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Title:
PURGING NON-FUSED BUILD MATERIAL
Document Type and Number:
WIPO Patent Application WO/2017/194117
Kind Code:
A1
Abstract:
A build material management system for a 3D printing system is described in which a non- fused purged build material port is to output purged non-fused build material from a build material transportation system. An emptying of substantially all non-fused build material from at least a portion of the build material transportation system to the non-fused purged build material port in response to a received purge signal is controlled by processing circuitry of the build material management system.

Inventors:
CHANCLON, Ismael (Cami de Can Graells, 1-21, Sant Cugat del Valles, 08174, ES)
ALONSO, Xavier (Cami de Can Graells, 1-21, Sant Cugat del Valles, 08174, ES)
NICOLAU, Marc (Cami de Can Graells, 1-21, Sant Cugat del Valles, 08174, ES)
MORROS, Marc (Cami de Can Graells, 1-21, Sant Cugat del Valles, 08174, ES)
MIGUEL, Xavier (Cami de Can Graells, 1-21, Sant Cugat del Valles, 08174, ES)
Application Number:
EP2016/060686
Publication Date:
November 16, 2017
Filing Date:
May 12, 2016
Export Citation:
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Assignee:
HEWLETT-PACKARD DEVELOPMENT COMPANY, L.P., (11445 Compaq Center Drive West, Houston, Texas, 77070, US)
CHANCLON, Ismael (Cami de Can Graells, 1-21, Sant Cugat del Valles, 08174, ES)
ALONSO, Xavier (Cami de Can Graells, 1-21, Sant Cugat del Valles, 08174, ES)
NICOLAU, Marc (Cami de Can Graells, 1-21, Sant Cugat del Valles, 08174, ES)
MORROS, Marc (Cami de Can Graells, 1-21, Sant Cugat del Valles, 08174, ES)
MIGUEL, Xavier (Cami de Can Graells, 1-21, Sant Cugat del Valles, 08174, ES)
International Classes:
B29C67/00; B08B5/04; B08B9/035
Attorney, Agent or Firm:
CUNDY, Jack (HGF Limited, Fountain Precinct,,Balm Green, Sheffield Yorkshire S1 2JA, S1 2JA, GB)
Download PDF:
Claims:
CLAIMS

1 . A build material management system, for a 3D printing system, the build material management system comprising:

a build material transportation system;

a non-fused purged build material port to output purged non-fused build material from the build material transportation system; and

processing circuitry to control an emptying of substantially all non-fused build material from at least a portion of the build material transportation system to the non-fused purged build material port in response to a received purge signal.

2. A build material management system as claimed in claim 1 , comprising:

a build material storage container connected to the build material transportation system, the build material storage container to store non-fused build material; and

processing circuitry to control a routing of substantially all non-fused build material from the build material storage container to the non-fused purged build material port, via the build material transportation system.

3. A build material management system as claimed in claim 1 , comprising:

a collection area;

a collection area port connected to the build material transportation system and to receive non-fused build material from the collection area; and

processing circuitry to control a routing of substantially all non-fused build material from the collection area to the non-fused purged build material port via the collection area port and the build material transportation system.

4. A build material management system as claimed in claim 1 , wherein the build material transportation system comprises:

a conduit network connected to the non-fused purged build material port; and a pump connected to the conduit network to provide a pressure differential across the conduit network,

wherein the processing circuitry to control a routing of substantially all non-fused build material comprises: processing circuitry to control the pump to transport the non-fused build material within the conduit network towards the non-fused purged build material port via the conduit network. 5. A build material management system as claimed in claim 4, wherein a first portion of the conduit network comprises a collection hose to be connected to a second portion of the conduit network, and wherein the pump is to provide the pressure differential across the second portion of the conduit network via the collection hose, and

wherein the processing circuitry to control the pump comprises processing circuitry to control the pump to transport the non-fused build material within the second portion of the conduit network towards the non-fused purged build material port via the collection hose of the conduit network.

6. A build material management system as claimed in claim 4, wherein the conduit network comprises at least one valve to selectively connect at least a portion of the conduit network to the non-fused purged build material port, and wherein the processing circuitry to control the emptying of substantially all non-fused build material comprises processing circuitry to control an operation of the valve(s) to selectively control the emptying of substantially all non-fused build material from at least a portion of the build material transportation system.

7. A build material management system as claimed in claim 1 , further comprising: a non-fused build material inlet port to connect to a further build material container; and

processing circuitry to produce the purge signal in response to the presence or absence of the further build material container.

8. A build material management system as claimed in claim 7, further comprising processing circuitry to produce the purge signal in response to the presence of a non- compatible build material in the further build material container, not compatible with the non-fused build material in the portion of the build material transportation system.

9. A build material management system as claimed in claim 1 , further comprising processing circuitry to control a cycling of substantially all the non-fused build material from at least the portion of the build material transportation system a plurality of times through the portion of the build material transportation system.

10. A build material management system as claimed in claim 9, wherein the processing circuitry controls the cycling in response to a non-compatible build material indicator indicative of the presence of a non-compatible build material in a further build material container to be connected to the build material management system, wherein the non- compatible material is not compatible with the non-fused build material in the portion of the build material transportation system. 1 1 . A build material management system as claimed in claim 1 , further comprising a sacrificial material inlet port to receive sacrificial material from a source of sacrificial material; and

processing circuitry to control a transporting of the sacrificial material to the portion of the build material transportation system comprising the non-fused build material.

12. A method of purging non-fused build material in a build material management system for a 3D printing system, the method comprising:

receiving a purge signal;

in response to the received purge signal, controlling an emptying of substantially all non-fused build material from at least a portion of a build material transportation system through a non-fused purged build material port, the non-fused purged build material port to output purged non-fused build material from the build material transportation system.

13. A method of purging non-fused build material as claimed in claim 12, wherein the build material transportation system comprises:

a conduit network connected to the non-fused purged build material port; and a pump connected to the conduit network to provide a pressure differential across the conduit network, wherein the method comprises:

controlling the pump to transport the non-fused build material within the conduit network towards the non-fused purged build material port via the conduit network.

14. A method of purging non-fused build material as claimed in claim 13, wherein a first portion of the conduit network comprises a collection hose to be connected to a second portion of the conduit network, and wherein controlling the pump to transport the non-fused build material comprises: controlling the pump to provide the pressure differential across the second portion of the conduit network via the collection hose to transport the non-fused build material within the second portion of the conduit network towards the non-fused purged build material port via the collection hose of the conduit network.

15. A method of purging non-fused build material as claimed in claim 13, wherein the conduit network comprises at least one valve to selectively connect at least a portion of the conduit network to the non-fused purged build material port, and wherein controlling the emptying of substantially all non-fused build material comprises:

controlling an operation of the valve(s) to selectively control the emptying of substantially all non-fused build material from at least a portion of the build material transportation system.

16. A method of purging non-fused build material as claimed in claim 12, wherein the method comprises cycling substantially all of the non-fused build material from at least the portion of the build material transportation system through the portion of the build material transportation system a plurality of times.

17. A method of purging non-fused build material as claimed in claim 16, further comprising determining a non-compatible build material indicator indicative of the presence of non-compatible build material in a further build material container to be connected to the build material management system, the non-compatible build material being not compatible with the non-fused build material in the portion of the build material

transportation system, and wherein the cycling is in response to the determination of the non-compatible build material indicator.

