Tool electrode, electric spark machining equipment and preparation method of ultra-fine grain tubular electrode

Abstract

The invention belongs to the technical field of electric spark machining, and provides a tool electrode, electric spark machining equipment and a preparation method of an ultra-fine grain tubular electrode, the tool electrode comprises an electrode body, and the electrode body is prepared from a copper material, a tungsten material or a copper-tungsten alloy material; the grain size of the copper material, the tungsten material or the copper-tungsten alloy material is 100-1000 nm; or the grain size of the copper material, the tungsten material or the copper-tungsten alloy material is 9-12 grades. The hardness and wear resistance of the tool electrode can be improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electric spark machining, and in particular to a tool electrode, an electric spark machining device and a preparation method of a super-fine-grain tubular electrode. BACKGROUND

[0002] Electric spark machining is a special machining method using high temperature generated by pulse discharge to remove materials, also known as electric erosion machining. In electric spark machining, a tool electrode is a core component for realizing material removal, and hardness and wear resistance of the tool electrode directly affect machining precision, efficiency and surface quality.

[0003] In related technologies, the hardness and wear resistance of the tool electrode cannot meet the requirements, so that the machining precision of the electric spark cannot meet the requirements. SUMMARY

[0004] The present application aims to provide a tool electrode, an electric spark machining device and a preparation method of a super-fine-grain tubular electrode, and aims to solve the technical problem that the precision of electric spark machining and the hardness and wear resistance of the electrode cannot meet the requirements.

[0005] In a first aspect, the present application provides a tool electrode, comprising an electrode body, the electrode body being prepared from copper material, tungsten material or copper-tungsten alloy material; the grain size of the copper material, tungsten material or copper-tungsten alloy material is 100-1000 nm; or, the grain size of the copper material, tungsten material or copper-tungsten alloy material is 9-12 levels.

[0006] In one of the embodiments, the electrode body extends along an axial direction by a preset length, and along the axial direction, a middle part of the electrode body has a through cavity.

[0007] In one of the embodiments, the electrode body is a tubular structure, and the thickness of the tubular structure is in a range of 0.3 mm-5 mm.

[0008] In a second aspect, the present application provides an electric spark machining device, comprising a power supply, a feeding device and the tool electrode according to any one of the above, the electrode body being installed on the feeding device and being electrically connected to the power supply.

[0009] In a third aspect, the present application provides a preparation method of a super-fine-grain tubular electrode, the preparation method being used for preparing the tool electrode according to any one of the above, and the preparation method comprises:

[0010] Preparation of an electrode blank, the electrode blank being a columnar structure;

[0011] Along the axial direction of the electrode blank, a through hole is machined, and the diameter of the through hole is in a range of 0.15 mm-1.0 mm;

[0012] The through hole is reamed by wire cutting.

[0013] In one of the embodiments, in the step of processing the through hole, the through hole is processed by electric spark drilling or liquid drilling.

[0014] In one of the embodiments, in the step of expanding the through hole by wire cutting, the voltage of the wire cutting is 60V-80V, the current is 0.3A-0.5A, and the pulse width ratio is 3:4.

[0015] In one of the embodiments, in the step of preparing the electrode blank, the electrode blank is formed by isometric extrusion, and the number of passes of the isometric extrusion is greater than or equal to 8.

[0016] In one of the embodiments, the electrode blank is extruded by an extrusion die, and the extrusion die comprises a die body, a first extrusion channel and a second extrusion channel formed on the die body and connected to each other, and the first extrusion channel and the second extrusion channel are arranged at a preset included angle, and the range of the preset included angle is 80°-120°.

[0017] In one of the embodiments, the range of the preset included angle is 90°.

[0018] The tool electrode, the electric spark machining device and the preparation method of the ultra-fine crystal pipe electrode have the following beneficial effects: the electrode body of the tool electrode is prepared by using copper material, tungsten material or copper-tungsten alloy material with ultra-fine grain size, so that the tool electrode has high hardness and wear resistance, can reduce wear and deformation in the machining process, and improve machining precision and stability; the tool electrode is used for machining, which can improve machining efficiency and surface quality of workpieces.

[0019] The above description is only a summary of the technical solutions of the present application, in order to more clearly understand the technical means of the present application, the specific embodiments of the present application can be implemented according to the content of the specification, and in order to make the above and other purposes, characteristics and advantages of the present application more obvious and easy to understand, the following will describe the specific embodiments of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0020] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments of the present application or the prior art description. Obviously, the drawings described below are only some embodiments of the present application, and those skilled in the art can obtain other drawings according to these drawings without creating any creative labor.

[0021] Figure 1 The structural schematic diagram of the tool electrode provided by some embodiments of the present application is shown in the figure;

[0022] Figure 2Structural schematic diagram of a tool electrode machining a workpiece provided for some embodiments of the present application;

[0023] Figure 3 Structural schematic diagram of an electrical discharge machining device provided for some embodiments of the present application;

[0024] Figure 4 Structural schematic diagram of an electrode blank of a tool electrode provided for some embodiments of the present application;

[0025] Figure 5 Structural schematic diagram of an electrode blank of a tool electrode provided for some embodiments of the present application after machining a through hole;

[0026] Figure 6 Structural schematic diagram of an extrusion die used in a method of manufacturing an electrode provided for some embodiments of the present application;

[0027] Figure 7 Structural schematic diagram of a microstructure (EBSD characterization) after 4 passes of extrusion of pure copper corresponding to Table 1 in a method of manufacturing an electrode provided for some embodiments of the present application;

[0028] Figure 8 Structural schematic diagram of a microstructure (EBSD characterization) after 6 passes of extrusion of pure copper corresponding to Table 1 in a method of manufacturing an electrode provided for some embodiments of the present application;

[0029] Figure 9 Structural schematic diagram of a microstructure (EBSD characterization) after 8 passes of extrusion of pure copper corresponding to Table 1 in a method of manufacturing an electrode provided for some embodiments of the present application.

