the material support (1) being translationally moved between a first position and a second position, a material introduction device (3) applies a material to the material support (1) in a defined layer thickness while the material support (1) is moving from the first position to the second position, the applied material between the build platform (8) and the material support (1) is position- and / or time-selectively irradiated with a radiation source to solidify, and then the material is removed from the material support (1) by the material introduction device (3) while the material support (1) is moving from the second position to the first position; The material is applied or removed by first and second doctor blades (5, 6), A material reservoir (2) is formed between the first and second doctor blades (5, 6). A method characterized by:

2. 2. The method according to claim 1, wherein the material is applied or removed by a static material introduction device (3).

3. 2. The method according to claim 1, characterized in that during or before the movement of the material support (1) from the second position to the first position, a first doctor blade (5) is moved away from the material support (1) perpendicular to the direction of movement of the material support (1).

4. 4. The method according to claim 3, characterized in that during or before the movement of the material support (1) from the first position to the second position, a movement towards the material support (1) is made to adjust the defined layer thickness.

5. 2. The method according to claim 1, wherein during the movement of the material support (1) from the first position to the second position, the material is applied from the material reservoir (2) through a gap defined between a first doctor blade (5) and the material support (1) with a layer thickness defined by the gap and a translational speed of the material support (1).

6. 6. A method according to any one of claims 1 to 5, characterized in that the material is introduced into the material reservoir (2) by means of a conveying device (9).

7. 7. A method according to any one of claims 1 to 6, characterized in that the second doctor blade (6) is held adjacent to the material support (1) by a return device (7).

8. The method according to claim 7, characterized in that the return device (7) is a spring.

9. 8. The method according to any one of claims 1 to 7, characterized in that during the movement of the material support (1) from the first position to the second position, the material removed from the material support (1) is at least partially returned to the material reservoir (2).

10. 10. The method according to any one of claims 1 to 9, characterized in that the build platform (8) is tilted during the movement of the material support (1) from the second position to the first position.

11. 11. A method according to any one of claims 1 to 10, characterized in that the material is heated in the material introduction device (3).

12. 12. An apparatus for lithography-based layer-by-layer manufacturing of three-dimensional bodies for carrying out the method according to any one of claims 1 to 11, comprising: The apparatus comprises a source of electromagnetic radiation, a material support (1) that is transparent to the radiation of the source in at least some areas for a material that can be solidified by exposure to the radiation, and a build platform (8) held at a distance from the material support (1), The material support (1) is translatable between a first position and a second position; Furthermore, a material introduction device (3) is provided, which is configured to apply a material of a defined layer thickness during the movement of the material support (1) from the first position to the second position, and to remove material from the material support (1) during the movement of the material support (1) from the second position to the first position, the material introduction device (3) comprises at least first and second doctor blades (5, 6), the first doctor blade (5) being height adjustable perpendicular to the direction of movement of the material support (1); An apparatus characterized in that a material reservoir (2) is formed between said first and second doctor blades (5, 6).

13. 13. Apparatus according to claim 12, characterized in that the second doctor blade (6) cooperates with a return device (7).

14. The device described in Claim 13, characterized in that the return device (7) is a spring.

15. 13. Apparatus according to claim 12, characterized in that the building platform (8) is arranged tiltably.

16. 16. Apparatus according to any one of claims 12 to 15, characterized in that the material introduction device (3) comprises a heating device for heating the material.

17. 13. Apparatus according to claim 12, characterized in that the material reservoir (2) is connected to a conveying device so as to enable material to be introduced into the material reservoir (2).

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