Multilayer composites having variable layer thicknesses and related methods - Patents.com

Abstract

Three-dimensional multi-layer composite structures fabricated by additive manufacturing techniques and methods of fabricating structures by additive manufacturing techniques are described, where the multi-layer structures have layers of at least two different and precise thicknesses.

Description

[Technical field]

[0001] The described invention relates to a three-dimensional multi-layer composite structure produced by additive manufacturing techniques and to a method of producing a structure by additive manufacturing techniques, the multi-layer structure having at least two layers of different thickness and a precise thickness. [Background technology]

[0002] Metal or ceramic rigid bodies, of which one exemplary type is a porous sintered metal body or membrane, are used in a wide variety of industrial applications. Porous metal membranes can be used as filter membranes in the microelectronics and semiconductor manufacturing industries, as well as other industries that require high purity raw materials for processing. For example, in the semiconductor and microelectronics industries, in-line filters are often used to remove particulate matter from fluids to prevent the introduction of particulate matter into the manufacturing process. The fluids can be in the form of gas or liquid.

[0003] Currently, the common method of commercially making porous sintered metal bodies includes forming and sintering steps that involve manually moving and handling intermediate (in-process) forms of the porous bodies. These steps are labor intensive. Furthermore, the porous bodies are fragile and the forming steps can be imprecise. These features make the method prone to significant waste, undesirably low efficiency, and undesirably high cost. Furthermore, many rigid bodies must be formed to very precise shapes or sizes (e.g., thickness). Metal bodies may be formed at an early stage and then processed by machining steps to achieve the required accuracy of shape or dimensional features. However, machining steps add cost and complexity in making any type of rigid body. Furthermore, some types of metal bodies are negatively affected by machining steps, for example, machining steps can clog the pores of a porous membrane. Summary of the Invention

[0004] The following description relates to additive manufacturing methods useful for producing multi-layer composites that exhibit high precision in at least one dimension, such as the thickness direction (the "z-direction").

[0005] The described method uses additive manufacturing techniques to form a multi-layer body (i.e., a "multi-layer composite") by a process that includes forming layers of different thicknesses to achieve a desired level of precision or "thickness tolerance" for the thickness of the body. The layer thicknesses are selected to produce a multi-layer composite having a measured thickness equal to the target thickness within the thickness tolerance range. If the thickness tolerance is 0.1 millimeters (denoted as + / - 0.1 mm), an acceptable multi-layer composite may have a measured thickness within 0.1 millimeters above the target thickness and within 0.1 millimeters below the target thickness.

[0006] By forming at least some of the layers of the multi-layer composite to have a thickness less than the magnitude of the thickness tolerance, the measured thickness can be controlled to some extent within the thickness tolerance relative to the target thickness. In an exemplary method, the method can include forming one or more layers to have a thickness less than the magnitude of the thickness tolerance. Other layers can be formed to have a thickness greater than the magnitude of the thickness tolerance.

[0007] Thus, to produce a multi-layer composite by the described additive manufacturing methods, where the composite has an actual (measured) thickness that is within a predetermined thickness tolerance of a target thickness, the method includes forming a plurality of layers by additive manufacturing, the plurality of layers having at least two different thicknesses, for example one or more "fine" layers having a relatively smaller thickness and one or more coarse layers having a relatively larger thickness.

[0008] The combination of coarse and fine layers results in a combination of precise thickness and manufacturing efficiency. Coarse layers formed at greater thickness improve manufacturing efficiency by reducing the number of layers that must be formed to produce a multi-layer composite of a particular thickness. Fine layers can be used to control the thickness of the composite to a desired tolerance.

[0009] The multi-layer composite formed by the additive manufacturing process can have any size, shape and purpose, particularly structures formed to a desired high level of dimensional accuracy. In an exemplary method, the multi-layer composite is a green body that is a precursor to a derived structure having a desired utility. After the green body is formed, it can be processed to produce a derived structure, such as a rigid inorganic body, e.g., a porous metal film. By forming the green body to exhibit precise thickness dimensions, the derived structure (e.g., metal film) also has a precise thickness.

[0010] In one aspect, the invention relates to a method of forming a three-dimensional body by an additive manufacturing process, the method including forming a coarse feedstock layer having a coarse feedstock layer thickness, solidifying a portion of the coarse feedstock layer to form a solidified coarse feedstock layer having a solidified coarse feedstock layer thickness, forming a fine feedstock layer having a fine feedstock layer thickness less than the coarse feedstock layer thickness before or after forming the solidified coarse feedstock layer, and solidifying a portion of the fine feedstock layer to form a solidified fine feedstock layer having a solidified fine feedstock layer thickness less than the solidified coarse feedstock layer thickness.

[0011] The foregoing will become apparent from the following more particular description of exemplary embodiments of the present disclosure, as illustrated in the accompanying drawings, in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating embodiments of the present disclosure. [Brief description of the drawings]

[0012] [Figure 1] A through E show examples of the multilayer composites described. [Diagram 2] A and B show examples of post-treatment bodies formed from the described multi-layer composites. [Figure 3A] 1 illustrates exemplary steps of the described method of forming the described multi-layer composite or derivative. [Figure 3B]1 illustrates exemplary steps of the described method of forming the described multi-layer composite or derivative. [Figure 4A] 1 illustrates exemplary steps of the described method of forming the described multi-layer composite or derivative. [Figure 4B] 1 illustrates exemplary steps of the described method of forming the described multi-layer composite or derivative. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] The following description relates to methods useful for producing multi-layer three-dimensional structures by additive manufacturing, including methods commonly referred to as "3D printing" techniques.

[0014] Various forms of additive manufacturing techniques are known. These methods, as applied herein, generally involve a series of layering steps (e.g., "passes") that individually and sequentially form multiple layers of a solidified feedstock composition that includes particles dispersed in a solidified binder composition. The solidified binder composition acts as a structure that holds the particles together within the solidified feedstock composition. Using a series of additive manufacturing steps, the multiple layers of the solidified feedstock are sequentially formed into a multi-layer composite that includes multiple layers of the solidified feedstock composition.

[0015] Illustrative examples of additive manufacturing techniques include those commonly referred to as "powder bed" additive manufacturing, including various "binder jet printing" techniques, and also those referred to as stereolithography (SLA). The methods and materials described herein may be useful in conjunction with these types of additive manufacturing methods and are described with respect to these exemplary techniques.

[0016] In accordance with the present disclosure, additive manufacturing techniques can be used to fabricate three-dimensional bodies having a desired level of accuracy in thickness (i.e., the "measured thickness" or the "actual thickness"). As described, the body can have a thickness that is within a thickness tolerance range of the target thickness.

[0017] During manufacturing, structures (or "parts") created by a manufacturing process must often meet desired size and shape requirements, including dimensional requirements such as thickness requirements. Thickness requirements can be described using two factors, one factor is a nominal thickness, called the "target thickness," which is the specific thickness dimension desired. The second factor is the "thickness tolerance," which is the range of maximum allowable deviations of the actual (measured) thickness from the target thickness, either greater than or less than the target thickness. Thickness tolerances are shown as values ​​having a "plus" ("+") sign, a "minus" ("-") sign, or a "plus-minus" ("+ / -") sign followed by a unit of length to indicate whether the tolerance provides for deviations from the target thickness greater than, less than, or in a greater or lesser direction than the target thickness value, respectively. A tolerance of + / -0.1 millimeters provides for a difference of up to 0.1 millimeters greater than the target thickness and a difference of up to 0.1 millimeters less than the target thickness. A tolerance of +0.1 millimeters provides for a difference of up to 0.1 millimeters greater than the target thickness, but not less than the target thickness. Similarly, a tolerance of -0.1 millimeters allows for a maximum difference of 0.1 millimeters less than the target thickness, but no difference more than the target thickness.

