CN115026362B - Electrolysis device and method for micro-electrolytic machining of tungsten carbide hard alloy - Google Patents
Electrolysis device and method for micro-electrolytic machining of tungsten carbide hard alloy Download PDFInfo
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- B23H3/00—Electrochemical machining, i.e. removing metal by passing current between an electrode and a workpiece in the presence of an electrolyte
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Abstract
The invention discloses an electrolysis device and a method for micro-electrolytic machining of tungsten carbide hard alloy, wherein the electrolysis device comprises a tool electrode, a workpiece electrode, an auxiliary electrode, a first circuit structure and a second circuit structure which are arranged in an electrolytic cell; a neutral electrolyte is arranged in the electrolytic cell; the auxiliary electrode and the tool electrode are separated by an insulating layer; the first circuit structure comprises an adjustable direct current power supply E1, a gallium nitride power transistor Q1 and a gallium nitride power transistor Q2; the second circuit structure comprises an adjustable direct current power supply E2, a gallium nitride power transistor Q3 and a gallium nitride power transistor Q4; the continuous electrochemical dissolution of the tungsten carbide hard alloy is realized by applying positive pulse voltage and negative pulse voltage to alternately act in the electrolysis device. The electrolytic device can protect the tool electrode from being corroded by sacrificing the auxiliary electrode under neutral electrolyte, thereby obtaining better machining and forming precision.
Description
Technical Field
The invention relates to the field of electrolytic machining, in particular to an electrolytic device and method for micro-electrolytic machining of tungsten carbide hard alloy.
Background
Micro-electrochemical machining (Electrochemical micromachining, micro-ECM) is a method based on the dissolution of anodic metal in the form of "ions" to remove materials, theoretically achieving machining accuracy in the micrometer and even nanometer scale. The micro electrolytic machining process has the advantages of no tool loss, no heat influence layer on the surface of the machined workpiece electrode, smooth structure surface, no internal stress, no crack, no limitation of material hardness in machining, etc. and the micro parts including micro gears, micro shafts, etc. are produced in the method.
Cemented tungsten carbide is a composite material obtained by sintering a hard compound (WC) and a metal binder (e.g. Co) by a powder metallurgy process, and is generally used for manufacturing wear-resistant parts such as dies, cutters, etc. because of its very high hardness and excellent wear resistance. However, this material has great difficulty in micro-machining. In view of the outstanding advantages of no tool loss, no material hardness limitation in machining and the like of micro electrolytic machining, the method for machining the tungsten carbide hard alloy has obvious advantages.
At present, some research methods for micro-electrolytic machining of tungsten carbide hard alloy mainly aim at research on different dissolution behaviors of the material in different electrolytes. Electrolytic processing typically employs neutral conductive solutions (aqueous NaCl or NaNO) 3 Aqueous solution), in which case, however, tungsten carbide cemented carbide is used as the workpiece anode, the surface thereof produces tungsten oxide with high resistance (WO 3 ) A passivation film, which may hinder the progress of the electrolytic reaction. In order to remove the passivation film, an acidic or alkaline solution may be used as an electrolyte for processing because the acidic solution easily dissolves cobalt (Co) and the alkaline solution easily dissolves tungsten oxide (WO 3 ). In the electrolytic grinding method, the passivation film can be scraped off by using abrasive particles in the conductive grinding wheel, or an Electrochemical Slurry Jet Micromachining (ESJM) method is adopted, namely, the passivation film on the surface of the workpiece electrode is impacted by using high-kinetic-energy abrasive particles in a neutral electrolyte. In addition, in the neutral electrolyte and two-electrode (workpiece electrode and tool electrode) processing system, tungsten oxide can be removed by bipolar pulse voltage (WO 3 ) Passivation film because the work electrode as a cathode can generate OH on its surface during the negative pulse phase - Thereby with tungsten oxide (WO 3 ) The reaction is dissolved.
When the electrolytic machining of the tungsten carbide hard alloy adopts strong acid or strong alkali electrolyte, the electrolyte has corrosion to experimental equipment, has safety risk to operators and is not environment-friendly; the passivation film on the surface of the tungsten carbide hard alloy can be removed by adopting a method of electrolytic grinding by using suspended abrasive particle flow, but the abrasive particles can strike the tool electrode, so that the tool electrode is damaged; although electrolytic machining of the tungsten carbide hard alloy can be performed by using bipolar pulse voltage and neutral electrolyte, tool electrode loss is caused, and the shape of a tool electrode is changed during copy molding machining, so that the machining morphology is inconsistent.
