Construction platform for additive manufacturing and related methods

Abstract

A build platform for metal additive manufacturing methods and related methods are disclosed. The build platform includes a base including a first metal and an upper surface. The build platform also includes a surface layer on the upper surface of the base, the surface layer including a second metal different from the first metal. The surface layer has a graded porosity having a densest region at an upper surface of the surface layer and a densest region at a lower surface of the surface layer. The lower surface of the surface layer is in contact with the upper surface of the base.

Description

Technical Field

[0001] This disclosure relates generally to additive manufacturing, and more specifically to a build platform and related methods for additive manufacturing. Background Technology

[0002] Additive manufacturing has become a reliable method for creating three-dimensional (3D) parts. Some additive manufacturing methods use lasers or electron beams to sequentially sinter layers of metal to form 3D parts. When using lasers, this method may be referred to as, for example, direct laser metal melting (DMLM) or selective laser melting (SLM), and when using electron beams, it may be referred to as, for example, electron beam melting (EBM). Both additive manufacturing methods utilize a metal powder bed that supplies layers of metal powder to a build platform as the base of the 3D printed part. The metal powder layers are sintered or melted together using a laser or electron beam. The build platform, typically made of steel, stainless steel, or any form of nickel-based alloy, is configured to contain the powder material used to form the 3D part; this powder material is called the printing material. The choice of build platform material depends on its compatibility with the printing material. Notably, it is advantageous for the printing material to be able to wet and bond (weld) to the build platform. If the printing material does not bond (weld) well to the build platform, it may result in peeling / fracture at the interface, leading to the failure of the 3D part build. The compatibility of the coefficient of thermal expansion (CTE) between the build platform and the printing material is another characteristic to consider. Significant differences in CTE can lead to the separation of the bond between the printing material and the build platform, resulting in build failure. The CTE issue is particularly challenging in additive manufacturing environments with relatively high temperatures (e.g., above 150°C (~302℉)).

[0003] To address these challenges, the build platform is constructed entirely from materials compatible with the printing materials. For applications requiring stainless steel and nickel-based alloys for 3D parts, this approach results in significant initial and operational costs. Another approach uses lower-cost materials, such as certain types of steel, for the build platform; these materials are inexpensive and easy to process. However, for the reasons stated above, these materials are often incompatible with many more advanced printing materials, such as nickel-based alloys, superalloys, etc. Summary of the Invention

[0004] All aspects, examples, and features mentioned below can be combined in any technically possible way.

[0005] One aspect of this disclosure includes a build platform for a metal additive manufacturing method, the build platform comprising: a base including a first metal and an upper surface; and a surface layer on the upper surface of the base, the surface layer including a second metal different from the first metal, wherein the surface layer has a graded porosity having a densest region at the upper surface of the surface layer and a least dense region at a lower surface of the surface layer, the lower surface of the surface layer being in contact with the upper surface of the base.

[0006] Another aspect of this disclosure includes any of the foregoing aspects, and the surface layer has a thickness of at least 0.2 mm.

[0007] Another aspect of this disclosure includes any of the foregoing aspects, and the surface layer covers the upper surface of the base, except for the exposed portion of the upper surface surrounding the surface layer, the exposed portion having a width in the range of 1.2 mm to 1.8 mm.

[0008] Another aspect of this disclosure includes any of the foregoing aspects, wherein the densest region has a porosity in the range of 0% to 4.9%, and the least dense region has a porosity in the range of 5% to 25%.

[0009] Another aspect of this disclosure includes any of the foregoing aspects, and the first metal comprises a single chemical element or alloy, and the second metal comprises different alloys of two or more chemical elements.

[0010] Another aspect of this disclosure includes any of the foregoing aspects, and the graded porosity between the upper surface of the surface layer and the lower surface of the surface layer includes a constant porosity variation rate from the upper surface of the surface layer to the lower surface of the surface layer, the constant porosity variation rate being in the range of 0.5% to 4% per millimeter.

[0011] Another aspect of this disclosure includes any of the foregoing aspects, and the graded porosity between the upper surface and the lower surface of the surface layer includes a plurality of stepped porosity layers having pores of different volumes in a stepped manner from the upper surface to the lower surface of the surface layer, wherein the diameter of the pores is in the range of 0.028 mm to 0.036 mm below the upper surface of the surface layer and in the range of 1.8 mm to 2.2 mm adjacent to the lower surface of the surface layer.

[0012] Another aspect of this disclosure includes any of the foregoing aspects, and the graded porosity between the upper surface and the lower surface of the surface layer includes a plurality of open pillars in a solid material extending from the upper surface of the surface layer to the lower surface of the surface layer, wherein each open pillar has a narrower upper portion adjacent to but below the upper surface of the surface layer and a wider lower portion adjacent to the lower surface of the surface layer.

[0013] Another aspect of this disclosure includes any of the foregoing aspects, and each open post has a lower width in the range of 0.5 mm to 2.0 mm at the lower surface of the surface layer, an upper width in the range of 0.05 mm to 0.3 mm below the upper surface of the surface layer, and a taper angle in the range of 1° to 4°.

