Powder bed fusion additive manufacturing method and apparatus

Abstract

The present invention relates to a powder bed fusion additive manufacturing method, which includes forming layers L1, L2 of powder of a powder bed and exposing these layers L1, L2 to one or more energy beams to melt the powder to form an object. Each layer L1, L2 is exposed to the energy beam or each energy beam forms a molten pool 300a to 300i in a conduction or transition mode, wherein the exposure distance HD between adjacent exposures in the layer L1, L2 is 40% to 60% of the width of the molten pool 300a to 300i produced by these exposures, and the offset OD of the exposures between the successively melted layers L1, L2 in the direction taken to measure the exposure distance HD is 40% to 60% of the exposure distance OD.

Description

Technical Field

[0001] The present invention relates to a powder bed fusion additive manufacturing method and apparatus, and in particular to a method and apparatus for forming an object in a layer-by-layer manner by melting powder of a powder bed so that the object has a single crystal or single crystal-like microstructure. Background Art

[0002] The powder bed fusion additive manufacturing method for producing an object includes the layer-by-layer solidification of a powder (e.g., a metal powder material) using a high energy beam (e.g., a laser beam or an electron beam). The powder layer is deposited on a powder bed in a build chamber, and the laser beam or electron beam is scanned across a portion of the powder layer corresponding to the cross section of the object being constructed. The laser beam or electron beam melts the powder to form a solidified layer. After the selective solidification of the layer, the powder bed is lowered by the thickness of the newly solidified layer, and another layer of powder is spread on the surface as needed and solidified.

[0003] WO 2014 / 13114444 A1 describes a device for producing three-dimensional workpieces by selective laser melting, which device comprises a control unit which is suitable for controlling the operation of a powder application device and an irradiation device to produce the desired microstructure, i.e. a polycrystalline spherical microstructure or a directional / dendritic solidification microstructure, including essentially dendrites and / or single crystals.

[0004] WO 2018 / 029478 A1 discloses an additive manufacturing system in which a series of energy pulses is determined to achieve a cooling rate to produce a specified microstructure such as a dendritic or honeycomb structure.

[0005] "Excellent mechanical and corrosion properties of austenitic stainless steel with unique crystal lamellar microstructure by selective laser melting" (S. Sun, T. Ishimoto, K. Hagihara, Y. Tsutsumi, T. Hanawa, T. Nakano, Scriptia Materialsia, 159, (2019) 89-93) discloses a method for forming a quasi-single crystal structure. The laser beam is scanned bidirectionally along the x-axis without rotation. Samples manufactured at higher energy densities have columnar units oriented only at + / -45°. The shape of the molten pool formed at these high energy densities has a shape close to that of a keyhole. The authors believe that due to the increased curvature of the molten pool in the keyhole mode, the lateral migration of the solid-liquid interface dominates at the bottom of the molten pool, and there is little chance that the units will grow in the build direction at the bottom of the molten pool. If vertically growing units are formed by chance, their growth will also be blocked by lateral solid-liquid interface migration. Fragments with (001) orientation along the build direction were partially observed in the lower part of the samples manufactured at higher energy densities, however, these fragments did not extend across multiple molten pools. Summary of the invention

[0006] According to a first aspect of the invention, there is provided a powder bed fusion additive manufacturing method, comprising forming layers of powder of a powder bed and exposing the layers to one or more energy beams to melt the powder to form an object, wherein each layer is exposed to the energy beam or each energy beam forms a molten pool in a conduction or transition mode, wherein the exposure distance between adjacent exposures within a layer is 40% to 60% of the width of the molten pool produced by the exposures, and the exposures between successively melted layers are offset by 40% to 60% of the exposure distance in the direction taken to measure the exposure distance.

[0007] It has been found that this exposed geometry produces a single crystal or quasi-single crystal microstructure. It is believed that this exposed geometry promotes the growth of grains in a direction 45° to the build direction (the build direction is perpendicular to the powder layer). This can form a crystalline microstructure with <110> The orientation is substantially parallel to the build direction.

