Method of controlling irradiation system, irradiation system, computer program product and apparatus for producing three-dimensional work piece

Abstract

To produce a high-quality three-dimensional work piece by an irradiation system for irradiating layers of a raw material powder with a radiation beam.SOLUTION: A method of controlling an irradiation system 10 for irradiating layers of a raw material powder with a radiation beam 14 in order to produce a three-dimensional work piece 110 comprises the steps of defining, for at least one raw material powder layer to be irradiated, a scanning pattern comprising a plurality of irradiation sections 20, where, within each of the plurality of irradiation sections 20, a plurality of scanning vectors V is defined, in which the radiation beam 14 is scanned across the raw material powder layer according to the scanning vectors V; determining, for each of the plurality of irradiation sections 20, whether the irradiation section 20 contains a down skin area 22; and defining, for each of the plurality of irradiation sections 20, a scanning order direction S in which the scanning vectors V within the irradiation sections 20 are scanned one after another according to the determination as to whether the irradiation section 20 contains the down skin area 22.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention is directed to a method of controlling an irradiation system for irradiating a layer of raw material powder with a radiation beam to manufacture a three-dimensional workpiece. Further, the present invention is directed to such an irradiation system and to a computer program product including program portions for implementing the method of controlling the irradiation system when the computer program product is run on one or more computing devices. Finally, the present invention is directed to an apparatus for manufacturing a three-dimensional workpiece. [Background technology]

[0002] Additive manufacturing processes produce a workpiece layer-by-layer by solidifying to produce a series of interconnected workpiece layers. Such processes may be distinguished by the type of feedstock material and / or the method by which the feedstock material is solidified to produce the workpiece.

[0003] For example, powder bed fusion is an additive manufacturing process that can process powder, particularly metal and / or ceramic, raw materials into three-dimensional workpieces with complex shapes. To achieve this, a layer of raw powder is applied to a carrier and laser irradiation is performed selectively depending on the desired shape of the workpiece to be manufactured. The laser radiation that penetrates the powder layer causes heating, resulting in the raw powder particles melting or sintering. Further layers of raw powder are then applied successively to the previously laser-treated layer on the carrier until the workpiece has the desired shape and size. Powder bed fusion may be employed based on CAD data to manufacture or repair prototypes, tools, replacement parts, high-value parts, or medical prostheses, such as dental or orthopedic prostheses.

[0004] In an exemplary method and apparatus for producing three-dimensional workpieces by powder bed fusion, such as that described in EP 2786858, a protective gas flow is directed through the processing chamber to establish a desired atmosphere within the processing chamber and to evacuate impurities therein. The operation of an irradiation device is controlled to direct a radiation beam emitted by at least one radiation source of the irradiation device across the layer of raw material powder according to a radiation pattern including a plurality of scanning vectors. The scanning vectors are oriented according to the flow direction of the gas stream flowing through the processing chamber.

[0005] At the start of the scan vector, pores or defects are likely to be formed. Such pores or defects can affect the quality of the produced workpiece, especially if they are located in the overhang region, also known as the downskin region. An overhang region is understood as a region of the workpiece layer that is produced by irradiating a powder layer that is above unsolidified powder, but not above a previously solidified workpiece layer. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] European Patent No. 2786858 Summary of the Invention

[0007] It is an object of the present invention to provide a method for controlling an irradiation system for irradiating a layer of raw material powder with a radiation beam to manufacture three-dimensional workpieces, and an irradiation system of this type, and a computer program product that enables the manufacture of high-quality workpieces.Furthermore, the present invention is directed to an apparatus for manufacturing three-dimensional workpieces that enables the manufacture of high-quality workpieces.

[0008] The invention is set out in the independent claims, and preferred embodiments of the invention are outlined in the dependent claims.

[0009] A method for controlling an irradiation system for irradiating a layer of raw material powder with a radiation beam to manufacture a three-dimensional workpiece is described. The method includes defining a scan pattern for at least one raw material powder layer to be irradiated, the scan pattern including a plurality of irradiation zones. Within each of the plurality of irradiation zones, a plurality of scan vectors are defined, and the radiation beam is scanned across the raw material powder layer according to the scan vectors. The radiation beam may be a beam of electromagnetic radiation or particle radiation that is directed across the raw material powder layer in a site-selective manner according to the shape of the corresponding layer of the workpiece to be manufactured.

[0010] The irradiation system may comprise a radiation beam source, in particular a laser beam source. Here, the laser beam source may be configured to emit a continuous laser beam, a modulated laser beam, or a pulsed laser beam. Furthermore, the irradiation system may comprise at least one optical unit for splitting, guiding, and / or processing at least one radiation beam emitted by the radiation beam source. The optical unit may comprise optical elements such as an objective lens and a scanner unit, which preferably comprises a diffractive optical element and a deflection mirror. The irradiation system may irradiate the raw material powder layer with a single radiation beam. However, it is also conceivable that the irradiation system irradiates the raw material powder layer with two or more radiation beams.

[0011] The raw material powder layer may be applied to the surface of the carrier using a powder application device that moves across the carrier to distribute the raw material powder. The carrier may be a rigidly fixed carrier. However, preferably, the carrier is designed to be vertically movable so that the carrier can move vertically downward as the build height increases when the workpiece is built up layer by layer from the raw material powder. The carrier and powder application device may be housed in a processing chamber that can be sealed against the ambient atmosphere. A protective gas flow may be conducted through the processing chamber to establish a desired atmosphere within the processing chamber and to evacuate impurities from the processing chamber. The raw material powder applied to the carrier in the processing chamber is preferably a metal powder, particularly an alloy powder, but may also be a ceramic powder or a powder containing a different material. The powder may 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.

