Method for preparing electrode for forming honeycomb extrusion die

Abstract

A method for forming an electrode for forming a honeycomb extrusion die. The method includes forming an electrode by means of an additive manufacturing process, the electrode including a base having a network extending from the base. The network defines a matrix of cell openings. The method also includes forming a secondary electrode having a plurality of pins. The plurality of pins are shaped and arranged to match the matrix of cell openings defined by the network of the electrode. The method also includes machining the electrode using the secondary electrode to smooth the surface of the electrode formed by the additive manufacturing process.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority under 35 U.S.C. §119 to U.S. Provisional Application No. 62 / 851,973, filed on May 23, 2019, the entirety of which is incorporated herein by reference. Technical Field

[0003] Embodiments described herein generally relate to methods of forming electrodes and electrodes formed thereby. Specifically, embodiments described herein relate to methods of preparing electrodes for forming an extrusion die having a honeycomb pattern. Background Art

[0004] Wire electrical discharge machining (wire EDM) is used to form the features of some honeycomb extrusion dies. However, wire EDM may be impractical or inappropriate for forming honeycomb extrusion dies with certain styles that are not conducive to being formed by using linear wires. Insert electrical discharge machining (insert EDM) and electrochemical machining (ECM) are alternative processes that can be used to form extrusion dies (including honeycomb extrusion dies that are not conducive to being manufactured by wire EDM). Insert EDM and ECM require the use of specially constructed electrodes that are shaped to provide the desired style to the extrusion die. As a result, forming electrodes for insert EDM or ECM may require additional time, materials, and costs.

[0005]

[0006] Therefore, there is a need in the art for methods of forming electrodes that can be used to produce honeycomb extrusion dies with rapidly changing geometries and reduced costs. Summary of the invention

[0006] In a first aspect, a method for additively manufacturing a copper-tungsten electrode comprises: forming the electrode as a series of layers, wherein each layer is formed by depositing a powder layer onto a build platform or onto a previous layer in the series, wherein the powder layer comprises tungsten powder and copper powder; and applying about 1 to about 10 J / mm 2 of a laser to the powder layer. 2 The laser energy causes the powder layers to fuse, and wherein the electrode comprises an interconnected network of tungsten infiltrated with copper formed by the series of layers being fused together.

[0007] In the second aspect according to the preceding paragraph, the electrode may have a relative density of at least about 75%.

[0008] In a 3rd aspect according to any preceding paragraph, the electrode may have a relative density of at least about 90%.

[0009] In a 4th aspect according to any preceding paragraph, the tungsten powder and the copper powder can each have a particle size distribution of about 15 μm to about 55 μm.

[0010] In the 5th aspect according to any preceding paragraph, the tungsten powder and the copper powder can each have a particle size distribution of about 25 μm or less.

[0011] In a 6th aspect according to any preceding paragraph, the amount of tungsten powder present in the powder layer may be about 70 wt % to about 90 wt %.

[0012] In a 7th aspect according to any preceding paragraph, the tungsten powder may be present in the powder layer in an amount of 75 wt %, and the copper powder may be present in an amount of 25 wt %.

[0013] In the 8th aspect according to any preceding paragraph, the depositing of the powder layer may include depositing one of tungsten powder or copper powder and subsequently depositing the other of tungsten powder or copper powder.

[0014] In a 9th aspect according to any preceding paragraph, the depositing of the powder layer may include depositing a mixture of copper powder and tungsten powder.

[0015] In a 10th aspect according to any preceding paragraph, forming the electrode may include forming the electrode having a base with a network extending from the base, wherein the network defines a matrix of cell openings.

[0016] In the 11th aspect according to any preceding paragraph, forming the electrode may further comprise forming one or more internal channels in a base of the electrode.

[0017] In a 12th aspect according to any preceding paragraph, the method may include smoothing the electrode by insert electro-discharge machining or electro-chemical machining using the secondary electrode.

[0018] In a 13th aspect according to any preceding paragraph, smoothing the electrode may include smoothing the electrode so that the surface roughness of the electrode is about 1 to about 50 μm.

[0019] In a 14th aspect, the electrode may be formed by a method according to any preceding paragraph.

[0020] In a fifteenth aspect, a method for manufacturing an electrode comprises: forming a porous tungsten structure in a layer-by-layer manner, wherein each layer is formed by depositing a layer of tungsten powder; and before depositing a subsequent layer, applying a laser energy of about 1 to about 10 J / mm 2 selectively fusing tungsten powder with a laser; and infiltrating the porous tungsten structure with molten copper to form an electrode, wherein the electrode includes a porous tungsten structure infiltrated with copper.

[0021] In the 16th aspect according to the preceding paragraph, the porous tungsten structure can have a relative density level of at least about 75%.

[0022] In the 17th aspect according to any of the preceding 2 paragraphs, the tungsten powder may have a particle size distribution of about 15 μm to about 55 μm.

[0023] In the 18th aspect according to any of the preceding 3 paragraphs, infiltration of the porous tungsten structure with molten copper may be performed by one of the following: spontaneous or pressure infiltration, centrifugal infiltration, ultrasonically driven or assisted infiltration, or Lorentz force infiltration.

[0024] In a 19th aspect according to any of the preceding 4 paragraphs, the electrode may have a base having a network extending from the base, wherein the network defines a matrix of pore openings.

[0025] In the 20th aspect according to any of the preceding 5 paragraphs, the method may further comprise smoothing the electrode by insert electro-discharge machining or electro-chemical machining using the secondary electrode.

[0026] In aspect 21, a method for forming an electrode for forming a honeycomb extrusion die comprises: forming an electrode by an additive manufacturing process, the electrode comprising a base having a network extending from the base, wherein the network defines a matrix of pore openings; and smoothing the surface of the electrode using a secondary electrode having a plurality of pins, wherein the plurality of pins are shaped and arranged to match the matrix of pore openings defined by the network of the electrode.

