Method and apparatus for additive manufacturing of three-dimensional shaped bodies based on photolithography

Abstract

Method for additive manufacturing of three-dimensionally shaped bodies on the basis of photolithography, wherein a construction platform (8) is positioned spaced apart from a material support (1) of a material which is at least locally permeable to the radiation of a radiation source and which is capable of being solidified by the action of the radiation, wherein the material support (1) is moved in translation between a first position and a second position, characterized in that during the movement of the material support (1) from the first position to the second position material is applied in defined layer thicknesses, subsequently the applied material between the construction platform (8) and the material support (1) is irradiated position-selectively and / or time-selectively by the radiation source and solidified, and subsequently the material is removed from the material support (1) during the movement of the material support (1) from the second position to the first position.

Description

Technical Field

[0001] The present invention relates to a method for fabricating a three-dimensional molded body based on photolithography, wherein a construction platform is positioned at intervals with a material support for a material that can be cured by radiation, at least partially permeable to radiation from a radiation source, wherein the material support translates between a first position and a second position.

[0002] The present invention also relates to an apparatus for performing this method. Background Technology

[0003] In photolithography or stereolithography additive manufacturing, photopolymerizable raw materials are processed layer by layer into a shaped body. Here, layer information is selectively transferred to the material to be polymerized, either by means of an optical mask, a projected image surface, or by scanning with a laser beam, depending on the position and time. A fundamental difference arises in the selection of exposure and structuring methods: on the one hand, the photopolymerizable material can be exposed from above in a (immersion) pool, where the patterned object is gradually immersed in the liquid material during manufacturing (SLA); on the other hand, the material reservoir (filled material tank) can be exposed from below through a transparent tank bottom, where the object is removed from above from the material pool (DLP, laser stereolithography). In the latter case, the object is structurated layer by layer by moving up and down, where the corresponding distance between the object and the bottom of the material tank ensures high-precision layer thickness. In newer methods, this type of structuring can also be performed continuously (without alternating up and down movements), where additional special requirements must be placed on the tank bottom. A major advantage of exposure via a material tank compared to the aforementioned immersion process (SLA) is, in particular, the material consumption for initiating the process is significantly lower. Because the impregnation process requires a large amount of reactive consumable material, this is an inherent disadvantage in terms of operating and process costs.

[0004] The common thread among all the process methods mentioned is the high geometric quality of additively structured products. This surface quality is particularly crucial in the field of plastics technology, in order to compete with commonly used methods, such as injection molding applications. Photolithography-based 3D printing therefore differs significantly from all other available 3D printing processes in terms of both surface and shape quality. The high viscosity requirement of the original material (photopolymer mixture) is considered a drawback in this regard. Therefore, the dynamic viscosity currently required during processing should not exceed a few Pa·s (Pa·s). This barrier to layer-by-layer processing severely limits the selection of available photopolymers, resulting in the greatest weakness of photolithography-based additive layer processes: the typically strongly limited material properties of the processed plastics.

[0005] Especially for technological applications, and also in the realm of end-user products, material quality is paramount, in addition to the geometric quality of an object. In additively processed plastics, known defects manifest particularly in heat resistance (a significant loss of rigidity / modulus of elasticity at elevated temperatures—mostly from 40°C to 50°C) or toughness (impact toughness / resistance to fatal fracture or cracking) at ambient temperatures. Stereolithically processable materials possessing a combination of strength, toughness, and sufficient heat resistance (e.g., sufficient rigidity up to 80°C) are currently considered prerequisites for the successful and widely economical integration of additive stereolithography into existing manufacturing technologies. However, to date, these materials have not been available, or have only been partially available, at the desired quality.

[0006] To develop novel photopolymer systems for stereolithography processes, the aforementioned viscosity requirements of known processing techniques are problematic. Process control at elevated temperatures has proven to be a viable solution. By significantly increasing the process temperature relative to normal room temperature (20°C), the viscosity of most photopolymers has been drastically reduced. This results in a substantial increase in the amount of the original polymer material to be selected, which in turn leads to novel 3D printing materials.

