Process chamber for additive manufacturing device and method of operating the process chamber - Patents.com

Abstract

A process chamber housing (1) for an additive manufacturing apparatus, the process chamber having a bottom (9), a ceiling (10), and side walls (11, 12, 13) that together enclose a volume (51) of the process chamber (5), an inert gas inlet (6) at a front wall (11) of the side walls (11, 12, 13) configured to provide an inert gas to the process chamber (5), and an inert gas outlet (7) at a rear wall (12) of the side walls (11, 12, 13) configured to discharge the inert gas from the process chamber (5), provides improved beam quality if the inert gas inlet (6) and the inert gas outlet (7) are arranged on opposite sides of an opening (94) and face each other, thereby generating an inert gas flow (2) in a main flow direction (2) from the inert gas inlet (6) across the opening to the inert gas outlet (7).

Description

[Technical field]

[0001] The present invention relates to additive manufacturing by powder bed fusion. In particular, the present invention relates to a process chamber housing for an additive manufacturing apparatus. The process chamber housing has a process chamber with a bottom, a ceiling, and side walls that together enclose a volume of the process chamber. An inert gas inlet in one of the side walls, e.g., a front wall, allows for the supply of inert gas into the process chamber, and an inert gas outlet in one of the side walls, e.g., a rear wall, is provided for discharging the inert gas from the process chamber.

[0002] 2. Description of Related Art Additive manufacturing is an increasingly important method that can produce three-dimensional workpieces. There are various additive manufacturing methods, but this document focuses on methods and apparatus for bonding powder particles, for example by selectively heating the powder particles at the top surface of a powder particle bed to cause some of the particles to adhere to each other. The powder particles are attached to each other by sintering, fusion bonding, and / or welding (hereinafter, collectively, "fusion bonding"). Heat for these processes is typically provided by focused radiation, for example by an electron beam or a laser beam. These beams selectively heat parts of the upper layer of the powder bed, thereby causing the particles of the upper layer to adhere to the particles of the previously formed layer. This process is generally referred to as a powder bed fusion bonding process, or simply a powder fusion bonding process. In this document, no distinction is made between different types of radiation, and they are simply referred to as "beams."

[0003] Modern devices for powder bed fusion bonding have a housing with a process chamber. The process chamber has a support opening for accommodating a movable support. First, a thin powder layer is applied to the support. This is mainly done by a recoater (see, for example, WO 2018 / 156264, WO 2017 / 143145, EP 1234625 and DE 102006056422, to name a few). Once the layer has been beam treated, a subsequent powder layer is applied, which is then selectively fusion bonded again. This process is repeated until the additive manufacturing of the workpiece is completed. Further processing of the workpiece may still be necessary, for example grinding, cutting, milling, etc.

[0004] As taught, for example, by EP 3321003, the process chamber is advantageously filled with an inert gas. During the additive manufacturing process, the inert gas flows from a gas inlet, over the bottom surface, and then over the upper layer of powder on the support, to a gas outlet. EP 3321003 aims to create a substantially laminar flow of inert gas, thereby removing fumes, smoke, or other by-products (hereinafter collectively "fume") of the fusion bonding process. For this purpose, the inlet opening is formed from a porous material, which releases a substantially uniform flow of inert gas through the process chamber. The selection of the inert gas is described in WO 2012 / 3828, WO 2020 / 064147, WO 2020 / 064148, or WO 2020 / 126086, and specifically, an argon (Ar) or nitrogen (N2) atmosphere with an oxygen concentration of less than 1000 ppm (parts per million) is proposed. The addition of helium (He) to the inert gas atmosphere has also been proposed to enable high laser scanning speeds.

[0005] The early powder bed fusion processes had the problem of being time-consuming, and there were many attempts to reduce the production time, for example by using multiple beam sources simultaneously, and thus the costs associated with a given additively manufactured workpiece. The difficulty with this approach is that the second beam does not melt-bond any part of the powder bed while the smoke plume resulting from the operation of the first beam is located between the second beam source and the corresponding part of the powder bed without significantly compromising the quality of the workpiece. Such smoke plumes appear to deform, absorb and scatter the beam, and thus many concepts have been developed to avoid melt-bonding parts of the powder bed that are shadowed by the smoke plume resulting from scanning the powder bed with other beams (see, for example, WO 2016 / 075026 or WO 2020 / 178216).

[0006] Summary of the Invention The problem to be solved by the present invention is to improve powder bed processes.

[0007] The solution to this problem is set forth in the independent claims. The dependent claims relate to further developments of the invention.

[0008] The process chamber housing has a process chamber with a bottom, a ceiling, and a sidewall. The bottom, the ceiling, and the sidewall together enclose the volume of the process chamber. In a preferred embodiment, at least one inert gas inlet is provided in the front wall of the sidewall and configured to supply inert gas into the volume of the process chamber. At least a portion of the inert gas supplied to the volume can be removed via at least one inert gas outlet in the rear wall of the sidewall, and thus the inert gas outlet is configured to discharge the inert gas from the process chamber. Alternatively or additionally, the gas inlet and / or the gas outlet may be provided in the ceiling, the bottom, different sidewalls, or the same sidewall. The gas inlet and the gas outlet may preferably be located on opposite sides of the process chamber.

[0009] The bottom surface may have an opening. The opening may be defined by an opening wall. Preferably, a vertically movable support for supporting the powder bed, and thus the three-dimensional (3D) object produced by selective powder bed fusion, may be located between the opening walls. As already clear, the support is preferably movably supported within the opening. For example, the support may be retracted further into the opening (i.e., lowered, assuming a horizontal support surface) before adding a new powder layer to the powder bed.

