Preparation method and application of gradient material electrode

Abstract

The invention relates to the technical field of electric spark machining, and discloses a gradient material electrode preparation method and application thereof.The gradient material electrode preparation method comprises the steps that beryllium copper alloy foil is selected as a base body, and an electroplating metal layer is selected according to the requirement for the profile shape of the section of a micro-groove; the electroplated foil is placed in a vacuum furnace cavity to be subjected to thermal diffusion treatment, and the gradient material foil is prepared; and cutting the gradient material foil into electrodes by adopting wire cut electrical discharge machining equipment. The application comprises the steps that a gradient material electrode is subjected to multi-round electric spark machining on a sacrificial material, and the specific stable contour is gradually formed on the working face of the electrode in the machining loss by means of the loss rate difference of all components of the gradient material in the thickness direction; and replacing the sacrificial material with a final workpiece, accurately reproducing the stable contour to the final workpiece by adopting the same machining parameters, and continuously machining the micro-groove. The metallurgical bonding gradient layer is constructed through thermal diffusion, and active regulation and control of the electrode contour are achieved through the material loss difference.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electric spark machining, in particular to a preparation method of a gradient material electrode and application thereof. BACKGROUND

[0002] Micro-groove structure is widely used in micro-electro-mechanical systems, precision molds and micro-fluidic chips. For machining micro-grooves in high-hardness materials, the traditional contact-type micro-milling method faces physical bottlenecks. When a micro-milling cutter is cutting high-hardness materials, it bears high cutting force, and the cutter is prone to vibration, accelerated wear and even chipping. This leads to unstable machining precision, poor surface quality of the groove sidewall, and serious cutter consumption and high production cost. Electric spark machining is a non-contact machining method that uses the thermal energy of pulse discharge to remove materials, and there is no macro cutting force in the machining process, so it is suitable for precision manufacturing of high-hardness materials.

[0003] The precision and efficiency of electric spark machining are highly dependent on the performance of the electrode. In micro electric spark machining applications, electrode wear is a core technical problem. Common electrode materials are quickly worn under the high-temperature thermal shock generated by continuous pulse discharge. In particular, when machining complex microstructures, the discharge is concentrated at the sharp edges of the electrode, and the heat accumulation causes the local material to melt and evaporate, resulting in rapid distortion of the electrode working surface profile. Degradation of the electrode shape will directly reproduce on the workpiece, making the machined micro-groove shape maintainability poor. In order to improve the durability, some technologies try to deposit a functional layer on the electrode substrate. However, the ordinary deposited layer and the substrate are mostly physically combined, with low bonding strength, and are prone to liquid phase peeling under the thermal shock of discharge, which cannot fundamentally solve the problem of electrode durability.

[0004] In addition, there is an objective initial running-in stage when the electrode is put into use. During the initial machining of the first few workpieces, the electrode profile changes dramatically and is in an unstable wear state. After the electrode has machined a certain number of workpieces, the electrode wear gradually enters a dynamic balance steady state. The existing process usually uses the newly prepared electrode directly for machining the final workpiece. This method results in large size deviation of the first batch of workpieces, poor geometric consistency and high scrap rate. It is necessary to wait until the electrode profile is stable to obtain a size-qualified product. This phenomenon causes serious precision control difficulties and waste of machining materials in batch micro-groove manufacturing requiring micron-level precision. SUMMARY

[0005] In view of the deficiencies of the prior art, the present application provides a preparation method of a gradient material electrode and application thereof, which solves the problems of short electrode life caused by weak bonding force of the conventional electrode coating and poor thermal shock resistance in micro electric spark machining, and low machining precision caused by unstable initial profile wear of the electrode.

[0006] To achieve the above object, the application is implemented by the following technical solutions: a preparation method of a gradient material electrode and application thereof.

[0007] In the first aspect, the application provides a preparation method of a gradient material electrode, which adopts the following technical solutions: The preparation method of the gradient material electrode comprises the following steps: S1, selecting a beryllium copper alloy foil as an electrode substrate, electroplating a metal layer on a main surface of the electrode substrate according to the cross-sectional profile shape requirement of a micro groove to be processed, the metal layer being selected from at least one of a pure tin layer and an oxygen-free copper layer, the thickness of the metal layer being 5-20 μm, and obtaining an electroplated foil; S2, horizontally placing the electroplated foil between two high-purity graphite plates, loading into a vacuum furnace cavity, vacuumizing to 0.5-1.5 Pa, introducing argon as a protective gas to 0.12-0.18 MPa, heating at a rate of 8-12 ℃ / min to 750-850 ℃, and keeping the temperature for 8-12 hours, and cooling with the furnace to obtain a gradient material foil; S3, cutting the gradient material foil into a tooth-shaped disc electrode by using an electric spark wire cutting device, and performing ultrasonic cleaning on the tooth-shaped disc electrode.

