GB2532518A

GB2532518A - Manufacturing method and manufacturing apparatus

Info

Publication number: GB2532518A
Application number: GB1420886.2A
Authority: GB
Inventors: Kimblad Hans
Original assignee: Digital Metal AB
Current assignee: Digital Metal AB
Priority date: 2014-11-24
Filing date: 2014-11-24
Publication date: 2016-05-25
Also published as: WO2016083234A1; TW201622963A; GB201420886D0

Abstract

An additive manufacturing apparatus comprises a build region 12; a construction material deposition unit 15b arranged for relative reciprocating movement in at least a first direction x across the build region for depositing a construction material (preferably powder) incrementally in layers from a construction material deposition position; first 15c and second 15a binding units arranged for relative reciprocating movement in at least the first direction across the build region for binding construction material selectively at positions on the layers of construction material from first and second binding positions respectively; wherein the first binding position, construction material deposition position and second binding position are arranged in order in the first direction. An alternate embodiment comprises a first construction material deposition unit, a binding unit and second construction material deposition unit arranged in order in the first direction. The units may be provided on a common carriage 15 or separate carriages. Preferably, a smoothing element is arranged between each deposition and binding position. The apparatus and method allow for material to be deposited and printed in the forward and reverse, or negative, pass of the units increasing the speed of object production.

Description

MANUFACTURING METHOD AND MANUFACTURING APPARATUS

Technical Field

The present disclosure relates to methods of manufacturing an object, and particularly to methods of manufacturing object in which the object is constructed from a series of layers of construction material, regions of each of which are selectively bound together during or after the deposition of the layer, and before the deposition of a successive layer. The present disclosure also relates to manufacturing apparatus suitable for implementing such methods.

Background

Three-dimensional printing is a class of additive manufacturing technologies in which sequential layers of material are deposited into a build region, portions of each layer being joined together so that a desired object is constructed by the joined portLons of the sequential layers.

One three-dimensional printing technique employs a process in which sequential layers of a granular material, such as a powder, are deposited into a build region from a print head which passes over and across the build region.

After or during deposition of the layer, portions of the build material are selectively bound together. For example, a liquid binder may be jetted from the print head onto the powder using a technique similar to ink-jet printing. Such a binder may be an adhesive which solidifies or cures, thereby to bind the granules of the granular material together, over time, for example by contact with the air in the case of an air-drying adhesive, or after curing, for example using ultraviolet light in the case of a UV-curable adhesive. Alternatively, radiation may be selectively applied to portions of each layer to locally bind regions of the layer together, for example by the application of a suitably high-intensity laser beam or focussed infrared radiation.

The deposited layers of powder are made sufficiently thin such that, when successive layers of powder are deposited having selective regions bound together, the bound parts of each layer extend through the layer to the boundary with an underlying layer so as to form a contiguous three-dimensional structure extending through the layers.

For 3D printing to be competitive with other manufacturing processes, 3D printing must be able to manufacture a desired object rapidly.

summary

According to a first aspect of the present disclosure there is provided an additive manufacturing apparatus. The apparatus comprises a build region. The apparatus comprises a construction material deposition unit arranged for relative reciprocating movement in at least a first direction across the build region for depositing a construction material incrementally in layers on the build region from a construction material deposition position on the construction material deposition unit. The apparatus comprises a first binding unit arranged for relative reciprocating movement in at least the first direction across the build region for binding construction material selectively at positions on the layers of construction material deposited on the build region from a first binding position on the first binding unit. The apparatus comprises a second binding unit arranged for relative reciprocating movement in at least the first direction across the build region for binding construction material selectively at positions on the layers of construction material deposited on the build region from a second binding position on the second binding unit. The first binding position, the construction material deposition position and the second binding position are arranged in order in the first direction.

