Copper infiltrated graphite electrode and method of manufacturing the same

Abstract

The application discloses a copper-infiltrated graphite electrode for electric spark machining and a manufacturing method thereof. The copper-infiltrated graphite electrode is composed of a porous graphite preform, a Cr layer and copper alloy infiltrated into the porous graphite preform. The manufacturing process comprises the following steps: powder mixing, porous graphite preform forming (unit layer preparation, organic network construction and multiple repetitions), high-temperature carbonization, direct-current magnetron sputtering of the Cr layer, vacuum high-temperature copper infiltration, mechanical processing and ultrasonic cleaning and drying. The method can realize the rapid combination of graphite and copper alloy and control the content and distribution of the copper alloy in the graphite matrix. The prepared copper-infiltrated graphite electrode has the characteristics of high strength, high electrical conductivity and long service life and is used for electric spark machining, and the density of the electrode is not less than 1.9 g / cm3. The electrode overcomes the shortcomings of poor mechanical properties of traditional graphite electrodes and weak anti-electric corrosion capacity of copper electrodes.

Description

Technical Field

[0001] This invention relates to a method for manufacturing a copper-impregnated graphite electrode, belonging to the field of forming and manufacturing technology. Specifically, it relates to a method for incorporating a high-temperature copper alloy liquid into a porous graphite preform under vacuum pressure to obtain a high-strength, high-conductivity, and long-life copper-impregnated graphite electrode. Background Technology

[0002] Currently, modern manufacturing primarily uses copper and graphite electrodes in electrical discharge machining (EDM). Compared to copper and tungsten electrodes, graphite electrodes are widely used in EDM technology due to their advantages such as low cost, high temperature resistance, low consumption, fast processing speed, low coefficient of thermal expansion, and high processing accuracy. However, the organic matter in graphite leaves many micropores during the carbonization process, resulting in low structural strength, easy detachment, and poor shape retention, affecting processing accuracy. Furthermore, its electrical conductivity is lower than copper, impacting production efficiency. Its poor oxidation resistance leads to rapid electrode consumption, significantly reducing lifespan and increasing costs.

[0003] To ensure the smooth operation of the equipment and achieve cost reduction and efficiency improvement, it is necessary to take measures to prevent electrode oxidation, reduce the number of electrode adjustments, reduce the labor intensity of workers, and reduce electrode consumption.

[0004] Current research on improving the performance of graphite electrodes in electrical discharge machining mainly focuses on the following three aspects:

[0005] 1. Material performance optimization: such as using chemical reagents or physical methods to remove impurities and improve the purity of graphite to enhance its conductivity; preparing high-density, high-smoothness graphite electrode materials by using small-diameter graphite particles or by pressing under extreme pressure to improve the structural strength and processing accuracy of the electrodes; and treating graphite electrode materials at low temperatures to improve the conductivity of graphite.

[0006] 2. Improved forming process: For example, using isostatic pressing instead of molding and extrusion can improve the mechanical properties of graphite, resulting in graphite with a uniform internal structure and high strength, high density, and high conductivity. However, the disadvantages are long cycle time, large investment, and expensive equipment.

[0007] 3. Composite electrode materials: such as copper-based / graphite composite electrodes. It has been found that the addition of a small amount of graphite is beneficial to the processing of positive electrodes, and a smoother and cleaner surface can be obtained. However, copper-based electrodes are more expensive, and there is a lack of research on graphite-based copper composite electrodes.

[0008] Current research abroad not only focuses on optimizing the performance of electrode materials, but also emphasizes the service life and environmental performance of electrodes, and studies ways to improve electrode wear mechanisms and surface treatment technologies.

[0009] For example, the wear of graphite electrodes can be investigated by changing electrode parameters and the medium; carbon nanotubes can be used to enhance the mechanical strength and conductivity of graphite electrodes; complex chemical reagents can be used to treat the surface of graphite to enhance the structural strength and oxidation resistance of graphite after forming; high-density, high-smoothness, and high-precision graphite electrodes can be prepared using ultrafine particle technology; and graphite electrode formulations can be improved to reduce pollution caused by production.

