Protective device for an exposure unit of an additive manufacturing device

Abstract

A protective device (40) is used for an exposure unit (18) of a manufacturing device (1) for producing a three-dimensional object (2) by selectively solidifying a building material (15) layer by layer. The exposure unit (18) is arranged in a process chamber (3) of the manufacturing device, the exposure unit (18) comprises at least two exposure units (30, 31, 32), each exposure unit generating a beam of light that can be directed at least onto one pixel in a working plane (7), and the exposure unit has, on its underside facing the working plane (7), a lower boundary (18a), which bounds the exposure unit (18) towards the working plane (7). The protective device (40) can be attached to the lower boundary (18a) of the exposure unit (18) and is designed to keep the lower boundary (18a) of the exposure unit at least partially free of contamination.

Description

[0001] The present invention relates to a protective device for an exposure unit of an additive manufacturing device, an additive manufacturing device with such a protective device, a flow method for an exposure unit of an additive manufacturing device and a method for producing a three-dimensional object.

[0002] Devices and processes of this type are used, for example, in rapid prototyping, rapid tooling, or additive manufacturing. One example of such a process is known as "selective laser sintering or laser melting." In this process, a thin layer of a powdered build material is repeatedly applied, and the build material is selectively solidified in each layer by selectively irradiating areas corresponding to a cross-section of the object to be manufactured with a laser beam.

[0003] WO 2015 / 091485 A1 discloses a 3D laser printing system for additive manufacturing, which contains a plurality of laser modules, each with at least two laser arrays. Each laser array comprises a plurality of semiconductor lasers, for example, VCSELs (Vertical Cavity Surface-Emitting Lasers), whose laser light is imaged onto a work plane by an optical element. By selectively switching the laser arrays on and off and moving the exposure unit across the work plane, a layer of build material applied in the work plane can be selectively exposed.

[0004] In the device of WO 2015 / 091485 A1, the exposure unit is provided in a process chamber in which the object is manufactured. During the build process, particularly during the selective solidification of the build material layers, contaminants or process byproducts, such as smoke, vapors, spatter, particles of the build material, etc., can arise. These can spread into the process chamber atmosphere and deposit on the exposure unit. Contaminants accumulating on the exposure unit can have a detrimental effect on the build process and the quality of the object being manufactured, as they can impair the laser radiation being imaged onto the work plane.

[0005] The object of the present invention is to provide an alternative or improved protective device for an exposure unit of an additive manufacturing device or an alternative or improved additive manufacturing device or an improved or alternative flow method for an exposure unit of an additive manufacturing device or an alternative or improved method for producing a three-dimensional object, with which or with which in particular the exposure unit of the additive manufacturing device can be reliably kept free of process by-products and the quality of the object to be produced can be improved.

[0006] This object is achieved by a protective device according to claim 1, a manufacturing device according to claim 9, a flow method according to claim 13 and a manufacturing method according to claim 14. Further developments of the invention are specified in the respective subclaims. The manufacturing device can also be further developed by the features of the protective device below or set out in the subclaims, and vice versa. The manufacturing method can also be further developed by the features of the flow method below or set out in the subclaims, and vice versa. Likewise, the methods can be further developed by the features of the devices below or set out in the subclaims, and vice versa.

[0007] A protective device according to the invention serves for an exposure unit of a manufacturing device for producing a three-dimensional object by selectively solidifying a building material layer by layer. The exposure unit is arranged in a process chamber of the manufacturing device, the exposure unit comprises at least two exposure units, each exposure unit generating a beam of light that can be directed at least onto one pixel in a working plane, and the exposure unit has a lower boundary on its underside facing the working plane, which boundary delimits the exposure unit from the working plane. The protective device can be attached to the lower boundary of the exposure unit and is designed to keep the lower boundary of the exposure unit at least partially free of contaminants. The term "contaminants" is used here and below as a synonym for the term "process by-products."

[0008] The exposure unit of the additive manufacturing device can in particular be an exposure unit that is provided in the process chamber so as to be movable above the working plane. The exposure unit can be provided with its lower boundary, for example, at a short distance of less than 10 cm, preferably less than 5 cm, particularly preferably substantially 1 cm, above the working plane in the process chamber. A height of the process chamber can be, for example, at least 20 cm, preferably at least 50 cm, particularly preferably at least 60 cm and / or at most 150 cm, preferably at most 100 cm, particularly preferably at most 80 cm. A travel speed of the exposure unit can be, for example, at least 0.05 m / s, preferably at least 0.1 m / s, particularly preferably 0.6 m / s and / or at most 5 m / s, preferably at most 3 m / s, particularly preferably at most 1.2 m / s.Thus, the exposure unit for which the protective device is suitable can be distinguished, in particular, from exposure units that are provided outside a process chamber of the additive manufacturing devices and / or stationary with respect to the process chamber. The exposure unit is preferably designed for large-area and / or selective exposure of a layer of the build material applied in the working plane. The "lower boundary" of the exposure unit preferably refers to a boundary of the exposure unit that faces the working plane.

[0009] Preferably, the exposure unit is movable or is moved in the process chamber at a speed corresponding to the speed at which a melt front is moved in the working plane, in particular on a powder bed. A melt front can refer to an area in the working plane or the powder bed in which the build-up material is partially or completely melted at a specific time due to the action of the beams. After cooling, the build-up material can then be present as a solid body at the locations scanned by the beams.

[0010] In order to keep the lower boundary of the exposure unit at least partially free from contamination, the protective device can be designed in particular according to at least one of the following measures: - The protective device can be designed to cover areas of the lower boundary of the exposure unit through which beam bundles do not pass during operation of the exposure unit. This can, for example, cover areas through which beam bundles do not pass during operation of the exposure unit and thus protect them from contamination. This can, for example, implement a shielding function of the protective device. The term "during operation of the exposure unit" refers in particular to a state of the exposure unit in which a number of beam bundles are directed onto the working plane, i.e. in particular activated, or the corresponding exposure unit(s) is / are switched on. The protective device can have a number of openings, each of which is designed as a channel designed to deflect a gas flow occurring in the process chamber away from the lower boundary of the exposure unit. This allows, for example, a flow-repellent function of the protective device to be realized. For example, contaminants occurring in the process chamber and carried along by the gas flow can be deflected away from the lower boundary of the exposure unit. - The protective device can have a number of openings, each opening being designed such that, in interaction with a movement of the protective device and the exposure unit in the process chamber, in particular a movement across the working plane, it generates a (gas) flow near the opening of the protective device, which moves a process chamber gas away from the opening. - The protective device can have at least one gas inlet for supplying a gas, which is designed to flow a gas at least partially over the lower boundary of the exposure unit. This can, for example, be used to blow out the protective device. In particular, the gas supply can actively prevent contaminants from reaching the lower boundary of the exposure unit.

[0011] Here and in the following, the term “number” can mean both “one” (here: one opening) and “a plurality of” (here: a plurality of openings), i.e. at least two.

[0012] The protective device can, for example, keep the lower edge of the exposure unit free of contaminants, allowing the radiation generated by the exposure unit to impinge on the working plane essentially unhindered. This can, for example, provide a sufficient energy supply for the complete solidification of the areas of a build-up material layer corresponding to the object's cross-section.

