RU2740936C1 - Electric spark coating application method and device for implementation thereof - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: group of inventions relates to method and device for electrospark deposition of coating on part surface used for production of wear-resistant, anticorrosive and heat-resistant coatings on parts and units of machines. Method includes treatment of surface by vibrating electrode, moving at an angle to processed surface, at which at moment of contact of electrode and part current flow pulse is supplied and part of surface formed by contact spot electrode-part is processed. Preliminary contact surface is prepared with high-frequency current pulses with variable duration of pulses from 0.5 to 20 mcs and variable duty cycle from 1 % to 80 % of their duration, besides, simultaneously with supply of current pulses voltage is stabilized on contact spot by control of electrode pressure on processed surface by change of amplitude and frequency of its vibration within 40–800 Hz. During the coating process, the process is controlled using information on the value of electric energy consumed in the spark gap measured on the contact spot.

EFFECT: obtaining homogeneous coatings having high continuity and thickness.

3 cl, 6 dwg

Description

The invention relates to the field of electrophysical methods of processing materials, in particular to electroerosive methods of hardening and alloying of electrically conductive materials can be used in machine building and repair production to obtain wear-resistant coatings on the surfaces of parts of friction units and fixed joints.

As is known, when using existing electrophysical methods for processing materials, for example, electrospark coating on parts at the beginning of the discharge, from 10 to 100% of the total amount of energy accumulated by the capacitor is released in the form of heat at electrical contacts and in the interelectrode gap (see, for example, Burumkulov F.Kh. et al. Electrospark technologies for restoration and hardening of machine parts and tools (Saransk, Krasny Oktyabr, 2003, p. 17). Often, in practice, with a short circuit (electrode and parts), the released heat is not enough to erode the electrode and it is spent on heating the electrode (Efimenko N.G., Doschechkina I.V. Electrospark alloying (ESA) of working surfaces of cast iron products. Kharkov, Vestnik KhNTUSK named after Vasilenko, 2011, Issue 110, p. 52). That is, a significant part of the energy of the pulsed technological current when the electrode and the surface of the part are closed is spent on heating the electrode and the part and does not participate in the transfer of the electrode material to the surface of the part.

When electrospark deposition of coatings on the surface of a part, for example, alloying, a sharp jump in the thickness and roughness of coatings is achieved at high currents "(Burumkulov F.Kh. et al. Electrospark technologies for the restoration and hardening of machine parts and tools. Saransk, Krasny Oktyabr, 2003, P.69 ).

The known method of electrospark deposition of metal coatings SU 89933, B23P 1/18, published 01.01.1950, in which the process of transferring the electrode material to the surface of the part is carried out by applying an electric current pulse to the electrode when the electrode end touches the surface of the part.

Known device for electrospark alloying RU 2245767 C1, B23N 1/02, published 02/10/2005, consisting of a pulse generator of technological current and a hand working body - an electromagnetic vibrator. A process current pulse is applied to the vibrator electrode by the signal that the electrode touches the workpiece surface.

The disadvantage of the known method and device is the supply of a current pulse on the signal of the electrode touching the surface of the part, that is, the process current pulse is supplied only when the electrode and the surface of the workpiece are closed, which leads to a loss of energy of the process current pulse.

There is a known method of electrospark alloying RU 2140834 C1, B23H 9/00, published on 11/10/1999, which consists in the fact that oscillations are reported to the electrode and the moment when the electrode contacts the surface of the workpiece in each oscillation period is recorded. At the moment of contact, an auxiliary current pulse is applied to the electrodes. Its duration corresponds to the contact time of the electrode with the surface of the part. Then, with a time delay relative to the moment when the electrode contacts the workpiece surface, a process current pulse is applied to the electrode.

Known device for electrospark alloying RU 2140834 C1, B23H 9/00, published 10.11.1999, providing the implementation of this method. It contains a manual working body - an electromagnetic vibrator, an auxiliary and process current pulse generator. The positive outputs of the generators are connected to the electrode, and the negative outputs of the generators are connected to the workpiece. In this case, the control inputs of the generators are connected to the output of the touch sensor connected between the electrode and the workpiece, and a delay unit is included in the connection of the touch sensor output and the input of the process current pulse generator.

The disadvantage of this method and device is the loss of energy of the pulse of the technological current, spent on heating the electrode and the workpiece, during the contact of the electrode with the surface of the workpiece. An electromagnetic vibrator is used in the device as a hand-held working body, which has a significant mass, a relatively narrow frequency range, which requires non-ferrous metals and special steel for the coil's magnetic circuit to manufacture.