[0008] The term "single-crystal-like microstructure" is used herein to mean that a majority of an object, in particular at least 65%, preferably at least 70%, even more preferably at least 90%, and most preferably at least 95% of the object has a single-crystal microstructure. Some regions of a component are considered to have a single-crystal microstructure when all grains within the region have an orientation difference of less than 15 degrees away from the single-crystal orientation.

[0009] It should be understood that "conduction mode" is used herein to refer to the energy of the energy beam being coupled into the powder bed primarily by thermal conduction, thereby producing a molten pool whose width is greater than its depth. This is in contrast to the keyhole mode in which the material in the molten pool is vaporized by exposure to the energy beam and holes are formed in the molten pool. The molten pool formed in the keyhole mode has a deep and narrow profile with an aspect ratio greater than 1.5. There is a transition mode between the conduction mode and the keyhole mode, in which the energy is not dissipated quickly enough and the processing temperature is raised above the vaporization temperature. The depth of the molten pool increases and penetration of the molten pool can begin. Preferably, the method includes exposing the layer to the energy beam or each energy beam to form a molten pool in a conduction or transition mode, having an aspect ratio of less than 1.5, preferably less than 1, more preferably less than 0.75, and most preferably less than or equal to 0.5.

[0010] It should be understood that "adjacent" is used herein to refer to some of the features that are the subject of the adjective "adjacent" (eg, exposures, weld pools, or hatches) being directly adjacent to (ie, next door to) each other.

[0011] The method may include scanning the energy beam or at least one of the energy beams along preferably parallel shadow lines on each layer, wherein the exposure distance is the shadow line distance between adjacent shadow lines. The shadow line distance between adjacent shadow lines may be 40% to 60% of the width of the molten pool (in a direction perpendicular to the direction of travel of the energy beam along the adjacent shadow lines) produced by exposing the adjacent shadow lines to one or more energy beams. The method may include scanning adjacent shadow lines one by one. The method may include scanning the shadow lines with the energy beam or at least one of the energy beams so that the heat accumulated in the area of ​​the powder bed does not cause the molten pool to deviate from the desired (conduction or transition mode) molten pool shape. The geometry of the section of the object being built may result in shadow lines of different lengths. In such a scenario, in order to maintain the desired molten pool shape, the method may include changing the scanning parameters to achieve different energy densities for different shadow lines, such as by changing the laser powder, scanning speed, exposure time and / or point distance, and / or scanning non-adjacent shadow lines continuously.

[0012] The hatching lines on the successively melted layers are parallel. The hatching lines of the layers may be scanned bidirectionally, i.e., back and forth along the hatching lines of the successive scans, or may be scanned unidirectionally. Unidirectional scanning may help dissipate heat and thus help maintain the desired melt pool shape.

[0013] Each layer may have a layer thickness that is less than half of the average (mean) melt pool depth (e.g., the average melt pool depth of at least 10 melt pools, preferably all melt pools). Each layer may have a layer thickness that is less than 50 microns, less than 40 microns, or less than 30 microns. In one embodiment, the layer thickness is about 20 microns. It has been found that the desired melt pool arrangement can be achieved with such layer thicknesses.

[0014] According to a second aspect of the present invention, a powder bed fusion additive manufacturing method is provided, comprising forming layers of powder of a powder bed and exposing the layers to one or more energy beams to melt the powder to form an object, wherein each layer is exposed to the energy beam or each energy beam forms a molten pool with an aspect ratio less than 1.5, wherein adjacent molten pools overlap so that the (average) spacing between the centers of the adjacent molten pools is 40% and 60% of the (average) width of the molten pools, and the center of each molten pool of the next layer is offset from the center of the molten pool of the immediately previous layer in a direction parallel to the layer by 40% to 60% of the spacing between the centers of the adjacent molten pools.

