An adaptive array functionally-graded electrode and method of manufacture

Abstract

The application relates to a self-adaptive array type function gradient electrode and a manufacturing method thereof, and belongs to the technical field of mechanical processing. The electrode is provided with equidistantly arranged conical discharge ends; the inner core is sequentially provided with a refractory layer, a high-conductivity layer, a stress release layer and a red copper base body from outside to inside; and the four circumferential sides of the inner core are sequentially coated with a side wall refractory layer and a fine-grain transition layer from outside to inside. The electrode structure has the advantages of controllable cost, high structural reliability, high hole manufacturing yield and consistency, can effectively prolong the service life of the electrode, and promotes efficient and low-consumption spark machining manufacturing of group hole structures.

Description

Technical Field

[0001] This invention relates to an adaptive array-type functional gradient electrode and its manufacturing method, belonging to the field of machining technology. Background Technology

[0002] Electrical discharge machining (EDM) is a specialized electrical machining technology that removes material through a high-temperature, continuous pulsed discharge process between an electrode and a workpiece. It boasts a wide range of applications and high processing efficiency, making it the primary method for creating shaped holes in metal parts in the aerospace field. It can efficiently and accurately create blind holes, curved irregular holes, and through holes according to design structure and performance requirements. With the development of aerospace equipment, the number and types of holes in large, integrated components are increasing. Correspondingly, EDM hole-making primarily uses arrayed electrodes as the discharge end, where the surface of a copper electrode contains several uniformly long discharge teeth. These equidistant, uniformly distributed discharge teeth simultaneously arc and discharge near the workpiece surface, ablating the material to create the shaped hole. Benefiting from the multi-electrode tooth characteristic of arrayed electrodes, it has significant advantages in batch hole-making. Studies show that for large curved components containing thousands or even tens of thousands of irregular holes, the hole-making time accounts for more than one-third of the entire component's forming time. Therefore, to meet the demand for efficient component processing, EDM hole-making equipment needs to possess long-term, continuous operational stability. Arrayed electrodes, as a crucial component in batch hole making, play a key role in determining processing efficiency and quality. However, copper electrodes are prone to severe discharge and burn-off during arc erosion. After cathode spots form on the copper surface, they tend to remain locally, leading to burn-off and shape changes on the electrode tooth surface under extremely high heat input. More seriously, when multiple electrode teeth in a localized area burn off simultaneously, the arc plasma can easily ignite between the teeth, inducing cross-arcs and causing the formation of interconnected holes on the workpiece surface, deteriorating processing quality, and making these interconnected hole defects difficult to repair. Severe arc erosion of the electrodes has become a major factor restricting the long-term operational stability of EDM hole making. Therefore, there is an urgent need to develop new electrode materials and structures with excellent arc erosion resistance.

[0003] Currently, the known arc erosion mechanisms of metal cathodes include evaporation-splash ablation, oxide exfoliation ablation, and non-uniform arc erosion caused by cathode spots. The main approaches to improving the arc erosion resistance of metal cathodes fall into two categories: material modification and structural design. Material modification largely relies on experience, such as replacing the copper electrode with a tungsten electrode (which has a higher melting point and lower work function), or adding 5–10% low work function ceramic phase to the existing copper electrode to resist the severe ablation caused by the arc plasma. Studies show that a low work function phase uniformly distributed in the copper matrix can preferentially act as an electron emission site to ignite the arc during electrode discharge, thereby dispersing the concentrated arc root across the entire electrode surface and reducing the input heat flux density. Furthermore, cathode spots induced by non-metallic phases such as ceramics are classified as Type 1 cathode spots, which have shorter lifetimes and higher migration rates than Type 2 cathode spots on metal surfaces, thus mitigating cathode ablation. When modifying electrodes using a structural design approach, the main focus is on optimizing the structure of the bulk electrode. For example, adding fine cooling channels on the back can facilitate the timely dissipation of arc-input heat through active cooling. Simultaneously, an appropriate anti-ablation layer can be sprayed / electroplated onto the electrode discharge surface to resist arc erosion.

