Recoating device and method for applying a layer of build material capable of solidification on a working surface

Abstract

A recoater for applying a layer of build material capable of solidification on a working surface, wherein the recoater comprises a discharge port and a flattening member, wherein the discharge port is configured to discharge build material to form a heap of build material ahead of the flattening member, wherein the flattening member is configured to spread material from the heap of build material along the working surface in order to form the layer of build material on top of the working surface through a gap formed between a lower surface of the flattening member and the working surface by relative movement of the flattening member and the working surface, wherein the recoater further includes a shutter distanced from the discharge port, wherein the shutter is configured to be movable between a closed position in which build material is not dispensed onto the working surface, and an opened position in which build material is dispensed onto the working surface, wherein the shutter is configured to close an adjacent area ahead of the lower surface of the flattening member in the closed position.

Claims

1. A recoater for forming a layer of build material capable of solidification on a working surface, wherein the recoater comprises: a discharge port; a flattening member; and a shutter distanced from the discharge port, wherein the discharge port is configured to discharge a build material to form a heap of build material for subsequent spreading by the flattening member, wherein the flattening member is configured to spread material of the heap of build material along the working surface to form the layer of build material on top of the working surface, through a gap formed between a lower surface of the flattening member and the working surface, by relative movement of the flattening member and the working surface, wherein the shutter is configured to be movable between: a closed position in which build material is not dispensed onto the working surface, and an opened position in which build material is dispensed onto the working surface, and wherein the shutter is configured to close an adjacent area ahead of the lower surface of the flattening member in the closed position.

2. The recoater according to claim 1, wherein in the closed position the shutter is configured to carry the heap of build material.

3. The recoater according to claim 1, wherein in the closed position a lower surface of the shutter is aligned with respect to the lower surface of the flattening member.

4. The recoater according to claim 1, wherein the shutter is slidingly displaceable between the opened position and the closed position.

5. The recoater according to claim 1, wherein the shutter is switchable between the opened position and closed position, and/or vice versa, at least during relative movement of the recoater and the surface.

6. The recoater according to claim 1, wherein the shutter is switchable between the opened position and closed positon, and/or vice versa, at a speed larger or equal to a recoating speed.

7. The recoater according to claim 1, wherein the shutter is switchable between the opened position and closed position, and/or vice versa, with a speed equal to a recoating speed.

8. The recoater according to claim 1, wherein the recoater further includes a scraper having a raised edge, wherein the raised edge is arranged to scrape off build material resting on the shutter during retraction of the shutter from the closed position to the opened position.

9. The recoater according to claim 1, wherein the shutter includes a flexible film held by one or more ribs.

10. A method for applying, by a recoater, a layer of build material capable of solidification on a working surface, wherein the recoater comprises: a discharge port; a flattening member; and a shutter distanced from the discharge port, wherein the method includes: discharging, by the discharge port, a build material to form a heap of build material for subsequent spreading by the flattening member, spreading, by the flattening member, material of the heap of build material along the working surface to form the layer of build material on top of the working surface through a gap formed between a lower surface of the flattening member and the working surface by relative movement of the flattening member and the working surface, wherein the shutter is movable between: a closed position in which build material is not dispensed onto the working surface, and an opened position in which build material is dispensed onto the working surface, and wherein the shutter is configured to close an adjacent area ahead of the lower surface of the flattening member in the closed position.

11. An additive manufacturing system including the recoater according to claim 1.

12. An additive manufacturing system including at least a conveyer, a plurality of build units moveable along the conveyor, and a recoater according to claim 1, wherein one or more of the plurality of build units are arranged to subsequently pass along the recoater by use of the conveyor.

13. The additive manufacturing system according to claim 12, further including a solidification chamber, and at least one of a preheating and/or postheating chamber, wherein the plurality of build units are movable to said chambers by the conveyor.

14. A method of layerwise forming an object from a medium capable of solidification, whereby the object is built up layer per layer by repeatedly providing a layer of the medium on a support and/or an already formed part of the object and by subsequently solidifying one or more predetermined areas of the layer of the medium according to a specific pattern before a successive layer is formed in a same manner, wherein the successive layers of medium are applied using a recoater according to claim 10.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) The invention will further be elucidated on the basis of exemplary embodiments which are represented in a drawing. The exemplary embodiments are given by way of non-limitative illustration. It is noted that the figures are only schematic representations of embodiments of the invention that are given by way of non-limiting example.