[0015] The exposed layers may include more than three layers, a majority of the layers, and preferably all of the layers formed when building the object.

[0016] Exposing each layer to the energy beam or each energy beam can form a molten pool spanning the layers arranged relative to each other, so that for multiple pairs of adjacent first molten pools formed in one of the layers, columnar grains formed during the solidification of the pair of adjacent molten pools at an angle of approximately 45 degrees to the build direction coincide with the bottom of the second molten pool formed in the next layer, thereby partially remelting the material melted during the formation of the pair of adjacent molten pools.

[0017] Each layer is exposed to the energy beam or each energy beam can form a molten pool across the layers arranged relative to each other, so that the lowest points on the molten pools in the successively solidified layers are offset relative to each other by an average value (mean) of about 45 degrees (such as between 40 degrees and 50 degrees) to the build direction. The average value can be calculated for at least 10 pairs of molten pools, and preferably all molten pools, extending across three or more layers in the layer, and preferably all layers. The average value can be calculated for molten pools that do not form the surface of the object, preferably molten pools that are two, three or more molten pool widths away from the surface of the object. For objects formed by exposing multiple shadow lines, the molten pool width is calculated perpendicular to the shadow lines.

[0018] It is believed that such a melt pool arrangement will produce a single crystal or single crystal-like microstructure.

[0019] According to a third aspect of the present invention, a powder bed fusion additive manufacturing device is provided, comprising a building platform for supporting a powder bed, a layer forming device for forming layers of powder to form a powder bed, a scanner for directing one or more energy beams to each layer to melt the powder in a selected area of ​​each layer, and a controller configured to control the scanner and the layer forming device to perform the method of the first aspect and / or the second aspect of the present invention.

[0020] According to a fourth aspect of the present invention, building instructions stored on a data carrier are provided, which, when executed by a controller of a powder bed fusion additive manufacturing device, enable the powder bed fusion additive manufacturing device to build an object according to the method of the first aspect and / or the second aspect of the present invention.

[0021] According to a fifth aspect of the invention, there are provided instructions stored on a data carrier which, when executed by a processor, cause the processor to generate building instructions for building an object using a powder bed fusion additive manufacturing apparatus according to the fourth aspect of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is a schematic diagram of a powder bed fusion additive manufacturing apparatus according to an embodiment of the present invention;

[0023] Figure 2 is a hatch exposure strategy for use in a method according to an embodiment of the present invention;

[0024] Figure 3 is a diagrammatic representation of a molten pool formed using a method according to an embodiment of the present invention;

[0025] Figure 4 shows a cross section of a part built in IN625 using a prior art exposure strategy in a plane parallel to the build direction of the part;

[0026] Figure 5 shows a cross-section of a part built in IN625 using an exposure strategy according to an embodiment of the present invention in a plane parallel to the build direction of the part; and

[0027] Figure 6 is an image obtained using electron backscatter diffraction (EBSD), showing a cubic single-crystal-like structure built in SS316L using a method according to an embodiment of the present invention. DETAILED DESCRIPTION

[0028] refer to Figure 1 , a powder bed fusion additive manufacturing apparatus according to an embodiment of the present invention includes a build chamber 101, which can be sealed from the external environment so that an inert atmosphere can be maintained therein. The build chamber 101 has partitions 115 and 116 defining a build sleeve 117. The build platform 102 is lowerable in the build sleeve 117. When a workpiece is built by selective laser melting of powder, the build platform 102 supports the powder bed and the workpiece 103. As successive layers of the workpiece 103 are formed, the platform 102 is lowered in the build sleeve 117 under the control of a drive (not shown).

