Formation of single crystal structures during additive manufacturing

Abstract

A layer of metal powder is spread on a powder bed and sintered. A portion of the layer is melted into the cross-sectional shape of an additively manufactured 3D printed part. Sintered powder adjacent to the melted edge of the shape is removed. That portion is remelted. The spreading, sintering, melting, removal, and remelting steps are repeated for each layer. In another embodiment, a layer of metal powder is spread on a powder bed. A portion of the layer is melted into the cross-sectional shape of the part. The spreading and melting steps are repeated for L-1 consecutive powder layers corresponding to L-1 layers of the part. After spreading and melting the top layer, the polycrystalline shell adjacent to the melted edge of each layer is removed with a tool to a depth of L layers relative to the current layer.

Description

Technical Field

[0001] Cross - reference to Related Applications This patent application claims the benefit and priority of U.S. Provisional Patent Application No. 63 / 507,051, filed on June 8, 2023, entitled "Forming a Single Crystal Structure During Additive Manufacturing", the entire content of which is incorporated herein by reference as if fully set forth below in its entirety and for all applicable purposes.

[0002] Aspects described herein generally relate to additive manufacturing, and more specifically, to the formation of single crystal structures during additive manufacturing.

Background Art

[0003] In the additive manufacturing of single crystals (also called monocrystals) using powder bed techniques such as laser powder bed fusion (L - PBF) and electron beam melting (EBM), parts may be produced that have a single crystal (SX) region adjacent to a polycrystalline (PX) region. The polycrystalline region is undesirable. In some examples, the polycrystalline region effectively forms a shell around the single crystal region. In some examples, the thickness of the shell can be about 1 - 2 mm. In some examples, the powder bed at the periphery of the single crystal region may function as a nucleation site for the polycrystalline region.

[0004] Engineers and scientists may be working on problems related to the growth of polycrystals, but effective methods to avoid polycrystalline shells, convert polycrystalline shells to single crystals, or remove polycrystalline shells in - situ during additive manufacturing have not yet been found.

Summary of the Invention

[0005] The following summary is provided to facilitate understanding of some of the innovative features specific to the disclosed embodiments and is not intended as a complete description. A full understanding of the various aspects of the embodiments can be gained by considering the entire specification, claims, drawings, and abstract as a whole.

[0006] As an example, a method for additive manufacturing a three-dimensional (3D) printed part is disclosed. In the embodiment, the method includes the steps of: spreading a layer of unmelted metal powder onto a powder bed; melting a portion of the layer to the cross-sectional shape of a corresponding layer among a plurality of layers of an additively manufactured 3D printed part; removing metal powder adjacent to a first melted edge of the shape using a tool; remelting the first melted edge or at least one portion of the layer of the cross-sectional shape of a corresponding layer among a plurality of layers of the additively manufactured 3D printed part; and repeating the spreading, melting, removing, and remelting steps in each of the consecutive layers of the plurality of layers of the additively manufactured 3D printed part.

[0007] In one embodiment, an apparatus is described. In this embodiment, the apparatus may comprise a powder bed, a recoater head configured to recoat the powder bed with unmelted metal powder, a tool actuator coupled to the recoater head, and a tool coupled to the tool actuator. In this embodiment, the apparatus is configured to use the recoater head to spread a layer of unmelted metal powder onto the powder bed, to melt a portion of the layer into the cross-sectional shape of a corresponding layer among a plurality of layers of an additive manufacturing 3D printed part, to use the tool to remove metal powder adjacent to a first melted edge of the shape, to remelt the first melted edge or at least one portion of the layer into the cross-sectional shape of a corresponding layer among a plurality of layers of the additive manufacturing 3D printed part, and to repeat the spreading, melting, removing, and remelting steps in each of the consecutive layers of the plurality of layers of the additive manufacturing 3D printed part.

[0008] In one embodiment, a system is described. In this embodiment, the system comprises one or more processors, one or more memories coupled to the one or more processors, a powder bed, a laser or electron beam gun coupled to the one or more processors and focused on the powder bed, a recoater head coupled to the one or more processors, a tool actuator coupled to the recoater head and the one or more processors, and a tool coupled to the tool actuator. In this embodiment, one or more processors are configured to individually or collectively spread a layer of unmelted metal powder onto a powder bed using a recoater head, based at least partially on information stored in one or more memories, melt a portion of the layer into the cross-sectional shape of a corresponding layer among a plurality of layers of an additive manufacturing 3D printed part, remove metal powder adjacent to a first melted edge of the shape using a tool, remelt the first melted edge or at least one of the portions of the layer into the cross-sectional shape of a corresponding layer among a plurality of layers of the additive manufacturing 3D printed part, and repeat the spreading, melting, removing, and remelting steps in each of the consecutive layers of the plurality of layers of the additive manufacturing 3D printed part.

[0009] One embodiment describes a method for additive manufacturing a three-dimensional (3D) printed part. In this embodiment, the method includes the steps of spreading a layer of unmelted metal powder onto a powder bed; melting a portion of the layer to the cross-sectional shape of a corresponding layer among a plurality of layers of an additively manufactured 3D printed part, wherein the portion of the layer has a melted edge; and repeating the spreading step and the melting step for L-1 consecutive layers of metal powder corresponding to each of the L-1 layers of the plurality of layers of the additively manufactured 3D printed part, where L is an integer greater than 1. The method further includes, after the spreading and melting steps of the top layer, using a first tool to remove polycrystalline shell adjacent to the melted edge of each layer to a depth of L layers relative to the top layer.

[0010] In one embodiment, an apparatus is described. In this embodiment, the apparatus comprises a powder bed, a recoater head configured to recoat the powder bed with unmelted metal powder, a tool actuator coupled to the recoater head, and a tool coupled to the tool actuator. In this embodiment, the apparatus uses the recoater head to spread a layer of unmelted metal powder onto the powder bed, melting a portion of the layer to the cross-sectional shape of a corresponding layer among a plurality of layers of an additive manufacturing 3D printed part, where the portion of the layer has a melted edge, and the spreading and melting steps are repeated for L-1 consecutive layers of metal powder corresponding to each of the L-1 layers of the plurality of layers of the additive manufacturing 3D printed part, where L is an integer greater than 1. The apparatus is further configured to use a first tool to remove the polycrystalline shell adjacent to the melted edge of each layer to a depth of L layers relative to the uppermost layer after the spreading and melting steps of the uppermost layer.

[0011] In one embodiment, a system is described. In this embodiment, the system comprises one or more processors, one or more memories coupled to the one or more processors, a powder bed, a laser or electron beam gun coupled to the one or more processors and focused on the powder bed, a recoater head coupled to the one or more processors, a tool actuator coupled to the recoater head and the one or more processors, and a tool coupled to the tool actuator. In this embodiment, one or more processors, individually or collectively, use the recoater head to spread a layer of unmelted metal powder onto the powder bed, at least partially based on information stored in one or more memories, and melt a portion of the layer to the cross-sectional shape of a corresponding layer among a plurality of layers of an additive manufacturing 3D printed part, where the portion of the layer has a melted edge, and the spreading step and the melting step are repeated for L-1 consecutive layers of metal powder corresponding to each of L-1 layers of the plurality of layers of the additive manufacturing 3D printed part, where L is an integer greater than 1. The apparatus is further configured to use a first tool to remove the polycrystalline shell adjacent to the melted edge of each layer to a depth of L layer relative to the top layer, after the steps of spreading and melting the top layer.

[0012] These and other embodiments will be fully understood by reading the detailed description below. Other embodiments, features, and examples will be apparent to those skilled in the art by reading the following description of a particular embodiment in conjunction with the accompanying drawings. Features are described in relation to the following specific embodiments and drawings, but all embodiments may include one or more of the features described herein. In other words, one or more embodiments are described as having a particular advantageous feature, but one or more such features may be used in other embodiments described herein. Similarly, embodiments are described below in terms of a particular apparatus, device, system, or method, but it should be understood that such embodiments can be carried out in a variety of other apparatuses, devices, systems, and methods. [Brief explanation of the drawing]

[0013] The accompanying drawings, where the same reference numerals indicate identical or functionally similar elements in separate drawings, are incorporated into this specification and constitute part of this specification, further illustrating the embodiments and serving to illustrate the embodiments disclosed herein, together with the detailed description. [Figure 1] Figure 1 is a micrograph of a sample of a single-crystal nickel-based superalloy, not limited to Alloy 5, showing a polycrystalline shell according to several aspects of the present disclosure. [Figure 2] Figure 2 shows a pair of three-dimensional printed metal products formed using an electron beam melting process according to some aspects of the present disclosure. [Figure 3] Figure 3 is a simplified, non-scale, expert drawing of the top layers of a cross-section of a sample of a metal product being manufactured using an electron beam fused metal additive manufacturing process, according to some aspects of this disclosure. [Figure 4] Figure 4 shows a second sample of a metal product manufactured using a laser powder bed fused metal additive manufacturing process according to some aspects of the present disclosure. [Figure 5] Figure 5 is a diagram that combines a series of images that can be used to illustrate the manufacture of metal products using a powder bed fused metal additive manufacturing process according to some aspects of the present disclosure. [Figure 6] Figure 6 is a diagram that combines a series of images that can be used to illustrate the manufacture of metal products using a powder bed fused metal additive manufacturing process according to some aspects of the present disclosure. [Figure 7] Figure 7 is a block diagram of an example of a system that may be used to remove unmelted metal powder from the edges of one or more additively printed layers of a 3D printed metal part during manufacturing, according to some aspects of the present disclosure. [Figure 8] Figure 8 is a flowchart illustrating exemplary processes for metal 3D printing using additive manufacturing and electron beam melting processes according to several aspects of this disclosure. [Figure 9]Figure 9 is a flowchart illustrating an exemplary process of metal 3D printing using an additive manufacturing process, such as a laser powder bed fusion process or an electron beam fusion process, according to several aspects of the present disclosure. [Modes for carrying out the invention]

[0014] The specific values ​​and configurations described in the following non-limiting embodiments can be varied and are cited merely to illustrate one or more embodiments, and are not intended to limit their scope.

[0015] Embodiments are described below in detail with reference to the drawings. The embodiments disclosed herein are modifiable within the scope of the disclosure and should not be constrained; rather, these embodiments are provided to ensure that the disclosure is thorough and complete and to fully convey the scope of the disclosure to those skilled in the art. The same figures refer to the same elements throughout.

[0016] The detailed descriptions provided below in relation to the attached drawings are intended to illustrate various configurations and are not intended to show only the configurations in which the concepts described herein can be implemented. The detailed descriptions include specific details necessary for a complete understanding of the various concepts. However, it will be apparent to those skilled in the art that these concepts can be implemented without specific details. In some examples, well-known structures and components are shown in block diagram form to avoid obscuring such concepts.

[0017] The terms used herein are for illustrative purposes only and are not intended to be limiting. The singular forms “a,” “an,” and “the” as used herein are intended to include the plural form unless the context clearly indicates otherwise. It will be further understood that, as used herein, the terms “include” and / or “encompass” identify the presence of a described feature, value, step, operation, element, component, and / or group thereof, but do not exclude the presence or addition of one or more other features, values, steps, operations, elements, components, and / or groups thereof.

