Patent Description:
Additive manufacturing or rapid prototyping methods for producing components comprise layer-by-layer consolidation of a material, such as a powder material, using a focussed laser beam or an electron beam. In SLM or SLS, a powder layer is deposited in a build chamber and a focussed laser beam is scanned across portions of a powder layer that correspond to a cross-section of the component being constructed such that the powder at the points where the laser scans is consolidated either by sintering or fusion. After consolidation of a layer, a build surface is lowered by a thickness of the newly consolidated layer and a further layer of powder is spread over the surface and consolidated as required. Typically, the laser beam will enter into the chamber through a window in the chamber.

During SLM/SLS of material, in particular metals, a significant amount of condensate can be produced in the build chamber. This condensate should be removed from the build chamber to prevent undesirable effects, such as the condensate settling on and being integrated into the component being built and/or the condensate blocking the window through which the laser beam enters into the chamber. It is known to remove condensate from the build chamber by introducing a gas flow through the chamber in which the condensate is entrained, the condensate exiting the chamber along with the gas flow through an exhaust.

<CIT> discloses directing a protective gas stream to the melting point via a nozzle. The nozzle travels together with the laser beam.

<CIT> discloses providing an annular device having a plurality of suction apertures. Nozzles are provided to provide a gas flow to the interior of the annular device.

<CIT> discloses a first inlet and outlet apertures for providing a protective gas stream across a bottom of a process chamber and second inlet apertures adjacent a beam injection window to protect the beam injection window from being soiled by gaseous components rising from a zone interaction.

<CIT> discloses a ring nozzle arranged adjacent to the image-side surface of the lens facing a working plane. The ring nozzle having its outlet oriented relative to the image-side surface so that a discharged stream strokes tangentially along the image-side surface towards the centre. The gas flows radially towards the centre of the lens and therefrom in direction towards the working plane.

<CIT> discloses a device for providing gas flow across a coupling window through which a laser enters a processing chamber. A first gap supplies a first gas that substantially strokes tangentially over the surface of a coupling window. A second gap is provided in a wall section, which has a shape of a hollow cylinder section so that gas escaping from the second gap at first flows into the groove that is formed by the section and obtains a downward momentum towards the working plane. After passing an edge of the hollow cylinder section, the gas flows with a distance to the surface of the coupling window substantially in parallel alongside the surface. The device allegedly generates two substantially laminar flows across the window that marginally mix.

<CIT> discloses a lamination moulding device comprising a chamber <NUM> and a fume diffusion unit <NUM> attached to the top face of the chamber <NUM>. The fume diffusion unit <NUM> comprises: a housing 17a having an open end 17b which is as small as possible not to shut off laser beam L irradiated to the moulding area R; and an inert gas feed passage 17d filling the inside of the housing 17a with inert gas.

<CIT> discloses a method for protecting a gas curtain of a selective laser sintering window mirror, wherein protective gas is introduced through a gas pipeline to a work chamber of a selective laser sintering machine, the gas is heated around the work chamber in the pipeline, then enters a window mirror protective plate and is blown out from a gas outlet on the protective plate to form the protective gas curtain covering the window mirror.

It has been found that arrangements that generate gas flows parallel to a window can entrain condensate carrying gas into the flow bringing the condensate in close proximity to the window. Furthermore, it is desirable to provide a gas nozzle that provides an equal gas velocity across its width in order to achieve uniform gas flow through the build chamber.

According to a first aspect of the invention there is provided an additive manufacturing apparatus in accordance with claim <NUM>.

In this way, condensate produced by the consolidation process that is not captured by the gas knife is prevented from settling on the internal surface of the window by the jet of gas (the stream of gas formed directly from the pressurised gas forced out of an aperture in the upper gas nozzle). It has been found that directing a jet of gas from a location adjacent to the window away from the internal surface of the window reduces a quantity of condensate that settles on the window compared to directing the jet of gas parallel with the internal surface.

An upper gas flow nozzle may be oriented for generating a jet of gas in the build chamber directed towards the exhaust. For example, the jet of gas may be directed at an acute angle to the working plane. A further upper gas flow nozzle may be oriented for generating a jet of gas in the build chamber at a normal to the working plane. By directing the jet of gas downwards towards the exhaust and away from the internal surface of the window, condensate entrained in the jet is carried away from the internal surface to an extraction point rather than along a path that includes traversal of the internal surface of the window.

The or each upper gas nozzle comprises apertures for generating the jet of gas. The upper gas nozzle may comprise a passageway leading to the or each aperture, a tangent to a wall of the passageway at the aperture being angled relative to the internal surface of the optical window to generate the jet of gas in the required direction.

