RU2558700C2 - Device and method for electromagnetic drawing and elimination of dents - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention relates to magnetic-pulse processing of materials and can be used for forming of thin-sheet parts and elimination of dents, primarily, on aircraft elements and for processing, for example, of vehicle body steel sheets. Proposed device comprises electromagnetic system for generation of pulse magnetic fields in processed part, primary slow pulse current source and secondary fast pulse current source. There is secondary magnetic field direction , mainly, opposite the primary magnetic field direction. Secondary current source generates the train of two or more current pulses. Working head is composed of a separate moving assembly with handles or holders for its retention relative to the part.

EFFECT: lower peak working voltages, higher reliability of working head.

17 cl, 2 dwg

Description

The invention relates to techniques for magnetic pulse processing of materials and can be used for molding thin-walled metal parts and eliminate dents on metal elements.

A device is known for deformation of thin-walled metal parts by a pulsed magnetic field ([1] H.H. Kolm, patent US No. 3703958, 11/1972), consisting of an electromagnetic system (in the form of two solenoids) and two pulsed current sources connected to an electromagnetic system. The first current source creates a constant or slowly changing magnetic field in the part, which penetrates the part, the second current source creates a rapidly changing magnetic field in the part, which causes intense eddy currents in the metal part and its deformation. Moreover, depending on the mutual direction of the magnetic fields created by the first and second current sources (or the polarity of their current), the nature of the force acting on the part can be both repulsive from the electromagnetic system and attracting to it.

A device for straightening dents on metal sheets is known ([2] BSChoe et al., US patent No. 7607332 B2, 10/2009), consisting of a high-frequency generator, an electromagnetic system connected to the generator and generating intense induction currents in the metal sheet, and sheet cooling systems by blowing it, for example, with air. Moreover, the electromagnetic system in the form of a coil is combined with a cooling system in a movable working head. Induction currents heat the metal sheet near the head evenly across the thickness of the sheet, and blowing the sheet cools it from the side of the head. In this case, a temperature gradient in thickness occurs in the sheet, which, due to the thermal expansion of the metal, uneven in thickness, straightens the dent. The disadvantages of this method include the following. The material of the straightened sheet must have a large coefficient of linear thermal expansion, the contact of the heat-removing elements on the back side of the sheet with respect to the head impedes straightening or leads to unpredictable deformation of the sheet, the nature of the deformation changes if they are adjacent to the sheet (maybe not even close) metal elements that distort the high-frequency magnetic field.

The closest device and method for the electromagnetic drawing of metal parts and removing dents on them (prototype) are the device and method proposed in the work ([3] K.A. Hansen, I.G. Hendrickson, US patent No. 3998081, 12/1976). The device comprises an electromagnetic system, a primary current source connected to the electromagnetic system, a secondary current source also connected to the electromagnetic system. The electromagnetic system of the prototype is made in the form of a coil wound by an electric current conductor, and its coils are isolated from each other and from the workpiece. Coil winding can be performed in various ways: a flat spiral, a multilayer flat spiral, spirals (including multilayer ones) lying in several planes at an angle to each other, etc. The primary current source connected to the electromagnetic system creates a slowly changing current pulse and, accordingly, the primary magnetic field in the area of the part. The pulse duration was chosen so that the magnetic field could penetrate through the conductive part without the appearance of noticeable ponderomotive forces in the part. Then a short secondary current pulse and, accordingly, a secondary magnetic field were generated by the secondary current source. In this case, the polarity of the secondary current pulse was opposite to the primary one; therefore, the generated secondary magnetic field was mainly opposite in direction to the primary one. The duration of the secondary pulse was chosen so that the secondary pulse did not penetrate the metal part (due to the skin effect). In this case, the magnetic field between the electromagnetic system and the part decreased due to partial compensation of the primary and secondary magnetic fields, and behind the part it remained the same. This created the ponderomotive force of the pulsed magnetic field, attracting the part to the electromagnetic system. Such a method and a device based on it can effectively work for relatively thin-walled parts (the thickness is much less than the characteristic dimensions along the surface) with good electrical conductivity when using strong magnetic fields (of the order of 10 T).