18. A method of purging non-fused build material as claimed in claim 12, wherein the build material management system further comprises a sacrificial material inlet port to receive a sacrificial material from a source of sacrificial material, the sacrificial material inlet port connected to at least the portion of the build material transportation system, and wherein the method comprises:

in response to the received purge signal, controlling a routing of the sacrificial material through the non-fused purged build material port via at least the portion of the build material transportation system, whereby to output substantially all the non-fused build material from at least the portion of the build material transportation system.

19. A non-transitory machine-readable storage medium encoded with instructions executable by a processor in a build material management system for a 3D printing system, the machine-readable storage medium comprising:

instructions to control a routing of substantially all non-fused build material from at least a portion of a build material transportation system to a non-fused purged build material port in response to a received purge signal, the non-fused purged build material port to output purged non-fused build material from the build material transportation system. 20. A non-transitory machine-readable storage medium as claimed in claim 19, the build material management system comprising:

a conduit network connected to the non-fused purged build material port; and a pump connected to the conduit network to provide a pressure differential across the conduit network, and

wherein the non-transitory machine-readable storage medium comprises:

instructions to control the pump to transport the non-fused build material within the conduit network towards the non-fused purged build material port via the conduit network.

21 . A non-transitory machine-readable storage medium as claimed in claim 20, wherein a first portion of the conduit network comprises a collection hose to be connected to a second portion of the conduit network, and wherein the pump is to provide the pressure differential across the second portion of the conduit network via the collection hose, and wherein the instructions to control the pump comprises:

instructions to control the pump to transport the non-fused build material within the second portion of the conduit network towards the non-fused purged build material port via the collection hose of the conduit network.

Description:
PURGING NON-FUSED BUILD MATERIAL

BACKGROUND

[0001] Additive manufacturing systems that generate three-dimensional objects on a layer-by-layer basis have been proposed as a potentially convenient way to produce three- dimensional objects in small quantities.

[0002] The cleaning of additive manufacturing systems varies. Generally, low quality objects are produced by additive manufacturing systems that receive limited cleaning.

BRIEF DESCRIPTION

[0003] Examples of the present disclosure are further described hereinafter with reference to the accompanying drawings, in which:

Figure 1 A is a diagram of an example 3D printing system which may make use of the present disclosure;

Figure 1 B is a schematic illustrating the material management station shown in the example shown in Figure 1A;

Figure 1 C is a diagram of an example of a working area of the material management station in the example shown in Figure 1 B;

Figure 2A is an internal circuit diagram of an example of a material management system shown in Figures 1A, 1 B and 1 C;

Figure 2B is a table schematically illustrating valve setting information for the material management station internal circuit of Figure 2A;

Figure 2C schematically illustrates a build material trap geometry used in containers of the material management station internal circuit of Figure 2A;

Figure 3 is a simplified illustration of a build material management system according to one example; and

Figure 4 is a flow diagram outlining a method of operating a build material management system according to one example.

DETAILED DESCRIPTION

[0004] As shown in Figure 1A, the 3D printing system 100 (or additive manufacturing system) according to one example comprises: a trolley 102, a 3D printer 104 and a material management system in the form of a material management station 106. The material management station 106 manages build material. [0005] The trolley 102 is arranged to slot into a docking position in the printer 104 to allow the printer 104 to generate a 3D object within the trolley. The trolley is also arranged to also slot (at a different time) into a docking position 107 in the material management station 106. The trolley 102 may be docked in the material management station 106 prior to a 3D printing process to load the trolley with build material in preparation for a subsequent 3D printing process.

[0006] The build material loaded into the trolley may include recycled or recovered build material from a previous printing process, fresh build material or a portion of fresh and recycled build material. Some build materials may be non-recyclable and hence in this case no recovered build material will be used to load the trolley. The build material may be or include, for example, powdered metal materials, powdered composited materials, powder ceramic materials, powdered glass materials, powdered resin material, powdered polymer materials and the like. In some examples where the build material is a powder- based build material, the term powder-based materials is intended to encompass both dry and wet powder-based materials, particulate materials and granular materials. It should be understood that the examples described herein are not limited to powder-based materials, and may be used, with suitable modification if appropriate, with other suitable build materials. In other examples, the build material may be in the form of pellets, or any other suitable form of build material, for instance.

[0007] Returning to Figure 1A, the trolley 102 may also be docked in the docking position 107 in the material management station 106 (shown without the trolley 102 docked in Figure 1A) to clean up at least some components of the trolley 102 after it has been used in a 3D printing production process. The clean-up process may involve recovery and storage in the material management station 106 of non-fused build material from the previous print job for subsequent reuse. During a 3D printing process a portion of the supplied build material may be fused to form the 3D object, whilst a remaining portion of the supplied build material may remain non-fused and potentially recyclable, depending upon the type of build material used. Some processing of the non-fused build material may be performed by the material management station 106 prior to storage for recycling, to reduce any agglomeration for example.

[0008] It will be understood that the material management station 106 may also include an access panel (not shown) to cover the docking position 107 when the trolley 102 is fully docked with the material management station 106 and when the trolley 102 is fully removed from the material management station 106.

[0009] One material management station 106 can be used to service any number of different 3D printers. A given 3D printer may interchangeably use any number of trolleys 102, for example, utilising different trolleys for different build materials. The material management station 106 can purge a trolley 102 of a given build material after a 3D printing production process, allowing it to be filled with a different build material for a subsequent 3D printing production run. Purging of the trolley 102 may also involve purging of the material management station 106 or alternatively, it may involve separation of different build materials in the material management station 106 to prevent contamination of one build material type with another.

[0010] The trolley 102 in this example has a build platform 122 on which an object being manufactured is constructed. The trolley 102 also comprises a build material store 124 situated beneath a build platform 122 in this example. The build platform 122 may be arranged to have an actuation mechanism (not shown) allowing it, when it is docked in the printer 104 and during a 3D printing production process, to gradually move down, such as in a step-wise manner, towards the base of the trolley 102 as the printing of the 3D object progresses and as the build material store 124 within the trolley 102 becomes depleted. This provides progressively more distance between the base level of the build platform 122 and the print carriages (not shown) to accommodate the 3D object being manufactured. The size of an object being printed may increase progressively as it is built up layer-by- layer in the 3D printing process in this example.

[0011] The 3D printer 104 of this example can generate a 3D object by using a build material depositor carriage (not shown) to form layers of build material onto the build platform 122. Certain regions of each deposited layer are fused by the printer 104 to progressively form the object according to object-specifying data. The object-specifying data are based on a 3D shape of the object and may also provide object property data such as strength or roughness corresponding to the whole object or part(s) of the 3D object. In examples, the desired 3D object properties may also be supplied to the 3D printer 104 via a user interface, via a software driver or via predetermined object property data stored in a memory.

[0012] After a layer of the build material has been deposited on the build platform 122 by the printer 104, a page-wide array of thermal (or piezo) printheads on a carriage (not shown) of the 3D printer 104 can traverse the build platform 122 to selectively deposit a fusing agent in a pattern based on where particles of the build material are to fuse together. Once the fusing agent has been applied, the layer of build material may be exposed to fusing energy using a heating element (not shown) of the 3D printer 104. The build material deposition, fusing agent and fusing energy application process may be repeated in successive layers until a complete 3D object has been generated. The material management station 106 may be used with any additive manufacturing technique and is not limited to printers using printheads on a carriage to deposit a fusing agent as in the example described above. For example, the material management station 106 may be used with a selective laser sintering additive manufacturing technique.

