WO2022025933A1

WO2022025933A1 - Sacrificial parts defined with agents including binders

Info

Publication number: WO2022025933A1
Application number: PCT/US2020/044621
Authority: WO
Inventors: Mackensie C. SMITH; Jennifer L. Wu
Original assignee: Hewlett Packard Development Co LP
Current assignee: Hewlett Packard Development Co LP
Priority date: 2020-07-31
Filing date: 2020-07-31
Publication date: 2022-02-03
Anticipated expiration: 2023-01-31

Abstract

According to examples, a processor may identify, from a digital model of a part to be defined, selected first portions of layers of build material particles in a build volume at which sections of the part are to be defined, determine second portions of layers at which sections of a sacrificial part are to defined, the second portions being separated from and within a predefined distance below the first portions, in which the second portions are related to layers at which the sections of the part are to be defined. The processor may also generate print control data including instructions to define the sections of the part in the selected first portions and the sections of the sacrificial part in the determined second portions through deposition of an agent, the agent including a binder that is to bind the build material particles on which the agent is deposited.

Description

SACRIFICIAL PARTS DEFINED WITH AGENTS INCLUDING BINDERS

BACKGROUND

[0001] In three-dimensional (3D) printing, an additive printing process may be used to make 3D solid parts from a digital model. 3D printing techniques are considered additive processes because they involve the application of successive layers or volumes of a build material, such as a powder or powder-like build material, to an existing surface (or previous layer). 3D printing often includes solidification of the build material, which for some materials may be accomplished through use of heat, a chemical binder, and/or an ultra-violet or a heat curable binder.

BRIEF DESCRIPTION OF THE DRAWINGS

[0002] Features of the present disclosure are illustrated byway of example and not limited in the following figure(s), in which like numerals indicate like elements, in which:

[0003] FIG. 1 shows a block diagram of an example apparatus that may generate print control data for defining a 3D part and a sacrificial part using an agent including a binder:

[0004] FIG, 2 shows an example 3D fabrication system that may define the 3D part and the sacrificial part according to the generated print control data;

[0005] FIGS. 3A and 3B, respectively, depict cross-sectional side views of a build volume of the 3D fabrication system depicted in FIG. 2 during two example states in the defining of a sacrificial part and a 3D part; [0006] FSG. 4 depicts a flow diagram of an example method for generating print control data for defining a 3D part and a sacrificial part using an agent including a binder; and

[0007] FIG. 5 shows a block diagram of an example computer-readable medium that may have stored thereon computer-readable instructions for generating print control data including instructions for defining the sections of a part in a first set of layers and the sections of a sacrificial part in a second set of layers through deposition of an agent including a binder.

DETAILED DESCRIPTION

[0008] For simplicity and illustrative purposes, the present disclosure is described by referring mainly to examples. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present disclosure. It will be readily apparent however, that the present disclosure may be practiced without limitation to these specific details. In other instances, some methods and structures have not been described in detail so as not to unnecessarily obscure the present disclosure.

[0009] Disclosed herein are apparatuses, 3D fabrication systems, and methods in which a processor may generate print control data including Instructions to define sections of a pari in first portions of layers and to define sections of a sacrificial part in second portions of layers through deposition of an agent including a binder that is to bind the build material particles on which the agent is deposited. The second portions may be separated from and within a predefined distance below the first portions such that vapors from the agent deposited onto the build material particles in the second portions to seep between the build material particles in a few bottom layers of the first portions. The vapors may cause those build material particles in the few bottom layers of the first portions over which the sacrificial part has (or parts have) been defined to be wetted, which may improve properties, e.g., reduce surface irregularities, of a bottom surface (or bottom surfaces) of the part, !n some instances, a liquid carrier in the agent may cause wetting through movement of the liquid carrier through capillary action

[0010] In some instances, when a liquid is deposited through jetting onto dry powder, surface irregularities may occur on the first few layers of the dry powder. After the liquid is deposited onto the first few layers, powder wetting interactions may become less erratic and the number of surface irregularities may diminish in additional layers upon which the liquid is deposited. This may occur due to interactions caused by the liquid deposited in the first few layers with the liquid deposited in the additional layers. As a result, the first few layers at which sections of a part may be defined may have surface irregularities as the initial layers are normally dry or nearly dry when the liquid is applied to those layers while the subsequent layers may not have the irregularities.

