SU1593817A1 - Method and apparatus for forming a.c.welding current - Google Patents

Abstract

The invention relates to mechanical engineering and can be used as a power source for an alternating current welding arc mainly in argon-arc welding of light alloys. The aim of the invention is to improve the quality of welding, the reliability of the switching process and the reduction of switching losses at the power source. The process of switching the current when changing polarity occurs in three stages: initially reduce the current to the minimum level of steady arc, then switch the polarity of the current while maintaining its absolute value, and after fixing the presence of arc voltage of the other polarity increase the current to given polarity values. The device contains a controlled direct current source, a low-frequency bridge inverter and a control unit. The control unit is equipped with a current switching control unit and a programmer. The switching control unit of the polarity unit includes the inverter control pulse shaper, the elements for fixing the minimum welding current and arc voltage, and the delay element. The first output of the programmer is used to set the amplitude and duration of the current flow during direct and reverse polarity, the second output - to set the amplitude of the minimum current of steady arc burning. In each arm of the bridge low-frequency inverter, a powerful thyristor and a low-power transistor, designed for the minimum current of stable arc, are installed in parallel. The invention makes it possible to reduce the mass of the device and improve the quality of the welded joint by forming rectangular pulses of the welding current. 2 sec. and 5 hp f-ly, 4 ill.

Description

The invention relates to the field of welding production and is intended as an AC power source primarily for argon arc welding of light alloys.

The goal is to improve the quality of welding, the reliability of the switching process and the reduction of switching losses at the power source.

Fig. 1 is a block diagram of the power supply of the welding circuit from a source of a permanent welding current through a low-frequency inverter; Fig. 2 are time diagrams of the voltage setting Uj. of the direct current, the current at the output of the direct current source i- and alternating current of almost rectangular form i- in the welding circuit at the output of the inverter; in fig. 3 is a block diagram of a device for forming a variable current; in fig. t is a block diagram of a device with a thyristor-transistor-inverter.

Controlled direct current source 1 through a low frequency inverter

2 connected to the welding circuit 3. In FIG. 1 shows the welding electrode and the product 5 V welding circuit

3An alternating current is supplied after the inverter. The value of the direct current at the output of the controlled direct current source 1 is determined by the magnitude of the voltage and the current reference from the current (fig 2).

The method is carried out as follows.

At the moment of time tg (Fig. 2), a voltage setting is set, which determines the magnitude of the current Ig, n in the alternating current period of direct polarity. The growth of the direct current i at the source output and the corresponding increase in the alternating current i in the welding circuit begin. At time t, the current increase terminates and a current with amplitude is established in the welding circuit. The interval t, - t (J depends on the speed of the source: the higher the speed, the smaller the interval, At time tj, after the end of the direct polarity current interval, the voltage U d is set, which determines the value of the minimum steady-state current of the arc IMHIC of constant and alternating currents up to the value of At the moment of time t, when the current drops to the Ifti value, with some delay (instant tj}), the low-frequency inverter switches the polarity of the current. After fixing the constant excitation of the arc At another Polarity (moment 15-), the voltage UQ of the reference is set, which determines the current amplitude during the period of inverse polarity IQ. In the interval tj-tg, the current increases to i (, „. After the end of the current interval

polarities (tt moment) again set the voltage of the task to 4. . Further, the process of switching the polarity of the current is carried out according to the previously discussed method.

A device for implementing the proposed method (FIG. 3) contains a controlled source of direct current 1, a low-frequency inverter 2, a welding circuit 3, a unit 6 for controlling the device. The device control unit 6 contains the programmer 7 - and the current switching polarity control unit 8. The programmer 7 has two outputs and one clock input. The first output of programmer 1 (7) is the output of the amplitude and duration of the current during the periods of direct and reverse polarity, and it is connected to the input of the controlled direct current source 1, to the second output (Vyho 2) - signal set the amplitude of the minimum current steady arc and it is connected to the input of the node 8 control switching current polarity. The current polarization control node 8 contains the driver of the inverter control pulses 9, latching elements of the minimum current 10 and arc voltage 11 with corresponding current sensors 12 and voltage 13. Between the output of the latching element 10 and the inverter control pulses 9, the inverter pulses can be set-delay element.

A controlled direct current source can be a welding rectifier, as in a known device or to reduce weight and improve the quality of a welded joint by reducing the duration of current pulse fronts (t, - tgj t - t, figure 2) can be made on the basis of high-speed high-frequency thyristor or transistor converter welding converter.

Low-frequency bridge inverter 2 can be implemented on various elemental base, for example, on powerful thyristors with inductive-capacitive switching, on powerful transistors. Inverter 2 can be performed on the basis of a more reliable and cost-effective thyristor-transistor circuit. In each arm of the bridge low-frequency inverter 2, a powerful thyristor connected in parallel is installed

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(), calculated on the full welding current of the installation and low-power transistor (19-22), calculated on the minimum current of a stable arc. In this case, a delay element lA must be entered into the current switching control unit 8. This will allow the moment when the current reaches the minimum level of powering on switching on low-power transistors and turning off powerful thyristors in the operating arms of low-frequency inverter 2 (Fig.) And after restoring the locking properties of off thyristors to switch the polarity of low-power transistors; After fixing the arc voltage at a different polarity, the thyristors are turned on, the transistors are turned off in the inverter shoulders operating at this polarity, and the current is further increased to a predetermined value. The time delay of the delay element 1 must be matched with the time of switching off the thyristors, but for reasons of stable arc burning during argon-arc welding, it should not exceed 100 µs.