[0018] Throughout this specification and the claims, terms may have nuances implied or suggested in context beyond their expressly stated meanings. Similarly, the expression “in one embodiment” as used herein does not necessarily refer to the same embodiment, and the expression “in another embodiment” as used herein does not necessarily refer to a different embodiment. The scope of this disclosure is intended to encompass all or part of the subject matter of one or more embodiments.

[0019] Unless otherwise specified, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by those skilled in the art. Furthermore, terms as defined in commonly used dictionaries should be interpreted as having the meaning consistent with their meaning in the context of the relevant art, and it will be understood that they should not be interpreted in an idealized or overly formal sense unless expressly defined herein.

[0020] It will be understood that the specific examples described herein are presented for purposes of illustration and not of limitation. The aspects described herein can be employed in various embodiments without departing from the scope of the disclosure. One of ordinary skill in the art will recognize or be able to ascertain many equivalents to the specific aspects and procedures described herein. Such equivalents are considered to be within the scope of this disclosure and are contemplated to be covered by the claims.

[0021] When used with the term “comprising,” the words “a” or “an” may mean “one.” Nevertheless, the use of the words “a” or “an” can be consistent with the meaning of “one or more,” “at least one,” and “one or more than one” when used in conjunction with the term “comprising.” This disclosure supports only definitions that indicate alternatives or “and / or,” and the word “or” is used to mean “and / or” unless explicitly indicated to refer to alternatives only or unless the alternatives are mutually exclusive. Throughout this application, the term “about” is used to indicate that a value includes the inherent variability of error for the device, the method of determining the value, or the variability that exists among the test subjects.

[0022] As used herein and in the claims, the terms “comprising” (and any form of comprising, such as “comprise,” “comprises,” etc.), “having” (and any form of having, such as “have,” “has,” etc.), “including” (and any form of including, such as “includes,” “include,” etc.), or “containing” (and any form of containing, such as “contains,” “contain,” etc.) are inclusive or open-ended and do not exclude additional, unrecited elements or method steps.

[0023] As used herein, the terms "or combination thereof" refer to all permutations and combinations of the items preceding the term. For example, "A, B, C, or combination thereof" is intended to include at least one of A, B, C, AB, AC, BC, or ABC, and also includes BA, CA, CB, CBA, BCA, ACB, BAC, or CAB if the order is important in the particular context. Continuing this example, combinations that explicitly include repetitions of one or more items or terms are included, such as BB, AAA, AB, BBC, AAABCCCC, CBBAAA, CABABB, etc. A person skilled in the art will understand that, unless it is evident from the context, there is generally no limit to the number of items or terms in any combination.

[0024] All embodiments disclosed and claimed herein can be manufactured and performed without excessive experimentation in light of this disclosure. While embodiments are described in terms of preferred embodiments, it will be apparent to those skilled in the art that modifications can be applied to the embodiments described herein without departing from the concepts, spirit, and scope of this disclosure and claims. All similar modifications, alternatives, and changes that are apparent to those skilled in the art are deemed to be within the spirit, scope, and concepts of this disclosure as defined by the appended claims.

[0025] In metal additive manufacturing, a desired (e.g., finished, final) metal part can be mathematically represented by thousands of horizontal cross-sectional "slices" stacked one on top of the other (e.g., one on top of another). A three-dimensional (3D) printer may be configured to direct a laser beam or electron beam onto a horizontal floor of unmolten metal powder and use the energy generated at the focal point of the laser or electron beam to melt shapes corresponding to the cross-sectional layers of the desired metal part into the top layer of unmolten metal powder. After melting these shapes into the layer, the next layer of unmolten metal powder is added on top of the newly processed layer. Each shape corresponding to a cross-sectional slice of the metal part layer is melted into the next layer. The process of adding the next layer of unmolten metal powder and melting the next shape corresponding to each slice of the metal product into the next layer with the laser or electron beam is repeated until the desired 3D metal part is manufactured.

[0026] Today, there are several categories of metal additive manufacturing processes. One category is called powder bed fusion or powder bed melting. This category has two subcategories. The first subcategory is called selective laser fusion or laser powder bed fusion (L-PBF). In L-PBF, a high-power laser beam is used to selectively melt metal powder to form one of thousands of slices of the desired (e.g., finished, final) metal part, resulting in a corresponding cross-sectional shape. The high-power laser beam selectively joins or welds the particles of the metal powder. Once all layers have been printed, the metal part is removed from the unmelted metal powder. Many parts made with the L-PBF process require heat treatment to strengthen the final metal product.

[0027] The second subcategory is called electron beam melting (EBM). Electron beam melting processes do not use high-power lasers. Instead, as the name suggests, they use a high-power electron beam to selectively melt metal powders. Unlike laser processes, which can be carried out at room temperature, room pressure, in normal air, or in an inert gas environment, electron beam melting processes must be carried out in a vacuum chamber that can be maintained at very high temperatures (e.g., 1,000–1,500 degrees Celsius).

[0028] Figure 1 is a micrograph of a first sample 100 of a nickel-based superalloy (hereinafter referred to as "SX superalloy") of a single crystal 102, which is, for example, Alloy 5, but is not limited to, a polycrystalline shell 104 according to several embodiments of the present disclosure. As used herein, the terms single crystal (as used in engineering terminology) and single grain (as used in metallurgical terminology) are synonymous. The first sample 100 was manufactured using an additive manufacturing process in which multiple layers of unmolten SX superalloy metal powder were melted into multiple cross-sections (e.g., shapes) corresponding to each of the multiple layers of a desired metal product. In the additive manufacturing process, an electron beam melting process was used to melt each cross-sectional shape of the desired metal product, one on top of the other, one after the other. After each slice was melted (e.g., printed), a new layer of unmolten metal powder was added on top of the newly solidified layer. Next, a new cross-sectional slice was melted into the new layer of unmolten metal powder and at least a portion of the previously solidified layer. The finished metal product is formed of multiple solidified cross-sectional slices that are continuously mixed together.

[0029] However, the multiple solidified cross-sectional slices, which are continuously intermingled, contain discontinuities that appear as polycrystalline shells 104. Note that the entire central region 108 is single-crystal, despite the presence of some random discoloration (i.e., whitish droplets, spots, and linear streaks seen in the first sample 100). The random discoloration in the central region 108 of the first sample 100 is due to the handling of the first sample 100.

[0030] The polycrystalline shell 104 appears in the region between the solidified single crystal 102 SX superalloy (central region 108) and the unmelted metal powder (not shown) outside the polycrystalline shell 104. The first sample 100 was obtained using a cross-sectional microscope. The cross-sectional microscope process involved embedding the first sample 100 in epoxy resin 106, cross-sectional processing, and polishing in the YZ plane (the X axis pointing in the plane of paper perpendicular to the YZ plane). Next, the first sample 100 was etched using an etching solution. Etching allows for the visualization of various particles in the first sample 100.

[0031] The first sample 100 shows the microstructure of an SX superalloy (having a polycrystalline shell 104) of single crystal 102 produced by an electron beam melting process according to several aspects of the present disclosure. The first sample 100 includes a plurality of horizontal layers (indistinguishable in the figure) on the XY plane. Each layer is formed on top of a preceding layer using the additive manufacturing process described, such that the layer is formed in the positive Z-axis direction from the bottom of the first sample 100 (e.g., the Z-axis origin) toward the top of the first sample 100.

[0032] Edge particles of the polycrystalline shell 104 may be formed by nucleation from metal powder adhering to the surface of the desired finished metal product (i.e., adhering to the outer boundary of the metal powder intentionally melted using an electron beam). According to the embodiments described herein, nucleation of edge particles can be prevented by removing the metal powder from the surface of the desired finished product.

[0033] As those skilled in the art know, the term grain can be used to refer to various, randomly distributed, small-sized crystals that make up a solid metal piece. Grain boundaries define the surface areas where various grains come into contact with each other. Grain boundaries are generally weak points of the material (i.e., weak points of solid metal pieces). Because grain boundaries where two grains meet have a disordered structure, the strength of the metal is reduced compared to a solid metal sample where the grains have a regular structure (i.e., a single crystal). Therefore, removing grain boundaries is considered advantageous, at least in terms of producing a metal with superior strength (compared to a sample with multiple grain boundaries).

[0034] One method of casting metal products involves growing the cast metal as a single particle. This method is sometimes commonly referred to as investment casting or lost-wax casting. In the investment casting process, a precise casting can be formed within a mold formed around a copy of a wax (or similar material) of the desired final metal product. The wax is melted and removed, and molten metal is poured into the mold in its place. Investment casting in single-particle metal final products can be used in high-performance metal applications, such as the first stage of a jet engine turbine blade, where the first-stage blade is located behind a combustor that emits extremely hot gases (exceeding the melting point of the metal used to manufacture the turbine blade) and rotates at high speeds under heavy loads around the shaft of the jet engine. However, the chemical composition of investment-cast metals is optimized, investment-cast products have no particle boundaries, and the metal parts can withstand high temperatures and heavy loads.

[0035] One challenge of investment casting is the limited range of shapes that engineers can create. For example, complex shapes may be designed to be aerodynamically, coolly, or functionally superior. However, such shapes may be impractical or impossible to manufacture using the investment casting process (for instance, an internal copy of the desired part within the investment mold would lose important details of the desired part when melted). Furthermore, creating investment molds is time-consuming. While it is possible to cast multiple finished products in a single investment mold, after filling the mold with molten metal to produce one or more finished products, the investment mold must be destroyed to remove the one or more finished products from the mold.

[0036] Therefore, significant advantages can be realized by manufacturing metal parts using an additive manufacturing process (different from the investment casting process), which produces additively manufactured metal parts where the entire metal part is a single-crystal metal with one particle. Furthermore, the additive manufacturing process is suitable for forming complex shapes, incorporating cooling channels, speed and ease of modeling and prototyping, speed and ease of shape modification for prototyping, and reproducibility with accuracy that depends on the 3D printer forming the finished metal part, rather than the accuracy that depends on each iteration or copy of the investment mold. Moreover, there are very few companies in the world that can manufacture high-quality, high-precision single-crystal metal parts using the investment casting method. In addition to the small number of companies, the demand for high-quality, high-precision single-crystal metal parts is high, so lead times can sometimes exceed one year.

[0037] As the scale in Figure 1 shows, the thickness of the polycrystalline shell 104 is approximately 1 mm (1000 μm). Certain components, such as high-performance turbine blades, may require an outer wall thickness of 1 mm. Given that the desired single-crystal outer wall thickness and the thickness of the undesirable polycrystalline shell undesirably bonded to that outer wall are of the same order, chemical etching may not be a viable method for removing the polycrystalline shell. For example, due to differences in the local concentration of the chemical etching solution, the formation of bubbles (as a byproduct of the etching process), surface contaminants, and the surface characteristics of the component, chemical etching may remove 1 mm of material from one area and 2 mm of material from an area adjacent to that area within any given unit time. Such differences in the depth of material removed by the chemical etching process could result in the removal of both the desired single-crystal outer wall and the undesirable polycrystalline shell.

