Metal ceramic gradient composite electric spark machining electrode and preparation method and application thereof

Abstract

The invention discloses a metal ceramic gradient composite electric spark machining electrode and a preparation method and application thereof.The electrode comprises a metal matrix and a gradient transition layer and a surface function layer.The metal matrix is covered with the gradient transition layer and the surface function layer.The high-hardness ceramic is arranged on the electrode, so that insulativity and electric corrosion resistance are provided; and reduction of machining precision and abnormal loss of the electrode caused by the secondary discharge phenomenon between the side wall of the tool electrode and the workpiece are effectively avoided. Meanwhile, a metal-ceramic gradient transition layer is arranged, the gradient layer has continuously changing components and performance, slow release of thermal stress is achieved, and the problem of interface stripping caused by mismatching of thermal expansion coefficients of an electrode side wall insulating layer is solved. The electrode prepared by the invention can resist the impact of electric spark discharge high temperature (greater than or equal to 2500 DEG C), the uniformity of the side wall gap and the processing efficiency can be improved, and the electrode loss rate is reduced.

Description

Technical Field

[0001] This invention relates to the field of electrical discharge machining (EDM) tool electrode technology, and more specifically, to a metal-ceramic gradient composite EDM electrode, its preparation method, and its application. Background Technology

[0002] Electrical discharge machining (EDM) is a specialized machining technique that uses the principle of electro-erosion to remove conductive materials. It involves using high temperatures generated by pulsed discharges from electrodes to locally melt and vaporize the material. In this method, the electrode and workpiece do not directly contact each other, the machining process does not rely on mechanical force, and there is no macroscopic cutting force. It is suitable for machining thin-walled, fine, and low-rigidity parts. The electrodes used in EDM must be able to withstand high temperatures and possess excellent wear resistance at the discharge temperatures. Furthermore, during machining, the electrode may be subjected to the pressure of the flushing medium, clamping forces, and discharge impact forces. Therefore, the electrode needs to maintain sufficient strength and hardness to prevent bending, vibration, or deformation, thereby ensuring machining accuracy and stability.

[0003] In addition, during the machining of deep and narrow grooves or casings, after the electrode completes one discharge, the metal particles (electro-erosion products) and carbon slag generated may not be discharged from the working area in time. These conductive impurities may adhere to the workpiece surface or remain suspended in the discharge gap, easily leading to secondary discharge between the electrode and the workpiece. This can result in decreased machining accuracy and surface quality, as well as accelerated electrode wear. Therefore, when machining deep holes or deep grooves using electrical discharge machining, it is also necessary to avoid the problem of secondary discharge on the sidewalls caused by the difficulty in removing eroded particles from the discharge gap.

[0004] CN204639369U discloses a separable electrode for electrical discharge machining. The electrode includes a first cylindrical electrode, a second cylindrical electrode, and a third cylindrical electrode. The first cylindrical electrode is located at the upper end of the second cylindrical electrode and the two are arranged perpendicularly and integrally. The third cylindrical electrode is located at the lower end of the second cylindrical electrode and the two are arranged perpendicularly. The second cylindrical electrode and the third cylindrical electrode are threadedly connected. The first cylindrical electrode, the second cylindrical electrode, and the third cylindrical electrode are arranged coaxially. The bottom end face of the third cylindrical electrode is the discharge machining area. The upper end face of the first cylindrical electrode has a plurality of first working fluid outlet holes evenly opened along the circumference. The first cylindrical electrode, the second cylindrical electrode, and the third cylindrical electrode have second working fluid outlet holes opened at the axial positions of the first cylindrical electrode, the second cylindrical electrode, and the third cylindrical electrode. This patent describes a method where, during electrical discharge machining (EDM), working fluid from multiple first working fluid outlets on the first cylindrical electrode completely encapsulates the sidewalls of the third cylindrical electrode, while working fluid from the second working fluid outlet completely encapsulates the bottom of the third cylindrical electrode. The rapid flow of the working fluid effectively flushes away etched particles generated within the discharge gap, thus solving the problem of secondary discharge. However, this method relies on physical isolation by an external working fluid. The working fluid cannot achieve uniform and sufficient flow in all complex geometric areas (especially deep and narrow sections). It suffers from dead zones, turbulent instability, and geometric limitations, easily leading to localized accumulation of etched products. The accumulation of etched products in dead zones causes a sharp increase in concentration, resulting in high-concentration etched particles suspended in the gaps. This significantly increases the probability of "short-circuiting" the discharge channel or forming secondary discharges through particle bridging. Simultaneously, the etched particles also affect electrode performance, leading to unstable electrode discharge and impacting the quality of the machined workpiece. Summary of the Invention

[0005] The main technical problem to be solved by this invention is to address the shortcomings of secondary discharge between the tool electrode sidewall and the workpiece, which leads to decreased machining accuracy and abnormal electrode wear. This invention provides a metal-ceramic gradient composite EDM electrode and its application.

