BACKGROUND

[0001] Some additive manufacturing or three-dimensional printing systems selectively solidify portions of successive layers of a powdered build material. In some examples, selective solidification may be achieved by selectively applying an energy absorbing fusing agent over each formed layer of build material and applying a fusing energy to the build material layer to cause portions thereof on which fusing agent was printed to heat up sufficiently to melt, coalesce, sinter, or otherwise fuse, and then to solidify upon cooling. Other examples directly apply energy in a point-to-point manner to portions of each layers to be solidified, for example using a laser.

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] Fig. 1 is a schematic diagram showing an example of an additive manufacturing apparatus. [0004] Fig. 2 is a flow diagram illustrating an example method of generating barriers in additive manufacturing.

[0005] Fig. 3A is a schematic diagram showing an example of an additive manufacturing apparatus.

[0006] Fig. 3B is a schematic diagram showing an example of an additive manufacturing apparatus.

[0007] Fig. 3C is a schematic diagram showing an example of an additive manufacturing apparatus. [0008] Fig. 4A is a schematic diagram showing a build chamber front view according to an example.

[0009] Fig. 4B is a schematic diagram showing a build chamber top view according to an example. [0010] Fig. 4C is a schematic diagram showing a build chamber front view according to an example.

[0011] Fig. 4D is a schematic diagram showing a build chamber front view according to an example.

[0012] Fig. 4E is a schematic diagram showing a build chamber front view according to an example.

[0013] Fig. 4F is a schematic diagram showing a build chamber top view according to an example.

[0014] Fig. 5A is a schematic diagram showing an example of a barrier.

[0015] Fig. 5B is a schematic diagram showing another example of a barrier. [0016] Fig. 6 is a block diagram illustrating an example of a processor-based system to generate barriers in additive manufacturing.

[0017] Fig. 7 is a flow diagram illustrating an example method of generating barriers in additive manufacturing.

DETAILED DESCRIPTION

[0018] The following description is directed to various examples of additive manufacturing, or three-dimensional printing, apparatus and processes to generate high quality 3D objects. While a limited number of examples have been disclosed, those skilled in the art may appreciate numerous modifications and variations therefrom. It is intended that the appended claims cover such modifications and variations as fall within the scope of the claims. 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.

[0019] Suitable powder-based build materials for use in examples herein may include, where appropriate, at least one of polymers, crystalline plastics, semi-crystalline plastics, polyethylene (PE), polylactic acid (PLA), acrylonitrile butadiene styrene (ABS), amorphous plastics, polyvinyl alcohol plastic (PVA), polyamide, thermo(setting) plastics, resins, transparent powders, colored powders, metal powder, ceramics powder such as for example, glass particles, and/or a combination of at least two of these or other materials, wherein such combination may include different particles each of different materials, or different materials in a single compound particle. Example blended build materials include alumide, which may include a blend of aluminum and polyamide. Some additive manufacturing systems use build material in, for example, a powdered or granular form. A suitable material may be Nylon 12, which is available, for example, from Sigma-Aldrich Co. LLC. Another suitable material may be PA 2200 which is available from Electro Optical Systems EOS GmbH. Other examples of suitable build materials may include PA12 build material commercially known as V1R10A "HP PA12" available from HP Inc, PA11, TPU, or any other suitable polymeric build material. In yet other examples the build material may be any suitable metallic or ceramic build material.

[0020] Different powders may have different characteristics, such as different average particle sizes, different minimum and maximum particle sizes, different coefficients of friction, different angle of repose, and the like. In some examples non-powdered build materials may be used such as gels, pastes, and slurries. Additionally, or alternatively from the above, some examples build materials may be formed from, or may include, short fibers that may, for example, have been cut into short lengths from long strands or threads of material.

