RU2707672C2 - Method for electroerosion-chemical piercing of holes of small diameter and device for its implementation - Google Patents

Abstract

FIELD: technological processes.

SUBSTANCE: invention relates to the field of electrophysical and electrochemical machining methods, mainly to piercing holes of small diameter in parts from high-strength and hard steels and alloys. Proposed method comprises billet processing in flow electrolyte at electrode-tool movement in billet direction and performing electroerosion and electrochemical removal of billet material by means of periodic feed of initiating pulses and the following power pulses to inter-electrode gap. At the electroerosion removal of the material, the erosion hole is produced in the workpiece, the diameter of which exceeds the diameter of the working end of the tool electrode by selecting values of the amplitude and duration of the discharge current in the initiating pulse, determined from the conditions: 0.8K_m<d_e ²/(K_fI_a√t_i)<K_m, where d_e is diameter of working end of electrode-tool; K_f is current pulse form coefficient; I_a is a discharge current pulse amplitude; t_i is duration of discharge current in initiating pulse; K_m is empirical coefficient, and for electrode-tool from tungsten and workpiece from chrome-nickel steel K_m=0.21⋅10^-6 m²/As^0.5, and electrochemical removal is carried out using power pulses of bipolar current, and before each power pulse of direct current of high density is fed pulse low-density reverse current.

EFFECT: providing, when piercing holes of small diameter, high quality of the surface of holes at high rate of piercing of 100 mm/min and more, by ensuring absence of a layer with a modified structure, burrs and sharp edges at R_a 0,2–0,8 mcm.

10 cl, 11 dwg

Description

The invention relates to the field of electrophysical and electrochemical processing methods, mainly to flashing holes of small diameter in parts of high strength and hard steels and alloys.

A known method of electroerosive and chemical dimensional processing of metals and alloys in a flowing electrolyte (a.s. USSR No. 193877, C25D 5/34, 06/05/1976), in which, in order to increase productivity, the processing is performed with a graphite electrode in a mode in which electrochemical processing accompanied by sparking.

The disadvantage of this method is that the use of graphite electrode tools is unacceptable for flashing holes of small diameter due to the fact that they will have high fragility and high electrical resistance. Also, the authors of the patent have not determined the principles of selecting the parameters of the mode at which the processing in the sparking mode ensured maximum productivity and surface quality. The method does not exclude the initiation of electrical discharges along the lateral surface of the electrode - tool (EI), which leads to a deterioration in the quality of the surface of the hole, increases the wear of EI.

There is a method of electroerosive and chemical sizing of metals and alloys in a flowing electrolyte (AS USSR No. 233806 / additional to AS USSR No. 193877 / MKI ² V23P 1/06, 09/30/1978), in which to increase accuracy processing products on finishing operations, increase the frequency of oscillations of the electric current, and the amplitude voltage at the electrodes is maintained somewhat higher than the arc burning voltage.

The disadvantage of this method is that the use of graphite electrode - tools is impractical for flashing holes of small diameter due to the fact that they will have high fragility and high electrical resistance. Also, the processing in this way does not exclude the initiation of electric discharges along the lateral surface of the EI, which leads to a deterioration in the quality of the surface of the hole, increases the wear of the EI. The principles of selecting the mode parameters at which processing would ensure maximum productivity and surface quality have not been determined.

A known method of electrical contact erosion and chemical treatment (RF patent No. 2428287, V23H 5/02, 09/10/2011), in which, in order to eliminate the etching of the untreated surface, improve the quality of the surface being treated while reducing environmental pollution, when it is carried out in a flowing electrolyte with an electrode feed- the instrument when it vibrates until it touches the surface being machined in each oscillation period. An aqueous solution of sodium nitrate with a concentration of 1-5 g / l is used as the electrolyte, and the time of exposure to anodic dissolution and erosion destruction is determined by the amplitude and frequency of vibration of the cathode-tool, depending on the required roughness of the treated surface.

The disadvantage of this method is that it does not exclude the initiation of electrical discharges along the lateral surface of the EI, which leads to a deterioration in the quality of the surface of the hole, increases the wear of the EI.

A known method of electrical discharge machining (a.s. USSR No. 585032, B23P 1/00, 12/25/1977), in which, in order to increase the processing productivity, by using the DC component energy at the stage of material erosion, the DC voltage component is set to be greater or equal to the arc burning voltage.

The disadvantage of this method is that it does not exclude the initiation of electrical discharges along the lateral surface of the EI, which leads to a deterioration in the quality of the surface of the hole, increases the wear of the EI. Also, the authors of the patent have not determined the principles of selecting the mode parameters at which processing ensures maximum productivity and surface quality.

A known method of electrochemical treatment with bipolar pulses and a device for its implementation (Eurasian patent No. 000069, B23H 3/02, 09/07/1996), in which, in order to improve processing performance, by depassivation of the surface of the part, the process of electrochemical processing is carried out with the supply of bipolar current, in which one or more pulses of direct / normal polarity alternate with voltage pulses of reverse polarity.

The disadvantage of this method is that it does not include voltage pulses initiating electrical discharges. There are no rules limiting the amplitude and duration of forward current pulses to prevent electric discharges during electrochemical processing.

A known method of combined electroerosion-electrochemical processing (EECP) by current pulses of electrically conductive materials coated during processing with a passivating film (AS USSR No. 309789, B32H 5/02, 01/01/1971), in which, with the aim of improving accuracy and reducing wear of the tool on the interelectrode gap periodically serves initiating pulses that carry out electroerosive removal of a passivating film, and then power pulses that carry out electrochemical removal.