[0010] In summary, modern manufacturing places higher demands on graphite electrodes, and improving surface finish, structural strength, and service life are key technical challenges. Currently, there is a lack of effective processing methods to achieve both guaranteed processing results and reduced electrode wear. Summary of the Invention

[0011] To address the shortcomings of current graphite electrodes, such as low working accuracy, low structural strength, poor shape retention, high wear, and short lifespan, this invention provides a copper-infiltrated graphite electrode for electrical discharge machining (EDM) and its manufacturing method. The basic process is as follows: This invention provides a copper-infiltrated graphite electrode for EDM and its manufacturing method. First, graphite powder is pretreated by coating using a fluidized bed coating dryer. After fine crushing and sieving, it is uniformly mixed in a ball mill. Then, a graphite preform is rapidly prepared using micro-thermal pressing technology. During the unit layer preparation process, multiple printed organic networks are placed and the process is repeated multiple times. Next, the graphite preform is carbonized at high temperature to obtain the preform. Using DC magnetron sputtering technology, Cr interlayers are sputtered into the impregnation channels within the graphite preform. The graphite preform is placed in an impregnation furnace, and a copper alloy solution is impregnated into the impregnation channels inside the graphite under high temperature, vacuum, and pressure conditions. Finally, it is machined, shaped, cleaned, and dried to obtain the copper-infiltrated graphite electrode.

[0012] A copper-infiltrated graphite electrode is obtained by sintering an organic network within a graphite preform to form a network channel, attaching a chromium film to the inner wall of the network channel by magnetron sputtering, and then impregnating the channel with a copper alloy.

[0013] The organic network is a mesh-like organic network printed by a 3D printer, and the organic material includes polylactic acid; the graphite preform includes artificial graphite.

[0014] The copper alloy is composed of Cu, Sn, Al2O3, and Zn, all with a purity greater than 99.5%. Sn accounts for 1-3% of the mass fraction of the copper alloy, Al2O3 accounts for 0.3-1% of the mass fraction of the copper alloy, Zn accounts for 1-2% of the mass fraction of the copper alloy, and the remainder is Cu.

[0015] The method for manufacturing the copper-impregnated graphite electrode allows for control of the number and distribution of impregnation channels within the graphite preform by designing an organic network, thereby controlling the copper alloy content in the graphite preform. The method includes the following steps:

[0016] (1) Preparation of organic networks: Multiple mesh-like organic networks were 3D printed;

[0017] (2) Powder pretreatment: Graphite powder is pretreated by coating with phenolic resin, then crushed and ball-milled to obtain graphite powder.

[0018] In some embodiments, a fluidized bed coating dryer is used to coat graphite powder, allowing the graphite particles to be coated with phenolic resin, ensuring sufficient bonding between the graphite particles in the subsequent process.

[0019] The graphite powder is crushed to obtain graphite particles with smaller particle sizes. The smaller the particle size, the smoother the surface of the resulting preform, i.e., the higher the smoothness, the higher the density, and the higher the structural strength of the preform. The graphite preform is composed of high-strength artificial graphite powder and natural flake graphite powder.

[0020] (3) Micro-hot pressing to form porous graphite preform: graphite powder is spread to prepare unit layers, and the organic network in step (1) is added. This process is repeated multiple times, and the graphite preform is prepared using micro-hot pressing technology.

[0021] The organic network decomposes after high-temperature sintering, and the resulting channels become the channels for subsequent impregnation with copper alloy liquid; the graphite preform with the required structure can be quickly prepared using micro-hot pressing forming technology.

[0022] (4) High-temperature carbonization: The graphite preform prepared in the high-temperature sintering step (3) forms a network channel;

[0023] (5) DC magnetron sputtering of Cr layer: DC magnetron sputtering is performed on the sintered graphite preform in step (4) to form a Cr interlayer in the network channel of the graphite preform.

[0024] Using physical vapor deposition (PVD), a small amount of Cr is sputtered into the channels inside the graphite preform using DC magnetron sputtering technology to form a Cr interlayer to solve the problem of poor bonding between C and Cu.

[0025] (6) Vacuum high-temperature copper infiltration: The graphite preform from step (5) is impregnated with a copper alloy solution under high temperature and vacuum pressure conditions.

[0026] Impregnating copper alloy solutions under high temperature, vacuum, and pressure conditions can effectively improve the impregnation efficiency.

