Method of operating an irradiation system, irradiation system and apparatus for producing three-dimensional workpieces with polarization control

Abstract

In a method of operating an irradiation system (10) for irradiating layers of a raw material powder with laser radiation to produce a three-dimensional workpiece (110), linearly polarized laser radiation is selectively irradiated to at least a portion of a layer (11) of the raw material powder applied to a carrier (102). An orientation of a plane of polarization of the linearly polarized laser radiation is controlled in dependence on an orientation of an incident plane of the linearly polarized laser radiation on the raw material.

Description

Technical Field

[0001] This invention relates to a method of operating an irradiation system for producing three-dimensional workpieces by irradiating multiple layers of raw material powder with laser radiation. Furthermore, this invention relates to such an irradiation system. Finally, this invention relates to an apparatus for producing three-dimensional workpieces. Background Technology

[0002] Powder bed melting is a layered additive manufacturing process that can process powdered, particularly metallic and / or ceramic, raw materials into complex three-dimensional workpieces. To do this, layers of raw material powder are applied to a carrier and then laser-irradiated in a site-selective manner according to the desired geometry of the workpiece to be produced. The laser radiation penetrating the powder layers heats the raw material powder particles, thus causing melting or sintering. Further layers of raw material powder are then sequentially applied to the laser-treated layers on the carrier until the workpiece has the desired shape and dimensions. Based on CAD data, powder bed melting can be used to produce or repair prototypes, tools, replacement parts, high-value components, or medical prostheses, such as dental or orthopedic implants.

[0003] An exemplary apparatus for producing three-dimensional workpieces by powder bed melting, as described in WO 2019 / 141381 A1, includes: a carrier configured to receive multiple layers of raw material, and an irradiation unit configured to selectively irradiate laser radiation onto the raw material on the carrier to produce the workpiece. The irradiation unit is provided with a spatial light modulator configured to split a laser beam into at least two sub-beams. To provide a linearly polarized laser beam to the spatial light modulator, a polarization device for performing the linear polarization of the laser beam is provided upstream of the spatial light modulator.

[0004] When constructing a three-dimensional workpiece on a carrier in a powder bed fusion apparatus, the absorption of laser radiation impacting the raw material powder causes the powder to melt and / or sinter, thereby creating a molten pool of raw material. Furthermore, the evaporation of the raw material leads to the formation of a vapor capillary through which the laser beam penetrates deeper into the raw material. Summary of the Invention

[0005] The object of this invention is to provide a method for operating an irradiation system and such an irradiation system for producing three-dimensional workpieces by irradiating multiple layers of raw material powder with laser radiation. This method and irradiation system allow for the efficient production of high-quality workpieces. Furthermore, this invention relates to an apparatus for producing three-dimensional workpieces, equipped with an irradiation system that allows for the efficient production of high-quality workpieces.

[0006] In a method of operating an irradiation system for producing three-dimensional workpieces by irradiating a layer of raw material powder with laser radiation, at least a portion of the raw material powder layer applied to a carrier is selectively irradiated with linearly polarized laser radiation. The raw material powder layer can be applied to the surface of the carrier by a powder application device that moves through the carrier to distribute the raw material powder. The carrier can be a rigidly fixed carrier. However, preferably, the carrier is designed to be vertically displaceable, such that as the workpiece is constructed from layers of raw material powder, the carrier can move downwards in the vertical direction as the construction height of the workpiece increases. Furthermore, the carrier can be provided with cooling and / or heating devices, configured as a cooling and / or heating carrier.

[0007] The carrier and powder application device can be housed in a sealing chamber that is airtight to the surrounding atmosphere. An inert gas environment can be established within the processing chamber by introducing airflow through a gas inlet. After being guided through the processing chamber and across the layer of raw material powder applied to the carrier, the airflow can exit from the processing chamber through a gas outlet. The raw material powder applied to the carrier within the processing chamber is preferably a metal powder, particularly a metal alloy powder, but it can also be a ceramic powder or a powder containing different materials. The powder can have any suitable particle size or particle size distribution. However, it is preferable to process powders with a particle size of less than 100 μm.

[0008] An irradiation system may include a laser beam source that emits at least one linearly polarized laser beam. Specifically, the laser beam source of the irradiation system may emit linearly polarized laser light with a wavelength of 532 nm, i.e., “green” laser light. However, it is also conceivable that the laser beam source of the irradiation system emits at least one randomly polarized (i.e., unpolarized) laser beam, which is converted into a linearly polarized laser beam by a suitable polarization device (e.g., a polarizer or polarization beam splitter cube). If the laser beam is split into two or more partial beams with different polarizations using one or more beam splitter cubes, only one partial beam can be used as the irradiation beam while blocking the other partial beams. Alternatively, one or more partial beams may be directed to different irradiation systems in one or more additive manufacturing apparatuses. Additionally or alternatively, one or more partial beams may be modified, particularly their polarization may be changed. Additionally or alternatively, multiple beams may be modified to obtain the same polarization and may be combined before being co-directed to the irradiation system.