[0014] Another aspect of this disclosure includes any of the foregoing aspects, and the construction platform further includes a filler that attaches the surface layer to the base, the filler including the second metal.

[0015] Another aspect of this disclosure includes a method comprising: forming a build platform for an additive manufacturing method by means of the following steps: providing a base including a first metal and an upper surface; and forming a surface layer on the upper surface of the base, the surface layer including a second metal different from the first metal, wherein the surface layer has a graded porosity having a densest region at the upper surface of the surface layer and a least dense region at the lower surface of the surface layer, the lower surface of the surface layer contacting the upper surface of the base, wherein the surface layer has a thickness of at least 0.2 mm.

[0016] Another aspect of this disclosure includes any of the foregoing aspects, and forming the surface layer includes: forming a solid layer separated from the base, forming the hierarchical porosity in the solid layer to form the surface layer, and attaching the surface layer to the upper surface of the base.

[0017] Another aspect of this disclosure includes any of the foregoing aspects, and the connection includes brazing, friction welding or fillet welding around the periphery of the surface layer.

[0018] Another aspect of this disclosure includes any of the foregoing aspects, and forming the surface layer includes forming a solid layer on the upper surface of the base, and forming the hierarchical porosity in the solid layer to form the surface layer.

[0019] Another aspect of this disclosure includes any of the foregoing aspects, and forming the graded porosity includes at least one of electrical discharge machining (EDM), electrochemical machining (ECM), and shaped tube electrical discharge machining (STEM), and the solid layer.

[0020] Another aspect of this disclosure includes any of the foregoing aspects, and forming the surface layer includes performing a second metal powder bed additive manufacturing on the upper surface of the base.

[0021] Another aspect of this disclosure includes any of the foregoing aspects, and the first metal comprises a single chemical element or alloy, and the second metal comprises different alloys of two or more chemical elements.

[0022] Another aspect of this disclosure includes any of the foregoing aspects, and the graded porosity between the upper surface of the surface layer and the lower surface of the surface layer includes a constant porosity variation rate from the upper surface of the surface layer to the lower surface of the surface layer, the constant porosity variation rate being in the range of 1% to 4% per millimeter.

[0023] Another aspect of this disclosure includes any of the foregoing aspects, and the graded porosity between the upper surface and the lower surface of the surface layer comprises a plurality of layers having pores of different volumes in a stepped manner from the upper surface to the lower surface of the surface layer, wherein the diameter of the pores is in the range of 0.028 mm to 0.036 mm below the upper surface of the surface layer and in the range of 1.8 mm to 2.2 mm adjacent to the lower surface of the surface layer.

[0024] Another aspect of this disclosure includes any of the foregoing aspects, and the graded porosity between the upper surface and the lower surface of the surface layer includes a plurality of open pillars in a solid material extending from the upper surface to the lower surface of the surface layer, wherein each open pillar has a narrower upper portion adjacent to but below the upper surface of the surface layer and a wider lower portion adjacent to the lower surface of the surface layer, wherein each open pillar has a lower width in the range of 0.5 mm to 2.0 mm at the lower surface of the surface layer, an upper width in the range of 0.05 mm to 0.3 mm below the upper surface of the surface layer, and a taper angle in the range of 1° to 4°.

[0025] Two or more aspects described in this disclosure (including those described in this overview section) may be combined to form specific embodiments not specifically described herein. That is, all embodiments described herein may be combined with each other.

[0026] Details of one or more specific embodiments are set forth in the following figures and description. Other features, objects, and advantages will be apparent from the specification, figures, and claims. Attached Figure Description

[0027] These and other features of the present disclosure will be more readily understood from the following detailed description of various aspects of the present disclosure, taken in conjunction with the accompanying drawings depicting various embodiments thereof, in which:

[0028] Figure 1 A schematic block diagram of an exemplary additive manufacturing system using a construction platform to perform additive manufacturing according to an embodiment of the present disclosure is shown;

[0029] Figure 2A A cross-sectional view of a construction platform according to an embodiment of this disclosure is shown;

[0030] Figure 3A A top view of a construction platform according to other embodiments of this disclosure is shown;

[0031] Figure 2B A cross-sectional view of a construction platform according to other embodiments of this disclosure is shown;

[0032] Figure 3B A top view of the construction platform according to an embodiment of this disclosure is shown;

[0033] Figure 4 A cross-sectional view of the surface layer of a construction platform according to an embodiment of the present disclosure is shown;

[0034] Figure 5 A cross-sectional view of the surface layer of a construction platform according to other embodiments of this disclosure is shown; and

[0035] Figure 6 A cross-sectional view of the surface layer of a construction platform according to an additional embodiment of this disclosure is shown.