[0027] (7) Post-processing: Clean and dry the copper-impregnated graphite material in step (6) to complete the preparation of the electrode.

[0028] In some embodiments, the pre-printed organic network is manufactured using a high-voltage electrostatic fusion 3D printer. The network comprises polylactic acid, and its radial dimensions match the graphite matrix, ranging from 25 to 30 mm. The line diameter is 40 to 400 μm, and the minimum feature size is 10 to 20 nm. The shape is shown in the attached figure. Figure 1 As shown, the shapes include: ring, snowflake, V, and Y, and their dimensions can be adjusted.

[0029] The graphite powder is artificial graphite powder with a carbon content greater than 99%; the coating solution is a mixture of liquid phenolic resin with a concentration of 35-40 mass% and anhydrous ethanol to obtain a liquid phenolic resin mixture with a phenolic resin mass fraction of 10-20 wt.%, and the mixture and graphite powder are mixed in a kneader for 5-11 hours; the graphite powder is crushed and sieved to obtain the material through a 1750-6250 mesh sieve, and then put into a ball mill for uniform mixing for 5-8 hours.

[0030] The thickness of the unit layer mentioned in step (3) is 5mm-8mm; the machine used is a micro hot press molding machine, the impact speed of the electromagnetic pressure head is 110~160 times / min, the forming pressure is 10~15MPa, the holding time is 15~20min, the heating temperature is 100-120℃, and the density of the prepared graphite preform is 1.9-2.0g / cm3.

[0031] In step (4), under a vacuum of -0.1 Pa and an inert atmosphere, the temperature is increased from room temperature to 400°C at a rate of 30-60°C / h, then increased to 600°C at a rate of 100-120°C / h, and finally increased to 800°C at a rate of 180-200°C / h. The temperature is held for 30 minutes, and then the furnace is cooled to room temperature before being removed. The above process is repeated at least once.

[0032] The inert atmosphere includes argon or nitrogen with a purity of 99% or higher.

[0033] In the process of DC magnetron sputtering deposition of the Cr layer in step (5), the graphite preform is first placed in NaOH solution for roughening, and then Cr is sputtered onto the graphite preform under the conditions of sputtering voltage of 300-350V, sputtering current of 0.2-0.4A, sputtering pressure of 1.0-1.5Pa, sputtering time of 5-10min, argon concentration of 99%, and temperature of 300-350℃. The thickness of the Cr sputtered interlayer is 1.5-2.0μm.

[0034] The graphite preform was roughened using NaOH solution to increase its specific surface area and the adhesion of the coating.

[0035] In step (6) of the vacuum high-temperature copper infiltration process, the graphite preform is placed in a vacuum impregnation kettle, vacuumed to below -0.1Pa and pressurized, heated to 1400~1600℃, and then the copper alloy solution is impregnated into the impregnation channel in the graphite preform under pressure of 1~2MPa and high temperature for 10~15min. Then it is dried in a hot air drying oven at 70~90℃. The above process is repeated at least once.

[0036] The copper alloy is composed of Cu, Sn, Al2O3, and Zn, all with a purity greater than 99.5%. Sn accounts for 1-3% of the mass fraction of the copper alloy, Al2O3 accounts for 0.3-1% of the mass fraction of the copper alloy, Zn accounts for 1-2% of the mass fraction of the copper alloy, and the remainder is Cu.

[0037] In some embodiments, the post-processing steps further include machining and shaping, i.e., machining the graphite preform to create mounting holes and working cone surfaces.

[0038] The copper-infiltrated graphite electrode used in electrical discharge machining is prepared according to the method described above. The copper-infiltrated graphite electrode comprises graphite, copper alloy, and chromium, wherein the volume percentage of graphite powder is 90-95%, the volume percentage of copper alloy is 2-8%, and the volume percentage of chromium is 1-3%. The copper alloy is regularly distributed in the impregnation channels in the graphite preform to form a high-strength, high-conductivity, and long-life copper-infiltrated graphite electrode.

[0039] The above-mentioned technical method has the following advantages:

[0040] 1. The present invention uses polylactic acid (melting point 105°C) as an organic material during the pressing process. During high-temperature sintering, the organic material forms pore channels before the phenolic resin is pyrolyzed, thus artificially constructing impregnation channels. Furthermore, the content and distribution of copper alloy in the graphite preform are designed and controlled to regulate the performance of the graphite electrode.

