WO2014011074A1

WO2014011074A1 - Electrochemical processing method

Info

Publication number: WO2014011074A1
Application number: PCT/RU2012/000566
Authority: WO
Inventors: Вячеслав Александрович ЗАЙЦЕВ; Насих Зиятдинович ГИМАЕВ; Тимур Рашитович ИДРИСОВ
Original assignee: Общество С Ограниченной Ответственностью "Есм"
Priority date: 2012-07-13
Filing date: 2012-07-13
Publication date: 2014-01-16

Abstract

The invention relates to electrochemical dimensional processing of parts consisting of chromium-containing steels and alloys. First, processing of a part is implemented by working current pulses of direct polarity, and then said current pulses and the power supply to a tool electrode are switched off, wherein a group of high-frequency test current pulses of direct polarity is switched on, and the value of the residual polarization in the interelectrode space is measured. Then, current pulses of reverse polarity are switched on and are fed synchronously with the phase of maximum convergence of the oscillating tool electrode and the part, and deposition of chromium onto the surface is performed, with alternation of the current pulses of reverse polarity with high-frequency test current pulses of direct polarity, wherein the deposition of chromium is controlled on the basis of the increase in the value of the residual polarization relative to the value thereof after processing with working current pulses of direct polarity. The invention makes it possible to increase the processing quality by means of providing a layer with a high lustre on a processed surface and to reduce the concentration of toxic hexavalent chromium ions in the processed electrolyte solution.

Description

Electrochemical processing method

Description of the invention

The present invention relates to the field of metalworking, in particular, to electrochemical dimensional processing and can be used in the manufacture of complex shaped surfaces of machine parts and forming tools from chromium-containing steels and alloys operating in an aggressive environment and high friction. In particular, it is aimed at creating a protective chrome layer on a machined surface of a part during one technological operation, which has a low roughness - a mirror gloss, and provides high corrosion resistance and a low friction coefficient, as well as a decrease in the concentration of toxic hexavalent chromium ions in the spent electrolyte solution .

A known method of pulsed electrochemical processing (ECHO) with the supply of constant voltage to the electrodes in the pauses between the working pulses, in which the constant voltage is set below the decomposition potential of the electrolyte [A. C. USSR N ° 506484, B 23 H 3/00, Bulletin of inventions, N10, 1976]

The disadvantage of this method is that the application to the interelectrode gap (MEP) of a constant voltage below the decomposition potential of the electrolyte, firstly, does not improve accuracy, since the localization of the process decreases due to the constant charge of the double electric layer at the metal-electrolyte interface anodic dissolution and, secondly, does not provide an increase in surface quality (decrease in roughness and increase corrosion resistance), due to the fact that the conditions for creating the surface of the part of a high-quality lame layer. Disadvantage is also the lack of information about when and under what conditions a layer of chromium should be created and how to control its occurrence.

A known method of electrochemical processing of chromium-containing 5 steels in electrolytes based on alkali metal nitrates, in which the amplitude of the positive half-wave current (direct polarity) is greater than negative [Electrochemical processing of metals. Moroz I.I. et al., Moscow: Mechanical Engineering, 1969, pp. 64-65, 130].

A disadvantage of the known method is that the conditions for creating a chrome layer having a mirror shine and a decrease in the concentration of toxic hexavalent chromium ions in the spent electrolyte solution in the treatment of chromium-containing steels and alloys are not defined. In addition, the constant alternation of the forward and backward half-waves will lead to the anode

15 dissolution of the surface of the part, therefore, the direct half-wave will simply dissolve the layer of chromium even if it arises there with the reverse previous half-wave. There is also no information about at what point and under what conditions a layer of chromium should be created and how to control its occurrence.

20 Known electrochemical processing method [United States Patent,

Patent Number 4,213,834, B23H3 / 02; B23NZ / 00 / Jul. 22, 1980], in which a signal characterizing the distortion of the shape of the voltage pulse (when using a current source) is used to conduct the process at small interelectrode gaps. In particular, they use a signal

25 is proportional to the maximum value of the second derivative of the voltage in the pulse.

