A superhard polycrystalline electrode and its preparation method and application

Abstract

The present invention belongs to the technical field of electrodes for electric spark machine tools, and in particular relates to a superhard polycrystalline electrode, a preparation method and application thereof. By optimizing the composition and component ratio, the present application obtains a superhard polycrystalline electrode with both wear resistance and electrical conductivity, thereby achieving the purpose of completing the composite processing of grinding and electricity in one go, and can also improve the high-temperature softening resistance and sharpness of the polycrystalline composite material, and can meet the requirements of high-efficiency, high-speed and high-precision composite processing of PDC surfaces.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrodes for electric spark machine tools, and in particular relates to a superhard polycrystalline electrode and a preparation method and application thereof. Background Art

[0002] In electrical discharge machining (EDM), the trade-off between machining efficiency and surface quality remains a key challenge. The goal is to simultaneously achieve high machining efficiency and excellent workpiece surface quality. In traditional EDM, the balance between machining efficiency and workpiece surface quality is achieved by adjusting discharge energy parameters, such as feed rate, tool lift angle, electrode rotation speed, and other non-discharge parameters. However, simply adjusting process parameters can only facilitate optimization and cannot fundamentally resolve this conflict. Consequently, hybrid EDM (Electro-Discharge Machining) has rapidly developed. Applications such as ultrasonic vibration, functional discharge media, and grinding wheels have been applied to EDM, resolving some of these challenges. However, these technologies still suffer from low efficiency, inconvenient operation, and complex processes. For the surface machining of polycrystalline diamond (PDC), in particular, a grinding wheel-based EDM (Electro-Discharge Machining) technique, combining EDM and mechanical grinding, is often employed. This technique, known as diamond grinding-EDDG (EDDG), uses a diamond grinding wheel as the tool electrode, resolving some of these challenges. However, these techniques still present complex processes, inconvenient operation, and uneven discharge patterns. Summary of the Invention

[0003] The purpose of the present invention is to provide a superhard polycrystalline electrode and its preparation method and application to solve the problem of processing efficiency in electrospark machining, that is, to obtain a new superhard polycrystalline electrode by sintering, and realize grinding-electric spark composite machining by one clamping; its one-piece molding structure solves the problems of complex procedures and inconvenient operation, as well as the assembly and contact problems in composite machining.

[0004] In order to achieve the above object, the technical solution adopted by the present invention is:

[0005] A method for preparing a superhard polycrystalline electrode comprises the following steps:

[0006] S1. First mixing process: The raw materials are mixed and placed in a ball mill for pre-alloying treatment, followed by vacuum high-pressure pressing, and then vacuum pre-sintering. The pressed powder is mechanically ball-milled to obtain a first mixed powder. The raw materials are composed of the following mass percentages: diamond 45-90%, cobalt powder 5-25%, titanium powder 5-15% or cubic boron nitride 45-90%, aluminum powder 5-25%, titanium powder 5-15%, the particle size of diamond and cubic boron nitride is 5-100μm, and the particle size of cobalt powder, aluminum powder, and titanium powder is 1-10μm;

[0007] S2. Second mixing process: According to the first mixing ratio of 60-80%, copper powder 10-30%, chromium powder 5-15% of the ingredients are mixed and placed in a ball mill for pre-alloying treatment, followed by vacuum high-pressure pressing, and then vacuum pre-sintering. The pressed powder is mechanically ball milled to obtain a second mixed powder, wherein the particle size of the copper powder and chromium powder is 10~50 μm;

[0008] S3 third mixing process: according to the second mixed powder 30 to 60%, ceramic powder 10 to 60%, pore-forming agent 5-35% of the ratio of the ingredients mixed into the ball mill pre-alloying treatment, after vacuum high-pressure pressing, and then vacuum pre-sintering, the pressed powder by mechanical ball milling to obtain a third mixed powder;