[0006] Another technical problem solved by the present invention is to provide a method for preparing a metal-ceramic gradient composite electrical discharge machining electrode.

[0007] The objective of this invention is achieved through the following technical solution: A metal-ceramic gradient composite electrical discharge machining electrode includes a metal substrate and a gradient transition layer and a surface functional layer covering the metal substrate. The metal substrate includes a working section and clamping ends and electrode ends located at both ends of the working section. The electrode ends are exposed metal substrates of 1-2 mm. The sidewalls of the working section are covered with a gradient transition layer, and the surface functional layer is covered on the gradient transition layer. The gradient transition layer material includes metal powder, ceramic particles, and sintering aids, wherein the ceramic particles are at least one of Al2O3, ZrO2, and SiC. The gradient transition layer has a thickness of 2-3 mm and includes a near-substrate region, a transition region, and a near-ceramic region. The volume fraction of ceramic particles increases from 0% to 80% in the direction from the metal substrate to the surface functional layer. The thickness of the near-matrix region is 0.5~1mm, and the volume fraction of its ceramic powder particles increases from 0% to 20%. The thickness of the transition zone is 1~2mm, and the volume fraction of ceramic powder particles increases from 20% to 60%. The thickness of the near-ceramic region is 0.5~1mm, and the volume fraction of ceramic powder particles increases from 60% to 80%. The surface functional layer raw materials include ceramic particles and sintering aids. The ceramic particles are at least one of Al2O3, ZrO2, and SiC, wherein the volume fraction of the ceramic particles is ≥90%, and the thickness of the surface functional layer is 0.2~0.5mm.

[0008] Furthermore, the metal matrix is ​​copper, tungsten-copper alloy, or molybdenum-copper alloy, with a conductivity ≥50 MS / m.

[0009] Furthermore, the volume fraction of ceramic particles is increased by 2% for every 50 μm of thickness in the near-matrix region, by 4% for every 50 μm of thickness in the transition region, and by 2% for every 50 μm of thickness in the near-ceramic region.

[0010] Furthermore, the sintering aid is MgO, which can promote ceramic densification and inhibit high-temperature grain growth.

[0011] Furthermore, the particle size of the ceramic particles in the gradient transition layer and the surface functional layer is 50~100nm.

[0012] A method for preparing a metal-ceramic gradient composite electrical discharge machining electrode, comprising the following steps: S1. A gradient unit layer is deposited on a metal substrate using a laser powder bed melting process. Metal powder and ceramic powder are simultaneously delivered through a dual powder feeding system. The layers are deposited one by one with the ceramic particle content increasing in a gradient manner to obtain a gradient transition layer. S2. Perform cold spray pretreatment on the surface of the gradient transition layer, and deposit ceramic particles on the surface of the gradient transition layer to form a ceramic particle pre-layer; S3. A laser cladding process is used to remelt the pre-placed ceramic particles to eliminate pores and strengthen the interfacial bonding, forming a dense surface functional layer.

[0013] This invention first utilizes a laser powder bed with a dual powder feeding system to simultaneously deliver metal and ceramic powders. By dynamically adjusting the powder mixing ratio, a gradient structural composition is achieved. A high-energy laser beam is then used to melt the powder in this region, enabling precise fusion and layer-by-layer accumulation, thus achieving gradient control of the composition, structure, and properties of the gradient transition layer. Then, using a cold spray-laser cladding method, a dense metal transition layer is first solid-deposited on the substrate surface via cold spraying. Subsequently, a laser beam melts the surface of this transition layer and simultaneously clads functional material powder, forming a dense metallurgically bonded top layer. This invention effectively solves the problems of poor wettability, substrate thermal damage, and oxidation control in laser cladding through the cold spray transition layer. It combines the high deposition efficiency of cold spraying with the excellent metallurgical bonding and microstructure control capabilities of laser cladding, significantly improving the coating interface reliability, geometric integrity, and overall performance.