[0038] According to some embodiments, the thickness of the polycrystalline shell 104 does not depend on the thickness of the single-crystal metal beneath the polycrystalline shell 104. Taking Figure 1 as an example, the thickness in the Y-axis direction of the single crystal 102 (i.e., the metal of the central region 108) is approximately 10 mm. In contrast, the thickness in the Y-axis direction of each left and right portion of the polycrystalline shell 104 is approximately 1 mm. It has been confirmed that the thickness of the polycrystalline shell 104 remains approximately 1 mm even if the thickness of the single crystal 102 in the central region 108 increases (e.g., to 100 mm) or decreases (e.g., to 3 mm).

[0039] In practice, unless nucleating material (e.g., unmelted metal powder adjacent to solidified metal powder) is at least partially removed from the desired outer wall surface, it is difficult, if not impossible, to produce a single-crystal metal wall with a thickness of approximately 1 mm by growing a polycrystalline shell 104.

[0040] Figure 2 is a diagram (e.g., photograph) showing a pair of 3D printed metal products 200 formed using an electron beam melting process according to some aspects of the present disclosure. The 3D printed metal products 200 exhibit a polycrystalline shell 204, such as the polycrystalline shell 104 shown and described in relation to Figure 1. Edge particles (i.e., polycrystalline shell 204) may be formed by nucleation of metal powder adhering to the outer surfaces 202 (e.g., outer surfaces) of each of the pair of 3D printed metal products 200. The polycrystalline shell 204 formed on the outer surfaces 202 of each of the pair of 3D printed metal products 200 may penetrate (erosion, spread) to the final (net) surface of each of the pair of 3D printed metal products 200. An accumulation of unmelted metal powder 206 is shown between the pair of 3D printed metal products 200. The thickness of the polycrystalline shell 204 in the example of Figure 2 is approximately 1 mm, as shown.

[0041] During solidification, when a metal melts and solidifies, solidification begins at a surface colder than the molten metal. The first atoms of the molten metal land on the cold surface, cool, solidify, and remain in place. This atom and / or the surface to which it is attached can be called a nucleation site. Other atoms attach to the nucleation site, cool, solidify, and remain in place, thus building up the solidified portion of the metal from the original cold surface to the residual molten metal.

[0042] More specifically, as is known to those skilled in the art, nucleation is understood as the initial process that occurs when a crystal is formed from a solution, liquid, or vapor, in which a small number of ions, atoms, or molecules are arranged in a characteristic pattern of the crystalline solid, and as the crystal grows, sites are formed where additional ions, atoms, or molecules deposit.

[0043] Figure 3 is a simplified, non-scaled, expert drawing of multiple top layers (the multiple layers are not individually distinguished to avoid drawing clutter) of a cross-section of a second sample 300 of a metal product being manufactured using an electron beam fused metal additive manufacturing process according to some aspects of the present disclosure. The second sample 300 may be similar to the first sample 100 shown and described in relation to Figure 1. The second sample 300 includes a single crystal 302 (e.g., single-crystal metal), a polycrystalline shell 304 (e.g., polycrystalline metal shell), an unmelted metal powder bed 306 on which the finished metal product is manufactured, and an intermixing region 308 (e.g., molten pool) of molten metal powder and remelted single crystal 302 drawn on top of the top layer of single crystal 302. Note that the width of the molten pool is exaggerated. In reality, the molten pool may be localized around the electron beam focal point on the surface of the metal product.

[0044] In the additive manufacturing process, an unmelted metal powder layer 306 is spread over a processed layer of the metal part to be manufactured. A portion of the unmelted metal powder 306 (corresponding to the cross-section of the desired metal part slice to be manufactured) is completely melted together with a portion of the top layer of the single crystal 302. As the unmelted metal powder 306 and a portion of the top layer of the single crystal 302 melt simultaneously, both the molten metal powder and the remelted single crystal form a mixed region 308 of molten metal powder and remelted single crystal metal.

[0045] The entire thickness (in the Z-axis direction) and width (in the XY plane) solidifies, and one layer is constructed on top of the next layer in the Z-axis direction. Each time a layer of unmolten metal powder 306 is added, and that layer of unmolten metal powder 306 (corresponding to a cross-sectional slice of the finished metal product) is melted and mixed with the remolten portion of the single crystal 302, it will be understood that the atoms in the mixed region 308 solidify from the atoms of the already solidified single crystal 302 (e.g., surface atoms). Since the atoms of the single crystal 302 are already aligned with each other, the atoms of the molten metal powder and remolten single crystal in the mixed region 308 will align with the atoms of the single crystal 302 that are already aligned in the solidification process. The newly solidified atoms will have the same alignment as the already aligned atoms of the single crystal 302. In other words, if the nucleation of atoms in the mixed region 308, which contains newly molten metal powder and remolten single crystal 302, begins on the surface of already aligned atoms in the solidified single crystal 302, then the newly solidified atoms, by their nature, will align with and maintain that alignment with atoms already present in the solidified single crystal 302.

[0046] However, the manufactured parts are constructed on a powder bed table that is covered with unmolten metal powder 306 each time a new layer is added. With each new layer, atoms of the molten metal in the mixed region 308 adjacent to the side region 310 come into contact with particles or grains of the unmolten metal powder 306 (at the left and right ends of the side region 310 of the second sample 300) and nucleate on those particles or grains. Thus, metal particles begin to grow toward the existing surface 312 of the single crystal 302, forming a polycrystalline shell 304. Meanwhile, atoms adjacent to the existing surface of the single crystal 302 nucleate on that existing surface and begin to grow from that existing surface.

[0047] This book describes examples of manufacturing metal parts formed as single-crystal metal 302 by additive manufacturing using a 3D metal printer. The additive manufacturing process may be an electron beam melting process, a high-power laser process (e.g., L-PBF), or a similar process that melts metal powder or metal-containing material at the edges (e.g., walls) of the metal part. In the examples, the polycrystalline shell 304 may be prevented, converted to a single crystal, or removed.

[0048] According to the first embodiment, metal powder remaining as unmelted metal powder 306 after printing a given layer of a desired metal part can be removed after spreading the layer of unmelted metal powder 306 and before printing (e.g., melting) the unmelted metal powder 306 into a shape corresponding to the cross-section of the desired metal product slice. By removing the unmelted metal powder 306 before melting (from the unmelted region of the entire layer and from the region adjacent to the melted region), the possibility of atoms of the molten metal (which will become the mixed region 308 of molten metal powder and remelted single crystal 302) using the particles of unmelted metal powder 306 as nucleation sites is eliminated, and thus the formation of a polycrystalline shell 304 before it is generated is prevented.

[0049] According to a second embodiment, if a polycrystalline shell 304 is formed, the polycrystalline shell 304 may be mechanically removed from a desired surface of the single crystal 302 using one or more tools (rather than chemical removal by etching). Mechanical removal can be carried out using, for example, cutting tools or polishing tools. The above list is illustrative and not limiting.

[0050] In practice, in electron beam melting processes, unmolten metal powder can be spread in layers, and then the layers of unmolten metal powder can be sintered. For example, the electron beam may be configured to scan the layers at an output level that is insufficient to melt the metal powder but sufficient to accrete the metal powder particles together. In other words, as is well known to those skilled in the art, the sintering process can agglomerate unmolten metal powder into a solid or porous mass without liquefying it by heating. In electron beam melting processes, sintering can be used because electrons from the electron beam gun are emitted into a printer device and a vacuum chamber holding the metal powder. The particles of unmolten metal powder can be negatively charged by electrons. Sintering, which accretes adjacent particles, can be used to prevent adjacent negatively charged particles from repelling each other electrostatically. In some examples, sintering can be avoided by introducing a positive charge into the vacuum chamber to counteract and neutralize the negative charge emitted from the electron gun.

[0051] As a result, in electron beam melting processes using sintering, unmelted (but coalesced) metal powder particles adhere to the part being printed. Therefore, unmelted metal particles are present and can act as (undesirable) nucleation sites.

[0052] In contrast, in laser powder bed fusion processes, metal powder is spread in layers but does not sinter. The metal powder does not coalesce before printing (e.g., melting). However, in laser powder bed fusion processes, unmelted metal powder particles adjacent to the molten pool, which should remain as unmelted metal powder 306 after printing a given layer, do not remain in place but are drawn into (or blown into) the molten pool. The molten pool contains the intended molten metal powder, remelted single-crystal metal, and unintended unmelted metal powder particles adjacent to (or drawn into) the molten pool. Because the loose unmelted metal powder particles adjacent to the molten pool are drawn into (or blown into) the molten pool, these particles are not available as nucleation sites for molten metal atoms within the molten pool (e.g., within the mixed region 308).

[0053] In at least one aspect, it may be found that a “wind” is generated or produced that draws (or blows) unmolten metal powder particles adjacent to the molten pool into the molten pool. For example, the wind (also called a local airflow or convection) can be generated by the convection of an inert gas (e.g., argon) surrounding the molten pool itself. To explain, because the molten pool is very hot, the inert gas near the molten pool is locally heated, and the heated inert gas rises rapidly (circulates by convection). As the heated inert gas rises rapidly (e.g., quickly) above the molten pool, the inert gas is drawn in from the sides of the molten pool. The drawn-in inert gas (wind) draws in unmolten metal powder particles adjacent to the molten pool into the molten pool.

[0054] In another embodiment, a directional jet or stream of inert gas may be directed into the molten pool to blow loose, unmolten metal powder particles adjacent to the molten pool into the molten pool. The jet or stream of inert gas may be introduced at a flow rate that moves the unmolten metal powder particles adjacent to the molten pool into the molten pool, but not at a rate that cools (or significantly cools) the molten pool itself. The inert gas may be introduced (blown) into the work area by a tool referred to herein as a positive pressure inert gas nozzle.

[0055] In another embodiment, physical properties associated with the molten pool, such as surface tension, may act to move loose, unmolten metal powder particles adjacent to the molten pool into the molten pool. The embodiments described above are illustrative and not limiting.

[0056] An inert gas envelops the molten pool and can remove oxygen, nitrogen, and air pollutants that could cause instability in the final product. In some examples, the inert gas is called a shielding gas. In some laser powder bed fusion systems, the inert gas may be at a pressure close to atmospheric pressure (e.g., very slightly above atmospheric pressure). Some laser powder bed fusion systems include a gas flow pump that delivers the inert gas over the surface of the powder bed at a flow rate of approximately 1 to 3 meters per second (m / s). This flow rate may be fast enough to remove soot generated during the melting process, but not fast enough to blow (e.g., move) free particles of metal powder in any direction. Other flow rates are also within the scope of this disclosure.