[0018] The "magnitude" of a thickness tolerance is the numerical value of the tolerance. For a thickness tolerance of + / -0.1mm, the magnitude of the thickness tolerance is 0.1mm. The "range" of a thickness tolerance is equal to the magnitude or twice the magnitude. The range of thicknesses allowed by a thickness tolerance of + / -0.1mm is between 0.1mm less than the target thickness and 0.1mm more than the target thickness, spanning a total of 0.2mm. The range of thicknesses allowed by a thickness tolerance of +0.1mm is between the target thickness and 0.1mm more than the target thickness, equal to 0.1mm.

[0019] The described structures can be of the type that are manufactured according to a preselected target thickness and thickness tolerance. Additive manufacturing methods can manufacture structures with a wide range of dimensions, including thickness. Multilayer composites prepared according to the present disclosure can have thicknesses in the micron range, e.g., less than 100 microns, to the fractional inch range, e.g., 0.25 inches, 0.5 inches, or inch range, e.g., 1, 2 inches or more.

[0020] As an illustrative example, a manufacturing process may be designed to produce parts having a desired thickness in the range of a fraction of an inch, such as 1 / 10 of an inch, or 2.54 millimeters. This desired (desired) thickness may be referred to as the "target thickness" and may be preselected for producing the part. Along with the preselected target thickness, the manufacturing process may also preselect a "thickness tolerance" that defines a range of acceptable thicknesses above and below the preselected target thickness value.

[0021] According to this example, an acceptable part may be considered to be one having a thickness greater than or less than the target thickness by no more than the magnitude of the thickness tolerance. An acceptable part has a thickness that differs from the target thickness by no more than the magnitude of the thickness tolerance. For a part with a target thickness of 2.54 millimeters and a tolerance of 0.1 millimeters (denoted as + / - 0.1 mm), an acceptable part may have a thickness in the range of 2.44 to 2.64 millimeters. For a part with a target thickness of 2.54 millimeters and a tolerance of 0.05 millimeters (denoted as + / - 0.05 mm), an acceptable part may have a thickness in the range of 2.49 to 2.59 millimeters.

[0022] The methods herein use additive manufacturing techniques to form a multi-layer body (i.e., a "multi-layer composite") by a process that includes forming multiple layers of the multi-layer body with different layers having different thicknesses to achieve a desired precision in terms of the thickness of the body (forming a multi-layer body having a thickness that is within a predetermined thickness tolerance relative to a target thickness). The layer thicknesses are selected to produce a finished multi-layer composite having a measured thickness that is equal to the target thickness within the thickness tolerance. If the thickness tolerance is 0.05 millimeters (denoted as + / - 0.05 mm), an acceptable multi-layer composite may have a measured thickness that is within 0.05 millimeters above the target thickness and within 0.05 millimeters below the target thickness.

[0023] By forming at least some of the layers of the multi-layer composite to have a thickness less than the magnitude of the thickness tolerance, the measured thickness can be controlled to a precision that allows the measured thickness of the multi-layer composite to be within the thickness tolerance relative to the target thickness. In an exemplary method, the method can include forming one or more layers to have a thickness less than the magnitude of the thickness tolerance. Other layers can be formed to have a thickness greater than the magnitude of the thickness tolerance.

[0024] Thus, to produce a multi-layer composite by additive manufacturing as described above, where the composite has an actual (measured) thickness that is within a predetermined thickness tolerance of a target thickness, the method includes forming a plurality of layers by additive manufacturing, the plurality of layers having at least two different thicknesses, for the purposes of this specification, these layers are referred to as fine layers, referring to the layers having a smaller thickness, and coarse layers, referring to the layers having a larger thickness.

[0025] Forming multiple fine layers having smaller thicknesses during an additive manufacturing process slows down the production rate of the multilayer composite, i.e., increases the number of steps and amount of time required to produce a multilayer composite having a particular thickness because a larger number of finer (thinner) layers must be formed, meaning that more additive manufacturing steps are required to build a multilayer composite of a given thickness. However, forming a composite with one or more fine layers advantageously allows for control of the thickness of the multilayer composite.

[0026] The thickness of the microlayer may be within a typical range of thicknesses for layers formed by additive manufacturing processes, particularly at the lower end of the range, such as a thickness in the range of 30 microns to 100 microns, for example 30 to 50, 60, 70, 80 or 90 microns. The thickness of the microlayer may also be selected based on thickness tolerance values.

[0027] In an exemplary method, the thickness of the fine layer can be less than the magnitude of the thickness tolerance. By using a fine layer having a thickness less than the magnitude of the thickness tolerance, the multilayer composite can be manufactured to a level of accuracy approximately equal to the thickness of the fine layer. To achieve an accuracy of 0.1 millimeters and form a multilayer body having a thickness within a thickness tolerance of + / - 0.1 millimeters, a useful thickness of the fine layer can be 0.1 millimeters. In other exemplary methods, the thickness of the fine layer can be a fraction of the magnitude of the thickness tolerance, such as 3 / 4, 1 / 2, 1 / 3 or 1 / 4 of the magnitude of the thickness tolerance. That is, for a thickness tolerance of 0.1 millimeters, the fine layer can have a thickness of 0.075, 0.05, 0.033 or 0.025 mm to form a multilayer composite having a thickness within 0.1 mm of the target thickness.

[0028] In combination with one or more fine layers, one or more coarse layers having a relatively greater thickness (compared to the fine layers) can be formed using additive manufacturing techniques to increase the production rate of the multi-layer composite. The use of relatively thicker layers to form the multi-layer composite increases the production rate (requires less time) to make the multi-layer composite by reducing the total number of layers and the number of layer formation steps required to produce a multi-layer composite of a particular thickness. The rough layer thickness can be within the typical range for layers formed by additive manufacturing processes, such as between 100 microns and 500 microns in thickness. A thicker rough layer reduces the number of steps and the amount of time required to form a finished multi-layer composite of a given total thickness.

[0029] A multilayer composite made according to the described method can have layers of different thicknesses, including layers having a relatively greater thickness (referred to as "coarse" layers) and layers having a relatively smaller thickness (referred to as "fine" layers). The location of the one or more fine layers as part of the multilayer composite relative to the coarse layers can be any useful location. Similarly, the order in which the one or more fine layers are formed relative to the one or more coarse layers can be any useful order. Various locations of the coarse and fine layers, as well as various orders of forming the coarse and fine layers, can be effective for the purpose of providing a multilayer composite having a thickness that is within a predetermined thickness tolerance relative to a predetermined target thickness.

[0030] As an example, and for purposes of illustration, a fine layer or a series (or groups) of fine layers (which may optionally all be formed to the same thickness) may be formed first at the "bottom" of the multilayer composite. After forming one or a group of fine layers, one or a group of coarse layers (which may optionally all be formed to the same thickness) may be formed after ("on top") one or more of the fine layers. FIG. 1A (schematic and not to scale) shows an example of a multilayer composite 10 having a group of three fine layers 30 formed at the bottom of the composite 10 and a subsequently formed group 20 of five coarse layers 22 formed after and on top of the fine layers 32. As shown, the target thickness of the composite 10 may be 600 microns (0.6 millimeters (mm)), with a tolerance of + / - 50 microns (+- 0.05 mm). Each coarse layer 22 may be formed to a thickness of 100 microns (0.1 mm) and each fine layer 32 may be formed to a thickness of 30 microns (0.03 mm). The total thickness of the fine and coarse layers combined is 590 microns (0.590 mm), which is within a thickness tolerance of + / - 50 microns from the target thickness of 600 microns.

[0031] In another exemplary method shown in Figure 1B, a multi-layer composite 12 may be formed by first forming a group 20 of coarse layers 22, followed by a group 30 of fine layers 32. The coarse layers are formed first and are located in the multi-layer composite below the fine layers at the bottom of the composite. Exemplary thicknesses may be the same as or different from the composite 12 of Figure 1A.