[0030] Explanation of reference signs:

[0031] 100, electrical discharge machining device; 110, tool electrode; 111, electrode body; 112, cavity; 113, electrode blank; 114, through hole; 120, extrusion die; 121, die body; 122, first extrusion channel; 123, second extrusion channel; 124, extrusion rod; 130, workpiece; 131, protruding structure; 140, working fluid; 150, power supply; 160, feeding device; a, preset included angle; X, radial direction; Y, axial direction; L, pipe wall thickness. DETAILED DESCRIPTION

[0032] The embodiments of the technical solutions of the present application will be described in detail below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present application, and therefore only serve as embodiments, but cannot limit the protection scope of the present application.

[0033] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of this application; the use of the terms "including," "comprising," or "having" and variations thereof herein is intended to be broad and encompass the terms "consisting of" and "consisting essentially of" and variations thereof. Unless otherwise required by context, singular terms shall include pluralities and vice versa. Unless otherwise required by context, the use herein of the singular is also to be construed as a use of the plural and vice versa.

[0034] In the description of the embodiments of the present application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "multiple" is more than two, unless otherwise explicitly and specifically limited.

[0035] Reference herein to "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the application. The appearance of the phrase in various places in the specification is not necessarily all referring to the same embodiment, or to a particular embodiment, or to a particular set of embodiments. It will be explicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0036] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship of the associated objects, which means that there can be three relationships, for example, A and / or B, which can represent the three cases of A alone, A and B together, and B alone. In addition, the character " / " herein generally represents an "or" relationship between the front and rear associated objects.

[0037] In the description of the embodiments of the present application, the term "multiple" refers to more than two (including two), and similarly, "multiple groups" refers to more than two groups (including two groups), and "multiple pieces" refers to more than two pieces (including two pieces).

[0038] In the description of the embodiments of the present application, the technical terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the embodiments of the present application and simplifying the description, and therefore cannot be understood as limiting the embodiments of the present application, which do not indicate or imply that the indicated devices or elements must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the embodiments of the present application.

[0039] In the description of the embodiments of the present application, unless otherwise explicitly specified and limited, the technical terms "mounting", "connecting", "connecting", "fixing" and the like should be understood in a broad sense, for example, can be fixedly connected, or can be detachably connected, or can be integrated; can be mechanically connected, or can be electrically connected; can be directly connected, or can be indirectly connected through an intermediate medium, or can be the internal communication of two elements or the interaction relationship between two elements. For those skilled in the art, the specific meanings of the above terms in the embodiments of the present application can be understood according to the specific circumstances.

[0040] Electrical discharge machining is a special machining method using high temperature generated by pulse discharge to remove material, also known as electrical erosion machining. In electrical discharge machining, the tool electrode is the core component to realize material removal, energy transmission and shape copying, and the hardness, wear resistance and the like of the tool electrode directly affect the machining precision, efficiency and surface quality.

[0041] In the related art, the hardness and wear resistance of the tool electrode cannot meet the requirements, so that the machining precision of the electrical discharge cannot meet the requirements. For example, the traditional tool electrode mostly uses ordinary copper electrode or graphite electrode, but has many defects.

[0042] The ordinary copper electrode has low hardness (Shore hardness 25-35HS) and poor wear resistance, and is easy to produce plastic deformation and wear due to discharge impact and mechanical friction in the machining process, resulting in a decrease in electrode shape precision, especially in the large-current rough machining scene, the electrical erosion wear rate is high. At the same time, the thermal expansion coefficient of copper is high (about 17x10 -6 / ℃), which is easy to deform in high-temperature machining environment, affecting the machining precision.

[0043] Although the graphite electrode has high hardness (Shore hardness 60-80HS), it is brittle and has poor impact resistance, and is easy to crack and fall off during clamping, handling and machining, and a large amount of dust is generated during machining, which not only pollutes the environment, but also may affect the machine precision and the health of the operator.

[0044] In order to overcome the above defects, the present application provides a tool electrode, an electrical discharge machining device and a preparation method of the electrode, the tool electrode uses copper material, tungsten material or copper-tungsten alloy material with grain size of 100-1000nm or grain size of 9-12 grade, the grain size grade of the copper material, tungsten material or copper-tungsten alloy material reaches ultra-fine grain size, so that the tool electrode has high hardness and wear resistance, which can reduce wear and deformation in the machining process, and improve the machining precision and stability.

[0045] According to some embodiments of the present application, the tool electrode 110 comprises an electrode body 111 made of copper material, tungsten material or copper-tungsten alloy material, wherein the grain size of the copper material, tungsten material or copper-tungsten alloy material is 100-1000 nm, or the grain size of the copper material, tungsten material or copper-tungsten alloy material is grade 9-12.

[0046] Specifically, the grain size is an index for describing the size of the crystal grains in a polycrystalline material, which reflects the refinement degree of the crystal grains inside the material and is an important parameter for measuring the microstructure of the material.

[0047] In a metal material (such as copper, tungsten, copper-tungsten alloy in the present application), the crystal grain is a basic unit of the material, which is formed by regular arrangement of a large number of atoms. The smaller the grain size, the more the number of crystal grains in a unit volume, and the larger the grain boundary area.

[0048] The "100-1000 nm" mentioned in the present application is directly described in terms of the size range of the crystal grains, which belongs to the category of nanoscale ultra-fine grains. Such ultra-fine grains can significantly improve the hardness, strength and wear resistance of the material.

[0049] The "grade 9-12" is based on the ASTM (American Society for Testing and Materials) grain size rating standard. The higher the rating, the finer the grain. The average grain diameter corresponding to grade 9 is about 1 μm, and the average grain diameter corresponding to grade 12 is about 0.125 μm, which also belongs to the category of ultra-fine grain size and corresponds to the size range of 100-1000 nm.

[0050] In the tool electrode 110 of electric spark machining, the material with ultra-fine grain size can effectively hinder the movement of dislocations by refining the crystal grains, thereby improving the hardness and wear resistance of the electrode, and improving the toughness of the material, reducing the loss and deformation of the electrode during machining. This is the core reason why the grain size is limited to a specific range in the present application.

