Online film coating method for side wall of micro electrode in electric spark micro hole machining process

Abstract

The invention provides an online film coating method for the side wall of a micro electrode in the electric spark micro-hole machining process, and belongs to the technical field of non-traditional machining. A bipolar pulse power supply is used for continuously emitting pulses with positive and negative polarities, and in-situ online film coating is carried out on the surface of the micro electrode in the electric spark micro-hole machining process; the high-resistivity nanoscale oxide film is formed by the oxide of the material of the micro electrode, the secondary discharge phenomenon caused by electric corrosion particles can be reduced, and meanwhile, the thickness of the oxide film is nanoscale, so that the size error of the micro electrode is hardly caused, and the influence on the processing result is relatively small; in addition, in-situ online film coating is synchronous in the electric spark micropore machining process and the film coating treatment process, the electrode is kept in situ in the film coating treatment process, and the micro electrode cannot generate motion errors due to clamping in the machining process.

Description

Technical Field

[0001] The invention belongs to the technical field of special processing, and in particular relates to a method for online coating of a micro-electrode side wall in an electrospark micro-hole processing process. Background Art

[0002] In the fields of aerospace, biomedicine, automobiles, etc., EDM micro-hole machining technology is widely used in micro-hole machining of various parts in different fields such as various fuel injectors, turbine blades, and drug delivery orifices due to its characteristics of no contact force, high machining accuracy, and suitability for difficult-to-machine materials. However, when facing deep micro-holes, especially micro-holes with extreme characteristics, EDM micro-hole machining technology has problems such as low machining efficiency, difficult chip removal, and serious secondary discharge. Among them, the secondary discharge phenomenon caused by electro-erosion particles is the main reason for the serious electrode loss. Since the size of the fine electrodes used in EDM micro-hole machining is small, they must be replaced once they are worn out, which seriously affects the production efficiency of EDM micro-hole machining.

[0003] In view of the above problems, there is an urgent need for a method for online coating of the side wall of a micro-electrode during electrospark micro-hole machining, which will not affect the electrospark micro-hole machining and effectively protect the micro-electrode body. Summary of the invention

[0004] In order to solve the shortcomings and deficiencies of the prior art, a method for online coating of the side wall of a fine electrode during electrospark micro-hole machining is provided, thereby solving the problem of serious electrode loss caused by secondary discharge caused by electro-erosion particles in electrospark micro-hole machining technology.

[0005] To achieve the purpose of the present invention, a method for online coating of the side wall of a fine electrode during electrospark micro-hole machining is provided, comprising the following steps:

[0006] Step 1: Place the workpiece on the processing table of the EDM micro-hole machining machine and clamp it, and use the fixture in the EDM micro-hole machining machine to clamp the fine electrode, and connect the fine electrode and the workpiece to the two poles of the bipolar pulse power supply respectively;

[0007] Step 2: Adjust the distance between the microelectrode and the bottom of the micropore in the workpiece, and continuously introduce a 2% KNO3 solution into the gap between the microelectrode and the wall of the micropore in the workpiece;

[0008] Step 3: Adjust the micro-electrode to the positive pole of the bipolar pulse power supply, adjust the workpiece to the negative pole of the bipolar pulse power supply, set the voltage of the bipolar pulse power supply to 30V, turn on the bipolar pulse power supply to coat the surface of the micro-electrode, so that the micro-electrode undergoes an oxidation reaction with the nitrate ions in the solution to form an oxide film;

[0009] Step 4: When no more bubbles appear on the surface of the micro-electrode, stop introducing the KNO3 solution into the gap between the micro-electrode and the workpiece;

[0010] Step 5: Adjust the fine electrode to the negative pole of the bipolar pulse power supply, adjust the workpiece to the positive pole of the bipolar pulse power supply, and measure the discharge gap between the fine electrode and the workpiece;

[0011] Step 6: Repeat steps 2 to 5 for multiple times, and finally make the discharge gap between the micro-electrode and the workpiece 1-2 μm;

[0012] Step 7: Make the bipolar pulse power supply emit two different pulses, so that the polarity of the micro-electrode and the workpiece changes accordingly, and at the same time, KNO3 solution is continuously introduced into the gap between the micro-electrode and the micro-pore wall in the workpiece to perform electrospark micro-hole machining.