[0004] However, existing electrode material design and structural optimization methods for improving the arc erosion resistance of copper electrodes have certain limitations. While refractory metals such as tungsten and zirconium possess excellent high-temperature resistance and discharge performance, their conductivity is poor, only 1 / 20th that of copper. Furthermore, most refractory metals are hard and brittle, making machining bulk electrodes difficult, leading to increased costs and reduced efficiency. Adding low work function ceramic phases to the copper matrix can improve discharge erosion performance by controlling cathode spot formation and migration behavior, but often results in a deterioration of the electrode's electrical and thermal conductivity. The conductivity and arc erosion resistance of homogeneous alloy electrodes exhibit an intrinsic "inverse relationship," limiting the widespread application of material modification in optimizing electrode service performance. In terms of structural design, existing research mostly focuses on single rod-shaped electrodes or simple sheet cathodes. The bonding strength between the reinforcing layer formed by methods such as cold spraying and the substrate is limited, and the reinforcing layer is prone to detachment and failure after a certain number of cyclic interruptions. Furthermore, surface strengthening techniques such as spraying are unsuitable for EDM electrodes with narrow-diameter irregular holes. After coating preparation, the thickness uniformity of the electrode rod's sidewalls and bottom is poor, and the narrow spacing between the arrayed electrode teeth makes secondary machining difficult. Therefore, current electrode modification methods are not suitable for improving the service performance of arrayed electrodes. Summary of the Invention

[0005] The purpose of this invention is to provide an adaptive array-type functionally graded electrode and its manufacturing method. The array-type electrode comprises several equidistantly arranged conical discharge ends. Each conical structure is a functionally graded structure along both the axial and radial directions. Axially, from the discharge surface inwards, the layers are sequentially a refractory layer, a highly conductive layer, a stress-relieving layer, and a copper substrate. Radially, from the surface inwards, the layers are a refractory layer and a fine-grained transition layer. Utilizing the two-phase functionally graded structure in both the axial and radial directions, a low ablation rate and continuous processing stability are achieved during long-term electrical discharge machining of the array-type electrode, alleviating the severe ablation and interconnection problems encountered in the existing array-type electrode hole-making process.

[0006] The specific manufacturing steps for the corresponding adaptive functional gradient electrode structure are as follows: pretreatment of the copper substrate, alternating deposition of stress relief layer and high conductivity layer, controllable cladding of refractory layer with low heat input, fabrication of arrayed conical structure, deposition of functional layer on the surface of the conical rod, and post-processing. Using this electrode structure can effectively alleviate electrode ablation problems and extend electrode service life, promoting the efficient and low-power electrical discharge machining (EDM) manufacturing of multi-hole structures.

[0007] According to one aspect of this application, an adaptive array functional gradient electrode is provided, the adaptive array functional gradient electrode having equally spaced conical discharge ends;

[0008] The inner core of the cone-shaped discharge end consists of, from the outside to the inside, a refractory layer, a highly conductive layer, a stress-relieving layer, and a copper substrate.

[0009] The inner core is covered from the outside in with a refractory sidewall layer and a fine-grained transition layer.

[0010] When the size of the electrode surface is greater than 500mm×500mm, the height of the cone-shaped discharge end is not less than 55% of the thickness of the electrode, the thickness of the refractory layer is at least 25% of the height of the cone-shaped discharge end, the thickness of the high conductivity layer is 40-80% of the thickness of the refractory layer, the thickness of the stress relief layer is 60-80% of the thickness of the refractory layer, the thickness of the sidewall refractory layer is 6-8% of the short diagonal length of the cross-section of the cone-shaped discharge end, and the thickness of the fine grain transition layer is 4-6% of the short diagonal length of the cross-section of the cone-shaped discharge end.

[0011] When the size of the electrode surface is less than 500mm×500mm, the height of the cone discharge end is not less than 50% of the electrode thickness, the thickness of the refractory layer is at least 20% of the height of the cone discharge end, the thickness of the high conductivity layer is 35-75% of the thickness of the refractory layer, the thickness of the stress relief layer is 50-75% of the thickness of the refractory layer, the thickness of the sidewall refractory layer is 4-6% of the short diagonal length of the cross section of the cone discharge end, and the thickness of the fine grain transition layer is 2-4% of the short diagonal length of the cross section of the cone discharge end.

[0012] The materials of the refractory layer, the sidewall refractory layer, and the fine-grained transition layer are selected from at least one of zirconium, titanium, and tantalum; all of them are high-melting-point, thermochemical electrode materials, which can inhibit arc erosion and adaptively generate a refractory oxide layer to resist long-term ablation.

[0013] The material of the highly conductive layer is selected from at least one of copper-based conductive materials and silver-based conductive materials;

[0014] Optionally, the material of the highly conductive layer is selected from CuCrZr alloy, CuCr2 alloy, AgCu5 alloy, and AgCu10 alloy;

[0015] The material of the stress relief layer is selected from at least one of nickel-based high-toughness materials and niobium-based high-toughness materials;

[0016] Optionally, the material of the stress relief layer is selected from at least one of Ni60 alloy, Ni30 alloy, Nb-1Zr alloy, and Nb-10W-10Ta alloy;

[0017] The fine-grained transition layer contains submicron or nanometer-sized grains. The small grains primarily accelerate the migration of the cathode spot, reducing its dwell time and thus resisting arc erosion. The actual material composition can be considered as a mixture of the refractory layer and the inner matrix.