[0009] S4. Preparation of super-hard polycrystalline electrodes: The third mixed powder is first subjected to vacuum pre-sintering treatment, and then sintered at high temperature and high pressure to prepare a super-hard polycrystalline electrode; the final super-hard polycrystalline sintered electrode is obtained by mixing the raw materials three times, pressing twice and then crushing, and sintering twice. The main purpose is to achieve the sintering of the diamond and the cobalt powder with good affinity in the first mixing; the second mixing is to achieve the uniform distribution and sintering between the metal copper and the super-hard tissue; the third mixing is to achieve the organizational structure of the ceramic diamond grinding wheel; the first two vacuum pressings and then crushing are mainly for granulation, and the micron-sized diamond and metal powder are pre-alloyed by ball milling to form larger particle agglomerates, and then the granulated particle agglomerates are sent to the next process.

[0010] Furthermore, the ball mill pre-alloying treatment adopts a planetary ball milling process with a rotation speed of 50~900r / min and a transmission ratio of 1:2; the main effects of the pre-alloying treatment are: when the metal powder is mixed with superhard materials such as diamond or cubic boron nitride, the pre-alloying treatment of mechanical ball milling can be used to achieve uniform dispersion, metal particle refinement and participation of pre-alloyed powder in sintering, mainly to promote sintering to form a uniform organizational structure; the two pre-alloying treatments are both based on the mechanical alloying mechanism of high-energy ball milling and are carried out through a mechanical ball milling process, that is, during the high-speed rotation of the ball mill, the grinding balls are stirred in the mixed raw materials and form mutual grinding, and the added metal powders such as cobalt, aluminum, copper, chromium, etc. are uniformly dispersed, refined, and solid-solved.

[0011] Furthermore, the vacuum degree of the vacuum high pressure pressing is 10 -1 Pa, pressure is 30~50MPa.

[0012] Furthermore, the vacuum degree of the vacuum pre-sintering is 6.63×10 -3 Pa, temperature is 900℃; the pressure of high temperature and high pressure sintering is 5GPa, temperature is 1200~1400℃.

[0013] Furthermore, the ceramic micropowder is at least one of copper oxide, silicon dioxide, titanium carbide, and zirconium oxide, and the pore-forming agent is at least one of carbon particles, hollow aluminum oxide balls, glass balls, boron carbide, and boron nitride. The particle size of the ceramic micropowder is 20-100 μm; the particle size of the pore-forming agent is 15-65 μm.

[0014] The super-hard polycrystalline electrode prepared by the preparation method of super-hard polycrystalline electrode is super-hard mainly because the composition of the electrode contains micron-sized diamond or cubic boron nitride particles. During the discharge-grinding composite processing, as the metal bonding layer wears off, the diamond or cubic boron nitride particles are gradually exposed and then worn off, thereby exerting the wear resistance of super-hard materials. The entire wear to exposure process makes the electrode surface have a certain sharpness.

[0015] The application of super-hard polycrystalline electrode is to connect it with the alloy base and then install it on the EDM machine. The alloy base is connected with a motor, and the motor is connected to the spark machine joint to obtain a self-spinning super-hard polycrystalline electrode, which is used in the surface processing of PDC hard conductive materials.

[0016] The advantages of the present invention are as follows: in the sintered microstructure of the superhard polycrystalline electrode prepared by the present invention, conductive phases such as metallic cobalt are distributed around the diamond particles, forming a uniform distribution with copper, chromium, etc., and then forming a continuous dispersed structure with metals, ceramics, and pores. The metal phase forms a grid-like uniform distribution, providing a conductive structure that facilitates uniform discharge in the later stage, while the dense sintered structure formed by the diamond or cubic boron nitride particles ensures wear resistance during high-precision grinding. Uniform discharge ensures high-precision grinding-EDM hybrid processing while effectively ensuring surface processing quality and the generation of environmental hazards. The molten state at high temperature during EDM reduces the surface hardness of the workpiece material, and the diamond contained in the polycrystalline electrode can remove the workpiece material under low cutting force conditions under micro-contact surface conditions. In specific use, after connecting the superhard polycrystalline electrode to the original spark machine joint, it has an adjustable rotation function, increasing the relative motion between the electrode and the workpiece, and realizing a composite processing process of uniform EDM on the PCD surface and high-speed rotation grinding. The process is simple and easy to operate, and it takes into account the balance between processing efficiency and surface processing quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a schematic diagram of the microstructural morphology of the discharge region of the superhard polycrystalline electrode prepared in Example 2 of the present invention.

