WO2024263546A1

WO2024263546A1 - Systems and methods for gas flow in additive manufacturing

Info

Publication number: WO2024263546A1
Application number: PCT/US2024/034435
Authority: WO
Inventors: Yiannis KAPAROS; Corey MURPHY; Joseph D. SANDT; Jeffrey M. LEBLANC; Richard A. WESSEL, Jr.; Piotr LIEBERSBACH
Original assignee: Vulcanforms Inc.
Priority date: 2023-06-23
Filing date: 2024-06-18
Publication date: 2024-12-26

Abstract

Systems and methods for providing gas flow characteristics for gas heads for additive manufacturing. A gas head may have a tubular arrangement with proximal and distal openings to allow flow through the gas head from the distal to proximal opening. A gas head may draw gas including process ejecta into and through the gas head in two different directions, which may be along corresponding scan directions and transverse to a plane of a proximal opening or proximal edge of the gas head. A gas head may include an inlet at a bottom wall of the gas head to receive process ejecta between the bottom wall and a build surface and/or to influence movement of process ejecta in the gas head interior volume. Various levels of gas flow may be provided for exhaust ports of a gas head and/or for different gas heads by operating one or more flow control valves.

Description

SYSTEMS AND METHODS FOR GAS FLOW IN ADDITIVE MANUFACTURING

RELATED APPLICATIONS

[0001] This application claims priority under 35 U.S.C. § 119(e) to U.S. Provisional Application No. 63/509,853, filed June 23, 2023, the content of which is incorporated by reference in its entirety for all purposes.

FIELD

[0002] Inventive features relate to systems and methods for gas flow in additive manufacturing.

BACKGROUND

[0003] In some selective laser melting processes for additive manufacturing, one or more laser spots may be scanned over a thin layer of powder material. The powder that is scanned with the laser spot is melted and fused into a solid structure. Once a layer is completed, the structure is indexed vertically, a new layer of powder is laid down and the process is repeated. If an area is scanned with the laser spot on the new layer that is above a previous scanned area on the prior layer, the powder is melted and fused onto the solid material from the prior layer. This process can be repeated many times in order to build up a three-dimensional shape of almost any form.

[0004] Both single laser and multi-laser systems are used in selective laser melting processes. Some systems use a pair of galvanometer mounted mirrors to scan each laser beam over the desired pattern on the build surface. Some systems use motion stages to scan the laser over the build surface. Moreover, some systems use a combination of motion stages and galvanometers to scan the laser over the build surface.

SUMMARY

[0005] In some embodiments, a gas head assembly for an additive manufacturing system may include a tubular body defining an interior volume extending from a proximal opening at a proximal side of the body to a distal opening at a distal side of the body opposite the proximal side. The assembly may include an exhaust flow port in fluid communication with the interior volume, and the exhaust flow port may be configured to be fluidly coupled to a gas flow generator to create an exhaust gas flow. The exhaust gas flow may be configured to carry process ejecta out of the interior volume through the exhaust flow port. The exhaust flow port may be fluidly coupled to the interior volume at a position on the tubular body above the proximal opening and the distal opening.

[0006] In other embodiments, an additive manufacturing system may comprise a build surface on which a printed part is formable by fusing powder material supported on the build surface, and a gas head assembly positioned over the build surface and out of contact with the powder material. The gas head assembly may include a first tubular body defining an interior volume extending from a proximal opening at a proximal side of the body to a distal opening at a distal side of the body opposite the proximal side. The gas head assembly may further include a first exhaust flow port in fluid communication with the interior volume, and the first exhaust flow port may be configured to be fluidly coupled to a gas flow generator to create an exhaust gas flow. The exhaust gas flow may be configured to carry process ejecta out of the interior volume through the first exhaust flow port. The first exhaust flow port may be fluidly coupled to the interior volume at a position on the tubular body above the proximal opening and the distal opening.

[0007] In some embodiments, a method for additive manufacturing may include receiving a proximal gas flow into a gas head through a proximal side of the gas head. The proximal gas flow may include process ejecta from a melt pool of an additive manufacturing system. The method may further include receiving a distal gas flow into the gas head through a distal side of the gas head opposite the proximal side, and removing the proximal gas flow and the distal gas flow from the gas head through an exhaust flow port of the gas head. The exhaust flow port may be disposed between the proximal side and the distal side.

[0008] In further embodiments, a method for additive manufacturing may include directing energy from an optics assembly toward a build surface to melt and fuse powder material on the build surface, and moving a first gas head and the optics assembly in a first direction relative to a build surface. The first gas head may be on a leading side of the energy directed from the optics assembly toward the build surface. The method may further include receiving a distal gas flow into the first gas head at a distal side of the first gas head, and conducting at least some of the distal gas flow through the first gas head from the distal side to a proximal side of the first gas head. At least some of the distal gas flow may exit the first gas head at the proximal side, the proximal side being nearer to the energy than the distal side.

[0009] In other embodiments, a method for additive manufacturing may include directing energy from an optics assembly toward a build surface to melt and fuse powder material on the build surface, and moving a first gas head, a second gas head, and the optics assembly in a first direction relative to a build surface. The first gas head may be on a leading side of the energy directed from optics assembly toward the build surface, and the second gas head may be on a trailing side of the energy. Further, a lowermost surface of the first gas head and the second gas head may be at a same height above the build surface. The method may further include receiving a first distal gas flow into the first gas head at a distal side of the first gas head.

[0010] In some embodiments, a gas head for a gas head assembly of an additive manufacturing system may comprise a body which defines an interior volume and has a proximal opening at a proximal side of the body. A distal side of the body may be opposite the proximal side. A top wall may extend from the proximal side to the distal side, and a bottom wall may extend from the proximal side to the distal side. First and second exhaust passages may extend between the distal side and the proximal side, each of the first and second exhaust passages coupled respectively to first and second exhaust ports.

[0011] In other embodiments, a gas head for a gas head assembly of an additive manufacturing system may comprise a body which defines an interior volume and has a proximal opening at a proximal side of the body. A distal side of the body may be opposite the proximal side. A top wall may extend from the proximal side to the distal side, and a bottom wall may extend from the proximal side to the distal side. A first exhaust passage may be coupled to a first exhaust port, and a first inlet in the bottom wall may be positioned between the proximal side and the first exhaust passage. The first exhaust port may be configured to be fluidly coupled to a gas flow generator to create a first exhaust gas flow to carry process ejecta from an additive manufacturing process through the proximal opening, into the interior volume and out of the first exhaust port and to draw gas through the first inlet, into the interior volume and out of the first exhaust port.

[0012] In further embodiments, an additive manufacturing system may comprise a build surface on which a printed part is formable by fusing powder material supported on the build surface, and a gas head comprising a body which defines an interior volume and has a proximal opening at a proximal side of the body. A distal side of the body may be opposite the proximal side. A top wall may extend from the proximal side to the distal side, and a bottom wall may extend from the proximal side to the distal side. First and second exhaust passages may extend between the distal side and the proximal side, each of the first and second exhaust passages coupled respectively to first and second exhaust ports.

[0013] In some embodiments, a method for additive manufacturing may include receiving a first gas flow into a gas head through a proximal opening at a proximal side of the gas head. The first gas flow may include first process ejecta from an additive manufacturing process. The method may further include conducting the first gas flow through an interior volume of the gas head in a first direction and to a first exhaust port of the gas head. The method may also include receiving a second gas flow into the gas head through the proximal opening, the second gas flow including second process ejecta from the additive manufacturing process, and conducting the second gas flow through the interior volume of the gas head in a second direction and to a second exhaust port of the gas head, the second direction being transverse to the first direction.

[0014] In other embodiments, a method for additive manufacturing may include providing a gas head which includes a body having an interior volume, first and second exhaust ports, and an opening. The method may further include receiving a first gas flow into the interior volume of the gas head through the opening. The first gas flow may include process ejecta from a melt pool of an additive manufacturing process. The method may also include exhausting the first gas flow from the interior volume through the first exhaust port at a first flow rate that may be larger than a second flow rate through the second exhaust port. [0015] In some embodiments, a method for additive manufacturing may include providing a gas head which includes a body having an interior volume, a bottom wall having a proximal edge, a first exhaust port fluidly connected to the interior volume, a proximal opening defined at least in part by the proximal edge, and a first inlet opening in the bottom wall. The method may further include receiving a proximal gas flow into the interior volume of the gas head through the proximal opening, the gas flow including process ejecta from a melt pool of an additive manufacturing process. The method may also include receiving a first inlet gas flow into the interior volume through the first inlet opening, and exhausting the proximal gas flow and the first inlet gas flow from the interior volume through the exhaust port.

[0016] In other embodiments, a gas flow control for an additive manufacturing system may include a first exhaust flow port for fluid communication with a gas flow generator. The first exhaust flow port may be configured to conduct a first exhaust gas flow from a build volume of the additive manufacturing system towards the gas flow generator. The gas flow control may further include a second exhaust flow port for fluid communication with the gas flow generator. The second exhaust flow port may be configured to conduct a second exhaust gas flow from the build volume towards the gas flow generator. The gas flow control may further include a gas flow valve fluidly coupled between the gas flow generator and the first and second exhaust flow ports. The gas flow valve may be configured to control flow from the first and second exhaust flow ports to the gas flow generator. The gas flow valve may include a valve element movable to selectively impede and allow flow from the first exhaust flow port to the gas flow generator, and to selectively impede and allow flow from the second exhaust flow port to the gas flow generator.

[0017] It should be appreciated that the foregoing concepts, and additional concepts discussed below, may be arranged in any suitable combination, as the present disclosure is not limited in this respect. Further, other advantages and novel features of the present disclosure will become apparent from the following detailed description of various nonlimiting embodiments when considered in conjunction with the accompanying figures.

[0018] In cases where the present specification and a document incorporated by reference include conflicting and/or inconsistent disclosure, the present specification shall control. If two or more documents incorporated by reference include conflicting and/or inconsistent disclosure with respect to each other, then the document having the later effective date shall control.

BRIEF DESCRIPTION OF DRAWINGS

[0019] In the drawings, each identical or nearly identical component that is illustrated in various figures may be represented by a like numeral. For purposes of clarity, not every component may be labeled in every drawing. In the drawings: [0020] FIG. 1 is a schematic perspective view of an additive manufacturing system in an illustrative embodiment;

[0021] FIG. 2 is a schematic side view of an additive manufacturing system illustrating an optics unit and gas head assembly in an illustrative embodiment;

[0022] FIG. 3 is a perspective view of a gas head assembly including gas heads having a tubular body with distal and proximal openings;

[0023] FIG. 4 is a cross sectional view of a gas head assembly taken along the scan direction;

[0024] FIG. 5 is a perspective view of a proximal side of a gas head from FIG. 4;

[0025] FIG. 6 is a cross sectional top view of a gas head from FIG. 4;

[0026] FIG. 7 is an upper rear perspective view of a gas head configured to draw gas into and through the gas head in two directions;

[0027] FIG. 8 is an upper front perspective view of the FIG. 7 gas head;

[0028] FIG. 9 is a top view of the FIG. 7 gas head positioned in relation to a lineshaped area of laser incidence in some embodiments;

[0029] FIG. 10 is a side view of the FIG. 7 gas head;

[0030] FIG. 11 is a cross sectional top view of a gas head including one or more inlets on a bottom wall;

[0031] FIG. 12 is a cross sectional view of the FIG. 11 gas head along the flow direction 21b in FIG. 11;

[0032] FIG. 13 shows a side view of a gas head assembly configured to adjust a height of the gas heads above a build surface;

[0033] FIG. 14 is a schematic view of a gas head assembly and associated gas flow arrangement in an illustrative embodiment;

[0034] FIG. 15 is a schematic view of a gas head assembly and associated gas flow arrangement configured to provide a greater gas flow to one exhaust port of a gas head than other exhaust ports of the same and another gas head;

[0035] FIG. 16 is a schematic view of a gas head assembly and associated gas flow arrangement configured to provide a different levels of gas flow for exhaust ports of gas heads; [0036] FIG. 17 is a perspective view of a valve configured to control flow between two inlet ports and an outlet port;

[0037] FIG. 18 is a cross sectional view of the valve of FIG. 17 configured to permit flow between two inlet ports and the outlet port;

[0038] FIG. 19 is a top view of the valve of FIG. 17 configured to permit flow between two inlet ports and the outlet port;

[0039] FIG. 20 is a cross sectional view of the valve of FIG. 17 configured to impede flow between two inlet ports and the outlet port; and

[0040] FIG. 21 is a top view of the valve of FIG. 17 configured to impede flow between two inlet ports and the outlet port.

