An Apparatus and Method for Additive Manufacturing

Technical Field of the Disclosure

The present disclosure relates to a method and apparatus for additive manufacturing, particularly but not exclusively, to a method and apparatus for the localised preparation of an additive manufacturing powder bed and environmental chamber.

Background of the Disclosure

Known commercial powder based additive manufacturing (AM) systems for metals or polymers utilise a layer-wise powder handling strategy that apply a powder feed system (a hopper and delivery mechanism) in conjunction with a levelling device such as wiper blade or roller to establish the required powder layer height before laser or inkjet methods are employed to consolidate the powder layer into a solid object. Furthermore, current systems employ build-pistons which are lowered for each layer onto which the object is built. Therefore, objects that are constructed of 1000s of layers must establish each powder layer with the above approach. This layer-step is non-productive and can amount to around 20% of the processing duration for a particular build since the process is split into two stages: 1) powder layering and 2) powder consolidation (usually achieved through laser melting or ink jetting of binder inks).

Summary of the Disclosure

A method and apparatus is described that locally prepares a level bed of powder for use in multi-layer additive manufacturing systems. The apparatus can be positioned in three dimensions with translation in either directional or omnidirectional mode with powder being preplaced or added locally to the site of powder consolidation.

The proposed technology seeks to simplify additive manufacturing machine architectures and improve process scalability in powder based Additive Manufacturing (AM) technologies. This is achieved by simplifying the process of powder handling when applied to layer-wise building of powder-based metal or polymer AM technologies. The proposed disclosure describes a powder handling and processing solution that integrates both powder layer control and powder consolidation into a single process operation.

Existing additive manufacturing systems have the following disadvantages:

• An unproductive phase of powder layering and levelling which limits build rates.

• Complicated machine structure which cannot easily be scaled to build 3D parts with volumes of several cubic metres.

• Limited control of the local atmosphere within the powder consolidation zone as only the entire atmosphere within the build chamber can be controlled.

• Limited control of process fumes.

• Limited control of the local temperature of the powder consolidation zone.

• Large volumes of unprocessed powder within the additive manufacturing machine.

The method and apparatus disclosed has the following advantages over state-of-the- art:

• Removing the unproductive phase of powder based AM systems, and thereby increasing the build rates accordingly.

• Greatly simplifying the machine structure which allows the AM machine to be easily scaled to build volumes of several cubic metres.

• Effective control of the local atmosphere within the processing chamber.

• Effective control of fumes generated within the processing chamber.

• Effective control of the local temperature of the processing chamber.

• Minimisation of unprocessed powder volume within the additive manufacturing machine.

• The ability to scale the concept to build volumes of many cubic metres

• Application to a wide range of powder materials including polymers and metals.

• Application to a wide range of consolidation techniques such as scanning laser beams, diode laser arrays, electron beams and inkjet-based systems. According to a first aspect of the present disclosure there is provided an apparatus for an additive manufacturing process, the apparatus comprising: a scanner, wherein the scanner comprises an open ended processing chamber and an optical device for forming a layer of a three dimensional (3D) part; and a controller configured to move the scanner over a target area. The open ended processing chamber may be a chamber with one face removed or missing, for example a cube with 5 faces. In use, the side of the cube without a solid face can be in contact with the powder bed such that a volume is formed between the open ended processing chamber and the powder bed underneath. The optical device allows consolidation of the powder directly underneath the processing chamber.

Advantageously, as the open ended processing chamber moves across the surface of the powder bed, it pushes the powder and levels the powder out. This removes the need for a separate powder levelling system. The movement of the open ended processing chamber levels out the powder within the processing chamber. In conventional techniques, the size of the part is limited by the size of levelled powder bed that can be achieved. The present disclosure allows for large scale manufacture as there is no limit imposed by the size of the powder bed.

The apparatus may further comprise a structure for supporting a powder bed for producing the 3D part. The structure for supporting a powder bed may be a build chamber.

The apparatus may further comprise a structure for providing a target area of the powder bed.