This method allows processing at the minimum possible interelectrode gaps, providing high copy accuracy when performing copy-and-flash operations using a hard electrode - tool (EI). However, there are no conditions in this method. creating a chromium layer on the treated surface, which ensures the creation of a specular gloss on the treated surface, as well as reducing the concentration of toxic hexavalent chromium ions in the spent electrolyte solution during the treatment of chromium-containing steels and alloys. It is also not determined at what point and under what conditions a layer of chromium should be created and how to control its occurrence.

There is also known a method of electrochemical dimensional processing [RF Patent N_> 2038928, 10.10.1990], in which when using a switching power supply with a steeply dc current-voltage characteristic, the processing is performed by vibration of one of the electrodes, in which the current value of voltage pulses is controlled, highlighting voltage surges in sections rapprochement and dilution of the electrodes and at the same time increase the feed rate of the electrode-tool to the formation of a third local voltage extreme in the middle of the pulse and support t this speed subject to the ratio

, 0 <(.e - Umin) / Umin <0.2, where il.u> hshh is the voltage amplitude of the third local extremum;

Umin is the minimum voltage value.

This method allows processing at the minimum possible interelectrode gaps, providing high copy accuracy when performing copy-firmware operations using hard EI. However, it is impossible to form a local voltage extreme in the middle of the voltage pulse by increasing the feed rate under the conditions of using electrode-tools made of a plate (foil) with a thickness of 0.2 - 0.3 mm. This is because the low stiffness of such electrodes does not allow to increase the electrolyte pressure in the interelectrode gap and to obtain a signal for controlling the processing process, the form of a third local voltage extreme in the middle momentum. In this method, there are also no conditions for creating a chromium layer on the treated surface, which provides a mirror gloss on the treated surface, as well as reducing the concentration of toxic hexavalent chromium ions in the spent electrolyte solution at

5 processing chromium-containing steels and alloys. There is also no information about at what point and under what conditions a layer of chromium should be created and how to control its occurrence.

A known method is ECHO of an electrically conductive part in an electrolyte by applying bipolar pulses between the part and the electrically conductive electrode, in which one or more current pulses of direct polarity alternate with voltage pulses of reverse polarity [United States Patent, Patent Number 5,833,835, B23H3 / 02; B23H3 / 00; Nov. 10, 1998].

This method is the closest to the claimed method and

15 adopted by us as the closest analogue.

The disadvantage of this method is that although this method allows processing at the minimum possible interelectrode gaps, providing high copy accuracy when performing copy-and-flash operations using hard EI, but

20 in the case of using electrode-tools made of a plate (foil) with a thickness of 0.2 ... 0.3 mm, it is impossible to form a local voltage extreme in the middle of the voltage pulse by increasing the feed rate. This is because the low stiffness of such electrodes does not allow increasing the electrolyte pressure in the interelectrode

25 gap and get a signal to control the processing process, the form of a third local voltage extreme in the middle of the pulse.

In addition, when implementing this method, a reverse polarity pulse is supplied at relatively large interelectrode gaps, when the oscillating electrode is removed from the surface of the workpiece being processed over a large distance, and this reduces the efficiency of the pulses reverse polarity to obtain a shiny surface by precipitation of chromium from an electrolyte. So, at large gaps, the hydraulic resistance of the MEC decreases, the electrolyte speed increases and the flow is turbulized, which prevents relatively slow cathodic deposition processes. Changing the external pressure at the entrance to the MEP with a frequency of 10-100 Hz is technically difficult to implement. And the supply of pulses of reverse polarity immediately after the end of the pulses of direct polarity during dilution of the electrodes leads to the fact that at this moment the pressure of the electrolyte in the interelectrode gap decreases and intensive gas filling of the interelectrode medium begins due to boiling of the overheated electrolyte and an increase in the volume of the gas phase accumulated in the electrolyte during the period of positive half waves. The properties of such a gas-vapor electrolyte mixture become substantially inhomogeneous over the treated surface, which worsens the conditions for the uniform deposition of chromium. In addition, the constant alternation of the forward and backward half-waves will lead to the anodic dissolution of the surface of the part, therefore, the direct half-wave will simply dissolve the layer of chromium even if it occurs there in the previous previous half-wave.

