WO2018227229A1

WO2018227229A1 - Improved additive manufacturing of metallic components

Info

Publication number: WO2018227229A1
Application number: PCT/AU2017/051241
Authority: WO
Inventors: Jack Martinich
Original assignee: AmPro Innovations Pty Ltd
Priority date: 2017-06-15
Filing date: 2017-11-13
Publication date: 2018-12-20

Abstract

Apparatus for the deposition of successive layers of a powder material onto a print bed to enable the production of components by additive manufacturing, such as laser-based additive manufacturing from CAD files, in which each layer is subjected in turn to selective heating, such as to above the melting temperature for the metal powder material, by focussed electromagnetic radiation providing selective melting, includes a housing defining a processing chamber in which a non-reactive or inert atmosphere is able to be maintained and, within the chamber, a system for the deposition of successive layers of powder material onto a print bed of the apparatus. The system has an elongate, powder material spreader member disposed in a first direction over and close to the print bed; a mounting member by which the spreader member is supported at an end for reversible lateral movement normal to the first direction between opposite sides of the print bed; and a powder material supply device above one side of the print bed and operable to discharge successive charges of the powder material and to spread a charge of the powder material over the upper surface in being moved from one to the other of the opposite sides.

Description

Improved Additive Manufacturing of Metallic Components

[0001] Technical Field

[0002] This invention relates to a method and apparatus for the production of metailic components by additive manufacturing, such as laser-based additive manufacturing, also known as 3D printing.

[0003] Background to the invention

[0004] Apparatus for the production of metallic components by additive manufacturing, or three dimensional printing, has progressed rapidly over the last two decades. An early development in the technology is that disclosed by the patent US 6,215,093 to Meiners et ai, assigned to Fraunhofer-Gesellschaft. The US'093 patent provides a method for manufacturing a component by using 3D CAD data of a model of the component to control deposition of successive layers of a metallic powder, one on top of the other, with each layer heated by a focused laser beam applied to a given area corresponding to a selected area of the model, to achieve selective laser melting, before depositing the next layer, with the laser beam guided over each layer of powder in accordance with the CAD cross-sectional data of the selected cross-sectional area of the model whereby each layer is fixed to the layer below. The method is distinguished in that the metailic powder is free of binding and fluxing agents and is fully melted throughout its layer thickness at the point of impact of the laser beam, the laser beam is guided in runs so each run partially overlaps the preceding run, while a protective atmosphere is maintained above the interaction zone beam of the laser beam and the metallic powder. A process similar to that of the US'093 patent is disclosed by patent US 6,676,892 to Das et al, assigned to the Board of Regents, The University of Texas System. The method of the US'892 patent is conducted with a partial pressure and a scanning energy beam, preferably a laser beam, is directed to melt each of successive layers of metallic powder in turn at selected locations comprising a continuous vector scan path that never intersects itself, for example such as by the path being helical.

[0005] Common to each of the US^!892 and US'093 patents is the requirement to build up successive layers of metallic powder. The US'892 patent provides little detail on how the layers are to be built up but suggests a layer thickness of about 0.005 inches (0.127 mm). The US'093 ambiguously suggests a layer thickness of from 0.05 to 0.02 mm, such as about 0.1 mm, but does show an elongate member that is caused to sweep laterally to spread the metallic powder across a target surface. However a number of alternatives have been proposed, although critical need for precision in the thickness and uniformity of the metallic powder layers is such that improved devices for forming the layers continue to be developed. Examples of are provided by the patents US 5,647,931 ; US 7,537,722; and US 8,308,466 and by patent application US 2017/0106570, each of which provides a method of producing a component layer by layer on a support, using a powdery material able to be solidified by irradiation with electromagnetic radiation such as a laser beam, in which the layers are applied by moving a wiper member laterally across the support to obtain a predetermined thickness of the material.

[0006] In patent US'931 to Retallick et al, assigned to EOS GmbH, the wiper member is vibrated and is carried by, and movable with, an elongate trough to which the material is charged and from which the powder material issues in advance of the wiper member. At one or each end of a path traversed by the wiper member, the trough is positioned under a reservoir means that holds a supply of the powder material with the reservoir having a feeder for replenishing the quantity of powder material held in the trough.

[0007] The patents US'551 to Wallgren et al and US'446 to Ackelid et al, both assigned to Arcam AB, disclose related respective arrangements for distributing powder material in a layer on a working table. The patent US'551 has an elongate rake member that moves laterally and, at each end of a path it traverses, it moves to displace over its upper edge a sufficient powder material to be spread to form a layer on moving back to the other end. The patent US'466 differs in that the working table has a depressible strip that enables powder material to be forced below the main surface of the table by the elongate rake member, and then enables the material to be raised to that surface after the elongate rake member has passed the depressible strip, with the material again being spread to form a layer by reversal of movement of the rake member.