[0014] Furthermore, the laser powder bed melting process employs a four-laser LPBF system with a wavelength of 1070 nm, a laser power of 400 W, and a scanning speed of 800-1200 mm / s.

[0015] Furthermore, the gas pressure for cold spraying is 5 MPa, with the main gas nitrogen at 5 MPa and a temperature of 550°C, and the auxiliary gas helium at 0.8 MPa, with a spray distance of 25 mm.

[0016] Furthermore, the porosity of the ceramic particle pre-placed layer is ≤5%.

[0017] Furthermore, the energy density of the laser cladding process is 150 J / mm². 2 The overlap rate is 40%, and the protective gas flow rate is 15L / min.

[0018] The aforementioned metal-ceramic gradient composite EDM electrode is used for EDM finishing of electrode diffuser blades and impeller blades, or for machining deep and narrow grooves in mold cavities.

[0019] Compared with existing technologies, the beneficial effects are: This invention uses a gradient material forming method to prepare a high-bonding-strength surface insulating layer on the side of the electrode. On the one hand, the insulating layer on the side of the electrode forces the electrode discharge to occur between the uninsulated front end and the workpiece, effectively suppressing harmful side discharge and concentrating the discharge energy on the front working surface, thereby improving the efficiency and processing stability of workpiece removal in this area, while eliminating electrode wear caused by side discharge. On the other hand, the ceramic-formed surface insulating layer has high strength, which can improve the electrode's resistance to the impact of the rinsing medium and discharge, preventing the electrode from bending, vibrating, or deforming.

[0020] This invention employs a gradient layered structure between a metal substrate and a ceramic functional layer on its surface. By precisely controlling the content of metal powder and ceramic powder in the gradient layer, the thermal expansion coefficient and elastic modulus between the metal substrate and the ceramic functional layer transition smoothly at the interface. This significantly reduces thermal stress, improves the adhesion and thermal shock resistance of the surface functional layer, effectively absorbs and dissipates the thermal shock energy of the electrode under repeated and drastic temperature changes, buffers the direct impact between the substrate and the surface ceramic, uniformly distributes thermal stress, avoids stress concentration points, effectively inhibits the initiation and propagation of microcracks, ensures the stability of the surface functional layer under long-term, harsh discharge environments, suppresses the potential hazards of thermal stress generated during electrical discharge machining leading to peeling of the bonding surface, and improves the reliability and service life of the tool electrode. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the overall structure of the tool electrode; 201 Pure metal layer, 202 Metal-ceramic hybrid layer, 203 Ceramic enrichment layer; Figure 2 The electric field distribution diagram of the metal-ceramic gradient composite EDM tool electrode during the machining of deep and narrow grooves; Figure 3 This is a diagram showing the electric field distribution of a conventional pure copper EDM tool electrode during deep and narrow groove machining. Detailed Implementation

[0022] The following examples further explain and clarify the invention, but the specific examples do not limit the invention in any way.

[0023] Example 1 This embodiment provides a metal-ceramic gradient composite electrical discharge machining electrode, such as... Figure 1 As shown, it includes a metal substrate and a gradient transition layer with a thickness of 2-3 mm and a surface functional layer with a thickness of 0.2-0.5 mm covering the metal substrate. The metal substrate includes a working section and clamping ends and electrode terminals located at both ends of the working section. The electrode terminals are exposed metal substrate with a thickness of 1-2 mm. The gradient transition layer covers the sidewall of the working section of the metal substrate.

[0024] The gradient transition layer consists of a pure metal layer 201, a metal-ceramic hybrid layer 202, and a ceramic enrichment layer 203, which are deposited sequentially from the metal substrate to the surface functional layer. The volume fraction of ceramic particles in the layer increases from 0% in the pure metal layer to 80% in the ceramic enrichment layer. The metal-ceramic hybrid layer 202 is obtained by depositing multiple gradient unit layers of 20-50 μm, and the volume fraction of ceramic particles increases by 2-4% for every 50 μm or 100 μm thick gradient unit layer.