[0057] Figure 4 is a diagram (e.g., photograph) showing a third sample 400 of a metal product manufactured using a laser powder bed fusion (L-PBF) metal additive manufacturing process according to several aspects of the present disclosure. During the manufacture of the third sample 400, wind was generated by the inert gas surrounding the molten pool (e.g., by the convection described above), which could draw (or blow) unmelted metal powder particles into the molten pool (these particles would have remained unmelted after the melting process because they were adjacent to areas defined by the shape of the cross-sectional slice to be printed). Therefore, these metal powder particles could not be utilized as nucleation sites for growing polycrystalline shells such as polycrystalline shells 104 and / or 204 as shown and described in relation to Figure 1 and / or Figure 2, respectively.

[0058] As shown and explained in relation to Figure 1, the third sample 400, like the first sample 100, was also prepared using a cross-sectional microscopy process, and the third sample 400 was cross-sectional (from larger portions), polished, and etched to reveal the particles within the third sample 400. Particles with different orientations exhibit different reactions to the etching solution used to prepare the third sample 400.

[0059] For illustrative purposes only, the first particle 402 contains metal atoms, all having a first crystal orientation, characterized by vertical "spikes" whose color (or hue) differs from that of the second particle 404 adjacent to the first particle 402. The particle boundary 406 between the first particle 402 and the second particle 404 is shown by a dashed line in the magnified section of Figure 4. The second particle 404 contains the same metal atoms (as the first particle 402) all having a second crystal orientation (the second crystal orientation is different from the first crystal orientation). Observation of the third sample 400 reveals that the metal in the third sample 400 is not a single-crystal example (for example, from the amount of vertical spikes mixed with more or less homogenized horizontal regions).

[0060] However, the third sample, 400, shows an example where no polycrystalline shells (such as polycrystalline shells 104 and 204 as shown and described in Figures 1 and 2) are present. In the third sample, 400, the heat of the molten pool generates a "wind" (as described above) due to the convection of the inert gas surrounding the molten pool, drawing in (or blowing into) (undesirable) unmolten metal particles adjacent to the molten pool during the melting process, and consequently removing the unmolten metal particles adjacent to the molten pool that would serve as nucleation sites for the growth of polycrystalline shells during the solidification process. As shown in the example in Figure 4, there is no evidence of nucleation of new particles that form polycrystalline shells. In the example in Figure 4, prepared using the L-PBF process, only particles that grow outward toward the edge and form the edge are shown in the third sample, 400.

[0061] Figure 5 is a diagram of a series of images that can be used to illustrate the manufacture of metal products (e.g., metal parts, components) using a powder bed fused metal additive manufacturing process according to several embodiments of the present disclosure. In the example of Figure 5, the powder bed fused process may be an electron beam fused process. However, the powder bed fused process may also be a laser powder bed fused process, in which case the sintering aspect may be omitted. For example, in one embodiment, the apparatus for performing the method shown in Figure 5 comprises an electron beam gun focused on the powder bed, and the apparatus may be configured to sinter a layer of unfused metal powder before melting and to perform sintering, melting, and remelting using an electron beam emitted from the electron beam gun. In another embodiment, the apparatus for performing the method shown in Figure 5 comprises a laser, and the laser beam may be focused on the powder bed. In this embodiment, the apparatus may be configured to perform melting and remelting in a laser powder bed fused process.

[0062] The first Figure 500 illustrates at least two processes. In the first process (which has already been completed), a recoater head (not shown) traverses the powder bed 502, depositing and leveling a first layer of unmolten metal powder 504 (e.g., SX superalloy metal powder) on it. The term “first layer” as used in relation to Figure 5 is a relative term. The illustrated first layer 504 of unmolten metal powder may be the uppermost layer of several already processed layers below the first layer (i.e., traversing the Z-axis toward the origin). In the second process (in progress), an electron beam gun sinters the first layer 504 of unmolten metal powder, transforming it into a sintered layer of unmolten metal powder (referred to as the sintered layer 506 in this document for brevity).

[0063] The second figure, 508, shows a shape 510 corresponding to a cross-section of a layer (e.g., a slice) of a metal part, after the electron beam has melted the shape 510 into a sintered layer 506 (and any portion of single-crystal metal directly beneath the sintered layer 506). The shape 510 contains both single-crystal and polycrystalline metals.

[0064] The single-crystal metal may be the center of shape 510 and may be a first portion of the single-crystal metal (or a first portion of the sintered layer 506) that approaches the first molten edge 512-1 from within shape 510. The first molten edge 512-1 may correspond to the projection of the outer wall of shape 510 on the sintered layer 506 (e.g., the projection of the desired net outer surface of the outer wall of shape 510, the final outer wall dimensions of shape 510). The first portion may be nucleated on an existing surface of the single-crystal metal.

[0065] The polycrystalline metal may be a second portion of the polycrystalline metal (or a second portion of the sintered layer 506) that is close to shape 510 and approaches the first molten edge 512-1 from outside shape 510. The second portion may be nucleated during the sintering of the unmolten metal powder rather than being an existing surface of the single-crystal metal.

[0066] The zone including the first molten edge 512-1 surrounds the shape 510 and may include at least one of a single-crystal metal and a polycrystalline metal.

[0067] The third figure, 514, shows the processed region 516 after the sintered metal powder adjacent to the first molten edge 512-1 has been removed with a tool (not shown). The tool may be, for example, a brush, a comb, multiple whiskers, a paddle or beam of any cross-section or combination of cross-sections (e.g., circular, rectangular, elliptical, D-shaped, etc.), or a negative pressure vacuum nozzle, or a positive pressure inert gas nozzle. The above list is illustrative and not limiting.

[0068] The fourth figure, 518, shows the shape 510 after the electron beam remelts the first melted edge 512-1. The remelted edge is identified as the remelted edge 512-2. The remelted edge 512-2 is shown with a black dashed line to distinguish it from the black solid line used to represent the first melted edge 512-1 (e.g., the second figure, 508). The dashed line of the remelted edge 512-2 does not indicate that the remelting stops and starts intermittently. The remelted edge 512-2 completely and seamlessly surrounds the shape 510. Furthermore, the dashed line of the remelted edge 512-2 does not indicate that the edge or shape 510 is arbitrary.

[0069] When the edge is remelted, the polycrystalline shell that has grown on the first molten edge 512-1 melts. Remelting a portion of the cross-sectional shape corresponds to remelting only the first molten edge 512-1 to form a second molten edge (i.e., remelted edge 512-2). The polycrystalline metal may be absent from the second molten edge (i.e., remelted edge 512-2). When the metal of the polycrystalline shell is remelted without the sintered layer 506 and removed from the processed region 516 (e.g., by brushing, moving, blowing, or suction), nucleation of atoms of the remelted metal on the surface of the single crystal is promoted. Upon solidification, these nucleated atoms adopt the orientation of the single crystal atoms, so that the single crystal extends to the edge of the part (e.g., the net edge). By utilizing the process described in this document, the net shape of the part can be obtained in situ (e.g., while remaining in its original location) without requiring subsequent machining or etching.

[0070] Fifth Figure 520 shows the powder bed 502 after a recoater head (not shown) has crossed the powder bed 502 and deposited a second layer of unmolten metal powder 504 on top of the sintered layer 506 and the shape 510 (both covered and not visible in fifth Figure 520), and then leveled the powder bed 502. According to some embodiments, the amount of unmolten metal powder 504 deposited on top of the sintered layer 506 and the shape 510 needs to be sufficient to fill the processed area 516 surrounding the shape 510.

[0071] As indicated by the arrows returning from the fifth figure, Figure 520, to the first figure, Figure 500, the process described and illustrated in Figure 5 may be repeated until all layers of the part are printed.

[0072] In one example, Figure 5 shows a method for additive manufacturing a three-dimensional (3D) printed part. This method may include the step of spreading a layer of unmelted metal powder 504 on a powder bed 502. This method may include the step of melting a portion of the layer into the shape 510 of the cross-section of a corresponding layer among several layers of the additively manufactured 3D printed part. In this example, the method may include the step of removing metal powder adjacent to a first molten edge of the shape using a tool (not shown). For example, if the layer of unmelted metal powder 504 sintersects to form a sintered layer 506, the third Figure 514 shows the processed area 516 after a tool (not shown) has removed the sintered metal powder adjacent to the first molten edge 512-1. This method may include the step of remelting at least one of the portions of the layer into the shape 510 of the cross-section of a corresponding layer among several layers of the additively manufactured 3D printed part. This method may further include repeating the steps of spreading, melting, removing, and remelting in each of the multiple consecutive layers of the additively manufactured 3D printed part.

[0073] In one example, this method may include sintering a layer of unmelted metal powder before the melting step, and performing the sintering, melting, and remelting with an electron beam (e.g., an electron beam used in an electron beam melting process). In another example, this method may include performing the melting and remelting in a laser powder bed melting process. In one example, the tool is not limited to but is at least one of a brush, comb, multiple whiskers, paddle, or beam.

[0074] In one embodiment, the method may further include the steps of spreading a layer of unmelted metal powder 504 onto a powder bed 502 using a recoater head (not shown), and positioning a tool (not shown) adjacent to a first melting edge 512-1 of the shape 510 using a tool actuator (not shown) coupled to the recoater head.

[0075] In one example, the shape 510 before remelting includes a first portion of single-crystal metal approaching a first melting edge from within the shape at the center of the shape, and a second portion of polycrystalline metal approaching the first melting edge from outside the shape at the proximal end of the shape, the second portion of which may be nucleated on unmelted metal powder rather than on an existing surface of single-crystal metal. In this example, the first melting edge may correspond to the projection of the outer wall of the 3D printed part on one of the layers of the additively manufactured 3D printed part (or on the sintered layer 506). In this example, the first melting edge 512-1 surrounds the shape 510 and may include at least one of single-crystal metal and polycrystalline metal.

[0076] In some examples, the step of remelting a portion of the layer with cross-sectional shape 510 corresponds to remelting only the first molten edge 512-1 to form a remelted edge 512-2 (e.g., a second molten edge). In such examples, the remelted edge 512-2 may be one in which the polycrystalline metal is absent (e.g., lacking).

[0077] Figure 6 is a set of images that can be used to illustrate the manufacture of metal products (e.g., metal parts, components) using a powder bed fused metal additive manufacturing process according to some aspects of the present disclosure. In the example in Figure 6, the powder bed fused process may be a laser powder bed fused process or an electron beam fused process. In an electron beam fused process, each layer of unmelted metal powder is sintered before printing a predetermined layer shape (e.g., after recoating (e.g., subsequent, subsequently) and before melting (e.g., prior)). In Figure 6, the sintering process is not shown to avoid drawing complexity. Of course, the example in Figure 6 is not limited to an electron beam fused process. In some aspects, the powder bed fused process may be a laser powder bed fused process, in which case the sintering aspect may be omitted.

[0078] In other words, in one embodiment, the apparatus for performing the method shown in Figure 6 may include an electron beam gun focused on the powder bed, and the apparatus may be configured to sinter a layer of unmelted metal powder before melting, and to perform sintering, melting, and remelting using an electron beam emitted from the electron beam gun. In another embodiment, the apparatus for performing the method shown in Figure 6 may include a laser, and the laser beam may be focused on the powder bed. In this embodiment, the apparatus may be configured to perform melting and remelting in a laser powder bed melting process.

