Co-sintering

Abstract

The present invention includes a novel sintered member (1) and method for manufacturing the same. The method includes forming (100) a plurality of sub-members (10) using binder jet additive manufacturing. The sub-members (10) have an outer surface (20) including one or more protrusions (22, 24) including one or more joining surfaces (26) configured to interface with at least one of the one or more joining surfaces (26) of an adjacent sub-member. Recesses (28) are formed between the sub-members (10) of the sintered member (1) to define cavities (30). The method includes heating the plurality of sub-members (10) in a first heating step (104), assembling the sub-members (10) (106), and heating the assembly of sub-members (108) in a second heating step (108).

Description

[Technical field]

[0001] THIN-WALLED SINTERED COMPONENTS AND METHODS FOR MANUFACTURING SAME FIELD OF THEINVENTION The present invention relates to thin-walled sintered components and methods for manufacturing same, and more particularly to co-sintered modular structures and methods for manufacturing same. [Background technology]

[0002] Parts produced by powder processes need to be sintered so that the shaped powder preform can be consolidated into a bulk material. The production of parts by sintering of powder materials is well known and usually involves forming the part from the powder material using a binder to maintain its shape. This is known as a green body. The binder is then partially removed in a process known as debinding to increase the proportion of powder material in the final part, once removed the part is known as a Brown body, which is the body ready for sintering. Alternatively, powder compacts can be produced by avoiding the green body stage and using a non-consumable functional binder product, as described in European Patent Application EP 3 661 673 A1.

[0003] The Brownian body is sintered by heating, which causes the particles of the powder material to coalesce and form a homogenous part. The final density of the part is governed by how much of the Brownian body is sintered through the duration and temperature of heating, and is expressed as a percentage of the density of the pure powder material. That is, if the final part has half the material density of the powder material, it is expressed as 50% density, which is what a powder material of the same density would be if it were 100% or fully sintered.

[0004] One way to form a green body is to use a powder bed manufacturing process, such as binder jet additive manufacturing. Binder jet additive manufacturing is done by building up the part in layers. A layer of powder material is spread over the entire area of ​​the build platform, and a binder is added to the powder over the cross section of the part, binding the powder within that cross section. Another layer of powder is added, and binder is added again over the cross section of the part. The binder bonds any subsequent layers of powder required for the part to the previous layers. This process is repeated until the part reaches its full height, leaving components contained within the body of powder material that were not used. Excess powder that was not given a binder remains free and unmoved, and therefore needs to be removed before the part is sintered to prevent the components from being included in the final part during the sintering process. During sintering, the part is heated, and the particles of powder coalesce to form the final part. The final sintered part is smaller than the green or brown body, as the voids between the powder particles are reduced or eliminated during the sintering process. Summary of the Invention [Problem to be solved by the invention]

[0005] Sintering, particularly of brown bodies formed by binder jet additive manufacturing, also known as binder jetting, is limited in size and / or complexity. More complex parts are limited in size that can be produced using the aforementioned sintering process. In particular, binder jetting is limited in the physical dimensions of the parts it can build, on the order of 60 mm in any one direction. Larger parts suffer from fracture issues during sintering, as shrinkage over the entire length of the feature results in stresses that lead to breakage. Thus, larger parts cannot be easily produced using conventional binder jet manufacturing. [Means for solving the problem]

[0006] High-resolution additive manufacturing, considered in this application as a minimum wall thickness of less than 0.2 mm, requires the use of powder bed manufacturing processes such as binder jetting, where powders are bonded together to form a non-uniform bulk material. When manufacturing green bodies using powder bed manufacturing, if there are internal voids in the design, the manufacturing process requires filling these voids with powder at the completion of the initial powder bonding step. This is difficult or impossible to avoid. In the method of the present invention, these internal voids can be transferred to the surface of the green body and then bonded to a complementary green body to form a uniform part. This reduces the minimum achievable channel diameter, allowing for relatively large cavities with small openings, and intricate details on the internal cavity surface. Otherwise, the powder is removed from the open areas without any difficulty and the powder is retained.

[0007] In particular, powder bed binder jetting with powder metal materials allows for high resolution parts with relatively small scale overall part dimensions. Current techniques capable of producing larger parts make it difficult to achieve high resolution features without costly, complex subtractive machining, or chemical treatments to remove excess material.

[0008] Additionally, removal of excess powder after the binder jet additive manufacturing process may not be straightforward or possible when complex internal cavities are present, especially when these cavities have small openings, contain internal surface detail, or form non-linear passages through the part.

[0009] The present invention therefore addresses two main challenges in the production of large, highly precise parts by additive manufacturing: 1 Binder jetting allows for the production of larger part sizes, overcoming the limitations imposed by sintering processes. 2. Reduced powder removal challenges, allowing the use of thin section tubes and thin wall features 3 High resolution features combined with large overall dimensions.

[0010] Thin walls of the binder jet components could be less than 2 mm, although 0.45 mm walls are possible, allowing for non-fluid retaining structures such as 0.1 mm heat sink fins.