This method is the closest to the claimed and adopted as a prototype.

The disadvantage of this method is that it does not exclude the initiation of electrical discharges along the lateral surface of the EI, which leads to a deterioration in the quality of the surface of the hole, increases the wear of the EI. Also, the authors of the patent have not determined the parameters of the mode under which the ECM will provide maximum performance and surface quality.

Thus, the known methods of electroerosive-electrochemical processing cannot provide

high-performance piercing of small-diameter holes with high quality of the processed surface (low roughness, without a defective layer). Since they do not exclude the initiation of electrical discharges along the lateral surface of the EI, which leads to a deterioration in the quality of the surface of the hole, increases the wear of EI. Also, the authors of the patents did not determine the parameters of the regime in which the treatment provides maximum productivity and surface quality. In particular, the electrochemical treatment is carried out at gaps substantially larger than the traditional one, the surface being treated is heated by previous discharges and has a structure changed relative to the base, which obviously requires a change in the conditions and modes of its implementation for effective anodic dissolution of the defective layers, reduction of roughness and rounding of sharp edges .

Known switching power supply mainly for electroerosive and electroerosive-chemical processing of metals (A.S. USSR No. 1281352, НОМ 7/515, В23Н 1/02, 01/07/1987), containing inverters made on parallel connected first groups of thyristors and diodes, connected by a bridge circuit with successive LC circuits in the diagonals of bridges, and connected to the anodes of the thyristors and cathodes of the diodes of the first groups by the primary winding of the output transformer, the middle point of which is connected through the input filter choke to the positive DC voltage, and a secondary winding with a midpoint is introduced into the output transformer, to which the cathodes of the second group of inverter thyristors are connected, forming the first output of the power source, and the extreme terminals of the secondary winding of the output transformer are connected via additional diodes to the anodes of the second group of diodes connected to the negative the pole of the constant voltage, forming the second output terminal of the power source.

The disadvantage of this power source is the impossibility of separately setting the voltage of the initiating pulses and the discharge current, and the power is regulated only by the frequency of the pulses, and also does not allow working on a bipolar current.

A known power source for electrochemical processing of materials (RF patent No. 2455131, B23H 3/02, B23H 7/16, 07/10/2012), made in the form of parallel-connected current generators, in which each current generator is connected to the load through a current switch with the possibility of closing the current generator at a time when the generator current has not yet reached the set value or it is necessary to pause between the pulses and the current switch to the load to form a pulse of a given duration on the load, the current switch of which is connected to the output the current generator in such a way that the normally closed contact is connected to a common point, while the total internal inductance of the current generator and the wire connecting the current generator to the current switch is significantly larger than the total inductance of the load and the wires connecting the current switch to the load, and the normally open contact a current switch is connected to a current source through a diode, while transistors are used as normally closed and normally open contacts of the current switch Protected against breakdown by voltage limiters. Such a pulsed power supply allows you to receive current pulses, adjustable in magnitude and duration, including pulses of microsecond duration.

This power source / generator is the closest to the claimed and adopted as a prototype.

The disadvantage of the prototype is the limited functionality due to the lack of initiating pulses of high voltage and the inability to work on a bipolar current.

The problem to which the invention is directed, is to increase processing productivity and the quality of the processed surface of the holes of small diameter.

The technical result is the provision when flashing holes of small diameter of high quality (absence of a layer with a changed structure, burrs and sharp edges at R a 0.2 ... 0.8 μm) of the surface of the holes at a high firmware speed of 100 mm / min or more.

The problem is solved, and the technical result is achieved by the method of electroerosive and chemical piercing of small diameter holes in a workpiece from high strength and hard steels and alloys, including processing the workpiece in a flowing electrolyte when the tool electrode moves in the direction of the workpiece and performing erosion and electrochemical removal of the workpiece by periodic feeding initiating pulses and subsequent power pulses to the interelectrode gap, in which, according to retention, during electroerosive removal of the material, an erosion hole is obtained in the workpiece, the diameter of which exceeds the diameter of the working end of the electrode-tool, by choosing the amplitude and duration of the discharge current in the initiating pulse, determined from the conditions:

Where

d _e - the diameter of the working end of the electrode-tool;

Kf - current pulse shape factor;

I a is the amplitude of the discharge current pulse;

tи is the duration of the discharge current in the initiating pulse;

Km is the empirical coefficient (for a tungsten electrode-tool and a workpiece made of chromium-nickel steel, Km = 0.21⋅10 ^-6 m ² / A s ^0.5 ),

and electrochemical removal is carried out using power pulses of a bipolar current, and a low-density reverse current pulse is supplied before each high-density forward current pulse.

больше Км, и уменьшают, если

меньше или равно 0,8Км.In addition, according to the invention, the duration of the initiating current pulses is increased if

more Km, and decrease if

less than or equal to 0.8 km.

In addition, according to the invention, a predetermined voltage value of the power pulse of direct polarity is maintained by changing the magnitude of the current of direct polarity, while the current value of pulses of reverse polarity is increased or decreased so that the current value of the power pulse of direct polarity is maximum.