[0011] According to examples of the present disclosure, to reduce or prevent the defining of the surface irregularities (such as crazing) in the bottom section of the part, the sacrificial part may be defined in some of the build material layers that are beneath, e.g., within a predefined distance below, the first portions of layers at which the part is to be defined. The predefined distance may be a certain number of build material layers and may be sufficiently small to cause a reduction or elimination of the surface irregularities in the bottom of the part. In some examples, multiple sacrificial parts may be defined beneath multiple portions of the part. Thus, for instance, in an example in which the part includes bottom sections on multiple levels, the multiple sacrificial parts may be defined for the bottom sections on the multiple levels. In addition, some of the lower set of layers for a sacrificial part may overlap with some of the higher set of layers for a portion of a pari such that sections of the sacrificial part and sections of the part may be defined in the same set of layers. [0012] In any regard, the sacrificial part may reduce or prevent the defining of the surface irregularities due to a crosstalk effect between a freshly-spread dry powder layer and a layer upon which the agent has been deposited. In addition, or alternatively, the previously patterned layers may contain volatile components of liquid formulation jetted onto the powder (water, solvent, surfactants with measurable vapor pressure). The volatile component vapors may percolate upward from the sacrificial part and into the initial layers of the first set of build material layers as the sacrificial part may be defined in layers that are below the layers at which the part may be defined. The percolating vapors and/or solvents may pretreat the initial layers, which may precondition the build material particles for improved wetting. The improved infiltration of the liquid droplets into the vapor- preconditioned initial layers may prevent coagulation of the liquid droplets on the initial layers and may minimize surface irregularities in the bottom section of the part.

[0013] Before continuing, it is noted that as used herein, the terms "includes" and "including" mean, but is not limited to, "includes" or "including" and "includes at least" or "including at least." The term "based on" means "based on" and "based at least in part on."

[0014] Reference is first made to FIGS. 1, 2, 3A and 3B. FIG. 1 shows a block diagram of an example apparatus 100 that may generate print control data for defining a 3D part and a sacrificial part using an agent including a binder. FIG. 2 shows an example 3D fabrication system 200 that may define the 3D part and the sacrificial part according to the generated print control data. FIGS. 3A and 3B, respectively, depict cross-sectional side views of a build volume of the 3D fabrication system 200 depicted in FIG. 2 during two example states In the defining of a sacrificial part and a 3D part. It should be understood that the example apparatus 100 depicted in FIG. 1, the 3D fabrication system 200, and/or the example various stages depicted in FIGS. 3A and 3B may include additional features and that some of the features described herein may be removed and/or modified without departing from the scopes of the features depicted in those figures.

[0015] The apparatus 100 depicted in FIG. 1 may be a computing system such as a server, a laptop computer, a tablet computer, a desktop computer, or the like. As shown, the apparatus 100 may include a processor 102, which may be a semiconductor-based microprocessor, a central processing unit (GPU), an application specific integrated circuit (ASIC), a field-programmable gate array (FPGA), and/or other suitable hardware device. In other examples, the apparatus 100 may be a 3D fabrication system, a 3D printer, a 3D fabricator, or the like. In these examples, the apparatus 100 may be equivalent to the 3D fabrication system 200 depicted in FIG. 2 and thus common features are depicted in both FIGS. 1 and 2. In other examples, the apparatus 100 may be separate from the 3D fabrication system 200 and may communicate instructions to the 3D fabrication system 200 to define a part 302 and to define a sacrificial part 306.

[0016] The apparatus 100 may also include a memory 110 that may have stored thereon machine-readable instructions (which may equivalently be termed computer-readable instructions) that the processor 102 may execute. The memory 110 may be an electronic, magnetic, optical, or other physical storage device that contains or stores executable instructions. The memory 110 may be, for example, Random-Access memory (RAM), an Electrically Erasable Programmable Read-Only Memory (EEPROM), a storage device, an optical disc, and the like. The memory 110, which may also be referred to as a computer- readable storage medium, may be a non-transiiory machine-readable storage medium, where the term “non-transiiory” does not encompass transitory propagating signals.

[0617] As shown in FIG. 1, the memory 110 may have stored thereon machine-readable instructions 112-116 that the processor 102 may execute. Although the instructions 112-116 are described herein as being stored on the memory 110 and may thus include a set of machine-readable instructions, the apparatus 100 may include hardware logic blocks that may perform functions similar to the instructions 112-118. For instance, the processor 102 may include hardware components that may execute the instructions 112-118. In other examples, the apparatus 100 may include a combination of instructions and hardware logic blocks to implement or execute functions corresponding to the instructions 112-118. In any of these examples, the processor 102 may implement the hardware logic blocks and/or execute the instructions 112-116. As discussed herein, the apparatus 100 may also include additional instructions and/or hardware logic blocks such that the processor 102 may execute operations in addition to or in place of those discussed above with respect to FIG. 1.