The processing chamber may comprise at least one sidewall. The at least one sidewall may be inclined with respect to a plane formed between the lower edges of the at least one sidewall. In other words, the at least one sidewall may be inclined with respect to the surface of the levelled powder bed formed. This external geometry of the processing chamber reduces powder drag on the processing chamber as the processing chamber moves over the powder. At least one end of at least one sidewall may have a tapered shape. The lower ends of the sidewalls, closest to the powder bed may have a pointed end. This creates a rake angle, f, between the surface of the powder bed and the edge of the processing chamber side walls.

At least one sidewall may be shorter than at least one other sidewall. The at least one shorter sidewall may extend from the top of the processing chamber down to a predetermined distance above a powder bed, or a predetermined distance from a top surface of the processing chamber. The predetermined distance above the powder bed may be greater than or equal to twice a diameter of a powder particle within a powder bed. This leaves a clearance of twice the particle diameter, preventing build-up of powder within the processing chamber. Alternatively, the processing chamber may be tilted to leave a clearance of at least twice the particle diameter.

At least one sidewall may comprise an upper sidewall portion and a lower sidewall portion. In use, the lower sidewall portion may be coupled with the powder bed, and the lower sidewall portion may be configured to be movable between a first configuration and a second configuration. The lower sidewall may be moveable by a hinge, or the sidewall may be flexible to allow movement.

In the first configuration the lower sidewall portion may extend substantially parallel to the upper sidewall portion. In the first configuration the lower sidewall extends in the same direction as the upper sidewall. In the second configuration the lower sidewall portion may be inclined such that the lower sidewall portion extends away from the processing chamber. This allows the lower portion to be deflected outwards from the processing chamber but does not allow the lower portion to be deflected inwards. The outwards deflection prevents a build-up of powder inside the processing chamber, whereas the sidewall still impacts a force in order to level the powder bed.

The processing chamber may have a frustoconical or frustopyramidal shape. The processing chamber may be wider at an end configured to be closer to the powder bed. This reduces powder drag on the processing chamber as the processing chamber moves over the powder. The apparatus may further comprise means configured to control an atmospheric composition within the processing chamber. The means for controlling the atmospheric composition may comprise means for injecting a gas into the processing chamber. The injection of inert gases such as argon, nitrogen, or reactive gases such as oxygen, allows control of the consolidation of the 3D part within the processing chamber.

The apparatus may further comprise means for controlling a pressure within the processing chamber. The pressure of inert or reactive gases within the processing chamber may be controlled such that a positive pressure exists between the pressure within the processing chamber and the build chamber. This reduces disruption to the levelled powder bed caused by processing fumes.

The apparatus may further comprise means for controlling a temperature within the processing chamber. The means for controlling a temperature may comprise any of infrared heaters, laser beams, light emitting diodes, or inductive heating. This allows control of the temperature of the powder layer within the processing chamber to a temperature below the melting point of the powder through the use of radiant energy such as for example infrared heaters, laser beams, light emitting diodes, or inductive heating. The temperature may be close to the melting point to allow the powder to be melted efficiently using the laser. This reduces the power of laser required.

The apparatus may further comprise means for dispensing a powder outside of the processing chamber. The means for dispensing a powder may comprises any of through Archimedes feeders, vibration feeders, volumetric dose feeders, or other powder feeders. The means for dispensing a powder may be open loop or controlled by a height sensor. In an open loop system, excess powder may be drawn from behind the direction of travel of the processing chamber and dispensed in front of the direction of travel of the processing chamber.

The means for dispensing a powder may be configured to dispense a powder around an outside perimeter of the processing chamber. The means for dispensing a powder may comprise a plurality of powder feeders located around an outside perimeter of the processing chamber. The powder dispensed may be a volumetric dose preplaced around the chamber or may be powder dispensed in all directions around the chamber. Alternatively, the means for dispensing a powder may be configured to dispense powder in front of the direction of travel of the processing chamber. This reduces the amount of powder required and reduces the build of powder in the build chamber.

The apparatus may comprise three or more powder feeders located around an outside perimeter of the processing chamber. Each of the powder feeders may be substantially equidistant from each of the other powder feeders. The powder feeders may be, for example, vibration feeders or Archimedes thread feeders.