[0013] The protective device preferably comprises at least one gas inlet for supplying a gas, wherein the at least one gas inlet is configured such that the gas flowing out of it exits substantially parallel to a plane of the lower boundary of the exposure unit when the protective device is attached to the exposure unit. This makes it possible, for example, to supply a gas to at least some of the lower boundary of the exposure unit, in particular to actively keep the lower boundary of the exposure unit free of contaminants. The gas supplied through the at least one gas inlet can be nitrogen, for example.

[0014] Preferably, the protective device is essentially designed as a cover, preferably a plate, with openings, wherein exactly one opening is provided at each point on the cover that corresponds to a region of the lower boundary of the exposure unit through which beam bundles pass during operation of the exposure unit when the protective device is attached to the exposure unit. Further preferably, the protective device is designed such that it at least partially covers regions of the lower boundary of the exposure unit through which beam bundles pass during operation of the exposure unit when the protective device is attached to the exposure unit. In this way, for example, regions of the lower boundary of the exposure unit through which beam bundles pass during operation of the exposure unit can be covered and thus protected from contamination.For example, the protective device for the beam bundles can form essentially impermeable and permeable regions at the lower boundary of the exposure unit, such as a mask. Due to the plate-like design of the protective device, it can, for example, have a small thickness, so that even existing exposure units located a short distance from the working plane in the process chamber can be equipped or retrofitted with the protective device.

[0015] A total area of the openings of the protective device in relation to a total area covered by the protective device can be, for example, less than 20%, preferably less than 15%, more preferably less than 10%, particularly preferably substantially 5%.

[0016] Preferably, a wall of the opening forms a flow channel for the gas to flow around the lower boundary of the exposure unit. Such a wall can, for example, keep a gas flow occurring in the process chamber away from the lower boundary of the exposure unit. Alternatively, the openings can be separated from one another by their walls so that, in particular, contaminants can be prevented from passing from one opening to another. Preferably, a flow velocity generated in the flow channel by supplying a gas through a gas inlet (see below) is lower than gas flows in the process chamber atmosphere occurring outside the flow channel in the process chamber, for example caused by the movement of the exposure unit across the working plane.

[0017] Preferably, the gas inlet is substantially slit-shaped, and a length of the slit-shaped gas inlet more preferably extends over the entire dimension of the opening in a direction parallel to the length of the slit-shaped opening. In other words, it is preferred that the slit-shaped gas inlet extends substantially over the entire opening. This makes it possible, for example, to flow the gas over the entire area of the opening. Preferably, the at least one gas inlet is configured such that the gas flowing out of it forms a laminar flow.

[0018] Preferably, the opening has two or more gas inlets arranged at a distance from one another in a direction perpendicular to a plane of the lower boundary of the exposure unit. This allows, for example, contaminants to be more effectively kept away from the lower boundary of the exposure unit, particularly in the area of the opening.

[0019] Preferably, the protective device further comprises at least one gas supply line, more preferably a plurality of gas supply lines, for supplying a gas to the at least one gas inlet, and more preferably for distributing the gas to a plurality of gas inlets.Further preferably, the openings of the protective device are arranged in cascades, and a gas supply line is provided between each two adjacent cascades of openings in order to supply all gas inlets of the openings of the respective cascade with gas, and / or the gas supply line further preferably has a first end and a second end opposite the first end, and both ends are connected to a gas supply, and wherein even more preferably a volume ratio of a gas supplied through the first end to a gas supplied through the second end is adjustable, in particular depending on a direction of travel of the exposure unit, and / or the gas supply line further preferably has a tapered line section between the first and second ends. This makes it possible, for example, to achieve the most even distribution possible of the inflowing gas volume between the various openings of the protective devices.

[0020] The protective device preferably comprises a protective gas heating device for heating the gas supplied through the gas supply line. This can be designed, for example, passively, e.g., as a heat exchanger, or actively, e.g., as a separate heating element, for example, in the form of two aluminum protective gas distributors with direct contact with the process chamber atmosphere. This makes it possible, for example, to heat the lower boundary of the exposure unit and / or to reduce a temperature difference between the lower boundary of the exposure unit or the inflowing gas and a build-up material layer applied in the working plane.

[0021] Preferably, a first line section, preferably a prechamber, is provided upstream of the gas inlet for supplying a gas to the gas inlet, and the first line section has a larger cross-section perpendicular to the flow direction than the gas inlet. Further preferably, a second line section is provided upstream of the first line section, preferably a flat channel, which has a smaller cross-section perpendicular to the flow direction than the first line section. The second line section can, for example, accelerate the flow and / or distribute the inflowing gas volume as evenly as possible between different gas inlets. The first line section can, for example, serve to ensure good pressure equalization of the flow and to calm the flow.

[0022] Preferably, the at least one gas inlet is designed and / or the gas is supplied during operation in such a way that at least in a region of the lower boundary of the exposure unit, preferably in the region of an opening in the protective device, a mixing zone is formed in which the gas flowing out of the gas inlet mixes with a gas atmosphere prevailing in the process chamber, wherein the mixing zone is formed at a distance from the lower boundary of the exposure unit, in particular at a distance of at least 1 mm, preferably of at least 2 mm, more preferably of at least 3 mm. As a result, impurities occurring in the process chamber and / or entrained in the gas atmosphere, for example, can be kept away from the lower boundary of the exposure unit.In particular, the mixing zone can be achieved by a slot-shaped design of the at least one gas inlet, and / or its arrangement at a defined distance from the lower boundary of the exposure unit, and / or a corresponding gas flow rate of the gas flowing in through the at least one gas inlet.

[0023] Preferably, each of the openings is designed as a channel with an inlet opening facing the lower boundary of the exposure unit and an outlet opening facing away from the lower boundary of the exposure unit, and a wall connecting the inlet opening and outlet opening. The wall can, in particular, form the above-mentioned flow channel for the gas flow to the lower boundary of the exposure unit. Further preferably, the wall runs essentially parallel to an envelope formed by the beam bundles that pass through the respective opening during operation of the exposure unit, and / or essentially parallel to a radiation cone formed by the beam bundles that pass through the respective opening during operation of the exposure unit, preferably at a distance of less than 1 mm from the envelope.the radiation cone, and / or each channel has a substantially frustoconical shape, and / or an area of the inlet opening is larger than an area of the outlet opening, and / or an area of the inlet opening and an area of the outlet opening have similar shapes, in particular substantially rectangular shapes. This can, for example, provide a protective device that allows the beam bundles or the solidification radiation of the exposure unit to pass largely unhindered. In addition, the wall can keep gas flows occurring, for example, in the process chamber, which may carry contaminants, from the lower boundary of the exposure unit.

[0024] Preferably, the protective device further comprises an edge that protrudes from a plane of the protective device toward the working plane, wherein the edge encloses a number of openings, preferably a plurality of openings. This can, for example, prevent or at least reduce the gas atmosphere and / or gas flow prevailing in the process chamber, which is caused, for example, by a movement of the exposure unit in the process chamber, from flowing into the opening(s).