[0018] With reference to FIGS. 1, 2, 3A, and 3B, the processor 102 may execute the instructions 112 to identify, for instance, from a digital model 202 of a part 302 to be defined, selected first portions of layers 304 of build material particles 204 in a build volume 208 of a three-dimensional (3D) fabrication system 200 at which sections of the part 302 are to be defined. The processor 102 may access the digital model 202, which may be a digital file, e.g., a computer aided design (CAD) file, or other digital representation, that may define properties of the part 302 to be defined within the build volume 208 during a 3D fabrication operation. The digital model 202 may identify features of the part 302, such as the shape, the size, the color, the texture, mechanical property, and/or the like, of the part 302. The processor 102 may access the digital model 202 from a data store (not shown) or some other source, e.g., directly from a user, from an online source, etc. In addition, the processor 102 may process the digital model 202 to determine how fabrication components 208 of the 3D fabrication system 200 are to be operated to define the part 302 from build materia! particles 204 in selected portions of layers 304. For instance, the processor 102 may process the digital model 202 In a printing pipeline, in which the output of the printing pipeline may be used to control the components in the 3D fabrication system 200 to define the part 302. In other examples, however, the processor 102 may generate the digital mode! 202 of the part 302,

[0019] The processor 102 may process the digital model 202 to determine how the fabrication components 206 are to be operated to define the part 302 from build materia! particles 204 in a build volume 208 of the 3D fabrication system 200. This may include determining in which build material layers 210 within the build volume 208 sections of the part 302 are to be defined as well as the areas in each of those build material layers 210 at which the sections of the part 302 are to be defined. Thus, for instance, the processor 102 may determine the build materia! layers 210 within the build volume 208 at which the part 302 is to be defined as well as the patterns of sections of the part 302 to be defined in those build material layers 210.

[0020] The processor 102 may execute the instructions 114 to determine second portions of layers 308 of build material particles 204 in the build volume 208 at which sections of a sacrificial part 306 are to defined. The second portions of layers 308 at which the sections of the sacrificial part 306 are to be defined may be related to the first portions of layers 304 of build material particles 204 at which the sections of the part 302 are to be defined. Particularly, the second portions of layers 308 at which the sections of the sacrificial part 306 are to be defined may correspond to, e.g., match, the areas in a bottom portion of the first portions of layers 304 at which a section of the part 302 is to be defined. That is, the second portions of layers 308 may have the same pattern as the bottom section of the part 302. As a result, the areas at which an agent 214 is to be applied to define the bottom portion of the first portions of layers 304 may be directly above areas at which the agent 214 is to be applied, which may reduce or prevent surface irregularities in the bottom section of the part 302 as discussed herein. As also discussed herein, the sacrificial part 306 may be defined to reduce or prevent the defining of surface irregularities on a bottom surface of the part 302 and may be discarded following the defining of the part 302. [0021] In some examples, the processor 102 may determine other portions of the layers, for instance, in some of the first portions of layers 304, at which an additional sacrificial part 312 may be defined. The other portions may be, for instance, portions beneath a section 314 of the part 302 that overhangs the bottom portion of the part 302 as shown in FIG. 3B. The additional sacrificial part 312 may thus reduce or prevent the defining of surface irregularities on a bottom surface of the section 314 of the part 302 that overhangs the bottom portion of the part 302.

[0022] The processor 102 may execute the instructions 116 to generate print control data 212 including instructions to define the sections of the part 302 in the first portions of layers 304 and the sections of the sacrificial part 306 are to be defined in the second portions of layers 308 through deposition of an agent 214 including a binder that is to bind the build material particles 204 on which the agent 214 is deposited.

[0023] As shown in FIG. 3B, the second portions of layers 308 may be separated from and within a predefined distance below the first portions of layers 304. That is, an intermediate set of layers 310 of build material particles 204 may be defined between the second portions of layers 308 and the first portions of layers 304. In this regard, the processor 102 may also generate the print control data 212 to include instructions to define an intermediate set of layers 310 of build material particles 204 between the second portions of layers 308 and the first portions of layers 304. As shown, the build material particles 204 in the intermediate set of layers 310 may be free of the agent 214. However, vapors from the agent 214 deposited onto the build material particles 204 in the second portions of layers 308 may seep through the intermediate set of layers 310 and to the bottom layers of the first portions of layers 304, which may cause the reduction or prevention of surface irregularities in the bottom surface of the part 302. [0024] According to examples, the build material particles 204 may have sizes that may range anywhere between about 1 micron to about 100 microns. In other examples, the build material particles 204 may have dimensions that are anywhere generally between about 30 pm and about 60 pm. In addition, the build material particles 204 may be a metal or a metal alloy that, when sintered, may coalesce and become a continuous metal part. Suitable metal powders, metal alloy powders, or mixtures of different metal powders, may include, but not limited to, stainless steel alloys 303, 304L, 310, 316L, 321, 347, 410, 420, 430, 440, 13- 8PH, 17-4PH; low carbon steel and tool steel alloys, magnetic alloys including, but not limited to, Fe/Ni, Fe/Si, Fe/AI, Fe/Si/A!, Fe/Co, Fe/CoN; cobalt alloys including, but not limited to as well as other ferrous metal alloys, copper, copper alloys, bronze (Cu/Sn), brass (Cu/Zn), tin, lead, gold, silver, platinum, palladium, iridium, titanium, tantalum, iron, aluminum alloys, magnesium alloys, iron alloys, nickel alloys, chromium alloys, silicon alloys, zirconium alloys, gold alloys, and any appropriate combinations thereof.