[0051] For the electrode body 111 made of copper material, the copper material has excellent electrical conductivity (conductivity 58 x 106 S / m) and thermal conductivity (401 W / (m·K)) and moderate cost, but the grain size of ordinary copper is relatively large (usually > 5 μm) and the hardness is only 25-35 HS. By refining to ultra-fine grain size (100-1000 nm), the hardness can be increased to 40-50 HS, the wear resistance can be increased by more than 30%, and the problem of easy deformation of ordinary copper is solved, so that the tool electrode 110 has high hardness and high wear resistance.

[0052] For the electrode body 111 made of tungsten material, the tungsten material has a high melting point of 3422℃, a hardness of 350-400 HV at room temperature, and excellent wear resistance, but is very brittle (impact toughness < 10 J / cm 2); after ultra-fine crystallization, the grain boundary can hinder crack propagation, and the impact toughness is improved to 15-20 J / cm 2 At the same time, the hardness is maintained at 400-450 HV, which is suitable for high temperature and high pressure processing scenarios, so that the tool electrode 110 has high hardness and high wear resistance.

[0053] For the electrode body 111 of the copper-tungsten alloy material, the copper-tungsten alloy (such as CuW50) combines the electrical conductivity of copper (conductivity 30x106S / m) and the wear resistance of tungsten, and after ultra-fine crystallization, the interfacial bonding strength is improved by 20%, and the loss rate is only 1 / 5 of that of ordinary copper electrode when discharging a large current (>50A), so that the tool electrode 110 has high hardness and high wear resistance.

[0054] 100-1000 nm corresponds to grain size 9-12 (9-level grain size about 1 μm, 12-level about 0.125 μm), which belongs to the ultra-fine crystal range. The above grain size can be achieved by equal-diameter extrusion. After 8 times of equal-diameter extrusion, the copper material grain can be refined from the initial 5 μm to 500 nm, and the tungsten material can be refined from 10 μm to 800 nm. The electrode body 111 prepared by copper material and tungsten material has high hardness and high wear resistance, which can meet the demand of machining precision, and the surface finish of the workpiece 130 is improved.

[0055] The microstructure of the material seriously affects its own macroscopic performance. When the grain size of the material reaches the ultra-fine crystal range (100-1000 nm), the material will exhibit unique physical, chemical and mechanical properties, and the strength of the material will be greatly improved. For example, ordinary pure copper is prepared into ultra-fine crystal copper (i.e. the copper material with grain size of 100-1000 nm as described above), and the ultra-fine crystal pure copper is processed into the shape of the electrode body 111, which can solve the problems of low strength and large wear of ordinary copper electrode.

[0056] In the embodiment, the electrode body 111 in the tool electrode 110 is prepared by using copper material, tungsten material or copper-tungsten alloy material with ultra-fine grain size, so that the tool electrode 110 has high hardness and wear resistance, which can reduce wear and deformation during processing, improve processing precision and stability; using the tool electrode 110 can improve processing efficiency and surface quality of the workpiece 130.

[0057] In some embodiments, referring to Figure 1 As shown in the figure, the electrode body 111 extends along the axial direction Y by a predetermined length, and the middle part of the electrode body 111 has a through cavity 112 along the axial direction Y.

[0058] Specifically, the axial direction Y is the extension direction of the electrode body 111, and can also be understood as the height direction of the electrode body 111. It can be understood that the outer part of the electrode body 111 is in a columnar shape. In the radial direction X, the outer contour of the electrode body 111 can be circular, elliptical or polygonal, and the radial direction X is perpendicular to the axial direction Y.

[0059] Taking the electrode body 111 in a cylindrical shape as an example, a through cavity 112 is formed in the middle part of the electrode body 111 along the axial direction Y. The cavity 112 can be understood as a through hole structure opened along the central axis of the electrode body 111, so that the electrode body 111 forms a tubular electrode.

[0060] Referring to Figure 2 It can be seen that the electrode body 111 in the above tubular form can process the protruding structure 131 on the surface of the workpiece 130. The core structure of the tubular electrode is a hollow pipe body through the axial direction Y, which takes into account the mechanical properties and processing requirements.

[0061] The electrode body 111 forms a tubular shape and has a through cavity 112 along the axial direction Y. The diameter of the cavity 112 can be 1 / 3-9 / 10 of the outer diameter of the electrode. For example, the outer diameter of the electrode body 111 is φ10mm, and the diameter of the cavity 112 is φ3-9mm.

[0062] The electrode body 111 is a tubular electrode, and the electrode body 111 is made of ultra-fine grain copper, tungsten or copper-tungsten alloy (grain size 100-1000nm). The pipe wall section is dense and is not easy to form defects such as pores and cracks. Through the equal-diameter extrusion process (≥8 passes of extrusion), the material density is >99.5%.

[0063] As for the cavity 112 on the electrode body 111, the cavity 112 can also be used as a channel for the working liquid 140 to directly deliver kerosene or deionized water to the discharge area. The cavity 112 forms a forced chip removal channel, and the flow rate of the working liquid 140 can reach 5-10m / s. The chip removal efficiency can be improved by 40% compared with the solid electrode, and the short circuit problem caused by the accumulation of debris is reduced, and the probability of processing interruption caused by debris blockage is reduced. In addition, the cavity 112 can expand the heat dissipation area by more than 30%, so that the working temperature of the working electrode is reduced by 10-15℃, and the thermal deformation is reduced. (Especially suitable for copper materials, the thermal expansion coefficient is reduced to 12×10 -6 / ℃ or less).

[0064] In the embodiment, the tubular structure and the ultrafine-grained material can achieve a synergistic effect. After the tubular structure is combined with the ultrafine-grained material (hardness 40-50HS), the wear resistance can be improved by 30%. Under the same processing conditions, the service life of the tool electrode 110 is 2-3 times that of a common solid copper electrode, and the advantage is particularly significant in a large current (>50A) scenario. The tubular tool electrode 110 balances processing efficiency, precision, and cost through structural innovation and material optimization, and can become a key tool for coping with complex scenarios such as deep holes, microstructures, and large cavities in electric spark machining.

[0065] In some embodiments, with reference to Figure 1 As shown in the figure, the electrode body 111 is a tubular structure, and the thickness L of the tubular structure is in the range of 0.1mm-5mm.