[0036] It should be noted that the accompanying drawings of this disclosure are not necessarily drawn to scale. The drawings are intended to depict only typical aspects of this disclosure and should therefore not be considered as limiting the scope of this disclosure. In the drawings, similar numbers denote similar elements between figures. Detailed Implementation

[0037] First, in order to clearly describe this disclosure, it will be necessary to select certain terms when referring to and describing relevant machine parts within exemplary applications of additive manufacturing systems. In doing so, common industry terms will be used and adopted in a manner consistent with their accepted meanings, where possible. Unless otherwise stated, such terms should be given a broad interpretation consistent with the context of this application and the scope of the appended claims. Those skilled in the art will understand that several different or overlapping terms may generally be used to refer to a particular part. An object that can be described herein as a single part may include multiple parts and is referred to in another context as being composed of multiple parts. Alternatively, an object that can be described herein as comprising multiple parts may elsewhere be referred to as a single part.

[0038] Furthermore, several descriptive terms may be used regularly throughout this document, and it should prove helpful to define these terms at the beginning of this section. Unless otherwise stated, these terms and their definitions are as follows. The terms “first,” “second,” and “third” may be used interchangeably to distinguish one component from another and are not intended to indicate the location or importance of a single component.

[0039] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this disclosure. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that, when used in the specification, the terms “comprising” and / or “including” specify the presence of the stated features, integers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. “Optional” or “optionally” means that the events subsequently described may or may not occur, or the features subsequently described may or may not be present, and the description includes instances where the events occur (or the features are present) and instances where the events do not occur (or the features are not present).

[0040] When an element or layer is referred to as “on another element or layer,” “joined to another element or layer,” “connected to another element or layer,” “linked to another element or layer,” or “mounted to another element or layer,” it may be directly on, joined to, connected to, linked to, or mounted to another element or layer, or an intermediary element or layer may be present. In contrast, when an element is referred to as “directly on another element or layer,” “directly joined to another element or layer,” “directly connected to another element or layer,” or “directly linked to another element or layer,” an intermediary element or layer is not present. Other terms used to describe the relationship between elements should be interpreted in a similar manner (e.g., “between” vs. “directly between,” “adjacent” vs. “directly adjacent,” etc.). As used herein, the term “and / or” includes any and all combinations of one or more of the associated listed items. The verb forms “link” and “mount” are used interchangeably herein.

[0041] As noted above, this disclosure provides a build platform and related methods for metal additive manufacturing (AM) methods. The build platform includes a base comprising a first metal and a top surface. The build platform also includes a surface layer on the top surface of the base, comprising a second metal different from the first metal. The surface layer has a hierarchical porosity, with the densest region at the top surface and the least dense region at the bottom surface. The bottom surface of the surface layer contacts the top surface of the base. Therefore, embodiments of this disclosure provide a bimetallic build platform in which the base is made of a first metal such as carbon steel, and the top surface layer bonded only to the printing material is made of a second metal compatible with the printing material. This bimetallic build platform provides a system compatible with the printing material in terms of adhesion strength and relative to CTE. Therefore, even at elevated temperatures, this build platform eliminates concerns about the aforementioned build failure. Furthermore, this build platform is cheaper to manufacture than a build platform made entirely of a material compatible with the printing material.

[0042] Figure 1A schematic / block diagram of an exemplary computerized metal powder additive manufacturing system 210 (hereinafter referred to as "AM system 210") using a build platform 220 for generating part 202 is shown. A single layer of part 202 is shown. The build platform 220 is shown in dashed lines because it is below the printing material layer 272. As will be further described herein, AM system 210 can use build platform 220 according to embodiments of this disclosure. AM system 210 will be described with respect to the construction of one or more parts 202A, 202B using multiple melting beam sources 212, 214, 216, 218, but it should be emphasized and readily appreciated that the teachings of this disclosure are equally applicable to the construction of one or more parts 202 using any number of melting beam sources. In this example, AM system 210 is arranged for direct metal laser melting (DMLM). It should be understood that the general teachings of this disclosure are equally applicable to other forms of metal powder additive manufacturing, such as, but not limited to, powder bed melting, direct metal laser sintering (DMLS), electron beam melting (EBM), selective laser sintering (SLS), selective laser melting (SLM), and other possible forms of additive manufacturing (i.e., other than metal powder applications). Parts 202A and 202B are illustrated as rectangular elements; however, it should be understood that the additive manufacturing method can be readily adapted to manufacture parts of any shape, a wide variety of different parts, and a large number of parts on the build platform 220.

[0043] AM system 210 generally includes additive manufacturing control system 230 (“control system”) and AM printer 232. As will be described, control system 230 executes a set of computer-executable instructions or code 234 to generate part 202 using multiple melt beam sources 212, 214, 216, 218. In the example shown, the four melt beam sources 212, 214, 216, 218 may include four lasers. However, the teachings of this disclosure are applicable to any melt beam source, such as an electron beam, laser, etc. Control system 230 is shown as implemented as computer program code on computer 236. To this extent, computer 236 is shown as including memory 238 and / or storage system 240, processor unit (PU) 244, input / output (I / O) interface 246, and bus 248. Furthermore, computer 236 is shown as communicating with external I / O devices / resources 250. Generally, processor unit (PU) 244 executes computer program code 234 stored in memory 238 and / or storage system 240. When executing computer program code 234, processor unit (PU) 244 may read and / or write data to / from memory 238, storage system 240, I / O device 250 and / or AM printer 232. Bus 248 provides a communication link between each component in computer 236, and I / O device 250 may include any device that enables a user to interact with computer 236 (e.g., keyboard, pointing device, display, etc.). Computer 236 refers only to various possible combinations of hardware and software. For example, processor unit (PU) 244 may include a single processing unit or one or more processing units distributed across one or more locations (e.g., on clients and servers). Similarly, memory 238 and / or storage system 240 may reside in one or more physical locations. The memory 238 and / or storage system 240 may include any combination of various types of non-transitory computer-readable storage media, including magnetic media, optical media, random access memory (RAM), read-only memory (ROM), etc. The computer 236 may include any type of computing device, such as an industrial controller, network server, desktop computer, laptop computer, handheld device, etc.

