An additive manufacturing device having optical means for diffusing / scattering the projected UV light towards a photocurable resin

Abstract

The present invention relates to an additive manufacturing apparatus (1) for additively manufacturing a part (2), comprising a resin tank unit (3) having a reservoir (4) for storing a UV light photocurable resin (5) and a UV-transparent window (6-4) at the bottom of the reservoir (4), wherein said UV-transparent window (6-4) comprises a UV-transparent plate (6-4a) and a UV-transparent anti-adhesive flexible foil (6-4b), a projection unit (7) for projecting UV light (8) through the UV-transparent window (6-4) into the reservoir (4), and a movable build platform (9) having a surface (9a) on which said part (2) can be formed through layer-by-layer curing of said resin (5). The UV-transmitting window (6-4) further comprises optical means (6-5) adapted to diffuse the projected UV light (8) towards the build platform (9) to an area (R) where the UV light curable resin (5) is to be cured in layers, wherein the optical means (6-5) is positioned in the optical path of the projected UV light (8).

Description

[Technical field]

[0001] The present invention relates to an additive manufacturing apparatus for additively manufacturing 3D parts, such as dental restorations and dental appliances. [Background technology]

[0002] In additive manufacturing techniques such as stereolithography (SLA) or digital light processing (DLP), 3D (three-dimensional) parts are printed layer by layer through light-based curing of a liquid printing medium, i.e., a photocurable resin, which is selectively cured under the influence of UV radiation. The photocurable resin may eventually become transparent or opaque / colored after the curing / polymerization process, depending on the type of photocurable resin material used. In a commonly known variant of additive manufacturing, the 3D part is preferably pulled upside down from the photocurable resin in a resin vat by a build platform. Other variants of additive manufacturing are also known to those skilled in the art.

[0003] Figure 2 shows a comparative example, the right side of which shows a vertical cross-sectional partial view of an additive manufacturing device according to the prior art. The additive manufacturing device of the prior art comprises a resin bath unit (3') with a reservoir (4') for storing a UV light photocurable resin (5') and a UV-transparent window (6-4') at the bottom of the reservoir (4'), where said UV-transparent window (6-4') comprises a UV-transparent plate (6-4a') and a UV-transparent adhesive-preventing flexible foil (6-4b'), a projection unit (7') for projecting UV light (8') through the UV-transparent window (6-4') into the reservoir (4'), and a movable build platform (9') with a surface (9a') on which a 3D part can be manufactured through layer-by-layer curing of said resin (5').

[0004] A problem with the prior art additive manufacturing apparatus of FIG. 2 is that the printed 3D parts then require mechanical surface treatment, such as polishing, grinding, etc., to obtain a smooth surface. Generally, dental restorations and instruments cannot be used directly after 3D printing without such mechanical surface treatment, as this would cause discomfort to the user. Thus, the prior art has the disadvantage that additional staff, working time, and consumables are required for the mechanical surface treatment of the printed 3D parts, thus all of which have their own costs. Furthermore, when the 3D parts are printed from a transparent light-curable resin, this results in a translucent 3D part due to the rough surface, which affects the light transmission and creates a certain degree of opacity. However, 3D parts such as dental aligners need to be clear to give a natural impression. Therefore, some mechanical surface treatment is also usually required to remove the opacity.

[0005] FIG. 10B shows a comparative example in which a 3D part (2') is printed using a transparent photocurable resin through a prior art additive manufacturing device. In this comparative example, the 3D part (2') is not subjected to any mechanical surface treatment. The eagle in the background shows that the 3D part (2') has a certain degree of opacity due to the rough surface.

[0006] Figure 11C shows another comparative example in which a dental aligner (2a') is printed using a transparent light-curable resin through a prior art additive manufacturing device. Also, in this comparative example, the aligner (2a') is not subjected to any mechanical surface treatment and is placed directly on the denture model (D). It can be seen that the aligner (2a') has a certain degree of opacity due to the rough surface, and the teeth cannot be clearly seen.

[0007] In the prior art, anti-aliasing software is commonly used to improve edge smoothness so that any mechanical surface treatment can be omitted. In principle, such anti-aliasing software is based on the use of 2D / 3D digital filters, which are commonly known in the art. However, the prior art has the drawback that anti-aliasing software increases the computational cost and is also limited by the geometry and magnification of the light source, such as the laser point diameter or pixel size. These physical limitations reduce the practical effect that can be achieved with anti-aliasing software. Summary of the Invention

[0008] The inventors are not aware of any additive manufacturing machine technology in which optical means, such as milky foils and / or milky plates, are used to diffuse / scatter the projected UV light towards the UV light curable resin (5) to produce parts with improved smoothness and transparency to visible light.

[0009] The object of the present invention is to overcome the above-mentioned problems of the prior art and to provide an additive manufacturing device that allows printing of 3D parts with improved smoothness and transparency to visible light, such that any mechanical surface treatment and software-based anti-aliasing may be unnecessary.

[0010] This object is achieved through an additive manufacturing device according to claim 1 and a UV-transparent anti-adhesive flexible foil according to claim 10. The dependent claims relate to further embodiments and developments.