The method proposed in the prototype [3], contains the following sequence of actions: (1) positioning the working surface of the working head of the device containing the electromagnetic system in the form of a coil relative to the part, (2) passing through the coil a slow primary current pulse with such a duration that ponderomotive forces the primary magnetic field did not deform the part, (3) passing through the coil a secondary rapidly changing current pulse with an amplitude of 50% to 80% of the amplitude of the primary current, and the secondary current must be opposite to the primary, so the primary and secondary magnetic fields are predominantly in the opposite direction. The duration of the secondary current pulse must be short enough to create strong deformations in the part.

The prototype suggested the use of several possible options. Between the electromagnetic system and the workpiece, an arrangement of a dielectric template was additionally allowed, the surface shape of which on the part side approximately corresponds to the desired final shape of the workpiece. An electromagnetic system can be integrated into the dielectric base, and the shape of the working surface of the dielectric base adjacent to the workpiece should approximately correspond to the desired final shape of the workpiece. To increase the efficiency of the electromagnetic system, it was proposed to use a pulsed magnetic field concentrator. The electromagnetic system was also proposed to be implemented as a separate movable unit (working head) for the convenience of working with the device.

Subsequently, individual elements of the prototype were developed and refined in a series of patents. In ([4] KAHansen, IGHendrickson, US patent No. 4061007, 12/1977), ([5] KAHansen, IGHendrickson, US patent No. 4127933, 12/1978), ([6] RFOlsen, US patent No. 7068134 B2, 06/2006) and ([7] FPBerg, DBSmith, US patent No. 7114242 B2, 10/2006) present electromagnetic systems in the form of a coil made of a rolled flat conductive sheet with an insulating gasket, moreover these rolls are additionally provided with cutouts for the concentration of magnetic flux in the dent area on the workpiece. The work ([8] K.A. Hansen, I.G. Hendrickson, US patent No. 4986102, 01/1991) used an electromagnetic system consisting of two coils connected in series. In this case, one common conclusion of both coils and two external ones is formed. Moreover, the common and one of the external terminals are connected to the secondary current source, and both external terminals are connected to the primary current source.

The works ([9] PBZieve, US patent No. 5046345, 09/1991) and ([10] DBSmith et al., US patent No. 6639781, 10/2003) described in detail the design of current sources based on capacitive energy storage, in In the electric circuit, additional blocking inductances are used, connected in series with the primary current source for electrical isolation of two current sources. Crowbar diode and thyristor circuits were also used in these works to prevent the oscillatory process of discharging capacitors to inductive load and recharging capacitors included in the sources of primary and secondary currents. In the works ([11] KAHansen, IGHendrickson, US patent No. 4148091, 04/1979) and ([12] KAHansen, IGHendrickson, US patent No. 4116031, 09/1978) the electromagnetic system was made in the form of two separate coils with a single-turn magnetic flux concentrator magnetically connected to both coils.

A known method and device ([13] O. Gafri, Y. Livshiz, US patent No. 6630649, 10/2003), which creates a primary (slow) and secondary (fast) alternating magnetic fields. However, their mutual polarity is not defined.

The prototype is intended primarily to eliminate dents on aircraft components (wings, fuselage, air intakes).

The disadvantages of the prototype include the need to use powerful high-voltage pulsed sources of secondary current. High voltages are needed to quickly change the current in the inductance (electromagnetic system) in the secondary current pulse. In this case, the upper voltage values are in practice limited to values of the order of 30 kV for a compact portable head. Therefore, the device and method proposed in the prototype are not used to eliminate dents for poorly conductive and durable materials (steel), which require very short intense pulses of a secondary magnetic field and, as a result, a high voltage amplitude of a secondary source. All this reduces the effectiveness of the prototype.

In this regard, the technical problem arises of increasing the processing efficiency, as well as increasing the compactness and reliability of the working head.

The technical result consists in increasing the processing efficiency (namely, in increasing the ratio of the mechanical impulse invested in the workpiece to the electric energy of the sources) and in reducing the amplitude of the voltage that occurs when the secondary current flows through the electromagnetic system, which makes it possible to make the working head of the device more compact and more reliable. Reducing the amplitude of the voltage allows you to create a device and method for drawing and removing dents of poorly conductive and durable materials, such as sheet steel automobile bodies.

The technical result is achieved as follows. In the claimed device and method, the secondary current and, accordingly, the secondary magnetic field are formed in the form of a sequence of pulses in contrast to a single pulse in the prototype.