[0018] The surface roughness Ra of the refractory layer and the sidewall refractory layer is no higher than 1.6 μm.

[0019] According to another aspect of this application, a method for fabricating the above-mentioned adaptive array functionally graded electrode is provided, comprising the following steps:

[0020] 1) Pretreatment of copper substrate: For bulk copper blanks, electrode blanks are made by machining and the surface to be discharged is milled until the roughness meets the requirements.

[0021] 2) Stress-relieving layers and highly conductive layers are deposited alternately;

[0022] 3) Controllable cladding with low heat input for refractory layers;

[0023] 4) Fabrication of arrayed cone-shaped structures;

[0024] 5) Deposition of the refractory layer and fine-grained transition layer on the sidewall;

[0025] 6) Post-processing. Based on the array electrodes obtained in the above steps, the electrode tooth surfaces are appropriately trimmed to ensure that the surface roughness of each electrode tooth is consistent during the discharge process.

[0026] 2) Includes the following steps:

[0027] After clamping the electrode blank in a special fixture and ensuring that the upper surface is level, a stress relief layer and a high conductivity layer are successively deposited on the discharge surface of the electrode blank using a dual-powder-barrel high-speed laser cladding equipment; after any layer is deposited, appropriate surface polishing treatment is required.

[0028] 3) Includes the following steps:

[0029] On the surface of a highly conductive layer, a high-speed laser cladding process is controlled to promote strong interfacial bonding and cladding of the refractory layer under low heat input conditions, and corresponding surface treatment is performed to meet the roughness requirements, resulting in a layered bulk material.

[0030] 4) Includes the following steps:

[0031] The layered block is clamped in a wire EDM machine and machined along a parallel array path using a fast wire EDM process. After unidirectional machining is completed, the layered block is tilted and the parallel array machining is repeated until an array of conical structures is formed, resulting in a block blank with an array of conical structures. The purpose of using the fast wire EDM process is to appropriately increase the roughness of the sidewalls of the array electrode teeth to meet the adhesion requirements of subsequent surface deposition.

[0032] 5) Includes the following steps:

[0033] A bulk blank with an array-shaped conical structure is used as the cathode and placed in an ionic liquid for pulsed ionic liquid electroplating to obtain a refractory layer on the sidewalls and a fine-grained transition layer. This controls the thermal damage to the electrode tooth substrate caused by the surface coating deposition, while the pulsed discharge promotes the refinement of the coating microstructure.

[0034] The array electrode teeth possess a functionally graded structure in both the radial and axial directions. In the axial dimension of the cone rod, the surface ablation-resistant layer resists ablation by relying on its high melting point and adaptive oxidation properties. A highly conductive layer located at the bottom of the surface accelerates electro-thermal conduction along the axial direction to regulate the temperature of the cone rod. The stress-relieving layer utilizes its moderate coefficient of thermal expansion and mechanical properties to act as an interlayer transition in the multi-layered graded structure. The copper substrate ensures the overall conductivity of the electrode. In the radial dimension, the surface refractory layer also resists ablation caused by localized arcing on the outer surface of the workpiece. The fine-grained transition layer accelerates cathode spot migration and strengthens the bonding force between heterogeneous layers.

[0035] The array electrode possesses "adaptive" properties, primarily due to the refractory metal layer on the surface of its arbitrary discharge teeth. Refractory metals such as zirconium, titanium, and tantalum not only have low work functions but also generate a high-temperature resistant oxide film on their surfaces almost synchronously during dense electron emission and arc combustion. Once formed, the oxide film hinders the ablation of the underlying substrate by the arc plasma and inhibits the diffusion and erosion of reactive oxygen atoms from the surface inward. Consequently, the array electrode exhibits adaptive anti-oxidation and anti-ablation properties.

[0036] The arrayed electrode features a functionally graded structure. Along the axial direction of the electrode teeth, from the surface inwards, are a refractory layer, a highly conductive layer, a stress-relieving layer, and a copper substrate. Each layer works synergistically and complements the others, with different specific functions: 1) The refractory layer resists arc erosion and protects the bottom electrode substrate, spontaneously forming a refractory oxide layer during discharge; 2) The highly conductive layer accelerates the directional migration of electrons at the interface and reduces the scattering obstruction of electron waves by the interface element mixing layer; 3) The stress-relieving layer, located between the copper substrate and the top reinforcing layer, strengthens the interfacial bonding of the multilayer structure; 4) The copper substrate serves as the base of the electrode tooth structure, maintaining the overall electrical and thermal conductivity of the gradient structure.