(2) In the drawing:

(3) FIG. 1 shows a schematic diagram of a recoater;

(4) FIG. 2 shows a schematic diagram of a recoater;

(5) FIG. 3 shows a schematic diagram of a recoater;

(6) FIG. 4 shows a schematic diagram of a recoater;

(7) FIG. 5 shows a schematic diagram of a recoater;

(8) FIG. 6 shows a schematic diagram of a recoater;

(9) FIG. 7 shows a schematic diagram of a recoater;

(10) FIG. 8 shows a schematic diagram of a recoater;

(11) FIG. 9 shows a schematic diagram of a recoater;

(12) FIG. 10 shows a schematic diagram of a shutter;

(13) FIG. 11 shows a schematic diagram of an additive manufacturing system;

(14) FIG. 12 shows a schematic diagram of an additive manufacturing system;

(15) FIG. 13 shows a schematic diagram of a recoating process in an additive manufacturing system; and

(16) FIG. 14 shows a flow chart of a method.

DETAILED DESCRIPTION

(17) FIG. 1 shows a schematic diagram of a recoater 1 for applying a layer 3 of build material 5 capable of solidification on a working surface 7. The working surface 7 may be formed by a holder of a build unit or a previously formed layer of build material 5 (e.g. powder bed). The recoater 1 comprises a discharge port 9 and a flattening member 11. The discharge port 9 is configured to discharge build material 5 to form a heap of build material 13 ahead of the flattening member 11. The flattening member 11 is configured to spread material from the heap of build material 13 along the working surface 7 in order to form the layer of build material 3 on top of the working surface 7 through a gap 15 formed between a lower surface 17 of the flattening member 11 and the working surface 7 by relative movement of the flattening member 11 and the working surface 7. In this example, the relative movement between the recoater 1 and the working surface 7 for sweeping the flattening member 11 across the working surface 7 is obtained by providing a translating movement X of the working surface 7 with respect to the recoater 1. The recoater 1 may thus remain stationary while the working surface 7 is moved. It will be appreciated that additionally or alternatively, the recoater 1 may be moved.

(18) The recoater 1 further includes a shutter 19 distanced from the discharge port 9, wherein the shutter 19 is configured to be movable between a closed position in which build material 5 is not dispensed onto the working surface 7, and an opened position in which build material 5 is dispensed onto the working surface 7. The shutter 19 is configured to close an adjacent area 21 ahead of the lower surface 17 of the flattening member 11 in the closed position. In this way, an interface through which build material 5 is provided onto the working surface 7 can be selectively covered by means of the shutter 19.

(19) In a closed position, the heap of build material 13 can be at least partially intercepted such that at least a remaining portion of the heap of build material 13 can rest on the shutter. Different shutter arrangements can be employed. In an example, a shutter blade is used for obtaining selective closing of the adjacent area.

(20) FIG. 2 shows a schematic diagram of a recoater 1. In this embodiment, the shutter 19 is slidingly displaceable between the closed position (cf. FIG. 2A) and opened position (cf. FIG. 2B). The shutter 19 includes a shutter blade 23 for selectively covering the adjacent area 21. In the closed position, the heap of build material 13 can rest on the shutter blade 23. The recoater 1 includes a sliding arrangement enabling sliding displacement between the opened position and the closed position, and vice versa. The shutter blade 23 is connected with a slider 25 which can slide along a slider line 27.