[0011] The present invention provides an additive manufacturing apparatus for additively manufacturing 3D parts, comprising: a resin vat unit comprising a reservoir for storing a UV light photocurable resin and a UV-transmitting window at the bottom of the reservoir, where the UV-transmitting window comprises a UV-transmitting plate and a UV-transmitting adhesive-preventing flexible foil, a projection unit for projecting UV light through the UV-transmitting window into the reservoir, and a movable build platform having a surface on which the 3D part can be formed through layer-by-layer curing of the resin. The UV-transmitting window further comprises optical means adapted to diffuse the projected UV light towards the build platform to an area where the UV light photocurable resin should be layer-by-layer cured, where the optical means is arranged in the optical path of the projected UV light.

[0012] The main advantageous effect of the present invention is that the projected UV light can be diffused through the optical means, and thus the polymerization of the photocurable resin near adjacent pixels at the edge sites becomes smoother. This can also reduce the overall scattering of visible light throughout the printed 3D part, and thus prevent any opacity due to surface roughness, especially when the 3D part is printed with a transparent photocurable resin material. Another main advantageous effect of the present invention is that the need for any mechanical surface treatment after printing or any software-based anti-aliasing during printing can be eliminated, and thus the printed 3D parts, such as dental restorations and appliances such as clear aligners, can be directly and immediately used by patients while giving a comfortable feeling and having a clear appearance. Another main advantageous effect of the present invention is that the cost, processing time, and consumables for mechanical surface treatment can be saved. Yet another main advantageous effect of the present invention is that the cost and processing time for the computational effort for software-based anti-aliasing can also be saved.

[0013] The optical means mentioned above can be realized through frosting the surface of the UV-transmitting adhesive-free flexible foil or the surface of the UV-transmitting plate, or by adding light-diffusing / scattering particles to said foil or plate, or by using a matrix of microlenses or similar structures or mechanisms for diffusing the projected UV light, thus resulting in a milky white foil and / or milky white plate.

[0014] In one embodiment, at least one of the upper and lower surfaces of the UV-transmitting anti-adhesive flexible foil is frosted. Thus, the frosted surface of the UV-transmitting anti-adhesive flexible foil can diffuse the projected UV light toward the photocurable resin, resulting in smoothing between adjacent pixels to be cured. In an alternative embodiment, the UV-transmitting anti-adhesive flexible foil includes light-diffusing / scattering particles. The light-diffusing / scattering particles can be introduced into the UV-transmitting anti-adhesive flexible foil during its manufacture by adding small impurities or cavities. The projected UV light can additionally or alternatively be actively diffused by using liquid crystals or electrochromic glass.

[0015] In another alternative embodiment, at least one of the upper and lower surfaces of the UV-transmitting plate is frosted. Thus, the frosted surface of the UV-transmitting plate can diffuse the projected UV light toward the photocurable resin, resulting in smoothing between adjacent pixels to be cured. In another alternative embodiment, the UV-transmitting plate includes light-diffusing / scattering particles. The light-diffusing / scattering particles can be introduced into the UV-transmitting plate during its manufacture by adding small impurities or cavities.

[0016] In another alternative embodiment, the optical means is realized through a matrix of light-diffusing microlenses. Such a matrix can be manufactured as a separate transparent foil with a 2D array of microlenses. The 2D array of microlenses can be located below the UV-transmitting anti-adhesive flexible foil and further either above or below the UV-transmitting plate. The 2D array of microlenses can be provided integrally with the UV-transmitting plate or the UV-transmitting anti-adhesive flexible foil.

[0017] According to the invention, it is also desirable that the additive manufacturing machine may be retrofitted / equipped with said optical means for diffusing the projected UV light. Thus, in one embodiment, the vat unit is provided as a removable unit that may be completely removed from the additive manufacturing machine in order to allow replacing an existing vat unit with another vat unit including said optical means. Thus, the user may selectively install a vat unit with any of the desired optical means as described above in order to achieve a print with a smooth surface. Furthermore, in another embodiment, the removable vat unit is preferably provided with an RFID tag that contains information about the presence / absence of said optical means in the UV-transmitting window. In this embodiment, the additive manufacturing machine is provided with an RFID reader / writer. Thereby, the additive manufacturing machine may recognize that the installed vat unit comprises such optical means, inform the user and apply the required print mode. Alternatively, the user may input the type of the installed vat unit via a user interface before the printing process. Alternatively, instead of an RFID tag, other sensing elements commonly known in the art may be used.