[0009] An irradiation system can irradiate a raw material powder layer with a single laser beam. However, it is also conceivable that the irradiation system irradiates the raw material powder layer with two or more laser beams. In the case where the irradiation system irradiates the raw material powder layer with two or more laser beams, at least one laser beam can be a linearly polarized laser beam, and at least one additional laser beam can be a randomly polarized laser beam, a radially polarized laser beam, and / or an azimuth-polarized laser beam. The multiple laser beams irradiated onto the raw material powder layer by the irradiation system can be emitted by suitable sub-units of a laser beam source.

[0010] The irradiation system may also include at least one optical unit for splitting, guiding, and / or processing at least one laser beam emitted by a laser beam source. The optical unit may include optical elements, such as objective lenses and scanner units, the scanner unit preferably including diffractive optical elements and deflecting mirrors.

[0011] In the method of operating the irradiation system, the orientation of the polarization plane of the linearly polarized laser radiation is controlled according to the orientation of the incident plane of the linearly polarized laser radiation on the raw material. The term "polarization plane" as used herein refers to the plane defined by the propagation vector of the incident laser beam and the electric field vector of the electromagnetic laser wave, and therefore coincides with the vibration plane of the electric field of the electromagnetic laser wave. The term "incident plane" as used herein refers to the plane defined by the propagation vector of the incident laser beam and the surface normal extending perpendicularly to the surface of the raw material impacted by the incident laser beam.

[0012] The orientation of the polarization plane of linearly polarized laser radiation relative to the incident plane of the laser radiation on the raw material has a strong influence on the absorption of laser energy by the raw material. Therefore, by controlling the orientation of the polarization plane according to the incident plane of the linearly polarized laser radiation on the raw material, the absorption of linearly polarized laser energy by the raw material can be controlled.

[0013] By considering and actively controlling the absorption of laser energy by raw materials, improved process stability can be achieved in the production of three-dimensional workpieces. Furthermore, by increasing laser energy absorption in a controllable manner, process productivity can be improved. Therefore, high-quality workpieces can be produced in a particularly efficient way. Moreover, materials such as Cu and Cu alloys, which are currently difficult to process by laser or sintering / melting, can be made processable by irradiating the corresponding raw material powder with linearly polarized laser radiation, while controlling the orientation of the polarization plane of the linearly polarized laser radiation according to the orientation of the incident plane of the linearly polarized laser radiation on the raw material.

[0014] In a preferred embodiment of the method for operating the irradiation system, the orientation of the polarization plane of the linearly polarized laser radiation is controlled according to the orientation of the incident plane of the linearly polarized laser radiation on the raw material, such that the polarization plane is oriented substantially parallel to the incident plane. In other words, the orientation of the polarization plane of the linearly polarized laser radiation is controlled relative to the orientation of the incident plane of the linearly polarized laser radiation on the raw material to achieve a p-pol state.

[0015] In the p-pol state, the absorption of linearly polarized laser radiation by the raw material is typically higher than that in the s-pol state, where the polarization plane extends perpendicular to the incident plane. Furthermore, the absorption of linearly polarized laser radiation in the p-pol state is also typically higher than that of randomly polarized laser radiation. Therefore, by controlling the orientation of the polarization plane relative to the incident plane to achieve the p-pol state, the absorption of laser energy can be increased in a controllable manner.

[0016] Preferably, the orientation of the polarization plane of the linearly polarized laser radiation is controlled according to the orientation of the incident plane of the linearly polarized laser radiation on the inner wall surface of the capillary. The capillary extends from the surface of the raw material powder layer into the volume of the raw material powder layer and is formed due to the interaction between the linearly polarized laser radiation and the raw material. The capillary can be a vapor capillary, which is formed by the evaporation of the raw material heated by absorbing the energy of the laser beam impacting the raw material layer. The size and shape of the capillary can depend on at least one parameter of various parameters (e.g., the power of the incident laser beam, the focal diameter, and the focal shape), the scanning speed and scanning direction of the laser beam, and / or the airflow guided through the raw material powder layer, to establish a controlled atmospheric environment in the processing chamber and remove particulate impurities (e.g., splatter particles, smoke particles, or soot particles) generated during the irradiation of the raw material powder.

[0017] A laser beam irradiating a raw material powder layer enters a capillary and strikes the inner wall surface of the capillary, which has an orientation different from the upper surface of the raw material powder layer. For example, the inner wall surface of the capillary struck by the laser beam may extend at an angle of approximately 45° to 90°, preferably approximately 60° to 80°, relative to the upper surface of the raw material powder layer, which is generally oriented substantially parallel to the surface of the carrier on which the raw material powder layer is applied. By taking into account the orientation of the incident plane of the linearly polarized laser radiation on the inner wall surface of the capillary, formed by the interaction between the laser beam and the raw material, when controlling the orientation of the polarization plane of the linearly polarized laser radiation, particularly reliable and precise control over the absorption of laser energy by the raw material can be achieved.