[0032] In a different exemplary multi-layer composite shown in FIG. 1C (schematic and not to scale), the exemplary multi-layer composite 14 includes a bottom group 30 of three fine layers 32 formed at the bottom of the composite 14, a subsequently formed group 20 of five coarse layers 22 formed after and on the fine layers 32, and a second group 30 of three fine layers 32 formed on the top of the composite 14. In this embodiment, there is a group of fine layers 32 on each of the two exposed surfaces of the composite 14 (e.g., as the outer "skin" layers). The coarse layers 22 are disposed at interior locations of the composite (e.g., as the "core" layers). As shown, the target thickness of the composite 10 may be 700 microns (0.7 millimeters (mm)) with a tolerance of + / - 50 microns (+- 0.05 mm). Each coarse layer 22 may be formed to a thickness of 100 microns (0.1 mm) and each fine layer 32 may be formed to a thickness of 30 microns (0.03 mm). The total thickness of the fine and coarse layers combined is 680 microns (0.680 mm), which is within a thickness tolerance of + / - 50 microns from the target thickness of 700 microns.

[0033] In yet another exemplary multilayer composite shown in FIG. 1D (schematic and not to scale), the multilayer composite 16 includes a bottom group 20 of three coarse layers 22 formed at the bottom of the composite 16, a subsequently formed group 30 of three fine layers 32 formed after and on top of the coarse layers 22, and a second group 20 of five coarse layers 22 formed at the top of the composite 16.

[0034] For example, in another embodiment shown in FIG. 1E (schematic and not to scale), an exemplary multilayer composite 18 may include a first group 20 of coarse layers 22 forming a center of the multilayer composite 18 and a second group 30 of fine layers 32 forming an outer surface of the multilayer composite 18.

[0035] As shown in Figures 1A-1E, the fine layer 32 may form at least a portion of the exterior of the multi-layer composite 10, 12, 14, 16 and 18. The embodiments shown in Figures 1A-1E may also be combined such that the fine layer 32 forms the entire exterior of the multi-layer composite, including the top, bottom and sides. In some embodiments, the fine layer 32 may form part or all of the top, bottom and / or sides. In some embodiments, as described in more detail below, when the fine layer 32 and the coarse layer 22 have a binder, the binder saturation is different between the fine layer 32 and the coarse layer 22. In an embodiment such as Figure 1E, where there is a fine layer forming an exterior surface, the multi-layer composite may be formed by alternately depositing a first layer of powder to the thickness of the fine layer, depositing binder only in the areas corresponding to the fine layer, and then depositing a second layer of powder with binder deposited throughout the second layer, but with a higher binder saturation in the areas corresponding to the coarse layer 22 than in the areas corresponding to the fine layer 32. In some embodiments, such as FIG. 1E, where the fine layer forms the outer surface, there may be a gradient in porosity and / or density from the outer surface to the interior.

[0036] As shown, any of a variety of arrangements of fine and coarse layers can be effective in producing a multi-layer composite having a thickness within a predetermined thickness tolerance of a target thickness.

[0037] The multi-layer composites formed directly by the described additive manufacturing processes generally consist of a plurality of separately formed layers, each of which includes particles held together by a solidified binder composition. The multi-layer composites initially formed by the additive manufacturing process can be of any useful structure. In a particular example, the multi-layer composites can be of a structure commonly referred to as a "green body."

[0038] A multi-layer composite in the form of a green body includes particles dispersed throughout a solidified binder material that are useful materials during an additive manufacturing process to form the multi-layer composite. In a typical process, the green body is not a desired or functional end product, but instead may be an intermediate product, referred to herein as a "post-processed body," that requires further processing to form a useful derived structure.

[0039] The post-processed body can be of any structure, form or composition that can be produced by additive manufacturing techniques that form a green body and then process the green body to form a derived product (post-processed body). Examples of post-processed bodies include rigid (e.g., free-standing) bodies, such as rigid inorganic bodies made of materials that include at least a portion of an inorganic material, such as a metallic material or a ceramic material, where either the metallic material or the ceramic material is made from particles that are used to form a multi-layered composite in the form of a green body. The post-processed body made according to the method is made from a green body (multi-layered composite) that is formed to a precise thickness dimension, meaning a thickness that is within a certain tolerance range relative to the target thickness of the green body. Advantageously, the post-processed body made from a green body (having a precise thickness dimension) can also exhibit a precise thickness dimension, meaning a thickness that is within a certain tolerance range relative to the target thickness of the post-processed body.

[0040] In one particular example, the post-treatment body can be a rigid inorganic body, such as a rigid inorganic body made of a material including a metal, a metal alloy, or a ceramic. Examples of rigid organic bodies can be useful for a variety of purposes, including some purposes where a precise thickness of the rigid inorganic body can be useful or advantageous. These include porous inorganic (e.g., metal) membranes in the form of a relatively thin, optionally flat structure having two opposing surfaces and a relatively uniform and precise thickness over the area of ​​the membrane. The membrane can be in the form of a flat sheet, disk, or another structure with a uniform thickness.

[0041] More specifically, a post-treatment body in the form of a porous sintered metal body (membrane) for use as a filter (of any shape) may typically include two opposing major surfaces and a thickness between the two opposing major surfaces through which fluid flows during use of the membrane as a filter in a filtration process. The thickness of an exemplary porous metal membrane used as a filter membrane (e.g., the thickness of a disk, sheet or cup, or the thickness of a body wall of a tube or cylinder) may be within a range effective for use of the porous body as a filter membrane, providing desired flow characteristics, e.g., sufficient flow at a given pressure drop, and filtration characteristics, e.g., particle retention, while having sufficient strength and structural integrity to be handled, installed, and used as part of a filter system. Examples of useful thicknesses (target thicknesses) may range from 0.5 to 5 millimeters, e.g., 1 to 4 millimeters. Exemplary thickness tolerances for this type of post-treatment body may be less than + / -0.1 mm. Exemplary thickness tolerances may be + / -0.09 mm or less, + / -0.08 mm or less, + / -0.06 mm or less, or + / -0.05 mm or less.

[0042] An example of a derivative that can be made according to the methods described herein is shown in Figures 2A and 2B. The disk 40 is illustrated as a porous sintered metal body (membrane) having a configuration with two opposing flat surfaces and a thickness between the surfaces. The disk (e.g., a porous sintered metal membrane) is made of sintered metal particles (e.g., metal or metal alloy, alternatively ceramic), has a diameter, and has been made according to the methods described herein to have a measured thickness within a desired (preselected) thickness tolerance range relative to a target thickness.

[0043] Specifically, the disk 40 is a derivative (post-processed body) formed by processing a green body in the form of a multi-layer composite formed by the described additive manufacturing method. The green body is formed to exhibit a thickness within a thickness tolerance of the target thickness of the green body. The disk (post-processed body) can also have a precise thickness, meaning a thickness within a thickness tolerance of the target thickness of the post-processed body. To form the post-processed body to have a precise thickness within a target thickness tolerance, the green body is formed to a target thickness that is slightly greater than the target thickness of the post-processed body. During one or more post-processing steps, the thickness of the green body is slightly reduced. The thickness of the post-processed body is slightly less than the thickness of the green body. By taking into account this thickness reduction, the target thickness of the green body can be selected to be slightly greater than the target thickness of the post-processed body, taking into account the thickness reduction that occurs during post-processing. The amount of thickness reduction due to the post-processing step can be determined empirically. The thickness tolerance range of the post-processed body can be equal or approximately equal to the thickness tolerance range of the green body, and can be a thickness tolerance equal to any of the thickness tolerances described herein useful for multi-layer composites or green bodies.

[0044] A "measured thickness" that is within a tolerance range of a target thickness can be measured as the thickness at one location of a body (e.g., a multi-layer composite, e.g., a green body or a post-treated body), or preferably, can be measured at multiple locations of the body. As shown in FIG. 2B, the thickness of a post-treated body (e.g., a porous sintered metal membrane) can be measured at multiple locations (e.g., five locations identified as numbers 1-5), such as a central location and four locations equidistantly spaced around the periphery. Preferably, the measured thickness of the body at the multiple (e.g., five) measurement locations is within a preselected thickness tolerance range of the target thickness at all measurement locations.

[0045] Typically, the green bodies are further processed after formation to form the desired post-processed product from the multi-layer composite in the form of a green body. The green bodies may be subjected to one or more post-processing steps, including a curing step in which elevated temperatures are used to cure (e.g., crosslink) the binder composition, a debinding step in which the solidified binder is removed, and a sintering step in which the particles of the composite are fused together to form a sintered body.