[0008] By adopting the above technical solutions, the application constructs a corrosion-resistant gradient layer on the surface of a conventional beryllium copper substrate by using the heat diffusion principle. The technical mechanism and beneficial effects are as follows: First, the profile regulation mechanism based on the loss rate difference: Under the specific thermodynamic conditions of high temperature (750-850 ℃) and long time keeping (8-12 hours), the surface plating layer atoms and the substrate atoms diffuse with each other, eliminating the obvious physical interface between the traditional electroplating layer and the substrate, and forming a Sn-Cu solid solution or intermetallic compound diffusion layer with a continuous transition of composition concentration from the surface layer to the core.

[0009] Second, the metallurgical bonding ensures the structural stability: The gradient structure solves the problem of peeling or evaporation of the low-melting-point plating layer (such as pure tin) at the moment of electric spark discharge due to high temperature. The gradient layer acts as a wear-resistant framework, significantly inhibiting the expansion of the discharge pits, so that the electrode can maintain the geometric sharpness of the edges and corners for a long time in micro machining, greatly prolonging the service life.

[0010] Third, the process ensures the flatness of the material: The raw materials used in the method are all general metal materials on the market, without the need for complex material synthesis steps. The gradient layer depth can be accurately regulated by controlling the heat diffusion parameters, which is suitable for industrial production.

[0011] Preferably, in the electroplating process, the electroplating solution temperature is maintained at 23-27 ℃.

[0012] Preferably, in the heat diffusion treatment, the inert atmosphere is argon.

[0013] Preferably, the selection of the metal layer according to the requirement of the cross-sectional profile shape of the micro-groove to be processed comprises: when a micro-groove profile with a shallower or smoother edge is required, a pure tin layer with a higher plating loss rate than the electrode base is selected; when a micro-groove profile with a deeper or steeper edge is required, an oxygen-free copper layer with a lower plating loss rate than the electrode base is selected.

[0014] Preferably, the plating treatment is asymmetric plating for preparing a micro-groove with an asymmetric cross-sectional profile, specifically plating a pure tin layer on the first major surface of the electrode base and plating an oxygen-free copper layer on the second major surface.

[0015] Preferably, in the electrode shaping step, the parameters of the wire-cut electrical discharge machining device include: pulse width 2-4 μs, pulse interval 25-35 μs, and voltage 100-120 V.

[0016] Preferably, in the electrode shaping step, the ultrasonic cleaning uses an ethanol medium with a power of 250-350 W and a time of 8-12 minutes.

[0017] In a second aspect, the present application provides an application of a gradient material electrode, which adopts the following technical scheme: An application of a gradient material electrode, the application is a micro-groove electrical discharge machining method, the method comprises the following steps: (a) mounting the gradient material electrode on the main shaft of a machine tool and setting a sacrificial material identical to the final workpiece material on the worktable; (b) setting the machining parameters and driving the gradient material electrode to perform multiple rounds of micro electrical discharge rotary machining on the sacrificial material; using the difference in electrical discharge loss rate of each component of the gradient material electrode in the thickness direction to gradually form a specific stable profile in the machining loss of the electrode working surface, to obtain a shaped electrode; (c) replacing the sacrificial material with the final workpiece and using the same machining parameters as in step (b) to continuously machine the micro-groove using the shaped electrode, to reproduce the stable profile of the shaped electrode on the final workpiece, to obtain a micro-groove with a specific cross-sectional profile shape.

[0018] By adopting the above technical scheme, the present application solves the problem of unstable profile of the gradient electrode in the initial stage of machining by introducing a sacrificial material shaping step. The technical mechanism and beneficial effects are as follows: First, self-shaping and stabilization of the electrode profile: By taking advantage of the difference in loss rate of each layer of the gradient material electrode, the electrode working surface will experience a self-shaping process from a plane to a specific curved surface during the multi-pass processing of the sacrificial material. When the loss of each point reaches a dynamic balance, the electrode forms a stable specific profile. This method ingeniously converts the loss of the electrode into the driving force for electrode shaping, solving the problem of single material electrode difficult to process complex cross-section micro-groove.

[0019] Second, high consistency of profile replication: By pre-completing the nonlinear loss shaping process of the electrode on the sacrificial material, the electrode is already in a stable profile state when it contacts the final workpiece. With the same processing parameters in step (c), the stable shape of the electrode can be accurately replicated to the workpiece surface. This not only guarantees the machining accuracy of the first product, but also ensures the high consistency of the micro-groove cross-section shape (such as R angle size, side wall slope) in batch processing.