[0013] Figure 1 B schematically illustrates the material management station 106 of the example of Figure 1A, with the trolley 102 of Figure 1A docked therein.

[0014] As shown in the example of Figure 1 B, the material management station 106 has two interfaces for receiving two fresh build material supply containers (or cartridges) 1 14a, 1 14b, which may be releasably insertable in the material management station 106. In this example, each fresh build material supply container 1 14a, 1 14b has a capacity of between about thirty and fifty litres. In one example, the build material may be a powdered semi- crystalline thermoplastic material. The provision of two fresh build material supply containers 1 14a, 1 14b allows "hot swapping" to be performed such that if a currently active container becomes empty or close to empty of build material when the trolley 102 is being filled with build material by the material management station 106 in preparation for an additive manufacturing process, a fresh build material supply source can be dynamically changed to the other of the two containers. The material management system 106 may have any number of weight measurement devices to assess how much fresh build material is present at a given time in any of the fresh build material supply containers 1 14a, 1 14b. The fresh build material from the containers 1 14a, 1 14b, may be consumed, for example, when loading the trolley 102 with build material prior to the trolley 102 being installed in the printer 104 for a 3D printing production run.

[0015] Build material is moved around within the material management station 106 in this example using a vacuum system (described below with reference to Figure 2A), which promotes cleanliness within the system and allows for recycling of at least a portion of build material between successive 3D printing jobs, where the type of build material selected for use is recyclable. References to a vacuum system in this specification include a vacuum that is partial vacuum or a pressure that is reduced, for example, relative to atmospheric pressure. The vacuum may correspond to "negative pressure", which can be used to denote pressures below atmospheric pressure in a circuit surrounded by atmospheric pressure.

[0016] A total trolley-use time for printing of a 3D object before trolley 102 can be reused may depend upon both a printing time of the printer 104 when the trolley 102 is in the printer 104 and a cooling time of the contents of the build volume of the trolley 102. It will be understood that the trolley 102 can be removed from the printer 104 after the printing operation, allowing the printer 104 to be re-used for a further printing operation using build material within a different trolley before the total trolley-use time has elapsed. The trolley 102 can be moved to the material management station 106 at the end of the printing time. The vacuum system can be used, in some examples, to promote more rapid cooling of the contents of the build volume following a 3D print production process than would otherwise occur without the vacuum system. Alternative examples to the vacuum system such as a compressed air system can create excess dust, potentially making the clean-up process more difficult.

[0017] The material management station 106 in this example has a recovered build material container 108 (see Figure 1 B), located internally, where build material recovered from the trolley 102 by the vacuum system is stored for subsequent reuse, if appropriate. Some build materials may be recyclable whilst others may be non-recyclable. In an initial 3D printing production cycle, 100% fresh build material may be used. However, on second and subsequent printing cycles, depending upon build material characteristics and user choice, the build material used for the print job may comprise a proportion of fresh build material (e.g. 20%) and a portion of recycled build material (e.g. 80%). Some users may elect to use mainly or exclusively fresh build material on second and subsequent printing cycles, for example, considering safeguarding a quality of the printed object. The internal recovered build material container 108 may become full during a post-production clean-up process, although it may become full after two or more post-production clean up processes have been performed, but not before. Accordingly, an overflow container in the form of an external overflow container 1 10 can be provided as part of the material management station 106 to provide additional capacity for recovered build material for use once the internal recovered build material container 108 is full or close to full capacity. Alternatively, the external overflow container 1 10 can be a removable container. In this example, any number of ports can be provided as part of the material management station 106 to allow for output of or reception of build material to and/or from the external overflow container 1 10. A sieve 1 16 or alternative build material refinement device may be provided for use together with the internal recovered build material container 108 to make non-fused build material recovered from a 3D printing production process for recycling more granular, that is, to reduce agglomeration (clumping).

[0018] The material management station 106 in this example has a mixing container (or blending container) 1 12 comprising a mixing blade (not shown) for mixing recycled build material from the internal recovered build material container 108 with fresh build material from one of the fresh build material supply containers 1 14a, 1 14b for supply to the trolley 102 when it is loaded prior to a printing production process. The mixing container (or blending container) 1 12, in this example, is provided on top of the material management station 106, above the location of the build platform 122 when the trolley 102 is docked therein. The mixing container 1 12 is connected to a mixer build material trap 1 13 (described below with reference to Figure 2A) for input of build material into the mixing container 1 12.

[0019] The fresh build material supply containers 1 14a, 1 14b, the external overflow container 1 10 and the main body of the material management station 106 may be constructed to fit together in a modular way, permitting a number of alternative geometrical configurations for the fully assembled material management station 106. In this way, the material management station 106 is adaptable to fit into different housing spaces in a manufacturing environment.

[0020] The fresh build material supply containers 1 14a, 1 14b may be releasably connected to the main body of the material management station 106 via respective supply container connectors 134a, 134b. These supply container connectors 134a, 134b may incorporate a security system to reduce the likelihood of unsuitable build material being used in the 3D printing system. In one example, suitable fresh build material supply containers 1 14a, 1 14b are provided with a secure memory chip, which can be read by a chip reader (not shown) or other processing circuitry on the main body of the material management station 106 to verify the authenticity of any replacement supply container (cartridge) 1 14a, 1 14b that has been installed. In this example, the chip reader may be provided on the supply container connectors 134a, 134b and upon attachment of the fresh build material supply containers 1 14a, 1 14b to the respective connector 134a, 134b, an electrical connection may be formed. The processing circuitry in the material management station 106 may also be used to write a measured weight of build material determined to be in the respective fresh build material supply container(s) 1 14a, 1 14b onto the secure memory chip of the container to store and/or update that value. Thus, the amount of build material remaining in the fresh build material supply container(s) 1 14a, 1 14b at the end of a trolley loading process can be recorded. This allows re-filling of a fresh build material supply container to be detected.

[0021] The secure memory chip of the fresh build material supply containers 1 14a, 1 14b can store a material type of the build material contained within the fresh build material supply containers. In one example, the material type is the material (e.g. ceramic, glass, resin, etc.). In this way, the material management station 106 can determine the material type to be used by the material management station 106.

[0022] Figure 1 C schematically illustrates a working area of the material management station 106 of the example of Figure 1 B, showing the build platform 122 of the trolley 102 and a build material loading hose 142, which provides a path between the mixing container 1 12 of Figure 1 B and the build material store 124 of the trolley 102. The loading hose 142 is used for loading the trolley 102 with build material prior to the trolley 102 being used in the printer 104. Figure 1 C also shows a recycling hose 144 for unpacking manufactured 3D objects, cleaning the build platform 122 of the trolley 102 and a surrounding working area within the material management station 106. In one example, the recycling hose 144 operates by suction provided via a pump 204 (see Figure 2A) and provides an enclosed path to the recovered build material container 108 (see Figure 1 B) for receiving and holding build material for re-use in a subsequent 3D printing process. The recycling hose 144 may, in one example, be operated manually by a user to recover recyclable build material from and/or to clean up a working area of the material management station 106.

[0023] Figure 2A schematically illustrates an internal circuit diagram 200 of one example of a build material management system in the form of a material management station 106. The material management station 106 can be used in conjunction with the trolley 102 of Figure 1A.