[0046] In an exemplary method, the debinding and sintering steps may be performed in a single apparatus (e.g., oven or furnace) or may be performed as a sequence, a debinding step in a first apparatus, a subsequent sintering step performed in a second (different) apparatus. The temperature used for the debinding step is lower than the temperature used for the sintering step. The temperature of the debinding step may typically be in the range of less than 600°C, for example in the range of 100 to 550 or 600°C. The temperature selected for any particular debinding step for a particular multilayer composite may depend on the binder chemistry. The temperature of the sintering step may generally be higher than the temperature of the debinding step, for example higher than 550 or 600°C.

[0047] The term "sintering" as used herein has a meaning consistent with that given when the term is used in the art of porous sintered metal or ceramic structures. Consistent with this, the term "sintering" can be used to refer to a process of bonding together (e.g., "solid-state welding" or "fusion") a collection of small sinterable particles of one or more different types (sizes, compositions, shapes, etc.) by the application of heat, in a non-oxidizing environment, to the particles formed in a green body to a temperature at which the surfaces of the particles are fused together by physical (mechanical) bonds between the particle surfaces, but do not melt the particles (i.e., neither metallic material reaches its melting temperature).

[0048] The sintering process is carried out at a temperature higher than the sintering point of the particles of the body, but lower than the melting temperature of the particles. As used herein, the "sintering point" of a particle is the temperature at which the material of the particle can sinter, i.e., the particle starts to adhere to other particles of the body being sintered and can fuse to another particle at a certain pressure, e.g., atmospheric pressure. The sintering point of a material (e.g., a metal) usually refers to the temperature below the melting temperature of the material, at which the material becomes liquid.

[0049] Thus, useful temperatures for carrying out the sintering and debinding steps can depend on the composition of the solidified binder for the debinding step, the composition of the particles and the sintering point of the particles, and the size of the particles being sintered, e.g., whether the particles are "coarse" (larger) or "fine" (smaller). The sintering step can be carried out in a furnace or oven in a non-oxidizing atmosphere that does not react with or otherwise deleteriously affect the particles of the body being sintered, such as in a vacuum or an atmosphere of concentrated or pure hydrogen, concentrated or pure inert gas, or a combination of concentrated or pure hydrogen and inert gas.

[0050] In order to produce the described multi-layer composites having a precise thickness relative to a preselected target thickness, certain types of additive manufacturing methods have been found to be useful or advantageous. In general, additive manufacturing processes are known to be useful for producing structures exhibiting a wide range of shapes and sizes. Additive manufacturing processes can also be highly automated and relatively efficient and cost-effective.

[0051] The additive manufacturing process for forming a multi-layer composite requires components including particles, e.g., inorganic particles such as metal particles, and one or more components that are combined to form a binder composition. The binder composition may be combined with the particles, and the binder composition may be solidified (hardened, cured, etc.) to produce a solidified feedstock composition that includes the solidified binder composition that acts as a physical support structure (matrix) for the particles. The process of combining the particles with the binder composition and solidifying the binder composition as a layer of the composite may differ for various types of additive manufacturing techniques, for example, the process of combining the particles with the binder composition may differ for powder bed techniques and for various forms of powder bed techniques compared to stereolithography techniques.

[0052] Useful particles according to the present invention can be any particles that can be processed to form the useful multilayer composites, useful green bodies, or useful post-processed bodies described. The particles can be included in the feedstock in the form of a powder or as part of a slurry of particles (in powder form) in combination with other components, such as one or more components of the binder composition.

[0053] Examples of useful particles include inorganic particles that are considered to be "sinterable", such as inorganic particles that can be formed into green bodies as described and then treated by a sintering process to fuse the particles together. The particles can be any sinterable material, such as a metal or ceramic material.

[0054] The particles can be of any effective size (e.g., average particle size) or size range, including small or relatively small particles on the scale of microns (e.g., having an average size of less than 500 microns, less than 100 microns, less than 50 microns, less than 10 microns, or less than 5 microns). Preferably, the average particle size of the particles can be less than the thickness of the layer formed during the described additive manufacturing techniques.

[0055] The term "metal" as used herein refers to any metallic or metalloid chemical element or an alloy of two or more of these elements. Useful or preferred particles may be comprised of metals including nickel, nickel alloys, and stainless steels, among others.

[0056] The particles can be selected to achieve effectiveness in the described processes, to be included in feedstocks, formed into feedstock layers, formed into consolidated feedstocks and multi-layer composites, and then optionally further processed, such as by sintering, to form porous sintered bodies having the desired utility, for example, as porous filter membranes. The size, shape, and chemical makeup of the particles can be any that are effective for these purposes.

[0057] With regard to the binder component of the method, materials that may be useful as binders or components of binders include materials that are polymeric, organic (eg, liquid solvents), and inorganic.

[0058] Examples of inorganic materials that may be useful as binder components include particles such as clays that can be suspended in a liquid and dried to form a solid material. Useful clays or other inorganic particle-type binder components can be combined with inorganic particles (e.g., metal or ceramic as described), solvent (water or organic solvent) and polymer in such a way that the inorganic binder particles and the inorganic particles (of the feedstock) are suspended together in the polymer and liquid (e.g., water, organic solvent or a combination of both), and the liquid can then be removed, for example, by evaporation. When the liquid evaporates, the inorganic particles of the binder and the polymer form a solidified binder composition that supports the inorganic particles of the feedstock as part of the solidified feedstock composition.

[0059] Other binder compositions include curable polymer binder materials. The curable polymer binders can be combined as a liquid with the particles formed in the feedstock layer and then solidified. Examples of curable polymer binders include materials that can be chemically cured, for example by reacting and solidifying when exposed to high temperature (thermosetting) or by reacting and solidifying when exposed to electromagnetic radiation, such as from a laser, for example a UV laser. Other examples of polymer binders can be applied as a liquid in a liquid solvent, and then the solvent can be evaporated to leave the polymer binder as a structure supporting the particles. The polymer component of the binder can be optionally cured after the multilayer composite is fully formed, i.e., after all layers of the multilayer composite are formed, using a single cure that cures the polymers contained in all layers of the multilayer composite by a chemical reaction initiated by heat (high temperature), exposure to radiation, or another reaction mechanism.

[0060] The curable liquid binder composition may include curable materials containing chemical monomers, oligomers, polymers, crosslinkers, etc., and may further contain small amounts of functional ingredients or additives that enable or promote the flow, solidification, or hardening of the curable binder composition. These may include any of the following: flow aids, surfactants, emulsifiers, dispersants to prevent particle agglomeration, and initiators to start the hardening of the polymer when exposed to electromagnetic (e.g. ultraviolet) radiation or elevated temperatures.

[0061] In additive manufacturing techniques called "powder bed" techniques, including various techniques called "binder jet printing" techniques, particles are contained in a bed of "feedstock" that can be formed into a uniform layer known as a "feedstock layer". The feedstock layer contains the particles and can optionally contain one or more additional components, such as one or more components of a binder composition. Other optional components can include flow aids or polymer spacer particles. These methods include allowing or solidifying a binder composition, where one or more components can be included in the feedstock layer or can be selectively applied to portions of the feedstock layer, to form a solidified binder composition in selected portions (areas) of the feedstock layer. The mechanism by which the binder composition (or a separate portion thereof) becomes located in the selected portion of the feedstock layer and the mechanism by which the binder composition in the selected portion of the feedstock layer becomes solidified can vary.

[0062] Powder bed additive manufacturing techniques can generally include a series of multiple individual layering steps, each step being used to form a single cross-sectional layer of a multi-layer composite. After forming a first (bottom) layer, each subsequent layer is formed on top of the preceding layer. This series of multiple individual layering steps is effective to form a multi-layer composite of multiple individually formed layers of solidified feedstock. Powder bed additive manufacturing techniques can be used as described to create multi-layer composites including multiple layers of different thicknesses, including one or more fine layers and one or more coarse layers, to produce a composite having a thickness that is within a predetermined thickness tolerance relative to a thickness target.