DETAILED DESCRIPTION

[0041] The incidence of one or more lasers on a layer of powder material in a selective laser melting additive manufacturing system may create a melt pool at the point of incidence (also referred to as a laser spot). The inventors have recognized and appreciated that dynamics within the melt pool may result in the generation of fumes and some degree of gasification of the molten material. Moreover, the heating, gasification, and rapid expansion of powder and molten material can also cause the melt pool and areas around the melt pool to eject particles upward and away from the melt pool. Such process ejecta emitted from a melt pool or otherwise as a result of the incident laser energy (e.g., individual powder particles, partially fused powder particles, cooled molten droplets, fumes from the melt pool, etc.) may cause problems during a build process. For example, process ejecta may result in delamination between build layers, inclusions, overbuilds, voids, and/or distortion in a final built component. Process ejecta may also result in damage to components of the system, including damage to a recoating blade or other portion of a powder deposition system, and/or to an optical component of the system.

[0042] The inventors have recognized and appreciated numerous benefits associated with additive manufacturing systems constructed and arranged to remove process ejecta emitted from a laser fusion process. These systems may mitigate the problems associated with process ejecta by preventing ejecta from depositing on other portions of the system (e.g., the build surface, powder bed, optical assembly, powder deposition system, etc.). In particular, the inventors have recognized and appreciated benefits associated with gas head assemblies that produce localized gas flows near a melt pool. Such gas head assemblies may cause process ejecta to be entrained and carried away from the area near the melt pool and may do so while maintaining a relatively low overall volume of circulating gas in the gas flow system, and/or while reducing disturbances to the powder surface.

[0043] The inventors have further observed that when laser energy is moved across a powder layer in a particular direction of motion (or scan direction), more ejecta may be emitted in a direction along but opposite from the scan direction than in the scan direction. In other words, more ejecta may be emitted behind a melt pool than ahead of a melt pool in relation to the direction of motion that laser energy is scanned or otherwise moved across the powder material on the build surface. In this regard, ejecta may be said to be emitted asymmetrically with respect to the direction of motion of the laser energy and melt pools. Accordingly, the inventors have recognized and appreciated the benefits associated with systems constructed and arranged to produce a correspondingly asymmetric gas flow or otherwise accommodate asymmetric ejecta creation in the area around the melt pool and/or the area of laser energy incidence. In this regard, a velocity, a flow rate, and/or an entrainment capacity of a gas flow used to remove ejecta from a laser incidence area may be greater behind the melt pool than ahead of the melt pool (or may be greater in an area trailing an area of laser energy incidence than ahead of the area of laser incidence in relation to a direction in which the laser energy is moved relative to the build surface), such that the greater volume of process ejecta emitted behind the melt pool may be carried away more effectively.

[0044] Some systems and methods for creating such localized and/or asymmetric gas flows have previously been described in our U.S. Patent Application No. 18/184,251 (filed March 15, 2023) and U.S. Patent No. 11,453,087 (filed August 5, 2019), both of which are incorporated herein by reference for all purposes in their entireties.

[0045] Some systems and methods for creating gas flows in additive manufacturing systems may include gas head assemblies having one or more gas heads coupled to or couplable to one or more gas flow generator(s). The gas head(s) may be positioned at or near the melt pool or laser incidence area to allow the gas flow generator(s) to produce a flow of gas that entrains and removes process ejecta from areas around the melt pool. In some systems, a gas head assembly may include a first gas head on a first side of the melt pool and a second gas head on a second side of the melt pool. For example, the first gas head may be behind or on a trailing side of laser energy used to create a melt pool with respect to a direction of motion of the laser energy relative to the build surface, while the second gas head may be ahead of or on a leading side of the laser energy with respect to the direction of motion. Additionally, in some systems, the two gas heads may produce gas flows having flow velocities, flow rates, and/or entrainment capacities that are non-uniform and/or asymmetric and/or otherwise different from each other (e.g., to accommodate the asymmetric distribution of process ejecta discussed above).

[0046] In some systems, including systems having gas heads on opposing sides of a melt pool (e.g., on trailing and leading sides of laser energy) as well as any system which uses a single gas head, the movement of a gas head across the build surface may produce aerodynamic disturbances and/or turbulence in areas ahead of, behind, and/or otherwise near the gas head. In addition to the potential for disrupting the powder material on the build surface, these aerodynamic disturbances may detract from the gas head’s entrainment performance. For example, in some systems in which a first gas head moves ahead of the melt pool and a second gas head moves behind the melt pool, detrimental effects on entrainment performance by the trailing gas head may be experienced because, as the first (leading) gas head moves in front of the second (trailing) gas head, the trailing gas head may move through a wake and/or other disturbances caused by the leading gas head.

[0047] In view of the above, the inventors have recognized and appreciated the benefits of gas heads and/or gas flow arrangements produced by one or more gas heads configured to reduce aerodynamic disturbances during gas head movement and/or improve process ejecta removal. In some embodiments, a gas head may be constructed to have a flow-through arrangement which permits gas to flow through a hollow or tubular body of the gas head during movement. Such flow-through arrangements may produce a smaller and/or less disruptive wake for a leading gas head than arrangements which force gas to flow around the gas head, and may provide benefits for a trailing gas head as well. In some cases, a gas head may be configured so that an exhaust port is fluidly coupled to an interior volume of the gas head at a location above both proximal and distal openings of the gas head. In some embodiments, a leading gas head may be configured to permit gas to flow through the gas head from a distal to a proximal side, and into a proximal opening of a trailing gas head for exhausting from the work area. These and/or other features may permit a gas head to improve pick up of process ejecta and/or reduce disturbance of a powder material on a build surface, e.g., leading and trailing gas heads may be positioned at a same height over a build surface thus avoiding any need to adjust a height of the gas heads with change in movement or scan direction.

[0048] In some other cases, a gas head may be configured to accommodate movement or scanning in a direction that is transverse to a proximal edge or to a plane of a proximal opening of the gas head. This may enable the gas head to operate with laser energy that is incident on a line-shaped area of the build surface that is transverse to the scan direction. In some embodiments, a gas head may be configured to cause gas flow into and/or through an interior volume of the gas head in a direction that is transverse to a plane of an opening through which process ejecta is drawn into the gas head and/or that is along a movement or scan direction of the gas head relative to a build surface. As noted above, process ejecta may be largely produced in a direction opposite to a scan direction in which laser energy is moved across a build surface. By configuring the gas head to generate gas flow into and/or through an interior volume of the gas head so as to be generally along the scan direction, process ejecta may be more effectively drawn into the gas head and removed from the work area. In some cases, laser energy may be incident on powder material on a build surface along a lineshaped area that is transverse to the scan direction, e.g., the line-shaped area may be at an angle of 45 degrees relative to the scan direction. Since it may be desirable to position an opening of the gas head into which process ejecta is drawn as near as possible to the lineshaped area (or other melt pool) to enhance pick up of process ejecta, the gas head opening may be arranged at an angle transverse to the scan direction. By arranging the gas head to cause gas flow into and/or through the interior volume of the gas head in a direction transverse to a plane of the gas head opening and generally along the scan direction, the gas head may more effectively pick up and remove process ejecta. In some cases, a gas head may have two exhaust ports and flow through the exhaust ports may be different from each other, e.g., depending on a movement direction of the gas head. This feature may allow the gas head to pick up process ejecta more effectively and depending on a direction of scanning. [0049] In some embodiments, a gas head may include an inlet opening in a bottom wall of the gas head, e.g., to help draw process ejecta into the gas head that is not picked up via a gas head opening adjacent the laser energy and/or melt pool. Alternately, or in addition, the inlet opening in the bottom wall of the gas head may help reduce turbulence or other disruption to powder material on the build surface that may be caused by movement of the gas head. As described more below, these features and others may be used together in any suitable combination or alone, e.g., a gas head may include a flow through configuration as well as be arranged to produce a gas flow into and/or through the gas head that is transverse to an opening of the gas head and/or be arranged to have an inlet opening in a bottom wall of the gas head. To the extent features described herein are not mutually exclusive, they may be combined and used together in any suitable arrangement.

[0050] It will be appreciated that any embodiments of the systems, components, methods, and/or programs disclosed herein, or any portion(s) thereof, may be used to form any part suitable for production using additive manufacturing. For example, a method for additively manufacturing one or more parts may, in addition to any other method steps disclosed herein, include the steps of selectively fusing one or more portions of a plurality of layers of precursor material deposited onto the build surface to form the one or more parts. This may be performed in a sequential manner where each layer of precursor material is deposited on the build surface and selected portions of the upper most layer of precursor material is fused to form the individual layers of the one or more parts. This process may be continued until the one or more parts are fully formed.

[0051] Turning to the figures, specific non-limiting embodiments are described in further detail. It should be understood that the various systems, components, features, and methods described relative to these embodiments may be used either individually and/or in any desired combination as the disclosure is not limited to only the specific embodiments described herein.

[0052] FIG. 1 shows a schematic view of an additive manufacturing system 100 including an optical assembly such as optics unit 1 that may direct one or more laser beams 4 onto a build surface 3 which may carry powder material to be operated on by the laser energy. The laser energy 4 may produce one or more melt pools 5 on the build surface, e.g., by selectively melting portions of the powder material on the build surface 3. The locations where melt pools 5 are formed on the build surface 3 may be controlled by moving the optics unit 1 and/or the laser energy 4 relative to the build surface 3, e.g., along scan directions 6 and/or 7 relative to the build surface 3, for example using motion stages, robotic systems or any other suitable drive. As will be appreciated, the scan direction is not limited to those illustrated by scan directions 6 and 7, as a scan direction may take any appropriate angle across the build surface 3. In some embodiments, the optics unit 1 may use movable elements such as galvomirrors, or other appropriate methods and systems for moving the laser energy relative to the build surface 3 in addition to or instead of moving the optics unit 1 itself. The system 100 may include one or more gas heads 2 to draw process ejecta into the gas head 2 for removal from the build surface 3 or other work area where laser energy is incident. The gas head 2 may move with the optics unit 1 along the directions 6 and/or 7, e.g., so at least one gas head 2 is adjacent a melt pool or other area where process ejecta are generated. The gas head 2 may be attached to the optics unit 1 for movement in the scan directions, or may be moved by a separate drive at least for some gas head movement. For example, the optics unit 1 and the gas head 2 may be coupled to a gantry system or other drive that moves the optics unit 1 and gas head 2 in a desired way. The additive manufacturing system 100 may include one or more controllers 8, e.g., operatively coupled with one or more controllable portions of the system such as the optics unit 1, the gas head 2 and/or other components such as actuators, valves, gas flow generators, and/or any other appropriate component. The controller 8 may include one or more processors 9 and associated non-transitory computer readable memory 10. The memory may include computer readable instructions that when executed by the one or more processors cause the additive manufacturing system to perform any of the methods and processes disclosed herein.