[0020] Third, wide processing applicability: This method uses non-contact electric spark processing, which is not limited by the hardness of the workpiece, and by adjusting the combination of the electrode base and the plating layer, a variety of micro-grooves with different cross-sections can be customized, greatly expanding the processing freedom of micro-structures.

[0021] Preferably, the processing parameters include: voltage 120-200V, pulse width 1-10us, pulse interval 15-25us, spindle speed 1000-4000rpm.

[0022] Preferably, in step (c), kerosene-based electric spark oil is used as the cooling liquid with a flow rate of 1.5-2.5L / min.

[0023] Preferably, in step (b), the working surface profile of the gradient material electrode reaches a stable state, and the determination standard is: through laser confocal microscope measurement, the profile change of the gradient material electrode after two consecutive processing is 0.01-0.15um, or the error between the cross-section profile of the processed micro-groove and the designed profile is 1%-5%.

[0024] The present application provides a preparation method of a gradient material electrode and its application. It has the following beneficial effects: 1、The present application combines electroplating treatment with thermal diffusion treatment to build a composition gradient diffusion layer with specific electric spark loss characteristics on the surface of the electrode base. By selecting electroplated high-loss rate materials (such as pure tin) or low-loss rate materials (such as oxygen-free copper), a controllable loss rate difference is established in the thickness direction of the electrode, enabling the electrode to undergo non-uniform etching according to a preset rule during processing, thereby achieving active regulation of the micro-geometric shape of the electrode working surface. At the same time, the metallurgical bonding layer formed by thermal diffusion eliminates the physical interface, solving the problem of easy peeling of conventional coatings under high discharge temperature, and ensuring the structural integrity of the gradient functional layer throughout the processing.

[0025] 2、The present application uses the loss rate difference of each component of the gradient material to convert the loss of the electrode into the power of self-shaping by setting a sacrificial material and a working surface forming step. The evolution process of the electrode from an initial simple shape to a specific complex stable profile is completed on the sacrificial material in advance, so that the electrode is in a dynamic balance state of profile accuracy when it contacts the final workpiece, ensuring the accurate reproduction of the asymmetric or complex cross-section machining profile and improving the size consistency and first-piece qualification rate of batch manufacturing of micro-grooves.

[0026] 3、The present application combines the preparation of gradient material electrodes with working surface forming applications, breaking through the limitations of traditional single material electrodes that are difficult to process complex cross-section micro-grooves. This method uses low-loss diffusion layers as a skeleton to maintain key dimension accuracy and uses high-loss diffusion layers to quickly build chamfer or inclined features, achieving high-precision forming of complex micro-nano structures. At the same time, using electric spark non-contact processing, it is not limited by the hardness of the workpiece material, avoiding the tool chipping problem when processing high-hardness materials by traditional contact cutting. DETAILED DESCRIPTION

[0027] The technical solutions in the embodiments of the present application will be described below in conjunction with the preparation examples, embodiments, comparative examples and tests of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0028] Preparation Examples 1-3: Preparation Example 1: The present preparation example provides a preparation method of a gradient material electrode, specifically relates to a symmetric structure electrode for preparing a double-sided chamfer or circular arc transition cross-section micro-groove, comprising the following steps: Electroplating treatment: A beryllium copper foil (C17200 beryllium copper) with a thickness of 0.1 mm is taken as the electrode base body. In order to obtain a micro-groove profile with smooth edges in subsequent processing, pure tin with high electrical spark loss rate characteristics is selected as the plating material. A conventional electroplating process is used to electroplate a pure tin layer on both main surfaces respectively. The electroplated layer thickness is controlled to be 5 μm, the electroplating solution temperature is maintained at 25±2℃, the current density is 2 A / dm2, and the electroplating time is 15 minutes.

[0029] Thermal diffusion treatment: The electroplated foil is placed horizontally between two high-purity graphite plates (the flatness of the graphite is used to constrain the warping deformation of the foil at high temperature), and is loaded into a vacuum furnace cavity. After vacuumizing to 1.0 Pa, argon gas (purity ≥ 99.99%) is introduced as a protective gas to a furnace pressure of 0.15 MPa. The temperature is raised to 750℃ at a rate of 10℃ / min, and after 8 hours of heat preservation, the heating is stopped, and the furnace is cooled to room temperature. In this process, the surface tin atoms diffuse inward to form a high-loss gradient diffusion layer.