[0018] Figure 2 This is a schematic diagram of the microstructure morphology of the grinding area of ​​the superhard polycrystalline electrode in Example 2 of the present invention.

[0019] Figure 3These are the curves of PDC material removal rate, PDC surface roughness and tool electrode wear rate corresponding to electrodes with different diamond particle sizes during rough, semi-finish and finish machining in the application examples of the present invention.

[0020] Figure 4 These are the curves of the PDC material removal rate, PDC surface roughness and tool electrode wear rate corresponding to the roughing, semi-finishing and finishing of the superhard polycrystalline electrode at different rotation speeds in the application example of the present invention.

[0021] Figure 5 It is a graph showing the interaction between process discharge parameters and grinding parameters regarding the response factors PDC material removal rate and PDC surface roughness mean. DETAILED DESCRIPTION

[0022] Example 1

[0023] A method for preparing a superhard polycrystalline electrode comprises the following steps:

[0024] S1. First Mixing Process: The raw materials are mixed and placed in a ball mill for pre-alloying. They are then vacuum pressed under high pressure and pre-sintered in vacuum. The pressed powder is then mechanically ball-milled to obtain a first mixed powder. The raw materials are composed of the following percentages by weight: 65% diamond, 20% cobalt powder, and 15% titanium powder. The diamond particle size is 5-100 μm, and the aluminum and titanium powders have particle sizes of 1-10 μm.

[0025] S2. Second mixing process: The first mixed powder was mixed in a ratio of 65%, copper powder 25%, and chromium powder 10%, and then placed in a ball mill for pre-alloying. After vacuum high-pressure pressing and vacuum pre-sintering, the pressed powder was mechanically ball-milled to obtain a second mixed powder, wherein the particle size of the copper powder and chromium powder was 10-50 μm;

[0026] S3. The third mixing process: according to the second mixed powder 50%, copper oxide 15%, silicon dioxide 12%, titanium carbide 15%, alumina hollow spheres 5%, boron carbide 3% of the ingredients ratio after mixing into a ball mill pre-alloying treatment, followed by vacuum high-pressure pressing, and then vacuum pre-sintering, the pressed powder is mechanically ball milled to obtain a third mixed powder, the particle size of the ceramic powder is 20~100μm; the particle size of the pore-forming agent is 15~65μm;

[0027] S4. Preparation of super-hard polycrystalline electrodes: The third mixed powder is first subjected to vacuum pre-sintering treatment, and then sintered at high temperature and high pressure to prepare a super-hard polycrystalline electrode; the final super-hard polycrystalline sintered electrode is obtained by mixing the raw materials three times, pressing twice and then crushing, and sintering twice. The main purpose is to achieve the sintering of the diamond and the cobalt powder with good affinity in the first mixing; the second mixing is to achieve the uniform distribution and sintering between the metal copper and the super-hard tissue; the third mixing is to achieve the organizational structure of the ceramic diamond grinding wheel; the first two vacuum pressings and then crushing are mainly for granulation, and the micron-sized diamond and metal powder are pre-alloyed by ball milling to form larger particle agglomerates, and then the granulated particle agglomerates are sent to the next process.