In addition, according to the invention, the process of electrochemical processing by power pulses of a current with a voltage equal to the voltage of the initiating pulses is carried out, the duration of the pre-breakdown part of the previous initiating pulse is measured, and the duration of the subsequent power pulse of direct polarity is reduced by 10 ... 15%

In addition, according to the invention, at the time of the initiation of the initiating current pulse until the breakdown, the amount of electricity supplied to the interelectrode gap is measured and proportional-integral-differential regulation of this value is carried out by changing the electrode feed rate.

In addition, according to the invention, in the absence of a pre-breakdown stage in the process of supplying an initiating current pulse, the interelectrode gap is considered close to zero, and the electrodes are short-circuited, while the current power pulses are stopped, and the direction of electrode supply is chosen so as to increase the gap, save the selected direction as long as a short circuit condition is present, then the supply of current power pulses is resumed and the working feed of the electrode is restored.

In addition, according to the invention, after the end of the stage of electro-erosion-chemical flashing and complete opening of the hole, the supply of the electrode-tool is turned off, and the initiating pulses are turned off and only bipolar current pulses supplying electrochemical dissolution of the layer with changed structure on the side surface of the hole and a decrease in its roughness.

In addition, according to the invention, power bipolar current pulses are supplied in groups, filling the gap between the initiating pulses as much as possible.

In addition, according to the invention, power bipolar current pulses turn on after the discharge stage of the previous initiating pulse after a time greater than or equal to the time required for deionization of the interelectrode space and turn off also before the start of the subsequent initiating pulse for a time greater than or equal to the time required for deionization of the interelectrode space.

The problem is solved, and the technical result is also achieved by a device for electroerosive and chemical piercing of small diameter holes in a workpiece of high strength and hard steels and alloys, containing first and second current generators connected in parallel, in which each current generator is connected to the load through a current switch with the possibility circuit of the current generator at a time when the generator current has not yet reached the set value or it is necessary to pause between the pulses and the current switch to the load for generating a pulse of a given duration on the load, and the current switch is connected to the output of the current generator so that the normally closed contact is connected to a common point, while the total internal inductance of the current generator and the wire connecting the current generator to the current switch is significantly larger than the total inductance load and wires connecting the current switch with the load, and the normally open contact of the current switch is connected to the current generator through a diode, and as normally closed and normally open contacts of the current switch, transistors are used that are protected against breakdown by voltage limiters, which according to the invention contains an additional initiating voltage source connected to the load through the key and the inductor, and a diode is connected between the output of the key and the negative terminal of the initiating voltage source, the control system connected to the load, the source of the initiating voltage, the first and second current generators, the key, the first and second switches current, while the positive terminal of the second current generator is connected to the negative terminal of the load, and the negative terminal is positive.

The invention is illustrated by drawings.

In FIG. 1 shows a hole-cell microprofile of the side surface of the hole after traditional EECHO firmware.

In FIG. 2 shows a wavy-circular microprofile of the side surface of the hole after the ECM firmware according to the proposed method.

In FIG. Figure 3 shows an example of a lubricant hole obtained by the proposed EEEHO method in the outer ring of a roller bearing made of ШХ15 steel: the firmware speed is 120 mm / min; calibration time in ECHO mode was 40 s; the surface roughness of the holes after calibration R a = 0.8 μm; the processing error is 0.1 mm, EI with a diameter of 0.8 mm, the electrolyte is 5% NaNO ₃ + 1% NaNO ₂ , the electrolyte pressure is 8 Bar.

d_л - о; Ua=120 В, τ_P=400 мкс; s_T - 0,1 мм; I_A=450А; электролит - 8% NaNO₃,Тэ=293К; материал анода - сталь 12Х18Н10Т; материал ЭИ - вольфрам.In FIG. 4. presents the dependence of the diameter and depth of a single erosion hole on the anode on the diameter of the working end of the EI:

d _l - o; Ua = 120 V, τ _P = 400 μs; s _T - 0.1 mm; I _A = 450A; electrolyte - 8% N a NO ₃ , Te = 293K; anode material - steel 12X18H10T; EI material is tungsten.

In FIG. 5. The dependences of the volume of a single erosion hole on the anode on the diameter of the working end of the EI are presented: U _A = 120 V, τ _P = 400 μs; s _T = 0.1 mm; I _A = 450A; electrolyte - 8% NaNO ₃ ; Te = 293K; anode material - steel 12X18H10T; EI material is tungsten.

360 мкс-о; U_A=100В, s_T=0,15 мм; I_A=450А; электролит - 5% NaNO₃; Тэ=293К; материал анода - сталь 12Х18Н10Т; материал ЭИ - вольфрам.In FIG. 6. The dependences of the diameter of a single erosion hole on the anode (electrode-billet) on the diameter of the working end of the cathode (electrode-tool) for various durations of the discharge stage of the voltage pulse are presented: tp:

360 μs-o; U _A = 100V, s _T = 0.15 mm; I _A = 450A; electrolyte - 5% NaNO ₃ ; Te = 293K; anode material - steel 12X18H10T; EI material is tungsten.

U_A=100В, s_T=0,15 мм; τ_P=360 мкс; электролит - 5% NaNO₃; Тэ=293К; материал анода - сталь 12Х18Н10Т; материал ЭИ - вольфрам.In FIG. 7. the dependences of the diameter of a single erosion hole on the anode (electrode - workpiece) on the diameter of the working end of the cathode (electrode - tool) for various amplitudes of the discharge current pulse are presented: Ip: 450 A-o, 840 A-Δ,

U _A = 100V, s _T = 0.15 mm; τ _P = 360 μs; electrolyte - 5% NaNO ₃ ; Te = 293K; anode material - steel 12X18H10T; EI material is tungsten.