The or each upper gas nozzle may be located adjacent to the optical window.

The jet of gas may block a direct path of condensate from the working plane to the window.

The or each upper gas flow nozzle may comprise one or more apertures for generating a sheet-like jet of gas that extends across a width of the window. Preferably, the or each upper gas flow device comprises a plurality of outlet apertures extending across a width of the build chamber.

The or each upper gas nozzle may comprise a first member having at least one inlet aperture therein and a second member having three or more downstream apertures therein, the downstream apertures in fluid communication with the inlet aperture such that a shortest fluid path from the inlet aperture to each downstream aperture is substantially the same.

Also described is a flow device for an additive manufacturing apparatus, in which material is consolidated in a layer-by-layer manner to build a part, the flow device comprising a first member having at least one inlet aperture therein and a second member having three or more downstream apertures therein, the first and second members connected such that the downstream apertures of the second member are in fluid communication with the inlet aperture of the first member with a shortest fluid path from the inlet aperture to each downstream aperture being substantially the same.

The or each upper gas nozzle/flow device may comprise at least one intermediate member between the first member and the second member, the at least one intermediate member having a plurality of intermediate apertures therein, two or more of the intermediate apertures in fluid communication with the inlet aperture of the first member and each intermediate aperture in fluid communication with two or more of the downstream apertures of the second member.

The upper gas nozzle/flow device may comprise a plurality of intermediate members, two or of more of the intermediate apertures of each intermediate member in fluid communication with the same intermediate aperture of the intermediate member or the inlet aperture of the first member that immediately precedes that intermediate member in the upstream direction.

In one embodiment, the members of the upper gas flow nozzle/flow device comprises a series of concentric cylinders with the apertures spaced along a length of the concentric cylinders. The apertures of each cylinder may be offset about a central axis of the concentric cylinders by <NUM> degrees from the apertures of adjacent cylinders in the series.

In another embodiment, the members of the upper gas flow nozzle/flow device comprises a plurality of plates with a dividing member sandwiched between each pair of plates, the dividing member providing a passageway for the flow of gas between the apertures in each plate of the pair. The or each dividing member may comprise a plate having one or more slots therein for defining the one or more passageways. The or each slot may comprise a set of connected longitudinal arms, the arms being of equal length and extending in different directions with equal angles between each pair of adjacent arms (as would be the case for a complete set of radii of a regular polygon).

In one embodiment, each downstream aperture of the upper gas nozzle/flow device comprises an aperture in a roof of a build chamber of the additive manufacturing apparatus. In one embodiment, each member of the upper gas nozzle/flow device is fixed together to form a roof of the build chamber.

In another embodiment, the or each upper gas nozzle/flow device may comprise a gas flow device separate from the build chamber and located in the build chamber. In this way, the upper gas nozzle/flow device may be removable from the build chamber for cleaning/replacement and/or repositioning an aperture of the flow device in the build chamber. For example, in one embodiment, an outer member of the upper gas nozzle/flow device that defines the one or more apertures may be rotatable to change an orientation of the aperture, altering a direction of the jet of gas generated by the aperture.

The flow device may comprise a heating and/or cooling device for heating/cooling material of the first, second and/or intermediate members.

There is described an additive manufacturing apparatus, in which material is consolidated in a layer-by-layer manner to build a part, the additive manufacturing apparatus comprising a flow device as described above.

In this way, condensate produced by the consolidation process that is not captured by the gas knife is prevented from settling on the internal surface of the window by the gas stream. It has been found that directing a stream of gas from a location adjacent to the window away from the internal surface of the window reduces a quantity of condensate that settles on the window compared to directing the stream of gas parallel with the internal surface.

The upper gas flow nozzle is oriented for generating a stream of gas in the build chamber directed towards the exhaust. For example, the stream of gas may be directed at an acute angle to the working plane. A further upper gas flow nozzle may be oriented for generating a stream of gas in the build chamber at a normal to the working plane. By directing the stream of gas downwards towards the exhaust and away from the internal surface of the window, condensate entrained in the stream is carried away from the internal surface to an extraction point rather than along a path that includes traversal of the internal surface of the window.

The or each upper gas nozzle comprises apertures for generating the stream of gas. The upper gas nozzle may comprise a passageway leading to the or each aperture, a tangent to a wall of the passageway at the aperture being angled relative to the internal surface of the optical window to generate the stream of gas in the required direction.

By locating the gas flow nozzle on a side of the window opposite to that of the exhaust the stream of gas may block a direct path of condensate from the working plane to the window.

The or each upper gas flow nozzle may comprise one or more apertures for generating a sheet-like stream of gas that extends across a width of the window. Preferably, the or each upper gas flow device comprises a plurality of outlet apertures extending across a width of the build chamber.