[0030] Electrode forming: The gradient material after thermal diffusion treatment is cut into a tooth-shaped disc electrode with an outer diameter of 8 mm and a tooth depth of 0.5 mm using a wire electrical discharge machining device (parameters: pulse width 3 μs, interval 30 μs, voltage 110 V). After cutting, the machining residues are removed by ultrasonic cleaning (ethanol medium, power 300 W, time 10 minutes).

[0031] Preparation Example 2: The present preparation example provides a preparation method of a gradient material electrode, and specifically relates to an asymmetric structure electrode for preparing an asymmetric inclined cross-section micro-groove, and comprises the following steps: Electroplating treatment: A beryllium copper foil (C17200 beryllium copper) with a thickness of 0.1 mm is taken as the electrode base body. According to the forming requirements of the asymmetric cross-section profile, a high-loss pure tin layer is electroplated on the first main surface (for forming a large chamfer or a shallow edge), and a low-loss oxygen-free copper layer is electroplated on the second main surface (for maintaining a right angle or a deep edge as a wear-resistant framework). The thickness of the electroplated layer on both sides is controlled to be 10 μm, the electroplating solution temperature is maintained at 25±2℃, the tin layer electroplating current density is 2 A / dm2 (time 20 minutes), and the copper layer electroplating current density is 3 A / dm2 (time 15 minutes).

[0032] Thermal diffusion treatment: The electroplated foil is placed horizontally between two high-purity graphite plates, and is loaded into a vacuum furnace cavity. After vacuumizing to 1.0 Pa, argon gas (purity ≥ 99.99%) is introduced to a furnace pressure of 0.15 MPa. The temperature is raised to 800℃ at a rate of 10℃ / min, and after 10 hours of heat preservation, the heating is stopped, and the furnace is cooled to room temperature.

[0033] Electrode forming: The gradient material after thermal diffusion treatment is cut into a tooth-shaped disc electrode with an outer diameter of 8 mm and a tooth depth of 0.5 mm by using a wire-cut electrical discharge machining device (parameters: pulse width 3 μs, interval 30 μs, voltage 110 V). After cutting, the machining residues are removed by ultrasonic cleaning (ethanol medium, power 300 W, time 10 minutes).

[0034] Preparation Example 3 The present preparation example provides a preparation method of a gradient material electrode, and particularly relates to increasing the thickness of a plating layer in an asymmetric structure to adapt to a larger slope requirement, comprising the following steps: Electroplating treatment: A beryllium copper foil material (C17200 beryllium copper) with a thickness of 0.1 mm is taken as an electrode substrate, and an asymmetric electroplating strategy is also adopted: a pure tin layer (high loss rate material) is electroplated on the first major surface, and an oxygen-free copper layer (low loss rate material) is electroplated on the second major surface. The thickness of the double-sided electroplated layer is controlled to be 20 μm, the electroplating liquid temperature is maintained at 25±2℃, the tin layer electroplating current density is 2 A / dm2 (time 35 minutes), and the copper layer electroplating current density is 3 A / dm2 (time 25 minutes).

[0035] Thermal diffusion treatment: The electroplated foil is horizontally placed between two high-purity graphite plates and loaded into a vacuum furnace cavity. After vacuumizing to 1.0 Pa, argon gas (purity ≥ 99.99%) is introduced to the furnace pressure of 0.15 MPa. The temperature is raised to 850℃ at a rate of 10℃ / min, and the heating is stopped after 12 hours of heat preservation, and the furnace is cooled to room temperature.

[0036] Electrode forming: The gradient material after thermal diffusion treatment is cut into a tooth-shaped disc electrode with an outer diameter of 8 mm and a tooth depth of 0.5 mm by using a wire-cut electrical discharge machining device (parameters: pulse width 3 μs, interval 30 μs, voltage 110 V). After cutting, the machining residues are removed by ultrasonic cleaning (ethanol medium, power 300 W, time 10 minutes).

[0037] Examples 1-3 Example 1 The present example provides an application of a gradient material electrode, and particularly relates to a micro-groove machining method using process parameters, comprising the following steps: Electrode clamping: The double-sided high-loss (tin) gradient electrode prepared in Preparation Example 1 is installed on the spindle of a precision electrical discharge machine, and the SKD11 sacrificial material with the same material as the final workpiece is fixed on the workbench. The gap between the electrode and the workpiece is adjusted to 50 μm.