[0011] Particularly advantageous applications of the method of the invention are as follows: A highly efficient heat exchanger that transfers thermal energy between a liquid and a gas, two liquids, or two gases. To achieve the scale of thermal energy transfer required in highly efficient heat exchangers for most applications, the maximum dimensions of the exchanger are much larger than can currently be achieved using binder jetting. One example is the lubricating oil coolant for the gearbox of an ultra-high bypass ratio turbofan. A second example is the design of a two-phase flow heat exchanger, such as a condenser or evaporator. The large surface area of ​​the confined volume promotes highly efficient phase change.

[0012] The method is also suitable for fabricating high complexity structures of heat sinks, examples of which include heat sinks for power electronic devices, nuclear fusion heat sinks, and battery cooling heat sinks.

[0013] The efficiency of a heat exchanger is determined by how much thermal energy it can transfer from one gas or liquid to a given volume of another fluid, collectively referred to herein as fluid. Factors that affect this efficiency are the surface area of ​​the heat exchange surface exposed to the fluid, the rate and type of flow through the core, and the thermal mass of the heat exchanger.

[0014] Traditionally, heat exchangers, and especially the cores of heat exchangers, include aluminum or other metal tubes with high thermal conductivity through which fluids flow and fins on the outer surface to increase the surface area over which heat is transferred on the outside of these tubes. Such fins must be bonded to the tubes, which unavoidably increase the thermal mass at the fins and at the joints, slowing down the rate at which heat is transferred between the fluids. The geometry of traditional heat exchangers is also constrained by their construction techniques. Because tubes are essentially straight, sheet-like materials and fins are essentially constructed flat, complex geometries, especially those with member curvature, are difficult to achieve, as are non-uniform structures. These arrangements also provide little room for flow control, especially within the tubes.

[0015] The present invention allows the creation of heat exchangers with novel structures that have low thermal mass, increased surface area relative to volume, and control over the flow type and path of each fluid moving through the core. An added advantage is that the heat exchanger can be manufactured to any shape.

[0016] In accordance with aspects and / or embodiments of the present invention, an improved method of producing a powder processed component is provided, in particular a component is provided using a binder jet additive manufacturing technique.

[0017] In a first aspect, there is provided a method of manufacturing a thin-walled sintered component comprising: forming a plurality of sub-components using binder jet additive manufacturing; heating the plurality of sub-components in a first heating step to at least partially sinter the sub-components; assembling the sub-components to form an assembly of sub-components having one or more bonding interfaces, where bonding surfaces of adjacent sub-components merge; and heating the assembly of sub-components in a second heating step to bond the sub-components to one another and form the sub-components.

[0018] The sub-member comprises a molded powder preform including a powder material and a binder, the sub-member has an outer surface including one or more protrusions having one or more joining surfaces configured to interface with at least one of the one or more joining surfaces of an adjacent sub-member, and a recess defining a cavity between the sub-members in the sintered member.

[0019] In one embodiment, the sintered sub-parts joined during the second heating step can provide sintered parts having a size and complexity greater than parts obtained using conventional processes, with certain shapes including intricate internal details or passages.

[0020] If necessary, a first heating step partially sinters the sub-member and a second heating step further sinters the member.

[0021] In some embodiments, it is preferred that the sub-components are partially sintered in a first heating step, thereby achieving the above-listed advantages while maintaining a low density of the sintered component.

[0022] If necessary, the first heating step includes fully sintering the sub-member.

[0023] In some embodiments, complete sintering of the sub-members during the first heating step can provide improved precision and increased adhesion at the bond interface, and the second heating step improves the bond between the sub-members.

[0024] Optionally, the sub-member further has an inner surface defining a first passage, a first end, and a second end, the first passage extending through the sub-member from the first end to the second end, and having a central axis A extending from the first end to the second end.

[0025] If necessary, the sub-members have a first protrusion and a second protrusion, the first protrusion of each sub-member extending radially at or near a first end and the second protrusion of each sub-member extending radially at or near a second end, the protrusions tesselated at their respective faying surfaces within the sintered member to form a cavity in a second passage perpendicular to the central axis A.

[0026] If necessary, the second heating step may include sealing the bond interfaces between the sub-members such that the first passageway and / or the second passageway are individually fluid-tight.

[0027] In some embodiments, the first passageway and / or the second passageway are individually made fluid-tight by sealing the bonded interfaces between the sub-members such that the interfaces are fluid-tight, thus providing first and second fluid flow paths, respectively, for example, when the sintered member is a fluid-to-fluid heat exchanger.

[0028] If desired, the protrusion may be formed to have an outer surface defining a polygonal cross-section, said outer surface being a joining surface, with the advantage being that a tight interface is provided between the joining surfaces of adjacent sub-members in an assembly of sub-members.

[0029] If necessary, the method may include the step of partially debinding the sub-member prior to the second heating step.

[0030] In some embodiments, the step of debinding the sub-member prior to the second heating step includes the step of debinding the member prior to the first heating step, which is advantageous in providing a sintered member having a higher percentage of powder material, which may improve the properties of the sintered member.

[0031] If desired, the assembly of the sub-members may further include adding a bonding material to the bond interface between the sub-members prior to the second heating step, and if desired, the bonding material may include another powder material or a mixture of another powder material and another binder.

[0032] In some embodiments, the strength of the bond at the bond interface may be improved by adding another powder material, or a powder material and a binder.

[0033] If necessary, a non-powder processing feature is added to the sub-components prior to assembly of the sub-components to form an assembly of sub-components. The non-powder processing feature may be a foil structure.