[0018] A change in the scanning direction of the laser beam on the raw material powder layer typically leads to a change in the orientation of the incident plane of the linearly polarized laser radiation on the raw material. Therefore, when controlling the orientation of the polarization plane of the linearly polarized laser radiation based on the orientation of the incident plane of the linearly polarized laser radiation on the raw material, the orientation of the polarization plane of the linearly polarized laser radiation is preferably updated according to the scanning direction of the linearly polarized laser radiation on the raw material powder layer.

[0019] To update the orientation of the polarization plane of linearly polarized laser radiation, a polarization device, such as a waveplate, particularly a half-waveplate, can be rotated. Alternatively, a collimator, positioned downstream of the polarization device in the optical path of the laser emitted from the radiation beam source, can be rotated. Furthermore, at least one deflector, particularly a pair, can be used to deflect the linearly polarized laser beam as needed. Alternatively, two pairs of deflectors can be used to deflect the linearly polarized laser beam: one pair for rotating the polarization plane and the other for deflecting the beam. In a preferred embodiment, mirrors with a metallic coating (e.g., aluminum, silver, gold, etc.) are used.

[0020] The orientation of the polarization plane of linearly polarized laser radiation, which is guided through a layer of raw material powder, can be updated based on analysis of the scanning pattern. By analyzing the scanning pattern, the variation in the scanning direction of the laser beam across the raw material powder layer can be determined. Therefore, the orientation of the polarization plane of the linearly polarized laser radiation can be updated as needed and synchronized with the operation of the scanner unit, which scans the laser beam across the raw material powder layer. The analysis of the scanning pattern can be performed before the start of 3D workpiece production and / or in situ during 3D workpiece production.

[0021] The absorption of energy from linearly polarized laser radiation by a raw material is strongly dependent on the angle of incidence of the laser beam on the material. In the p-pol state, absorption increases with increasing angle of incidence, at least for angles of incidence between approximately 10 and 80°. The term "angle of incidence" as used herein refers to the angle between the propagation vector of the incident laser beam and the surface normal extending perpendicularly to the surface of the raw material struck by the incident laser beam.

[0022] To selectively irradiate the raw material powder layer, i.e., to allow the laser beam to scan across the raw material powder layer, the laser beam is deflected relative to the surface normal extending perpendicular to the upper surface of the raw material powder layer. Therefore, the incident angle depends on the deflection angle of the incident laser beam relative to the surface normal extending perpendicular to the upper surface of the raw material powder layer, and thus on the operating state of the scanner unit. Furthermore, the incident angle depends on the orientation of the raw material surface struck by the incident laser beam.

[0023] Besides the incident angle of the linearly polarized laser beam, many other process parameters can affect the absorption of laser energy by the raw material. These parameters can include the power, focal diameter, and focal shape of the linearly polarized laser beam. Furthermore, the scanning pattern, scanning speed, (front or back) scanning mode, and scanning direction by which the laser beam is guided through the raw material powder layer can influence the absorption of laser energy by the raw material. Additionally, the airflow guided through the processing chamber and across the surface of the raw material powder layer, particularly the volumetric flow rate and velocity, as well as the type of gas, can affect absorption.

[0024] Therefore, in a preferred embodiment of the method of operating the irradiation system, at least one of the power, focal diameter, and focal shape of the linearly polarized laser beam is controlled according to the incident angle of the linearly polarized laser beam on the raw material, and / or at least one of the scanning pattern, scanning speed, scanning mode, and scanning direction on which the linearly polarized laser beam is guided through the raw material powder layer, and / or at least one parameter of the airflow guided through the raw material powder layer.

[0025] By correlating the incident angle of a linearly polarized laser beam with one or more other process parameters that affect the absorption of laser energy by the raw material, highly reliable control over absorption can be achieved, and overheating of the raw material can be avoided. Furthermore, process efficiency can be improved. For example, a reduction in absorption caused by a decrease in laser power and / or an increase in scanning speed can be compensated for by increasing absorption at an appropriate incident angle. Moreover, for a specific raw material, the energy applied to the material can be increased in a controlled manner by appropriately controlling the incident angle, for example, to allow for the processing of these materials.

[0026] A linearly polarized laser beam can be scanned on a raw material powder layer using the following scanning strategy: before scanning at least one scanning vector pointing in a second vector direction different from the first vector direction, multiple scanning vectors pointing in the first vector direction are scanned sequentially. The scanning vector pointing in the first vector direction v1 can be scanned "forward" in direction +v1 and "backward" in direction -v1 without changing the orientation of the polarization plane of the linearly polarized laser radiation. Similarly, the scanning vector pointing in the second vector direction v2 can be scanned "forward" in direction +v2 and "backward" in direction -v2 without changing the orientation of the polarization plane of the linearly polarized laser radiation. Therefore, the orientation of the polarization plane of the linearly polarized laser radiation only needs to be changed when the vector direction, i.e., the direction of vector extension, is changed. Using this scanning strategy, the "update times" of the orientation of the polarization plane of the linearly polarized laser radiation can be reduced. Therefore, the update process can be simplified.