[0025] Example 2 This embodiment provides a method for preparing a metal-ceramic gradient composite electrical discharge machining electrode, the steps of which include: S1. A gradient transition layer was deposited layer by layer on a CuW80 alloy metal substrate using a laser powder bed melting process. A four-laser LPBF system with a wavelength of 1070 nm, a laser power of 400 W, and a scanning speed of 800-1200 mm / s was used to deposit a 25 μm thick gradient unit layer on the metal substrate. Then, a dual powder feeding system was used to simultaneously deliver copper metal powder and SiC ceramic powder, which also contained 2 wt% MgO sintering aid. By dynamically adjusting the powder mixing ratio, a 2 mm thick gradient transition layer was obtained.

[0026] Specifically, in the near-matrix region, i.e., within the thickness h1 = 0~0.5 mm, the volume fraction of ceramic powder increases from 0% to 20%, and the volume fraction of ceramic powder per 50 μm unit layer increases by 2%. In the transition region, i.e., within the thickness h2 = 0.5~1.5 mm, the volume fraction of ceramic powder increases from 20% to 60%, and the volume fraction of ceramic powder per 50 μm unit layer increases by 4%. In the near-ceramic region, within the thickness h3 = 1.5~2.0 mm, the volume fraction of ceramic powder increases from 60% to 80%, and the volume fraction of ceramic powder per 50 μm unit layer increases by 2%.

[0027] S2. A cold spray pretreatment is performed on the surface of the gradient transition layer. The cold spray gas pressure is 5 MPa, using nitrogen (main gas pressure 5 MPa / temperature 550℃) and helium (auxiliary gas pressure 0.8 MPa), with a spray distance of 25 mm. A mixed powder containing 98 wt.% 80 nm nano-SiC powder and 2 wt.% MgO is deposited on the surface of the transition layer by cold spray to form a ceramic particle pre-layer with a porosity ≤5%.

[0028] S3. Eliminating porosity and strengthening interfacial bonding through laser cladding, with laser energy density strictly controlled at 150±30 J / mm². 2 (Power 1200 W, spot diameter 1.2 mm, scanning speed 800 mm / s), overlap rate 40%, argon protection (flow rate 15 L / min), molten pool temperature 2200±50℃, laser cladding process is used to remelt the pre-placed layer to form a 0.5 m thick dense surface ceramic functional layer, thus preparing a metal-ceramic gradient composite EDM electrode.

[0029] Example 3 This embodiment provides a method for preparing a metal-ceramic gradient composite electrical discharge machining electrode, the steps of which include: S1. A gradient transition layer was deposited layer by layer on a CuW80 alloy metal substrate using a laser powder bed melting process. A four-laser LPBF system with a wavelength of 1070 nm, a laser power of 400 W, and a scanning speed of 800-1200 mm / s was used to deposit a 50 μm thick gradient unit layer on the metal substrate. Then, a dual powder feeding system was used to simultaneously deliver copper metal powder and SiC ceramic powder. By dynamically adjusting the powder mixing ratio, a 3 mm thick gradient transition layer was obtained.

[0030] Specifically, in the near-matrix region, i.e., within the thickness h1 = 0~1 mm, the volume fraction of ceramic powder increases from 0% to 20%, and the volume fraction of ceramic powder per 100 μm unit layer increases by 2%. In the transition region, i.e., within the thickness h2 = 1~2 mm, the volume fraction of ceramic powder increases from 20% to 60%, and the volume fraction of ceramic powder per 100 μm unit layer increases by 4%. In the near-ceramic region, within the thickness h3 = 2~3 mm, the volume fraction of ceramic powder increases from 60% to 80%, and the volume fraction of ceramic powder per 100 μm unit layer increases by 2%.

[0031] S2. A cold spray pretreatment is performed on the surface of the gradient transition layer. The cold spray gas pressure is 5 MPa, using nitrogen (main gas pressure 5 MPa / temperature 550℃) and helium (auxiliary gas pressure 0.8 MPa), with a spray distance of 25 mm. Nano-SiC powder with a particle size of 80 nm is deposited on the surface of the transition layer by cold spray to form a ceramic particle pre-layer with a porosity ≤5%.

[0032] S3. Eliminating porosity and strengthening interfacial bonding through laser cladding, with laser energy density strictly controlled at 150±30 J / mm². 2 (Power 1200 W, spot diameter 1.2 mm, scanning speed 800 mm / s), overlap rate 40%, argon protection (flow rate 15 L / min), molten pool temperature 2200±50℃, laser cladding process is used to remelt the pre-placed layer to form a 0.5 m thick dense surface ceramic functional layer, thus preparing a metal-ceramic gradient composite EDM electrode.