[0021] In the present disclosure, the term "to treat" shall be understood as comprising, where appropriate, at least one of: to fuse, to melt, to solidify, to coalesce, to bind, to cure, and to sinter. For simplicity, the terms "treat", "treating", and "to treat" may be used throughout the disclosure. The term "process module" shall be read to include "melting module", "solidifying module", "coalescing module", "binding module", "curing module" and "sintering module". [0022] Some examples of additive manufacturing comprise a chamber of build material on a build platform to move within a build unit with rigid walls. The build material movement may cause friction to the build unit rigid walls that may lead to agitation of the build material of the chamber. This agitation may cause defects in the object to be generated.

[0023] Referring now to the drawings, Fig. 1 shows an example of an additive manufacturing apparatus 100. The apparatus 100 comprises a process module 110, a powder distribution module 120, and a controller 130.

[0024] Examples herein comprise a build chamber 140, illustrated in dotted lines for clarity, in which the object may be generated. The build chamber 140 comprises a build platform 150 therein. The build platform 150 is moveable within the build chamber 140. In an example, the build platform 150 is to move substantially vertically , for example the build platform 150 may move along the axis 155 (illustrated as a vertical dotted arrow). The build platform 150 may be placed in a high position (as illustrated) at the beginning of the printing operation and may be lowered a vertical distance corresponding to the thickness of each layer to be formed. In some examples, the thickness of the subsequent layer may be in the range of about 40 microns to 120 microns, for example 80 microns. The build chamber 140 may, for example, be a generally open cuboid structure in which the build platform 150 forms a vertically movable base. In an example, the build chamber 140 is part of a removable build unit (not shown) that may be removed from the additive manufacturing apparatus 100 after the generation of the object. In another example, the build chamber 140 is integrated into the 3D printing system 100.

[0025] In some examples of additive manufacturing, the walls from the build unit may be rigid. As the print platform 150 is lowered to generate each build material layer, the friction between the build unit walls and the build material on top of the build platform 150 may lead to agitation of the build material in the build chamber. This agitation may cause object imperfections such as deformations, especially to the objects generated near the build unit walls.

[0026] The powder distribution module 120 is to form successive layers of build material on the build platform 150, or on a previously formed layer. In the example herein, the powder distribution module 120 may be a roller, a wiper, or any suitable mechanism to spread build material on the build platform 150 in the form of a build material layer. The powder distribution module 120 may be mounted on a carriage (not shown) that is movable over the build platform 150 to generate a layer of build material. The powder distribution module 120 may move over the build platform 150, for example, through a guide or track as indicated by the dotted arrow 125. The build material may be supplied from a build material reservoir (not shown) using a suitable build material supply mechanism (not shown).

[0027] The process module 110 is to selectively treat portions of a layer of build material formed in the build chamber 140, e.g. the uppermost layer of build material on the build platform 150. In the present disclosure, the term "treat" and similar terms should be read in their respective broad definition, therefore including "partially solidify", and "totally solidify". In some examples, the process module 110 may be fixed above the build platform 150. In other examples, the process module 110 may be moveable over the build platform 150, for example, through a carriage (not shown) scannable over the build platform 150. In yet another example, the process module 110 and the powder distribution module 120 may be installed in the same carriage. In some examples, the process module 110 may be also to selectively jet a printing fluid, such as an energy absorbing fusing agent, or a binder agent, on a build material layer.