[0044] As noted, AM system 210, and particularly control system 230, executes code 234 to generate metal part 202 (among other things). Among other things, code 234 may include a computer-executable instruction set 234S (also referred to herein as 'code 234S') for operating AM printer 232, and a computer-executable instruction set 234O (also referred herein as 'code 234O') defining the metal part 202 to be physically generated by AM printer 232. As described herein, the additive manufacturing method begins with storing code 234 in a non-transitory computer-readable storage medium (e.g., memory 238, storage system 240, etc.). The computer-executable instruction set 234S for operating AM printer 232 may include any software code now known or later developed capable of operating AM printer 232.

[0045] The computer-executable instruction set 234O defining the metal part 202 may include a precisely defined 3D model of the part, and may be executed by a variety of well-known computer-aided design (CAD) software systems (such as...). Any of the following generation methods (DesignCAD, 3D Max, etc.). In this regard, code 234O can include any file format now known or developed later. Furthermore, code 234O representing metal part 202 can be converted between different formats. For example, code 234O can include a Standard Subdivision Language (STL) file created by a stereolithography CAD program for a 3D system or an Additive Manufacturing File (AMF) as an ASME standard, which is a format based on Extensible Markup Language (XML) designed to allow any CAD software to describe the shape and composition of any three-dimensional object to be manufactured on any AM printer. Code 234O representing metal part 202 can also be converted into a set of data signals as needed, and transmitted, received, converted into code, stored, etc., as a set of data signals. Code 234O can be configured according to embodiments of this disclosure to allow the formation of boundaries and internal segments in overlapping field areas, as will be described. In any case, code 234O can be input to AM system 210 and can originate from a part designer, intellectual property (IP) provider, design firm, operator or owner of AM system 210, or from other sources. In any case, control system 230 executes codes 234S and 234O to divide metal part 202 into a series of thin slices, which are assembled as continuous material layers using AM printer 232. As will be described herein, in addition to constructing part 202 and possibly using printing material 272 different from the printing material used for part 202, control system 230 can also execute codes 234S and 234O to divide surface layer 312 for building platform 220 into a series of thin slices, which are assembled as continuous material layers on base 300 of building platform 220 using AM printer 232.

[0046] AM printer 232 may include a processing chamber 260, which is sealed to provide a controlled atmosphere for printing metal parts 202. A build platform 220 on which one or more metal parts 202 are built is positioned within the processing chamber 260. A plurality of melt beam sources 212, 214, 216, 218 are configured to melt a layer of metal powder on the build platform 220 to generate parts 202. Although four melt beam sources 212, 214, 216, 218 are shown, it should be emphasized that the teachings of this disclosure are applicable to systems employing any number of sources (e.g., one, two, three, or five or more). As understood in the art, each melt beam source 212, 214, 216, 218 may each have a field including a non-overlapping field region in which the melt beam source can exclusively melt the metal powder, and the melt beam source may include at least one overlapping field region in which two or more sources can melt the metal powder. In this respect, each melting beam source 212, 214, 216, 218 can generate a melting beam that melts the particles of each slice, as defined by code 234O. For example, in Figure 1 In the diagram, melt beam source 212 is shown forming a layer of metal part 202 in one region using melt beam 262, while melt beam source 214 is shown forming a layer of metal part 202 in another region using melt beam 262'. Each melt beam source 212, 214, 216, 218 is calibrated in any manner now known or later developed. That is, each melt beam source 212, 214, 216, 218 already has an expected position of its laser or electron beam relative to the build platform 220, related to the actual position of the laser or electron beam, in order to provide individual position corrections (not shown) to ensure their individual accuracy. In one embodiment, each of the plurality of melt beam sources 212, 214, 216, 218 may form melt beams having the same cross-sectional dimensions (e.g., shape and size in operation), power, and / or scanning speed, such as 262, 262'.