(21) As shown in FIG. 2A, in the closed position the shutter blade 23 of the shutter 19 is configured to carry the heap of build material 13. The heap of build material 13 can be carried along with the recoater 1 for later use. In this way, it can be prevented that the remainder of the heap of build material after a recoating stroke is spread on the surface. Wasting of build material can thus be reduced since the recoater can selectively apply a layer of building material 3 onto the working surface 7. In this embodiment, the lower surface 29 of the shutter blade 23 is substantially aligned with respect to the lower surface 17 of the flattening member 11. The shutter blade 23 of the shutter 19 can be moved against the flattening member 11 such that their lower surfaces 29, 17, respectively, are substantially aligned forming a smooth flat surface. In this way, it can be prevented that the shutter blade is pushed underneath the flattening member which may result in undesirable disruption of the formed layer 3 of build material (e.g. powder bed). The bottom surface 29 of the shutter blade 23 may be at a same height as the bottom surface 17 of the flattening member 11 (with respect to the working surface 7). The shutter blade 23 may rest against a side portion of the flattening member 11 in the closed position (see FIG. 2A). In an example, the shutter blade 23 is configured to rest against a bottom edge of the flattening member 11 facing the front side of the flattening member 11. The flattening member 11 in this embodiment is a recoater blade. Other types of flattening members 11 may also be used. The flatting member 11 may have various shapes and dimensions. In an example (not shown) the flattening member 11 is a roller.

(22) In the shown embodiment of FIG. 2, the lower surface of the flattening member 11 is flat, wherein the shutter blade 23 of the shutter 19 is parallel to the lower surface 17 of the flattening member 11.

(23) FIG. 3 shows a schematic diagram of a recoater 1. The recoater 1 is configured to apply a uniform layer 3 of build material 5 onto the working surface 7. The working surface 7 may for instance be a previous applied layer of building material. The recoater 1 may be used for enabling a layer-by-layer processing in an additive manufacturing process wherein a powder is employed. The discharge port 9 is configured to provide a supply of build material 5 towards a front side of the flattening member 11, with respect to the relative direction of movement of the recoater 1. In this embodiment, the working surface 7, for example held on a build unit of an additive manufacturing system, is moved along the running direction X. The discharge port 9 can be arranged to control the supply of build material 5, for instance coming from a reservoir or hopper (not shown). A heap of build material 13 is formed below the discharge port at the front side the flattening member 11. Optionally, a sensor is used for monitoring a level of the heap of build material 13.

(24) By means of the recoater, build material 5 can be spread across the working surface 7 for selectively forming at at least a portion of the working surface 7 the layer 3 of build material 5. Build material 5 from the heap of build material 13 is guided through the gap formed between the bottom side 17 of the flattening member 11 and an upper side of the working surface 7.

(25) The build material 5 discharged from the discharge port 9 can be collected in a walled heap chamber 31. The walled heap chamber can be selectively closed off by means of the shutter 19. In this embodiment, the shutter includes a sliding shutter blade 23. It will be appreciated that other shutter 19 mechanisms may also be employed. In closed position of the shutter 19, the shutter blade intercepts the heap of build material 13, such that the portion of the heap of build material 13 above the shutter blade 23 can be maintained. Hence, a large portion of the initial heap of build material 13 can rest on the shutter blade 23 and be used for a subsequent coating by the recoater 1. Advantageously, the transition between layer and non-layer portions on the working surface 7 can be improved. A sudden and accurate transition can be obtained. Furthermore, for the purpose of subsequent recoating, refilling the heap chamber 31 for obtaining the heap of build material 13 may no longer be required, resulting in improved process efficiency and time savings.

(26) The shutter blade 23 is distanced from the discharge port 9. The shutter is configured to be movable between a closed position (not shown) in which build material is not dispensed onto the working surface, and an opened position (shown) in which build material is dispensed onto the working surface. The shutter 19 is configured to close the adjacent area 21 ahead or upstream of the lower surface 17 of the flattening member 11, in the closed position. The upstream location is related to the relative motion of the recoater or the flattening member with respect to the working surface 7. In this embodiment, the working surface 7 is translated with respect to the recoater 1 in the running direction X. However, it may also be additionally or alternatively possible that the recoater 1 is moved with respect to the working surface 7.

(27) FIG. 4 shows a schematic diagram of a recoater 1. The recoater is configured to apply a layer 3 of build material 5 capable of solidification on a working surface 7. The recoater 1 comprises a discharge port 9 and a flattening member 11. The discharge port 9 is configured to discharge build material 5 in order to form a resulting heap of build material 13 ahead of the flattening member 11, i.e. upstream the flattening member with respect to the relative movement of the recoater 1 and the working surface 7. The flattening member 11 may be configured to spread build material 5 from the heap of build material 13 along the working surface 7 in order to form the layer of build material 3 on top of the working surface 7 through a gap 15 formed between a lower surface 17 of the flattening member 11 and the working surface 7 by means of relative movement of the flattening member 11 and the working surface 7. The recoater 1 further includes a shutter 19 distanced from the discharge port 9. In this embodiment, the shutter includes a shutter blade 23 movable arranged by means of a sliding arrangement. The shutter 19 is configured to be movable between a closed position in which build material 5 is not dispensed onto the working surface 7, and an opened position in which build material 5 is dispensed onto the working surface 7. The shutter 19 is configured to close an adjacent area 21 ahead of the lower surface 17 of the flattening member 11, in the closed position.