[0008] The patent US'722 to Andersson et al, also assigned to Arcam AB, is similar to patent US'931 in terms of how powder layers are formed, although the advance is provides resides more in the determination of determination of powder melting temperature, fused metai temperature and the temperature of the powder material prior to exposure to the ray gun used (which may be a laser source).

[0009] The patent application US'570 by Kaiisson, assigned to Arcam AB, is directed to overcoming deficiencies with each of Patents US'551 and US'446. This is indicated as enabled by a pivoted powder-pushing device that has a part that passes under a device for powder spreading, and enables powder to be pushed from a curved support surface below the working table surface and pass beyond the spreading device.

[0010] The present invention seeks to provide a method and apparatus that, at least in preferred forms, enable complications that arise with the arrangements of the prior art to be overcome or at least ameliorated.

[0011] Broad Summary of the Invention

[0012] The present invention provides apparatus, and a corresponding method, for the deposition of successive layers of a powder material onto a print bed in the course of the production of components by additive manufacturing, such as laser-based additive manufacturing from CAD files, in which each layer is subjected in turn to selective heating, such as to above the melting temperature for the powder material, by focussed electromagnetic radiation. The invention principally relates to the use of metal powder material and the production of metallic components by selective laser melting and, for ease of description, the invention is described in that context. However it is to be understood that the different aspects of the invention have more general application.

[0013] in one form, the invention provides apparatus for additive manufacturing, such as laser additive manufacturing, in which the apparatus includes a housing defining a processing chamber in which a non-reactive or an inert atmosphere is able to be maintained and, within the processing chamber, a system for the deposition of successive layers of powder material onto a print bed of the apparatus, wherein the system has an elongate, powder material spreader member that has its longitudinal extent disposed in a first direction over, and in close juxtaposition to, an upper surface of the print bed; at least one mounting member by which the spreader member is supported, at an end of the spreader member, for reversible movement of the spreader member in a second direction normal to the first direction across and between opposite sides of the upper surface of the print bed; and a powder material supply device located above one side of the print bed and operable to discharge , via an outlet member, successive charges of the powder material such that the spreader member is able to spread a charge of the powder material over the upper surface in being moved from the one of the opposite sides to the other of the opposite sides.

[0014] The powder material supply device may be operable to discharge successive charges under gravity. However other arrangements are possible, such as discharge using gas pressure acting on powder material held by the supply device.

[0015] The elongate, powder material spreader member may be in the form of an elongate vessel, such as an open-topped trough of U- or V-shape in transverse cross- sections. The arrangement may be such that the vessel is movable to the one side of the opposite sides of the upper surface of the print bed so as to be locatable under the outlet member of the powder material supply device for receiving a charge of the powder discharged from the supply device. In that event, the vessel comprising the spreader member preferably is provided with a slit forming a narrow elongate opening through which the powder material of the charge is able to flow onto the upper surface of the print bed and form a layer of the powder material as the spreader member is moved from the one, to the other, of the opposite sides of the print bed. The spreader member may have a capacity for holding a charge sufficient for forming a single layer of the powder material as the spreader member is moved from the one, to the other, of the opposite sides. Where that is the case, the arrangement may be such that the spreader member is required to return to the one side in order to receive a respective further charge of powder material for forming each of successive layers. Alternatively, a respective powder delivery supply device may be provided above each side of the print bed to enable successive charges to be received from alternative supply devices. In a preferred form, the spreader member has a capacity enabling it to hold a larger charge of powder material sufficient to form two successive layers, comprising a first layer formed as the spreader member is moved from the one, to the other, of the opposite sides, and a second layer formed as the spreader member returns to the one side. In each arrangement, powder material of each layer is subjected to heating to selectively fuse powder material of the layer prior to a respective next layer being formed.