[0027] In embodiments of the method for operating the irradiation system, a first portion of the raw material powder layer can be selectively irradiated with linearly polarized laser radiation, and a second portion of the raw material powder layer can be selectively irradiated with random laser radiation, radially polarized laser radiation, and / or azimuthally polarized laser radiation. The second portion may be a part of the raw material powder layer intended to be irradiated according to a scanning strategy that requires frequent and / or rapid updates to the orientation of the polarization plane of the linearly polarized laser radiation. For example, the second portion may be a part of the raw material powder layer intended to be irradiated according to a scanning pattern comprising high-density short scan vectors and / or scan vectors pointing in multiple directions, and / or intended to be irradiated at a high scan rate.

[0028] Specifically, the first part of the raw material powder layer can be a hatch portion of the workpiece layer produced by selectively irradiating the raw material powder layer. The second part of the raw material powder layer can be a contour portion of the workpiece layer produced by selectively irradiating the raw material powder layer. Therefore, the advantages of irradiating the raw material powder layer with linearly polarized laser radiation as described above can be achieved in the hatch portion, which typically forms most of the workpiece layer. At the same time, difficulties that may arise when updating the orientation of the polarization plane in the contour portion can be avoided.

[0029] In another embodiment of the method for operating the irradiation system, multiple linearly polarized laser beams can be scanned over the overlapping portion of the raw material powder layer according to a scanning strategy in which all scan vectors are scanned according to the same scanning mode. The term "overlapping portion" as used herein defines a portion of the raw material powder layer that can be irradiated by more than one laser beam. For example, in the overlapping portion of the raw material powder layer, all scan vectors are scanned according to a later scan mode or a previous scan mode. Therefore, in the overlapping portion, the absorption of laser radiation by the raw material is not affected by the scanning mode and can thus be controlled more reliably.

[0030] An irradiation system for producing three-dimensional workpieces by irradiating a layer of raw material powder with laser radiation is configured to selectively irradiate at least a portion of the raw material powder layer applied to a carrier with linearly polarized laser radiation. The irradiation system includes a control device configured to control the orientation of the polarization plane of the linearly polarized laser radiation based on the orientation of the incident plane of the linearly polarized laser radiation on the raw material.

[0031] The control device of the irradiation system can be configured to control the orientation of the polarization plane of the linearly polarized laser radiation based on the orientation of the incident plane of the linearly polarized laser radiation on the raw material, such that the polarization plane is oriented substantially parallel to the incident plane. Therefore, a p-pol state can be achieved.

[0032] The control device can also be configured to control the orientation of the polarization plane of the linearly polarized laser radiation based on the orientation of the incident plane of the linearly polarized laser radiation on the inner wall surface of the capillary, which extends from the surface of the raw material powder layer into the volume of the raw material powder layer and is formed due to the interaction between the linearly polarized laser radiation and the raw material.

[0033] Furthermore, when the control device controls the orientation of the polarization plane of the linearly polarized laser radiation based on the orientation of the incident plane of the linearly polarized laser radiation on the raw material, it can be configured to update the orientation of the polarization plane of the linearly polarized laser radiation based on the scanning direction of the linearly polarized laser radiation as it scans through the raw material powder layer.

[0034] Specifically, the control device can be configured to update the orientation of the polarization plane of the linearly polarized laser radiation based on an analysis of a scanning pattern according to which the linearly polarized laser radiation beam is guided through the raw material powder layer. The analysis of the scanning pattern can be performed before the start of production of the three-dimensional workpiece and / or in situ during production.

[0035] The control device can also be configured to control at least one of the power, focal diameter, and focal shape of the linearly polarized laser beam based on the incident angle of the linearly polarized laser beam on the raw material, and / or at least one of the scanning pattern, scanning speed, scanning direction, and scanning mode on which the linearly polarized laser beam is guided through the raw material powder layer, and / or at least one parameter of the airflow guided through the raw material powder layer.

[0036] Alternatively or additionally, the control device may be configured to control the scanner unit such that the linearly polarized laser radiation beam scans the raw material powder layer according to a scanning strategy in which multiple scanning vectors pointing to the first vector direction are scanned consecutively before scanning at least one scanning vector pointing to a second vector direction different from the first vector direction.

[0037] Furthermore, the control device can be configured to control the irradiation system such that a first portion of the raw material powder layer is selectively irradiated with linearly polarized laser radiation, and a second portion of the raw material powder layer is selectively irradiated with random laser radiation, radially polarized laser radiation, and / or azimuthally polarized laser radiation.