[0007] The application of heating process systems is well-known. Another feasible approach to handling high-viscosity systems lies in the process control itself, where, for example, alternative methods of material delivery (e.g., coating systems) can be used to replace existing impregnation systems (material tanks with filling heights of a few millimeters or centimeters). In these approaches, increased process temperatures can also offer decisive advantages; however, the temperature sensitivity of the photopolymer being processed must always be considered. Complex heating of individual process elements or the entire process chamber can provide a remedy, but this typically leads to significant electromechanical costs and, if implemented incorrectly, can reduce the long-term stability of the photopolymer mixture and thus significantly jeopardize process stability. Summary of the Invention

[0008] Therefore, the object of the present invention is to find a process control for processing high-viscosity resins that combines the advantages of selective heating of each process stage with the advantages of limited material delivery to the process zone and can be implemented as a long-term stable production system.

[0009] To address this task, the present invention essentially specifies, in a method of the type described at the beginning, that a material is applied to a defined layer thickness during the movement of a material support from a first position to a second position, and then the material applied between the construction platform and the material support is selectively irradiated and cured by a radiation source at a position and / or at a time, and then the material is removed from the material support during the movement of the material support from the second position to the first position.

[0010] This invention comprises a coating and cycling process in which a photosensitive material in thin layer form can be delivered to an exposure area. Here, the process utilizes a translationally movable material support, constructed, for example, as a material tank, which primarily serves as a support plate for the process-related thin layer of the photosensitive material. A photopolymerizable material is then delivered to this movable support plate, which can refer to a pure photosensitive monomer compound or oligomer compound, or it can refer to the same compound including a photoinitiator component. Furthermore, such a compound may also contain organic or inorganic fillers and / or have other organic or inorganic additives or other substances, colorants, absorbers, or other functional or non-functional components. Additionally, other photopolymerizable materials may be used, provided that photolithographic interaction with the material is possible within a wavelength range between 150 nm and 950 nm.

[0011] The material is preferably coated or removed by means of a fixed material introduction device, and has a process position fixed relative to a movable material support.

[0012] The preferred method is to apply or remove material using a first scraper and a second scraper.

[0013] Preferably, before or during the movement of the material support from the second position to the first position, the first scraper is moved away from the material support perpendicular to its direction of movement. More preferably, during or before the material support moves from the first position to the second position, the first scraper is moved toward the material support to adjust the defined layer thickness. The first scraper is configured such that its height is variablely adjustable in the z-direction (perpendicular to the x-direction of the material support's movement), wherein this height adjustment can be controlled either actively (e.g., by a scraper motor) or passively by a process mechanism. The height of the first scraper is preferably adjusted such that, in its lowest position, no scraper gap is allowed between the first scraper and the material support, thus completely closing the material introduction device; or, in its elevated position, the first scraper allows a gap height of a few micrometers to a few millimeters.

[0014] The second scraper constitutes a pulling mechanism and can be passively or actively adjusted in its feed height (z-direction). Preferably, the second scraper is held in contact with the material support by means of a reset element, such as a spring. Thus, the material introduction device is at least partially sealed relative to the photosensitive material therein at all times.

[0015] Furthermore, it is preferably specified that a material reservoir is formed between the first and second scrapers. Particularly preferably, during the movement of the material support from the second position to the first position, at least partially, material removed from the material support is returned and guided into the material reservoir. Particularly preferably, during the movement of the material support from the first position to the second position, material is applied from the material reservoir through a gap defined between the first scraper and the material support, with a layer thickness defined by the gap and an adjusted translational movement speed of the material support.

[0016] Here, according to the method of the invention, the linear movement of the material support below the material introduction device, i.e. below the first and second scrapers, is performed in such a way that, during the forward movement of the material support (i.e., from the first position to the second position), a defined thin layer of photopolymerizable material is at least partially coated onto the material support and onto each portion of the material support, and during the backward movement of the material support (i.e., from the second position to the first position), the remaining photosensitive material film is at least partially peeled off or removed from each portion of the material support, thereby, on the one hand, the material support in the peeled portion has a pure or at least partially clean surface, and on the other hand, the previously remaining photosensitive material is at least partially returned to be guided back into the material reservoir.