[0027] In the 22nd aspect according to the preceding paragraph, the forming of the electrode may include forming the electrode from a powder mixture of tungsten and copper, and wherein the additive manufacturing process is laser powder bed fusion.

[0028] In the 23rd aspect according to the preceding paragraph, the mixture of tungsten and copper can include tungsten particles and copper particles each having a particle size distribution of about 15 to about 55 microns.

[0029] In the 24th aspect according to any of the preceding two paragraphs, 1 J / mm 2 Up to 10J / mm 2 Laser energy can be used for laser powder bed fusion.

[0030] In a 25th aspect according to any of the preceding 4 paragraphs, forming the electrode may include: forming a porous body using tungsten powder by laser powder bed fusion, and infiltrating the porous body with molten copper.

[0031] In a 26th aspect according to any of the preceding 5 paragraphs, forming the electrode may include forming a first region of channel openings having a first size, and a second region of channel openings having a second size different from the first size.

[0032] In the 27th aspect according to any of the preceding 6 paragraphs, forming the electrode may include forming a first region of channel openings having a first shape, and a second region of channel openings having a second shape different from the first shape.

[0033] In a 28th aspect according to any of the preceding 7 paragraphs, forming the electrode may include forming a network such that each cell opening in the matrix of cell openings has a hexagonal cross-sectional area.

[0034] In a 29th aspect according to any of the preceding 8 paragraphs, forming the electrode may include forming the base to define one or more internal passages configured for circulation of a fluid used in electrospark machining.

[0035] In a 30th aspect according to any of the preceding nine paragraphs, forming the secondary electrode may include forming the secondary electrode by machining a metal blank using an electrode in pulsed salt electrochemical machining.

[0036] In the 31st aspect according to the preceding paragraph, smoothing the surface of the electrode may include machining the electrode using the secondary electrode in pulsed salt electrochemical machining.

[0037] In a 32nd aspect according to any of the preceding 11 paragraphs, the smoothing of the electrode surface may include plunge electro-discharge machining.

[0038] In a 33rd aspect according to any of the preceding 12 paragraphs, the smoothing of the electrode surface may include wire electrical discharge machining.

[0039] In a 34th aspect according to any of the preceding 13 paragraphs, the method may further include applying an electrically insulating coating to the electrode after smoothing the surface of the electrode.

[0040] In a 35th aspect, an electrode may be formed by a method according to any of the preceding 14 paragraphs.

[0041] In aspect 36, a method for forming an electrode for forming a honeycomb extrusion die by electrospark machining comprises: forming an electrode by an additive manufacturing process, the electrode comprising a base and a network extending from the base, wherein the network defines a matrix of cell openings and is configured to form a pattern corresponding to the matrix of cell openings in the extrusion die; and smoothing the electrode so that the surface roughness (Ra) of the electrode is about 1 to about 50 μm.

[0042] In the 37th aspect according to the preceding paragraph, the smoothing of the electrode may include insert electro-discharge machining the electrode using a secondary electrode.

[0043] In the 38th aspect according to any of the preceding two paragraphs, smoothing the surface of the electrode may include machining the electrode using a secondary electrode in a pulsed salt electrochemical machining process.

[0044] In a 39th aspect according to any three of the preceding paragraphs, smoothing the electrode may include smoothing the electrode so that the surface roughness of the electrode is about 1 to about 20 μm.

[0045] In aspect 40, an additively manufactured electrode capable of forming a honeycomb extrusion die comprises: a base having one or more internal passages configured for circulation of a fluid used in electrospark machining, and a network extending from the base and defining a matrix of cell openings, wherein the matrix of cell openings comprises a first zone of cell openings and a second zone of cell openings, wherein at least one of the size and shape of the first zone of cell openings and the second zone of cell openings are different, and wherein the network is configured to form a pattern on the extrusion die corresponding to the matrix of cell openings.

[0046] In a 41st aspect, a method for manufacturing an electrode comprises: applying laser energy to an initial layer of a forming powder comprising tungsten powder and copper powder to form a fused layer of tungsten infiltrated by copper; depositing an additive layer of the forming powder on the fused layer and applying laser energy to the additive layer to form another fused layer of tungsten infiltrated by copper, which is also fused to the previous fused layer; and repeating the deposition of additive layers and corresponding application of laser energy to form a multi-layer fused layer in the form of an interconnected network of tungsten infiltrated by copper, wherein the applied laser energy is about 1 to about 10 J / mm 2 . BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 is a top view of an electrode according to an embodiment.

[0048] Figure 2 is a perspective view of an electrode according to an embodiment.

[0049] Figure 3 is a perspective view of a portion of an extrusion die formed using electrodes according to an embodiment.

[0050] Figure 4 is a top view of an electrode according to an embodiment.

[0051] Figures 5A-5F is a diagram of a pattern of electrodes according to an embodiment.

[0052] Figure 6 is a diagram of electrodes for an electrospark machining operation according to an embodiment.

[0053] Figure 7 is a diagram of the microstructure of a mixture of tungsten and copper according to an embodiment.

[0054] Figure 8 is a picture of an unpolished surface of a mixture of tungsten and copper having holes according to an embodiment.

[0055] Fig. 9 is a diagram of a continuous tungsten matrix according to an embodiment.

[0056] Fig.10 is a perspective view of a portion of a network of electrodes after the electrodes have been smoothed according to an embodiment.

[0057] Fig.11 is a picture of the rough surface of the electrode network before smoothing.

[0058] Fig.12 is a perspective view of a secondary electrode for smoothing an electrode according to an embodiment.