Consider the mechanical action of a pulsed magnetic field on a conductive non-magnetic part in the form of a metal sheet. Note that, since the amplitude of the magnetic field is assumed to be very high (above 1 T), there is practically no difference between the behavior of non-magnetic and magnetic metals, because the magnetic metal is in a state of saturation of magnetization. It is assumed that the electromagnetic system consists of a single coil to which primary and secondary current sources are connected. The coil is located near the surface of the metal sheet. We consider the primary current pulse to be very slow and, for simplicity, we assume that the primary magnetic field does not create induction currents.

First, we examine the secondary magnetic field in the form of a single pulse, as is the case in the prototype [3]. The bulk force acting on the part in this case has the form ([14] A.S. Lagutin, V.I. Ozhogin, Strong pulsed magnetic fields in a physical experiment, M: Energoatomizdat, 1988)

$$\text{f (r}\text{, t)}={\text{f}}_{\text{21}}\text{(r}\text{, t)}+{\text{f}}_{\text{2}}\text{(r}\text{, t)}\text{,}\text{(one)}$$

и $${\text{f}}_{\text{2}}\text{(r}\text{,t)}=\frac{\text{1}}{{\mu }_{\text{0}}}{\text{ rot(B}}_{\text{2}}\text{)}\times {\text{B}}_{\text{2}}$$

, B₁ и B₂ - вектора индукции первичного и вторичного магнитных полей, µ₀ - магнитная проницаемость вакуума, r - радиус-вектор точки, t - время. Распределение вторичного магнитного поля с учетом создаваемых им индукционных токов в детали определяется уравнением диффузии [14]Where $${\text{f}}_{\text{21}}\text{(r}\text{, t)}=\frac{\text{one}}{{\mu }_{\text{0}}}{\text{rot (B}}_{\text{2}}\text{)}\times {\text{B}}_{\text{one}}$$

and $${\text{f}}_{\text{2}}\text{(r}\text{, t)}=\frac{\text{one}}{{\mu }_{\text{0}}}{\text{rot (B}}_{\text{2}}\text{)}\times {\text{B}}_{\text{2}}$$

, B ₁ and B ₂ are the induction vectors of the primary and secondary magnetic fields, μ ₀ is the magnetic permeability of the vacuum, r is the radius vector of the point, and t is time. The distribution of the secondary magnetic field, taking into account the induction currents it creates in the part, is determined by the diffusion equation [14]

where σ is the electrical conductivity of the material of the part.

The total force applied to the part is found by integration over the volume of the part

$$\text{F (t)}={\displaystyle \int \text{[}}{\text{f}}_{\text{21}}\text{(r}\text{, t)}+{\text{f}}_{\text{2}}\text{(r}\text{, r)] dr *}={\text{F}}_{\text{21}}\text{(}t)+{\text{F}}_{\text{2}}\text{(t)}\text{.}\text{(3)}$$

Note that in the case when the primary and secondary current pulses have opposite polarity, the components of the forces F ₂₁ and F ₂ normal to the surface of the sheet have different signs (moreover, F ₂₁ acts in the direction of the electromagnetic system, and F ₂ in the opposite direction) :

$${\text{F}}_{\text{N}}\text{(f)}={\text{F}}_{\text{N21}}{\text{(t) -F}}_{\text{N2}}\text{(t)}\text{.}\text{(four)}$$

where F _N21 (t)> 0 and F _N2 (t)> 0.

Then the normal component of the mechanical impulse embedded in the part by the Ampere force and directed towards the electromagnetic system can be estimated as

$$\text{p}={\displaystyle \int {\text{F}}_{\text{N}}\text{dt}}={\displaystyle \int {\text{(F}}_{\text{N21}}{\text{-F}}_{\text{N2}}\text{) dt}>\text{0}}\text{.}\text{(5)}$$

. Заметим, что в силу линейности уравнения (2) вторичное магнитное поле каждого из импульсов последовательности просто в N раз меньше одиночного импульса при сохранении временной зависимости и пространственного его распределения как вне, так и внутри детали $$B_2^{\text{'}}(r,t)=\raisebox{1ex}{$B_2(r,t)$}\!\left/ \!\raisebox{-1ex}{$N$}\right.$$

. Тогда последовательность из N импульсов тока передаст детали механический импульсNow, instead of a single pulse of a secondary current, we consider a sequence of pulses. Moreover, for simplicity, we assume that N identical pulses of the secondary current (magnetic field) have the same shape as a single one, considered above, but have a current amplitude N times smaller: $$I_2^{\text{'}\text{'}}=\raisebox{1ex}{$I_2$}\!\left/ \!\raisebox{-1ex}{$N$}\right.$$