[0016] The apparatus may have only one mounting member by which the elongate spreader member is mounted for reversible movement between opposite sides of the print surface. Where that is the case, the other end of the spreader member may rest on a support surface extending between those opposite sides so the spreader member is able to slide over the support surface as the one mounting member moves the spreader member. However, there may be two mounting members supporting the spreader member, with each mounting member at a respective end of the spreader member and the two mounting members operable in unison to move the spreader member between the opposite sides of the upper surface of the print bed. The one mounting member, or each mounting member, may comprise a carriage device that is moveable along a track, or along a respective track, extending between the opposite sides of the print surface, under the action of a drive device, or a respective drive device. The drive device, or each drive device, may be located within the processing chamber but, most preferably is located externally of the housing and is operable through a wall, or a respective wall, of the housing. In a particularly preferred embodiment the, or each, housing is of a ferromagnetic material and the, or each, drive device is magnetically coupled to the carriage, or a respective carriage, through the wall or the respective wall of the housing. In that embodiment, the or each drive device may include a magnet and a linear drive for reversibly moving the magnet along a path along the wall, or the respective wall, of the housing, with the carriage, or the respective carriage of a ferromagnetic material or comprising a magnet that is magnetically coupled to the, or a respective, magnet of the drive device through the wall, or the respective wall, of the housing. The arrangement is such that the magnet of the drive device, or the respective magnet of each drive device, is movable to thereby move the carriage with which it is magnetically coupled, and to thereby advance the spreader member across the print surface, as required for spreading a layer of powder material across the print surface.

[0017] The powder material supply device may be in the form of a hopper that has an inlet at or towards a top level, with the outlet member at or adjacent to a lower level. The supply device may be fully contained within the housing, with a supply conduit or other suitable feed device providing communication between the inlet of the hopper and a supply source for powder material that is located outside the housing, to enable a flow of make-up powder material from the source to the hopper, as required. Alternatively, the hopper may have an upper end portion that projects through an upper part of the housing such that the inlet is outside the housing for similarly receiving make-up powder material from the supply source. The hopper may be in the form of a container separable from the housing, or it may be defined in part by a wall of the housing on which is mounted a fitting that, with the wall, forms a container comprising the hopper.

[0018] The outlet member may be of elongate form and, where that is the case, the outlet member may have a length that is the same, or substantially the same, as an elongate open top of a vessel comprising the powder material spreader member. The outlet member may have an elongate valve member that is rotatable on a longitudinal axis between a first position in which it enables powder material to flow from the hopper into the vessel and a second position in which it prevents such flow. In one convenient form, the outlet member comprises an elongate rod of circular cross-section through which a plurality of longitudinally spaced transverse holes extend through the rod, such as in a common longitudinal plane, with the holes enabling the flow of powder material from the hopper when the rod is rotated to the first position. An outlet member of that form facilitates the discharge of powder material through the transverse holes in a controlled amount and fashion, while it also enables the discharge to be uniform along the vessel comprising the spreader member.

[0019] In one convenient arrangement, the housing of the apparatus has an upstanding periphery defined by a first and a second, mutually perpendicular pairs of opposed walls, such as with the walls of each pair substantially parallel. The housing also has a base across an upper surface of which the print surface extends, and also has a top cover. For ease of further description, the walls of the first pair are taken to be sidewal!s, with the walls of the second pair comprising a front wall and a rear wall. In that arrangement, the hopper is located within the container adjacent to and along one sidewall, or a respective hopper is located adjacent to and along each sidewall. The powder material spreader member is supported above, but close to, the print surface. The elongate extent of the spreader member extends between the front and rear walls and so that the spreader member is movable laterally in a direction extending between the sidewalls. Most conveniently the spreader member is supported at each of its ends by a respective mounting member and is laterally movable by a respective drive system acting on each mounting member. A respective drive system for each mounting member may include a linear drive, such as a stepper motor, that is located within the housing to engage directly with the respective mounting member.

[0020] In a preferred form, the drive system is located externally of the housing and operable to engage indirectly with the mounting member, an arrangement that has the important benefit of facilitating the maintenance of a non-reactive or inert atmosphere in the processing chamber. In the preferred external form, the drive system may be operable to move a magnet device that provides a magnetic coupling with a respective mounting member, by the coupling acting through a respective one of the front and rear wails. Thus, as the drive system acts to move the magnet device, the magnetic coupling causes the mounting member to move in unison with the magnet device thereby to move the spreader member laterally across the print surface. The mounting member preferably is movable along a rail secured within the housing, adjacent to the respective one of the front and rear walls. The drive system may be secured below the base across which the print surface extends, with a magnet of the magnet device supported on and movable along an upper surface of the base, such as on a rail fixed on the base outside the respective one of the front and rear walls. The drive system preferably consists of a stepper motor mounted below a corner of the base, with the motor having an output shaft connected end-to-end to a threaded shaft mounted under the base and fixed against movement in the direction of its axis. The magnet device has a depending arm that extends below the base from the magnet while the arm has a threaded bore through which the shaft extends in threaded engagement. The arrangement is such that, with actuation of the stepper motor, the shaft is rotated on its axis, thereby causing the magnet and arm of the magnet device to progress along the shaft, in a direction determined by the direction of rotation of the threaded shaft.