[0010] The aperture wall may be and / or may provide a linear bearing that limits movement to a direction at least substantially perpendicular to the edge formed by the transition between the bottom surface and the aperture wall. At least substantially perpendicular means that it is preferably perpendicular, but can tolerate small deviations, for example deviations of less than 1°, 2.5°, 5° and / or 10°. The aperture wall may enclose a space, for example a box or a cylinder. This space can accommodate the already fused portion of the powder bed. The aperture wall may be configured to be removable from the process chamber housing. This allows the aperture walls to be easily replaced with a set of empty walls after the workpiece has been produced.

[0011] Preferably, the inert gas inlet and the inert gas outlet are arranged on opposite sides of the opening and face each other. This therefore makes it possible to provide a main inert gas flow in the main flow direction by ejecting the inert gas from the (first) inert gas inlet during removal of the inert gas from the volume via the (first) inert gas outlet, or in other words by providing a pressure gradient from the inert gas inlet to the inert gas outlet. This main inert gas flow is preferably at least substantially parallel to the bottom surface and / or the upward facing surface of the optional support. The main inert gas flow may include an upward or downward component. In a preferred example, the direction of the main inert gas flow has a non-vanishing component parallel to the bottom surface and / or the support. This non-vanishing component provides a direction in which the smoke plume generated when scanning the powder bed with the beam is inclined with respect to the vertical.

[0012] In a preferred example, the gas inlet is connected to an inert gas source that provides an inert gas containing He. The inert gas source is preferably configured to supply an inert gas that contains at least helium (He) and one of other noble gases (i.e., at least one of neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), radon (Rn)) and / or nitrogen (N2). The inert gas source is configured to supply the inert gas containing He from the inert gas source into the volume of the process chamber. Particularly preferably, the inert gas source supplies a gas containing He and / or Ne in at least one percentage of 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%, 98%, 99%, where the percentage relates to the molar amount of He and / or Ne, respectively, relative to the total molar amount of gas.

[0013] It has been unexpectedly found that by replacing Ar or N2 with He and / or Ne, a portion of the powder bed can be melt-bonded by a second beam emitted by a second beam source when smoke generated by a first beam emitted by a first beam source is located between the beam outlet of the second beam source and the portion of the powder bed to be melt-bonded. Thus, in one embodiment, the invention comprises melt-bonding a powder bed using at least two beams while at least one second beam is controlled to melt-bond a portion of the powder bed covered by a smoke plume resulting from melt-bonding another portion of the powder bed by another beam (at least one first beam), where the smoke plume is removed from the process chamber by a main inert gas flow, where the main inert gas flow comprises at least 20% He and / or Ne and / or 1.4 kg / m 3 , 1.2kg / m 3 , 1kg / m 3 , 0.6kg / m 3 , 0.4kg / m 3 , and 0.2 kg / m 3The main inert gas flow is generated by an inert gas having a density less than the density of at least one of the densities of the powder bed. The density is preferably based on normal conditions (0° C., 1013 hPa), but may also be based on the actual conditions in the process chamber. In other words, at least one second beam source operates downstream of the beam spot of another beam source, where downstream refers to the main inert gas flow direction above the powder bed. Covered is intended to express the presence of a smoke plume in the beam path of at least one second beam. As already mentioned, the beam source is preferably, but not limited to, a laser beam source. The use of the term "laser beam" or "laser beam source" in this specification should be understood as a preferred example of "beam" or "beam source". In operation, the beam source may be swiveled to scan the positions to be fused on the powder bed. For example, a mirror swiveled to project a laser beam to the aforementioned positions on the powder bed can be considered as a beam source even if this beam is not generated by the mirror itself. In such applications, the location of the beam towards a location on the powder bed is important, not the type of beam or the beam generator.

[0014] Contrary to any teachings of the prior art, the replacement of at least a portion of the Ar and / or N2 with He and / or Ne allows the manipulation of the smoke plume resulting from the scanning of a portion of the powder bed by a first beam. Moreover, studies have revealed that the smoke in these plumes has a relatively low effect on the quality of the fusion bonded area fusion bonded by penetrating the plume produced by another beam. As is evident from these observations, the thermally induced density changes in the plume lead to distortion of the laser beam, which leads to defocusing of an otherwise well-focused beam and / or changes in the beam profile and / or changes in the beam intensity distribution across the beam profile. The reduced density of He and / or Ne combined with the increased thermal conductivity of He and / or Ne results in a lower density gradient between the hot and cold parts of the inert gas flow, which in turn reduces the effects of defocusing. The beneficial effect of reducing the laser beam distortion due to thermal inhomogeneities in the inert gas flow can be further enhanced by reducing the amount of gas in the volume, i.e., by operating the process chamber at a pressure lower than ambient pressure. By lowering the pressure significantly, it is also possible to use Ar and / or N2 as the inert gas (or simply use air), i.e. omitting He and / or Ne. An additional advantage of lowering the pressure (i.e. reducing the amount of gas molecules in the volume) is that the flow rate of the inert gas stream can be increased without the powder particles previously deposited in the powder bed being displaced (blown away) by the inert gas stream.

[0015] Particularly preferably, the inert gas has a thermal conductivity at normal conditions (0°C, 1013 hPa) of at least one of 0.15 W / m·K, 0.1 W / m·K, 0.05 W / m·K, 0.025 W / m·K, and 0.02 W / m·K, and / or at conditions within the process chamber of at least one of 0.15 W / m·K, 0.1 W / m·K, 0.05 W / m·K, 0.025 W / m·K, and 0.01 W / m·K.

[0016] In a preferred example, the inert gas flow may have a flow velocity in the main flow direction, the average flow velocity measured at 1013 hPa and 0.5 cm above the opening being higher than 0.75 m / s, preferably higher than 1 m / s, and / or lower than 4 m / s, preferably lower than 3 m / s, more preferably lower than 2.5 m / s. These boundaries may preferably be raised if the gas pressure in the volume of the process chamber is reduced and / or if the molar mass of the gas is reduced.