[0053] FIG. 2 depicts a schematic side view of the additive manufacturing system 100 of FIG. 1. As noted above, the gas head 2 may be attached to the optics unit 1 with a mounting bracket 11 or other appropriate attachment. Attachment of the gas head 2 to the optics unit 1 may help maintain the gas head 2 in a fixed or other desired position relative to the optics unit 1, at least in one direction such as along the directions 6 and/or 7. In this manner, as the optics unit 1 scanned over or otherwise moved relative to the build surface 3, the gas head 2 may also move over the build surface along a direction 6 and/or 7 at substantially a same velocity as the optics unit 1. Thus, the gas head 2 may move with laser energy as the laser energy moves across the build surface 3 to selectively melt powder material and form a printed or built part. Two or more gas heads 2 may be provided, e.g., a first gas head 2 on one side of the laser energy and a second gas head 2 on an opposite side of the laser energy 4. For example, the gas heads 2 may be positioned so that the first gas head 2 is on a leading side of the laser energy 4 and the second gas head 2 is on a trailing side of the laser energy 4 for movement in a first scan direction along the direction 6 and/or 7, and such that the first gas head 2 is on a trailing side of the laser energy 4 and the second gas head 2 is on a leading side of the laser energy 4 for movement in a second scan direction opposite the first scan direction. The laser energy 4 may pass through a space or gap 22 between the gas heads 2, e.g., such that one or both openings of the gas heads 2 proximal to the melt pool 5 may receive process ejecta. A gas flow generator 12 may be used to generate an exhaust gas flow 21 at the gas heads, e.g., to draw a flow of gas into and through the gas head 2 to evacuate process ejecta including particles, fumes, and/or gasses ejected from the melt pool 5 or otherwise created by the laser energy 4. For example, in FIG. 2 the gas flow generator 12 includes a first vacuum supply 121 which may draw a first flow of gas through the gas head 2 on the left and a second vacuum supply 122 may draw a second flow of gas through the gas head 2 on the right. Any suitable source of vacuum or otherwise relatively low pressure may be employed, such as fans, pumps, bellows, blowers, compressed gas sources, etc., and any appropriate number of vacuum supplies may be used, including a single vacuum supply or more than two vacuum supplies. The gas flow generator 12 may include one or more valves or other components to suitably control flow for one or more exhaust ports of the gas heads 2. [0054] In some cases, configurations that employ a gas head on a leading side of laser energy relative to a scan direction of the laser energy can disrupt powder material on the build surface, e.g., by causing turbulence or other gas movement as the leading side gas head moves across the powder material on the build surface. Such movement in gasses around the leading side gas head can cause disruption to powder material on the build surface and/or disturb exhaust gas flow into the trailing gas head, which may cause imperfections or inconsistencies in the printed part and/or cause suboptimal removal of process ejecta. In some cases, a leading side gas head can be configured to help reduce turbulence or other gas movement around the gas head. For example, in some cases a leading side gas head can be configured to include a hollow or tubular body which defines an interior volume of the gas head. The hollow body may have a proximal side adjacent the laser energy/melt pool and a distal side opposite the proximal side. As used herein, the terms distal and proximal with respect to a gas head may be understood to indicate relative positions with respect to a melt pool or laser energy during operation of the additive manufacturing system. In other words, for an additive manufacturing system configured to create a melt pool in a particular area, a proximal side of a gas head may be configured to be disposed closer to the melt pool and/or laser energy incidence area than the distal side. The body may be of generally tubular construction, having one or more flow ports or openings at the distal and proximal sides and at least one wall extending between the distal and proximal flow openings. Thus, in some cases, distal and proximal openings of the gas head may allow gas to flow through the gas head from the distal side to the proximal side as the gas head moves ahead of the laser energy during scanning movement. By permitting gas flow through the gas head, or at least into the gas head from the distal side into the interior volume of the gas head, gas movement around the gas head caused by movement of the gas head may be reduced.

[0055] FIG. 3 shows an illustrative embodiment of a gas head assembly including first and second gas heads 2, where each gas head 2 is configured to allow gas flow into, and optionally through, the gas head from a distal side to a proximal side. Each gas head 2 may include a tubular body 23 that defines an interior volume extending from a proximal opening 24 at a proximal side of the body to a distal opening 25 at a distal side of the body opposite the proximal side. In some embodiments, the proximal opening 24 may be arranged in a proximal plane (e.g., that is oriented vertically) and the distal opening 25 may be arranged in a distal plane (e.g., that is oriented vertically), and the proximal plane and the distal plane may be parallel to each other. In some cases, the body 23 may be configured to provide a straight line flow path from the distal opening 25 to the proximal opening 24. Thus, as the gas head 2 moves along a scan direction 6, e.g., to the right in FIG. 2, gas may move into and through the distal opening 25 of the leading side gas head 2 (on the right in FIG. 2 in this example) and optionally through the body 23 to the proximal opening 24. A flow path length through the gas head 2 from the proximal opening 24 to the distal opening 25 may be relatively short in relation to (e.g., to be less than) a width and/or height of the proximal and/or distal openings 24, 25. The gas head 2 can also include an exhaust flow port 26 in fluid communication with the interior volume. The exhaust flow port 26 can be configured to be fluidly coupled to a gas flow generator 12 to create an exhaust gas flow configured to carry gas and/or process ejecta out of the interior volume through the exhaust flow port 26. In FIG. 2, the gas heads 2 each include two exhaust flow ports 26, but may include one or more than two exhaust flow ports 26. In some cases, the exhaust flow port 26 may be positioned on the tubular body 23 above the proximal opening 24 and the distal opening 25, e.g., the exhaust flow port 26 may be coupled to a top wall 27 of the body 23. The exhaust flow port 26 may be fluidly coupled to the interior volume of the body 23 at a location above both the proximal and distal openings 24, 25 and/or so that gas entering at least a portion of the proximal and distal openings 24, 25 flow upwardly to the location of fluid coupling between the interior volume and the exhaust port 26. The top wall 27 may define the interior volume of the gas head 2 along with first and second sidewalls 28 disposed on opposing sides of the tubular body 23, e.g., which may extend vertically downwardly from the top wall 27, and a bottom wall 29. The top wall 27, first and second sidewalls 28 and/or the bottom wall 29 may extend from the proximal opening 24 to the distal opening 25, e.g., proximal and distal edges of the walls 27, 28, 29 may define the proximal and distal openings 24, 25, respectively. In some cases, the body 23 may have a rectangular shape in cross section perpendicular to a line extending from the proximal opening 24 to the distal opening 25 and/or the proximal and distal openings 24, 25 may have a rectangular shape. An inner surface of the bottom wall 29 may define a floor that extends from the proximal opening 24 to the distal opening 25, and the floor may be shaped to influence flow in the interior volume in any suitable way, e.g., to help accelerate and/or decelerate flow in the interior volume in desired areas of the gas head 2 and/or to reduce turbulence of flow from the proximal opening 24 to the exhaust flow port 26 and from the distal opening 25 to the exhaust flow port 26. Similar is true of inner surfaces of the sidewalls 28 and the top wall 27, which may include a first ceiling portion extending from the proximal opening 24 to the exhaust flow port 26, and a second ceiling portion extending from the exhaust flow port 26 to the distal opening 25. [0056] FIG. 4 shows a cross sectional view of gas heads 2 which are similar in many respects to those of FIG. 3. The cross sectional view of FIG.4 may be taken along a line extending in the scan direction 6, and helps illustrate several inventive features that may be employed and/or enabled by a gas head. The gas heads 2 of Fig. 4 differ from those in FIG. 3 in that they comprise multiple components assembled together (e.g., using fasteners 40), rather than being formed as a single piece as shown in FIG. 3. In FIG. 4, the leading side gas head 2 (on the right) and the trailing side gas head 2 (on the left) are shown moving along the scan direction 6 from left to right relative to the build surface 3. Such movement of the gas heads 2 may be with the optics unit 1 and may enable the optics unit 1 to direct laser energy 4 to powder material on the build surface 3 to create one or more melt pools 5 in selective areas to form a printed part. FIG. 4 illustrates that as the leading side gas head 2 moves to the right, gas may be received into the gas head 2 through the distal opening 25 at the distal side of the gas head 2. At least some of this distal gas flow may be conducted through the gas head 2 from the distal side to the proximal side, e.g., such that at least some of the distal gas flow exits the gas head at the proximal opening 24 at the proximal side. A part of the distal gas flow that exits the proximal opening 24 of the leading gas head 2 may flow over or near the melt pool 5 and be received into the proximal opening 24 of the trailing gas head 2. Flow into the trailing gas head 2 (e.g., including process ejecta from or near the melt pool 5) may be exhausted from the trailing gas head 2 via the exhaust port 26, e.g., the trailing gas head 2 exhaust port 26 may be coupled to the gas flow generator 12 to pull gas and process ejecta from the interior volume of the trailing gas head 2. FIG. 4 shows that a gas flow is also generated at the distal opening 25 of the trailing gas head 2, e.g., so that gas is drawn into the interior volume of the trailing gas head 2 at the distal opening 25 and exhausted via the exhaust port 26. This flow may be enabled by providing suitably high vacuum or other low pressure at the exhaust gas port 26. Such flow into the distal opening 25 of the trailing gas head 2 may help ensure that process ejecta that enter via the proximal opening 24 are exhausted from the gas head 2, e.g., and do not exit the trailing gas head 2. Alternately, or in addition, flow into the distal opening 25 of the trailing gas head 2 may draw process ejecta into the gas head 2 that were not received at the proximal opening 24, e.g., process ejecta that somehow passed by the proximal opening 24. However, in some cases, at least some gas in the trailing gas head 2 may flow through the trailing gas head 2 to exit the distal opening 25, e.g., there may be at least some flow out of the gas head 2 via the distal opening 25.

[0057] Although FIG. 4 illustrates gas flow from the interior volume of the leading side gas head 2 to and through the proximal opening 24 (which may be received at the proximal opening 24 of the trailing side gas head), in some cases gas may flow into the proximal opening 24 of the leading side gas head 2 and such gas may be exhausted via the exhaust flow port 26. In some cases, no gas in the interior volume of the leading side gas head 2 may exit via the proximal opening 24 and instead gas may flow only into the proximal opening 24 of the leading side gas head 2, e.g., caused by suitable vacuum or otherwise low pressure at the exhaust flow port 26. Note that the flow described is generally in relation to using the gas heads 2 as a frame of reference. However, depending on the frame of reference, gas may not flow at all. For example, when using the build surface 3 as a frame of reference, gas that enters the distal opening 25 of the leading gas head 2 and exits the proximal opening

24 of the leading gas head 2 may not move at all, but rather the leading gas head 2 may simply move through or past stationary gas over the build surface 3. Note as well that the example described above is in relation to the gas heads 2 moving along the scan direction 6 to the right in FIG. 4. However, the gas heads 2 can be configured to operate as both a leading side gas head and a trailing side gas head. Thus, the description above is equally applicable to movement of the optics unit 1 and gas heads 2 along the scan direction 6 to the left in FIG. 4.

[0058] Another feature illustrated in FIG. 4 is that a gas head 2 may include an exhaust flow port 26 positioned between proximal and distal openings 24, 25, and in some cases the exhaust flow port 26 may be positioned above the proximal and distal openings 24, 25. By coupling or otherwise positioning the exhaust flow port 26 between the proximal and distal openings 24, 25, the gas head 2 can support operation such that gas flow is received into the interior space of the gas head 2 from both proximal and distal openings 24, 25 and exhausted via the exhaust flow port 26. As noted above, this may help reduce disturbance or other gas movement around the gas head 2 as the gas head moves across a build surface, and/or may help ensure that process ejecta are removed from the gas head and surrounding areas. Thus, for example, a trailing side gas head may operate to receive a proximal gas flow into the gas head through a proximal side of the gas head, e.g., where the proximal gas flow includes process ejecta from a melt pool, to receive a distal gas flow into the gas head through a distal side of the gas head opposite the proximal side, and to remove the proximal gas flow and the distal gas flow from the gas head through an exhaust flow port of the gas head. Since the gas head includes a tubular body 23, the gas head 2 includes a bottom wall 29 positioned between interior space of the gas head 2 and the build surface 3. Thus, proximal and distal flow received into the gas head via the proximal and distal openings 24,

25 may be conducted along a surface of the gas head positioned between the proximal gas flow and a build surface. This may help the gas head influence flow in the interior volume, e.g., direct the flow toward the exhaust port 26 at the top wall 27 and/or help reduce any effect of flow to the exhaust port 26 on powder material on the build surface 3. For example, without a bottom wall 29 positioned between the interior volume and the build surface 3, relatively high vacuum or other flow at the exhaust port 26 may disrupt relatively small and light powder material at the build surface 3. The presence of the bottom wall 29 may help reduce such effects and shield the powder material from relatively high vacuum or other gas flow.