U_A=120В,; τ_P=360 мкс;Ia=450А; электролит - 5% NaNO₃; Тэ=293К; материал анода - сталь 12Х18Н10Т; материал ЭИ - вольфрам.In FIG. 8. the dependences of the diameter of a single erosion hole on the anode (electrode-blank) on the diameter of the working end of the cathode (electrode-tool) for various values of the end MEZ are presented: s _Tt : 0.08 mm-o,

U _A = 120V; τ _P = 360 μs; Ia = 450A; electrolyte - 5% NaNO ₃ ; Te = 293K; anode material - steel 12X18H10T; EI material is tungsten.

In FIG. Figure 9 shows the dependences of the change in V _k — the feed rate of EI during electrochemical processing on the amplitude of the reverse polarity pulse for a group of bipolar pulses: electrolyte - 8% N a NO ₃ , workpiece material — steel 40X13; t _un (pulse width of direct polarity) = 100 μs; the number of pulses of direct polarity in the group = 10; jn (current density of direct polarity) = 100 A / cm ² ; t _uo (current pulse duration of reverse polarity) = 2 ms; tп (pause between pulses) = 50 μs.

In FIG. 10 shows a block diagram of a power source for electro-erosion-chemical flashing holes of small diameter.

In FIG. 11 shows a functional diagram of a process control system for ECHO firmware of small diameter holes.

The essence of the method is as follows.

Processing is carried out in a flowing electrolyte when the electrode - tool moves in the direction of the workpiece. In this case, the workpiece is connected to the positive pole of the pulsed power source, and EI to the negative.

From time to time, initiating voltage pulses of direct polarity are applied to the interelectrode gap, creating a gas-vapor surface film on the surface of the cathode (end of the electrode-tool), i.e. necessary conditions for low-voltage electrical breakdown of the electrolyte (this is the pre-breakdown stage of the initiating pulse). They initiate an electrical breakdown in the interelectrode space (MEP), followed by a spark-arc discharge, accompanied by electrical discharge erosion (this is the discharge stage of the initiating pulse). Moreover, at the time of the breakdown, the discharge current from the additional current generator begins to arrive at the MEP.

Following the initiating pulses, power bipolar current pulses are supplied that carry out electrochemical removal.

In this case, the amplitude and duration of the cascade stage of the initiating pulses are selected so that the diameter of the erosion hole from each single discharge exceeds the diameter of the working end of the electrode - the tool, and electrochemical removal is carried out by bipolar current pulses, so that a low-density reverse current pulse is supplied before each direct current power pulse , contributing to an increase in the rate of electrochemical anodic dissolution of the side surface of the stitched hole on the enlarged inter cathodic gaps formed by electroerosion holes.

The mode of electroerosive-chemical flashing of small-diameter holes can qualitatively change the nature of the formation of the microprofile of the processed surface. So, depending on the ratio of the diametrical dimensions of a single erosion hole on the anode and the working end of the EI, the following two schemes are possible for the formation of a microprofile of the side surface of the hole (Fig. 1, 2):

По известным способам ЭЭХО, диаметр единичной эрозионной лунки на аноде, как правило, многоменьше диаметра рабочего торца ЭИ. В этом случае формирование профиля боковой поверхности отверстия и линейная скорость прошивки обусловлены электрическими разрядами, как в торцовом, так и в боковом МЭП. Окончательное формирование ячеисто-луночного микропрофиля боковой поверхности отверстия будет в большей степени определяться электрическими разрядами в боковом МЭП (фиг. 1);

According to known EECHO methods, the diameter of a single erosion hole on the anode, as a rule, is much smaller than the diameter of the working end of the EI. In this case, the formation of the profile of the side surface of the hole and the linear speed of the firmware are due to electric discharges, both in the end and in the side MEP. The final formation of a mesh-well microprofile of the side surface of the hole will be more determined by electrical discharges in the side MEP (Fig. 1);

По предлагаемому способу ЭЭХО диаметр единичной эрозионной лунки на аноде превышает диаметр рабочего торца ЭИ на величину большую, чем максимальный пробойный МЭЗ при данной амплитуде импульса напряжения. В этом случае электрические разряды инициируются, в основном, в торцовом МЭП, и после каждого разряда ЭИ получает возможность внедрения в тело заготовки на величину, соизмеримую с глубиной лунки. Микропрофиль боковой поверхности в этом случае образован кольцеобразными выступами, представляющими диаметральные кромочные границы эрозионных лунок (фиг. 2).

According to the proposed EEE method, the diameter of a single erosion hole on the anode exceeds the diameter of the working end of the EI by an amount greater than the maximum breakdown MEZ at a given voltage pulse amplitude. In this case, electric discharges are initiated mainly in the end MEP, and after each discharge EI gets the opportunity to introduce the workpiece into the body by a value commensurate with the depth of the hole. The microprofile of the lateral surface in this case is formed by ring-shaped protrusions representing the diametrical edge boundaries of the erosion holes (Fig. 2).

