BACKGROUND

[0001] Some additive manufacturing or three-dimensional printing systems generate 3D objects by selectively solidifying portions of successively formed layers of build material on a layer-by- layer basis. After object generation the build material which has not been solidified is separated from the 3D objects.

BRIEF DESCRIPTION OF THE DRAWINGS

[0002] The present application may be more fully appreciated in connection with the following detailed description of non-limiting examples taken in conjunction with the accompanying drawings, in which like reference characters refer to like parts throughout and in which:

[0003] Figures 1A-1D are schematic diagrams showing an example of an apparatus for cleaning a set of 3D printed objects;

[0004] Figure 2 is a schematic diagram showing an example of another apparatus for cleaning a set of 3D printed objects;

[0005] Figure 3 is a flowchart of an example method of controlling an apparatus for cleaning a set of 3D printed objects;

[0006] Figure 4 is a flowchart of another example method of cleaning a set of 3D printed objects; and

[0007] Figure 5 is a flowchart of another example method of cleaning a set of 3D printed objects. DETAILED DESCRIPTION

[0008] The following description is directed to various examples of additive manufacturing, or three-dimensional printing, apparatus and processes involved in the generation of 3D objects. Throughout the present disclosure, the terms "a" and "an" are intended to denote at least one of a particular element. In addition, as used herein, the term "includes" means includes but not limited to, the term "including" means including but not limited to. The term "based on" means based at least in part on.

[0009] As used herein, the term "about" is used to provide flexibility to a range endpoint by providing that a given value may be, for example, an additional 15% more or an additional 15% less than the endpoints of the range. In another example, the range endpoint may be an additional 30% more or an additional 30% less than the endpoints of the range. The degree of flexibility of this term can be dictated by the particular variable and would be within the knowledge of those skilled in the art to determine based on experience and the associated description herein.

[0010] For simplicity, it is to be understood that in the present disclosure, elements with the same reference numerals in different figures may be structurally the same and may perform the same functionality.

[0011] 3D printers generate 3D objects based on data in a 3D virtual model of an object or objects to be generated, for example, using a CAD computer program product. 3D printers may generate 3D objects by selectively processing layers of build material. For example, a 3D printer may selectively treat portions of a layer of build material, e.g. a powder, corresponding to a layer of a 3D object to be generated, thereby leaving the portions of the layer un-treated in the areas where no 3D object is to be generated. The combination of the generated 3D objects and the un-treated build material may also be referred to as a build volume. The volume in which the build bed is generated may be referred to as a build chamber.

[0012] Suitable powder-based build materials for use in additive manufacturing include polymer powder, metal powder or ceramic powder. In some examples, non-powdered build materials may be used such as gels, pastes, and slurries. [0013] 3D printers may selectively treat portions of a layer of build material by, for example, ejecting a printing liquid in a pattern corresponding to the 3D object. Examples of printing liquids may include fusing agents, detailing agents, curable binder agents or any printing liquid suitable for the generation of a 3D object. Additionally, the chemical composition of some printing liquids may include, for example, a liquid vehicle and/or solvent to be at least partially evaporated once the printing liquid have been applied to the build material layer. For simplicity, the liquid vehicle and/or solvents may be referred hereinafter as solvents.

[0014] Some three-dimensional printing systems use fusing agents to treat the portions of the layer of build material. The portions in which the fusing agent is applied are further heated so that the fusing agent absorbs such energy to heat up and melt, coalesce and solidify upon cooling the portions of build material on which the fusing agent was ejected. The three-dimensional printing system may heat the build material by applying energy from an energy source to each layer of build material.

[0015] Some three-dimensional printing systems use a thermally curable binder agent which has to be heated to a predetermined temperature to cause components of the liquid binder agent to bind together particles of build material on which it is applied. Such a liquid binder agent may comprise latex particles and curing of the binder may occur, for example, at a temperature above 40 degrees Celsius, above 70 degrees Celsius, above 100 degrees Celsius, or above 120 degrees Celsius, or above 150 degrees Celsius.

[0016] Such binder agents may be applied to successive layers of powdered build material, such as powdered stainless steel (e.g. SS316L) build material, and the curing of the binder agent leads to the generation of so-called "green parts". Green parts are generally relatively low-density objects formed by a matrix of metal build material particles and cured binder. Green parts are transformed into highly dense final objects by heating them in a sintering furnace to a temperature close to the melting point of the build material used.