[0018] According to the present invention, it is also desirable that the resin bath unit may be retrofitted / equipped with optical means for diffusing the projected UV light. This allows the degree of diffusion through the optical means to be pre-adjusted depending on the desired target transparency of the 3D part. In addition, if the resin bath has an RFID tag, the RFID tag may be further updated by an RFID reader / writer via a user interface after retrofitting. Alternatively, a new suitable RFID tag may be attached to the resin bath unit. According to the present invention, a UV-transmitting anti-adhesive flexible foil having one or more frosted surfaces, or having light diffusing particles, or having a microlens array may also be provided separately to the user for retrofitting to the resin bath unit for the purpose of smoothing the surface of the 3D printed part. Thus, in one embodiment, the UV-transmitting anti-adhesive flexible foil with UV light diffusing optical means may be removably attached to the frame assembly of the resin bath unit. This allows the user to replace the prior art UV-transmitting anti-adhesive flexible foil with the UV light diffusing optical means, or vice versa, according to the printing requirements. In another alternative embodiment, the user may replace the prior art UV-transmitting plate with a UV-transmitting plate having UV light diffusing optical means, or vice versa, by the frame assembly according to the printing requirements. In another alternative embodiment, an additional transparent foil with a microlens array may be attached to the frame assembly. The resin bath unit may also be provided as a partially integrated unit with the additive manufacturing apparatus.

[0019] In the following description, further aspects and advantages of the invention are explained in more detail by means of exemplary embodiments and with reference to the drawings. [Brief description of the drawings]

[0020] [Figure 1] FIG. 1 is a schematic partial cross-sectional vertical view of an additive manufacturing apparatus according to one embodiment of the present invention. [Diagram 2]FIG. 2 is a schematic side-by-side comparison of a partial vertical cross-section of an additive manufacturing apparatus according to one embodiment (see EMB) and a partial vertical cross-section of an additive manufacturing apparatus according to the prior art, for comparison purposes. [Diagram 3] FIG. 3 is a schematic perspective view of a fully removable resin vat unit of an additive manufacturing apparatus according to one embodiment. [Figure 4] FIG. 4 is a schematic perspective exploded view of the resin vat unit of FIG. [Diagram 5] 5 is a schematic perspective top surface view of an inner frame of a frame assembly of the resin vat unit of FIG. 4. FIG. [Figure 6] FIG. 6 is a schematic perspective bottom view of the inner frame of FIG. [Figure 7] FIG. 7 is a schematic cross-sectional view of the inner frame of FIG. 6 taken along line II. [Figure 8] FIG. 8 is a schematic enlarged view of detail II of FIG. [Figure 9] FIG. 9 is a schematic bottom view of a UV transparent adhesive-resistant flexible foil having a frosted lower surface. [Figure 10A] FIG. 10A is a schematic diagram of a 3D part printed with a translucent photocurable resin through an additive manufacturing apparatus according to one embodiment. [Figure 10B] FIG. 10B is a schematic diagram of a 3D part printed with a translucent photocurable resin through a prior art additive manufacturing apparatus. [Figure 11A] FIG. 11A is a schematic diagram of a clear aligner printed with a translucent photocurable resin through an additive manufacturing apparatus according to one embodiment. [Figure 11B] FIG. 11B is a schematic diagram of the clear aligner of FIG. 11A placed on a denture model. [Figure 11C] FIG. 11C is a schematic diagram of an aligner printed with a clear light-curable resin through a prior art additive manufacturing device and placed on a denture model. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] The reference numbers shown in the drawings indicate the elements listed below and will be referenced in the following description of the exemplary embodiments. 1. Additive Manufacturing Equipment 2.3D parts 2a. Dental aligners 3.Resin tank unit 4.Storage tank 4a.Opening 4b. Grip 5.UV photocurable resin 6.Frame Assembly 6-1.Inner frame 6-1a.Inner frame elements 6-1b.Inner frame elements 6-1c.Screw 6-1d. Screw hole 6-2.Outer frame 6-2a.Air vent 6-2b.Air flow path 6-2c. Hose 6-2d.Screw 6-2d' screw 6-2e. Screw hole 6-2e' screw hole 6-3.Ceiling 6-4.UV Transmitting Window 6-4a.UV transmission plate 6-4b.UV transparent adhesion prevention flexible foil 6-5.Optical means (diffuser) 7.Projection unit 8.UV light 9. Movable modeling platform 9a.Surface D: Denture model

[0022] FIG. 1 shows an embodiment of an additive manufacturing apparatus (1) for additively manufacturing a 3D part (2). The additive manufacturing apparatus (1) has a resin bath unit (3) including a reservoir (4) for storing a UV light photocurable resin (5) and a frame assembly (6) for holding a UV-transparent window (6-4) at the bottom of the reservoir (4). The reservoir (4) can be heated to a suitable operating temperature by a heater (not shown). The UV-transparent window (6-4) includes a UV-transparent plate (6-4a) and a UV-transparent anti-adhesive flexible foil (6-4b). The UV-transparent plate (6-4a) is preferably a glass plate. Alternatively, a PMMA plate can be used. Furthermore, the additive manufacturing apparatus (1) has a projection unit (7) for projecting UV light (8) through the UV-transparent window (6-4) into the reservoir (4). The additive manufacturing apparatus (1) includes a transport unit with a movable build platform (9) having a surface (9a) facing the bottom of the resin bath unit (3) on which the 3D part (2) can be formed through layer-by-layer curing of the resin (5) through the projection unit (7). The build platform (9) can be moved into and out of the reservoir (4) for layer-by-layer curing and for peeling the cured layer from the foil (6-4b). The build platform (9) can also be moved laterally within the reservoir (4) by the transport unit. The additive manufacturing apparatus (1) also includes a computer-implemented control unit (not shown) for controlling the overall operation, including controlling the projection unit (7) and the transport unit. The UV-transmitting window (6-4) further includes optical means (6-5) adapted to diffuse the projected UV light (8) towards the build platform (9) in the area (R) where the UV light photocurable resin (5) should be cured in layers. The optical means (6-5) is positioned in the optical path of the projected UV light (8).