[0025] The agent 214 may include a binder that is to bind the build material particles 204 on which the agent 214 has been deposited. The binder may be any suitable material that may physically bind the metallic build material particles 204 together. For instance, the binder may be a water-based binder containing dispersed polymer, e.g., latex, particles. In these examples, when the temperature of the agent 214 is heated to a certain elevated temperature, the binder may coalesce and may thus cause the metallic build material particles 204 upon which the agent 214 has been deposited to bind together. In other examples, the binder may include other types of binders that may, for instance, be activated through receipt of light, such as UV light. The part 302 at this stage of fabrication may be termed a green part and a later stage of fabrication may include a debinding and/or sintering operation to finish the fabrication of the part 302.

The agent 214 may include water to reduce viscosity and increase jettabiliiy of the agent 214. The agent 214 may also include additives to improve jettability, such as, surfactants, humectants, co-solvents, etc. The agent 214 may further include other additives, such as a biocide, an anti-kogation agent, and/or the like. In some examples, the agent 214 may be heated to a certain elevated temperature as discussed herein to cause the water and the other additives to evaporate while causing the binder in the agent 214 to coalesce. Particularly, the agent 214 may be heated to the certain elevated temperature following the defining of both the sacrificial part 306 and the part 302. in other examples, UV light may be applied to cause liquid in the agent 214 to evaporate.

[0027] According to examples, the fabrication components 206 may include an agent delivery system 216 that is to deliver the agent 214. The agent delivery system 216 may include delivery devices 226, 228 that may deliver the agent 214 as droplets, which are represented as dashed lines, onto the build material layers 210. By way of particular example, the agent delivery system 216 may be a printhead (or multiple printheads) having delivery devices 226, 228 (e.g., nozzles) in which droplet ejectors, e.g., resistors, piezoelectric actuators, and/or the like, may he provided to eject droplets of the agent 214 through the delivery devices 226, 228.

[0028] It has been found that in some instances, when a liquid, such as the agent 214, is deposited through jetting onto dry powder, such as dry build material particles 204, surface irregularities may occur. After the liquid is deposited onto a first few layers to define the part 302, powder wetting interactions may become less erratic and the number of surface irregularities may diminish in additional layers upon which the liquid is deposited. This may occur due to interactions caused by the liquid deposited in the first few layers with the liquid deposited in the additional layers such as may occur due to vaporization of agent 214 (and/or migration of a liquid carrier/solvent) deposited on the second portions of layers 308 to define the sacrificial part 306. [0029] As a result, the first few build material layers 210 at which sections of the part 302 may be defined may have surface irregularities as the initial build material layers 210 are normally dry or nearly dry when the agent 214 is applied to those layers while the subsequent layers may not have the irregularities. The surface irregularities may become especially pronounced at high printed fluid flux densities and jetted drops land onto a dry build material layer 210 at close proximities to each other. This may be because the jetted drops that are in dose proximities to each other may start merging into shallow pools on the surface of the build material layer 210. The longer it takes for the liquid to start wetting the build material particles 204 and infiltrate between the build material particles 204, the more likely it is that the shallow pools will form into larger individual droplets. As the droplets are formed, surface adhesive forces between the droplets and the build material particles 204 may cause the positions of some of the build material particles 204 to shift. This shift may cause formations of peaks (particles randomly driven together and agglomerated by beading liquid) and valleys (spaces between the agglomerated particles) in the build material layer 210.