[0079] Figure 600 shows the powder bed 602 after a recoater head (not shown) has crossed it and deposited a first layer of unmolten metal powder (hereinafter referred to as "first layer") 604 (e.g., SX superalloy metal powder) on top of it, and then leveled it. The term "first layer" as used in relation to Figure 6 is a relative term. The first layer 604 may be the uppermost layer of several already processed layers below the first layer (i.e., crossing the Z-axis toward the origin).

[0080] The second Figure 606 shows a shape 610 corresponding to a cross-section of a layer (e.g., a slice) of a metal part, after the electron beam has melted the shape 610 into the first layer 606 (and any portion of single-crystal metal directly beneath the first layer 604). Similar to the shape 510 shown and described in relation to Figure 5, the shape 610 includes single-crystal metal and polycrystalline metal. A zone including the melted edge (e.g., the first melted edge 612) surrounds the shape 610 and may include at least one of the single-crystal metal and polycrystalline metal. In some examples, the shape 610 may be slightly larger in size (e.g., near-net shape) to facilitate tooling in the field (e.g., in its original location, fixed position) as described herein. The process shown in the second Figure 606 can be repeated a predetermined number of times. For example, let L be the total number of repetitions, where L is an integer greater than or equal to 1. In the example in Figure 6, this process is repeated 10 times, and numbers less or greater than 10 are also within the scope of this disclosure. An example of 10 repetitions of the process shown in the second Figure 606 is indicated by a box containing the letters "X10" and an arrow looping from the first Figure 600 to the second Figure 606 and back to the first Figure 600.

[0081] The third figure, 608, shows the processed region 616 after a tool (not shown) has removed a polycrystalline shell (not shown) adjacent to the first molten edge 612 of the shape to a depth corresponding to a predetermined number of layers (e.g., 10 layers) corresponding to at least a predetermined number of repetitions (e.g., 10 repetitions). The tool may be a cutting tool such as an end mill or router bit, or a grinding tool such as a burr grinder or die grinder. The grinding tool may be cylindrical or of other shapes.

[0082] The process shown in the third figure, 608, may be performed once every predetermined number of repetitions. For example, in relation to Figure 6, the process shown in the third figure, 608, can be executed once every 10 repetitions. In the third figure, 608, the box labeled "After 10 Repetitions" indicates that the repetition occurs once every 10 times. This box is associated with an arrow that loops from the second figure, 606, to the third figure, 608. A box containing the text "X1" is associated with an arrow that loops from the third figure, 608, to the first figure, 600.

[0083] In one example, Figure 6 shows a method for additive manufacturing a three-dimensional (3D) printed part. This method may include the step of spreading a layer of unmelted metal powder (for example, a first layer 604 of unmelted metal powder as illustrated and described in relation to the first Figure 600) on a powder bed 602.

[0084] This method includes the step of melting a portion of a layer having a cross-sectional shape 610 of a corresponding layer among multiple layers of a layer-formed 3D printed part, wherein the portion of the layer has a melted edge (e.g., a first melted edge 612).

[0085] This method may include repeatedly spreading and melting L-1 consecutive layers of metal powder corresponding to each of the L-1 layers of a multilayer 3D printed part (where L is an integer greater than 1), and after spreading and melting the top layer (e.g., the L-th layer), using a first tool (not shown) to remove polycrystalline shell (not shown) adjacent to the melted edge (e.g., the first melted edge 612) of the melted edges of each layer of the shape up to a depth of L layers relative to the top layer.

[0086] In one example, this method may include sintering a layer of unmelted metal powder before melting, and performing the sintering, partial melting of the layer, melting of the subsequent L-1 layer, and melting of the top layer in an electron beam melting process. In another example, this method may include performing the partial melting of the layer, melting of the subsequent L-1 layer, and melting of the top layer in a laser powder bed melting process.

[0087] For example, in response to a decision that additional layers should be printed to correspond to multiple layers of an additively manufactured 3D printed part, this method may include spreading and melting the next L consecutive layers of metal powder corresponding to each of the next L layers of the additively manufactured 3D printed part until all layers corresponding to the multiple layers of the additively manufactured 3D printed part have been printed, and then repeating the step of removing the polycrystalline shell adjacent to the melted edge of each layer of the shape to a depth of L layers for the next top layer using a first tool.

[0088] In one example, this method may involve using a laser powder bed melting process to perform the melting of a portion of the layer, the melting of the subsequent L-1 layer, and the melting of the top layer.

[0089] In another example, this method may involve using an electron beam melting process to perform the melting of a portion of the layer, the melting of the subsequent L-1 layer, and the melting of the top layer.

[0090] In an example using an electron beam melting process, this method may involve spreading each layer of unmelted metal powder onto a powder bed (for example, after spreading) and then sintering each layer of unmelted metal powder. In some cases, the first tool can be a cutting tool or a grinding tool. Examples of cutting tools include end mills and router bits. Examples of grinding tools include burr grinders and die grinders.

[0091] For example, this method may involve using a second tool (not shown) to remove unmelted metal powder adjacent to the melted edge of each layer of the shape (e.g., the first melted edge 612) to a depth of L of the current layer. In some examples, the second tool is, but is not limited to, at least one of a brush, comb, multiple whiskers, paddle, beam, negative pressure vacuum nozzle, and positive pressure inert gas nozzle.

[0092] In some cases, the 3D printed parts are single-crystal 3D printed parts that do not contain polycrystalline metal, and the polycrystalline shell is removed in place (for example, in its original location).

[0093] Figure 7 is a block diagram of an example of a system 701 that may be used to remove unmelted metal powder from the edges of one or more additively printed layers of a 3D printed metal part (hereinafter referred to as "part" 702) during (on-site) manufacturing, according to several aspects of the present disclosure. The system 701 includes an apparatus 700 that can be used in an electron beam melting process or a laser powder bed melting process. The apparatus 700 may include a recoater head 704, a tool actuator 706 slidably coupled to the recoater head 704, and a tool 708 that can be fixedly or optionally rotatably coupled to the tool actuator 706.

[0094] In the example in Figure 7, the apparatus 700 is located within the vacuum chamber 714 of the electron beam melting 3D printer 716 and is therefore configured for the electron beam melting process. The same apparatus 700 can be used in a laser powder bed melting process, in which case the vacuum chamber 714 and the electron beam melting 3D printer 716 are removed from Figure 7, and a laser (not shown) is used instead of the electron beam gun 718. Alternatively, the apparatus 700 (including the recoater head 704, tool actuator 706, and tool 708), as well as the gantry driver 712, worm drive 710, powder bed 720, part 702, and gantry (not shown) (which may be configured to produce specific movements of the recoater head 704), can be used in either the electron beam melting process or the laser powder bed melting process. The coupling of the tool and / or tool actuator to the gantry is for illustrative and non-limiting purposes, and other apparatuses, devices, etc., that enable any tool, apparatus, mechanism, etc., to interact with the part, such as, but not limited to, an independent gantry, mechanical arm, multi-axis articulated structure, etc., are also within the scope of this disclosure.

[0095] The recoater head 704 may include one or more servos, motors, linear stepping motors, etc., or combinations thereof (not shown) to achieve vertical (up and down) motion (i.e., movement along the Z-axis). The tool actuator 706 may include one or more servos, motors, linear stepping motors, etc., or combinations thereof (not shown) to achieve vertical (up and down) motion (i.e., movement along the Z-axis) and optionally rotational motion of the tool 708 (i.e., rotation about the Z-axis).

[0096] In some examples, if the tool 708 is configured to move unmolten metal powder (e.g., sintered or unsintered metal powder adjacent to the outer edge of the boundary of part 702) by displacement, the tool 708 may be, for example, a brush, a comb, multiple whiskers, a paddle or beam of any cross-section or combination of cross-sections (e.g., circular, rectangular, elliptical, D-shaped, etc.). In some examples, if the tool 708 is configured to move unmolten metal powder (e.g., sintered or unsintered metal powder adjacent to the outer edge of the boundary of part 702) by displacement, the tool 708 may be, for example, a positive pressure inert gas nozzle that delivers a gas to blow the unmolten metal powder away from the outer edge of the boundary of part 702 during manufacturing, or a gas to blow into the molten pool, onto the surface of the unmolten metal powder. If the tool 708 is configured to remove polycrystalline metal (e.g., molten metal powder nucleated on a surface other than the desired single-crystal surface) by cutting or polishing, the tool 708 may be, for example, a cutting tool such as an end mill, a router bit, or a polishing cylinder. For tools such as end mills, router bits, and grinding cylinders, the tool actuator 706 may optionally be configured to rotate the tool 708, as shown in Figure 7.

[0097] The tool actuator 706 may be configured to rotate the tool 708 in either direction at a predetermined or variable speed. Figure 7 shows only the clockwise direction to avoid drawing complexity. If the tool 708 is configured to remove unmolten metal powder, sintered metal powder, and / or crushed, routed, or polished particles of polycrystalline metal and / or sintered metal powder by vacuum action (e.g., during or after on-site machining), the tool 708 may be, for example, a vacuum nozzle coupled to a vacuum, vacuum pump, or other negative pressure device. The above list is illustrative and not limiting. Although not shown to avoid drawing complexity, the tool 708 may be any combination of the above types of tools, and the tool actuator 706 may be configured to transport one or more of the tools 708, or any combination of two or more tools. For example, the tool 708 may be a spaced, adjacent, or coaxial combination of a cutting tool and a vacuum nozzle, or a cutting tool and a brush, or a cutting tool, a brush, and a vacuum nozzle. The above combinations are illustrative and non-exclusive. Any combination of two or more tools is within the scope of this disclosure.

[0098] In some embodiments, the recoater head 704 may be coupled to a worm drive 710. The worm drive 710 may be rotatably coupled to a gantry driver 712. The gantry driver may include one or more servos, motors, linear stepping motors, etc. (not shown). The gantry driver 712 may be configured to rotate the worm drive 710 clockwise and counterclockwise (at different times) around its longitudinal axis (e.g., the Y-axis) to produce lateral motion of the recoater head 704 (i.e., movement along the Y-axis). The gantry driver 712 may be coupled to a gantry (not shown) and configured to produce longitudinal motion of the recoater head 704 (i.e., movement along the X-axis (the X-axis is perpendicular to the plane of the figure)) by moving the gantry in the longitudinal direction. The worm gear and / or track that realize the longitudinal motion of the gantry, and the gantry itself, are omitted from Figure 7 to avoid drawing complexity.

[0099] Figure 7 shows the apparatus 700 inside a vacuum chamber 714 within an electron beam melting (EBM) 3D printer 716. The electron beam gun 718 is shown above the powder bed 720. However, the apparatus 700 is not limited to placement inside the vacuum chamber 714 or the placement of the EBM 3D printer 716 inside the vacuum chamber 714. For example, the apparatus 700 can be used with a laser (instead of the electron beam gun 718) outside the vacuum chamber 714 in the case of a laser powder bed fusion (L-PBF) 3D printer (not shown).