[0047] Continue to refer to Figure 1The coater (or recoater blade) 270 can form a thin layer of raw printing material 272 (from the printing material supply chamber 268), which is spread out as a blank canvas to form each successive slice of the final part on the build platform 220. Various parts of the AM printer 232 can be moved to accommodate the addition of each new layer; for example, after each layer, the build platform 220 can be lowered and / or the processing chamber 260 and / or the coater 270 can be raised using the actuator system 264. Any form of actuator system 264 can be used to move the build platform 220 and / or other parts of the AM printer 232. The method can use different printing materials 272 in the form of fine-grained metal powder, reserves of which can be maintained in the printing material supply chamber 268 accessible by the coater 270. In this case, the part 202 can be made of metal, which can include pure metals or alloys. In one example, the metal may include virtually any non-reactive metal powder, i.e., a non-explosive powder, such as, but not limited to: cobalt-chromium-molybdenum (CoCrMo) alloys; stainless steel; austenitic nickel-chromium based alloys, such as nickel-chromium-molybdenum-niobium alloys (NiCrMoNb) (e.g., Inconel 625 or Inconel 718); nickel-chromium-iron-molybdenum alloys (NiCrFeMo) (e.g., available from Haynes International, Inc.). X); or a nickel-chromium-cobalt-molybdenum alloy (NiCrCoMo) (e.g., Haynes 282, available from Hastelloy International, USA). Other possibilities include, for example, René 108, CM 247, Mar M 247, and any precipitation-hardening (PH) nickel alloy. As will be described herein, the build platform 220 is configured to address compatibility with any printing material 272 used.

[0048] Processing chamber 260 is filled with an inert gas such as argon or nitrogen and is controlled to minimize or eliminate oxygen. Control system 230 is configured to control the flow rate of gas mixture 274 from inert gas source 276 within processing chamber 260. In this case, control system 230 may control pump 280 and / or flow valve system 282 for the inert gas to control the content of gas mixture 274. Flow valve system 282 may include one or more computer-controllable valves, flow sensors, temperature sensors, pressure sensors, etc., capable of precisely controlling the flow rate of a particular gas. Pump 280 may or may not be equipped with valve system 282. If pump 280 is omitted, inert gas may simply enter a pipe or manifold before being introduced into processing chamber 260. Inert gas source 276 may take the form of any conventional source for the materials contained therein, such as a tank, reservoir, or other source. Any sensors (not shown) required to measure gas mixture 274 may be provided. Gas mixture 274 may be filtered in a conventional manner using filter 286.

[0049] In operation, a build platform 220, on which raw material 272 metal powder is disposed, is located within a processing chamber 260, and a control system 230 controls the flow rate of a gas mixture 274 from an inert gas source 276 within the processing chamber 260. According to an embodiment of this disclosure, the control system 230 also controls an AM printer 232, particularly a coater 270, and melting beam sources 212, 214, 216, 218, to sequentially melt the metal powder layer on the build platform 220, thereby generating a metal part 202. Upon completion, the metal part 202 has multiple re-cured metal layers therein.

[0050] While a specific AM system 210 has been described herein, it should be emphasized that the teachings of this disclosure are not limited to any particular additive manufacturing system or method.

[0051] Figure 2A A cross-sectional view of the construction platform 220 is shown, and Figure 3A A top view of a build platform 220 for an AM (Ampere) method for metal powders, as previously described herein, is shown. The build platform 220 includes a base 300 comprising a first metal and an upper surface 302. The base 300 may include any now-known or later-developed system for operatively coupling the base 300 to an AM system 210, for example, within a processing chamber 260. For example, the base 300 may include one or more recesses 304 and / or openings 306, the AM system 210 ( Figure 1 ) actuator system 264 ( Figure 1The base 300 can be connected to these grooves and / or openings. The first metal of the base 300 may include a single metallic chemical element, such as, but not limited to, nickel (Ni), titanium (Ti), aluminum (Al), or copper (Cu). Alternatively, the first metal may include a metal alloy, such as, but not limited to, steel alloys or stainless steel.

[0052] like Figure 2A As shown, the build platform 220 also includes a surface layer 312 on the upper surface 302 of the base 300. The surface layer 312 has a thickness T of at least 0.2 mm. The surface layer 312 includes a second metal different from the first metal. The second metal of the surface layer 312 may include a single metallic chemical element or may include a metal alloy. In some embodiments, the first metal of the base 300 includes a single chemical element or alloy, and the second metal of the surface layer 312 includes different (metallic) alloys of two or more chemical elements. In one example, the first metal includes carbon steel, and the second metal includes one of stainless steel and a nickel-based alloy. Various alternative first and second metals may also be used. In any case, the second metal of the surface layer 312 is used in conjunction with the printing material 272 for building / printing the part 202. Figure 1 Compatibility. For example, the second metal of surface layer 312 wets and bonds to printing material 272 to prevent peeling / fracture at the interface, which would otherwise cause part 202 to fail. The second metal of surface layer 312 may also have a coefficient of thermal expansion (CTE) compatible with printing material 272. That is, even in high-temperature additive manufacturing environments (e.g., above 150°C (~302℉)), any difference in CTE between surface layer 312 and printing material 272 is small enough to prevent printing material 272 ( Figure 1 The separation of the integration between the platform 220 and the building platform.