[0059] In some embodiments, a gas head may have inner surfaces that define the interior volume of the gas head configured to control or otherwise influence flow of gas in the interior volume in any suitable way. For example, as can be seen in FIG. 4, the bottom wall 29 can include a lower inner surface extending from the proximal opening 24 to the distal opening 25 that has a proximal portion and a distal portion. The proximal portion of the lower inner surface can be sloped inwardly and upwardly towards a central portion of the body 23 and the distal portion of the lower inner surface can be sloped inwardly and upwardly towards the central portion of the body 23. This arrangement can help influence flow in the interior volume in one or more ways. For example, the proximal and distal portions of the lower inner surface of the bottom wall 29 may help accelerate the flow of gas in the interior volume, which may help ensure that particulate matter entrained in the gas flow is exhausted to the exhaust port 26. In addition, the lower inner surface may help direct inward flow from the proximal and distal openings 24, 25 upwardly and toward the exhaust port 26. Thus, a proximal gas flow can be conducted upwardly in the gas head to the exhaust flow port, and a distal gas flow can be conducted upwardly in the gas head to the exhaust flow port. A lower outer surface of the bottom wall 29, e.g., that extends from the proximal opening 24 to the distal opening 25, may be planar, e.g., to have a minimal effect on powder material on the build surface 3 as the gas head moves along the build surface.

[0060] Another feature illustrated in FIG. 4 is that a lowermost surface of a leading side gas head 2 may be at a same height over the build surface as a lowermost surface of a trailing side gas head 2. In some configurations, including some gas head arrangements discussed herein, a leading side gas head may disrupt or otherwise cause unwanted gas movement as the leading side gas head moves across the build surface. To help reduce such effects, the leading side gas head may be raised above the build surface so the lowermost surface of the leading side gas head is above that of the trailing side gas head. However, in a configuration like that shown in FIG. 4 where a leading side gas head permits gas flow into the distal side, and optionally to and through the proximal side, the leading side gas head may have minimal effect on powder material on the build surface as it moves across the build surface. Thus, the leading side and trailing side gas heads may be arranged at a same height over the build surface, and gas heads on opposing sides of the laser energy may be configured to be positioned at a same height above the powder material on the build surface for movement in opposite scan directions. This arrangement can help reduce system complexity, e.g., because no system is required to move the gas heads vertically depending on the direction of movement. With the leading side and trailing side gas heads arranged at a same height above the build surface, the gas heads may be operated in any suitable way with respect to gas flow into and out of the gas heads, e.g., as discussed herein. For example, the leading side gas head may receive gas flow into a distal opening, may receive gas flow into a proximal opening, may exhaust gas received from the distal and/or proximal openings via an exhaust flow port (e.g., that is positioned between and/or above the distal and proximal openings), may permit gas flow from the interior volume to and through the proximal opening, and so on. Similar is true for the trailing side gas head which may receive gas flow into a distal opening, may receive gas flow into a proximal opening, may exhaust gas received from the distal and/or proximal openings via an exhaust flow port (e.g., that is positioned between and/or above the distal and proximal openings), may permit gas flow from the interior volume to and through the distal opening, and so on.

[0061] In some embodiments, various portions of the gas head 2 may be configured to influence gas flow (e.g., including process ejecta) into and/or within the gas head in a desired way. For example, inner surfaces of the tubular body 23, such as ceiling and floor surfaces of the top wall 27 and bottom wall 29 may be curved or otherwise configured to provide desired flow characteristics, e.g., to reduce particle buildup, to accelerate or decelerate gas flow, and/or provide desired flow turbulence levels. The proximal and/or distal edges of the top wall 27, sidewalls 28 and/or bottom wall 29 that define the proximal and distal openings 24, 25 may be positioned, beveled, rounded, curved, tapered or otherwise shaped to have a desired effect on gas flow through the proximal and distal openings 24, 25, e.g., to help reduce collection of particulate matter in process ejecta from collecting on these and other surfaces, and/or to provide other desired flow characteristics. For example, FIG. 5 shows a perspective view of the proximal side of a gas head configured like that in FIG. 4. As shown in FIG. 5, the gas head 2 of FIGs. 4 and 5 may further differ from those of FIG. 3 in that a divergence point 41 at which the exhaust ports 26 diverge to form separate flow paths is spaced further from the proximal opening 24 than in the gas heads of FIG. 3. This spacing may reduce the amount of process ejecta which may deposit at the divergence point 41. In some embodiments, a divergence point between two or more exhaust ports may be any appropriate distance from the proximal opening, including 1 cm, 2 cm, 5 cm, 10 cm, 15 cm, or any other appropriate distance. As can further be seen in FIG. 5, a proximal edge of the bottom wall 29 that partially defines the proximal opening 24 may be recessed or positioned closer to a central portion of the body 23 than proximal edges of the sidewalls 28 and/or the top wall 27. Such an arrangement may help improve receipt of process ejecta into the proximal opening 24. FIG. 6 shows a top cross sectional view of the FIGs. 4-5 gas head and illustrates that the sidewalls 28 may be shaped to influence flow into and/or within the interior volume of the gas head. For example, the first and second sidewalls 28 flare outwardly near the distal opening 25, e.g., to help guide flow into the interior volume when the gas head 2 is operating as a leading side gas head and/or to accelerate a flow rate of gas flow in the interior volume as the gas flow moves from the distal side toward a central portion of the body 23. Taper angles between 20 and 120 degrees may be employed as measured between corresponding inner surface locations on the opposed sidewalls 28. The inner surfaces of the sidewalls 28 may also be tapered at and/or near the proximal opening 24, although the taper angle between corresponding inner sidewall surface may be less than that for areas at and/or near the distal opening 25. Taper angles between corresponding inner surface portions of the sidewalls may be between 5 and 25 degrees for portions at and/or near the proximal opening 25. In some cases, the first and second sidewalls 28 may be configured such that the distal opening 25 is wider than the proximal opening 24. In some cases, the distal opening 25 may have an area (e.g., defined by the distal edges of the top wall 27, sidewalls 28 and bottom wall 29) that is larger than an area of the proximal opening 24 (e.g., defined by the proximal edges of the top wall 27, sidewalls 28 and bottom wall 29). In some cases, an area of the distal opening 25 may be 100 to 150% of an area of the proximal opening 24. [0062] In some embodiments, a gas head may be configured to create gas flow into and/or through the gas head that is transverse to a plane of an opening through which process ejecta are received into the gas head and/or that is transverse to a proximal edge of the gas head. Such an arrangement may permit the gas head to support different configurations for laser energy application to a build surface and/or enhance the ability of the gas head to remove process ejecta from a melt pool or other area where laser energy is incident on a build surface. For example, FIGs. 7 and 8 show upper rear and upper front perspective views of a gas head 2 configured to create gas flows into and/or through the gas head in two directions that are both transverse to a plane of a proximal opening 24 or proximal edge of the gas head 2. In some embodiments, the gas head 2 may include a body 23 defining an interior volume and having a proximal opening 24 at a proximal side of the body. The proximal opening 24 may be positioned adjacent a melt pool or laser energy incident on a build surface so process ejecta can be received through the proximal opening 24. The body 23 may have a distal side opposite the proximal side, a top wall 27 extending from the proximal side to the distal side, and a bottom wall 29 extending from the proximal side to the distal side. First and second exhaust passages 32 may extend between the distal side and the proximal side, with each of the first and second exhaust passages 32 coupled respectively to first and second exhaust ports 26. For example, the first and second exhaust passages 32 may extend from the distal side of the body 23 to the proximal side of the body 23. The first and second exhaust passages 32 may each have a proximal end adjacent the proximal opening 24 (e.g., proximal edges of the first and second exhaust passages 32 may define the proximal opening 24 in part) and a distal end adjacent the distal side of the body 23, with the distal ends of the first and second exhaust passages 32 being adjacent each other at the distal side of the body 23. In some cases, the interior volume of the body 23 may be open only to the proximal opening 24 and the first and second exhaust ports 26, e.g., the body 23 may not have a distal side opening as in the embodiments in FIGs. 3-6. In some embodiments, the top and bottom walls 27, 29 may be planar and may be parallel to each other. For example, the top wall 27 and the bottom wall 29 may each have a triangular shape with a proximal edge extending along the proximal side, e.g., defining the proximal opening 24 in part, a first edge extending along the first exhaust passage 32 and a second edge extending along the second exhaust passage 32. In some cases, the proximal opening 24 may be arranged in a proximal plane, e.g., parallel to a vertical plane, and the first and second exhaust passages 32 may be configured such that movement of gas out of the first exhaust port 26 causes movement of gas in the interior space in a first direction transverse to the proximal plane and movement of gas out of the second exhaust port 26 causes movement of gas in the interior space in a second direction transverse to the proximal plane. For example, the first direction may be approximately 45 degrees to the proximal plane, and the second direction may be approximately 45 degrees to the proximal plane. In some examples, the first and second directions may be transverse, e.g., may be perpendicular to each other.

[0063] FIG. 9 shows a top view of the gas head 2 of FIGs. 7 and 8 and helps illustrate the configuration and potential use of the gas head. FIG. 9 shows a line-shaped array of melt pools 5 that may be formed by an optics unit 1. That is, the optics unit 1 used with the gas head 2 may be configured to direct laser energy to be incident along a line- shaped portion of powder material on a build surface adjacent to a proximal side of the gas head 2. As can also be seen in FIG. 9, the line-shaped portion may be arranged to be transverse to the scan directions 6 and 7, which may be perpendicular to each other. As those of skill in the art will appreciate, arranging laser energy 4 to be incident on spots of powder material that are arranged along a line that is at an angle (such as 45 degrees) to a scan direction may assist in forming a more accurate and higher quality printed part. This is, at least in part, because creating immediately adjacent melt pools 5 that touch each other can create inconsistences in part geometry and make part accuracy difficult to achieve. For example, if two melt pools are formed so as to touch each other, the melted powder material (such as a molten metal) in the two pools 5 can flow together, causing variability in the size and/or shape of the combined melt pool. In contrast, if melt pools 5 can be made adjacent each other, but not touching while in a molten or liquid state, part accuracy can be improved. However, to ensure proper strength and/or other characteristics, at least some melt pools 5 must be bonded together. To achieve these objectives, melt pools 5 may be formed along a line-shaped area like that in FIG. 9 so the adjacent melt pools 5 are near but not touching each other while molten. To bond melt pools 5 to each other, a first melt pool 5 may be formed and then solidified before a second melt pool 5 to be bonded to the first melt pool 5 is formed. As an example, the melt pools 5a and 5b in a single line-shaped area may be formed and solidified. The optics unit 1 may be moved, e.g., to the right along scan direction 6 at a second line- shaped area, and a third melt pool 5c formed which contacts one or both of the now solidified melt pools 5a and 5b. This enables bonding of melt pools together while avoiding problems created by having adjacent melt pools contact each other while both are molten or otherwise in liquid form. As described above, process ejecta tend to be largely emitted from melt pools 5 in a direction opposite to the scan direction, e.g., to the left in FIG. 9 for scanning of the laser energy 4 to the right along scan direction 6. For gas heads configured to draw gas including process ejecta into a proximal opening of the gas head in a direction perpendicular to a plane of the proximal opening, a configuration like that in FIG. 9 can allow gas and process ejecta to be drawn into the gas head in a direction transverse to the direction in which process ejecta are primarily produced. For example, in embodiments in which a gas head configured like those in FIGs. 3-6 is arranged so the proximal opening is parallel to the lineshaped area of incidence of the laser energy 4, the gas head will tend to draw gas into the gas head in a direction perpendicular to the line-shaped area. However, process ejecta will primarily be produced in a direction to the left along the scan direction 6. Although a gas head assembly and/or additive manufacturing system may be configured this way in some embodiments, other embodiments may allow the direction in which gas is drawn into the gas head to be more closely aligned with the direction in which process ejecta is produced.

[0064] For example, a gas head configured like that in FIGS. 7-9 can improve whether and how process ejecta are drawn into a gas head for arrangements in which laser energy is incident on a line-shaped area that is transverse to the scan direction. In this example, the gas head 2 may be adjacent the line- shaped area of incidence of the laser energy 4 and the proximal opening 24 and/or a proximal edge of the gas head 2 may be parallel to the line- shaped area. The laser energy 4 and the gas head 2 may be moved so the gas head is on a trailing side of the laser energy for movement to the right along scan direction 6 and movement downwardly along the scan direction 7 as seen in FIG. 9. For example, a first exhaust passage 32a can be configured so that when gas is drawn out of the corresponding exhaust port 26a, the first exhaust passage 32a can create a first exhaust gas flow 21a in the interior volume of the body 23 to carry process ejecta through the proximal opening 24, into the interior volume and out of the first exhaust port 26a. Such operation can be particularly effective for movement of the laser energy 4 (and its line-shaped area of incidence) and the gas head 2 to the right along the scan direction 6. Similarly, a second exhaust passage 32b can be configured so that when gas is drawn out of the corresponding exhaust port 26b, the second exhaust passage 32b can create a second exhaust gas flow 21b in the interior volume of the body 23 to carry process ejecta through the proximal opening 24, into the interior volume and out of the second exhaust port 26b. Such operation can be particularly effective for movement of the laser energy 4 (and its line-shaped area of incidence) and the gas head 2 downwardly along the scan direction 7.