. Note that due to the linearity of equation (2), the secondary magnetic field of each of the pulses in the sequence is simply N times less than a single pulse while maintaining the time dependence and its spatial distribution both outside and inside the part $$B_2^{\text{'}\text{'}}(r,t)=\raisebox{1ex}{$B_2(r,t)$}\!\left/ \!\raisebox{-1ex}{$N$}\right.$$

. Then a sequence of N current pulses will transmit a mechanical impulse to the part

$$p\text{'}\text{'}={\displaystyle \int F_{N}dt={\displaystyle \int \left(F_{N21}-\frac{F_{N2}}{N}\right)dt>p.\left(6\right)}}$$

A comparison of expressions (5) and (6) for mechanical pulses shows that a sequence of N pulses of a secondary current allows a larger mechanical pulse and, therefore, a greater strain energy of the part to be enclosed than a single current pulse. This result is valid only in the case of predominantly opposite directions of the magnetic field. In option [13], the crushing of the secondary pulse, on the contrary, leads to a decrease in efficiency.

, где L - индуктивность электромагнитной системы. Отсюда мы видим, что при уменьшении амплитуды тока в N раз соответственно уменьшается и амплитуда напряжения в каждом из импульсов последовательности. Тогда энергия, вложенная вторичным источником тока во всю последовательность импульсов оказывается в N раз меньше, чем энергия для одиночного импульса вторичного тока. Таким образом, мы показали, последовательность импульсов вторичного тока более эффективна, чем одиночный импульс.The voltage amplitude of the secondary current pulse can be estimated as $$\text{U}=\text{L}{\dot{I}}_2$$

where L is the inductance of the electromagnetic system. From here we see that with a decrease in the amplitude of the current N times, the voltage amplitude in each of the pulses of the sequence also decreases. Then the energy invested by the secondary current source in the entire sequence of pulses turns out to be N times less than the energy for a single pulse of the secondary current. Thus, we have shown that the sequence of pulses of the secondary current is more efficient than a single pulse.

The amplitude of a single pulse in a sequence cannot be reduced indefinitely, since a single pulse of a secondary current in a sequence must create a mechanical force leading to plastic deformation of the part.

The electromagnetic system can be made in the form of a conventional wire coil of strong magnetic fields [14] or in the form of a roll of metal sheet with an insulating pad, possibly with special cutouts for magnetic flux concentration [4-7]. It is also possible to use flat spiral coils, including multilayer and complex shapes, as proposed in the prototype [3].

To increase the efficiency of the electromagnetic system, it can be equipped with a single-turn magnetic flux concentrator, which is widely used in the technique of strong pulsed magnetic fields [14] and, in particular, in magnetic pulse processing of materials ([15] I.V. Bely, S.M. Fertik, L.T. Khimenko, Handbook of magnetic-pulse processing of metals, Kharkov, Vishcha School, 1977). Hubs used in patents can be used [11, 12].

In some cases, it is convenient to make a system in the form of two coils [8, 11, 12]. This does not fundamentally change the operation of the device, but it can increase its flexibility. For example, coils with a different number of turns can be made. A coil with a large number of turns is connected to the primary slow current source, and with a smaller number to the secondary one. Coils can be made isolated from each other or connected in series. A convenient option may be a coaxial coil arrangement [8].

To create a primary current pulse, you can use the sources proposed in the prototype [3] and subsequent works [8-10].

To create a sequence of powerful pulses of the secondary current, semiconductor elements capable of performing controlled switching on and off (IGBT transistors, lockable thyristors) can also be used. The second option of the secondary current source is a parallel connection of single pulse generators, which are now well developed in pulse technology. Each of these generators can consist, for example, of a capacitor and a controlled closing key made on the basis of a vacuum or gas-filled (thyratron) spark gap or semiconductor device (thyristor, reversibly switched dinistor). When the generators are triggered at different points in time, a sequence of pulses is formed.

It should be noted that to isolate the primary and secondary power sources, you can use the blocking inductance, connected in series with the primary source [8-10]. Its value is selected in such a way as to block the flow of secondary current in the circuit of the primary source. Crowbar circuit should also be used to block the recharging of capacitors of primary and secondary current sources [8-10]. To control the entire system as a whole, you should use a controller.