In the aspect of micro electrolytic machining power supply, a pulse power supply can be adopted, and the pulse power supply is a power supply which is controlled to be turned on or off by a switch type power device and is used for converting direct current into a sequence pulse with a certain frequency, providing energy required by electrochemical reaction for electrolytic machining, further removing materials from a workpiece electrode and controlling the machining process. The conventional main circuit adopted by the current micro-electrochemical machining power supply comprises two topological structures of a chopper type and a power amplification type, wherein the chopper type is based on a switch on-off principle, an ultra-short pulse signal is generated by a signal generator to drive a single-path or double-path chopper device, and a stable and single direct-current voltage is output by the on-off action of the chopper device to be the ultra-short pulse voltage with the same frequency as the signal; the power amplification type is to directly amplify the ultrashort pulse signal generated by the pulse generator through a power amplifier, so as to obtain the ultrashort pulse voltage required by micro electrolytic machining.
In the aspect of bipolar pulse micro-electrochemical machining power supply:
the Nanjing engineering institute application discloses an invention patent application (application number is 201010502233.3) of a programmable nanosecond double-pulse integrated power supply, which mainly comprises voltage regulation, rectification, filtering and chopper circuits; CPLD is used for generating control pulse and driving a switching tube to chop and output positive and negative pulse voltages through voltage amplification.
The application of Qinghua university discloses a micro-electrolytic machining power supply with auxiliary electrode inter-pulse output and a machining method (application number is 201410743850.0), wherein the power supply can output two paths of positive pulse signals with equal period and unequal amplitude by controlling the switching state of three paths of MOSFET (metal oxide semiconductor field effect transistor) tubes, and the auxiliary electrode is utilized to guide complete depolarization current into an electrolytic cell so as to quickly eliminate the primary cell effect between a workpiece electrode and a solution to be machined, reduce the inter-electrode maintaining voltage to zero and quickly remove a passivation film on the interface between the workpiece electrode and the electrolyte. The invention patent application 201711147097.9 discloses that unipolar or bipolar pulse voltages can be output by adjusting the on and off of four-way transistors by using one or two direct current power supplies. Namely, when the pulse power supply is used for electrolytic machining at pulse intervals, the electrode of the workpiece is connected with a short-circuit tool to accelerate the elimination of the voltage between electrodes, or the reverse voltage with adjustable duty ratio and amplitude is added between electrodes to accelerate depolarization.
In micro electrochemical machining test, in order to precisely control localized removal of workpiece material to achieve the goal of high localized material removal rate, a pulse power source with pulse frequency up to kHz or even MHz level and pulse width generally at nanosecond level is required to meet machining requirements. For micro-electro-machining power supplies, chopper switching devices on the main power are usually insulated gate field effect transistors (MOSFETs), and such devices are usually made of silicon (Si) or silicon carbide (SiC). In development and application of the SiC MOSFET, compared with Si MOSFETs with the same power level, the on-resistance and the switching loss of the SiC MOSFET are greatly reduced, and the SiC MOSFET is suitable for higher working frequency. GaN devices can operate at higher switching frequencies than SiC devices, and proper power class design can achieve significantly higher power output for GaN. In addition, the programmable nanosecond double-pulse integrated power supply in the patent application of the application number 201010502233.3 can not output positive and negative pulses of different voltages due to the fact that a single power supply is adopted to provide direct current voltage required by chopping, and therefore experimental research is still limited.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide an electrolytic device for micro-electrolytic machining of tungsten carbide hard alloy, which can realize that a tool electrode is protected from corrosion by sacrificing an auxiliary electrode when the tungsten carbide hard alloy is machined by adopting a bipolar pulse power supply under the condition of neutral electrolyte, so that better machining and forming precision is obtained.
A second object of the present invention is to provide an electrolytic method for micro-electrolytic machining of cemented tungsten carbide.
