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[0024]Methods of additive manufacturing, binder compositions for additive manufacturing, and articles produced by and/or associated with methods of additive manufacturing are generally described. Some of the methods of additive manufacturing described herein employ a binder composition described herein having one or more advantageous features.
[0025]For instance, some binder compositions described herein have one or more advantages for use in combination with particular types of metal powders. By way of example, in some embodiments, a binder composition as a whole is configured to interact with a metal powder such that the metal powder undergoes minimal amounts of deleterious chemical reactions. For instance, a binder composition may have a pH that reduces corrosion of the relevant metal powder. In some embodiments, a binder includes relatively low amounts of (or lacks) species that are highly reactive with the metal powder and/or undesirably reactive with the metal powder. Binder compositions having this property may desirably allow for the formation of metal-based composite structures and/or metal objects in which the metal component(s) has a chemical composition close to (or identical to) its composition in powder form and/or in which the metal powder has a desirable chemical composition.
[0026]As a second example, in some embodiments, a binder composition as a whole is configured to interact with a layer of metal powder such that it penetrates the layer of metal powder and/or spreads within the layer of metal powder in a desirable manner. The binder composition may be configured to readily penetrate through the depth of the layer of metal powder, which may assist with adhering the layer of metal powder together and/or may reduce the amount of undesired pores in a metal-based composite structure formed therefrom prior to sintering. In some embodiments, a binder composition is configured to spread laterally to a relatively low extent within a layer of metal powder. As excessive spreading is believed to cause the formation of metal objects that are oversized and/or rough, this property may assist with the formation of metal objects having fine features and/or that are smooth.
[0027]In some embodiments, a binder composition described herein is configured to be compatible with one or more components of an additive manufacturing system. By way of example, in some embodiments, a binder composition as a whole is configured to interact with one or more components of the additive manufacturing system such that the component(s) of the additive manufacturing system undergo minimal amounts of deleterious chemical reactions. For instance, a binder composition may have a pH that is non-corrosive to the component(s) of the additive manufacturing system, such as non-corrosive to the print head of the additive manufacturing system (e.g., a print head comprising steel, such as a print head comprising a steel face plate). As another example, in some embodiments, a binder composition as a whole has is configured such that it can be printed by an additive manufacturing system in a desirable manner. For instance, the binder composition as a whole may be configured to allow for the formation of droplets of a desired size and/or uniformity by a print head of the additive manufacturing system. Such properties may allow for additive manufacturing system to be capable of facilely printing the binder composition in a manner that results in the formation of desirable metal-based composite structures without appreciable wear and tear of the on-demand printer.
[0028]In some embodiments, a binder composition described herein is configured to be stored for an appreciable amount of time without undergoing undesirable transformations. For instance, in some embodiments, a binder composition described herein has a composition that retards and/or prevents the growth of biological contaminants therein. As another example, a binder composition described herein may be provided in a container that is configured to resist degradation by the binder composition. These advantages may allow for some of the binder compositions described herein to be prepared well in advance of anticipated use and stored until needed.
[0029]It should be understood that some binder compositions described herein may have all of the above-described advantages, some binder compositions described herein may have a subset of the above-described advantages, and binder compositions described herein may have none of the above-described advantages. Similarly, some binder compositions described herein may have advantages not described above and/or may be desirable for use in a variety of applications for reasons not described above. Particular features of binder compositions that may promote one or more of the above-described advantages are described in further detail below.
[0030]Some embodiments relate methods of additive manufacturing, binder compositions for additive manufacturing, and/or articles formed by additive manufacturing (e.g., three-dimensional compositions, metal-based composite structures, metal objects). For instance, a binder composition having one or more of the advantageous properties described herein may be employed in a method of additive manufacturing described herein to form a three-dimensional composition, metal-based composite structure, and/or metal object described herein. An overview of steps that may be included in methods of additive manufacturing is provided below. It should be understood that some methods of additive manufacturing may comprise some of the steps described below but lack over the steps described below, that some methods of additive manufacturing may comprise all of the steps described below, that some methods of additive manufacturing may comprise none of the steps described below, and that some methods of additive manufacturing may comprise further steps not described below.