[0021] Genera! Description of the Drawings

[0022] in order that the invention may more readily be understood, description now is directed to the accompanying drawings, in which: [0023] Figure 1 shows a front perspective view of a process unit of a machine for the production of components by additive manufacturing, incorporating apparatus according to the present invention for use in the deposition of successive layers of powder material;

[0024] Figure 2 is an exploded view corresponding to Figure 1 , showing sub-units of the process unit;

[0025] Figure 3 is a perspective view of the unit of Figure 1 , but with removal of a housing and associated devices of the apparatus of the invention;

[0026] Figure 4 is a sectioned view if the unit as shown in Figure 3;

[0027] Figure 5 shows on an enlarged scale and upper part of the unit as seen in Figure 3;

[0028] Figure 6 shows an exploded view showing an uninstalled component of the unit as seen in Figure 5;

[0029] Figure 7 corresponds to Figure 6, but provides an exploded view of the uninstalled component;

[0030] Figure 8 is a front elevation of the sectioned view of Figure 4 on the enlarged scale;

[0031] Figure 9 corresponds generally to Figure 3, but shows a modified form of processing unit; and

[0032] Figure 10 shows a sectioned view of the unit of Figure 9. [0033] Detailed Description of the Drawings

[0034] With reference to Figures 1 , there is a processing unit U(a) of a machine suitable for use in the production of components by additive manufacturing, incorporating apparatus A according to the present invention for use in the deposition of successive layers of metal powder material. Components of the apparatus A are shown and described if relation to Figures 2 to 8, while an alternative form of processing unit U(b) is shown in Figures 9 and 10. The other parts of a complete machine with which processing unit U(a) or unit U(b) is able to be used, that are not shown, include:

(a) an electronics and computer unit, including a power source for electromagnetic radiation sources, such as laser sources, a scanner control system, a computer system and other general electrical systems required for operation of the complete machine;

(b) a gas/powder unit, containing a recirculation filter and powder feeding system, through which powder would be loaded into unit U(a) or unit U(b);

(c) parts associated with unit U(a) or unit U(b) to form a process unit in which a part is to be built under a supplied protective atmosphere;

(d) a glovebox in which a build job, comprising a built part, is able to be unloaded and powder reclaimed and sieved under the protective atmosphere; and

(e) water coolers and post processing facilities.

However, these other parts readily will be understood by those skilled in the technology.

[0035] The unit U(a) as shown in Figure 1 has a rectangular footing 10 on which other parts are supported. The other parts include an upper housing 12 that defines a processing chamber 14. The housing 12 has a box-like form with a front wall 16, a rear wall 17 opposed to the front wall 16, opposed sidewalls 18 joining the front and rear walls 16 and 17, a top cover 19 and a base 20. The front wall 16 has an access panel 15 in which an inspection window 15a is provided. A print bed 21 extends across an upper surface of base 20 within the processing chamber 14. The base 20 comprises an outer frame 22 that has an inner periphery defining a central, substantially rectangular opening 24. In the condition shown in Figure 1 , the outer periphery of print bed 21 is formed by the upper surface of frame 22 and, within opening 24, a main operative part of the print bed is formed by the upper surface of a substantially rectangular platform 26 when platform 26 is received into opening 24. A sub-housing 28 is secured below the build chamber 14, and platform 26 can be lowered progressively into a build chamber 29 defined within the sub-housing 28 by stepwise movement from an upper position in which platform 26 provides a continuation of the upper surface of frame 22. With each step by which platform 26 is lowered, the print bed 21 is able to be reformed so as to comprise the upper surface of frame 22 and material from a previous layer of powder material, so that a fresh layer, of successive layers, of powder material formed on the print bed 21 , including over and above the platform 26. Material progressively lowered into the build chamber 29 comprises metal that has been selectively melted in successive layers of powder material, by at least one electromagnetic beam, in building up a metallic component, as well as unmelted powder material from each of the successive layers.

[0036] The platform 26 can be lowered by vertically adjustable mechanism, with the steps by which platform 26 is lowered, and the thickness of successive layers of powder material, each being about 20 to 50 μιη or greater. In the arrangement shown, the adjustable mechanism comprises hydraulic devices 30 operable under the action of hydraulic motor 32. However vertically adjustable mechanisms can be used, such as an electric or hydraulic scissor lift device.