[0038] The first part of the raw material powder layer can be the filling portion of the workpiece layer produced by selectively irradiating the raw material powder layer. The second part of the raw material powder layer can be the contour portion of the workpiece layer produced by selectively irradiating the raw material powder layer.

[0039] The control device can also be configured to control the scanner unit such that multiple linearly polarized laser radiation beams are scanned over the overlapping portion of the raw material powder layer according to a scanning strategy in which all scanning vectors are scanned according to the same scanning mode.

[0040] An apparatus for producing three-dimensional workpieces is equipped with the aforementioned irradiation system. Attached Figure Description

[0041] Preferred embodiments of the invention will be described in more detail with reference to the accompanying drawings, in which:

[0042] Figure 1 An apparatus for producing three-dimensional workpieces by irradiating multiple layers of raw material powder with laser radiation is shown.

[0043] Figure 2 for Figure 1 The irradiation system used in the equipment;

[0044] Figure 3 The diagram illustrates the interaction between a linearly polarized laser beam and the raw material.

[0045] Figure 4 The study shows the dependence of the absorption of laser radiation by the raw material on the polarization state of the laser radiation and the incident angle of the laser beam on the raw material. Detailed Implementation

[0046] Figure 1 An apparatus 100 for producing three-dimensional workpieces using a layered additive manufacturing process is shown. The apparatus 100 includes a carrier 102 and a powder application device 104 for applying raw material powder to the carrier 102. The carrier 102 and the powder application device 104 are housed within a processing chamber 106, which is sealable from the surrounding atmosphere. The carrier 102 can be vertically displaced into a constructed cylinder 108 such that the carrier 102 can move downwards as the structural height of the workpiece 110 increases, since the workpiece is constructed layer by layer from the raw material powder on the carrier 102. The carrier 102 may include a heater and / or a cooler.

[0047] The device 100 also includes an irradiation system 10 for selectively irradiating laser radiation onto a layer 11 of raw material powder applied to a carrier 102. Figure 1In the embodiment of the illustrated device 100, the irradiation system 10 includes two laser beam sources 12a, 12b, each configured to emit a laser beam 14a, 14b. Optical units 16a, 16b are associated with each of the laser beam sources 12a, 12b for guiding and processing the laser beams 14a, 14b emitted by the laser beam sources 12a, 12b. However, it is also conceivable that the irradiation system 10 may be equipped with only one laser beam source and one optical unit, and thus emit only a single laser beam. A control device 18 is provided to control the operation of the irradiation system 10 and other components of the device 100 (e.g., powder application device 104).

[0048] A controlled gas environment, preferably an inert gas environment, is established within the processing chamber 106 by supplying a protective gas to the processing chamber 106 via the processing gas inlet 112. After being guided through the processing chamber 106 and passing through the raw material powder layer 11 applied to the carrier 102, the gas exits the processing chamber 106 via the processing gas outlet 114. The flow direction of the protective gas from the processing gas inlet 112 through the processing chamber 106 to the processing gas outlet 114 is indicated by arrow F. The processing gas can be recirculated from the processing gas outlet 114 back to the processing gas inlet 112, and thus can be cooled or heated.

[0049] During operation of the equipment 100 for producing three-dimensional workpieces, a raw material powder layer 11 is applied to a carrier 102 by a powder application device 104. To apply the raw material powder layer 11, the powder application device 104 moves traversing the carrier 102 under the control of a control device 18. Then, again under the control of the control device 18, the raw material powder layer 11 is selectively irradiated with laser radiation by an irradiation device 10 according to the geometry of the corresponding layer of the workpiece 110 to be produced. The steps of applying the raw material powder layer 11 to the carrier 102 and selectively irradiating the raw material powder layer 11 with laser radiation according to the geometry of the corresponding layer of the workpiece 110 to be produced are repeated until the workpiece 110 achieves the desired shape and size.

[0050] At least one of the laser beams 14a and 14b irradiating the raw material powder layer 11 by the irradiation system 10 is a linearly polarized laser radiation beam. A more detailed description of the laser beam source 12a and the optical unit 16a is as follows: Figure 2As shown. Laser beam source 12a emits linearly polarized laser light, such as a laser with a wavelength of 450 nm, i.e., a "blue" laser, or a laser beam with a wavelength of 532 nm, i.e., a "green" laser, or a laser with a wavelength in the range of 1000 nm to 1090 nm or in the range of 1530 nm to 1610 nm, such as an "infrared" laser. Polarization device 20 is used for rotating the polarization plane and can be designed, for example, as a rotatably mounted waveplate, particularly a half-wave plate. The linearly polarized laser beam (i.e., laser beam 14a) scans the raw material powder layer 11 through scanner unit 22.