[0013] As a further improvement of the above scheme, the bipolar pulse power supply includes power supplies U1-U2, MOS field effect transistors M1-M3, resistor R1 and discharge capacitor C1; the negative electrode of the power supply U1 is connected to the drain of the MOS field effect transistor M1, and the positive electrode is connected to the source of the MOS field effect transistor M2, one end of the discharge capacitor C1 and the workpiece; the negative electrode of the power supply U2 is connected to the drain of the MOS field effect transistor M2, and the positive electrode is connected to the source of the MOS field effect transistor M1 and one end of the resistor R1; the other end of the resistor R1 is connected to the drain of the MOS field effect transistor M3 and the other end of the discharge capacitor C1, and the source of the MOS field effect transistor M3 is connected to the tungsten electrode; the power supplies U1-U2 are respectively controlled by the MOS field effect transistors M1-M2, and at the same time, the MOS field effect transistor M3 controls the discharge capacitor C1 to discharge.

[0014] As a further improvement of the above scheme, during the film coating process in step three, the MOS field effect transistor M1 is disconnected and the MOS field effect transistor M2 is closed. At this time, the discharge capacitor C1 is charged by the power supply U2. During the discharge process of the discharge capacitor C1, the micro-electrode is the positive electrode and the workpiece is the negative electrode.

[0015] As a further improvement of the above scheme, when measuring the discharge gap between the micro-electrode and the workpiece in step five, the MOS field effect transistor M1 is closed and the MOS field effect transistor M2 is disconnected. At this time, the discharge capacitor C1 is charged by the power supply U1. During the discharge process of the discharge capacitor C1, the micro-electrode is the negative electrode and the workpiece is the positive electrode.

[0016] As a further improvement of the above scheme, when the bipolar pulse power supply emits two different pulses in step seven, the MOS field effect transistor M1 is disconnected and the MOS field effect transistor M2 is closed. At this time, the power supply U2 charges the discharge capacitor C1. During the discharge process of the discharge capacitor C1, the micro-electrode is the positive electrode and the workpiece is the negative electrode; the MOS field effect transistor M1 is closed and the MOS field effect transistor M2 is disconnected. At this time, the power supply U1 charges the discharge capacitor C1. During the discharge process of the discharge capacitor C1, the micro-electrode is the negative electrode and the workpiece is the positive electrode.

[0017] As a further improvement of the above solution, the microelectrode is a tungsten electrode.

[0018] The beneficial effects of the present invention are:

[0019] Compared with the prior art, the present invention provides a method for online coating of the side wall of a micro-electrode during electrospark micro-hole machining, which utilizes a bipolar pulse power supply to continuously emit pulses of positive and negative polarities, and performs in-situ online coating on the surface of the micro-electrode during the electrospark micro-hole machining process to generate a high-resistivity nano-scale oxide film. The high-resistivity nano-scale oxide film is composed of the oxide of the micro-electrode's own material, which can reduce the secondary discharge phenomenon caused by the electro-etching particles. At the same time, the thickness of the oxide film is nanometer-level, so it will hardly cause micro-electrode size error and has little effect on the machining results. In addition, the in-situ online coating is a simultaneous electrospark micro-hole machining process and a coating process, and the electrode remains in place during the coating process, and the micro-electrode will not produce motion errors due to clamping during the machining process. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a structural schematic diagram of step 1 in the present invention;

[0021] Figure 2 This is a schematic diagram of the present invention in which the fine electrode is the positive electrode and the workpiece is the negative electrode;

[0022] Figure 3 This is a schematic diagram of the present invention in which the fine electrode is the negative electrode and the workpiece is the positive electrode;

[0023] Figure 4 It is a circuit connection diagram of the bipolar pulse power supply in the present invention. DETAILED DESCRIPTION

[0024] The specific embodiments of the present invention are further described in detail below in conjunction with the accompanying drawings:

[0025] Embodiment 1

[0026] The present invention provides a method for online coating of the side wall of a micro-electrode during electrospark micro-hole machining, comprising the following steps:

[0027] Step 1: If Figure 1 As shown, the workpiece is placed on the processing table of the EDM micro-hole machining machine and clamped, and the tungsten electrode is clamped by the fixture in the EDM micro-hole machining machine, and the tungsten electrode and the workpiece are respectively connected to the two poles of a bipolar pulse power supply;

[0028] Step 2: If Figure 2-3 As shown, the distance between the tungsten electrode and the bottom of the micropore in the workpiece is adjusted, and a KNO3 solution with a concentration of 2% is continuously introduced into the gap between the tungsten electrode and the wall of the micropore in the workpiece;

[0029] Step 3: If Figure 2 As shown, the tungsten electrode is adjusted to the positive pole of the bipolar pulse power supply, the workpiece is adjusted to the negative pole of the bipolar pulse power supply, the voltage of the bipolar pulse power supply is set to 30V, and the bipolar pulse power supply is turned on to coat the surface of the tungsten electrode, so that the tungsten electrode undergoes an oxidation reaction with the nitrate ions in the solution to form an oxide film;