[0024] As previously described, printed parts along with non-fused build material can be transported from the 3D printer 104 to the material management station 106 via the trolley 102. The material management station 106 can then be used to process build material and printed parts from the trolley 102.

[0025] In another example, printed parts along with non-fused build material can be transported from the 3D printer 104 to the material management station 106 via another suitable container, e.g. a box or cartridge (not shown) instead of the trolley 102. The material management station 106 may then be used to process the powder-based material and printed parts from the container.

[0026] A build material transportation system in the form of a material management station circuit 200 includes a conduit (or guide-channel) network and a pump 204 to provide a pressure differential across the conduit network to transport non-fused build material between different components, as described below with reference to Figure 2A. In this example, the pump 204 is a suction pump which operates to create a pressure differential across the suction pump to produce air flow from an air inlet at substantially atmospheric pressure through the conduit network towards an upstream side of the suction pump (at a pressure below atmospheric pressure or at "negative pressure"). The pump 204 may be provided as an integral part of the material management station 106 in one example, but in another example, the material management station 106 provides a negative/reduced pressure interface, via which a suction pump may be detachably coupled or coupled in a fixed configuration. Although the description below refers to first conduit, second conduit, third conduit, etc. of the conduit network, there is no implied ordering in the number of the conduits other than to distinguish one conduit from another. [0027] A collection hose 206 is connected to a recovered build material container (RBMT) 208 via a working area port in a working area 203 in the form of a working area inlet port 273 and a first conduit (hose-to-RBMT conduit) 272 of the conduit network. The recovered build material container 208 includes a recovered build material container (RBMT) inlet area comprising a recovered build material container (RBMT) build material trap 218b and a recovered build material container (RBMT) material outlet. The RBMT inlet area is where a fluidised flow of build material is received for storage in the recovered build material container 208. The first conduit 272 provides a path between the working area inlet port 273 and the RBMT inlet area. The working area inlet port 273 is to receive build material from the collection hose 206 and is provided at an end of the first conduit 272 connected to the collection hose 206. In other examples, the RBMT inlet area may communicate directly with the working area 203 or the collection hose 206 without a first conduit 272 between.

[0028] The recovered build material container 208 in this example is provided internally to the material management station 106. A hose-to-RBMT valve 242 is positioned along the first conduit 272 for opening and closing the path through the first conduit 272. The collection hose 206 extends from the working area inlet port 273 into the working area 203. The working area 203 includes at least a portion of the trolley 102 (or other container) and can be maintained at substantially atmospheric pressure. Build material from the trolley 102 can be collected by the collection hose 206 and transported to the recovered build material container 208 through the first conduit 272. The recovered build material container 208 can be used for storing any non-fused build material from the trolley 102 that is suitable for being used again in a further 3D printing (additive manufacturing) process. In this way, the recovered build material container 208 can be used as a buffer storage container to temporarily store non-fused build material prior to supplying the non-fused build material for use in a further 3D printing (additive manufacturing) process.

[0029] A second conduit 274 (hose-to-overflow conduit) of the conduit network connects the collection hose 206 to an overflow container 210. The overflow container 210 includes an overflow inlet area and the second conduit 274 provides a path between the collection hose 206 and the overflow inlet area comprising, in this example, an overflow build material trap 218a (a filter). An overflow container port in the form of an overflow container outlet port 275 may also be provided at an end of the second conduit 274. The overflow container 210 can be selectively sealed by an openable lid (not shown). In a sealed configuration, the overflow container 210 is in fluid communication with one or more overflow inlet ports and overflow outlet ports of the conduit network. Furthermore, in the sealed configuration, the overflow container 210 is not directly open to the atmosphere. Build material from the working area 203 can be transported through the second conduit 274 and overflow container outlet port 275 into the overflow container 210. A hose-to- overflow valve 244 is positioned along the second conduit 274 for opening and closing a path through the second conduit 274. Non-fused build material from the trolley 102 (or other container) can be collected by the collection hose 206 and transported to the overflow container 210 through the first conduit 272. The overflow container 210 is an external container that is removable and that can be used for storing excess recoverable (recyclable) build material when the recovered build material container 208 is full. Alternatively, the overflow container 210 can be used as a waste storage container to store non-fused build material from the trolley 102 that is not suitable for recycling. In a further alternative, the overflow container 210 can be used as a purged build material storage container to store non-fused build material from the trolley 102 and from elsewhere in the material management station 106 when the material management station 106 is purged of non-fused build material.

[0030] The pump 204 is connected via a third conduit (pump-to-RBMT conduit) 276 of the conduit network to the recovered build material container 208. The third conduit 276 provides a path between the pump 204 and the RBMT inlet area. A RBMT-to-pump valve 246 is positioned along the third conduit 276 for opening and closing the path through the third conduit 276.

[0031] The pump 204 is also connected to the overflow container 210 via a fourth conduit (pump-to-overflow conduit) 278 of the conduit network. The fourth conduit 278 provides a path between the pump 204 and the overflow inlet area. An overflow container port in the form of an overflow container vacuum port 279 may also be provided at an end of the fourth conduit 278. Fluid, e.g. air, can transmit through the overflow container vacuum port 279 from the overflow inlet area towards the pump 204. An overflow-to-pump valve 248 is positioned along the fourth conduit 278 for opening and closing a path through the fourth conduit 278.

[0032] Non-fused build material in the trolley 102 can be collected using the collection hose 206 and transported either to the recovered build material container 208 or to the overflow container 210, or both. The container to be used at a given time can be selected by opening appropriate valves along the conduits of the circuit of Figure 2A.

[0033] The valves described herein with reference to Figure 2A may be controlled by a controller 295, which may be, for example a programmable logic controller forming a part of processing circuitry of the build material management station 106. The controller 295 may electronically open any number of valves to open any number of paths in respective conduits based on the material transport operation being performed. The controller 295 may also electronically close any number of valves to close any number of paths in respective conduits. The valves may be, for example, butterfly valves and may be actuated using compressed air. In another example, any number of valves may be opened and closed manually by a user.

[0034] The controller controls the general operation of the material management system 200. The controller may be a microprocessor-based controller that is coupled to a memory (not shown), for example via a communications bus (not shown). The memory stores machine executable instructions. The controller 295 may execute the instructions and hence control operation of the build material management system 200 in accordance with those instructions.

[0035] Figure 2B is a table schematically illustrating for each of a number of different build material source locations and build material destination locations, an appropriate valve configuration corresponding the valves as labelled in Figure 2A. A tick in an appropriate column of the table indicates that the corresponding valve is controlled to be open by the controller 295 for the particular build material transport operation. For example, when transporting build material from the recovered build material container 208 to the mixing container 212, the valves 256, 258 and 254 are set by the controller 295 to be open, whereas the valves 250, 244, 276, 248, 242, 262, 260, 252a and 252b are set to be closed. In alternative examples, some valves may be set to be open by simultaneity.

[0036] In an example, a recyclability indicator is determined by processing circuitry of the build material management station 106. The recyclability indicator can be indicative of whether the build material in the trolley 102 (or other container) includes recyclable or recoverable material. When it is determined that the non-fused build material in the trolley 102 is not recyclable or when the recovered build material container 208 is full, the non- fused build material can be transported to the overflow container 210.