[0100] Figure 7 also shows a controller 722 employing one or more processors (collectively represented as processor 724) that can be coupled to one or more memories (collectively represented as memory / computer-readable medium 728), according to several aspects of the present disclosure. Examples of processor 724 include microprocessors, microcontrollers, digital signal processors (DSPs), field-programmable gate arrays (FPGAs), programmable logic devices (PLDs), state machines, gate logic, discrete hardware circuits, and other suitable hardware configured to perform various functions described throughout the present disclosure. In various examples, one or more processors (collectively represented as processor 724) used in the controller 722 may be configured to perform (e.g., execute) any one or more of the functions, methods, processes, or embodiments described and illustrated, for example, in Figures 1, 2, 3, 4, 5, and / or 6, individually or collectively, based at least in part on information stored in one or more memories (collectively represented as memory / computer-readable medium 728).

[0101] In this example, the controller 722 may be implemented in a bus architecture represented collectively by bus 726. Bus 726 may include any number of interconnect buses and bridges, depending on the specific application and overall design constraints of the controller 722. Bus 726 communicatively connects various circuits, including one or more processors (represented collectively by processor 724) and one or more memories (represented collectively by memory / computer-readable media 728). Bus 726 may also link various other circuits, such as timing sources, peripheral circuits, voltage regulators, and power management circuits, which are well known to those skilled in the art and therefore not described further.

[0102] The bus interface 730 provides an interface between the bus 726, the gantry driver 712, the recoater head 704, and the tool actuator 706. The bus interface 730 may also provide an interface between the bus 726 and a user interface 732 (e.g., a keypad, display, touchscreen, speaker, microphone, control functions, vibration circuit / device, etc.). Of course, such a user interface 732 is optional and may be omitted in some examples.

[0103] One or more processors, individually or collectively represented by processor 724, may be responsible for general operations, including managing bus 726 and executing software stored in / on memory / computer-readable medium 728. Software is broadly interpreted to mean instructions, instruction sets, code, code segments, program code, programs, subprograms, software modules, applications, software applications, software packages, routines, subroutines, objects, executable files, execution threads, procedures, functions, etc., whether they are called software, firmware, middleware, microcode, or hardware description languages, etc. When executed by processor 724, software (e.g., instructions) causes controller 722, via gantry driver 712, recooler head 704, tool actuator 706, and tool 708, to perform various processes and functions described herein for any particular device.

[0104] Memory / computer-readable media 728 may be non-temporary computer-readable media, also called computer-readable storage media or non-temporary computer-readable media. Non-temporary computer-readable media may store computer-executable code (e.g., processor-executable code). Computer-executable code may include code that causes a computer (e.g., a processor) to perform one or more of the various processes and functions described herein. Non-temporary computer-readable media may include, for example, magnetic storage devices (e.g., hard disks, floppy disks, magnetic strips), optical disks (e.g., compact discs (CDs), digital multipurpose discs (DVDs)), smart cards, flash memory devices (e.g., cards, sticks, key drives), random access memory (RAM), read-only memory (ROM), programmable ROM (PROM), erasable PROM (EPROM) including electrically erasable PROM (EEPROM), registers, removable disks, and any other suitable media for storing software and / or instructions that a computer can access and read. The memory / computer-readable medium 728 may reside within the controller 722, or outside the controller 722, or may be distributed across multiple entities including the controller 722. The memory / computer-readable medium 728 may be implemented in a computer program product or manufactured product. For example, a computer program product or manufactured product may include the computer-readable medium in its packaging. A person skilled in the art will recognize the best way to implement the functions described throughout this disclosure, depending on the specific application and the overall design constraints imposed on the entire system. The memory / computer-readable medium 728 may be used to store data that is manipulated by the processor 724 when executing software (instructions 729).

[0105] For example, the controller 722 may be configured to perform an electron beam melting process (for example, in the vacuum chamber 714 of an electron beam melting 3D printer 716, using a recoater head 704 to spread and flatten a layer of unmelted metal powder, sinter the layer of unmelted metal powder, and melt the shape corresponding to the layer (e.g., slice) that will become the (finished) 3D printed part). At the end of each melting process, before recoating the layer that has just been treated with a new layer of unmelted metal powder, the controller may use a brush device on the recoater head 704 to remove the sintered metal powder from around the top layer of the part (for example, the brush may be a tool 708 directly coupled to the recoater head 707 or indirectly coupled via a tool actuator 706). After removing the sintered metal powder from around the top layer of the part, the controller may be configured to remelt the top layer (e.g., the top layer portion including the printed slice) without adding additional metal powder, or to remelt the periphery edge of the top layer of the part to remelt any polycrystalline shell that may have formed during the initial melting, thereby generating a single crystal (to replace the polycrystalline shell). Once complete, the controller 722 may be configured to return to the process of recoating, flattening, sintering, and melting the next shape corresponding to the next layer that will become the (finished) 3D printed part. Note that more metal powder than usual may be needed to "replenish" the parts removed by brushing.

[0106] More specifically, the controller 722 may be configured to cause the recoater head 704 to spread a first layer of unmelted metal powder (e.g., SX superalloy metal powder) onto the powder bed 720. The controller 722 may further be configured to cause the electron beam gun 718 to sinter the first layer of unmelted metal powder. The controller 722 may further be configured to cause the electron beam gun 718 to perform a first melt of a portion of the first layer of unmelted metal powder in the shape of one cross-section of one of several layers (e.g., slices) of a additively fabricated 3D printed metal part (e.g., part 702). The first melt may form a single-crystal volume (similar to single crystals 102 and / or 302 shown and described in relation to Figures 1 and / or 3, respectively) and adjacent polycrystalline shells (similar to polycrystalline shells 104, 204, and / or 304 shown and described in relation to Figures 1, 2, and / or 3, respectively).

[0107] Following the first melting, the controller 722 may further configure the tool 708 to remove sintered metal powder adjacent to the edges of the molten metal powder (where the outer edge of the molten metal powder at this joint may include at least a portion of the polycrystalline shell), where each edge corresponds to a desired edge of part 702. After removal, the controller 722 may further configure the electron beam gun 718 to re-perform the first melting (either over the entire molten metal powder or around the outer edges). Re-performing the first melting melts any polycrystalline shell that may have grown adjacent to the outer edges corresponding to the desired edges of part 702. Re-melting the metal of the polycrystalline shell in the absence of removed sintered metal powder promotes nucleation of atoms of the re-melted metal on the surface of the single-crystal volume. Upon solidification, these nucleated atoms will have the same orientation as the atoms of the single crystal. After re-melting, the controller 722 may further configure the recoater head 704 to spread a second layer of unmelted metal powder onto the powder bed 720.

[0108] For example, the controller 722 may be configured to perform either a laser powder bed melting process or an electron beam melting process. For example, when using a laser powder bed melting process, the controller may be configured to use a recoater head 704 to spread and flatten a layer of unmelted metal powder and to use a laser (not shown) to melt the layer of unmelted metal powder into a shape corresponding to the layer that will become the (finished) part (e.g., a slice). For example, when using an electron beam melting process, the controller may be configured to use a recoater head 704 to spread and flatten a layer of unmelted metal powder in the vacuum chamber 714 of the electron beam melting 3D printer 716, to sinter the layer of unmelted metal powder and melt the shape corresponding to the layer that will become the (finished) part (e.g., a slice). The laser powder bed melting process or the electron beam melting process may be repeated for a predetermined number of layers (e.g., 10 layers). The controller 722 may then optionally be configured to remove metal powder from around the molten area using a vacuum cleaner or brush, to scrape off edge particles (e.g., particles that form a polycrystalline shell around the single-crystal portion of the molten area) using a cutting tool, and to repeatedly perform a laser powder bed melting process (e.g., repeated recoating and melting) or an electron beam melting process (e.g., repeated recoating, sintering, and melting) on ​​another layer of a predetermined number of layers (e.g., 10 more layers), and to continue this until all layers of the part are completed.

[0109] More specifically, the controller 722 may be configured to cause the recoater head 704 to spread a first layer of unmelted metal powder (e.g., SX superalloy metal powder) onto the powder bed 720. The controller 722 may further be configured to cause the electron beam gun 718 to sinter the first layer of unmelted metal powder. The controller 722 may further be configured to cause a laser (not shown) or the electron beam gun 718 to perform a first melting of a portion of the first layer of unmelted metal powder in the shape of one cross-section of one of several layers (e.g., slices) of a finished 3D printed metal part (e.g., part 702) that has been additively fabricated. The first melting may form a single-crystal volume (similar to single crystals 102 and / or 302 shown and described in relation to Figures 1 and / or 3, respectively) and adjacent polycrystalline shells (similar to polycrystalline shells 104, 204, and / or 304 shown and described in relation to Figures 1, 2, and / or 3, respectively). After the first melting, the controller 722 may be configured to further repeat the recoating and melting process a given number of times (e.g., 10 times), and thereafter cause the tool 708 to remove the polycrystalline shell formed adjacent to the outer edges of the shape to a depth of at least a given number of layers (e.g., 10 layers). According to some embodiments, the tool may be a cutting tool such as an end mill or routing bit, or a grinding tool such as a bar bit or grind bit.

[0110] After removing the polycrystalline shell, the controller 722 may be configured to repeat the recoating and melting process a predetermined number of times (e.g., 10 times), and then use a cutting or polishing tool to remove the polycrystalline shell to a predetermined number of layers (e.g., 10 layers), repeating this individual process many times until all layers of the part are printed.

[0111] The controller 722 may also be configured to execute instructions 729 (e.g., software) stored in memory / computer-readable medium 728 to perform one or more of the functions described herein.

[0112] Figure 8 is a flowchart illustrating an exemplary process 800 (e.g., method) of metal 3D printing using additive manufacturing and electron beam melting processes according to several aspects of the present disclosure. As described below, in certain embodiments within the scope of the present disclosure, some or all of the illustrated features may be omitted, and some of the illustrated features may not be essential for the implementation of all embodiments. In some examples, process 800 may be performed by system 701, as shown and described in relation to Figure 7. In some examples, process 800 may be performed by any suitable apparatus or means for performing the functions or algorithms described below.

[0113] In block 802, the system may set the value of variable N to 1 (where N is a non-negative integer). For example, one or more processors (collectively referred to as processor 724, as shown and described in relation to Figure 7) may individually or collectively provide means for setting the value of variable N to 1.

[0114] In block 804, the system can spread the Nth layer of unmelted metal powder onto the powder bed. For example, as shown and described in relation to Figure 7, the recoater head 704 of the apparatus 700 may provide means for spreading the Nth layer of unmelted metal powder onto the powder bed. The powder bed 720 of system 701 is an example of a powder bed.