Thus, each of the known ECHO methods separately when processing parts of chromium steels does not provide, within the framework of a single technological operation, the achievement of high copying accuracy, and the creation of a chromium layer having a specular gloss on the treated surface, as well as a decrease in the concentration of toxic hexavalent ions in the spent electrolyte solution chromium.

The objective of the present invention is to improve the quality of processing by creating on the treated surface a layer having a specular gloss, and reducing the concentration of toxic hexavalent chromium ions in the spent electrolyte solution by processing on. small interelectrode gaps with pulses of direct polarity at high current density, creating a polished surface and subsequent deposition of chromium pulses of reverse polarity on the treated surface to create a mirror shine.

The problem is solved by the fact that by the method of electrochemical treatment of chromium-containing steels and alloys in electrolytes based on aqueous solutions of alkali metal nitrates, including the processing of the part by current pulses supplied synchronously with the phase of maximum approximation of the oscillating electrode-tool and the part when adjusting the feed speed of the electrode-tool or the parts according to the invention first carry out electrochemical treatment with working pulses of current of direct polarity, forming in the electrolyte zone the layer adjacent to the surface of the part enriched with chromium ions, then, upon reaching the specified processing depth, shape and size of the part, the working pulses of the current of direct polarity and the electrode supply of the tool are turned off, a group of test high-frequency pulses of current of the direct polarity are turned on, and the value of the residual polarization is measured on the interelectrode gap, then reverse current pulses are turned on, supplied synchronously with the phase of maximum approximation of the oscillating electrode-tool and part, and cathodic deposition of chromium on the treated surface of the part, alternating pulses of current of reverse polarity with test high-frequency pulses of current of direct polarity, and control the deposition of chromium by incrementing the value of residual polarization relative to its value after processing by working pulses of current of direct polarity

In addition, according to the invention, the upper limit of the amplitude and duration of current pulses of reverse polarity is limited from the condition that there is no raster of the working surface of the electrode-tool, and the lower limit of the amplitude and duration of reverse current pulses polarity is limited due to the formation of a continuous chrome layer on the treated surface of the part.

In addition, according to the invention, the duration of the test high-frequency current pulses of direct polarity is set in the 5th range of 10-50 μs with a frequency of 5-10 kHz, and the voltage amplitude of 6 - 8 V.

In addition, according to the invention, the value of the increment of the residual polarization relative to its value after the working pulses of the current of direct polarity is established empirically on the first 2-3 parts from the batch.

In addition, according to the invention, when applying current pulses of reverse polarity, the pressure of the electrolyte at the inlet of the interelectrode gap is reduced to 50-150 kPa and chromium is deposited.

In addition, according to the invention, when processing by working pulses of current of direct polarity, the interelectrode gap

15 is reduced by gradually increasing the feed rate of the electrode - the tool or part until the first breakdown of the interelectrode gap occurs, then reduce the feed rate by 3-10% relative to the speed at which the breakdown occurred and continue processing, repeating if necessary act.

20 In addition, according to the invention, the processing of working current pulses of direct polarity is carried out under the following conditions: voltage at the MEP 5-15V, the pressure of the electrolyte at the input of the MEP 50-500kPa, the concentration of the electrolyte 7-15% and the temperature of the electrolyte 18-40 ° C, providing current density 50-1000A / cm2.

25 In addition, according to the invention, the value of the residual polarization is measured at the end of the last test pulse at the starting point of the decay curve of the residual polarization, while the duration of the group of test high-frequency pulses of the current of direct polarity is selected from the condition that the residual polarization value reaches a steady state value. The proposed method for the electrochemical treatment of chromium-containing steels and alloys allows to improve the quality of processing and to obtain a surface having a specular gloss, to reduce the concentration of toxic hexavalent chromium ions in the spent electrolyte solution.