[0037] The arrayed electrode also possesses functionally graded properties in the radial direction of the electrode teeth, consisting of a refractory layer and a fine-grained transition layer from the outside in. The refractory layer and the fine-grained transition layer respectively resist arc erosion of the sidewalls and accelerate cathode spot migration. In the initial stage of hole fabrication, arc plasma easily forms between the outer edge of the hole and the sidewall of the electrode teeth, ablating the electrode sidewalls. At this time, the refractory layer effectively protects the structural integrity of the electrode sidewalls. During long-term hole fabrication, local burn-off and peeling of the refractory layer on the sidewalls are inevitable. In this case, the exposed fine-grained transition layer still protects the electrode substrate and accelerates cathode spot migration to reduce concentrated heat input erosion.

[0038] The dimensions of the array electrode can be flexibly designed according to the number of holes, hole diameter, and workpiece material. Taking a 400mm×400mm×80mm electrode as an example, it is mainly used for the processing and manufacturing of porous structures in thin-walled metal components. The length of the electrode teeth should not be less than 50% of the overall thickness. The 400mm×400mm surface is the electrode discharge surface, corresponding to an array of 64 electrode teeth, each 30mm long. Specifically, it includes an 8-10mm refractory metal layer, a 4-6mm high conductivity layer, a 5-7mm stress relief layer, and the remainder is a 10-12mm copper substrate.

[0039] The stress relief layer is dense and pore-free. During cladding preparation, a combination of parameters including negative defocus, high laser power, and low scanning rate is used to enhance the penetration depth into the substrate and stir the molten pool, thereby expanding the interfacial bonding range.

[0040] The highly conductive layer is designed to strictly control defects such as pores and cracks. During cladding preparation, a moderate combination of deposition parameters—low laser power, low scanning rate, and low powder feed rate—is used to control the thickness of the element-mixed layer at both interfaces of the conductive layer, thereby reducing the adverse effects of fine interfacial precipitation on conductivity.

[0041] During the preparation of the refractory layer cladding, the initial 2 to 4 layers are prepared with a low powder feeding rate to ensure interface flatness, and then the laser power and powder feeding rate are gradually increased.

[0042] The adaptive array-type functional gradient electrode can be an array electrode, or it can be extended to single-bar electrodes, ring electrodes, etc.

[0043] The manufacturing of the multi-layered structure involved can be achieved through laser cladding, or through powder metallurgy, high-temperature melting and infiltration, and high-temperature diffusion forming.

[0044] The adaptive array functional gradient electrode is suitable for hole making of metal workpieces such as titanium alloys, aluminum alloys, high-temperature alloys, and metal matrix composites. It is suitable for various hole shapes, including rhomboid, rectangular, and circular structures.

[0045] The present invention has the following advantages:

[0046] 1) Cost controllable. The use of a new type of electrode with bidirectional functional gradient can extend the service life compared to existing copper electrodes. The continuous discharge processing time of a single electrode can be extended by 1 to 2 times, reducing electrode consumable consumption and replacement frequency, thereby effectively alleviating the cost surge caused by severe electrode ablation.

[0047] 2) High structural reliability. The structural design of the novel array-type functionally graded electrode is based on service performance requirements, significantly improving material utilization and structural efficiency. Furthermore, relying on the multilayer structure fabricated by high-speed laser cladding, the layer thickness, intralayer microstructure, and interlayer metallurgical bonding are highly controllable, resulting in high structural reliability.

[0048] 3) High yield and consistency of hole fabrication. The array electrode has a functional gradient structure in the radial direction of the electrode teeth, which can suppress the change of electrode shape caused by lateral arc erosion during long-term electrical discharge, thereby avoiding the hole connection defects caused by the arcing of multiple electrode teeth, and improving the yield and structural consistency of batch hole fabrication. Attached Figure Description

[0049] Figure 1 The diagram shows an adaptive array functional graded electrode structure, where a is a schematic diagram of the adaptive array functional graded electrode, b and c are schematic diagrams of the inner core of the cone-shaped discharge end, and d is a cross-sectional view of the cone-shaped discharge end.

[0050] Figure 2 This is a schematic diagram of the fabrication process of an array electrode structure, where a, b, c, d, e, and f correspond to steps 1), 2), 3), 4), 5), and 6 of the fabrication method, respectively.

[0051] Figure 3 The diagram illustrates the hole-making mechanism of EDM with arrayed electrodes. In the diagram, a is a schematic diagram of the mechanism by which adaptive arrayed functional graded electrodes ensure long-term service stability during EDM, and b is a schematic diagram of the mechanism by which adaptive arrayed functional graded electrodes avoid bridging defects between adjacent hole-making positions.

[0052] Figure 4 a and b are for filtering and capturing the spark discharge process of array-type functional gradient electrodes.