[0041] 2. Using physical vapor deposition (PVD), a small amount of Cr is sputtered into the impregnation channels in the graphite preform using DC magnetron sputtering technology. This avoids the characteristics of C and Cu being non-wetting and having poor bonding, and forms a Cr interlayer that enhances the bonding. Attached Figure Description

[0042] The present invention will be further described below with reference to the accompanying drawings:

[0043] Figure 1 To generate a printed organic network diagram, four shapes are provided: A is a ring, B is a snowflake, C is a V-shape, and D is a Y-shape.

[0044] Figure 2 The diagram shows a graphite preform containing an organic network, with a ring-shaped organic network as an example.

[0045] Figure 3 This is a diagram of the graphite preform after machining.

[0046] Figure 4 The basic process flow for manufacturing copper-impregnated graphite electrodes according to embodiments of the present invention is as follows. Detailed Implementation

[0047] The following is a specific embodiment provided by the inventor.

[0048] Example 1:

[0049] A copper-impregnated graphite electrode for electrical discharge machining and its manufacturing method are disclosed. The graphite is artificial graphite. The copper alloy is composed of Cu, Sn, Al₂O₃, and Zn, all with a purity greater than 99.5%. Sn accounts for 1% of the mass fraction of the copper alloy, Al₂O₃ accounts for 0.3% of the mass fraction, Zn accounts for 1% of the mass fraction, and the remainder is Cu. The Cr powder has a purity greater than 99.5%.

[0050] The volume percentage of graphite powder is 93%, copper alloy is 5%, and chromium is 2%.

[0051] The specific preparation steps are as follows:

[0052] (1) Design and preparation of organic networks

[0053] Based on the shape of the electrodes, different shapes of organic materials in a ring-like mesh were designed, as shown in the attached figure. Figure 1 The ring-shaped organic network shown in Figure A was printed using a high-voltage electrostatic melting 3D printer. Eleven organic networks were printed, with the radial dimension of the network matching the graphite matrix at 30 mm and the line diameter at 40 μm.

[0054] (2) Preparation of mixed powders

[0055] The graphite powder is artificial graphite powder with a carbon content greater than 99%; the coating solution is a mixture of 40 mass% liquid phenolic resin and anhydrous ethanol to obtain a liquid phenolic resin mixture with a phenolic resin mass fraction of 18~20 wt.%, and the mixture and graphite powder are placed in a kneader and mixed for 10 hours; the graphite powder is crushed and sieved to obtain the material through a 1750~6250 mesh sieve, and then placed in a ball mill and mixed evenly for 5~8 hours.

[0056] (3) Preparation of porous graphite preforms

[0057] The machine used is a micro thermoforming machine. The impact speed of the electromagnetic pressure head is 150 times / min, the forming pressure is 12~15MPa, the holding time is 15~20min, the unit layer thickness is 5mm, the heating temperature is 100℃, and the density of the prepared graphite preform is 1.9~2.0g / cm3. During the pressing process, 11 printed organic networks are placed in the graphite preform. The graphite preform is cylindrical with a height of 60mm and a diameter of 30mm.

[0058] (4) High-temperature carbonization

[0059] The graphite preform is evacuated to below -0.1 Pa in a carbonization furnace, and then heated from room temperature to 400°C at a rate of 60°C / h while 99% pure argon or nitrogen is introduced; then the temperature is increased to 600°C at a rate of 120°C / h; finally, the temperature is increased to 800°C at a rate of 200°C / h and held for 30 minutes. Finally, it is cooled to room temperature with the furnace and removed.

[0060] (5) DC magnetron sputtering of Cr layer

[0061] The graphite preform was roughened in a 200 g / L NaOH solution, and then Cr was sputtered onto the graphite preform using an FJL520 high-vacuum composite sputtering device. The sputtering voltage was 350 V, the sputtering current was 0.4 A, the sputtering pressure was 1.0~1.5 Pa, the sputtering time was 5~10 min, the argon concentration was 99%, the temperature was 300 ℃, and the Cr sputtering interlayer thickness was 1.5~2.0 μm.