(28) The build material 5 can be discharged by means of the discharge port 9 ahead (upstream) of the flattening member 11 such that it can pile up to form the heap of build material 13. In this embodiment, the build material is made out of powder. The flattening member 11 traverses relative to the working surface 7, which is formed by a powder bed, such that the build material 5 is distributed as a uniform layer over the working surface 7 (powder bed).

(29) The recoater 1 can be employed for forming the powder layer onto the powder bed in a build chamber. The build chamber may for instance be part of a build unit of an additive manufacturing system. By depositing the heap of powder 13 adjacent to the powder bed and spreading the heap of powder with a flattening member 11 across (from one side to another side of) the powder bed the uniform powder layer can be formed. The flattening member 11 may thus act as a wiper, configured to spread upstream build material collected in the heap of build material 13.

(30) Optionally, a laser beam can be scanned across portions of the powder layer that correspond to a cross-section of the object being constructed. The laser beam can melt or sinter the powder to form a solidified layer. After selective solidification of a layer, the powder bed can be lowered by a thickness of the newly solidified layer and a further layer of powder can be spread over the surface and solidified, as required.

(31) The heap of build material 13 may be a detached heap. Detachment of the heap of build material 13 can be obtained by means of a distance provided between the discharge port 9 and working surface 7 on which the build material is disposed. The shutter 19 is arranged such that in the closed position, the shutter blade 23 is aligned with the lower surface 17 of the flattening member 11.

(32) In the shown embodiment, the recoater 1 includes a first chamber 33 and a second chamber 35 different than the first chamber 33, the first chamber 33 holding a quantity of build material 5. A discharge port 9 is arranged between the first chamber 33 and the second chamber 35. The discharge port 9 is configured to provide build material 5 to the second chamber 35 such as to form a heap of build material 13 ahead of the flattening member 11 (upstream in the relative direction of movement of the recoater and working surface). In this example, the working surface 7 is moved in the running direction X. Other ways of relative translations between the recoater 1 and the working surface 7 may also be employed for obtaining the relative movement of the recoater 1 across the top of the working surface 7. The first chamber 33 may for instance be a reservoir containing build material 5, such as a hopper. A clearance or gap is provided between the flattening member 11 and the working surface 7, such that during relative movement of the recoater 1 across the working surface 7, a layer of build material 5 is formed on the working surface 7. Build material from the heap of build material 13 is guided through the clearance/gap to form a smooth layer of build material on the powder bed.

(33) The recoater 1 further includes adjustment means 37 configured for adjusting an opening area of the discharge port 9. In this example, the adjustment means 37 are arranged to adjust an angle of a side wall 39 for adjusting the opening area of the discharge port 9. The adjustment means 37 enable a rotational movement of the side wall 39. The adjustment of the opening area of the discharge port 9 can significantly influence the formed detached heap of build material 13 in the second chamber 35.

(34) Further, the recoater includes an optional level sensor 41 configured to determine a level of build material at the first chamber 33.

(35) Further, the recoater 1 includes an optional scraper 43 having a raised edge. The raised edge is arranged to scrape off build material 5 resting on the shutter blade 23 during retraction of the shutter blade 23 from the closed position to the opened position.

(36) In the closed position, the heap of build material 13 is resting on the shutter blade 23. When subsequently the shutter blade is moved from the closed position to the opened position, with the heap of material 13 resting on it, build material can be carried along with the shutter blade 23. By means of the scraper 43, it can be prevented that remaining build material is carried too far away with the shutter blade 23. When the powder remains attached to the shutter blade 23, it can be effectively scraped off such that it may fall off towards the working surface 7 through the adjacent area 21. The scraper 43 is slidingly arranged above the shutter blade 23. The shutter blade 23 is configured to slide along a bottom side of the scraper 43 for enabling scraping of remaining residual build material when the shutter blade 23 is moved from the closed position to the opened position. It will be appreciated that other types of scrapers may also be used. For instance, attachment of build material of the shutter blade 23 may be reduced using vibrations.