[0017] After the completion of the green part generation process, the build volume comprises a set of weakly bound green parts surrounded by generally unbound build material. Before green parts are transferred to the sintering oven, the unbound build material is separated from the green parts. In some examples, vibration and air-blowing techniques may be used to remove unbound build material. The application of vibration and air blowing techniques cause the green parts to move and/or collide with each other and thereby potentially causing some damage on them.

[0018] Referring now to the drawings, Figures 1A-1D are schematic diagrams showing an example of an apparatus 100 for cleaning a set of 3D printed objects. In some examples, the apparatus 100 is a stand-alone module that interacts with other elements of a 3D printing system (e.g., 3D printer, build material management station). In other examples, however, the apparatus 100 is an integral part of an element of a 3D printing system, such as a 3D printer.

[0019] The apparatus 100 comprises a platform 120. In some examples, the platform 120 is a vertically moveable platform. In other examples, however the platform 120 moves horizontally. In yet other examples, the platform 120 is a static platform. The platform 120 is to receive and hold a set of 3D printed objects 130 with build material 135 attached thereto. In some examples, wherein the apparatus is part of a 3D printer, the 3D printed objects 130 may be generated directly on the platform 120. In other examples, the 3D printed objects 130 with the build material attached thereto 135 are transferred from a build chamber with the 3D printer to the platform 120. In some examples, the 3D printed objects 130 are green parts. In other examples, the 3D printed objects 130 are not bound green parts but may be, for example, thermally fused polymer-based parts which may be fragile, for example, due to their geometry, thickness, etc.

[0020] The 3D printed objects 130 to be received on the platform 120 may comprise build material in which a thermally curable binder agent has been applied in a 3D printer to define the 3D objects 130. The 3D object 130 is surrounded by some agglomerated build material (e.g., partially fused, or partially bound), which is in turn surrounded by generally free-flowing build material. In the examples herein, the agglomerated build material and the free-flowing build material is referred hereinafter as loose build material.

[0021] The apparatus 100 comprises a porous media supply module 110 to contain a porous media 115. The porous media supply module 100 may be positioned above the platform 120 in such a way that once the porous media 115 is installed in the porous media supply module 110, the porous media 115 faces the upper surface of the platform 120. In an example, the porous media supply module 110 is a frame or a support to which a porous media 115 may be attached. In the above examples, once the porous media 115 is installed in the porous media supply module 100. It is to be understood, however, that the porous media 115 may not be an integral part of the apparatus 100, as the apparatus 100 may not include the porous media 115 during, for example, apparatus 100 cleaning or transporting operations. When in use, the porous media 115 is embedded within the porous supply module 110 from the apparatus 100.

[0022] The porous media 115 is a media that enables a gas flow to flow therethrough. In an example, the porous media 115 comprises pores located at a distribution of about 4 to 12 pores per inch (ppi). In another example, the porous media comprises pores located at a distribution of about 6 to 10 ppi. During the cleaning operation, the porous media 115 may be positioned to at least partially surround the 3D printed objects 130 and build material 135 so that the 3D printed objects 130 are restrained on the platform 120 to substantially inhibit relative movement between the 3D printed objects 130 and the platform 120 during a cleaning operation. In the examples herein, the term "restrain" should be understood as holding between the platform 120 and the porous media 115 by some pressure that is not sufficient to damage the 3D printed objects 130. During the cleaning operation, once the 3D printed objects 130 are secured with the porous media 115, a gas flow may be initiated to flow through the porous media 115 to remove the build material 135 attached to the 3D printed objects 130 while securing the 3D printed objects 130 . Using this technique removes the risk of damage from objects colliding with each other or with elements of the cleaning module. Further, since the objects are secured, this allows for higher pressure gas flows to be used which in turn improves the effectiveness of the cleaning operation. Providing an automated cleaning system, such as apparatus 100, reduces the cost, labor and time spent by manual cleaning of the 3D objects 130.

