Electrode for electric discharge machining of micro-holes with large depth-diameter ratio and preparation method thereof

Abstract

The application discloses an electrode for electric spark machining of a micro-hole with a large depth-diameter ratio and a preparation method thereof, and belongs to the technical field of tool electrode preparation. The electrode comprises a tungsten wire rod, and the diameter of the tungsten wire rod is 0.1-0.4 mm. The tungsten wire rod is characterized in that a uniform and stable zirconium oxide insulation layer is arranged on the peripheral wall of the tungsten wire rod. The electrode selects the stable zirconium oxide layer as the insulation layer, which can enhance the insulation property of the peripheral wall of the electrode. On one hand, the electrode can reduce the discharge removal between the peripheral wall of the electrode and the side wall of the hole in the electric spark machining process, thereby improving the forming precision of the micro-hole. On the other hand, the electrode can reduce the skin effect of the current in the electrode and increase the current density of the center of the end surface of the electrode. Meanwhile, the end surface of the insulation layer has the conductivity in the electric spark discharge, electric spark discharge is generated to remove the material, and the electric spark machining efficiency is improved.

Description

Technical Field

[0001] This invention belongs to the field of tool electrode preparation technology, specifically relating to an electrode for electrical discharge machining of micro-holes with large aspect ratio and its preparation method. Background Technology

[0002] With the development of precision manufacturing technology, the demand for machining microporous structures in parts such as precision filtration equipment, chemical fiber spinnerets, jet engine nozzles, automotive engine fuel injectors, aerospace gyroscope instrument components, and aircraft turbine blades is increasing. There is even a demand for machining micropores with a depth-to-diameter ratio greater than 10 and an aperture less than 0.5 mm. Traditional machining methods are almost incapable of machining such microporous structures. Electrical discharge machining (EDM), however, is a non-contact machining process. During machining, the tool electrode does not come into contact with the workpiece, and the tool electrode does not deform under stress. Furthermore, EDM is almost unaffected by the workpiece's structure, strength, and hardness, making it particularly suitable for machining conductive materials.

[0003] Therefore, people sought to apply electrical discharge machining (EDM) technology to the machining of micro-holes with large aspect ratios. Patent application CN110695474A discloses a device for efficient EDM machining of small micro-holes with large aspect ratios. This device has a cavity at the bottom of the central shaft of the fixed electrode for mounting a transducer. A connecting hole for placing the transducer lead is formed inside the central shaft, communicating with the cavity. An insulating sleeve is coaxially fitted on the upper part of the central shaft, and a conductive slip ring for supplying power to the transducer is coaxially fitted outside the insulating sleeve. The conductive slip ring is coaxially fitted outside the conductive slip ring. The first sleeve is fitted with a housing, and the outer shell is fitted on the outside of the first sleeve. Transducer lead wire outlet holes are made on the housing, the first sleeve, and the insulating sleeve. The transducer lead wire is led out from the housing and connected to the ultrasonic power supply. Although this device can add an ultrasonic device to the central axis of the fixed electrode, thereby increasing the ultrasonic vibration function of the electrode and enhancing the chip removal effect, it can improve the efficiency of large aspect ratio micro-hole machining to a certain extent. However, the machined micro-holes are tapered holes with a larger outer diameter and a smaller inner diameter, which reduces the accuracy of micro-hole machining and cannot be applied to precision manufacturing.

[0004] Therefore, it is still necessary to fundamentally improve the machining accuracy of micro-holes with large depth-to-diameter ratios. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide an electrode for electrical discharge machining of micro-holes with large aspect ratio and a method for preparing the same, which can enhance the insulation of the electrode peripheral wall and reduce the electrical discharge removal of the electrode peripheral wall on the sidewall of the micro-hole.

[0006] To solve the above-mentioned technical problems, the technical solution of the present invention is: to design an electrode for electrical discharge machining of micro-holes with large aspect ratio, comprising a tungsten wire rod with a diameter of 0.1 to 0.4 mm, characterized in that: a uniform stabilized zirconium oxide insulating layer is provided on the peripheral wall of the tungsten wire rod.

[0007] Preferably, the stabilized zirconia insulating layer is a yttrium-stabilized zirconia coating.