[0029] When the workpiece 103 is built by the layer forming device (in this embodiment, the distribution device 108 and the wiper 109), a layer of powder 104 is formed. For example, the distribution device 108 can be a device as described in WO 2010 / 007396. The distribution device 108 distributes the powder onto the upper surface defined by the partition 115 and is spread across the powder bed by the wiper 109. The position of the lower edge of the wiper 109 defines a working plane 190, at which the powder is consolidated.

[0030] A plurality of laser modules 105a, 105c generate laser beams 118a, 118c for melting the powder 104, which are directed by corresponding optical modules 106a, 106c as needed. The laser beams 118a, 118c enter through a common laser window 107. Each optical module includes a steering optical device 121 (such as two mirrors mounted on a galvanometer) for steering the laser beam 118 across the working plane in a vertical direction and a focusing optical device 120 (such as two movable lenses for changing the focus of the laser beam 118). The scanner is controlled so that the focal position of the laser beam 118 remains in the working plane as it moves across the working plane. Instead of using a dynamic focusing element, an f-θ lens can be used to maintain the focal position of the laser beam in a plane.

[0031] The inlet and outlet (not shown) are arranged to generate a gas flow across the powder bed formed on the build platform 102. The inlet and outlet are arranged to generate a laminar flow with a flow direction from the inlet to the outlet. The gas is recirculated from the outlet to the inlet by a gas recirculation loop (not shown).

[0032] The controller 140 (including a processor 161 and a memory 162) communicates with the modules of the additive manufacturing device (i.e., laser modules 105a, 105b, 105c, 105d, optical modules 106a, 106b, 106c, 106d, building platform 102, dispensing device 108, and wiper 109). As described below, the controller 140 controls these modules based on software stored in the memory 162.

[0033] In use, the computer receives a geometric model, such as an STL file, describing a three-dimensional object to be constructed using a powder bed fusion additive manufacturing device. The computer slices the geometric model into a plurality of slices based on a defined layer thickness, which will be constructed as layers in the powder bed fusion additive manufacturing device. In this embodiment, the defined layer thickness L is less than 30 microns, preferably less than 20 microns.

[0034] The laser exposure sequence is then determined for the melt zone of each layer to form the corresponding cross-section (slice) of the object. Figure 2 In this embodiment, a plurality of parallel hatching lines 201a to 201e, 202a to 202e are determined for each layer, which hatching lines define the path that one or more lasers follow when melting a region of the powder layer to form the object. Figure 2 In FIG. 1 , the dark hatching 201a to 201e shows the hatching of the first layer, while the light grey hatching 202a to 202e shows the hatching of the next second layer. It should be understood that the hatching of all other layers will be substantially aligned in the build direction BD (see, for example, FIG. Figure 3 ).

[0035] The hatches are spaced within the layer at a predetermined exposure (hatch) distance HD. The hatch distance HD is set to 40% to 60% of the molten pool width w (the width of the molten pool perpendicular to the hatches). The molten pool width w is predetermined for a set of laser parameters selected for use, such as laser power, scanning speed (or spot distance PD and exposure time in the spot scanning mechanism used in ReniShaw's AM400 machine) and laser spot size (1 / e) (focal length). Typically, the laser parameters are selected to form a molten pool with a width of 80 microns to 200 microns, more typically about 130 microns to 170 microns. The laser parameters (and scanning mechanism) are also selected to ensure that the molten pool is formed in a conduction or transition mode, where the ratio of the depth d to the width w of the molten pool is less than one. In this embodiment, the laser parameters are selected so that the depth-to-width ratio of the molten pool is about 0.5 (taking into account fluctuations due to process variability).