[0062] (6) Vacuum high-temperature impregnation of copper alloy

[0063] The graphite preform is placed in an impregnation vessel. The process is as follows: the graphite preform is placed in a vacuum impregnation vessel, and a vacuum is drawn to below -0.1 Pa. Then, the temperature is increased to 1400℃ at a rate of 200℃ / h. A copper alloy solution is impregnated into the impregnation channel in the graphite preform under a pressure of 1 MPa for 10-15 minutes. Subsequently, it is dried in a hot air drying oven at a temperature below 100℃. The above process is repeated twice.

[0064] (7) Machining and shaping

[0065] The graphite preform is machined by cutting, and mounting holes are machined on one end face of the cylindrical graphite preform, while a conical surface for electrical discharge machining is machined on the other side.

[0066] (8) Post-processing

[0067] The copper-impregnated graphite electrodes were cleaned using an ultrasonic cleaner and then dried using a dryer.

[0068] The prepared copper-impregnated graphite electrode was found to have a density of 2.10 g / cm³, a Vickers hardness of 382 HV, a flexural strength of 52 MPa, a compressive strength of 102 MPa, and a resistivity of 6.32 μΩ·m.

[0069] Example 2:

[0070] This is basically the same as Example 1, except that the shape of the prepared organic network is different, and an attachment is used. Figure 1 B: Snowflake-shaped organic network. Graphite powder accounts for 95% of the volume, copper alloy accounts for 3%, and chromium accounts for 2%. Experimentally, the prepared copper-impregnated graphite electrode has a density of 2.12 g / cm³, a Vickers hardness of 357 HV, a flexural strength of 46 MPa, a compressive strength of 92 MPa, and a resistivity of 7.83 μΩ·m.

[0071] Example 3:

[0072] This is basically the same as Example 1, except that the shape of the prepared organic network is different, and an attachment is used. Figure 1 C: V-shaped organic network. Graphite powder accounts for 90% of the volume, copper alloy accounts for 7%, and chromium accounts for 3%. Experimentally, the prepared copper-impregnated graphite electrode has a density of 2.08 g / cm³, a Vickers hardness of 361 HV, a flexural strength of 48 MPa, a compressive strength of 97 MPa, and a resistivity of 7.62 μΩ·m.

[0073] Example 4:

[0074] This is basically the same as Example 1, except that the shape of the prepared organic network is different, and an attachment is used. Figure 1 D: Y-shaped organic network. Graphite powder accounts for 91% of the volume, copper alloy accounts for 8%, and chromium accounts for 1%. Experimentally, the prepared copper-impregnated graphite electrode has a density of 2.09 g / cm³, a Vickers hardness of 348 HV, a flexural strength of 44 MPa, a compressive strength of 87 MPa, and a resistivity of 8.57 μΩ·m.

[0075] Counterexample 1:

[0076] The method is basically the same as in Example 1, except that the volume percentage of graphite powder is 90%, the volume percentage of copper alloy is 5%, and the volume percentage of chromium is 5%, resulting in a Cr sputtering interlayer thickness of 1.8~2.3μm. Experimental measurements showed that the prepared copper-infiltrated graphite electrode had a density of 2.11g / cm³, a Vickers hardness of 315HV, a flexural strength of 38MPa, a compressive strength of 76MPa, and a resistivity of 7.57μΩ·m.

[0077] Counterexample 2:

[0078] The process is basically the same as in Example 1, except that pure copper liquid was used for vacuum high-temperature impregnation. Experimental results showed that the prepared copper-impregnated graphite electrode had a density of 2.22 g / cm³, a Vickers hardness of 287 HV, a flexural strength of 33 MPa, a compressive strength of 69 MPa, and a resistivity of 9.69 μΩ·m.