[0030] As discussed herein, and according to examples of the present disclosure, to reduce or prevent the formation of the surface irregularities in the bottom section of the part 302, a sacrificial part 306 may be defined in some of the build material layers 210 that are beneath, e.g., within a predefined distance below, the first portions of layers 304 at which the part 302 is to be defined. The predefined distance may be a certain number of build material layers 210 and may be sufficiently small to cause a reduction or elimination of the surface irregularities in the bottom of the part 302. The predefined distance may be based on the type of build material particles 204, the type of agent 214 being deposited, environmental conditions, and/or the like, and may be determined through testing.

[0031] According to examples, the processor 102 may generate the print control data 212 to include instructions for an energy source 224 to apply energy onto the first portions of layers 304 and the second portions of layers 308 in the build volume 208 after the agent 214 Is delivered to both the first portions of layers 304 and the second portions of layers 308. The application of the energy may cause the build material particles 204 in the second portions of layers 308 and the first portions of layers 304 upon which the agent 214 has been deposited to bind together. In other words, the processor 102 may generate the print control data 212 to include instructions for the energy source 224 to apply the energy into the build volume 208 after the sections of the sacrificial part 306 and the sections of the part 302 are defined. In other words, the print control data 212 may include instructions to define the sections of the sacrificial part 306 without causing the energy source 224 to apply energy onto the layers of the second portions of layers 308 during defining of the sections of the sacrificial part 306 to raise the temperature of the build material particles 204 defining the sections of the sacrificial part 306 above a temperature of the build material particles 204 prior to defining of the sections of the sacrificial part 306. In other words, the sections of the sacrificial part 306 may be defined without increasing the temperature of the build material particles 204 above a temperature of the build material particles 204 prior to defining of the sections of the sacrificial part 306. The energy source 224 may be any suitable type of energy source 224, such as a resistive heater, a UV light source, and/or the like. In other examples, the print control data 212 may include instructions for the energy source 224 to apply energy, e.g., heat, UV light, or the like, onto the build material layers 210 prior to, during, and/or following application of the agent 214 and prior to the formation of respective subsequent build material layers 210, such that, for instance, the liquid in the agent 214 may partially or completely be evaporated prior to the formation of the respective subsequent build material layers 210.

[0032] With particular reference to FIG. 2, the 3D fabrication system 200 may also include a recoater 230, which may spread, spray, or otherwise define the build material particles 204 into a build material layer 210 as the recoater 230 is moved, e.g., scanned, across a build platform 232 as indicated by the arrow 234. The build platform 232 may provide the build volume 208 for the build material particles 204 to he spread into successive layers 210 of build material particles 204. The build platform 232 may be movable in a direction away from the recoafer 230 during defining of successive build material layers 210.

[0033] According to examples, the 3D fabrication system 200 may include a deck 238 or multiple decks 236, 238 from which build material particles 204 may be supplied for formation into the build material layers 210. For instance, the deck 236 may supply an amount of build material particles 204 on top of the deck 236 that the recoater 230 may push over the build platform 232 as the recoater 230 is moved across the build platform 232 as denoted by the arrow 234 to define a build material layer 210 on the build platform 232 or on a previously defined build material layer 210.

[0034] The processor 102 may control operations of the recoater 230 via, for instance, the generation and implementation of the print control data 212. In other examples, however, the 3D fabrication system 200 may include a separate controller (not shown) that may control operations of the recoater 230 in which the processor 102 may communicate with the controller. The processor 102 and/or another controller (not shown) may control other components of the 3D fabrication system 200 using the print control data 212.

[0035] Various manners in which the processor 102 may operate are discussed in greater detail with respect to the method 400 depicted in FIG. 4. Particularly, FIG. 4 depicts a flow diagram of an example method 400 for generating print control data 212 for defining a 3D part 302 and a sacrificial part 306 using an agent 214 including a binder. It should be understood that the method 400 depicted in FIG. 4 may include additional operations and that some of the operations described therein may be removed and/or modified without departing from scope of the method 400. The description of the method 400 is made with reference to the features depicted in FIGS. 1-3B for purposes of illustration.

[0036] At block 402, the processor 102 may identify selected first portions of layers 304 of build material particles 204 in a build volume 208 at which sections of a part 302 are to be defined. In some examples, the processor 102 may make this identification based on a digital model 202 of the part 302, while in other examples, the processor 102 may identify the selected first portions of layers 304 from another source, such as data in other forms. In the latter examples, the processor 102 may generate the digital model 202 of the part 302.