[0059] Fig.13 is a flow chart of a method for forming an electrode for preparing a honeycomb extrusion die according to an embodiment. DETAILED DESCRIPTION

[0060] The present invention will now be described in detail with reference to the embodiments shown in the accompanying drawings. References to "one embodiment", "an embodiment", "an exemplary embodiment", etc. indicate that the embodiment described may include specific features, structures, or characteristics, but not every embodiment necessarily includes the specific features, structures, or characteristics. In addition, such expressions do not necessarily refer to the same embodiment. In addition, when a specific feature, structure, or characteristic is described in conjunction with an embodiment, it means that a person skilled in the art has the ability to affect such features, structures, or characteristics in conjunction with other embodiments, whether or not explicitly described.

[0061] In some wire EDM manufacturing processes, linear metal (or other conductive material) wires are used to cut features (e.g., slots or grooves) in the discharge face of an extrusion die. Since the wire is linear, only linear slots can be formed on the face of the extrusion die, which limits the types of patterns and geometric morphologies that can be formed in the die face. For example, using wire EDM, a honeycomb extrusion die with a matrix of hexagonal cell openings cannot be produced. Using wire EDM, an extrusion die that forms different cell opening areas with varying sizes or cross-sectional shapes is also shown. However, it may be desirable to have an extrusion die with other geometric morphologies to form extruded products with complex honeycomb shapes (e.g., hexagonal cells, circular cells, varying sizes / shapes, etc.). Such extruded products can be used in a variety of applications, such as for the treatment of fluid flows (e.g., vehicle engine exhaust flows). For vehicle engine exhaust flows, the extruded products can be arranged as wall-flow filters (which have channels that are alternately blocked at the inlet and outlet ends) and / or catalyst substrates for catalytic converters. Modification of the extruded article geometry can be used to provide improved performance parameters such as air flow, soot loading capacity, filtration efficiency, and pressure drop under different operating conditions.

[0062] Insertion or "immersion" EDM (referred to herein as "insert EDM") can be used to form a honeycomb extrusion die head with a more complex honeycomb pattern (which cannot be manufactured by wire EDM). In insert EDM, an electrode is provided with a specific structure for forming a honeycomb pattern in a workpiece. The workpiece is placed in a dielectric fluid (e.g., oil or deionized water). A power source generates an electric potential between the electrode and the workpiece. As the electrode approaches the workpiece, a series of discharges between the electrode and the workpiece erode the surface of the workpiece to provide the workpiece with a structure based on the electrode structure (e.g., forming a narrow groove that is a "negative mold" of the electrode pattern).

[0063] Similarly, electrochemical machining (ECM) can be used to prepare extrusion dies with complex geometries. In ECM, an electric current is passed through an electrode (cathode) and a workpiece (anode). An electrolyte fluid is introduced between the electrode and the workpiece, and the electrolyte fluid transfers charge between the electrode and the workpiece. As the electrode approaches the workpiece, the workpiece corrodes, and the corroded part of the workpiece is carried away by the electrolyte fluid. This process continues until the workpiece has a shape corresponding to the electrode. ECM can be performed using a continuous current or a pulsed current (p-ECM).

[0064] Although insert EDM and ECM can form honeycomb extrusion dies with complex geometric morphology, these processes have defects. For example, it may be very time-consuming to prepare electrodes (for example, by a combination of drilling, grinding, wire EDM and / or other operations). In addition, such subtractive manufacturing methods cannot be used to form electrodes with internal channels. Due to the time, cost and complexity of forming electrodes, electrodes corresponding to the entire discharge face of the expected extrusion die cannot be manufactured. On the contrary, electrodes corresponding to only a portion of the discharge face can be used, which must be repeatedly moved to form each part of the extrusion die individually until the entire face of the extrusion die has the desired style. As a result, the slots in the various parts of the extrusion die, or the interfaces or boundaries between adjacent parts may have slight changes, asymmetry, discontinuity and other irregularities or defects, which is undesirable.

[0065] Embodiments of the present invention relate to methods of forming an electrode by means of additive manufacturing techniques. The additively manufactured electrode comprises a base and a network of matrices defining pore openings, such that the electrode can be used to form a honeycomb extrusion die. The method also includes smoothing the network of additively manufactured electrodes to reduce the surface roughness of the additively manufactured electrodes.

[0066] For example, Figure 1 1 is an embodiment of an additively manufactured electrode 100 for forming a honeycomb extrusion die. The electrode 100 includes a base 120 and a network 140 extending from the base 120. Specifically, the network 140 extends from a surface 122 of the base 120 and may be perpendicular to the surface 122 of the base 120. The base 120 may be any of a variety of shapes, such as a cylindrical block or plate, or a square or rectangular block, such as Figure 2 The base 120 is configured to connect the electrode 100 to a device for performing an EDM or ECM operation.

[0067] The network 140 of electrodes 100 defines a matrix of pore openings 160, such as Figure 1as best shown. When the electrode 100 is used for EDM or ECM, the network 140 provides a honeycomb pattern to a workpiece (e.g., an extrusion die) that corresponds to the shape and construction of the network 140. As described herein, additive manufacturing of the electrode 100 facilitates flexible size and shape adjustment of the network 140, thereby forming the entire face of the extrusion die at one time, which greatly reduces the amount of time required to machine the extrusion die while minimizing defects compared to the EDM or ECM methods described above. The matrix of cell openings 160 can be of uniform size and shape, so that each cell opening 160 has the same shape and scale. The cell openings 160 of the network 140 can have any of a variety of transverse cross-sectional shapes, such as: triangles, circles, ellipses, squares, rectangles, pentagons, hexagons, or wedge-shaped cakes, etc. In Figure 1 In some embodiments, the electrode 100 is formed to have a network 140 that defines a matrix of pore openings 160, each pore opening having a hexagonal transverse cross-section. However, in some embodiments, the network 140 defines a matrix of non-uniform pore openings 160. Thus, the matrix of pore openings 160 can include openings of different sizes, for example: a matrix of pore openings that alternate between a first size and a second size. In some embodiments, the thickness of the network 140 is gradually tapered toward the base 120, which can help improve fluid distribution when the electrode 100 is used for EDM or ECM. In addition, the thickness of the network 140 can vary in different portions of the network 140, so that the network 140 has regions of different geometric morphologies intermingled (e.g., thereby facilitating the transition from a pore opening having a first size / shape to an adjacent pore opening having a different size / shape).