[0063] These techniques, like other additive manufacturing techniques, produce three-dimensional objects described or defined by digital data such as CAD (computer-aided design) files. The three-dimensional body is built up sequentially layer by layer using a series of individual steps that combine to produce a composite ("multilayer composite") consisting of many thin cross-sectional layers of solidified feedstock. Each layer formation step may include forming a single feedstock layer on a surface that includes a feedstock containing particles. In some exemplary methods, the feedstock layer may contain a binder composition or components thereof. In other exemplary methods, the feedstock layer does not contain a binder composition or components of a binder composition. In these methods, the binder composition is selectively added to portions of the feedstock layer.

[0064] As an example, a roller or other spreading device applies the feedstock composition in the form of a powder or slurry evenly onto a surface by applying a single amount of the feedstock composition in one pass, or by applying multiple separate amounts of the feedstock in multiple passes over the surface. A "feedstock layer" can be formed from the feedstock composition by one or more steps of applying the feedstock composition to a surface using a roller or other application method to form a smooth, uniform feedstock layer having a desired useful depth.

[0065] The useful depth of the feedstock layer can be a depth for forming a coarse layer or a depth for forming a fine layer, as desired. The range of depths that can be formed by a particular process and system can depend on factors such as the composition of the feedstock and the resolution of the printhead or other device used to apply the liquid material to the feedstock layer. As one non-limiting example, a printhead with a resolution of 100 microns can be used with a feedstock layer having a depth of about 10 microns.

[0066] After the feedstock layer is formed, portions of the feedstock layer are selectively treated to form a solidified feedstock composition as part of the feedstock layer. Following these steps to form the solidified feedstock composition, an additional thin layer of the feedstock composition is spread on top of the completed layer, which contains the solidified feedstock composition surrounded by a quantity of unsolidified (original) feedstock composition.

[0067] This process is repeated to form multiple layers comprising the solidified feedstock, with each new layer (after the first layer) of the solidified feedstock composition being formed on and adhering to the previous layer of the solidified feedstock composition. Multiple feedstock layers are deposited, with multiple layers of the solidified feedstock composition being formed one after the other in succession on each completed layer to form a multi-layer composite. The layers may have different thicknesses. Each layer may be composed of the same feedstock material, or different layers may be composed of different feedstock materials. After all layers of the multi-layer composite have been deposited, the portion of the feedstock layer comprising the original feedstock material not used to make the solidified feedstock composition may be separated from the multi-layer composite.

[0068] If desired or useful, the feedstock layer used in powder bed additive manufacturing techniques may contain one or more optional components that are part of the binder composition or are otherwise useful as part of the solidified feedstock layer. These may include, for example, flow aids to improve the flow of the feedstock in the printer bed and improve the ability of the feedstock to form a uniform (uniform, height, homogeneous) feedstock layer. Alternatively or in addition, the feedstock layer may optionally contain a solid polymeric material that acts as a spacer between the particles, for example, as a "pore-forming" material. Such a solid polymer may be a thermoplastic (solid form at room temperature) pore-forming polymer and may be present in the feedstock layer in any desired amount, for example, 0.5 to 15% by weight based on the total weight of the feedstock, for example, 1 to 12 or 2 to 10% by weight based on the total weight of the feedstock, with the remainder of the feedstock (by weight) being particles.

[0069] More specifically, one specific example of a powder bed approach is referred to as “jet binder printing.” According to these exemplary additive manufacturing methods, the feedstock layer includes particles and may or may not include a binder composition or components of a binder composition.

[0070] The solidified feedstock layer is formed by selectively applying a liquid material to portions of the feedstock layer to selectively form a solidified feedstock composition in the portions of the feedstock layer. A printhead or other device useful for selectively dispensing and applying a desired amount of liquid to the feedstock layer moves over the top surface of the feedstock layer. The printhead or other useful device ejects the liquid and applies the liquid to selected portions of the top surface of the feedstock layer. The liquid flows into the feedstock layer and is useful for forming a solidified binder composition at the locations of the feedstock layer where the liquid was selectively applied. The solidified feedstock composition contains particles dispersed throughout the solidified binder composition.

[0071] There are different variants of this general description of the jet binder technology: according to one variant, the feedstock layer contains particles and the binder composition or a part of the binder composition, and the liquid selectively applied to the feedstock layer is a liquid useful in the process of solidifying the binder composition or its components in the feedstock layer.

[0072] In more exemplary detail, without being limiting herein, such methods may use a feedstock containing particles and components of a binder composition that are dissolved, suspended, or otherwise activated upon contact with the discharged liquid, and the combined binder composition may then solidify as a matrix surrounding the particles.

[0073] The components of the binder composition contained in the feedstock may be organic, such as polymers (e.g., polyvinyl alcohol) or phenolic resins, or inorganic, such as inorganic particles such as clay. The liquid may be any liquid effective to dissolve, disperse, or chemically react with the binder composition initially present in the feedstock layer. In some instances, the liquid or a portion of the liquid may be subsequently removed (e.g., evaporated) leaving behind a solidified feedstock composition that includes the solidified binder composition as a matrix structure surrounding and supporting the particles.

[0074] In another variation of the powder bed additive manufacturing technique, the feedstock layer does not contain (or does not require) any components that are part of the binder composition. In this variation, the liquid selectively applied to the feedstock layer may contain all the necessary components of the binder composition, which may be in the form of a chemically curable polymer in liquid form. In this variation, the liquid binder composition is selectively applied to the feedstock layer and allowed to solidify or solidify in place to produce a solidified feedstock layer.

[0075] According to examples of such systems, the feedstock layer may contain particles and need not contain other materials. For example, the feedstock layer may contain at least 70, 80, 90, or 95% by weight of particles. However, as described herein, other components such as pore-forming particles, flow aids, etc. may be desirable.

[0076] The liquid binder composition applied to the feedstock layer can include all the components of the binder composition that are necessary to selectively distribute and apply the binder composition in liquid form to the feedstock layer, and for the liquid binder composition to optionally solidify by further processing such as evaporation or chemical reaction. The liquid binder can include, for example, a polymeric material that can be solidified by either a chemical hardening mechanism (by exposure to electromagnetic radiation) or by removal of a solvent by evaporation.

[0077] Yet another variety of additive manufacturing techniques is called stereolithography. This method uses similar steps and equipment as powder bed techniques. With these techniques, the feedstock layer contains particles dispersed in a curable liquid binder composition. The feedstock layer may be contained in a shallow bed, similar to binder jet techniques. Multiple layers of solidified feedstock composition are successively formed by selectively curing (hardening) each layer by exposure to electromagnetic radiation, such as ultraviolet (UV) radiation. Compared to selectively applying liquid to a powder feedstock layer and solidifying the feedstock layer (as described above with respect to the jet binder technique), stereolithography selectively solidifies (hardens) portions of a liquid feedstock layer by exposing portions of the feedstock layer to electromagnetic radiation that induces chemical hardening.

[0078] Each of these different types of additive manufacturing techniques for use in making multilayer composites requires a binder composition, particles (e.g., in the form of powder or particle aggregates), and a useful equipment for carrying out the additive manufacturing process. The equipment can be (generally) an automated 3D printer capable of forming the multilayer composite by powder bed technology, jet binder printing technology, stereolithography printing technology, or another useful additive manufacturing method. The useful equipment and associated methods are effective for forming the multilayer composite by sequentially depositing multiple layers of solidified feedstock one on top of the previous layer.

[0079] An example of a binder jet printing additive manufacturing technique (100) useful for producing multi-layer composites is shown in Figures 3A and 3B.

[0080] FIG. 3A shows a sequence of steps for a useful binder jet printing additive manufacturing technique, demonstrating that the method can be used independently with different forms of feedstock 102 fed to the printer bed of the additive manufacturing system and different liquids 104 fed to the print head of the additive manufacturing system.