(37) The side wall 39 further includes an optional vibrator 45 configured to vibrate the at least a portion of the side wall such that a more continuous flow of build material 5 towards the discharge port 9 can be obtained. In this way, the obtained heap of build material 13 may be better maintained during the recoating process.

(38) In the exemplary embodiment, the recoater 1 further includes an optional environment barrier 47. The environment barrier 47 may be arranged for preventing gasses, such as oxygen from entering the second chamber 39 from the first chamber 33. The build unit in which the recoater 1 is employed may for instance operate under elevated temperature or a desired atmosphere. The environment barrier 47 may prevent contamination of the environment within the build unit in which the recoater 1 is operating. The recoater 1 further includes an optional frame 49 arranged holding various features of the recoater 1.

(39) The recoater 1 according to the embodiment of FIG. 4 may be used for achieving automatic feeding. The recoater 1 may include a combined first chamber (hopper) with an automatic build material (e.g. powder) feeder. The recoater 1 can be highly adjustable by means of adjustment means for controlling the flow of build material towards the second chamber 35. A substantially constant density in the powder bed can be obtained by means of the adjustment means. Furthermore, a large range of layer thicknesses can be achieved using the recoater 1.

(40) Alternatively, instead of a sliding shutter blade, a rotating shutter blade can be arranged, wherein the shutter blade is rotatably switchable between the opened position and closed position, and vice versa. In the closed position, the heap of medium/powder can rest on the shutter blade. It is also envisaged that a pivotally switchable shutter blade can be arranged. Other shutter movement mechanisms can also be used, such as for example diaphragm shutters. Many variants are possible.

(41) FIG. 5 shows a schematic diagram of a recoater 1. Similar to the embodiment of FIG. 4, the recoater 1 includes a first chamber 33 and a second chamber 35, with a discharge port 9 therebetween. The discharge port allows a controlled supply of build material 5 towards the second chamber 35. The discharge port may provide a periodic supply of build material 5 by rotation of gear 9a. Other types of discharge ports 9 may also be used. For instance a gear pump with two gears may be used. The build material is disposed upstream of the flattening member 11 such as to form a heap of build material 13. In this example, an optional sensor 41 is arranged in the flattening member 11 for measuring a level of the heap of build material 13. It will be appreciated that level sensor 41 may be positioned differently. Furthermore, a different number of sensors may be used. It may also be possible to employ different kind of sensors for indicating the presence of an adequate heap of build material 13.

(42) A detached heap of build material 13 is obtained which is spread over the working surface 7. In this example, the build material is a powder, and the layer of build material 5 is disposed on a powder bed. In this example, the working surface 7 is moved in the running direction X while the recoater 1 remains stationary. Additionally or alternatively, the recoater 1 may be moved for obtaining the relative movement for applying the layer of build material 3 onto the working surface 7.

(43) The recoater 1 includes a shutter 19 distanced from the discharge port 9. The shutter 19 is configured to be movable between a closed position in which build material is not dispensed onto the working surface 7, and an opened position in which build material is dispensed onto the working surface 7. The shutter is configured to close an adjacent area 21 ahead/upstream of the lower surface 17 of the flattening member 11, in the closed position.

(44) A larger hopper may result in a larger pressure at the formed heap of build material if the build material within the hopper is directly guided to the discharge port 9. However, in this exemplary embodiment, the discharge port controls the amount of build material supplied to the second chamber 35 for forming the heap of build material 13. In this way, the influence of the weight of the build material within the hopper on the formed heap of build material 13 can be reduced and/or eliminated. Therefore, different pressures and densities in the formed layers of build material (e.g. powder bed), which could result in different local mechanical properties of the created object, can be prevented. In this example, the first chamber (hopper) may be refilled or replaced easily. It may be even replaced during recoating. The first chamber may be detachable.