In the future, the invention is illustrated by specific examples of its implementation and the accompanying drawings, confirming the possibility of its implementation, in which:

figure 1 depicts a process diagram according to the invention; figure 2 depicts the waveform of the voltage and current in the MEP at the stage of forming pulses of direct polarity and at the finish stage when the deposition of chromium on the treated surface, according to the invention; where: S is the trajectory of the oscillating electrode - the tool, mm depending on the time t, sec, U is the voltage of the pulses of direct polarity, V, U _A is the voltage of the residual polarization after the test pulses after the shaping stage, V; 1 / _B - residual polarization voltage determined by test high-frequency pulses after the finishing stage of chromium deposition, V; j is the technological current density of pulses of direct polarity, A / cm ² .

FIG. Za depicts the waveforms of the residual polarization voltage after the pulses of direct polarity determined by high-frequency pulses of direct polarity (curve 1), and the waveforms of the current of high-frequency pulses (curve 2) in the MEP at the stage of shaping by pulses of direct polarity,

FIG. 36 shows the waveforms of the residual polarization voltage after pulses of reverse polarity determined by high-frequency pulses of direct polarity (curve 1), and the waveforms of the current of high-frequency pulses (curve 2) in the MEP on the final stage when processing pulses of reverse polarity during the deposition of chromium on the treated surface,

figure 4. depicts the structure of a control system for a technological current generator and a reverse polarity current source of an electrochemical machine according to the invention; where: 3 -controlled source of technological current; 4 - controlled current source of reverse polarity; 5 - controlled source of test pulses of current of direct polarity; 6 - electronic key to turn on the technological current source; 7 - electronic key to turn on the current source of reverse polarity; 8 - electronic key to turn on the source of test pulses, 9 - automatic process control system, 10 - generator control unit.

Figure 5 depicts the appearance of the surfaces of the machined parts with their corresponding profilograms after ECHO using unipolar current pulses of direct polarity (A) and after reverse polarity pulses of ECHO (B) according to the proposed method;

6 depicts the ratio of the concentration of chromium to the concentration of iron in the surface layer after ECHO by unipolar pulses of direct polarity (A) and ECHO with pulses of reverse polarity (B) according to the proposed method, obtained by the method of secondary ion mass spectroscopy.

SUMMARY OF THE INVENTION

The essence of the technological scheme of pulsed bipolar electrochemical processing (ECHO) by vibrating EI used on machines of the ET series is as follows (Figure 1). The electrode-tool 1 makes periodic oscillations S (t) relative to the workpiece surface of the electrode-workpiece (parts) 2, coaxial with the feed direction V, First, in the region of the phase of closest proximity of the electrodes, a working pulse or a group of current pulses of direct polarity, high density (in the range of 50 ... 1000 A / cm) is supplied, then, upon reaching the specified processing depth at the finishing stage of the process, the working pulses of the current of direct polarity are turned off and EI supply, determine the value of the residual polarization UA after applying a group of test high-frequency pulses (Figure 2), and include low-voltage current pulses of reverse polarity, and synchronize the time of supply of reverse polarity pulses and also with the phase of closest approach of the electrodes and perform the cathodic deposition of chromium on the treated surface of the electrolyte at small interelectrode gaps. After that, test high-frequency pulses of direct polarity current are switched on again to determine the residual polarization voltage after reverse polarity pulses U _E. Then, low-voltage pulses of reverse polarity current are turned on again, and cathodic deposition of chromium onto the treated surface from the electrolyte is repeated at small interelectrode gaps. After that, test high-frequency pulses of direct polarity current are switched on again to determine the total value of the residual polarization after the reverse polarization pulses UE, this is repeated until the necessary increment of the residual polarization value is obtained.