The technical scheme for solving the technical problems is as follows:
an electrolytic device for micro-electrolytic machining of cemented tungsten carbide, comprising a tool electrode, a workpiece electrode, an auxiliary electrode, a first circuit structure for connecting the tool electrode and the workpiece electrode, and a second circuit structure for connecting the auxiliary electrode, which are arranged in an electrolytic cell,
a neutral electrolyte is arranged in the electrolytic cell; the auxiliary electrode is arranged outside the tool electrode, and the auxiliary electrode and the tool electrode are separated by an insulating layer;
the first circuit structure comprises an adjustable direct current power supply E1, a gallium nitride power transistor Q1 and a gallium nitride power transistor Q2, wherein the positive electrode of the adjustable direct current power supply E1 is sequentially connected with the gallium nitride power transistor Q1 and the end A of a workpiece electrode in the electrolytic cell; the negative electrode of the adjustable direct current E1 is connected with the C end of a tool electrode in the electrolytic cell and is grounded at the same time; the C end of the tool electrode is grounded; one end of the gallium nitride power transistor Q2 is connected with the negative electrode of the adjustable direct current E1, and the other end of the gallium nitride power transistor Q2 is connected with the end part of the gallium nitride power transistor Q1 connected with the end A of the workpiece electrode in the electrolytic cell;
the second circuit structure comprises an adjustable direct current power supply E2, a gallium nitride power transistor Q3 and a gallium nitride power transistor Q4, wherein the positive electrode of the adjustable direct current power supply E2 is sequentially connected with the gallium nitride power transistor Q3 and the end B of an auxiliary electrode in the electrolytic cell; the negative electrode of the adjustable direct current power supply E2 is grounded; one end of the gallium nitride power transistor Q4 is connected to the negative electrode of the adjustable direct current E2, and the other end is connected to the end of the gallium nitride power transistor Q3 connected to the B end of the auxiliary electrode in the electrolytic cell.
Preferably, a current limiting resistor R is further disposed between the gallium nitride power transistor Q4 and the negative electrode of the adjustable dc power source E2.
Preferably, the tool electrode and the auxiliary electrode are electrically isolated by an insulating layer to prevent mutual conduction, and are coaxially arranged; so that the distance between the end face of the auxiliary electrode and the end face of the tool electrode is within 1 mm.
Preferably, the servo motor drives the tool electrode to move vertically so as to adjust the gap between the tool electrode and the workpiece electrode.
An electrolysis method for micro-electrolytic machining of a tungsten carbide hard alloy, wherein continuous electrochemical dissolution of the tungsten carbide hard alloy is realized by applying positive pulse voltage and negative pulse voltage to alternately act in the electrolysis device,
at t of positive pulse voltage p During the period, the gallium nitride power transistor Q1 and the gallium nitride power transistor Q4 are respectively turned on under the control of the driving signal G1 and the driving signal G4, and the gallium nitride power transistor Q2 and the gallium nitride power transistor Q3 are respectively turned off under the control of the driving signal G2 and the driving signal G3; at the moment, the workpiece electrode of the tungsten carbide hard alloy is subjected to the action of high level from the adjustable direct current power supply E1, and the tool electrode is grounded; the workpiece electrode and the tool electrode form an electrolytic machining loop; at positive pulse processing voltage U AC Under the action of (a), the main circuit generates a processing current I AC Co on the surface of the workpiece electrode is dissolved, WO 3 A passivation film is formed on the surface of the workpiece electrode; the tool electrode can generate hydrogen evolution reaction; the electrochemical reactions that occur at this time are as follows:
workpiece electrode:
Co→Co 2+ +2e - (1)
WC+5H 2 O→WO 3 +CO 2 ↑+10H + +10e - (2)
tool electrode:
2H 2 O+2e - →H 2 ↑+2OH - (3)
at t of negative pulse voltage n During the period, the gallium nitride power transistor Q1 and the gallium nitride power transistor Q4 are turned off under the control of the driving signal G1 and the driving signal G4, respectively, and the gallium nitride power transistor Q2 and the gallium nitride power transistor Q3 are turned on under the control of the driving signal G2 and the driving signal G3, respectively; at this time, the potential between the workpiece electrode and the tool electrode is zero; meanwhile, the auxiliary electrode is kept at a high potential when being connected to the adjustable direct current power supply E2; and because the negative poles of the adjustable direct current power supply E1 and the adjustable direct current power supply E2 are grounded, the workpiece electrode and the auxiliary electrode form an electrolytic machining loop, and the workpiece is electrically poweredThe electrode serves as a cathode, and the auxiliary electrode serves as an anode; at negative pulse voltage U AB The main circuit generates a current I BA The method comprises the steps of carrying out a first treatment on the surface of the Under this condition, the hydrogen evolution reaction occurs on the surface of the workpiece electrode, and the electrochemical reaction occurring at this time is as follows:
workpiece electrode:
2H 2 O+2e - →H 2 ↑+2OH - (4)
auxiliary electrode
M-ne - →M n+ (6)。
Preferably, at t of the negative pulse voltage n During this time, the auxiliary electrode acts as an anode, and the electric double layer between the auxiliary electrode and the neutral electrolyte is charged by the current; when the negative pulse voltage is removed, the auxiliary electrode should be grounded.