[0066] The tubular thickness L is in the range of 0.3mm-1mm, and the tubular wall can be understood as a thin wall. The electrode body 111 in this data range is suitable for micro-machining (such as semiconductor lead frame molds); the diameter of the tubular structure can be as small as 0.3mm, and the flexibility is good, which can adapt to complex curved surface machining; in the case of using copper-tungsten alloy material (tensile strength >600MPa), the probability of bending (deflection <0.01mm / m) due to insufficient rigidity during machining can be better reduced.

[0067] The tubular thickness L is in the range of 1mm-5mm, and the tubular wall can be understood as a thick wall. The electrode body 111 in this data range is suitable for machining large workpieces 130. The diameter of the tubular structure can reach 50mm, and the rigidity is high (elastic modulus >100GPa). The deformation amount is <0.005mm when machining under a large current (30-50A).

[0068] For example, the tubular wall thickness L and the outer diameter of the electrode body 111 need to meet the following relationship. For example, the electrode body 111 is φ20mm, and the corresponding wall thickness is 0.5-4mm. Through finite element analysis verification, the maximum stress of the electrode body 111 is <200MPa (material yield strength >300MPa) under this ratio, and the plastic deformation risk is small.

[0069] In the embodiment, the thickness L of the tubular structure is controlled in the range of 0.1mm-5mm, so that the electrode body 111 has sufficient rigidity under the premise of having sufficient hardness, to reduce the risk of plastic deformation of the electrode body 111.

[0070] The application also provides an electric spark machining equipment 100, with reference to Figure 3 As shown in the figure, the electric spark machining equipment 100 includes a power supply 150, a feeding device 160, and the tool electrode 110 in the above-mentioned embodiments. The electrode body 111 is installed on the feeding device 160 and is electrically connected with the power supply 150.

[0071] Specifically, the power supply 150 is configured to provide working current for the tool electrode 110, so that the electrode body 111 generates electric spark. For example, the power supply 150 outputs adjustable waveform with pulse width of 0.1-100 μs, and when the power supply 150 is matched with the ultra-fine-grained electrode body 111, the ratio of pulse interval / pulse width is recommended to be 3:4, so as to reduce the risk of electrode overheating. For example, when processing alloy, the power supply 150 outputs 60 V voltage and 0.5 A current, and is matched with copper-tungsten alloy electrode, so that the material removal rate reaches 15 mm / min. 3

[0072] The feeding device 160 is connected with the electrode body 111, and the feeding device 160 is configured to realize high-precision motion control of the tool electrode 110. The feeding device 160 can include a driving system, which can adopt the structure form of servo motor connected with ball screw transmission, so that the positioning accuracy of the feeding device 160 reaches ±0.0005 mm, the repeat positioning accuracy reaches ±0.0002 mm, and the feeding speed reaches 0.1-500 mm / min, which can meet the smooth feeding when deep hole machining (depth-diameter ratio > 200 mm).

[0073] When the workpiece 130 is machined, it is also necessary to detect the gap between the electrode body 111 and the surface to be machined of the workpiece 130. The detection method is to monitor the discharge gap in real time by a high-frequency current sensor (sampling frequency 1 MHz), and when the gap deviates from the set value (±0.005 mm), the feeding system completes adjustment within 10 ms to ensure stable discharge and achieve the effect of real-time compensation of the discharge gap.

[0074] The feeding device 160 further includes a clamping assembly of the tool electrode 110, which is rigidly connected with the electrode body 111. The clamping assembly can adopt three-point positioning self-centering clamping mode with the electrode body 111, and the clamping force can be adjusted between 50-500 N. For thin-walled electrode (for example, 0.1 mm wall thickness), a flexible clamping pad can be further added to reduce damage to the electrode body 111.

[0075] The electric spark machining device 100 can further include a calibration assembly capable of calibrating the feeding direction of the electrode body 111. The calibration assembly can adopt a laser interferometer, and the calibration assembly can automatically correct the perpendicularity error (≤0.002 mm / 100 mm) of the axis of the electrode body 111 and the feeding direction, so as to ensure machining accuracy.

[0076] The electric spark machining device 100 can further include a working liquid circulating system, which is configured to provide working liquid 140. During electric spark machining, the working liquid 140 can immerse the surface to be machined of the workpiece 130 and the machining end of the electrode body 111. The working liquid circulating system can also cooperate with the cavity 112 of the tool electrode 110 to realize efficient chip removal and cooling. ​

[0077] In the embodiment, the electrode body 111 is prepared by using a copper material, a tungsten material or a copper-tungsten alloy material with ultra-fine grain size, so that the electrode body 111 has high hardness and wear resistance, can reduce wear and deformation in the processing process, and improve the processing precision and stability; the use of the electric spark processing equipment 100 can improve the processing efficiency and the surface quality of the workpiece 130.

[0078] The application further provides a preparation method of the ultra-fine grain tubular electrode, and the preparation method of the electrode is used to prepare the tool electrode 110 in the above-mentioned embodiments, and the preparation method comprises the following steps: S01, preparing an electrode blank 113, the electrode blank 113 is a column structure; S02, processing a through hole 114 along the axial direction Y of the electrode blank 113, the diameter of the through hole 114 ranges from 0.15 mm to 1.0 mm; and S03, expanding the through hole 114 by using a wire cutting method.

[0079] In the step S01, the electrode blank 113 is prepared, and the electrode blank 113 is a column structure, as shown in Figure 4

[0080] There are many ways to prepare the electrode blank 113, one way is to put the powder-shaped copper material, tungsten material or copper-tungsten alloy material (the copper-tungsten alloy material can be mixed by ball milling first) into a mold, and then high-pressure pressing is performed at room temperature to obtain a rod, the pressing pressure can be 100 MPa, the pressure is maintained for 60 s and then released, demolding is performed, and the electrode blank 113 is extruded into a column structure. Another way is to directly use a rod structure of the copper material, the tungsten material or the copper-tungsten alloy material, and the rod structure needs to be annealed (the copper material is annealed at 300℃ for 1 h, and the tungsten material is annealed at 1000℃ for 2 h), so as to eliminate the rolling stress (residual stress < 50 MPa) and reduce the risk of cracking during extrusion.