The practical use of one of the known methods of electrospark alloying, RF patent 2482943, has shown that its efficiency, namely, the transfer coefficient of the electrode material, productivity, and coating continuity depend on many factors. One of the main factors is the need to obtain information about the ongoing process directly on the spark gap between the electrode and the part and its further use to stabilize the process and improve the coating technology. The known method has a large error, since when it is carried out, the energy consumed at the contact gap is measured at a constant voltage equal to 20 Volts. In fact, in the process of surface treatment, conditions arise when this voltage takes on different values, especially during manual processing, where the quality of the coating depends on the qualifications of the operator.

In fig. 1 shows the dependence of the change in voltage across the spark gap electrode - part during the processing of the part.

In fig. 2 shows the amplitudes of the process current and the voltage across the spark gap at point A, characterized by a resistance close to a short circuit.

Obviously, the energy control at this point (A) gives an overestimate. In this case, almost all of the energy is spent on the supply conductors, and not on the electrode gap.

There is a known method of electrospark coating on the surface of a part (patent RU 2 679 160 C1 according to class B23H 9/00, published 02/06/2019), including processing the surface of the part with an electrode when applying technological and auxiliary current pulses, in which an auxiliary current pulse is applied to the interelectrode gap formed by the end of the electrode and the surface of the workpiece. At the same time, at the moment of contact of the electrode with the surface of the workpiece, the end of the electrode is removed from the surface of the workpiece at a distance of up to 15 μm by supplying an auxiliary current pulse with an energy of 0.05-1.5 J and a duration of 5-100 μs, and the technological current pulse is supplied to the moment of the end of the auxiliary current pulse.

The known device for electrospark coating on the surface of a part, which implements this method, is equipped with a manual working body with an electrode holder, a generator of auxiliary and technological current pulses. In this case, the positive outputs of the generators are connected to the electrode fixed in the electrode holder, the negative outputs of the generators are connected to the workpiece, and a touch sensor is connected to the electrode and the workpiece, equipped with an additional generator of process current pulses, the positive output of which is connected to the electrode, and the negative output to the workpiece, and the output of the touch sensor is connected to the input of the vibrator triggered by the leading edge of the touch sensor signal. The vibrator output is connected to the control input of the auxiliary current pulse generator. Moreover, a current sensor is included in the positive circuit of the auxiliary current pulse generator, the output of which is connected to the input of the comparator, the output of which is connected to the input of the vibrator triggered by the trailing edge of the comparator signal, and the output of the vibrator is connected to the control input of the trigger unit, the outputs of which are connected to the control inputs of the generators process current pulses, while the manual working body contains an electrode holder made of a conductive material in the form of a rod and a handle made of a dielectric material, which are pivotally connected through a horizontal axis with the possibility of moving the electrode holder relative to the handle in the vertical plane.

However, in the process of coating with this method, the electrode remains on the treated surface for a rather long time, and this increases the likelihood of the electrode being welded to the workpiece. The second disadvantage is that with this method of coating, a strong heating of the workpiece occurs, which can lead to a change in its physical properties.

The known method of electrospark coating is patent RU 2708196 C1, adopted in the proposed technical solution for a prototype, which consists in the fact that the surface treatment process is performed by step-by-step motion of the electrode located at an angle of 30 ÷ 50 ° to the surface to be treated. At the moment the electrode touches the workpiece, a technological set of discharge current pulses is supplied, thus, the part of the surface formed by the contact spot of the electrode-workpiece is processed. Known device for electrospark alloying patent RU 2708196 C1, providing the implementation of this method - a prototype, the block diagram of which is shown in Fig. 3.

The device contains a process current generator 1, a vibrating device 2 generator, for example ultrasonic, a vibrator 3, a current shunt 4, an amplifier 5, an integrator 6, a current generator control device 7, an electrode 8, part 9, an engine control unit 10 and an engine 11, for example, stepping.

The operation of the device is carried out as follows: from the generator 1, the process current pulses are fed to the electrode 8, fixed on the vibrator 3. The second output of the generator 1 through the current shunt 4 is connected to the part 9. The signal from the shunt goes to the amplifier 5, then to the integrator 6, at the output which produces a signal proportional to the energy consumed in the spark gap. Surface treatment takes place in accordance with the movement of the electrode 8, for example, step by step using the motor control device 10 and the motor 11.

The disadvantage of this method and device is that the energy consumed in the contact gap is determined taking into account the stable voltage of the electrode-part, which is possible only at a certain value of the electrode pressure. However, mechanical devices that make it possible to implement this task have a finite inertia that does not allow monitoring the process with a sufficient degree of accuracy. This is especially noticeable when processing parts with noticeable irregularities (about 2-4 mm). The use of electrode vibrations at an ultrasonic frequency to stabilize the contact spot gives acceptable results only when processing materials with low hardness and a discharge current duration of the order of 0.5-2 ms.