[0038] Work surface forming: The machining parameters are set as voltage 120 V, pulse width 1 μs, pulse interval 15 μs, and spindle speed 1000 rpm. The first round of machining is performed on the surface of the sacrificial material, and the feed depth is 10 μm. Since the two sides of the electrode are tin diffusion layers with high wear rate, and the center is a beryllium copper matrix, the wear rate of the two side edges of the electrode is significantly faster than the center during the discharge process, so that the originally rectangular electrode cross section gradually evolves into a double-side circular arc shape. After translating the workpiece by 0.5 mm, the same parameters are repeated for machining, and a total of 6 rounds are performed.

[0039] Profile stability confirmation: After shaping, the electrode is detected by a laser confocal microscope, and the profile change of the working surface is ≤0.1 μm (comparison between the 3rd round and the 6th round), which is determined to reach a stable state.

[0040] Batch processing: The final workpiece (SKD11) is replaced, and 100 micro-groove structures are continuously machined using the same parameters as the working surface shaping step. The single groove length is 5 mm, and the cooling liquid during the machining process is kerosene-based EDM oil (flow rate 2 L / min). The final micro-groove accurately reproduces the stable shape of the electrode, and presents a double-side smooth transition cross section feature.

[0041] Example 2: The present embodiment provides an application of a gradient material electrode, specifically a micro-groove machining method using process parameters, including the following steps: Electrode clamping: The asymmetric (tin / copper) gradient electrode prepared in Preparation Example 2 is installed on the spindle of a precision EDM machine, and the SKD11 sacrificial material is fixed on the workbench. The gap between the electrode and the workpiece is adjusted to 50 μm.

[0042] Working surface shaping: The machining parameters are set as voltage 160 V, pulse width 5 μs, pulse interval 20 μs, and spindle speed 2500 rpm. The first round of machining is performed on the surface of the sacrificial material, and in this process, the first surface of the electrode (high wear tin diffusion layer) quickly retreats, while the second surface (low wear copper diffusion layer) remains as a wear-resistant skeleton, thereby shaping the working surface of the electrode into a specific asymmetric inclined profile. A total of 6 rounds are performed.

[0043] Profile stability confirmation: After shaping, the electrode is detected by a laser confocal microscope, and the profile change of the working surface is ≤0.1 μm (comparison between the 3rd round and the 6th round), which is determined to reach a stable state.

[0044] Batch processing: The final workpiece (SKD11) is replaced, and 100 micro-grooves are continuously machined using the same parameters. The obtained micro-grooves present a specific asymmetric inclined cross section structure, and have good consistency.

[0045] Example 3: This embodiment provides an application of a gradient material electrode, specifically a micro-groove processing method using process parameters, including the following steps: Electrode clamping: The asymmetric structure gradient electrode prepared in Preparation Example 3 was installed on the main shaft of a precision electric spark machine tool, and the SKD11 sacrificial material was fixed on the workbench. The gap between the electrode and the workpiece was adjusted to 50 μm.

[0046] Working surface forming: The processing parameters were set as voltage 200 V, pulse width 10 μs, pulse interval 25 μs, and spindle speed 4000 rpm. The first round of processing was performed on the surface of the sacrificial material. The thickened plating layer and higher discharge energy allowed the electrode to form an asymmetric profile with a larger slope.

[0047] Profile stability confirmation: After forming, the electrode was detected by a laser confocal microscope, and the profile change of the working surface was ≤0.1 μm (comparison between the 3rd round and the 6th round), which was determined to reach a stable state.

[0048] Batch processing: The final workpiece (SKD11) was replaced, and 100 micro-groove structures were continuously processed using the same parameters as the working surface forming step, with a single groove length of 5 mm. The cooling liquid during processing was kerosene-based electric spark oil (flow rate 2 L / min).

[0049] Comparative Examples 1-4: Comparative Example 1: Compared with Example 2, the difference lies in that a single material electrode is used instead of a gradient material electrode, specifically a disc electrode with the same tooth-like structure is directly made from a beryllium copper alloy foil (C17200 beryllium copper) with a thickness of 0.1 mm by electric spark wire cutting (without electroplating and thermal diffusion treatment). Due to the uniform material, it is not possible to form a specific slope by utilizing the difference in wear. The remaining processing steps and parameters (voltage 160 V, pulse width 5 μs, speed 2500 rpm, sacrificial material forming 20 rounds, batch processing 100 micro-grooves) are the same as those of Example 2.

[0050] Comparative Example 2: Compared with Example 2, the difference lies in that the thermal diffusion treatment step is omitted, and the electroplated beryllium copper alloy foil (double-sided electroplated layer thickness 10 μm) is directly wire-cut formed. The remaining processing steps and parameters (voltage 160 V, pulse width 5 μs, speed 2500 rpm, sacrificial material forming 8 rounds, batch processing 100 micro-grooves) are the same as those of Example 2.