[0037] To transport the non-fused build material from the trolley 102 (or other container) to the overflow container 210, the hose-to-overflow valve 244 in the second conduit 274 between the collection hose 206 and the overflow container 210 and the overflow-to-pump valve 248 in the fourth conduit 278 between the pump 204 and the overflow container 210 can be opened, e.g. electronically by the controller 295. When the pump is active, a differential pressure is provided from the pump to the collection hose 206. That is, a pressure at the pump 204 is lower than a pressure at the collection hose 206. The differential pressure enables build material from the trolley 102 (or container) to be transported to the overflow container 210. Build material (and air) in proximity with an end of the collection hose 206 (at approximately atmospheric pressure) is transported from the collection hose 206, along the second conduit 274 and through the hose-to-overflow valve 244 to overflow container 210. The overflow container 210 is provided in the sealed configuration. At the overflow container 210, build material separates from air flow and drops from the overflow inlet area into the overflow container 210. Air (and any residual build material) continues along the fourth conduit 278 and through the overflow-to-pump valve 248 towards the pump 204, which is at a reduced pressure.

[0038] To help prevent non-fused build material traveling through the overflow inlet area of the overflow container 210 into the fourth conduit 278 towards the pump 204, the overflow inlet area can include an overflow build material trap 218a (e.g. a powder trap). The overflow build material trap 218a is arranged to collect build material from the second conduit 274 and divert the build material (e.g. powder) into the overflow container 210. Thus, the overflow build material trap 218a helps prevent build material conveying past the overflow inlet area of the overflow container 210 and entering the fourth conduit 278 via the overflow container vacuum port 279 to travel towards the pump 204.

[0039] The overflow build material trap 218a may include a filter (e.g. a mesh), which collects build material transported from the overflow container 210. Thus, the filter separates build material from air flow in the overflow inlet area. Holes in the filter are small enough to prevent the passage of at least 95% of build material but allow relatively free flow of air through the filter. Holes in the filter may be small enough to prevent the passage of at least 99% of build material, whilst still allowing relatively free flow of air through the filter. Build material collected by the filter may drop from the overflow inlet area into the overflow container 210.

[0040] Recoverable non-fused build material in the trolley 102 (or other container) can be transported to the recovered build material container 208 in a similar way. To transport the non-fused build material from the trolley 102 to the recovered build material container 208, the hose-to-RBMT valve 242 in the first conduit 272 between the collection hose 206 and the recovered build material container 208 and the RBMT-to-pump valve 246 in the third conduit 276 between the pump 204 and the recovered build material container 208 can be opened electronically by the controller 295 as described above. When the pump is active, a differential pressure is provided from the pump to the collection hose 206. That is, a pressure at the pump 204 is lower than a pressure at the collection hose 206. The differential pressure enables build material from the trolley 102 (or container) to be transported to the recovered build material container 208. Build material (and air) in proximity with an end of the collection hose 206 (at approximately atmospheric pressure) is transported from the collection hose 206, along the first conduit 272 and through the hose- to-RBMT valve 242 to the recovered build material container 208. At the recovered build material container 208, build material separates from air flow and drops from the RBMT inlet area into the recovered build material container 208. Air (and any residual build material) continues along the third conduit 276 and through the RBMT-to-pump valve 246 towards the pump 204, which is at reduced pressure relative to atmospheric pressure.

[0041] Each of the recovered build material container 208, the overflow container 210, and the mixing container 213 has a build material trap 218b, 218a and 218c respectively. These build material traps 218a, 218b, 218c perform cyclonic filtration of an incoming fluidised flow of build material and air as schematically illustrated in Figure 2C. An inlet 296 of the build material trap 218 receives the fluidised flow of build material and the build material is pushed by a centrifugal force created by suction of the pump 204 to an outer wall 297 of the build material trap 218. In one example, the outer wall 297 of the build material trap 218 has a circular cross-section and the incoming build material migrates via a cyclonic action to the outer wall 297 of the build material trap 218 until the incoming air reaches an exit below, whereupon the build material particles drop down into a vacuum sealed recipient 299 in the build material trap 218. Thus the build material trap 218 separates a fluidised flow of build material into a powder component, which is deposited in the associated container and an air component, which is sucked towards the pump 204 via an air outlet 298 in the build material trap 218 providing an interface to the pump 204. A filter (not shown) may be provided in the air outlet 298 of the build material trap 218 to reduce the likelihood of any remaining build material reaching the pump 204 in the separated air flow. The build material trap 218 provides efficient powder separation via its geometry that promotes formation of a cyclone within the build material trap in use. It offers transportation of build material in an air flow and storage of the powder in a container, whilst diverting an air flow out of the container towards the pump 204. The build material trap provides a filter to capture residual powder in an air flow emerging from the cyclone to prevent it from reaching the pump 204. The build material trap 218 is one example of a build material filter having a function of separating an air from a build material flow at a corresponding container inlet area. In other examples, the air flow is separated from the fluidised build material upon arrival at a destination container using a filter other than a cyclonic filter. For example, a diffusion filter may be used.

[0042] Returning to Figure 2A, the RBMT inlet area of the recovered build material container 208 may also include the RBMT build material trap 218b (e.g. a powder trap) or another type of RBMT build material filter to separate build material and air from an incoming fluidised flow of build material. The RBMT build material trap 218b operates in the same or a similar way as the overflow build material trap 218a in the overflow container 210, to help collect and divert build material into the recovered build material container 208 to help prevent build material from traveling through the third conduit 276 towards the pump 204.

[0043] When collecting material from the trolley 102 via the collection hose 206, as described above, a user can move the end of the collection hose 206 around the working area 203 including the trolley 102 to collect as much build material from the trolley 102 as possible.

[0044] The recovered build material container 208 is also connected via a fifth conduit (overflow-to-RBMT conduit) 280 of the conduit network. An overflow container port in the form of an overflow container inlet port 281 may also be provided at an end of the fifth conduit 280. Build material from the overflow container 210 can be transported through the fifth conduit 280 and overflow container inlet port 281 into the recovered build material container 208.

[0045] The fifth conduit 280 between the recovered material container 208 and the overflow container inlet port 281 includes an overflow-to-RBMT valve 250 in the path leading to the RBMT build material trap. In the event that the recovered build material container 208 is to be refilled with recovered build material, the overflow-to-RBMT valve 250 in the fifth conduit 280 between the recovered build material container 208 and the overflow container 210 can be opened, along with the RBMT-to-pump valve 246 in the third conduit 276 between the recovered build material container 208 and the pump 204. Each of the valves can be opened electronically by the controller 295, as described above. When the pump is active, a differential pressure is provided from the pump to the overflow container 210. That is, a pressure at the pump 204 is lower than a pressure at the overflow container 210. In this example, the overflow container 210 is provided in an unsealed configuration and includes an air inlet (not shown) open to atmosphere to maintain approximately atmospheric pressure within the overflow container 210. The differential pressure enables build material from the overflow container 210 to be transported to the recovered build material container 208. Air flows into the overflow container 210 through the air inlet. Build material (and air) in the overflow container is transported from the overflow container 210, along the fifth conduit 280 and through the overflow-to-RBMT valve 250 to the recovered build material container 208. At the recovered build material container 208, build material separates from air flow and drops from the RBMT inlet area into the recovered build material container 208. Air (and any residual build material) continues along the third conduit 276 and through the RBMT-to-pump valve 246 towards the pump 204, which is at a reduced pressure.