[0037] At block 404, the processor 102 may determine second portions of layers 308 of build material particles 204 in the build volume 208 at which sections of a sacrificial part 306 are to be defined. The second portions of layers 308 may be separated from and within a predefined distance below the first portions of layers 304. In addition, the second portions of layers 308 may include a certain number of layers to thus cause the sacrificial part 306 to have a predefined height. The predefined height of the sacrificial part 306 to be defined may be based on the type of build material particles 204, the type of agent being deposited, environmental conditions, and/or the like, and may be determined through testing. In some examples, the predefined height of the sacrificial part 306 to be defined may not be affected by the height of the part 302 to be defined. That is, the height of the sacrificial part 306 to be defined may be the same regardless of the height of the part 302 to be defined. In some examples, the height of the sacrificial part 306 to be defined may be significantly smaller than the height of the part 302 to be defined. As a particular non-limiting example, the predefined height of the sacrificial part 306 to be defined may be around 2 mm or less.

[0038] According to examples, a shape of the second portions of layers 308 may match a shape of a portion of the part 302 to be defined. For instance, the shape of the second portions of layers 308 may be based on a projection of a portion of the digital model 202 of the part 302. In other words, the area of a bottom portion of the part 302 to be defined on a first few layers of the first portions of layers 304 may be projected onto an area that the sacrificial part 306 is to encompass. The shape of the sacrificial part 306 may correspond to, e.g., match, the projection of the bottom portion of the part 306. In other examples, the widest portion of the part 302 may be projected onto the area that the sacrificial part 306 is to encompass. In these examples, the shape of the sacrificial part 306 may correspond to, e.g., match, the projection of the widest portion of the part 306. In other examples, the sacrificial part 306 may correspond to other widths of the part 302, such as a width of the part 302 at a certain distance from a bottom surface of the part 302.

[0039] At block 406, the processor 102 may generate print control data 212 including instructions to deposit an agent 214 onto the determined second portions of layers 308 at which the sections of the sacrificial part 306 are to be defined and instructions to deposit the agent 214 onto the selected first portions of layers 304 at which the part 302 is to be defined. In some examples, the processor 102 may generate the digital model 202 of the part 302 to also include a digital model of the sacrificial part 306. The processor 102 may generate the digital model 202 outside of a printing pipeiine.

[0040] As discussed herein, the agent 214 may include a binder that is to bind the build material particles 204 on which the agent 214 is deposited. The processor 102 may generate the print control data 212 such that the instructions are to cause the sections of the sacrificial part 306 as well as the sections of the part 302 to be defined without causing an energy source 224 to apply energy onto the first and second portions of layers 304, 308 during defining of the sections of the sacrificial part 306 and the part 302. However, the instructions may cause the energy source 224 to apply energy onto the first portions of layers 304 and the second portions of layers 308 after the sections of the sacrificial part 306 and the sections of the part 302 are respectively defined in the second portions of layers 308 and the first portions of layers 304,

[0041] According to examples, the processor 102 may also generate the print control data 212 to include instructions to define an intermediate set of layers 310 of build material particles 204 between the second set of layers 308 and the first set of layers 304. The build material particles 204 in the intermediate set of layers 310 are to be free of the agent 214 such that a number of layers having no joined areas may be provided between the second portions of layers 308 and the first portions of layers 304 and thus, the sacrificial part 308 may be separate from the part 302.

[0042] At block 408, the processor 102 may cause the sections of the sacrificial part 306 to be defined in the determined areas of the second portions of layers 308 through execution of the print control data 212. The processor 102 may also cause the intermediate set of layers 310 to be defined above the sections of the sacrificial part 308 through execution of the print control data 212. In addition, at block 410, the processor 102 may cause sections of the part 302 to be defined in the selected areas in the first portions of layers 304 through execution of the print control data 212 following defining of the sections of the sacrificial part 302 and the defining of the intermediate set of layers 310.

[0043] In some examples, the processor 102 may send the print control data 212 to a 3D fabrication system 200, for instance, to a controller of the 3D fabrication system 200, in which the controller may control the fabrication components 206 to define the sections of the sacrificial part 306 in the determined areas in the second portions of layers 308 and to define the part 302 in the selected areas in the first portions of layers 304. In other examples, the processor 102 may control the fabrication components 206 of the 3D fabrication system 200 to define the sections of the sacrificial part 308 in the areas in the second portions of layers 308 according to the print control data 212 and control the fabrication components 206 to define the intermediate layers 310 of dry build material particles above the second portions of layers 308 according to the print control data 212. The processor 102 may also control the fabrication components 206 to define the part 302 in the selected areas in the first portions of layers 304 according to the print control data 212.

[0044] The processor 102 or the separate controller may also execute the print control data 212 to cause the energy source 224 to apply energy onto the build volume 208 to cause the build material particles 204 defining the part 302 and the sacrificial part 306 to bind together. As discussed herein, application of the energy may cause the liquids in the agent 214 to evaporate and the binder in the agent 214 to coalesce thereby causing the build material particles 204 in contact with the binder from the agent 214 to coalesce.