[0028] Furthermore, the ball mill pre-alloying treatment adopts a planetary ball milling process with a rotation speed of 50~900r / min and a transmission ratio of 1:2; the main effects of the pre-alloying treatment are: when the metal powder is mixed with superhard materials such as diamond or cubic boron nitride, the pre-alloying treatment of mechanical ball milling can be used to achieve uniform dispersion, metal particle refinement and participation of pre-alloyed powder in sintering, mainly to promote sintering to form a uniform organizational structure; the two pre-alloying treatments are both based on the mechanical alloying mechanism of high-energy ball milling and are carried out through a mechanical ball milling process, that is, during the high-speed rotation of the ball mill, the grinding balls are stirred in the mixed raw materials and form mutual grinding, and the added metal powders such as cobalt, aluminum, copper, chromium, etc. are uniformly dispersed, refined, and solid-solved.

[0029] Furthermore, the vacuum degree of the vacuum high pressure pressing is 10 -1 Pa, pressure is 30~50MPa.

[0030] Furthermore, the vacuum degree of the vacuum pre-sintering is 6.63*10 -3 Pa, temperature is 900℃; the pressure of high temperature and high pressure sintering is 5GPa, temperature is 1200~1400℃.

[0031] The super-hard polycrystalline electrode prepared by the preparation method of super-hard polycrystalline electrode is super-hard mainly because the composition of the electrode contains micron-sized diamond or cubic boron nitride particles. During the discharge-grinding composite processing, as the metal bonding layer wears off, the diamond or cubic boron nitride particles are gradually exposed and then worn off, thereby exerting the wear resistance of super-hard materials. The entire wear to exposure process makes the electrode surface have a certain sharpness.

[0032] The application of super-hard polycrystalline electrode is to connect it with the alloy base and then install it on the EDM machine. The alloy base is connected with a motor, and the motor is connected to the spark machine joint to obtain a self-spinning super-hard polycrystalline electrode, which is used in the surface processing of PDC hard conductive materials.

[0033] Example 2

[0034] The difference between Example 2 and Example 1 is that the first mixed powder is composed of the following components in mass percentage: 70% diamond, 20% cobalt powder, and 10% titanium powder, the diamond particle size is selected to be 40 μm, and the particle sizes of aluminum powder and titanium powder are 2-4 μm;

[0035] The second mixed powder is composed of the following components in percentage by mass: 60% of the first mixed powder, 25% of copper powder, and 15% of chromium powder, and the particle size of the copper powder and the chromium powder is 20 μm;

[0036] The third mixed powder is composed of the following components in volume percentage: 65% of the second layer mixed powder, 10% of copper oxide, 12% of titanium carbide, 8% of zirconium oxide, 2% of hollow aluminum oxide balls, and 3% of boron carbide. The particle size of the ceramic micropowder is 25 μm; the particle size of the pore-forming agent is 20 μm.

[0037] Furthermore, in the mixing process, the planetary ball mill has a rotation speed of 450 r / min and a transmission ratio of 1:2; the operation time is 12 h; the vacuum degree of the vacuum high pressure pressing is 10 -1 Pa, the pressure is 30MPa; the vacuum degree of the vacuum pre-sintering is 6.63*10 -3 The pressure of high temperature and high pressure sintering is 5GPa and the temperature is 1400℃.

[0038] Application example description:

[0039] The present invention's superhard polycrystalline electrode is connected to an alloy substrate and then installed on an EDM machine as a tool electrode. The alloy substrate is connected to a motor, which is then connected to the EDM machine connector to produce a self-spinning superhard polycrystalline electrode. A PDC hard conductive material serves as the workpiece electrode for surface machining. After setting discharge and grinding parameters, machining is performed, and parameters such as PDC material removal rate, PDC surface roughness, and tool electrode wear rate are collected for comparative analysis of rough machining, semi-finish machining, and finish machining. During the experiments, the diamond particle sizes used in the superhard polycrystalline electrode were 10µm, 14µm, 28µm, 40µm, and 45µm, respectively; the tool electrode rotation speeds were 14, 16, 18, 20, and 22 m / s, respectively. The three parameters exhibited varying degrees of change as the diamond particle size varied. Appropriate adjustment of the process parameters can achieve the optimal option for efficient finish machining while ensuring tool electrode life. Increasing the tool electrode speed will increase the PDC material removal rate and tool electrode wear rate. Under the combined action of discharge and grinding, the PDC surface roughness can be optimized to meet the finishing requirements. Discharge and grinding have a significant mutual promotion effect. Interaction between discharge parameters and grinding parameters Figure 5In the figure, the curves of different colors represent the mean values ​​of the response factors corresponding to the four-level values ​​of different factors in the orthogonal experiment. This figure can show how the relationship between a categorical factor and a continuous response factor depends on the value of the second categorical factor. Usually, the horizontal average value of an influencing factor is shown on the horizontal axis, and a separate line is shown for each level of the other factor. The influencing factors include discharge parameters (discharge pulse width, breakdown voltage and peak current) and grinding parameters (diamond particle size and tool electrode speed). The vertical axis is the sample mean of the response factor. The parallel lines and non-parallel lines shown in the figure respectively indicate that the two factors do not interact and interact with each other. The higher the non-parallelism between the non-parallel lines, the stronger the interaction between the corresponding two factors. As the values ​​of each parameter increase, the interaction is more significant, indicating that the interaction between the discharge and grinding parameters has a significant impact on the processing effect, that is, the super-hard polycrystalline electrode of the present invention can effectively improve the processing efficiency in actual discharge and grinding composite processing.

Claims

1. A method for preparing a superhard polycrystalline electrode, characterized in that: The following steps are involved: S1. First Mixing Process: The raw materials are mixed and placed in a ball mill for pre-alloying, followed by vacuum high-pressure compaction and vacuum pre-sintering. The pressed powder is then mechanically ball-milled to obtain a first mixed powder. The raw materials are composed of the following percentages by weight: 45-90% diamond, 5-25% cobalt powder, 5-15% titanium powder or 45-90% cubic boron nitride, 5-25% aluminum powder, and 5-15% titanium powder. S2 second mixing process: according to the first mixing powder 60-80%, copper powder 10-30%, chromium powder 5-15% of the ratio of the ingredients were placed in a ball mill pre-alloying treatment, after vacuum high pressure pressing, and then vacuum pre-sintering, the pressed powder was mechanically milled to obtain a second mixed powder; S3 third mixing process: according to the second mixed powder 30 to 60%, ceramic powder 10 to 60%, pore-forming agent 5-35% of the ratio of the ingredients mixed into the ball mill pre-alloying treatment, after vacuum high-pressure pressing, and then vacuum pre-sintering, the pressed powder by mechanical ball milling to obtain a third mixed powder; S4. Preparation of super-hard polycrystalline electrodes: The third mixed powder is first subjected to vacuum pre-sintering treatment, and then sintered at high temperature and high pressure to prepare super-hard polycrystalline electrodes.

2. The method for preparing a superhard polycrystalline electrode according to claim 1, wherein: The ball mill pre-alloying treatment adopts a planetary ball milling process with a rotation speed of 50-900 r / min and a transmission ratio of 1:

2.

3. The method for preparing a superhard polycrystalline electrode according to claim 1, wherein: The vacuum degree of the vacuum high pressure pressing is 10 -1 Pa, pressure is 30~50MPa.

4. The method for preparing a superhard polycrystalline electrode according to claim 1, wherein: The vacuum degree of the vacuum pre-sintering is 6.63×10 -3 Pa, temperature is 900℃; the pressure of high temperature and high pressure sintering is 5GPa, temperature is 1200~1400℃.

5. The method for preparing a superhard polycrystalline electrode according to claim 1, wherein: The ceramic powder is at least one of copper oxide, silicon dioxide, titanium carbide and zirconium oxide, and the pore-forming agent is at least one of carbon particles, hollow aluminum oxide balls, glass balls, boron carbide and boron nitride.

6. A superhard polycrystalline electrode prepared by the method for preparing a superhard polycrystalline electrode according to any one of claims 1 to 5.

7. The use of the superhard polycrystalline electrode according to claim 6, characterized in that: After connecting it to the alloy substrate, it is installed on the EDM machine and used in the surface processing of PDC hard conductive materials.

Images