[0012] The scanning pattern may be a stripe pattern, where each illumination section forms a stripe of the stripe pattern. However, it is also conceivable that the scanning pattern is a checkerboard pattern or any other suitable scanning pattern comprising a plurality of illumination sections in which blocks of scanning vectors are arranged. The illumination sections may be arranged adjacent to each other or overlapping each other. The scanning vectors within an illumination section typically, but not necessarily, extend substantially parallel to each other. Within an illumination section, the scanning vectors may be unidirectional, i.e., within an illumination section, all scanning vectors may point in the same direction. However, it is also conceivable that within an illumination section, adjacent scanning vectors may point in opposite directions. When the scanning pattern is a stripe pattern, the scanning vectors within a stripe may extend substantially perpendicular to the longitudinal axis of the stripe. However, other directions of the scanning vectors relative to the longitudinal axis of the stripe are also conceivable.

[0013] In a preferred embodiment, for at least some of the plurality of irradiation sections, preferably for each of the plurality of irradiation sections, it may be determined whether the irradiation section includes a down skin region. By "down skin region" is understood a region of the irradiation section that is located above unsolidified powder, but not above a previously solidified workpiece layer region. Thus, in the down skin region, at least one scanning vector extends across at least a portion of its length through unsolidified, unconsolidated powder. The down skin region is intended to form an overhang region of the resulting workpiece layer.

[0014] For each of the plurality of irradiation sections, a scan sequence direction in which the scan vectors in the irradiation section are scanned one after the other may be defined depending on whether the irradiation section includes a down skin region. The scan sequence direction may extend substantially perpendicular to the scan vectors in the irradiation section. For example, if the scan pattern is a stripe pattern in which the scan vectors are substantially parallel to each other and arranged substantially perpendicular to the longitudinal axes of the stripes, the scan sequence direction will be substantially perpendicular to the scan vectors and thus substantially parallel to the longitudinal axes of the stripes. The above-defined method steps may be performed for at least one, preferably each, of the workpiece layers to be manufactured.

[0015] In an alternative embodiment, the regions of the workpiece that contain overhang or downskin regions, or regions of the workpiece where part growth direction exists, may be determined first, and the location of the irradiation patch may then be compared with the results of this determination.

[0016] The method described herein takes into account the presence of a down-skin region in the irradiation section when defining the scan sequence direction, thereby addressing quality issues such as pore formation or warping that may occur when forming an overhang region of a workpiece. Taking into account the presence of a down-skin region in the irradiation section when defining the scan sequence direction of the irradiation section is particularly advantageous in the manufacture of workpieces that include overhangs, especially overhangs with low angles, such as overhangs with an overhang angle of less than 40°, less than 30°, or less than 20° relative to the horizontal plane, when the overhang needs to be formed without being supported by a support structure.

[0017] The scan sequence direction may be determined according to a prior determination of whether the irradiation section already includes a down-skin region, i.e., by setting the layer (slicing) and scan pattern (hatching) of the workpiece to be manufactured. This may be achieved, for example, by using an appropriate simulation and / or slicing / hatching tool. However, it is also conceivable to determine a preliminary scan sequence direction without taking into account the presence of a down-skin region in the irradiation section of the workpiece layer to be manufactured, and then re-determine, i.e., change, the scan sequence direction as necessary.

[0018] For at least one irradiation section including a down skin region, the scanning order direction is defined to point from the solid-on region toward the down skin region. This may particularly apply to all irradiation sections including a down skin region. For an irradiation section including both a down skin region and a solid-on region, the vector defining the scanning order direction may include a start point located in the solid-on region and an end point located in the down skin region. When an irradiation section is composed of a down skin region, i.e., does not include a solid-on region, the start point of the vector defining the scanning order direction may be located closer to the solid-on region than the end point of the vector.

[0019] In either case, the defined scan sequence direction pointing from the solid-on region toward the down-skin region ensures that irradiation of the down-skin region begins as close as possible to the solid-on region, rather than on unconsolidated powder. As a result, each scan vector in the down-skin region is directly adjacent to or at least close to a previously irradiated scan vector, and thus directly adjacent to or at least close to a previously solidified region of the irradiation section. This improves the connection between the workpiece layer region built on the solid-on region and the workpiece layer region built on the down-skin region, as well as the overall quality of the workpiece layer region built on the down-skin region.

[0020] For an irradiation section that does not include a down-skin region, i.e., that is composed of a solid-on region, the scan order direction may be defined to point from the solid-on region toward the down-skin region of another irradiation section, for example, an adjacent irradiation section. However, for an irradiation section that does not include a down-skin region, the scan order direction may also be defined according to the direction of gas flow across the raw material powder layer. Specifically, the scan order direction may be defined to include a component that is opposite to the direction of gas flow across the raw material powder layer. As a result, the interfering effect of particulate impurities that may absorb radiation energy and / or block the radiation beam can be reduced or avoided in the processing zone where the radiation beam impinges on the raw material powder.

[0021] For an irradiation section including a down-skin region, the scan sequence direction may be defined such that the angle between the scan sequence direction and the component growth direction is 90° or less. In the context of this application, the term "component growth direction" defines the direction in which a component boundary moves between two layers. This may be defined relative to the entire workpiece layer. That is, the component growth direction corresponds to the direction of movement of the center of gravity or the direction of a region / boundary of the workpiece. In this case, there may be multiple component growth directions. For example, the component growth direction may extend substantially perpendicular to the boundary between the solid-top region and the down-skin region of the irradiation section. An angle of 90° or less between the scan sequence direction and the component growth direction ensures that the vector defining the scan sequence direction has a component extending in the same direction as the component growth direction, thereby pointing from the solid-top region toward the down-skin region.

[0022] The setting of the scan sequence so that the angle between the scan sequence direction and the component growth direction is less than or equal to 90° may be performed in advance, i.e., during the slicing and hatching procedures. However, it is also conceivable to define a preliminary scan sequence direction in a first step, consider in a second step whether there is an irradiation section including a down-skin region where the angle between the preliminary scan sequence direction and the component growth direction is greater than 90°, and finally change the scan sequence direction so that the criterion that the angle between the scan sequence direction and the component growth direction is less than or equal to 90° is met.