[0045] Following execution of the method 400, the part 302 may be removed from the build volume 208 and excess build material particles 204 may be removed from the part 302. The part 302 may also undergo additional finishing operations, such as sintering. However, the sacrificial part 306 may be discarded.

[0046] Some or all of the operations set forth in the method 400 may be Included as utilities, programs, or subprograms, In any desired computer accessible medium. In addition, the method 400 may be embodied by computer programs, which may exist in a variety of forms both active and inactive. For example, they may exist as machine readable instructions, including source code, object code, executable code or other formats. Any of the above may be embodied on a non-transitory computer readable storage medium.

[6047] Examples of non-transitory computer readable storage media include computer system RAM, ROM, EPROM, EEPROM, and magnetic or optica! disks or tapes, it Is therefore to be understood that any electronic device capable of executing the above-described functions may perform those functions enumerated above. [0048] Turning now to FIG. 5, there is shown a block diagram of an example computer-readable medium 500 that may have stored thereon computer-readable instructions for generating print control data including instructions for defining the sections of a part 302 in first portions of layers 304 and the sections of a sacrificial part 308 in second portions of layers 308 through deposition of an agent 214 including a binder. It should be understood that the example computer-readable medium 500 depicted in FIG. 5 may include additional instructions and that some of the instructions described herein may be removed and/or modified without departing from the scope of the computer- readable medium 500 disclosed herein. The computer-readable medium 500 may be a non-transitory computer-readable medium, in which the term “non-transitory” does not encompass transitory propagating signals. Additionally, FIG. 5 is described with reference to FIGS. 1-4 for purposes of illustration.

[0049] The computer-readable medium 500 may have stored thereon computer-readable instructions 502-506 that a processor, such as the processor 102 depicted in FIG. 1, may execute. The computer-readable medium 500 may be an electronic, magnetic, optical, or other physical storage device that contains or stores executable instructions. The computer-readable medium 500 may be, for example, Random Access memory (RAM), an Electrically Erasable Programmable Read-Only Memory (EEPROM), a storage device, an optical disc, and the like.

[0050] The processor may fetch, decode, and execute the instructions 502 to identify selected areas in first portions of layers 304 of build material particles 204 in a build volume 208 at which sections of a part 302 are to be defined, for instance, based on a digital model 202 of the part 302. The processor may fetch, decode, and execute the instructions 502 to determine second portions of layers 308 of build material particles 204 in the build volume 208 at which sections of a sacrificial part 302 are to be defined, the second portions of layers 308 being separated from and within a predefined distance below the first portions of layers 304, and in which a shape of the second portions of layers 308 is based on a projection of a section of the digital model 202 of the part 302, The processor may fetch, decode, and execute the instructions 506 to generate print control data 212 including instructions for defining the sections of the sacrificial part 306 in the second portions of layers 308 and the sections of the part 302 in the first portions of layers 304 through deposition of an agent 214 including a binder that is to bind the build material particles 204 on which the agent 214 is deposited. The processor may generate the print control data 212 to include instructions for defining the sections of the sacrificial part 306 without increasing a temperature of the build material particles 204 defining the sections of the sacrificial part 306 above a temperature of the build material particles 204 prior to defining of the sections of the sacrificial part 306 through deposition of the agent 214.

[0051] Although described specifically throughout the entirety of the instant disclosure, representative examples of the present disclosure have utility over a wide range of applications, and the above discussion is not intended and should not be construed to be limiting, but is offered as an illustrative discussion of aspects of the disclosure.

[0052] 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 only and are not meant as limitations. Many variations are possible within the spirit and scope of the disclosure, which is intended to be defined by the following claims — and their equivalents -- in which all terms are meant in their broadest reasonable sense unless otherwise indicated.

Claims

What is claimed is:

1. An apparatus comprising: a processor; and a memory on which is stored instructions that when executed by the processor cause the processor to: identify, from a digital model of a part to be defined, selected first portions of layers of build material particles in a build volume at which sections of the part are to be defined; determine second portions of layers of build material particles in the build volume at which sections of a sacrificial part are to defined, the second portions being separated from and within a predefined distance below the first portions, wherein the second portions are related to the first portions of layers at which the sections of the part are to be defined; and generate print control data including instructions to define the sections of the part in the selected first portions and the sections of the sacrificial part in the determined second portions through deposition of an agent, the agent including a binder that is to bind the build material particles on which the agent is deposited.