[0053] In some implementations, such as Figure 2A and Figure 3A As shown, the surface layer 312 can cover the entire upper surface 302 of the base 300, that is, the surface layer is vertically aligned with the outer periphery of the upper surface. Figure 2B and Figure 3B As shown, in other embodiments, the surface layer 312 may cover the upper surface 302 of the base 300, except for the exposed portion 308 of the upper surface 302 of the base 300 surrounding the surface layer 312. Figure 2B As shown, in some embodiments, the exposed portion 308 may have a width W1 (on each side) ranging from 1.2 mm to 1.8 mm. In other embodiments not shown, the exposed portion 308 may include any radial difference between the outer periphery 310 of the base 300 and the coverage area of ​​the printed part 202. (As only...) Figure 2BAs shown on the right, surface layer 312 can be joined to base 300 via filler 313. More specifically, the corner between the vertical sidewall 311 of surface layer 312 and the exposed portion 308 of base 300 may include filler 313 to join surface layer 312 to base 300. Filler 313 may be formed together with surface layer 312 and extend along any extent of surface layer 312; for example, the filler may be continuous or discontinuous. Filler 313 comprises a second metal, i.e., the same metal as surface layer 312. In any case, where provided, exposed portion 308 allows some thermal expansion / contraction between surface layer 312 and base 300 of construction platform 220.

[0054] The surface layer 312 also has a graded porosity, which has a densest region 314 at the upper surface 316 of the surface layer 312 (i.e., in or directly below the upper surface 316) and a least dense region 318 at the lower surface 320 of the surface layer 312 (i.e., in or directly above the lower surface 320). Figures 4 to 6 This graded porosity provides a solid or very dense upper surface 316 and a more flexible lower surface 320, on which the printing material 272 for part 202 is printed. Figure 1 The lower surface of the component 202 is fully wetted / bonded at the interface with the base 300 of the building platform 220 to allow for thermal expansion / contraction. As shown, the lower surface 320 of the surface layer 312 contacts the upper surface 302 of the base 300, that is, the lower surface of the surface layer is in direct contact with the upper surface of the base without intervening material.

[0055] As used herein, “porosity” is the ratio of the volume of open spaces to the total volume of a stated structure (e.g., surface layer 312 or a region thereof). Generally, for this purpose, porosity is stated as the percentage of the volume of open spaces to the total volume or total volume of the stated structure. For example, in some embodiments, the densest region 314 has a porosity ranging from 0% to 4.9%, and the least dense region 318 has a porosity ranging from 5% to 25%. As noted, the densest region 314 can also be considered solid, i.e., 0% porosity. In some cases, open spaces are empty regions in the form of “pores” 332 in a solid material (see, for example...). Figure 5 This refers to a small, individual open space, which may include interconnecting channels in the material of the described structure, such as three-dimensional channels. In other cases, an open space is an empty region in the form of a larger opening in a solid material (see, for example...). Figure 6 The open space may include elongated channels in the material of the stated structure, such as open columns 334. Figure 6Therefore, the porous regions in surface layer 312 are less than 100% solid and include open spaces in the form of pores or other openings and / or interconnecting channels. Surface layer 312 may include solid regions, but also one or more porous regions that are less than 100% solid. As used herein, the three-dimensional boundaries of a porous region or subregion for identifying its “total volume” can be identified by a porosity variation of more than 0.1% relative to adjacent regions or subregions occurring within surface layer 312. “Open space volume” is collectively referred to as empty three-dimensional space (i.e., voids, gaps, empty spaces) and / or unfilled material within a region or subregion. As used herein, “different porosity” or “porosity difference” generally means any kind of characteristic such as: the percentage of open space volume to total volume, the number of pores or other open spaces in a given volume, the volume (i.e., size) of pores or other open spaces, the shape of pores or open spaces, and variations in connecting channels between pores or other open spaces that may not be considered actual discrete pores or open spaces. As a non-limiting example only, the aperture can be, for example, 1.715 x 10⁻⁶. -5 cubic millimeters up to 6.542 x 10 -2 cubic millimeters (1.000x10) -9 cubic inches up to 3.992 x 10 -6 The porosity ranges from cubic inches. In some embodiments, the pores may be spherical and may have a diameter ranging from 0.030 mm to 0.50 mm (0.0012 inches to 0.0197 inches). In some embodiments, the diameter of the pores ranges from 0.028 mm to 0.036 mm below the upper surface 316 of the surface layer 312 and from 1.8 mm to 2.2 mm adjacent to (i.e., directly above or within) the lower surface 320 of the surface layer 312. Other porosity shapes are also possible for graded porosity arrangements, as long as the percentages and variations fall within the stated ranges. In cases with differences, such as pore shape or pore connection channels, it will be appreciated that the difference in porosity may not be solely based on the percentage of open space volume to total volume. However, in cases where differences in porosity are compared in terms of degree (e.g., higher or lower), the difference mentioned is merely a difference in volumetric characteristics, i.e., the percentage of open space volume to total volume.