[0068] The electrode 100 is configured to form a honeycomb pattern in the discharge face 310 of the extrusion die 300, a portion of which is as shown in FIG. Figure 3 The discharge face 310 includes a plurality of pins 330 separated by a plurality of slots 320 through which the extrudable material can flow. Figure 3 Only a few pins 330 are shown, but it is apparent that the extrusion die may include hundreds or even thousands of pins 330 arranged in a desired pattern relative to the slots 320 at the discharge face 310. The extrusion die 300 also includes a plurality of feed holes 360 that provide extrudable material to the slots 320 of the discharge face 310, so that the extrudable material flows through the slots 320 and around the pins 330, producing an extruded product having a honeycomb pattern corresponding to the pattern of the slots 320.

[0069] When the electrode 100 is used to produce an extrusion die, such as by EDM or ECM, the honeycomb pattern of the extrusion die corresponds to the geometry of the network 140 and the matrix of cell openings 160 of the electrode 100. Specifically, the network 140 of the electrode 100 forms slots (e.g., slots 320 of the extrusion die 300), while the pins (e.g., pins 330 of the extrusion die 300) are shaped like the cell openings 160 of the electrode 100. In this way, the electrode 100 can be used to form an extrusion die whose geometry is a negative or negative mold of the network 140 and the cell openings 160 of the electrode 100.

[0070] Since additive manufacturing can be used to manufacture electrodes with complex geometries, electrodes with multiple regions, each with different geometries and dimensions, can be formed. Figure 4 , an electrode 400 is shown having a first zone 450 of a channel opening 460 and a second zone 470 of a channel opening 480. The first zone 450 is annular and surrounds the circular second zone 470 in a concentric manner. In other embodiments, the zones of the electrode occupy various other shapes, sizes, or areas of the electrode. For example, the first zone can be the first half or quarter of the electrode, while the second zone or other zones can occupy the opposite half or separate quarter of the electrode. In addition, in some embodiments, the height of the network in the first zone (which is measured as the distance that the network extends from the base surface in a direction perpendicular to the base surface) is less than the height of the network in the second zone, thereby promoting uniform distribution of the dielectric fluid or electrolyte fluid throughout the electrode during the EDM or ECM process, respectively.

[0071] exist Figure 4 In the embodiment, the first zone 450 of the electrode 400 includes a network 440a defining a matrix of pore openings 460, which includes a first cross-sectional shape and a first size or dimension. The second zone 470 includes a network 440b defining a matrix of pore openings 480, which includes a second cross-sectional shape and a second size or dimension. The pore openings 460, 480 of the first and second zones 450, 470 have square transverse cross-sectional shapes, respectively. However, the size or dimension of the pore openings 460 of the first zone 450 is smaller than the pore openings 480 of the second zone 470. The size of the pore openings refers to the transverse cross-sectional area of ​​the pore openings defined by the networks 440a, 440b, for example, the pore openings 460, 480 are in Figure 4In other words, the density of the cell openings 460 of the first zone 450 is higher than that of the second zone 470. In some embodiments, the cross-sectional shape of the cell openings 460 of the first zone 450 is different from the cross-sectional shape of the cell openings 480 of the second zone 470. For example, the first zone may have cell openings of a first cross-sectional shape (e.g., square), while the second zone may have cell openings of a second cross-sectional shape (e.g., triangle) that is different from the first cross-sectional shape.

[0072] Using electrodes as described herein, an extrusion die can be formed. For example, Figures 5A-5F Various styles of extrusion dies are shown. Figure 5A In the embodiment, the extrusion die 510 has a plurality of hexagonal pins 515. Figure 5B In the embodiment, the extrusion die 520 includes a first pin 522 of a first size and a second pin 524 of a second size, wherein the first size is different from the second size, and the first and second pins are arranged in an alternating pattern. Figure 5C In the embodiment, the extrusion die 530 has a mesh pattern of wedge-shaped pins 535 defining concentric circular slots and radially extending slots. Figure 5D In FIG. 5 , the extrusion die 540 includes a square pin 542 and a triangular pin 544. Figure 5E In the embodiment, the extrusion die 550 includes circular pins 555, which may be connected by ribs that provide structural support to the circular pins 555. Fig. 5F In FIG. 5 , the extrusion die 560 includes a series of square pins 562 and rectangular pins 564 .

[0073] In some embodiments, the electrode 600 is formed so that the base 620 has an internal channel 610, such as Figure 6 As shown. Electrodes with internal channels cannot be easily formed using conventional wire EDM methods. The internal channel 610 may be useful for a fluid 1000 (e.g., a dielectric fluid used in electrospark machining using the electrode 600). The internal channel 610 may have an inlet 612 for connection to an external device (e.g., a pump or a vacuum source), and an outlet 614 on a surface 622 of the electrode 600 on which the network 640 is placed. The fluid 1000 may be circulated through the internal channel 610 to flush or remove material eroded from the workpiece 300 by the machining process. For example, a pump may provide a dielectric fluid through the internal channel 610 to the network 640 of the electrode 600, thereby providing a dielectric fluid in a cutting zone where the network 640 meets the workpiece 300, and a vacuum source may suck away the used dielectric fluid and eroded material from the cutting zone through a separate internal channel 610.