[0023] The working principle of the additive manufacturing device (1) is explained in more detail with reference to the comparative example in FIG. 2, which shows a schematic side-by-side arrangement of an additive manufacturing device according to the embodiment of FIG. 1 and an additive manufacturing device according to the prior art. As can be seen on the left side of FIG. 2, the optical means (6-5) (shown through the grey / milky areas) diffuse the projected UV light so that the photocurable resin (5) in the vicinity of the adjacent pixels hit by the diffused UV light is polymerized more smoothly. Thus, the curing process through the diffused UV light has an anti-aliasing effect. As can be seen on the right side of FIG. 2, the UV-transmitting anti-adhesive flexible foil (6-4b') does not have a diffusing effect. This results in a rough surface where the cured pixels form sharp edges.

[0024] In an alternative embodiment of the invention, said optical means (6-5) can be realized through frosting the upper and / or lower surface of the UV-transmitting anti-adhesive flexible foil (6-4b). Figure 3 shows an embodiment in which only the lower surface of the UV-transmitting anti-adhesive flexible foil (6-4b) is frosted. It should be understood that in this specification, the lower surface faces the projection unit (7) and is averted from the interior of the reservoir (4) so ​​as not to come into contact with the photocurable resin (5). In the embodiment of Figure 3, the upper surface of the UV-transmitting anti-adhesive flexible foil (6-4b) is smooth and therefore not frosted in order to allow easy peeling of said flexible foil (6-4b) from the 3D part (2) attached to the surface (9a) of the mobile build platform (9). During the printing process, after each time a layer is polymerized through the projected UV light, peeling can be achieved by moving the build platform (9) upwards / downwards so that new light-curable resin (5) can refill the gap between the 3D part (2) and the UV-transmitting anti-adhesive flexible foil (6-4b) on the bottom of the reservoir (4) for printing the next layer. Alternatively, both the upper and lower surfaces of the UV-transmitting anti-adhesive flexible foil (6-4b) or only the upper surface can be frosted.

[0025] In another alternative embodiment of the present invention (not shown), the optical means (6-5) can be realized through the provision of light diffusing / scattering particles in the UV-transmitting anti-adhesive flexible foil (6-4b). Also, in this embodiment, the upper surface of the UV-transmitting anti-adhesive flexible foil (6-4b) containing the light diffusing / scattering particles is preferably smooth (not frosted) to allow easy peeling. Alternatively, the upper and / or lower surface of the UV-transmitting anti-adhesive flexible foil (6-4b) with the light diffusing / scattering particles can be additionally frosted.

[0026] In other alternative embodiments of the invention (not shown), said optical means (6-5) may be realised through frosting the upper and / or lower surface of the UV-transmitting plate (6-4a) and / or by including light diffusing / scattering particles in the UV-transmitting plate (6-4a). In the embodiment shown in Figure 4, the UV-transmitting plate (6-4a) is completely transparent and therefore not frosted and is provided without light diffusing / scattering particles.

[0027] The frame assembly (6) will be described in more detail below. As shown in FIG. 4, the frame assembly (6) comprises an inner frame (6-1) and an outer frame (6-2) mounted on the inside and outside of the opening (4a) of the resin vat unit (3), respectively. A seal (6-3) is preferably disposed between the interface between the inner frame (6-1) and the resin vat unit (3). Another seal (6-3) is preferably disposed between the interface between the inner frame (6-1) and the outer frame (6-2). As shown in FIG. 8, the inner frame (6-1) has two inner frame elements (6-1a; 6-1b) attached to each other through screws (6-1c). As shown in FIG. 8 in more detail, a UV-transmitting anti-adhesive flexible foil (6-4b) can be attached by the frame assembly (6). The UV-transmitting anti-adhesive flexible foil (6-4b) is sandwiched / clamped between the two inner frame elements (6-1a; 6-1b). The screw (6-1c) can be easily removed by the user to replace the removable UV-transmitting anti-adhesive flexible foil (6-4b). Figure 9 shows a UV-transmitting anti-adhesive flexible foil (6-4b) with a frosted lower surface. Compared to the transparent foil (6-4b'), the frosted foil (6-4b) in Figure 9 appears milky white and preferably has a smooth upper surface to allow easy peeling. Alternatively, the foil (6-4b) can be completely smooth on both sides but has a milky optical appearance to achieve smoothing. As shown in FIG. 4, the UV-transmitting window (6-4) has air holes (6-2a) for communicating the interface between the UV-transmitting anti-adhesive flexible foil (6-4b) and the UV-transmitting plate (6-4a) with the atmosphere to more easily enable the peeling process during layered printing. As shown in FIG. 4, the UV-transmitting plate (6-4a) is fixed on the outer frame (6-2), for example with an adhesive, alternatively, the UV-transmitting plate (6-4a) can be removably seated on a sealing (not shown). The outer frame (6-2) has air holes (6-2a) at each corner, which are preferably connected to each other through an air passage (6-2b) extending around the periphery. The air holes (6-2a) are preferably connected to the atmosphere through a hose (6-2c).The outer frame (6-2) has a screw hole (6-2e) for passing a screw (6-2d) that is screwed into the screw hole (6-1d) (see FIG. 6). The outer frame (6-2) also has a screw hole (6-2e') for passing a screw (6-2d') that is screwed into the screw hole (not shown) on the outside of the resin tank unit (3). In the assembled state, the UV-transmitting anti-adhesive flexible foil (6-4b) and the UV-transmitting plate (6-4a) are stacked on top of each other, thereby together defining the UV-transmitting window (6-4). Optionally, a frame-like spacer foil (not shown) of a desired thickness, preferably 100 micrometers, can be placed between the UV-transmitting anti-adhesive flexible foil (6-4b) and the UV-transmitting plate (6-4a) to ensure more space to allow easier peeling. The weight of the photocurable resin (5) in the resin bath unit (3) will cause the UV-transmitting anti-adhesive flexible foil (6-4b) to bend. The screw (6-2d) can also be used to adjust the tension on said flexible foil (6-4b) when the inner frame (6-1) is clamped to the outer frame (6-2) with the elastic sealing (6-3) located between them. The tighter the screw (6-2d) is tightened to fix, the higher the tension on the flexible foil (6-4b). As the screw (6-2d) is tightened, the UV-transmitting anti-adhesive flexible foil (6-4b) is stretched across the UV-transmitting plate (6-4a) and is accordingly pressed against the UV-transmitting plate (6-4a) by the relative movement of the inner frame (6-1) towards the outer frame (6-2).