[0017] In a preferred example, the process chamber has at least one oxygen sensor and / or gas density sensor and / or thermal conductivity sensor and / or heat capacity sensor configured to measure values ​​representative of the thermal conductivity and / or heat capacity of the inert gas, respectively. At least one of these sensors is preferably located in the bottom part of the volume. For example, at least one of these sensors may be located on the bottom surface and / or in a recess in the bottom surface and / or at a distance of less than 5 cm above the bottom surface and / or on the support and / or below the support and / or within at least one of the following distances of 10 cm, 5 cm, 2.5 cm, 1 cm, 0.5 cm from the edge surrounding the opening. In another example, at least one of these sensors is preferably located in the (first) inert gas outlet, preferably in the bottom surface of the (first) inert gas outlet and / or within at least one of the following distances of 10 cm, 5 cm, 2.5 cm, 1 cm, 0.5 cm from the edge surrounding the (first) inert gas outlet. Each of these exemplary locations allows the measurement of the oxygen concentration in the vicinity of the powder bed. If He (4u) and / or Ne (10u) are used as inert gases (usually u is the unified atomic mass unit), oxygen will accumulate at the bottom of the volume since it has a higher mass per molecule (16u). Potential leaks or impurities originating from gas sources can therefore be quickly detected. Moreover, the measurement is as representative as possible of the oxygen level immediately above the powder bed. Additionally or alternatively, at least one of the sensors may be located in a duct connecting at least one inert gas outlet to at least one inert gas inlet.

[0018] At least one oxygen sensor and / or gas density sensor and / or thermal conductivity sensor and / or heat capacity sensor is preferably located in the inert gas flow through the chamber, and particularly preferably each sensor is oriented at least substantially parallel to the inert gas flow, where at least substantially parallel means that parallel is preferred, but deviations within a few degrees (e.g., ±30°, ±20°, ±10°, ±5°, ±2.5°, ±1° or 0°) are acceptable.

[0019] At least one oxygen sensor and / or gas density sensor is preferably connected to a process chamber control device, i.e., to an electronic circuit for controlling the operation of the process chamber and / or to the entire additive manufacturing apparatus comprising the process chamber (hereinafter simply "controller"). In particular, for example, if the oxygen level is above a predetermined threshold, the controller may increase the flow rate of the inert gas flow above the opening, for example, by increasing the power supplied to the vacuum pump connected to the inert gas outlet and / or by opening a throttle valve upstream of the inert gas inlet. Furthermore, prior to powder bed fusion bonding, the process chamber is preferably filled with inert gas. When the oxygen level falls below a predetermined threshold, an inert gas pump may be used to circulate the inert gas from the inert gas outlet to the inert gas inlet, thereby forming an inert gas flow.

[0020] In a preferred example, the process chamber may have a gas component concentration sensor configured to measure a value representative of at least one of the concentrations of O2, N2, He, Ne, Ar, Kr, Xe, Rn and / or a value representative of the ratio of at least two of these gases in the inert gas. The gas component sensor may be located at the position described above for the oxygen sensor or may have a gas inlet at the position. The above-mentioned sensors may be considered as examples of gas component concentration sensors. In other words, the gas component concentration sensor may be or may include at least one of an oxygen sensor and / or a gas density sensor and / or a thermal conductivity sensor and / or a heat capacity sensor and / or a gas chromatograph and / or a spectrometer and / or a gas analyzer, in particular a He analyzer. It should be further noted that if the total pressure is known, the partial pressure values ​​of O2, N2, He, Ne, Ar, Kr, Xe, Rn may be considered to represent at least one of the concentrations of these gases. Therefore, a simple yet effective way to measure the concentration is to measure the partial pressure of at least one of these gases, for example by the diffusion rate through a semipermeable membrane. For example, if the semipermeable membrane is permeable only to He, the diffusion rate through the membrane at a given pressure difference between the spaces separated by the membrane can be used to measure the partial pressure of He in the inert gas.

[0021] The gas constituent concentration sensor is preferably connected to the process chamber control device by a data line, so that values ​​obtained by the gas constituent concentration sensor may be available to the process chamber control device.

[0022] In any embodiment, the method may include supplying at least a portion of the inert gas removed through the inert gas outlet to the process chamber through the inert gas inlet, also referred to as recycling or circulating the inert gas.

[0023] Thus, a method for melt bonding at least a portion of a powder bed may include controlling the composition of an inert gas flow generated above the powder bed.

[0024] The method may include measuring the concentration and / or partial pressure of at least one of O2, N2, He, Ne, Ar, Kr and Xe in the inert gas stream generated above the powder by detecting the concentration and / or partial pressure of at least one of O2, N2, He, Ne, Ar, Kr and Xe in the inert gas present in the process chamber and / or removed from the process chamber via at least one inert gas outlet and / or provided to the process chamber via the inert gas inlet. The method may further include obtaining a measurement representative of the concentration and / or partial pressure of at least one of O2, N2, He, Ne, Ar, Kr and Xe in the inert gas and comparing the measurement to lower and / or upper limit values ​​for the concentration and / or partial pressure of each of at least one of N2, He, Ne, Ar, Kr and Xe in the inert gas. It should be noted that O2 is not inert and therefore should not be included in the inert gas. However, monitoring of unintentional O2 concentration can be used to increase the concentration of the inert components of the inert gas, thereby reducing the partial pressure and concentration of O2, which can be viewed as effectively removing unintentional O2 from the process chamber and thus from the fusion bonding process.

[0025] If the aforementioned comparison indicates that the measured value is less than the lower limit, the method may include the step of adding a corresponding reduced component to the inert gas stream in the process chamber, for example by circulating the inert gas stream from the inert gas outlet to the inert gas inlet through the process chamber, while not adding or adding only a relatively small amount of at least one other component of the inert gas mixture to the inert gas mixture. In this context, "relatively small" refers to the amount of the reduced component, i.e., the amount of at least another added component added is less than the amount of the reduced component added.