The experiments showed that with a decrease in the diameter d _{T of the} working end of the EI (with other constant parameters: the amplitude and duration of the discharge current) less than some critical value d _cr , a decrease in diameter and an increase in the depth of individual erosion holes on the anode are observed (Fig. 4). Moreover, the dependence of the volume of the erosion hole on the diameter of the end face of the EI is extreme (Fig. 5). The position of the point d _cr (Fig. 4), i.e. the points of the area of commensurability between the diameters of the EI and the cathode spot of the discharge channel, depending on the amplitude and duration of the discharge current, can vary over a fairly wide range and, with certain combinations of these parameters, the diameter of the hole may exceed the diameter of the EI zone 1, FIG. 4..8).

It should also be noted that the volume of the hole at the extremum point is significantly (3-5 times) higher than the volume that the hole has with the same pulse parameters in the region d _T > d _cr (Fig. 5).

Thus, for d _T <d _{cr, the} diameter of the working end of the electrode-tool (for given values of the amplitude and duration of the discharge current) can be chosen in such a way as to achieve maximum performance.

This phenomenon can be explained as follows: for diameters of the working end of the electron beam exceeding the steady-state dimensions of the near-cathode region of the discharge channel, its change does not affect the density of the discharge current and, therefore, the density of the heat flux that determines the nature of erosion holes. Reducing the diameter of the EI, we come to a situation where the size of the EI becomes smaller than the steady-state dimensions of the near-cathode region of the discharge channel. In this case, the near-cathode region is artificially limited by the dimensions of the end face of the electron beam, which at a constant discharge current causes an increase in the heat flux density. An increase in the heat flux density leads to an increase in the depth of erosion holes, and a narrowing of the area over which it is distributed leads to a decrease in its diameter. The mutually contradictory nature of the change in the diameter and depth of the hole determines the existence of a maximum in the change in its volume (Fig. 5) and, accordingly, the conditions for achieving the greatest productivity.

Experimental studies (Zone 1, Fig. 6, 7, 8) showed that the values of the amplitude and duration of the discharge stage current, at which the diameter of the erosion hole exceeds the diameter of the working end of the electrode of the tool, can be determined from the following system of inequalities:

where d _e is the diameter of the working end of the electrode - tool;

Kf - current pulse shape factor;

Ia is the amplitude of the discharge current pulse;

tи is the duration of the discharge current in the initiating pulse;

Km - empirical coefficient (for ee of tungsten and workpiece CNS Km = 0,21⋅10 ^-b m ² / A ^0.5).

становится больше Км, то длительность разрядного тока увеличивают, если

становится меньше или равно 0,8Км, то длительность разрядного тока уменьшают.Moreover, in order to achieve the effect of commensurability of the diameter of the end face of the EI and to reach the volume of the erosion hole close to the maximum value, proceed as follows: if

becomes more Km, then the duration of the discharge current is increased if

becomes less than or equal to 0.8 km, the duration of the discharge current is reduced.

It was experimentally established that the range of values of the coefficient Km (Km ... 0.8Km) corresponds to a certain region in zone 1 (Fig. 5), in which the maximum volume of the holes is reached.

During the period of electrochemical surface refinement, the process is carried out by current power pulses with a voltage equal to the voltage of the initiating pulses, and to reduce the likelihood of electric breakdown of the MEP by power pulses, the duration of the prebreakdown stage of the previous initiating pulse is measured and the duration of the subsequent direct pulse of direct polarity is reduced by 10.15% . This value is determined by us experimentally.

As already noted above, another distinctive feature of the proposed new EECP method is that the electrochemical removal is carried out by bipolar current pulses, so that a low-density reverse current pulse is applied before each direct current power pulse, which contributes to an increase in the rate of electrochemical anode dissolution of the side surface of the pierced hole on increased (due to the electrical discharge components of the process) interelectrode gaps. In this case, a predetermined voltage value of the power pulse of direct polarity is maintained by changing the magnitude of the current of direct polarity, and the current value of pulses of reverse polarity is increased or decreased so that the current value of the power pulse of direct polarity is maximum.

The choice of parameters of current pulses of reverse polarity must satisfy two conflicting requirements:

с одной стороны, плотность j_n импульса тока не должна превышать величины, при которой энергетически становится возможным процесс "анодного" растворения рабочей поверхности электрод - инструмента, а количество электричества Q_n не должно вызывать критической величины подщелачивания приповерхностного слоя заготовки, при которой могут начаться процессы ее пассивации,

on the one hand, the current pulse density j _n must not exceed the value at which the process of "anodic" dissolution of the electrode - tool working surface becomes energetically possible, and the amount of electricity Q _n should not cause a critical value of alkalization of the surface layer of the workpiece, at which processes can begin her passivation

с другой стороны, длительность импульса обратной полярности должна определяться количеством электричества Q_n, необходимым, для выделения такого количества водорода, которого достаточно для механического разрушения поверхностных солевых пленок и протекания реакций восстановления во всем объеме оксидной пленки блокирующей обрабатываемую поверхность заготовки. Как видно из фиг. 9 при определенных значениях тока j_n обратной полярности скорость V анодного электрохимического растворения достигает максимума, а ее значение при этом существенно превышает скорость, которая достигается только при униполярном токе (сравните точки j_n=0 и j_n=8 А/см², фиг. 9).

on the other hand, the pulse width of the reverse polarity should be determined by the amount of electricity Q _n necessary to release such an amount of hydrogen that is sufficient for the mechanical destruction of surface salt films and the occurrence of reduction reactions in the entire volume of the oxide film blocking the workpiece surface. As can be seen from FIG. 9, for certain values of current j _{n of} reverse polarity, the speed V of the anodic electrochemical dissolution reaches a maximum, and its value in this case significantly exceeds the speed that is achieved only with a unipolar current (compare points j _n = 0 and j _n = 8 A / cm ² , FIG. . nine).