[0025] The protective device is preferably a component made of a metallic material. The protective device is preferably made of a material that allows for substantial dimensional stability under the temperature fluctuations that occur during operation of the manufacturing device. The protective device can, for example, be made of INVAR36, an iron-based alloy with 36% nickel. The protective device is preferably a component manufactured using an additive manufacturing process. This makes it possible, for example, to produce a protective device with great geometric complexity.

[0026] Preferably, the protective device further comprises at least one fastening element for the preferably reversible fastening of the protective device to the exposure unit, wherein the fastening element is more preferably designed as a quick-release connection. This makes it possible, for example, to easily attach the protective device to the exposure unit, for example, to retrofit the exposure unit with the protective device, and / or to remove the protective device from the exposure unit.

[0027] A manufacturing device according to the invention serves to produce a three-dimensional object by selectively solidifying a building material layer by layer. It comprises a process chamber in which the three-dimensional object can be produced in a build field in a working plane, and an exposure unit for, preferably selectively, exposing a layer of the building material applied in the build field, wherein the exposure unit is arranged in the process chamber. The exposure unit comprises at least two exposure units, and each exposure unit generates a beam of light that can be directed onto at least one pixel in the working plane. The exposure unit has, on its underside facing the working plane, a lower boundary that delimits the exposure unit from the working plane. The manufacturing device further comprises a protective device as described above, which is or can be attached to the lower boundary of the exposure unit.With such a manufacturing device, for example, the same or similar effects can be achieved as with a protective device described above.

[0028] The exposure unit is preferably provided in the process chamber so as to be movable in one direction of movement across the working plane. Alternatively or additionally, each exposure unit of the exposure unit is preferably individually controllable. Alternatively or additionally, the lower boundary of the exposure unit is preferably designed as a plate that is at least partially translucent, in particular transparent, in particular as a glass plate. Alternatively or additionally, the exposure unit preferably further comprises a heating device for heating the lower boundary. Alternatively or additionally, the exposure units of the exposure unit are preferably arranged in mutually offset rows and / or columns, or in cascades, and the protective device is essentially designed as a cover with openings, wherein the openings are arranged at locations corresponding to the exposure units of the exposure unit in mutually offset rows and / or columns, or in cascades.Alternatively or additionally, the exposure units are preferably designed as laser modules, wherein each laser module is formed from a plurality of laser arrays, and each laser array is formed from a plurality of individual lasers, preferably VCSELs and / or VECSELs.

[0029] According to the invention, a flow method is provided for an exposure unit of a manufacturing device for producing a three-dimensional object by selective layer-by-layer solidification of a building material, wherein the exposure unit is arranged in a process chamber of the manufacturing device, and the exposure unit comprises at least two exposure units and each exposure unit generates a beam of light that can be directed at least onto one pixel in a working plane, and the exposure unit has a lower boundary on its underside facing the working plane, which boundary delimits the exposure unit towards the working plane, and wherein preferably a protective device as described above is attached to the lower boundary of the exposure unit.The flow method comprises at least one step of supplying a gas such that the gas flows out essentially parallel to a plane of the lower boundary of the exposure unit in order to keep the lower boundary of the exposure unit at least partially free of contaminants. This makes it possible, for example, to allow the beam bundles to pass through the lower boundary of the exposure unit largely unhindered, which can improve the quality of the object to be produced. All inert gases are particularly suitable as gases, e.g. nitrogen, carbon dioxide, argon and many more. The gas can also be nitrogen, for example. It is also possible to mix several gases in order to achieve specific properties of the gas mixture. In particular, an inert gas mixture produced by combustion of combustion gases can be advantageously used.

[0030] A method according to the invention for producing a three-dimensional object by selectively solidifying a build material layer by layer in an additive manufacturing device, wherein the object is produced in a process chamber of the manufacturing device, comprises the steps of: applying a layer of the build material in a build field in a working plane, and exposing, preferably selectively exposing, the layer of the build material applied in the build field with an exposure unit, wherein the exposure unit is arranged in the process chamber, wherein the exposure unit comprises at least two exposure units and each exposure unit generates a beam of light that can be directed onto at least one pixel in the working plane, and the exposure unit has a lower boundary on its underside facing the working plane, which boundary delimits the exposure unit from the working plane, and wherein a protective device as described above is attached to the lower boundary of the exposure unit,and / or wherein the manufacturing device is a manufacturing device described above, and / or wherein a flow process described above is carried out at least temporarily. This makes it possible, for example, to achieve the effects described above with regard to the protective device even in an additive manufacturing process.

[0031] Preferably, the manufacturing method further comprises a step of transferring thermal energy, in particular heat, within the exposure unit to an exterior of the exposure unit, in particular to a process chamber region outside the exposure unit facing the working plane, and / or to the outflowing gas. This makes it possible, for example, to dissipate heat generated in the exposure unit to the outside or to cool the exposure units of the exposure unit, and / or to reduce a temperature difference between a build-up material layer applied in the working plane and the exposure unit.

[0032] Further features and advantages will become apparent from the description of an embodiment with reference to the attached figures. Fig. 1 shows a schematic, partially sectioned view of an additive manufacturing device in which the protective device according to the invention is used; Fig. 2a shows a schematic view of an exposure unit of the Fig. 1 shown additive manufacturing device from below, wherein the exposure unit has several laser modules; Fig. Figure 2b shows schematically an arrangement of laser arrays in a Fig. Laser module shown in Figure 2a; Fig. Figure 2c shows schematically an arrangement of lasers in a Fig. Laser array shown in Figure 2b; Fig. 3 shows a schematic view of a protective device according to the invention, looking at the top of the protective device; Fig. 4 shows a schematic perspective view of the Fig. 3 shown guard with a view of the underside of the guard; Fig. Figure 5a shows a schematic, perspective and partially sectioned view of the Fig. 3 and Fig. 4, wherein a cutting plane is perpendicular to the top and bottom of the protective device; Fig. 5b shows a detailed view of the Fig. 5a, if the protective device is attached to the lower limit of the exposure unit; Fig. 6 shows a schematic representation of a gas flow during operation of the Fig. 3 to 5b, if this is attached to the exposure unit of the type shown in Fig. 1 shown additive manufacturing device; and Fig. Figure 7 shows a schematic representation of a purity level of the gas atmosphere during operation of the Fig. 3 to 5b, if this is attached to the exposure unit of the type shown in Fig. 1 shown additive manufacturing device.

[0033] The following is based on Fig. 1 describes an embodiment of an additive manufacturing device 1 to which the present invention is applicable. Fig. The device shown in Figure 1 is a laser sintering or laser melting device 1. For building an object 2, it contains a process chamber 3 with a chamber wall 4.

[0034] Arranged in the process chamber 3 is an upwardly open container 5 with a container wall 6. A working plane 7 is defined by an upper opening of the container 5, wherein the area of the working plane 7 located within the opening, which can be used to build the object 2, is referred to as the build field 8.

[0035] In the container 5, a support 10 is arranged, which is movable in a vertical direction V and to which a base plate 11 is attached, which closes off the container 5 at the bottom and thus forms its bottom. The object 2 to be manufactured can be built on the base plate 11 as a construction base, or on a construction platform 12, which is attached to the base plate 11 as a construction base, as in Fig. 1 shown. In Fig. 1, the object 2 to be formed in the container 5 on the construction platform 12 is shown below the working plane 7 in an intermediate state with several solidified layers, surrounded by unsolidified building material 13.