[0030] Step 4: When no more bubbles appear on the surface of the tungsten electrode, stop introducing KNO3 solution into the gap between the tungsten electrode and the workpiece;

[0031] Step 5: If Figure 3 As shown, the tungsten electrode is adjusted to the negative pole of the bipolar pulse power supply, the workpiece is adjusted to the positive pole of the bipolar pulse power supply, and the discharge gap between the tungsten electrode and the workpiece is measured;

[0032] Step 6: Repeat steps 2 to 5 several times until the discharge gap between the tungsten electrode and the workpiece is 1-2 μm;

[0033] Step 7: If Figure 2-3 As shown, the bipolar pulse power supply emits two different pulses, so that the polarity of the tungsten electrode and the workpiece changes accordingly. At the same time, KNO3 solution is continuously introduced into the gap between the tungsten electrode and the micropore wall in the workpiece to perform electrospark micropore machining.

[0034] like Figure 4As shown, the bipolar pulse power supply includes power supplies U1-U2, MOS field effect transistors M1-M3, resistor R1 and discharge capacitor C1; the negative electrode of power supply U1 is connected to the drain of MOS field effect transistor M1, and the positive electrode is connected to the source of MOS field effect transistor M2, one end of discharge capacitor C1 and the workpiece; the negative electrode of power supply U2 is connected to the drain of MOS field effect transistor M2, and the positive electrode is connected to the source of MOS field effect transistor M1 and one end of resistor R1; the other end of resistor R1 is connected to the drain of MOS field effect transistor M3 and the other end of discharge capacitor C1; the source of MOS field effect transistor M3 is connected to the tungsten electrode; power supplies U1-U2 are respectively controlled by MOS field effect transistors M1-M2, and at the same time, MOS field effect transistor M3 controls discharge capacitor C1 to discharge.

[0035] During the coating process in step 3, the MOS field effect transistor M1 is disconnected and the MOS field effect transistor M2 is closed. At this time, the power supply U2 charges the discharge capacitor C1. During the discharge process of the discharge capacitor C1, the tungsten electrode is the positive electrode and the workpiece is the negative electrode.

[0036] Step 5: When measuring the discharge gap between the tungsten electrode and the workpiece, the MOS field effect transistor M1 is closed and the MOS field effect transistor M2 is disconnected. At this time, the power supply U1 charges the discharge capacitor C1. During the discharge of the discharge capacitor C1, the tungsten electrode is the negative electrode and the workpiece is the positive electrode.

[0037] When the bipolar pulse power supply emits two different pulses in step seven, the MOS field effect transistor M1 is disconnected and the MOS field effect transistor M2 is closed. At this time, the power supply U2 charges the discharge capacitor C1. During the discharge process of the discharge capacitor C1, the tungsten electrode is the positive electrode and the workpiece is the negative electrode; the MOS field effect transistor M1 is closed and the MOS field effect transistor M2 is disconnected. At this time, the power supply U1 charges the discharge capacitor C1. During the discharge process of the discharge capacitor C1, the tungsten electrode is the negative electrode and the workpiece is the positive electrode.

[0038] The present invention provides a method for online coating of the side wall of a micro-electrode during electrospark micro-hole machining, wherein a bipolar pulse power supply is used to continuously emit pulses of positive and negative polarities, and in-situ online coating is performed on the surface of the micro-electrode during the electrospark micro-hole machining process to generate a high-resistivity nano-scale oxide film; the high-resistivity nano-scale oxide film is composed of an oxide of the micro-electrode's own material, which can reduce the secondary discharge phenomenon caused by electro-etching particles, and the oxide film thickness is nanometer-level, so it almost does not cause a micro-electrode size error, and has little effect on the machining result; in addition, the in-situ online coating is that the electrospark micro-hole machining process and the coating treatment process are carried out simultaneously, and the electrode remains in place during the coating treatment process, and the micro-electrode will not produce a motion error due to clamping during the machining process.

[0039] In the bipolar pulse power supply, since the reverse polarity pulse value used in the coating process is smaller than the positive polarity pulse value, the gap generated in the positive polarity EDM micro-hole machining process is greater than the discharge condition in the coating process. Therefore, no discharge occurs between the micro-electrode and the workpiece during the coating process, thereby ensuring that the integrity of the film is not destroyed during the coating process. In the EDM process, the feeding of the micro-electrode reduces the gap between the micro-electrode end face and the bottom of the small hole, causing spark discharge between the micro-electrode end face and the bottom of the small hole, and the oxide film on the micro-electrode end face is removed.