[0034] In some embodiments, the inclusion of non-powder-machined structures provides structural improvements or functional benefits to the sintered member, such as improved or increased surface area for heat transfer or improved fluid flow characteristics around or through the sintered member.

[0035] If necessary, the step of adding the non-powder structure may include a supplemental heating step to bond the non-powder structure to the sub-member.

[0036] If necessary, a compressive force is applied to the bond interface between the sub-members during the second heating step, and if necessary, the bond surfaces of the sub-members may be positioned such that gravity provides said compressive force.

[0037] Further, if necessary, the sub-member assembly is placed in a fixture to provide a compressive force during the second heating step. The fixture may have a lower coefficient of thermal expansion than the material of the members to provide a compressive force at the bond interface. The fixture may include a diffusion-preventing coating, if necessary, to prevent adhesion of the members to the fixture.

[0038] In some embodiments, applying a compressive force to the bond interface during the second heating step advantageously improves the strength of the bonds between the sub-components in the sintered part.

[0039] If necessary, the sub-members are sintered to 80 to 100% of their full density during the first heating step.

[0040] If necessary, the sub-members are sintered to 98 to 100% of their full density during the first heating step.

[0041] If necessary, the sub-members are sintered to 80 to 95% of their full density during the first heating step.

[0042] If necessary, the sub-members are sintered to 95 to 99% of their full density during the first heating step.

[0043] In another aspect, the present invention provides singulated, thin-walled, sintered components having greater detail and more intricate internal structures.

[0044] In a second aspect of the present invention, 1. A singulated thin-walled heat exchanger core having a sintered material, comprising: a plurality of first passages each having a first end, a second end, an inner surface, and an outer surface; the inner surface connects the first end and the second end, and a wall extends between the outer surface and the inner surface; Each first passage defines a central axis A extending from the first end to the second end; the outer surface having a first protrusion at or near the first end and a second protrusion at or near the second end; the first protrusions extend radially and the second protrusions extend radially, each connected to one or more adjacent sub-members at a bonding interface; the outer surface further includes a recess defining a cavity between the first passages; The cavity is a second passage perpendicular to the central axis A, providing a heat exchanger core.

[0045] If necessary, the first protrusion and the second protrusion are brought together at their respective bond interfaces, said bond interfaces being continuous such that the first passageway and / or the second passageway are separated and fluid-tight.

[0046] Where desired, the first passage provides a first fluid flow path and the second passage provides a second fluid flow path that is separate and perpendicular to the first fluid flow path.

[0047] If necessary, each first passageway has a polygonal cross-section extending along the axis A.

[0048] If desired, one or more of the interior and / or exterior surfaces of the first passageway may have protrusions, such as fins, complex fins, protrusions, or triple periodic minimal surface lattice structures, to further increase surface area or modify fluid flow characteristics.

[0049] If desired, non-powdered structures bonded to the interior or exterior surfaces may be included within the first and / or second passages, respectively, to improve heat transfer or direct fluid flow.

[0050] Optionally, the non-powder handling structure comprises a plurality of foil sheets disposed in the first passage or the second passage.

[0051] Optionally, the heat exchanger core is a cellular structure, each of the first passages forming a cell, the cellular structure having a plurality of non-uniform cells arranged to enhance heat transfer by manipulating fluid flow in the second passages.

[0052] If desired, the first protrusion extends radially and is connected to a first protrusion of an adjacent first passage, and the second protrusion extends radially and is connected to a second protrusion of an adjacent first passage at a joint interface. If desired, the first protrusion and the second protrusion are connected to one or more first protrusions and second protrusions, respectively, of the adjacent first passage.

[0053] Optionally, each first passage has a polygonal wall extending between the inner surface and the outer surface. Further, optionally, the first opening has a first perimeter at a first end and the second opening has a second perimeter at a second end, connected by the first passage, the first projection extends from the first perimeter to a joining interface, and the second projection extends from the second perimeter to a joining interface, said joining interface having a polygonal cross-section.

[0054] If desired, the sintered material may be a sinterable pure metal, alloy, ceramic, or composite material.

[0055] In yet another aspect, there is provided a unitized, thin-walled, sintered member made by the method of the present invention, comprising a plurality of joined sub-members, each having a first end, a second end, an inner surface, and an outer surface, and each sub-member has a first passage defined by the inner surface connecting the first end and the second end, the first passage defining a central axis A extending from the first end to the second end (14).

[0056] The outer surface has a first protrusion at or near a first end and a second protrusion at or near a second end, the first and second protrusions extending radially and connected to one or more adjacent sub-members at a joint interface. The outer surface may further have a recess defining a cavity between the sub-members. The recess may be between the first protrusion and the second protrusion.

[0057] In one embodiment, multiple joined sub-pieces including protrusions and recesses provide the sintered part with more complex internal details including narrow, non-linear internal passages.

[0058] If necessary, the protrusions are joined at their respective bond interfaces such that the cavity forms a second passage perpendicular to the central axis A.

[0059] If desired, the bond interface is sealed and continuous such that the first passageway and / or the second passageway are separated and fluid tight.Further, if desired, the sintered member is the core of a heat exchanger, the first passageway being configured to provide a first fluid flow path and the second passageway being configured to provide a separated second fluid flow path perpendicular to the first passageway.