[0081] In the step S02, the through hole 114 is processed along the axial direction Y of the electrode blank 113, and the diameter of the through hole 114 ranges from 0.15 mm to 1.0 mm, as shown in Figure 5

[0082] ​​In view of the material properties of the ultra-fine-grained electrode body 111, the high strength and low plasticity of the electrode body 111 made of a copper material, a tungsten material or a copper-tungsten alloy material with a grain size of the ultra-fine-grained level are contradictory. Taking the ultra-fine-grained copper as an example, the hardness of the ultra-fine-grained copper is increased to 40-50 HS through grain refinement (100-1000 nm), the yield strength reaches 300 MPa (about 100 MPa for ordinary copper), but the elongation is reduced from 50% for ordinary copper to 15%-20%, and the plasticity is significantly reduced. If the large-diameter cavity 112 (such as φ3 mm) is directly machined, a large amount of material needs to be removed at one time, the radial X force generated by the tool (or the discharge electrode) on the tube wall can reach 200-300 MPa (close to the yield strength of the material), and the tube wall is prone to plastic deformation (such as local depression) or micro-cracks (through scanning electron microscopy, the surface crack rate of the tube wall after direct machining is 15%).

[0083] Therefore, in the present example, a smaller-diameter through hole 114 needs to be machined first, and the diameter of the through hole 114 ranges from φ0.15 mm to φ1.0 mm, and further reaming is performed through the through hole 114. In step S03, the through hole 114 is reamed in a wire cutting manner, and in the reaming process, a multiple reaming manner can be used, for example, the amount of reaming each time is <0.5 mm, and the single radial X force can be controlled to 50-100 MPa, so as to reduce the plastic damage to the electrode body 111.

[0084] In addition, taking the electrode body 111 made of ultra-fine-grained copper material as an example, the high strength of the ultra-fine-grained copper depends on the dense grain boundaries (the grain boundary density is 10-100 times that of ordinary copper), but high temperature or high stress can cause grain coarsening. When the large-diameter cavity 112 is directly machined, the local temperature generated by the discharge or cutting can reach 500-800°C (exceeding the recrystallization temperature 300-400°C of the ultra-fine-grained copper), and the duration is long (>100 ms), which easily causes the surface layer to be coarsened to more than 2000 nm, and the hardness to be reduced by 20%.

[0085] The step-by-step reaming controls the single machining energy (such as wire cutting voltage 60-80 V, energy 0.018-0.04 J), so that the local temperature is <300°C, the machining time is shortened to 5-10 ms, the grain size change is <50 nm, and the material performance is stable.

[0086] Furthermore, the elastic modulus (110 GPa) of the ultra-fine-grained copper is slightly higher than that (100 GPa) of ordinary copper, but it still belongs to a low-rigidity material. When the large-diameter cavity 112 is directly machined, the thickness L of the tube wall is deviated by 0.05-0.1 mm due to the difference in the amount of material removed (such as a 0.01 mm center offset).

[0087] And with the smaller diameter through hole 114 as the "reference guide", the concentricity correction can be realized through the wire cutting reaming spiral path. Each time the reaming is performed, the electrode wire is slowly fed along the center of the through hole 114 to automatically compensate for the initial deviation, and the final wall thickness uniformity can reach ±0.005 mm, thereby being able to guarantee the machining precision and structural consistency and reduce the size deviation and wall thickness unevenness.

[0088] In addition, the electrode body 111 of the ultra-fine grain copper has a high natural frequency (for example, 500-1000 Hz), and when the large-diameter cavity 112 is directly machined, the high-frequency friction between the tool and the material can easily cause resonance (amplitude > 0.005 mm), which can cause ripples on the inner wall of the cavity 112, thereby affecting the surface finish of the cavity wall of the cavity 112.

[0089] The "rigid support" effect of the relatively small-diameter through hole 114 can reduce the vibration amplitude (<0.002 mm), and in combination with the low-speed feeding (0.1-0.5 mm / min) during reaming, the surface roughness can be controlled to Ra≤0.8 μm, thereby meeting the requirements of the electrode surface quality for the electric spark machining.

[0090] In the example, the machining of the small-diameter through hole 114 with a diameter of φ0.15-1.0 mm belongs to the category of micro-machining, and needs to rely on high-precision electric spark piercing (positioning accuracy ±0.001 mm) or high-pressure liquid piercing (jet diameter deviation <0.02 mm). When the large-diameter cavity 112 with a diameter of φ3 mm or more is directly machined, the existing equipment is difficult to balance "large size" and "high precision". For example, the tool diameter error of mechanical drilling is >0.01 mm, and the electrode loss rate of electric spark forming is >5%, which cannot meet the precision requirements of the tubular electrode body 111 (or tool electrode 110).

[0091] In the example, the machining of the cavity 112 adopts a step-by-step process, which reduces the limitation of the equipment capacity bottleneck through the combination of "small size high precision piercing + controllable reaming", and is especially suitable for machining micro-tubular electrodes with a diameter of <5 mm.

[0092] In the reaming process, the wire cutting method can be used. The wire cutting can use a helical wire cutting path (pitch 0.05 mm) to remove the material layer by layer from the inner wall of the through hole 114. Compared with the straight line cutting, the wire cutting is beneficial to reducing the electrode vibration (amplitude from 0.005 mm to 0.002 mm) and ensuring the uniformity of the tube wall thickness L (deviation <0.01 mm).

[0093] In the embodiment, the preparation method of first preparing the smaller-diameter through hole 114 and then reaming can provide machining precision, reduce machining difficulty, guarantee machining quality, and balance the process feasibility and economy.

[0094] In some embodiments, in the step of processing the through hole 114, the through hole 114 is processed by electric spark drilling, or the through hole 114 is processed by liquid drilling.

[0095] Specifically, for electric spark drilling, electric spark machining is based on the principle of "pulse discharge ablation", for example, through high-frequency pulse discharge (0.5-2 μs pulse width) between a φ0.1 mm molybdenum electrode and the workpiece 130, a high temperature of more than 20000 °C is generated instantaneously, which makes the material locally melt and vaporize, and forms the through hole 114. The whole process relies on the conversion of electric energy into heat energy to realize material removal, and belongs to the category of "thermal processing".