[0031]In some embodiments, a method of additive manufacturing comprises a step of depositing a layer of metal powder. This step may comprise dispersing a metal powder to form a layer thereof. The metal powder may initially not be in the form of layer (e.g., it may be in the form of a source of metal powder enclosed in a container, in the form of a pile, etc.). FIG. 1 shows one non-limiting embodiment of a method of depositing a layer of metal powder in which a metal powder 10 is deposited to form a layer of metal powder 20. In some embodiments, a metal powder is deposited to form the layer thereof by one or more tools, non-limiting examples of which include rollers, doctor blades, and sifters. Depositing a metal powder to form a layer thereof is typically performed such that the resultant layer of metal powder is formed on a substrate. Appropriate examples of substrates include bases on which the article formed by the additive manufacturing method is designed to be formed (e.g., platforms comprising metals and/or ceramics, sheets comprising metals and/or ceramics) and layers disposed on such bases (e.g., one or more layers of metal powder disposed on a base on which the article formed by the additive manufacturing method is designed to be formed, one or more layers formed in an additive manufacturing process, such as one or more of the layers formed by one or more of the processes described below). Layers disposed on such bases may include layer(s) configured to be incorporated into an article formed by additive manufacturing (e.g., in the case of layer(s) themselves formed by additive manufacturing and/or layer(s) not configured to be incorporated into an article formed by additive manufacturing (e.g., in the case of layer(s) of metal powder).
[0032]Once a layer of metal powder is obtained, a method of additive manufacturing may comprise depositing a binder composition onto at least a portion of the layer of metal powder. FIG. 2A shows one example of this method step, as it depicts the deposition of a binder composition 100 on a layer 200 of metal powder. The metal powder comprises a plurality 210 of metal particles. In some embodiments, like the embodiment shown in FIG. 2A, the binder composition may be deposited on the metal powder in the form of droplets, such as in the form of a plurality of droplets formed by a print head. By way of example, a method of additive manufacturing described herein may comprise performing a binder jet printing process.
[0033]An additive manufacturing method may comprise performing the steps shown in FIGS. 1 and 2A multiple times successively. For instance, a method of additive manufacturing may comprise depositing a first layer of metal powder, then depositing a binder composition on at least a portion of the first layer of metal powder, and then depositing a second layer of metal powder on the first layer of metal powder. As another example, a method of additive manufacturing may comprise depositing a binder composition on at least a portion of a first layer of metal powder, then depositing a second layer of metal powder on the first layer of metal powder, and then depositing a binder composition on at least a portion of the second layer of metal powder. It can be seen that some methods of additive manufacturing may comprise performing these two steps in an alternating manner at least twice, at least three times, at least four times, at least five times, at least ten times, at least a hundred times, or a number of times sufficient to build up a metal-based composite structure.
[0034]Methods comprising performing successive steps of depositing a layer of metal powder and depositing a binder composition onto at least a portion of the layer of metal powder may be performed in a variety of manners. By way of example, FIG. 2B shows a method step of depositing a second powder layer 252 on the first powder layer onto which a binder composition had been deposited.
[0035]In some embodiments, the sequential steps of depositing a layer of metal powder and depositing a binder composition thereon may be performed in a manner in which the binder deposited on at least a portion of a first layer of metal powder is not dried or cross-linked prior to depositing a second layer of metal powder on the first layer of metal powder (e.g., the second layer of metal powder is deposited on the first layer of metal powder prior to drying or cross-linking the binder composition). The article formed by such successive steps may be referred to elsewhere herein as a “three-dimensional composition”. In some embodiments, the sequential steps of depositing a layer of metal powder and depositing a binder composition thereon may be performed in a manner in which the binder deposited on at least a portion of a first layer of metal powder is dried and/or cross-linked prior to depositing a second layer of metal powder on the first layer of metal powder.