[0028] The selection of the suitable process module 110 may be based on the build material and the 3D printing technology to be used. In an example, the process module 110 may comprise an array of ultraviolet (UV) Light Emitting Diodes (LED) that emit electromagnetic energy in about the 300nm to 410nm range. In another example, the process module 110 may comprise at least one infrared lamp that emits electromagnetic energy in about the 700nm to 1mm range. In yet another example, the process module 110 may comprise at least one lighting element that emits electromagnetic energy in about the 380nm to 750nm range. [0029] In an example, the object is to be generated using a polymeric build material. In the example, the powder distribution module 120 is to form subsequent layers of the polymeric build material and the process module 110 is to selectively raise the temperature of the layer of polymeric build material above the melting point of the polymeric build material, so that the melted parts can solidify upon cooling. [0030] In another example, the object is to be generated using a metallic build material. In the example, the powder distribution module 120 is to form subsequent layers of the metallic build material and the process module 110 is to selectively cure the layer of the metallic build material. Some additive manufacturing systems comprising metallic build materials, selectively jet curable binding agents including, for example, a polymeric binder or a chemical binder dissolved in a liquid carrier. The curing of the curable binding agents may cause the particles from the binding agent to bind together. In some examples, however, before the curing operation, the process module 110 may heat the build material layer with the curable binding agent applied, so that the liquid carrier from the binding agent is evaporated, or partially evaporated, therefore leading to layers of metallic build material in the build chamber 140 free, or partially free, of the liquid carrier.

[0031] In some examples, the curing operation may be performed through an ultraviolet energy source. In other examples, the curing operation may be performed by a thermal energy source. The process module may cure the build material from the build chamber 140 in a layer-by-layer basis in the apparatus 100, or in an external heating entity. In some examples, the printed objects may be subject to an additional post-processing after the curing, for example, a sintering process in a furnace.

[0032] As mentioned above, the apparatus 100 may further comprise a controller 130. The controller 130 may be any combination of hardware and programming to implement, for example, the functionalities resulting from the execution of the method 200 of Fig. 2. In some examples herein, such combinations of hardware and programming may be implemented in a number of different ways. For example, the programming of modules may be processor- executable instructions stored on 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, as described above. In other examples, the functionalities of the controller 130 may be, at least partially, implemented in the form of electronic circuitry.

[0033] Fig. 2 is a flow diagram illustrating an example method of generating barriers in additive manufacturing according to an example. Method 200 is described below as being executed or performed by a controller, such as the controller 130 of FIG. 1. Method 200 may be implemented in the form of executable instructions stored on a machine-readable storage medium and executed by a single processor or a plurality of processors, and/or in the form of any electronic circuitry, for example digital and/or analog ASIC. In some implementations of the present disclosure, method 200 may include more or less elements than are shown in FIG. 2. In some implementations, some of the elements of method 200 may, at certain times, be performed in parallel and/or may repeat.

[0034] At block 210, the controller 130 may receive object data 135 corresponding to the object to be generated. The data 135 to print the object may be derived from a 3D object model of the object. In an example, the 3D object model may be a Computer Aid Design (CAD) file. The data 135 may, in an example, comprise a plurality of 2D slices corresponding to virtual cross sections of the object to be generated. Each slice may correspond to a physical build material layer. The 3D object model may be defined in a vector-type format in which 2D rasterized images may be generated from each slice of the object model. The data 135 may also comprise instructions or data indicating which locations of the build material layer are to be treated, e.g. solidified, to generate the object.

[0035] At block 220, the controller 130 may also define control data to generate a physical barrier to be located between the object and a sidewall of the build chamber 140. The barrier generation control data is not in the data 135 as such, but may be defined by the controller 130 based on the object to be generated comprised in the data 135. As such, the controller 130 may define the barrier control data including the location of the barrier, the number of barriers to be generated and the thickness of the barrier, based on the data 135 and the additive manufacturing technology used. This description comprises additional examples and details for generating the barrier control data hereinafter.

[0036] As mentioned above, the controller 130 may define a barrier, which is not encoded in the data 135 corresponding to the object to be generated, to mitigate the build material agitation within the build chamber. In an example, the barrier is to mitigate the agitation of the build material with which the object is to be generated. In an example, the barriers are intended to solidify and reduce the build material agitation generated by, for example, the friction between the movement of the build platform and the build unit (or build chamber 140) sidewalls. In some examples, the controller 130 may define control data to generate a plurality of barriers surrounding at least part of the object to mitigate the build material agitation generated in each of the sidewalls of the build chamber 140. In further examples, the controller 130 is to generate additional barriers for other purposes, for example the purposes explained below.

