Superhard polycrystalline electrode and preparation method and application thereof

Abstract

The invention belongs to the technical field of electrodes for electric spark machine tools, and particularly relates to a superhard polycrystalline electrode and a preparation method and application thereof.The superhard polycrystalline electrode with abrasion resistance and electrical conductivity is obtained by optimizing components and the component proportion, the purpose of completing combined machining of grinding and electric machining at a time is achieved, and the service life of the superhard polycrystalline electrode is prolonged. And the high-temperature softening resistance and sharpness of the polycrystalline composite material can be improved, and the use requirements of high-efficiency, high-speed and high-precision composite machining of the PDC surface can be met.

Description

Technical Field

[0001] The 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 EDM technology, the contradiction between machining efficiency and surface quality has always been a key problem that needs to be solved, that is, to obtain high machining efficiency and excellent workpiece surface quality at the same time. In traditional EDM, the balance between machining efficiency and workpiece surface quality is achieved by adjusting discharge energy parameters such as feed speed, tool lifting angle, electrode rotation speed and other non-discharge parameters. However, simple process parameter adjustment can only promote optimization, and cannot fundamentally solve the contradiction. Therefore, EDM technology has been rapidly developed. For example, ultrasonic vibration, functional discharge medium and grinding wheel grinding are applied to EDM, which solves some problems but still has shortcomings such as low efficiency, inconvenient operation and complex process. Especially for the surface processing of polycrystalline diamond (PDC), grinding wheel grinding-EDM technology, which is a diamond grinding EDM (EDDG) that performs EDM and mechanical grinding at the same time, is often used. It uses diamond grinding wheel as tool electrode to solve certain problems, but still has complex process and inconvenient operation, and there is a problem of uneven discharge. Summary of the invention

[0003] The purpose of the present invention is to provide a superhard polycrystalline electrode and its preparation method and application, so as to solve the problem of machining efficiency in electrospark machining, that is, to obtain a new superhard polycrystalline electrode by sintering, and realize grinding-electrospark composite machining by one clamping; its one-piece molded structure solves the problems of complicated 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: A method for preparing a superhard polycrystalline electrode comprises the following steps: S1. The first mixing process: the raw materials are mixed and placed in a ball mill for pre-alloying, followed by vacuum high-pressure pressing, and then vacuum pre-sintering. The pressed powder is finely crushed by mechanical ball milling to obtain the first mixed powder. The raw materials are composed of the following mass percentages: 45-90% diamond or cubic boron nitride, 5-25% cobalt powder or aluminum powder, and 5-15% titanium powder. The particle size of diamond and cubic boron nitride is 5-100 μm, and the particle size of cobalt powder, aluminum powder, and titanium powder is 1-10 μm; S2. Second mixing treatment: according to the first mixed powder 60-80%, copper powder 10-30%, chromium powder 5-15% of the ingredients ratio mixed into a ball mill pre-alloying treatment, then vacuum high pressure pressing, and then vacuum pre-sintering, the pressed powder by mechanical ball milling to obtain the second mixed powder, wherein the copper powder, chromium powder particle size of 10 ~ 50 μ m; S3. The third mixing process: according to the second mixed powder 30-60%, ceramic powder 10-60%, pore-forming agent 5-35% 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 by mechanical ball milling to obtain the third mixed powder; S4. Preparation of superhard polycrystalline electrode: The third mixed powder is first subjected to vacuum pre-sintering treatment, and then high temperature and high pressure sintering molding to prepare superhard polycrystalline electrode; the final superhard polycrystalline sintered electrode is obtained by three mixing of raw materials, two pressings and then crushing, and two sintering processes. The main purpose is to achieve the organizational sintering of diamond and cobalt powder with good affinity in the first mixing; the second mixing is to achieve the uniform distribution and sintering between metal copper and superhard tissue; the third mixing is to achieve the organizational structure of 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 enter the next process.

[0005] 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 pre-alloyed powder participation 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 cobalt, aluminum, copper, chromium and other metal powders are uniformly dispersed, refined, and solid-dissolved.

[0006] Furthermore, the vacuum degree of the vacuum high pressure pressing is 10 -1 Pa, pressure is 30~50MPa.

