Powder bed fusion apparatus and method

Abstract

A method for determining the irradiation sequence of a powder bed melting process, wherein each of a plurality of scanners is operated such that a corresponding energy beam travels across a powder bed (104) such that when a recoater (109) is above the powder bed (104), a plurality of energy beams (118a, 118b, 118c, 118d) irradiate the powder bed (104) and form powder layers (104a, 104b) with the recoater (109) such that the movement of the recoater (109) along the powder layer forming path is different for different powder layers (104a, 104b). The method includes taking into account that the movement of the recoater (109) on the powder layer formation journey is different for different powder layers in the powder layer (104a), determining the irradiation sequence of the powder layers (104a, 104b) by assigning each scanner to the irradiation area (1a, 2a, 3a, 4a, 1b, 2b, 3b, 4b), such that the irradiation of each irradiation area (1a, 2a, 3a, 4a, 1b, 2b, 3b, 4b) is completed before the irradiation area (1a, 2a, 3a, 4a, 1b, 2b, 3b, 4b) is covered during the formation of the next powder layer (104b).

Description

Technical Field

[0001] This invention relates to a powder bed melting apparatus and method. The invention is particularly applicable to powder bed melting apparatus and methods in which an energy beam scans across a powder bed while a powder layer is formed using a recoater. The invention is also applicable to powder bed melting apparatus and methods in which an energy beam scans across a powder bed to melt powders of varying thicknesses. Furthermore, the invention is applicable to powder bed melting apparatus and methods in which an energy beam scans across an area of ​​the powder bed, wherein the area is divided into multiple regions, each region containing multiple scanning paths, the length of which is defined by the boundaries of the region. Background Technology

[0002] Powder bed fusion equipment produces objects by solidifying powder materials (such as metallic powders) layer by layer (through melting or sintering) using a high-energy beam (such as a laser beam). Powder layers are formed in a build chamber across a powder bed by depositing powder adjacent to the bed and spreading the deposited powder across the bed (from side to side) using a wiper. A laser beam is then swept across the portion of the powder layer corresponding to the cross-section of the object being constructed. The laser beam irradiates the powder at selected locations to melt or sinter the powder to form a solidified material. After selective solidification of the layers, the powder bed is lowered, and another layer of powder is spread on the surface and solidified as needed.

[0003] WO 2015 / 140547 A1 discloses an apparatus in which a scanner causes an energy beam to scan across the powder bed to solidify powder material on either side of the wiper as the wiper is moving across the powder bed. The scanner can be controlled to cause the energy beam to scan across at least one powder layer during two or more strokes of the wiper across the powder bed (e.g., a stroke in which the wiper forms a powder layer and one or more subsequent strokes).

[0004] In one embodiment, the device includes a wiper arrangement (hereinafter referred to as a "bidirectional wiper") configured to spread powder in two directions of travel across a powder bed. The wiper unit includes two wipers installed at a fixed distance from each other. Powder is dispensed into the gap between the wipers, with one wiper spreading the powder into a layer as the wiper unit moves from a first side of the powder bed to a second side, and the other wiper spreading the powder into a layer as the wiper unit moves from the second side of the powder bed to the first side.

[0005] The problem with using a bidirectional wiper is that the time for irradiating different portions of the powder layer varies depending on the direction in which the bidirectional wiper travels to spread the layer. Specifically, the last portion of the powder layer formed has the least irradiation time because it is the first portion covered by the next powder layer formed by the bidirectional wiper. In Figure 7 of WO 2015 / 140547 A1, using a bidirectional wiper to limit the scanning of the layer to time slots 1 to 5 (or time slots 6 to 10 for the next layer) results in a significantly longer time available to irradiate one portion (part A for time slots 1 to 5 or time slot C for the next layer) than another portion (such as part C for time slots 1 to 5 or time slot A for the next layer). Therefore, the bidirectional wiper's back-movement across the powder bed to form the next powder layer may have to be delayed to allow sufficient time to irradiate this other portion of the powder layer, thus reducing the build-up time advantage of scanning the energy beam across the powder bed to consolidate the powder material on either side of the wiper while the wiper is moving across the powder bed.

[0006] Ideally, the wiping motion to spread the layer and irradiate the powder bed should be continuous, with minimal or no interruptions, to achieve the fastest build time. Summary of the Invention

[0007] According to a first aspect of the invention, a method is provided for determining the irradiation sequence of a powder bed melting process, wherein each of a plurality of scanners is operated such that a corresponding energy beam travels across the powder bed, such that when a recoater is above the powder bed, the plurality of energy beams irradiate the powder bed and form a powder layer with the recoater, such that the movement of the recoater in the powder layer forming stroke is different for different powder layers in the powder layer.

[0008] This method may include determining the irradiation sequence of powder layers by assigning each scanner to an irradiation area, taking into account the different movements of the recoater during the powder layer formation process for different powder layers. The irradiation sequence may be determined such that irradiation of each irradiation area is completed during the formation of the next powder layer before the irradiation area is covered.

[0009] The method may include determining irradiation areas of a powder layer, wherein the size of at least one irradiation area is based on the movement of the recoater during the powder layer formation stroke of the recoater. Two or more irradiation areas may have different sizes.

[0010] The method may include determining the irradiation area of ​​a powder layer and determining the irradiation sequence by assigning multiple irradiation areas to each scanner based on the movement of the recoater along the powder layer formation path, such that irradiation of each irradiation area is completed during the formation of the next powder layer before the irradiation area is covered. In one embodiment, different numbers of irradiation areas may be assigned to at least one scanner among the scanners on consecutive powder layers. (Secondly) different numbers of irradiation areas may be assigned to two or more scanners within one powder layer of the powder layer. The irradiation times for different scanners in one powder layer of the powder layer may be different. The number of irradiation areas may be allocated such that the differences in irradiation times of the scanners on two or more powder layers are all within a predetermined difference threshold (although based on differences in irradiation times per powder layer or outside the difference threshold).

[0011] Determining the irradiation sequence may include assigning each scanner to an irradiation area based on a parameter indicating the available irradiation time between the formation of a powder layer across the irradiation area and the covering of the irradiation area during the formation of the next powder layer, wherein the available irradiation time varies for different irradiation areas. This parameter may be the available irradiation time between the formation of a powder layer across the irradiation area and the covering of the irradiation area during the formation of the next powder layer. This parameter may also be the position of the recoater at a specific time, for example, if the movement of the recoater is predetermined.

[0012] In this way, the irradiation area allocated to the scanner can be adjusted based on the available irradiation time for the recoater to move during the formation of the powder layer, in order to reduce or eliminate inactivity and / or excessive delay of the energy beam when the next powder layer is laid.

[0013] Each of the multiple scanners can be operated to make the corresponding energy beam travel across the powder bed, such that multiple energy beams irradiate the powder bed while the recoater is moving across the powder bed to form a powder layer.

[0014] The movement of the recoater can be predetermined, and the irradiation sequence can be determined before the build begins using the irradiation sequence. For example, build preparation software can be used to determine the irradiation sequence. The method may include receiving input from a user that identifies the predetermined movement of the recoater. For example, the user may identify a specific powder bed melting machine on which the build will be performed, allowing the software to identify the predetermined movement of the recoater for that machine, for example, from a lookup table. Alternatively, the user may input one or more parameters for the recoater movement, such as the recoater speed and the time period for forming the powder layer.

[0015] In one embodiment, in a powder bed melting process, a powder layer is formed using a recoater such that the start and / or finish positions of the recoater on one or more of the powder layer forming strokes differ for different powder layers, and the method includes determining an irradiation area of ​​the powder layer, wherein the size of at least one irradiation area is based on the start and / or finish positions of the recoater on one or more of the powder layer forming strokes during powder layer formation. An irradiation area closer to the finish position (and further from the start position) may include an area that can be irradiated in a shorter time period (e.g., a smaller area) compared to an irradiation area further from the finish position (and closer to the start position). Irradiation of multiple smaller irradiation areas can be segmented between multiple energy beams to ensure timely completion of irradiation (even if this requires the energy beams to operate together more densely than a preferred spacing and / or more switching between scanners), while a larger irradiation area further from the finish position (and closer to the start position) ensures the preferred spacing between energy beams and / or reduces switching between scanners. It will be understood that area can represent irradiation time, but other factors that may affect irradiation time, such as scan speed and / or the presence of boundary scans, can be considered.

[0016] Adjacent irradiation areas are assigned to different scanners (i.e., the boundary of an irradiation area is the location where an assigned scanner switches to another scanner and / or beyond the boundary no powder is irradiated). Adjacent irradiation areas may partially overlap, for example, to allow the energy beams guided by different scanners to melt or sinter the solidified material to bond together. The irradiation sequence can be determined such that adjacent irradiation areas are irradiated at least partially simultaneously. Determining the irradiation sequence may include assigning each scanner to one or more non-adjacent irradiation areas, such that irradiation of each irradiation area is completed during the formation of the next powder layer before the irradiation area is covered.

[0017] The method may include assigning at least one scanner to irradiate multiple separate irradiation regions of a powder layer to solidify (e.g., melt or sinter) the powder. The multiple separate irradiation regions may include the irradiation region closest to the completion position of the recoater in the powder layer forming stroke of the powder layer. In this way, when the irradiation region closest to the completion position of the recoater is unavailable for irradiation (because, for example, it has been covered by the recoater, but a portion of the next powder layer has not yet been formed to allow for irradiation of the next powder layer), the scanner assigned to this irradiation region may direct a corresponding energy beam to begin irradiating the powder in another irradiation region of the multiple separate irradiation regions of the powder layer.

[0018] The dimension can be the width of the irradiated area in the direction of travel of the recoater across the powder bed. The dimension can also be the area of ​​the irradiated area (which is the area measured in the plane of the powder layer).

[0019] This method may include forming continuous powder layers, wherein a first powder layer is formed by movement of a recoater across a powder bed in a first direction, and a second continuous powder layer is formed by movement of the recoater across the powder bed in a second direction opposite to the first direction (hereinafter referred to as "bidirectional recoating"). In one embodiment, the recoater may form the powder layer by linear movement across the powder bed, with the first and second directions in opposite directions along a straight line. In another embodiment, the recoater may form the powder layer by rotation of the recoater relative to the powder bed about a fixed axis perpendicular to a plane of the powder layer, with the first and second directions in opposite circumferential directions. Therefore, the finishing positions of the recoater differ for continuous powder layers. In one embodiment, the finishing position of each powder layer is on one side of the powder bed, wherein, for continuous layers, the finishing positions of the recoater are on different sides of the powder bed (opposite sides of the linear movement). In this method, for continuous powder layers, the irradiation time for irradiating points on the powder bed that are not equidistant from the finishing positions of the continuous powder layers will be different. Therefore, this method can accommodate such variations in irradiation time for different powder layers. For example, the size of the irradiated area of ​​the first powder layer can be determined based on the completion position of the recoater on one side of the powder bed, and the size of the irradiated area of ​​the second powder layer can be determined based on the completion position of the recoater on the other side of the powder bed.

[0020] In an alternative embodiment, the method may include forming a continuous powder layer, wherein a first powder layer and a second continuous powder layer are formed by moving a recoater across a powder bed in the same direction (hereinafter referred to as "unidirectional recoating"). The movement of the recoater (e.g., one or more starting and / or finishing positions) may differ when forming the first and second powder layers.

[0021] This method may include forming a first powder layer that extends partially (incompletely) across a powder bed and a second continuous powder layer that extends partially or completely across a powder bed using a recoating device, wherein the area of ​​the first powder layer (in terms of size or position on the powder bed) differs from the area of ​​the second powder layer. The size of the irradiated area of ​​the first powder layer can be determined based on the movement of the recoating device for the first powder layer (e.g., the starting and / or finishing position), and the size of the irradiated area of ​​the second powder layer can be determined based on the movement of the recoating device for the second powder layer. The size of the irradiated area of ​​the first powder layer can be determined based on the starting position of the recoating device for the second powder layer. For example, if a portion of the first powder layer is not covered by the second powder layer, more time is available to irradiate this portion of the first powder layer because this portion can continue to be irradiated during and after the formation of the second layer. Therefore, taking this into consideration, the size of the irradiated area of ​​this portion of the first powder layer can be determined (e.g., to be larger than the case where the second powder layer covers this portion of the first powder layer). This method can be performed using bidirectional or unidirectional recoating. In powder bed fusion processes, it may be desirable to form powder layers that extend only partially across the powder bed, allowing for different layer thicknesses in different regions of the area to be consolidated. For example, it may be desirable to form some parts of an object with thinner layers (e.g., to manage thermal stress, produce a desired surface finish, and / or construct low-angle overhangs), while other parts of the object can be formed using thicker layers. Therefore, thinner layers may only need to be formed on the powder bed where the object requires a thinner layer.

[0022] Irradiation of powder within each irradiation area can be assigned to the same scanner. Alternatively, the method may assign only one scanner to each irradiation area.