The apparatus may further comprise at least one powder height sensor configured to measure a height of a powder bed. The height of the powder bed may be measured in comparison to a sidewall of the processing chamber. The height sensors allow control of the powder flow rate and/or powder bed height.

The apparatus may further comprise a plurality of fins formed on an outside surface of the processing chamber. The fins may be placed around the outside of the perimeter of the processing chamber, allowing delivery of a more directional drag of powder across the powder bed, reducing the amount of powder that is pushed around the side, hence reducing the amount of powder that is required to be dispensed.

The apparatus may further comprise means configured to remove one or more waste gases from the processing chamber.

The apparatus may further comprise means for producing a transverse gas flow within the processing chamber. This allows a positive pressure to be generated between the pressure within the processing chamber and the build chamber. This reduces disturbance to the powder bed caused by the process fumes. The pressure of the gas at the base of the processing chamber may be controlled to have a pressure only slightly above that of the external atmosphere, in order to maintain the composition of the atmosphere within the processing chamber whilst at the same time preventing powder from blowing out of the processing chamber. In addition, fumes from the consolidation process can be managed for the protection of the laser optics or inkjet heads. The means for producing a transverse gas flow may be configured to produce a first gas flow in a first portion of the processing chamber and a second gas flow in a second portion of the processing chamber. In use, the second portion may comprise a portion of the processing chamber in contact with a powder bed and the first portion may comprise a portion of the processing chamber above the second portion, and wherein the first gas flow has a substantially larger velocity than the second gas flow. This removes process fumes from the surface of the powder bed and forces them up into the processing chamber.

The apparatus may further comprise means configured to produce a gas flow through the processing chamber. The internal structure of the processing chamber may be configured such that atmosphere and fume control can be managed through the creation of a gas vortex. A laminated construction may be used to control the speed of gas flow in different layers within the internal structure, with gas flow being parallel to optical surface at the top of the processing chamber. A narrow throat section ensures low volume flow, with a larger diameter section for low speed flow near the powder layer.

The means configured to produce a gas flow through the processing chamber may comprise one or more apertures through a surface of the processing chamber. This allows process fumes to exit the processing chamber.

The apparatus may further comprise means configured to extract excess powder from the processing chamber. Powder not extracted from the processing chamber may interfere with production of a 3D part as it would reduce how level the powder bed is.

The processing chamber may be fitted with flexible baffles to prevent a build of powder inside the trailing edge of the processing chamber. The processing chamber may be configured such that it allows a build-up of powder at the rear of the processing chamber to be ejected through means of movement or gas flow. The aperture formed by the flexible baffles may be shaped to guide powder from the processing chamber. Alternatively, the means configured to extract excess powder from the processing chamber may comprise a powder flow path formed along an internal surface of the processing chamber. The powder flow path directs powder away from the processing chamber. The excess powder may be extracted (for example by vacuum) from the processing chamber.

The apparatus may further comprise one or more deflectors configured to direct a flow of powder.

According to a further aspect of the present disclosure, we also provide a method for additive manufacturing of a three dimensional (3D) part, the method comprising: positioning a scanner, wherein the scanner comprises: an open ended processing chamber; and an optical device for forming a layer of the 3D part.

The method may further comprise: translating the processing chamber across a powder bed such that powder is displaced by the processing chamber; and consolidating powder within the processing chamber to form a layer of the 3D part.

Positioning the scanner may comprise positioning the processing chamber such that a lower edge of the open ended processing chamber is at a predetermined height.

The method may further comprise introducing a powder outside of the processing chamber such that a top surface of the powder is higher than a lower edge of the processing chamber. This allows powder to be moved and levelled by the processing chamber

The step of introducing a powder outside the processing chamber may comprise dispensing a powder around an outside perimeter of the processing chamber.

Alternatively, the step of introducing a powder outside the processing chamber may comprise dispensing a powder in front of the processing chamber. The front of the processing chamber may be the side of the processing chamber in front of the direction of travel of the processing chamber. This means that powder placed in front of the processing chamber may then be levelled out by movement of the processing chamber. The back of the processing chamber may be behind the direction of travel of the processing chamber where the processing chamber has levelled the powder bed.