[0037] The inter-connected housing 12 and sub-housing 28 are supported above footing 10 by front and rear upright supports 34. The sub-housing 28 has a front wall 35, a rear wall 36 and opposed sidewalls 37 each parallel with, but inset from the corresponding wail 16, 17 and 18 of housing 12 such that the periphery of sub-housing 28 closely follows the outline of opening 24 of base 22. The sub-housing 28 also includes a bottom wail 38 through which the devices 30 project upwardly from footing 10 to the underside of platform 26, with devices 30 enabling platform 26 to be lowered stepwise and, after completion of manufacture of a metallic component, the devices 30 also enable platform 26 to be returned to the position shown in Figure 1 in which the upper surface of platform 26 again forms part of the print bed 21. The devices 30 comprise a parallel pair of upstanding telescopic hydraulic masts 41 each encased in a protective bellows 44. The masts 30 are vertically contracttble in a stepwise manner to progressively lower platform 18 and material thereon into the build chamber 29 within sub-housing 28, and also extendible for the return elevation of platform 26, in each case under the action of hydraulic motor 32.

[0038] Mounted above the print bed 21 , each of the units U(a) and U(b) includes a dosing unit 40 and a re-coater unit 42. As viewed in Figure 1 , the dosing unit 40 is adjacent to the right side of print bed 21. The unit U(b) of Figures 9 and 10 is the same overall as unit U(a) of Figure 1 , except for having a respective dosing unit 40 adjacent to each of the right and left sides of bed 21.

[0039] Each dosing unit 40 is of elongate form in the direction of spacing between the front wall 16 and rear wall 17 of upper housing 12 and print bed 21. Each unit 40 consists of a hopper 44 for holding a quantity of metal powder material and a valve housing 46 by which charges of the powder material are able to be dispensed periodically to the re-coater unit 42. The hopper 44 is mounted on the top of the valve housing 46, while a flange 48 depending from the outermost side of the valve housing 46 is mounted on frame 22 of base 20 to space the valve housing 46, by a clearance 49 below valve housing 46, above the frame 18 and the print bed 21. The valve housing 46 has a longitudinal slot 50 that is located below an elongate opening 51 along the bottom of hopper 44, while a flow control valve cylinder 52 is held captive in slot 50. Hopper 44 is secured to the top of valve housing 46 by a peripheral flange 54 secured around the opening 51. A respective resilient seal 56, such as of rubber or neoprene, is clamped between the flange 54 and valve housing 46, along each side of slot 50, so each seal 56 bears against and provides a seal along a respective side of the valve cylinder 52. A parallel series of uniformly spaced transverse through holes 58, in a common plane through the axis of valve cylinder 52, are provided so valve cylinder 52 either enables or precludes the flow of a required dose of powder material from hopper 44 through the valve housing 46. A control motor (not shown) is associated with unit 40 for rotating valve cylinder 52 at intervals for alternatively enabling or stopping such flow, with the motor either providing rotation at intervals in one direction, or for providing rotation in alternate directions. The required flow is allowed by seals 56, although the seals 56 otherwise hold back a reserve of powder material held in hopper 44.

[0040] The re-coater 42 comprises a system for the deposition of successive layers of powder material onto the print bed 21 , and includes an elongate, powder material spreader member 60 that extends in along a first line between and substantially perpendicular to the front and rear walls 16,17 of upper housing 12. The longitudinal extent of spreader member 60 is disposed along the first line over, and in close juxtaposition to, an upper surface of the print bed 21. A respective mounting member 61 , by which the spreader member 60 is supported, is provided at each end of the spreading member 60, with the mounting members 61 enabling reversible movement of the spreader member 60 along a second line normal to the first line, across and between opposite sides of the upper surface of the print bed. In the case of Figures 1 to 8, movement of spreader member 60 to the side at which dosing unit 40 is located enables the spreader member 60 to move into clearance 49, below valve housing 46, so spreader member 60 can receive a quantity of powder material discharged from hopper 44. The arrangement preferably is such that spreader member 60 is able to receive sufficient quantity of powder material to enable the spreading of successive layers of powder material over the print bed, by a first layer put down in a first traversal as spreader member 60 moves away from dosing unit 40 and a second layer put down in the next traversal of spreader member moving back to dosing unit 40. Thus, production time is not lost in needing the second traversal simply to enable spreader member to move back to dosing unit 40 to receive a further quantity of powder material for a second layer. In the case of Figures 9 and 10, spreader member 60 requires only a sufficient quantity of powder material for a single traversal, as successive quantities of powder material can be received form alternate dosing units, again with the ability to spread a layer of powder material during each traversal of the print bed 21 by spreader member 60.