The measurement of the polarization values UA and U is determined after turning off the current, due to which the ohmic component is excluded from the measured voltage value and the reliability of measuring the difference between U A and U _B , which is taken as an informative parameter about the enrichment of the treated surface with chromium, is increased (Fig. 3).

Test pulses provide a recharge of the capacitance of the double electric layer, establishing the polarization value, the components of which are the anodic and cathodic potentials. In this case, the cathode potential is established faster than the anode one and its steady-state value at a fixed current density has a stable value, and the value of the anode potential depends on the properties of the treated surface and makes the main contribution to the increment of the residual polarization U _A and U _E. In this case, the duration of the group of test high-frequency current pulses of direct polarity is selected from the condition that the residual polarization of the steady state is achieved.

In addition, test high-frequency pulses of current of direct polarity, alternating with current pulses of reverse polarity, can provide more favorable conditions for the deposition of chromium on the treated surface, as it is considered (Povetkin V.V. Structure of electrolytic coatings / V.V. Povetkin, I. M. Kovensky. - M .: Metallurgy, 1989. - 136 s), that the best way to prepare the surface for metal deposition is electrolytic polishing, which provides a large number of nuclei and good adhesion to the substrate.

The invention is implemented as follows:

The proposed method for the electrochemical treatment of chromium-containing steels in electrolytes based on aqueous solutions of alkali metal nitrates is carried out in a flowing electrolyte with superposition of vibrations on one of the electrodes (Fig. 1). As a power source 3 of direct polarity, a source with a steeply falling current-voltage characteristic (Fig. 4) is used, which is periodically connected to the MEP by an electronic switch to turn on the technological current source 6 in the region of the phase of closest proximity of the electrodes. The closed-state time of the electronic switch on the technological current source 6 determines the duration of the current pulse of direct polarity. ,

The flow of reverse current polarity pulses through the MEP is ensured by the inclusion of an electronic switch to turn on the reverse polarity current source 7 (see FIG. 4). As a generator of test pulses 5, a source with a steeply falling current-voltage characteristic (Fig. 4) is used, which is periodically connected to the MEP using an electronic switch to turn on the source of test pulses 8.

An increase in the amount of chromium on the treated surface after bipolar electrochemical treatment of chromium-containing steels is confirmed by the results of determining the composition of the surface layer carried out using various methods.

Investigations were made of the surface of an electrode made of 40X13 steel after a unipolar ECHO and a bipolar ECHO with the supply of an additional current pulse of reverse polarity after a working current pulse of direct polarity, when significant changes in the quality of the treated surface occur (Fig. 5).

The experiments were carried out in a 9.5% solution of sodium nitrate NaNO ₃ at a current pulse density of ~ 100 A / cm and a pulse duration of 1.5 ms, current density and reverse polarity pulse duration of ~ 5 A / cm and 2 ms, respectively. The moment of supply of working pulses and pulses of reverse polarity was synchronized with the phase of maximum approximation of the EI with the surface being treated. The duration of the test pulses was 50 μs, the voltage amplitude was selected no more than 8 V.

The results of studies of the surface layer by the method of secondary ion mass spectroscopy showed an increase in the concentration of chromium in relation to the concentration of iron after a bipolar ECHO compared to a unipolar ECHO.

When using this kind of surfaces in conjugated pairs of friction, forming equipment (punches, dies), etc., the friction coefficient decreases and the fatigue strength, wear resistance and corrosion resistance increase. For example, the resistance of a tool steel punch for the manufacture of Togh recesses in steel screws increased by more than 2 times compared to a similar punch made by traditional technology (metalwork-mechanical method) and coated with titanium nitride. Similar results are expected when using punches in the manufacture of tablets (pharmaceutical industry).

It should be noted that during conventional unipolar processing, the surface layers of chromium-containing steels are usually depleted in chromium. Due to the specifics of bipolar processing, according to the invention, they form chromium-containing layers on a wide range of chromium-containing steels and automatically control this process.