The step of translating the processing chamber across the powder bed may comprise levelling a volume of the powder bed. This removes the production step of producing a large, levelled bed of powder. The powder within the processing chamber is continuously levelled by the movement of the processing chamber.

The method may further comprise injecting a gas into the processing chamber.

The method may further comprise controlling the pressure of the gas within the processing chamber.

The method may further comprise controlling the temperature of the gas within the processing chamber.

The method may further comprise redistributing powder from a back side of the processing chamber to a front side of the processing chamber.

The method may further comprise measuring a value of a height of the top surface of a powder bed.

The method may further comprise comparing the measured value of height with a predetermined value; and dispensing a powder in response.

The method may further comprise generating a transverse gas flow within the processing chamber. The transverse gas flow may have high speeds at the top of the processing chamber (near the optics) and low speeds at the bottom of the processing chamber, adjacent to the surface of the powder bed. This allows control of the pressure of the gas at the base of the processing chamber to have a pressure only slightly above that of the external atmosphere, in order to maintain the composition of the atmosphere within the processing chamber whilst at the same time preventing powder from blowing out of the processing chamber. In addition, fumes from the consolidation process are managed for the protection of the laser optics or inkjet heads within the processing chamber.

The method may further comprise removing process fumes from the processing chamber.

The method may further comprise generating a gas flux within the processing chamber.

The method may further comprise removing excess powder within the processing chamber.

Removing excess powder may comprise directing excess powder through a powder flow path.

Brief Description of the Preferred Embodiments

Some preferred embodiments of the invention will now be described by way of an example only and with reference to the accompanying drawings, in which:

Figure 1 illustrates a schematic view of the additive manufacturing apparatus according to the present disclosure;

Figure 2 illustrates a schematic view of the additive manufacturing apparatus according to a further embodiment of the disclosure;

Figure 3 shows a schematic view of the steps of the powder layering and part consolidation process;

Figure 3(a) shows a first step in the process in which the processing chamber is positioned in order to define the layer thickness of the powder layer to be consolidated;

Figure 3(b) shows a second step in the process in which a volume of powder is introduced to the build chamber; Figure 3(c) shows a third step in the process in which the processing chamber is translated across the build plate;

Figure 4 shows a fourth step in the process in which the powder layer is consolidated to form a layer of a 3D part.

Figure 5 illustrates a schematic view of the additive manufacturing system according to a further embodiment in which the processing chamber has angled side walls;

Figure 6 illustrates a schematic view of the additive manufacturing system according to a further embodiment in which the walls of the processing chamber have a tapered lower edge;

Figure 7 illustrates a schematic view of the additive manufacturing system according to a further embodiment in which the powder is dispensed either in front of, or around, the processing chamber;

Figure 8 shows a top-view of the processing chamber according to one embodiment of the disclosure in which projections, such as fins, are located around the perimeter of the processing chamber;

Figure 9 illustrates a schematic view of the additive manufacturing system according to a further embodiment in which a transverse gas flow is generated within the processing chamber;

Figure 10 illustrates a schematic view of the additive manufacturing system according to a further embodiment in which a gas vortex is generated within the processing chamber;

Figure 11 illustrates a schematic view of the additive manufacturing system according to a further embodiment in which the processing chamber has a system for removing excess powder; Figure 12 illustrates a schematic view of the additive manufacturing system according to a further embodiment in which there is a clearance between the lower edge of a back sidewall of the processing chamber and the powder bed;

Figure 13 illustrates a schematic view of the additive manufacturing system according to a further embodiment in which the sidewalls of the processing chamber are hinged or flexible;

Figure 14 illustrates a schematic view of the additive manufacturing system according to a further embodiment in which powder at the trailing edge of the processing chamber is ejected from the processing chamber;

Figure 15 shows a top-view of the processing chamber according to one embodiment of the disclosure in which powder sensors and powder dispensers are located around the processing chamber; and

Figure 16 illustrates a schematic view of the additive manufacturing system according to a further embodiment in which a deflector is used to improve distribution of powder outside the processing chamber.