According to a second aspect of the present disclosure, there is provided an additive manufacturing apparatus. The apparatus comprises a build region. The apparatus comprises a first construction material deposition unit arranged for relative reciprocating movement in at least a first direction across the build region for depositing a first construction material incrementally in layers on the build region from a construction material deposition position on the first construction material deposition unit. The apparatus comprises a binding unit arranged for relative reciprocating movement in at least the first direction across the build region for binding construction material selectively at positions on the layers of construction material deposited on the build region from a binding position on the binding unit. The apparatus comprises a second construction material deposition unit arranged for relative reciprocating movement in at least the first direction across the build region for depositing a second construction material incrementally in layers on the build region from a second construction material deposition position on the second construction material deposition unit. The first construction material deposition position, binding position and second construction material deposition position are arranged in order in the first direction.

In one embodiment, the deposition and binding units are provided on a common carriage arranged for reciprocating 35 movement in the first direction.

In one embodiment, the deposition and binding units are provided on respective separate carriages, each being arranged for reciprocating movement in the first direction.

In one embodiment, a smoothing element is arranged between each deposition and binding position of the deposition and binding positions and the next deposition or binding positions of the deposition and binding positions in order.

In one embodiment, each binding unit is a binder deposition unit arranged to deposit binder material selectively at positions on previously-deposited construction material thereby to bind the construction material selectively.

In one embodiment, the construction material deposition units are arranged for obtaining construction material from a common reservoir.

According to a third aspect of the present disclosure, there is provided an additive manufacturing method. The method comprises a process of depositing construction material in a second layer on a build region from a construction material deposition position on a construction material deposition unit while the construction deposition material deposition unit relatively moves in at least a first direction across the build region. The method comprises a process of binding selectively positions on the first layer of construction material from a first binding position on a first binding unit while the first binding unit relatively moves in at least the first direction across the build region. The first binding position is arranged on a first side of the construction material position. The first side is a side in a direction opposite to the first direction. The method comprises a process of depositing construction material in a second layer on the first layer from the construction material deposition position on the construction material deposition unit while the construction material deposition unit relatively moves in a direction opposite to the first direction across the build region. The method comprises a process of binding selectively positions on the second layer of construction material from a second binding position of a second binding unit while the second binding unit relatively moves in the direction opposite to the first direction across the build region. The second binding deposition position is arranged on a second side of the construction material deposition position. The second side is a side in the first direction.

According to a third aspect of the present disclosure, there is provided an additive manufacturing method. The method comprises a process of depositing construction material in a layer on a build region from a first construction material deposition position on a first construction material deposition unit while the first construction material deposition unit relatively moves in a first direction across the build region. The method comprises a process of binding selectively positions on the first layer from a binding position on a binding unit while the binding unit relatively moves in the first direction across the build region. The first construction material deposition position is arranged on a first side of the binding position. The first side is a side in a direction opposite to the first direction. The method comprises a process of depositing construction material in a second layer on the first layer from a second construction material deposition position of a second construction material deposition unit while the second construction material deposition unit relatively moves in a direction opposite to the first direction across the build region. The second construction material deposition position is arranged on a second side of the binder material deposition position. The second side is a side in the first direction. The method comprises a process of binding selectively positions on the second layer from the binding position on the binding unit while the binding unit relatively moves in the direction opposite to the first direction across the build region.

In one implementation, the deposition and binding units are provided on a common carriage arranged for reciprocating movement in the first direction.

In one implementation, the deposition and binding units are arranged on respective separate carriages, each of which is arranged for reciprocating movement in the first direction.

In one implementation, the method comprises a process of, after depositing each layer of construction material, smoothing the deposited layer of construction material with a smoothing element arranged between the deposition position for the deposited layer and the binding position of deposited layer.

In one implementation, each binding unit deposits binder material selectively at positions on previously-deposited construction material thereby to bind the construction 25 material selectively.

In one implementation, the construction material deposited by each construction material deposition unit is obtained from a common reservoir.