[0046] The material management station circuit 200 also includes a mixing container 212. The mixing container 212 can be used to mix recovered build material from the recovered build material container 208 with fresh build material from a fresh build material supply container 214a or 214b, ready to be used in a 3D printing process.

[0047] Although two fresh build material supply containers 214a, 214b are shown in this example, in other examples, any number of fresh build material supply containers 214a, 214b may be used. More fresh build material supply containers 214a, 214b may be used when appropriate.

[0048] Each fresh build material supply container 214a, 214b is connected to the mixing container 212 via a sixth conduit (a fresh build material conduit) 282 of the conduit network and a fresh build material supply container port 283a, 283b. The fresh build material supply container port 283a, 283b is to output build material from the respective fresh build material supply container 214a, 214b. Each fresh build material supply container 214a, 214b has an associated material supply container cartridge-to-mixer valve 252a, 252b in the sixth conduit 282 between the respective fresh build material supply container 214a, 214b and the mixing container 212. Each fresh build material supply container 214a, 214b also includes an air inlet valve whereby to ensure air can enter the fresh build material supply container 214a, 214b to maintain air pressure within the fresh build material supply container 214a, 214b at approximately atmospheric pressure.

[0049] The mixing container 212 is connected via a seventh conduit (pump-to-mixer conduit) 284 of the conduit network to the pump 204. The seventh conduit 284 between the mixing container 212 and the pump 204 includes a mixer-to-pump valve 254, which may be opened or closed to open and close the passage through the seventh conduit 284.

[0050] To transport fresh build material from the fresh build material supply container 214a or 214b to the mixing container 212, the material supply container cartridge-to-mixer valve 252a or 252b and the mixer-to-pump valve 254 in the seventh conduit 284 between the mixing container 212 and the pump 204 are opened. Each of the valves can be opened electronically by the controller 295, as described above. When the pump 204 is active, a differential pressure is provided from the pump 204 to the fresh build material supply container 214a or 214b. That is, a pressure at the pump 204 is lower than a pressure at the fresh build material supply container 214a or 214b. The differential pressure enables build material from the fresh build material supply container 214a or 214b to be transported to the mixing container 212. Build material (and air) in the fresh build material supply container 214a or 214b is transported from the fresh build material supply container 214a or 214b, along the sixth conduit 282 and through the cartridge-to-mixer valve 252a or 252b to the mixing container 212. At the mixing container 212, build material separates from air flow and drops from the mixer inlet area into the mixing container 212. Air (and any residual build material) continues along the seventh conduit 284 and through the mixer-to- pump valve 254 towards the pump 204, which is at a reduced pressure.

[0051] The mixer inlet area of the mixing container 212 can also include a mixer build material trap 218c (e.g. a powder trap) or any type of mixer build material filter to separate an air flow from a build material flow, which operates in the same or similar manner to as the overflow build material trap 218a and the RBMT build material trap 218b. The mixer build material trap 218c helps to collect and divert build material into the mixing container 212, and help prevent the build material from travelling through the seventh conduit 284 towards the pump 204.

[0052] The mixing container 212 is also connected to the recovered build material container 208 via an eighth conduit (RBMT-to-mixer conduit) 286 of the conduit network and a ninth conduit 288 of the conduit network extending sequentially from the recovered build material container 208 to the mixing container 212. The ninth conduit 288 may be part of the RBMT-to-mixer conduit 286.

[0053] A sieve 216 may, in some examples, be located in the RBMT to mixer conduit 286 or between the eighth and ninth conduits 286 and 288 between the recovered build material container 208 and the mixing container 212. The sieve 216 may be used to separate agglomerates and larger parts of material from the recycled or recovered build material that is transported from the recovered build material container 208. Often, agglomerates and larger parts of material are not suitable for recycling in a further 3D printing process, so the sieve may be used to remove these parts from the build material. The sieve 216 includes an air inlet (not shown) to ensure air can enter the sieve 216 to maintain air pressure within the sieve 216 at approximately atmospheric pressure. In some examples, the RBMT-to-mixer conduit 286 may not be connected to a build material outlet of the recovered build material container 208. In other examples a conduit connecting an outlet of the recovered build material container 208 to a build material inlet in the mixer build material trap 218c of the mixing container 212 may form a closed circuit.

[0054] A RBMT-to-sieve valve 256 is located in the eighth conduit 286 between the recovered build material container 208 and the sieve 216, and a sieve-to-mixer valve 258 is located in the ninth conduit 288 between the sieve 216 and the mixing container 212. The RBMT-to-sieve valve 256 and sieve-to-mixer valve 258 may be opened or closed to open and close the passages through the eighth and ninth conduits 286, 288 between the recovered build material container 208 and the mixing container 212. The valves may be opened or closed electronically by the controller 295.

[0055] To transport build material from the recovered build material container 208 to the mixing container 212 both the RBMT-to-sieve valve 256 and the sieve-to-mixer valve 258 in the eighth and ninth conduits 286, 288 between the recovered build material container 208 and the mixing container 212 can be opened as well as the mixer-to-pump valve 254 in the seventh conduit 284 that connects the mixing container 212 to the pump 204. Build material in the recovered build material container 208 may drop down into the sieve 216 through the eighth conduit 286 by gravity, for example. When the pump 204 is active, a differential pressure is provided from the pump 204 to the sieve 216. That is, a pressure at the pump 204 is lower than a pressure at the sieve 216. The differential pressure enables build material from the recovered build material container 208 to be transported to the sieve 216 by gravity and to the mixing container 212 by suction. Build material in the recovered build material container 208 is transported through the RBMT material outlet, along the eighth conduit 286 and through the RBMT-to-sieve valve 256 to the sieve 216. Build material (and air) in the sieve 216 is transported from the sieve 216, along the ninth conduit 288 and through the sieve-to-mixer valve 258 to the mixing container 212. At the mixing container 212, build material separates from air flow and drops from the mixer inlet area into the mixing container 212. Air (and any residual build material) continues along the seventh conduit 284 and through the mixer-to-pump valve 254 towards the pump 204, which is at a reduced (negative) pressure.

[0056] A currently selected ratio of recycled build material from the recovered build material container 208 and fresh build material from the fresh build material supply container 214a or 214b can be transported to the mixing container 212 as described above. The ratio of fresh build material to recovered build material may be any selected ratio. The ratio may depend on the type of build material and/or the type of additive manufacturing process. In a selective laser sintering process the ratio could be, for example 50% fresh to 50% recovered build material. In one example of a printhead cartridge 3D printing process, the ratio may be 80% recovered to 20% fresh build material. For some build materials 100% fresh build material may be used, but for other build materials up to 100% recovered build material may be used. The fresh build material and the recovered build material can be mixed together within the mixing container 212 using, for example, a rotating mixing blade 213.

[0057] Once the fresh build material and the recovered build material are sufficiently mixed, the mixed build material can be transported from the mixing container 212 through a mixer-to-trolley valve 260, a tenth conduit (mixer-to-trolley conduit) 290 of the conduit network, a working area port in the form of a working area outlet port 291 , to the working area 203 and into the trolley 102. Build material from the mixing container 212 can pass through the working area outlet port 291 into the working area 203. The trolley 102 (or other container) can be located substantially beneath the mixing container 212 so that gravity can aid the transport of mixed build material from the mixing container 212, through the mixer-to-trolley valve 260, the tenth conduit 290, the working area outlet port 291 and the working area 203 to the trolley 102.