Referring to <FIG> and <FIG>, an additive manufacturing apparatus according to an embodiment of the invention comprises a build chamber <NUM> having therein partitions <NUM>, <NUM> that define a build volume and a surface onto which powder can be deposited. A build platform <NUM> defines a working area in which an object <NUM> is built by selective laser melting powder <NUM>. The platform <NUM> can be lowered within the build volume <NUM> using a suitable mechanism <NUM> as successive layers of the object <NUM> are formed. A build volume available is defined by the extent to which the build platform <NUM> can be lowered. Layers of powder <NUM> are formed as the object <NUM> is built by dispensing apparatus <NUM> and a wiper <NUM>. For example, the dispensing apparatus <NUM> may be apparatus as described in <CIT>. A laser module <NUM> generates a laser for melting the powder <NUM>, the laser directed onto the powder bed <NUM> as required by optical module <NUM> under the control of a computer <NUM>. The laser enters the chamber <NUM> via a window <NUM>. The window may be a window having a flat internal surface 107a or a curved internal surface, for example in the case wherein the window comprises a lens, such as an f-theta lens.

A gas flow system for controlling condensate produced during the laser melting process comprises a first gas nozzle <NUM> comprising a plurality of gas outlets 112a and a gas exhaust <NUM> comprising a gas inlet 110a. The gas outlets 112a and gas inlet 110a are arranged for generating a horizontal gas flow (a gas knife) across a working surface of the powder bed <NUM> formed on the build platform <NUM>. The nozzle <NUM> and exhaust <NUM> produce a laminar flow having a flow direction from the nozzle <NUM> to the exhaust <NUM>, as indicated by arrows <NUM>. Gas is re-circulated from the exhaust <NUM> to the nozzle <NUM> through a gas recirculation loop (not shown). A pump maintains the desired gas pressure at gas inlet <NUM> and gas outlet <NUM>. A filter is provided in the recirculation loop to filter condensate that has become entrapped in the flow.

The gas flow system further comprises an upper gas nozzle <NUM> located in the top corner of the build chamber <NUM> adjacent the window <NUM>. Outlets 113d from the upper gas nozzle <NUM> are oriented to generate a gas flow through the build chamber <NUM> directed downwards away from an internal surface 107a of the window <NUM> towards the exhaust <NUM> (as indicated by arrow <NUM>). The gas flow is directed in a direction that is angled relative to the working surface 104a such that the gas flow traverses the space between the powder bed <NUM> and the window <NUM>. In this way, condensate that rises above the gas knife <NUM> is entrapped by the flow <NUM> and is carried to the exhaust <NUM>.

A further upper gas nozzle <NUM> is located in the opposite top corner of the build chamber <NUM> above the exhaust <NUM>. Outlets 114d from the further upper gas nozzle <NUM> are oriented to generate a gas flow directed vertically downwards away from an internal surface 107a of the window <NUM> towards the exhaust <NUM> (as indicated by arrow <NUM>). The gas flow <NUM> is directed along a wall of the build chamber <NUM> to the exhaust <NUM> limiting circulation of gas of the gas knife <NUM> and flow <NUM> that carries condensate to an upper region of the build chamber <NUM> adjacent the internal surface 107a of window <NUM>.

Referring to <FIG>, a flow device is shown used for the upper gas nozzles <NUM>, <NUM>. The flow device comprises a series of, in this embodiment four, concentric tubes 121a to 121d. Tubes 121b to 121d are closed at both ends and tube 121a is closed at one end with the other open end <NUM> providing an inlet into the flow device for gas. The tubes 121a to 121d comprise corresponding apertures 113a to 113d. <FIG> illustrates the relative angular orientation of apertures <NUM> of the tubes 121a to 121d. It will be understood that <FIG> should not be interpreted as showing that the apertures 113a to 113d are located at the same longitudinal location along the flow device but in fact, the locations of the apertures 113a to 113d along a length of the tubes <NUM> are offset, as shown in <FIG>.

Tube 121a comprises a single (inlet) aperture 113a located centrally along a length of the tube 113a. Tube 121b comprises two intermediate apertures 113b, one located a quarter of the way along tube 113b and the other located three-quarters of the way along the tube 113b. Tube 121c comprises four intermediate apertures 113c located one-eighth, three-eighths, five-eighths and seven-eighths of the way along the length of the tube 121c. Tube 121d comprises eight outlet apertures located one-sixteenth, three-sixteenths, five-sixteenths, seven-sixteenths, nine-sixteenth, eleven-sixteenths, thirteen-sixteenths and fifteen-sixteenths of the way along the length of the tube 121d. It will be understood that in other embodiments, further concentric tubes can be provided with apertures spaced following the pattern of apertures described above. Furthermore, the first tube 121a may be open at both ends to provide two inlets and comprise two equally spaced apertures with a corresponding increase in the number of apertures in the following outer tubes 121b to 121d.