[0023] In some examples, the porous media 115 is an elastic media that adapts, at least partially, to the geometry of the 3D printed objects 130 when brought into contact with the objects. In an example, the porous media 115 is an open cell foam. In another example, the porous media 115 is a lattice structure which has similar properties already mentioned in terms of porosity, for example, a 3D printed lattice structure (e.g., made of a suitable polyamide, such as PA11; or a polyurethane, such as TPU). Additionally, the lattice structure may be customized or customizable for the type of 3D printed parts 130 that are to be cleaned. In yet further examples, the porous media 115 may be in the form of a net or a mesh, or may be in the form of a textile made from any suitable synthetic and/or natural fiber or fiber mix.

[0024] The apparatus 100 further comprises a mechanism 117 to position the porous media 115 over the platform 120 to restrain the 3D printed objects 130 thereon. The mechanism 117 enables a relative movement between the porous media supply module 110 and the platform 120, such as a vertical movement. In an example, the mechanism 117 may move the porous media supply module 110 towards the platform 120 so that the porous media 115 restrains the 3D printed objects 130 on the platform. In another example, the mechanism 117 may move the platform 120 towards the porous media supply module 110 so that the porous media 115 restrains the 3D printed objects 130 on the platform. In yet another example, the mechanism 117 may move the porous media supply module 110 towards the platform 120 and the platform 120 towards the porous media supply module 110 so that the porous media 115 restrains the 3D printed objects 130 on the platform.

[0025] The mechanism 117 may be implemented in a number of different ways. For example, the mechanism 117 may be a frame mechanism, a roller blind, a pin passive mechanism, a platform impelling mechanism, a motor with a guide, a pneumatic piston, or any other suitable mechanism to enable a relative movement between the porous media supply module 110 and the platform 120.

[0026] The apparatus 100 further comprises a gas flow conduit 140 connectable to a gas flow source (not shown). In some examples, the gas flow source may be part of the apparatus 100. In other examples, however, the gas flow source may be external from the apparatus 100 and connectable to gas flow conduit 140. The gas flow conduit 140 is a channel to direct a gas flow through the porous media 115 to clean any 3D printed objects 130 restrained thereby. Some examples of the gas flow conduit may include a static blowing nozzle, a directional blowing nozzle, an airknife or a combination thereof. In the present disclosure, an airknife may be implemented as a pressurized air plenum containing a series of holes (e.g., nozzles) or continuous slots through which pressurized air exits in a laminar flow. In some examples, the gas flow is an air flow. In other examples, the gas from the gas flow may be another gas, such as nitrogen.

[0027] Additionally, in some examples, the apparatus 100 may further comprise a controllable vibration element (e.g., vibration plate, eccentric motor) coupled to a controller (not shown) that causes the vibration element to vibrate the platform 120. The vibration causes the fluidization of the build material 135 which can be directed to an external reservoir and thereby be extracted from the apparatus 100 to the external reservoir. In some examples, the external reservoir is used a source of recycled build material for a subsequent print job. The fluidized build material 130 may be directed to the external reservoir by means of, for example, a drain, an airflow or a sieve. In some examples, a controller may control the vibration element to vibrate at very high frequencies (e.g., ultrasounds) for example at 20kHz, and at low amplitudes, for example of 20 microns. Vibrating at high frequencies and low amplitudes enables gentle removal of build material 135 from 3D objects 130. However, the controller may control the vibration element to vibrate at lower frequencies, for example 35 Hz, and higher amplitudes, for example 1mm.

[0028] In some examples, the apparatus 100 may further comprise a controller (not shown). The controller comprises a processor and a memory with specific control instructions stored therein to be executed by the processor. The controller may be coupled to the mechanism 117 and/or the gas flow generator. The controller may control at least some of the operations of the elements that it is coupled therewith. The functionality of the controller is described further below with reference to Figures 3-5.

[0029] In the examples herein, the controller may be any combination of hardware and programming that may be implemented in a number of different ways. For example, the programming of modules may be processor-executable instructions stored in at least one non- transitory machine-readable storage medium and the hardware for modules may include at least one processor to execute those instructions. In some examples described herein, multiple modules may be collectively implemented by a combination of hardware and programming. In other examples, the functionalities of the controller may be, at least partially, implemented in the form of an electronic circuitry. The controller may be a distributed controller, a plurality of controllers, and the like.