[0026] Similarly, if the comparison indicates that the measured value exceeds the upper limit, the method may include adding at least one component other than the component having a measured value exceeding the upper limit to the inert gas in the process chamber, for example by adding the other component to the inert gas flow supplied from the inert gas outlet through a duct to the inert gas inlet (and thus into the process chamber), while not adding or adding only relatively little of the component having a measured value exceeding the upper limit. As above, "relatively little" refers to the amount of the at least one other component added. In other words, the at least one other component is added in a larger amount than the component having a measured value exceeding the upper limit.

[0027] This method allows partial and selective replenishment of only those components of the inert gas that are shown to be insufficient in a given composition as defined by the upper and lower limits of each component. This helps to keep the operating costs low while maintaining a high quality of the workpiece. Such method steps are based on the consideration that for practical purposes, the inert gas is often substantially a mixture of He and / or Ne with Ar and / or N2, where the concentrations of He, Ne, Ar, and N2 in the mixture are well defined. However, He and Ne diffuse through the duct walls and other defining structures of the process chamber housing at a significantly high rate. Thus, this method allows the partial pressure of He and / or Ne in the inert gas and / or the concentration of He and / or Ne to be maintained within the defined limits, while not replacing the inert gas depleted of He and / or Ne from the process chamber by (expensive) "new" inert gas. For example, values ​​representing the concentrations (and / or partial pressures) of He and / or Ne are measured, and if a decrease in He and / or Ne below the respective lower limits is observed, then only He and / or Ne is added to the inert gas circulating through the process chamber housing. Such an approach can also be used for all other inert gases mentioned above, i.e., the correction of He and / or Ne decrease is merely a preferred example. All other decreases can also be eliminated by adding the decreased component, preferably only.

[0028] These steps of controlling the composition of the inert gas flow generated above the powder bed may be performed by a process chamber control device, also referred to as a “controller.” In other words, the process chamber control device may be configured to perform any of the above-mentioned method steps directly or by controlling and / or communicating with corresponding components, such as gas component concentration sensors.

[0029] The corresponding process chamber housing may therefore have a process chamber control device. The process chamber control device may be connected to at least one gas component concentration sensor, for example via a data line and / or any other data transmission means. Such a gas component concentration sensor may be located in the process chamber. Alternatively or additionally, this (or another) gas component concentration sensor may be located in and / or attached to and / or integrated into a duct connecting an inert gas outlet to an inert gas inlet.

[0030] The process chamber may further comprise an inert gas component supply source that contains only one component or only a limited number of components of the inert gas in the process chamber. For example, the inert gas component supply source may contain only He and / or Ne, but no Ar or N2, if the inert gas is a mixture of three gases in total. In practice, it is sufficient if the concentration of the reduced inert gas component in the gas provided by the inert gas component supply source is higher than the preset or intended concentration of the reduced component in the inert gas, because in this case, the addition of the gas mixture from the inert gas component supply source increases the concentration of the reduced component in the inert gas circulating through the process chamber and the duct connecting the inert gas outlet to the inert gas inlet.

[0031] The process chamber may have two or more inert gas component sources, each containing a different inert gas component and / or containing different inert gas mixtures.

[0032] Typically, a "limited number of components" means that at least one component of the (intended) inert gas mixture is not included or is insufficient in the inert gas component source. The inert gas component source may be fluidly connected to the inert gas inlet via at least one inert gas component valve or to a separate gas inlet, for example via a branch of a duct. Fluid connection via a duct is preferred, since it results in a uniform concentration of the components of the inert gas supplied to the process chamber. In other words, the inert gas in the process chamber has a more uniform composition.

[0033] The process chamber control device may be connected to the inert gas component valve, for example via at least one control line and / or a contactless data connection, to open and close the inert gas component valve.

[0034] In another preferred example, the process chamber includes a heater configured to heat the temperature of at least a portion of the inert gas flow through the process chamber to at least one of 25° C., 40° C., 60° C., 80° C., 100° C., 150° C., 250° C., 300° C., 350° C., 400° C., 450° C., 500° C., 600° C., 700° C., 800° C., 900° C., 1000° C. or higher. When higher temperatures are used, the process chamber housing is preferably thermally insulated. Such an increase in gas temperature reduces the temperature gradient in the plume and therefore reduces, if not negligibly small, the beam distortion of the plume.

[0035] As already mentioned above, the process chamber preferably comprises a pressure control device configured to maintain the pressure inside the process chamber below the ambient pressure outside the process chamber and / or below at least one of the following pressures: 1000 hPa, 900 hPa, 800 hPa, 700 hPa, 600 hPa, 500 hPa, 400 hPa, 300 hPa, 200 hPa, 100 hPa. The pressure control device may be integrated into the process chamber control device or may form part of the process chamber control device. In another preferred example, the pressure in the process chamber is higher than the ambient pressure, thereby ensuring that oxygen is not accidentally sucked into the process chamber. In another example, the process chamber is contained in a separate housing, the pressure in the process chamber is lower than the ambient pressure, while the pressure in the volume defined by the boundary between the process chamber and the separate housing is higher than the ambient pressure, the gas in this volume also being an inert gas, preferably the same as in the process chamber. This allows the volume between the boundary of the process chamber and the separate housing to be filled with an inert gas having a pressure higher than ambient pressure, thereby reducing the risk of oxygen being accidentally drawn into the process chamber while ensuring a low pressure in the process chamber.