[0017] A thin layer of photosensitive material is conveyed to an exposure zone as a material support moves forward, where exposure information is selectively delivered positionally and temporally from the side of the material support opposite to the material. In a preferred embodiment, this is done, for example, from below, where the exposure information must pass over the material support. For this purpose, the material support is designed to be transparent or at least partially transparent relative to the light information used. After exposure and selective intensification of the photopolymerizable material, the photopolymerizable material is peeled off from the material support, whereby the unpolymerized portion of the photosensitive material exists as a discontinuous film or as material deposits, material islands, or other layer patterns. During backward movement of the material support, the material is again conveyed to a material reservoir. To facilitate this, a first squeegee can be actively or passively raised during backward movement of the material support so that any unpolymerized material residue passes beneath the blade of the first squeegee. After the backward movement of the material support ends, the first squeegee can be lowered directly and actively or passively to prevent leakage of the photopolymerizable material from the material reservoir. As the material support moves backward, the photosensitive material detaches from the bottom of the material support by means of a second scraper, thereby allowing the photosensitive material to be retained in the material reservoir at least temporarily.

[0018] The process can be repeated any number of times, thereby ensuring that a newly applied layer of photopolymerizable material is consistently coated onto the material support and then conveyed to the exposure area. The height or thickness of these applied photosensitive material layers can now be steplessly adjusted via the height of the first doctor blade and the linear movement speed of the material support. For example, the height adjustment of the photosensitive layer can be made in the range of a few micrometers to a few millimeters. Furthermore, the final achievable layer thickness of the photosensitive material depends on its viscosity and flow characteristics, which are themselves largely temperature-dependent. To address this, it is preferable to heat the material in the material introduction device. Moreover, in a preferred embodiment, all relevant process components, such as the first and / or second doctor blades and / or the material support, can be configured to be selectively and / or individually adapted for heating.

[0019] The construction platform used in actual stereolithography printing processes is preferably designed to be heated, which mechanically adjusts the interlayer gap (along the z-axis) for polymerization and ensures that the selectively polymerized material layer is stripped from the linearly movable material support after polymerization.

[0020] During the process, preferably always, the photosensitive reserve material is located in the material reservoir. Alternating linear movement of the material support beneath the material reservoir causes the photosensitive reserve material in the reservoir to circulate in the form of a movable or surrounding material shaft or a roller of photosensitive material. To optimize process control, it is now advantageous to continuously or at defined intervals actively or passively detect the material state of the photosensitive reserve material, which, in embodiments according to the invention, can be done using ultrasonic sensors, optical sensors, or contact sensors. Other feedback systems not mentioned, such as switches, buttons, fill level probes, or the like, can also be used to measure the fill level of the photosensitive reserve material. To maintain the desired fill level of the photosensitive reserve material, it is preferably specified that the material is introduced into the material reservoir by means of a conveying device. For example, it can be specified that new photosensitive material can be continuously or at desired time intervals fed to the material reservoir. This conveying device can be implemented to be selectively and individually heated.

[0021] Furthermore, the linearly moving material support can also actively or passively support the desired detachment of the selectively strengthened photosensitive material from the material support within the exposure zone. This is achieved by combining the linear movement of the material support with an active or passive tilting movement of the entire process structure relative to the construction platform, or also with an active or passive tilting movement of the construction platform itself relative to the process structure. This results in a defined or undefined multiaxial detachment process of the strengthened photosensitive material from the material support, wherein this combined detachment movement approximates the ideal peeling process as closely as possible. Therefore, it is preferably specified that the construction platform tilts during the movement of the material support from the second position to the first position. In a preferred embodiment, this peeling process of the selectively strengthened photosensitive material layer is determined by the linear travel (z-direction) of the construction platform, the passive or active rotation of the construction platform about a rotation point carried by the construction platform, and the active or passive linear translational movement of the material support, which generally allow for a multiaxial peeling process. To support this peeling process, the material support may be provided with a special anti-stick coating and / or consist of laminates of materials that are transparent or at least partially transparent to the working wavelengths used in photopolymerizable exposure processes.