In one implementation, the binding is performed simultaneously with the deposition for each of the first direction and the second direction, respectively.

Brief Description of the Drawings

For a better understanding of the present invention, and to show how the same may be carried into effect, reference will 5 be made, by way of example only, to the accompanying Drawings, in which: Figures 1 to 3 show steps in one implementation of the present disclosure in a schematic manufacturing apparatus; Figure 4 shows a schematic view of a print head used in the present disclosure; and Figures 5 to 7 show steps in another implementation of the 15 present disclosure in a schematic manufacturing apparatus

Detailed Description

The present disclosure relates to 3D printing 20 technologies in which an object is constructed from a series of successively deposited layers, portions of which are joined together both within the layer and with portions of an underlying layer. In particular, the present disclosure relates to powder bed 3D printing, in which layers of powder are successively deposited, regions of each layer being bound together to form portions of a desired object before the next successive layer is deposited.

The present disclosure will be exemplified in relation to a powder bed and ink jet head 3D printing system, in which binder is selectively jetted from a scanning ink jet head onto a previously-deposited powder bed. However, the disclosure is not to be so limited, and the concepts disclosed herein are applicable to other additive manufacturing techniques involving the binding together of a previously-deposited powder layer, including selective laser sintering and local melting manufacturing.

Figure 1 shows a schematic view of a powder bed and ink jet head 3D printing apparatus 10. 3D printing apparatus 10 has a print table 11, into an upper surface of which well 12 5 is formed. Within well 12 is formed displaceable platform 13, which is arranged to be displaceable within well 12 in a first direction Z which, in the configuration of Figure 1, is perpendicular to a surface plane of Table 11. Platform 13 is supported by retractable supports, not shown, which are 10 retractable in a controlled manner to effect the lowering of platform 13 into well 12. For example, the retractable supports may be provided with toothed portions which enable the supports to be retracted.n a controlled manner through the operation of toothed wheels, in the manner of a rack and pinion drive. Alternatively, retractable supports may be hydraulically retractable or retractable by some other means, as may be desired.

Apparatus 10 also includes print head 15, which is arranged to traverse above well 12 in a first direction X, while being supported above the well as it translates. In the embodiment of Figure 1, print head 15 is supported on rail 16, along which it is arranged to move. Print head 16 may be moved in a reciprocating fashion over well 12 by, for example, a drive belt, a drive screw, an internal drive motor or any other suitable means. Importantly, print head 15 is able to transverse the full extent of well 12 in the X-direction.

It must be noted that, while the illustration of Figure 1 depicts the X-Z plane in transverse section, well 12 has extent in a third direction Y perpendicular to the X and Z directions and, for example, extending out of the page. Table 11, well 12 and platform 13 have extent in this direction also, but have no further special limitation as to the shape or dimension in this direction. For example, when viewed along the Z-direction, well 12 could have a rectangular or square shape in plan view, but also could have other shapes, including polygonal or circular. The cross-section of well 12 does not vary with extent in the Z direction, while platform 13 has a plan view so as to be a close fit to the vertical walls of well 12 relative to which platform 13 moves. Accordingly, a volume exists below the surface of table 11 between the vertical walls of well 12 and platform 13 into which powder can be dispensed such that substantially no powder leaks between sides of well 12 and the edges of platform 13. Platform 13 may be provided with seals, such as resilient wipers, at each edge to allow such a seal to be provided.

Print head 15 also has extent in the Y direction such that print head 15 is able to pass across the entire X-Y cross-sectional extent of well 12. This can be achieved by providing a print head 15 which extends the full length of the well in the Y-direction. Alternatively, this can be achieved by providing a print head, one or more components of which are arranged to reciprocate in the Y-direction to scan the surface of the well in a raster fashion, such that, as the print head traverses the well in the X-direction, whether continuously or stepwise, the component of the print head which scans in the Y-direction passes across every point of the well.

The configuration outlined above is common to conventional powder bed and ink jet head 3D printers as known in the art.