To straighten dents on a metal sheet (part), it is necessary to have a surface that gives the part its final shape [3]. For this, a replaceable dielectric template is used, the surface of which on the part side has a surface close to the desired shape. It is necessary to take into account the elastic unloading of the part after the impulse, therefore the shape of this surface of the template does not have to coincide exactly with the given one. Instead of the template, it is possible to form the required shape of the working surface of the dielectric base, in which the electromagnetic system is integrated.

The proposed device and method can be used to process parts from poorly conductive and dielectric materials. To do this, use a metal sheet superimposed on the part (satellite) [15]. As a rule, a soft sheet of copper is used as a satellite. The electromagnetic system acts on the satellite, which in turn carries away the workpiece. For the proposed device, a metal sheet (satellite) should be superimposed on the part from the side of the opposite electromagnetic system, i.e. The part must be between the satellite and the electromagnetic system. Then the movement of the satellite in the direction of the electromagnetic system will lead to deformation of the part.

The invention is illustrated by drawings.

In FIG. 1 schematically shows a device for drawing metal and removing dents,

in FIG. 2 - pulse shapes of primary, secondary and full currents.

A device for drawing metal and removing dents (Fig. 1) contains:

(a) the charger of the primary current source 1,

(b) the charger of the secondary current source 2,

(c) managed keys 3, 4, 5, and 6,

(g) a primary current source 7, consisting of a capacitor bank 8, a thyristor switch 9, and a cube diode 10,

(e) a secondary current source consisting of three sources of single current pulses 11, 12, 13, each of which consists of a capacitor bank 14, 15, 16 and a thyristor switch 17, 18, 19,

(e) blocking inductance 20,

(g) a controlled crowbar consisting of a thyristor switch 21 and a resistor 22,

(h) an electromagnetic system in the form of a coil 23, made of a roll of copper sheet with a dielectric gasket, which has a cutout for magnetic flux concentration, and adjacent to the part 24, which is a flat metal sheet with a dent,

(i) a dielectric template 25, which is a flat thin sheet of solid dielectric located between the electromagnetic system and the part,

(k) a controller 26 that controls the operation of keys 3, 4, 5, 6 and thyristor keys 9, 17, 18, 19,21.

The electromagnetic system 23 in this example is the working head. Previously, the working head 23 should be positioned relative to the workpiece 24 so that the dent to be removed is in the region of magnetic flux concentration (magnetic field lines are schematically shown in Fig. 1 by dashed ovals). The working head should fit snugly to the template 25, and the template to the workpiece.

An example of the construction of the device, including for implementing the method of drawing metal and removing dents, is presented in FIG. 1. Charger 1 has a charging voltage of 3 kV, charger 2 has a charging voltage of 15 kV, and the polarity of charger 2 is opposite to the polarity of charger 1. Charging capacitors 8, 14, 15, 16 is done before the start of the work cycle. Since charging time is not limited, charging currents may be small (less than 1 A). Therefore, controlled keys 3, 4, 5, 6 can be made on the basis of mechanical relay switches with a maximum permissible open-circuit voltage of 3 kV for a key 3 and 15 kV for keys 4, 5, 6. The capacitor 8 has a capacitance of 10 mF and a maximum allowable voltage 3 kV, capacitors 14, 15 and 16 have capacities of 1 μF at a maximum permissible voltage of 15 kV. The controlled key 9 is made on the basis of the thyristor T453-630 (32 cells). The DI153 diode is used as a crowbar diode 10. The keys 17, 18, 19, 21 are thyristor columns of TBI371-160 thyristors (at least 10 cells), 16 pieces each. Ballast inductance 20 has a nominal inductance of 60 μH and a maximum allowable voltage of 20 kV, resistor 22 has a nominal resistance of 0.5 ohms. The coil 23 is wound with a flat copper tape 0.45 mm thick with a 50 micron thick Kapton strip gasket (Kapton, Du Pont) similar to the design of the coil in the patent [4]. The coil length is 100 mm, the inner diameter is 20 mm, the outer diameter is 40 mm, and the cross section of the coil in the region of the maximum magnetic flux concentration is 20 × 10 mm. The effective inductance of the electromagnetic system is approximately 27 μH for the primary current pulse and 20 μH for the secondary current (at a frequency of 50 kHz). The calculation was carried out according to the methodology ([16] P.L. Kalantarov, L.A. Tsetlin, Calculation of inductances (reference book), L .: Energoatomizdat, 1986). The decrease in inductance for the secondary current pulse is due to the skin effect in the part. The inner frame of the coil is made of structural fiberglass, outside the coil is bandaged with ARMOS high-modulus high-strength para-aramid thread, the entire electromagnetic system is filled with an epoxy compound based on epoxy resin SEDM-3 with boron nitride filler. The polymerization should be carried out under vacuum with heating the resin to 80 ° C. As a template, a flat sheet of structural fiberglass 0.5 mm thick is used. The workpiece is a steel sheet (St.20) with a thickness of 0.8 mm, with a dent in the linear dimensions of not more than 20 mm and a depth of 5 mm. The controller is based on the National Instruments industrial modular control complex.