[0008] Preferably, the thickness of the stabilized zirconium oxide insulating layer is 14.8–18.8 μm.

[0009] The present invention also provides a method for preparing the above-mentioned electrode for electrical discharge machining of micro-holes with large aspect ratio, characterized by comprising the following steps:

[0010] (1) Roughening: Tungsten wire rods with a diameter of 0.1 to 0.4 mm are placed in hydrogen peroxide solution for roughening, and the roughened tungsten wire rods are ultrasonically cleaned and dried;

[0011] (2) Motion: Rotate the tungsten wire rod processed in step (1). The rotating tungsten wire rod also vibrates along the axial direction of the tungsten wire rod with a vibration frequency of 20KHz.

[0012] (3) Spraying: Plasma spraying stabilized zirconium oxide powder onto the peripheral wall of the tungsten wire rod in the state of step (2) to obtain a stabilized zirconium oxide insulating layer on the peripheral wall of the tungsten wire rod. The particle size of the stabilized zirconium oxide powder is 30-45 μm.

[0013] In plasma spraying, the voltage is 60V, the current is 500-700A, the main gas flow rate is 40L / min, the secondary gas flow rate is 9L / min, the powder feeding speed is 1.5r / min, and the spraying distance is 70-110mm.

[0014] Preferably, in plasma spraying, argon is used as the primary gas and hydrogen as the secondary gas.

[0015] Preferably, a cleaning step is included before roughening, in which the tungsten wire rod is placed in a potassium hydroxide solution for surface cleaning.

[0016] Preferably, the volume percentage concentration of the potassium hydroxide solution is 25-35%.

[0017] Preferably, the cleaning temperature is 20-28℃ and the cleaning time is 7-12 minutes.

[0018] Preferably, in step (1), the volume percentage concentration of the hydrogen peroxide solution is 25-35%.

[0019] Preferably, in step (1), the roughening time is 7–12 min.

[0020] Preferably, in step (2), the tungsten wire rod is placed in an alternating electromagnetic field for plasma spraying, the direction of the magnetic field lines in the electromagnetic field is consistent with the direction of plasma spraying, and the intensity of the electromagnetic field is 100-200mT.

[0021] Preferably, in step (2), the amplitude of the axial vibration is 2 to 3 μm.

[0022] Compared with the prior art, the beneficial effects of the present invention are:

[0023] 1. This invention uses a stabilized zirconia layer as an insulating layer, which can enhance the insulation of the electrode peripheral wall. On the one hand, it can reduce the discharge removal between the electrode peripheral wall and the hole sidewall during the electrical discharge machining process, thereby improving the forming accuracy of the microhole. On the other hand, it can reduce the skin effect of the current in the electrode and increase the current density at the center of the electrode end face. At the same time, it also makes the end face of the insulating layer conductive in the electrical discharge, generating electrical discharge to remove material, thus improving the efficiency of electrical discharge machining.

[0024] 2. The stabilized zirconia insulation layer uses a yttrium-stabilized zirconia coating with low thermal conductivity, which can improve the insulation layer's resistance to electrolytic corrosion and effectively extend its service life.

[0025] 3. The present invention uses high-hardness tungsten wire rods as the electrode substrate, which not only has certain conductivity to meet the requirements of micro-hole processing, but also has certain resistance to deformation to resist the deformation caused by subsequent spraying processing, and is also easy to chemically roughen using hydrogen peroxide solution.

[0026] 4. Cleaning and roughening the tungsten wire rod before plasma spraying can increase the bonding force between the insulation layer and the tungsten wire rod, enhance the adhesion strength of the insulation layer, and extend the protective life of the insulation layer for the tungsten wire rod.

[0027] 5. The preparation of the insulation layer using the mature plasma spraying technology is not only easy to implement, but also enables the cladding preparation of the insulation layer, which helps to enhance the bonding strength between the coating and the substrate.

[0028] 6. During the spraying process, rotation enables uniform spraying of the tungsten wire rod's periphery, while high-frequency vibration along the axial direction of the tungsten wire rod can agitate the molten droplets sprayed onto the tungsten wire rod by the plasma jet, causing the droplets to tend to spread out, which helps to improve the uniformity of the insulation layer thickness and enhance the density of the insulation layer, so that all parts of the tungsten wire rod's periphery obtain equal strength of insulation.