[0023] This method may include generating a gas flow across a powder bed. The method may include generating the gas flow in a direction perpendicular to the direction of movement of the recoater. Each irradiation area may extend across the powder bed in the direction of the gas flow. Each irradiation area may extend from one side of the powder bed to the opposite side of the powder bed in the direction of the gas flow. The width of the irradiation area in the direction of movement of the recoater may be based on the movement of the recoater during powder layer formation. In powder bed melting involving multiple laser beams, it is known to divide the powder bed into channels (sometimes called "lanes") extending longitudinally across the powder bed in the direction of the gas flow, with each laser beam assigned to a different channel to mitigate the effect of debris and condensate generated by one laser beam on the other. The lanes separate the processing performed by each laser beam, thus avoiding significant adverse effects in most cases. Conventionally, the width of each lane remains the same for each powder layer. A problem with applying this method to an irradiated powder bed when the movement of the recoater differs for different powder layers during powder layer formation is that the scanner may not be able to irradiate all these areas within a single channel before the desired area is covered during the formation of the next powder layer. For bidirectional recoating, the last channel forming the powder layer must be irradiated faster than the other channels. Furthermore, during the movement of the recoator across the powder bed, each channel can be gradually covered by the recoator, during which time the scanner assigned to that channel may not be used to irradiate the powder bed. The method for determining the irradiation sequence according to the invention can mitigate or avoid this problem by adjusting the size of the irradiation area (e.g., lane) based on the movement of the recoator during powder layer formation. For example, the last irradiation area (e.g., the last lane forming the powder layer) can be smaller, or narrower, than the other irradiation areas (e.g., other lanes that complete the powder layer earlier).

[0024] The scanner can be assigned to an irradiation area so that when the irradiation area assigned to the scanner becomes unavailable, another irradiation area (in the same or a different powder layer) assigned to the scanner can be used for irradiation. In this way, scanner downtime is reduced.

[0025] According to a second aspect of the invention, a powder bed melting process is provided, the powder bed melting process comprising: forming a powder layer of a powder bed with a recoater such that the movement of the recoater in the powder layer forming stroke is different for different powder layers in the powder bed; and operating each of a plurality of scanners to cause a corresponding energy beam to travel across the powder bed such that when the recoater is above the powder bed, the plurality of energy beams irradiate the powder bed according to an irradiation sequence determined by the method of the first aspect of the invention.

[0026] According to a third aspect of the invention, a powder bed melting process is provided, comprising: forming a powder layer of a powder bed using a recoater, such that the movement of the recoater during the powder layer forming stroke differs for different powder layers; and operating each of a plurality of scanners to cause a corresponding energy beam to travel across the powder bed, such that when the recoater is above the powder bed, the plurality of energy beams irradiate the powder bed according to an irradiation sequence, each energy beam irradiating a selected area within an irradiation region in that irradiation sequence. The irradiation regions may have different sizes, such that irradiation of each irradiation region is completed during the formation of the next powder layer before the irradiation region is covered.

[0027] At least one powder layer can be irradiated over two or more passes of the recoating apparatus. The two or more passes may include a powder layer forming pass and a powder layer forming pass for forming the next powder layer. The passes can be in opposite directions (bidirectional recoating).

[0028] The energy beam can be a laser beam. Each scanner may include at least one movable optical element for guiding the corresponding laser beam across the powder bed. Irradiating the powder with the energy beam can solidify the powder by melting or sintering it.

[0029] The recoater may include at least one wiper for spreading powder across the powder bed. The wiper may be a brush, roller, blade, or selective powder deposition drum, such as the device disclosed in WO 2019 / 185626 A1, which is incorporated herein by reference in its entirety. The recoater may include a pair of spaced-apart parallel wipers arranged such that powder can be metered into the gap between the wipers. In this arrangement, as the recoater moves in one direction, one wiper spreads powder, and as the recoater moves in another direction, the other wiper spreads powder.

[0030] According to a fourth aspect of the invention, a powder bed melting process is provided, comprising forming powder layers of a powder bed using a recoater, and operating at least one scanner to cause a corresponding energy beam to travel across the powder bed while the recoater is moving across the powder bed to form each of a plurality of powder layers, such that the energy beam irradiates the powder bed to melt the powder. Multiple regions of the powder layer can be solidified by melting the powder in each region together with powder from at least one other powder layer by irradiating the powder bed with the energy beam, to form a solidified segment together within the powder layer. Powder from different regions within the area can be melted together with powder from different other powder layers.

[0031] In this way, different regions within the powder layer can be consolidated after the formation of different powder layers, thereby reducing the irradiation time of the energy beam within each stroke of the recoater. This allows for, for example, maintaining a preferred spacing and sequence of irradiation relative to the gas flow direction, since it is no longer necessary to complete the consolidation of the powder layer before the area to be consolidated is covered during the formation of the next powder layer. Irradiation melting corresponds to the powder thickness of two or more powder layers (multiple powder thicknesses) (causing the powder to consolidate into a “block” comprising two or more powder layers), forming a molten pool to consolidate the areas of the powder layer offset in the build direction (i.e., forming the upper surfaces of different molten pools in the plane of different powder layers). This method can increase the number of powder layer formation strokes for the recoater used in the build (because the molten powder thickness is formed by multiple strokes of the recoater), but this may not delay the build, as for a typical build, the irradiation time of the powder layer is longer than the time it takes for the recoater to complete two or more strokes.

[0032] Furthermore, this method can reduce or even eliminate significant residual stress caused by the shrinkage of the consolidated material. Voids created by powder agglomeration / stripping during material melting can be filled before other areas within the molten powder layer. Therefore, this method can simultaneously mitigate warping and the presence of porosity within the object. Additionally, the powder blocks formed during the formation of each region extend across different groups of layers for different regions, potentially reducing the weakening lines caused by prior art methods that immediately consolidate all (or most) regions of the layer after formation.

[0033] The first region within the area can be melted by direct irradiation of the powder layer, while the second region can be melted by direct irradiation of a subsequent powder layer. In this way, the gaps in the powder layer formed during the formation of the first region are filled by the formation of the subsequent layers, and then the other regions within the area are melted. This reduces porosity in the object.

[0034] The powder in the first region of the powder layer can be melted together with the powder in the first powder layer. The powder in the second region of the powder layer can be melted together with the powder in the second powder layer. The first powder layer can be different from the second powder layer.

[0035] The first region within the area can melt during the first powder layer formation stroke of the recoater, and the second region within the area can melt during a second subsequent stroke of the recoater. The first and second strokes can be consecutive strokes of the recoater.

[0036] Before the second region of the molten region, the first region of the region can be melted to form discrete regions of powder with powder layers therebetween, wherein the solidification of the second region connects the first regions of the region together. In this way, each discrete first region can shrink individually during cooling, thereby reducing residual stress in the object.

[0037] The region can be solidified to form part of the core of an object. This method can include forming a boundary by melting the material surrounding the region, for example, as typically performed in shell and core scanning strategies. The boundary can be formed by melting a powder thickness different from that of the region. For example, the boundary powder thickness could be the thickness of a single powder layer. The powder at the boundary can be melted at each powder layer.

[0038] In an alternative embodiment, the melting of the powder layer at the boundary can be skipped, allowing at least a portion of the boundary to be formed by melting multiple powder layers. Different segments of the boundary region can be melted together with powder from different other powder layers. For example, a first segment of the boundary can be melted by direct irradiation of the powder layer, while a second segment of the boundary can be melted by direct irradiation of subsequent powder layers. The first segment of the boundary can form an overhang of the object in its construction orientation, wherein, when forming subsequent powder layers, the component of the recoater direction is in the overhang direction of the overhang. When forming powder layers, the component of the recoater direction can be opposite to the overhang direction of the overhang. The overhang direction is a vector perpendicular to the edge of the area to be consolidated in the powder layer, having a direction from the consolidation material of that area to the powder. Therefore, the consolidation of the boundary can transition from a first segment of the boundary melted by direct irradiation of the powder layer to a second segment melted by direct irradiation of subsequent powder layers, because the overhang direction changes relative to the recoater direction for different points along the edge of the area. This method can reduce or eliminate the adverse effects caused by partial jamming of the overhang on the recoater as it moves across the powder bed during the formation of subsequent powder layers. For example, movement of the recoater across the solidified material layer in a direction opposite to the overhang direction may cause the layer to shift or otherwise adversely affect it, such as by pushing powder beneath the layer. Movement of the recoater in the opposite direction can avoid this adverse effect. Therefore, this method can facilitate the construction of thin layers and / or low-angle overhangs.

[0039] Different regions within a given area can be melted together with varying numbers of other layers. This can be achieved by varying the power of the at least one energy beam. Alternatively, all regions melted together with other layers can be melted together with the same number of other powder layers.

[0040] This method may include forming powder layers of varying thicknesses. The thickness of each powder layer may depend on the geometry of the object being formed. The thickness of each powder layer may be based on the angle of the overhangs oriented during construction. The method may include selecting the powder layer thickness based on the angle of the overhangs. For powder layers to be consolidated, a thinner thickness may be selected to form overhangs at a smaller angle to the horizontal plane / plane of the powder layer. The powder layer thickness may be selected based on the length of the overhangs in the powder layer (which is a function of the angle of the overhang to be formed). The powder layer thickness may be selected such that the length of the overhang is below a predetermined threshold length.

[0041] An overhang is the area of ​​a powder layer to be consolidated, which has unconsolidated powder from the previous layer immediately below it. An overhang is a section of an object that includes a surface oriented upwards during construction.

[0042] The recoater may include a bidirectional recoater as described above.

[0043] According to a fifth aspect of the invention, a method is provided for determining the irradiation sequence of a powder bed melting process according to a fourth aspect of the invention. The method may include determining the area to be consolidated within the powder layer based on the geometry of the object to be constructed, and determining a first region of the powder layer to be melted together with powder from a first group of powder layers by direct irradiation of the powder layer by the at least one energy beam, and a second region of the powder layer to be melted together with powder from a second group of powder layers by direct irradiation of subsequent powder layers by the at least one energy beam. The first group of powder layers may be different from the second group of powder layers. The method may include determining the irradiation sequence of the powder layers and subsequent powder layers based on the first and second regions.

[0044] The first region can be determined by identifying areas in the powder layer to be melted that coincide with areas in the adjacent previous powder layer to be melted in the build direction. The second region can be determined by identifying areas in subsequent powder layers to be melted that coincide with regions in the powder layer in the build direction. In this way, regions in the powder layer can be melted together with regions in the adjacent previous and subsequent powder layers.

[0045] The irradiation sequence can be determined based on the predetermined movement of the recoater across the powder bed. The recoater can be a bidirectional recoater.

[0046] According to a sixth aspect of the invention, a method for determining the irradiation sequence of a powder bed melting process is provided, the method comprising: determining the construction orientation of an object to be constructed in the powder bed melting process; determining the geometric characteristics of the surface of the object at different locations in the construction direction based on geometric data describing the object; selecting different powder layer thicknesses for powder layers based on the geometric characteristics; and determining the irradiation sequence based on the selected layer thickness and the geometric data.

[0047] The thickness of each powder layer can be determined based on the angle of the object's surface (such as the angle of the overhang oriented during construction). The method can include selecting the powder layer thickness based on the angle of the overhang. For powder layers to be consolidated, a thinner thickness can be selected to form overhangs at a smaller angle to the horizontal plane / powder layer plane. The powder layer thickness can be selected based on the length of the overhang in the powder layer (which is a function of the angle of the overhang to be formed). The powder layer thickness can be selected such that the length of the overhang is below a predetermined threshold length.

[0048] This method may include selecting different layer thicknesses based on maintaining the distance between adjacent exposures on a continuous powder layer within a predefined acceptable range, wherein adjacent exposures form the surface of the object (the exposure of the object's "skin"). The acceptable range of distances between adjacent exposures may depend on the angle of the vector between adjacent exposures relative to the build plane. The exposure of the skin is located in part based on the geometry of the object's surface. If a constant layer thickness (as is conventional) is used, the distance between adjacent exposures of the skin becomes larger as the surface geometry becomes shallower relative to the build plane, which may lead to build failure. This aspect of the invention avoids such build failure by selecting different layer thicknesses to maintain the distance between adjacent exposures of the skin on adjacent layers within a predefined acceptable range.

[0049] Different powder layer thicknesses can be selected such that the powder layer thickness varies between different pairs of adjacent exposures, each pair of adjacent exposures occurring on successively formed powder layers, and the material solidified due to the exposure forms the surface of the object (e.g., exposure of the object's "skin"). Adjacent exposures can extend the surface in the horizontal build direction. Different layer thicknesses between different pairs of adjacent exposures can include zero-thickness powder layers (powder layers formed in the same location as previous powder layers in the build direction) and non-zero-thickness powder layers. Zero-thickness powder layers can be located between adjacent exposures oriented in the same horizontal plane of the object during its build. It has been found that irradiating a powder layer can cause powder to peel off from the irradiated area. If an adjacent area is subsequently irradiated to melt the powder, this can lead to undesirable results because the area lacks powder. When parts are grown in the vertical build direction using a fixed powder layer thickness, the peeled powder is replaced by a new powder layer. However, when exposure extends the surface of the object in the horizontal build direction, a powder layer for replacing the peeled powder is not conventionally provided. By forming a powder layer of variable thickness between adjacent exposures on the surface, flaking powder is replaced with fresh powder before each subsequent exposure, while the vertical growth can be appropriately adjusted based on the object geometry. It will be understood that, as used herein, the thickness of the powder layer refers to its thickness relative to a previous powder layer. The powder layer is formed by the movement of the recoating device. The thickness of the powder layer is defined by the relative movement between the build platform supporting the powder bed and the recoating device. Multiple powder layers can be melted during exposure.

[0050] Adjacent exposures may include adjacent contour scan paths forming the surface of an object. The method may include selecting to form a powder layer between each pair of adjacent contour scan paths forming the surface of the object. Therefore, the powder layer thickness may be selected based on the location of each adjacent contour scan path.

[0051] The powder bed melting process may include operating at least one scanner to cause a corresponding energy beam to travel across the powder bed, such that the energy beam irradiates the powder bed to solidify the powder while a recoater is moving across the powder bed to form a powder layer.

[0052] According to a seventh aspect of the invention, a powder bed melting process is provided, comprising forming powder layers of varying thicknesses to form a powder bed, and operating at least one scanner to allow a corresponding energy beam to travel across the powder bed, such that the energy beam irradiates the powder bed to melt the powder. The thickness of each powder layer is based on the geometry of the surface of the object being formed. The powder bed melting process can be performed according to an irradiation sequence determined according to a sixth aspect of the invention.