[0023] Alternatively or additionally, the method may include determining, for a first edge scan vector within a down-skin region of the illumination section, the number of end points of the first edge scan vector that contact or lie on a solid-on region. Furthermore, for a second edge scan vector within the down-skin region, the number of end points of the second edge scan vector that contact or lie on a solid-on region may be determined. In the context of the present application, the term "edge scan vector" defines a scan vector that is at the edge of a down-skin region of the illumination section, i.e., a scan vector that is adjacent to the boundary of the down-skin region.

[0024] The scan order direction may be defined such that the first or second edge scan vector having more end points that contact or are located on the solid region is defined as the starting scan vector, and / or the first or second edge scan vector having fewer end points that contact or are located on the solid region is defined as the final scan vector.

[0025] If it is determined that neither the first nor the second edge scan vector has an end point that contacts the solid region, i.e., if each of the first and second edge scan vectors starts and ends within the down-skin region, the method may further include determining, for the first edge scan vector, the number of solid scan vector points that are near the end point of the first edge scan vector. Furthermore, for the second edge scan vector, the number of solid scan vector points that are near the end point of the second edge scan vector may be determined. In the context of this application, the term "solid scan vector point" defines, for example, a point on a vector that is within the solid region of an adjacent irradiation section.

[0026] The scan order direction may be determined such that the first or second edge scan vector having the most solid scan vector points near its end point is defined as the starting scan vector, and / or the first or second edge scan vector having the fewest solid scan vector points near its end point is defined as the final scan vector. For example, a region having a particular radius, e.g., 0.25 mm, may be formed around the end points of the first and second edge scan vectors, and the number of solid scan vector points located within that region may be determined. However, it is of course possible to form a non-circular region of any suitable shape and size around the end points of the first or second edge scan vector, and analyze the number of solid scan vector points within such region.

[0027] The scan order may be set in advance, i.e., based on a slicing and hatching procedure, depending on the number of end points of the first and second edge scan vectors that contact the solid region and / or the number of solid scan vector points near the end points of the first and second edge scan vectors. However, it is also possible to determine a preliminary scan order direction in the first step, consider whether there is an irradiation section including a down-skin region that does not satisfy the above criteria of the number of end points and / or the above criteria of the number of solid scan vector points, and finally change the scan order direction to satisfy the above criteria.

[0028] The definition of the scan sequence direction according to the number of end points of the first and second edge scan vectors that contact the solid-surface region and / or the number of solid-surface scan vector points that are near the end points of the first and second edge scan vectors is particularly suitable for an irradiation section that consists only of a down-skin region, i.e., an irradiation section that does not include a solid-surface region. However, it is also conceivable to use such a criterion to set the scan sequence direction for an irradiation section that includes a down-skin region and a solid-surface region.

[0029] Alternatively, a down skin region may span several down skin vector blocks. Each down skin vector block may include one start vector, one end vector, and a scan order direction. For example, a down skin region may have several down skin stripes, where each stripe forms a down skin vector block including a start vector and an end vector. The scan order direction may be determined for each down skin vector block. Scanning may be performed using the scan order direction for each block determined as described above by using the block-to-block order (solid-to-powder direction).

[0030] When it is determined that neither the first nor the second edge scan vector has an end point that contacts the solid-on-solid region, the illumination section may be divided into a first partial illumination section and a second partial illumination section within the solid-on-solid region, such that each of the first and second partial illumination sections comprises a solid-on-solid region formed by a portion of the undivided illumination section's solid-on-solid region and a down-skin region formed by a portion of the undivided illumination section's down-skin region.

[0031] A first scan order direction may be defined for a first partially irradiated section, pointing from the solid upper region of the first partially irradiated section toward the down skin region of the first partially irradiated section. A second scan order direction may be defined for a second partially irradiated section, pointing from the solid upper region of the second partially irradiated section toward the down skin region of the second partially irradiated section. The first scan order direction and the second scan order direction may point in opposite directions.

[0032] The scanning vector may be oriented in one direction, pointing from the solid-up region to the down-skin region. Therefore, in order to further improve the quality of the overhanging workpiece region, not only the scanning sequence direction in the irradiation section plane but also the orientation of the scanning vector may be specified to follow the "solid-to-powder" rule.

[0033] Furthermore, for at least one raw powder layer to be irradiated, it is also conceivable to define an irradiation order direction for sequentially irradiating multiple irradiation sections in the raw powder layer, such that the irradiation order direction points from the first irradiation section to the second irradiation section, where the second irradiation section has a down skin area range greater than the down skin area range of the first irradiation section. In the context of this application, the expression "down skin area range" refers to the proportion of the irradiation section that is covered by the down skin area. In this embodiment of the method, the irradiation order direction for sequentially irradiating multiple irradiation sections is also defined to follow the "solid to powder" rule, in order to further improve the quality of the overhanging workpiece area.

[0034] An irradiation system for irradiating a layer of raw material powder with a radiation beam to manufacture a three-dimensional workpiece is provided with a control unit. The control unit may be exclusively coupled to the irradiation system. However, it is also conceivable that the control unit forms part of an overall control system for controlling the operation of an apparatus equipped with the irradiation system to manufacture a three-dimensional workpiece. The control unit is configured to define a scan pattern for at least one raw material powder layer to be irradiated, the scan pattern including a plurality of irradiation zones, wherein within each of the plurality of irradiation zones, a plurality of scan vectors are defined by which the radiation beam is scanned across the raw material powder layer.

[0035] Further, the control unit may be configured to determine, for at least a portion of the plurality of irradiation sections, preferably for each of the plurality of irradiation sections, whether the irradiation section includes a downskin region, and to specify, for each of the plurality of irradiation sections, a scanning order direction in which scanning vectors within the irradiation section are scanned one after another depending on the determination of whether the irradiation section includes a downskin region.

[0036] For the irradiation section including the down skin region, the control unit is configured to define the scan sequence direction to point from the solid-top region toward the down skin region.

[0037] For irradiation sections that do not include a downskin region, the control unit may be configured to define the scan sequence direction depending on the direction of gas flow across the raw material powder layer. In particular, the scan sequence direction may be defined to include a component oriented opposite to the direction of gas flow across the raw material powder layer.