Preferably, at t of positive pulse voltage p During the process, the electrochemical reaction is reduced by controlling the diameter of the auxiliary electrode and the distance between the auxiliary electrode and the workpiece electrode; at the same time, a current limiting resistor R is added in the second circuit structure of the electrolytic device to reduce the current I between the workpiece electrode and the auxiliary electrode AB 。
Preferably, during the electrolytic machining, a voltage U is applied between the workpiece electrode and the auxiliary electrode AB For bipolar pulse voltage, a voltage U is applied between the workpiece electrode and the tool electrode AC Is a unipolar pulsed voltage, while the potential of the tool electrode remains zero at all times.
Preferably, the main control chip FPGA in the electrolytic device adopts EP4CE6E22C8 of the Cyclone IV of Altera to send out an ultrashort pulse signal, and after isolation and driving of the amplifying circuit, the gallium nitride power transistors Q1, Q2, Q3 and Q4 are controlled to chop the adjustable dc power supplies E1 and E2 to output an adjustable pulse voltage.
Preferably, a current sensor is added in the electrolytic device so as to detect the current in the electrolytic machining process in real time, when a short circuit occurs, the current sensor detects that a current signal is changed greatly, the processed voltage is output and compared with the threshold voltage of the numerical control system, and a pulse signal is sent to control the servo motor, so that the tool electrode is retracted to an initial machining gap and then fed at a preset speed, and the continuous electrolytic machining is ensured.
Compared with the prior art, the invention has the following beneficial effects:
1. at present, under the condition of neutral electrolyte, when a two-electrode (workpiece electrode and tool electrode) processing mode and a bipolar pulse power supply are adopted to process the tungsten carbide hard alloy, the tool electrode abrasion problem exists. Therefore, the electrolytic device for micro electrolytic machining of the tungsten carbide hard alloy introduces the auxiliary electrode into the two electrodes (the workpiece electrode and the tool electrode), takes the workpiece electrode as the cathode under the action of negative pulse voltage, promotes the surface of the workpiece electrode to generate hydrogen evolution reaction, on one hand, weakens the adhesive force of oxidation products on the surface of the workpiece electrode through periodical generation, movement, collision and collapse of bubbles, generates hydrodynamic force flow, strengthens the mass and heat transfer process, and accelerates the discharge of the electrolysis products out of a processing area; on the other hand, OH is generated on the surface of the workpiece electrode - This may dissolve WO generated at the surface of the workpiece electrode during positive pulse voltage 3 Thereby exposing the new processing surface to achieve efficient removal of workpiece material; the positive pulse voltage and the negative pulse voltage alternately act on the electrolytic device to realize continuous electrochemical dissolution of the tungsten carbide hard alloy, and can avoid electrochemical corrosion of a tool electrode, so that better machining and forming precision is finally obtained.
2. Currently, an electrolysis device with conveniently controllable parameters usually adopts an insulated gate field effect transistor (MOSFET) as a power switch device, but with the increase of pulse frequency, the current carrying capacity of the electrolysis device is reduced, and the loss is larger at high frequency. Therefore, in order to meet the requirement of micro-electrolytic machining using high-frequency ultrashort pulse voltage, the electrolytic method for micro-electrolytic machining of tungsten carbide hard alloy of the present invention adopts gallium nitride (GaN) transistor as power transistor, because the switching speed of gallium nitride (GaN) transistor can be much faster than MOSFET, lower switching loss can be realized, and power can be improved, which is advantageous to improve the power of micro-electrolytic machining power supply.
Drawings
FIG. 1 is a schematic diagram of the circuit structure of an electrolytic device for micro-electrolytic machining of cemented tungsten carbide according to the present invention.
Fig. 2 is a schematic circuit diagram of the circuit structure when a positive pulse voltage is applied.
Fig. 3 is a schematic circuit diagram of the circuit structure when negative pulse voltage is applied.
FIG. 4 shows the gate driving signals and the power supply output voltage U of GaN power transistors Q1, Q2, Q3, Q4 AB And U AC Is a waveform diagram of (a).
Fig. 5 is a schematic control diagram of an electrolytic apparatus for micro-electrolytic machining of cemented tungsten carbide according to the present invention.
Detailed Description
The present invention will be described in further detail with reference to examples and drawings, but embodiments of the present invention are not limited thereto.