[0074] According to the embodiments disclosed herein, an electrode 100 having a honeycomb pattern is formed by an additive manufacturing process (also referred to as a three-dimensional (3D) printing process), such as Figure 1 Additive manufacturing can form electrodes 100 with complex geometries that cannot be achieved using conventional subtractive manufacturing or machining techniques (e.g., EDM, ECM, or milling and drilling operations) used to form electrodes. Additive manufacturing can also enable faster electrode production than using conventional subtractive techniques.

[0075] Any of a variety of additive manufacturing processes can be used to form the electrode 100, including: laser or electron beam powder bed fusion (PBF) techniques, including: selective laser melting (SLM), selective laser sintering (SLS), direct metal laser sintering (DMLS) and electron beam melting (EBM), powder-free bed directed energy deposition (DED) schemes, material jetting, binder jetting, and other additive manufacturing techniques such as stereolithography, as well as hybrid schemes that combine additive manufacturing and conventional machining. In addition, the electrode 100 can be formed from any of a variety of materials, including: brass, bronze, copper, tungsten, nickel, rhenium, thorium, lanthanum, silver, zinc, silicon or carbide (e.g., silicon carbide, brass-infiltrated silicon carbide, tungsten carbide) or blends, composites or alloys thereof, as well as other materials suitable for forming electrodes.

[0076] In some embodiments, the electrode 100 is made of a powder mixture of tungsten and copper. Tungsten-copper (W-Cu) mixtures are well suited for forming electrodes for insert EDM because copper is conductive and tungsten provides wear resistance and spark erosion resistance. However, tungsten-copper may be difficult to use in additive manufacturing processes. For example, copper and tungsten are immiscible and do not form a binary alloy system. In addition, there is no temperature at which copper and tungsten are in equilibrium in the same phase because, due to the high melting point of tungsten, copper is vapor or gaseous when tungsten is in a liquid state. Existing processes for forming a tungsten body and subsequently infiltrating the tungsten body with copper are time-consuming and expensive. In addition, such processes cannot select the resulting shape or geometry, and instead, the resulting tungsten-copper solid block must be processed by additional forming techniques (e.g., wire EDM and insert EDM, etc.).

[0077] In some embodiments, the electrode 100 is additively manufactured using a tungsten-copper mixture by direct additive manufacturing of a mixture of pure tungsten and copper powders (eg, by laser powder bed fusion (PBF) technology).

[0078] Laser PBF is a method of forming a three-dimensional object in a layer-by-layer manner using thermal energy sufficient to induce fusion of one or more materials. A digital representation of the object is produced, which presents the object as a series of layers or cross-sections. In laser PBF, a layer of a first material (e.g., a metal powder (e.g., tungsten powder or copper powder, etc.)) can be deposited on the surface of a manufacturing platform. A second material (e.g., a metal powder (e.g., copper powder or tungsten powder, etc.)) can be deposited after or simultaneously with the first material. The metal powder can also be deposited on the platform as a mixture of metal powders (e.g., a mixture of copper and tungsten powders). The deposited materials are deposited as an unfused layer on the surface of the platform. Then, using a laser-based heat source, energy is selectively directed to the layer to induce fusion of the metal powder (e.g., tungsten and copper powder), thereby forming a first fused layer having a desired shape based on the digital representation. Subsequent layers of metal powder can then be deposited on top of the first fused layer, and the subsequent layers are selectively fused by the laser based on the digital representation of the object. The process of depositing layers and fusing each layer is repeated until all layers of the article are formed, thereby producing an object corresponding to the digital representation.

[0079] However, in other embodiments, alternative additive manufacturing techniques as described herein may be used. The mixture may contain about 70 to 90 weight percent tungsten, with the remainder being copper. In some embodiments, the tungsten-copper mixture may contain 75 weight percent tungsten and 25 weight percent copper. It will be appreciated by those skilled in the art that the amounts of tungsten and copper may be selected based on the desired properties of the resulting electrode.

[0080] In some embodiments, the particle size distribution of tungsten and copper particles used in laser powder bed fusion techniques is about 15 to 55 microns. In some embodiments, the particle size distribution includes particles of 25 microns or less. A fine particle size (e.g., less than 25 microns) can be used to help form a continuous network of tungsten in the electrode. A continuous network of tungsten is required to provide spark erosion resistance to the resulting electrode.

[0081] In the direct additive manufacturing technique described herein, tungsten and copper are subjected to two processing modes: liquid phase sintering (LPS) and tungsten melting. In LPS, the molten copper rearranges the unmelted tungsten particles. As a result, a mixture 700 is formed, which includes isolated tungsten particles 720 dispersed in a continuous copper matrix 710, such as Figure 7 As shown. The mixture 700 formed in LPS provides good electrical conductivity due to the copper matrix. However, in LPS, the tungsten is still solid, and therefore the tungsten particles are not fused together and a continuous network of tungsten is not formed.

[0082] When tungsten melts, it melts, thereby forming a continuous network of tungsten necessary for forming an electrode with good wear resistance. However, in the case of high concentrations of tungsten, the tungsten may melt and form spheres 760, which may result in a mixture 750 having pores 770, such as Figure 8 As a result, the density of the mixture 750 may be lower than that of the mixture formed in LPS. Therefore, in order to obtain a continuous network of tungsten without significant density loss, it may be desirable to perform additive manufacturing using a laser energy window in which both LPS and tungsten melting can occur simultaneously.

[0083] According to the embodiments disclosed herein, the laser energy used for laser PBF may be about 1 to about 10 J / mm 2 In this range, a relatively dense and continuous tungsten network can be achieved. When the laser energy drops below about 1J / mm 2 , no tungsten melting may occur. In contrast, when the laser energy is higher than about 10 J / mm 2 When tungsten is melted, the tungsten-copper binary system mainly undergoes tungsten melting.