[0081] The feedstock 102 is a powder (or alternatively a slurry) containing particles and any additional components. In an exemplary method, the feedstock 102 does not contain (e.g., does not require) a binder composition or components thereof, and the liquid 104 contains a binder composition. In another exemplary method, the feedstock 102 contains a binder composition or components of a binder composition, and the liquid 104 contains a liquid component that is effective or aids in solidifying the binder composition in the feedstock by any process such as evaporation or by causing a chemical reaction of the binder. This process can be carried out using a commercially available binder jet printing device, the particles described herein, along with a liquid (heated thermoplastic) polymer binder (104) dispensed from the printhead of the device.

[0082] According to an exemplary step of the method (FIG. 3A), a feedstock (e.g., 102) is introduced into the bed of a powder bed additive manufacturing system and formed into a uniform feedstock layer of a desired depth on the build plate of the device (110). In a next step (112), a print head selectively deposits a liquid binder (104) onto a portion of the first layer. The liquid binder (104) can be solidified after being placed onto the feedstock layer. For example, the liquid binder (104) can contain a polymer dissolved or dispersed in a liquid solvent that can be removed to solidify the polymer. After the liquid binder (104) is selectively applied to the feedstock layer, the liquid binder (104) can be solidified, for example, by applying heat to the liquid binder to remove the solvent from the binder and form a solidified feedstock in the portion. Alternatively, the liquid binder (104) can be a curable polymer that can be applied to the feedstock layer in liquid form and then chemically reacted to solidify.

[0083] The liquid binder is applied to the feedstock layer in an amount effective to fix the position of the particles of the feedstock layer. The method does not require that the liquid binder be applied in an amount or manner that fills the spaces between the particles of the feedstock, but may be applied in an amount that connects or "bridges" adjacent or neighboring particles in the feedstock layer to fix the position of the particles relative to other particles, without necessarily filling the void spaces of the feedstock layer. A "solidified" feedstock is "solid" in the sense that it has been sufficiently stiffened, rigidified, or hardened to act as a structure that supports and maintains the position of the particles, but may contain openings, void spaces, or pores between the connected particles. A solidified feedstock may include particles connected by, for example, a dried, hardened, or otherwise continuous (meaning that it is not necessarily solid, but is free of pores) polymeric material that connects and maintains the position of the particles within the solidified feedstock structure.

[0084] The portion of the applied feedstock layer that is not formed into solidified feedstock remains as the original powder feedstock.

[0085] The build plate is moved downward (114) and a second layer of the feedstock is formed as a second uniform feedstock layer over the first feedstock layer including a portion of the solidified feedstock (116). The printhead then selectively deposits a second amount of liquid polymer binder (104) onto portions of the second feedstock layer (118), and the second amount of liquid binder is solidified, for example, by using heat to remove solvent and form a dry (solidified) polymer binder, or by another relevant mechanism based on the type of binder composition, to form a solidified feedstock from the second layer.

[0086] The portion of the second layer that is not formed relative to the solidified feedstock remains as the original powder feedstock.

[0087] Steps 114, 116 and 118 are repeated (120) to form a finished multi-layer composite (e.g., green body) surrounded by the original feedstock (102 or 104). The multi-layer composite is a multi-layer body that includes the solidified feedstock of each layer formed and is composed of particles dispersed in a solidified (solid) binder. Optionally, if the polymer binder is thermosetting, the multi-layer composite can be heated, optionally in the presence of the surrounding original powder feedstock, to crosslink and harden the liquid polymer binder (122). The original (loose) powder feedstock (102 or 104) can be removed and separated from the multi-layer composite (124). According to the present specification, any one or more layers of the feedstock can be a fine layer or a coarse layer.

[0088] The multi-layer composite can be moved to a location for any type of subsequent processing (post-processing) that may be useful or desirable to convert the multi-layer composite (e.g., green body) into a derived product, such as a rigid inorganic body. Exemplary steps not shown may include a debinding step, in which solidified binder is removed from the multi-layer composite, and a sintering step, in which particles of the multi-layer composite are sintered to bind the particles together and form a rigid inorganic body.

[0089] FIG. 3B shows a schematic of the steps of the technique 100 with the associated process equipment and feedstocks.

[0090] Referring to FIG. 3B, an exemplary process can be carried out using a commercially available binder jet printing apparatus (130), a feedstock (132) as described herein, and a liquid (133) dispensed from a printhead (136) of the apparatus (130). According to an exemplary step of the method, the feedstock (132) is formed as a feedstock layer (134) of uniform thickness and height on a build plate (138) of the apparatus (130). The feedstock layer (134) can be formed using a single pass or multiple passes to uniformly form and distribute the feedstock (132) to the desired depth using a roller or other leveling device. The feedstock layer (134) can be a fine layer or a coarse layer as described herein. The printhead (136) selectively deposits the liquid (133) onto a portion of the first layer (134).

[0091] The liquid 133 can be, for example, a liquid binder composition (as described with respect to FIG. 3A) or another liquid as described herein. The liquid (133) in the form of a liquid binder composition is solidified, for example, by drying with heat to evaporate the binder solvent and form a first solidified feedstock (140) containing a solid polymer in the part, or by causing a chemical reaction to solidify the feedstock.

[0092] The portions of the feedstock layer 134 that are not formed into a solidified feedstock (140) remain as the original feedstock (132). The build plate (138) is moved downward (114) and a second or subsequent feedstock layer (142) is formed on the first layer (134) and the first solidified feedstock (140). The print head (136) then selectively deposits a second amount of liquid polymer binder (133) onto the portions of the second layer (142) and solidifies the second amount of liquid polymer binder (133) to form a solidified feedstock from the second layer. The portions of the second layer that are not formed into a solidified feedstock remain as the original feedstock. The feedstock layer (142) can be a fine layer or a coarse layer as described herein.

[0093] This sequence of steps of applying a feedstock layer over the previous layer and applying a binder to the new feedstock layer to produce a solidified feedstock for the new feedstock layer is repeated (150) to form a finished multi-layer composite (152) surrounded by the original powder feedstock (132). The multi-layer composite (152) is a body containing the solidified feedstock of each formed layer, and is composed of particles from the feedstock dispersed in a solidified (solid) polymer binder. The composite (152) is formed to include layers of different thicknesses, including one or more fine layers and one or more coarse layers. If desired, the multi-layer composite can be further processed, such as by post-processing including debinding and sintering to convert the multi-layer composite in the form of a green body into a rigid organic body (e.g., a porous sintered metal film) to produce a derived product.

[0094] For example, as shown, the multi-layer composite (152), optionally in the presence of the surrounding original powder feedstock (132), can be heated to cure the liquid polymer binder (122).

[0095] The original (loose) powder feedstock (132) may be removed and separated from the multi-layer composite (152). The multi-layer composite (152) may be transferred to an oven and heated to a temperature effective to remove the solidified binder (debinding) from the multi-layer composite (152). Optionally, following the debinding step, the multi-layer composite (152) may be further processed by a sintering step in a furnace to form a derived structure, such as a rigid inorganic body (160).

[0096] A technique called stereolithography (SLA) is a form of additive manufacturing technology that can be used to build multi-layer composites layer by layer and involves a photochemical process that uses light (electromagnetic radiation) to selectively polymerize, crosslink, or otherwise chemically react reactive chemical components such as monomers, oligomers, crosslinkers, etc. (together referred to as "polymers" or "liquid polymer binders") of a layer of a liquid feedstock to form a hardened polymeric reaction product ("solidified polymer") of the solidified feedstock of the feedstock layer. The liquid polymer binder is selectively curable by exposure to electromagnetic radiation such as ultraviolet (UV) light. The feedstock is in liquid form and contains a hardenable liquid polymer ("liquid polymer binder") in combination with particles.