[0041] The powder material spreader member 60 is in the form of an elongate, open- topped vessel 64 comprising a trough of V-shape in transverse cross-sections. The vessel 64 has oppositely inclined sidewalls 65 between the lower edges of which a narrow elongate slit or opening 66 is defined. The vessel 64 is laterally movable between the opposite sides of the upper surface of the print bed 21 so as to be locatable under the valve cylinder 52 of the valve housing 46 of the dosing unit 40 for receiving a quantity of the powder material discharged from hopper 44, as permitted and controlled by operation of valve cylinder 52. Also, in moving laterally from one to the other side of the print bed 21 while containing a quantity of the powder material, the vessel 64 is able to lay down a layer of powder material. The thickness of the layer is controlled primarily by the narrow spacing between the lower edges of sidewalls 65 from the print surface, with that spacing and the layer thickness able to be from about 20 to 50 μτη, but able to range up to about 100 μηι. As indicated, vessel 64 may have a capacity for holding a charge sufficient for forming a single layer of the powder material as the spreader member 60 is moved from the one, to the other, of the opposite sides. Where that is the case, the arrangement may be such that the spreader member 60 is required to return to the one side in order to receive a respective further charge of powder material for forming each of successive layers. Alternatively, a respective powder material dosing unit 40 may be provided above each side of the print bed 21 to enable successive charges to be received from alternative supply devices. In a preferred form, the spreader member 60 has a capacity enabling it to hold a larger charge of powder material sufficient to form two successive layers, comprising a first layer formed as the spreader member 60 is moved from the one, to the other, of the opposite sides, and a second layer formed as the spreader member 60 returns to the one side. In each arrangement, powder material of each layer is subjected to heating to selectively fuse powder material of the layer prior to a respective next layer being formed.

[0042] As shown, the re-coater 42 preferably has a respective mounting member 61 at each end of the spreader member 60 by which the spreader member 60 is moved laterally. While less preferred, there may be a single mounting member 61 at one end of the spreader member 60, with the other end of the spreader member 60 resting on a support surface, such as of a support rail, extending between those opposite sides. Thus, as the one mounting member 61 moves the spreader member 60 laterally, the other end of the spreader member 60 is able to slide over the support surface. However, two mounting members 61 supporting the spreader member 60 enhances the stability and precision of operation, particularly as a result of the two mounting members 61 being able to operate in unison to move the spreader member 60 laterally. The one mounting member 61 , or each mounting member 61 , may comprise a carriage device 63 that is moveable along an inner rail track 62, or along a respective inner rail track 62, within the processing chamber 14. The or each inner track 62 extends between the opposite sides of the print surface, parallel to a respective one of walls 16 and 17 of upper housing 12, and the or each carriage device 3 moves under the action of a drive device 68, or a respective drive device 68. The drive device 68, or each drive device 68, may be located within the processing chamber 14 but, most preferably is located externally of the upper housing 12 and is operable through a wall 16 or 17, or a respective one of walls 16 and 17, of the upper housing 12. In the particularly preferred embodiment illustrated, the upper housing 12, or at least each of the walls 16 and 17, is of a ferromagnetic material and the, or each, drive device 68 is magnetically coupled to a respective carriage device 63, through the respective one of walls 16 and 17 of the upper housing 12. Each drive device 68 includes a magnet 70 and a linear drive 72, with the drives 72 operable in unison for reversibly moving each magnet 70 along an outer rail track 71 secured on the upper surface of base 20, outside and parallel to the respective one of walls 16 and 17 of the upper housing 12. The respective carriage device 63 is made of a ferromagnetic material, or comprising a magnet, and can be magnetically coupled to the respective magnet 70 of the drive device 68 through the respective on of walls 16 and 17 of the upper housing 12. The arrangement is such that the respective magnet 70 of each drive device 68 is movable to thereby move the carriage device 63 with which it is magnetically coupled, and to advance the spreader member 60 across the surface of the print bed 21 , as required for spreading a layer of powder material across the print bed 21.

[0043] In the arrangement shown, each drive device 68 is secured below the base 20 across which the print bed 21 extends, with a magnet 70 of the drive device 68 supported on and movable along an upper surface of the base 20, on a respective rail track 71 fixed on the base 20 outside the respective one of the front and rear walls 16 and 17 of sub-housing 12. The drive device consists of a motor 73, such as a stepper motor, mounted below a corner of the base 20, by being attached to one end of an elongate frame member 74 that is secured along and below a respective edge of base, parallel to a respective one of walls 16 and 17. The motor 73 has an output shaft (not shown) connected end-to-end to a threaded shaft 76 mounted under the frame member 74 and fixed against longitudinal movement in the direction of its axis. The drive device 68 has a depending arm 77 that extends below the base 20 from the magnet 70, with the lower end of arm 77 having a threaded bore through which the shaft 76 extends in threaded engagement. The arrangement is such that, with actuation of the motor 73, the shaft 76 is rotated on its axis, thereby causing the magnet 70 and arm 77 to progress along the shaft 76, in a direction determined by the direction of rotation of the shaft 76. A control system regulates operation of motor 73 to achieve the required direction of rotation of shaft 76 and, hence the required direction of movement of carriage with resultant movement of magnet 70 to enable the laying down of a layer of powder material as the spreader member traverses the print bed.