[0029] 7. The spraying process is carried out in an alternating electromagnetic field, which can use the alternating magnetic field to disturb the molten droplets and further enhance the uniformity and density of the insulation layer.

[0030] 8. The present invention is ingenious in conception. It can add an insulating layer on the peripheral wall of the tool electrode while retaining the discharge capability of the tool electrode end face. This can avoid the discharge between the peripheral wall of the tool electrode and the side wall of the hole as much as possible, thereby fundamentally improving the processing accuracy of the micro hole and facilitating its promotion and application in the field. Attached Figure Description

[0031] Figure 1 This is an electron microscope scan of the electrode in this invention;

[0032] Figure 2 Electron microscopy scan of the insulating coating surface Figure 1 ;

[0033] Figure 3 Electron microscopy scan of the insulating coating surface Figure 2 ;

[0034] Figure 4 This is a metallographic microscope image of micropores fabricated using the electrodes of this invention via electrical discharge machining.

[0035] Figure 5 This is a metallographic microscope image of a micropore fabricated using a comparative electrode electrical discharge machining process. Detailed Implementation

[0036] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0037] In this invention, the working surface perpendicular to the electrode axis is defined as the end face, and the side wall located on the outer periphery of the electrode axis is defined as the peripheral wall.

[0038] Example 1

[0039] This embodiment obtains an electrode for electrical discharge machining of micro-holes with large aspect ratios via the following steps:

[0040] (1) Cleaning: Place a 0.1 mm diameter tungsten wire rod into a 25% potassium hydroxide solution for surface cleaning for 12 min.

[0041] (2) Roughening: The tungsten wire rod treated in step (1) is placed in a hydrogen peroxide solution with a volume percentage concentration of 35% for 7 minutes for chemical reaction. The tungsten wire rod immersed in the hydrogen peroxide solution is ultrasonically cleaned and dried to obtain a roughened tungsten wire rod.

[0042] (3) Motion: Fix the tungsten wire rod treated in step (2) on the amplitude rod of the ultrasonic vibrator. The tungsten wire rod can vibrate along its own axial direction with an amplitude of 2μm. The vibration frequency of the ultrasonic vibrator is 18KHz. The ultrasonic vibrator is installed on a rotating shaft with a rotation speed of 200r / min. This is how the tungsten wire rod treated in step (2) is rotated. The rotating tungsten wire rod also vibrates along the axial direction of the tungsten wire rod. Of course, it is not limited to the specific method of realizing high-frequency vibration of the tungsten wire rod by the ultrasonic vibrator. Other methods can also be used to realize high-frequency vibration. Here, the means of realizing high-frequency vibration are not specifically limited, as long as the vibration frequency can reach 18KHz.

[0043] (4) Spraying: The tungsten wire rod in the state of step (3) is placed in an alternating electromagnetic field for plasma spraying. The direction of the magnetic field lines in the electromagnetic field is consistent with the direction of plasma spraying. The intensity of the electromagnetic field is 200mT. Yttrium-stabilized zirconia powder is plasma sprayed onto the peripheral wall of the tungsten wire rod, so that the yttrium-stabilized zirconia powder forms a yttrium-stabilized zirconia insulating layer on the peripheral wall of the tungsten wire rod, and an electrode for high aspect ratio microholes is obtained by electrical discharge machining.

[0044] In plasma spraying, the yttrium-stabilized zirconia powder used has a particle size of 45 μm, the operating voltage is 60V, the operating current is 500A, the main gas flow rate is 38L / min, the secondary gas flow rate is 7L / min, the powder feed speed is 1.5r / min, and the spraying distance is 110mm. The selection of the main and secondary gases is the same as in existing technologies, with no special features; argon and hydrogen, commonly used in plasma spraying, are employed, with argon as the main gas and hydrogen as the secondary gas.

[0045] Example 2

[0046] The difference between this embodiment and Embodiment 1 is that:

[0047] In step (1), the diameter of the tungsten wire rod used is 0.2 mm, the volume percentage concentration of the potassium hydroxide solution is 28%, and the surface cleaning time is 11 min.

[0048] In step (2), the volume percentage concentration of hydrogen peroxide solution is 32%, and the roughening time through chemical reaction is 8 minutes.