Studies of changes in the amount of dichromate ions in the electrolyte acquire an important role due to the high requirements for protecting service personnel and the environment from harmful emissions from the electrochemical treatment (ECHO) of chromium-containing steels and alloys. This becomes even more important because the need to reduce losses, from an economic point of view (switching to a closed cycle) leads to a sharp increase in the time of use of the electrolyte solution and, therefore, to an increase in the content of dichromate ions in the solution, which will require measures to regeneration or replacement of the solution.

You can reduce the content of dichromate ions in solution by depositing them on a pre-treated surface at high current densities (for example, more than 100 A / cm ² ) by applying pulses of reverse polarity according to the proposed method. Since the dichromat ions are Cr ₂ 0 ₇ , in which metal atoms already have a maximum oxidation number, they cannot be oxidized on a positively charged anode, therefore, having a high standard potential (p (Cr ₂ 0 ₇ ² 7C ³⁺ ) = +1, 33 V, they are reduced at the cathode. Therefore, in order to discharge the chromium ions on the treated surface of the part to metallic chromium, they reverse the polarity of the part to negative. to create appropriate conditions, for example, small interelectrode gaps of 10 ... 100 μm, and apply a voltage of pulses of reverse polarity that does not allow the working surface of the electrode-tool to be torn, but sufficient to discharge chromium ions on the treated surface, chromium will be deposited by the reaction:

Cr ₂ O ₇ ^{2 ~} + 14H ^ + 12e -> 2Cr + 7H ₂ 0.

Implementation example

A specific example of the implementation of the proposed method of electrochemical processing, according to the invention.

The proposed method of ECM by current pulses was implemented on an electrochemical copy-piercing machine model ET500 of the company ESM LLC, the material of the sample (part) and electrode-tool was 40X13 steel. The treatment was carried out in a 9.5% aqueous solution of sodium nitrate to a depth of 5 mm with an area of 200 mm2.

Before starting the processing, the oscillating electrode-tool 1 (Fig. 1) and the workpiece (part) 2 were brought together until they touched in the absence of technological voltage and were taken to the predetermined minimum interelectrode gap S _t = 20 μm (Fig. 1).

Then, the following processing regime was established with pulses of direct polarity at the first processing stage:

-frequency of rectangular current pulses and oscillations of the tool electrode, (Hz) - 49;

- voltage pulse duration, (ms) - 1.5;

-the amplitude of the oscillation of the electrode-tool, (mm) -0, 15;

The amplitude of the rectangular voltage pulse at the time of the smallest distance between the electrodes, (V) -10.5;

. The electrolyte pressure at the inlet of the interelectrode gap, (kPa) -

one hundred; Electrolyte temperature, (° С) - 20.

The electrolyte supply is direct through the central hole of the tool electrode.

In the process of embedding the electrode-tool 1 (Fig. 1) into the workpiece 2 to a depth of 0, 1 ... 0.3 mm, the feed rate was 0.1 mm / min. Then, as the electrode-tool 1 further deepens into the workpiece 2, the electrolyte pressure is gradually increased to 350 kPa. In the process of processing by pulses of direct polarity, the feed rate was gradually increased until the first breakdown occurred, which corresponded to the feed rate of EI - 0.16 mm min, then the feed rate of EI was reduced by about 7% and the further processing was continued to a predetermined depth.

Upon reaching a predetermined depth of 5 mm, the working pulses of the current of direct polarity were turned off,. EI supply, measured the value of the residual polarization by turning on the test high-frequency pulses of the current of direct polarity with a voltage amplitude of 8 V and a pulse duration of 50 μs. Then, low-voltage rectangular pulses of reverse polarity voltage were turned on, creating a current density of 5 A / cm and a duration of 2 ms, synchronizing the time of supply of reverse polarity current pulses with the phase of maximum electrode proximity and performing cathodic deposition of chromium onto the treated surface from the electrolyte at small interelectrode gaps periodically measuring the value of residual polarization with test high-frequency pulses of current of direct polarity. At the same time, at the stage of chromium deposition, reverse polarity current pulses alternated with test high-frequency pulses of direct polarity current, providing control of chromium deposition to the necessary increment of the residual polarization value relative to its value after direct polarity pulses, the value of which was previously determined on 2 ... 3 details this party. , When current pulses of reverse polarity were applied, the electrolyte pressure was reduced to 10 ° C, creating a laminar flow in the interelectrode gap, which provided good conditions for the deposition of chromium from the electrolyte composition onto the treated surface. In this case, the amplitude and duration of the reverse polarity current pulses were limited from the condition that there is no raster of the working surface of the electrode-tool, but sufficient for the discharge of chromium ions on the treated surface of the part.