Referring to fig. 1 to 5, the electrolytic device for micro-electrolytic machining of cemented tungsten carbide of the present invention comprises a tool electrode 3, a workpiece electrode 4, an auxiliary electrode 1, a first circuit structure for connecting the tool electrode 3 and the workpiece electrode 4, and a second circuit structure for connecting the auxiliary electrode 1, which are arranged in an electrolytic cell, wherein a neutral electrolyte 5 is arranged in the electrolytic cell; the auxiliary electrode 1 is arranged outside the tool electrode 3 and coaxially arranged; the auxiliary electrode 1 and the tool electrode 3 are separated by an insulating layer 2; the first circuit structure comprises an adjustable direct current power supply E1, a gallium nitride power transistor Q1 and a gallium nitride power transistor Q2, wherein the positive electrode of the adjustable direct current power supply E1 is sequentially connected with the gallium nitride power transistor Q1 and the end A of a workpiece electrode 4 in the electrolytic cell; the negative electrode of the adjustable direct current E1 is connected with the C end of the tool electrode 3 in the electrolytic cell and is grounded, namely the C end of the tool electrode 3 is grounded; one end of the gallium nitride power transistor Q2 is connected with the negative electrode of the adjustable direct current E1, and the other end of the gallium nitride power transistor Q2 is connected with the end part of the gallium nitride power transistor Q1 connected with the end A of the workpiece electrode 4 in the electrolytic cell; the second circuit structure comprises an adjustable direct current power supply E2, a gallium nitride power transistor Q3 and a gallium nitride power transistor Q4, wherein the positive electrode of the adjustable direct current power supply E2 is sequentially connected with the gallium nitride power transistor Q3 and the end B of the auxiliary electrode 1 in the electrolytic cell; the negative electrode of the adjustable direct current power supply E2 is grounded; one end of the gallium nitride power transistor Q4 is connected to the negative electrode of the adjustable dc power supply E2, and the other end is connected to the end of the gallium nitride power transistor Q3 connected to the B end of the auxiliary electrode 1 in the electrolytic cell. And a current limiting resistor R is also arranged between the gallium nitride power transistor Q4 and the negative electrode of the adjustable direct current power supply E2.
In the embodiment, the auxiliary electrode 1 and the tool electrode 3 are coaxially arranged, and the end face distance between the auxiliary electrode and the tool electrode is within 1 mm; and the tool electrode 3 can be driven by a servo motor to move vertically so as to adjust the gap between the tool electrode 3 and the workpiece electrode 4. In addition, because the micro electrolytic machining environment is severe, spark discharge and even short circuit often occur in the machining process, the electrolytic device adopts the high-precision current sensor to detect the machining abnormal signal, and transmits the signal to the numerical control system for information interaction after processing, so that whether the short circuit occurs or not is judged, the main shaft of the servo motor is controlled to retract finally, the long-time short circuit state is avoided, and the continuous electrolytic machining is ensured.
Referring to FIG. 2, at t, where a positive pulse voltage is applied p During this time, the gallium nitride power crystals Q1 and Q4 are turned on under the control of the driving signals G1 and G4, respectively, and the gallium nitride power crystals Q2 and Q3 are turned off under the control of the driving signals G2 and G3, respectively. At this time, the workpiece electrode 4 of cemented tungsten carbide is affected by the high level from the adjustable dc power supply E1, and the tool electrode 3 is grounded (zero potential). The workpiece electrode 4 and the tool electrode 3 form an electrolytic machining circuit. At positive pulse processing voltage U AC Under the action of (a), the main circuit generates a processing current I AC Co dissolution occurs on the surface of the workpiece electrode 4, WO 3 A passivation film is formed on the surface of the workpiece electrode 4. While the tool electrode 3 generates hydrogen evolution reactionThe reaction is carried out; the electrochemical reactions that occur at this time are as follows:
workpiece electrode 4:
Co→Co 2+ +2e - (1)
WC+5H 2 O→WO 3 +CO 2 ↑+10H + +10e - (2)
tool electrode 3:
2H 2 O+2e - →H 2 ↑+2OH - (3)