[0007] Furthermore, the vacuum degree of the vacuum pre-sintering is 6.63*10 -3 Pa, the temperature is 900℃; the pressure of high temperature and high pressure sintering is 5GPa, the temperature is 1200~1400℃.

[0008] Furthermore, the ceramic powder is at least one of copper oxide, silicon dioxide, titanium carbide, and zirconium oxide, 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 powder is 20-100 μm; the particle size of the pore-forming agent is 15-65 μm.

[0009] The superhard polycrystalline electrode prepared by the preparation method of superhard polycrystalline electrode is superhard mainly because 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 achieving the wear resistance of superhard materials. The entire wear to exposure process makes the electrode surface have a certain sharpness.

[0010] The application of super-hard polycrystalline electrode is to connect it with alloy substrate and install it on electric spark machine. The alloy substrate is connected with motor, and the motor is connected with the joint of spark machine to obtain the self-spinning super-hard polycrystalline electrode, which is used in the surface processing of PDC hard conductive materials.

[0011] 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 metal cobalt are distributed around the diamond particles, and are evenly distributed with copper, chromium, etc., and then form a continuous dispersed organizational structure with metals, ceramics and pores, etc., wherein the metal phase forms a grid-like uniform distribution to provide a conductive organization to facilitate uniform discharge in the later stage, and the dense sintered organization formed by diamond or cubic boron nitride particles ensures the wear resistance in high-precision grinding. Uniform discharge ensures high-precision grinding-electric spark composite processing, while effectively ensuring the surface processing quality and the generation of environmental harmful substances; the molten state at high temperature during discharge processing reduces the surface hardness of the workpiece material, and the diamond contained in the polycrystalline electrode can remove the workpiece material under the condition of small cutting force on the micro-contact surface; when used specifically, after the superhard polycrystalline electrode is connected to the joint of the original spark machine, it has an adjustable rotation function, increases the relative movement of the electrode and the workpiece, and realizes the composite processing technology of uniform discharge processing and high-speed rotation grinding of the PCD surface, with simple procedures and convenient operation, taking into account the balance between processing efficiency and surface processing quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 It 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.

[0013] Figure 2 It is a schematic diagram of the microstructure morphology of the grinding area of ​​the superhard polycrystalline electrode in Example 2 of the present invention.

[0014] Figure 3These are the curves of PDC material removal rate, PDC surface roughness and tool electrode wear rate corresponding to electrodes with different diamond grain sizes during rough, semi-finish and finish machining in the application examples of the present invention.

[0015] Figure 4 These are the curves of PDC material removal rate, PDC surface roughness and tool electrode loss rate corresponding to rough, semi-finish and finish machining of the superhard polycrystalline electrode at different rotation speeds in the application example of the present invention.

[0016] Figure 5 It is the interaction relationship diagram between process discharge parameters and grinding parameters on the response factor PDC material removal rate and PDC surface roughness mean. DETAILED DESCRIPTION

[0017] Example 1 A method for preparing a superhard polycrystalline electrode comprises the following steps: S1. The first mixing process: the raw materials are mixed and placed in a ball mill for pre-alloying, followed by vacuum high-pressure pressing, and then vacuum pre-sintering. The pressed powder is finely crushed by mechanical ball milling to obtain the first mixed powder. The raw materials are composed of the following mass percentages: 65% diamond, 20% aluminum powder, and 15% titanium powder. The diamond particle size is 5-100 μm, and the particle sizes of aluminum powder and titanium powder are 1-10 μm. S2. Second mixing treatment: 65% of the first mixed powder, 25% of the copper powder, and 10% of the chromium powder 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 finely crushed by mechanical ball milling to obtain the second mixed powder, wherein the particle size of the copper powder and the chromium powder is 10~50 μm; S3. The third mixing process: according to the second mixed powder 50%, copper oxide 15%, silicon dioxide 12%, titanium carbide 15%, aluminum oxide hollow sphere 5%, boron carbide 3% of the proportion of mixing and placing into a ball mill for pre-alloying treatment, and then vacuum high pressure pressing, and then vacuum pre-sintering, the pressed powder is mechanically ball milled to obtain the third mixed powder, the particle size of the ceramic powder is 20~100μm; the particle size of the pore-forming agent is 15~65μm; S4. Preparation of superhard polycrystalline electrode: The third mixed powder is first subjected to vacuum pre-sintering treatment, and then high temperature and high pressure sintering molding to prepare superhard polycrystalline electrode; the final superhard polycrystalline sintered electrode is obtained by three mixing of raw materials, two pressings and then crushing, and two sintering processes. The main purpose is to achieve the organizational sintering of diamond and cobalt powder with good affinity in the first mixing; the second mixing is to achieve the uniform distribution and sintering between metal copper and superhard tissue; the third mixing is to achieve the organizational structure of 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 enter the next process.