[0037] At block 230, the controller 130 may control the powder distribution module 120 to form successive layers of build material on the build platform 150. In some examples, the powder distribution module 120 is to form successive layers of build material. In some examples herein, the layers may be complete layers that span from a wall of the build chamber 140 to an opposite wall of the build chamber 140. In other examples, however, the powder distribution module 120 is to form successive layers which may not be complete, for example, in the case of having a reduced build chamber 140. At blocks 240 and 250, the controller 130 is further to control the process module 110 to selectively treat portions of the formed layers to generate the object based on the received data 135 and the barrier based on the defined control data.

[0038] Fig. 3A to 3C illustrate an example of the generation of a first object 370 and a second object 370' by the additive manufacturing apparatus 100 from Fig. 1.

[0039] The example may start from the apparatus illustrated in Fig. 1. The controller 130 (not shown hereinafter for simplicity) receives the object data 135 corresponding to a first object 370 and a second object 370' and defines control data to generate a barrier 380 (shown in Fig. 3B) located between a first sidewall from the build chamber 140 and the first object 370.

[0040] The controller 130 may control the powder distribution module 120 to form the first build material layer 361 on the build platform 150 as illustrated in Fig. 3A. In some examples, the first layer 361 or a plurality of first layers may not be solidified. The controller 130 may instruct the build platform 150 to lower by a height corresponding to the thickness of a second build material layer 362 to be formed, e.g. 80 microns. In some examples, the thickness of the second layer 362 may be the same thickness as of the first layer 361. The controller 130 may control the powder distribution module 120 to form the second build material layer 362 on the first build material layer 361. The controller 130 may further control the process module 110 to treat portions 370 and 370' to generate the first object 370 and the second object 370' respectively based on the object data 135. The controller 130 may further control the process module 110 to treat the portion 380 to generate the barrier 380 based on the defined control data. Fig. 3B illustrates the progression of the process after the solidification of the corresponding portions of the second layer 362.

[0041] The controller 130 controls the build platform 150, the powder distribution module 120, and the process module 110 based on the control data and the object data 135 up to the completion of the generation of objects 370 and 370'. Fig. 3C illustrates the progression of the process after the completion of the generation of objects 370 and 370'. In the example shown, to generate the objects 370 and 370', the controller controlled the powder distribution module 120 to generate seven build material layers 361-367 and controlled the process module 110 to treat the corresponding portions of each build material layer 361-367 to generate the first object 370 (illustrated as a "H" shape), the second object 370' (illustrated as a "P" shape), and a barrier 380 located between the first object 370 and a sidewall from the build chamber 140. In the example from Fig. 3A-3C, the controller 130 defined control data to generate the barrier 380 in a substantially vertical orientation.

[0042] Fig. 4A-4F illustrate different examples of the build chamber 140 from apparatus 100 at the completion of the generation of the object or objects. For clarity purposes, in the following illustrations, the plurality of build material layers is shown as a single layer of build material 360. However, it is noted that the single layer 360 is for illustrative purposes as such, and should be interpreted as a plurality of thin build material layers, for example, build material layers of 80 microns thickness. Throughout the examples herein, it should be understood that the controller 130 has defined the control data to generate the barrier or barriers 380 and controlled the corresponding elements to generate them, i.e. process module 110, powder distribution module 120, and build platform 150. The features of the examples may be combined and split without departing from the scope of the present disclosure.