[0030] Figure 1A shows the apparatus 100 in a configuration prior to the build material 135 extraction operation. At Figure 1A configuration, the platform 120 holds the 3D objects 130 with build material 135 attached thereto and the porous media 115 is embedded in the porous media supply module 110, which is located above the 3D printed objects 130. Then, the mechanism 117 is to move the porous media supply module (e.g., vertically downwardly) and/or the platform 120 (e.g., vertically upwardly) such that the porous media 115 restrains the 3D printed objects 130 on the platform 120 (i.e., Figure IB configuration). Once 3D printed objects 130 are restrained on the platform 120, the gas flow conduit 140 is to direct a gas flow 145 towards and through the porous media 115 to remove the build material 135 attached on the restrained 3D printed objects 135 surface. Once the 3D printed objects 135 are clean or substantially clean (i.e., Figure 1C configuration), the mechanism 117 may move the porous media supply module (e.g., vertically upwardly) and/or the platform 120 (e.g., vertically downwardly) such that the porous media 115 does not restrain the 3D printed objects 130 on the platform 120 anymore (i.e., Figure ID configuration); Then, the cleaned 3D printed objects 130 may be further removed from the platform 120.

[0031] Figure 2 is a schematic diagram showing an example of another apparatus 200 for cleaning a set of 3D printed objects 130. In some examples, the apparatus 200 may be an alternative implementation to the apparatus 100 from Figures 1A-1D. The apparatus 200 may comprise previously disclosed elements from Figures 1A-1D referred to with the same reference numerals. The apparatus 200 comprises the porous media supply module 110, the mechanism 170 and the gas flow conduit 140. In use, the apparatus 200 may further comprise the porous media 115 installed within the porous media supply module 110.

[0032] The apparatus 200 further comprises a platform 220. The platform 220 may be structurally and functionally similar to the platform 120 from Figures 1A-1D. However, the platform 120 comprises a plurality of perforations 225 (e.g., apertures) extending from the top surface of the platform 220 to the bottom surface of the platform 220. In alternative examples, the plurality of perforations 225 may extend from the top surface of the platform 220 to a side surface of the platform 220. The size of the perforation may be bigger than the size of a build material particle and smaller than the size of a 3D printed object 130, for example, about 50 microns.

[0033] The apparatus 200 further comprises a vacuum source 250 (e.g., a pump or a fan) fluidically connected to the plurality of perforations 225 to generate vacuum conditions at the platform 220. In some examples, the vacuum conditions may be a negative relative pressure on the platform 220. The vacuum conditions may be a lower pressure than the pressure above the platform 220. In the build material extraction operation (e.g., cleaning operation), the build material 135 particles may be removed from the surface of the restrained 3D printed objects 130 through the gas flow 145 and may be further driven, and thereby exhausted, to an external build material reservoir through the plurality of perforations 225 assisted by the vacuum conditions generated by the vacuum source 250 (e.g., arrow 260). In additional examples, the gas flow 145 and vacuum conditions may be generated in the opposite directions (e.g., vertically upwardly gas flow and vacuum conditions above the platform 220)

[0034] Figure 3 is a flowchart of an example method 300 controlling an apparatus to cause cleaning of build material 135 from the surface of a set of 3D printed objects 130. The method 300 may involve previously disclosed elements from Figures 1A-1D referred to with the same reference numerals. In some examples, parts of method 300 may be executed by a controller of the apparatus 100.

[0035] At block 320, a set of 3D printed objects 130 are received on the platform 120 of the apparatus 100. In an example, the 3D printed objects 130 may be already generated on the platform 120 in a 3D printer and then the platform 120 is conveyed to the apparatus 100. In another example, the 3D printed objects 130 are manually placed from a build volume to the platform 120. In yet another example, the 3D printed objects 130 are automatically placed from a build volume to the platform 120, for example, through robotic means.

[0036] At block 340 the set of 3D printed objects 130 are restrained on the platform 120 with a porous media 115. In an example, at block 340, the controller controls the mechanism 117 to move the platform 120 (e.g., vertically upwardly) towards the porous element supply module 110 to cause the porous media 115 to restrain the 3D printed objects 130 on the platform 120. In another example, at block 340, the controller controls the mechanism 117 to move the porous media supply module 110 (e.g., vertically downwardly) towards the platform 120 to cause the porous media 115 to restrain the 3D printed objects 130 on the platform 120. In yet another example, at block 340, the controller controls the mechanism 117 to move the platform 120 (e.g., vertically upwardly) and the porous media supply module 110 (e.g., vertically downwardly) to cause the porous media 115 to restrain the 3D printed objects 130 on the platform 120.