[0065] To effect the different exhaust gas flows 21a and 21b, flow through the exhaust ports 26a, 26b may be suitably controlled, e.g., by actuating a gas flow generator to provide a suitable level of flow for each of the ports 26 depending on the scan direction. For example, for movement along the scan direction 6, flow in the first exhaust port 26a may be greater than flow in the second exhaust port 26b (which may be zero or non-zero but lower than that for the first exhaust port 26a). For movement along the scan direction 7, flow in the second exhaust port 26b may be greater than flow in the first exhaust port 26a (which may be zero or non-zero but lower than that for the second exhaust port 26b). This adjustment in flow (such as flow rate and/or volume) can be effected by operating one or more valves, one or more pumps, etc. of the flow generator 12. For example, one or more valves may be fluidly coupled between a vacuum pump and the exhaust ports 26a, 26b and operated to provide a desired flow for each of the ports 26a, 26b. This inventive feature of providing different flow rates or other flow characteristics for two or more exhaust ports 26 of a gas head 2 is not limited to use in a gas head like that in FIGs. 7-9, but can be used with any gas head with any suitable configuration including those in FIGs. 3-6.

[0066] As will be understood from the description above, use of a gas head like that in FIG. 9 may involve receiving a first gas flow into a gas head through a proximal opening at a proximal side of the gas head, e.g., where the first gas flow includes first process ejecta from a melt pool formed by laser energy configured to be incident on a line- shaped area of powder material on a build surface. The line-shaped area may be parallel to a plane of the proximal opening and/or to a proximal edge of the gas head. The first gas flow may pass through the proximal opening in a direction transverse to a plane of the proximal opening and be conducted through an interior volume of the gas head in a first direction to a first exhaust port of the gas head. The first direction may be parallel to or otherwise along a first scan direction that the gas head and laser energy are moved across a build surface. A second gas flow may be received into the gas head through the proximal opening, and may include second process ejecta. The second gas flow may be pass through the proximal opening in a direction transverse to the plane of the proximal opening and/or to the proximal edge of the gas head. The second gas flow may be conducted through the interior volume of the gas head in a second direction and to a second exhaust port of the gas head. The second direction may be transverse to the first direction, e.g., the second direction may be parallel to or otherwise along a second scan direction that the gas head and laser energy are moved across a build surface. In some cases, the first and second scan directions may be perpendicular to each other, and the first and second directions may be arranged at about 45 degrees to a plane of the proximal opening and/or a proximal edge of the gas head.

[0067] FIG. 10 shows a side view of the gas head of FIG. 9 along the scan direction 7. As can be seen, the inner surfaces of the second exhaust passage 32b may be configured to draw gas into the proximal opening 24 along the gas flow path or direction 21b into the passage 32b. As discussed above, edges of the top, bottom and sidewalls of the gas head (e.g., that define the proximal opening 24) and/or inner surfaces of the gas head may be configured to provide desired flow characteristics, e.g., to reduce particle buildup, to accelerate or decelerate gas flow, and/or provide desired flow turbulence levels, and so on. Flow along the gas flow path 21b may bypass the first exhaust passage 32a, e.g., due to a relatively low vacuum or negative pressure applied at the first exhaust port 26a and relatively higher vacuum or negative pressure applied at the second exhaust port 26b. The gas head may be similarly configured with respect to a side view along the gas flow path or direction 21a.

[0068] In some arrangements, a gas head may include one or more inlet openings in a bottom wall of the gas head, e.g., between a proximal side and a distal side of the gas head. Such an inlet opening on a bottom wall of a gas head may provide advantages such as helping to remove process ejecta that are not picked up at a proximal opening of the gas head. In addition, since the gas head may have a bottom wall, disruption of powder material on the build surface, e.g., that may be caused by relatively high vacuum or other flow in the gas head to an exhaust port, may be reduced. That is, the bottom wall may provide a barrier between relatively high speed or volume flow in the gas head, while the inlet opening in the bottom wall may pick up process ejecta between the bottom wall and the build surface. When implementing an inlet opening in a bottom wall, a gas head may include a body defining an interior volume and having a proximal opening at a proximal side of the body, a distal side of the body opposite the proximal side, a top wall extending from the proximal side to the distal side, a bottom wall extending from the proximal side to the distal side, an exhaust port coupled to the interior volume, and an inlet in the bottom wall positioned between the proximal side and the distal side. The exhaust port may be configured to be fluidly coupled to a gas flow generator to create an exhaust gas flow to carry process ejecta through the proximal opening, into the interior volume and out of the first exhaust port and to draw gas through the inlet, into the interior volume and out of the exhaust port.

[0069] FIG. 11 shows a cross sectional top view of a gas head that includes an inlet in the bottom wall of the gas head. While the gas head in FIG. 11 is configured like that in FIGs. 7-10, a gas head having any suitable configuration may employ an inlet in the bottom wall, such as a gas head configured like those in FIGs. 3-6 and others. The inlet 33 may be located in the bottom wall 29 between a proximal side and a distal side of the gas head, e.g., between a proximal opening 24 and an exhaust gas passage 32 of the gas head. In FIG. 11, the gas head includes two exhaust gas passages 32 and exhaust ports 26 and thus two inlets 33 may be provided, one for each exhaust port 26. In some cases, the inlet 33 may be arranged as an elongated slot that extends along a leading end of a corresponding exhaust passage 32, e.g., adjacent a side of the bottom wall 29 that is adjacent the exhaust passage 32. In some embodiments, the inlet may be arranged as an elongated slot that extends between the distal side and the proximal side of the body 23. The inlet 33 may be transverse to a proximal edge of the bottom wall 29 that defines, at least in part, the proximal opening 24. In some cases, the inlet 33 may be transverse, e.g., perpendicular, to a gas flow direction 21 generated by the corresponding exhaust gas passage 32 in response to suitable vacuum or other low pressure applied to the corresponding exhaust port 26.

[0070] As can be seen in FIG. 12, the inlet 33 may operate to draw gas, e.g., including process ejecta, from a space between the bottom wall 29 and the build surface 3 into the gas head. (FIG. 12 shows a cross sectional view of the gas head 2 approximately along the line of the exhaust gas flow direction 21b in FIG. 11 or along the line of exhaust gas flow direction 21a in FIG. 9.) For example, a gas head 2 including an inlet 33 at the bottom wall may be operated so that a proximal gas flow is received into the interior volume of the gas head 2 through the proximal opening 24, with the gas flow including process ejecta from a melt pool 5. An inlet gas flow may be received into the interior volume through the inlet opening 33 in the bottom wall, and both the proximal gas flow and the inlet gas flow may be exhausted from the interior volume through the exhaust port 26. In some cases, the inlet gas flow may help guide or direct process ejecta received at the proximal opening 24 to the exhaust gas passage 32 and/or to the exhaust port 26. For example, the inlet gas flow may help keep process ejecta from striking a distal or rear portion of the exhaust gas passage 32, and instead steer the process ejecta to flow upwardly to the exhaust port 26. The inlet opening 33 may be shaped to provide flow into the gas head 2 in any suitable direction, velocity, volume and/or other characteristics.

[0071] As noted above, in some arrangements, when scanning or otherwise moving a gas head assembly including leading and trailing gas heads, the leading side gas head may be raised relative to the trailing side gas head, e.g., to help reduce disruption of powder material on a build surface by the leading side gas head, help improve reception of process ejecta by the trailing side gas head and/or provide other benefits. FIG. 13 shows a side view of one configuration in which gas heads 2 configured like that in FIGS. 7-12 are mounted to a bracket 11 via respective actuators 111. The bracket 11 may be coupled directly or indirectly to the optics unit 1 so the gas head assembly moves with the optics unit 1 and the laser energy produced. The actuators 111 may be operated, e.g., under control of the controller 8, to raise a leading side gas head 2 (e.g., on the right in FIG. 13) and/or lower a trailing side gas head 2 (e.g., on the left in FIG. 13). The leading side gas head may be positioned to provide little or no obstruction or other impedance of gas flow into the proximal opening of the trailing side gas head.

[0072] In some embodiments, flow in two or more exhaust ports, whether in a same or different gas head, may be different from each other and may be controlled so as to be variable. For example, flow in a first exhaust port may be greater than a second exhaust port, e.g., for movement in a first scanning direction, and then may be adjusted such that flow in the second exhaust port is greater than the first exhaust port, e.g., for movement in a second scanning direction different from the first direction. This arrangement may permit a gas head, or two or more gas heads, to operate to receive process ejecta in a desired way and/or provide other gas flow characteristics. For example, FIG. 14 shows a schematic view of an arrangement like that in FIG. 2, e.g., in which first and second gas heads 2a, 2b are on opposed leading and trailing sides of laser energy 4. The laser energy 4 may be configured to be incident on a line-shaped portion of powder material on a build surface 3 at a gap or space 22 between the gas heads 2. In some cases, when the gas heads 2a, 2b are moved in a scan direction 6, the gas flow generator 12 may be configured to provide a greater gas flow for the exhaust ports 26 of the first or trailing gas head 2a than for the exhaust ports 26 of the second or leading gas head 2b. This difference in gas flow may be provided in different ways, such as by operating a pump, blower or other first gas mover 122 at a higher flow rate and/or vacuum than a second gas mover 121. Alternately, a first valve 124 may be operated to provide greater gas flow for the first gas head 2a and a second valve 123 may be operated to provide a relatively lower gas flow for the second gas head 2b. such cases, the gas movers 121, 122 need not be adjusted in operation. Where valves 123, 124 are operated to provide a desired gas flow, a single gas mover 121 or 122 may be coupled to both valves 123, 124 to provide vacuum or other flow for both gas heads 2a, 2b. Note as well that a single valve and single gas mover can be employed to provide the different gas flows for the gas heads 2a, 2b and/or exhaust ports 26, e.g., where the single valve is a three-way valve that can selectively control flow for the exhaust ports, e.g., by coupling one, both or neither of the exhaust ports of the gas heads 2a, 2b to a single gas mover. For movement of the gas heads 2a, 2b in a different scan direction, such as up as viewed in FIG. 14, the gas mover(s), valve(s) or other components of the gas flow generator 12 may be adjusted to provide the second gas head 2b with greater flow than the first gas head 2a, or other flow characteristics.

[0073] FIG. 15 shows another illustrative embodiment in which different, and optionally controllable, levels of gas flow may be provided to one or more exhaust ports of one or more gas heads. In some embodiments, two or more exhaust ports 26 may be fluidly coupled to or otherwise be in fluid communication with a valve that may be operated to provide different flow levels for the exhaust ports 26. For example, exhaust ports 26c, 26d of a first gas head 2a may be coupled to a valve 124 and exhaust ports 26a, 26b of a second gas head 2b may be coupled to a valve 123, and both valves 123, 124 may be coupled to a single gas mover 121 (although two or more gas movers can be employed). The gas heads 2 may be configured like that in FIGs. 7-12, and for movement along a scan direction 6 the valve 123 may be operated (e.g., by the controller 8) to provide greater gas flow for the exhaust port 26a than for the exhaust port 26b. (Relative flow velocity and/or volume is depicted in FIG. 15 by the relative thickness of the arrows illustrating gas flow direction.) Also, the valve 124 may be operated to provide a same level of gas flow for the exhaust ports 26c and 26d, which may be less than that for the exhaust port 26a and/or less than (or greater than) that for the exhaust port 26b. Again, the valves 123, 124 may be operated to provide variable levels of gas flow for the exhaust ports 26, e.g., corresponding to a change in scan direction, such as movement in a direction along, but opposite to the scan direction 6 shown in FIG. 15. In some cases, the valves 123, 124 may include a valve element movable to selectively impede and allow flow from one exhaust flow port to the gas flow generator and selectively impede and allow flow from another exhaust flow port to the gas flow generator. (Impeding gas flow may include a complete prevention of flow as well as reduced but non-zero levels of flow, and may include various levels of impedance.) Any suitable relative levels of gas flow may be provided for one or more exhaust ports. For example, FIG. 16 shows the configuration of FIG. 15 controlled to provide a greatest flow for the exhaust port 26a, a lower level of flow for the exhaust ports 26b and 26c, and a lowest level of flow for the exhaust port 26d. The valves 123, 124 may be operated to provide these different levels of flow, and each valve may be configured to provide two or more discrete levels of flow for each exhaust port 26 or an infinite number of different levels of flow for each exhaust port 26. FIG. 16 shows only one possible option but any number of relative levels of flow for the exhaust ports 26 may be provided, such as where flow for the exhaust ports 26a and 26b are equal but greater than that for exhaust ports 26c and 26d (which may be useful for gas head arrangements like those in FIGs. 3-6).