[0044] The hopper 44 of the powder material dosing unit 40 may, as shown, have an open top comprising an inlet 74. Also, unit 40 may be fully contained within the upper housing 12, as shown, with a supply conduit or other suitable feed device (not shown) providing communication between the inlet 74 of the hopper and an external supply source (not shown) for powder material, to enable a flow of make-up powder material from the source to the hopper 44. as required. Alternatively, the hopper 44 may have an upper end portion that projects through the top cover 19 of the upper housing 12 such that the inlet 74 is outside the upper housing 12 for similarly receiving make-up powder material from the supply source. Rather than being in a form separable from the upper housing 12, as shown, the hopper 44 may be defined in part by the adjacent sidewall 18 of the upper housing 12 on which is mounted a fitting that, with the adjacent wall 18, forms a container comprising the hopper 44.

[0045] The lower edge of each of walls 16, 17 and 18 of upper housing 12 is received in a corresponding section of a rectangular channel 20a formed in the upper surface of the base 20 of housing 12, around the print bed 21. This arrangement, as well as the fitting of top cover 19 on the upper edge of each wall 16, 17 and 18, enables oxygen to be flushed from the processing chamber 14 by a maintained flow of a non-reactive gas such as nitrogen, or an inert gas such as argon. While not shown, the processing chamber 14 accordingly has an inlet and an outlet enabling such through-flow of non-reactive or inert gas.

[0046] As indicated, each layer of powder material formed is to be selectively melted to form a respective layer of a component being progressively built up, prior to the next layer being formed. To enable this, each of units U(a) and U(b) shows a pair of optical head devices 78, incorporating a motion system operable on at least an X-Y co-ordinate system, by which a respective laser beam received via optical fibres 79 from a laser source (not shown) is able to be focused on and directed over required areas of the print bed 21 , as required for compliance with controlling CAD files, as shown by the cones 80 in Figure 2, depicting the areas over which respective laser beams can be directed.

Claims

1. Apparatus for the deposition of successive layers of a powder material onto a print bed to enable the production of components by additive manufacturing, such as laser- based additive manufacturing from CAD files, in which each layer is subjected in turn to selective heating, such as to above the melting temperature for the metal powder material, by focussed electromagnetic radiation providing selective melting; wherein apparatus includes a housing defining a processing chamber in which a non-reactive or inert atmosphere is able to be maintained and. within the processing chamber, a system for the deposition of successive layers of powder material onto a print bed of the apparatus, wherein the system has an elongate, powder material spreader member that has its longitudinal extent disposed in a first direction over, and in close juxtaposition to, an upper surface of the print bed; at least one mounting member by which the spreader member is supported, at an end of the spreader member, for reversible movement of the spreader member in a second direction normal to the first direction across and between opposite sides of the upper surface of the print bed; and a powder material supply device located above one side of the print bed and operable to discharge under gravity or gas pressure, via an outlet member, successive charges of the powder material such that the spreader member is able to spread a charge of the powder material over the upper surface in being moved from the one of the opposite sides to the other of the opposite sides.

2. The apparatus of claim 1 , wherein the spreader member is in the form of an elongate vessel, such as an open-topped trough of U- or V-shape in transverse cross-sections, such that the vessel is movable to the one side of the opposite sides of the upper surface of the print bed so as to be locatable under the outlet member of the powder material supply device for receiving a charge of the powder discharged from the supply device, with the vessel provided with a slit forming a narrow elongate opening through which the powder material of the charge is able to flow onto the upper surface of the print bed and form a layer of the powder material as the spreader member is moved from the one, to the other, of the opposite sides of the print bed.

3. The apparatus of claim 2, wherein the spreader member has a capacity for holding a charge sufficient for forming a single layer of the powder material as the spreader member is moved from the one, to the other, of the opposite sides such that the spreader member is required to return to the one side in order to receive a respective further charge of powder material, or a respective powder delivery supply device is provided above each side of the print bed to enable successive charges to be received from alternative supply devices.

4. The apparatus of claim 2, wherein the spreader member has a capacity enabling it to hold a charge of powder material sufficient to form two successive layers, comprising a first layer formed as the spreader member is moved from the one, to the other, of the opposite sides, and a second layer formed as the spreader member returns to the one side.

5. The apparatus of any one of claims 1 to 4, wherein there is only one mounting member by which the elongate spreader member is mounted for reversible movement between opposite sides of the print surface, with the other end of the spreader member resting on a support surface extending between those opposite sides so the spreader member is able to slide over the support surface as the one mounting member moves the spreader member.