[0036]It should be noted that some embodiments may comprise both of the above-referenced sequences of steps. For instance, the steps of sequentially depositing a layer of metal powder and then depositing a binder composition onto at least a portion of the layer of metal powder may be repeated a number of times without performing any drying or heating process on the binder composition (e.g., one or more layers of metal powder may be deposited prior to cross-linking or drying the binder composition previously deposited, binder composition may be deposited onto at least a portion of a layer of metal powder deposited prior to the cross-linking or drying of the binder composition previously deposited). These steps may result in the formation of a three-dimensional composition. Then, the binder composition may be dried and/or cross-linked to form a metal-based composite structure from the three-dimensional composition. After which, further steps of sequentially depositing a layer of metal powder and then depositing a binder composition onto at least a portion of the layer of metal powder may be performed thereon. The second three-dimensional composition may also be dried and/or cross-linked. This drying and/or cross-linking may result in the formation of a new metal-based composite structure comprising the prior metal-based composite structure and the dried and/or cross-linked three-dimensional composition formed thereon.
[0037]In some embodiments, a step of depositing a binder composition on at least a portion of a layer of metal powder like that shown in FIG. 2A or FIG. 2B comprises depositing a binder composition on a layer of metal powder such that it contacts some portions of the layer of metal powder and does not contact other portions of the layer of metal powder. The binder composition may penetrate into and/or spread into portions of the layer of metal powder that it contacts and may not penetrate or spread into portions of the layer of metal powder that it does not contact. This process may result in the formation of a layer having a morphology like that shown in FIG. 2C. In FIG. 2C, a layer 304 comprises a portion 354 comprising both a binder composition and a portion of the layer of metal powder and a portion 364 comprising a portion of the layer of metal powder but lacking the binder composition. The portions of the layer of metal powder through which the binder composition has penetrated and/or spread may be adhered together by one or more components of the binder composition (e.g., a polymer) upon deposition thereof and/or during later processing steps. The portions of the layer of metal powder through which the binder composition has not penetrated or spread may remain unadhered to each other.
[0038]During formation of a three-dimensional composition, deposition of a binder composition on a layer or metal powder may also comprise depositing a portion of the binder composition onto layer positioned therebeneath. Advantageously, this may adhere together layers in the three-dimensional composition with the layers to which they are directly adjacent, which may result in the formation of a three-dimensional object, metal-based composite structure, or combination of metal-based composite structures adhered together in all three dimensions and/or having a continuous morphology.
[0039]As described above, some methods of additive manufacturing comprise forming a metal-based composite structure (e.g., from a layer comprising a binder composition, from a three-dimensional composition) (e.g., in a process comprising drying and/or cross-linking a binder composition). As also described above, the binder composition may be a binder composition present in a three-dimensional composition and/or may be a binder composition present in a layer disposed on a metal-based composite structure.
[0040]Drying the binder composition may comprise exposing the binder composition to a stimulus that causes one or more volatile components therein to evaporate (e.g., free water, organic solvents, volatile pH modifiers). Other, non-volatile and/or less volatile components of the binder composition may not be removed by a drying process (e.g., bound water, a polymer, a cross-linking agent).
[0041]Cross-linking the binder composition may comprise exposing the binder composition to a stimulus that causes one or more portions thereof to undergo a cross-linking reaction (e.g., a polymer, a cross-linking agent). Non-limiting examples of suitable stimuli include heat and light (e.g., microwave radiation, UV light), wherein heat transfer may include any combination of conduction, convection and/or radiation. Convective heat transfer may include, but is not limited to, forced convection through the powder bed. Heat and/or light stimuli may be suitable both for drying the binder composition and cross-linking the binder composition; other such stimuli may only be suitable for one or the other. In some embodiments, a binder composition may be dried and then cross-linked. The drying step may comprise removing one or more components that would interfere with the cross-linking step. For instance, a drying step may comprise removing water (e.g., water that causes the equilibrium of the cross-linking reaction to favor breaking cross-links instead of forming cross-links) and/or may comprise removing a pH modifier (e.g., a pH modifier that would interfere with the cross-linking reaction).
[0042]FIG. 3 shows one example of a step of drying and/or cross-linking a binder composition, in which a stimulus is applied to a layer 306 to form a metal-based composite structure 406. In some embodiments, a method like that shown in FIG. 3 is performed on a single layer comprising a layer of metal particles and a binder (and/or a layer of metal particles on which a binder is disposed). In some embodiments, a method like that shown in FIG. 3 is performed on a series of such layers disposed on each other in a three-dimensional composition simultaneously.