[0051] The laser energy introduced into the raw material powder by the impact of the laser beam 14a onto the raw material powder layer 11 causes the raw material powder to melt and / or sinter. Specifically, a molten pool of raw material is generated in the region where the laser beam 14a impacts the raw material powder. Furthermore, vapor capillaries 24 are formed due to the evaporation of the raw material heated by absorbing the energy of the laser beam 14a impacting the raw material. Figure 3 As shown.

[0052] The laser beam 14a penetrates the capillary 24 and impacts the inner wall surface 26 of the capillary 24, which has a different orientation than the upper surface 28 of the raw material powder layer 11. Figure 3 In the exemplary embodiment shown, the inner wall surface 26 of the capillary struck by the laser beam is at an angle of approximately 75° to 80° relative to the upper surface 28 of the raw material powder layer 11, which is oriented substantially parallel to the surface of the support member 102. extend.

[0053] exist Figure 3 In the exemplary embodiment shown, the laser beam 14a scans the raw material powder layer 11 in the scanning direction indicated by arrow S in the forward scanning mode. The incident plane of the laser beam 14a on the raw material (i.e., on the inner wall surface 26 of the capillary 24) is defined by the propagation vector P of the laser beam 14a and the surface normal N extending perpendicularly to the raw material surface struck by the laser beam 14a. The incident angle α is defined between the propagation vector P of the laser beam 14a and the surface normal N.

[0054] During the operation of the irradiation system 10, the control device 18 controls the orientation of the polarization plane of the linearly polarized laser beam (i.e., laser beam 14a) based on the orientation of the incident plane of the linearly polarized laser beam (i.e., laser beam 14a) on the raw material. Specifically, the control device 18 controls the orientation of the polarization plane of the linearly polarized laser beam (i.e., laser beam 14a) based on the orientation of the incident plane of the linearly polarized laser beam (i.e., laser beam 14a) on the inner wall surface 26 of the capillary 24.

[0055] from Figure 4It is evident that the orientation of the polarization plane of the linearly polarized laser radiation relative to the incident plane of the linearly polarized laser radiation on the raw material has a significant impact on the absorption of laser energy by the raw material. In the p-pol state, defined by the orientation of the polarization plane of the linearly polarized laser beam (i.e., laser beam 14a), which is parallel to the orientation of the incident plane of the linearly polarized laser radiation on the raw material, the absorption of laser energy by the raw material is higher than that in the s-pol state, which is defined by the orientation of the polarization plane of the linearly polarized laser beam (i.e., laser beam 14a), which is perpendicular to the orientation of the incident plane of the linearly polarized laser radiation on the raw material. In the p-pol state, the absorption of laser energy by the raw material is also higher than that of the randomly polarized laser beam. Therefore, the control device 18 controls the orientation of the polarization plane of the linearly polarized laser beam (i.e., laser beam 14a) according to the orientation of the incident plane of the linearly polarized laser beam (i.e., laser beam 14a) on the raw material, so that the polarization plane is substantially parallel to the incident plane, i.e., achieving the p-pol state.

[0056] The change in the scanning direction S of the laser beam 14a as it passes through the raw material powder layer 11 causes a change in the orientation of the incident plane of the linearly polarized laser beam (i.e., laser beam 14a) on the raw material. Therefore, when the control device 18 controls the orientation of the polarization plane of the linearly polarized laser beam (i.e., laser beam 14a) based on the orientation of the incident plane of the linearly polarized laser beam (i.e., laser beam 14a) on the raw material, it updates the orientation of the polarization plane of the linearly polarized laser beam (i.e., laser beam 14a) based on the scanning direction S of the laser beam 14a as it passes through the raw material powder layer 11.

[0057] exist Figure 2 In the exemplary arrangement, the orientation of the polarization plane of the linearly polarized laser beam (i.e., laser beam 14a) is updated by appropriately rotating the polarization device 20. The control device 18 performs the update of the polarization plane orientation of the linearly polarized laser beam (i.e., laser beam 14a) based on the analysis of the scanning pattern, according to which the linearly polarized laser beam (i.e., laser beam 14a) is guided through the raw material powder layer 11. The analysis of the scanning pattern can be performed before the start of production of the three-dimensional workpiece 110 and / or in situ during the production of the three-dimensional workpiece 110.

[0058] To simplify the updating of the polarization plane orientation of the linearly polarized laser beam (i.e., laser beam 14a), the linearly polarized laser beam (i.e., laser beam 14a) is scanned across the raw material powder layer 11 according to a scanning strategy in which multiple scanning vectors pointing to the first direction are scanned consecutively before at least one scanning vector pointing to a second direction different from the first direction is scanned. This scanning strategy reduces the number of changes in the scanning direction S, and thus reduces the number of rotations of the polarization device 20 that must be performed to update the polarization plane orientation of the linearly polarized laser beam (i.e., laser beam 14a).