[0084] In some embodiments, the additive manufacturing of the electrode includes: additively manufacturing the porous tungsten structure 900 (such as Fig. 9 ), followed by infiltration of the porous tungsten structure with molten copper to form an electrode. Various methods of infiltrating a porous tungsten structure with molten copper are known, including: spontaneous or pressurized infiltration, centrifugal infiltration, ultrasonically driven or assisted infiltration, or Lorentz force infiltration. In contrast to the direct additive manufacturing of a mixture of tungsten and copper powders described above, additive manufacturing of the porous tungsten structure and subsequent copper infiltration ensures the formation of a continuous network of tungsten 910. Copper infiltration can be performed using any of a variety of conventional methods, such as by placing the porous tungsten structure in a mold and filling the mold with molten copper. To facilitate copper infiltration, the infiltration can be performed under pressure.

[0085] In some embodiments, a porous tungsten structure is additively manufactured using a powder bed additive manufacturing technique (e.g., laser PBF). The porous tungsten structure can be additively manufactured to provide an electrode having a desired shape and configuration, wherein the porous tungsten structure includes an interconnected network of pores. The particle size distribution of the tungsten particles can be about 15 to about 55 microns, and can be about 25 microns or less. In addition, in order to control the porosity or density of the porous tungsten structure, the laser energy range used for laser PBF or other similar additive manufacturing techniques can be about 1 to 10 J / mm 2 The inventors have found that as the laser energy increases, the relative density of the porous tungsten structure generally decreases, for example as a result of tungsten balling. To enable subsequent copper infiltration, the resulting porous tungsten structure can be produced to have a relative density level of about 75%, about 80%, about 85%, about 90%, or about 95%.

[0086] In some embodiments, the electrode formed by the additive manufacturing process as described herein has not only the desired geometry and configuration (e.g., a network defining a matrix of cell openings and any internal channels), but also has a high surface roughness (e.g., a high surface roughness that is undesirable for manufacturing an extrusion die for a particular application). As used herein, the term "surface roughness" or "roughness" shall refer to the arithmetic mean roughness Ra. Fig.10 A network 140 of a portion of an electrode 100 formed by additive manufacturing is shown. An inner surface 144 of the network 140 produced by additive manufacturing may have a surface roughness Ra of about 100 μm or more. For example, Fig.11 The enlarged view shows that the inner surface of the electrode 100 obtained by additive manufacturing has high surface roughness. According to the embodiments disclosed herein, in order to use the electrode 100 for the subsequent extrusion die manufacturing process, the electrode 100 formed by additive manufacturing is smoothed to reduce the surface roughness.

[0087] Specifically, the inner surface 144 of the network 140 surrounding the cell openings 160 can be smoothed. For example, if the electrode 100 has a high surface roughness, an extrusion die formed using a rough electrode will also have a high surface roughness. The smooth surface of the features of the extrusion die (e.g., the pins of the extrusion die near the discharge face) can be useful for promoting more uniform flow throughout the die and / or for extruding a more uniformly sized product due to the interaction of the extrudable material flowing through the channels of the extrusion die defined between the side surfaces of the pins.

[0088] In some embodiments, the additively manufactured electrode 100 is smoothed to provide a network 140 having a surface roughness Ra of about 1 to about 50 μm, about 1 to about 40 μm, about 1 to about 30 μm, about 1 to about 20 μm, or about 1 to about 10 μm. However, other roughness values ​​may be used in other embodiments depending on the parameters of the extrusion process (e.g., the composition or batch mixture of the material to be extruded, the dimensions of the slots / pins in the extrusion die, and other parameters).

[0089] The electrode 100 formed by additive manufacturing can be smoothed by any of a variety of methods, including: insert EDM, wire EDM, electrochemical machining (ECM), pulsed salt electrochemical machining (p-ECM), grinding, micromachining, or a combination thereof. Specifically, the inner surface 144 of the network 140 of the electrode 100 can be smoothed by the methods listed above. Compared to forming the entire electrode using EDM or ECM methods, the operation of smoothing the electrode obtained by additive manufacturing can be performed in a faster and less expensive manner. The smoothing operation can also serve to reduce the size of the electrode 100 (e.g., the thickness t1 of the network) to the final size required for the electrode 100 (e.g., achieving a deliberate "rough cut" of an oversized extrusion die head and then smoothing to reduce the thickness).

[0090] In some embodiments, the secondary electrode 200 is used to smooth the electrode 100 by EDM or ECM, for example, Fig.12 As shown. The secondary electrode 200 includes a base 220 and a plurality of pins 260 extending from a surface 222 of the base 220. The pins 260 of the secondary electrode 200 are shaped and arranged so as to match the matrix of the channel openings 160 and the network 140 of the electrode 100. "Matching" means that the pins 260 generally correspond to the size and shape of the channel openings 160. For example, if the electrode 100 has a matrix of channel openings with hexagonal cross-sectional areas, the pins 260 of the secondary electrode 200 are also formed to have hexagonal cross-sectional areas. The size of the pins 260 is adjusted to fit within the channel openings 160 of the electrode 100 with a close tolerance, thereby smoothing the inner surface 144 of the network 140. Therefore, when the pins 260 of the secondary electrode 200 are inserted into the channel openings of the electrode 100, the surface 264 of the pins 260 will be adjacent to the inner surface 144 of the network 140 of the electrode 100.

[0091] The secondary electrode 200 may be formed by any of the various methods described herein, such as by additive manufacturing, wire EDM (depending on the desired pin shape), pulsed EDM, ECM, or p-ECM. In addition, the secondary electrode 200 may be formed from any of a variety of materials. The secondary electrode 200 may have a low surface roughness to produce an electrode with low roughness. The secondary electrode may be relatively smooth, i.e., have a low surface roughness (e.g., relative to the surface roughness of the electrode 100), such as particularly when the secondary electrode 200 is used in an insert EDM process to smooth the electrode 100.