[0051] Comparative Example 3: Compared with Example 2, the difference is that the working surface forming step (sacrificial material pre-processing) is omitted, and the asymmetric gradient electrode prepared in Preparation Example 2 is directly used for batch processing of the final workpiece (SKD11), and the rest of the processing parameters (voltage 160V, pulse width 5μs, rotation speed 2500rpm, continuous processing of 100 microgrooves) are the same as Example 2.

[0052] Comparative Example 4: Compared with Example 2, the difference is that conventional micro-milling processing is used instead of electric spark processing, specifically using a diameter of 0.5mm hard alloy end mill (brand K20) to process the same size microgroove (length 5mm) on the same SKD11 workpiece. The processing parameters are set as spindle speed 20000rpm, feed speed 100mm / min, axial cutting depth 0.1mm (layered processing), cooling method is water-based cutting fluid (flow rate 2L / min), the rest of the conditions (groove number 100) are consistent with Example 2.

[0053] Test Example 1-2: Test Example 1: Feasibility test of the scheme Experimental explanation: This test aims to verify the performance of the technical scheme (gradient electrode + working surface forming) in the forming ability and processing consistency of microgrooves with specific cross section, especially compared with the performance of conventional electrode, untreated electrode and conventional processing method.

[0054] Test object: The electrodes (or tools) prepared in Examples 1-3 and Comparative Examples 1-4 and the SKD11 workpiece samples processed (100 microgrooves per group).

[0055] Test equipment: Laser confocal microscope (model: Keyence VK-X3000); Tool microscope (model: Nikon MM-400); Surface roughness meter (model: Mahr MarSurf PS10).

[0056] Experimental steps: Electrode loss rate detection (or tool replacement statistics): For the electrodes of Examples 1-3 and Comparative Examples 1-3, use the laser confocal microscope to measure the working surface profile after processing 100 grooves, and compare it with the profile data after forming (or before processing) to calculate the relative loss rate of the electrode.

[0057] Processing precision detection (focus on shape consistency): Using tool microscope, measure the width and depth of each of the 100 microgrooves at the beginning, middle and end of the groove. Calculate the average and standard deviation (SD) of the width of each group of 100 grooves, and evaluate the consistency of processing by standard deviation.

[0058] Cross-sectional shape verification: Using laser confocal microscope to observe the cross-section of the microgroove, to determine whether the expected non-rectangular complex cross-section (such as chamfer, tilt) is formed.

[0059] Surface quality detection: Using surface roughness meter, randomly select 10 grooves from each group of groove samples, measure the surface roughness (Ra) of the groove side wall, and calculate the average value.

[0060] Experimental data: Table 1. Comparison of comprehensive performance of examples and comparative examples

[0061] Note: N / A means not applicable.

[0062] Conclusion: Based on the innovative mechanism and the test data in Table 1, the following conclusions can be drawn: Mechanism of gradient material for complex cross-section forming (comparative example and comparative example 1): The electrode loss rate of Example 1 (double-sided plated high-loss tin) (52.4%) is higher than that of single beryllium copper electrode (46.3%) of Comparative Example 1, which verifies the core design logic of the present application: not blindly pursuing low loss, but using the high loss characteristics of pure tin layer to make the electrode wear back quickly on both sides, so as to process microgrooves with double-sided smooth chamfer characteristics.

[0063] In contrast, Comparative Example 1 has uniform material, and the loss of the electrode is relatively uniform, so it can only process ordinary approximately rectangular grooves and cannot realize the preparation of complex cross-section microstructures.

[0064] The loss rate of Example 2 (one side high-loss tin / one side low-loss copper) (38.6%) is between tin and beryllium copper, which successfully utilizes the difference in loss on both sides to process non-symmetrical tilt cross-section microgrooves.

[0065] Necessity of metallurgical bonding (comparison between Example 2 and Comparative Example 2): The comparative example 2 (electroplating only, without diffusion, loss 72.5%) has the worst performance. The data prove that the Sn-Cu structure without forming a diffusion layer cannot withstand the discharge. The mechanism lies in that the Sn layer with low melting point (melting point 231.9°C) will have liquid phase peeling or severe evaporation at the moment of discharge, leading to unstable arc, aggravating the substrate loss, and seriously deteriorating the processing precision (SD 11.74 μm) and surface quality (Ra 0.95 μm).

[0066] On the contrary, the thermal diffusion treatment in the embodiment forms a metallurgical bond, realizes the performance gradient transition from the high loss rate material to the substrate, and effectively improves the thermal shock resistance.