[0036] For a single laser that exposes multiple adjacent hatches having a length above a predetermined threshold (e.g., longer than 0.5 mm), the laser beam scans the hatches sequentially in a bidirectional manner (scanning adjacent hatches in the opposite direction to the immediately preceding hatch). For shorter hatches, the laser beam may expose the hatches in an orderly but unidirectional manner, or the laser beam may expose the hatches in a disordered manner so that adjacent hatches are not processed sequentially. For such small segments, the order in which the hatches are irradiated may be randomized, with a specified minimum number of hatches between successively irradiated hatches and / or a specified minimum time delay between the processing of adjacent hatches. This may allow time for energy dissipation so that a molten pool of the desired size continues to be formed. In a multi-laser system, assigning hatches to different lasers enables more complex exposure strategies, but the overall purpose of any such exposure strategy is to form a molten pool with a desired aspect ratio. In addition, exposure strategies that do not include hatch scanning may be used, such as spaced point scanning as disclosed in WO 2016 / 079496, which is incorporated herein by reference.

[0037] The orientation of the object relative to the build direction can be selected based on a preferred hatch length for forming the desired microstructure. For example, an object comprising a rod- or bar-like structure can be oriented so that the hatch is not parallel (e.g., greater than 45 degrees) to the longitudinal direction of the rod- or bar-like structure. It may be preferred that the hatch is substantially perpendicular to the longitudinal direction.

[0038] In an alternative embodiment, the hatching is aligned with the longest direction of the cross-section of the part to be printed.

[0039] The hatches 201a to 201e and 202a to 202e between successively melted layers (or discrete exposures in the case of spaced spot scanning) are offset by an offset distance OD that is 40% to 60% of the exposure / hatch distance HD, and most preferably 50% of the exposure / hatch distance HD. The hatches across all layers are parallel.

[0040] Once calculated, the instructions are sent to the powder bed fusion additive manufacturing machine for execution.

[0041] It has been found that components formed using this exposure strategy have a substantially single crystal microstructure. Without being bound by any theory, the applicant believes that due to the present reference Figure 3 Explain the reasons for the formation of a single crystal microstructure. Figure 3 A typical melt pool arrangement that can be achieved when using such an exposure strategy is illustrated. Figure 3 The shape of the molten pool perpendicular to the hatching is shown. When one or more laser beams are scanned in the hatching to form the molten pools 300a to 300c, the first layer L1 is exposed to the one or more laser beams. Each molten pool overlaps the adjacent molten pool or each adjacent molten pool by 50% of its width w. Columnar grains 301a to 301i are formed in each molten pool along the steepest thermal gradient, which is generally orthogonal to the surface of the molten pool. The molten pool portion that is re-melted after solidification due to the overlap of the molten pools will be reformed to have grains based on the geometry of the molten pool subsequently formed. For the first layer L1, columnar grains 301a, 301b can be formed at the bottom of each molten pool aligned along the build direction BD. Due to the shape of the molten pool, the columnar grains 301c, 301d, 301e, 301f formed on the side of the molten pool (away from the center of the molten pool) will generally be more closely aligned at 45 degrees to the build direction BD. Therefore, columnar grains 301c, 301d, 301e, 301f formed toward the center of the molten pools 300a, 300b, 300c are formed. <100> Oriented grains. Formed away from the center of the molten pool <110> Oriented grains.

[0042] For the next layer L2 (and subsequent layers), the molten pool is offset from the center of the molten pool of the immediately preceding layer by an offset distance OD, which is 50% of the hatch spacing HD between the centers of adjacent molten pools in the immediately preceding layer. As a result, the bottom of each molten pool coincides with columnar grains 301c, 301d, 301e, 301f, which were formed during solidification of the molten pool in the immediately preceding layer and are oriented at 45 degrees to the build direction BD. These columnar grains 301c, 301d, 301e, 301f "seed" the molten pool so that grains with this orientation continue in the molten pool of the next layer, even at the bottom / center of the molten pool. This "seeding" and continuation of columnar grains 301c, 301d, 301e, 301f oriented at 45 degrees to the build direction BD results in a molten pool having a substantially parallel build direction. <110> Oriented single crystal microstructure.

[0043] like Figure 3 As shown in , in order to maintain this directional growth of columnar grains, the line between corresponding points (such as the bottom) of the melt pools of successively melted layers should form an angle A of about 45 degrees with the build direction BD. This will be controlled by the melt pool shape and the layer thickness.