[0092] In some embodiments, Fig.13As shown, a method of forming an electrode by additive manufacturing 1300 is provided. An additively manufactured electrode 1310 is used to form a secondary electrode from a metal blank (e.g., a stainless steel blank). In such embodiments, the additively manufactured electrode is used as a cathode in a p-ECM process, thereby machining a honeycomb pattern in the metal blank to form a secondary electrode having a negative mold pattern of the additively manufactured electrode 1320. The secondary electrode is then used to smooth the additively manufactured electrode 1330. The secondary electrode can be used as a cathode in a p-ECM process to smooth the electrode. The secondary electrode used for p-ECM can smooth the network of the additively manufactured electrode so that the electrode has a desired surface roughness Ra within about ±0.05 μm. Using p-ECM to smooth the electrode can smooth the electrode more quickly than conventional machining methods (e.g., wire EDM that requires smoothing each channel at a time), and by using p-ECM, a matrix of channel openings can be smoothed simultaneously.

[0093] In some embodiments, a coating is applied to the surface of the smoothed electrode 1340. In some embodiments, the coating is applied by chemical vapor deposition, physical vapor deposition, or by atomic layer precipitation. The coating can also be applied by an electrostatic coating process (e.g., by electrostatic painting or powder coating). In an electrostatic coating process, an electric charge is used to create a magnetic bond between the paint (e.g., a coating material) and the object to be coated (e.g., an electrode). In powder coating, after the coating is applied to the substrate, the coating is further baked in an oven. In some embodiments, the coating is an electrically insulating coating that is applied to the inner surface of the smoothed electrode (e.g., such as Fig.10 The coating is preferably amorphous silicon, polyparaxylene, aluminum oxide, silicon carbide, or diamond-like carbon (DLC), among other coatings.

[0094] Unless otherwise expressly stated, it is not intended that any method described herein be construed as requiring that its steps be performed in a specific order. Therefore, when a method claim does not actually state that its steps follow a certain order or it does not specifically indicate in any other way in the claims or description that the steps are limited to a specific order, it is not intended to imply any particular order.

[0095] It will be apparent to those skilled in the art that various modifications and variations may be made without departing from the spirit or scope of the illustrated embodiments. Because those skilled in the art may conceive of various modifications, combinations, sub-combinations, and variations of the disclosed embodiments that incorporate the spirit and substance of the embodiments, the disclosed embodiments should be considered to include all of the contents within the scope of the appended claims and their equivalents.

[0096] Unless otherwise noted in a specific case, the numerical ranges stated herein include upper and lower limits, and the range is intended to include its endpoints and all integers and fractions within the range. When a range is defined, it is not intended to limit the scope of the claim to the specific values ​​stated. In addition, when a certain amount, concentration, or other value or parameter is stated in the form of a range, one or more preferred ranges, or a preferred upper numerical limit and a preferred lower numerical limit, it should be understood that it is equivalent to specifically revealing any range by combining any pair of upper range limits or preferred numerical values ​​with any lower range limit or preferred numerical value, without considering whether this paired combination is specifically disclosed. Finally, when the term "about" is used to describe the value or endpoint of a range, it should be understood that the disclosure includes the specific value or endpoint referenced. Regardless of whether the endpoint of a numerical value or range is stated "about", the endpoint of the numerical value or range is intended to include two embodiments: one is modified with "about", and one is not modified with "about".

[0097] As used herein, the term "about" indicates that amounts, sizes, ranges, formulations, parameters and other variables and characteristics are not and need not be exact, but may be approximate and / or larger or smaller as necessary, reflecting tolerances, conversion factors, rounding and measurement errors, etc., and other factors known to those skilled in the art.

[0098] As used herein, the terms "substantially," "substantially," and variations thereof are intended to indicate that the described feature is the same or approximately the same as the value or description. For example, a "substantially planar" surface is intended to indicate a planar or approximately planar surface.

[0099] The embodiments of the present invention have been described above by means of functional building blocks that show the execution of specific functions and their relationships. For ease of description, the boundaries of these functional building blocks are arbitrarily defined herein. Alternative boundaries can be defined as long as the specified functions and their relationships are appropriately executed.

[0100] It is to be understood that the phraseology and terminology used herein is for the purpose of description rather than limitation.The breadth and scope of the present disclosure should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.

Claims

1. A method for additively manufacturing a copper-tungsten electrode, the method comprising: The first electrode is formed as a series of layers, each layer of the series of layers being formed as follows: depositing a powder layer on the build platform or on a previous layer in the series, the powder layer comprising tungsten powder and copper powder; and Laser applied 1J / mm to the powder layer 2 Up to 10J / mm 2 The laser energy causes the powder layers to fuse; wherein the first electrode comprises an interconnected network of tungsten infiltrated with copper formed by the series of layers fused together, the first electrode further comprising a base and a network extending therefrom, the network defining a matrix of cell openings; forming a second electrode through the first electrode, the second electrode comprising a negative mold pattern of the first electrode; and The second electrode is inserted into the matrix of the channel openings of the first electrode and the surface of the first electrode is smoothed by the second electrode.

2. The method of claim 1, wherein: The relative density of the first electrode is at least 75%.

3. The method of claim 2, wherein: The relative density of the first electrode is at least 90%.

4. The method according to any one of claims 1 to 3, wherein: The tungsten powder and the copper powder each have a particle size distribution of 15 μm to 55 μm.

5. The method according to any one of claims 1 to 3, wherein: The tungsten powder and the copper powder each have a particle size distribution of 25 μm or less.

6. The method according to any one of claims 1 to 3, wherein: The amount of tungsten powder present in the powder layer is 70 wt % to 90 wt %.

7. The method according to any one of claims 1 to 3, wherein: The amount of tungsten powder present in the powder layer was 75% by weight, and the amount of copper powder present was 25% by weight.