[0067] Necessity of the working surface forming step (comparative example 2 vs. comparative example 3): Comparative example 3 (not formed) and example 2 (formed) both use gradient electrodes, and the electrode loss rates of the two are close (12.8% vs. 10.2%), which proves the durability of the gradient material itself.

[0068] However, there is a huge difference in processing precision: the groove width standard deviation of comparative example 3 (9.45 μm) is 7.4 times that of example 2 (1.27 μm).

[0069] The data prove the core mechanism of the scheme: the gradient electrode must be matched with the working surface forming step. This step uses sacrificial material to make the electrode discharge under controllable conditions to achieve a dynamic balance of profile loss. After the electrode profile is stable, it is used to process the final workpiece, so as to reproduce this stable state to the workpiece, ensuring the high consistency of batch processing. Without this step, the electrode will experience severe profile changes in the early stage of processing (first 10-20 grooves), leading to precision disaster.

[0070] Applicability of the electrical discharge machining route (comparative example 2 vs. comparative example 4): Comparative example 4 (micro-milling) has 11 tool changes when machining high-hardness SKD11, and the precision (SD 7.91 μm) and roughness (Ra 0.84 μm) are not ideal. This exposes the physical bottleneck of traditional contact cutting when machining microstructures of high-hard materials, i.e. tool vibration and edge collapse caused by cutting force.

[0071] The scheme (example 2) uses electrical discharge non-contact machining, which is not limited by material hardness and has no macro cutting force, achieving excellent precision (SD 1.27 μm) and surface quality (Ra 0.21 μm).

[0072] Summary: The data show that a single gradient material (such as Comparative Example 3) or a single forming process (such as Comparative Example 1) cannot achieve high precision and low loss microprocessing. The technical solution combines the preparation of a gradient material electrode with the working surface forming process, solves the influence of the profile change of the electrode before reaching the stable loss state (i.e. the forming stage) on the precision of the workpiece, and realizes the unification of low loss of the electrode and high precision (1.27 μm) of the workpiece.

[0073] Test Example 2: Performance comparison test Experimental description: This test aims to further evaluate the cross-sectional profile retention capability of the technical solution in long-time continuous processing, focusing on the influence of the gradient structure and the pre-forming process on the processing life of complex microstructures.

[0074] Test object: The electrodes prepared by Example 2 (asymmetric forming), Comparative Example 1 (single material cannot be formed), and Comparative Example 3 (not formed by sacrificial material) are selected.

[0075] Test equipment: Scanning electron microscope and energy dispersive spectrometer (SEM-EDS, model: ZEISS Sigma300); High-precision image measuring instrument (model: Hexagon Optiv Classic 321).

[0076] Experimental steps: Long-term processing stability test: Set up a continuous processing task, and each electrode processes 200 microgrooves (workpiece material SKD11) continuously.

[0077] Sampling detection: samples are extracted at the 1st, 10th, 50th, 100th, 150th, and 200th groove nodes.

[0078] Measurement index: Cross-sectional profile error: The actual processed microgroove cross-sectional profile is fitted with the designed target profile (Example 2 is an inclined profile, and Comparative Example 1 is a rectangular profile), and the maximum profile deviation is measured.

[0079] Microscopic composition analysis of the electrode surface: After the completion of the processing task, the working end face of the electrode of Example 2 is cut off, and line scanning is performed using EDS energy spectrum to analyze the element (Sn, Cu, Be) distribution concentration change from the surface to the core to verify the existence of the thermal diffusion layer and its retention after processing.

[0080] Experimental data: Table 2. Profile error evolution data in long-term processing

[0081] Conclusion: Through long-term processing tests and microscopic analysis, combined with Table 2, the following technical conclusions are drawn: Steady-state reproduction mechanism of sacrificial material shaping (Example 2 vs. Comparative Example 3): The data of Comparative Example 3 clearly shows the self-shaping process of the electrode. Its profile error is as high as 8.7 μm at the first workpiece, because at this time the electrode is still rectangular and has not been able to process the designed inclined groove. With the progress of processing, the electrode is gradually ground into an inclined shape by using the difference in wear rate, and it reaches stability (1.5 μm) at the 50th workpiece. This means that if the sacrificial material shaping step of the present application is not used, the first 50 products will be scrapped due to profile inconsistency.

[0082] Example 2 has completed this process in advance, and the profile error is controlled at 1.2 μm from the first workpiece, realizing zero-waste start.

[0083] Gradient layer's ability to maintain complex profile (Example 2 vs. Comparative Example 1): Although Comparative Example 1 (single material) can process rectangular grooves at the beginning, it cannot resist the concentration of sharp end discharge, and its corners quickly round, leading to a linear deterioration of profile error and short service life.