In the embodiment of Figure 1, print head 15 includes powder dispenser 15b adapted to dispense a layer of powder into well 12 as print head 15 traverses the well. In the present embodiment, powder dispenser 15b may have a dispensing orifice which extends the full width of well 12 in the Y-direction such that, when the print head 15 traverses well 12, a full layer of powder may be dispensed from the orifice. In alternative configurations, the powder dispenser 15b may be formed as a scanning component which dispenses successive rows of powder in the Y-direction, the rows being arranged sequentially in the X-direction. Print head 15 also includes two binding units 15a and 15c, respectively arranged on each side of powder dispenser 15b in the X-direction. In the present embodiment, each binding unit 15a, 15c includes an ink jet head arranged to jet binder into well 12 as print head 15 passes across well 12. By selectively jetting the binder as the print head 15 traverses well 12, portions of each layer of powder deposited by powder dispenser 15b can be selectively bound together, in order to form one layer of the object to be manufactured.

Print head 15 may additionally include one or more smoothing devices, such as a doctor blade or smoothing roller, arranged thereon and adapted to level the upper surface of the dispensed powder layer as print head 15 traverses well 12. For example, such a smoothing device could be arranged between powder dispenser 15b and binding unit 15c and/or between powder dispenser 15b and binding unit 15a. Such a smoothing device may be fixed or have an adjustable position in at least the Z direction.

Further, for use with binders which require active curing, for example by a UV light, print head 15 may include a curing unit, such as a UV lamp, associated with either or both binding units. Such a curing unit may be provided on either side of the respective binding unit, such that the curing unit acts to cure either binder that has just been dispensed by the binding unit or binder of the previous layer to the layer onto which binder is being dispensed in the present printing pass.

Each binder unit 15a, 15c could, in one configuration, be provided as a scanning ink-jet head which is operable to deposit drops of binder at predetermined locations in a single row in the Y-direction before or while the print head advances in the X-direction so that the binder dispenser can selectively deposit binder at locations on each successive row. Alternatively, each binder dispenser may comprise a single ink-jet head extending in the Y-direction the full extent of the well and having a plurality of binder dispensing orifices arranged in a row in at least the Y-direction such that, by activating individual orifices of the binder dispenser while the print head 15 translates across well 12 in the X-direction, binder may be deposited to selected locations in the X-Y plane of the well. A combination of these approaches is also possible, in which each binder dispenser may be arranged to translate in the Y-direction, but may also include plural orifices arranged in at least the Y-direction. The orifices of the print head 15 may also be arranged in the X direction, for example as a tilted linear array, for example in order to achieve closer spacing in the Y-direction as between the orifices.

The operation of the embodiment of Figure 1 will now be described. In Figure 1, the upper surface of platform 13 which, in the embodiment of Figure 1 is flat and parallel to the X-Y plane, has been retracted a short distance below the surface of table 11 to provide a build region (or build volume) into which a layer of powder may be dispensed. The depth of the build region, and consequently the depth of the layer of powder to be dispensed above platform 13, may be selected such that the entirety of the depth of the layer may be selectively bound at a particular location through the action of the binding units, in order that one layer may be bound to a bound portion of the previous layer, without undesirably binding together substantial portions of the previous layer.

From the configuration shown in Figure 1, print head 15 traverses well 12 in the X-direction to deposit a layer of powder into the well on the surface of platform 13 from the

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dispensing orifice of the powder dispenser. Also, as the print head traverses in the X-direction, binder dispenser 15a selectively deposits binder onto portions of the deposited layer to selectively bind portions of that layer together.

In the configuration of Figure 1, the powder and binder are simultaneously dispensed in the same pass, the powder being dispensed to a location relatively advanced in the X-direction as compared with the location at which the binder dispenser is able to dispense binder, although other printing patterns are possible. In particular, where time is required to allow the powder to settle before the binder is deposited, the powder can be deposited in a first pass in the X-direction, while the binder can be deposited in a reverse pass in the -X direction.