A direct current source 1 is connected via a current sensor 12 to a low-frequency inverter 2, which is connected to Welding circuit 3 via an arc voltage sensor. Programmer 7 is connected to the input of controlled DC source 1 by its first output, and the second output is connected to element 10 of fixing the minimum current, which directly or each element of the delay element I is connected to the shaper 9 of the inverter control pulses. The arc voltage clamping element 11 is connected to the clock input of the programmer 7. The current sensors 12 and voltage 13 are connected respectively to the inputs of the 10 and 11 elements of the minimum current clamping and arc voltage.

The device works as follows. i

Initially, the programmer 7 is set to the minimum steady arc current, and the position of the keys of the low-frequency bridge inverter 2 ensures that the current of the direct polarity passes through the welding circuit 3. When the welding circuit is closed, it establishes the minimum direct current

0

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five

0 5 0 5

0

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polarities, the voltage sensor 13 and the minimum arc voltage fixing element 11 are triggered. The programmer receives a signal at the clock input and outputs to the first output a reference signal Unn of amplitude t „duration t, - - 12 currents of direct polarity (Fig. 2). There is an increase (over time t,) of the current of the direct polarity to the specified amplitude value Ipj ,,. At the end of the duration of the current of the direct polarity (time t-), the programmer changes the current command by, In the time interval, t, the current drops to I , v, n. The element of minimum current fixation 10 triggers and sends a signal to the shaper 9 of the inverter control pulses, which, in the case of using a thyristor or transistor inverter, provides switching of the inverter shoulders and, therefore, polarity of the current. In the case of using a thyristor-transistor inverter (Fig. I), the driver turns off the thyristors and turns on parallel transistors in the inverter's working arms (for example, in the arms with keys 15, 19 and 1b, 20 in FIG.). Then, with a delay t - t (Fig 2), given by the delay element lA, the driver 9 of the inverter control pulses gives a signal for switching the polarity:. in the inverter 2, the transistors 19 and 20 are turned off and the transistors 21 and 22 are turned on. The minimum steady arc current with reverse polarity is set. The element 11 fixes the minimum arc voltage, which gives a signal to the clock input of the programmer 7, which gives the task U ,, amplitude i of duration tj- t-, reverse current :: th polarity. During the time, the current of reverse polarity increases to a given amplitude value of I cc, etc.

Due to the fact that the interval t (100 X) is incommensurably small compared to the duration of the pulse current t, - t and tj-- tg (about 10,000 ISS each), and the interval tj may be practically absent, the proposed method and device provide current of almost rectangular shape with instant polarity change at minimum current.

The implementation of the polarity change at minimum current allows to increase reliability and reduce losses when

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commutation. In the case of using a high-frequency converter, the mass is significantly reduced and the quality of the welded connection is improved. When using a thyristor-transistor inverter, the cost is reduced and the reliability of the power switching element (inverter) increases.

Example. Method of forming current in argon-arc welding at rated current IHOM 250 A.

Frequency of alternating current f ii ITs, T 25000 µs; ratio

between the forward and reverse polarity current tf, 0.6 T, tp O. i T.

The duration of the fronts and decays of the current at the direct polarity tc.n ti | J at the opposite polarity .o 0,1tp.

Delay duration: tijrCt, - C, FIG. 2) "On the ISS (for the circuit of Fig. With thyristors with a shutdown time of up to 32 μs); t, j (t4- tg, fig. 2) 10 μs

The minimum current of steady burning of the arc IMHH is 0.06 1 „, then t„ “CilSOOO μs; tq t 10,000 μs; t (p, -, tcn 1050 µs; tmo 0 UOOOO µs ;.

- 10 μs; 1m „n 15 A.

  tO μs;

H.

The proposed method and device can reduce the cost and improve the reliability of the power switching current device.

invention formula

Claims (7)

1. A method of forming an alternating welding current, which consists in inverting a constant welding current, so that it is, in order to improve the quality of welding, the reliability of the switching process and reduce the switching losses in the source power supply, when changing the field, 45 currents reduce the current to the minimum level of steady arc, then switch the polarity of the current, keeping I. its absolute value, And after fixing the presence of an arc voltage of opposite polarity, increase the current to magnitudes of magnitude. 2. The method according to p. 1, about t l and c a - y u and with the fact that the duration eight 0 five 0 five about 45 reducing the current and the duration of its increase set no more than 10 of the duration of the current pulse of the corresponding polarity. 3. Method of pop, 1, characterized in that the switching of the polarity is made with a time delay relative to the moment when the current reaches the minimum level of steady arc burning. t. A method according to claim 1 and 3, characterized in that the time delay of switching the polarity of the current during argon-arc welding is set to not more than 100 µs. 5. A device for forming an alternating welding current, comprising a controlled direct current source, current sensors and arc voltages, a low-frequency bridge inverter and a control unit, characterized in that, in order to improve the quality of welding, the reliability of the switching process and reduce switching losses, it is equipped with a programmer, and the control unit is made of series-connected elements for fixing the minimum current, the delay element and the driver for controlling the inverter, the second input of which is connected It is connected with the first output of the minimum arc voltage clamping element, the second output of which is connected to the clock input of the programmer, the first output connected to the input of the controlled DC source, and the second to the first input, the minimum current clamping element whose second input is connected to the output of the current sensor, and the input of the latching element of the minimum arc voltage is connected to the output of the arc voltage sensor. 6. The device according to claim 5, characterized in that the controlled source of welding current is designed as a high-speed high-frequency converter. 7. The device according to claim 5, characterized in that in each arm of the low-frequency bridge inverter there are installed connected in parallel a thyristor for the full installation current and a transistor for the minimum current of steady arc.