[0074] In some embodiments, a valve used to control flow for two or more exhaust ports may include a valve element movable to provide any suitable level of control of flow between the exhaust ports and a gas mover or other source of gas flow. FIGs. 17-21 show an embodiment of a valve that can be operated to control flow for two exhaust ports with respect to a source of gas flow or movement. In some embodiments, the valve may include a valve body 9 that includes first and second inlet ports 91 , 92 and an outlet port 93. In use, the first inlet port 91 of the valve may be coupled to a first exhaust port, and the second inlet port 92 may be coupled to a second exhaust port, e.g., of a same gas head or different gas heads. The outlet port 93 may be coupled to a gas flow generator, such as a conduit that is fluidly coupled to a pump, blower or other gas mover. A valve element 94 may be movable in the valve body 9 to selectively impede or allow flow from the first inlet port 91 to the outlet port 93, and to impede or allow flow from the second inlet port 92 to the outlet port 93. The valve element 94 may be moved by an actuator 95, such as a pneumatic motor or other drive, and may be controlled by the controller 8. The valve element 94 may be operable to completely or partially open and/or close flow between the inlet ports 91, 92 and the outlet port 93, and may be operable to provide two or more variable levels of flow between the ports 91, 92 and the outlet port 93. For example, the valve element 94 may be rotatable to at least partially open a passage between one or both of the inlet ports 91, 92 and the outlet port 93 and/or to at least partially block a passage between a bypass opening 96 and the outlet port 93. FIGs. 18 and 19 show such a condition in which a passage between the outlet port 93 and the inlet ports 91, 92 is at least partially open and a passage between the outlet port 93 and the bypass opening 96 is at least partially blocked. This may permit the valve to provide a relatively maximum, and equal, flow for both of the inlet ports 91, 92 and the corresponding exhaust ports. FIGs. 20 and 21 show a condition in which a passage between the outlet port 93 and the inlet ports 91, 92 is at least partially blocked and a passage between the outlet port 93 and the bypass opening 96 is open. This may permit the valve to provide a relatively minimum (e.g., zero or non-zero flow), and equal, flow for both of the inlet ports 91, 92 and the corresponding exhaust ports. Those of skill will appreciate that different levels of flow may be provided by the valve for different positions of the valve element 94, such as higher flow for one inlet port 91, 92 than the other inlet port 91, 92 as well as variable levels of flow for each port 91, 92. Control of flow to exhaust ports of a gas head using an arrangement like that in FIGs. 17-21 may enable a controller 8 to provide relatively rapid adjustment of flow for one or more exhaust ports 26, and so may enable more rapid scanning and/or change in scan direction and/or accommodate varying conditions that require adjustment of flow for exhaust ports. This is in contrast to systems that rely on changing a speed of operation of a gas mover, such as a pump or blower, which may have a relatively long start up and/or speed adjustment time. In contrast, a controller need only move a valve element of a valve to make suitable flow adjustment, which can be done relatively rapidly. Also, the controller 8 may be enabled to employ feedback control, e.g., where process ejecta conditions are monitored and gas flow adjusted for exhaust ports of one or more gas heads to accommodate for varying conditions.

[0075] The above-described embodiments of the technology described herein can be implemented in any of numerous ways. For example, one or more functions of the embodiments may be implemented using hardware, software or a combination thereof. When implemented in software, the software code can be executed on any suitable processor or collection of processors, whether provided in a single computing device or distributed among multiple computing devices. Such processors may be implemented as integrated circuits, with one or more processors in an integrated circuit component, including commercially available integrated circuit components known in the art by names such as CPU chips, GPU chips, microprocessor, microcontroller, or co-processor. Alternatively, a processor may be implemented in custom circuitry, such as an ASIC, or semicustom circuitry resulting from configuring a programmable logic device. As yet a further alternative, a processor may be a portion of a larger circuit or semiconductor device, whether commercially available, semicustom or custom. As a specific example, some commercially available microprocessors have multiple cores such that one or a subset of those cores may constitute a processor. Though, a processor may be implemented using circuitry in any suitable format.

[0076] Also, a computing device may have one or more input and output devices. These devices can be used, among other things, to present a user interface. Examples of output devices that can be used to provide a user interface include display screens for visual presentation of output and speakers or other sound generating devices for audible presentation of output. Examples of input devices that can be used for a user interface include keyboards, individual buttons, and pointing devices, such as mice, touch pads, and digitizing tablets. As another example, a computing device may receive input information through speech recognition or in other audible format.

[0077] Such computing devices may be interconnected by one or more networks in any suitable form, including as a local area network or a wide area network, such as an enterprise network or the Internet. Such networks may be based on any suitable technology and may operate according to any suitable protocol and may include wireless networks, wired networks or fiber optic networks. [0078] Also, the various methods or processes outlined herein may be coded as software that is executable on one or more processors that employ any one of a variety of operating systems or platforms. Additionally, such software may be written using any of a number of suitable programming languages and/or programming or scripting tools, and also may be compiled as executable machine language code or intermediate code that is executed on a framework or virtual machine.

[0079] In this respect, the embodiments described herein may be embodied as a computer readable storage medium (or multiple computer readable media) (e.g., a computer memory, one or more floppy discs, compact discs (CD), optical discs, digital video disks (DVD), magnetic tapes, flash memories, RAM, ROM, EEPROM, circuit configurations in Field Programmable Gate Arrays or other semiconductor devices, or other tangible computer storage medium) encoded with one or more programs that, when executed on one or more computers or other processors, perform methods that implement the various embodiments discussed above. As is apparent from the foregoing examples, a computer readable storage medium may retain information for a sufficient time to provide computer-executable instructions in a non-transitory form. Such a computer readable storage medium or media can be transportable, such that the program or programs stored thereon can be loaded onto one or more different computing devices or other processors to implement various aspects of the present disclosure as discussed above. As used herein, the term "computer-readable storage medium" encompasses only a non-transitory computer-readable medium that can be considered to be a manufacture (i.e., article of manufacture) or a machine. Alternatively or additionally, the disclosure may be embodied as a computer readable medium other than a computer-readable storage medium, such as a propagating signal.

[0080] The terms “program” or “software” are used herein in a generic sense to refer to any type of computer code or set of computer-executable instructions that can be employed to program a computing device or other processor to implement various aspects of the present disclosure as discussed above. Additionally, it should be appreciated that according to one aspect of this embodiment, one or more computer programs that when executed perform methods of the present disclosure need not reside on a single computing device or processor, but may be distributed in a modular fashion amongst a number of different computers or processors to implement various aspects of the present disclosure . [0081] Computer-executable instructions may be in many forms, such as program modules, executed by one or more computers or other devices. Generally, program modules include routines, programs, objects, components, data structures, etc. that perform particular tasks or implement particular abstract data types. Typically the functionality of the program modules may be combined or distributed as desired in various embodiments.

[0082] While several embodiments of the present invention have been described and illustrated herein, those of ordinary skill in the art will readily envision a variety of other means and/or structures for performing the functions and/or obtaining the results and/or one or more of the advantages described herein, and each of such variations and/or modifications is deemed to be within the scope of the present invention. More generally, those skilled in the art will readily appreciate that all parameters, dimensions, materials, and configurations described herein are meant to be exemplary and that the actual parameters, dimensions, materials, and/or configurations will depend upon the specific application or applications for which the teachings of the present invention is/are used. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the invention described herein. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, the invention may be practiced otherwise than as specifically described and claimed. The present invention is directed to each individual feature, system, article, material, kit, and/or method described herein. In addition, any combination of two or more such features, systems, articles, materials, kits, and/or methods, if such features, systems, articles, materials, kits, and/or methods are not mutually inconsistent, is included within the scope of the present invention.

Claims

1. A gas head assembly for an additive manufacturing system, the gas head assembly comprising: a tubular body defining an interior volume extending from a proximal opening at a proximal side of the body to a distal opening at a distal side of the body opposite the proximal side; and an exhaust flow port in fluid communication with the interior volume, the exhaust flow port configured to be fluidly coupled to a gas flow generator to create an exhaust gas flow configured to carry process ejecta out of the interior volume through the exhaust flow port, wherein the exhaust flow port is fluidly coupled to the interior volume at a position on the tubular body above the proximal opening and the distal opening.

2. The gas head assembly of claim 1, wherein the tubular body includes a bottom wall extending from the proximal opening to the distal opening.

3. The gas head assembly of claim 1, wherein the tubular body includes a top wall with a first portion extending from the proximal opening to the exhaust flow port, and a second portion extending from the exhaust flow port to the distal opening.

4. The gas head assembly of claim 1, wherein the tubular body includes a first sidewall and a second sidewall disposed on opposing sides of the tubular body, each of the first sidewall and the second sidewall extending from the proximal opening to the distal opening.

5. The gas head assembly of claim 4, wherein the first and second side walls flare outwardly near the distal opening.

6. The gas head assembly of claim 4, wherein the first and second side walls are configured such that the distal opening is wider than the proximal opening.

7. The gas head assembly of claim 4, wherein the first and second side walls flare outwardly near the proximal opening.

8. The gas head assembly of claim 4, wherein the tubular body includes a bottom wall extending from the proximal opening to the distal opening, the bottom wall having a proximal edge at least in part defining the proximal opening, wherein the first and second sidewalls each have a proximal edge at least in part defining the proximal opening, and wherein the proximal edge of the bottom wall is recessed relative to the proximal edges of the first and second sidewalls.

9. The gas head assembly of claim 1, wherein the tubular body includes a lower inner surface extending from the proximal opening to the distal opening and having a proximal portion and a distal portion, the proximal portion of the lower inner surface sloped inwardly and upwardly towards a central portion of the tubular body and the distal portion of the lower inner surface sloped inwardly and upwardly towards the central portion of the tubular body.

10. The gas head assembly of claim 9, wherein the tubular body includes a lower outer surface that extends from the proximal opening to the distal opening and is planar.

11. The gas head assembly of claim 1, wherein the tubular body is rectangular in shape in cross section transverse to a line extending from the distal opening to the proximal opening.

12. The gas head assembly of claim 1, wherein the tubular body has an inner surface that defines the interior volume and is configured to reduce turbulence of flow from the proximal opening to the exhaust flow port and from the distal opening to the exhaust flow port.

13. The gas head assembly of claim 1, wherein the proximal opening is arranged in a proximal plane and the distal opening is arranged in a distal plane, and wherein the proximal plane and the distal plane are parallel.

14. The gas head assembly of claim 1, wherein the tubular body is configured to provide a straight line flow path from the distal opening to the proximal opening.

15. The gas head assembly of claim 1, wherein the proximal opening has a proximal area and the distal opening has a distal area, and wherein the distal area is between 100-150% of the proximal area.

16. The gas head assembly of claim 1, wherein the distal opening is larger than the proximal opening.

17. The gas head assembly of claim 1, wherein the proximal opening and the distal opening are generally rectangular in shape.

18. The gas head assembly of claim 1, wherein the proximal opening and the distal opening are separated by a distance that is less than a width of the proximal opening and that is less than a width of the distal opening.

19. The gas head assembly of claim 1, wherein the tubular body has a bottom wall, opposed sidewalls and a top wall that extend from the proximal opening to the distal opening.