Once layer 2a has been deposited, platform 13 is further lowered, for example by the intended thickness of the next layer, and print head 15, travelling in the reverse (-X) direction, deposits a further layer 2b on top of the first layer 2a as shown in Figure 3. To enable the binder and powder to be dispensed in the same pass for both the forward and reverse print directions across build region 12, whereas on the forward pass when moving between Figure 1 and Figure 2 powder dispenser 15b and binder dispenser 15a are active, in the reverse pass between Figure 2 and Figure 3, powder dispenser 15b and binder dispenser 15c are active. Accordingly, in contrast to known apparatus in which printing is completed only on the forward pass, and time is wasted while the print head returns to the original position shown in Figure 1 before a further layer may be deposited and bound, the embodiment of Figure 1 makes use of both a forward and a reverse pass for the depositing and binding of a layer. Accordingly, two layers can be deposited and bound within the time available for deposition of a single layer in known apparatus. Accordingly, printing with the disclosed embodiment can be significantly faster.

In some configurations, binder may not be deposited at all on the first layer above table 13, in order to allow the printed object to be easily released from the upper surface of table 13.

Figure 4 shows a schematic view of print head 15, showing clearly the twin binding units 15a and 15c as well as powder dispenser 15b. Each binding unit 15a, 15c has an ink-jet head 15f, 15k providing a binder-dispensing orifice which is connected via a supply tube 15e, 15j to an external reservoir for binder. The binder reservoir may be distinct for each binding unit, or may be a common reservoir shared between the binding units. Print head 15 may be connected to the external reservoir, for example, by suitable length of flexible tubing. Positioned between binding unit 15a and binding unit 15c is powder dispenser 15b, which is connected via supply duct 15g to a powder reservoir. Powder reservoir may be provided supported on print head 15 or may be external to print head 15 and the powder, which may be appropriately fluidised, may be delivered from the external reservoir to supply channel 15g. Dispenser 15b also includes blade valve unit 15h, which functions to actuate the dispensing of the powder from the supply channel 15g through supply orifice 15i. However, the supply of powder through orifice 15a may be selectively actuated by other means such as are known in the art.

Print head 15 may be driven along rail 16 in the X-direction by pairs of drive rollers 15d, which respectively in pairs clamp rail 16 between them, and which are, for example, electrically drivable to effect movement in the forward and reverse X-direction of print head 15. The entirety of print head 15 is in the disclosed embodiment enclosed within external shell 151, such that binding units 15a and 15c and powder dispenser 15b share a common carriage.

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However, an implementation is possible in which, for example, print head 15 shown in Figure 4 is divided into three separate carriages, each being provided with its own drive means, the carriages respectively containing binding unit 15a, powder dispenser 15b, and binding unit 15c. The driving of each of the separate carriages in the X-direction may be thereby be independently effected, and particularly may be effected at respectively different speeds.

For example, as shown in Figure 5, printing apparatus 20 has three carriages 25a, 25b and 25c each arranged to translate along common rail 26 in the X-direction above well 22 formed in Table 21 so as to deposit and bind layers of material arranged on movable support platform 23. Whereas carriages 25a and 25c are provided respectively with binding units, carriage 25b is provided with a powder dispenser. From the configuration shown in Figure 5, carriages 25b and 25c traverse in the X-direction across well 22 such that a layer of powder is deposited from powder dispenser 25b, the stage shown in Figure 6. Carriages 25b and 25c may travel together at the same speed and in an adjacent formation, or binder unit 25c may depart earlier or may move faster than powder unit 25b, as may be desired.