[0022] The process control described according to the invention allows for the precise processing of high-viscosity photosensitive raw materials, which can also have high molecular weights and exist as non-flowable or even as solids at room temperature. Furthermore, the refill system provides high process reliability because only a small amount of photosensitive material must remain in the process zone, as required for a stable printing process. Other photosensitive reserve material can be kept outside the process zone until its use, minimizing the potential adverse long-term effects due to process temperature or other environmental influences. Additionally, the delivery of photosensitive material to the exposure zone defined in the thin layer on the material support allows for control over potential air bubbles in the reinforced photopolymer layer. The linear movement speed of the material support, the filling level of the photosensitive material in the material reservoir, and the movement height of the doctor blade can thus influence the circulating material rollers in the material reservoir, optimizing the mixing between fresh and already stripped photosensitive material from the material support, and minimizing the unwanted introduction of air or air bubbles into the material reserve within the material reservoir.

[0023] According to another aspect of the invention, an apparatus for fabricating a three-dimensional molded body based on photolithography is provided. The apparatus includes a radiation source of electromagnetic radiation, a material support for a material that can be cured by radiation and is at least partially permeable to the radiation from the radiation source, and a construction platform spaced apart from the material support, wherein the material support is translatably movable between a first position and a second position. The apparatus is characterized by providing a material introduction device configured to apply material to the material support at a defined layer thickness during the movement of the material support from the first position to the second position and to remove material from the material support during the movement of the material support from the second position to the first position.

[0024] Preferably, the material introduction device has at least one first and a second scraper, wherein the first scraper is preferably height-adjustable perpendicular to the moving direction of the material support.

[0025] Furthermore, it is preferably specified that the second scraper cooperates with a reset element, such as a spring.

[0026] In a preferred embodiment, the construction platform is configured to be tilted.

[0027] Preferably, the material introduction device has a heating device for heating the material.

[0028] Furthermore, it is preferably specified that a material reservoir is formed between the first and second scrapers, which are preferably arranged in parallel with each other.

[0029] Preferably, the material storage container is connected to the conveying device so that the material can be introduced into the material storage container. Attached Figure Description

[0030] The invention is further illustrated below with reference to embodiments schematically shown in the accompanying drawings. Wherein are shown:

[0031] Figure 1 and Figure 2 A schematic side sectional view of the apparatus according to the invention in successive stages of the method flow is shown. Detailed Implementation

[0032] exist Figure 1 In this diagram, the material support is labeled 1, and material layers 11 are arranged on this material support. A structural platform 8 is arranged spaced apart from the material support 1; this structural platform is height-adjustable along the z-direction and can be tilted about axis 4. Several material layers 11 have been constructed between the structural platform 8 and the material support 1. The material support 1 can translate along the x-direction, which is perpendicular to the z-direction.

[0033] Furthermore, a material introduction device 3 is provided, comprising a first scraper 5 and a second scraper 6. The first scraper 5 is height-adjustable in the z-direction by means of a scraper motor 10, and the second scraper 6 has a spring 7 that keeps the second scraper 6 in contact with the material support 1 in the z-direction. A material reservoir 2 is constructed between the two scrapers 5 and 6, and the material reservoir can be supplied with material by means of a conveying device 9.

[0034] exist Figure 1 In the method phase shown, the material support 1 is in the second position. The construction platform 8 descends along the direction of the material support 1, thereby forming a new material layer 11 by selectively irradiating and curing the material layer 11 on the material support 1 from below through the position of the material support 1 using a radiation source (not shown). The material layer 11 is applied by a first scraper 5 while the material support 1 is in the second position.

[0035] Figure 2 The stage after the curing of material layer 11 is completed is shown. Now, material support 1 moves from the second position toward the first position in the direction of arrow 12. Simultaneously, construction platform 8 is slightly raised in the z-direction, wherein the combined lifting movement of construction platform 8 and the movement of material support 1 in the direction of arrow 12 causes construction platform 8 to tilt about axis 4, thereby facilitating the multiaxial detachment of material layer 11 from material support 1 in a peeling process. For this purpose, the position of axis 4 on construction platform 8 can also be arranged on one side of construction platform 8 opposite to it in the x-direction, as long as this additionally facilitates the peeling process. As material support moves from the second position to the first position, the remaining material 11 on material support 1 is removed by the second scraper 6 and thereby collected in material reservoir 2, and replenished with fresh material as needed by a conveying device, ensuring sufficient material is always available.