[0036] The laser sintering device 1 further contains a storage container 14 for a building material 15 which can be solidified by electromagnetic radiation, e.g. in powder form, and a coater 16 which can be moved in a horizontal direction H for applying the building material 15 within the construction field 8. The coater 16 preferably extends transversely to its direction of movement over the entire area to be coated (not shown in the figures).

[0037] Various types of powder can be used as build-up material, in particular metal powder or metal-containing powder, plastic powder, ceramic powder, sand, filled or mixed powders. Instead of powder, other suitable materials can also be used as build-up material, e.g., particles, pastes, liquids, etc.

[0038] Optionally, a radiant heater 17 is arranged in the process chamber 3, which serves to heat the applied build material 15. An infrared radiator, for example, can be provided as the radiant heater 17.

[0039] In the process chamber 3 there is also a horizontal direction B (see Fig. 2a) arranged above the working plane 7 is an exposure unit 18 which is movable and generates laser radiation 19 which is focused onto the working plane 7. The exposure unit 18 is preferably designed as a line exposure unit which is designed to expose an area extending transversely to its direction of movement B, which area extends transversely to the direction of movement B over the entire area to be exposed. On its side facing the build field 8 or the working plane 7, i.e. its underside, the exposure unit 18 has a lower boundary 18a which delimits the exposure unit towards the working plane 7. The lower boundary 18a can, for example, be a plate which is at least partially translucent, in particular transparent, for the laser radiation 19, e.g. a glass plate. Optionally, a heating device (not shown in the figures) can be provided on or near the lower boundary 18a of the exposure unit for heating the lower boundary 18a.

[0040] The direction of movement B (see Fig. 2a) of the exposure unit 18 can be parallel to the direction of movement H of the coater 16, as in Fig. 1. However, the directions of movement of the exposure unit 18 and the coating unit 16 may also be different directions of movement, e.g., perpendicular to one another; preferably, they are each horizontal directions of movement, ie, perpendicular to the vertical direction V in which the carrier 10 is movable.

[0041] The laser sintering device 1 further contains a control unit 20, via which the individual components of the device 1 are controlled in a coordinated manner to carry out the building process. Alternatively, the control unit can also be mounted partially or entirely outside the device. The term “control unit” refers in particular to any computer-based control device that is capable of controlling the operation of the additive device or a component thereof. For example, the control unit can be a computer. The control unit can contain a CPU whose operation is controlled by a computer program (software). The computer program can be stored separately from the additive manufacturing device in a storage device, from where it can be loaded into the additive manufacturing device, in particular into the control unit, e.g. via a network or by wireless transmission.

[0042] During operation, to apply a build material layer, the carrier 10 is first lowered by a height corresponding to the desired layer thickness. The coater 16 first moves to the storage container 14 and takes from it a quantity of build material 15 sufficient to apply one or more layers. It then moves over the build area 8 and applies a thin layer of build material 15 to the build substrate or an already existing build material layer. The application takes place at least over the entire cross-section of the object 2 to be produced, preferably over the entire build area 8, i.e. the area delimited by the container wall 6. Optionally, the build material 15 is heated to a working temperature by means of the radiant heater 17.

[0043] The exposure unit 18 then moves over the applied and optionally preheated build material layer and solidifies the build material 15 at the locations corresponding to the cross-section of the object 2 to be produced by selectively exposing these locations to the laser radiation 19. In the case of a powdered build material, the energy introduced by the radiation partially or completely melts the powder grains at these locations, so that after cooling, they are bonded together as a solid. These steps are repeated until the object 2 is finished and can be removed from the process chamber 3.

[0044] The exposure of the areas to be solidified is preferably carried out in such a way that the exposure unit is in the direction of movement B (see Fig. 2a) moves across the build field 8 and simultaneously exposes all areas of the build material layer to be solidified, each of which lies below the current position of the exposure unit 18. For this purpose, the exposure unit is designed to generate different exposure profiles in the direction transverse to its direction of movement. In the present embodiment, this is achieved by a plurality of independently controllable exposure units in the form of laser arrays 31 (see below).

[0045] The Fig. 2a to 2c schematically show a view of the exposure unit 18 from below, i.e., a plan view of its lower boundary 18a. The direction of movement of the exposure unit 18 across the build field 8 (see Fig. 1) is represented by an arrow B. Fig. Figure 2a shows how a plurality of laser modules 30 are arranged in offset rows on the underside of the exposure unit 18. Fig. Figure 2b shows how each laser module 30 is formed from a plurality of laser arrays 31, which represent the exposure units. Fig. Figure 2c shows how each laser array 31 is formed from a plurality of individual lasers 32.

[0046] The individual lasers 32 can be designed, for example, as semiconductor diode lasers of the VCSEL (Vertical Cavity Surface Emitting Laser) or VECSEL (Vertical External Cavity Surface Emitting Laser) type. These laser sources have a radiation direction perpendicular to the main extension (wafer plane) and a circularly symmetric beam divergence and are particularly well suited for arrangement in two-dimensional arrays. Fig. In the laser array 31 shown in Figure 2c, the individual lasers 32 are offset from one another, for example, arranged in a diamond shape, although any other arrangements are also possible. All lasers 32 of a laser array 31 are preferably controlled simultaneously. The smallest individually controllable exposure unit of the exposure unit 18 is then the laser array 31. This has the advantage that if a single laser fails, the entire exposure unit does not fail immediately, but rather the power drop can be compensated for by the other lasers of the laser array. Alternatively, each laser or a plurality of lasers can be controlled individually.

[0047] Several laser arrays 31 are combined to form a laser module 30. The Fig. The laser module 30 shown in Figure 2b comprises, purely by way of example, two rows of 12 laser arrays 31 each. A row of laser arrays is defined here as laser arrays arranged next to one another transversely, preferably perpendicularly, to the direction of movement B. For each laser module 30, an optical element (not shown in the figures) is also provided, with which the laser light of the laser arrays 31 is imaged onto the working plane 7. The laser light of a laser array 31 is imaged as a beam bundle onto a pixel in the working plane 7. Each laser module 30 is directed onto a specific area in the working plane 7. When the exposure unit 18 is moved in its direction of movement B, the pixels of the switched-on laser arrays 31 form a track.

[0048] In the Fig. In the laser module 30 shown in Figure 2b, the individual laser arrays 31 are arranged in two offset rows such that the tracks of their pixels in the working plane adjoin one another when the laser module 30 moves in the direction of movement B. For example, if the laser arrays 31 have a width of 0.1 mm transverse to the direction of movement and are imaged onto the build field at a reduced image scale of 1:5, the adjacent tracks of the laser arrays 31 have a width of 0.02 mm. In other words, the exposure unit 18 has a resolution of 0.02 mm in a direction transverse to its direction of movement B.