[0043]In some embodiments, a metal-based composite structure may undergo one or more further steps. By way of example, portion(s) of a layer of metal powder (and/or layers of metal powder forming a metal powder bed) onto which the binder has been deposited may be incorporated into the metal-based composite structure while other portion(s) (e.g., portions onto which the binder composition was not deposited) may not be incorporated into the metal-based composite structure. One or more portion(s) of the layer(s) of metal powder and/or metal powder bed not incorporated into the metal-based composite structure may be removed therefrom. This may be accomplished by, for example, removing the metal-based composite structure from a powder bed.
[0044]As another example, a metal-based composite structure may be heated. The heating may comprise positioning the metal-based composite structure in an environment at a temperature that results in the removal of one or more components of the binder composition previously retained in the composite structure. For instance, the heating may remove a polymer from the binder composition retained in the composite structure and/or one or more other components of the binder composition not removed from the composite structure by prior drying and/or cross-linking steps. In some embodiments, heating the composite structure may cause thermal decomposition of these components of the binder composition that are then volatilized or retained as solids (e.g., as char) positioned within the resultant structure. The resultant structure may also be referred to herein as a “de-bound metal structure”. FIG. 4 shows one example of a heating step, in which heat is applied to a metal-based composite structure 408 to form a de-bound metal structure 608. During a heating step, the particles present in the metal-based composite structure may adhere together directly as the portion(s) of the binder composition are being removed.
[0045]In some embodiments, a metal-based composite structure and/or a de-bound metal structure undergoes a heating step to form a metal object. This heating step may comprise heating an environment in which the metal-based composite structure and/or de-bound metal structure is positioned to a temperature that allows for diffusion of metal components within the metal-based composite structure and/or de-bound metal structure but that does not melt the metal-based composite structure and/or de-bound metal structure to an undesirable extent. For example, this heating step may comprise heating the environment to a temperature that promotes sintering of the metal-based composite structure and/or de-bound metal structure. Advantageously, diffusion that occurs during sintering may further bond together the resultant metal object and/or may reduce (and/or eliminate) any porosity present in the metal-based composite structure and/or de-bound metal structure. This diffusion may also cause the metal-based composite structure and/or de-bound metal structure to densify, which may enhance its surface finish, mechanical properties, and/or electrical conductivity. FIG. 5 shows one example of a step of heating a de-bound metal structure, in which heat is applied to a de-bound metal structure 610 to form a metal object 710.
[0046]In some embodiments, one or more of the method steps described above may be performed in an additive manufacturing system. FIGS. 6A and 6B show two similar versions of an exemplary additive manufacturing system 1100. The various components of this additive manufacturing system and its operation are described below.
[0047]The additive manufacturing system 1100 shown in FIGS. 6A and 6B may be used to form an article 1102 from a metal powder 1104. The article 1102 may be a three-dimensional composition as described elsewhere herein. For instance, it may comprise a binder composition and a metal powder comprising a plurality of metal particles (e.g., as shown in FIGS. 2A-2C). As also described elsewhere herein, the three-dimensional composition 1102 can undergo subsequent steps to form a metal object. While the additive manufacturing system shown in FIGS. 6A and 6B is suitable for performing a binder jetting process to form a three-dimensional composition (e.g., by selectively joining portions of layers of metal powder with a binder composition in a sequential manner), it should be understood that the current disclosure is not limited to any particular type of additive manufacturing process or powder process (e.g., any particular type of powder metallurgical process) involving a binder. For example, other suitable processes that may be employed to form a three-dimensional composition to form a three-dimensional composition include, but are not limited to injection molding processes and powder fusion processes (e.g., selective laser melting processes).
[0048]The additive manufacturing system 1100 shown in FIGS. 6A and 6B can include a powder deposition mechanism 1106 (e.g., shown in FIG. 6B) and a print head (e.g., shown as print head 1118 in FIG. 6A and print head 1108 in FIG. 6B), which may be coupled to and moved across the print area by a unit 1107 (e.g., as shown in FIG. 6B). The powder deposition mechanism 1106 may be operated to deposit a layer of metal powder by depositing powder 1104 onto the powder bed 1114.