2. The apparatus of claim 1 , wherein the instructions are further to cause the processor to: generate the print control data to: cause an agent delivery system of a three-dimensional (3D) fabrication system to deliver the agent including the binder into a pattern onto some of the selected first portions of the layers to define the sections of the part; and cause the agent delivery system to selectively deliver the agent in a matching pattern onto the determined second portions of the layers to define the sections of the sacrificial part.

3. The apparatus of claim 2, wherein the instructions are further to cause the processor to: generate the print control data to include instructions for an energy source to apply energy onto the first portions of the layers and the second portions of the layers after the sections of the sacrificial part and the sections of the part are respectively defined in the second portions and the first portions of the layers.

4. The apparatus of claim 2, wherein the instructions are further to cause the processor to: generate the print control data to include instructions to define an intermediate set of layers of build material particles between the second portions and the first portions of the layers, wherein the build material particles in the intermediate set of layers are to be free of the agent.

5. The apparatus of claim 1, wherein the print control data includes instructions to define the sections of the sacrificial part without increasing a temperature of the build material particles defining the sections of the sacrificial part above a temperature of the build material particles prior to defining of the sections of the sacrificial part.

6. The apparatus of claim 1 , wherein the instructions are further to cause the processor to: identify a projection of a portion of the digital model of the part to be defined; and determine the second portions at which the sections of the sacrificial part are to be defined based on the identified projection of the portion of the digital model.

7. The apparatus of claim 1 , wherein the instructions are further to cause the processor to: send the print control data to a three-dimensional (3D) fabrication system to: cause the sections of the sacrificial part to be defined in the determined second portions of the layers; and cause the part to be defined in the selected first portions of the layers following defining of the sections of the sacrificial part and defining of an intermediate set of layers of dry build material particles above the sections of the sacrificial part,

8. The apparatus of claim 1 , wherein the instructions are further to cause the processor to: control fabrication components of a three-dimensional (3D) fabrication system to define the sections of the sacrificial part in the determined second portions according to the print control data; control the fabrication components to define intermediate layers of dry build material particles above the determined second portions according to the print control data; and control the fabrication components to define the part in the selected first portions according to the print control data.

9. A method comprising: identifying, by a processor, selected first portions of layers of build material particles in a build volume at which sections of a part are to be defined; determining, by the processor, second portions of layers of build material particles in the build volume at which sections of a sacrificial part are to be defined, the second portions being separated from and within a predefined distance below the first portions, and wherein a shape of the second portions matches a shape of a portion of the part to be defined; and generating, by the processor, print control data including instructions to deposit an agent onto the determined second portions at which the sections of the sacrificial part are to be defined and instructions to deposit the agent onto the selected first portions at which the part is to be defined, wherein the agent includes a binder that is to bind the build material particles on which the agent is deposited.

10. The method of claim 9, wherein generating the print control data comprises generating the print control data to include Instructions for defining the sections of the sacrificial part without increasing a temperature of the buiid material particles defining the sections of the sacrificial part above a temperature of the build material particles prior to defining of the sections of the sacrificial part.

11. The method of claim 9, further comprising: generating the print control data to include instructions for an energy source to apply energy onto the first portions and the second portions after the sections of the sacrificial part and the sections of the part are respectively defined in the second portions and the first portions.

12. The method of claim 9, further comprising: sending the print control data to a three-dimensional (3D) fabrication system to: cause the sections of the sacrificial part to be defined in the determined second portions; and cause the part to be defined in the selected first portions following defining of the sections of the sacrificial part and defining of intermediate layers of dry build material particles above the sections of the sacrificial part.

13. The method of claim 9, further comprising: controlling fabrication components of a three-dimensional (3D) fabrication system to define the sections of the sacrificial part in the determined second portions according to the print control data; controlling the fabrication components to define an intermediate set of layers of build material particles above the second portions; and controlling the fabrication components to define the part in the selected first portions according to the print control data.

14. A non-transitory computer readable medium on which is stored instructions that when executed by a processor, cause the processor to: identify selected first portions of layers of build material particles in a build volume at which sections of a part are to be defined; determine second portions of layers of build material particles in the build volume at which sections of a sacrificial part are to be defined, the second portions being separated from and within a predefined distance below the first portions, and wherein a shape of the second portions matches a shape of a portion of the part to be defined; and generate print control data including instructions for defining the sections of the sacrificial part in the second portions and the sections of the part in the first portions through deposition of an agent including a binder that is to bind the build material particles on which the agent is deposited.

15. The non-transitory computer readable medium of claim 14, wherein the instructions are further to cause the processor to: generate the print control data to include instructions for defining the sections of the sacrificial part without increasing a temperature of the build material particles defining the sections of the sacrificial part above a temperature of the build material particles prior to defining of the sections of the sacrificial part through deposition of the agent,