[0053] According to an eighth aspect of the invention, a powder bed melting process is provided, the powder bed melting process comprising forming powder layers of a powder bed with a recoater, and irradiating the area of ​​each powder layer to melt the powder to form an object, wherein, when solidified, the area of ​​the overhang portion of the object in the construction orientation is formed by irradiating selected powder layers in the powder layers, and when forming the next powder layer across the overhang portion, the component of the recoater direction is in the overhang direction of the overhang portion.

[0054] Different overhangs formed in a powder layer can be melted together with powder from other powder layers. For example, a first overhang can be melted by direct irradiation of the powder layer with at least one energy beam, while a second powder layer can be melted by direct irradiation of subsequent powder layers with the same energy beam. When forming the next powder layer, the component of the recoating direction can be in the overhang direction of the first overhang. When forming a powder layer, the component of the recoating direction can be opposite to the overhang direction of the first overhang. The overhang direction is a vector perpendicular to the edge of the area of ​​the object to be formed by the powder layer, having a direction from the solidified material of that area to the powder. Therefore, the solidification of the first and second overhangs can transition from the first overhang melted by direct irradiation of the powder layer to the second overhang melted by direct irradiation of the next powder layer, because the overhang direction changes relative to the recoating direction for different points along the edge of the area to be solidified. This method can reduce or eliminate the adverse effects caused by parts of the overhang getting stuck on the recoating as the recoating moves across the powder bed during the formation of the next powder layer. This method can help construct thin layers and / or low-angle overhangs.

[0055] The at least one scanner can be operated to cause the corresponding energy beam to travel across the powder layer, such that the energy beam irradiates the powder bed to melt the powder while the recoater is moving across the powder bed to form a powder layer and / or the next powder layer.

[0056] According to a ninth aspect of the invention, a method for determining the irradiation sequence of a powder bed melting process is provided, the method comprising determining the construction orientation of an object to be constructed in the powder bed melting process; selecting, based on geometric data describing the object, a powder layer in which an overhang area is to be consolidated, the overhang area forming an overhang portion of the object in the orientation during construction, such that when the next powder layer is formed on the overhang area, the component of the recoating direction is in the overhang direction of the overhang area.

[0057] According to a tenth aspect of the invention, a powder bed melting apparatus is provided, the powder bed melting apparatus including a controller arranged to control the powder bed melting apparatus to perform a powder bed melting process according to a second, third, fourth, seventh and / or eighth aspect of the invention.

[0058] According to an eleventh aspect of the present invention, a data carrier is provided that stores instructions, wherein when executed by a processor, the instructions cause the processor to perform the methods of the first, fifth, sixth, and / or ninth aspects of the present invention.

[0059] Data carriers can be suitable media used to provide instructions to machines, such as non-transitory data carriers, such as floppy disks, CD ROMs, DVD ROM / RAM (including -R / -RW and +R / +RW), HD DVDs, Blu-ray™ optical discs, memory (such as Memory Stick™, SD cards, compact flash memory cards, etc.), disk drives (such as hard disk drives), magnetic tapes, any magnetic / optical memory; or transient data carriers, such as signals on wires or optical fibers, or wireless signals, such as signals transmitted over wired or wireless networks (such as internet downloads, FTP transfers, etc.).

[0060] It will be understood that the term “adjacent” as used in this article in conjunction with two similar elements (e.g., two irradiated areas, two exposures, or two layers) means that the two similar elements are close to each other and / or one of these elements is adjacent to the other of these elements, where there is no intermediary element of this type. Attached Figure Description

[0061] Figure 1 This is a schematic diagram of a powder bed melting device according to an embodiment of the present invention;

[0062] Figure 2 This is a plan view of a powder bed melting device, showing multiple scanners;

[0063] Figure 3 It is a schematic diagram showing the gas flow across the powder bed and dividing the powder bed into channel-shaped irradiation areas (also known as "lanes") allocated to each scanner;

[0064] Figure 4a and Figure 4b This is a schematic diagram illustrating a method for determining a channel-shaped irradiation area and assigning a corresponding scanner to each irradiation area, taking into account the gas flow direction according to an embodiment of the present invention.

[0065] Figure 5 This is a schematic diagram illustrating a method for determining a channel-shaped irradiation region by taking into account the direction of gas flow, wherein the width of the channel-shaped irradiation region is based on the area to be consolidated;

[0066] Figure 6 This is a schematic diagram illustrating a method for determining a channel-shaped irradiation area and assigning one or more scanners to each irradiation area, taking into account the gas flow direction according to another embodiment of the present invention.

[0067] Figure 7a and Figure 7b This is a schematic diagram illustrating a method for determining an irradiation area and assigning a corresponding scanner to each irradiation area according to another embodiment of the present invention;

[0068] Figure 8 It is a demonstration of Figure 7a A schematic diagram of a modification to the method described in Figure 7c, the modification including assigning multiple irradiation zones to each scanner;

[0069] Figure 9 This is a schematic diagram illustrating a method for determining an irradiation area and assigning a corresponding scanner to each irradiation area according to another embodiment of the present invention;

[0070] Figure 10a and Figure 10b This is a schematic diagram illustrating a method for allocating a fixed-size irradiation area (in this example, a fixed-size square irradiation area) according to yet another embodiment of the present invention;

[0071] Figure 11a and Figure 11b This is a schematic diagram illustrating a method for determining a strip irradiation area and assigning a scanner to each strip irradiation area according to yet another embodiment of the present invention;

[0072] Figure 12 This is a schematic diagram illustrating a powder bed melting method according to an embodiment of the present invention;

[0073] Figure 13 This is a schematic diagram illustrating a powder bed melting method using variable layer thickness according to an embodiment of the present invention;

[0074] Figure 14 This is a schematic diagram illustrating a powder bed melting method using variable layer thickness according to another embodiment of the present invention;

[0075] Figures 15a to 15f Displayed layer by layer Figure 14 How the powder bed melting process is performed; and

[0076] Figure 16 This is a schematic diagram illustrating a powder bed melting method using variable layer thickness according to yet another embodiment of the present invention. Detailed Implementation

[0077] refer to Figure 1 and Figure 2The powder bed melting apparatus according to an embodiment of the present invention includes a build chamber 101 having a processing plate 115 having a hole, and a build sleeve 116 extending downward from the hole. A build platform 102 is lowerable within the build sleeve 116 such that the build sleeve 116 and the build platform 102 together define a build volume 117. When a workpiece is built by selective laser melting of powder, the build platform 102 supports a build substrate 102a, a powder bed 104, and a workpiece (object) 103. As successive layers 103a, 103b of the workpiece 103 are formed, the platform 102 is lowered within the build volume 117 under the control of a drive mechanism (not shown).

[0078] When workpiece 103 is constructed using dispensing device 108 and recoater 109, a powder layer 104 is formed. Recoater 109 includes a pair of spaced-apart wiper blades, each blade for spreading powder across powder bed 104 in opposite directions. This recoater 109 can be referred to as a bidirectional recoater because it spreads the powder layer by moving in opposite directions. When recoater 109 is positioned below powder dispenser 108, dispensing device 108 dispenses powder 104a into the gaps between the spaced-apart wiper blades. Mechanisms for achieving this timely dispensing are disclosed in US 6672343 B1. Movement of recoater 109 spreads the dispensed powder into a powder layer within the powder bed. The position of the lower edge of each blade of recoater 109 defines a working plane 110 where the powder is melted.

[0079] Multiple laser modules generate laser beams 118a, 118b, 118c, and 118d for melting powder 104. Each laser module includes optical fibers 128a, 128b, 128c, and 128d, and beam transmission optics (BDOs) 105a, 105b, 105c, and 105d for transmitting the laser beams 118a, 118b, 118c, and 118d to corresponding optical scanners 106a, 106b, 106c, and 106d. The optical scanners 106a, 106b, 106c, and 106d guide the laser beams 118a, 118b, 118c, and 118d to selected areas of the powder bed 104 to construct an object. The laser beams 118a, 118b, 118c, and 118d enter through a common laser window 107.

[0080] Each optical scanner 106a, 106b, 106c, 106d includes movable manipulating optics 121 (e.g., two mirrors mounted on a galvanometer) for traveling the laser beam 118 across the working plane 110 in the vertical directions (X and Y), and focusing optics 120 (e.g., two movable lenses for changing the focal point of the laser beam 118). The optical scanners are controlled such that the focal position of the laser beam 118 is maintained in the same plane 110 as the laser beam 118 moves across the working plane 110. In this embodiment, each scanner can cause the corresponding laser beam 118 to travel across the working area covering the entire powder bed 104. However, in other embodiments, such as Figure 7a and Figure 7b as well as Figure 8 In the illustrated embodiment, each scanner 106 has a working field that only partially covers the powder bed 104. As used herein, the term "addressable field" refers to an area in the working plane 110 across which the scanner 106 can cause a corresponding laser beam 118 to travel in response to a demand signal. The working field of the scanner 106 is an area in the working plane and can correspond to an addressable field. However, additional limitations may be imposed on the working field due to the physical constraints of the powder bed melting apparatus or the physical constraints of the calibration process. For example, the demand position of the scanner 106 may be limited to not extending beyond the edge of the powder bed 104 (referred to herein as the "working area") or beyond the area where the scanner 106 is calibrated (referred to herein as the "scanning field"). The extent of the working field is defined at the time of machine setup and is construction-independent.

[0081] The powder bed melting apparatus includes a controller 160 for controlling the movement of the apparatus's modules (including lasers, scanners 106a, 106b, 106c, 106d) and recoater 109. The controller includes a processor 161 and a memory 162 storing a computer program that, when executed by the processor, controls the powder bed melting apparatus in the manner described below. The software may include instructions generated by build-up preparation software. This build-up preparation software may be located on or off the apparatus, such as on a general-purpose computer. The build-up preparation software generates instructions, such as scan paths, scan parameters, and / or scan sequences, based on the geometry of the object 103 to be built, and these instructions are sent to the controller for execution. Scan parameters may include laser power, scan speed (or spot distance and exposure time), spot size, and / or other parameters affecting the shape of the melt pool. For all powder layers, the layer thickness is conventionally the same and set by the user. However, for some embodiments described below, the powder layer thickness is also a variable to be selected based on the geometry of the object 103 to be built.

[0082] refer to Figure 3The powder bed melting apparatus further includes a gas nozzle 111 for delivering gas into the build chamber 101 and a gas exhaust end 112 for extracting gas from the build chamber 101, so as to generate a gas flow from one side of the powder bed 104 to the opposite side in the gas flow direction G. The build preparation software can conceptually divide the powder bed 104 into channel-shaped irradiation zones 1, 2, 3, and 4 (sometimes referred to as "lanes"), with each scanner 106a, 106b, 106c, and 106d assigned to a different irradiation zone within the channel-shaped irradiation zones 1, 2, 3, and 4, such that the irradiation of the powder bed 104 by the scanner 106a, 106b, 106c, and 106d is limited to the area to be solidified falling within the assigned irradiation zone 1, 2, 3, and 4. The scanning of the areas to be consolidated falling within the assigned irradiation zones 1, 2, 3, and 4 is sequenced such that the scans of the assigned scanners 106a, 106b, 106c, and 106d are performed in the direction opposite to the gas flow (as indicated by the non-solid arrows). (WO 2014 / 125280 and WO 2014 / 125258 (which are incorporated herein by reference in their entirety) describe the selection of the scan sequence based on the gas flow direction, and these principles are applied to each scanner assigned to each irradiation zone 1, 2, 3, and 4). In this way, simultaneous scanning of the powder bed 104 can be performed while mitigating problems caused by melting downstream of the gas flow direction of the upstream laser beam, because condensate clouds and spatter will be primarily confined downstream of the laser beam within the corresponding channel-shaped irradiation zones 1, 2, 3, and 4 that have already been melted by the laser beam. As used herein, "downstream" means within or considered to be within the debris flow generated by melting through the upstream point or region. As used herein, the term "downwind" refers to a region or point further along the gas flow direction G, regardless of whether it falls within or is considered to fall within debris generated by the melting of the upwind point or region. The use of channel-shaped irradiation zones 1, 2, 3, and 4 approximates the rule for avoiding downstream scanning of the powder bed in multi-scanner powder bed melting machines.