[0038] For the irradiation section including the down skin region, the control unit may be configured to prescribe the scan sequence direction such that the angle between the scan sequence direction and the part growth direction is less than or equal to 90°.

[0039] The control unit may be further configured to determine, for a first edge scan vector in the down-skin region of the irradiation section, a number of end points of the first edge scan vector that contact or are located on the solid-on region, and to determine, for a second edge scan vector within the solid-on region, a number of end points of the second edge scan vector that contact or are located on the solid-on region. The control unit may be further configured to determine a scan order direction such that one of the first and second edge scan vectors that has more end points that contact or are located on the solid-on region is defined as a starting scan vector and / or one of the first and second edge scan vectors that has fewer end points that contact or are located on the solid-on region is defined as a final scan vector.

[0040] When it is determined that neither the first nor the second edge scan vector has an end point that contacts a solid region, the control unit may be further configured to: determine, for the first edge scan vector, a number of on-solid scan vector points near an end point of the first edge scan vector; and determine, for the second edge scan vector, a number of on-solid scan vector points near an end point of the second edge scan vector. The control unit may be further configured to determine a scan order direction such that one of the first and second edge scan vectors having more on-solid scan vector points near its end point is defined as a starting scan vector and / or one of the first and second edge scan vectors having fewer on-solid scan vector points near its end point is defined as a final scan vector.

[0041] When it is determined that neither the first nor the second edge scan vector has an end point that contacts the solid-on-solid region, the control unit may be further configured to divide the illumination section in the solid-on-solid region into a first partial illumination section and a second partial illumination section. The control unit is further configured to define a first scan order direction for the first partial illumination section, the first scan order direction pointing from the solid-on-solid region of the first partial illumination section to the down-skin region of the first partial illumination section, and to define a second scan order direction for the second partial illumination section, the second scan order direction pointing from the solid-on-solid region of the second partial illumination section to the down-skin region of the second partial illumination section. The first scan order direction and the second scan order direction may be opposite to each other.

[0042] The scanning vector may be oriented in one direction, pointing from the solid-on region towards the down-skin region.

[0043] For at least one raw powder layer to be irradiated, the control unit may be configured to define an irradiation sequence direction in which irradiation sections in the raw powder layer are scanned one after the other from a first irradiation section toward a second irradiation section, where the second irradiation section has a down skin area extent greater than the down skin area extent of the first irradiation section.

[0044] The computer program product includes program portions for performing the methods outlined according to any one or more of the implementations as described throughout this disclosure when the computer program product is executed on one or more computing devices.

[0045] An apparatus for manufacturing a three-dimensional workpiece by irradiating a layer of raw material powder with a radiation beam comprises an irradiation system as described above and / or a computer-readable recording medium having stored thereon a computer program product as described above. [Brief explanation of the drawings]

[0046] Preferred embodiments of the present invention will now be described in more detail with reference to the accompanying schematic drawings. [Figure 1] FIG. 1 shows an apparatus for producing a three-dimensional workpiece by irradiating a layer of raw material powder with a radiation beam. [Figure 2] FIG. 2 shows the definition of the scanning sequence direction of the irradiation section of the stripe scanning pattern, which points from the solid upper region to the down skin region. [Figure 3] FIG. 3 illustrates the definition of scan sequence directions depending on part growth direction for two example workpieces having overhang regions. [Figure 4a] FIG. 4a illustrates the definition of a scan order direction as a function of determining the number of endpoints of the first and second edge scan vectors in an exemplary down skin region that contacts a solid on region. [Figure 4b] FIG. 4b illustrates the definition of a scan order direction as a function of determining the number of endpoints of the first and second edge scan vectors in an exemplary down skin region that contacts a solid on region. [Figure 4c] FIG. 4c illustrates the definition of a scan order direction as a function of determining the number of endpoints of the first and second edge scan vectors in an exemplary down skin region that contacts a solid top region. [Figure 5a] FIG. 5a illustrates the definition of scan order direction as a function of determining the number of endpoints of first and second edge scan vectors in an additional exemplary down skin region that contacts a solid on region. [Figure 5b] FIG. 5b illustrates the definition of scan order direction as a function of determining the number of endpoints of the first and second edge scan vectors in an additional exemplary down skin region that contacts a solid on region. [Figure 5c] FIG. 5c illustrates the definition of scan order direction as a function of determining the number of endpoints of the first and second edge scan vectors in an additional exemplary down skin region that contacts a solid on region. [Figure 5d] FIG. 5d illustrates the definition of scan order direction as a function of determining the number of endpoints of the first and second edge scan vectors in an additional exemplary down skin region that contacts a solid on region. [Figure 6]FIG. 6 illustrates the definition of a scan order for an illumination section that includes a down-skin region and a solid-on region, and in which neither the first nor second edge scan vector has an end point that contacts the solid-on region. [Figure 7] FIG. 7 shows the definition of the irradiation sequence direction of the grid scanning pattern irradiation sections, which points from a first irradiation section to a second irradiation section that includes a downskin area larger than the downskin area of ​​the first irradiation section. DETAILED DESCRIPTION OF THE INVENTION

[0047] 1 shows an apparatus 100 for manufacturing three-dimensional workpieces by an additive manufacturing process. The apparatus 100 includes a carrier 102 and a powder application device 104 for applying raw material powder onto the carrier 102. The carrier 102 and the powder application device 104 are housed in a process chamber 106 that can be sealed against the ambient atmosphere. The carrier 102 is vertically movable within a built-up cylinder 108, such that as the workpiece 110 is built up layer by layer from raw material powder on the carrier 102, the carrier 102 can be moved downward as the build height of the workpiece 110 increases. The carrier 102 may include a heater and / or a cooler.