referring to FIG. 3, at t of the negative pulse voltage n During this time, the gallium nitride power crystals Q1 and Q4 are turned off under the control of the driving signals G1 and G4, respectively, and the gallium nitride power crystals Q2 and Q3 are turned on under the control of the driving signals G2 and G3, respectively. At this time, the potential between the workpiece electrode 4 and the tool electrode 3 is zero, and thus the depolarization between these two electrodes can be accelerated. Meanwhile, the auxiliary electrode 1 is kept at a high potential when connected to the adjustable direct current power supply E2. Since the cathodes of the adjustable direct current power supplies E1 and E2 are grounded in common, the workpiece electrode 4 and the auxiliary electrode 1 form an electrolytic machining circuit in which the workpiece electrode 4 becomes the cathode and the auxiliary electrode 1 becomes the anode. At negative pulse voltage U AB The main circuit generates a current I BA . Under the condition, the surface of the workpiece electrode generates hydrogen evolution reaction, on one hand, bubbles are periodically generated, moved, collided and collapsed, thereby being beneficial to weakening the adhesive force of oxidation products on the surface of the workpiece electrode 4, being beneficial to generating hydrodynamic flow, strengthening the mass and heat transfer process, simultaneously generating scouring on the surface of the workpiece and promoting the smooth elimination of electrolysis products; on the other hand OH is generated on the surface of the workpiece electrode 4 - This can dissolve WO generated on the surface of the workpiece electrode 4 during the positive pulse 3 Thereby exposing a new working surface and the auxiliary electrode 1 is corroded. The electrochemical reactions that occur at this time are as follows:
workpiece electrode 4:
2H 2 O+2e - →H 2 ↑+2OH - (4)
M-ne - →M n+ (6)
It is to be noted that during application of a negative pulse voltage during electrolytic processing, the auxiliary electrode 1 acts as an anode, and the electric current charges the electric double layer between the auxiliary electrode 1 and the neutral electrolyte. When the negative pulse voltage is removed, the electric charge of the electric double layer remains for a period of time, resulting in distortion of the output pulse waveform. In order to accelerate the removal of electric double layer charges and reduce waveform distortion of output pulses, the auxiliary electrode 1 should be grounded (zero potential). In addition, during the application of the positive pulse voltage, in order to reduce the electrochemical reaction between the workpiece electrode 4 and the auxiliary electrode 1 as much as possible. On the one hand, by controlling the diameter of the auxiliary electrode 1 and the distance between the end face and the surface of the workpiece electrode 4, the electrochemical reaction can be reduced; on the other hand, a current limiting resistor R is added in the circuit to reduce the current I between the electrodes AB . Thus at t of positive pulse voltage p During this time, the electrochemical reaction is concentrated in the region between the tool electrode 3 and the workpiece electrode 4.
When positive pulse voltage and negative pulse voltage alternately act on the electrolysis device, continuous electrochemical dissolution of the tungsten carbide hard alloy can be realized. FIG. 4 shows the gate drive signal and the power supply output voltage U of each GaN power transistor AB And U AC Is a waveform of (a). To prevent the upper and lower bridge GaN power transistors from being simultaneously turned on due to different switching speeds of each power transistor, a dead time t is specially added in the gate driving signal d . During the whole electrolytic machining process, a voltage U is applied between the workpiece electrode 4 and the auxiliary electrode 1 AB For bipolar pulse voltages, the voltage U between the workpiece electrode 4 and the tool electrode 3 AC The electric potential of the tool electrode 3 is always kept to be zero (the lowest electric potential) and is a unipolar pulse voltage, so that electrochemical corrosion of the tool electrode 3 can be avoided, and finally, better machining and forming precision is obtained.
Referring to fig. 5, the main control chip FPGA of the electrolytic device of the present invention adopts EP4CE6E22C8 of the Cyclone IV of Altera to send out an ultrashort pulse signal, and after isolation and driving of the amplifying circuit, the multichannel gallium nitride (GaN) power transistor is controlled to chop and output an adjustable pulse voltage to an adjustable direct voltage. In order to conveniently control the frequency and the duty ratio of the pulse voltage and meet the requirement of adjusting the processing parameters, 4 keys for adjusting the frequency and the duty ratio are added in the electrolysis device. In order to detect whether the tool electrode 3 and the workpiece electrode 4 are short-circuited in the electrolytic machining process, a current sensor is added in the electrolytic device so as to detect the current in machining in real time, when the short-circuited occurs, the current sensor detects that a current signal is greatly changed, the processed voltage is output and compared with the threshold voltage of a numerical control system, a pulse signal is sent to control a servo motor, the tool electrode 3 is retreated to an initial machining gap and fed at a preset speed, continuous machining is ensured, and real-time interaction of a micro-electrolytic machining power supply and an electrolytic machining motion control system is realized.