[0037] At block 360, the controller controls the gas flow source to generate a gas flow through the gas flow conduit 140, so that the gas flow conduit 140 directs the gas flow through the porous media 115 to clean any 3D printed object 130 restrained thereby. Additionally, in some examples, the controller may further control the gas flow conduit 140 to move and/or rotate based on the position of the 3D objects 130 with respect to the gas flow conduit 140. Alternatively, the controller controls a valve between the gas flow source and the gas flow conduit 140 so that the gas flow conduit 140 directs the gas flow through the porous media 115 to clean any 3D printed object 130 restrained thereby.

[0038] Additionally, the controller may further control a vacuum source 250 (see, e.g., apparatus 200 from Figure 2) to generate a negative relative pressure on the platform 120 and thereby remove any build material 135 particle cleaned by the gas flow. In some examples, the build material 135 particles are pneumatically conveyed through a conduit to a build material reservoir.

[0039] Figure 4 is a flowchart of another example method 400 of cleaning a set of 3D printed objects 130. The method 300 may involve previously disclosed elements from Figures 1A-1D referred to with the same reference numerals. In some examples, parts of method 400 may be executed by a controller of the apparatus 100. In some examples, method 400 may be executed after block 360 from Figure 3.

[0040] At block 420, the controller may determine that the 3D objects 130 are clean from build material 135. In an example, the removed build material is conveyed to a build material container the weight of which is determined a weighing device (e.g., a load cell). The weighing device may send data to the controller indicative that the 3D objects 130 are clean from build material 135, for example, by detecting that no more build material reaches the container or by detecting that of the height level of build material in the container is over a predeterminable level threshold. Other examples, however, may comprise un-restraining the 3D objects 130 from the porous media 115, capturing images of the 3D objects 130 through imagining devices which may then send the images to the controller, which then detects that the 3D objects 130 are clean from build material 135. Yet other examples may comprise alternative mechanisms to detect that the 3D objects 130 are clean from build material, for example, optical or capacitive sensors.

[0041] At block 440, the controller may control the gas flow to cease generating the flow. In an example, the controller may control the gas flow source to cease generating the gas flow. In other examples, however, the controller may control a valve between the gas flow generator and the gas flow conduit 140 to close, or partially close.

[0042] At block 460, the cleaned 3D objects 130 are un-restrained from the porous media 115 and released from the platform 120. In some examples, the controller may control a conveyor belt and/or robotic means to move the 3D objects 130 from the platform 120.

[0043] Figure 5 is a flowchart of another example method 500 of cleaning a set of 3D printed objects 130. The method 300 may involve previously disclosed elements from Figures 1A-1D referred to with the same reference numerals. In some examples, parts of method 500 may be executed by a controller of the apparatus 100. In some examples, method 500 may be executed along with blocks 340 and/or 360 from Figure 3.

[0044] As the cleaning operation is being executed, and thereby the build material 135 attached on the surface of the 3D objects 130 is being removed, the overall volume of the 3D objects 130 and the build material 135 attached thereto decreases. Accordingly, based on the resiliency and elasticity of the media, a new sub-volume of air (i.e., not comprising build material nor 3D object), corresponding to the removed build material, appears between the porous media 115 and the 3D objects 130. Such inter-volume may enable the gas flow 145 to move the 3D objects 130 and thereby increasing the risk of a potential breakage of the 3D objects 130. [0045] At block 520, the controller may adjust the pressure in which the porous media 115 restrains the 3D printed objects 130 to the platform 120 as the 3D printed objects 130 are being cleaned, thereby inhibiting or reducing the generation of the above-mentioned inter-volumes.

[0046] In one example, the binder agent can include a binder in a liquid carrier or vehicle for application to the particulate build material. For example, the binder can be present in the binding agent at from about 1 wt% to about 50 wt%, from about 2 wt% to about 30 wt%, from about 5 wt% to about 25 wt%, from about 10 wt% to about 20 wt%, from about 7.5 wt% to about 15 wt%, from about 15 wt% to about 30 wt%, from about 20 wt% to about 30 wt%, or from about 2 wt% to about 12 wt% in the binding agent.

[0047] In one example, the binder can include polymer particles, such as latex polymer particles. The polymer particles can have an average particle size that can range from about 100 nm to about 1 pm. In other examples, the polymer particles can have an average particle size that can range from about 150 nm to about 300 nm, from about 200 nm to about 500 nm, or from about 250 nm to 750 nm.