[0049]In some embodiments, a powder deposition mechanism comprises a metal powder supply 1112, a metal powder bed 1114, and a spreader 1116 (e.g., as shown in FIG. 6A). When present, the spreader 1116 can be movable from the metal powder supply 1112 to the metal powder bed 1114 and along the metal powder bed 1114 to deposit a metal powder onto the metal powder bed 1114 and to deposit successive layers of the metal powder across the metal powder bed 1114. As discussed in more detail below, the additive manufacturing apparatus 1100 and/or the spreader 1116 therein may be configured to deposit layers of metal powder on the powder bed having any suitable geometry (e.g., layers of metal powder having a homogeneous, planar geometry; layers of metal powder having a morphology other than a homogeneous, planar geometry). Depending on the particular embodiment, the spreader 1116 may include, for example, a roller rotatable about an axis perpendicular to an axis of movement of the spreader 1116 across the powder bed 1114. The roller can be, for example, substantially cylindrical. In use, rotation of the roller about the axis perpendicular to the axis of movement of the spreader 1116 can deposit the metal powder from the metal powder supply 1112 to the metal powder bed 1114 and form a layer of the metal powder along the metal powder bed 1114. It should be appreciated, therefore, that a plurality of sequential layers of the material 1104 can be formed in the metal powder bed 1114 through repeated movement of the spreader 1116 across the metal powder bed 1114.
[0050]The print head 1108 (in FIG. 6B) and/or 1118 (in FIG. 6A) can be movable (e.g., in coordination with movement of the spreader 1116) across the metal powder bed 1114 and/or can be stationary (e.g., in embodiments in which the platform 1105 is movable). In some embodiments, the print head 1108 and/or 1118 includes one or more orifices through which a liquid (e.g., a binder composition) can be delivered from the print head 1118 to each layer of the metal powder along the metal powder bed 1114. In certain embodiments, the print head 1108 and/or 1118 can include one or more piezoelectric elements, and each piezoelectric element may be associated with a respective orifice and, in use, each piezoelectric element can be selectively actuated such that displacement of the piezoelectric element can expel liquid from the respective orifice. In some embodiments, the print head 1108 and/or 1118 may be arranged to expel a single liquid formulation from the one or more orifices. In other embodiments, the print head 1108 and/or 1118 may be arranged to expel a plurality of liquid formulations from the one or more orifices. For example, the print head 1108 and/or 1118 can expel a plurality of liquids (e.g., a plurality of solvents), a plurality of components of a binder composition, or both from the one or more orifices. Moreover, in some instances, expelling or otherwise delivering a liquid from the print head may include emitting an aerosolized liquid (i.e., an aerosol spray) from a nozzle of the print head.
[0051]In general, the print head 1108 in FIG. 6B and/or 1118 in FIG. 6A may be controlled to deliver liquid such as a binder composition to the metal powder bed 1114 in predetermined two-dimensional patterns, with each pattern corresponding to a respective layer of the three-dimensional composition 1102. In this manner, the delivery of the binder composition may be a printing operation in which the metal powder in each respective layer of the three-dimensional composition is selectively joined along the predetermined two-dimensional layers. After each layer of the three-dimensional composition is formed as described above, the platform 1105 may be moved down and a new layer of metal powder deposited, binder composition again applied to the new metal powder, etc. until the object has been formed.
[0052]In some embodiments, the print head 1108 (in FIG. 6B) and/or 1118 (in FIG. 6A) can extend axially along substantially an entire dimension of the metal powder bed 1114 in a direction perpendicular to a direction of movement of the print head 1108 and/or 1118 across the metal powder bed 1114. For example, in such embodiments, the print head 1118 can define a plurality of orifices arranged along the axial extent of the print head 1108 and/or 1118, and liquid can be selectively jetted from these orifices along the axial extent to form a predetermined two-dimensional pattern of liquid along the metal powder bed 1114 as the print head 1108 and/or 1118 moves across the metal powder bed 1114. In some embodiments, the print head 1108 and/or 1118 may extend only partially across the metal powder bed 1114, and the print head 1108 and/or 1118 may be movable in two dimensions relative to a plane defined by the powder bed 1114 to deliver a predetermined two-dimensional pattern of a liquid along the powder bed 1114.