20. The gas head assembly of claim 19, wherein the opposed sidewalls are vertical and the bottom wall is horizontal.

21. The gas head assembly of claim 19, wherein the exhaust flow port is coupled to the top wall.

22. An additive manufacturing system comprising: a build surface on which a printed part is formable by fusing powder material supported on the build surface; and a gas head assembly positioned over the build surface and out of contact with the powder material, the gas head assembly including: a first tubular body defining an interior volume extending from a proximal opening at a proximal side of the body to a distal opening at a distal side of the body opposite the proximal side; and a first exhaust flow port in fluid communication with the interior volume, the first exhaust flow port configured to be fluidly coupled to a gas flow generator to create an exhaust gas flow configured to carry process ejecta out of the interior volume through the first exhaust flow port, wherein the first exhaust flow port is fluidly coupled to the interior volume at a position on the tubular body above the proximal opening and the distal opening.

23. The system of claim 22, wherein the gas head assembly includes: a second tubular body defining an interior volume extending from a proximal opening at a proximal side of the body to a distal opening at a distal side of the body opposite the proximal side; and a second exhaust flow port in fluid communication with the interior volume, the second exhaust flow port configured to be fluidly coupled to a gas flow generator to create an exhaust gas flow configured to carry process ejecta out of the interior volume through the second exhaust flow port, wherein the second exhaust flow port is positioned on the tubular body above the proximal opening and the distal opening, and wherein the first and second tubular bodies are arranged with the proximal opening of the first tubular body facing the proximal opening of the second tubular body and separated by a gap.

24. The system of claim 23, further comprising: an optics system configured to move relative to the build surface and to direct laser energy to a portion of the build surface located immediately below the gap to fuse powder material at the portion of the build surface, wherein the first and second tubular bodies are configured to move with the optics system.

25. The system of claim 24, wherein the first and second tubular bodies are configured to move with the optics system such that the distal opening of the first tubular body is at a leading end of a first direction of movement of the optics system relative to the build surface and the distal opening of the second tubular body is at a leading end of a second direction of movement of the optics system relative to the build surface.

26. The system of claim 25, wherein the first and second tubular bodies are configured to be positioned at a same height above the powder material on the build surface for movement in both the first and second directions.

27. The system of claim 25, further comprising a gas flow generator coupled to the first and second exhaust flow ports, wherein the gas flow generator is configured to provide a higher volume flow for the second exhaust flow port than the first exhaust flow port for movement in the first direction, and configured to provide a higher volume flow for the first exhaust flow port than the second exhaust flow port for movement in the second direction.

28. The system of claim 27, wherein the gas flow generator includes first and second flow valves associated respectively with the first and second exhaust flow ports, the first and second flow valves being configured to provide adjustable volume flow for the respective first and second exhaust flow ports.

29. The system of claim 25, wherein the first and second tubular bodies are configured such that a line extending from the distal opening of the first tubular body to the distal opening of the second tubular body extends along the first and second direction of movement.

30. A method for additive manufacturing, the method comprising: receiving a proximal gas flow into a gas head through a proximal side of the gas head, the proximal gas flow including process ejecta from a melt pool of an additive manufacturing system; receiving a distal gas flow into the gas head through a distal side of the gas head opposite the proximal side; and removing the proximal gas flow and the distal gas flow from the gas head through an exhaust flow port of the gas head, the exhaust flow port disposed between the proximal side and the distal side.

31. The method of claim 30, wherein receiving the proximal gas flow includes conducting the proximal gas flow through a tubular portion of the gas head toward the exhaust flow port.

32. The method of claim 30, wherein receiving the distal gas flow includes conducting the distal gas flow through a tubular portion of the gas head toward the exhaust flow port.

33. The method of claim 30, wherein receiving the proximal gas flow includes conducting at least a portion of the proximal gas flow along a surface of the gas head positioned between the proximal gas flow and a build surface.

34. The method of claim 30, wherein receiving the distal gas flow includes conducting at least a portion of the distal gas flow along a surface of the gas head positioned between the distal gas flow and a build surface.

35. The method of claim 30, wherein receiving the proximal gas flow includes conducting the proximal gas flow toward the distal side of the gas head, and receiving the distal gas flow includes conducting the distal gas flow toward the proximal side.

36. The method of claim 30, wherein receiving the proximal gas flow includes conducting the proximal gas flow upwardly in the gas head to the exhaust flow port, and receiving the distal gas flow includes conducting the distal gas flow upwardly in the gas head to the exhaust flow port.

37. The method of claim 30, wherein receiving the proximal gas flow includes accelerating the proximal gas flow in the gas head in movement to the exhaust flow port, and/or receiving the distal gas flow includes accelerating the distal gas flow in the gas head in movement to the exhaust flow port.

38. The method of any one of claims 30-37, further comprising: directing laser energy to a precursor material on a build surface of the additive manufacturing system to form the melt pool; and fusing the precursor material with the laser energy to form one or more parts on the build surface.

39. A part manufactured using the method of any one of claims 30-38.

40. A method for additive manufacturing, the method comprising: directing energy from an optics assembly toward a build surface to melt and fuse powder material on the build surface; moving a first gas head and the optics assembly in a first direction relative to a build surface, the first gas head being on a leading side of the energy directed from the optics assembly toward the build surface; receiving a distal gas flow into the first gas head at a distal side of the first gas head; and conducting at least some of the distal gas flow through the first gas head from the distal side to a proximal side of the first gas head, at least some of the distal gas flow exiting the first gas head at the proximal side, the proximal side being nearer to the energy than the distal side.

41. The method of claim 40, further comprising moving a second gas head with the first gas head and the optics assembly in the first direction, the second gas head being on a trailing side of the energy; and receiving at least a portion of the distal gas flow into the second gas head via a proximal side of the second gas head.

42. The method of claim 41, further comprising exhausting the at least a portion of the distal gas flow from the second gas head via an exhaust flow port of the second gas head.

43. The method of claim 42, further comprising receiving a second distal gas flow into the second gas head at a distal side of the second gas head; and exhausting the second distal gas flow with the at least a portion of the distal gas flow from the second gas head via the exhaust flow port of the second gas head.

44. The method of claim 42, wherein receiving at least a portion of the distal gas flow into the second gas head includes receiving process ejecta from a melt pool formed by the energy incident on the powder material; and exhausting the process ejecta from the second gas head via the exhaust flow port of the second gas head.

45. The method of claim 44, further comprising moving the first gas head, the second gas head and the optics assembly in a second direction opposite the first direction while directing energy from the optics assembly toward the build surface to melt and fuse powder material on the build surface; receiving a second distal gas flow into the second gas head at a distal side of the second gas head; and conducting at least some of the second distal gas flow through the second gas head from the distal side to a proximal side of the second gas head, at least some of the second distal gas flow exiting the second gas head at the proximal side, the proximal side being nearer to the energy than the distal side.

46. The method of claim 45, further comprising receiving at least a portion of the second distal gas flow into the first gas head via a proximal side of the first gas head.

47. The method of claim 40, further comprising exhausting at least a part of the distal gas flow from the first gas head via an exhaust flow port of the first gas head.

48. The method of any one of claims 40-47, wherein directing the energy from the optics assembly toward the build surface to melt and fuse the powder material on the build surface comprises forming one or more parts on the build surface.

49. A part manufactured using the method of any one of claims 40-48.

50. A method for additive manufacturing, the method comprising: directing energy from an optics assembly toward a build surface to melt and fuse powder material on the build surface; moving a first gas head, a second gas head, and the optics assembly in a first direction relative to a build surface, the first gas head being on a leading side of the energy directed from optics assembly toward the build surface; and the second gas head being on a trailing side of the energy, a lowermost surface of the first gas head and the second gas head being at a same height above the build surface; and receiving a first distal gas flow into the first gas head at a distal side of the first gas head.

51. The method of claim 50, further comprising exhausting the first distal gas flow from the first gas head via an exhaust flow port of the first gas head.

52. The method of claim 51, further comprising receiving a second distal gas flow into the second gas head at a distal side of the second gas head; receiving a second proximal gas flow into the second gas head at a proximal side of the second gas head, the proximal side being nearer the energy than the distal side of the second gas head; and exhausting the second distal gas flow from the second gas head via an exhaust flow port of the second gas head.

53. The method of claim 52, wherein receiving the second proximal gas flow into the second gas head includes receiving process ejecta from a melt pool formed by the energy incident on the powder material; and exhausting the process ejecta from the second gas head via the exhaust flow port of the second gas head.

54. The method of any one of claims 50-53, wherein directing the energy from the optics assembly toward the build surface to melt and fuse the powder material on the build surface comprises forming one or more parts on the build surface.

55. A part manufactured using the method of any one of claims 50-54.

56. A gas head for a gas head assembly of an additive manufacturing system, the gas head comprising: a body defining an interior volume and having a proximal opening at a proximal side of the body, a distal side of the body opposite the proximal side, a top wall extending from the proximal side to the distal side, a bottom wall extending from the proximal side to the distal side, and first and second exhaust passages extending between the distal side and the proximal side, each of the first and second exhaust passages coupled respectively to first and second exhaust ports.

57. The gas head of claim 56, wherein the interior volume is open only to the proximal opening and the first and second exhaust passages.

58. The gas head of claim 56, wherein the top and bottom walls are planar and are parallel to each other.

59. The gas head of claim 56, wherein the proximal opening is arranged in a proximal plane, and the first and second exhaust passages are configured such that movement of gas out of the first exhaust port causes movement of gas in the interior space in a first direction transverse to the proximal plane and movement of gas out of the second exhaust port causes movement of gas in the interior space in a second direction transverse to the proximal plane.

60. The gas head of claim 59, wherein the first direction is approximately 45 degrees to the proximal plane, and the second direction is approximately 45 degrees to the proximal plane.

61. The gas head of claim 59, wherein the first direction is transverse to the second direction.

62. The gas head of claim 61, wherein the first direction is perpendicular to the second direction.

63. The gas head of claim 56, wherein the top wall and the bottom wall have a triangular shape with a proximal edge extending along the proximal side, a first edge extending along the first exhaust passage and a second edge extending along the second exhaust passage.

64. The gas head of claim 56, wherein the first and second exhaust passages extend from the distal side to the proximal side.

65. The gas head of claim 56, wherein the bottom wall includes a first inlet positioned in the bottom wall between the proximal side and the first exhaust passage and a second inlet in the bottom wall positioned between the proximal side and the second exhaust passage.

66. The gas head of claim 65, wherein the first and second inlets are arranged as elongated slots oriented transverse to the proximal opening.

67. The gas head of claim 65, wherein the first and second inlets are arranged as elongated slots that extend between the distal side and the proximal side.

68. The gas head of claim 65, wherein the first and second exhaust ports are configured to be fluidly coupled to the at least one gas flow generator to respectively create first and second exhaust gas flows to carry process ejecta from an additive manufacturing process through the proximal opening, into the interior volume and out of the first or second exhaust port and to draw gas through the first and second inlets, into the interior volume and out of the first or second exhaust port.

69. The gas head of claim 56, wherein the first and second exhaust ports are configured to be fluidly coupled to the at least one gas flow generator to respectively create first and second exhaust gas flows to carry process ejecta from an additive manufacturing process through the proximal opening, into the interior volume and out of the first and second exhaust port.

70. The gas head of claim 56, wherein first and second exhaust passages each have a proximal end adjacent the proximal opening and a distal end adjacent the distal side of the body, the distal ends of the first and second exhaust passages being adjacent each other.

71. A gas head for a gas head assembly of an additive manufacturing system, the gas head comprising: a body defining an interior volume and having a proximal opening at a proximal side of the body, a distal side of the body opposite the proximal side, a top wall extending from the proximal side to the distal side, a bottom wall extending from the proximal side to the distal side, a first exhaust passage coupled to a first exhaust port, and a first inlet in the bottom wall positioned between the proximal side and the first exhaust passage, wherein the first exhaust port is configured to be fluidly coupled to a gas flow generator to create a first exhaust gas flow to carry process ejecta from an additive manufacturing process through the proximal opening, into the interior volume and out of the first exhaust port and to draw gas through the first inlet, into the interior volume and out of the first exhaust port.

72. The gas head of claim 71, wherein the first inlet is arranged as an elongated slot that extends along a leading end of the first exhaust passage.

73. The gas head of claim 71, wherein the first inlet is arranged as an elongated slot that extends between the distal side and the proximal side.