From the configuration shown in Figure 6, binding unit 25a then travels in the X-direction across deposited powder layer 2a to selectively bind portions of layer 2a together. After binding unit 25a has completed its transit of well 22, the configuration shown in Figure 7 is achieved, in which all carriages 25a, 25b and 25c are together arranged on one side of well 12. Of course, it is not required to wait for powder dispenser 25b to arrive on the other side of well 22 before binder unit 25a begins its transit. Indeed, in some situations, where for example when the speed of transit of powder dispenser 25b is reduced, for example to allow an even layer or sufficient depth of powder to be deposited, as compared with the transit speed of binding unit 25a, it may be preferable for binder unit 25a to begin its transit before dispenser unit 25b has completed its transit. In such configurations, it may be selected that binder unit 25a completes its transit at the same time as, or shortly after, 5 powder dispenser 25b completes its transit.

In the above, curing units or smoothing units, where present, can be provided also on independent carriages, or can be suitably arranged on one or more of the binder unit or 10 powder dispenser carriages.

In some implementations, the print head may be configured to dispenser different binders or to use different binding methods for binder unit 25a and binder unit 25c.

Although the above disclosure has been made with regard to a print head which reciprocates in at least a first linear direction above a well defining the printing region, the above disclosure is also applicable to applications in which a print head is arranged to extend radially from the central axis of a build region and to sweep a circular pass around the axis to deposit powder into the circular build region and to selectively bind regions of the powder together.

Although the above disclosure has been exemplified with regard to situations in which two binding units are provided on either side of a powder dispenser in a reciprocating transit direction of the powder dispenser, the above disclosure can be equally implemented in a configuration in which two powder dispensers are arranged on either side of a single binder unit. Such a configuration may be constructed as shown and described with reference to Figure 1, except that elements 15a and 15c are to be considered as powder dispensers while element 15b is to be considered as a binding unit configured to, for example, to dispense a binder. In such a configuration, the powder dispensers could be configured to dispense either the same or different powders. In one example, a ceramic powder and a metal powder could be * used as the two different powders; or alternatively two different ceramics, two different metal powders, or two different powders of the same material but, for example, having different grain sizes. All the above disclosure may be equivalently implemented, therefore, in such a configuration.

Particularly, the above disclosures are applicable to a wide variety of 3D printing technologies other than those specifically described, including the use of ceramic, polymer and metal powder construction materials, reactive, DV-curable, contact-curable or other jetted binders, or other binding techniques such as laser or thermal binding. One particular embodiment uses a metal powder and a polymer binder. In such implementations, a sintering process may be applied to the metal powder after the object is removed from the printing apparatus.

The above disclosures are considered only exemplary. It is expected that those skilled in the art would be able to implement the above disclosure with such modifications, substitutions, alternatives or variations as may be required to meet particular engineering requirements without undue burden.