[0059] Figure 4 The illustration further illustrates that the absorption of energy from linearly polarized laser radiation by the raw material largely depends on the incident angle α of the laser beam 14a on the raw material. The incident angle α, in turn, depends on the deflection angle of the laser beam 14a relative to the surface normal extending perpendicular to the upper surface 28 of the raw material powder layer 11, and thus on the operating state of the scanner unit 22. Furthermore, the incident angle α depends on the orientation of the raw material surface struck by the laser beam 14a. In the p-pol state, and at least for incident angles α between approximately 10° and 80°, absorption increases with increasing incident angle α. The relationship between absorption, incident angle, and polarization may also be material-dependent and temperature-dependent.

[0060] In order to reliably control the absorption of laser energy by the raw material, the control device 18, when controlling the operation of the irradiation system 10, considers many other process parameters that may affect the absorption of laser energy by the raw material, in addition to the incident angle α of the linearly polarized laser beam (i.e., laser beam 14a). Specifically, the control device 18 controls at least one of the power, focal diameter, and focal shape of the linearly polarized laser beam (i.e., laser beam 14a), and / or at least one of the scanning pattern, scanning speed, scanning mode, and scanning direction S on which the linearly polarized laser beam (i.e., laser beam 14a) is guided through the raw material powder layer 11, and / or at least one parameter of the airflow guided through the raw material powder layer 11, based on the incident angle α of the linearly polarized laser beam (i.e., laser beam 14a) on the raw material.

[0061] The laser beam source 12b and optical unit 16b can have the same design as the laser beam source 12a and optical unit 16b, such that the laser beam 14b is also a linearly polarized laser beam. In this case, the control device 18 controls the operation of the irradiation system 10 so that the linearly polarized laser beams (i.e., laser beams 14a, 14b) scan the overlapping portion of the raw material powder layer 11 according to a scanning strategy in which all scanning vectors are scanned according to the same scanning mode. In particular, in the overlapping portion of the raw material powder layer 11, all scanning vectors are scanned according to a rear scanning mode or a front scanning mode to eliminate the influence of the scanning mode on the absorption of laser energy by the raw material.

[0062] However, it is also conceivable that the laser beam source 12b and optical unit 16b are configured to emit random laser beams, radially polarized laser beams, and / or azimuth-polarized laser beams. In this case, a first portion of the raw material powder layer 11 can be selectively irradiated with linearly polarized laser radiation, and a second portion of the raw material powder layer 11 can be selectively irradiated with random laser radiation, radially polarized laser radiation, and / or azimuth-polarized laser radiation. Specifically, the first portion of the raw material powder layer 11 can be a filling portion of a workpiece layer produced by selectively irradiating the raw material powder layer 11, and the second portion of the raw material powder layer 11 can be a contour portion of a workpiece layer produced by selectively irradiating the raw material powder layer 11.

Claims

1. A method of operating an irradiation system (10) for producing a three-dimensional workpiece (110) by irradiating multiple layers of raw material powder with laser radiation, wherein at least a portion of the raw material powder layer (11) applied to a carrier (102) is selectively irradiated with linearly polarized laser radiation, and wherein, The orientation of the polarization plane of the linearly polarized laser radiation is controlled based on the orientation of the incident plane of the linearly polarized laser radiation on the raw material. The orientation of the polarization plane of the linearly polarized laser radiation is controlled according to the orientation of the incident plane on the inner wall surface (26) of the capillary (24). The capillary extends from the surface (28) of the raw material powder layer (11) into the volume of the raw material powder layer (11) and is formed due to the interaction between the linearly polarized laser radiation and the raw material.

2. The method according to claim 1, in, The orientation of the polarization plane of the linearly polarized laser radiation is controlled according to the orientation of the incident plane of the linearly polarized laser radiation on the raw material, so that the polarization plane is oriented substantially parallel to the incident plane.

3. The method according to claim 1, in, When controlling the orientation of the polarization plane of the linearly polarized laser radiation according to the orientation of the incident plane of the linearly polarized laser radiation on the raw material, the orientation of the polarization plane of the linearly polarized laser radiation is updated according to the scanning direction (S) of the linearly polarized laser radiation scanning through the raw material powder layer (11).

4. The method according to claim 3, in, The orientation of the polarization plane of the linearly polarized laser radiation is updated based on the analysis of the scanning pattern, and the linearly polarized laser radiation beam is guided through the raw material powder layer (11) according to the scanning pattern, wherein the analysis of the scanning pattern is performed before the start of production of the three-dimensional workpiece (110) and / or in situ during the production of the three-dimensional workpiece (110).

5. The method according to claim 1, in, The power, focal diameter, and focal shape of the linearly polarized laser beam are controlled based on the incident angle (α) of the linearly polarized laser beam on the raw material, and / or at least one of the scanning pattern, scanning speed, scanning direction (S), and scanning mode on which the linearly polarized laser beam is guided through the raw material powder layer (11), and / or at least one parameter of the gas flow guided through the raw material powder layer (11).