[0048] The apparatus 100 further comprises an irradiation system 10 for selectively irradiating the raw material powder layer 11 applied on the carrier 102 with laser radiation. In the embodiment of the apparatus 100 shown in FIG. 1 , the irradiation system 10 comprises a radiation beam source 12 configured to emit a radiation beam 14. The radiation beam source 12 may be a laser beam source configured to emit a laser beam. An optical unit 16 is associated with the radiation beam source 12 for guiding and processing the radiation beam 14 emitted by the radiation beam source 12. However, it is also conceivable that the irradiation system 10 is configured to emit more than one radiation beam. A control unit 18 is provided for controlling operation of the irradiation system 10 and of further components of the apparatus 100, such as, for example, the powder application device 104. The control unit 18 comprises a computer-readable storage medium on which a computer program product including program code portions is stored.

[0049] A controlled gas atmosphere, preferably an inert gas atmosphere, is established within the processing chamber 106 by supplying a shielding gas to the processing chamber 106 via the process gas inlet 112. The gas is directed through the processing chamber 106, across the raw material powder layer 11 applied to the carrier 102, and then exits the processing chamber 106 via the process gas outlet 114. The flow direction of the shielding gas from the process gas inlet 112, through the processing chamber 106, and to the process gas outlet 114 is indicated by arrow F. The process gas may be recirculated from the process gas outlet 114 back to the process gas inlet 112, where it may be cooled or heated.

[0050] During operation of the apparatus 100 for manufacturing a three-dimensional workpiece, a layer 11 of raw material powder is applied onto the carrier 102 by the powder application device 104. To apply the layer 11 of raw material powder, the powder application device 104 moves across the carrier 102 under the control of the control unit 18. Then, again under the control of the control unit 18, the layer 11 of raw material powder is selectively irradiated by the irradiation device 10 in accordance with the shape of the corresponding layer of the workpiece 110 to be manufactured. The steps of applying the layer 11 of raw material powder onto the carrier 102 and selectively irradiating the layer 11 of raw material powder with laser radiation in accordance with the shape of the corresponding layer of the workpiece 110 to be manufactured are repeated until the workpiece 110 reaches the desired shape and size.

[0051] The radiation beam 14 is scanned across the raw material powder layer 11 according to a scan pattern defined by the control unit 18. The scan pattern may be a stripe pattern as shown in FIGS. 2 and 6, a checkerboard pattern as shown in FIG. 7, or another suitable scan pattern as shown in FIGS. 4 and 5, and includes a plurality of irradiation sections 20 in which blocks of scan vectors V are arranged. Typically, as shown in FIGS. 2 to 7, the scan vectors V extend substantially parallel to one another. The control unit 18 determines, for each of the plurality of irradiation sections 20, whether the irradiation section 20 includes a downskin region 22, i.e., a region located above the unconsolidated powder and intended to form an overhang region of the workpiece layer to be produced by irradiating the raw material powder layer 11.

[0052] Based on the above determination, the control unit 18 defines, for each of the plurality of irradiation sections 20, a scanning order direction S for sequentially scanning the scanning vectors V within the irradiation section 20, particularly adjacent scanning vectors V within the irradiation section 20, depending on whether the irradiation section 20 includes a down skin region 22. In the exemplary configurations shown in Figures 2 to 7, the scanning order direction S extends substantially perpendicular to the scanning vectors V within the irradiation section. Specifically, for an irradiation section 20 including a down skin region 22, the scanning order direction S is preferably defined to point in the direction from the solid-surface region 24 to the down skin region 22.

[0053] FIG. 2 shows a raw material powder layer 11 intended to form a workpiece layer including an overhang region. The scanning pattern in which the radiation beam 14 is scanned across the raw material powder layer 11 is a stripe pattern, which includes a plurality of stripe-shaped irradiation sections 20. The scanning vectors V within each of the plurality of irradiation sections 20 extend substantially parallel to each other and substantially perpendicular to the longitudinal axis of the stripe-shaped irradiation section 20. Adjacent scanning vectors V point in opposite directions. Although all irradiation sections 20 are extensively covered by the scanning vectors V, for clarity, the schematic diagram in FIG. 2 shows the scanning vectors V in only a selected portion of the irradiation sections 20.

[0054] The down-skin region 22 of the irradiation section 20, which is intended to form the overhang region of the workpiece layer produced by irradiating the raw material powder layer 11, is built on the unsolidified portion of the previously applied raw material powder layer. Conversely, the solid-on region 24 of the irradiation section 20, which is intended to form the volume region of the workpiece layer produced by irradiating the raw material powder layer 11, is built on the solidified portion of the previously applied raw material powder layer, i.e., on a part of the previously constructed workpiece layer.

[0055] The scanning order direction S is defined to follow the general rule of "from solid to powder," i.e., for each irradiation section 20 consisting of a down-skin region 22 and an on-solid region 24, it is defined to run from the on-solid region 24 to the down-skin region 22. Therefore, the vector defining the scanning order direction S includes a start point located in the on-solid region 24 and an end point located in the down-skin region 22. Therefore, for the irradiation section 20 shown in the upper part of Figure 2, the scanning order direction S is defined to point to the left side of Figure 2, while for the irradiation section 20 shown in the lower part of Figure 2, the scanning order direction S is defined to point to the right side of Figure 2.

[0056] For an irradiation section 20 that does not include the down skin region 22, the scan order direction S may be defined to point from the solid-on region 24 toward an additional irradiation section, for example, the down skin region 22 of an adjacent irradiation section 20. However, for an irradiation section 20 that does not include the down skin region 22, the scan order direction S may alternatively be defined according to the flow direction F of the gas flow that is guided through the processing chamber 106 and across the raw material powder layer 11. Specifically, the scan order direction S may be defined to include a component that is opposite to the flow direction F of the gas flow.

[0057] Figure 3 shows a further example for defining the scan sequence direction S to follow the general rule "from solid to powder." Figure 2 shows two workpieces 110a, 110b built on a carrier 102. The build direction is indicated by arrow B. Each of the workpieces 110a, 110b includes an overhang region O. The lower part of Figure 3 shows irradiation sections 20 of the raw material powder layer 11 that are irradiated by the radiation beam 14 to produce the layers of the workpieces 110a, 110b, shown in dashed lines in the upper part of Figure 3. Each of the irradiation sections 20 comprises a down-skin region 22 and a solid-on region 24.