[0096] Electric spark drilling can be controlled by a grating ruler closed loop (sampling frequency 1 MHz), and a φ0.15 mm micro hole can be processed, with a hole wall perpendicularity error of <0.002 mm / 100 mm.

[0097] For electric spark drilling, the positioning accuracy can be ±0.001 mm, the hole diameter deviation can be ±0.003 mm, the surface roughness can be Ra≤0.8 μm, and burrs are not easy to be generated after thermal ablation; the surface quality is stable, the hole wall has no mechanical stress after thermal ablation, and the work hardening layer caused by cold processing (hardness fluctuation <5%) is not easy to be generated, which is conducive to reducing the tool damage problem during subsequent hole expansion.

[0098] The liquid drilling method has high efficiency, and the processing efficiency can be 3-6 times that of electric spark drilling, which is suitable for large batch production scenes such as automobile molds. In addition, the liquid drilling method has low processing cost, no electrode loss, and only consumes deionized water (or abrasive), and the single-hole processing cost is about 1 / 10 of that of electric spark drilling. In addition, the liquid drilling method has no thermal damage, and the cold processing process does not change the metallographic structure of the material, which is especially suitable for heat-sensitive ultra-fine grain copper, and reduces the risk of grain coarsening.

[0099] In the present embodiment, both electric spark drilling and liquid drilling can be used to process the through hole 114 on the electrode body 111, and the selection can be adapted according to the use scene.

[0100] In some embodiments, in the step of expanding the through hole 114 by wire cutting, the voltage of the wire cutting is 60V-80V, the current is 0.3A-0.5A, and the pulse width ratio is 3:4, for example, the voltage of the wire cutting is 70V, and the current is 0.4A.

[0101] Specifically, the core of wire cutting is the pulsed discharge between the electrode wire (usually φ0.1mm molybdenum wire) and the workpiece 130, and the voltage directly determines the discharge gap size. Take kerosene medium as an example for illustration, according to the breakdown characteristics of kerosene medium; when the voltage is 60V, the breakdown gap is about 0.02mm; when the voltage is 70V, the breakdown gap is about 0.035mm; when the voltage is 80V, the breakdown gap is about 0.05mm. This range matches the pipe wall thickness L (0.3mm-5mm) of the electrode body 111, so that the discharge only occurs between the outer surface of the electrode body 111 and the workpiece 130, which is beneficial to reduce the risk of false discharge of the wall surface of the cavity 112 in the electrode body 111.

[0102] If the voltage <60V, the breakdown gap <0.02mm, it is easy to cause short circuit due to electrode wire vibration (amplitude ±0.005mm); if the voltage >80V, the gap >0.05mm, the discharge energy is dispersed, which will increase the hole wall surface roughness from Ra0.8μm to Ra1.6μm, which does not meet the subsequent processing requirements.

[0103] For example, the resistivity of ultra-fine crystal copper (resistivity 1.7×10 -8 Ω·m), tungsten (5.3×10 -8 Ω·m) and copper-tungsten alloy (2.5×10 -8 Ω·m) are lower than that of ordinary metals, and 60V-80V voltage can ensure that the current density (J=I / S) is in a reasonable range (10 4 -10 5 A / m 2 ). For high-resistance tungsten materials, 80V voltage can provide sufficient electric field strength to ensure stable discharge. For low-resistance copper materials, 60V voltage can reduce the risk of electrode wire overheating (temperature <300℃, lower than the oxidation temperature of molybdenum wire 400℃) caused by excessive current.

[0104] For wire cutting, the current control, the current range is 0.3A-0.5A, for example, the current is 0.4A. Specifically, the single pulse energy E of wire cutting = U×I×t (t is the pulse width), under 4μs pulse width, 60V×0.3A×4μs=0.000072J, 80V×0.5A×4μs=0.00016J, this energy range can realize "micro-etching". This current range can not only remove materials (about 10 -12 mm 3 per pulse etching amount) to ensure the reaming efficiency (0.1-0.5mm / min), but also will not cause the surface of the electrode body 111 to melt due to excessive energy (the melting point of ultra-fine crystal copper is 1083℃, and the corresponding melting energy threshold is 0.0002J), thereby reducing the probability of slag on the hole wall.

[0105] For pulse width ratio, pulse width ratio is a key parameter in wire cutting machining to describe the time distribution of pulse signal, and pulse width ratio refers to the ratio of pulse interval time to pulse width. In this scenario, pulse width ratio 3:4 specifically refers to "pulse interval time is 3μs and pulse width is 4μs".

[0106] Pulse width ratio 3:4 reflects the reasonable distribution of time for heat dissipation and chip removal of wire cutting. Specifically, pulse width 4μs can ensure sufficient energy to remove materials, and the formed chips (size <5μm) can be removed in the subsequent interval time. Interval 3μs provides backflow time for working fluid 140 (such as kerosene), quickly removes the hole wall heat (local temperature >1000℃), and reduces the surface temperature of electrode body 111 to below 300℃ (thermal conductivity of copper 401W / (m·K), 3μs can reduce temperature by 700℃), thereby reducing the risk of coarse grain of ultra-fine grain due to continuous high temperature.

[0107] In this embodiment, the combination of the above data parameters is the result of optimization for the characteristics of ultra-fine grain electrode material, which not only ensures the reaming accuracy and efficiency, but also reduces the risk of damage to material performance, and is a key process parameter for high-quality machining of tubular electrode body 111.

[0108] In some embodiments, referring to Figure 6 As shown, in the step of preparing electrode blank 113, the electrode blank 113 is formed by equal-diameter extrusion. The pass of equal-diameter extrusion is greater than or equal to 8 times.

[0109] Specifically, equal-diameter extrusion is a processing technology that applies pressure to copper material, tungsten material or copper-tungsten alloy material through a die, so that the material plastically deforms while maintaining the cross-sectional area unchanged. It is a core technology for preparing ultra-fine grain electrode blank 113.