[0049] In order to utilize the entire width of the exposure unit 18, several laser modules 30 are arranged in a row in the direction transverse to the direction of movement B. A row of laser modules is defined as laser modules 30 arranged next to one another transversely, preferably perpendicularly, to the direction of movement B. In the Fig. In the exposure unit shown in Figure 2a, purely by way of example, each row comprises eleven laser modules 30. Due to the optical reduction in size of the laser modules 30 by the optical element (not shown in the figures), the total width of a track formed from the pixels of all laser arrays 31 of the laser module 30 when a laser module 30 moves in the direction of movement B is narrower than the laser module 30 itself by the reduction scale. The grid spacing of the tracks of all laser modules in a row, i.e. the center-to-center distance between the tracks, corresponds to the (unreduced) grid spacing of the laser modules 30. Thus, a non-exposure area remains between the tracks that can be exposed by a single row of laser modules 30.

[0050] In order to enable continuous exposure of the working plane 7 in the direction transverse to the direction of movement B, several rows of laser modules 30 are arranged offset from one another. Fig. 2a comprises, purely by way of example, five rows of laser modules 30 offset from one another. In other words, the laser modules 30 are arranged in cascades in a stepped manner one behind the other in the direction of movement B of the exposure unit, wherein the laser modules 30 of a cascade are arranged offset or staggered from one another in the direction transverse, preferably perpendicular, to the direction of movement B. In Fig. In Figure 2a, for example, the leftmost laser modules 30 of the five rows form a first cascade. Several such cascades are then arranged next to one another in the direction transverse to the direction of movement B. Within each cascade, the laser modules 30 are offset from one another to such an extent that the tracks of the pixels of their laser arrays 31 are adjacent to one another.

[0051] In another exemplary embodiment, the exposure unit includes 108 laser modules, each laser module includes 32 laser arrays, and each laser array includes 282 VCSELs. In this case, the exposure unit includes 3456 individually controllable exposure units (laser arrays).

[0052] Further on, Fig. 2a shows the lower boundary 18a of the exposure unit 18. Due to the arrangement of the individual lasers 32 in laser arrays 31 and laser modules 30, laser light does not pass through all areas of the lower boundary 18a during operation of the exposure unit 18. Thus, there are areas of the lower boundary 18a through which laser light or beams pass or can pass during operation of the exposure unit 18, in Fig. 2a, these correspond to the areas of the laser modules 30. No laser light or beam passes through the remaining areas of the lower boundary 18a during operation of the exposure unit 18.

[0053] The following is based on Fig. 2 to 5b, a protective device 40 is described which can be attached or is attached to the lower limit 18a of the exposure unit 18.

[0054] The protective device 40 is designed to keep the lower boundary 18a of the exposure unit 18 at least partially free from contamination.

[0055] The protective device 40 is essentially designed as a cover in the form of a plate with an upper side 41 and a lower side 42. The upper side 41 faces the exposure unit, and the lower side 42 faces away from the exposure unit or, in the installed state, faces the working plane 7. Fig. 3 shows a plan view of the top side 41 of the plate, Fig. 4 on the underside 42 of the plate, and Fig. Figure 5a shows a perspective and partially sectioned view of the protective device 40, with the underside 42 of the protective device 40 facing upward. The protective device 40 is thus attached to the lower boundary 18a of the exposure unit 18 (see Fig. 1, Fig. 2a) so that its upper side 41 rests against the lower limit 18a of the exposure unit 18 (see e.g. Fig. 5b).

[0056] The protective device 40 has a plurality of openings 43 in the form of channels, each of which penetrates the protective device from the top side 41 to the bottom side 42, as well as gas supply lines 50 arranged between the openings or channels 43.

[0057] Each channel 43 has an inlet opening 43a on the upper side 41 of the protective device, an outlet opening 43b on the lower side 42 of the protective device, and a wall 44 connecting the inlet opening 43a and the outlet opening 43b. The wall 44 of a channel 43 forms a flow channel for the flow of a gas to the lower boundary 18a of the exposure unit 18, as described below. As best seen from Fig. 4, Fig. 5a, the wall 44 of each channel is essentially frustoconical, for example, with the channel tapering from the inlet opening 43a to the outlet opening 43b. An area of the inlet opening 43a is thus larger than an area of the outlet opening 43b of the channel 43. The ratio of the areas of an inlet opening to an outlet opening can also be reversed, or the areas can be the same size. The area of the inlet opening 43a and the area of the outlet opening 43b have similar shapes, in the present embodiment essentially rectangular shapes or the shape of a rectangle with rounded corners. Instead of rectangular shapes, other shapes, such as circles, ovals, ellipses and polygons, are also possible as cross-sections of the channels and the inlet and / or outlet openings.

[0058] As in Fig. 3, the upper side 41 of the protective device 40 is essentially planar, i.e., flat. The plane of the upper side 41 defines a plane of the protective device 40. Fastening elements, here in the form of holes 46, can be provided on the sides of the protective device 40, which serve to fasten the protective device 40 to the lower boundary 18a of the exposure unit 18. The holes 46 can be designed, for example, to receive screws, fastening pins, or the like. Instead of the holes 46, any other fastening elements can be provided which are suitable for fastening the protective device 40 to the lower boundary 18a of the exposure unit 18, preferably for fastening it detachably or reversibly, such as, for example, magnetic fastening elements, snap-in connections, etc. In a preferred embodiment, the fastening elements are designed as quick-action clamp connections.In another embodiment, click bars, clamps, or suction cups can be used. In another embodiment, chemical compounds, such as removable adhesives, can also be used. This eliminates the need for mounting holes or holes 46 on the protective device.

[0059] The number and arrangement of the openings 43 in the protective device 40 is selected such that exactly one opening 43 is provided at each point on the protective device 40 that corresponds to a region of the lower boundary 18a of the exposure unit 18 through which beams or laser light pass during operation of the exposure unit when the protective device 40 is attached to the exposure unit 18. In other words, the inlet openings 43a of the channels 43 are provided on the upper side 41 of the protective device at the locations that correspond to the regions of the laser modules 30 of the exposure unit 18 (see Fig. 2a). The areas of the lower boundary 18a of the exposure unit 18, through which no beam or laser radiation passes during operation of the exposure unit, are covered by the protective device 40 when the protective device is attached to the exposure unit 18. The channels 43 thus form regions of the protective device 40 that are permeable to the laser light of the exposure unit 18. The frustoconical shape of the channels 43 is preferably adapted to the converging radiation path of the laser radiation due to the reducing image scale (see above), ie an envelope formed from the beam bundles during operation of the exposure unit. Fig. 5b is a purely schematic representation of the envelope of the beam bundles of a laser module (see Fig. 2a, Fig. 2b) by dashed lines 33. In other words, the envelope 33 preferably delimits a region which is passed by the laser radiation 19 of a laser module 30 during operation of the exposure unit 18. The arrows of the lines 33 in Fig. 5b indicate the direction in which the laser radiation passes through the respective channel 43. Preferably, the wall 44 of the channel 43 is slightly larger than the envelope 33, for example, with a distance of at most one millimeter (e.g., 0.8 mm) from the envelope 33.

[0060] Thus, the openings or channels 43 of the protective device 40 are arranged in offset rows or in stepped cascades (columns), corresponding to the arrangement of the laser modules 30 of the exposure unit 18 (see Fig. 2a). Fig. 3, Fig. 4 shows, purely by way of example, a protective device with nine rows of 12 openings 43 each, ie 12 cascades with nine openings 43 each, whereby the protective device 40 shown is suitable, for example, for an exposure unit 18 of nine rows of 12 laser modules 30 each.