[0060] Advantageously, if desired, each sub-member has a polygonal cross-section extending along axis A to provide good alignment for the bonding surfaces at the bonding interface, enhancing the strength of the bonding interface.

[0061] If desired, the inner and / or outer surfaces of one or more sub-members may have other protrusions, also referred to as functional structures, such as fins, complex fins, protrusions, or triple periodic minimal structures, to increase surface area or to tailor fluid flow characteristics.

[0062] If desired, the sintered member may further include a non-powdered structure bonded to an inner or outer surface within the first and / or second passages, respectively, for improved heat transfer or fluid flow guidance. If desired, the non-powdered structure may further include a plurality of foil sheets disposed within the first or second passages.

[0063] In some embodiments, the non-powder processed structure improves strength and / or provides improved surface area for heat transfer to the sintered member.

[0064] Optionally, the sintered members are of a cellular structure, each of the members defining a cell, the cellular structure having a plurality of non-uniform cells arranged to optimize fluid flow in the second passageway. If desired, each sub-member has a polygonal wall extending between the inner and outer surfaces, a first opening having a first perimeter at a first end and a second opening having a second perimeter at a second end connected by a first passageway, the first projection extending from the first perimeter to a joining interface and the second projection extending from the second perimeter to a joining interface, said joining interface having a polygonal cross-section.

[0065] If desired, the powder material is a sinterable pure metal, alloy, ceramic, or composite material.

[0066] Example embodiments will now be described with reference to the accompanying drawings, in which like reference numbers refer to like elements. [Brief description of the drawings]

[0067] [Figure 1] FIG. 1 illustrates the method of the present invention. [Diagram 2] FIG. 2 illustrates a second embodiment of the method of the present invention. [Diagram 3] FIG. 3 illustrates a third embodiment of the method of the present invention. [Figure 4] FIG. 4 illustrates a fourth embodiment of the method of the present invention. [Diagram 5] FIG. 1 is a diagram showing the steps in the method of the present invention. [Figure 6] FIG. 1 illustrates a sintered component having a uniform structure constructed according to the present invention. [Figure 7] FIG. 2 shows a sintered part having a non-uniform structure according to the present invention. [Figure 8] FIG. 2 is a diagram showing a sub-part of a sintered part according to the present invention. [Figure 9] 13A and 13B are diagrams showing functional structures included in a sub-member according to the present invention. [Figure 10] FIG. 2 shows a functional structure, which is a three-period minimal structure according to the present invention. [Figure 11] FIG. 1 illustrates a functional structure that is a variable density three-period minimal structure according to the present invention. [Figure 12] FIG. 1 shows a heat exchanger according to the present invention. [Figure 13] FIG. 2 illustrates the flow path of fluids through a heat exchanger according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0068] In the present invention, a method is provided for producing a uniform, single sintered part 1 composed of a plurality of small sub-parts 10 by co-sintering in a series of successive steps as shown in Figs. 1 to 4 as follows.

[0069] First, at 100, a number of sub-components 10 are constructed in the form of a moulded powder preform 10a of the desired shape having a density between 50% and 99.5%. This can be achieved by producing the green body powder components 10a by an indirect additive manufacturing process 100, in which powder material particles 3 are bound together with a binder 4 to produce the moulded powder preform 10a. The moulded powder preform 10a, known in this state as a green body compact 10a, is then debindered at 102, by partial removal of the binder 4 to form a brown body compact 10b. Alternatively, if a functional binder 4 is used, the debindering step 102 can be omitted to avoid the green body stage.

[0070] Second, the sub-piece 10 is at least partially sintered by the application of heat in a first heating step 104. The heating process causes the powder particles to cohere and sinter together due to diffusion between the powder particles, resulting in shrinkage.

[0071] Thirdly, a plurality of sub-members 10 are assembled to form a sub-member 2 assembly.

[0072] Finally, further heat is applied in a second heating step 108 to form the integrated part 1 from the multiple individual sub-members 10 of the assembly of sub-members 2. The second heating step 108 further sinters the assembly of sub-members 2, bonding the sub-members 10 together to form a single sintered part 1. The sub-members 10 have bonding surfaces 26 that are complementary to the bonding surfaces 26 of one or more other sub-members 10. The sub-members 10 are assembled in step 106 and during the sintering process of the second heating step 108, the bonding surfaces 26 of adjacent sub-members 10 are brought into intimate contact with each other, such that the powder compacts are sintered together and the powder particles are sintered together at the surfaces to form a whole. The bonding surfaces 26 are complementary in that they are intimately joined over the entire area of ​​the bonding surfaces 26, and the sintering bonds the bonding surfaces 26 together. A first embodiment of the present invention will now be described with reference to Figure 1. Figure 1 shows a sintering assembly sintering process according to the following steps: a) The green sub-members 10, 10a are debindered to provide the brown sub-members 10, 10b. b) At 104, the brown components 10, 10b are sintered to full or near full density, typically 98-100%. c) In 104, the sintered sub-pieces 10 are assembled. If necessary, an excess of powder 3 or a mixture of powder 3 and binder 4 may be introduced at the joining interface to improve bonding. d) The assembly is returned to high temperature in a second heating step 108 to sinter the bond interface 5 .