[0097] Multilayer composites are constructed by a series of steps that produce multiple thin cross-sections ("solidified feedstock" of "layers" herein) of a larger three-dimensional structure (composite). An electromagnetic radiation source (e.g., a laser) selectively applies electromagnetic radiation over a portion of a layer of liquid feedstock, the liquid feedstock comprising, according to the present specification, particles and a liquid polymer binder that can be solidified by chemically hardening upon exposure to electromagnetic radiation. Electromagnetic radiation, for example provided by a laser, selectively irradiates a portion of the layer of liquid feedstock at the surface of the layer. The electromagnetic radiation solidifies (i.e., cures) the liquid polymer binder by chemical reaction to form a solidified feedstock containing particles and solidified (hardened) polymer.

[0098] After the initial layer of solidified feedstock is formed, an additional thin layer of liquid feedstock is deposited on top of the completed layer containing solidified feedstock, and the process is repeated to form multiple layers, each layer on top of and attached to the top of the previous layer. Multiple layers are deposited one on top of each other in succession to form a multilayer composite that is a composite of each layer of solidified feedstock. The multiple layers can include one or more fine layers and one or more coarse layers as described herein. After all layers of the multilayer composite are formed, the portion of the layer containing the original liquid feedstock that was not used to prepare the solidified feedstock is separated from the multilayer composite. The multilayer composite can then be processed if necessary, for example, by a process including removal of the solidified (cured) polymer from the particles (i.e., "debinding") and optional sintering to form a derived structure, such as a rigid inorganic body (e.g., a porous sintered metal membrane).

[0099] Stereolithography additive manufacturing techniques may be used as described to create multi-layer composites including multiple layers of differing thicknesses, including one or more fine layers and one or more coarse layers, to produce a composite having a thickness that is within a predetermined thickness tolerance relative to a thickness target.

[0100] An example of a stereolithography additive manufacturing technique (200) useful for producing the described multi-layer composites is shown in Figure 4A. The feedstock 202 is a liquid containing particles in combination with a liquid curable polymer binder.

[0101] This process can be carried out using commercially available stereolithography additive manufacturing equipment and a liquid polymer binder combined with particles to form a feedstock. According to the exemplary steps of the exemplary method (steps numbered in parentheses as shown in FIG. 4A), a liquid feedstock (202) received by a stereolithography additive manufacturing device is formed as a uniform layer on the build plate of the device (204, 206). In the next step (208), an electromagnetic radiation source (e.g., a UV (ultraviolet) laser) selectively irradiates a portion of this first layer with radiation of a wavelength that chemically cures and solidifies the liquid polymer binder of the feedstock. The solidified liquid polymer binder forms a solidified feedstock in the irradiated portion. The layer of liquid feedstock can be a fine layer or a coarse layer.

[0102] The portions of the layer that are not formed relative to the solidified feedstock remain as the original liquid feedstock.

[0103] The build plate is moved down (210) and a second layer (either a fine layer or a coarse layer) of liquid feedstock is formed as a second uniform layer (212) over the first feedstock layer and over the solidified feedstock of the first feedstock layer. An electromagnetic irradiation source then selectively irradiates portions of the second layer (214) to solidify (cure) portions of the liquid feedstock of the second layer to form solidified feedstock in the portions of the second layer. Portions of the second layer that are not formed into solidified feedstock remain as the original liquid feedstock. Steps 212, 214, and 216 are repeated (218) to form a completed multi-layer solidified feedstock composite ("final part") surrounded by the original liquid feedstock (202).

[0104] The multi-layered solidified feedstock composite is a body containing the solidified feedstock of each layer formed, which is composed of particles dispersed in the solidified (solid) polymer binder of the liquid feedstock. The original liquid feedstock (202) can be removed and separated from the multi-layered composite (218). The multi-layered composite can then be further processed to form derived structures, such as rigid inorganic bodies.

[0105] Referring to FIG. 4B, an exemplary process may be performed using a commercially available stereolithography additive manufacturing apparatus (230) using a liquid feedstock (232) according to the present disclosure. According to an exemplary step of the method, the liquid feedstock (232) is formed as a uniform feedstock layer (234) on a build plate (238) of the apparatus (230). A laser (236) applies electromagnetic radiation (233) to a portion of the first layer (234) to form a first solidified feedstock (240) thereon. The portion of the feedstock layer (234) that is not formed into a solidified feedstock (240) remains as the original liquid feedstock (232). The build plate (238) is moved downward (214) to form a second or subsequent liquid feedstock layer (242) on the first layer (234) and the first solidified feedstock (240). A laser (236) then selectively irradiates portions of the second layer (242) with electromagnetic radiation (233) to form a solidified feedstock from the second layer. Portions of the second layer not formed into a solidified feedstock remain as the original liquid feedstock. This sequence is repeated (250) to form a completed multi-layered solidified feedstock composite (252) surrounded by the original liquid feedstock (232). The multi-layered solidified feedstock composite (252) is a body containing the solidified feedstock of each layer formed, and is composed of particles from the feedstock dispersed in the solidified (solid) hardened polymer of the feedstock.

[0106] The original liquid feedstock (232) can be removed and separated from the multi-layered composite (252), which can then be further processed by a sintering step in a furnace to form a derived structure, such as a rigid inorganic body (260).

[0107] Aspects In a first aspect, a method of forming a three-dimensional body by an additive manufacturing process includes forming a coarse feedstock layer having a coarse feedstock layer thickness, solidifying a portion of the coarse feedstock layer to form a solidified coarse feedstock layer having a solidified coarse feedstock layer thickness, forming a fine feedstock layer having a fine feedstock layer thickness less than the coarse feedstock layer thickness, either before or after forming the solidified coarse feedstock layer, and solidifying a portion of the fine feedstock layer to form a solidified fine feedstock layer having a solidified fine feedstock layer thickness less than the solidified coarse feedstock layer thickness.

[0108] The second embodiment of the first embodiment, wherein forming the solidified coarse feedstock layer includes forming a coarse feedstock layer, applying a liquid to a portion of the coarse feedstock layer, and solidifying the portion of the coarse feedstock layer to form the solidified coarse feedstock layer, and forming the solidified fine feedstock layer includes forming a fine feedstock layer, applying a liquid to a portion of the fine feedstock layer, and solidifying the portion of the fine feedstock layer to form the solidified fine feedstock layer.

[0109] The third embodiment of the first embodiment, wherein forming the solidified coarse feedstock layer comprises forming a coarse feedstock layer and solidifying a portion of the coarse feedstock layer by irradiating a portion of the coarse feedstock layer to form the solidified coarse feedstock layer, and forming the solidified fine feedstock layer comprises forming a fine feedstock layer and solidifying a portion of the fine feedstock layer by irradiating a portion of the fine feedstock layer to form the solidified coarse feedstock layer.

[0110] A fourth embodiment according to any of the first to third embodiments, wherein the solidified fine feedstock layer forms at least a part of an exterior of the three-dimensional body.

[0111] The fifth embodiment according to the fourth embodiment, wherein the solidified fine feedstock layer forms an exterior top surface of the three-dimensional body.

[0112] The sixth embodiment of the present invention relates to a method for manufacturing a three-dimensional body, the method comprising the steps of: forming a layer of solidified fine feedstock on an exterior surface of the three-dimensional body;

[0113] A seventh embodiment according to any of the fourth to sixth embodiments, wherein the solidified fine feedstock layer forms at least a part of an exterior side of the three-dimensional body.

[0114] An eighth embodiment according to any of the fourth to seventh embodiments, wherein the solidified feedstock layer forms the entire exterior of the three-dimensional body.

[0115] A ninth embodiment according to any of the first to eighth embodiments, wherein the thickness of the solidified fine feedstock layer is no more than 70% of the thickness of the solidified coarse feedstock layer.

[0116] A tenth embodiment according to any of the first to ninth embodiments, wherein the fine feedstock layer comprises sinterable metal particles or sinterable ceramic particles and the coarse feedstock layer comprises sinterable metal particles or sinterable ceramic particles.

[0117] An eleventh aspect of any of the first to tenth aspects, further comprising specifying a target thickness and a thickness tolerance for the body; forming a plurality of solidified coarse layers, each having a thickness greater than the magnitude of the thickness tolerance; forming at least one solidified fine layer having a thickness less than the magnitude of the thickness tolerance; and forming the three-dimensional body to have a measured thickness that differs from the target thickness by no more than the magnitude of the thickness tolerance.