[0049] In step (3), the amplitude is 2.5 μm, the vibration frequency of the ultrasonic vibrator is 19 kHz, and the rotation speed of the rotating shaft is 300 r / min.

[0050] In step (4), the electromagnetic field strength is 170mT, the particle size of the yttrium-stabilized zirconia powder used is 35μm, the working current is 550A, the main gas flow rate is 39L / min, the secondary gas flow rate is 8L / min, the powder feeding speed is 1.5r / min, and the spraying distance is 100mm.

[0051] The rest are the same as in Example 1.

[0052] Example 3

[0053] The difference between this embodiment and Embodiment 1 is that:

[0054] In step (1), the diameter of the tungsten wire rod used is 0.3 mm, the volume percentage concentration of the potassium hydroxide solution is 30%, and the surface cleaning time is 10 min.

[0055] In step (2), the volume percentage concentration of hydrogen peroxide solution is 30%, and the roughening time through chemical reaction is 10 min.

[0056] In step (3), the amplitude is 3μm, the vibration frequency of the ultrasonic vibrator is 120KHz, and the rotation speed of the rotating shaft is 350r / min.

[0057] In step (4), the electromagnetic field strength is 150mT, the particle size of the yttrium-stabilized zirconia powder used is 40μm, the working current is 600A, the main gas flow rate is 40L / min, the secondary gas flow rate is 9L / min, the powder feeding speed is 1.5r / min, and the spraying distance is 90mm.

[0058] The rest are the same as in Example 1.

[0059] Example 4

[0060] The difference between this embodiment and Embodiment 1 is that:

[0061] In step (1), the diameter of the tungsten wire rod used is 0.4 mm, the volume percentage concentration of the potassium hydroxide solution is 35%, and the surface cleaning time is 7 min.

[0062] In step (2), the volume percentage concentration of hydrogen peroxide solution is 25%, and the roughening time through chemical reaction is 12 min.

[0063] In step (3), the amplitude is 2.5 μm, the vibration frequency of the ultrasonic vibrator is 23 kHz, and the rotation speed of the rotating shaft is 500 r / min.

[0064] In step (4), the electromagnetic field strength is 100mT, the particle size of the yttrium-stabilized zirconia powder used is 30μm, the working current is 700A, the main gas flow rate is 42L / min, the secondary gas flow rate is 11L / min, the powder feeding speed is 1.5r / min, and the spraying distance is 70mm.

[0065] The rest are the same as in Example 1.

[0066] Example 5

[0067] The difference between this embodiment and Embodiment 1 is that:

[0068] In step (1), the diameter of the tungsten wire rod used is 0.25 mm, the volume content of potassium hydroxide in the potassium hydroxide solution is 32%, and the surface cleaning time is 8 min.

[0069] In step (2), the volume percentage concentration of hydrogen peroxide solution is 28%, and the roughening time through chemical reaction is 11 min.

[0070] In step (3), the amplitude is 3μm, the vibration frequency of the ultrasonic vibrator is 21KHz, and the rotation speed of the rotating shaft is 400r / min.

[0071] In step (4), the electromagnetic field strength is 130mT, the particle size of the yttrium-stabilized zirconia powder used is 35μm, the working current is 650A, the main gas flow rate is 41L / min, the secondary gas flow rate is 10L / min, the powder feeding speed is 1.5r / min, and the spraying distance is 80mm.

[0072] The rest are the same as in Example 1.

[0073] The insulation layer of the electrode prepared in the above embodiment was tested for thickness uniformity (thickness range), porosity and insulation. The insulation was tested for conductivity at 25°C, 800°C (temperature of the electrode peripheral wall during EDM) and 2000°C (temperature of the working surface during EDM) to reflect the insulation of the insulation layer at room temperature and the sidewall and endwall of the electrode during EDM.

[0074] The thickness range of the insulation layer was tested according to the national standard GB 11374-1989 "Non-destructive Measurement Method for Thickness of Thermal Spray Coatings". Porosity testing was conducted according to the national standard GB / T 41898-2022 "Electrochemical Method for Determination of Corrosion Resistance and Density of Coatings for Inner Walls of Food Metal Containers". Conductivity testing was conducted according to the aerospace industry standard QJ 2220.2-1992 "Test Methods for Electrical Insulation Performance of Coatings: Insulation Resistance, Surface Resistivity, and Volume Resistivity". The test results are as follows:

[0075]

[0076] It can be seen that the insulating layer of the electrode made by the present invention has good uniformity and is relatively dense, which is conducive to achieving uniformity of insulation strength on the peripheral wall of the electrode.