[0073] The production of a uniform single sintered part 1 is shown, moving continuously from left to right through various stages of production. On the left side, one of several sub-parts 10 is shown, produced using a high-resolution additive powder bed manufacturing technique 100a, such as binder jet additive manufacturing 100b. The sub-part 10 is a molded powder preform 10a formed from a powder material 3 and a binder 4. The powder material 3 is a sinterable pure metal, alloy, ceramic, or composite material. In FIG. 1, the left side view shows the sub-part 10 partially debindered to provide a brown sub-part 10b. This involves removing a portion of the binder 4, resulting in an increased percentage of the powder material 3 in the final part 1. In another embodiment, the binder 4 used in the sub-part 10 may be a functional binder 4 suitable for inclusion in the final product 1. In this case, debindering of the sub-part 10 is not required.

[0074] Once created, the plurality of sub-members 10 are heated in a first heating step 104 to sinter the sub-members 10. In the first heating step 104, the sub-members 10 are fully sintered or at least partially sintered. During sintering in the first heating step 104, the sub-members 10 shrink and stresses are created within the sub-members 10. The size of the sub-members 10 needs to be limited so that these stresses do not fracture or destroy the sub-members 10. Preferably, the sub-members are less than 60 mm in any one dimension.

[0075] A plurality of sub-members 10 are then assembled to form an assembly of green bodies 2. The sub-members 10 have an outer surface 20 including one or more joining surfaces 26 configured to interface with at least one of the one or more joining surfaces 26 of an adjacent sub-member 10 at one or more joining interfaces 5. The assembly of sub-members 2 includes another powder material 3, or the powder material 3 and a binder 4, between the sub-members 10, which coalesce and promote bonding during a second heating step 108. Preferably, once sintered, the part 1 is homogenous at the joining interfaces 5.

[0076] Once assembled, the assembly of sub-members 2 is heated in a second heating step 108 such that the sub-members 10 are bonded together at the bond interfaces 5 to provide a single sintered member 1. This step is also referred to as co-sintering 108. The second heating step 108 may also further sinter the sub-members 10 and the additional powder material 3 and, if included, the binder 4. 2 shows the method of FIG. 1, but after assembly step 106, the sub-member 2 assembly is placed in a fixture 60, which restrains the sub-member 2 assembly during a second heating step 108. The following steps are involved: a) The green part is debindered to provide a brown part. b) The brown part is sintered to obtain a higher density, typically 95-99%. c) The partially sintered part is assembled into a fixture. i The fixture is selected to have a lower coefficient of thermal expansion than the component material. ii An anti-diffusion coating is applied to the fixture, allowing it to be reused. iii) Additional binder or powder / binder mixture may be inserted at the joint interface. d) The assembly is exposed to high temperatures and sintered. i The fixture does not expand with temperature, applying load to the bond interface and improving sintering.

[0077] The fixture 60 restrains the sub-member 2 assembly during the second heating step 106. Preferably, the thermal expansion coefficient of the fixture 60 is made lower than the thermal expansion coefficient of the sub-member 2 assembly, so that the sub-member 2 assembly expands more within the fixture than the fixture 60 due to the heat of the second heating step 108, and therefore the fixture 60 exerts a compressive force on the sub-member 2 assembly during the second heating step 108.

[0078] Figure 3 shows the method as shown in Figure 1, but where the sub-piece 10 is only partially sintered during a first heating step 104 and further sintered during a second heating step 108. The following steps are present: a) The green part is debindered to provide a brown part. b) The brown part is partially sintered to obtain a high density, typically 80-95%. c) The sintered components are assembled with excess powder or a powder / binder mixture is inserted at the joint interface. d) The assembly is returned to high temperature to sinter the interface.

[0079] FIG. 4 shows the method of FIG. 1, but now with another step of adding 103 a non-powder structure 50 to the sub-member 10. The non-powder structure 50 is a structure that is not formed in a powder process via sintering, such as a homogenous metal that may be rolled, cast or forged in the form of a foil structure 52. The non-powder structure 50 may be added to the sub-member 10 prior to the first heating step 104 and bonded to the sub-member 10 during the first heating step 104, as shown in FIG. 4. Alternatively, it may be added 103 during the assembly 106 of the sub-members 2 and bonded to the sintered member 1 during the second heating step 108. The non-powder structure 50 may be placed inside the cavity 30 of the sub-member 10 or between the sub-members 10. The non-powder structure 50 is bonded to the sub-member 10 or member 2 by diffusion bonding or is held in place by the sub-member 10 shrinking around the non-powder member 50 due to sintering shrinkage during the first heating step 104 or the second heating step 108. The process of FIG. 4 has the following steps: a) The brown member is debindered to provide a brown member. b) A foil structure is inserted into a void in the heat exchanger. c) The foil structured component is partially sintered to obtain a high density, typically 80-95%, which constrains the foil structure and allows diffusion bonding. d) The sintered parts are assembled with excess powder or powder / binder mixture introduced at the joint interface.

[0080] e) The assembly is returned to high temperature to sinter the interfaces between the parts.

[0081] Figure 5 shows the steps of the process.

[0082] 1 to 4 all show sub-members 10 having a triangular cross section, and six of the sub-members 10 being assembled to form an assembly of sub-members 2. FIG.