[0056] Figures 4 to 6 Cross-sectional views of various embodiments of surface layer 312 are shown. Figure 4The diagram illustrates the graded porosity between the upper surface 316 and the lower surface 320 of surface layer 312. This graded porosity includes a constant porosity variation rate from the upper surface 316 to the lower surface 320 (i.e., the contact base 300) of surface layer 312. Here, this graded porosity variation can have a constant porosity variation rate from the upper surface 316 to the lower surface 320 of surface layer 312, which is in the range of 1% to 4% per millimeter. Figure 5 A stepped porosity is shown between the upper surface 316 and the lower surface 320 of surface layer 312, comprising multiple stepped porosity layers 330A to 330F, each having pores 332 of varying volumes arranged in a stepped manner from the upper surface 316 to the lower surface 320 (i.e., the contact base 300) of surface layer 312. While six stepped porosity layers 330A to 330F are shown, any number can be used. The pores 332 in each stepped porosity layer (e.g., 330F) are larger and / or more than those in the stepped porosity layer above it (e.g., 330E). Figure 6 The diagram illustrates a graded porosity between the upper surface 316 and the lower surface 320 of surface layer 312, comprising a plurality of open pillars 334 in solid material 336. The plurality of open pillars 334 extend from near the upper surface 316 of surface layer 312 to the lower surface 320 of surface layer 312. Each open pillar 334 has a narrower upper portion 340 adjacent to but below the upper surface 316 of surface layer 312, and a wider lower portion 342 adjacent to the lower surface 320 of surface layer 312 (i.e., contact base 300). The lower width W2 of the open pillar 334 at the lower surface 320 of surface layer 312 (i.e., the wider lower portion 342) can range, for example, from 0.5 mm to 2.0 mm. The upper width W3 (i.e., the narrower upper portion 340) of the open post 334 below the upper surface 316 of the surface layer 312 can be in the range of, for example, 0.05 mm to 0.3 mm. The open post 334 can have a taper angle α in the range of, for example, 1° to 4°.

[0057] The method according to embodiments of this disclosure may include forming a construction platform 220 for the AM method as described herein. This formation may include providing a base 300 comprising a first metal and an upper surface 302, and forming a surface layer 312 on the upper surface 302 of the base 300. As indicated, the surface layer 312 comprises a second metal different from the first metal. Further, the surface layer 312 has a hierarchical porosity having a densest region 314 at the upper surface 316 and a least dense region 318 at the lower surface 320 of the surface layer 312. Figure 2Aand Figure 2B As shown, the lower surface 320 of the surface layer 312 is in contact with the upper surface 302 of the base 300. The surface layer 312 has a thickness T of at least 0.2 mm.

[0058] Surface layer 312 can be formed in a variety of different ways. Since the various techniques listed herein are generally well-known in the art, details of these techniques are largely omitted unless otherwise necessary. Regardless of the formation method, surface layer 312 comprises only the second metal as described herein.

[0059] In some embodiments, forming the surface layer 312 may include forming a solid layer separate from the base 300, then forming a hierarchical porosity in the solid layer to form the surface layer 312, and attaching the surface layer to the upper surface of the base. In this embodiment, the surface layer 312 may initially comprise a solid layer, which may then be made porous using any of a variety of techniques according to this disclosure, such as, but not limited to, electrical discharge machining (EDM), electrochemical machining (ECM), and / or forming tube electrical discharge machining (STEM) or similar processes. These processes may be applied to one or both sides of the solid, pre-formed surface layer 312. The pre-formed surface layer 312 may then be attached to the base 300 using, for example, brazing, friction welding, or fillet welding around the periphery of the surface layer 312.

[0060] In another method according to this embodiment, forming the surface layer 312 may include forming a solid layer on the upper surface 302 of the base 300, and then forming a graded porosity in the solid layer to form the surface layer 312. Initially, the solid layer may be formed on the base 300 using, for example, laser cladding or other bonding methods. The surface layer 312 may then be processed to form the porosity according to the present disclosure. For example, the pre-formed surface layer 312 may be made porous using any of a variety of techniques according to the present disclosure, such as, but not limited to, electrical discharge machining (EDM), electrochemical machining (ECM), and / or forming tube electrical discharge machining (STEM) and / or similar processing.

[0061] In other embodiments, forming the surface layer 312 may include providing a second metal powder bed and additive manufacturing the surface layer 312 on the upper surface 302 of the base 300. That is, the surface layer 312 may use the same or similar AM system as described herein, but may be formed using a printing material 272 comprising a second metal having a different desired porosity and gradation profile (in-situ formation) than the printing material 272 used to print the part 202.

[0062] Once formed, surface layer 312 may include either the second metal or the hierarchical porosity form described herein. After surface layer 312 is formed, any necessary heat treatments may be performed, and build platform 220 may be machined to the desired dimensions and surface layer 312 finish.

[0063] Return to Figure 1 As shown in Figure 2, an embodiment of the method may further include additively manufacturing parts 202 on a build platform 220 using printing material 272. Once parts 202 are completed, they can be removed from the bimetallic build platform along the upper surface 316 of the surface layer 312, i.e., the surface layer 312 is not on the final part 202.

[0064] This disclosure provides various technical and commercial advantages, examples of which are discussed herein. The bimetallic build platform offers compatibility with the printing material in terms of bonding / welding to it and with CTE. Therefore, even at elevated temperatures, this build platform eliminates concerns about the aforementioned build failure. Furthermore, this build platform is less expensive to manufacture than build platforms made entirely of materials compatible with the printing material. The teachings of this disclosure are applicable to any metal powder bed additive manufacturing method and / or AM system.