[0053] Figure 5 The surface morphology of the burned functional gradient electrode.

[0054] Figure 6 a, b, and c are the filtering and capture of the spark discharge process of the copper array electrode.

[0055] Figure 7 The surface morphology of the burned copper array electrode is shown.

[0056] In the figure: 1. Conical electrode teeth, 2. Refractory layer, 3. High conductivity layer, 4. Stress relief layer, 5. Copper substrate, 6. Refractory layer on the sidewall, 7. Fine grain transition layer, 8. Copper billet, 9. CNC machining center milling, 10. High-speed laser cladding deposition head, 11. Array structure, 12. Insulating layer, 13. Ionic liquid electroplating tank, 14. Pulse power supply, 15. CNC machining / manual shaping, 16. Dense oxide film. Detailed Implementation

[0057] The present application is described in detail below with reference to the embodiments, but the present application is not limited to these embodiments.

[0058] Example 1

[0059] The array-type functionally graded electrode involved in this invention, such as Figure 1 As shown in Figure a, the overall structure is a cubic block, with several pointed cone-shaped electrode teeth (1) distributed in an XOY planar array on a copper substrate. The spacing between adjacent electrode teeth is consistent. Each electrode tooth is parallel to the Z-axis direction. Regarding a single electrode tooth, as shown in Figure a... Figure 1 As shown in b, the electrode teeth exhibit a functionally graded structure in both the axial and radial directions. Axial direction ( Figure 1 c) From the self-discharge surface inwards, the layers are sequentially a refractory layer (2), a highly conductive layer (3), a stress-relieving layer (4), and a copper substrate (5), with metallurgical bonding between each layer. Radial direction ( Figure 1 d), from the outside to the inside, are the refractory layer (6) and the fine-grained transition layer (7).

[0060] Based on a bidirectional functional gradient structure, a low ablation rate and continuous machining stability are achieved during long-term EDM of array electrodes, alleviating workpiece hole defects that occur during long-term service of copper electrodes, and promoting the efficient and low-consumption EDM manufacturing of multi-hole structures.

[0061] Specifically, the functional characteristics of the axial multilayer material are as follows: 1) The refractory layer spontaneously oxidizes during air discharge to generate a high-viscosity, dense oxide film, which then inhibits arc ablation and suppresses the diffusion and erosion of active oxygen atoms, thereby reducing cathode ablation and ensuring long-term service stability; 2) The highly conductive layer is located between the refractory layer and the stress relief layer, accelerating the directional migration of electron beams at the heterogeneous interface, reducing the scattering and obstruction of electron waves by the interface element mixing layer, and improving the overall electrical and thermal conductivity; 3) The stress relief layer has high toughness and is located between the copper substrate and the top reinforcing layer, strengthening the interfacial bonding of the multilayer structure; 4) The copper substrate serves as the base of the electrode tooth structure, maintaining the electrical and thermal conductivity of the overall structure.

[0062] This invention relates to the fabrication process of array-type functionally graded electrodes, such as... Figure 2 As shown, the main steps are: 1) pretreatment of copper substrate; 2) alternating deposition of stress relief layer and high conductivity layer; 3) controllable cladding of refractory layer with low heat input; 4) preparation of array cone structure; 5) deposition of functional layer on cone rod surface; 6) post-processing.

[0063] Pre-processing of copper substrates. Based on the number and duration of holes to be drilled, the three-dimensional dimensions, number, shape, and spacing of the array electrodes are designed to ensure that the drilling allowance meets the component design requirements. For example... Figure 2 As shown in Figure a, the copper blank (8) is cut according to the three-dimensional dimensions of the electrode. The block blank is milled by a CNC machining center (9) to ensure that the surface roughness is less than 1.6μm and the six sides are flat. The discharge surface is flat without protrusions or depressions.

[0064] Stress-relieving layers and highly conductive layers are deposited alternately. After substrate pretreatment, alternating laser cladding deposition of stress-relieving layers and highly conductive layers is performed, such as... Figure 2 As shown in b. After clamping the electrode blank in the cladding intensifier and leveling the upper surface, a stress relief layer is first deposited on the copper surface using a high-speed laser cladding deposition equipment (10). After traversing the upper surface of the copper, the stress relief layer manufacturing is completed. Moderate surface polishing is performed, followed by secondary deposition of a high conductivity layer. The manufacturing requirements for the stress relief layer are: 1) The material is a high-toughness metal such as nickel-based or niobium-based; 2) The thickness is at least 50% of the thickness of the refractory layer, and the interior is dense and free of pores; 3) The cladding process design is based on negative defocusing, high laser power, and low scanning rate. Correspondingly, the manufacturing requirements for the high conductivity layer are: 1) The material is a copper-based or silver-based conductive metal; 2) The thickness should be between 35% and 75% of the thickness of the refractory layer, and the interior is strictly controlled for defects such as pores and cracks; 3) The cladding process design is based on low laser power, low scanning rate, and low powder feeding rate.