Claims

Claims 1. An additive manufacturing apparatus comprising: a build region; a construction material deposition unit arranged for relative reciprocating movement in at least a first direction across the build region for depositing a construction material incrementally in layers on the build region from a construction material deposition position on the construction material deposition unit; a first binding unit arranged for relative reciprocating movement in at least the first direction across the build region for binding construction material selectively at positions on the layers of construction material deposited on the build region from a first binding position on the first binding unit; and a second binding unit arranged for relative reciprocating movement in at least the first direction across the build region for binding construction material selectively at positions on the layers of construction material deposited on the build region from a second binding position on the second binding unit, the first binding position, construction material 25 deposition position and second binding position being arranged in order in the first direction.
2. An additive manufacturing apparatus comprising: a build region; a first construction material deposition unit arranged for relative reciprocating movement in at least a first direction across the build region for depositing a first construction material incrementally in layers on the build region from a construction material deposition position on the first construction material deposition unit; * * a binding unit arranged for relative reciprocating movement in at least the first direction across the build region for binding construction material selectively at positions on the layers of construction material deposited on 5 the build region from a binding position on the binding unit; and a second construction material deposition unit arranged for relative reciprocating movement in at least the first direction across the build region for depositing a second 10 construction material incrementally in layers on the build region from a second construction material deposition position on the second construction material deposition unit, the first construction material deposition position, binding position and second construction material deposition 15 position being arranged in order in the first direction.
3. The additive manufacturing apparatus according to claim 1 or 2, wherein the deposition and binding units are provided on a common carriage arranged for reciprocating movement in 20 the first direction.
4. The additive manufacturing apparatus according to claim 1, 2 or 3, wherein the deposition and binding units are provided on respective separate carriages, each being 25 arranged for reciprocating movement in the first direction.
5. The additive manufacturing apparatus according to any one of claims 1 to 4, wherein a smoothing element is arranged between each deposition and binding position of the deposition and binding positions and the next deposition or binding positions of the deposition and binding positions in order.
6. The additive manufacturing apparatus according to each 35 of claims 1 to 5, wherein each binding unit is a binder deposition unit arranged to deposit binder material selectively at positions on previously-deposited construction material thereby to bind the construction material selectively.
7. The additive manufacturing apparatus according to claim 2 or according to each of claims 3 to 6 as dependent on claim 2, wherein the construction material deposition units are arranged for obtaining construction material from a common reservoir.
8. An additive manufacturing method comprising: depositing construction material in a second layer on a build region from a construction material deposition position on a construction material deposition unit while the construction deposition material deposition unit relatively moves in at least a first direction across the build region; binding selectively positions on the first layer of construction material from a first binding position on a first binding unit while the first binding unit relatively moves in at least the first direction across the build region, the first binding position being arranged on a first side of the construction material position, the first side being a side in a direction opposite to the first direction; depositing construction material in a second layer on the first layer from the construction material deposition position on the construction material deposition unit while the construction material deposition unit relatively moves in a direction opposite to the first direction across the build region; and binding selectively positions on the second layer of construction material from a second binding position of a second binding unit while the second binding unit relatively moves in the direction opposite to the first direction across the build region, the second binding deposition position being arranged on a second side of the construction material deposition position, the second side being a side in the first direction.
9. An additive manufacturing method comprising: depositing construction material in a layer on a build region from a first construction material deposition position on a first construction material deposition unit while the first construction material deposition unit relatively moves in a first direction across the build region; binding selectively positions on the first layer from a binding position on a binding unit while the binding unit relatively moves in the first direction across the build region, the first construction material deposition position being arranged on a first side of the binding position, the first side being a side in a direction opposite to the first direction; depositing construction material in a second layer on the first layer from a second construction material deposition position of a second construction material deposition unit while the second construction material deposition unit relatively moves in a direction opposite to the first direction across the build region, the second construction material deposition position being arranged on a second side of the binder material deposition position, the second side being a side in the first direction; and binding selectively positions on the second layer from the binding position on the binding unit while the binding unit 25 relatively moves in the direction opposite to the first direction across the build region.
10. The additive manufacturing method according to claim 8 or 9, wherein the deposition and binding units are provided 30 on a common carriage arranged for reciprocating movement in the first direction.
11. The additive manufacturing method according to claim 8, 9 or 10, wherein the deposition and binding units are 35 arranged on respective separate carriages, each of which is arranged for reciprocating movement in the first direction. *
12. The additive manufacturing method according to any one of claims 8 to 11, comprising, after depositing each layer of construction material, smoothing the deposited layer of construction material with a smoothing element arranged between the deposition position for the deposited layer and the binding position of deposited layer.
13. The additive manufacturing method according to each of claims 8 to 12, wherein each binding unit deposits binder material selectively at positions on previously-deposited construction material thereby to bind the construction material selectively.
14. The additive manufacturing method according to claim 9 or according to each of claims 10 to 13 as dependent on claim 9, wherein the construction material deposited by each construction material deposition unit is obtained from a common reservoir.
15. The additive manufacturing method according to any one of claims 8 to 14, wherein the binding is performed simultaneously with the deposition for each of the first direction and the second direction, respectively.M