[0058] The arrow G indicates the component growth direction of the workpiece layer produced "from solid to powder." For each irradiation section 20, the component growth direction G extends from the solid-on-solid region 24 toward the down-skin region 22. FIG. 3 illustrates a case in which the same scan sequence direction S, which includes a component opposite to the gas flow direction F, is defined for both irradiation sections 20. For the workpiece 110a on the left side of FIG. 3, the scan sequence direction S is defined such that the angle α between the scan sequence direction S and the component growth direction G is approximately 45°, and therefore less than 90°. As a result, the vector defining the scan sequence direction S has a component extending in the same direction as the component growth direction G. As a result, the scan sequence direction G points from the solid-on-solid region 24 toward the down-skin region 22. Therefore, the workpiece 110a is expected to meet high quality standards.

[0059] Conversely, for the workpiece 110b on the right side of FIG. 3 , the scan sequence direction S is defined such that the angle α between the scan sequence direction S and the part growth direction G is approximately 135°, and thus greater than 90°. As a result, the vector defining the scan sequence direction S does not have a component extending in the same direction as the part growth direction G. As a result, the scan sequence direction G points from the down-skin region 22 to the solid-on region 24. Therefore, it cannot be denied that the workpiece 110b may be expected to have quality defects. To avoid this, the direction of the scan sequence direction S needs to be changed, i.e., rotated 180°.

[0060] 4 and 5 show various exemplary irradiation sections 20 that are comprised only of a downskin region 22, i.e., that do not include a solid upper region 24. The irradiation sections 20 shown in Figures 4a-4c and 5a, 5b, and 5d are positioned adjacent to the solid upper region 24 of an adjacent irradiation section 20', while the irradiation section 20 shown in Figure 5c is not in contact with the solid region of the adjacent irradiation section.

[0061] The following describes an exemplary strategy for determining an appropriate scan sequence direction S for the exclusively down-skin irradiation section 20 shown in Figures 4 and 5. However, this strategy may also be applied to other irradiation sections 20 that include both a down-skin region 22 and a solid-on region 24, such as the irradiation section shown in Figure 2.

[0062] This strategy involves determining, for a first edge scan vector VE1 within a down-skin region 22 of an illumination section 20, the number of end points of the first edge scan vector VE1 that contact a solid region 24 of the same or adjacent illumination section 20. Additionally, for a second edge scan vector VE2 within the down-skin region 22, the number of end points of the second edge scan vector VE2 that contact a solid region 24 of the same or adjacent illumination section 20 is determined. The edge scan vectors VE1 and VE2 define opposite ends of the down-skin region 22 of the illumination section 20. A scan order direction S is defined such that either the first or second edge scan vector VE1 or VE2 that has more end points that contact a solid region 24 is defined as the starting scan vector, and / or the first or second edge scan vector VE1 or VE2 that has fewer end points that contact a solid region 24 is defined as the final scan vector.

[0063] 4a, the first edge scan vector VE1 has two end points that contact the solid region 24 of the adjacent illumination section 20′. The second edge scan vector VE2 has only one end point that contacts the solid region 24 of the adjacent illumination section 20′. As a result, the scan order direction S is defined such that the first scan vector VE1 is defined as the starting scan vector and the second scan vector VE2 is defined as the final scan vector.

[0064] 4b, the first and second edge scan vectors VE1, VE2 each have one end point that contacts the solid region 24 of the adjacent illumination section 20′. As a result, the scan order direction S may be defined such that either one of the first scan vectors VE1, VE2 is defined as the starting scan vector.

[0065] 4c, the first edge scan vector VE1 has two end points that contact the solid region 24 of the adjacent illumination section 20'. Conversely, none of the end points of the second edge scan vector VE2 contact the solid region 24 of the adjacent illumination section 20'. As a result, the scan order direction S is defined such that the first scan vector VE1 is defined as the start scan vector and the second scan vector VE2 is defined as the end scan vector.

[0066] 5a, the first edge scan vector VE1 has one end point that contacts the solid region 24 of the adjacent illumination section 20′, but none of the end points of the second edge scan vector VE2 contact the solid region 24 of the adjacent illumination section 20′. As a result, the scan order direction S is defined such that the first scan vector VE1 is defined as the starting scan vector and the second scan vector VE2 is defined as the final scan vector.

[0067] 5b, each of the first and second edge scan vectors VE1, VE2 has two end points that contact the solid region 24 of the adjacent illumination section 20′. As a result, the scan order direction S may be defined such that any one of the first scan vectors VE1, VE2 is defined as the starting scan vector.

[0068] 5c and 5d, neither the first nor the second edge scan vectors VE1, VE2 have any end points that contact the solid region 24 of the adjacent illumination section 20′, so essentially the scan order direction S may be defined such that either one of the first scan vectors VE1, VE2 is defined as the starting scan vector.

[0069] 5d, an additional determination step is used to determine the number of solid scan vector points near the end point of the first edge scan vector VE1, and the number of solid scan vector points near the end point of the second edge scan vector VE2. For example, a region having a specific radius, e.g., 0.25 mm, may be defined around the end points of the first and second edge scan vectors VE1 and VE2, and the number of solid scan vector points located in that region may be determined. Based on this additional determination step, the first scan vector VE1 is defined as the starting scan vector, and the second scan vector VE2 is defined as the final scan vector.

[0070] 6 shows an additional exemplary raw material powder layer 11 intended to form a workpiece layer including an overhang region. Similar to the configuration of FIG. 2, the scan pattern in which the radiation beam 14 is scanned across the raw material powder layer 11 is a stripe pattern including a plurality of stripe-shaped irradiation sections 20. The irradiation section 20, shown in FIG. 6 as including a plurality of substantially parallel scanning vectors V, includes a down-skin region 22 and a solid-on region 24.