[0040] The above embodiments are not limited to the technical solutions of the embodiments themselves, and the embodiments can be combined with each other to form new embodiments. The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Any modification or equivalent replacement that does not deviate from the spirit and scope of the present invention shall be included in the scope of the technical solutions of the present invention.

Claims

1. A method for online coating of the side wall of a micro-electrode during electrospark micro-hole machining, characterized in that: The steps include: Step 1: Place the workpiece on the processing table of the EDM micro-hole machining machine and clamp it, and use the fixture in the EDM micro-hole machining machine to clamp the fine electrode, and connect the fine electrode and the workpiece to the two poles of the bipolar pulse power supply respectively; Step 2: Adjust the distance between the microelectrode and the bottom of the micropore in the workpiece, and continuously introduce a 2% KNO3 solution into the gap between the microelectrode and the wall of the micropore in the workpiece; Step 3: Adjust the micro-electrode to the positive pole of the bipolar pulse power supply, adjust the workpiece to the negative pole of the bipolar pulse power supply, set the voltage of the bipolar pulse power supply to 30V, turn on the bipolar pulse power supply to coat the surface of the micro-electrode, so that the micro-electrode undergoes an oxidation reaction with the nitrate ions in the solution to form an oxide film; Step 4: When no more bubbles appear on the surface of the micro-electrode, stop introducing the KNO3 solution into the gap between the micro-electrode and the workpiece; Step 5: Adjust the fine electrode to the negative pole of the bipolar pulse power supply, adjust the workpiece to the positive pole of the bipolar pulse power supply, and measure the discharge gap between the fine electrode and the workpiece; Step 6: Repeat steps 2 to 5 for multiple times, and finally make the discharge gap between the micro-electrode and the workpiece 1-2 μm; Step 7: Make the bipolar pulse power supply emit two different pulses, so that the polarity of the micro-electrode and the workpiece changes accordingly, and at the same time, KNO3 solution is continuously introduced into the gap between the micro-electrode and the micro-pore wall in the workpiece to perform electrospark micro-hole machining.

2. The method for online coating of the side wall of a micro-electrode during electrospark micro-hole machining according to claim 1, characterized in that: The bipolar pulse power supply includes power supplies U1-U2, MOS field effect transistors M1-M3, resistor R1 and discharge capacitor C1; the negative electrode of the power supply U1 is connected to the drain of the MOS field effect transistor M1, and the positive electrode is connected to the source of the MOS field effect transistor M2, one end of the discharge capacitor C1 and the workpiece; the negative electrode of the power supply U2 is connected to the drain of the MOS field effect transistor M2, and the positive electrode is connected to the source of the MOS field effect transistor M1 and one end of the resistor R1; the other end of the resistor R1 is connected to the drain of the MOS field effect transistor M3 and the other end of the discharge capacitor C1, and the source of the MOS field effect transistor M3 is connected to the tungsten electrode; the power supplies U1-U2 are controlled by the MOS field effect transistors M1-M2 respectively, and the MOS field effect transistor M3 controls the discharge capacitor C1 to discharge. 。 3. The method for online coating of the side wall of a micro-electrode during electrospark micro-hole machining according to claim 2, characterized in that: During the coating process in step three, the MOS field effect transistor M1 is disconnected and the MOS field effect transistor M2 is closed. At this time, the power supply U2 charges the discharge capacitor C1. During the discharge process of the discharge capacitor C1, the fine electrode is the positive electrode and the workpiece is the negative electrode.

4. The method for online coating of the side wall of a micro-electrode during electrospark micro-hole machining according to claim 3, characterized in that: When measuring the discharge gap between the fine electrode and the workpiece in step 5, the MOS field effect transistor M1 is closed and the MOS field effect transistor M2 is disconnected. At this time, the discharge capacitor C1 is charged by the power supply U1. During the discharge of the discharge capacitor C1, the fine electrode is the negative electrode and the workpiece is the positive electrode.

5. The method for online coating of the side wall of a micro-electrode during electrospark micro-hole machining according to claim 4, characterized in that: When the bipolar pulse power supply emits two different pulses in step seven, the MOS field effect transistor M1 is disconnected and the MOS field effect transistor M2 is closed. At this time, the power supply U2 charges the discharge capacitor C1. During the discharge process of the discharge capacitor C1, the fine electrode is the positive electrode and the workpiece is the negative electrode; the MOS field effect transistor M1 is closed and the MOS field effect transistor M2 is disconnected. At this time, the power supply U1 charges the discharge capacitor C1. During the discharge process of the discharge capacitor C1, the fine electrode is the negative electrode and the workpiece is the positive electrode.

6. The method for online coating of the side wall of a micro-electrode during electrospark micro-hole machining according to claim 5, characterized in that: The microelectrode is a tungsten electrode.

Images