Analysis of the processing results showed that when using the proposed method there is a significant decrease in the concentration of hexavalent chromium in the spent electrolyte and obtaining a stable specular gloss of the treated surface (Ra <0, 15 μm), the error in copying EI did not exceed 0.01 mm, the feed rate during processing pulses of direct polarity was 0.15 mm / min.

Claims

Claim

1. The method of electrochemical treatment of chromium-containing steels and alloys in electrolytes based on aqueous solutions of alkali metal nitrates, comprising treating the part with current pulses supplied synchronously with the phase of maximum convergence of the oscillating tool electrode and the part when adjusting the feed speed of the tool electrode, characterized in that at first carry out electrochemical treatment with working pulses of current of direct polarity, forming a layer in the electrolyte zone adjacent to the surface of the part filled with chromium ions, then, upon reaching the specified processing depth, shape and size of the part, the working pulses of the current of direct polarity are turned off and the electrode supply of the tool is turned on, a group of test high-frequency pulses of current of the polarity are turned on and the value of the residual polarization at the interelectrode gap is measured, then the current pulses reverse polarity supplied synchronously with the phase of maximum approximation of the oscillating electrode-tool and the part, and carry out cathodic deposition of chromium on the treated surface parts, alternating current pulses of reverse polarity with test high-frequency pulses of current of direct polarity, and control the deposition of chromium by incrementing the value of residual polarization relative to its value after processing by working pulses of current of direct polarity.

2. The method according to claim 1, characterized in that the upper limit of the amplitude and duration of the pulses of current of reverse polarity is limited from the condition that there is no raster of the working surface of the electrode-tool, and the lower limit of the amplitude and duration of pulses of current of the reverse polarity is limited from the condition of formation of a solid chrome layer on surface finish of the part.

3. The method according to claim 1, characterized in that the duration of the test high-frequency current pulses of direct polarity is set in the range of 10-50 μs with a frequency of 5-10 kHz, and the voltage amplitude of 6 - 8 V.

4. The method according to claim 1, characterized in that the value of the increment of the residual polarization relative to its value after the working pulses of the current of direct polarity is established empirically on the first 2-3 parts from the batch.

5. The method according to claim 1, characterized in that when applying current pulses of reverse polarity, the pressure of the electrolyte at the input of the interelectrode gap is reduced to 50-150 kPa and chromium is deposited.

6. The method according to claim 1, characterized in that when the working pulses are processed with direct polarity current, the interelectrode gap is reduced by smoothly increasing the feed rate of the electrode tool or part until the first breakdown of the interelectrode gap occurs, then the feed rate is reduced by 3-10% relative to the speed at which the breakdown occurred and continue processing, repeating this action if necessary.

7. The method according to claim 1, characterized in that the processing of the working pulses of current of direct polarity is carried out under the following modes: voltage at the interelectrode gap of 5-15V, the pressure of the electrolyte at the inlet of the interelectrode gap of 50-500kPa, the electrolyte concentration of 7-15% and the temperature of the electrolyte 18-40 ° C, providing a current density of 50-1000 A / cm2.

8. The method according to claim 1, characterized in that the residual polarization value is measured at the end of the last test pulse at the starting point of the decay curve of the residual polarization, while the duration of the group of test high-frequency current pulses of direct polarity is selected from the condition that the residual polarization value reaches a steady state.