[0071] In the step of analyzing how many of the end points of the first and second edge scan vectors VE1, VE2 contact the solid-on-solid region 24 of the irradiation section 20, it is determined that neither the first nor the second edge scan vector VE1, VE2 has an end point that contacts the solid-on-solid region 24. Therefore, the irradiation section 20 is divided into a first partial irradiation section 20a and a second partial irradiation section 20b along the dashed lines in the solid-on-solid region 24. Therefore, each of the first and second partial irradiation sections 20a, 20b includes a solid-on-solid region 24a formed by a portion of the undivided irradiation section 20's solid-on-solid region 24 and a down skin region 22a formed by a portion of the undivided irradiation section 20's down skin region 22.

[0072] For the first partial irradiation section 20a, a first scanning order direction S1 is defined, which is the direction from the solid-surface region 24a of the first partial irradiation section 22a to the down-skin region 24a of the first partial irradiation section 22a, i.e., points to the left in Fig. 6. For the second partial irradiation section 22b, a second scanning order direction S2 is defined, which is the direction from the solid-surface region 24b of the second partial irradiation section 22b to the down-skin region 24b of the second partial irradiation section 22b, i.e., points to the right in Fig. 6. The first scanning order direction S1 and the second scanning order direction S2 are oriented in opposite directions.

[0073] In the exemplary configurations shown in Figures 2 to 7, adjacent scanning vectors V point in opposite directions. However, it is also possible to orient the scanning vector V in one direction, pointing from the solid-on region 24 toward the down-skin region 22. The solid-on region 24 may form part of the irradiation section 20 that also includes the down-skin region 22, or may be part of an adjacent irradiation section 20. For example, in the configuration of Figure 5d, the scanning vector V may be redirected to point in one direction, from the solid-on region 24 of the irradiation section 20' toward the down-skin region 22 of the irradiation section 20.

[0074] 7 shows an additional exemplary raw material powder layer 11 intended to form a workpiece layer including an overhang region. The scan pattern in which the radiation beam 14 is scanned across the raw material powder layer 11 is a checkerboard pattern, which in turn includes a plurality of rectangular irradiation sections 20. The scan vectors V within each of the plurality of irradiation sections 20 extend substantially parallel to one another. Adjacent scan vectors V point in opposite directions.

[0075] The irradiation sequence direction I for sequentially irradiating multiple irradiation sections 20 in the raw material powder layer 11 is defined as pointing from the first irradiation section 20 indicated by symbol 1 in Figure 7 to the second irradiation section 20 indicated by symbol 2 in Figure 7, and further to the third irradiation section 20 indicated by symbol 3 in Figure 7.

[0076] The second irradiation section 20 has a down skin area range (about 90%) larger than the down skin area range (about 20%) of the first irradiation section 20. Furthermore, the third irradiation section 20 has a down skin area range (100%) larger than the down skin area range (about 90%) of the second irradiation section 20. Therefore, in addition to this, the irradiation sequence direction I in which the multiple irradiation sections 20 are irradiated one after another is specified to follow the rule of "from solid to powder".

Claims

1. 1. A method of controlling an irradiation system (10) for irradiating a layer of raw material powder with a radiation beam (14) to produce a three-dimensional workpiece (110), comprising: - forming a scanning pattern for at least one raw material powder layer to be irradiated, the scanning pattern comprising a plurality of irradiation sections (20), within each of the plurality of irradiation sections (20), defining a plurality of scanning vectors (V), and the radiation beam (14) being scanned across the raw material powder layer according to the plurality of scanning vectors (V); - for each of the plurality of irradiation sections (20), defining a scanning order direction (S) in which the scanning vectors (V) within the irradiation section (20) are scanned one after the other, wherein for at least one irradiation section (20) including a down skin region (22), the scanning order direction (S) is defined to point in a direction from the solid-on region (24) to the down skin region (22).

2. 2. The method according to claim 1, wherein for at least one irradiation section (20) that does not include a downskin region (22), the scanning sequence direction (S) is defined according to the direction of gas flow across the raw material powder layer, and the scanning sequence direction (S) is defined to include, in particular, a component that is opposite to the direction of gas flow across the raw material powder layer.

3. 3. The method according to claim 1 or 2, wherein for an irradiation section (20) including at least a downskin region (22), the scanning sequence direction (S) is defined such that an angle (α) between the scanning sequence direction (S) and a part growth direction (G) is less than or equal to 90°.

4. - determining, for a first edge scanning vector (VE1) in the downskin area (22) of the irradiation section, the number of end points of said first edge scanning vector (VE1) that contact or are located on the solid area (24); - for a second edge scan vector (VE2) in the down skin region (22), determining the number of end points of the second edge scan vector (VE2) that contact or are located on the solid region (24); 4. The method according to claim 1, further comprising the step of: defining the scan order direction (S) such that one of the first and second edge scan vectors (VE1, VE2) that has more end points that touch or are located on the solid region (24) is defined as a starting scan vector; and / or one of the first and second edge scan vectors (VE1, VE2) that has fewer end points that touch or are located on the solid region (24) is defined as a final scan vector.

5. If it is determined that, for the first and second edge scan vectors (VE1, VE2) within the down skin region (22) of the irradiation section, neither of the first and second edge scan vectors (VE1, VE2) has an end point that contacts the solid on region (24), the method includes: - determining, for said first edge scan vector (VE1), the number of on-solid scan vector points that are in the vicinity of said end point of said first edge scan vector (VE1); - determining, for said second edge scan vector (VE2), the number of on-solid scan vector points that are in the vicinity of said end point of said second edge scan vector (VE2); - defining the scan order direction (S) so that one of the first and second edge scan vectors (VE1, VE2) that has more solid scan vector points near its end points is defined as a starting scan vector, and / or one of the first and second edge scan vectors (VE1, VE2) that has fewer solid scan vector points near its end points is defined as a final scan vector.