[0083] It will be appreciated that each sub-member may be of any shape, including one or more joining surfaces 26 that form complementary interfaces with adjacent sub-members 10 in the assembly of sub-members 2, allowing the sub-members 10 to be joined during the second heating step 108. In a particularly advantageous configuration, the sub-members 10 have polygonal cross-sections and planar joining surfaces 26, facilitating a reliable bond between the sub-members 10 in the sintered member 1. However, an advantage of additive manufacturing methods is that any shape is possible. The method of the present invention can be applied to regularly and irregularly shaped sub-members 10 having complementary joining surfaces 26 configured to match at the joining interface 5.

[0084] The co-sintering step 108 is aided by applying a force to the faying surfaces 26 during the sintering process 108. This can be provided in a number of ways. ○ The design of the sub-member 10 may allow gravity to act on some or all of the bond interfaces 5 during the second heating step 108. o As explained with reference to FIG. 2 above, during the second heating step 108 a fixture 60 may be used to restrain the sub-member 10, so that a compressive force is applied to the interface. o Design of structures through additive manufacturing techniques to interconnect joining surfaces via non-planar structures or by separate inserts that bring the parts into intimate contact during sintering.

[0085] The fixture 60 may have a diffusion-preventing coating 62 to prevent adhesion of the component 1 to the fixture, either by sintering or diffusion bonding. The powder material 3 may be a ceramic or metallic material, depending on the needs of the particular application. Currently available metals suitable for use in this method include nickel superalloys, steel alloys, copper alloys, aluminum alloys, and titanium alloys. The method is not limited to these metals, but can be applied to any pure metal, alloy, ceramic, or composite material that can be sintered.

[0086] The method overcomes size limitations associated with sintering processes for powder bed defined parts, including binder jet parts. Multiple individually manufactured sub-pieces 10 are provided to one another at 106 to form a uniform single sintered part 1 after co-sintering 108. The multiple sub-pieces 10 mean that the inner surface of the final part 1 is accessible during manufacture, allowing the incorporation of geometric features therein that could not be manufactured due to molding and powder extraction difficulties.

[0087] The method allows the combination of high resolution features at the micrometer scale in macro-scale parts with minimal intervention and low cost. The method of the present invention is particularly suitable for the production of composite heat sinks and high efficiency fluid to fluid heat exchangers 7 for transferring thermal energy between a liquid and a gas, two liquids, or two gases. Using conventional manufacturing techniques, such heat sinks and heat exchangers are limited in efficiency as described above and are restricted to simple forms such as six-sided polyhedrons, usually flat rectangular prisms. If shaping is required, the heat exchanger is usually limited to small curvatures in a single plane, which are formed by bending the post-product of a flat heat exchanger. The method of the present invention allows the production of complex sintered heat exchangers 7 of any size and shape, tailored to the local flow characteristics and direction, and the available space.

[0088] The sintered member 1 according to the present invention comprises a plurality of sub-members 10 sintered together to form a single sintered member 1. Each sub-member 10 has an outer surface 20 having one or more protrusions 22, 24 including one or more joining surfaces 26. Each of the joining surfaces 26 is configured to interface at a joining interface 5 with one or more complementary joining surfaces 26 of one or more adjacent sub-members 10 in the sintered member 1. The outer surface 20 further comprises a recess 28 to define a cavity 30 between the sub-members 10 in the sintered member 1. The recess 28 is between the first protrusion 22 and the second protrusion 24. The cavity 30 may be closed or open on one or more sides to allow for the flow of fluid therethrough.

[0089] FIG. 6 illustrates the configuration of such a sintered member 1 in the form of a heat exchanger 7. The sintered member 1 has a plurality of sub-members 10, each forming a cell 16 of the heat exchanger 7. In the embodiment of FIG. 6, each of the sub-members 10 is in the form of a polygonal prism, has a first end 12 and a second end 14, and an inner surface 40, and defines a first passage 42 extending therethrough from the first end 12 to the second end 14. The first passage 42 defines a central axis A extending therethrough from the first end 12 to the second end 14. The sub-member 10 further has an outer surface 20, which has one or more mating surfaces 26 configured to interface with complementary mating surfaces 26 of one or more adjacent sub-members 10 of the sintered member 1. Each sub-member 10 has a wall 18 extending between the outer surface 20 and the inner surface 40.

[0090] Each sub-member 10 has an outer surface 20, which includes an interface surface 26 configured to interface with a complementary interface surface 26 of an adjacent sub-member 10 at an interface interface 5. In a preferred embodiment, the outer surface 20 includes a first protrusion 22 extending radially at the first end 12 and a second protrusion 24 extending radially at the second end 14. Preferably, the first protrusion 22 and the second protrusion 23 extend radially outwardly in a direction R from the outer surface 20 and / or wall 18 of the first passage 42. The first protrusion 22 and the second protrusion 23 may extend radially outward perpendicular to the inner surface 40 and / or axis A. Each radial extension 22, 24 includes an outer flat surface 23 that defines a polygonal shape in cross section, said outer flat surface 23 being the interface surface 26.

[0091] In another embodiment, the joining surfaces 26 may not be flat, but may have complementary protruding and penetrating features 27 to improve alignment and joint strength between the sub-members 10 .