In preparation for operation, the keys 3, 4, 5, 6 are closed, so the capacitors 8, 14, 15, 16 are charged to the rated voltage of the chargers. Directly before the operating cycle, the controller opens the keys 3, 4, 5, 6.

The duty cycle begins by turning on the thyristor switch 9. The capacitor 8 is discharged through the inductance 20 to the coil of the electromagnetic system 23 and creates a primary current in it. Upon reaching the maximum of the primary current, the Crowbar diode 10 is turned on, which prevents the polarity reversal of the voltage across the capacitor 8. The pulse duration of the primary current is about t ₁ = 4 ms (see Fig. 2). The maximum primary magnetic field in the part area is about 8 T at a primary current of 20 kA. The depth of the skin layer of steel St.20 at a frequency of 100 Hz is more than 20 mm [15], therefore, the primary magnetic field almost completely penetrates the part without noticeable weakening and without deforming the part. Near the maximum of the primary magnetic field, the controller turns on thyristor switches 17, 18, and 19 sequentially at intervals of 150 μs. In this case, a sequence of pulses of a secondary current is generated, which in the coil of the electromagnetic system has a direction opposite to the primary. Near the maximum current of each of the pulses, the controller includes a controlled crowbar 21 and puts the discharge into aperiodic mode. The resistor 22 serves to reduce the duration of the trailing edge of the pulse. The duration of each pulse is about t ₂ = 12 μs (see Fig. 2). Since the inductance of the coil 23 is much smaller than the inductance of the blocking inductance 20, the current flows almost completely through the coil 23. The amplitude of the secondary current in it is at least 3 kA, and the amplitude of the secondary magnetic field is not less than 1.3 T. In pauses of current between pulses, the Crowbar key is turned off. In FIG. 2 shows schematically the primary current pulse I ₁ , the pulses of the single pulse generators I ₂₁ , I ₂₂ , I ₂₃ and the total current pulse in the coil of the electromagnetic system /.

, что в нашем случае составляет 7МПа. Внутреннее напряжение на краю деформируемой области в детали может быть рассчитано по стандартным выражениям: для круглой пластинки радиуса a и толщины h, шарнирно опертой по краю

([17] И.А.Биргер, Р.Р.Мавлютов, Сопротивление материалов, М.: Наука, 1986). При размерах а=10 мм, h=0,8 мм максимальное радиальное напряжение составляет более 1000 МПа, что значительно превышает предел текучести стали Ст.20. Поэтому на каждом импульсе из последовательности вторичных импульсов будет происходить пластическая деформация детали.The depth of the skin layer of steel St.20 at a frequency of 50 kHz is 0.85 mm, so the secondary magnetic field effectively creates induction currents and deforms the part. Assuming that the secondary field is completely shielded by the part, while the primary field penetrates completely through the part and that the lines of magnetic field induction are parallel to the surface of the part, the magnetic pressure on the surface of the part can be estimated as $$P=\raisebox{1ex}{$\left(B_2{B}_{\mathrm{one}}-B_2^2\right)$}\!\left/ \!\raisebox{-1ex}{${\mu }_0$}\right.$$

, which in our case is 7MPa. The internal stress at the edge of the deformable region in the part can be calculated using standard expressions: for a circular plate of radius a and thickness h pivotally supported along the edge

([17] I.A. Birger, R.R. Mavlyutov, Resistance of materials, Moscow: Nauka, 1986). With dimensions a = 10 mm, h = 0.8 mm, the maximum radial stress is more than 1000 MPa, which significantly exceeds the yield strength of steel Art.20. Therefore, at each pulse from the sequence of secondary pulses, plastic deformation of the part will occur.