6. The method according to claim 1, in, The linearly polarized laser radiation beam scans the raw material powder layer (11) according to the following scanning strategy, in which multiple scanning vectors pointing to the first vector direction are scanned consecutively before scanning at least one scanning vector pointing to a second vector direction different from the first vector direction.

7. The method according to claim 1, in, The first portion of the raw material powder layer (11) is selectively irradiated with linearly polarized laser radiation, and the second portion of the raw material powder layer (11) is selectively irradiated with random laser radiation, radially polarized laser radiation and / or azimuth-polarized laser radiation.

8. The method according to claim 7, in, The first portion of the raw material powder layer (11) is a filling portion of a workpiece layer produced by selectively irradiating the raw material powder layer (11), and / or the second portion of the raw material powder layer (11) is a contour portion of a workpiece layer produced by selectively irradiating the raw material powder layer (11).

9. The method according to claim 1, in, Multiple linearly polarized laser radiation beams scan the overlapping portion of the raw material powder layer (11) according to the following scanning strategy, in which all scanning vectors are scanned according to the same scanning mode.

10. An irradiation system (10) for producing a three-dimensional workpiece (110) by irradiating multiple layers of raw material powder with laser radiation, wherein, The irradiation system (10) is configured to selectively irradiate at least a portion of a raw material powder layer (11) applied to a carrier (102) with linearly polarized laser radiation, and wherein the irradiation system (10) includes a control device (18) configured to control the orientation of the polarization plane of the linearly polarized laser radiation according to the orientation of the incident plane of the linearly polarized laser radiation on the raw material. The control device (18) is configured to control the orientation of the polarization plane of the linearly polarized laser radiation based on the orientation of the incident plane of the linearly polarized laser radiation on the inner wall surface (26) of the capillary (24), which extends from the surface (28) of the raw material powder layer (11) into the volume of the raw material powder layer (11) and is formed due to the interaction between the linearly polarized laser radiation and the raw material.

11. The irradiation system (10) according to claim 10. in, The control device (18) is configured to: - The orientation of the polarization plane of the linearly polarized laser radiation is controlled according to the orientation of the incident plane of the linearly polarized laser radiation on the raw material, so that the polarization plane is oriented substantially parallel to the incident plane.

12. The irradiation system (10) according to claim 10. The control device (18) is configured to update the orientation of the polarization plane of the linearly polarized laser radiation according to the scanning direction of the linearly polarized laser radiation as it scans through the raw material powder layer (11) when controlling the orientation of the polarization plane of the linearly polarized laser radiation according to the orientation of the incident plane of the linearly polarized laser radiation on the raw material.

13. The irradiation system (10) according to claim 12, wherein, The control device (18) is configured to update the orientation of the polarization plane of the linearly polarized laser radiation based on an analysis of a scanning pattern on which the linearly polarized laser radiation beam is guided across the raw material powder layer (11), wherein the analysis of the scanning pattern is performed before the start of production of the three-dimensional workpiece (110) and / or in situ during production of the three-dimensional workpiece (110).

14. The irradiation system (10) according to claim 10. in, The control device (18) is configured to: - Controlling at least one of the power, focal diameter, and focal shape of the linearly polarized laser beam based on the incident angle (α) of the linearly polarized laser beam on the raw material, and / or at least one of the scanning pattern, scanning speed, scanning direction, and scanning mode upon which the linearly polarized laser beam is guided through the raw material powder layer (11), and / or at least one parameter of the gas flow guided through the raw material powder layer (11); and / or - Control the scanner unit (22) so that the linearly polarized laser radiation beam scans the raw material powder layer (11) according to the following scanning strategy, in which multiple scanning vectors pointing to the first vector direction are scanned consecutively before scanning at least one scanning vector pointing to a second vector direction different from the first vector direction; and / or - Control the irradiation system (10) such that a first portion of the raw material powder layer (11) is selectively irradiated with linearly polarized laser radiation, and a second portion of the raw material powder layer (11) is selectively irradiated with random laser radiation, radially polarized laser radiation and / or azimuthally polarized laser radiation.

15. The irradiation system (10) according to claim 10. in, The control device (18) is configured to control the scanner unit (22) such that multiple linearly polarized laser radiation beams scan the overlapping portion of the raw material powder layer (11) according to the following scanning strategy, in which all scanning vectors are scanned according to the same scanning mode.

16. The irradiation system (10) according to claim 14. in, The first portion of the raw material powder layer (11) is a filling portion of the workpiece layer produced by selectively irradiating the raw material powder layer (11), and / or the second portion of the raw material powder layer (11) is a contour portion of the workpiece layer produced by selectively irradiating the raw material powder layer (11).

17. An apparatus (100) for producing three-dimensional workpieces (110), the apparatus being equipped with an irradiation system according to claim 10.

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