At present, under the condition of neutral electrolyte 5, when a two-electrode (workpiece electrode 4 and tool electrode 3) processing mode and a bipolar pulse power supply are adopted to process the tungsten carbide hard alloy, the problem of tool electrode abrasion exists. Therefore, the auxiliary electrode 1 is introduced into the electrolytic device of the two electrodes (the workpiece electrode 4 and the tool electrode 3), the workpiece electrode 4 is taken as a cathode in combination with the electrolytic device of the invention, so that the surface of the workpiece electrode 4 is promoted to generate hydrogen evolution reaction, on one hand, bubbles are periodically generated and collapsed to weaken the adhesive force of oxidation products on the surface of the workpiece electrode 4, and hydrodynamic flow is generated to strengthen the mass and heat transfer process, and meanwhile, scouring is generated on the surface of the workpiece to promote the smooth elimination of the electrolysis products; on the other hand, OH is generated on the surface of the workpiece electrode - This can dissolve WO generated at the surface of the workpiece electrode 4 during the positive pulse voltage 3 Thereby exposing the new processing surface, and realizing efficient removal of the workpiece material; in addition, the method can realize that the tool electrode does not generate electrochemical corrosion by sacrificing the auxiliary electrode so as to obtain better machining and forming precision; the continuous electrochemical dissolution of the tungsten carbide hard alloy is realized by alternately applying positive pulse voltage and negative pulse voltage in the electrolysis device.
The foregoing is illustrative of the present invention and is not to be construed as limiting thereof, but rather as various changes, modifications, substitutions, combinations, and simplifications which may be made therein without departing from the spirit and principles of the invention are intended to be included within the scope of the invention.
Claims (10)
1. An electrolytic device for micro-electrolytic machining of cemented tungsten carbide, characterized by comprising a tool electrode, a workpiece electrode, an auxiliary electrode, a first circuit structure for connecting the tool electrode and the workpiece electrode, and a second circuit structure for connecting the auxiliary electrode, which are arranged in an electrolytic cell,
a neutral electrolyte is arranged in the electrolytic cell; the auxiliary electrode is arranged outside the tool electrode, and the auxiliary electrode and the tool electrode are separated by an insulating layer;
the first circuit structure comprises an adjustable direct current power supply E1, a gallium nitride power transistor Q1 and a gallium nitride power transistor Q2, wherein the positive electrode of the adjustable direct current power supply E1 is sequentially connected with the gallium nitride power transistor Q1 and the end A of a workpiece electrode in the electrolytic cell; the negative electrode of the adjustable direct current E1 is connected with the C end of a tool electrode in the electrolytic cell and is grounded at the same time; the C end of the tool electrode is grounded; one end of the gallium nitride power transistor Q2 is connected with the negative electrode of the adjustable direct current E1, and the other end of the gallium nitride power transistor Q2 is connected with the end part of the gallium nitride power transistor Q1 connected with the end A of the workpiece electrode in the electrolytic cell;
the second circuit structure comprises an adjustable direct current power supply E2, a gallium nitride power transistor Q3 and a gallium nitride power transistor Q4, wherein the positive electrode of the adjustable direct current power supply E2 is sequentially connected with the gallium nitride power transistor Q3 and the end B of an auxiliary electrode in the electrolytic cell; the negative electrode of the adjustable direct current power supply E2 is grounded; one end of the gallium nitride power transistor Q4 is connected to the negative electrode of the adjustable direct current E2, and the other end is connected to the end of the gallium nitride power transistor Q3 connected to the B end of the auxiliary electrode in the electrolytic cell.
2. The electrolytic device for micro-electrolytic machining of cemented tungsten carbide according to claim 1, wherein a current limiting resistor R is further provided between the gallium nitride power transistor Q4 and the negative electrode of the adjustable dc power supply E2.
3. The electrolytic apparatus for micro-electrolytic machining of cemented tungsten carbide according to claim 1, wherein the tool electrode and the auxiliary electrode are electrically isolated from each other by an insulating layer and are coaxially arranged; so that the distance between the end face of the auxiliary electrode and the end face of the tool electrode is within 1 mm.
4. The electrolytic device for micro-electrolytic machining of cemented tungsten carbide according to claim 1, wherein a tool electrode is moved vertically by a servo motor to adjust a gap between the tool electrode and the workpiece electrode.