[0083] Figure 3 This demonstrates the movement of a bidirectional recoater 109 across a powder bed 104 while irradiating it with laser beams 118a, 118b, 118c, and 118d, simultaneously holding each laser beam 118a, 118b, 118c, and 118d within its corresponding channel-shaped irradiation zones 1, 2, 3, and 4. The formation of slices 103a and 103b of object 103 is shown for powder layers 104a and 104b, and the material so far consolidated within these slices is shown as darker areas. A problem with this method is that the available time for irradiating the material in each channel-shaped irradiation zone is unequal, and there may not be sufficient time to irradiate the material within channel-shaped irradiation zones 1, 2, 3, and 4 without delaying the recoater movement (or introducing an additional delay). This... Figure 3The diagram shows that powder layer 104b has been formed, and the recoating device is in the process of forming powder layer 104a by moving in direction W1. The formation of powder layer 104a gradually covers powder layer 104b, making it no longer usable for irradiation. Powder layer 104b is formed first across irradiation region 4, then across irradiation regions 3 and 2, and finally across irradiation region 1, while powder layer 104a is formed across irradiation regions in the reverse order 1, 2, 3, and 4. Therefore, irradiation region 1 of powder layer 104b is formed last, but it is first covered by powder layer 104a, followed by irradiation region 2, then irradiation region 3, and finally irradiation region 4. Therefore, the usable time of irradiation region 1 of powder layer 104b is less than that of all other irradiation regions 2, 3, and 4; the usable time of irradiation region 2 of powder layer 104b is less than that of irradiation regions 3 and 4; and the usable time of irradiation region 3 of powder layer 104b is less than that of irradiation region 4. This could result in laser beams 118c and / or 118d not being fully utilized, as these laser beams 118c, 118d may complete irradiation of the assigned irradiation areas 3, 4 in powder layer 104b before the corresponding irradiation areas in powder layer 104a become available. Furthermore, laser beams 118a and / or 118b may not have sufficient time to irradiate powder layer 104b before these irradiation areas are covered by powder layer 104a, necessitating the introduction of a recoating delay to provide sufficient time. Additionally, when the recoater 109 is above irradiation areas 1, 2, 3, 4, the assigned laser beams 118a, 118b, 118c, 118d may have to be turned off, as it can be assumed that no area of ​​irradiation areas 1, 2, 3, 4 can be processed during this time. For example, in addition to not scanning laser beams 118a, 118b, 118c, 118d across recoater 109, a safety zone can be implemented on one or both sides of recoater 109 in which scanning should not occur (as disclosed in WO 2015 / 140547). This is demonstrated by the interruption of irradiation of powder layer 104b by laser beam 118b due to recoater 109 moving into irradiation zone 2. These problems occur for each powder layer, but for alternating powder layers, these problems will occur in the opposite direction, such as when powder layer 104b is formed by movement of recoater in the opposite direction.

[0084] refer to Figure 4a and Figure 4bIn one embodiment of the invention, the irradiation areas, in this embodiment, are irradiation areas 1a, 2a, 3a, 4a, 1b, 2b, 3b, and 4b of powder layer 104a and irradiation areas 1a', 2a', 3a', 4a', 1b', 2b', 3b', and 4b' of powder layer 104b, respectively, determined based on the movement of recoater 109 during the stroke of forming powder layers 104a and 104b. Each scanner 106a, 106b, 106c, and 106d is assigned to an irradiation area within the irradiation areas 1a, 2a, 3a, 4a, 1b, 2b, 3b, 4b, 1a', 2a', 3a', 4a', 1b', 2b', 3b', and 4b', and irradiation is determined for each powder layer 104a and 104b. The sequence ensures that each irradiated region 1a, 2a, 3a, 4a, 1b, 2b, 3b, 4b, 1a', 2a', 3a', 4a', 1b', 2b', 3b', 4b' is irradiated before the irradiated regions 1a, 2a, 3a, 4a, 1b, 2b, 3b', 4b' are covered during the formation of the next powder layer.

[0085] The powder layers 104a and 104b shown in the attached figures represent alternating powder layers formed during the powder bed melting process. Therefore, multiple powder layers 104a are formed and dispersed among multiple powder layers 104b. Powder layers 104a are formed by the movement of the recoater 109 in the recoater direction W1, and powder layers 104b are formed by the movement of the recoater 109 in the recoater direction W2.

[0086] In this embodiment, multiple channel-shaped irradiation areas 1a, 2a, 3a, 4a, 1b, 2b, 3b, 4b; 1a', 2a', 3a', 4a', 1b', 2b', 3b', 4b' are defined for each powder layer 104a, 104b. Different irradiation areas within the channel-shaped irradiation areas 1a, 2a, 3a, 4a, 1b, 2b, 3b, 4b; 1a', 2a', 3a', 4a', 1b', 2b', 3b', 4b' have different sizes. In this embodiment, the channel-shaped irradiation areas have different widths in the moving directions W1 and W2 of the recoating device 109. Further away from the completion position of the recoating device 109 ( Figure 4a The completion location for powder layer 104a is shown, and Figure 4bThe channel-shaped irradiation areas 1a, 2a, 3a, 4a; 1a', 2a', 3a', 4a' shown for the finished position of powder layer 104b are wider in the recoating directions W1, W2 than the channel-shaped irradiation areas 1b, 2b, 3b, 4b; 1b', 2b', 3b', 4b' closer to the finished position. In this way, it is ensured that the laser beams 118a, 118b, 118c, 118d allocated to the irradiation areas 1a, 2a, 3a, 4a, 1b, 2b, 3b, 4b; 1a', 2a', 3a', 4a', 1b', 2b', 3b', 4b' can complete the scanning of one or more areas within the irradiation area before the area is covered by the next powder layer. In another embodiment, the width of each irradiation zone 1a, 2a, 3a, 4a, 1b, 2b, 3b, 4b; 1a', 2a', 3a', 4a', 1b', 2b', 3b', 4b' is based not only on the completion position but also on other factors, such as the predicted irradiation time for the area(s) to fall within the irradiation zone and / or for one of the areas(s) to be irradiated within the irradiation zone. Because these additional factors are considered, in the recoating directions W1, W2, the channel-shaped irradiation zone farther from the completion position of the recoating device 109 can be narrower than the channel-shaped irradiation zone closer to the completion position. However, it is permissible for each laser beam 118a, 118b, 118c, 118d to have unequal irradiation times within a single powder layer 104a, 104b, as long as the scanner can begin irradiating the area on the next powder layer 104a, 104b once the scanner has finished irradiating the allocated area(s) in the powder layers 104a, 104b.

[0087] exist Figure 4a and Figure 4bIn the illustrated embodiment, for each powder layer, more channel-shaped irradiation areas 1a, 2a, 3a, 4a, 1b, 2b, 3b, 4b, 1a', 2a', 3a', 4a', 1b', 2b', 3b', 4b' are determined than when scanners 106a, 106b, 106c, 106d are present in the device, and at least one scanner of scanners 106a, 106b, 106c, 106d is assigned to more than one channel-shaped irradiation area 1a, 1b; 2a, 2b; 3a, 3b and 4a, 4b; 1a', 1b'; 2a', 2b'; 3a', 3b' and 4a', 4b' for each powder layer. In the illustrated embodiment, for each powder layer 104a, 104b, each scanner 106a, 106b, 106c, 106d is assigned the same number (in this example, two) of channel-shaped irradiation areas 1a, 1b; 2a, 2b; 3a, 3b; 4a, 4b; 1a', 1b'; 2a', 2b'; 3a', 3b'; 4a', 4b'. However, this is not necessary, and different scanners 106a, 106b, 106c, 106d can be assigned to different numbers of channel-shaped irradiation areas. By assigning more than one irradiation zone 1a, 1b; 2a, 2b; 3a, 3b; 4a, 4b; 1a', 1b', 2a', 2b', 3a', 3b', 4a', 4b' in powder layers 104a, 104b to scanners 106a, 106b, 106c, 106d, if one of the assigned irradiation zones in powder layers 104a, 104b is unavailable for irradiation (because it has not yet been formed or is covered by recoater 109 and / or the next powder layer), the area to be solidified in another irradiation zone of these irradiation zones in scanners 106a, 106b, 106c, 106d can be directed. Irradiation areas 1a, 1b and 1a', 1b' are assigned to the first scanner 106a, irradiation areas 2a, 2b; 2a', 2b' are assigned to the second scanner 106b, irradiation areas 3a, 3b; 3a', 3b' are assigned to the third scanner 106c, and irradiation areas 4a, 4b; 4a', 4b' are assigned to the fourth scanner 106d.

[0088] exist Figure 4aAs powder layer 104a is formed, the irradiation zones become available for scanning in the order of 1a, 2a, 3a, 4a, 4b, 3b, 2b, 1b. When irradiation zones 1a, 2a, 3a, and 4a become available, scanners 106a, 106b, 106c, and 106d begin scanning one or more areas within these zones. The scanning of the areas to be solidified and / or the stripe formation direction within each irradiation zone (see WO 2014 / 125280 and WO 2014 / 125258) are arranged such that the scanning is performed in the direction opposite to the gas flow direction G. The dimensions of these irradiation zones 1a, 2a, 3a, and 4a are typically determined such that only a partial irradiation of the areas to be solidified within these zones is completed before irradiation zones 1b, 2b, 3b, and 4b become available for scanning. When irradiation zones 1b, 2b, 3b, and 4b become available for scanning, the assigned scanners 106a, 106b, 106c, and 106d switch the scanning to irradiation zones 1b, 2b, 3b, and 4b to ensure that the scanning of one or more areas of these irradiation zones 1b, 2b, 3b, and 4b is completed before they are covered during the formation of the next powder layer. The scanning in zones 1b, 2b, 3b, and 4b is performed in the direction opposite to the gas flow direction G.

[0089] When the irradiation of one or more areas to be solidified within the corresponding irradiation zones 1b, 2b, 3b, and 4b is completed, the assigned scanners 106a, 106b, 106c, and 106d switch back to the corresponding irradiation zones 1a, 2a, 3a, and 4a. Before the irradiation zones 1a, 2a, 3a, and 4a are covered during the formation of the next powder layer, the scanning of one or more areas within the zones 1a, 2a, 3a, and 4a is completed by scanning in the direction opposite to the gas flow direction G.

[0090] When the irradiation areas 1a, 2a, 3a, and 4a of powder layer 104a are completed, the assigned scanners 106a, 106b, 106c, and 106d switch to scanning the next powder layer 104b that is being formed or has already been formed. Figure 4bThe irradiation areas 1a', 2a', 3a', 4a', 1b', 2b', 3b', and 4b' of powder layer 104b are shown. Because the starting and ending positions of the recoating device 109 of powder layer 104b are reversed compared to the previous layer 104a, the widths of the irradiation areas 1a', 2a', 3a', 4a', 1b', 2b', 3b', and 4b' change accordingly. When the scanner completes irradiation of the corresponding irradiation areas 1a, 2a, 3a, and 4a of powder layer 104a to be solidified, scanners 106a, 106b, 106c, and 106d switch to scanning the corresponding irradiation areas 1a', 2a', 3a', and 4a' of powder layer 104b. Before the recoating unit 109 completes the formation of the powder layer 104b, the scanners 106b, 106c, and 106d assigned to the irradiation areas 2a, 3a, and 4a of the powder layer 104a can be switched to scan the corresponding irradiation areas 2a', 3a', and 4a' of the powder layer 104b. As the powder layer 104b is formed, the irradiation areas become available for scanning in the order of 1a', 2a', 3a', 4a', 4b', 3b', 2b', and 1b'. The dimensions of these irradiation areas 1a', 2a', 3a', and 4a' are determined such that, typically only a portion of the area(s) within these areas is irradiated before the irradiation areas 1b', 2b', 3b', and 4b' assigned to the same scanners 106a, 106b, 106c, and 106d become available for scanning. When irradiated areas 1b', 2b', 3b', and 4b' become available for scanning, the assigned scanners 106a, 106b, 106c, and 106d switch the scanning to irradiated areas 1b', 2b', 3b', and 4b' to ensure that the scanning of one or more areas to be consolidated in these irradiated areas 1b', 2b', 3b', and 4b' is completed before they are covered during the formation of the next powder layer 104a. The scanning in irradiated areas 1b', 2b', 3b', and 4b' is performed in the direction opposite to the gas flow direction G.

[0091] When the irradiation areas 1b', 2b', 3b', and 4b' are completed, the assigned scanners 106a, 106b, 106c, and 106d switch back to the corresponding irradiation areas 1a', 2a', 3a', and 4a'. Before the irradiation areas 1a', 2a', 3a', and 4a' are covered during the formation of the next powder layer 104a, the area(s) within the irradiation areas 1a', 2a', 3a', and 4a' are scanned by scanning in the direction opposite to the gas flow direction G.

[0092] When the corresponding irradiation areas 1a', 2a', 3a', and 4a' of powder layer 104b are completed, the assigned scanners 106a, 106b, 106c, and 106d switch to scanning the next powder layer 104a that is being formed or has already been formed (refer to the above reference). Figure 4a (Description of the scan order).

[0093] In this way, the irradiation time of irradiation zones 1b, 2b, 3b, 4b; 1b', 2b', 3b', 4b' closer to the completion position of the recoater 109 may be shorter than that of irradiation zones 1a, 2a, 3a, 4a; 1a', 2a', 3a', 4a' farther from the completion position, because the irradiation zones 1b, 2b, 3b, 4b; 1b', 2b', 3b', 4b' are narrower than the irradiation zones 1a, 2a, 3a, 4a; 1a', 2a', 3a', 4a', and the area(s) to be irradiated in each irradiation zone may be smaller. Therefore, the irradiation zones 1b, 2b, 3b, 4b; 1b', 2b', 3b', 4b' closer to the completion position of the recoater 109 will be completed quickly after formation, thereby reducing or minimizing the delay in the recoater 109 starting to form the next powder layer 104a, 104b. Furthermore, the scans in the channel-shaped irradiation zones 1a, 2a, 3a, 4a, 1b, 2b, 3b, 4b, 1a', 2a', 3a', 4a', 1b', 2b', 3b', and 4b' restrict or eliminate the simultaneous irradiation of two points, where one of these points is downstream of the other, in a direction opposite to the gas flow direction G. For example... Figure 4a and Figure 4b As shown, the irradiation area can be allocated to scanners 106a, 106b, 106c, and 106d such that the total size of the irradiation area allocated to each scanner 106a, 106b, 106c, and 106d for each powder layer 104a, 104b is approximately the same. In this embodiment, this is achieved by allocating both the widest irradiation areas 1a and 4a' and the narrowest areas 1b and 4b' to the same scanner 106a and 106d, allocating both the next widest irradiation areas 2a and 3a' and the next narrowest areas 2b and 3b' to the same scanner 106b and 106c, and so on.