[0043] Fig. 4A and 4B illustrate examples of a build chamber 140 (without side walls for illustrative purposes) after processing by the apparatus 100. Fig. 4A illustrates a front view of a cross-section of the middle of the object 370 of the example, and Fig. 4B illustrates a top view of the example corresponding to the cross-section A-A' from Fig. 4A. As can be seen in the illustrated example, the apparatus 100 has been controlled to generate an object 370, and a first and second barrier 380-380' both having a height corresponding to the height of the object 370. In an example, the height of the barrier 380 is smaller than the height of the object 370. In another example, the height of the barrier 380 is about the same height as the height of the object 370. In other examples, the first barrier 380 and a second barrier 380' have at least the height of the object 370 to be generated. In the example shown in Fig. 4B, the first barrier 380 and the second barrier 380' are a single barrier 380 surrounding the object 370. In additional examples, the barrier 380 surrounds the object 370 following the contour of the shape of the object 370.

[0044] In a further example, illustrated in Fig. 4C, a front view of the build chamber 140 (without side walls for illustrative purposes) of a cross-section of the middle of the object 370 after processing by the apparatus 100 is shown. As can be seen, the apparatus 100 has been controlled to generate an object 370, and a first barrier 380 located between a first sidewall of the build chamber 140 and the object 370. The controller 130 has, additionally, controlled the elements of the apparatus 100 to build a second barrier 380' between the object 370 and a second sidewall of the build chamber 140. The first barrier 380 and second barrier 380' have about the same height as the height of the build chamber 140.

[0045] In a further example, illustrated in Fig. 4D, a front view of the build chamber 140 (without side walls for illustrative purposes) of a cross-section of the middle of the object 370 after processing by the apparatus 100 is shown. As can be seen, the apparatus 100 has been controlled to generate an object 370, a first barrier 380 and, additionally, a second barrier 380.

[0046] In the present disclosure, the process module 110 may generate a barrier having a degree of solidification. A greater degree of solidification of a barrier involves a higher protection against agitation travelling though the barrier. In an example, the process module 110 may generate a barrier by ejecting a binding agent to the layers of build material, e.g. metallic build material, of the build chamber but without curing the binding agent. In this example, the barrier would have a generally low degree of solidification.

[0047] In another example, the process module 100 may generate a barrier by ejecting the binding agent to layers of build material of the build chamber and curing, or at least partially curing, the binding agent. In this example the barrier would have a generally higher degree of solidification than the previous example.

[0048] In another example, the process module 100 may generate a barrier by selectively ejecting a fusing agent and fusing the portions thereof from the layers of build material, in this example the barrier would have a higher degree of solidification than the previous examples, regardless the fact that the barrier may not be fully solidified until after an amount of time after the ejection of the fusing agent.

[0049] In another example, the process module 100 may generate a barrier by selectively laser sintering portions of the layers of build material in the build chamber, in this example the barrier would have a high degree of solidification although the barrier may not be fully solidified until after an amount of time after the laser sintering operation.

[0050] In some examples, the process module 110 may not completely solidify the barrier 380 and therefore some agitation from the friction between the walls of the build chamber 140 and the build material 360 may travel through the barrier 380 and reach the object 370. In these cases, the controller 130 may additionally, instruct the elements of the apparatus 100 to build a third barrier 385 located between the barrier 380 and the object 370 to mitigate the effects of the agitation that travelled through the first barrier 380. Additionally, the controller 130 may also control the elements of the apparatus 100 to build a fourth barrier 385' located between the barrier 380' and the object 370 for similar reasons as the third barrier 385.

[0051] Fig. 4E and 4F illustrate an example of a build chamber 140 (without side walls for illustrative purposes) after processing by the apparatus 100. Fig. 4E illustrates a front view of a cross-section of the middle of the object 370 of the example and Fig. 4F illustrates an example of top view of the example corresponding to the section B-B' from Fig. 4E. As can be seen, the apparatus 100 has been controlled to generate a plurality of objects, for example, a first object 370A, a second object 370B, a third object 370C, and a fourth object 370D. The build chamber 140 further comprises a first barrier 380A between the plurality of objects and a first build chamber sidewall, a second barrier 380C between the plurality of objects and a second build chamber sidewall, a third barrier 380E between the plurality of objects and a third build chamber sidewall, and a fourth barrier 380F between the plurality of objects and a fourth build chamber sidewall. The barriers 380A, 380C, 380E, and 380F may be connected to form a single wall or a fewer number of walls, surrounding at least part of the plurality of objects.