[0065] Controlled cladding of refractory layers with low heat input. Controlled deposition of refractory metal coatings on the surface of highly conductive layers. Figure 2 c) This step requires careful control of the interface fusion zone between the refractory layer and the highly conductive layer to minimize the stirring effect of the secondary cladding on the molten pool and reduce the melting depth. Let parameter combination A represent the conventional cladding process parameters for the refractory layer. Initially, when depositing 2-4 layers, a milder parameter combination of 75% powder feed rate, 50% laser power, and 120% scan rate compared to A is used. Subsequent depositions are gradually restored to parameters A for continuous layer-by-layer deposition. The requirements for refractory layer manufacturing are: 1) The material should be a high-melting-point, thermochemically sound material such as hafnium-based, tungsten-based, or zirconium-based; 2) The thickness should be no less than 8 mm and free of obvious internal defects; 3) When awaiting discharge machining, the surface roughness Ra should not exceed 1.6 μm.

[0066] Fabrication of arrayed conical structures. This primarily involves fabricating the arrayed electrode teeth using wire cutting, such as... Figure 2 As shown in d, the layered block is clamped in the wire EDM machine tool and removed along the parallel array path based on the fast wire EDM mode. After the unidirectional processing is completed, the block is tilted and the parallel array removal is repeated to complete the preparation of the array structure (11). The purpose of fast wire EDM is to increase the roughness of the electrode tooth sidewall to meet the bonding force requirements of subsequent surface deposition.

[0067] Functional layer deposition on the surface of the cone rod. After obtaining the array electrode by wire cutting, further functional gradient treatment of the sidewalls of arbitrary electrode teeth is required, mainly by ionic liquid electroplating. An insulating layer (12) is coated / attached to all parts of the array electrode except for the electrode teeth, such as... Figure 2 As shown in e, the electrode is then connected to the circuit and immersed in the ionic liquid plating tank (13) as a cathode. The pulse power supply (14) of the plating tank A is turned on to perform pulse discharge, which promotes the cations to accept electrons in the near-surface region of the electrode teeth and reduce them to grow into a plating layer. When preparing a fine-grained layer, a high pulse frequency and current are maintained to promote the refinement of the plating layer grains. When performing ionic liquid plating of a refractory layer, the array electrode is switched from tank A to tank B, and then a secondary ionic liquid plating of the refractory layer is performed.

[0068] Post-processing. For the array electrodes obtained in the above steps, the surface insulating layer is removed by CNC machining / manual shaping (15), and the electrode tooth surface is appropriately trimmed, such as... Figure 2 As shown in f, ensure that the surface roughness of the electrode teeth discharge is consistent. Simultaneously, threaded holes are machined on the backplate surface to meet electrode clamping requirements.

[0069] The mechanism by which the array-type functionally graded electrode, fabricated based on the above steps, ensures long-term service stability during the electrical discharge machining process is as follows: Figure 3As shown in Figure a. Taking a single electrode tooth as an example, during continuous discharge drilling, the refractory layer at the axial end of the electrode tooth preferentially contacts the workpiece surface. Under the action of pulsed high voltage, the gap breaks down to form an arc plasma, and the refractory layer then rapidly and spontaneously oxidizes to form a dense oxide film (16). Subsequently, the refractory layer and its surface dense oxide film bear the arc root, resist high-temperature ablation, and reduce the electrode ablation rate. At the same time, the high conductivity layer and the copper substrate accelerate the conduction of input heat flow and current inside the electrode tooth. Thus, the functional gradient structure efficiency is fully utilized, and the material utilization rate is improved. Under the action of the refractory layer-high conductivity layer-stress relief layer-copper functional gradient structure in the axial direction, the electrode can always work in a low ablation rate mode during long-term hole drilling, reducing electrode wear.

[0070] Furthermore, arrayed electrodes can also avoid interconnected hole defects near adjacent hole locations, the corresponding mechanism being as follows: Figure 3 As shown in b, the electrode teeth exhibit a functionally graded structure of a refractory layer followed by a fine-grained layer on the radial direction of the electrode tooth sidewall. During long-term operation of the array electrodes, some electrode teeth inevitably undergo tip shape changes, leading to narrowing of the spacing between multiple electrode teeth and potentially inducing arcing. By adopting a radial functionally graded design, the surface refractory layer can resist sidewall ablation caused by arcing, inhibiting arc erosion and thus avoiding the problem of interconnected holes on the workpiece surface caused by arcing, thereby improving the quality of the processed workpiece delivery.