[0110] Specifically, the columnar electrode blank 113 (such as ultra-fine grain copper, tungsten or copper-tungsten alloy) is placed in the feeding channel of the extrusion die 120, and the axial Y pressure (usually 100-500MPa) is applied through the extrusion rod 124, so that the material is forced to pass through the deformation channel (for example, the first extrusion channel 122 and the second extrusion channel 123 described below) of the extrusion die 120. Because the cross-sectional areas of the inlet and outlet of the extrusion are equal, it is called "equal-diameter" extrusion. The material only undergoes shape remodeling and internal organization change, without volume loss.

[0111] For example, the copper blank with a diameter of φ10mm is still φ10mm after equal-diameter extrusion, but the internal grain is refined from 5μm to 500nm, and the dislocation density is increased by 1-2 orders of magnitude.

[0112] The equal-diameter extrusion can adopt an extruder, the extruder adopts hydraulic drive, the pressure control precision is ±1 MPa, and constant-speed extrusion (0.1-1 mm / s) can be realized, so that uniform deformation is ensured.

[0113] The equal-diameter extrusion realizes grain refinement through “shear deformation + dynamic recrystallization”, when the material passes through the die included angle, is subjected to strong shear stress (the shear stress of copper material is 150 MPa when the included angle is 90°), the original coarse grains are broken into subgrains, and after multi-pass extrusion (≥8 times), the subgrains gradually evolve into ultrafine grains (100-1000 nm).

[0114] Experimental data show that after 8 times of equal-diameter extrusion, the grain size of the copper material is reduced from the initial 5 μm to 500 nm, and the hardness is increased from 25 HS to 45 HS, thereby forming the “ultrafine grain size” electrode body 111. Compared with rolling, forging and other processes, the deformation of equal-diameter extrusion is more uniform (deformation deviation <5%), which can eliminate internal defects such as porosity and segregation of the material (density is increased from 95% to 99.5%). Especially for copper-tungsten alloy, it can reduce the agglomeration of tungsten particles, increase the uniformity of particle distribution by 40%, and ensure the stability of energy distribution of the electrode body 111 during discharge.

[0115] The extrusion pass needs to be ≥8 times, specifically, in the first 4 passes, coarse grains are mainly broken, and the grain size is rapidly reduced (about 30% refinement per pass); in the 5th-8th pass, dynamic recrystallization is promoted, a stable ultrafine grain structure is formed, and the hardness and strength tend to be stable (the increase is <5%); >8 passes, the grain refinement slows down, but the material work hardening intensifies (the yield strength increases <3%), and the die loss increases by 20%, and the cost performance decreases.

[0116] The equal-diameter extrusion can refine the grains while retaining the high electrical conductivity of the material (the electrical conductivity of copper only decreases by 5%, which is much better than the 15% of the cold rolling process), solving the contradiction between “strength improvement and conductivity decrease”, and ensuring the energy transmission efficiency (>90%) of the electrode body 111 during discharge.

[0117] The billet extruded by equal-diameter extrusion has excellent size precision (diameter deviation ±0.01 mm) and straightness (<0.02 mm / m), which can reduce the processing allowance (from 0.5 mm to 0.1 mm) of subsequent piercing and expanding, reduce tool wear and processing time (30% shorter).

[0118] In the present embodiment, the equal-diameter extrusion is a key process for material ultrafine crystallization through multi-pass shear deformation, and its core value lies in significantly improving the mechanical properties while ensuring the electrical conductivity of the material, which provides a stable billet basis for preparing high-performance tool electrodes 110.

[0119] In some embodiments, reference is made to Figure 6As shown, the extrusion of the electrode green compact 113 adopts an extrusion die 120, which includes a die body 121 with a first extrusion channel 122 and a second extrusion channel 123 formed thereon and connected therewith, and the first extrusion channel 122 and the second extrusion channel 123 are arranged at a preset included angle a, and the preset included angle a ranges from 80° to 120°.

[0120] Specifically, the die body 121 is a carrier of the first extrusion channel 122 and the second extrusion channel 123, and the preset included angle a (80°-120°) between the first extrusion channel 122 and the second extrusion channel 123 in the extrusion die 120 is a core structural parameter for realizing equal-diameter grain refinement, and the design thereof directly affects the material deformation uniformity, shear stress size and die life.

[0121] The first extrusion channel 122 of the die body 121 can be considered as a feeding end, and the second extrusion channel 123 can be considered as a discharging end, and the first extrusion channel 122 and the second extrusion channel 123 have the same diameter (such as φ10 mm), which ensures the "equal-diameter" characteristic; and the channel length can be 5-10 times of the diameter (such as 50-100 mm). The electrode green compact 113 can be fully preheated before entering the included angle region, for example, by heating the die to 200-300°C, and the plasticity of copper material is increased by 30%.

[0122] The included angle region adopts a circular arc transition (radius 0.5-1 mm), which reduces the risk of stress concentration (stress concentration coefficient from 3.0 to 1.2) caused by sharp corners and reduces the risk of die cracking (the die material can be high-speed steel W18Cr4V, and the bending strength is 1800 MPa).

[0123] The preset included angle a refers to the included angle between the two channel axes (not the channel wall included angle), which is calibrated by a three-coordinate measuring instrument (accuracy ±0.1°). For example, when the included angle is 90°, the two channel axes form a right angle at the intersection point, and the material needs to complete a 90° directional turn when flowing through this point, thereby generating a circumferentially uniform shear deformation.

[0124] When the electrode green compact 113 passes through the included angle region, the shear stress τ received is negatively related to the included angle θ (the smaller θ is, the larger τ is), and the specific law is as follows:

[0125] Experimental verification: within the range of 80°-120°, the shear stress exceeds the critical shear stress of the material (copper 100 MPa, tungsten 200 MPa), which can trigger dynamic recrystallization, and exceeding this range (such as 70° or 130°) cannot balance the refinement efficiency and die life.

[0126] Specifically, in the case of 80° angle, the shear stress of copper material reaches 160 MPa, and that of tungsten material reaches 350 MPa, which can quickly break the coarse grains (single pass grain refinement rate 40%) but obvious local stress concentration (the maximum stress in the inner wall of the channel is 2000 MPa, close to the yield strength of the die).

[0127] In the case of 90° angle, the shear stress of copper material is 150 MPa, and that of tungsten material is 320 MPa, the shear stress distribution is the most uniform (radial X stress deviation <5%), the grain refinement rate is 35%, and the die stress is reduced to 1800 MPa.