[0052] As mentioned in the example above, the agitation effect may travel through the barriers. Additionally, the controller 130 may control the elements of the apparatus 100 to build additional barriers between the different objects from the plurality of objects to isolate a potential agitation effect between each object from the plurality of objects. For example, the apparatus 100 may be controlled to build the barrier 380B located between the first object 370A and a subset of objects from the plurality of objects formed by the second object 370B, the third object 370C, and the fourth object 370D. Additionally, or alternatively, the apparatus 100 may be controlled to build the barrier 380D located between the third object 370C and the fourth object 370D.

[0053] Fig. 5A and 5B illustrate examples of the barrier 380, and barriers 380A-380F (referred hereinafter as barrier 380). In the examples herein, the controller 130 may define the barrier control data to generate the barrier 380 based on the object data 135. In some examples, the generated barrier 380 may not be in direct contact, i.e. may not touch, with a sidewall of the build chamber 140. In an example, the gap between the sidewall of the build chamber 140 and the barrier 380 (referred hereinafter as "the gap") may range from about 0.5cm to about 5cm. In another example, the gap may range from about 1cm to about 4cm. In another example, the gap may range from about 0.5cm to about 1.5cm. In yet another example, the gap may be of about 1cm. The previous ranges may also apply to the examples of generated barriers located in between objects (e.g., barriers 380B and 380D) wherein the gap is defined as the gap between the barrier and an object.

[0054] As mentioned above, the agitation may travel through the barrier 380 due to, for example, how solidified is the barrier 380, i.e. the solidification degree of the barrier 380. In an example herein, the controller 130 may control the apparatus 100 elements to generate the barrier 380 with different thicknesses based on the solidification degree of the barrier 380. In an example in which the barrier 380 is not completely solidified, the apparatus 100 may generate a barrier 380 with a high thickness, e.g. 2cm. In another example in which the barrier 380 is completely solidified, the apparatus 100 may generate a barrier 380 with a low thickness, e.g. 1cm. The apparatus may generate the barrier 380 with a thickness of the range defined from about 0.5cm to about 2.5cm, or a range defined from about 1cm to about 2cm, or a range defined from about 0.5cm to 3cm. In an example, the controller 130 may select the thickness of the barrier 280 to be built as the lowest thickness that inhibits the agitation to travel through the barrier 280. In the examples herein, the term "inhibit" may comprise to completely inhibit or to partially inhibit, wherein partially inhibit may range from about 98% to 50%.

[0055] Fig. 5A is a schematic diagram showing an example of a side-view of a barrier 380. The vertical section of the barrier 380 comprises a solid pattern 382. In the example, the solid pattern 382 indicates that the apparatus 100 is to fuse substantially all the section of the barrier 380 without leaving unfused areas therein.

[0056] Fig. 5B comprises a schematic diagram showing another example of a side-view of a barrier 380. Precisely, Fig. 5B illustrates a vertical section of the barrier 380 that comprises a mesh-type pattern. The mesh-type pattern comprises a plurality of elements 384 arranged in a substantially horizontal orientation and a plurality of elements 386 arranged in a substantially vertical orientation. The arrangement of the plurality of elements 384 and 386 may generate a grid with holes 388 therein that may not be treated (e.g., may not be fused or otherwise solidified, or may not be treated with a print agent) in the generation of the barrier 380. The mesh-type structured barrier 380 may enable to recycle a higher amount of build material corresponding to the not treated build material, as opposed to the solid barrier 380 from Fig. 5A and, at the same time, mitigate an amount of the build material agitation within the build chamber 140 depending on the characteristics of the mesh.