Detailed Description of the Preferred Embodiments

Reference Numerals

100 - Additive manufacturing apparatus

105 - build chamber

110 - processing chamber

115 - Cartesian robot

120 - build plate

125 - volume of powder

130 - body of levelled powder

135 - consolidation means

140 - height sensor

145 - fins

150 - optic

155 - narrowing internal structure 160 - laminated internal structure

165 - powder extraction system

170 - hinge

175 - deflectable lower sidewall portion

180 - aperture or gap

185 - hinged flap

190 - powder feeder or dispenser

195 - front side wall

200 - back side wall

205 - apertures

210 - powder deflector

Figure 1 illustrates a schematic view of the additive manufacturing apparatus according to the present disclosure. In this embodiment, the apparatus 100 comprises a powder bed (not shown) and a processing chamber 110. The open-ended processing chamber 110 is mounted onto a multi-axis (x, y, z, Q) Cartesian robot within the additive manufacturing system 100. The processing chamber 110 is configured to move across the powder bed in the x and y dimensions of Cartesian space. The processing chamber 110 is also configured to move vertically in the z dimension over the powder bed, in other words in a direction substantially perpendicular to a top surface of the powder bed. The processing chamber 110 may also rotate about an angle, Q. The processing chamber 110 and the powder bed are located within a build chamber 105. A build plate (not shown) on which the additively manufactured part will be constructed is positioned within the build chamber 105 of the manufacturing system 100.

Figure 2 illustrates a schematic view of the additive manufacturing apparatus according to a further embodiment of the disclosure. Many of the features of figure 2 are the same as those shown in figure 1 and therefore carry the same reference numerals. In this embodiment the processing chamber 110 extends in the x direction of Cartesian space. The processing chamber 110 in this embodiment is configured to move in the y and z dimensions of Cartesian space.

Figure 3 shows a schematic view of the steps of the powder layering and part consolidation process. Figure 3(a) shows a first step in the process. Step-1 of the process sequence begins with the lower edge of the processing chamber 110 being moved to a set-point above the build plate 120 such that the distance between the lower edge of the processing chamber 110 and the top of the build plate 120 (or previously built layer) defines the layer thickness of the powder layer to be consolidated.

Figure 3(b) shows a second step in the process. Step-2 of the process introduces a volume of powder 125 to the build chamber 105 such that the surface of the build plate 120 is submerged in powder 125 and provides a powder surface level such that this level exceeds the height of the lower level of the processing chamber 110. Powder can also be dispensed at the leading edge of the processing chamber 110.

Figure 3(c) shows a third step in the process. Step-3 of the process is to translate the processing chamber 110 in single or omni-directional paths across the build plate 120 such that powder 125 is displaced by its motion leaving a body of levelled powder 130 within the body of the processing chamber 110 and/or behind the processing chamber 110 depending on the volume of powder with the system.

Figure 4 shows a fourth step in the process. Step-4 of the process is to consolidate the powder layer 130 created within the processing chamber 110 whilst it is in continuous motion or in step-wise motion through some consolidation means 135 such as melting by scanning a laser beam, melting through a diode laser array, consolidation through liquid binder deposition, or some other means. It will be appreciated that the processing chamber 110 in this embodiment, among others, is configured to move in a vertical and a horizontal direction. It will be appreciated that the processing chamber may also be configured to move in a third direction.

Step 1 to step 4 are repeated until the multi-layer object is consolidated to form the finished object.

Figure 5 illustrates a schematic view of the additive manufacturing system according to a further embodiment in which the processing chamber 110 has angled side walls 195, 200. Many features of Figure 5 are the same as those shown in Figure 1 and therefore carry the same reference numerals. The external walls 195, 200 of the processing chamber 110 are inclined with respect to the levelled powder bed 130 and build plate 120 underneath. This reduces the drag force imparted on the processing chamber 110 by the volume of powder 125.

Figure 6 illustrates a schematic view of the additive manufacturing system according to a further embodiment in which the walls 195, 200 of the processing chamber 110 have a tapered lower edge. Many features of Figure 6 are the same as those shown in Figure 1 and therefore carry the same reference numerals. The side walls 195, 200 of the processing chamber 110 are tapered at the bottom such that there is a rake angle f between the levelled surface of the powder bed 130 and the lower edge of the processing chamber side walls 195, 200.