[0128] In the case of 120° angle, the shear stress of copper material is 120 MPa, and that of tungsten material is 250 MPa, the stress concentration is the smallest (the die stress is 1500 MPa), but the grain refinement rate is reduced to 25%, and the extrusion pass needs to be increased to meet the requirement of ultra-fine grains.

[0129] Specifically, equal-diameter extrusion can be understood as equal-channel extrusion or equal-diameter angle extrusion. The electrode billets 113 are respectively extruded by different passes to prepare ultra-fine grain blocks with different grain sizes by using equal-channel extrusion process. The equal-channel extrusion adopts a special extrusion die 120. The working process of the equal-channel extrusion (or equal-diameter angle extrusion) process is as shown in Figure 6 The inner angle φ1 of the intersection of the two channels of the extrusion die 120 is 0°, and the die central angle φ2 (i.e. the preset angle a mentioned above) of the intersection of the two channels is 90°. The electrode billets 113 pass through the first extrusion channel 122 and the second extrusion channel 123 under the pressure of the extrusion punch (also known as extrusion rod 124), which have the same cross section and form a preset angle a. The inner die corner of the intersection of the two channels is equal to φ1, and the die central angle of the intersection of the two channels is equal to φ2. When the electrode billets 113 pass through the corner of the channel, pure shear deformation occurs inside the electrode billets 113. Since the shape of the cross section of the electrode billets 113 remains basically the same before and after deformation, the electrode billets 113 can be repeatedly extruded through the first extrusion channel 122 and the second extrusion channel 123 of the extrusion die 120. The strain accumulation of each pass deformation can obtain a larger total strain. The coarse grains in the original electrode billets 113 are broken by extrusion, and finally the grains with grain size in the ultra-fine grain level can be obtained.

[0130] Taking pure copper as an example, as shown in Figure 7 , the ultra-fine grains can be obtained by extruding to the fourth pass at room temperature. With the increase of the extrusion pass, the grain size is continuously refined and homogenized. As shown in Figure 9 , when extruded to the eighth pass, the grain size reaches the minimum, and even if the number of extrusion increases, the grain size changes little. The main advantages of the equal-diameter angle extrusion process include convenient operation, simple die and related equipment, and different grain sizes can be obtained by controlling the extrusion pass.

[0131] Table 1 is the average grain size of pure copper after 4, 6, 8 passes of extrusion detected by EBSD (electron backscatter diffraction) method; combined with Figures 7-9 Figure 1 shows the microstructure of pure copper after 4, 6, 8 passes of extrusion. Therefore, the electrode billets 113 of different grain sizes correspond to the electrode billets 113 after 4, 6, 8 passes of extrusion.

[0132] Table 1 Average grain size of pure copper after 4, 6, 8 passes of extrusion

[0133]

[0134] In terms of hardness, the microhardness of ordinary pure copper is about 110 HV, and when the 8th pass of extrusion is completed, the microhardness can reach 130 HV, and the microhardness is increased by about 20%.

[0135] In the present embodiment, the preset included angle a of 80°-120° is an optimized range of material properties, refinement requirements and die life, and the 90° included angle is preferred due to uniform shear stress and strong versatility, which provides a key structure for the equal-diameter extrusion of the ultra-fine grain electrode billet 113.

[0136] The above is only a preferred embodiment of the present application, and only the technical principles of the present application are specifically described. These descriptions are only for the purpose of explaining the principles of the present application and cannot be interpreted in any way as a limitation on the scope of protection of the present application. Based on the explanations herein, any modifications, equivalent replacements and improvements made within the spirit and principles of the present application, and other specific embodiments of the present application that can be conceived by those skilled in the art without creative labor, should be included within the scope of protection of the present application.

Claims

1. A tool electrode, characterized in that, The electrode body is made of copper material, tungsten material or copper-tungsten alloy material, and the grain size of the copper material, tungsten material or copper-tungsten alloy material is 100-1000 nm, or the grain size of the copper material, tungsten material or copper-tungsten alloy material is 9-12 grade.

2. The tool electrode of claim 1, wherein, The electrode body extends along an axial direction by a preset length, and a middle part of the electrode body has a through cavity along the axial direction.

3. The tool electrode of claim 1, wherein, The electrode body is a tubular structure, and the thickness of the tubular wall is 0.3-5 mm.

4. An electric discharge machining apparatus characterized by comprising: The EDM device comprises a power supply, a feeding device and the tool electrode according to any one of claims 1-3, the electrode body is installed on the feeding device and electrically connected to the power supply.

5. A method of producing an ultrafine-grained tubular electrode, characterized by, The electrode preparation method is used to prepare the tool electrode according to any one of claims 1-3, and the preparation method comprises: The electrode blank is prepared as a column structure; A through hole is processed along the axial direction of the electrode blank, and the diameter of the through hole is 0.15-1.0 mm; The through hole is reamed by wire cutting.

6. The method of claim 5, wherein the ultrafine-grained tubular electrode is prepared by the steps of: In the step of processing the through hole, the through hole is processed by EDM or liquid piercing.

7. The method for preparing the ultrafine crystalline tubular electrode as described in claim 5, characterized in that, In the step of reaming the through hole by wire cutting, the voltage of the wire cutting is 60-80 V, the current is 0.3-0.5 A, and the pulse width ratio is 3:

4.

8. The method of claim 5, wherein the ultrafine-grained tubular electrode is prepared by the steps of: In the step of preparing the electrode blank, the electrode blank is formed by equal-diameter extrusion, and the number of passes of the equal-diameter extrusion is greater than or equal to 8.

9. The method of claim 8, wherein the ultrafine-grained tubular electrode is prepared by the steps of: The electrode blank is extruded by an extrusion die, and the extrusion die comprises a die body, a first extrusion channel and a second extrusion channel are formed on the die body and are connected, the first extrusion channel and the second extrusion channel are arranged at a preset included angle, and the preset included angle is 80-120°.

10. The method of claim 9, wherein the ultrafine-grained tubular electrode is prepared by the steps of: The preset included angle is 90°.

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