[0094] refer to Figure 5In another embodiment, the width of each channel-shaped irradiation zone 1a, 2a, 3a, 4a, 1b, 2b, 3b, 4b is based on the movement of the recoater 109 and the size of the area to be consolidated within each irradiation zone 1a, 2a, 3a, 4a, 1b, 2b, 3b, 4b. Specifically, the total area of ​​the area(s) to be consolidated within the irradiation zones 1b, 2b, 3b, 4b allocated to the scanners 106a, 106b, 106c, 106d closer to the completion position of the recoater 109 is less than the total area of ​​the area(s) to be consolidated in the irradiation zones 1a, 2a, 3a, 4a allocated to the scanners 106a, 106b, 106c, 106d further away from the completion position of the recoater 109. As shown, this may result in the irradiation zones closer to the completion position being wider than those further away from the completion position, depending on the shape of the area(s) to be consolidated. In this embodiment, the total area of ​​the area(s) to be consolidated within the irradiation zone is used as an indicator of the irradiation time of the area by the scanner. However, instead of the total area, or other parameters besides the total area, other parameters may be used as an indicator of the irradiation time of the area by the scanner, such as the length of the perimeter of the area(s), the length of the scan path used to scan the area, the span between the end and start points of the scan path, etc.

[0095] exist Figure 6 In another embodiment shown, more than one scanner 106a, 106b, 106c, 106d is assigned to channel-shaped irradiation zones 1b and 2b, and 3b and 4b, closer to the completion position of the recoater 109, thereby potentially breaking the preferred condition that downstream points are not irradiated simultaneously with upstream points in order to achieve the desired irradiation rate in these irradiation zones. Sufficiently good part quality can still be achieved if the downstream point is within the maximum interval distance d from the upstream point. WO 2019211587 (incorporated herein in its entirety) discloses a method for determining downstream points for simultaneous irradiation with upstream points, and this method can be used herein to sequence scanners 106a, 106b, 106c, 106d assigned to the same channel-shaped irradiation zones 1b and 2b; 3b and 4b.

[0096] It has been found that in multi-laser-beam processes (such as those performed in the RenAM 500Q powder bed melting machine), when a downstream point on the powder bed is simultaneously exposed to an upstream point and within the maximum separation distance, the quality of the solidified downstream point is largely unaffected by airborne debris generated by the exposure of the upstream point. Outside these acceptable boundaries, simultaneous processing of two points on the powder bed can affect the quality of the solidified downstream point. Therefore, a downstream point can be a point within an airborne debris zone. The airborne debris zone can be a region of the powder bed where airborne debris generated by the solidification of the upstream point is considered to be carried by the gas flow. The airborne debris zone can be determined based on the location of the upstream point.

[0097] In some builds, the impact of condensate and spatter on downstream processing quality may not be a problem, for example, if the molten material produces very little condensate and / or spatter, if the gas flow is good enough to remove spatter and / or condensate to prevent unacceptable adverse effects, and / or if the adverse effects of condensate and / or spatter are acceptable for the build. In such cases, the gas flow direction G can be disregarded when determining the irradiation zone. Furthermore, it may be impossible to define a channel-shaped irradiation zone for each scanner, as the working field of each scanner may not extend across the entire powder bed 104 in the gas flow direction G.

[0098] Figure 7a and Figure 7b An example is shown of how the irradiation zone can be determined for each powder layer 104a, 104b. Figure 7a and Figure 7bIn the diagram, the working fields of each scanner 106a, 106b, 106c, and 106d in the x and y directions are defined by 130x1, 130x2, 130y1, and 130y2. The working field of scanner 106a is defined by the area of ​​130x1 and 130y1, the working field of scanner 106b is defined by the area of ​​130x2 and 130y1, the working field of scanner 106c is defined by the area of ​​130x1 and 130y2, and the working field of scanner 106d is defined by the area of ​​130x2 and 130y2. The irradiation areas 1, 2, 3, and 4 of powder layer 104a and the irradiation areas 1', 2', 3', and 4' of powder layer 104b are determined such that the irradiation areas fall within the assigned working fields of scanners 106a, 106b, 106c, and 106d. The dimensions of each irradiation zone 1, 2, 3, 4; 1', 2', 3', 4' are based on the completion position of the recoater 109 when forming the corresponding powder layers 104a, 104b. In this embodiment, the irradiation zones are determined as 1, 2, 3, 4; 1', 2', 3', 4', such that the irradiation time for completing one or more areas within irradiation zones 3, 4 and 1', 2' closer to the completion position of the recoater 109 when forming powder layers 104a, 104b is less than the irradiation time for irradiation zones 3, 4 and 1', 2' further away from the completion position. In this embodiment, the dimensions of the irradiation zones are based on the total area of ​​one or more areas to be consolidated falling within each irradiation zone 1, 2, 3, 4; 1', 2', 3', 4'. Specifically, in terms of the total area of ​​one or more of the areas falling within each of the irradiated zones 1, 2, 3, 4; 1', 2', 3', 4', the irradiated zones 3, 4 and 1', 2', which are closer to the completion position of the recoater 109 when forming powder layers 104a, 104b, are smaller than the irradiated zones 1, 2 and 3', 4', which are farther from the completion position. This can reduce or minimize the delay in recoater movement to begin forming the next powder layer 104a, 104b.

[0099] To consolidate the powder in layer 104a, when each irradiation zone 1, 2, 3, 4 becomes available for scanning and the recoater 109 has moved far enough to be able to scan at least a portion of irradiation zones 1, 2, 3, 4, the assigned laser scanners 106a, 106b, 106c, 106d begin scanning laser beams 118a, 118b, 118c, 118d across irradiation zones 1, 2, 3, 4. Upon completion of scanning of irradiation zones 1, 2, 3, 4 in powder layer 104a, laser scanners 106a, 106b, 106c, 106d begin scanning laser beams 118a, 118b, 118c, 118d across irradiation zones 1', 2', 3', 4' of the next powder layer 104b. Upon completion of scanning of irradiation zones 1', 2', 3', and 4', laser scanners 106a, 106b, 106c, and 106d begin scanning laser beams 118a, 118b, 118c, and 118d across irradiation zones 1, 2, 3, and 4 of the next powder layer 104a, and so on. It will be understood that the size and shape of irradiation zones 1, 2, 3, and 4 can vary for each powder layer 104a, for example, due to variations in the geometry of the slice 103a to be solidified, and the size and shape of irradiation zones 1', 2', 3', and 4' can vary for each powder layer 104b, for example, due to variations in the geometry of the slice 103b to be solidified.

[0100] The irradiation zones 1, 2, 3, 4; 1', 2', 3', 4' are not determined based on the gas flow direction. In one embodiment, the gas flow direction may be disregarded when determining the scanning order of each irradiation zone 1, 2, 3, 4; 1', 2', 3', 4'. However, the scans are sequenced such that the scan of each irradiation zone 1, 2, 3, 4; 1', 2', 3', 4' begins with the portion first formed by the recoater 109, for that powder layer 104a, 104b, proceeds in the recoater directions W1, W2 to the last portion formed by the recoater 109, and then proceeds backwards in the recoater directions W1, W2 for the next powder layer 104b, 104a (this is illustrated by the curved arrows across each irradiation zone 1, 2, 3, 4; 1', 2', 3', 4'). In this manner, at least some of the irradiated areas 1, 2, 3, 4; 1', 2', 3', 4' are scanned while the recoater 109 is forming powder layer 104a and while the recoater 109 is forming powder layer 104b. Furthermore, the scanning sequence ensures that each portion of the irradiated areas 1, 2, 3, 4; 1', 2', 3', 4' is scanned before the area is covered during the formation of the next powder layer 104a, 104b, while ensuring that the assigned scanners 106a, 106b, 106c, 106d have an area available for scanning on the already formed powder layers 104a, 104b or the powder layers 104a, 104b being formed by the recoater 109. The sequence may include selecting the order in which the defined portions (scanning units) of each irradiated area 1, 2, 3, 4; 1', 2', 3', 4' are scanned. For example, as is known in the art, scanning of the consolidation area can be divided into stripes or a checkerboard pattern, and the squares of these stripes or checkerboards can serve as ordered scanning units. Therefore, the method may include selecting the order in which the stripes or squares fall within the irradiation areas 1, 2, 3, 4; 1', 2', 3', 4'. However, it will be understood that other scanning units can be ordered, such as groups of stripes or groups of squares or individual scanning paths.

[0101] The order in which the scanning units for irradiation zones 1, 2, 3, 4; 1', 2', 3', 4' are selected for scanning can take into account the gas flow direction G. Specifically, the method may include selecting scanning units that are further upstream in the gas flow direction for scanning zones 1, 2, 3, 4; 1', 2', 3', 4', followed by scanning units that are further downstream in the gas flow direction. A combination of selecting the scanning unit order based on both the wiper directions W1, W2 and the gas flow direction G can result in a sorting of scanning units typically indicated by curved arrows. Scanning can begin with the unit closest to the starting position of the recoater 109 during the formation of powder layers 104a, 104b and / or the upwind unit and / or the unit determined by a combination of these two factors. For example, if the unit closest to the starting position of the recoater 109 is not the upwind unit, and if both requirements cannot be met simultaneously, the selection algorithm will resolve the conflict between these requirements. For example, the algorithm may assign a weight to each requirement and determine the irradiation order based on the order that minimizes the penalty calculated according to the weights.

[0102] If the downstream point is within the maximum interval distance d from the upstream point, simultaneous scanning of the downstream and upstream points may be acceptable, wherein the laser beam passes through the airborne debris generated by the scanning of the upstream point in order to scan the downstream point, as described in WO2019211587. Even if one irradiation zone 1, 1', 3, 3' is downstream of another irradiation zone 2, 2', 4, 4', this situation can also be achieved using the scanning sequence described above if the scanning of the two irradiation zones is properly sequenced. If it is not possible for each scanner 106a, 106b, 106c, 106d to maintain simultaneous scanning within a distance d using a single irradiation zone, multiple irradiation zones can be provided for each scanner 106a, 106b, 106c, 106d across the slices 103a, 103b to be consolidated in the gas flow direction G, with each irradiation zone assigned to one of the scanners 106a, 106b, 106c, 106d alternating with the irradiation zone assigned to another of the scanners 106a, 106b, 106c, 106d. Figure 8 An example of this situation is shown, in which the irradiation areas assigned to each scanner 106a, 106b, 106c, 106d are scanned in the order of a to c.

[0103] Figure 9Another embodiment of the invention is illustrated, wherein a gas flow G is considered to avoid irradiating a region downstream of another irradiation region of scanners 106a, 106b, 106c, 106d, which have a working field that does not cover the entire powder bed. In this embodiment, two or more irradiation regions are assigned to each scanner 106a, 106b, 106c, 106d. The irradiation of the irradiation regions is sequenced such that when upwind irradiation regions 1a, 1b, 3a, 3b are being irradiated, any downwind irradiation regions 2a, 2b, 4a, 4b simultaneously irradiated are not downstream of upwind irradiation regions 1a, 1b, 3a, 3b. Figure 9 In the example shown, while upstream irradiation areas 1a and 3a are irradiated, downstream irradiation areas 2a and 4a are irradiated, these downstream irradiation areas being offset in the gas flow direction G so as not downstream of the upwind irradiation areas 1a and 3a (i.e., within the airborne debris). When scanners 106a and 106c irradiate upstream irradiation areas 1b and 3b respectively, scanners 106b and 106d irradiate downstream irradiation areas 2b and 4b so as not downstream of the upwind irradiation areas 1b and 3b (i.e., within the airborne debris). This scanning sequence may result in irradiation of areas where debris from one or more previously irradiated upwind areas(s) has already landed, but this trade-off may be acceptable. Processing through airborne debris may be less desirable for part quality than remelting debris that has landed on the powder bed.

[0104] For ease of sequencing, it may be desirable that the areas irradiated simultaneously (e.g., 1a and 2a, and 3a and 4a) have approximately the same size, such that the irradiation times for irradiated areas 1a and 2a, and 3a and 4a, are substantially the same. However, the irradiated areas 3a, 3b, 4a, and 4b closer to the completion position of the powder layer 104a in the recoater 109 are determined to be smaller, for example, than the irradiated areas 1a, 1b, 2a, and 2b further away from the completion position, such that the irradiation time for irradiated areas 3a, 4a, 4a, and 4a is shorter than the irradiation time for irradiated areas 1a, 1a, 2a, and 2b. In this way, the movement delay of the recoater for forming the next powder layer 104b can be reduced or completely avoided. For the next powder layer, scanners 106c and 106d can be assigned irradiation areas that take longer to irradiate than the irradiation areas assigned to scanners 106a and 106b, such that any difference in irradiation time between the two combined powder layers is less than the difference in irradiation time between each individual powder layer, i.e., within a difference threshold and / or substantially equal. Across multiple powder layers, the irradiation areas are determined such that the difference in irradiation time for each scanner 106a, 106b, 106c, 106d tends towards a common value, such as zero.

[0105] Figure 10a and Figure 10bAnother embodiment is shown, in which the slices 103a and 103b to be consolidated within the powder layers 104a and 104b are divided into irradiation areas of equal size (except where the irradiation area is bisected by the boundaries of the slices 103a and 103b to be consolidated). (In Figure 10a In the middle, the irradiation areas are 11, 12, 13, 21, 22, 23, 31, 32, 33, 34, 35, 41, 42, 43, 44, and 45, and in... Figure 10b In this embodiment, slices 103a and 103b are divided into a square grid (hereinafter referred to as a checkerboard). The checkerboard pattern may conform to the squares of the checkerboard pattern used to define the length of the grating scan path across the slices 103a and 103b to be consolidated (the width of each square defines the length of the scan path), or it may be defined separately from the scan path length (e.g., the scan path length may be defined by smaller squares or by stripes across the squares). Therefore, the irradiation area is not determined by the completion position of the recoater 109 when forming powder layers 104a and 104b, but by the preset size of the grid (e.g., squares) and the geometry of the slices 103a and 103b to be consolidated.