Figure 7 illustrates a schematic view of the additive manufacturing system according to a further embodiment in which the powder is dispensed either in front of, or around, the processing chamber 110. Many features of Figure 7 are the same as those shown in Figure 1 and therefore carry the same reference numerals. A volumetric dose of powder can be placed around the processing chamber 110. This can be done, for example, using Archimedes feeders, vibration feeders or volumetric dose feeders. Alternatively, as shown in Figure 7, the powder is dispensed in front of the direction of travel of the processing chamber 110.

The powder dispensation may be open-loop. This means that excess powder is collected from a first direction (e.g. behind the direction of travel of the processing chamber 110) and redistributed in a second opposing direction (e.g. in front of the direction of travel of the processing chamber 110). There is a height sensor 140 located on either the processing chamber 110 or the build chamber 105. This is configured to measure the height of the powder bed 125 in front of the direction of travel of the processing chamber 110. The volume of powder dispensed into the build chamber 105 can then be controlled to regulate the height of the powder bed 125.

Figure 8 shows a top-view of the processing chamber 110 according to one embodiment of the disclosure in which projections 145, such as fins, are located around the perimeter of the processing chamber 110. The fins 145 allow delivery of a more directional drag of powder across the powder bed, therefore reducing the amount of powder that is pushed around the side of the processing chamber 110. This reduces the amount of powder that is required to be dispensed in the build chamber 105.

Figure 9 illustrates a schematic view of the additive manufacturing system according to a further embodiment in which a transverse gas flow is generated within the processing chamber 110. Many features of Figure 9 are the same as those shown in Figure 1 and therefore carry the same reference numerals. The processing chamber 110 has an internal structure 155 such that the processing chamber 110 is tapered to be wider at the top and bottom of the processing chamber 110 and has a narrow throat section. This structure allows the formation of a transverse gas flow operating at high speeds near to the optic/inkjet head 150, and low speeds near the levelled powder layer 130. The pressure of the gas at the base of the processing chamber 110 is controlled to have a pressure only slightly above that of the external atmosphere within the build chamber 105. This maintains the composition of the atmosphere within the processing chamber 110, whilst at the same time preventing powder from dissipating out of the processing chamber 110. Process fumes from the consolidation process are drawn (sucked) up from the levelled powder bed 130 into the body of the processing chamber 110.

Figure 10 illustrates a schematic view of the additive manufacturing system according to a further embodiment in which the system is configured such that a gas vortex is generated within the processing chamber 110. Many features of Figure 10 are the same as those shown in Figure 1 and therefore carry the same reference numerals. The processing chamber 110 has an internal structure 160 such that atmosphere and fume control can be managed through the creation of a gas vortex within the processing chamber 110. The gas vortex forces process fumes from the powder bed 130 upwards into the processing chamber 110. In this case, a laminated construction of a layered structure 160 is used to control the speed of gas within each layer, with gas flow being substantially parallel to an optical surface 150 at the top of the processing chamber 110. The internal structure 160 of the processing chamber 110 has a narrow throat section which ensures low volume flow, with a larger diameter section for low speed flow near the powder layer 130. The processing chamber 110 has apertures or fluid flow paths 205 towards the top of the processing chamber 110 for removal of process fumes.

Figure 11 illustrates a schematic view of the additive manufacturing system according to a further embodiment in which the processing chamber 110 has a system for removing excess powder. Many features of Figure 11 are the same as those shown in Figure 1 and therefore carry the same reference numerals. The lower edge of the inside leading sidewall 195, trailing sidewall 200, or both sidewalls 195, 200 of the processing chamber 110 have a system 165 whereby excess powder can be extracted (for example by vacuum) from the processing chamber 110 and build chamber 105 and fed to a powder storage hopper (not shown). In Figure 11 the system 165 for removing excess powder includes a lip or ridge 165 on the lower edge of each sidewall 195, 200. Each ridge 165 forms a powder flow path to direct the excess powder away from the processing chamber 110.