5. An electrolytic method for micro-electrolytic machining of a cemented tungsten carbide, characterized in that continuous electrochemical dissolution of cemented tungsten carbide is achieved by applying a positive pulse voltage and a negative pulse voltage alternately acting in the electrolytic apparatus for micro-electrolytic machining of cemented tungsten carbide as claimed in any one of claims 1 to 4, wherein,
at t of positive pulse voltage p During the period, the gallium nitride power transistor Q1 and the gallium nitride power transistor Q4 are respectively turned on under the control of the driving signal G1 and the driving signal G4, and the gallium nitride power transistor Q2 and the gallium nitride power transistor Q3 are respectively turned off under the control of the driving signal G2 and the driving signal G3; at the moment, the workpiece electrode of the tungsten carbide hard alloy is subjected to the action of high level from the adjustable direct current power supply E1, and the tool electrode is grounded; the workpiece electrode and the tool electrode form an electrolytic machining loop; at positive pulse processing voltage U AC Under the action of (a), the main circuit generates a processing current I AC Co on the surface of the workpiece electrode is dissolved, WO 3 Passivation film on workpiece electrode surfaceForming a surface; the tool electrode can generate hydrogen evolution reaction; the electrochemical reactions that occur at this time are as follows:
workpiece electrode:
Co→Co 2+ +2e - (1)
WC+5H 2 O→WO 3 +CO 2 ↑+10H + +10e - (2)
tool electrode:
2H 2 O+2e - →H 2 ↑+2OH - (3)
at t of negative pulse voltage n During the period, the gallium nitride power transistor Q1 and the gallium nitride power transistor Q4 are turned off under the control of the driving signal G1 and the driving signal G4, respectively, and the gallium nitride power transistor Q2 and the gallium nitride power transistor Q3 are turned on under the control of the driving signal G2 and the driving signal G3, respectively; at this time, the potential between the workpiece electrode and the tool electrode is zero; meanwhile, the auxiliary electrode is kept at a high potential when being connected to the adjustable direct current power supply E2; the negative electrodes of the adjustable direct current power supply E1 and the adjustable direct current power supply E2 are grounded together, so that the workpiece electrode and the auxiliary electrode form an electrolytic machining loop, wherein the workpiece electrode serves as a cathode, and the auxiliary electrode serves as an anode; at negative pulse voltage U AB The main circuit generates a current I BA The method comprises the steps of carrying out a first treatment on the surface of the Under this condition, the hydrogen evolution reaction occurs on the surface of the workpiece electrode, and the electrochemical reaction occurring at this time is as follows:
workpiece electrode:
2H 2 O+2e - →H 2 ↑+2OH - (4)
auxiliary electrode
M-ne - →Mn + (6)。
6. The method for micro-machining a cemented tungsten carbide according to claim 5, wherein at t of the negative pulse voltage n During which the auxiliary electrode acts as an anode,the electric current charges an electric double layer between the auxiliary electrode and the neutral electrolyte; when the negative pulse voltage is removed, the auxiliary electrode should be grounded.
7. The method for micro-machining a cemented tungsten carbide according to claim 5, wherein at t of positive pulse voltage p During the process, the electrochemical reaction is reduced by controlling the diameter of the auxiliary electrode and the distance between the auxiliary electrode and the workpiece electrode; at the same time, a current limiting resistor R is added in the second circuit structure of the electrolytic device to reduce the current I between the workpiece electrode and the auxiliary electrode AB 。
8. The electrolytic method for micro-electrolytic machining of cemented tungsten carbide according to claim 5, wherein the voltage U applied between the workpiece electrode and the auxiliary electrode during the electrolytic machining AB For bipolar pulse voltage, a voltage U is applied between the workpiece electrode and the tool electrode AC Is a unipolar pulsed voltage, while the potential of the tool electrode remains zero at all times.
9. The electrolytic method for micro-electrolytic machining of the tungsten carbide hard alloy according to claim 5, wherein a main control chip FPGA in the electrolytic device adopts EP4CE6E22C8 of a Cyclone IV of Altera to send out an ultra-short pulse signal, and after isolation and driving of an amplifying circuit, the gallium nitride power transistors Q1, Q2, Q3 and Q4 are controlled to chopper-output adjustable pulse voltages to the adjustable direct current power supplies E1 and E2.
10. The electrolytic method for micro-electrolytic machining of cemented tungsten carbide according to claim 5, wherein a current sensor is added in the electrolytic device to detect the current in the electrolytic machining process in real time, when a short circuit occurs, the current sensor detects a large change in a current signal, the processed voltage is output and compared with a threshold voltage of a numerical control system, a pulse signal is sent to control a servo motor, so that a tool electrode is retracted to an initial machining gap and fed at a predetermined speed, and continuous electrolytic machining is ensured.
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