[0044] The direction in which the hatches are scanned may be selected based on the direction of gas flow across the powder bed. For example, the order in which the hatches are scanned may be selected such that (in a direction perpendicular to the hatches) one or more energy beams progressively scan the hatches in a direction at least partially opposite to the gas flow direction. Furthermore, for hatches that are scanned unidirectionally, the hatches themselves may be scanned in a direction at least partially opposite to the gas flow direction.

[0045] The orientation in which the object is built relative to the build direction can be selected so that the single crystal microstructure extends through the object in a desired direction.

[0046] Example 1

[0047] A 1cm x 1cm x 1cm cube was built in IN625 using a Renishaw AM400 additive manufacturing machine and a state of the art exposure strategy. A layer thickness of 20 microns and the following laser parameters were used:-

[0048] Laser power = 190W

[0049] Point distance = 120 microns

[0050] Exposure time = 120 microseconds

[0051] Shadow distance = 95 microns

[0052] Figure 4is an image of a cross section of one of the cubes. The solidified melt pools can be clearly seen, with overlapping melt pools within one layer. The melt pools for each layer are essentially aligned in the build direction (layer offset is 0). The cube was analyzed for grain orientation using EBSD and was found to have a polycrystalline microstructure.

[0053] Example 2

[0054] A 1 cm x 1 cm x 1 cm cube was built in IN625 using a Renishaw AM400 additive manufacturing machine and the exposure strategy according to the invention as described above. A layer thickness of 20 microns and the following laser parameters were used: -

[0055] Laser power = 160W

[0056] Point distance = 45 microns

[0057] Exposure time = 60 microseconds

[0058] Shadow distance = 55 microns

[0059] Layer offset = 27.5 microns

[0060] Figure 5 is an image of a cross section of one of the cubes. The solidified melt pools can be clearly seen, with overlapping melt pools within one layer, and the melt pool of one layer offset perpendicular to the build direction by about 50% relative to the melt pool of the previous layer. The grain orientation of the cube was analyzed using EBSD, and it was found to have a single-crystal-like microstructure.

[0061] Example 3

[0062] A 1 cm x 1 cm x 1 cm cube was built in SS316L using a Renishaw AM250 additive manufacturing machine and an exposure strategy according to the invention as described above. A layer thickness of 20 microns and the following laser parameters were used:-

[0063] Laser power = 170W

[0064] Point distance = 80 microns

[0065] Exposure time = 80 microseconds

[0066] Shadow distance = 80 microns

[0067] Layer offset = 40 microns

[0068] The grain orientation of one of the cubes was analyzed using EBSD and was found to have a single-crystal-like microstructure in which its <110> Oriented parallel to the build direction. Images obtained using EBSD are Figure 6 Shown in.

[0069] Example 4

[0070] The parts were built in Hastelloy X using a Renishaw AM400 additive manufacturing machine and the exposure strategy according to the invention as described above. A layer thickness of 20 microns and the following laser parameters were used: -

[0071] Laser power = 160W

[0072] Point distance = 44 microns

[0073] Exposure time = 60 microseconds

[0074] Shadow distance = 66 microns

[0075] Layer offset = 33 microns

[0076] The grain orientation of the parts was analyzed using EBSD and was found to have a single-crystal-like microstructure.

[0077] It will be appreciated that the above embodiments may be changed and modified without departing from the invention described herein. For example, other materials may be used, such as other alloys that are difficult to weld. For example, the present invention may be used to form components having a single crystal or quasi-single crystal microstructure from superalloys such as other Inconel, Waspaloy, other Rene alloys, Incoloy, MP98T, TMS alloys, and CMSX single crystal alloys. Examples of such alloys are RENE41, RENE77, IN738, and CM247.