[0028] In one embodiment, the reservoir (4) and the frame assembly (6) including the UV-transparent window (6-4) are configured to define a removable resin vat unit (3) that can be completely removed and manually removed from the additive manufacturing apparatus (1) through the user. The UV-transparent plate (6-4a) can also be provided separately from the resin vat unit (3) such that the frame assembly (6) holds only the UV-transparent anti-adhesive flexible foil (6-4b). In such an embodiment (not shown), the UV-transparent plate (6-4a) can be attached to the chassis of the additive manufacturing apparatus (1) below the removable resin vat unit (3). In this embodiment, the resin vat unit (3) preferably has a hand grip (4b) as shown in FIG. 3. The user can remove the resin vat unit (3) and retrofit the resin vat unit (3) with any desired UV-transparent anti-adhesive flexible foil (6-4b) or UV-transparent plate (6-4a) having optical means (5) for diffusing the projected UV light by means of the frame assembly (6).

[0029] In one embodiment, the removable vat unit (3) preferably has an RFID tag (not shown) containing information about the presence / absence of said optical means (6-5) in the UV-transmitting window (6-4). In this embodiment, the additive manufacturing device has a corresponding RFID reader / writer (not shown) to recognize the type of vat unit (3) and to update any information stored in the RFID tag. The additive manufacturing device (1) also preferably has a control panel (not shown) with a GUI to guide the user.

[0030] Figure 10A shows an embodiment in which a 3D part (2) is printed using a transparent photocurable resin through the additive manufacturing apparatus of the present invention. In this embodiment, the 3D part (2) is not subjected to any mechanical surface treatment. In Figure 10A, it can be seen that the 3D part (2) has a high transparency due to its smooth surface, and the eagle in the background can be clearly seen, in contrast to the prior art in Figure 10B.

[0031] Figures 11A and 11B show another embodiment in which a dental aligner (2a) is printed using a transparent photocurable resin through an additive manufacturing device according to the present invention. Also in this embodiment, the aligner (2a) is not subjected to any mechanical surface treatment and is placed on a denture model (D) with gingival areas and teeth. In Figure 11B, it can be seen that the aligner (2a) has a high transparency due to its smooth surface and the teeth can be clearly seen through the aligner (2a), in contrast to the prior art in Figure 11C.