[0048] The above examples may be implemented by hardware, or software in combination with hardware. For example, the various methods, processes and functional modules described herein may be implemented by a physical processor (the term processor is to be implemented broadly to include CPU, SoC, processing module, ASIC, logic module, or programmable gate array, etc.). The processes, methods and functional modules may all be performed by a single processor or split between several processors; reference in this disclosure or the claims to a "processor" should thus be interpreted to mean "at least one processor". The processes, method and functional modules are implemented as machine-readable instructions executable by at least one processor, hardware logic circuitry of the at least one processor, or a combination thereof.

[0049] The drawings in the examples of the present disclosure are some examples. It should be noted that some units and functions of the procedure may be combined into one unit or further divided into multiple sub-units. What has been described and illustrated herein is an example of the disclosure along with some of its variations. The terms, descriptions and figures used herein are set forth by way of illustration. Many variations are possible within the scope of the disclosure, which is intended to be defined by the following claims and their equivalents.

[0050] There have been described example implementations with the following sets of features:

[0051] Feature set 1: An apparatus for cleaning a set of 3D printed objects, the apparatus comprising: a platform to hold a set of 3D printed objects with build material attached thereto; a porous media supply module to contain a porous media; a mechanism to position the porous media over the platform to restrain any 3D printed objects thereon; and a gas flow conduit to direct a gas flow through the porous media to clean any 3D printed objects restrained thereby.

[0052] Feature set 2: An apparatus with feature set 1, further comprising the porous media within the porous media supply module.

[0053] Feature set 3: An apparatus with any preceding feature set 1 to 2, wherein the platform comprises a plurality of perforations, the apparatus further comprising a vacuum source to generate vacuum conditions at the platform, so that removed build material is exhausted through the perforations.

[0054] Feature set 4: An apparatus with any preceding feature set 1 to 3, wherein the porous media is an elastic media to adapt to the geometry of the 3D printed objects.

[0055] Feature set 5: An apparatus with any preceding feature set 1 to 4, wherein the porous media comprises pores having a distribution of about 4 to about 12 pores per inch (ppi).

[0056] Feature set 6: An apparatus with any preceding feature set 1 to 5, wherein the porous media is a foam.

[0057] Feature set 7: An apparatus with any preceding feature set 1 to 6, wherein the porous media is a 3D printed lattice structure. [0058] Feature set 8: An apparatus with any preceding feature set 1 to 7, further comprising a controller to: control the mechanism to move the platform and/or the porous media supply module to cause the porous media to restrain the 3D printed objects on the platform; and control a gas flow source to generate a gas flow through the gas flow conduit.

[0059] Feature set 9: A method to clean 3D printed objects to remove build material attached thereto, the method comprising: receiving a set of 3D printed objects with build material attached thereto on a platform; restraining the 3D printed objects to the platform with a porous media; and applying a gas flow through the porous media to clean the 3D printed objects.

[0060] Feature set 10: A method with feature set 9, further comprising generating a negative relative pressure to remove any build material cleaned by the gas flow.

[0061] Feature set 11: A method with any preceding feature set 9 to 10, wherein restraining the 3D printed objects to the platform comprises moving the porous element supply module towards the platform.

[0062] Feature set 12: A method with any preceding feature set 9 to 11, wherein restraining the 3D printed objects to the platform comprises moving the platform towards the porous element supply module.

[0063] Feature set 13: A method with any preceding feature set 9 to 12, further comprising: determining that the 3D printed objects are clean from build material; controlling a gas flow generator to cease generating the gas flow; and releasing the clean 3D objects from the platform.

[0064] Feature set 14: A method with any preceding feature set 9 to 13, further comprising adjusting the pressure in which the porous media restrains the 3D printed objects to the platform as the 3D printed objects are being cleaned.

[0065] Feature set 15: A 3D printer comprising: a platform with perforations to hold a set of 3D printed objects with build material attached thereto; a porous media supply module to contain a porous media; a mechanism to position the porous media over the platform to restrain any 3D printed objects thereon; a gas flow conduit to direct a gas flow through the porous media to clean any 3D printed objects restrained thereby; and a vacuum source to generate vacuum conditions at the platform so that removed build material is exhausted through the perforations.