Claims

1. A powder bed fusion additive manufacturing method comprising forming a layer of powder of a powder bed and exposing the layer to one or more energy beams to melt the powder to form an object, wherein, Each layer is exposed to the energy beam or each energy beam forms a molten pool in conduction or transition mode, wherein the exposure distance between adjacent exposures within the layer is 40% to 60% of the width of the molten pool produced by the exposure, and the exposure between successively melted layers is offset by 40% to 60% of the exposure distance in the direction in which the exposure distance is measured.

2. The powder bed fusion additive manufacturing method according to claim 1, comprising: The energy beam or at least one of the energy beams is scanned along hatch lines on each layer, wherein the exposure distance is a hatch line distance between adjacent hatch lines.

3. The powder bed fusion additive manufacturing method according to claim 2, wherein: The hatch distance between adjacent hatches is 40% to 60% of a width of the molten pool resulting from exposure of the adjacent hatches to the one or more energy beams.

4. The powder bed fusion additive manufacturing method according to claim 2 or claim 3, comprising scanning the adjacent shadow lines one by one.

5. The powder bed fusion additive manufacturing method according to any one of claims 2 to 4, wherein: The hatching lines on the successively melted layers are parallel.

6. The powder bed fusion additive manufacturing method according to any one of the preceding claims, wherein: The layer thickness of each layer is less than half of the average depth of the molten pool.

7. The powder bed fusion additive manufacturing method according to any one of the preceding claims, wherein: The layer thickness of each layer is less than 50 micrometers.

8. A powder bed fusion additive manufacturing method comprising forming a layer of powder of a powder bed and exposing the layer to one or more energy beams to melt the powder to form an object, wherein: Each layer is exposed to the energy beam or each energy beam forms a molten pool with an aspect ratio less than 1.5, wherein adjacent molten pools overlap so that the spacing between the centers of the adjacent molten pools is 40% and 60% of the width of the molten pool, and the center of each molten pool of the next layer is offset from the center of the molten pool of the immediately previous layer in a direction parallel to the layer by 40% to 60% of the spacing between the centers of the adjacent molten pools.

9. The powder bed fusion additive manufacturing method according to claim 8, wherein: Each layer is exposed to the energy beam or each energy beam forms a molten pool spanning the layers arranged relative to each other, so that for multiple pairs of adjacent first molten pools formed in one of the layers, columnar grains formed during the solidification of each pair of adjacent molten pools at an angle of approximately 45 degrees to the building direction coincide with the bottom of the corresponding second molten pool formed in the next layer, thereby partially remelting the material melted during the formation of the pair of adjacent molten pools.

10. The powder bed fusion additive manufacturing method according to claim 8, wherein: Each layer is exposed to the energy beam or each energy beam forms a melt pool across the layers arranged relative to each other so that the lowest points on the melt pools in successively solidified layers are offset relative to each other by an average of about 45 degrees to the build direction.

11. The powder bed fusion additive manufacturing method according to claim 9, wherein: Each layer is exposed to the energy beam or each energy beam forms a melt pool across the layers arranged relative to each other so that the lowest points on the melt pools in successively solidified layers are offset relative to each other by an average of about 45 degrees to the build direction.

12. A powder bed fusion additive manufacturing device, comprising a building platform for supporting a powder bed, a layer forming device for forming layers of powder to form the powder bed, a scanner for directing one or more energy beams to each layer to melt the powder in a selected area of ​​each layer, and a controller, the controller being configured to control the scanner and the layer forming device to perform a method as described in any of the preceding claims.

13. A data carrier having built instructions stored therein, which, when executed by a controller of a powder bed fusion additive manufacturing device, cause the powder bed fusion additive manufacturing device to build an object according to the method according to any one of claims 1 to 11.

14. A data carrier having instructions stored therein, which, when executed by a processor, cause the processor to generate building instructions for building an object using the powder bed fusion additive manufacturing device according to claim 13.

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