8. The method according to any one of claims 1 to 3, wherein: The depositing of the powder layer includes: depositing one of tungsten powder or copper powder, and subsequently depositing the other of tungsten powder or copper powder.

9. The method according to any one of claims 1 to 3, wherein: The deposited powder layer includes depositing a mixture of copper powder and tungsten powder.

10. The method of claim 1, wherein: Forming the first electrode also includes forming one or more internal channels in a base of the first electrode.

11. The method of claim 1, wherein: The smoothing of the first electrode by the second electrode comprises insert electric discharge machining or electrochemical machining.

12. The method of claim 11, wherein: Smoothing the first electrode includes smoothing the first electrode so that the surface roughness of the first electrode is 1 μm to 50 μm.

13. An electrode formed by the method according to any one of claims 1 to 3.

14. A method for manufacturing an electrode, comprising: The porous tungsten structure is formed in a layer-by-layer manner, wherein each layer is formed as follows: depositing a layer of tungsten powder; and Before deposition of subsequent layers, the laser energy used was 1 J / mm 2 Up to 10J / mm 2 The laser selectively fuses tungsten powder; infiltrating the porous tungsten structure with molten copper to form a first electrode comprising a porous tungsten structure infiltrated with copper, the first electrode comprising a base and a network extending therefrom, the network defining a matrix of cell openings; forming a second electrode through the first electrode, the second electrode comprising a negative mold pattern of the first electrode; and The second electrode is inserted into the matrix of the channel openings of the first electrode and the surface of the first electrode is smoothed by the second electrode.

15. The method of claim 14, wherein: The relative density level of the porous tungsten structure is at least 75%.

16. The method according to any one of claims 14 or 15, wherein: The tungsten powder has a particle size distribution of 15 μm to 55 μm.

17. The method according to any one of claims 14 to 15, wherein: Infiltration of the porous tungsten structure with molten copper is performed by one of the following means: spontaneous or pressurized infiltration, centrifugal infiltration, ultrasonically driven or assisted infiltration, or Lorentz force infiltration.

18. The method according to any one of claims 14 to 15, wherein: The smoothing of the first electrode comprises insert electric discharge machining or electrochemical machining.

19. A method for forming an electrode used in a honeycomb extrusion die, comprising: forming, by an additive manufacturing process, a first electrode comprising a base, the base including a network extending therefrom, the network defining a matrix of channel openings; forming a second electrode through the first electrode, the second electrode comprising a negative mold pattern of the first electrode; as well as The second electrode is inserted into the matrix of channel openings of the first electrode and the surface of the first electrode is smoothed using the second electrode, the negative mold pattern of the second electrode includes a plurality of pins, and the shape and arrangement of the plurality of pins match the matrix of channel openings.

20. The method of claim 19, wherein: Forming the first electrode includes forming the first electrode from a powder mixture of tungsten and copper in a laser powder bed fusion process.

21. The method of claim 20, wherein: The mixture of tungsten and copper includes tungsten particles and copper particles, each having a particle size distribution of 15 μm to 55 μm.

22. The method of any one of claims 20 or 21, wherein: Using 1J / mm 2 Up to 10J / mm 2 The laser can carry out the laser powder bed fusion process.

23. The method of claim 19, wherein: Forming the first electrode includes: Using tungsten powder to form a porous body by laser powder bed fusion process, and The porous body is infiltrated with molten copper.

24. The method of any one of claims 19 to 21, wherein: Forming the first electrode includes forming a first region of channel openings having a first size, and a second region of channel openings having a second size different from the first size.

25. The method of any one of claims 19 to 21, wherein: Forming the first electrode includes forming a first region of the channel opening having a first shape, and a second region of the channel opening having a second shape different from the first shape.

26. The method of any one of claims 19 to 21, wherein: Forming the first electrode includes forming a network such that each cell opening in the matrix of cell openings comprises a hexagonal cross-sectional area.

27. The method of any one of claims 19 to 21, wherein: Forming the first electrode includes forming a base to define one or more internal passages configured for circulation of a fluid used in electro-spark machining.

28. The method of any one of claims 19 to 21, wherein: Forming the second electrode includes machining a metal blank using the first electrode in a first pulsed salt electrochemical machining process.

29. The method of claim 28, wherein: Smoothing the surface of the first electrode includes machining the first electrode using the second electrode in a second pulsed salt electrochemical machining process.

30. The method of any one of claims 19 to 21, wherein: Smoothing the surface of the first electrode includes insert electric spark machining.

31. The method of any one of claims 19 to 21, wherein: Smoothing the surface of the first electrode includes wire electrical discharge machining.

32. The method of any one of claims 19-21, further comprising applying an electrically insulating coating to the first electrode after smoothing the electrode surface.

33. An electrode formed by the method of any one of claims 19-21.

34. A method for forming an electrode for use in a honeycomb extrusion die by electrospark machining, comprising: forming a first electrode by means of an additive manufacturing process, the first electrode comprising a base and a network extending therefrom, the network defining a matrix of cell openings and configured to form a pattern corresponding to the matrix of cell openings in an extrusion die; forming a second electrode through the first electrode, the second electrode comprising a negative mold pattern of the first electrode; The second electrode is inserted into the matrix of the channel openings of the first electrode and the first electrode is smoothed by the second electrode so that the surface roughness Ra of the first electrode is within ±0.05 μm of the predetermined surface roughness.

35. The method of claim 34, wherein: The smoothing of the first electrode includes insert electro-spark machining.

36. The method of any one of claims 34-35, wherein: The smoothing of the first electrode comprises a pulsed salt electrochemical machining process.

37. The method of any one of claims 34-35, wherein: The smoothing of the first electrode includes smoothing the first electrode so that the surface roughness of the first electrode is 1 to 20 μm.

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