[0058] Once the trolley 102 is filled with enough build material for a given 3D print run, the trolley 102 can be returned to the 3D printer 104. An appropriate quantity of build material to fill the trolley 102 for a print job may be controlled by the controller 295 of the material management station 106 based on the material management station 106 sensing how much build material is in the trolley when the trolley is docked in the material management station 106 at the beginning of a trolley fill workflow. The controller may then fill the trolley with a particular quantity (dose) of build material requested by a user for a particular print job intended by the user. The dosing is achieved by using a fill level sensor (not shown) such as a load cell in the mixing container 212 to output a fill level value indicative of an amount of non-fused build material in the mixing container. The fill level sensor can include a load cell, or any other type of sensor such as a laser-based sensor, a microwave sensor, a radar, a sonar, a capacitive sensor, etc.,. When the fill level sensor is a load cell, the fill level value can be an electrical signal indicative of a mass of the non- fused build material in the storage container.

[0059] A number of different workflows may be implemented in the material management station 106. These workflows are managed by the user, but some level of automation may be provided by a data processor on the material management station 106. For example, the user may select a workflow from a digital display on the material management station 106. For users having one material management station 106 and one printer 104 an example workflow cycle may be filling the trolley 102, followed by printing a 3D object, followed by unpacking the object from a build volume in the material management station 106 followed by a subsequent print operation and a corresponding unpacking of the build volume and so on. However, the material management station 106 may serve two or more printers so that successive unpacking and trolley filling operations may be performed by the material management station 106. The user may also choose to perform the trolley filling, printing and unpacking functions in a random order.

[0060] For each of the workflow operations, a user interface of the material management station 106 may guide the user to undertake particular manual operations that may be performed as part of the workflow operation. For example, to perform an unpack operation, the user interface may instruct the user to move the collection hose 206 around the collection area 203 as described previously. In addition, the material management station 106 can automatically initiate other functions of the workflow operation. For example, to perform the unpack operation, the material management station 106 can automatically operate the pump 204 whilst the user moves the collection hose 206 around the collection area 203 to recover build material from the trolley 102. Any workflow operations the material management station 106 can perform fully automatically may be signalled to the user through the user interface without requiring user confirmation to proceed. If the workflow operation could present a potential safety risk, the otherwise fully automatic workflow operation may require user confirmation to proceed.

[0061] For example, to load the trolley 102 with build material, the user sets this workflow operation then the material management station 106 automatically launches the different operations required sequentially. The material management station 106 is controlled to send build material from the recovered build material container 208 to the mixing container 212. The material management station 106 is further controlled to send fresh build material from at least one of the fresh build material supply containers 214a, 214b to the mixing container 212. The material management station 106 is subsequently controlled to blend the mixture in the mixing container 212. The mixed build material in the mixing container 212 can then be discharged to the trolley 102. In an example, this workflow operation is completed as a batch process, and so the cycle may be continuously repeated to completely fill the trolley 102.

[0062] In some processes, a small portion (e.g. 1 %) of build material can pass through the build material traps 218a, 218b, 218c (e.g. the powder traps) and can travel towards the pump 204.

[0063] An additional RBMT build material trap 220 (e.g. a powder trap) may, in some examples, be located in an eleventh conduit (pump feed conduit) 292 of the conduit network that connects each of the third, fourth and seventh conduits 276, 278 and 284 to the pump 204. The additional RBMT build material trap 220 is connected to the RBMT inlet area. The additional RBMT build material trap 220 collects build material that may have passed through any of the overflow build material trap 218a, RBMT build material trap 218b or mixer build material trap 218c to help prevent it from reaching the pump 204. Build material collected in the additional RBMT build material trap 220 can be transported into the recovered build material container 208 by opening a trap-to-RBMT valve 262. The trap- to-RBMT valve 262 may be opened electronically by the controller 295. The RBMT build material trap 220 may operate in the same or similar way to each of the overflow, RBMT, and mixer build material traps 218a, 218b and 218c. Build material can be transported from the RBMT build material trap 220 to the recovered build material container 208 by gravity.

[0064] A pump filter 222 may also be located in a twelfth conduit 294 of the conduit network adjacent the pump 204. This pump filter 222 helps to collect any build material that may have passed through any of the overflow build material trap 218a, RBMT build material trap 218b or mixer build material trap 218c as well as the additional RBMT build material trap 220. This helps prevent the build material from reaching the pump 204, thereby reducing the likelihood of the function of the pump 204 being impaired, which could happen if large quantities of build material were to reach it.

[0065] At any time, when the material management station 106 is to be used to process build material of a different material type, for example of a different material, the material management station circuit 200 can be controlled to implement a purging process to purge substantially all build material (e.g., greater than 90% of the build material) of a current material type from the material management station circuit 200 to the overflow container 210. The fresh build material supply containers 214a, 214b can be disconnected from the build material station circuit 200 and stored to prevent wastage of fresh building material of the current material type.

[0066] In one example, the purging process is carried out when non-fused build material in the trolley 102 has already been collected using the collection hose 206 and transported either to the recovered build material container 208 or to the overflow container 210, or both. Alternatively, the purge process can include using the collection hose 206 to transport any non-fused build material in the trolley 102 to the overflow container 210, as described previously.

[0067] The purge process includes transporting any non-fused build material in the recovered build material container 208 to the overflow container 210. To transport non- fused build material from the recovered build material container 208 to the overflow container 210, the RBMT-to-sieve valve 256 and the sieve-to-mixer valve 258 in the eighth and ninth conduits 286, 288 between the recovered build material container 208 and the mixing container 212 can be opened as well as the mixer-to-trolley valve 260 in the tenth conduit 290 and the hose-to-overflow valve 244 in the second conduit 274 between the collection hose 206 and the overflow container 210 and the overflow-to-pump valve 248 in the fourth conduit 278 between the pump 204 and the overflow container 210. Any build material in the recovered build material container 208 drops down into the sieve 216 through the eighth conduit 286 by gravity. The collection hose 206 can be connected directly to the tenth conduit 290 before or after any cleaning of the non-fused build material in the trolley 102 has been completed. When the pump 204 is active, a differential pressure is provided from the pump 204 to the sieve 216 via the overflow-to-pump valve 248, the overflow container 210, the hose-to-overflow valve 244, the collection hose 206, the mixer-to-trolley valve 260, the mixing container 212 and the sieve-to-mixer valve 258. Build material in the recovered material container 208 is transported to the sieve 216 by gravity via the eighth conduit 286 and the RBMT-to-sieve valve 256. That is, a pressure at the pump 204 is lower than a pressure at the sieve 216. The differential pressure enables build material from the recovered build material container 208 to be transported to the sieve 216 and on to the overflow container 210. At the overflow container, build material separates from air flow and drops from the overflow inlet area into the overflow container 210. Air (and any residual build material) continues along the fourth conduit 278 and through the overflow-to-pump valve 248 towards the pump 204, which is at a reduced pressure. It can be seen that any non-fused build material in the sieve 216, the mixing container 212 or in any of the eighth conduit 286, the ninth conduit 288, the tenth conduit 290 or the second conduit 274 may also be transported to the overflow container 210. In this way, substantially all non-fused build material in the material management station circuit 200 can be transported to the overflow container 210.