[0115] In block 806, the system can sinter the Nth layer of unmelted metal powder. For example, as shown and described in relation to Figure 7, the electron beam gun 718 of the electron beam fusion 3D printer 716 may provide means for sintering the Nth layer of unmelted metal powder. In block 808, the system may melt a portion of the Nth layer of unmelted metal powder into the shape of the cross-section of the Nth layer among multiple layers of the finished additively manufactured 3D printed part. For example, as shown and described in relation to Figure 7, the electron beam gun 718 of the electron beam fusion 3D printer 716 may provide means for performing a first melting of a portion of the Nth layer of unmelted metal powder into the shape of the cross-section of the Nth layer among multiple layers of the finished additively manufactured 3D printed part.

[0116] In block 810, the system may use a tool to remove sintered metal powder adjacent to the first molten edge of the shape. For example, as shown and described in relation to Figure 7, a tool 708 coupled to the recoater head 704 via a tool actuator 706 may provide a means for using the tool to remove sintered metal powder adjacent to the first molten edge of the shape. According to some embodiments, the tool may be, for example, a brush, a comb, multiple whiskers, a paddle or beam of any cross-section or combination of cross-sections (e.g., circular, rectangular, elliptical, D-shaped, etc.).

[0117] In block 812, the system may perform a second melting of a portion of the Nth layer to the shape of the cross-section of the Nth layer of the multiple layers of the finished additively manufactured 3D printed part (without spreading new metal powder before performing the second melting). For example, as shown and described in relation to Figure 7, the electron beam gun 718 of the electron beam fusion 3D printer 716 may provide means for performing a second melting of a portion of the Nth layer to the shape of the cross-section of the Nth layer of the multiple layers of the finished additively manufactured 3D printed part (without spreading new metal powder before performing the second melting).

[0118] In block 814, the system may determine whether all layers of a plurality of layers have been printed. For example, one or more processors (collectively referred to as processor 724, as shown and described in relation to Figure 7) may individually or collectively provide means for determining whether all layers of a plurality of layers have not been printed. In response to determining that all layers of a plurality of layers have not been printed, process 800 may proceed to block 816.

[0119] In block 816, the system may increment the variable N by 1 (for example, N = N + 1). For example, one or more processors (collectively represented by processor 724, as shown and explained in relation to Figure 7) may individually or collectively provide means to increment the value of variable N by 1. Process 800 then returns to block 804.

[0120] However, if block 814 determines that all layers of multiple layers have been printed, process 800 may terminate. Figure 9 is a flowchart illustrating an exemplary process 900 (e.g., method) of metal 3D printing using an additive manufacturing process such as a laser powder bed fusion process or an electron beam fusion process, according to several aspects of the present disclosure. As described below, in certain embodiments within the scope of the present disclosure, some or all of the illustrated features may be omitted, and some of the illustrated features may not be essential for the implementation of all embodiments. In some examples, process 900 may be performed by system 701, as shown and described in relation to Figure 7. In some examples, process 900 may be performed by any suitable apparatus or means for performing the functions or algorithms described below.

[0121] In block 902, the system may set a first value of variable N to 0 (where N is a non-negative integer) and a second value of variable L to 1 (where L is a non-negative integer). For example, one or more processors (collectively referred to as processor 724, as shown and described in relation to Figure 7) may individually or collectively provide means for setting a first value of variable N to 0 and a second value of variable L to 1.

[0122] In block 904, the system can spread the (N+L)th layer of unmelted metal powder onto the powder bed. For example, as shown and described in relation to Figure 7, the recoater head 704 of the apparatus 700 may provide means for spreading the (N+L)th layer of unmelted metal powder onto the powder bed. The powder bed 720 of system 701 is an example of a powder bed.

[0123] In block 906, the system may melt a portion of the (N+L)th layer of unmelted metal powder into the shape of the cross-section of the (N+L)th layer among multiple layers of the finished additively manufactured 3D printed part. For example, as shown and described in relation to Figure 7, the electron beam gun 718 of the electron beam fusion 3D printer 716 (or the laser (not shown) of a laser powder bed fusion system (not shown)) may provide means for performing a first melting of a portion of the (N+L)th layer of unmelted metal powder into the shape of the cross-section of the (N+L)th layer among multiple layers of the finished additively manufactured 3D printed part.

[0124] In block 908, the system may determine whether the variable L is equal to a predetermined number (e.g., L = 10) (e.g., a pre-set predetermined number). In the example of block 908, the predetermined number (e.g., a pre-set predetermined number) has a value of 10 for illustrative and non-limiting purposes. Other numerical values ​​are also within the scope of this disclosure. For example, one or more processors (collectively represented as processor 724, as shown and described in relation to Figure 7) may individually or collectively provide means for determining whether the variable L is equal to a predetermined number. If it is determined that L is not equal to a predetermined number (e.g., L ≠ 10), process 800 may proceed to block 910.

[0125] In block 910, the system may increment the variable L by 1 (for example, L = L + 1). For example, one or more processors (collectively represented by processor 724, as shown and explained in relation to Figure 7) may individually or collectively provide means to increment the value of variable L by 1. Process 800 then returns to block 904.

[0126] However, if block 908 determines that the variable L is equal to a predetermined number (for example, L=10), process 800 may optionally proceed to block 912, or, if the option in block 912 is not taken, the process may proceed to block 914.

[0127] In block 912, the system may optionally use a first tool to remove metal powder adjacent to the outer edges of the shape. For example, as shown and described in relation to Figure 7, a tool 708 coupled to the recoater head 704 via a tool actuator 706 may provide a means for using the first tool to remove metal powder adjacent to the outer edges of the shape. According to some embodiments, the first tool may be, for example, a brush, a comb, multiple whiskers, a paddle or beam of any cross-section or combination of cross-sections (e.g., circular, rectangular, elliptical, D-shaped, etc.).

[0128] In block 914, the system may use a second tool to remove polycrystalline shell adjacent to the outer edges of the shape. For example, as shown and described in relation to Figure 7, a tool 708 coupled to a recoater head 704 via a tool actuator 706 may provide a means for using the second tool to remove polycrystalline shell adjacent to the outer edges of the shape. According to some embodiments, the second tool may be a cutting tool such as an end mill or router bit, or a grinding tool such as a burr grinder or die grinder. The grinding tool may be cylindrical or of other shapes.

[0129] In block 916, the system may determine whether all layers of a plurality of layers have been printed. For example, one or more processors (collectively referred to as processor 724, as shown and described in relation to Figure 7) may individually or collectively provide means for determining whether all layers of a plurality of layers have not been printed. In response to determining that all layers of a plurality of layers have not been printed, process 900 may proceed to block 918.

[0130] In block 918, the system increments the variable N by 10 (e.g., N = N + 10) and resets the variable L to 1 (e.g., L = 1). In the example of block 918, the value of variable N is given as 10 and the value of variable L is given as 1 for illustrative and non-limiting purposes. Other values ​​of N and L are also within the scope of this disclosure. For example, one or more processors (collectively represented as processor 724, as shown and described in relation to Figure 7) may individually or collectively provide means for incrementing the value of variable N by 10 and resetting variable L to 1. The process 900 may then return to block 904.

[0131] However, if block 916 determines that all layers of multiple layers have been printed, process 900 may terminate.

[0132] Of course, in the example above, the circuitry included in the processor 724 in Figure 7 is provided merely as an example. Other means for carrying out the described processes or functions may be included in various aspects of this disclosure, but are not limited to, instructions 729 stored in the memory / computer-readable medium 728 in Figure 7, or any other suitable apparatus or means described in any one of Figures 5, 6, and / or 7 that utilizes the processes and / or algorithms described herein in relation to Figures 1, 3, 4, 5, 6, 8, and / or 9.

[0133] Several embodiments of 3D printing systems have been described with reference to exemplary examples. As will be readily apparent to those skilled in the art, the various embodiments described herein can be extended to other 3D printing systems.

[0134] According to one embodiment, a system is described. This system comprises one or more processors, one or more memories coupled to the one or more processors, a powder bed, an electron beam gun coupled to the one or more processors and focused on the powder bed, a recoater head coupled to the one or more processors, a tool actuator coupled to the recoater head and the one or more processors, and a tool coupled to the tool actuator. In this embodiment, one or more processors are configured to individually or collectively, at least partially based on information stored in one or more memories, to use the recoater head to spread a layer of unmelted metal powder onto the powder bed, to melt a portion of the layer into the cross-sectional shape of a corresponding layer among a plurality of layers of an additive manufacturing 3D printed part, to use the tool to remove metal powder adjacent to a first melted edge of the shape, to remelt the first melted edge or a portion of the layer of the cross-sectional shape of a corresponding layer among a plurality of layers of the additive manufacturing 3D printed part, and to repeat the spreading step, melting step, removal step, and remelting step for each of the consecutive layers of the plurality of layers of the additive manufacturing 3D printed part.

[0135] According to one embodiment, a system is described. This system may comprise one or more processors, one or more memories coupled to the one or more processors, a powder bed, a laser or electron beam gun connected to the one or more processors and focused on the powder bed, a recoater head coupled to the one or more processors, a tool actuator coupled to the recoater head and the one or more processors, and a tool coupled to the tool actuator. According to this embodiment, one or more processors are configured to spread a layer of unmelted metal powder onto a powder bed, melt a portion of the layer into the cross-sectional shape of a corresponding layer among a plurality of layers of an additive manufacturing 3D printed part, at least partially based on information stored in one or more memories individually or collectively, and to repeat the spreading and melting steps for L-1 consecutive layers of metal powder corresponding to each of the L-1 layers of the plurality of layers of the additive manufacturing 3D printed part, where L is an integer greater than 1, and to use a first tool to remove polycrystalline shell adjacent to the melted edge of each layer of the shape to a depth of L layers relative to the top layer, following the step of spreading and melting the top layer (e.g., the Lth layer).

[0136] According to one embodiment, an apparatus is described which can perform additive manufacturing of three-dimensional (3D) printed parts. The apparatus includes means for spreading a layer of unmelted metal powder onto a powder bed; means for sintering the layer of unmelted metal powder; means for melting a portion of the layer to the cross-sectional shape of a corresponding layer among a plurality of layers of an additively manufactured 3D printed part; means for removing sintered metal powder adjacent to a first melted edge of the shape using a tool; means for remelting a portion of the layer to the cross-sectional shape of a corresponding layer among a plurality of layers of the additively manufactured 3D printed part; and means for repeating the spreading step, the sintering step, the melting step, the removal step, and the remelting step in each of the plurality of consecutive layers of the additively manufactured 3D printed part.

[0137] According to one embodiment, an apparatus is described that can perform additive manufacturing of three-dimensional (3D) printed parts. The apparatus includes means for spreading a layer of unmelted metal powder onto a powder bed; means for melting a portion of the layer into the cross-sectional shape of a corresponding layer among a plurality of layers of an additively manufactured 3D printed part; and means for repeating the spreading and melting steps for L-1 consecutive layers of metal powder corresponding to each of the L-1 layers of the plurality of layers of the additively manufactured 3D printed part, where L is an integer greater than 1; and, following the step of spreading and melting the top layer, means for using a first tool to remove polycrystalline shell adjacent to the melted edge of each layer of the shape to a depth of L layers relative to the top layer.