[0036] For example, the inert gas outlet may be fluidly connected to a low pressure side inlet of a gas pump (e.g., a vacuum pump inlet), for example via the ducts described above, and / or the inert gas inlet may be fluidly connected to an inert gas supply (e.g., a high pressure side gas outlet of a gas pump), with a throttle valve disposed upstream of the inert gas inlet. The optional pressure controller may be configured to increase and / or decrease the power supplied to the gas pump. Furthermore, the pressure controller may be configured to open and / or close the throttle valve, for example by supplying power to an actuator. The optional pressure controller may therefore also control the flow rate of the inert gas flow. The optional pressure controller may be connected to at least one pressure sensor and / or flow rate sensor, and may control the pressure and / or flow rate in the process chamber in response to a signal provided by at least one of the pressure sensor and / or flow rate sensor.

[0037] Changes in the inert gas may affect the signal provided by the flow rate sensor and / or the pressure sensor. Such effects may require a recalibration of the sensor if the inert gas is changed during the production of the workpiece or between the production of two workpieces. For example, if an inert gas with increased heat capacity and / or increased thermal conductivity is used, the anemometer for measuring the flow rate may require a recalibration. For example, if the thermal conductivity of the inert gas is increased, the hot wire anemometer will have better cooling. Thus, if the increased thermal conductivity is not taken into account, the resistivity of the hot wire will decrease, which will likely directly lead to erroneous flow rate readings. Similarly, if a vane or cup anemometer is used, changes in the (average) molar mass and / or density of the inert gas may also require a recalibration of the flow rate sensor.

[0038] In a preferred example, the process chamber further comprises at least one second gas outlet provided on at least one of the bottom surface, the support, the opening wall, and the bottom surface of the opening. The second gas outlet may be used when replacing a gas (mixture) such as air with at least one of an inert gas, for example He and / or Ne and / or Ar and / or N2, which may then be preferably provided to the volume via at least one second inert gas inlet in the ceiling. The use of expensive He and / or Ne or other inert gases can be reduced by each of these measures.

[0039] The optional second gas outlet may be connected to a second gas outlet control valve, preferably a check valve configured to prevent gas from flowing into the process chamber through the second gas outlet. Further, the second gas outlet may be connected to a gas inlet of the second outlet vacuum pump via a tube or the like.

[0040] As already mentioned, the process chamber preferably comprises at least one (laser) beam entrance window, which may be located above the support. In a particularly preferred embodiment, the process chamber further comprises at least one inert gas jet inlet nozzle. As will be described in more detail below, the term "jet" is used only to indicate that this gas flow is a linguistically distinct second gas flow that flows above the inert gas flow. The inert gas jet inlet nozzle is preferably located in the upper part of the process chamber and is preferably oriented to provide an inert gas jet between the window and the support. Particularly preferably, the inert gas jet is attached to the window surface and / or directed downwards. This is obtained by orienting the inert gas jet inlet nozzle in such a way, for example by directing it towards the window surface and / or by utilizing the Coanda effect.

[0041] Preferably, at least one inert gas jet outlet nozzle may be located opposite the inert gas jet inlet nozzle and is therefore well positioned to provide an inert gas jet between the window and the support.

[0042] The inert gas jet counteracts the effect that smoke tends to rise higher in a reduced density atmosphere. The inert gas jet protects the window from contamination by condensed or sublimated smoke, which may degrade the beam quality and therefore the workpiece quality. Thus, the proposed measure allows to keep the vertical dimensions of the volume reasonable, which reduces the operating and installation costs, but ultimately reduces the quality of the workpiece, not least because the increased distance between the laser source and the powder makes imperfections in the beam focusing more apparent, which reduces the quality of the workpiece.

[0043] For example, at least one inert gas jet inlet nozzle is angled at an angle α from a parallel orientation to the (first) inert gas inlet. js and a nozzle outlet opening oriented within α js ∈A, A={30°, 20°, 10°, 5°, 2.5°, 1°, 0.5°, 0°}. By such measures, turbulence within the volume is reduced and therefore the efficiency of smoke removal from the volume is increased.

[0044] Preferably, the flow velocity of the inert gas jet relative to the window is at least 1.1, 1.25, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 7.5 and / or 10 times the flow velocity of the inert gas stream 0.5 cm above the opening. This increased flow velocity thus provides a flow velocity gradient from the base to the ceiling that allows for safe removal of fumes without blowing powder from the powder bed towards the inert gas outlet.

[0045] In a preferred example, the temperature of at least one optional inert gas jet is lower than the temperature of the main inert gas flow measured at least at the corresponding nozzle opening, so that residues in the smoke can condense before reaching the window, and residues in the smoke do not condense, or at least only to a small extent, on the window.

[0046] In another example, the temperature of at least one optional inert gas jet is higher than the temperature of the main inert gas flow, at least measured at the corresponding nozzle opening. This allows the powder bed to be efficiently cooled by the main inert gas flow, which preferably flows at least approximately directly above the powder bed. This is obtained by positioning the lower edge of the (first) inert gas inlet and / or the lower edge of the (first) inert gas outlet at the level of the edge of the support opening and / or at the level of the bottom surface or slightly above these levels. Slightly above means within at least one of the following heights above the corresponding reference height: 0.5 cm, 1 cm, 1.5 cm, 2 cm, and / or 2.5 cm. Furthermore, the temperature of the main (first) inert gas flow from the (first) inert gas inlet to the (first) inert gas outlet is preferably below ambient temperature, for example at least one of the following temperatures: 23° C., 20° C., 18° C., 10° C., 0° C., -5° C., -10° C., -20° C. The lower the temperature, the better the cooling, i.e., the better the heat transfer from the powder bed and / or workpiece to the main inert gas flow. The temperature of the inert gas jet may preferably be at or above ambient temperature, e.g., at or above at least one of 25°C, 40°C, 60°C, 80°C, 100°C, 150°C, 250°C, 300°C, 350°C, 400°C, 450°C. This particularly preferred combination of having a reduced temperature near the powder bed and an increased temperature above provides both good cooling and low beam distortion.