[0032] In a preferred embodiment, the UV-transmitting anti-adhesive flexible foil (6-4b), hereafter referred to as foil (6-4b) for short, is frosted only on its lower surface facing the projection unit (7). The upper surface of said foil (6-4b), facing the inside of the reservoir (4) and in contact with the UV light curable resin (5), is smooth (not frosted). Also, said foil (6-4b) does not have light diffusing particles mixed in. Alternatively, light diffusing particles can be mixed in during the manufacturing of the foil. Said foil (6-4b) may be made of any of the following plastic materials: Fluorinated ethylene propylene (FEP), Polytetrafluoroethylene (PTFE), Ethylene Tetrafluoroethylene (ETFE), Perfluoralkoxy- Polymer (PFA), fluoropolymers such as Teflon AFTM, Polyvinyl fluoride (PVF), Polyvinylidene fluoride (PVDF). This list is not exhaustive. The upper surface of the UV-transparent plate (6-4a) (hereafter referred to as plate (6-4a) for short), facing away from the projection unit (7), is smooth. Alternatively, the upper surface of the plate (6-4a) may also be frosted or roughened (for example by etching). The lower surface of the plate (6-4a) is also smooth. Additionally, the plate (6-4a) does not have any light diffusing particles mixed in. The plate (6-4a) can be float glass (white glass) with a specified light transmittance of >89% at 385 nm. The foil (6-4b) is placed directly on the plate (6-4a) on the side facing away from the projection unit (7). The foil (6-4b) rests directly on the plate (6-4a) which prevents the foil (6-4b) from sagging. This keeps the printing surface straight. Alternatively, a separate UV light diffusing / scattering foil (not shown), which will be described later, can be placed between the foil (6-4b) and the plate (6-4a). Additionally, the plate (6-4a) prevents the foil (6-4b) from being damaged / destroyed from the underside of the resin bath unit (3) during installation / removal or transportation by the user.Any of the above-mentioned frosted surfaces can be obtained by a mechanical or chemical post-process such as sandblasting or chemical etching. Alternatively, any of the above-mentioned frosted surfaces can be obtained during the molding process, where the mold has a frosted / rough surface. The degree of roughness (frost level) of the frosted surface is process adjustable according to the desired smoothing effect. The above-mentioned light-diffusing particles can be obtained by mixing calcium phosphate, fluoride, tin oxide, ash, or the like in a suitable low concentration. The foil (6-4b) with the mixture has a milky optical appearance. Alternatively, UV-scattering nanoparticles, e.g. TiO2, can be used. The UV-scattering nanoparticles can be dispersed in the resin (5) in a suitable concentration instead or in addition.

[0033] In this preferred embodiment, the resin bath unit (3) can be removed by the user by means of a release mechanism comprising a container for receiving the resin bath unit (3) and a latch for locking / unlocking the resin bath unit (3). The removable resin bath unit (3) is preferably equipped with an RFID tag containing information regarding the type of resin bath unit (3) and the presence / absence of said optical means (6-5) in the UV-transmitting window (6-4), in particular the UV light diffusion / scattering level that can be used to determine the achievable smoothness level and the amount of UV light to be compensated during exposure. In addition, the additive manufacturing device (1) is provided with an RFID reader / writer. Thereby, the additive manufacturing device (1) can recognize the type of the attached resin bath unit (3), the type of said optical means (6-5), for example whether said optical means (6-5) comprises a frosted / milky foil (6-4b) or not, retrieve said information on the foil (6-4b) and optionally display said information to a user via a user interface of the additive manufacturing device (1), and the control unit can apply the required printing mode based on such information. The information stored by the RFID tag can also include additional information, which will be explained later. The control unit is adapted to control according to such information read from the RFID tag. The information can indicate at least the amount of light to be compensated due to the diffusion of the projected UV light (8) caused by said optical means (6-5). For example, the frosted / milky foil (6-4b) depending on the degree of roughness and / or the light diffusing particles mixed depending on the concentration can lead to an amount of loss of 50% of the exposure light. The smoothing effect of the part (2) can be improved when the diffusion / scattering of the projected UV light (8) additionally induced by the optical means (5) is increased so as to cause a loss of at least 3% of the exposure light (projected UV light (8)), more preferably at least 3%-50%, and even more preferably a loss of 10%-25% of the exposure light, relative to the exposure light set for normal printing conditions.Herein, normal printing conditions may entail that the upper surface of the plate (6-4a) or the lower surface of the foil (6-4b) are very slightly roughened (without becoming milky) to achieve improved release, but this does not result in any observable smoothing of the part (2). This control is implemented through software. The control unit may compensate for the amount of light to be emitted by the projection unit (7) during layer-wise curing lost due to the diffusion / scattering effects of the frost and / or mixture. The amount of light is thus adjusted accordingly, i.e. increased or reduced. The control unit may prompt the user via a user interface to mount a foil (6-4b) with a particular frost level and / or mixture suitable for the print job, in particular the desired smoothness of the part (2) to be printed, and further adapt the amount of light emitted by the projection unit (7) accordingly.

[0034] The resin bath unit (3) may be provided with a removable refill cartridge (not shown) containing a specific UV light curable resin (5) for refilling the reservoir (4). One or more RFID tags may be provided on the wall of the reservoir (4) and / or directly on the refill cartridge. The RFID tag may also contain information about the specific UV light curable resin (5). Thereby, different UV light curable resins (5) may be recognized and used by the additive manufacturing device (1) for different dental applications. The control unit is adapted to control according to the type and exposure requirements of the recognized UV light curable resin (5).

[0035] The user may also edit the RFID tag via the user interface of the additive manufacturing device (1) according to any changes made to the resin bath unit (3), or any other components, or consumables such as the UV light curable resin (5), for example after retrofitting a foil (6-4b) or replacing it with a different foil.

[0036] Instead of or in addition to the above mentioned RFID tags, barcode or QR code labels or the like storing information may be used on the resin vat unit (3). Instead of or in addition to the above mentioned RFID reader / writers, optical reading devices such as scanners (camera / barcode readers etc.) may be used. Alternatively or additionally, a mobile phone camera or an intraoral scanner connectable to a system with the additive manufacturing device (1) may be used.