74. The gas head of claim 73, wherein the first exhaust passage extends between the distal side and the proximal side.

75. The gas head of claim 71, wherein the bottom wall includes a proximal edge that at least partially defines the proximal opening, and the first inlet is arranged as an elongated slot transverse to the proximal edge.

76. The gas head of claim 71, the body further comprising a second exhaust passage coupled to a second exhaust port, and a second inlet in the bottom wall positioned between the proximal side and the second exhaust passage,

77. The gas head of claim 76, wherein the first and second inlets are arranged as elongated slots oriented transverse to the proximal opening.

78. The gas head of claim 76, wherein the first and second inlets are arranged as elongated slots that extend between the distal side and the proximal side.

79. The gas head of claim 76, wherein the top wall and the bottom wall each have a triangular shape with a proximal edge extending along the proximal side, a first edge extending along the first exhaust passage and a second edge extending along the second exhaust passage.

80. An additive manufacturing system comprising: a build surface on which a printed part is formable by fusing powder material supported on the build surface; and a gas head comprising a body defining an interior volume and having a proximal opening at a proximal side of the body, a distal side of the body opposite the proximal side, a top wall extending from the proximal side to the distal side, a bottom wall extending from the proximal side to the distal side, and first and second exhaust passages extending between the distal side and the proximal side, each of the first and second exhaust passages coupled respectively to first and second exhaust ports.

81. The system of claim 80, further comprising: an optics system configured to move relative to the build surface and to direct laser energy to a portion of the build surface located adjacent the proximal side of the body to fuse powder material at the portion of the build surface, wherein the gas head is configured to move with the optics system along a first direction such that the gas head is on a trailing side of the energy and the proximal opening is adjacent the laser energy.

82. The system of claim 81, wherein the optics system is configured to direct the laser energy to be incident along a line- shaped portion of the powder material on the build surface, and wherein the gas head is oriented such that a plane of the proximal opening is parallel to the line-shaped portion.

83. The system of claim 82, wherein the first direction is transverse to the plane of the proximal opening and to the line- shaped portion.

84. The system of claim 83, further comprising a gas flow generator coupled to the first exhaust port and configured to create a first exhaust gas flow to carry process ejecta created by the laser energy and powder material through the proximal opening, into the interior volume and out of the first exhaust port, the first exhaust gas flow being oriented along a first exhaust gas flow direction that is along the first direction.

85. The system of claim 84, wherein the gas head is configured to move with the optics system along a second direction transverse to the first direction such that the gas head is on a trailing side of the energy and the proximal opening is adjacent the energy, and wherein the gas flow generator is coupled to the second exhaust port and configured to create a second exhaust gas flow to carry process ejecta created by the laser energy and powder material through the proximal opening, into the interior volume and out of the second exhaust port, the second exhaust gas flow being oriented along a second exhaust gas flow direction that is along the second direction.

86. The system of claim 84, wherein first and second exhaust passages each have a proximal end adjacent the proximal opening and a distal end adjacent the distal side of the body, the distal ends of the first and second exhaust passages being adjacent each other.

87. A method for additive manufacturing, the method comprising: receiving a first gas flow into a gas head through a proximal opening at a proximal side of the gas head, the first gas flow including first process ejecta from an additive manufacturing process; conducting the first gas flow through an interior volume of the gas head in a first direction and to a first exhaust port of the gas head; receiving a second gas flow into the gas head through the proximal opening, the second gas flow including second process ejecta from the additive manufacturing process; conducting the second gas flow through the interior volume of the gas head in a second direction and to a second exhaust port of the gas head, the second direction being transverse to the first direction.

88. The method of claim 87, wherein the first direction is perpendicular to the second direction.

89. The method of claim 87, wherein the first direction and the second direction are oriented at 45 degrees to a plane of the proximal opening.

90. The method of claim 87, further comprising, during the steps of receiving the first gas flow and conducting the first gas flow, directing laser energy to be incident along a lineshaped portion of powder material on a build surface located adjacent the proximal side of the gas head to fuse the powder material, wherein the line-shaped portion is transverse to the first direction.

91. The method of claim 90, wherein directing laser energy includes using an optics system to direct the laser energy to be incident along the line-shaped portion, the method further comprising moving the gas head and the optics system along the first direction such that the gas head is on a trailing side of the laser energy, the line-shaped portion is transverse to the first direction and a plane of the proximal opening is transverse to the first direction.

92. The method of claim 91, wherein the plane of the proximal opening is parallel to the line- shaped portion.

93. The method of claim 91, further comprising, during the steps of receiving the second gas flow and conducting the second gas flow, directing laser energy to be incident along a second line- shaped portion of powder material on the build surface located adjacent the proximal side of the gas head to fuse the powder material, wherein the line-shaped portion is transverse to the second direction.

94. The method of claim 93, further comprising, during the steps of receiving the second gas flow and conducting the second gas flow, moving the gas head and the optics system along the second direction such that the gas head is on the trailing side of the laser energy, the line-shaped portion is transverse to the second direction and the plane of the proximal opening is transverse to the second direction.

95. The method of any one of claims 87-94, further comprising at least one step of the additive manufacturing process, the at least one step of the additive manufacturing process comprising directing laser energy to a precursor material on a build surface to fuse the precursor material to form one or more parts on the build surface.

96. A part manufactured using the method of any one of claims 87-95.

97. A method for additive manufacturing, the method comprising: providing a gas head including a body having an interior volume, first and second exhaust ports and an opening; receiving a first gas flow into the interior volume of the gas head through the opening, the first gas flow including process ejecta from a melt pool of an additive manufacturing process; and exhausting the first gas flow from the interior volume through the first exhaust port at a first flow rate that is larger than a second flow rate through the second exhaust port.

98. The method of claim 97, further comprising conducting the first gas flow through the interior volume of the gas head in a first direction to the first exhaust port.

99. The method of claim 98, further comprising moving the gas head in a first scan direction that is opposite to and along the first direction.

100. The method of claim 99, further comprising directing laser energy to be incident on a portion of powder material on a build surface located adjacent the opening of the gas head to fuse the powder material, wherein the gas head is on a trailing side of the laser energy relative to the first scan direction.

101. The method of claim 97, further comprising: receiving a second gas flow into the interior volume of the gas head through the opening, the second gas flow including process ejecta from a melt pool of an additive manufacturing process; and exhausting the second gas flow from the interior volume through the second exhaust port at a third flow rate that is larger than a fourth flow rate through the first exhaust port.

102. The method of claim 101, further comprising conducting the second gas flow through the interior volume of the gas head in a second direction to the second exhaust port.

103. The method of claim 101, further comprising moving the gas head in a second scan direction that is opposite to and along the second direction.

104. The method of claim 103, further comprising directing laser energy to be incident on portion of powder material on a build surface located adjacent the opening of the gas head to fuse the powder material, wherein the gas head is on a trailing side of the laser energy relative to the second scan direction.

105. The method of claim 104, wherein directing the laser energy to be incident includes directing the laser energy to be incident along a line- shaped portion of powder material on the build surface located adjacent the opening of the gas head to fuse the powder material, wherein the line-shaped portion is transverse to the second direction.

106. The method of claim 97, further comprising directing laser energy to be incident on a portion of powder material on a build surface located adjacent the opening of the gas head to fuse the powder material; and moving the gas head in a first scan direction, wherein the first and second exhaust ports of the gas head are on a trailing side of the laser energy relative to the first scan direction.

107. The method of claim 106, wherein the gas head is a first gas head, the method further comprising: providing a second gas head including a body having an interior volume, first and second exhaust ports and an opening; and moving the second gas head with the first gas head, the second gas head being on a leading side of the laser energy.

108. The method of claim 107, further comprising positioning a lowermost surface of the first gas head closer to the build surface than a lowermost surface of the second gas head.

109. The method of any one of claims 97-108, further comprising at least one step of the additive manufacturing process, the at least one step of the additive manufacturing process comprising directing laser energy to a precursor material on a build surface to form the melt pool and to fuse the precursor material to form one or more parts on the build surface.

110. A part manufactured using the method of any one of claims 97-109.

111. A method for additive manufacturing, the method comprising: providing a gas head including a body having an interior volume, a bottom wall having a proximal edge, a first exhaust port fluidly connected to the interior volume, a proximal opening defined at least in part by the proximal edge, and a first inlet opening in the bottom wall; receiving a proximal gas flow into the interior volume of the gas head through the proximal opening, the gas flow including process ejecta from a melt pool of an additive manufacturing process; receiving a first inlet gas flow into the interior volume through the first inlet opening; and exhausting the proximal gas flow and the first inlet gas flow from the interior volume through the exhaust port.

112. The method of claim 111, wherein the first inlet opening is located between the proximal edge and a distal side of the body.

113. The method of claim 111, wherein the bottom wall is planar and spaced above a build surface that supports powder material used to form the melt pool.

114. The method of claim 111, further comprising: receiving a second inlet gas flow into the interior volume through a second inlet opening in the bottom wall; and exhausting a portion of the proximal gas flow and the second inlet gas flow from the interior volume through a second exhaust port of the body.

115. The method of any one of claims 111-114, further comprising at least one step of the additive manufacturing process, the at least one step of the additive manufacturing process comprising directing laser energy to a precursor material on a build surface to form the melt pool and to fuse the precursor material to form one or more parts on the build surface.

116. A part manufactured using the method of any one of claims 111-115.

117. A gas flow control for an additive manufacturing system, the gas flow control comprising: a first exhaust flow port for fluid communication with a gas flow generator, the first exhaust flow port configured to conduct a first exhaust gas flow from a build volume of the additive manufacturing system towards the gas flow generator; a second exhaust flow port for fluid communication with the gas flow generator, the second exhaust flow port configured to conduct a second exhaust gas flow from the build volume towards the gas flow generator; and a gas flow valve fluidly coupled between the gas flow generator and the first and second exhaust flow ports, the gas flow valve configured to control flow from the first and second exhaust flow ports to the gas flow generator, the gas flow valve comprising a valve element movable to selectively impede and allow flow from the first exhaust flow port to the gas flow generator and selectively impede and allow flow from the second exhaust flow port to the gas flow generator.

118. The gas flow control of claim 117, wherein the first and second exhaust flow ports are part of a same gas head.

119. The gas flow control of claim 118, wherein the gas flow valve is configured to simultaneously allow flow from the first exhaust flow port to the gas flow generator and impede flow from the second exhaust flow port to the gas flow generator.

120. The gas flow control of claim 117, wherein the first and second exhaust flow ports are part of respective first and second gas heads.

121. The gas flow control of claim 120, wherein the gas flow valve is configured to simultaneously allow flow from the first exhaust flow port to the gas flow generator and impede flow from the second exhaust flow port to the gas flow generator.

122. The gas flow control of claim 121, wherein the first and second gas heads are configured for positioning on opposite sides of a melt pool formed on a build surface of the additive manufacturing system.

123. The gas flow control of claim 117, wherein the gas flow valve includes a valve body with first and second inlet ports and an outlet port, the first inlet port being coupled to the first exhaust flow port, the second inlet port being coupled to the second exhaust flow port, and the outlet port being coupled to the gas flow generator, and the valve element is movable in the valve body to selectively impede or allow flow from the first inlet port to the outlet port, and to impede or allow flow from the second inlet port to the outlet port.

124. The gas flow control of claim 123, wherein the valve element is movable between positions in which flow from the first and second inlet ports to the outlet port is impeded, and in which flow from the first and second inlet ports to the outlet port is allowed.

125. The gas flow control of claim 123, wherein the valve element is movable between positions in which flow from the first inlet port to the outlet port is allowed and flow from the second inlet port to the outlet port is impeded, and in which flow from the first inlet port to the outlet port is impeded and flow from the second inlet port to the outlet port is allowed.

126. The gas flow control of claim 123, wherein the body includes a bypass opening and the valve element is movable to impede and allow flow between the bypass opening and the outlet port.

127. The gas flow control of claim 126, wherein the valve element is movable between positions in which flow from the first and second inlet ports to the outlet port is impeded and flow from the bypass opening to the outlet port is allowed, and in which flow from the first and second inlet ports to the outlet port is allowed and flow from the bypass opening to the outlet port is impeded.

128. The gas flow control of claim 123, wherein the gas flow valve includes an actuator to rotate the valve element between multiple positions relative to the valve body.