[0061] In the present embodiment, the gas supply lines 50 of the protective device 40 are each arranged between two adjacent cascades (columns) of openings 43. For example, one gas supply line can be assigned to each of the openings 43 of a cascade in order to supply them with a gas, as described below. Each gas supply line extends, as shown in Fig. 4, from a first end 51a of the gas supply line 50 to a second end 51b opposite the first end 51a. At least one of the two ends 51a, 51b, preferably both ends 51a, 51b, are connected to a gas supply (not shown in the figures) and optionally to a gas conveying device (likewise not shown), e.g., a turbine, in order to supply gas to the gas supply line 50. Preferably, a volume ratio of the gas supplied through the first end 51a to the gas supplied through the second end 51b is adjustable, in particular depending on the direction of movement B of the exposure unit. For this purpose, for example, corresponding control devices, e.g., valves for controlling a gas flow rate (not shown in the figures), can be provided. Furthermore, the protective device 40 can comprise a heating device (not shown in the figures) for heating the gas supplied through the gas supply lines 50. Nitrogen, for example, can be used as the gas.

[0062] The gas supply line 50 is tapered between the first end 51a and the second end 51b. In the present embodiment, a tapered line section 52 is provided in the central region of the gas supply line 50 between the two ends 51a, 51b, which has a cross-sectional area that continuously decreases from the respective end 51a, 51b toward the center.

[0063] The underside 42 of the protective device (see in particular Fig. 4, Fig. 5a) can be formed by the outlet openings 43b of the channels 43 and the gas supply lines 50, which in the present embodiment point downwards (ie in the direction of the working plane 7, see Fig. 1, when the protective device 40 is attached to the exposure unit) are formed protruding. According to a further development of the protective device not shown in the figures, the channels 43 and / or the gas supply lines 50 can also be integrated into the plate of the protective device, so that the protective device has a planar, i.e. flat, underside 42. In this case, the underside and the upper side are preferably parallel to one another. In a further embodiment, the underside of the protective device can be inclined, i.e. at an angle, to the upper side. The inclination of the underside to the upper side can in this case advantageously be implemented with respect to a gas flow of the process chamber atmosphere.

[0064] Furthermore, each opening or channel 43 in the present embodiment of the protective device 40 has two gas inlets 53, 54 for supplying a gas from the gas supply line 50 to the channel 43. The gas inlets 53, 54 are each slit-shaped, wherein a longitudinal direction of the slit extends in Fig. 5a, Fig. 5b extends into the plane of the drawing, ie runs parallel to the plane of the protective device 40 (or the plane of the upper side 41). The length of the slot-shaped opening of the respective gas inlet 53, 54 is essentially the same size as the dimension of the channel 43 parallel to the longitudinal direction of the slot (in Fig. 5a, Fig. 5b into the plane of the drawing) or parallel to the plane of the protective device 40. The length of the slot-shaped gas inlet 53, 54 thus extends over the entire dimension of the channel 43 in a direction parallel to the length of the slot-shaped opening 53 or 54. The gas inlets 53, 54 are designed such that gas flowing out of them exits essentially parallel to the plane of the protective device 40, and thus parallel to the lower boundary 18a of the exposure unit 18 (see Fig. 1, Fig. 2a) when the protective device 40 is attached to the exposure unit 18. In addition, gas escaping from the gas inlets 53, 54 flows through substantially the entire surface of the channel 43 parallel to the plane of the protective device 40.

[0065] The gas inlets 53 and 54 are spaced apart in a direction perpendicular to the plane of the protective device 40. In Fig. 5a, Fig. 5b, the first gas inlet 53 is closer to the lower boundary 18a of the exposure unit 18 than the second gas inlet 54 when the protective device 40 is attached to the exposure unit 18. Preferably, both gas inlets 53 and 54 are arranged closer to the upper side 41 of the protective device, i.e., the inlet opening 43a, than to the underside 42 of the protective device or the outlet opening 43b of the respective channel 43. For example, the gas inlets 53, 54 can be provided in a region of the channel adjacent to the inlet opening 43a, which corresponds to one-third of a total extension of the channel 43 from the inlet opening 43a to the outlet opening 43b.

[0066] To supply the gas to the gas inlets 53 and 54, the gas supply line 50 has a supply channel 55, which is connected in a gas-conducting manner to the gas reservoir (see above), not shown, and, starting from the supply channel 55, a second line section 56 and a first line section 57. The second line section 56 has a smaller cross-section perpendicular to the flow direction than the adjacent line sections, i.e., than the first line section 57 and the supply channel 55. The second line section 56 can, for example, be designed as a flat channel. In particular, the second line section 56 can have changes of direction in the flow direction of the gas, e.g., be wound, in order to guide the gas from the supply channel 55 towards the gas inlets 53, 54. Fig. 5a, Fig. 5b, the second line section 56 has a 180° turn, which connects the supply channel 55 to the first line section 57 in a gas-conducting manner. The second line section 56 forms, for example, a constriction for the gas flowing through it, which experiences a pressure loss and a homogenization of the flow properties as it flows through the second line section 56.

[0067] The first line section 57 has a larger cross-section perpendicular to the flow direction than the adjacent second line section 56 and the gas inlets 53, 54. The first line section 57 can, for example, be designed as a pre-chamber in front of the gas inlets 53, 54. Preferably, the first line section 57 has essentially a uniform direction in the flow direction of the gas, i.e., no changes in direction. The first line section 57 can thus serve to calm the flow of the gas flowing through. The slot-shaped gas inlets 53, 54 adjoining the first line section 57 can accelerate the gas flowing into the channel 43 again, i.e., increase its flow velocity.

[0068] The protective device 40 can be made of a metallic material, for example, INVAR36. It is not necessary to use a single type of metal exclusively. For example, two or more metallic materials can be combined. In addition to metal, other materials, as well as combinations thereof, can be used to manufacture the protective device, such as plastic, glass, or ceramic. Preferably, the protective device 40 is a component manufactured using an additive manufacturing process.

[0069] In the operation of the related Fig. 1, the protective device 40 is attached to the lower boundary 18a of the exposure unit 18. Thus, the protective device 40 covers the areas of the lower boundary 18a through which no beams pass during operation of the exposure unit 18, in particular during the selective exposure of an applied layer of the build-up material. This can prevent the accumulation of contaminants in these areas of the lower boundary 18a of the exposure unit 18. The areas of the lower boundary 18a of the exposure unit corresponding to the laser modules 30 are permeable to the beams, since the protective device 40 has openings 43 at the corresponding locations. The laser radiation 19 can pass through the openings 43 of the protective device 40 and be imaged onto the working plane 7. The three-dimensional design of the channels also makes it possible to detect gas flows occurring in the process chamber, e.g.caused by the movement of the exposure unit in the process chamber, from the lower boundary 18a of the exposure unit, which can also contribute to a cleaning effect of the protective device 40.

[0070] Furthermore, during operation, gas is introduced into the openings 43 through the gas supply lines and the gas inlets 53, 54. The gas is introduced at least during the step of selectively solidifying one or more building material layers, preferably also before and / or after, and particularly preferably throughout the entire manufacturing process. The gas flowing into the openings 43 allows the areas of the lower boundary 18a, through which beams pass during operation of the exposure unit, to be kept largely free of contaminants.