(45) Advantageously, the recoater 1 in the shown embodiment of FIG. 5 may achieve a direct dosing. The first chamber 33 (hopper) may be detachable with a (fine) dosing mechanism. The first chamber can be removed with powder inside. Further, a low level detection of the heap of powder can be achieved during recoating using the sensor 41.

(46) FIG. 6 shows a schematic diagram of a recoater 1. In the shown embodiment, the recoater 1 includes a first chamber 33 and a second chamber 35 different than the first chamber 33, the first chamber 33 holding a quantity of build material 5. A first discharge port 9a is arranged between the first chamber 33 and the second chamber 35, the first discharge port 9a being configured to provide build material 5 to the second chamber 35. Within the second chamber 35, a second discharge port 9b is arranged. The second discharge port 9b is similar to the discharge port arranged in the embodiment of FIG. 4. The second discharge port 9b is configured to form a heap of build material 13 ahead of the flattening member 11 (upstream in the relative direction of movement of the recoater and working surface).

(47) In this example, the working surface 7 is moved in the running direction X. Other ways of relative translations between the recoater 1 and the working surface 7 may also be employed for obtaining the relative movement of the recoater 1 across the top of the working surface 7.

(48) The shutter 19 can be translated into the opened position (FIG. 6a) and in the closed position (FIG. 6b), by means of a sliding mechanism. A detached (freestanding) heap of build material 13 can be obtained by means of the recoater 1. The heap of build material 13 can remain substantially intact when the shutter 19 is switched to the closed position. The heap can then be readily used in a later phase, for example in a subsequent recoating stroke, when the shutter 19 is witched from the closed position to an opened position.

(49) The recoater 1 shown in FIG. 6 may achieve a highly adjustable recoating. This embodiment may for instance be suitable for providing a constant density in the powder bed. The first chamber 33 (hopper) can be removed with powder therein. Furthermore, a large range of layer thicknesses may be achieved using the recoater 1.

(50) The recoater 1 may provide automatic feeding. The first chamber 33 (primary hopper) may be detachable with respect to the dosing mechanism of the recoater 1 (cf. second chamber 35). The second chamber 35 may be level controlled. The recoater 1 may further be used for a closed loop dosing to the second chamber 35. Advantageously, the recoating process may be independent from the level of powder in the first chamber 33. A relatively coarse dosing may be achieved if desired.

(51) FIG. 7 shows a schematic diagram of a recoater 1. An open area 51 is formed below the discharge port 9 such that a detached or freestanding heap of build material 13 can be obtained upstream the flattening member 11. By means of the resulting detached heap of build material 13, a more uniform density distribution may be obtained along the disposed layer of build material.

(52) Optionally, the shutter blade is flexible. A flexible shutter blade can for example provide better recoating when metal powders are used.

(53) FIG. 8 shows a schematic diagram of a recoater 1 at different time steps when the shutter 19 is switched from the opened position (step a) to the closed position (step c). Also an intermediate time step is shown (step b) between the opened positon (step a) and the closed position (step c) of the shutter 19. In this example the shutter 19 includes a shutter blade 23. Other shutter types may also be used, such as for example a diaphragm.

(54) The shutter may be switchable between the opened position and closed positon, and/or vice versa, with a speed v2 larger or equal to a recoating speed v1. In this way, a sufficiently fast switching of the shutter between the opened position and the closed position can be obtained resulting in a short cut-off portion 53 of the layer of build material 3.

(55) In an advantageous embodiment, the shutter is switchable between the opened position and closed position, and/or vice versa, with a speed substantially equal to a recoating speed. A more stable cut-off portion 53 of the layer of build material 3 can be obtained in this way.

(56) Advantageously, a relatively short transition region may be obtained between a layered region 55a and a non-layered region 55b. For instance, the surface 57 adjacent to the working surface 7 may not require a layer of build material 3 disposed thereon. Hence, the layer of build material may be selectively coated on the working surface 7.

(57) In case the speed v1 at which the working surface 7 is moved with respect to the stationary recoater 1 (i.e. recoating speed) is equal to the relative speed in which the shutter blade 23 of the shutter 19 is closed, it can be ensured that the shutter blade 23 is substantially stationary relative to the working surface 7 during the closing process. (moving at the same relative speed) when the shutter is changing from the opened position to the closed position. Since the shutter blade seemingly stands still relative to the working surface, the layer of build material can be cut-off at an improved substantially straight line on the working surface.