[0037] Before the printing process is started, the information is automatically obtained via the RFID tag and / or label, but the user may optionally manually input any of the above-mentioned information regarding the type of resin bath unit (3) installed, in particular the frost / mix level, the type of consumables, and the like, via a user interface. The control unit also manages the usage history of the resin bath unit (3), monitoring the wear of the foil (6-4b), etc. Data regarding the usage history and / or other look-up tables for decoding the information may be kept in a data store of the additive manufacturing device (1) and / or in a data store in the cloud, etc. The additive manufacturing device (1) is connectable to the internet and / or a local area network to receive / send data regarding the print job. This information may also be retrieved / updated by other additive manufacturing devices (1) that may be connected to each other directly or via a network.

[0038] A removable and replaceable frame-like spacer foil (not shown) having a desired thickness, preferably 100 micrometers or more, can be optionally placed between the foil (6-4b) and the plate (6-4a) to ensure more space, such as an air gap, to allow easier peeling. The air gap is preferably open to the atmosphere. The frame-like spacer foil can be made, for example, from any of the following plastic materials: plastic polymers such as polyethylene (PE), polypropylene (PP), polymethyl methacrylate (PMMA), polyvinyl chloride (PVC), polycarbonate (PC), etc. The frame-like spacer foil can also be made from metal, ceramic, or paper. The metal material can be metal, such as aluminum, aluminum-based alloy, copper-based alloy, stainless steel, etc. The ceramic material can be ceramic, such as alumina, zirconia, silicon carbide, silicon nitride, etc.

[0039] The foil (6-4b) preferably has a rectangular area of ​​about 107.7×166.5 mm and a thickness of preferably 0.127 mm. However, foils (6-4b) with different dimensions, larger or smaller, can also be used. The removable frame-like spacer foil is preferably provided with a thickness of at least 100 micrometers. This allows the specific pull-out force to be reduced below 30 N with an area utilization of 60% of the available projection foil area of ​​about 134.4 mm×75.6 mm, which is suitable for dental applications such as aligners, bite splints, models, drilling templates, dentures, and the like. Different area utilizations, larger or smaller, can be used. If the utilization of the available projection foil area is even smaller, the removable frame-like spacer foil can be provided with a smaller thickness, preferably at least 50 micrometers. A smaller height does not sufficiently meet the peeling requirements. Thus, said thickness is preferably in the range of 50-150 μm, more preferably in the range of 150-200 μm, or even more preferably at least 200 μm. The removable frame-like spacer foil (6-4c) preferably has a rectangular opening in its center to ensure an air gap in the assembled state. The foil (6-4b) preferably has the same outer contour as the removable frame-like spacer foil. The peripheral frame width of the removable frame-like spacer foil is preferably about 13 mm and also preferably has rounded corners. Different widths can be used. The removable frame-like spacer foil can be made of the same material as the UV-transmitting anti-adhesive flexible foil (6-4b). Alternatively, the removable frame-like spacer foil can be manufactured from a different material, such as plastic, metal, ceramic or paper, preferably in the form of a thin sheet.

[0040] Furthermore, the removable frame-like spacer foils and / or foils (6-4b) may be provided with different color codes (color markings) visible from the outside, allowing a user to distinguish between different sizes, thicknesses, materials, roughness and / or mixing levels of the removable frame-like spacer foils and / or foils (6-4b). Herein, the user may refer to a look-up table in a user manual or a user interface of the additive manufacturing device (1) for the color codes. The additive manufacturing device (1) may have a data storage device that stores such information or may retrieve such information from an external data storage device, preferably in the cloud.

[0041] The RFID tag or label may also include information regarding the presence / absence of a removable frame-like spacer foil in the UV-transmitting window (6-4). In addition, any combination of information regarding the thickness, size, material and / or color of the removable frame-like spacer foil (6-4c) may also be stored in the RFID tag.

[0042] The control unit can prompt the user via the user interface to attach a spacer foil (6-4c) having a required / sufficient minimum thickness suitable for the print job, in particular the area utilization, and further adapt the peeling force applied by the transport unit accordingly.

[0043] The present invention also provides a method for additively manufacturing a part (2) by using the additive manufacturing apparatus (1) of the present invention, in particular by using the above-mentioned optical means (6-5) of the removable resin bath unit (3) to diffuse / scatter the projected UV light (8) and smooth the surface of the part (2), wherein the control unit compensates for the amount of light to be irradiated by the projection unit (7) during layer-by-layer curing due to light lost by the diffusion / scattering effect.

[0044] After the exposure process, the resin (5) is cured on the exposed surface layer and adheres to the top surface of the foil (6-4b) and to the movable build platform (9) / part (2). The foil (6-4b) should preferably have a smooth top surface so that the cured resin (5) can be separated / peeled off from the foil (6-4b) as easily as possible through the transport unit. This results in lower peel forces, which provide higher part precision and longer hardware life, and also accelerates production.