6. The apparatus of any one of claims 1 to 4, wherein there is a respective mounting member supporting the spreader member at each end of the spreader member with the mounting members operable in unison to move the spreader member between the opposite sides of the upper surface of the print bed.

7. The apparatus of claim 5 or claim6, wherein the or each mounting member comprises a carriage device that is moveable along a track, or a respective track, extending between the opposite sides of the print surface, under the action of a drive device, or a respective drive device.

8. The apparatus of claim 7, wherein the drive device, or each drive device, is located within the processing chamber.

9. The apparatus of claim 7, wherein the drive device, or each drive device, is located externally of the housing and is operable through a wall, or a respective wall, of the housing.

10. The apparatus of claim 9, wherein the, or each, drive device is magnetically coupled to the carriage, or a respective carriage, through by the wall, or the respective wall, of a ferromagnetic material, with the or each drive device including a magnet and a linear drive for reversibly moving the magnet along a path along the wall, or the respective wall, of the housing, with the carriage, or the respective carriage, being of a ferromagnetic material or comprising a magnet that is magnetically coupled to the, or a respective, magnet of the drive device through the wall, or the respective wall, of the housing.

1 1.The apparatus of claim 10, wherein the arrangement is such that the magnet of the drive device, or the respective magnet of each drive device, is movable to thereby move the carriage with which it is magnetically coupled, and to thereby advance the spreader member across the print surface, as required for spreading a layer of powder material across the print surface. i 2.The apparatus of any one of claims 1 to 1 1 , wherein the powder material supply device is in the form of a hopper that, at or towards a top level, has an inlet, with the outlet member at or adjacent to a lower level, with the supply device fully contained within the housing, with a supply conduit or other suitable feed device providing communication between the inlet of the hopper and a supply source for powder material that is located outside the housing, to enable a flow of make-up powder material from the source to the hopper, as required, or with the supply device having an upper end portion that projects through an upper part of the housing such that the inlet is outside the housing for similarly receiving make-up powder material from the supply source; the hopper in each case being in the form of a container separable from the housing, or defined in part by a wall of the housing on which is mounted a fitting that, with the wall, forms a container comprising the hopper.

13.The apparatus of claim 12, wherein the outlet member is of elongate form and of a length that is the same, or substantially the same, as an elongate open top of a vessel comprising the powder material spreader member, the outlet member having an elongate valve member that is rotatable on a longitudinal axis between a first position in which it enables powder material to flow from the hopper into the vessel and a second position in which it prevents such flow.

14.The apparatus of claim 13, wherein valve member comprises an elongate rod of circular cross-section through which a plurality of longitudinally spaced transverse holes extend through the rod, such as in a common longitudinal plane, with the holes enabling the flow of powder material from the hopper when the rod is rotated to the first position.

15.The apparatus of claim 1 , wherein the housing has an upstanding peripheral wall defined by a first and a second, mutually perpendicular pairs of opposed walls, such as with the walls of each pair substantially parallel, a base on which the peripheral was stands, and a top cover, the walls of the first pair comprising sidewalls, with the walls of the second pair comprising a front wall and a rear wall; the powder material supply device comprises a hopper located within the container, adjacent to and along one sidewall, or a respective hopper located adjacent to and along each sidewall; the powder material spreader member is supported above but close to the print surface, with the extending between the front and rear walls and so that the spreader member is movable laterally in a direction extending between the sidewalls; the spreader member is supported at each of its ends by a respective mounting member and is laterally movable by a respective drive system acting on each mounting member; the respective drive system for each mounting member including a linear drive, such as a stepper motor, located externally of the housing and operable to engage indirectly with a respective mounting member and operable to move a magnet device that provides a magnetic coupling with a respective mounting member, by the coupling acting through a respective one of the front and rear walls such that as the drive system acts to move the magnet device, the magnetic coupling causes the mounting member to move in unison with the magnet device thereby to move the spreader member laterally across the print surface.

16.The apparatus of claim 15, wherein each mounting member is movable along a respective rail secured within the housing, adjacent to the respective one of the front and rear walls, with the drive system secured below the base defining the print surface, with a magnet of the magnet device supported on and movable along an upper surface of the base, such as on a rail fixed on the base outside the respective one of the front and rear walls; and wherein the drive system consists of a stepper motor mounted below the base, with the motor having an output shaft connected end- to-end to a threaded shaft mounted under the base and fixed against movement in the direction of its axis; the magnet device having a depending arm that extends below the base from the magnet with the arm having a threaded bore through which the shaft extends in threaded engagement; whereby with actuation of the stepper motor, the shaft is rotated on its axis, thereby causing the magnet and arm of the magnet device to progress along the shaft, in a direction determined by the direction of rotation of the threaded shaft.