Note that the mass of the electromagnetic system is about 1 kg, which allows the working head to be implemented as a separately moved and even portable unit.

Instead of using a source of secondary current, consisting of several parallel-connected generators of single current pulses, as shown above, it is possible to use a source of sequences of current pulses based on IGBT transistors. So, for the example discussed above, you can use the assembly of 7 sequentially connected modules MTKI-1000-25 manufactured by JSC "Electric rectifier". Note that, unlike thyristors, these IGBT modules have very short turn-on and turn-off times (less than 3 μs), which allows the formation of sequences of secondary current pulses that are diverse in number and duration using a single key.

Claims (17)

1. Device for electromagnetic extraction and elimination of dents, containing an electromagnetic system for creating pulsed magnetic fields in the workpiece, a primary pulse current source connected to an electromagnetic system to create a slowly varying primary magnetic field pulse, a secondary pulse current source also connected to an electromagnetic system to create a rapidly changing pulsed secondary magnetic field during the pulse of the primary magnetic field, and tion of the secondary magnetic field is preferably opposite to the direction of the primary magnetic field, characterized in that the secondary power source is a generator of a sequence of two or more current pulses. 2. The device according to claim 1, containing the above-mentioned electromagnetic system, made in the form of a coil, which is made of an electrically conductive material, the turns of which are electrically isolated from each other and from the workpiece, and the primary and secondary current sources are connected in parallel to its terminals. 3. The device according to claim 1, containing a magnetic flux concentrator in an electromagnetic system. 4. The device according to claim 1, characterized in that the electromagnetic system is made in the form of two coils made of electrically conductive material, the turns of which are electrically isolated from each other and from the workpiece, with a primary current source connected to the terminals of the first coils, and the terminals the second coil - secondary current sources. 5. The device according to claim 1, characterized in that the electromagnetic system is made in the form of two coils made of electrically conductive material, the turns of which are electrically isolated from each other and from the workpiece, while the coils are connected in series, forming one common conclusion for both coils and two external terminals, and have the same winding direction, with the common terminal of both coils and one of the external terminals connected to the secondary current source, and both external terminals to the primary current source. 6. The device according to claim 1, characterized in that the secondary current source is made in the form of a set of parallel-connected sources of single current pulses starting at different points in time. 7. The device according to any one of claims 1 to 6, containing a dielectric template that is installed between the electromagnetic system and the workpiece and the surface shape of which on the part side is approximately corresponding to the desired final shape of the workpiece. 8. The device according to any one of claims 1 to 6, containing a dielectric base, in which an electromagnetic system is integrated, the shape of the working surface of the dielectric base adjacent to the workpiece, approximately corresponds to the desired final shape of the workpiece. 9. The device according to any one of claims 1 to 6, containing a working head in which the electromagnetic system is located and which is made in the form of a separate movable unit equipped with handles or a holder for fixing its position relative to the part. 10. The device according to any one of claims 1 to 6, characterized in that it contains an additional inductance, which is connected in series with the primary current source for electrical isolation of the primary and secondary current sources. 11. The device according to any one of claims 1 to 6, containing a controller for controlling and synchronizing the operation of its nodes. 12. The method of electromagnetic extraction and elimination of dents, which consists in the fact that the working surface of the working head containing the electromagnetic system to create a pulsed magnetic field in the workpiece is positioned relative to the workpiece, and then by passing the primary current through the electromagnetic system create a pulse of slowly changing primary magnetic fields, then passing a secondary current through an electromagnetic system creates a rapidly changing secondary pulsed magnetic les within the primary pulse magnetic field, the direction of the secondary magnetic field is set mainly opposite direction of the primary magnetic field, characterized in that the secondary pulse magnetic field is formed as a series of two or more pulses. 13. The method according to p. 12, characterized in that the electromagnetic system is made in the form of two separate coils made of electrically conductive material, and the primary current is passed through one of the coils, and the secondary current is passed through the other. 14. The method of claim 12, comprising the step of manufacturing a magnetic flux concentrator in an electromagnetic system. 15. The method according to item 12, comprising the step of installing a dielectric template between the electromagnetic system and the workpiece. 16. The method according to any one of paragraphs.12-15, comprising the step of manufacturing a working head in the form of a separate movable assembly. 17. The method according to any one of paragraphs.12-15, characterized in that for processing the part with low electrical conductivity, a metal sheet is preliminarily applied to it from the side opposite to the location of the working head.

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