[0036] After material layer 11 is removed by the second scraper 6 and material support 1 reaches the first position, material layer 11 is re-coated from material reservoir 2 by moving the first scraper 5 to the second position against the direction of arrow 12 through material support 1, until reaching... Figure 1 The second position is shown. Then, the construction platform or structure formed by the already cured layer 11 is lowered into the material layer to adjust the thickness of the layer to be cured, after which further exposure and curing of the material layer 11 can be performed.

Claims

1. A method for fabricating three-dimensional shapes based on photolithography, wherein, The construction platform (8) is positioned at intervals with a material support (1) of a material that is at least partially permeable to radiation from a radiation source and is intended to be cured by the action of radiation, wherein the material support (1) is translated between a first position and a second position, characterized in that a material is applied to the material support (1) with a defined layer thickness during the movement of the material support (1) from the first position to the second position, and the material applied between the construction platform (8) and the material support (1) is subsequently irradiated and cured by the location and / or time-selective action of the radiation source, and the material is subsequently removed from the material support (1) during the movement of the material support (1) from the second position to the first position.

2. The method according to claim 1, characterized in that, The material is applied or removed by means of a fixed material introduction device (3).

3. The method according to any one of claims 1 or 2, characterized in that, The material is applied or removed by means of first and second scrapers (5, 6).

4. The method according to claim 3, characterized in that, Before or during the material support member (1) moving from the second position to the first position, the first scraper (5) moves away from the material support member (1) perpendicular to the direction of movement of the material support member (1), and preferably, during or before the material support member (1) moving from the first position to the second position, the first scraper moves toward the material support member (1) in order to adjust the defined layer thickness.

5. The method according to claim 3 or 4, characterized in that, A material reservoir (2) is formed between the first and second scrapers (5, 6).

6. The method according to claim 5, characterized in that, 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) via a gap defined between the first scraper (5) and the material support (1) to a layer thickness defined by the gap and the translational movement speed of the material support (1).

7. The method according to claim 5 or 6, characterized in that, The material is introduced into the material storage container (2) by means of the conveying device (9).

8. The method according to any one of claims 3 to 7, characterized in that, The second scraper (6) is held in contact with the material support (1) by means of a reset element (7), such as a spring.

9. The method according to any one of claims 5 to 8, characterized in that, During the movement of the material support (1) from the second position to the first position, the material removed from the material support (1) is at least partially returned and guided into the material reservoir (2).

10. The method according to any one of claims 1 to 9, characterized in that, The construction platform (8) tilts as the material support (1) moves from the second position to the first position.

11. The method according to any one of claims 2 to 10, characterized in that, The material is heated in the material introduction device (3).

12. An apparatus for fabricating a three-dimensional object based on photolithography, particularly an apparatus for performing the method according to any one of claims 1 to 11, the apparatus comprising a radiation source of electromagnetic radiation, a material support (1) of a material that is at least partially permeable to radiation from the radiation source and is capable of being cured by the action of radiation, and a construction platform (8) spaced apart from the material support (1), wherein, The material support (1) is translatably movable between a first position and a second position, characterized in that it is provided with a material introduction device (3) configured to apply material with 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.

13. The apparatus according to claim 12, characterized in that, The material introduction device (3) has at least one first and a second scraper (5, 6), wherein the first scraper (5) is preferably height-adjustable perpendicular to the moving direction of the material support (1).

14. The apparatus according to claim 13, characterized in that, The second scraper (6) works in conjunction with the reset element (7), such as a spring.

15. The apparatus according to claim 12 or 13, characterized in that, The construction platform (8) can be arranged at an angle.

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

17. The apparatus according to any one of claims 13 to 16, characterized in that, A material reservoir (2) is formed between the first and second scrapers (5, 6).

18. The apparatus according to claim 17, characterized in that, The material storage container (2) is connected to the conveying device so that the material can be introduced into the material storage container (2).

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