At the same time, in order to increase productivity, power bipolar current pulses are supplied in groups, filling the pause between the initiating pulses as much as possible.

In order to prevent the possibility of "picking up" the arc burning from the initiating pulse by subsequent power pulses, due to incomplete deionization of the electrode space, the power bipolar current pulses include, after the discharge stage of the previous initiating pulse, after a time greater than or equal to the time (experimentally determined) necessary for the deionization of the interelectrode space and, in order to prevent arc burning for a time longer than the time of one initiating discharge, force All bipolar current pulses are turned off before the start of the subsequent initiating pulse for a time longer or the time (experimentally determined) necessary for the deionization of the interelectrode space.

For guaranteed removal of the changed defective layer and reduction of surface roughness, after the end of the stage of electroerosive - chemical flashing and complete opening of the hole, the supply of the electrode-tool is turned off, at the same time, the initiating pulses are turned off and only bipolar current pulses that provide high-performance current are delivered for a specified time interval anodic electrochemical dissolution at the interelectrode gaps increased after the electroerosion - chemical stage.

Concrete implementation example

The proposed method of electroerosive - chemical flashing holes of small diameter can be demonstrated on the operations of flashing lubricant holes in the outer rings of rolling bearings.

The geometric parameters of the lubrication holes: d _o = 0.5 ... 2 mm with the ratio of the hole depth to its diameter h _o / d _o <l0 (Fig. 3)

The range of variation of the parameters of the electric and hydrodynamic modes of the ECHO: R _e = 5 ... 15 Bar; U _Au = 80..150 V; I _A = 250..500 A; ƒ = 300.1000 Hz; t _И = 100 .. 500 μs. Electrolyte: aqueous solutions of oxygen-containing mineral salts (usually N a NO ₃ ) with a specific conductivity of 4-16 S / m with passivating additives. Processing is carried out under a layer of electrolyte with a thickness of 20 ... 30 mm, which allows to reduce noise, stabilize the ECM process and eliminate electrolyte spatter. Electrolyte supply scheme: through the nozzle, it was provided with special technological equipment.

Electrode - tools with a diameter of d _e = 0.5 ... 2 mm are made of tungsten rods of grades VM, VRN and do not have side insulation.

The operation of electroerosive - chemical flashing of lubricant holes is carried out sequentially in two transitions: electroerosive-chemical flashing and electrochemical calibration / surface refinement, in order to reduce the roughness and remove the defective layer created by thermal erosion at the flashing stage. Electrochemical calibration is carried out in a pulsed ECHO mode with a stationary EI. In some cases, electrochemical calibration does not require changes in the electrical and hydrodynamic parameters of the EEE process installed at the firmware upgrade. In some cases, the calibration stage can produce EI with a larger diameter than those used for flashing, this allows rounding of sharp edges and refinement of the side surface of the hole with greater productivity.

To ensure stable hydrodynamic conditions from the side of the EI, a technological screen of non-conductive material is installed at a distance of 2 ... 3 mm from the surface of the part to reflect the electrolyte stream.

The operation of electroerosive - chemical flashing of lubricant holes in the outer rings of rolling bearings was used instead of drilling and metalwork (deburring and blunting sharp edges), carried out before heat treatment and ultrasonic descaling from the inner surfaces of the holes after heat treatment.

A specific example of hole firmware (see Fig. 3).

In the manufacture of holes with a diameter of d _o = 1.5 mm, a depth of h _o = 10 mm in the bearing rings of steel ШХ-15, the electrode is an instrument with a diameter of -1 mm, in the mode: R _e = 10 Bar; U _Au = 120 V; Ia = 250 A; ƒ = 300 Hz; t _И = 500 μs. Electrolyte: an aqueous solution of N a NO ₃ with a specific conductivity of 10 S / m with passivating additives of 0.5% N a NO ₂ , the accuracy of processing in a batch of parts was 0.1 mm, the surface roughness R a 1.25..2, 5 μm, the feed rate was V = 50 mm / min, the relative linear wear of the EI from tungsten alloy grade VM was 3%, the defective layer after the stage of electrochemical calibration lasting 20 seconds at a voltage of power pulses of direct polarity U _Ac = 120 V, duration t _Is = 500 μs, and the voltage of pulses of reverse polarity U _An = 5 V and their length lnnosti t _n - 50 μs is completely absent.

The power source for electroerosive and chemical piercing of small-diameter holes contains an initiating voltage source 1 connected to a load (MEP) 2 through a key 3 and a choke 4. A diode 5 is connected between the output of the key 3 and the negative terminal of the initiating voltage source 1. The first current generator 6 is connected with load 2 through the first current switch 7. The second current generator 8 is connected to load 2 through the second current switch 9, and its positive output is connected to the negative output of the load, and the negative output to positive. The control system 10 is connected to the load 2, the source of the initiating voltage 1, the first and second current generators 6 and 8, key 3, the first and second current switches 7 and 9.

The power source for electroerosive - chemical flashing holes of small diameter works as follows (Fig. 10). At the initial moment of time, the initiating voltage source 1, the first current generator 6 and the second current generator 8 are turned on. The key 3 is open. A circuit closing the current generators is included in the current switches 7 and 9. As soon as the voltage specified by the control system is established in the source of the initiating voltage, and the current is set in the current generators, the power source is ready for pulse formation.