[0057] FIG. 6 is a block diagram illustrating a processor-based system 600 that includes a machine-readable medium 620 encoded with example instructions to generate barriers in additive manufacturing. In some implementations, the system 600 is a processor-based system and may include a processor 610 coupled to a machine-readable medium 620. The processor 610 may include a single-core processor, a multi-core processor, an application- specific integrated circuit (ASIC), a field programmable gate array (FPGA), and/or any other hardware device suitable for retrieval and/or execution of instructions from the machine- readable medium 620 (e.g., instructions 625) to perform functions related to various examples. Additionally, or alternatively, the processor 610 may include electronic circuitry for performing the functionality described herein, including the functionality of instructions 625. With respect of the executable instructions represented as boxes in FIG. 6, it should be understood that part or all of the executable instructions and/or electronic circuits included within one box may, in alternative implementations, be included in a different box shown in the figures or in a different box not shown.

[0058] The machine-readable medium 620 may be any medium suitable for storing executable instructions, such as a random-access memory (RAM), electrically erasable programmable read-only memory (EEPROM), flash memory, hard disk drives, optical disks, and the like. In some example implementations, the machine-readable medium 620 may be a tangible, non-transitory medium, where the term "non-transitory" does not encompass transitory propagating signals. The machine-readable medium 620 may be disposed within the processor-based system 600, as shown in FIG. 6, in which case the executable instructions may be deemed "installed" on the system 600. Alternatively, the machine-readable medium 620 may be a portable (e.g., external) storage medium, for example, that allows system 600 to remotely execute the instructions or download the instructions from the storage medium. In this case, the executable instructions may be part of an "installation package". As described further herein below, the machine-readable medium may be encoded with a set of executable instructions 625.

[0059] The machine-readable medium is to receive data 630 corresponding to a print job to be printed.

[0060] In an example, instructions 625, when executed by the processor 610, may cause the processor 610 to execute the method of Fig. 2. In another example, instructions 625, when executed by the processor 610, may cause the processor 610 to execute the method of Fig. 7.

[0061] Fig. 7 is a flow diagram illustrating an example method of generating barriers in additive manufacturing according to an example. Method 700 is described below as being executed or performed by a controller, such as the controller 130 of FIG. 1. Method 700 may be implemented in the form of executable instructions 625 stored on a machine-readable storage medium 620 and executed by a single processor 610 or a plurality of processors, and/or in the form of any electronic circuitry, for example digital and/or analog ASIC. In some implementations of the present disclosure, method 700 may include more or less blocks than are shown in FIG. 7. In some implementations, some of the blocks of method 700 may, at certain times, be performed in parallel and/or may repeat.

[0062] At block 710, instructions 625, when executed by the processor 610, may cause the processor 610 to define barrier generation control data including data corresponding to a barrier to be located between the print job 370 and an edge of the build platform 150. At block 720, instructions 625 when executed by the processor 610, may cause the processor 610 to distribute a complete layer of build material 261-267 on the build platform 150. At block 730, instructions 625, when executed by the processor 610, may cause the processor 610 to selectively eject a printing fluid onto a first portion of build material corresponding to the print job. At block 740, instructions 625, when executed by the processor 610, may cause the processor 610 to selectively eject the printing fluid onto a second portion of build material corresponding to the barrier 280. At block 750, instructions 625, when executed by the processor 610, may cause the processor 610 to emit energy (by, e.g., the process module 110) to the layer of build material 261-267 to fuse the build material located at the first portion and the second portion. As mentioned above, blocks 710-750 may be also performed by a controller such as controller 130 from Fig. 1 instead of the processor 610.

[0063] 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 processors, or a combination thereof.

[0064] As used herein, the term "about" and "substantially" are used to provide flexibility to a numerical range endpoint by providing that a given value may be, for example, an additional 20% more or an additional 20% 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. [0065] 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.