[0092] The outer surface 26 further has recesses 28, which form cavities 30 between the sub-components 10 when the sub-components 10 are assembled. When the sintered component 1 is a heat exchanger 7, as shown in FIG. 6, the protrusions 22, 24 are mated protrusions 22, 24 that are fitted together without gaps at the joint interface 5 to form a continuous fluid-tight joint, and the cavities 30 form the second passages 32. Thus, the first passage 42 is the first fluid passage 44, and the second passage 32 is the second fluid passage 34 for exchanging thermal energy between the first and second fluids. The first fluid passage 35 and the second fluid passage 45 are fluid-tight and separated from each other. The first fluid passage 35, and therefore the axis A, is perpendicular to the second fluid passage 45.

[0093] In a preferred embodiment, each sub-member 10 has a wall 18 extending between the outer surface 20 and the inner surface 40. The wall 18 has a polygonal cross-section. For the heat exchanger 7, each sub-member 10 has a first opening 13 having a first perimeter 13' at a first end 12 and a second opening 15 having a second perimeter 15' at a second end 14. The first opening 13 and the second opening 15 are connected by a first passage 42 along the axis A. The first projection 22 may extend radially outward from the entire length of the first perimeter 13' and the second projection 24 may extend radially outward from the entire length of the second perimeter 15' to a respective bond interface 5. The bond interface 5 may also have a polygonal cross-section.

[0094] In more complex configurations, such as shown in FIG. 7, the submembers 10 may be non-uniform or irregular, and multiple fluid flow paths 35, 45 may be tailored and / or optimized through and between the cells 16 of the heat exchanger 7. For example, the polygonal prism submembers 10 may have different sized sides, different number of sides, or the polygonal profile may be irregularly shaped. The profile of the submembers 10 may be configured to straighten out the second fluid flow path 45 by reducing the angle θ through which the fluid must turn to enhance the flow of fluid. Alternatively, the profile of the submembers 10 may be configured to increase the angle θ through which the fluid must turn, or to increase the distance the fluid must take through the heat exchanger 7 to enhance heat transfer. An example of a fluid flow path is shown in FIG. 13.

[0095] The individual cells 16 can be molded by designing the member 1 to provide a curvature, conformally fitting within a predefined space, such as around a cylindrical core or a second degree of curvature. If a curved profile is required for the heat exchanger 7, the sub-members 10 may be tapered in one or more directions along the axis A to provide a sintered member with a single or compound curvature without introducing stresses into the member 1 through post-fabrication bending. Even if an irregular pattern is selected, the cells 16 may be combined into modules by repeating base cells 16 or by combinations of cells 16, so that the cells 16 may be stitched together for ease of manufacture.

[0096] The shape may be divided into repeating groups of sub-members for ease of manufacture, which form interlocking molded shapes, providing a modular level of internal shape, although this is not required.

[0097] In the example of a fluid heat exchanger, this method may provide particular advantages with respect to how it allows for the production of heat transfer and flow management structures by molding internal fluid passages.

[0098] FIG. 8 shows an example of a functional structure 25 in the form of an additional protrusion 25 for impeding fluid flow and enhancing surface area for heat transfer. FIG. 8 shows said functional structure 25 on the outer surface 20. The functional structure 25 protrudes therefrom into the second passage 32 for enhancing surface area for heat transfer and / or adjusting flow characteristics of the fluid flowing in the second passage 32 or the second passage 34. In another aspect of the invention, the functional structure 25 is disposed on the inner surface protruding into the first passage 42 for enhancing surface area for heat transfer and / or adjusting flow characteristics of the fluid flowing in the first passage 42 or the first fluid flow passage 44. These additional protrusions 25 can be formed during formation of the powder preform as part of the green body 10a and can be disposed on the outer surface 20 and / or inner surface 40 of the sub-piece 10. These additional protrusions 25 may be in the form of flow disrupting and surface area increasing structures 25, such as pins 25a, ribs 25b, and fins 25c, to improve heat transfer.

[0099] Also, in the method of the present invention, more complex functional structures 25 can be included in or added to the sub-member 10 to improve heat transfer through increased surface area or to modify or disrupt the flow of fluid through the passages 32, 42. For example, in a fluid-fluid heat exchanger 7, the optimum surface contact area of ​​the two fluids for best heat transfer may be significantly different, especially when one fluid is a gas and the other is a liquid. In such a situation, the liquid channel may be a second fluid flow path 34 around the outside of the cell 16, and a functional structure 25 including a high complexity gas-facing surface 27 with a high surface area to volume ratio may be included in the first fluid flow path 34. Such functional structures 25 are shown in Figures 9 and 10 and can take the form of complex fin-type structures 25d, pin array-type structures 25e, and periodic minimal surfaces 25f. These periodic minimum structures 25f may be of varying density, as shown in FIG. 11, and ideally have a reduced density and larger openings towards the center of the passages 32, 42, and smaller openings and higher density closer to the inner and / or outer surfaces.

[0100] The functional structure shown in FIG. 9 is designed to be included in a first passage 42 of a cell 16 having a hexagonal cross section.

[0101] These gas-facing surfaces may be sintered structures formed by powder processes such as binder jetting, or may be non-powder structures 50 produced by bulk additive manufacturing techniques. Binder jetting, and particularly metal binder jetting, of these complex functional structures allows a high degree of design freedom and takes advantage of high complexity thin-walled structures such as periodic minimal surfaces with fine fin structures to perform their functions. These structures can incorporate secondary functions such as flow direction surfaces that maintain ideal orientation for these functions or are used to perform actions on the fluid such as directional control.