[0047] Furthermore, it is preferred if the vertical thickness of the main inert gas flow or streams of the main inert gas is significantly smaller than the vertical thickness of the inert gas jet above the main inert gas flow. The vertical thickness of each stream can be adjusted, for example, by the vertical dimension of each inlet opening. Thus, the vertical dimension d2 of the inert gas jet inlet is preferably at least x times the vertical dimension d1 of the (first) inert gas inlet, where x∈{1.5, 2, 2.5, 5, 10, 15}, i.e. x·d1≦d2.

[0048] As is clear, the main inert gas flow from the inert gas inlet nozzle to the inert gas outlet nozzle and the inert gas jet are both "inert gas flows", and the terms main inert gas flow and inert gas jet are used only to make them linguistically distinct. Alternatively, the terms first gas flow and second gas flow can be used, but the first proposed term is considered to be clearer. As is clear, in a preferred example, the second inert gas flow (i.e. the inert gas jet) has a higher flow velocity throughout the volume than the first (main) inert gas flow. The flow rate of the second inert gas flow may be higher than the first (=main) inert gas flow. The word "main" therefore has no relevance with respect to the amount of gas flowing per unit time compared to the other inert gas flow.

[0049] The additive manufacturing apparatus according to the invention may of course be characterized in that it comprises a process chamber having at least one of the above mentioned features. In particular, the additive manufacturing apparatus may have one laser beam entry window and at least two (laser) beam sources each configured to emit at least one (laser) beam on the powder bed on the upper surface of the support outside the process chamber in front of the at least one window. It goes without saying that the windows are at least substantially transparent to the beams emitted by the (laser) beam sources through the at least one window to the support. In a preferred example, the additive manufacturing apparatus is configured to scan the surface of the powder bed below the plume generated by the operation of the first (laser) beam source. Such measures may also improve the workpiece quality, for example by optimizing the thermal stresses on the workpiece during production.

[0050] Description of the drawings The invention will be explained below by way of example, without limiting the general inventive concept, on the basis of several examples of embodiments in connection with the drawings. [Brief description of the drawings]

[0051] [Figure 1] FIG. 1 illustrates an exemplary process chamber of an additive manufacturing apparatus. [Diagram 2] FIG. 1 illustrates another exemplary process chamber of an additive manufacturing apparatus.

[0052] In FIG. 1, a simplified cross-sectional view of an exemplary additive manufacturing apparatus 1 having a process chamber 5 is shown. The process chamber 5 has a volume 51 bounded by side walls 11, 12, 13 (a fourth side wall is not visible), a ceiling 10, and a bottom surface 9. The bottom surface 9 has an opening 94 with an opening wall 93. The opening wall 93 may provide a linear bearing for a movably supported, liftable support 8. On top of the support 8, there may be an optional powder bed 99, within which a partially manufactured workpiece 4 may be embedded. The powder bed 99 and workpiece 4 are shown by way of example only, although the additive manufacturing apparatus 1 and / or process chamber 5 are typically delivered without a powder bed or a workpiece.

[0053] The ceiling 10 has windows 101, 102 that are transparent to the beams 81, 91 emitted by the beam sources 80, 90. A first beam source 80 and a second beam source 90 are shown emitting a first beam 81 and a second beam 91, respectively. Preferably, the process chamber 5 has three or more beam sources 80, 90. The windows 101, 102 may be integral, so that at least one window is provided above the opening 94 in the bottom surface.

[0054] The (first) inert gas inlet 6 in the front wall 11 and the (first) inert gas outlet 7 in the rear wall 12 make it possible to provide a main inert gas flow 20 across the opening 94 in the bottom surface 9, i.e. in the main inert gas flow direction 2. As can be seen, the main inert gas flow 20 is at least substantially parallel to the bottom surface 9 (i.e. ±α ms (α ms ∈{30°, 20°, 10°, 5°, 2.5°, 1°, 0.5°, 0°}), and thus at least substantially parallel to the powder bed surface and the powder bed support surface of the support 8. In the illustrated example, the main inert gas flow direction 2 has a small downward component. Preferably, the inert gas comprises at least 20% helium (He) and / or has a flow rate of 1.4 kg / m 3and / or a temperature above the dew point temperature of the gas. In one example, the pressure can be equal to or greater than ambient pressure. In another example, the pressure can be equal to or less than ambient pressure.

[0055] Above the main inert gas inlet 6 is at least one optional second inert gas inlet 256 and at least one optional third inert gas inlet 266. Above the main inert gas outlet 7 is at least one optional second inert gas outlet 257, which may also be referred to as an inert gas jet inlet or an inert gas jet outlet, respectively.

[0056] In operation, a second inert gas stream may flow above the main (first) inert gas stream from at least one optional second inert gas inlet 256 to at least one optional second inert gas outlet 257. As indicated by arrow 25, the volume per time, i.e., the flow rate and / or flow velocity, of the optional second inert gas stream 25 is preferably higher than the flow rate and / or flow velocity, respectively, of the main inert gas stream 20. Furthermore, the downward component of the flow direction of the second inert gas flow direction 252 is preferably greater than the downward component of the main inert gas flow direction 2. The temperature of the second inert gas stream 25 is preferably lower than the temperature of the main inert gas stream 20.

[0057] The optional third inert gas inlet 266 is preferably located proximate (within 10 cm, 5 cm, 2.5 cm and / or 1 cm) of the at least one window 101, 102 in the ceiling 10 and is positioned to deposit a third inert gas flow onto a surface of the at least one window 101, 102, thereby contributing to keeping the at least one window 101, 102 free of condensation. Preferably, the temperature of the inert gas leaving the third inert gas inlet is higher than the temperature of the second inert gas entering the volume 51 from the at least one second inert gas inlet 256.

[0058] As shown, each beam 81, 91 is directed at a different location on the powder bed 99, and the fusion bonding process generates first and second plumes 82, 92. As shown, the second beam 91 passes through the first plume 82, which is created by the interaction of the first beam 81 with the powder bed 99.