6. For first and second edge scan vectors (VE1, VE2) in a down skin region (22) of an irradiation section (20) that also includes a solid-on region (24), if it is determined that neither the first nor the second edge scan vector (VE1, VE2) has an end point that contacts the solid-on region (24), the method includes: - dividing the irradiated section (20) of the solid area (24) into a first partially irradiated section (20a) and a second partially irradiated section (20b); - defining for said first partial exposure section (20a) a first scanning sequence direction (S1) pointing in the direction from the solid top area (24a) of said first partial exposure section (20a) to the down skin area (22a) of said first partial exposure section (20a); The method according to any one of claims 1 to 5, further comprising a step of defining, for the second partial irradiation section (20b), a second scanning order direction (S2) pointing in a direction from the solid upper region (24b) of the second partial irradiation section (20b) to the down skin region (22b) of the second partial irradiation section (20b), wherein the first scanning order direction (S1) and the second scanning order direction (S2) point in particular in opposite directions.

7. 7. The method according to any one of claims 1 to 6, wherein the scanning vector (V) is oriented in one direction so as to point from the solid-on region (24) towards the down-skin region (22).

8. For at least one raw material powder layer to be irradiated, an irradiation order direction (I) in which the plurality of irradiation sections (20) in the raw material powder layer are irradiated one after another is defined to point in a direction from a first irradiation section (20) to a second irradiation section (20); 8. The method according to any one of claims 1 to 7, wherein the second irradiated section (20) has a down skin area extent that is greater than the down skin area extent of the first irradiated section (20).

9. 1. An irradiation system (10) for irradiating a layer of raw material powder with a radiation beam (14) to produce a three-dimensional workpiece (110), the irradiation system (10) comprising a control unit (18), the control unit (18) comprising: - defining a scanning pattern for at least one raw material powder layer to be irradiated, the scanning pattern comprising a plurality of irradiation sections (20), within each of the plurality of irradiation sections (20), defining a plurality of scanning vectors (V), the radiation beam (14) being scanned across the raw material powder layer according to the plurality of scanning vectors (V); - for each of the plurality of irradiation sections (20), a step of defining a scanning order direction (S) in which the scanning vector (V) within the irradiation section (20) is scanned one after the other, wherein for at least one irradiation section (20) including a down skin region (22), the control unit (18) is configured to define the scanning order direction (S) to point in a direction from a solid-on region (24) to the down skin region (22).

10. - For an irradiation section (20) that does not include a downskin region (22), the control unit (18) is configured to define the scanning sequence direction (S) depending on the direction of gas flow across the raw material powder layer, and the scanning sequence direction (S) is defined to include, in particular, a component that is directed opposite to the direction of gas flow across the raw material powder layer.

11. 11. The illumination system (10) of claim 9 or 10, wherein for an illumination section (20) including a downskin region (22), the control unit (18) is configured to define the scanning sequence direction (S) so that an angle (α) between the scanning sequence direction (S) and the part growth direction () is 90° or less.

12. The control unit (18) - determining, for a first edge scanning vector (VE1) in the downskin area (22) of the irradiation section, the number of end points of said first edge scanning vector (VE1) that contact or are located on the solid area (24); - for a second edge scan vector (VE2) in the down skin region (22), determining the number of end points of the second edge scan vector (VE2) that contact or are located on the solid region (24); defining the scan order direction (S) such that one of the first and second edge scan vectors (VE1, VE2) having more end points that touch or are located on the solid region (24) is defined as a start scan vector, and / or one of the first and second edge scan vectors (VE1, VE2) having fewer end points that touch or are located on the solid region (24) is defined as a final scan vector.

13. For first and second edge scanning vectors (VE1, VE2) in a down-skin region (22) of the irradiation section, if neither of the first and second edge scanning vectors (VE1, VE2) has an end point that is in contact with a solid-on region (24), the control unit (18) - determining, for said first edge scan vector (VE1), the number of on-solid scan vector points that are in the vicinity of said end point of said first edge scan vector (VE1); - determining, for said second edge scan vector (VE2), the number of on-solid scan vector points that are in the vicinity of said end point of said second edge scan vector (VE2); 13. The illumination system (10) of claim 9, further configured to perform the step of: defining the scan order direction (S) such that one of the first and second edge scan vectors (VE1, VE2) that has more solid-state scan vector points near its end points is defined as a start scan vector; and / or one of the first and second edge scan vectors (VE1, VE2) that has fewer solid-state scan vector points near its end points is defined as a final scan vector.

14. When it is determined that, for the first and second edge scanning vectors (VE1, VE2) in the down skin region (22) of the irradiation section (20) that also includes a solid-on region (24), neither of the first and second edge scanning vectors (VE1, VE2) has an end point that contacts the solid-on region (24), the control unit (18) - dividing the irradiated section (20) of the solid area (24) into a first partially irradiated section (20a) and a second partially irradiated section (20b); - defining for said first partial exposure section (20a) a first scanning sequence direction (S1) pointing in the direction from the solid top area (24a) of said first partial exposure section (20a) to the down skin area (22a) of said first partial exposure section (20a); 14. The illumination system (10) according to any one of claims 9 to 13, further configured to perform the step of: defining, for the second partial irradiation section (20b), a second scanning order direction (S2) pointing in a direction from the solid upper region (24b) of the second partial irradiation section (20b) to the down skin region (22b) of the second partial irradiation section (20b), wherein the first scanning order direction (S1) and the second scanning order direction (S2) point in particular in opposite directions.

15. 15. The illumination system (10) according to any one of claims 9 to 14, wherein the scanning vector (V) is oriented in one direction so as to point from the solid top region (24) towards the down skin region (22).

16. 16. The irradiation system of claim 9, wherein for at least one raw powder layer to be irradiated, the control unit (18) is configured to define an irradiation sequence direction (I), according to which the plurality of irradiation sections (20) in the raw powder layer are scanned one after another so as to point in a direction from a first irradiation section (20) to a second irradiation section (20), and the second irradiation section (20) has a down skin area range greater than the down skin area range of the first irradiation section (20).

17. 9. A computer program product comprising program portions for carrying out the method of any one of claims 1 to 8 when said computer program product is run on one or more computing devices.

18. An apparatus (100) for manufacturing a three-dimensional workpiece by irradiating a layer of raw material powder with a radiation beam (14), the apparatus (100) comprising an irradiation system according to any one of claims 9 to 16 and / or a computer-readable recording medium having stored thereon a computer program product according to claim 17.

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