[0066] There have been described example implementations with the following sets of features:

[0067] Feature set 1: An additive manufacturing apparatus comprising: a process module to selectively treat a layer of build material from a build chamber formed from at least one sidewall and comprising a build platform moveable within the build chamber; a powder distribution module to form a layer of build material in the build chamber; and a controller to: receive data corresponding to an object to be generated, define control data to generate a barrier to be located between the object and at least one of the at least one sidewall,

control the powder distribution module to form successive layers of build material on the build platform,

control the process module to selectively treat portions of the formed layers to generate the object based on the received data, and to generate the barrier based on the defined control data. [0068] Feature set 2: An additive manufacturing apparatus with feature set 1, wherein the controller is to define control data to generate a barrier having a height corresponding to the height of the object.

[0069] Feature set 3: An additive manufacturing apparatus with any preceding feature set 1 or 2, wherein the controller is to define control data to generate a barrier in a substantially vertical orientation.

[0070] Feature set 4: An additive manufacturing apparatus with any of feature sets 1 to 3, wherein the controller is to define control data to generate a barrier having a height of the barrier about the same as the height of the build chamber. [0071] Feature set 5: An additive manufacturing apparatus with any of feature sets 1 to 4, wherein the controller is to define control data to generate a barrier having a mesh-type structure

[0072] Feature set 6: An additive manufacturing apparatus with any of feature sets 1 to 5, wherein the controller is to define control data to generate an additional barrier located between the barrier and the object.

[0073] Feature set 7: An additive manufacturing apparatus with any of feature sets 1 to 6, wherein the controller is to receive data corresponding to a plurality of objects to be generated, the controller further to define the control data to further generate additional barriers to enclose at least part of the plurality of objects. [0074] Feature set 8: An additive manufacturing apparatus with any of feature sets 1 to 7, wherein the controller is to define control data to generate the barrier at a distance from about 0.5cm to about 5cm from a sidewall from the build chamber.

[0075] Feature set 9: An additive manufacturing apparatus with any of feature sets 1 to 8, wherein the controller is to define control data to generate the barrier with a thickness from about 0.5cm to about 2.5c.

[0076] Feature set 10: An additive manufacturing apparatus with any of feature sets 1 to 9, wherein the controller is further to: control the powder distribution module to form a layer of metallic build material; and control the process module to selectively apply a binder agent to the layer. [0077] Feature set 11: An additive manufacturing apparatus with any of feature sets 1 to 10, wherein the controller is to control the process module to apply curing energy to the layer.

[0078] Feature set 12: An additive manufacturing apparatus with any of feature sets 1 to 11, wherein the process module comprises at least one of an ultraviolet (UV) energy source, an infrared energy source, and a visible spectrum light energy source.

[0079] Feature set 13: An additive manufacturing apparatus with any of feature sets 1 to 12, wherein the powder distribution module is to form a layer of a polymeric build material and the process module is to selectively raise a temperature of the layer of polymeric build material above the melting point of the polymeric build material. [0080] There has also been described a method comprising: receiving a print job comprising data to generate an object within a build chamber; defining control data to generate a barrier to be located between the object and at least one sidewall of the build chamber; distributing successive layers of build material within the build chamber; treating a first subset of portions of the formed layers to form an object based on the print job; and treating a second subset of portions of the formed layers to form the barrier based on the defined control data, wherein the second subset of portions are not defined in the print job.

[0081] There has also been described a non-transitory machine-readable medium storing instructions executable by a processor, wherein the medium is to receive data corresponding to a print job to be printed, the non-transitory machine-readable medium comprising: instructions to define barrier generation data comprising data including a barrier to be located between the print job and an edge of a build platform based on the data corresponding to the print job; instructions to distribute a complete layer of build material on the build platform; instructions to selectively eject a printing fluid onto a first portion of build material corresponding to the print job; instructions to selectively eject the printing fluid onto a second portion of build material corresponding to the barrier; and instructions to emit energy to the layer of build material to fuse the build material located at the first portion and the second portion.