[0071] In this embodiment, equidistantly distributed rhomboid holes need to be fabricated on the surface of a large-sized thin-walled component, employing an array-type functional graded electrode structure. The array electrode is designed in terms of materials and structure. Considering the weak rigidity of the thin-walled component, an array electrode is used for EDM hole fabrication, with three-dimensional dimensions of 450mm × 450mm × 80mm, where the 450mm × 450mm plane serves as the EDM surface. Structurally, 64 rhomboid electrode teeth are arranged in an array, with a side length of 4mm and an included angle of 60° between adjacent edges. The electrode teeth are 30mm long, specifically comprising a 9mm refractory metal layer, a 5mm conductive layer, a 7mm stress-relieving layer, and a 9mm copper substrate. In terms of materials, considering the hole fabrication time and the material properties of the titanium alloy workpiece, hafnium metal is selected as the refractory layer, a silver-based conductive alloy as the high-conductivity layer, and a nickel-based alloy as the stress-relieving layer.

[0072] After the electrode fabrication was completed according to the array-type functional graded electrode preparation method, the surface roughness, cross-sectional dimensions, and other key features of 64 electrode teeth were randomly inspected. After confirming that they met the design requirements, electrical discharge machining (EDM) was started to create holes. The large-sized thin-walled component was clamped in a special tooling, and EDM was performed on the area to be processed. The processing parameters were set as follows: pulse width 36μs, pulse gap 8μs, current 25A, and tool lift relative speed 1.

[0073] When using a bidirectional functionally graded array electrode for hole fabrication, a high-speed filter camera is used for in-situ observation of the discharge surface, such as... Figure 4 As shown, several dispersed discharge clusters appeared in the field of view, with each cluster corresponding to an electrode tooth being processed during the positive discharge phase. The good separation of multiple discharge clusters indicates the stability of the array electrode EDM process. Simultaneously, the electrodes were subjected to morphological testing and microstructural characterization after 5 hours of continuous discharge processing. It was found that the refractory layer on the axial surface of the electrode teeth had a complete outline, with a remaining thickness of 5–6 mm after ablation. Most electrode teeth had intact outer contours, with only 3–4 teeth at the edge of the array electrode showing ablation-melting traces on their outer periphery. Representative electrode teeth were cut for scanning electron microscopy observation of the ablated surface, as shown... Figure 5 As shown, electrode ablation is minimal, with only localized surface cracking of the oxide layer due to rapid heating and cooling. Overall, the array electrode exhibits excellent resistance to arc erosion, ensuring stability during long-term, continuous processing.

[0074] Comparative Example 1

[0075] In this comparative example, the specific EDM (Electrical Discharge Machining) scenario for the array electrode is the same as in the embodiment. The difference is that the comparative example does not employ a multi-material functional gradient design, but instead uses a solid copper block as the electrode material, which is then fabricated into an array electrode with a consistent outer contour through wire cutting, CNC machining, and other methods. Accordingly, the three-dimensional dimensions of the array electrode are 450mm × 450mm × 80mm, with the 450mm × 450mm plane serving as the EDM surface. Structurally, 64 rhomboid electrode teeth are arranged in an array, with a side length of 4mm, an included angle of 60° between adjacent edges, and a tooth length of 30mm.

[0076] The workpieces processed in this comparative example are large-sized, thin-walled components, and the part type, wall thickness, and hole-making requirements are consistent with those in the embodiment. Similarly, the EDM parameters are set as follows: pulse width 36μs, pulse gap 8μs, current 25A, and tool lift-off relative speed 1.

[0077] After setup, initiate electrical discharge machining (EDM) on the copper array electrodes and use a high-speed filter camera to observe the electrode discharge in situ. For example... Figure 6 As shown, in addition to discrete spots, three clusters of highly overlapping discharge spots also appeared. Analysis revealed that the overlapping discharge spots were caused by arc discharge between adjacent electrode teeth, which may induce interconnected hole defects. Furthermore, the copper electrode after 5 hours of discharge machining was subjected to contour inspection and microstructure characterization. After discharge ablation, the remaining length of the electrode teeth was 18–20 mm, with a burn-off length exceeding 10 mm, indicating severe burn-off of the copper electrode. Even more serious was the burn-off surface of the copper electrode teeth (…). Figure 7 The presence of numerous deep ablation pits and severe non-uniform ablation of the electrodes confirms that using only copper as the array electrode material results in a surge in material ablation rate, making it difficult to meet the continuous and stable processing requirements of large-volume through-holes.