[0053]The additive manufacturing system 1100 generally further includes a controller 1120 in electrical communication with one or more other system components. For instance, in FIG. 6A, a controller 1120 is in electrical communication with the metal powder supply 1112, the metal powder bed 1114, the spreader 1116, and the print head 1118. In FIG. 6B, the controller 1120 is in electrical communication with the unit 1107, the powder deposition mechanism 1106, and the print head 1108. Also in FIG. 6B, the controller 1120 may be configured to control the motion of the unit 1107, the material deposition mechanism 1106, and the print head 1108 as described above.
[0054]A non-transitory, computer readable storage medium 1122 may be in communication with the controller 1120 and have stored thereon a three-dimensional model 1124 and instructions for carrying out any one or more of the methods described herein. Alternatively, the non-transitory, computer readable storage medium may comprise previously prepared instructions. With reference to FIG. 6B, such instructions, when executed by the controller 1120, may operate the platform 1105, the unit 1107, the material deposition mechanism 1106, and the print head 1108 to fabricate one or more three-dimensional compositions. For example, one or more processors of the controller 1120 can execute instructions to move the unit 1107 forwards and backwards along an x-axis direction across the surface of the powder bed 1114. One or more processors of the controller 1120 also may control the material deposition mechanism 1106 to deposit build material onto the metal powder bed 1114.
[0055]With reference toFIG. 6A, one or more processors of the controller 1120 can execute instructions to control movement of one or more of the metal powder supply 1112 and the metal powder bed 1114 relative to one another as the three-dimensional composition 1102 is being formed. For example, one or more processors of the controller 1120 can execute instructions to move the metal powder supply 1112 in a z-axis direction toward the spreader 1116 to direct the metal powder 1104 toward the spreader 1116 as each layer of the three-dimensional composition 102 is formed and to move the metal powder bed 1114 in a z-axis direction away from the spreader 1116 to accept each new layer of the metal powder along the top of the metal powder bed 1114 as the spreader 1116 moves across the metal powder bed 1114. One or more processors of the controller 1120 also may control movement of the spreader 1116 from the metal powder supply 1112 to the metal powder bed 1114 to move successive layers of the metal powder across the metal powder bed 1114.
[0056]In some embodiments, one or more processors of the controller 1120 can control movement of the print head 1108 (in FIG. 6B) and/or 1118 (in FIG. 6A) to deposit liquid such as a binder composition onto selected regions of the metal powder bed 1114 to deliver a respective predetermined two-dimensional pattern of the liquid to each new layer of the metal powder 1104 along the top of the metal powder bed 1114. In general, as a plurality of sequential layers of the metal powder 1104 are introduced to the metal powder bed 1114 and the predetermined two-dimensional patterns of the liquid are delivered to each respective layer of the plurality of sequential layers of the metal powder 1104, the three-dimensional composition 1102 is formed according to the three-dimensional model (e.g., a model stored in a non-transitory, computer readable storage medium coupled to, or otherwise accessible by, the controller 1120, such as three-dimensional model 1124 stored in the non-transitory, computer readable storage medium 1122). In certain embodiments, the controller 1120 may retrieve the three-dimensional model (e.g., three-dimensional model 1124) in response to user input, and generate machine-ready instructions for execution by the additive manufacturing system 1100 to fabricate the three-dimensional object 1102.
[0057]As described above, it will be appreciated that the illustrative additive manufacturing system 1100 is provided as one example of a suitable additive manufacturing system and is not intended to be limiting with respect to the techniques described herein for controlling the flow behavior of a metal powder. For instance, it will be appreciated that the techniques may be applied within an additive manufacturing apparatus that utilizes only a roller as a material deposition mechanism and does not include material deposition mechanism 1106.
[0058]According to some embodiments, the techniques described herein for controlling the flow behavior of a metal powder may be employed to control properties of a metal powder for a binder jet additive manufacturing system. Such a system may comprise additive manufacturing system 1100 in addition to one or more other apparatus for producing a completed part (e.g., a metal object as described herein). Such apparatus may include, for example, a furnace for sintering a three-dimensional composition fabricated by the additive manufacturing system 1100 (or for sintering such a three-dimensional composition subsequent to applying other post-processing steps upon the three-dimensional composition).
[0059]Techniques described herein may refer to a “metal powder,” although it will be appreciated that the techniques described herein are not necessarily limited to use cases in which the metal material employed to form one or more of the articles described herein comprises or c