[0071] The gas flows in the area of the openings or channels 43 are shown schematically in Fig. 6. A first gas partial stream 63 flows through the first gas inlet 53 into the flow channel formed by the wall 44 of the channel 43, and a second gas partial stream 64 flows through the second gas inlet 54 into the flow channel. The two gas partial streams 63, 64 exit the gas inlets 53, 54 essentially parallel to the plane of the lower boundary 18a of the exposure unit 18. At least in the region of the gas inlets 53, 54, the gas partial streams 63, 64 are preferably laminar flows. The partial gas streams 63, 64 allow a region of the flow channel formed by the wall 44 of the channel 43, adjacent to the lower boundary 18a of the exposure unit 18, to be flooded with the gas flowing in through the gas inlets 53, 54, i.e., a protective layer consisting of the introduced gas is created. This can prevent the process chamber atmosphere, which may carry contaminants, from penetrating the channels.

[0072] In general, a flow method for the exposure device 18 comprises at least one step of supplying a gas such that the gas flows out substantially parallel to a plane of the lower boundary 18a of the exposure device 18 in order to keep the lower boundary of the exposure device at least partially free of contaminants.

[0073] In particular, by supplying the gas through the two gas inlets 53, 54 into the respective channel 43, a mixing zone can be formed in the channel 43, in which the gas flowing out of the gas inlets 53, 54 mixes with a gas atmosphere prevailing in the process chamber (process chamber atmosphere). This mixing zone is formed at a distance from the lower boundary 18a of the exposure unit 18, in particular at a distance of at least 1 mm, preferably at least 2 mm, more preferably at least 3 mm.

[0074] Fig. Figure 7 schematically shows a purity level of the gas atmosphere in the area of a channel 43 and an immediately adjacent area of the process chamber 3. A purity level of 1 denotes in the illustration of the Fig. 7 a 100% portion of the process gas supplied through the gas inlets 53, 54. The degree of purity decreases with increasing mixing of the supplied process gas with the gas atmosphere prevailing in the process chamber. As in Fig. As shown in Figure 7, the area of the channel 43 immediately adjacent to the lower boundary 18a of the exposure unit 18 has a purity level of essentially 100%, i.e., essentially no gas from the process chamber, which may carry contaminants, reaches the lower boundary 18a of the exposure unit. Even at some distance (e.g., one-third of the extent of the channel from the inlet opening 43a to the outlet opening 43b) from the lower boundary 18a of the exposure unit, the purity level is still greater than 0.999990, i.e., here too, the partial gas streams 63, 64 still provide sufficient protection against penetrating contaminants. It should be noted that in Fig. 7 areas with a purity level of less than 0.999990 are shown uniformly, i.e. not further differentiated.

[0075] The mixing zone mentioned above can, for example, be reached via the Fig. 7 shown distribution of the purity level of the gas atmosphere in the area of a channel 43. In the example of Fig. 7 For example, a mixing zone can be defined as an area of the channel in which the purity of the gas atmosphere is between 0.999991 and 0.999997.

[0076] According to a study published in Fig. 6 and Fig. In the further development of the protective device 40 shown schematically in Figure 7, a circumferential edge 60 is formed on the underside 42 of the protective device 40, which protrudes from a plane of the protective device 40 toward the working plane 7. The circumferential edge 60 encloses a number of openings or channels 43, preferably a plurality of openings or channels. The circumferential edge 60 can, for example, have a flow-repellent function.

[0077] The present invention is not limited to the embodiment described with reference to the figures. Rather, modifications and further developments of the protective device and / or additive manufacturing device described with reference to the figures are possible.

[0078] In the protective device described above, the openings are formed as channels that penetrate the protective device from the top side 41 to the bottom side 42, i.e., the openings extend perpendicular to the plane of the plate-shaped protective device. However, the openings can also be formed as holes in a plate, particularly if the protective device has a smaller thickness perpendicular to the plane of the plate.

[0079] Also, in a number of the channels 43 of the protective device, only a single gas inlet, or more than two gas inlets, can be provided for introducing the gas into the flow channel formed by the wall 44. The gas inlets can, for example, also be provided on different sides of the wall forming the flow channel. The protective device can also be designed without gas inlets.

[0080] Furthermore, the protective device can be designed without the channels 43, and the protective device can have a number of gas inlets for flowing a gas to the lower boundary of the exposure device.

[0081] According to a further development, thermal energy, in particular heat, can be transferred from an area inside the exposure unit to an exterior of the exposure unit, in particular to a process chamber area outside the exposure unit facing the working plane, and / or to the escaping gas. This makes it possible, for example, to cool the exposure unit and simultaneously reduce occurring temperature differences.

[0082] Although the present invention has been described with reference to a laser sintering or laser melting device, it is not limited to laser sintering or laser melting. It can be applied to any method for the additive production of a three-dimensional object by layer-by-layer application and solidification, in particular selective solidification, of a build-up material using an exposure unit provided in the process chamber.

[0083] Any device that can selectively apply energy as wave or particle radiation to a layer of the build material can be used as an exposure unit. Instead of a laser or multiple lasers, one or more other light sources, one or more electron beams, or any other energy or radiation source suitable for solidifying the build material can be used. The invention can also be applied to selective mask sintering, in which an extended light source and a mask are used, or to high-speed sintering (HSS), in which a material is selectively applied to the build material that increases (absorption sintering) or decreases (inhibition sintering) radiation absorption at the corresponding locations, and then exposed non-selectively over a large area or using a movable line exposure unit.Furthermore, the invention is also applicable to manufacturing processes in which a layer prepared by selectively applying one or more different building materials is selectively exposed after the layer has been applied to the partially built-up component, in particular for the purpose of a pore-free connection of the applied layer to the partially built-up component.

[0084] In general, the invention can be applied to any device or method for additively manufacturing a three-dimensional object in which an exposure unit is arranged in a process chamber of the manufacturing device. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] WO 2015 / 091485 A1 [0003, 0004]