[0033] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A metal-ceramic gradient composite electrical discharge machining electrode, characterized in that, It includes a metal substrate and a gradient transition layer and a surface functional layer covering the metal substrate. The metal substrate includes a working section and clamping ends and electrode terminals located at both ends of the working section. The electrode terminals are exposed metal substrate with a thickness of 1-2 mm. The sidewalls of the working section are covered with a gradient transition layer, and the surface functional layer is covered on the gradient transition layer. The gradient transition layer material includes metal powder, ceramic particles, and sintering aids, wherein the ceramic particles are at least one of Al2O3, ZrO2, and SiC. The gradient transition layer has a thickness of 2-3 mm and includes a near-substrate region, a transition region, and a near-ceramic region. The volume fraction of ceramic particles increases from 0% to 80% in the direction from the metal substrate to the surface functional layer. The thickness of the near-matrix region is 0.5~1mm, and the volume fraction of its ceramic powder particles increases from 0% to 20%. The thickness of the transition zone is 1~2mm, and the volume fraction of ceramic powder particles increases from 20% to 60%. The thickness of the near-ceramic region is 0.5~1mm, and the volume fraction of ceramic powder particles increases from 60% to 80%. The surface functional layer raw materials include ceramic particles and sintering aids. The ceramic particles are at least one of Al2O3, ZrO2, and SiC, wherein the volume fraction of the ceramic particles is ≥90%, and the thickness of the surface functional layer is 0.2~0.5mm.

2. The metal-ceramic gradient composite EDM electrode according to claim 1, characterized in that, The metal matrix is ​​copper, tungsten-copper alloy, or molybdenum-copper alloy.

3. The metal-ceramic gradient composite EDM electrode according to claim 1, characterized in that, The volume fraction of ceramic particles is increased by 2% for every 50 μm of thickness in the near-matrix region, 4% for every 50 μm of thickness in the transition region, and 4% for every 50 μm of thickness in the near-ceramic region.

4. The metal-ceramic gradient composite EDM electrode according to claim 1, characterized in that, The particle size of ceramic particles in the gradient transition layer and surface functional layer is 50~100nm.

5. A method for preparing a metal-ceramic gradient composite electrical discharge machining electrode, characterized in that the step... include: S1. A gradient unit layer is deposited on a metal substrate using a laser powder bed melting process. Metal powder and ceramic powder are simultaneously delivered through a dual powder feeding system. The layers are deposited one by one with the ceramic particle content increasing in a gradient manner to obtain a gradient transition layer. S2. Perform cold spray pretreatment on the surface of the gradient transition layer, and deposit ceramic particles on the surface of the gradient transition layer to form a ceramic particle pre-layer; S3. A laser cladding process is used to remelt the pre-placed ceramic particles to eliminate pores and strengthen the interfacial bonding, forming a dense surface functional layer.

6. The method for preparing a metal-ceramic gradient composite electrical discharge machining electrode according to claim 5, characterized in that, The laser powder bed melting process uses a four-laser LPBF system with a wavelength of 1070nm, a laser power of 400W, and a scanning speed of 800-1200 mm / s.

7. The method for preparing a metal-ceramic gradient composite electrical discharge machining electrode according to claim 5, characterized in that, The gas pressure for cold spraying is 5 MPa, with the main gas nitrogen at 5 MPa and the temperature at 550℃, and the auxiliary gas helium at 0.8 MPa. The spray distance is 25 mm.

8. The method for preparing a metal-ceramic gradient composite electrical discharge machining electrode according to claim 5, characterized in that, The porosity of the ceramic particle pre-layer is ≤5%.

9. The method for preparing a metal-ceramic gradient composite electrical discharge machining electrode according to claim 5, characterized in that, The energy density of laser cladding process is 150 J / mm². 2 The overlap rate is 40%, and the protective gas flow rate is 15L / min.

10. A metal-ceramic gradient composite EDM electrode according to any one of claims 1 to 4, characterized in that, The aforementioned technology is applied to the precision machining of EDM bushings for electrode diffuser blades and impeller blades, or the machining of deep and narrow grooves in mold cavities.

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