(58) FIG. 9 shows a schematic diagram of a recoater 1. FIG. 9a shows a perspective view of the recoater 1. The shutter 19 includes a thin shutter blade 23 held by means of ribs 59. The discharge port 9 is distanced from the adjacent area 21 upstream the flattening member 11. The recoater 1 includes a sliding arrangement 27 for slidingly switching the recoater blade 23 from the opened position in which the adjacent area 21 is covered, to the closed position in which the adjacent area 21 is uncovered. FIG. 9b shows a cross-sectional perspective view of the recoater 1 with the shutter 19 in the opened position, and FIG. 9c shows a cross-section perspective view of the recoater 1 with the shutter 19 in the closed position.

(59) FIG. 10 shows a schematic diagram of a shutter 19. In this example, the shutter 19 includes a thin flexible film 61 being stretched and held by means of ribs 59. In this way, a thinner shutter blade may be obtained advantageously. Side ribs are attached to a sliding arrangement 27 allowing the shutter to be translated between the opened position and the closed position.

(60) FIG. 11 shows a schematic diagram of an additive manufacturing system 100 including a conveyer (not shown), and a plurality of build units 101a, 101b moveable along the conveyor. A recoater 1 is stationary arranged within the additive manufacturing system 100. Two successive build units 101a, 101b are shown in this example, however the system 100 may include more build units. The build units 101a, 101b are arranged to subsequently pass along the recoater 1 by means of the conveyor. In this way a relative movement is obtained between the working surface 7 and the recoater 1, wherein the build units 101a, 101b are moved and the recoater is remained stationary.

(61) The recoater includes a shutter 19 distanced from the discharge port 9. The shutter 19 is configured to be movable between a closed position in which build material is not dispensed onto the working surface 7, and an opened position in which build material is dispensed onto the working surface 7. The shutter is arranged to close/cover an adjacent area ahead (upstream) of the lower surface of the flattening member 11, in the closed position

(62) Advantageously, it may no longer be required to push remaining build material into waste bins, enabling a more efficient use of the build material. Hence, after the desired layer of build material is deposited on the working surface (e.g. on powder bed), the remaining heap of build material is not considered as a waste, but is kept intact by means of the shutter. Furthermore, the time required for building up the heap of build material by providing build material through the discharge port, can be avoided in successive runs. The additive manufacturing process may thus become faster in this way.

(63) A hopper or a reservoir can be arranged for providing build material 5 to the discharge port 9 of the recoater 1. The flattening member 11 can be configured to relatively move with respect to the working surface 7 when a layer of build material 3 is provided on the working surface 7. By means of selective illumination of selected portions, a layer of an object can be hardened.

(64) FIG. 12 shows a schematic diagram of an additive manufacturing system 100 including a build unit 101. The building unit 101 passed along the recoater 1 and different time steps are illustrated in FIG. 12. The build unit 101 can be moved by means of a conveyor. The recoater 1 may be stationary at a fixed position S, such that the relative movement between the recoater 1 and the working surface 7 on the build unit 100 is obtained by means of movement of the build unit 100.

(65) The recoater 1 comprises a shutter 19 distanced from the discharge port 9. The shutter 19 is configured to be movable between a closed position in which build material is not dispensed onto the working surface 7 of the build unit 101, and an opened position in which build material is dispensed onto the working surface 7 of the build unit 101. The shutter 19 can be configured to close an adjacent area 21 ahead of the lower surface of the flattening member 11, in the closed position. In this way, the layer of build material can be selectively applied on the working surface 7 of the build unit 101.

(66) In step A, the build unit 100 approaches the stationary recoater 1 in the running direction X. The shutter 19 of the recoater 1 is in a closed position, wherein a heap of build material 13 is resting on the shutter 19. In step B, the build unit 100 has reached the stationary recoater 1. The shutter 19 of the recoater 1 is then switched from the closed position to the opened position releasing the heap of build material. As a result, the layering process is initiated and a layer of build material is formed as the build unit is relatively moved with respect to the recoater 1. Subsequently, in step C, the recoater 1 passed across the working surface 7 with the shutter 19 remaining in the opened position. In step D, the stationary recoater 1 has reached a portion of the build unit 101 not requiring a layer of build material. At this point the shutter 19 is switched from the opened position to the closed position. In this way, the heap of build material 13 can remain substantially intact resting on the shutter 19. In step E, the build unit 101 has passed the recoater and the shutter remains in the closed position until initialization of a subsequent recoating process.