Claims

[1] Protective device for an exposure unit (18) of a manufacturing device (1) for producing a three-dimensional object (2) by selective layer-by-layer solidification of a building material (15), wherein the exposure unit (18) is arranged in a process chamber (3) of the manufacturing device, and the exposure unit (18) comprises at least two exposure units (30, 31, 32), each exposure unit generating a beam of light that can be directed at least onto one pixel in a working plane (7), and the exposure unit has, on its underside facing the working plane (7), a lower boundary (18a) that delimits the exposure unit (18) towards the working plane (7), wherein the protective device (40) can be attached to the lower boundary (18a) of the exposure unit (18), and the protective device (40) is designed to keep the lower boundary (18a) of the exposure unit at least partially free from contamination. [2] Protection device according to claim 1, comprising at least one gas inlet (53, 54) for supplying a gas, which is designed such that the gas flowing out of it exits substantially parallel to a plane of the lower boundary (18a) of the exposure unit when the protection device (40) is attached to the exposure unit (18). [3] Protection device according to claim 1 or 2, wherein the protection device is essentially designed as a cover, preferably a plate, with openings (43), wherein at each point on the cover which corresponds to a region of the lower boundary (18a) of the exposure unit (18) through which beams pass during operation of the exposure unit when the protection device (40) is attached to the exposure unit (189), exactly one opening (43) is provided, and wherein the protection device (40) preferably at least partially covers regions of the lower boundary (18a) of the exposure unit (18) through which no beams pass during operation of the exposure unit when the protection device is attached to the exposure unit. [4] Protection device according to claim 2 and 3, wherein a wall (44) of the opening (43) forms a flow channel for the flow of the gas to the lower boundary (18a) of the exposure unit, and / or wherein the gas inlet (53, 54) is substantially slit-shaped, and wherein preferably a length of the slit-shaped gas inlet extends over the entire dimension of the opening (43) in a direction parallel to the length of the slit-shaped opening, and / or wherein an opening (43) has two or more gas inlets (53, 54), and the gas inlets are arranged spaced apart from one another in a direction perpendicular to a plane of the lower boundary (18a) of the exposure unit. [5] Protection device according to claim 2 and 3, or claim 4, further comprising at least one gas supply line (50), preferably a plurality of gas supply lines, for supplying a gas to the at least one gas inlet (53, 54), and preferably distributing the gas to a plurality of gas inlets, wherein the openings (43) of the protective device are preferably arranged in cascades and a gas supply line (50) is provided between each two adjacent cascades of openings in order to supply all gas inlets of the openings of the respective cascade with gas, and / or wherein the gas supply line (50) preferably has a first end (51a) and a second end (51b) opposite the first end, and both ends are connected to a gas supply, and wherein more preferably a volume ratio of a gas supplied through the first end (51a) to a gas supplied through the second end (51b) is adjustable, in particular depending on a direction of travel (B) of the exposure unit, and / or the gas supply line has a tapered line section (52) between the first and the second end. [6] Protection device according to one of claims 2 to 5, wherein upstream of the gas inlet (53, 54) a first line section (57), preferably a pre-chamber, is provided for supplying a gas to the gas inlet and the first line section (57) has a larger cross-section perpendicular to the flow direction than the gas inlet (53, 54), and wherein preferably upstream of the first line section (57) a second line section (56) is provided, preferably a flat channel which has a smaller cross-section perpendicular to the flow direction than the first line section. [7] Protection device according to one of claims 2 to 6, wherein the at least one gas inlet (53, 54) is formed and / or the gas is supplied during operation in such a way that at least in a region of the lower boundary (18a) of the exposure unit, preferably in the region of an opening (43) of the protection device, a mixing zone is formed, in which the gas flowing out of the gas inlet (53, 54) mixes with a gas atmosphere prevailing in the process chamber (3), wherein the mixing zone is formed at a distance from the lower boundary (18a) of the exposure unit, in particular at a distance of at least 1 mm, preferably of at least 2 mm, more preferably of at least 3 mm. [8] Protection device according to one of claims 3 to 7, wherein each of the openings is designed as a channel (43) with an inlet opening (43a) facing the lower boundary (18a) of the exposure unit (18) and an outlet opening (43b) facing away from the lower boundary (18a) of the exposure unit and a wall (44) connecting the inlet opening and the outlet opening to one another, wherein the wall (44) extends substantially parallel to an envelope (33) formed from the beam bundles passing through the respective opening during operation of the exposure device (18), preferably at a distance of less than 1 mm from the envelope, and / or wherein preferably each channel (43) has a substantially frustoconical shape, and / or wherein preferably an area of the inlet opening (43a) is larger than an area of the outlet opening (43b), and / or wherein preferably a surface of the inlet opening (43a) and a surface of the outlet opening (43b) have similar shapes, in particular substantially rectangular shapes. [9] Manufacturing device (1) for producing a three-dimensional object (2) by selective layer-by-layer solidification of a building material (15), the manufacturing device comprising: a process chamber (3) in which the three-dimensional object (2) can be produced in a construction field (8) in a working plane (7), an exposure unit (18) for, preferably selectively, exposing a layer of the build material (15) applied in the build field (8), wherein the exposure unit is arranged in the process chamber (3), wherein the exposure unit (18) comprises at least two exposure units (30, 31, 32) and each exposure unit generates a beam of light that can be directed onto at least one pixel in the working plane (7), and the exposure unit has a lower boundary (18a) on its underside facing the working plane (7), which boundary delimits the exposure unit towards the working plane (7), and wherein the manufacturing device (1) further comprises a protective device (40) according to one of claims 1 to 8, which can be attached to the lower boundary (18a) of the exposure device. [10] Manufacturing device according to claim 9, wherein the exposure unit (18) is provided in the process chamber (3) so as to be movable in a direction of movement (B) over the working plane (7), and / or wherein each exposure unit (30, 31, 32) of the exposure unit (18) is individually controllable. [11] Manufacturing device according to claim 9 or 10, wherein the lower boundary (18a) of the exposure unit (18) is designed as a plate which is at least partially translucent, in particular transparent, in particular as a glass plate. [12] Manufacturing apparatus according to one of claims 9 to 11, wherein the exposure unit (18) further comprises a heating device for heating the lower boundary (18a). [13] A flow method for an exposure unit (18) of a manufacturing device (1) for producing a three-dimensional object (2) by selective layer-by-layer solidification of a building material (15), wherein the exposure unit (18) is arranged in a process chamber (3) of the manufacturing device, and the exposure unit (18) comprises at least two exposure units (30, 31, 32), each exposure unit (31) generating a beam of light that can be directed at least onto one pixel in a working plane (7), and the exposure unit has, on its underside facing the working plane (7), a lower boundary (18a) that delimits the exposure unit towards the working plane (7), and wherein preferably a protective device (40) according to one of claims 1 to 9 is attached to the lower boundary (18a) of the exposure unit, wherein the flow method comprises at least one step of supplying a gas,so that the gas flows out substantially parallel to a plane of the lower boundary (18a) of the exposure unit in order to keep the lower boundary of the exposure unit at least partially free of contaminants. [14] Method for producing a three-dimensional object by selective layer-by-layer solidification of a building material (15) in an additive manufacturing device (1), wherein the object is produced in a process chamber (3) of the manufacturing device, comprising the steps: Applying a layer of the building material in a building area (8) in a working plane (7), and Exposing the layer of the build material (15) applied in the build field (8) with an exposure unit (18), wherein the exposure unit is arranged in the process chamber (3), wherein the exposure unit (18) comprises at least two exposure units (30, 31, 32) and each exposure unit (31) generates a beam of light that can be directed onto at least one pixel in the working plane (7), and the exposure unit has a lower boundary (18a) on its underside facing the working plane (7), which boundary delimits the exposure unit towards the working plane (7), and wherein a protective device (40) according to one of claims 1 to 8 is attached to the lower boundary (18a) of the exposure unit (18), and / or wherein the production device (1) is a production device according to one of claims 9 to 12, and / or wherein at least temporarily a flow method according to claim 13 is carried out. [15] Method according to claim 14, further comprising a step of transferring thermal energy, in particular heat, within the exposure unit (18) to an exposure unit exterior, in particular to a process chamber region outside the exposure unit facing the working plane (7), and / or to the outflowing gas.

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