[0018] 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 pre-alloyed powder participation 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 cobalt, aluminum, copper, chromium and other metal powders are uniformly dispersed, refined, and solid-dissolved.

[0019] Furthermore, the vacuum degree of the vacuum high pressure pressing is 10 -1 Pa, pressure is 30~50MPa.

[0020] Furthermore, the vacuum degree of the vacuum pre-sintering is 6.63*10 -3 Pa, the temperature is 900℃; the pressure of high temperature and high pressure sintering is 5GPa, the temperature is 1200~1400℃.

[0021] The superhard polycrystalline electrode prepared by the preparation method of superhard polycrystalline electrode is superhard mainly because 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 achieving the wear resistance of superhard materials. The entire wear to exposure process makes the electrode surface have a certain sharpness.

[0022] The application of super-hard polycrystalline electrode is to connect it with alloy substrate and install it on electric spark machine. The alloy substrate is connected with motor, and the motor is connected with the joint of spark machine to obtain the self-spinning super-hard polycrystalline electrode, which is used in the surface processing of PDC hard conductive materials.

[0023] Example 2 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% aluminum powder, and 10% titanium powder, the diamond particle size is selected to be 40μm, and the particle sizes of aluminum powder and titanium powder are 2-4μm; 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; 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.

[0024] Furthermore, in the mixing process, the planetary ball mill has a rotation speed of 450 r / min, a transmission ratio of 1:2, an operation time of 12 h, and a vacuum degree of 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℃.

[0025] Application example description: The superhard polycrystalline electrode of the present invention 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, and the motor is connected to the joint of the EDM machine to obtain a self-spinning superhard polycrystalline electrode; the PDC hard conductive material is used as a workpiece electrode for surface processing. After setting the discharge parameters and grinding parameters, the processing is carried out, and the parameters such as PDC material removal rate, PDC surface roughness and tool electrode loss rate are collected to perform a comparative analysis of rough machining, semi-finish machining and finish machining. During the experiment, the diamond particle sizes in the superhard polycrystalline electrode were selected as 10µm, 14µm, 28µm, 40µm and 45µm respectively; the tool electrode speeds were 14, 16, 18, 20 and 22m / s respectively; with the change of the diamond particle size, the three parameters showed different degrees of change, and the adjustment of appropriate process parameters can achieve the optimal option of efficient finishing while ensuring the life of the tool electrode. Increasing the tool electrode speed will increase the PDC material removal rate and tool electrode loss 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 axis shows the horizontal mean value of an influencing factor, and a separate line is shown for each level of another 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. 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 effect on the processing effect, that is, the superhard polycrystalline electrode of the present invention can effectively improve the processing efficiency in the 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 pressing, vacuum pre-sintering, and the pressed powder is finely crushed by mechanical ball milling to obtain the first mixed powder. The raw materials are composed of the following mass percentages: 45-90% diamond or cubic boron nitride, 5-25% cobalt powder or aluminum powder, and 5-15% titanium powder; S2. The second mixing process: according to the first mixing powder 60-80%, copper powder 10-30%, chromium powder 5-15% of the ingredients ratio after the mixture 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 second mixed powder; S3. The third mixing process: according to the second mixed powder 30-60%, ceramic powder 10-60%, pore-forming agent 5-35% 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 by mechanical ball milling to obtain the third mixed powder; S4. Preparation of super-hard polycrystalline electrode: 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.

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

5. The method for preparing a superhard polycrystalline electrode according to claim 1, characterized in that: 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 as described in any one of claims 1 to 5.

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

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