(67) The build material may for instance be a powder. By means of the recoater, the powder can be layered to form a powder layer, wherein the powder of the powder layer is (selectively) bonded together to form a layer of the object. The layer of the object can be laminated on the previously formed layer of the object.

(68) FIG. 13 shows a schematic diagram of a recoating process in an additive manufacturing system 100 including a conveyer 103 and a plurality of build units 101. The plurality of build units 101 are moveable along the conveyor 103. The system 100 further includes a recoater compartment 105. Within the recoater compartment a recoater 1 is arranged for providing a layer of build material onto the working surface of the build unit 101 passing therethrough, if desired. One or more of the plurality of build units 101 are arranged to subsequently pass along the recoater compartment 105 by means of the conveyor 103. In this exemplary embodiment, the additive manufacturing system 100 further includes a preheating compartment 107 and a subsequent solidification compartment 109, for example for sintering. One or more additional compartments 111 may be arranged, such as for example for postheating. The plurality of build units 101 are movable arranged such as to subsequently pass the compartments. Other compartments may also be arranged in the additive manufacturing system 100. Advantageously, the recoater 1 has a shutter 19 such that wasting of build material can be reduced.

(69) The solidification process may require an elevated temperature. Additionally or alternatively, a vacuum may be required.

(70) FIG. 14 shows a flow chart of a method 1000 for applying a layer of build material capable of solidification on a working surface by means of a recoater, wherein the recoater comprises a discharge port and a flattening member. The recoater is provided with a shutter distanced from the discharge port, wherein the shutter is movable between a closed position in which build material is not dispensed onto the working surface, and an opened position in which build material is dispensed onto the working surface. In a first method step 1001, build material is discharged by means of the discharge port in order to form a heap of build material ahead of the flattening member. In a second method step 1002, material from the heap of build material is spread, by means of the flattening member, along the working surface in order to form the layer of build material on top of the working surface through a gap formed between a lower surface of the flattening member and the working surface by relative movement of the flattening member and the working surface. In a third method step 1003, the shutter is employed for selectively opening or closing an adjacent area ahead of the lower surface of the flattening member.

(71) The method can be used in an additive manufacturing process for forming at least a portion of a three-dimensional object, wherein a subsequent layer of the three-dimensional object, having a layer thickness, is formed over a previously formed layer of the object.

(72) The recoater 1 may include a primary reservoir and a second reservoir, wherein the primary reservoir is in communication with the secondary reservoir by means of the discharge port.

(73) In an example, the recoater 1 is a powder spreading device configured to spread powder over a working surface 7 such as a build plate and/or on a previous layer. Material needed for forming the layer of build material 3 can be drained from the heap of build material 13 ahead (upstream) of the flattening member of the recoater 1 during relative movement between the recoater and the working surface 7.

(74) Herein, the invention is described with reference to specific examples of embodiments of the invention. It will, however, be evident that various modifications, variations, alternatives and changes may be made therein, without departing from the essence of the invention. For the purpose of clarity and a concise description features are described herein as part of the same or separate embodiments, however, alternative embodiments having combinations of all or some of the features described in these separate embodiments are also envisaged and understood to fall within the framework of the invention as outlined by the claims. The specifications, figures and examples are, accordingly, to be regarded in an illustrative sense rather than in a restrictive sense. The invention is intended to embrace all alternatives, modifications and variations which fall within the spirit and scope of the appended claims. Further, many of the elements that are described are functional entities that may be implemented as discrete or distributed components or in conjunction with other components, in any suitable combination and location.

(75) In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word ‘comprising’ does not exclude the presence of other features or steps than those listed in a claim. Furthermore, the words ‘a’ and ‘an’ shall not be construed as limited to ‘only one’, but instead are used to mean ‘at least one’, and do not exclude a plurality. The mere fact that certain measures are recited in mutually different claims does not indicate that a combination of these measures cannot be used to an advantage.