[0102] Any system feature described herein may be provided as a method feature, and vice versa. Means-plus-function features used herein may be alternatively expressed in terms of their corresponding structures.

[0103] Any feature in one embodiment may be applied to other embodiments in any suitable combination. In particular, method embodiments may be applied to system or apparatus embodiments and vice versa. Furthermore, any, some, and / or all of the features in one embodiment may be applied to any, some, and / or all of the features in any other embodiment in any suitable combination.

[0104] It should also be understood that specific combinations of the various features described and defined in any embodiment may be implemented and / or provided and / or used independently.

Claims

1. A method for manufacturing a thin-walled sintered member, comprising: forming a plurality of sub-members using a binder jet additive manufacturing method, wherein the sub-member has a formed powder preform containing a powder material and a binder, the sub-member has an outer surface including one or more protrusions including one or more joining surfaces, and the joining surface is configured to interface with at least one of the one or more joining surfaces of an adjacent sub-member, a step; heating the plurality of sub-members in a first heating step to at least partially sinter the sub-members, assembling the sub-members to form an assembly of sub-members having one or more joining interfaces, wherein the joining surfaces of adjacent sub-members are joined together, heating the assembly of sub-members in a second heating step to bond the sub-members to each other to form the member, A method having the above steps.

2. The method according to claim 1, wherein the thin wall has a wall thickness of less than 2 mm.

3. The first heating step has a step of partially sintering the sub-members, The method according to claim 1 or 2, wherein the second heating step further has a step of sintering the member.

4. The method according to claim 1 or 2, wherein the first heating step has a step of completely sintering the sub-members.

5. The method according to claim 1 or 2, wherein the sub-member further has a recess defining a cavity between the sub-members in the sintered member.

6. The sub-member further includes an inner surface defining a first passage, a first end, and a second end, The first passage extends through the sub-member from the first end to the second end and has a central axis A extending from the first end to the second end. The method according to claim 1 or 2.

7. The sub-member has a first protrusion of each sub-member extending radially at or near the first end or near the first end, and a second protrusion of each sub-member extending radially at or near the second end or near the second end, The protrusions are joined together (tesselate) at each joining surface of the sintered member, and the cavity forms a second passage perpendicular to the central axis A. The method according to claim 6.

8. The second heating step has a step of sealing the bonding interface between the sub-members, and the first passage and / or the second passage are each fluid-tight. The method according to claim 1 or 2.

9. The method according to claim 1 or 2, further comprising a step of forming the protrusion having an external flat surface defining a polygonal cross-section, the external flat surface being the bonding surface.

10. The method according to claim 1 or 2, further comprising a step of partially debinding the sub-members before the second heating step.

11. The assembly of the sub-members further has a step of adding a binding material to the bonding interface between the sub-members before the second heating step. The method according to claim 1 or 2.

12. The method according to claim 11, wherein the binding material further comprises a powder material or a mixture of another powder material and another binder.

13. The method according to claim 1 or 2, having a step of adding a non-powder treatment structure to the sub-members before the step of assembling the sub-members, and an assembly of the sub-members is formed.

14. The method according to claim 13, wherein the non-powder structure is a foil structure.

15. The method according to claim 13, wherein the step of adding the non-powder structure has an auxiliary heating step for bonding the non-powder structure to the sub-members.

16. The method according to claim 1 or 2, having a step of applying a compressive force to the bonding interface between the sub-members during the second heating step.

17. The method according to claim 16, wherein the bonding surface of the sub-members is arranged such that the compressive force is provided by gravity.

18. The assembly of the sub-members is arranged in a fixture for the second heating step. The method according to claim 1 or 2.

19. The method according to claim 18, wherein the fixture has a lower coefficient of thermal expansion than the material of the member such that the compressive force is provided to the bonding interface.

20. The method according to claim 19, wherein the fixture has a diffusion prevention coating to prevent adhesion of the member to the fixture.

21. During the first heating step, the sub-members are sintered from 80 to 100% of the full density. The method according to claim 1 or 2.

22. The method according to claim 1 or 2, wherein during the first heating step, the sub-member is sintered to 98 to 100% of the total density.

23. The method according to claim 1 or 2, wherein the sub-member is sintered to 80 to 95% of the total density during the first heating step.

24. The method according to claim 1 or 2, wherein the sub-member is sintered to 95 to 99% of the total density during the first heating step.

25. The method according to claim 1 or 2, wherein the powder material is a sinterable pure metal, alloy, ceramic, or composite material.

26. A consolidated thin-walled heat exchanger core having a sintered material, having a plurality of first passages, each having a first end, a second end, an inner surface, and an outer surface, the inner surface connecting the first end and the second end, and a wall extending between the outer surface and the inner surface, each first passage defining a central axis A extending from the first end to the second end, the outer surface having a first protrusion at or near the first end and a second protrusion at or near the second end, the first protrusion extending radially, the second protrusion extending radially, each being connected at a joining interface to one or more adjacent sub-members, the outer surface further having a recess defining a cavity between the plurality of first passages, the cavity being a second passage perpendicular to the central axis A, the core being a heat exchanger core formed using a binder jet method.

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