[0106] The number of irradiation zones allocated to each scanner 106a, 106b, 106c, 106d is determined at least in part based on the completion position of the recoater 109 when forming the corresponding powder layers 104a, 104b. Specifically, compared to a set of irradiated areas 31, 32, 34, 35, 41, 42, 43, 45, 11', 12', 13', 15', 21', 22', 33', 36', 27' that are farther from the completion position (in this example, these irradiated areas are assigned to only two of the scanners 106a, 106b, 106c, 106d), a set of irradiated areas 11, 12, 22, 33, 43, 14', 24', 31', 42' that are closer to the completion position of the recoater 109 can be assigned to a larger number (e.g., all) of the scanners 106a, 106b, 106c, 106d to minimize the time spent irradiating these areas, so that the irradiation of these areas is completed before the recoater 109 covers these areas during the formation of the next powder layer 104b, 104a. Therefore, within a single powder layer 104a, 104b, the number of irradiation areas allocated to each scanner 106a, 106b, 106c, 106d may be unequal. However, across two or more powder layers 103a, 103b, the number (or percentage) of irradiation areas allocated to each scanner 106a, 106b, 106c, 106d will tend towards a common value. For example, the percentage of irradiation areas allocated to each scanner 106a, 106b, 106c, 106d may tend towards or equal to 100 x (1 / number of scanners). Therefore, for four scanners 106a, 106b, 106c, 106d, the percentage of irradiation areas allocated to each scanner 106a, 106b, 106c, 106d will tend towards or equal to 25%, considering the additional powder layers 104a, 104b. In this way, the time the scanners are not used is reduced. However, since more than one powder layer 104a, 104b can be scanned during the stroke of the recoater 109 across the powder bed, it is not required that the irradiation time of each scanner 106a, 106b, 106c, 106d be the same for any one powder layer 104a, 104b.

[0107] like Figure 10a , Figure 10b As shown, the pattern of the irradiated area can be rotated between powder layers 104a and 104b. The rotation angle can be an angle other than 0°, 90°, 180°, and 270°. Alternatively or additionally, the patterned irradiated area can be translated by a distance that is not an integer multiple of the square width. This avoids weakening lines that could appear if the boundaries between the irradiated areas are aligned across multiple powder layers 104a and 104b.

[0108] For powder layer 104a, scanners 106a, 106b, 106c, and 106d assigned to irradiation area group 1 irradiate these irradiation areas in sequence 11, 12, and 13. Scanners 106a, 106b, 106c, and 106d assigned to irradiation area group 2 irradiate these irradiation areas in sequence 21, 22, and 23. Scanners 106a, 106b, 106c, and 106d assigned to irradiation area group 3 irradiate these irradiation areas in sequence 31, 32, 33, 34, and 35, and scanners 106a, 106b, 106c, and 106d assigned to irradiation area group 4 irradiate these irradiation areas in sequence 41, 42, 43, 44, and 45.

[0109] For powder layer 104b, scanners 106a, 106b, 106c, and 106d assigned to irradiation area group 1 irradiate these irradiation areas in the order of 11', 12', 13', 14', 15', 16', and 17'. Scanners 106a, 106b, 106c, and 106d assigned to irradiation area group 2 irradiate these irradiation areas in the order of 21', 22', 23', 24', 25', 26', and 27'. Scanners 106a, 106b, 106c, and 106d assigned to irradiation area group 3 irradiate these irradiation areas in the order of 31', 32', and 33'. Scanners 106a, 106b, 106c, and 106d assigned to irradiation area group 4 irradiate these irradiation areas in the order of 41', 42', and 43'.

[0110] Therefore, for one powder layer 104a, irradiation groups 1 and 2 have fewer irradiation areas than groups 3 and 4, but for another (continuous) powder layer 104b, there are more irradiation areas than groups 3 and 4. Therefore, the percentage difference in irradiation time for each scanner 106a, 106b, 106c, 106d for two or more powder layers 104a, 104b is less than the percentage difference in irradiation time for each scanner 106a, 106b, 106c, 106d for powder layers 104a, 104b formed using bidirectional recoating.

[0111] For powder layer 104a, the irradiation of the irradiation areas is sequenced such that, before the recoating unit 109 has completed the formation of powder layer 104a, once irradiation area 31 in irradiation area group 3 and irradiation area 41 in irradiation area group 4 become available for scanning, that area is irradiated by the assigned scanners 106a, 106b, 106c, and 106d. During this time, scanners 106a, 106b, 106c, and 106d assigned to irradiation area groups 1 and 2 are scanning the irradiation area of ​​the previous powder layer 104b. When irradiation of one irradiation area within groups 3 and 4 is completed, the assigned scanners 106a, 106b, 106c, and 106d begin irradiation of the next irradiation area in groups 3 and 4. At some point during the formation of powder layer 104a, irradiation areas 11 and 21 become available for irradiation, and all scanners 106a, 106b, 106c, and 106d simultaneously irradiate powder layer 104a. When forming powder layer 104a, the irradiated areas 12, 22, 33, and 43 closest to the completion position of the recoater 109 can all be irradiated simultaneously to reduce the irradiation time of the area closest to the completion position of the completed section 103a compared to the area of ​​the section 103a further away from the completion position of the recoater 109. This is desirable because these irradiated areas have the shortest available irradiation time before being covered by the recoater 109 during the formation of the next powder layer 104b.

[0112] When the irradiation of irradiation zones 12, 22, 33, and 43 closest to the completion position is completed, scanners 106a, 106b, 106c, and 106d irradiate irradiation zones 13, 23, 34, 44, 35, and 45 further away from the completion position. Before scanners 106a, 106b, 106c, and 106d have completed irradiating all irradiation zones within groups 3 and 4, scanners 106a, 106b, 106c, and 106d assigned to group 1 and / or group 2 may begin irradiating the next powder layer 104b (starting from irradiation zones 11' and 21').

[0113] The powder layer 104b is irradiated in a similar manner based on the order of the irradiation zones, but the powder layer 104b begins and ends with the irradiation of the irradiation zones in groups 1 and 2, rather than with the irradiation of groups 3 and 4, wherein the irradiation zones of groups 3 and 4 occur before the recoater 109 reaches the end point of forming the powder layer 104b and is covered by the recoater 109 when forming the next powder layer 104a.

[0114] Figure 11a and Figure 11b It shows something similar to about Figure 10a and Figure 10b Another embodiment of the described example, but slices 103a, 103b are divided into stripe segments to define the irradiation area, rather than being divided into a square grid. (In Figure 11a In the middle, the irradiation areas are 11, 12, 13, 14, 21, 22, 23, 24, 31, 32, 33, 34, 35, 41, 42, 43, 44, 45, and 46, and in... Figure 11b In the diagram, irradiation areas 11', 12', 13', 14', 15', 21', 22', 23', 24', 25', 31', 32', 33', 41', 42', 43', and 44' are irradiated. The subscripts indicate the order of the irradiation stripes in each powder layer 104a, 104b. The stripes may conform to a stripe pattern used to define the length of the grating scan path across the slices 103a, 103b to be consolidated (the width of each stripe sets the length of the scan path). Like a square, the stripe formation direction (the longitudinal direction of the stripes) rotates between powder layers 104a, 104b. In this embodiment, the length of the stripe segments is determined based on the completion position of the recoater 109 when forming the corresponding powder layers 104a, 104b, wherein the stripe length of the irradiation area farther from the completion position is longer than the stripe length of the irradiation area closer to the completion position. However, in alternative embodiments, all stripe lengths are the same, or if the stripes intersect the boundaries of slices 103a, 130b, the stripe lengths are defined by the geometry of slices 103a, 103b, and the number of stripe segments assigned to each scanner 106a, 106b, 106c, 106d is determined based on the completion position of recoater 109 when forming the corresponding powder layers 104a, 104b.

[0115] exist Figure 10a and Figure 10b as well as Figure 11a and Figure 11b In the illustrated embodiment, a square or stripe can be irradiated by advancing a laser beam in a direction opposite to the gas flow direction across the square or stripe. The formation direction is the direction in which smaller scanning units (e.g., scanning paths) within the irradiation area are irradiated in sequence by the assigned scanners 106a, 106b, 106c, 106d.

[0116] Figure 12Another embodiment of the invention is illustrated. In this embodiment, multiple regions of each powder layer L1 to L11 are solidified by irradiating the powder bed with laser beams 118a, 118b, 118c, 118d, melting the powder in each region together with the powder of at least one other powder layer, to form a solidified segment together within the powder layer. To achieve this, the powder layers L1 to L11 have a thickness that is half or less than half of the maximum layer thickness to be solidified (e.g., melted) by laser beams 118a, 118b, 118c, 118d. This method reduces the irradiation time for each powder layer, thereby ensuring that the irradiation of each powder layer L1 to L11 can be completed during the formation of the next powder layer before the area to be irradiated is covered by the recoater 109.

[0117] An example of this method will now be described with reference to powder layer L3. The solidified section 141 of powder layer L3 is formed by solidified blocks 130 to 138. Each solidified block 130 to 138 solidifies a region of powder layer L3 together with a region of either powder layer L2 or powder layer L4. Each block 130, 132, 134, 136, and 138 is formed by directly irradiating powder layer L3 with one of laser beams 118a, 118b, 118c, and 118d, the laser parameters of which are sufficient to melt both powder layer L3 and powder layer L2, such that a solidified block is formed when the molten material solidifies. Each block 131, 133, 135, and 137 is formed by directly irradiating powder layer L4 with one of laser beams 118a, 118b, 118c, and 118d, the laser parameters of which are sufficient to melt both powder layer L4 and powder layer L3, such that a solidified block is formed when the molten material solidifies. Therefore, the consolidation segment 141 in each powder layer is formed by areas consolidated by direct irradiation of the powder layer and areas consolidated by direct irradiation of a later (e.g., the next) powder layer. Thus, the irradiation time for each powder layer is reduced compared to consolidating all areas by direct irradiation of the powder layer. Another way to consider this embodiment is that irradiation for each powder layer is distributed across two or more passes of the recoater 109 across the powder bed 104. The number of passes of the recoater 109 can be increased, but when two layers are consolidated by exposure, the irradiation time for forming the object is the same as or at least equivalent to the irradiation time for forming the object when the powder layer is formed at twice the layer thickness. If the irradiation time for each powder layer is greater than the time it takes for the recoater to complete a pass across the powder bed, there is typically no or very little penalty for the build time. However, since the consolidation of the powder layer can be completed even after the powder layer has been covered by the next powder layer, it may not be necessary to prioritize irradiating the areas of the powder layer near the completion position of the recoater when the powder layer is formed. If an area remains unconsolidated even after being covered by the next powder layer, it can be consolidated when the next powder layer is irradiated.

[0118] Furthermore, this method allows for maintaining, for example, preferred spacing and order of irradiation relative to the gas flow direction, since it is no longer necessary to complete the consolidation of the powder layer before the area to be consolidated is covered during the formation of the next powder layer. This method can also reduce or even eliminate significant residual stress due to shrinkage of the consolidated material. Voids created by powder aggregation during the melting of the material can be filled before other areas within the molten powder layer. Therefore, this method can simultaneously mitigate warping of the object and the presence of porosity within the object. Additionally, the powder blocks consolidated during the formation of each area extend across different groups of layers for different areas (e.g., blocks 130, 132, 124, 126, 138 are offset relative to adjacent (i.e., directly adjacent) blocks 131, 133, 135, 137), thereby potentially reducing the weakening lines caused by prior art methods that consolidate all (or most) areas of the layer immediately after the formation of the powder layer.

[0119] In this embodiment, some blocks (e.g., blocks 132, 134, and 136) are formed with non-uniform thicknesses, such as T-shapes. This can be achieved by adjusting the penetration depth of the laser beam. The penetration depth can be varied by adjusting the energy density of the irradiation (e.g., by adjusting laser and / or scanning parameters, such as laser power). The laser and / or scanning parameters can be adjusted from those suitable for consolidating a single powder layer thickness to those suitable for consolidating powder thicknesses equivalent to two or more powder layers. Using appropriate laser and / or scanning parameters, these parameters produce a consolidated material with greater than 99%, and preferably greater than 99.9%, of the theoretically fully dense material. The adjustment can be a step change (as illustrated) or a gradual change. In this way, weakening lines in the build direction (vertical direction) are avoided.

[0120] The method may include selecting blocks 130, 138, and 139 that comprise overhanging regions of object 103, such that when forming a next powder layer across overhanging portions 130, 138, and 139, the component of the direction W of the recoater 109 lies in the overhanging direction O. The overhanging direction O is a vector perpendicular to the edge of the area of ​​the object to be formed in the powder layer, having a direction from the solidified material of that area to the powder. In the example shown in FIG. 11, block 139 is solidified by irradiating layer L10 and forms an overhanging portion of object 103. The overhanging portion has an overhanging direction O. When forming the next powder layer L11 covering the overhanging portion, the movement direction W of the recoater 109 lies in the overhanging direction O (or has at least one component in the overhanging direction). Block 140 forms an overhanging portion having an overhanging direction opposite to that of block 139. Therefore, powder layer L11 is irradiated to form block 140. In the example where a bidirectional recoater 109 is used, the powder layer L11 is formed by the movement of the recoater in a recoater direction having a component opposite to the overhang direction of block 140. Any consolidation section of the powder layer will have overhang portions with opposite overhang directions. Thus, the overhang portions of the powder layer transition from overhang portions to overhang portions to be consolidated by direct irradiation of the powder layer to overhang portions to be consolidated by irradiation of the next powder layer. This method can reduce or eliminate the adverse effects caused by portions of the overhangs getting stuck on the recoater 109 as it moves across the powder bed during the formation of subsequent powder layers. For example, movement of the recoater across the consolidation material layer in a direction opposite to the overhang direction may cause the layer to move or otherwise adversely affect the layer, for example, by pushing the powder under the layer, while movement of the recoater in another direction can avoid such adverse effects.