[0077] The electrode prepared in Example 1 was also used for electrical discharge machining (EDM) of micropores. The EDM process parameters were: discharge current of 3A, pulse width of 60µs, and pulse interval of 20s. Using the original tungsten wire rod from Example 1 as a control electrode, under the same process conditions and with the same titanium alloy as the machining substrate, EDM was performed on different parts for comparison. The metallographic microscopy images of the micropores machined by the electrode of this invention are shown below. Figure 4 As shown, the metallurgical microscope image of the micropores fabricated by the contrast electrode is as follows: Figure 5 As shown, Figure 4 and Figure 5 The images were obtained using a metallurgical microscope in the same working state, with a magnification of 10x.

[0078] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing an electrode for electrical discharge machining of micro-holes with a large aspect ratio, comprising a tungsten wire rod with a diameter of 0.1–0.4 mm, wherein a uniform stabilized zirconium oxide insulating layer is provided on the peripheral wall of the tungsten wire rod, characterized in that: Includes the following steps: (1) Roughening: Tungsten wire rods with a diameter of 0.1 to 0.4 mm are placed in hydrogen peroxide solution for roughening, and the roughened tungsten wire rods are ultrasonically cleaned and dried; (2) Motion: Rotate the tungsten wire rod processed in step (1). The rotating tungsten wire rod also vibrates along the axial direction of the tungsten wire rod with a vibration frequency of 20KHz. (3) Spraying: Plasma spraying stabilized zirconium oxide powder onto the peripheral wall of the tungsten wire rod in the state of step (2) to obtain a stabilized zirconium oxide insulating layer on the peripheral wall of the tungsten wire rod. The particle size of the stabilized zirconium oxide powder is 30-45 μm. In plasma spraying, the voltage is 60V, the current is 500-700A, the main gas flow rate is 40L / min, the secondary gas flow rate is 9L / min, the powder feeding speed is 1.5r / min, and the spraying distance is 70-110mm.

2. The method for preparing an electrode for electrical discharge machining of micro-holes with a large aspect ratio according to claim 1, characterized in that: The roughening process includes a cleaning step, in which the tungsten wire rod is placed in a potassium hydroxide solution for surface cleaning.

3. The method for preparing an electrode for electrical discharge machining of micro-holes with a large aspect ratio according to claim 2, characterized in that: The potassium hydroxide solution has a volume percentage concentration of 25-35%.

4. The method for preparing an electrode for electrical discharge machining of micro-holes with a large aspect ratio according to claim 1, characterized in that: In step (1), the volume percentage concentration of the hydrogen peroxide solution is 25-35%.

5. The method for preparing an electrode for electrical discharge machining of micro-holes with a large aspect ratio according to claim 4, characterized in that: In step (1), the roughening time is 7 to 12 minutes.

6. The method for preparing an electrode for electrical discharge machining of micro-holes with large aspect ratios according to any one of claims 1 to 5, characterized in that: In step (3), the tungsten wire rod is placed in an alternating electromagnetic field for plasma spraying. The direction of the magnetic field lines in the electromagnetic field is consistent with the direction of plasma spraying. The intensity of the electromagnetic field is 100-200mT.

7. The method for preparing an electrode for electrical discharge machining of micro-holes with large aspect ratios according to any one of claims 1 to 5, characterized in that: In step (2), the amplitude of the axial vibration is 2 to 3 μm.

8. The method for preparing an electrode for electrical discharge machining of micro-holes with large aspect ratios according to any one of claims 1 to 5, characterized in that: The stabilized zirconium oxide insulating layer is a yttrium oxide stabilized zirconium oxide coating.

9. The method for preparing an electrode for electrical discharge machining of micro-holes with large aspect ratios according to any one of claims 1 to 5, characterized in that: The thickness of the stabilized zirconium oxide insulating layer is 14.8–18.8 μm.

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