[0059] The inert gas is removed by at least one pump 32, i.e. the first and second inert gas outlets 7, 257 are in fluid communication with the low pressure inlets of the gas pump 32, which then supplies the inert gas to at least one of the inert gas inlets 6, 256, 266 via duct 33. The temperatures of the different inert gas streams can preferably be controlled by optional indirect heat exchangers 201, 251, 261.

[0060] Data and / or power lines may connect the controller 3 to the beam sources 80, 90, sensors 30, pump 32, valves 38, etc. Example connections are indicated by dashed or dotted arrows.

[0061] FIG. 2 shows another simplified cross-sectional view of an exemplary additive manufacturing apparatus 1 with a process chamber 5. The description of FIG. 1 can also be read with respect to FIG. 2. Here, only the differences are described. As in FIG. 1, at least one of the inert gas outlets 7 and 257 of the process chamber 5 may be connected to at least one of the inert gas inlets 6, 256, 266 via a duct 33. The pump 32 may have a pump inlet in fluid communication with at least one of the inert gas outlets 6, 25, and the pump outlet may be in fluid communication with at least one of the inert gas inlets 6, 256, 266 via a duct 33. The duct may have a gas composition sensor 30. The values ​​measured by the gas composition sensor 30 may be supplied to the control device 3 by several data lines or any other communication means, regardless of its location. The control device may be referred to as the process chamber control device 3.

[0062] The process chamber housing preferably includes at least one of these gas composition sensors 30. In Figure 2, two gas composition sensors 30 are shown in preferred locations for illustrative purposes, although other numbers of gas composition sensors may be used.

[0063] The process chamber housing may further include at least one inert gas component supply 34. In one example, the inert gas component supply 34 may include a tank filled or configured to be filled with, for example, He and / or Ne or other inert gas or inert gas mixture.

[0064] The inert gas component source 34 is fluidly connected to at least one of the inert gas inlets 6, 256, 266 via an inert gas component valve 36.

[0065] The controller 3 is preferably configured to monitor the concentration and / or partial pressure of at least one of He and Ne in the inert gas in the process chamber 5 and / or duct 33 based on at least one measurement value. Such measurement value may be derived from at least one of the at least one inert gas component sensors 30. If the concentration of He and Ne in the inert gas in the process chamber 5 decreases below a predefined lower limit value, the controller may be configured to open the inert gas component valve 36, for example for a predetermined period of time. This period may be calculated based on the difference between the lower limit value and the measurement value. By opening the inert gas component valve 36, the inert gas being supplied to the process chamber may be supplied with the reduced inert gas component. This allows the concentration of the reduced component, in this example He and / or Ne, to be corrected. Similarly, if the measured concentration of another component of the inert gas in the process chamber 5 and / or duct is above an upper limit value, the controller may open the inert gas component valve 36, thereby reducing the concentration of the component having a concentration above the upper limit value. The process chamber may have multiple inert gas component supplies 34 filled with different inert gases and corresponding inert gas component valves 36 to selectively replenish depleted inert gas components. [Explanation of symbols]

[0066] 1 Additive manufacturing equipment 2 Main inert gas flow direction 3. Control device / process chamber control device 4. Workpiece / raw material bonding area 5. Process chamber 6 Gas inlet 7 Gas outlet 8 Support 9 Bottom 10. Ceiling 101 Window 102 Window 11 First side wall 12 Second side wall 13 Third Sidewall 20 Main inert gas flow 201 Heat exchanger 25 Second inert gas stream (inert gas jet) 251 Heat exchanger 252 Direction of second inert gas flow 256 Second inert gas inlet 257 Second inert gas outlet 26 Third inert gas stream 261 Heat exchanger 266 Third inert gas inlet 30 Gas component sensor, for example, an oxygen sensor and / or a gas density sensor and / or a gas component concentration sensor 32 Pump 33 Duct 34 Inert gas component supply source 35 Heater 36 Inert gas component valve 50 Recoater 80 First Beam Source 81 First beam / First laser beam 82 First Smoke Pillar 90 Second Beam Source 91 Second Beam / Second Laser Beam 92 Second Smoke Pillar 93 Opening Wall 94 Support opening in bottom surface 9, configured to receive support 8 99 Powder bed

Claims

**Claim 1**: An additive manufacturing apparatus having at least a first beam source (80) configured to emit at least a first beam (81), at least a second beam source (90) configured to emit at least a second beam (91), and a process chamber housing (1), wherein the process chamber housing (1) has a process chamber (5), and the process chamber (5) has at least the following components: A bottom surface (9), a ceiling (10), and side walls (11, 12, 13) that together surround the volume (51) of the process chamber (5); An inert gas inlet (6) configured to supply an inert gas into the process chamber (5); An inert gas outlet (7) configured to discharge the inert gas from the process chamber (5). It has, The bottom surface (9) has an opening (94) defined by a plurality of opening walls (93), and a vertically movable support (8) for supporting a three-dimensional object (4) disposed between the powder bed (99) and the plurality of opening walls (93), and The gas inlet (6) is configured to supply a lightweight inert gas having a density of less than 1.4 kg / m ３ into the process chamber (5). In the additive manufacturing apparatus, The additive manufacturing apparatus is controlled to, at least, Generate a first smoke column (82) by melting and bonding a first position of the powder bed (99) using the first beam (81), and Generate a second smoke column (92) by melting and bonding a second position of the powder bed (99) using the second beam (91). It is provided with a process chamber control device (3) configured to execute a melting and bonding step. Here, the first position is closer to the inert gas inlet (6) than the second position, the second position is closer to the inert gas outlet (7) than the first position, and the at least one second beam (91) is controlled to melt-bond the second position of the powder bed (99) covered by the first smoke column (82) generated by melting and bonding the first position of the powder bed (99) with the at least one first beam (81). The inert gas inlet (6) and the inert gas outlet (7) are configured to remove the smoke columns (82, 92) from the process chamber (5) by a main inert gas flow, and the main inert gas flow is generated by an inert gas containing at least 20% of He and / or Ne. An additive manufacturing apparatus, characterized by the above.