[0068] Alternatively, the non-fused build material in the recovered build material container 208 can be transported to the trolley 102 as described previously. Subsequently, the non-fused build material in the trolley 102 can be transported to the overflow container 210, also as described previously. Thus, an alternative way to transport non-fused build material from the recovered build material container 208 to the overflow container 210 can be provided without directly connecting the collection hose 206 to the tenth conduit 290.

[0069] The purge process can also include further purging process elements where a sacrificial material is transported through any part of the conduit network of the material management station circuit 200 which may still contain at least an amount of non-fused build material of a current material type. The sacrificial material can act to dislodge at least some of the current build material remaining in the material management station circuit 200. The sacrificial material in one example may be the build material of the different build material type to be subsequently used in the material management station 106. The sacrificial material may alternatively be an inert material (e.g., silica) which is not a build material. In this way, any small amount of sacrificial material remaining in the material management station 106 at the end of the purging process is unlikely to interfere with the further operation of the material management station 106. The sacrificial material can be introduced into the material management station 106 from one or both of the fresh build material supply containers 214a, 214b. In an example, the sacrificial material can be introduced into the material management station from a separate sacrificial material supply container to be connected to the conduit network. In a further example, the sacrificial material can be supplied into the working area 203 and transported into the material management station 106 using the collection hose 206 in a similar way to that described previously for recovering build material from the trolley 102 into the recovered build material container 208.

[0070] In an example, the particular purge process to be performed can be determined based on a future intended use of the material management station 106. For example, where the material management station 106 is to be used to handle a further build material not compatible with the current (or previous) build material, further purging involving the sacrificial material can be performed.

[0071] In one example, the purge process can include cycling the non-fused build material within the material management station circuit 200 through the material management station circuit 200 a plurality of times (for example at least 3 times).

[0072] The cycling process includes transporting any non-fused build material in the recovered build material container 208 back to the recovered build material container 208 a plurality of times. Firstly, non-fused build material is transported from the recovered build material container 208 to the sieve 216 as described previously. To transport non-fused build material from the sieve 216 to the recovered build material container 208, the sieve- to-mixer valve 258 in the ninth conduit 288 between the sieve 216 and the mixing container 212, the mixer-to-trolley valve 260 in the tenth conduit 290, the hose-to-RBMT valve 242 in the first conduit 272 between the collection hose 206 and the recovered build material container 208 and the RBMT-to-pump valve 246 in the third conduit 276 between the pump 204 and the recovered build material container 208 can be opened e.g., electronically by the controller as described above. The collection hose 206 can be connected directly to the tenth conduit 290 for the duration of the cycling process. When the pump 204 is active, a differential pressure is provided from the pump 204 to the sieve 216. That is, a pressure at the pump 204 is lower than a pressure at the sieve 216. The differential pressure enables build material from the sieve 216 to be transported to the recovered build material container 208. Build material (and air) in the sieve 216 (at approximately atmospheric pressure) is transported from the sieve 216, along the ninth conduit 288 and through the sieve-to-mixer valve 258 and the mixing container 212, along the tenth conduit 290 and through the mixer-to-trolley valve 260, along the collection hose 206, along the first conduit 272 and through the hose-to-RBMT valve 242 to the recovered build material container 208. At the recovered build material container 208, build material separates from air flow and drops from the RBMT inlet area into the recovered build material container 208. Air (and any residual build material) continues along the third conduit 276 and through the RBMT-to-pump valve 246 towards the pump 204, which is at reduced pressure. [0073] It can be seen that any non-fused build material in the sieve 216, the mixing container 212 or in any of the eighth conduit 286, the ninth conduit 288, the tenth conduit 290 or the first conduit 272 will also be transported to the recovered build material container 208. In this way, substantially all non-fused build material in the material management station circuit 200 can be cycled through the material management station circuit 200 a plurality of times, and any non-fused build material in the material management station circuit 200 can be dislodged. It will be appreciated that the cycling process can be followed by the purge process described previously to empty substantially all the non-fused build material from the material management station circuit 200 to the overflow container 210.

[0074] It will be understood that in other examples, for example where the further build material and the previous (or current) build material are compatible, the purge process may not include the cycling process.

[0075] After the purge process is completed, and substantially all the non-fused build material in the material management station circuit 200 is in the overflow container 210, the overflow container 210 can then be removed from the material management station 106, for example for storage or disposal and a further overflow container (not shown) can be connected to the material management station 106. The further overflow container can be empty or the further overflow container can contain build material previously purged from the (or another) material management station 106.

[0076] The purge process can be performed in response to a user input, or automatically. Where purging is performed automatically, the material management station circuit 200 can be controlled to implement the purging process when a trolley 102 containing a different material is slotted into the docking position 107 in the material management station 106. In this example, a material type is electronically recorded on a memory chip of the trolley 102 (or other container). The memory chip is readable by the processing circuitry of the material management station 106 to determine the material type of the material in the trolley 102 (or other container). Alternatively or additionally, the material management station circuit 200 can be controlled to implement the purging process when any of fresh build material supply containers 214a, 214b containing a different material type are connected to the material management station circuit 200. In this example, a material type is electronically recorded on a memory chip of the fresh build material supply containers 214a, 214b. The memory chip is readable by the processing circuitry of the material management station 106 to determine the material type of the material in the fresh build material supply containers 214a, 214b. In other examples, the material management station circuit 200 can be controlled to implement the purging process when both fresh build material supply containers 214a, 214b are removed from the material management station circuit 200. It will be appreciated that the material management station 106 may be controlled to provide an indication to a user that the purging process can be performed based on the criteria discussed previously.

[0077] Figure 3 shows a simplified illustration of a build material management system 300 according to an example of the present disclosure. The system 300 comprises a controller 302 that controls the general operation of the build material management system 300. In the example shown in Figure 3 the controller 302 is a microprocessor-based controller that is coupled to a memory 304, for example via a communications bus (not shown). The memory stores processor executable instructions 306. The controller 302 may execute the instructions 306 and hence control operation of the build material management system 300 in accordance with those instructions.

[0078] In one example, the controller 302 controls the material management station circuit 200 to implement the purging process described hereinbefore.

[0079] It will be appreciated that examples described herein can be realised in the form of hardware, or a combination of hardware and software. Any such software may be stored in the form of volatile or non-volatile storage such as, for example, a storage device like a ROM, whether erasable or rewritable or not, or in the form of memory such as, for example, RAM, memory chips, device or integrated circuits or on an optically or magnetically readable medium such as, for example, a CD, DVD, magnetic disk or magnetic tape. It will be appreciated that the storage devices and storage media are examples of machine-readable storage that are suitable for storing a program or programs that, when executed, implement examples described herein. Accordingly, examples provide a program comprising code for implementing a system or method as claimed in any preceding claim and a machine readable storage storing such a program.

[0080] Figure 4 is a flow diagram outlining a method of operating a build material management system according to one example. In the method of Figure 4, at 402, a purge signal is received in the build material management system. At 404, the build material management system is controlled to route substantially all non-fused build material from the build material transportation system. At 406, the build material management system is controlled to empty substantially all non-fused build material from the build material transportation system through a non-fused purged build material port.

[0081] Throughout the description and claims of this specification, the words "comprise" and "contain" and variations of them mean "including but not limited to", and they are not intended to (and do not) exclude other components, integers or steps. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

[0082] Features, integers or characteristics described in conjunction with a particular example are to be understood to be applicable to any example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. The disclosure is not restricted to the details of any foregoing examples. The disclosure extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.