[0084] Example 2 uses the copper diffusion layer as a low-wear skeleton to effectively maintain the key dimensions in the inclined profile, and uses the continuous high wear of the tin diffusion layer to maintain the clearance shape on the other side, so that this complex asymmetric profile can be kept stable for a long time (error only 2.1 μm at 200 times) in 200 times of processing.

[0085] Summary: Performance comparison tests confirm that the present application, through the combined process of material gradient design + sacrificial material self-shaping, not only solves the problem of single material unable to process complex micro-sections, but also eliminates the electrode running-in period in advance, realizing high-precision, high-consistency batch manufacturing of complex micro-grooves.

Claims

1. A method for preparing a gradient material electrode, characterized in that, Includes the following steps: S1. Select beryllium copper alloy foil as the electrode substrate. According to the cross-sectional contour shape requirements of the micro-groove to be processed, electroplate a metal layer on the main surface of the electrode substrate. The metal layer is selected from at least one of pure tin layer and oxygen-free copper layer. The thickness of the metal layer is 5-20μm, and the electroplated foil is obtained. S2. The electroplated foil is placed horizontally between two high-purity graphite plates and placed into a vacuum furnace cavity. The vacuum is evacuated to 0.5-1.5 Pa, and argon gas is introduced as a protective gas to 0.12-0.18 MPa. The temperature is then increased to 750-850°C at a rate of 8-12°C / min and held for 8-12 hours. The furnace is then cooled to obtain a gradient material foil. S3. The gradient material foil is cut into toothed disc electrodes using an electrical discharge wire cutting device, and the toothed disc electrodes are ultrasonically cleaned.

2. The method for preparing a gradient material electrode according to claim 1, characterized in that, In step S1, the temperature of the electroplating solution is maintained at 23-27°C.

3. The method for preparing a gradient material electrode according to claim 1, characterized in that, In step S1, selecting the metal layer according to the cross-sectional profile shape requirements of the micro-trench to be processed includes: when a shallow or smooth micro-trench profile is required, a pure tin layer with a higher electroplating loss rate than the electrode substrate is selected; when a deep or steep micro-trench profile is required, an oxygen-free copper layer with a lower electroplating loss rate than the electrode substrate is selected.

4. The method for preparing a gradient material electrode according to claim 1, characterized in that, The overall step S1 is an electroplating process used to prepare microgrooves with asymmetric cross-sectional profiles. Specifically, a pure tin layer is electroplated on the first main surface of the electrode substrate, and an oxygen-free copper layer is electroplated on the second main surface.

5. The method for preparing a gradient material electrode according to claim 1, characterized in that, In step S3, the parameters of the wire electrical discharge machining equipment include: pulse width 2-4μs, pulse interval 25-35μs, and voltage 100-120V.

6. The method for preparing a gradient material electrode according to claim 1, characterized in that, In the electrode forming step, ultrasonic cleaning is performed using ethanol as the medium, with a power of 250-350W and a time of 8-12 minutes.

7. An application of a gradient material electrode, characterized in that, The application is a microgroove electrical discharge machining method, which includes the following steps: (a) The gradient material electrode is mounted on the machine tool spindle, and a sacrificial material identical to the final workpiece material is placed on the worktable; (b) Set the processing parameters and drive the gradient material electrode to perform multiple rounds of micro-electrical discharge rotation processing on the sacrificial material; utilize the difference in the electric discharge loss rate of each component of the gradient material electrode in the thickness direction to make the electrode working surface gradually form a specific stable profile in the processing loss, and obtain the shaped electrode. (c) Replace the sacrificial material with the final workpiece, use the same processing parameters as in step (b), and continuously process the microgroove using the formed electrode to reproduce the stable profile of the formed electrode onto the final workpiece to obtain a microgroove with a specific cross-sectional profile shape.

8. The application of a gradient material electrode according to claim 7, characterized in that, The machining parameters in steps (b) and (c) include: voltage 120-200V, pulse width 1-10μs, pulse interval 15-25μs, and spindle speed 1000-4000rpm.

9. The application of a gradient material electrode according to claim 7, characterized in that, In step (c) of workpiece machining, kerosene-based EDM oil is used as the coolant, with a flow rate of 1.5-2.5 L / min.

10. The application of a gradient material electrode according to claim 7, characterized in that, In step (b), the working surface profile of the electrode reaches a stable state. The judgment criteria are: the profile change of the gradient material electrode after two consecutive processing cycles is 0.01-0.15 μm, as measured by a laser confocal microscope, or the profile of the processed microgroove cross section has an error of 1%-5% compared with the design profile.

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