2. The inert gas inlet (6) and the inert gas outlet (7) are arranged on opposite sides of the process chamber and / or the opening (94), whereby an inert gas flow (2) in the main flow direction (2) from the inert gas inlet (6), over the opening (94), and to the inert gas outlet (7) is generated. The additive manufacturing apparatus according to claim 1.

3. The inert gas flow in the main flow direction (2) has a flow velocity, and the average flow velocity measured 0.5 cm above the opening (94) is greater than 0.75 m / s and / or less than 4 m / s. The additive manufacturing apparatus according to claim 1.

4. The process chamber (5) has at least one gas component concentration sensor, and at least one of the at least one gas component concentration sensor (30) is on the bottom surface and / or in a recess of the bottom surface and / or below a distance of 5 cm above the bottom surface and / or On and / or below the support, and / or At least one or within at least one of 10 cm, 5 cm, 2.5 cm, 1 cm, 0.5 cm from the edge on the bottom surface surrounding the opening (94), and / or Within a duct (33) connecting the inert gas outlet (7) to the inert gas inlet (6), The additive manufacturing apparatus according to claim 1, which is arranged.

5. The process chamber housing further has at least one inert gas component supply source (34) fluidly connected to the inert gas inlet (6) of the process chamber (5) via an inert gas component valve (36), the additive manufacturing apparatus according to claim 4.

6. The process chamber (5) is provided with a heater (35) configured to heat at least a part of the temperature of the inert gas flow passing through the process chamber to at least one temperature among 25°C, 40°C, 60°C, 80°C, 100°C, 150°C, 250°C, 300°C, 350°C, 400°C, 450°C, the additive manufacturing apparatus according to claim 1.

7. The inert gas outlet (7) is in fluid communication with a vacuum pump, and / or the inert gas inlet (6) is in fluid communication with an inert gas supply source, and a throttle valve is arranged upstream of the inert gas inlet, the additive manufacturing apparatus according to claim 1.

8. The process chamber: At least one second gas outlet provided on at least one of the bottom surface, the support, the opening wall, and the bottom surface of the opening, and / or At least one second inert gas inlet provided on the ceiling The additive manufacturing apparatus according to claim 1, further comprising.

9. The second gas outlet is connected to a second gas outlet control valve, preferably a check valve configured such that gas cannot flow into the process chamber through the second gas outlet, and / or The second gas outlet is connected to the gas inlet of a second outlet vacuum pump, The additive manufacturing apparatus according to claim 8.

10. The process chamber housing (1) further comprises at least one beam entry window located above the opening (94), and optionally, At least one inert gas jet inlet nozzle arranged to supply an inert gas jet between the window and the support, and / or At least one inert gas jet outlet nozzle arranged to supply an inert gas jet between the window and the support The additive manufacturing apparatus according to claim 1, further comprising.

11. The at least one inert gas jet inlet nozzle has a nozzle outlet opening directed within an angle α from a direction parallel to the inert gas inlet, said α ｊｓ within, said α ｊｓ is ∈A, where A = {30°, 20°, 10°, 5°, 2.5°, 1°, 0.5°, 0°}, the additive manufacturing apparatus according to claim 10.

12. At least two beam sources of the additive manufacturing apparatus are arranged in front of the at least one beam entry window, Outside the process chamber (5), the at least two beam sources are each configured to emit at least one beam onto a powder bed (99) on the upper surface of the support (8). The additive manufacturing apparatus according to claim 10.

13. A method for fusing and bonding at least a part of a layer of a powder bed (99), comprising at least: Radiating at least two different beams (81, 91) that generate smoke columns (82, 92) respectively at at least two different positions of the powder bed (99) from at least two different beam sources (80, 90); Removing the smoke columns (82, 92) by generating a main inert gas flow from an inert gas inlet (6) to an inert gas outlet (7), wherein the main inert gas flow has a direction of a component parallel to the powder bed, and a first position where a first beam (81) from a first beam source (80) hits is closer to the inert gas inlet (6) than a second position where a second beam (91) from a second beam source (90) hits, and the second position is closer to the inert gas outlet (7) than the first position; Fusing and bonding the second position of the powder bed (99) by the second beam (91) from the second beam source (90), wherein at least a part of the first smoke column (82) exists between the second beam source (90) and the second position, and the density of the inert gas flow is 1.4 kg / m ３ or less under standard conditions and / or at a distance of 20 mm above the layer; Including, and the inert gas flow is generated by an inert gas containing at least 20% of He and / or Ne.

14. The method further includes providing an additive manufacturing apparatus according to any one of Claims 1 to 12, and / or The distance between the first position and the second position is smaller than at least one of 100 mm, 70 mm, 40 mm, 30 mm, 20 mm, and 10 mm, and / or The distance between the first position and the second position is less than at least one of 100 mm, 70 mm, 40 mm, 30 mm, 20 mm, 10 mm, and the time interval between the moment when the first beam and the second beam are radiated to the first position and the second position is less than at least one of 10%, 20%, 30%, 40%, 50%, 60%, 70%, and 80% of the maximum period during which the first beam (81) or the second beam (91) is radiated onto the layer, and / or The generated inert gas stream contains at least one percentage of He among 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%, 98%, 99%, and these percentages relate to the molar amount of He and / or Ne relative to the total amount of the gas, The method according to claim 13, characterized in that.

15. The generated inert gas stream has a temperature of at least one of 25°C, 40°C, 60°C, 80°C, 100°C, 150°C, 250°C, 300°C, 350°C, 400°C, 450°C or higher, the method according to claim 13.

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