[0045] The foil (6-4b) is preferably rough on the underside, so that (i) air can flow more easily between the foil (6-4b) and the plate (6-4a) and (ii) a scattering effect is achieved through the roughness and the optically opalescent structure. This scattering effect provides a smooth surface for the part (2), i.e. the printed body. To further ensure accuracy, the scattering effect should preferably occur as close as possible to the resin (5). The foil (6-4b) is therefore preferably frosted on the underside. Alternatively or additionally, the internal volume of the foil (6-4b) may be provided with light diffusing particles. The resin bath unit (3) is preferably replaceable. This is particularly advantageous, since if the resin bath unit (3) wears out or is to be printed with a different resin material, the resin bath unit (3) can be removed and replaced by another resin bath unit or retrofitted accordingly. The RFID tag is advantageous for uniquely registering the resin bath unit (3) and documenting the wear. This (i) avoids confusion and (ii) makes it possible to recognize information about the resin bath unit (3) and the foil (6-4b) used. This ensures that the correct process parameters (e.g. exposure time and individual over / under size correction) can be set and thus the print body can be produced as desired. In addition, (iii) the resin bath unit (3) and the performed print job as well as the wear can be documented as a usage history. Thus, the use of the hardware beyond the defined / permitted run time can be prohibited.

[0046] In one embodiment, a configuration may be used consisting of a transparent glass plate (6-4a) that is smooth on both sides (arranged in a predetermined order along the light path from the projection unit (7) to the resin (5)), a separate diffusing / scattering foil (not shown) with at least one of its upper and lower surfaces roughened and / or mixed with light diffusing / scattering particles, and a transparent foil (6-4b) that is smooth on both sides. The separate diffusing / scattering foil is preferably removably attached to the resin bath unit (3) and sandwiched between the plate (6-4a) and the foil (6-4b).

[0047] According to the present invention, "easy peeling", "protection of the upper surface of the foil (6-4b) from resin contamination", and "light diffusion / scattering to smooth the component surface" can be effectively achieved.

Claims

1. An additive manufacturing apparatus (1) for additively manufacturing a part (2), comprising: A resin tank unit (3) including a storage tank (4) for storing a UV light curable resin (5) and a UV-transmitting window (6-4) at the bottom of the storage tank (4), wherein the UV-transmitting window (6-4) includes a UV-transmitting plate (6-4a) and a UV-transmitting, adhesive-preventing, flexible foil (6-4b); a projection unit (7) for projecting UV light (8) into the reservoir (4) through the UV-transmitting window (6-4); a movable build platform (9) having a surface (9a) on which the part (2) can be formed through layer-by-layer curing of the UV light curable resin (5); Equipped with The UV-transmitting window (6-4) is An additive manufacturing device (1), further comprising optical means (6-5) adapted to diffuse the projected UV light (8) towards the movable build platform (9) to an area (R) where the UV light photocurable resin (5) is to be layer-cured, the optical means (6-5) being arranged in an optical path of the projected UV light (8).

2. Additive manufacturing device (1) according to claim 1, characterized in that at least one of the upper and lower surfaces of the UV-transparent, adhesive-preventing, flexible foil (6-4b) is frosted, and the optical means (6-5) are realized through said one or more frosted surfaces of the UV-transparent, adhesive-preventing, flexible foil (6-4b).

3. Additive manufacturing device (1) according to claim 1 or 2, characterized in that the UV-transparent adhesive-free flexible foil (6-4b) comprises light diffusing particles, and the optical means (6-5) are realized through the light diffusing particles inside the UV-transparent adhesive-free flexible foil (6-4b).

4. Additive manufacturing device (1) according to any one of claims 1 to 3, characterized in that at least one of the upper and lower surfaces of the UV-transparent plate (6-4a) is frosted, and the optical means (6-5) are realized through said one or more frosted surfaces of the UV-transparent plate (6-4a).

5. Additive manufacturing device (1) according to any one of claims 1 to 4, characterized in that the UV-transmitting plate (6-4a) comprises light-diffusing particles, and the optical means (6-5) are realized through the light-diffusing particles inside the UV-transmitting plate (6-4a).

6. Additive manufacturing device (1) according to any one of claims 1 to 5, characterised in that the optical means (6-5) comprise a matrix of light-diffusing microlenses.

7. The additive manufacturing device (1) according to any one of claims 1 to 6, characterized in that the reservoir (4) and the UV-transparent window (6-4) are configured to define a detachable resin vat unit (3) that can be removed from the additive manufacturing device (1) by a user.

8. An additive manufacturing device (1) as described in claim 7, further comprising an RFID reader / writer, characterized in that the removable resin vat unit (3) is provided with an RFID tag containing information regarding the presence / absence of the optical means (6-5) in the UV-transmitting window (6-4).

9. Additive manufacturing device (1) according to any one of claims 1 to 8, characterized in that the UV transparent anti-adhesive flexible foil (6-4b) is removably attached to the resin vat unit (3).

10. A UV-transmitting, adhesive-preventing, flexible foil (6-4b) suitable for use in an additive manufacturing device (1) according to claim 9, wherein at least one of the upper and lower surfaces of said UV-transmitting, adhesive-preventing, flexible foil (6-4b) is frosted and / or said UV-transmitting, adhesive-preventing, flexible foil (6-4b) comprises light diffusing particles.

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