[0078] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications or substitutions made by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. An adaptive array-type functionally graded electrode, characterized in that, The adaptive array functional gradient electrode is provided with equally spaced conical discharge ends; The inner core of the cone-shaped discharge end consists of, from the outside to the inside, a refractory layer, a highly conductive layer, a stress-relieving layer, and a copper substrate. The inner core is covered from the outside in with a refractory sidewall layer and a fine-grained transition layer.

2. The adaptive array-type functionally graded electrode according to claim 1, characterized in that, When the size of the electrode surface is greater than 500mm×500mm, the height of the cone-shaped discharge end is not less than 55% of the thickness of the electrode, the thickness of the refractory layer is at least 25% of the height of the cone-shaped discharge end, the thickness of the high conductivity layer is 40~80% of the thickness of the refractory layer, the thickness of the stress relief layer is 60~80% of the thickness of the refractory layer, the thickness of the sidewall refractory layer is 6~8% of the short diagonal length of the cross section of the cone-shaped discharge end, and the thickness of the fine grain transition layer is 4~6% of the short diagonal length of the cross section of the cone-shaped discharge end.

3. The adaptive array-type functionally graded electrode according to claim 1, characterized in that, When the size of the electrode surface is less than 500mm×500mm, the height of the cone discharge end is not less than 50% of the electrode thickness, the thickness of the refractory layer is at least 20% of the height of the cone discharge end, the thickness of the high conductivity layer is 35~75% of the thickness of the refractory layer, the thickness of the stress relief layer is 50~75% of the thickness of the refractory layer, the thickness of the sidewall refractory layer is 4~6% of the short diagonal length of the cross section of the cone discharge end, and the thickness of the fine grain transition layer is 2~4% of the short diagonal length of the cross section of the cone discharge end.

4. The adaptive array-type functionally graded electrode according to claim 1, characterized in that, The materials of the refractory layer, the sidewall refractory layer and the fine-grained transition layer are selected from at least one of zirconium, titanium and tantalum; The material of the highly conductive layer is selected from at least one of copper-based conductive materials and silver-based conductive materials; The material of the stress relief layer is selected from at least one of nickel-based high-toughness materials and niobium-based high-toughness materials; The grain size inside the fine-grained transition layer is at the submicron or nanometer level.

5. The adaptive array-type functionally graded electrode according to claim 4, characterized in that, The material of the highly conductive layer is selected from CuCrZr alloy, CuCr2 alloy, AgCu5 alloy, and AgCu10 alloy.

6. The adaptive array-type functionally graded electrode according to claim 4, characterized in that, The material of the stress relief layer is selected from at least one of Ni60 alloy, Ni30 alloy, Nb-1Zr alloy, and Nb-10W-10Ta alloy.

7. The adaptive array-type functionally graded electrode according to claim 1, characterized in that, The surface roughness Ra of the refractory layer and the sidewall refractory layer is not higher than 1.6 μm.

8. A method for fabricating an adaptive array-type functionally graded electrode according to any one of claims 1 to 7, characterized in that, Includes the following steps: 1) Pretreatment of copper substrate: For bulk copper blanks, electrode blanks are made by machining and the surface to be discharged is milled until the roughness meets the requirements. 2) Stress-relieving layers and highly conductive layers are deposited alternately; 3) Controllable cladding with low heat input for refractory layers; 4) Fabrication of arrayed cone-shaped structures; 5) Deposition of the refractory layer and fine-grained transition layer on the sidewall; 6) Post-processing.

9. The preparation method according to claim 8, characterized in that, 2) Includes the following steps: After clamping the electrode blank in a special fixture and ensuring that the upper surface is level, a stress relief layer and a high conductivity layer are successively deposited on the discharge surface of the electrode blank using a dual-powder-barrel high-speed laser cladding equipment; after any layer is deposited, appropriate surface polishing treatment is required.

10. The preparation method according to claim 9, characterized in that, 3) Includes the following steps: On the surface of a highly conductive layer, a high-speed laser cladding process is controlled to promote strong interfacial bonding and cladding of the refractory layer under low heat input conditions, and corresponding surface treatment is performed to meet the roughness requirements, resulting in a layered bulk material.

11. The preparation method according to claim 10, characterized in that, 4) Includes the following steps: The layered block is clamped in a wire EDM machine tool and processed along a parallel array path using fast wire EDM technology. After unidirectional processing is completed, the layered block is tilted and the parallel array processing is repeated until an array-shaped conical structure is formed, resulting in a block blank with an array-shaped conical structure.

12. The preparation method according to claim 11, characterized in that, 5) Includes the following steps: A bulk blank with an array-shaped conical structure is used as the cathode and placed in an ionic liquid for pulsed ionic liquid electroplating to obtain a refractory layer on the sidewall and a fine-grained transition layer.

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