The supply of pulses begins with the fact that the current switch 9 is activated. The key is opened, closing the current generator 8, and the key is closed, supplying current to the load 2. A reverse polarity current is transmitted through the load, which removes the passivating film from the workpiece. After a specified time, the control system 10 returns the current switch 9 to its original state and the current of the current generator 8 switches from load to squirrel-cage circuit. Then the key 3 is turned on and the initiating voltage is supplied to the load through the inductor 4. In the first (pre-breakdown) stage of the initializing pulse, a current flows through the load and electrochemical processing occurs. The initiating voltage is quite significant for electrochemical processing. This leads to the fact that after some time the breakdown of the interelectrode gap occurs and the second (discharge) stage of the initializing pulse begins. Inductor 4 prevents an instantaneous increase in current. The voltage on the MEP drops to the burning voltage of the arc (20 ... 40V). The current in the MEP increases at a speed limited by the inductor 4. The voltage drop is fixed by the control system 10, which turns off the key 3 and puts the current switch 7 in a state where the key closing the current generator 6 is opened, and the key supplying current to the load is closed, which leads to a very rapid increase in the current through the load to the value specified by the current control system of the current generator 6. The inductor 4 does not allow the current from the source of the initiating voltage 1 to disconnect instantly. After opening key 3, the current continues to flow along the circuit for some time: 4-load inductor 2 (MEP) - diode 5. Such a current shutdown delay makes it possible not to disturb the process (do not go out of the arc) if there are delays in the control system 10 and current switch 7 After the operation of the current switch 7, the load (the arc in the MEP) turns out to be connected to the current generator 6. The current-voltage characteristic of the current generator provides stable arc burning and allows you to control the discharge current in the discharge stage of the initializing pulse. During the discharge stage of the initiating pulse, erosion treatment occurs.

After a specified time, the control system 10 returns the current switch 7 to its initial state, and the load current switches to a short-circuited circuit, the arc goes out.

After restoration of the MEP resistance, the proposed power source can supply a power pulse of electrochemical processing or a group of microsecond power pulses or a group of bipolar power pulses.

To supply a power pulse of direct polarity, the control system puts the current switch 7 in a state where the key that closes the current generator 6 opens, and the key that connects the load closes.

To supply a power pulse of reverse polarity, the control system puts the current switch 9 in a state where the key closing the current generator 8 opens and the key connecting the load closes. Moreover, the proposed switching power supply allows you to apply power pulses of direct and reverse polarity with or without a pause. If, due to delays in the control system or delays in turning off the transistors, a current will be supplied to the load simultaneously from both switches, then no short circuits and overloads will occur, since the current switches are connected to current generators. Part of the load current at the time when both current switches supply current to the load will go from the current generator in which a larger current is set to the current generator in which a lower current is set, and the current difference will go through the load. As the current of one of the current switches is turned off, the load current quickly (with the switch-off speed in the current switch), without a pause, switches to a new preset state.

In FIG. 10 depicts one current generator of each type, but there may be several depending on the required power, as described in the prototype.

Thus, the proposed power source allows you to generate the required current pulses and bipolar (direct and reverse polarity) current pulses required for the implementation of the new method.

The power supply control system operates according to the functional diagram shown in FIG. 11 as follows. The current turn-on signal generator 20 provides pulse control signals to the keys and switches of the generator current, which are generated depending on the specified durations of the power current pulse and reverse current pulse, the signal from the current computer and the duration of the discharge stage 22 limits the duration of the initiating pulse according to the condition (1, 2 ) In addition, block 20 generates strobe signals to block 12 of the MEP voltage analyzer, the duration of the strobe pulses indicates the time periods of applying current pulses of the corresponding type to the electrode gap (initiating pulse, power pulse, and reverse polarity current pulse).

The voltage analyzer unit 12 with a frequency of 1 ... 5 μs (sampling period) receives from the analog-to-digital converter (ADC) unit 13 the measured voltage value at the electrodes, processes the values in accordance with the state of the gate signals and sets at its outputs: duration of the pre-breakdown stage, duration discharge stage, voltage pulse of current of direct polarity. The measured value of the duration of the pre-breakdown stage and the measured value of the current of the pre-breakdown stage are supplied to the input of the unit for calculating the amount of electricity 11, which generates the value of the measured value of the amount of electricity of the pre-breakdown phase and transfers this value to the input of the proportional-integral-differential (PID) controller 75, which, in accordance with the set value of the amount of electricity changes the feed rate, setting the speed value to the speed controller 19 of the servo system. The measured duration of the pre-breakdown stage is also fed to the input of the detector of the short-circuited state 16, where this value is compared with a predetermined threshold of the minimum duration of the pre-breakdown stage, and if the measured value becomes less than the threshold, it is considered that a short circuit condition of the electrodes is present, in this case, a signal is transmitted to disabling the PID block of the amount of electricity regulator of the pre-breakdown stage 15 and a value that changes the direction of movement is set at the input of the speed controller electrode to eliminate the short-circuited state.

The measured value of the voltage of the power current pulse from the block 12 is fed to the input of the PID regulator of the voltage of the power current pulse 17, this value is compared with the set value of the voltage of the power current pulse, the current value of the current of the power pulse is generated at the output of the controller, which is fed to the input of the generator 21 and to the calculator reverse polarity current 18.