Figure 12 illustrates a schematic view of the additive manufacturing system according to a further embodiment in which there is a clearance between the lower edge of a back sidewall 200 of the processing chamber 110 and the powder bed 130. Many features of Figure 12 are the same as those shown in Figure 1 and therefore carry the same reference numerals. The processing chamber 110 can be tilted or designed such that the lower edge of the trailing (or back) sidewall 200 leaves a clearance of at least twice the particle diameter (2 x 0) in order to prevent build-up of powder within the processing chamber 110. This can be achieved by tilting the processing chamber 110 or designing the processing chamber 110 such that a back sidewall 200 is shorter than a front sidewall 195.

Figure 13 illustrates a schematic view of the additive manufacturing system according to a further embodiment in which the sidewalls 195, 200 of the processing chamber 110 are hinged. Many features of Figure 13 are the same as those shown in Figure 1 and therefore carry the same reference numerals. The sidewalls 195, 200 of the processing chamber 110 are hinged or flexible such that are deflected or movable upon contact with powder. The flexibility of the sidewalls 195, 200 or hinges 170 allows a lower portion 175 of the sidewalls to be deflected outwards (away from the processing chamber 110), but not allow deflection inwards (towards the center of the processing chamber 110). The outwards deflection of the back sidewall 200 prevents a build of powder inside the trailing edge of the processing chamber 110. The front sidewall 195 of the processing chamber 110 is not deflected by the force of powder 125 on the processing chamber 110, and still can be used to level the powder bed.

Figure 14 illustrates a schematic view of the additive manufacturing system according to a further embodiment in which powder at the trailing edge of the processing chamber 110 is ejected from the processing chamber 110. Many features of Figure 14 are the same as those shown in Figure 1 and therefore carry the same reference numerals. The processing chamber 110 has an aperture 180 in the back sidewall 200 to allow a build-up of powder at the rear of the processing chamber 110 to be ejected through means of movement or gas flow. The aperture 180 may be shaped to guide powder from the processing chamber 110. Alternatively, the sidewalls 195, 200 may have hinged flaps 185 or flexible lower portions that can be deflected outwards (away from the processing chamber 110), but not allow deflection inwards (towards the center of the processing chamber 110). The flaps 185 are hinged from the lower edge of the sidewalls 195, 200 so that in a deflected position a gap 180 is formed in the back sidewall 200.

Figure 15 shows a top-view of the processing chamber 110 according to one embodiment of the disclosure in which powder sensors 140 and powder dispensers 190 are located around the processing chamber 110. Powder feeders 190 are located around an outside perimeter of the processing chamber 110. In this embodiment, three dispensers 190 are located substantially equidistant around the processing chamber 110. This allows omni-directional operation of the system. The dispensers 190 can be, for example, vibration or Archimedes thread dispensers 190. Powder height sensors 140 are also located around the perimeter of the processing chamber 110 to control dispensing flow rate and powder bed height. The sensors 140 can be, for example, point source sensors or line sensors. It will be appreciated that three dispensers 190 and sensors 140 are shown in this embodiment, however more or less dispensers and sensors can also be used.

Figure 16 illustrates a schematic view of the additive manufacturing system according to a further embodiment in which a deflector 210 is used to improve distribution of powder outside the processing chamber. A powder spreading system including a powder feeder 110 and a powder deflector 210 are located outside of the processing chamber. The powder spreading system employs deflectors 210 to direct the powder flow and provide a more evenly distributed mass of powder. While one powder feeder is shown in this figure, a number of powder dispensing ports could be distributed around the outside of the processing chamber to dispense powder at the correct location with respect to the levelling direction.

Although the invention has been described in terms of preferred embodiments as set forth above, it should be understood that these embodiments are illustrative only and that the claims are not limited to those embodiments. Those skilled in the art will be able to make modifications and alternatives in view of the disclosure which are contemplated as falling within the scope of the appended claims. Each feature disclosed or illustrated in the present specification may be incorporated in the invention, whether alone or in any appropriate combination with any other feature disclosed or illustrated herein.