Claims

1. A method for manufacturing a copper-impregnated graphite electrode, characterized in that, Includes the following steps: (1) Preparation of organic network: Multiple mesh-like organic networks are 3D printed; the organics include polylactic acid; (2) Powder pretreatment: Graphite powder is pretreated by coating with phenolic resin, then crushed and ball-milled to obtain graphite powder. (3) Micro-hot pressing to form porous graphite preform: graphite powder is spread to prepare unit layers, and the organic network in step (1) is added. This process is repeated multiple times. The graphite preform is prepared using micro-hot pressing technology. The organic network will decompose after high-temperature sintering, and the resulting channels are the impregnation channels for the copper alloy solution to be impregnated later. (4) High-temperature carbonization: The graphite preform prepared in the high-temperature sintering step (3) forms a network channel; (5) DC magnetron sputtering of Cr layer: DC magnetron sputtering is performed on the sintered graphite preform in step (4) to form a Cr interlayer in the network channel of the graphite preform. (6) Vacuum high-temperature copper infiltration: The graphite preform from step (5) is impregnated with a copper alloy solution under high temperature and vacuum pressure conditions, and the copper alloy solution is impregnated into the impregnation channel in the graphite preform. (7) Post-processing: Clean and dry the copper-impregnated graphite material in step (6) to complete the preparation of the electrode.

2. The method for manufacturing a copper-impregnated graphite electrode according to claim 1, characterized in that, The structure of the organic network includes any one or more combinations of ring-shaped, snowflake-shaped, V-shaped, and Y-shaped structures.

3. The copper-impregnated graphite electrode according to claim 1, characterized in that, The graphite preform includes artificial graphite.

4. The method for manufacturing a copper-impregnated graphite electrode according to claim 1, characterized in that, The thickness of the unit layer mentioned in step (3) is 5mm-8mm; Graphite preforms are obtained by using an electromagnetic indenter with an impact speed of 110-160 times / min, a forming pressure of 10-15 MPa, a holding time of 15-20 min, and a heating temperature of 100-120℃.

5. The method for manufacturing a copper-impregnated graphite electrode according to claim 1, characterized in that, In step (4), under a vacuum of -0.1 Pa and an inert atmosphere, the temperature is increased from room temperature to 400°C at a rate of 30-60°C / h, then increased to 600°C at a rate of 100-120°C / h, and finally increased to 800°C at a rate of 180-200°C / h. The temperature is held for 30 minutes, and then the furnace is cooled to room temperature before being removed. The above process is repeated at least once.

6. The method for manufacturing a copper-impregnated graphite electrode according to claim 1, characterized in that, In step (5), during the DC magnetron sputtering of the Cr layer, the graphite preform is first placed in a NaOH solution for roughening. Then, under the conditions of sputtering voltage of 300-350V, sputtering current of 0.2-0.4A, sputtering pressure of 1.0-1.5Pa, sputtering time of 5-10min, argon concentration of 99%, and temperature of 300-350℃, Cr is sputtered onto the graphite preform. The thickness of the Cr sputtered interlayer is 1.5-2.0μm.

7. The method for manufacturing a copper-impregnated graphite electrode according to claim 1, characterized in that, In step (6) of the vacuum high-temperature copper infiltration process, the graphite preform is placed in a vacuum impregnation kettle, vacuumed to below -0.1Pa and pressurized, heated to 1400~1600℃, and then the copper alloy solution is impregnated into the impregnation channel in the graphite preform under pressure of 1~2MPa and high temperature for 10~15min. Then it is dried in a hot air drying oven at 70~90℃. The above process is repeated at least once. The copper alloy is composed of Cu, Sn, Al2O3, and Zn, all with a purity greater than 99.5%. Sn accounts for 1-3% of the mass fraction of the copper alloy, Al2O3 accounts for 0.3-1% of the mass fraction of the copper alloy, Zn accounts for 1-2% of the mass fraction of the copper alloy, and the remainder is Cu.

8. The method for manufacturing a copper-impregnated graphite electrode according to any one of claims 1-6, characterized in that, The copper alloy is composed of Cu, Sn, Al2O3, and Zn, all with a purity greater than 99.5%. Sn accounts for 1-3% of the mass fraction of the copper alloy, Al2O3 accounts for 0.3-1% of the mass fraction of the copper alloy, Zn accounts for 1-2% of the mass fraction of the copper alloy, and the remainder is Cu.

9. A copper-impregnated graphite electrode used in electrical discharge machining, characterized in that, The copper-infiltrated graphite electrode prepared according to any one of claims 1-8 comprises graphite, copper alloy, and chromium, wherein the volume percentage of graphite powder is 90-95%, the volume percentage of copper alloy is 2-8%, and the volume percentage of chromium is 1-3%; the copper alloy is regularly distributed in the impregnation channels in the graphite preform to form a high-strength, high-conductivity, and high-life copper-infiltrated graphite electrode.

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