[0138] In this disclosure, the term “exemplary” is used to mean “serving as an example, illustration, or explanatory example.” Embodiments or aspects described “exemplary” in this specification are not necessarily construed to be preferable or advantageous to other embodiments or aspects of this disclosure. Similarly, the term “aspects” does not require that all aspects of this disclosure include the features, advantages, or modes of operation discussed. In this specification, the term “bonded” means a direct or indirect bond between two objects. For example, if object A is in physical contact with object B, and object B is in contact with object C, objects A and C are considered bonded to each other even if they are not in direct physical contact. For example, an object may be bonded to an object second even if it is not in direct physical contact with the object first. The terms “circuit” and “circuit” are used broadly and are intended to include both hardware implementations of electrical devices and conductors that, when connected and configured, enable the performance of the functions described in this disclosure, and software implementations of information and instructions that, when executed by a processor, enable the performance of the functions described in this disclosure, without being limited to types of electronic circuits.

[0139] One or more of the components, steps, features, and / or functions illustrated in Figures 1-9 may be rearranged and / or combined into a single component, step, feature, or function, or they may be embodied in multiple components, steps, or functions. Additional elements, components, steps, and / or functions may also be added without departing from the novel features disclosed herein. The apparatus, devices, and / or components illustrated in Figures 1-9 may be configured to perform one or more of the methods, features, or steps described herein. Furthermore, the novel algorithms described herein can be efficiently implemented in software or incorporated into hardware.

[0140] It should be understood that the specific order or hierarchy of steps in the disclosed method is illustrative of an exemplary process. It should be understood that the specific order or hierarchy of steps in this method may be rearranged based on design preferences. The method claims present elements of various steps in a sample order and are not intended to be limited to the specific order or hierarchy presented unless otherwise stated.

[0141] The above description is provided so that a person skilled in the art may carry out the various embodiments described herein. Various modifications to these embodiments will be obvious to a person skilled in the art, and the general principles set forth herein may be applied to other embodiments. For this reason, the claims are not intended to be limited to the embodiments shown herein, but the entire scope consistent with the language of the claims is permitted, and references to singular elements shall mean "one or more" and not "only" unless otherwise specified. Unless otherwise specified, the term "several" refers to one or more.

[0142] All structural and functional equivalents of elements of various aspects described herein, known to those skilled in the art, or to become known to those skilled in the art, are expressly incorporated herein by reference and are intended to be included in the claims. Furthermore, nothing disclosed herein is intended to be made available to the public, whether such disclosure is expressly included in the claims or not. No element of a claim should be construed under 35 U.S. SC § 112(f) unless it is expressly described in the phrase “means for” or, in the case of a method claim, in the phrase “step for.”

[0143] As used herein, the terms “determine” or “determine” encompass a wide range of actions, and therefore “determining” includes calculation, operation, processing, derivation, retrieval (such as retrieving in tables, databases, or other data structures), inference, confirmation, measurement, etc. “Determining” also includes receiving (such as receiving information), accessing (such as accessing data stored in memory), and transmitting (such as transmitting information). Furthermore, “determining” includes actions such as resolution, selection, retrieval, choice, and establishment.

[0144] Where used herein, the phrase “at least one” in a list of items refers to any combination of those items, including a single member. For example, “at least one of a, b, and c” means a, b, c, ab, ac, bc, and abc. Where used herein, “or” is intended to be interpreted in an inclusive sense unless otherwise explicitly indicated. For example, “a or b” includes a only, b only, or a combination of a and b. Similarly, the phrase A and / or B may include A only, B only, or a combination of A and B.

[0145] The various exemplary components, logic, logic blocks, modules, circuits, operations, and algorithmic processes described in relation to the embodiments disclosed herein can be implemented as electronic hardware, firmware, software, or a combination of hardware, firmware, and software, including the structures disclosed herein and their structural equivalents. The compatibility of hardware, firmware, and software is generally described in terms of functionality and is illustrated above for the various exemplary components, blocks, modules, circuits, and processes. Whether such functionality is implemented in hardware, firmware, or software depends on the specific application and the design constraints imposed on the overall system.

[0146] Various modifications to the embodiments described herein will be readily apparent to those skilled in the art, and the general principles defined herein can be applied to other embodiments without departing from the spirit or scope of this disclosure. Therefore, the claims are not intended to be limited to the embodiments described herein, but should be given to the broadest extent consistent with this disclosure, the principles, and the novel features disclosed herein.

[0147] Similarly, while the diagrams show operations in a specific order, this should not be understood as requiring that such operations be performed in the specific order shown, or in a sequential order, or that all illustrated operations be performed to achieve the desired result. Furthermore, the diagrams may schematically represent one or more exemplary processes in the form of flowcharts or flow charts. However, other operations not illustrated may be incorporated into the schematically shown exemplary process. For example, one or more additional operations may be performed before, after, simultaneously with, or in between the illustrated operations. In some situations, multitasking or parallel processing may be advantageous. Moreover, the separation of various system components in the embodiments described above should not be understood as requiring such separation in all embodiments, and the described program components and systems can generally be integrated into a single software product or packaged into multiple software products.

Claims

1. A method for additive manufacturing of three-dimensional (3D) printed parts, The steps include spreading a layer of unmelted metal powder on a powder bed, A step of melting a portion of a layer to form the cross-sectional shape of a corresponding layer among multiple layers of an additively manufactured 3D printed part, The steps include using a tool to remove metal powder adjacent to the first molten edge of the shape, The steps include: remelting the first molten edge, or at least one portion of the cross-sectional shape of a corresponding layer among a plurality of layers of an additively manufactured 3D printed part; A method comprising repeating the spreading step, the melting step, the removal step, and the remelting step in each of the multiple consecutive layers of an additively manufactured 3D printed part.

2. The method according to claim 1, further, The step of sintering a layer of unmelted metal powder before the melting step, A method comprising performing the sintering step, the melting step, and the remelting step with an electron beam.

3. The method according to claim 1, further, A method comprising performing the melting step and the remelting step in a laser powder bed melting process.

4. The method according to claim 1, wherein the tool is at least one of a brush, a comb, a plurality of whiskers, a paddle, and a beam.

5. The method according to claim 1, further, The steps include spreading a layer of unmelted metal powder onto the powder bed using a recoater head, A method comprising the step of positioning a tool adjacent to a first melting edge of the shape using a tool actuator coupled to the recoater head.

6. In the method according to claim 1, the shape is obtained before the remelting step, A first portion of the single-crystal metal at the center of the shape, approaching the first molten edge from the inside of the shape, wherein the first portion is nucleated on the existing surface of the single-crystal metal, The second portion of the polycrystalline metal proximal to the shape, approaching the first molten edge from the outside of the shape, and comprising a second portion nucleated on unmolten metal powder rather than on an existing surface of the single-crystal metal, The first molten edge corresponds to a protruding portion of the outer wall of a 3D printed part on one of the layers of the additively manufactured 3D printed part.

7. The method according to claim 6, wherein the first molten edge surrounds the shape and includes at least one of the single-crystal metal and the polycrystalline metal.

8. A method according to claim 1, wherein the step of remelting a portion of the layer having the shape of the cross-section corresponds to remelting only the first molten edge to form a second molten edge.

9. The method according to claim 8, wherein the second molten edge does not contain polycrystalline metal.

10. It is a device, Powder bed and A recoater head configured to recoat the powder bed with unmelted metal powder, The tool actuator coupled to the recoater head, The device comprises a tool coupled to the tool actuator, and the device is Using the recoater head, spread a layer of unmelted metal powder onto the powder bed. A portion of a layer is melted to form the cross-sectional shape of a corresponding layer among multiple layers of an additively manufactured 3D printed part. Using the tool, remove the metal powder adjacent to the first molten edge of the shape. The first melted edge, or at least one of the portion of the layer whose cross-sectional shape corresponds to one of the multiple layers of the additively manufactured 3D printed part, is remelted. An apparatus configured to repeatedly perform the processes of spreading, melting, removing, and remelting in each of the multiple consecutive layers of a 3D printed part produced by additive manufacturing.

11. A method for additive manufacturing of three-dimensional (3D) printed parts, The steps include spreading a layer of unmelted metal powder on a powder bed, A step of melting a portion of a layer to the shape of the cross-section of a corresponding layer among multiple layers of an additively manufactured 3D printed part, wherein the portion of the layer has a melted edge, For L-1 consecutive layers of metal powder corresponding to each of the L-1 layers of the additively manufactured 3D printed part, the step of spreading and the step of melting are repeated, where L is an integer greater than 1. A method comprising, after the steps of spreading and melting the uppermost layer, using a first tool to remove the polycrystalline shell adjacent to the melted edge of each layer to a depth of L layer relative to the uppermost layer.

12. In the method according to claim 11, further, The step of sintering a layer of unmelted metal powder before the melting step, A method comprising the steps of performing the sintering, melting a portion of the layer, melting L-1 consecutive layers, and melting the uppermost layer in an electron beam melting process.

13. In the method according to claim 11, further, A method comprising the steps of performing a laser powder bed melting process, including melting a portion of the layer, melting the L-1 consecutive layers, and melting the uppermost layer.

14. In the method of claim 11, in response to a decision that additional layers corresponding to multiple layers of the additively manufactured 3D printed part should be printed, the method further Until all layers corresponding to the multiple layers of the aforementioned additively manufactured 3D printed part are printed, The process involves spreading and melting L consecutive layers of metal powder corresponding to each of the L layers of the additively fabricated 3D printed part, A method comprising the step of subsequently using a first tool to repeat the step of removing polycrystalline shell adjacent to the molten edge of each layer of the shape up to the depth of the next uppermost layer.

15. The method according to claim 10, wherein the first tool is a cutting tool or a polishing tool.

16. The method according to claim 15, wherein the cutting tool is an end mill or a router bit, and the grinding tool is a burr grinder or a die grinder.

17. In the method according to claim 11, further, A method comprising the step of using a second tool to remove unmelted metal powder adjacent to the molten edge of each layer of the shape to a depth of L layer relative to the current layer.

18. The method according to claim 17, wherein the second tool is at least one of a brush, a comb, a plurality of whiskers, a paddle, a beam, a negative pressure vacuum nozzle, and a positive pressure inert gas nozzle.

19. The method according to claim 11, wherein the 3D printed part is a single-crystal 3D printed part that does not contain polycrystalline metal, and the polycrystalline shell is removed in situ.

20. It is a device, Powder bed and A recoater head configured to recoat the powder bed with unmelted metal powder, The tool actuator coupled to the recoater head, The device comprises a tool coupled to the tool actuator, and the device is Using the recoater head, spread a layer of unmelted metal powder onto the powder bed. A portion of a layer is melted to match the cross-sectional shape of a corresponding layer among multiple layers of an additively manufactured 3D printed part, and the portion of the layer has a melted edge. For L-1 consecutive layers of metal powder corresponding to each of the L-1 layers of the additively manufactured 3D printed part, the spreading and melting process is repeated, where L is an integer greater than 1. An apparatus configured to, after spreading and melting the top layer, use a first tool to remove the polycrystalline shell adjacent to the melted edge of each layer to a depth of L layer relative to the top layer.

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