The objective of the invention is to improve the technology of electrospark deposition of coatings on the surface of parts, which ensures the production of uniform coatings predictable in thickness with specified parameters and properties.

The method of electrospark deposition of coatings on the surface of a workpiece includes surface treatment with a vibrating electrode moving at an angle to the surface to be treated, in which, at the moment of touching the electrode and the workpiece, a technological current pulse is applied and a part of the surface formed by the contact spot of the electrode-workpiece is processed with the provision of coating. In this case, before applying a technological current pulse, the contact surface is pre-prepared by high-frequency current pulses with a variable pulse duration from 0.5 to 20 μs and a variable duty cycle from 1% to 80% of their duration, and simultaneously with the application of current pulses, the voltage on the contact spot is stabilized by regulation of the electrode pressure on the surface to be treated by changing the amplitude and frequency of its vibration in the range of 40 - 800 Hz, and the control of the coating process is carried out using information about the amount of electrical energy consumed in the spark gap, measured at the contact spot. The movement of the electrode at an angle to the surface to be treated is carried out in a step-by-step mode.

The device for electrospark coating on the surface of the part contains a generator of technological current, a vibrator powered by a vibration generator, an electrode motor located at an angle to the surface to be treated, and a control unit, while the positive terminals of the current generator are connected to the electrode fixed on the vibrator, and the negative terminals of the generator are made with the possibility of connection with the workpiece through the shunt. The device additionally contains a matching amplifier connected directly to the contact gap electrode - part, and the control unit is connected to a process current generator, a vibration generator and a matching amplifier and is configured to change parameters according to a signal from a matching amplifier, and the vibration generator is configured to change the frequency in the range of 40 - 800 Hz and voltage in the range from 0 to 50 V according to the signal from the matching amplifier.

The task is achieved by the fact that in the method of electrospark coating, the application process is controlled using information on the amount of electrical energy consumed in the spark gap, and the energy values are controlled directly within the contact spot.

To stabilize the contact spot and eliminate short-circuit currents, before applying the technological current pulse, the contact surface is preliminary prepared by supplying high-frequency current pulses with the possibility of changing their parameters in the range from 0.5 to 20 μs and with the possibility of changing the pulse duty cycle from 1% to 80% their duration.

Simultaneously with the supply of high-frequency pulses, a control signal is sent to the generator of the vibrating device, changing the frequency and intensity of vibrations of which allows you to quickly reduce the electrode pressure on the surface to be treated.

In this case, as in the prototype, the surface treatment process is performed by moving the electrode at an angle to the surface to be treated, for example, step by step.

This method is implemented using a device that allows you to process the surfaces of machine parts and tools.

The block diagram of the device is shown in Fig. 4.

The device for spark deposition of coatings on the surface of the part consists of a generator of technological current and heating currents 1, the positive leads of which are connected to the electrode 8, fixed on the vibrator 3. The negative leads of the generator through the current shunt 4 are connected to the workpiece 9. For the operation of the vibrator 3, a tunable frequency and voltage generator 2. Frequency tuning is provided in the range of 40 - 800 Hz, and the voltage varies, in the range from 0 to 50 V. The design of the generator allows you to change the parameters from an external signal coming from the matching amplifier 12 connected directly to the contact gap of the electrode - detail. To stabilize and measure electrical parameters, a control unit 7 is used, the parameters of which change depending on the signal coming from the matching amplifier 12, and the movement of the electrode 8 at an angle to the surface to be treated is carried out by the engine 11 through the control unit 10 connected to the electronic computing unit (e .v.m) 14 devices through an analog-to-digital converter (ADC) 13.

The device works as follows: before the coating process, the optimal value of the contact resistance of the electrode - part, proportional to the pressure of the electrode on the surface to be treated, and the heating currents of the contact spot are adjusted.

The optimal electrode pressure is determined by measuring the contact voltage of the electrode - part, resulting from the supply of heating current pulses to the contact area. The pulses come from the generator 1. The parameters are controlled by a preliminary selection of modes in block 7. In this case, the pulse repetition rate varies within 0.025 - 1 MHz, and the change in duty cycle is possible from 1% to 80% of the pulse duration.

The duty cycle of the pulses can be changed by changing the signal coming from the amplifier 5. At the same time, a control signal is generated in block 2, which changes the parameters of the oscillator of the vibrating device so that the electrode pressure on the treated surface decreases. Decreasing the pressure on the electrode increases the electrode-to-part contact resistance.

In fig. 5 shows the signal from the output of the generator 2, supplied to the vibrator windings.