[0118] A twelfth aspect according to the sixth aspect, wherein the target thickness is within the range of 1 to 5 millimeters, the thickness tolerance is no greater than + / - 0.08 mm, and the measured thickness is no greater than the magnitude of the thickness tolerance greater or less than the target thickness.

[0119] A thirteenth aspect according to the twelfth aspect, wherein the thickness tolerance is less than + / - 50 microns, the method comprising forming a plurality of solidified coarse layers, each having a thickness of at least 50 microns, and forming at least one solidified fine layer having a thickness less than 80 microns.

[0120] The fourteenth aspect of the present invention is directed to any one of the first to thirteenth aspects, wherein the feedstock for the coarse feedstock layer or the fine feedstock layer comprises metal particles and a binder composition or a component of a binder composition.

[0121] The fifteenth aspect of the present invention is directed to the fourteenth aspect, wherein the liquid in the coarse feedstock layer of the fine feedstock layer comprises one of water, an organic solvent, or both.

[0122] The sixteenth embodiment of any of the first to thirteenth embodiments, wherein the feedstock for the coarse feedstock layer or the fine feedstock layer comprises metal particles, and the liquid in the coarse feedstock layer or the fine feedstock layer comprises a polymer of the binder composition.

[0123] A seventeenth embodiment according to the sixteenth embodiment, wherein the binder composition comprises a curable polymer, and the method comprises selectively applying a liquid binder composition to portions of the feedstock layer and curing the liquid binder composition by chemical reaction.

[0124] An 18th embodiment according to any of the first to seventeenth embodiments, further comprising separating the portions of the solidified coarse and fine feedstock layers from the portions of the unsolidified coarse and fine feedstock layers, and sintering the solidified coarse and fine feedstock layers to form a solidified three-dimensional inorganic body.

[0125] The 19th embodiment of the present invention is described in the 18th embodiment, wherein the solidified coarse feedstock layer and the fine feedstock layer comprise inorganic particles, and the solidified coarse feedstock layer and the fine feedstock layer are sintered to cause the inorganic particles to form a sintered film.

[0126] A twentieth aspect of the nineteenth aspect of the present invention, further comprising specifying a target thickness for the film and a film thickness tolerance, forming a plurality of solidified coarse feedstock layers, forming at least one solidified fine feedstock layer, separating portions of the solidified coarse feedstock layers and the fine feedstock layers from portions of the coarse feedstock layers and the fine feedstock layers that are not solidified, and sintering the solidified coarse feedstock layers and the fine feedstock layers to form a sintered film, wherein the sintered film has a thickness that differs from the film target thickness by no more than the film thickness tolerance.

[0127] In a twenty-first aspect, a sintered membrane is formed according to the method of the twentieth aspect.

[0128] The twenty-second embodiment according to the twenty-first embodiment, wherein the membrane is a porous metal membrane.

[0129] In a twenty-third aspect, a three-dimensional object is formed by the method according to any one of the first to nineteenth aspects.

Claims

1. 1. A method for forming a three-dimensional body by an additive manufacturing process, comprising the steps of: forming a coarse feedstock layer having a coarse feedstock layer thickness; solidifying a portion of the coarse feedstock layer to form a solidified coarse feedstock layer having a solidified coarse feedstock layer thickness; forming a fine feedstock layer having a fine feedstock layer thickness less than a coarse feedstock layer thickness, either before or after forming the solidified coarse feedstock layer; solidifying a portion of the fine feedstock layer to form a solidified fine feedstock layer having a solidified fine feedstock layer thickness less than the solidified coarse feedstock layer thickness; Specifying a target thickness and thickness tolerance for the body; forming a plurality of solidified rough layers, each having a thickness greater than a magnitude of a thickness tolerance; forming at least one solidified microlayer having a thickness less than the magnitude of the thickness tolerance; forming the three-dimensional body to have a measured thickness that differs from the target thickness by no more than the magnitude of the thickness tolerance; Including, The target thickness is in the range of 1 to 5 millimeters; The thickness tolerance is ±0.08 mm or less; A method in which the measured thickness is less than or equal to the thickness tolerance magnitude and greater or less than the target thickness.

2. forming a solidified coarse feedstock layer; forming a crude feedstock layer; applying a liquid to a portion of the coarse feedstock layer; solidifying a portion of the coarse feedstock layer to form a solidified coarse feedstock layer; Including, forming a solidified fine feedstock layer; forming a fine feedstock layer; applying a liquid to a portion of the fine feedstock layer; solidifying a portion of the fine feedstock layer to form a solidified fine feedstock layer; The method of claim 1 , comprising:

3. forming a solidified coarse feedstock layer; forming a crude feedstock layer; solidifying a portion of the coarse feedstock layer by irradiating the portion of the coarse feedstock layer to form a solidified coarse feedstock layer. Including, forming a solidified fine feedstock layer; forming a fine feedstock layer; solidifying a portion of the fine feedstock layer by irradiating the portion of the fine feedstock layer to form a solidified coarse feedstock layer; The method of claim 1 , comprising:

4. 4. The method of claim 1, wherein the solidified fine feedstock layer forms at least a portion of the exterior of the three-dimensional body.

5. The method of claim 4 , wherein the solidified fine feedstock layer forms an exterior top surface of the three-dimensional body.

6. 6. The method of claim 5, wherein the solidified fine feedstock layer forms the exterior top and bottom surfaces of the three-dimensional body.

7. 7. The method of any one of claims 4 to 6, wherein the solidified fine feedstock layer forms at least a portion of an exterior side of the three-dimensional body.

8. 8. The method of claim 4, wherein the solidified feedstock layer forms the entire exterior of the three-dimensional body.

9. 9. The method of any one of claims 1 to 8, wherein the thickness of the solidified fine feedstock layer is no more than 70% of the thickness of the solidified coarse feedstock layer.

10. 10. The method of claim 1, wherein the fine feedstock layer comprises sinterable metal particles or sinterable ceramic particles and the coarse feedstock layer comprises sinterable metal particles or sinterable ceramic particles.

11. The thickness tolerance is less than + / - 50 microns, and the method comprises: forming a plurality of solidified rough layers, each having a thickness of at least 50 microns; forming at least one solidified microlayer having a thickness of less than 80 microns; The method of claim 1 , comprising:

12. 12. The method of claim 1, wherein the feedstock for the coarse feedstock layer or the fine feedstock layer comprises metal particles and a binder composition or a component of a binder composition.

13. 13. The method of claim 12, wherein the liquid in the coarse feedstock layer of the fine feedstock layer comprises water, an organic solvent, or both.

14. the feedstock for the coarse feedstock layer or the fine feedstock layer comprises metal particles; the liquid in the coarse feedstock layer or the fine feedstock layer comprises a polymer of a binder composition; 12. The method according to any one of claims 1 to 11.

15. The binder composition comprises a curable polymer, and the method comprises: selectively applying a liquid binder composition to portions of the feedstock layer; hardening the liquid binder composition by chemical reaction; 15. The method of claim 14, comprising:

16. separating the solidified coarse and fine feedstock layer portions from the unsolidified coarse and fine feedstock layer portions; sintering the solidified coarse feedstock layer and the fine feedstock layer to form a solidified three-dimensional inorganic body; 16. The method of claim 1, further comprising:

17. the solidified coarse feedstock layer and the fine feedstock layer comprise inorganic particles; sintering the solidified coarse feedstock layer and the fine feedstock layer to form a sintered film on the inorganic particles; 17. The method of claim 16.

18. Specifying a target thickness of the film and a thickness tolerance of the film; forming a plurality of solidified coarse feedstock layers; forming at least one layer of solidified fine feedstock; separating the solidified coarse and fine feedstock layer portions from the unsolidified coarse and fine feedstock layer portions; sintering the solidified coarse feedstock layer and the fine feedstock layer to form a sintered membrane; 20. The method of claim 17, further comprising: wherein the sintered film has a thickness that differs from the film target thickness by no more than a film thickness tolerance.

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