[0065] As used throughout the specification and claims, approximate language can be used to modify any quantitative expression that allows for variation without causing a change in its underlying function. Therefore, values ​​modified by one or more terms (such as “about,” “approximately,” and “substantially”) are not limited to specified exact values. In at least some cases, approximate language may correspond to the precision of the instrument used to measure the value. Range limitations may be combined and / or interchanged herein and throughout the specification and claims; unless otherwise indicated by context or language, these ranges are identified and include all subranges contained therein. The term “about” or “approximately” applied to a specific value within a range applies to both endpoints and may indicate + / - 10% of the value unless otherwise dependent on the precision of the instrument used to measure the value.

[0066] All means or steps plus functional elements in the following claims are intended to include any structure, material, action, and equivalent for performing a function in conjunction with other claimed elements of a particular claim. The present disclosure has been described for purposes of illustration and description, but it is not intended to be exhaustive or to limit the disclosure to the forms disclosed. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the disclosure. Embodiments have been chosen and described to best explain the principles and practical application of the disclosure and to enable others skilled in the art to understand the various embodiments of the disclosure and their various modifications suitable for the intended particular purpose.

Claims

1. A construction platform for a metal additive manufacturing method, the construction platform comprising: The base includes a first metal and an upper surface; and A surface layer, said surface layer on said upper surface of said base, said surface layer comprising a second metal different from the first metal. The surface layer has a graded porosity, wherein the graded porosity has the densest region at the upper surface of the surface layer and the least dense region at the lower surface of the surface layer, and the lower surface of the surface layer is in contact with the upper surface of the base.

2. The construction platform according to claim 1, wherein the surface layer has a thickness of at least 0.2 mm.

3. The construction platform according to claim 1 or 2, wherein the surface layer covers the upper surface of the base, except for an exposed portion of the upper surface surrounding the surface layer, the exposed portion having a width in the range of 1.2 mm to 1.8 mm.

4. The construction platform according to any one of the preceding claims, wherein the densest region has a porosity in the range of 0% to 4.9%, and the least dense region has a porosity in the range of 5% to 25%.

5. The construction platform according to any one of the preceding claims, wherein the first metal comprises a single chemical element or alloy, and the second metal comprises different alloys of two or more chemical elements.

6. The construction platform according to any one of the preceding claims, wherein the hierarchical porosity between the upper surface of the surface layer and the lower surface of the surface layer includes a constant porosity variation rate from the upper surface of the surface layer to the lower surface of the surface layer, the constant porosity variation rate being in the range of 1% to 4% per millimeter.

7. The construction platform according to any one of claims 1 to 5, wherein the graded porosity between the upper surface and the lower surface of the surface layer comprises a plurality of stepped porosity layers having pores of different volumes in a stepped manner from the upper surface to the lower surface of the surface layer, wherein the diameter of the pores is in the range of 0.028 mm to 0.036 mm below the upper surface of the surface layer and in the range of 1.8 mm to 2.2 mm adjacent to the lower surface of the surface layer.

8. The construction platform according to any one of claims 1 to 5, wherein the hierarchical porosity between the upper surface and the lower surface of the surface layer comprises a plurality of open pillars in a solid material extending from the upper surface of the surface layer to the lower surface of the surface layer, wherein each open pillar has a narrower upper portion adjacent to but below the upper surface of the surface layer and a wider lower portion adjacent to the lower surface of the surface layer.

9. The construction platform of claim 8, wherein each open column has a lower width at the lower surface of the surface layer in the range of 0.5 mm to 2.0 mm, an upper width below the upper surface of the surface layer in the range of 0.05 mm to 0.3 mm, and a taper angle in the range of 1° to 4°.

10. The construction platform according to any one of the preceding claims, the construction platform further comprising a filler that connects the surface layer to the base, the filler comprising the second metal.

11. A method, the method comprising: The following steps form a construction platform for additive manufacturing methods: Provides a base comprising a first metal and an upper surface; as well as A surface layer is formed on the upper surface of the base, the surface layer comprising a second metal different from the first metal. The surface layer has a graded porosity, with the densest region at the upper surface and the least dense region at the lower surface, the lower surface of which is in contact with the upper surface of the base. The surface layer has a thickness of at least 0.2 mm.

12. The method of claim 11, wherein forming the surface layer comprises: A solid layer is formed separate from the base, the hierarchical porosity is formed in the solid layer to form the surface layer, and the surface layer is attached to the upper surface of the base.

13. The method of claim 12, wherein the connection comprises brazing, friction welding or fillet welding around the periphery of the surface layer.

14. The method of claim 11, wherein forming the surface layer comprises forming a solid layer on the upper surface of the base, and forming the hierarchical porosity in the solid layer to form the surface layer; The formation of the graded porosity preferably includes at least one of electrical discharge machining (EDM), electrochemical machining (ECM), and shaped tube electrical discharge machining (STEM), and the solid layer.

15. The method of claim 11, wherein forming the surface layer comprises performing a second metal powder bed additive manufacturing on the upper surface of the base.

Images