[0121] Figure 13 Another embodiment of the invention is shown. In this embodiment, the powder layer thickness is selected based on the geometry of the surface of object 103 (hereinafter referred to as "variable layer thickness"). This embodiment is shown and will be described below in conjunction with the bidirectional recoater 109; however, it will be understood that variable layer thickness can also be implemented with a recoater that spreads the powder layer in only a single direction. Furthermore, variable layer thickness can be implemented where irradiation is not performed while the recoater moves across the powder bed to form the powder layer (e.g., scanning is not performed during wiping). However, a preferred embodiment irradiates the area of ​​the powder layer while it is being formed.

[0122] The dashed line 150 represents the desired geometry of the object to be formed. The build preparation software slices the geometry into layers to be formed in a powder bed fusion process, wherein these layers have a thickness based on the object's geometry 150. In this embodiment, the layer thickness is based on the shallowness of the overhanging portion of the object relative to the build plane 110. The thickness of the slice is determined based on the layer thickness, up to a maximum layer thickness Tmax, which results in the overhanging portion of the slice having a length up to a maximum length Dmax. As the angle of the overhanging surface on the object increases, thicker layers can be used while still meeting this requirement. This is in Figure 13 As shown, the layer thickness increases from Tmin to Tmax in a continuous layer. Tmin can be 0 μm. Therefore, for overhangs with very shallow angles in geometry and / or for overhangs parallel to the build plane 110, slices can be formed in a series of segments 151, 152, 153, each of which has a maximum length Dmax, wherein between the formation of each segment 151, 152, 153, a powder layer is formed by a recoater 109 at the same height as the previous powder layer. For example, the first segment 151 can be formed when the segment is connected to the consolidation material of the previous (lower) layer. Then a powder layer is formed (reformed) at the same height as the previous layer, and then the powder layer is irradiated to form segment 152. Then a powder layer is formed (reformed) at the same height as the previous layer, and then the powder layer is irradiated to form segment 153. By limiting the maximum length of the overhang of the slice, excessive heat buildup can be avoided and thus deformation or curling of the object that may lead to build failure can be avoided. In addition, for zero-thickness layers, the powder that was shed during the irradiation of the powder layer is replenished before the powder layer is irradiated to form the next segment of the slice.

[0123] The maximum length Dmax can be less than the width of a single track of the solidified material produced by irradiating the powder (e.g., the width of a single weld). Therefore, each segment 151, 152, 153 of the overhang can be formed by scanning a single laser beam along a single scanning path (profile) that extends around at least a portion of the material already solidified in the powder layer or a previous powder layer, such that the material solidified by the scanning profile is connected to the previously solidified material. To ensure the solidified material is connected to the previously solidified material, the track of the solidified material produced by irradiating the scanning path will overlap with the already solidified material, such that the segment of the overhang connects to a portion of the constructed object. Therefore, the length of the segment of the overhang will be less than the width of the track produced by scanning along the profile.

[0124] To determine the contours and / or areas to be scanned in the powder layer, the procedure first determines the required layer thickness based on the shallowest angle of overhang at each z-height (distance in the build direction) and determines slices of these layer thicknesses. Alternatively, slices are determined for the minimum layer thickness (e.g., 10 μm). Then, one or more complete (closed) contours are determined for each slice. It is determined whether there are segments of that contour or each contour that can be consolidated by irradiating a later powder layer, for example, because the overhang at that location is below a threshold distance Dmin / above a threshold angle. For example, segments of contours or areas between the minimum distances Dmin and Dmax can be consolidated by irradiating the current layer, while shorter segments of contours or areas below the minimum distance Dmin in the current powder layer may not be irradiated. Material in these shorter segments can be consolidated by irradiating contours in later powder layers. Therefore, the contours scanned by irradiating layers may be open (only a portion of the initially determined closed contours). One or more segments of a profile or area above Dmax (e.g., 152 and 153) can be solidified by irradiating a powder layer of zero thickness (i.e., a powder layer formed at the same z height as the previous powder layer).

[0125] Laser parameters (such as laser power) and / or scanning parameters can be varied for different layer thicknesses. For example, laser parameters and / or scanning parameters can be adapted to reduce the energy density of thinner layers. This reduction in energy density can help avoid overheating in overhanging regions, where the cooling rate may be lower compared to the core of the object.

[0126] like Figure 13 As shown, the portion of an object that does not form the object's surface (i.e., the object's core) can be formed with the maximum permissible layer thickness Tmax. The object's core can be formed by offset blocks, as shown in the reference. Figure 12 As described, irradiating a thicker region of powder within the core with the same layer thickness as the overhang can result in faster builds compared to processing the core with the same layer thickness as the overhang. However, for the portion of the core located above the overhang, this can help mitigate overheating of the overhang region during the irradiation of later layers, which could lead to build failure.

[0127] To form a powder layer with a thickness less than the maximum layer thickness Tmax, the recoater 109 may not move across the entire powder bed 104, but rather spread powder only at locations of the areas to be consolidated (e.g., in overhanging areas and areas overlapping with the consolidation material in the underlying layer). Therefore, build-up delays that may be caused by the formation of these thinner layers can be reduced or minimized. This approach is facilitated by using a bidirectional recoater 109 that retains powder between two wipers 109a, 109b. In this embodiment, the recoater 109 moves differently along the powder layer formation path for different powder layers within the thinner powder layer, and for different powder layers, the recoater 109 may have different finish positions, such as different finish positions above the powder bed 104. Consider the finish positions of the recoater 109 for each powder layer, as referenced above. Figures 3 to 1 As described in 1, the irradiation area can be defined for the powder layer and / or assigned to scanners 106a, 106b, 106c, 160d.

[0128] It is believed that by forming overhanging regions with thinner (including zero-thickness) layers, it is possible to construct overhanging regions without support, whereas support would be required when only thicker layers are used. Renishaw has constructed unsupported dome-shaped structures using variable layer thicknesses.

[0129] It will be understood that it may also be desirable to vary the powder layer thickness based on the geometry of another surface of the object (such as the upward-facing surface (in terms of build orientation)). This could be desired to improve surface finish.

[0130] Figure 14 Further embodiments of the invention implementing variable layer thickness are illustrated. Each shaded dot represents a scan path 170 of a powder layer. Each (short) dashed line represents a molten pool 180, which can be generated by irradiating the corresponding scan path 170 with a laser beam. The molten pool has a depth greater than the thickness of the irradiated powder layer, such that the resulting solidified material is bonded to the underlying solidified material. In the illustration, for clarity, the molten pool depth is shown as approximately two powder layers, but in practice, the molten pool depth can be much deeper, such as tens of powder layers. The molten pool has a width greater than the horizontal spacing d between adjacent scan paths, such that adjacent scan paths form a continuum of solidified material.

[0131] Scan path group 181 forms the outer surface of the object, hereinafter referred to as the "skin" of the object. Scan path groups 183a and 183b form a consolidation material that merges / connects with the consolidation material of the skin in the underlying layer, and are hereinafter referred to as the "shell" of the object (the shell is the internal region between the skin and the core). The scan paths for the skin 182 and the shells 183a and 183b can be contour scan paths, i.e., scan paths that follow at least a portion of the shape of the outer surface of the object. The skin at least forms the surface (overhang) of the object that is oriented upwards during construction. However, it will be understood that the contour scan forming the skin can also form other surfaces, such as horizontal surfaces and upward-facing surfaces. (The direction of the surface is the surface normal, which is in the direction from the consolidation material to the powder.)

[0132] The scan path that forms the solidified material within the skin and / or shell is referred to below as the "core" of the object. The scan path of the core can be a contour scan path, or it can be a scan path arranged in another pattern (such as a raster scan path, for example, a known zigzag, striped, or checkerboard pattern used in powder bed melting). Therefore, the scan path of the core may not be parallel to the scan paths of the shell and skin, although... Figure 13 For convenience, the scan path of the core is shown as a scan path parallel to the skin and shell.

[0133] Line 181 represents the outline of the geometry to be formed by irradiating the solidified material.

[0134] The core's scanning path is irradiated over a powder layer, wherein the thickness (at least substantially) of the powder (unconsolidated material) between the surface of the powder bed and the underlying consolidated material is equal to the maximum layer thickness Tmax to be consolidated in the build. Scanning parameters suitable for consolidating this thickness are used throughout the core, such that the material consolidated by irradiation is linked to the material in the underlying consolidation. However, this powder thickness can be achieved by forming one or more powder layers by a recoater 109, as now described.

[0135] Irradiation of each scan path of the epidermis 181 is performed after the formation of a powder layer, the thickness of which depends on the geometry of the object being constructed, for example, based on the angle of the downward-facing surface to be formed by irradiating the scan path. The thickness of the powder layer (relative to the height of the previous powder layer) can range from 0 μm (“zero layer thickness”) to a maximum layer thickness Tmax. In one embodiment, possible powder layer thicknesses selectable by planning software can be within a defined step size between 0 μm and Tmax, such that Tmax is a multiple of the minimum step size in the powder thickness. The minimum step size in the powder thickness can be less than or equal to 20 μm, and preferably less than or equal to 10 μm. The minimum step size can be greater than or equal to 1 μm, and preferably greater than or equal to 5 μm. Tmax can be greater than or equal to 50 μm, and preferably greater than or equal to 60 μm. Tmax can be greater than or equal to 100 μm, or even greater than or equal to 120 μm.

[0136] In this embodiment, the powder layer thickness is based on the angle of the downward-facing surface to be formed by the scanning path. The angle of the downward-facing surface can vary for different portions of the contour scanning path. The contour scanning path does not have to be a closed scanning path, but can be "open," having a start and an end point. For example, if the angle of the downward-facing surface to be formed is greater than a threshold, this steeper surface can be formed by irradiating the contour scanning path on a subsequent powder layer. Furthermore, if a bidirectional recoater 109 is used to form the powder layer, the contour scanning path can only form an overhang in the recoater direction when the next powder layer is formed.

[0137] The scanning paths of shells 183a and 183b continue over the same powder layer as the core, but the scanning parameters (such as laser power) are dynamically adjusted as the scanning path moves from the adjacent core toward the outer surface of the object. The scanning parameters can be dynamically adjusted to reduce the melt pool depth as the scanning path moves from the adjacent core toward the outer surface of the object. It has been found that even if the first layer of the overhang is formed without deformation that could lead to build failure, irradiating subsequent powder layers above the overhang with maximum energy density can still cause build failure. Therefore, build failure can be avoided by reducing the laser and / or scanning parameters within the shell.

[0138] The position of the scan path on each powder layer can be based on the maximum distance dmax and minimum distance dmin of the scan path from adjacent scan paths (both within the same powder layer and other powder layers). This is for different angular orientations between adjacent scan paths / adjacent exposures. The maximum distance dmax and the minimum distance dmin can be different (and will depend in part on the shape of the molten pool). Angular orientation is determined by the angle. Limited to vectors between exposures on adjacent scan paths. Pointing to the construction plane 110. Typically, the depth of the melt pool is greater than its width, and therefore, larger minimum and maximum distances can be used for the vertical direction than for the horizontal direction. However, melt pools produced in conduction or transition modes can have a width greater than their depth. The minimum and maximum distances can transition smoothly between the horizontal and vertical directions. This is schematically shown at 185, where the elliptical rings show the acceptable distance range at each angular orientation, and the dashed ellipse shows the center value. This acceptable range provides some leeway in selecting the layer thickness of the epidermis, as the scan path of the epidermis does not need to be located at a precise distance from the adjacent exposure on the previous / next layer. This is in Figure 13 As shown, the scanning path of the epidermis does not perfectly follow the shape of the expected geometry 181. Furthermore, the overhang has a threshold angle relative to the build plane 110. For angles greater than this threshold angle, a powder layer thickness Tmax equal to the powder layer thickness used for the core can be used, because the maximum acceptable distance for this angle and larger angles has a vertical component equal to or greater than Tmax. For overhang angles below the threshold angle, a powder thickness thinner than Tmax is used. The threshold angle can be less than 45° or even less than 15°.

[0139] US 2020 / 0269352 discloses an exposure scheme in the overhang region where not every powder layer is irradiated in at least a portion of the area forming the surface. Unbound by any single theory, this exposure scheme is believed to help prevent build failure because, during the formation of the first layer in the overhang region, as the overhang region cools during build, it deforms upwards, but not enough to cause immediate build failure (and could lead to build failure if a hard recoater that does not easily overcome protruding material is used). When forming subsequent powder layers, scanning parameters are selected for the expected powder thickness, but due to the upward deformation of the overhang region, the expected powder thickness is not the actual powder layer thickness. Therefore, the scanning parameters used to scan the next layer may cause overheating and unacceptable deformation of the overhang region. Not irradiating each powder layer in the overhang region serves to compensate for the powder thickness loss caused by deformation without having to change the scanning parameters. However, this scheme may result in a rougher / less accurate surface finish due to the larger step size in the build direction z between the scan paths forming the surface.