The apertures 113a to 113d in consecutive tubes 121a to 121d are angularly offset by <NUM> degrees. However, in another embodiment, the apertures 113a to 113d are all oriented in the same direction (with no angular offset).

The labyrinth design of the apertures 113a to 113d, wherein the path length for gas from the aperture 113a to apertures 113d is substantially the same for each aperture 113d, ensures that the gas velocity generated at each aperture 113d is substantially equal. In this way, gas can be introduced into the upper gas nozzles <NUM>, <NUM> from a side of the chamber <NUM> (as shown in <FIG>) whilst still ensuring uniform gas stream <NUM> across a width of the build chamber <NUM>.

The flow device <NUM>, <NUM> or an outermost tube 113d of the flow device <NUM>, <NUM> may be rotatable (manually or under the control of a motor) to adjust a direction of the gas flow from the flow device. In this way, the user can adjust the direction of the gas flow as desired.

<FIG> shows a further flow device in accordance with the invention that may be used as a roof or wall of the build chamber <NUM>. In this embodiment, rather than the aperture defining members being concentric tubes, the flow device comprises a series of parallel plates 221a to 221d having apertures 213a to 213d therein and a series of dividing plates 222a to 222c having slots 224a at 224c therein. The dividing plates 222a to 222c are sandwiched between plates 221a to <NUM> such that the slots 224a to 224c form passageways connecting the apertures 213a to 213d in adjacent plates 221a to 221d. The slots 224a to 224c are X-shaped such that one aperture 113a to 113c in an upstream plate 221a to 221c is fluidically connected to four apertures 113b to 113d in a downstream plate 221b to 221d. In this embodiment, the first plate 221a comprises a single inlet aperture 213a, the second plate 221b four equally spaced intermediate apertures 213b, the third plate 221c sixteen equally spaced intermediate apertures 213c and the fourth, final plate 221d sixty-four equally spaced outlet apertures 213d. As with the first embodiment of the flow device described with reference to <FIG>, the labyrinth design of the apertures 213a to 213d, wherein the path length for gas from the aperture 213a to apertures 213d is substantially the same for each aperture 213d, ensures that the gas velocity generated at each apertures 213d is substantially equal with a minimal pressure drop. In this way, gas can be introduced at a central location into the inlet aperture 213a whilst still ensuring uniform flow across a <NUM>-dimensional area of the build chamber <NUM>.

Suitable adjustments may be made for elements, such as the optical window <NUM>, that may be situated in the roof or wall of the build chamber <NUM>. Furthermore, it may be desirable for only some apertures 113d of the flow device to provide an equal flow velocity. This may be achieved through the appropriate design of slots and apertures in the plates.

Computer <NUM> comprises a processor unit <NUM>, memory <NUM>, display <NUM>, user input device <NUM>, such as a keyboard, touch screen, etc, a data connection to modules of the laser melting apparatus, such as optical module <NUM>, laser module <NUM> and motors (not shown) that drive movement of the dispensing apparatus <NUM>, wiper <NUM> and build platform <NUM> (and flow device if movable). An external data connection <NUM> provides for the uploading of scanning instructions to the computer <NUM>. The laser unit <NUM>, optical unit <NUM>, movement of build platform <NUM> and flow device are controlled by the computer <NUM> based upon the scanning instructions.

It will be understood that modifications and alteration scan be made to the above described embodiments without departing from the scope of the invention as defined in the claims.

Claim 1:
An additive manufacturing apparatus, in which material is consolidated in a layer-by-layer manner to build a part, the additive manufacturing apparatus comprising a build chamber (<NUM>) having a window (<NUM>) in a roof of the build chamber (<NUM>), a radiation source (<NUM>) for generating an energy beam deliverable through the window (<NUM>) for consolidating material in a working plane (104a), wherein a lower gas nozzle (<NUM>) and an exhaust (<NUM>) are arranged for generating a gas knife (<NUM>) across the working plane, and an upper gas flow device (<NUM>, <NUM>) comprising a plurality of apertures oriented such that a stream of gas expelled therefrom is directed downwards away from an internal surface of the window (<NUM>), characterised in that the plurality of apertures is in the roof of the build chamber (<NUM>) and wherein a normal to each aperture extends in a direction downwards towards the exhaust (<NUM>) and away from an internal surface of the window (<NUM>).