The operation of the heating current generator contributes to the stabilization of the size of the contact area due to the melting of microcontacts and an increase in the size of the contact surface. The selection of heating current parameters is carried out based on the chemical composition of the electrode material. By changing the values of the heating currents, the frequency and amplitude of the vibrating device, stabilization of the voltage at the contact gap obtained at the output of the amplifier 12 is achieved. This completes the tuning process, then the process current generator 1 is switched on and on this basis the electrical parameters of the current pulse are selected based on the specific requirements technological nature. The repetition rate, duration and amplitude of the current are controlled in block 7. The block allows you to change the frequency of the vibrating device within 50 - 800 Hz, duration from 10 μs to 2 ms, current amplitude from 5 to 800 A. 6 shows an oscillogram of a single discharge pulse of the process current together with the heating current.

To operate the device in automatic mode, the movement of the electrode 8, fixed on the vibrator 3, is carried out by a stepping motor 11. With the help of an analog-to-digital converter (ADC) 13, the signals coming from the shunt 4 and the matching amplifier 12 are digitized and fed to the electronic -computer unit (e.m.) 14, which calculates the energy supplied to the electrode gap during processing at a specific point on the surface. When certain energy values are reached, a signal is sent from the computing unit to the control unit of the stepping motor 10, and then to the stepping motor, through which the electrode moves. Thus, step-by-step processing is carried out. The amount of energy supplied to the electrode gap depends on the technological parameters. The magnitude of the step-by-step movement of the electrode is selected based on its size. All information about the energy parameters of processing is recorded in an electronic computing unit (computer) 14 to control and refine the coating technology.

Brief Description of Drawings

In fig. 1 shows the time dependence of the voltage of the current pulses on the spark gap electrode - part in the process of machining the part, measured at the output of the matching amplifier 12.

In fig. 2 shows the amplitudes of the process current and voltage across the spark gap at point A, corresponding to the resistance close to a short circuit, as a measure of the energy within the contact spot, measured at the output of the matching amplifier 12.

In fig. 3 shows a block diagram of a device for electrospark alloying, patent RU 2708196 C1, which provides the implementation of the prototype method.

In fig. 4 shows a block diagram of a device for electrospark coating on the surface of a part in accordance with the proposed method.

In fig. 5 shows the time dependence of the signal from the output of the control generator 2, supplied to the windings of the vibrator 3.

In fig. 6 shows an oscillogram of a single discharge pulse of the process current together with the heating current supplied to the electrode.

To work out the coating technology and study the process, all values of the energy parameters are digitized by an analog-to-digital converter (ADC) 13 and fed to an electronic computing unit (computer) 14. In this case, in the interests of optimizing the coating technology , further processing of information in the computing unit 14 is carried out by the MATLAB program.

The use of this method makes it possible to obtain homogeneous coatings with high continuity and thickness due to the stabilization of the parameters of the deposition process, carried out as a result of monitoring the energy parameters at the contact gap between the electrode and the part and using the results of monitoring in process control.

Claims (3)

1. A method of electrospark deposition of coatings on the surface of a part, including surface treatment with a vibrating electrode moving at an angle to the surface to be treated, in which, at the moment of touching the electrode and the part, a technological current pulse is applied and a part of the surface formed by the contact spot of the electrode-part is processed to ensure application coating, characterized in that before applying a technological current pulse, the contact surface is pre-prepared by high-frequency current pulses with a variable pulse duration from 0.5 to 20 μs and a variable duty cycle from 1% to 80% of their duration, and simultaneously with the application of current pulses, the voltage is stabilized on the contact spot by regulating the electrode pressure on the treated surface by changing the amplitude and frequency of its vibration in the range of 40-800 Hz, and the coating process is controlled using information about the amount of electrical energy, consumed in the spark gap, measured at the contact spot. 2. The method of electrospark deposition of coatings on the surface of a part according to claim 1, characterized in that the movement of the electrode at an angle to the surface to be treated is carried out in a stepwise mode. 3. A device for electrospark coating on the surface of a part by the method of claim 1, comprising a process current generator, a vibrator powered by a vibration generator, an electrode motor located at an angle to the surface to be treated, and a control unit, while the positive terminals of the current generator are connected to an electrode fixed on a vibrator, and the negative terminals of the generator are made with the possibility of connecting to the workpiece through a shunt, characterized in that it additionally contains a matching amplifier connected directly to the contact gap electrode - workpiece, and the control unit is connected to a process current generator, vibration generator and a matching amplifier and is configured to change parameters according to a signal from a matching amplifier, wherein the vibration generator is configured to change a frequency within 40-800 Hz and a voltage within a range from 0 to 50 V according to a signal from a matching amplifier.

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