[0140] In embodiments of the invention, a smoother / more accurate outer surface is achieved as the scanning paths of the skin remain closer together. However, overheating of the subsequent overhang is avoided in two ways. First, overheating of the overhang is avoided by reducing the energy density of the shell's scanning path. Second, if the powder layer thickness below the shell's scanning path is too thin, the shell's scanning path will not obtain a bonded material connected to the skin's scanning path for any given powder layer. This means that for overhangs below a certain angle, the bonded material formed by irradiating the shell's scanning path will separate in the plane of the powder layer from the bonded material formed by irradiating the skin's scanning path in the same powder layer. This gap in the bonded material of the powder layer is achieved by irradiating the shell's scanning path in subsequent powder layers. For example, the gap 184 between the shell scanning path group 183a and the skin scanning path 178 is bonded by irradiating the shell scanning path group 183a on subsequent powder layers.

[0141] Irradiation of the epidermal 182 scanning path can be performed using scanning parameters that are different from those used for the core scanning path.

[0142] In one embodiment, the shell scanning path may be an extension of the core scanning path, rather than a contour scan, wherein scanning parameters are adjusted to reduce the depth of the molten pool as the laser beam moves along the scanning path from the core to the shell.

[0143] refer to Figures 15a to 15f Now we will describe the layer-by-layer description of the irradiation scan path. Figure 15a The formation of the first four powder layers is shown. The first three powder layers L1, L2, and L3 are each formed with a powder thickness Tmax relative to the previous powder layer. The scan path is irradiated to form a vertical cross-section of the object. After irradiating the scan path 171, a fourth powder layer L4 is formed, which has zero layer thickness relative to the previous powder layer L3. This replenishes the powder that was shed due to irradiation by the scan path 171. The scan path 172 is then irradiated by a laser beam. Figure 15b and Figure 15c As shown, the process for the fourth powder layer is then repeated for the fifth and sixth powder layers, wherein powder layers L5 / L6 are formed to have zero layer thickness relative to the previous powder layers L4 / L5 to replenish the powder that has been stripped off due to the irradiation of scan paths 172 / 173, and then scan paths 173 / 174 are irradiated by a laser beam.

[0144] like Figure 15dAs shown, powder layers L7, L8, and L9 each have a powder thickness greater than zero but less than Tmax. Each powder layer is shown to have a different powder thickness relative to the previous powder layer. For each powder layer, scan paths 175, 176, and 177 are used to irradiate the skin. Since the combined powder thickness of layers L7, L8, and L9 is less than Tmax, no shell or core scan paths are irradiated on these powder layers.

[0145] Figure 15e A powder layer L10 is shown, which, together with layers L7, L8, and L9, forms a powder thickness substantially equal to Tmax from powder layer L6. Therefore, for layer L10, in addition to irradiating the skin scan path 178, the core scan path 190 and the shell scan path 183a are also irradiated. This leaves a gap 184 within powder layer L10 containing unconsolidated powder between the material consolidated via irradiation scan path 178 and the material consolidated via shell scan path 183a.

[0146] Additional powder layers L11, L12, and L13 are formed, and the epidermis is irradiated via scan paths 179, 193, and 194, as shown. Figure 15f As shown above, since the total thickness of powder layers L11, L12, and L13 adds up to a maximum of Tmax, the scan paths of the core 191 and shell 183b are irradiated on powder layer L13. The core scan path is irradiated using preset scan parameters for the core, and the shell scan path is irradiated using scan parameters adjusted for each shell scan path to produce different melt pool depths for each scan path. Irradiation of the shell scan path 183b consolidates the material within gap 184 on the previous powder layer L10. On powder layer L13, there is a gap 185 of unconsolidated material between shell 193b and the skin scan path 194.

[0147] During object formation, as the molten material cools, the overhanging areas can curl upwards. The wipers 109a, 109b on the recoater 109 are deformable or flexible (compliant), for example, made of deformable materials or comprising flexible bristles, allowing the wipers 109a, 109b to pass over any solidified material protruding above the build plane 110. Therefore, even if the object deforms upwards, a powder layer can still be formed. However, the upward deflection of the object alters the thickness of the powder to be exposed for solidification. This method can compensate for this deflection by adjusting the molten pool depth for the shell scan paths 183a, 183b and leaving the powder in the gaps 184, 185 between the shell scan paths and the skin, where the powder is solidified by irradiating the scan paths on a subsequent powder layer. In this way, overheating and build failure can be avoided.

[0148] Figure 16Alternative embodiments are shown in which the scan paths of core 191 and shell 183 are distributed across different powder layers, rather than limiting the scan paths of the shell and core to separate powder layers of Tmax. This allows the core and shell areas of material to be consolidated within a single layer to be consolidated by irradiating scan paths in powder layers and then irradiating scan paths on subsequent powder layers to melt the powder. The scan path of core 191 is distributed such that, for at least some powder layers, the area to be consolidated within a powder layer comprises multiple regions, each region being consolidated by irradiating the core scan path to melt the powder in that region together with the powder in at least one other powder layer to form the core within the powder layer. This is achieved by irradiating different regions within these powder layers with the powder in different other powder layers. For example, for powder layer L1, the powder of the core is consolidated by irradiating scan paths 170a and 170b, where scan path 170a is on powder layer L1 and scan path 170b is on powder layer L2. In this embodiment, to achieve this, the core scan path is irradiated with a powder thickness of half Tmax. However, it will be understood that core scan paths can be distributed with different powder thicknesses between adjacent core scan paths, which bind the powder in the same powder layer.

[0149] The scan path of the skin 183 is distributed across powder layers, some of which may not correspond to powder layers where the core scan path exists. Distributing the shell scan path across additional powder layers may be beneficial, as this reduces or eliminates the need to adjust scan parameters to change the melt pool depth. In particular, by positioning the shell scan path on appropriate powder layers to create a greater distance between the shell scan path and the skin, the irradiation effect of the shell scan path on the skin can be reduced, rather than changing the melt pool depth. Figure 16 An example of this situation is shown in the figure.

[0150] Usage Reference Figures 13 to 16 The described method allows for the formation of low-angle overhangs without support.

[0151] Where the shell scan ends (e.g., the size of the gap between the shell and the skin on a particular powder layer) and / or the adjustment of scan parameters (e.g., laser power) for different scan paths for the shell or as the laser beam moves along the scan path from the core to the shell, can be determined using a thermal model of the build, empirically based on previous builds of the object and / or based on feedback from sensors during the process, such as visible light or thermal cameras monitoring the build of the object and / or previous builds of the object. For example, based on images captured by a camera after each powder layer is formed, it can be determined whether areas of the object built so far protrude above the powder layer. Areas of the object protruding above the powder layer are identified as areas that should not be irradiated on that powder layer; for example, these areas become gaps between scan paths in the shell scan path and scan paths in the skin scan path. The thickness of the powder layer can also be predicted based on knowledge of the thickness of the powder layer formed above the protrusion, even after the area has been covered by powder during the formation of subsequent layers, and the adjustment of scan parameters for the shell scan path for subsequent layers is determined based on the predicted powder layer thickness. These determinations can be based on data obtained during one or more previous builds of the object to produce a final set of scan paths and scan parameters for the object's build; that is, adjustments are not necessarily made during the process, but can be made across builds.

[0152] When irradiation is performed during the formation of the powder layer using the recoater 109 Figure 16 The method can have advantages over Figure 14 The method shown has the advantage of more uniform irradiation across powder layers. This can reduce or eliminate the delay in irradiation when powder layer formation is complete, or the delay in the formation of the next powder layer when the current powder layer is irradiated. Furthermore, for both embodiments, if powder is locally spread in overhanging regions with angles below a threshold angle, the core can continue to be processed for the lower powder layer even when constructing powder layers with variable layer thicknesses in the overhanging regions. Further, with the possibility of variable powder layer thickness, adjusting the scanning parameters to change the melt pool depth and / or irradiating simultaneously with recoating, the scanning path can be arranged taking into account the movement of the recoater, particularly the starting and / or finishing positions of the recoater, so that if consolidation cannot be completed in time before the area within the powder layer is covered by the recoater during the formation of the next powder layer, that area (e.g., shell and / or core) can be consolidated by irradiating the scanning path in a later layer. This method can be compared with the reference... Figures 3 to 1 The method combination described in 0 is to avoid delays in powder layer formation and / or time when the material is not irradiated.

[0153] Will understand, refer to Figures 12 to 16The described method can be performed using a unidirectional recoater (a recoater that forms a powder layer during movement in only a single direction) and / or by not irradiating the powder layer during the movement of the recoater across the powder bed. Furthermore, see references... Figure 12 and Figure 16 The described method can be performed using a single scanner for guiding a laser beam.

[0154] It will be understood that modifications and alterations can be made to the above embodiments without departing from the scope of the invention as defined herein. For example, bidirectional spreading of the powder layer can be achieved, for instance, by providing powder feeders on opposite sides of the powder bed without using a pair of wipers 109a, 109b, wherein each feeder meterly feeds powder to different sides of a single wiper. Furthermore, Figures 1 to 1 The invention implemented in 1 is not limited to four scanners, but may include any number of scanners, more than one.

Claims

1. A method for determining the irradiation sequence in a powder bed melting process, wherein, The method involves operating each of a plurality of scanners to travel a corresponding energy beam across a powder bed, such that when a recoater is above the powder bed, the plurality of energy beams irradiate the powder bed and form a powder layer with the recoater, such that the movement of the recoater along the powder layer forming journey is different for different powder layers in the powder layer, the method including taking into account the different movement of the recoater along the powder layer forming journey for different powder layers in the powder layer, determining the irradiation sequence of the powder layers by assigning each scanner to an irradiation area, such that irradiation of each irradiation area is completed before the irradiation area is covered during the formation of the next powder layer.

2. The method of claim 1, further comprising determining the irradiation area of ​​the powder layer, wherein, The size of at least one of the irradiated areas is based on the movement of the recoater during the powder layer formation stroke of the recoater.

3. The method of claim 1 or claim 2, further comprising determining the irradiation area of ​​the powder layer, and determining the irradiation sequence by assigning a plurality of the irradiation areas to each scanner based on the movement of the recoating device on the powder layer forming stroke, such that irradiation of each irradiation area is completed before the irradiation area is covered during the formation of the next powder layer.

4. The method according to any one of the preceding claims, wherein, Different numbers of irradiation areas are assigned to at least one of the scanners on a continuous powder layer.

5. The method according to any one of the preceding claims, wherein, Within one of the powder layers, different numbers of irradiation areas are assigned to two or more scanners in the scanner.

6. The method according to any one of the preceding claims, wherein, The irradiation time for different scanners in one of the powder layers is different, wherein the number of irradiation areas can be allocated such that the total irradiation time of the scanners on two or more powder layers is all within a predetermined total irradiation threshold.

7. The method according to any one of the preceding claims, wherein, Determining the irradiation sequence includes assigning each scanner to the irradiation area based on a parameter indicating the available irradiation time between the formation of a powder layer across the irradiation area and the covering of the irradiation area during the formation of the next powder layer, wherein the available irradiation time differs for different irradiation areas, and wherein the parameter can be the available irradiation time between the formation of a powder layer across the irradiation area and the covering of the irradiation area during the formation of the next powder layer, and / or the position of the recoater at a specific time.

8. The method according to any one of the preceding claims, wherein, Each of the plurality of scanners is operated such that a corresponding energy beam travels across the powder bed, such that the plurality of energy beams irradiate the powder bed while the recoater is moving across the powder bed to form a powder layer.

9. The method according to any one of the preceding claims, wherein, In the powder bed melting process, a powder layer is formed using the recoater, such that one or more start and / or finish positions of the recoater on the powder layer forming journey are different for different powder layers, and the method includes determining an irradiation area of ​​the powder layer, wherein the size of at least one irradiation area is based on the one or more start and / or finish positions of the recoater on the powder layer forming journey during the formation of the powder layer, wherein an irradiation area closer to the finish position can include an area that can be irradiated in a shorter time period compared to an irradiation area further away from the finish position, and / or wherein the size is the width of the irradiation area in the direction of travel of the recoater across the powder bed or the area of ​​the irradiation area.

10. The method according to any one of the preceding claims, wherein, The powder bed melting process includes forming a continuous powder layer, wherein a first powder layer is formed by the recoating device moving across the powder bed in a first direction, and a second continuous powder layer is formed by the recoating device moving across the powder bed in a second direction opposite to the first direction, and wherein the completion position of each powder layer can be on one side of the powder bed, wherein for continuous layers, the completion position of the recoating device is on different sides of the powder bed, or the powder bed melting process includes forming a first powder layer extending partially across the powder bed and a second continuous powder layer extending across the powder bed with the recoating device, wherein the area of ​​the first powder layer is different from the area of ​​the second powder layer.

11. The method according to any one of the preceding claims, wherein, The powder bed melting process includes generating a gas flow across the powder bed in a direction perpendicular to the direction of movement of the recoater, and each irradiation area is defined to extend across the powder bed in the direction of the gas flow, and the width of the irradiation area in the direction of movement of the recoater is based on the movement of the recoater during the formation of the powder layer.

12. The method according to any one of the preceding claims, wherein, The scanner is assigned to the irradiation area such that when the irradiation area assigned to the scanner becomes unavailable for irradiation, another irradiation area assigned to the scanner becomes available for irradiation.

13. A powder bed melting process, the powder bed melting process comprising: A recoating device is used to form a powder layer in a powder bed, such that the movement of the recoating device during the powder layer forming stroke is different for different powder layers in the powder bed; And to operate each of the plurality of scanners to make the corresponding energy beam travel across the powder bed, such that when the recoater is above the powder bed, the plurality of energy beams irradiate the powder bed in an irradiation sequence determined according to the method of any one of claims 1 to 12.

14. A powder bed melting apparatus, the powder bed melting apparatus comprising a controller arranged to control the powder bed melting apparatus to perform the powder bed melting process according to claim 13.

15. A data carrier storing instructions, wherein, When the instructions are executed by the processor, the processor performs the method as described in any one of claims 1 to 12.

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