The reverse polarity current calculator 18 implements an algorithm for finding the maximum value of the current of direct polarity, the essence of which is as follows: the search starts with a zero value of the current of reverse polarity, then, for a given period of increment time, the current of reverse polarity increases by a specified amount of increment of the current of reverse polarity until , while the current pulse of direct polarity increases as a result of the impact on the processing of the pulse current of reverse polarity, if the current of reverse polarity begins To stop, the sign of the increment of the current of reverse polarity is reversed. The reverse polarity current calculated in this way is fed to the corresponding control input of the generator.

It is advisable to build a device that implements this functional diagram (see Fig. 11) using specialized digital computers - microcontrollers, the hardware structure of such a system can consist of two digital control units: a generator control unit (BUG) and a feed drive control unit ( BUPP). Together, both blocks are able to implement all the functionality of the proposed system programmatically.

So, the claimed invention improves the processing productivity and the quality of the processed surface of the holes of small diameter, and also provides high-quality when flashing holes of small diameter (absence of a layer with a changed structure, burrs and sharp edges at R a 0.2 ... 0.8 μm) of the surface holes at high firmware speeds of 100 mm / min or more.

Claims (18)

1. The method of electroerosive and chemical piercing of small diameter holes in a workpiece of high strength and hard steels and alloys, including processing the workpiece in a flowing electrolyte when the electrode-tool moves in the direction of the workpiece and performing electroerosive and electrochemical removal of the workpiece material by periodically feeding initiating pulses to the interelectrode gap and subsequent power pulses, characterized in that during electroerosive removal of the material provide erosio a hole in the workpiece, the diameter of which exceeds the diameter of the working end of the electrode-tool, by choosing the values of the amplitude and duration of the discharge current in the initiating pulse, determined from the conditions:

, Where d _e - the diameter of the working end of the electrode-tool; Kf - current pulse shape factor; I a is the amplitude of the discharge current pulse; tu is the duration of the discharge current in the initiating pulse; Km is an empirical coefficient, moreover, for a tungsten electrode-tool and a workpiece made of chromium-nickel steel, Km = 0.21⋅10 ^-6 m ² / A with ^0.5 , and electrochemical removal is carried out using power pulses of a bipolar current, and a low-density reverse current pulse is supplied before each high-density forward current pulse. 2. The method according to p. 1, characterized in that the duration of the initiating current pulses is increased if

more Km, and decrease if

less than or equal to 0.8 km. 3. The method according to p. 1, characterized in that it maintains a predetermined voltage value of the power pulse of direct polarity by changing the magnitude of the current of direct polarity, while the magnitude of the current pulses of reverse polarity increase or decrease providing the maximum current value of the power pulse of direct polarity. 4. The method according to p. 1, characterized in that the process of electrochemical processing by power pulses of a current with a voltage equal to the voltage of the initiating pulses is carried out, the duration of the pre-breakdown stage of the previous initiating pulse is measured, and the duration of the subsequent direct pulse of direct polarity is reduced by 10 ... 15%. 5. The method according to p. 1, characterized in that at the time of supplying the initiating current pulse until the breakdown, measure the amount of electricity supplied to the interelectrode gap, and carry out proportional-integral-differential regulation of this value by changing the electrode feed rate. 6. The method according to p. 1, characterized in that in the absence of a pre-breakdown stage in the process of supplying an initiating current pulse, the interelectrode gap is considered close to zero, and the electrodes are short-circuited, while stopping the supply of power current pulses, and the electrode feeding direction is chosen so that increase the gap, keep the selected direction until there is a short circuit condition, and then resume the supply of power current pulses and restore the working supply of the electrode. 7. The method according to p. 1, characterized in that after the end of the electro-erosion-chemical flashing and the hole is completely opened, the feed of the electrode-tool is turned off, the initiating pulses are turned off and only bipolar current pulses performing electrochemical flow during a specified time interval are turned off anodic dissolution of a layer with a changed structure on the side surface of the hole and a decrease in its roughness. 8. The method according to p. 1, characterized in that the power bipolar current pulses are supplied in groups, filling the gap between the initiating pulses as much as possible. 9. The method according to p. 1, characterized in that the power bipolar current pulses turn on after the discharge stage of the previous initiating pulse after a time greater than or equal to the time required for deionization of the interelectrode space and turn off also before the start of the subsequent initiating pulse for a time greater than or equal to time necessary for deionization of the interelectrode space. 10. A device for electroerosive and chemical piercing of small-diameter holes in a workpiece of high strength and hard steels and alloys, containing first and second current generators connected in parallel, in which each current generator is connected to the load through a current switch with the possibility of closing the current generator at a time the generator current has not yet reached the set value or it is necessary to pause between the pulses and the current switch to the load to form a pulse of a given duration on the load, and the current switch is connected to the output of the current generator in such a way that a normally closed contact is connected to a common point, while the total internal inductance of the current generator and the wire connecting the current generator to the current switch is significantly larger than the total inductance of the load and the wires connecting the current switch to the load moreover, the normally open contact of the current switch is connected to the current generator through the diode, and as a normally closed and normally open contact of the switch current transistors are used, protected from breakdown by voltage limiters, characterized in that it contains an additional source of initiating voltage connected to the load through the key and the inductor, and between the output of the key and the negative output of the initiating voltage source, a diode is connected, the control system connected to the load, the source initiating voltage, the first and second current generators, a key, the first and second current switches, while the positive terminal of the second current generator is connected to negative terminal of the load, and negative terminal with positive.

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