Welding is controlled by electronics. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / welding equipment

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Many metal structures are assembled using electric welding. I made several apparatuses for this purpose, and one turned out to be the most successful and convenient in operation. I bring to your attention a welding transformer with electronic current regulation. It has no moving parts that require high build quality and are subject to vibration. The control unit allows you to smoothly adjust the welding current by turning the potentiometer knob. At the same time, the arc burns stably over the entire range of changes.

Technical characteristics of the welding transformer with electronic current regulation:

• Supply voltage, V 220
• Limits of regulation of welding current, A 45 - 140
• Open circuit voltage of the power arc, V 42
• Open circuit voltage of the duty arc, V 87
• Make-up current, A 15

Figure 1 shows the electrical circuit of the welding machine. It includes: welding transformer T3; power rectifier on thyristors VS3, VS4; rectifier for powering the pilot arc on diodes VD6 - VD9, smoothing choke L1; control unit for power thyristors on transistors VT1 - VT5.

Rice. 1. Schematic diagram of a welding machine with electronic current control and mains power supply with a voltage of 220 V

The main arc is powered by a thyristor rectifier VS3, VS4; the value of the welding current is changed by changing the angle of switching on the thyristors.

When the power thyristors are closed, the welding arc current is provided by the feed circuit on the diodes VD6 - VD9 and the choke L1.

The power rectifier has a falling external characteristic. The pilot arc rectifier has a steeply falling external characteristic, and due to the inductor L1, a continuous current is maintained in the arc circuit, which ensures stable arc burning and prevents the electrode coating from shedding.

The control circuit consists of a power supply on transformer T1, a rectifier on diodes VD1, a synchronization circuit on transistors VT1 and VT5, a phase shifter on transistors VT3, VT4, a comparison unit on transistor VT2, a welding current meter circuit on a current transformer T4, power thyristor control circuits on thyristors VS1 and VS2.

The synchronization circuit on transistors VT1, VT5 is designed to discharge the capacitance C3 of the phase shifter at the beginning of each half-cycle of the mains supply voltage. At the moment when the mains voltage is 0, the base of the transistor VT1 will be 0 (it is closed), and VT5 is open and C3 is discharged; in all other cases, VT5 is closed.

At the beginning of each half-cycle of the supply voltage, the capacitor C3 is charged through VT2 and R8; at the moment when the voltage at C3 is equal to the voltage at the base of the transistor VTZ, it opens, VT4 and C3 are discharged to the I winding of the pulse transformer T2. From the windings II and III, a current pulse opens the thyristor VS1 or VS2 (the thyristor opens, on the anode of which there is a positive half-wave voltage). The control current from the winding III or IV of the transformer T1 through an open thyristor VS1 or VS2 is supplied to the power thyristor VS3 or VS4. Of these thyristors, one opens through the control electrode of which the control current flows. The latter is limited by resistors R14 or R15.

The welding arc current flows through the open thyristor VS3 (VS4), it is measured by the current transformer T4 and fed through the feedback circuit VD5, R17, C4, R18, R20, R7 to the comparison circuit on the transistor VT2. The voltage from the slider of the resistor R20 is compared with the voltage at point "A" of the comparison circuit. Transistor VT2 changes its internal resistance (it works in active mode) depending on the voltage difference at point "A" and on the engine of the resistor R20. If the current through the welding arc has grown more than set by the control unit, the internal resistance VT2 increases, the capacitor C1 charges more slowly, the switching angle of the power thyristors increases and, therefore, the current through the welding arc decreases.

If the welding current decreases below that set by the control unit, reverse processes occur: the switching angle of the power thyristors decreases and, consequently, the arc current increases. In this way, the welding current is regulated.

The welding arc current is set from the control panel by turning the R20 resistor slider. In the process of arc burning, the gap between the end of the electrode and the welding product changes, therefore, the voltage on the arc also changes. In some cases (with a large gap), it becomes greater than the no-load voltage of the power rectifier, and then the arc begins to be powered by the pilot arc rectifier, and the power thyristors close. In the event of a decrease in the length of the welding arc, the power thyristors will open again, since the control current flows through the control electrode of the thyristor during the entire half-cycle.

Transformer T1 can be of any power, but not less than 20 W, primary winding I - 220 volts, winding II - 24 volts, wire diameter not less than 0,13 mm, winding III and IV - 12 volts, wire diameter not less than 0,25 mm.

The T2 transformer is wound on a K20x10x5 core made of 2000NM ferrite. Its windings I, II, III - 50 turns of wire PEV-1 with a diameter of 0,2 mm.

The core of the T3 transformer is made of electrical cold-rolled steel grade 3404 with a thickness of 0,35 mm (dimensions are shown in Fig. 2). Winding I - 162 turns: two sections of 81 turns of copper wire with a cross section of 8 mm2 (2x4 mm). Each winding II and III - 32 turns each: consists of two sections of 16 turns of copper wire with a cross section of 15 mm2 (3x5 mm). Windings I, II, III are insulated with fiberglass impregnated with heat-resistant varnish. Winding IV, V - 93 turns of enameled wire with a diameter of 1,7 mm.

Rice. 2. Welding transformer T3 (electrical (a) and physical (b) layout of the windings on the magnetic circuit): 1 - winding I (two sections of 81 turns of copper wire with a cross section of 8 mm2); 2,3 - windings II and III (each - from two sections of 16 turns of copper wire with a cross section of 15 mm2); 4,7 - windings V and IV (93 turns of enameled wire with a diameter of 1,7 each); 5 - core (cold-rolled steel grade 3404, sheet s0,35); 6 - magnetic shunt

As a current transformer T4, a core was taken from a current transformer TK 200, 100/5. It has two primary

windings by one turn with a cross section of 15 mm2. As a wire, you can use a welding cable or other stranded wire in insulation. Secondary winding - 400 turns of enamel wire with a diameter of 0,5 mm. It is wound on the frame from the old secondary winding.

Choke core L1 - from electrical steel; the cross section of the magnetic circuit (passing through the winding) is at least 12 cm2 with a non-magnetic gap of 1 mm. The number of turns of enamel wire with a diameter of 2,24 mm is 68.

The electronic circuit is not critical to radio elements, with the exception of VTZ and VT4 (a pair of these transistors should be analogous to a dinistor). Resistor R20 must have a knob to control the welding current. Resistor R16 - PEV 10. Resistor R15 (R14) is assembled from three parallel-connected one-watt resistors of 47 ohms each.

Debugging of the welding transformer is carried out block by block. First, it is assembled and connected to the network through a fuse of at least 30 A. Then the voltage on the secondary windings is checked: on II and III - up to 45 volts, and it is necessary to turn them on according to; on windings IV and V - up to 90 volts (switching on also according to). In series with the power thyristors, the single-turn windings of the T4 current transformer are switched on so that it operates in the remagnetization mode.

After assembling the control unit, check the pulses at the output of T2 and the operation of the synchronization circuit. For convenience of testing, instead of the transistor VT2, parallel to R9, you should put a variable resistance of 20 kOhm and, by changing its value, check the change in the switching angle of the analog of the dinistor. Then the whole scheme is assembled. An ammeter with a total deflection current of 150 - 200 A is placed in the welding arc circuit. When welding metal, it is necessary to adjust the resistor R18 so that when the knob of the variable resistor R20 is turned, the welding current changes from 45 to 140 A.

Power thyristors are mounted on standard radiators; diodes VD6 - VD9 are installed on four radiators with an area of ​​30 cm2 each.

The welding transformer has been successfully and trouble-free in operation since 1993 to this day, the electronic control of the welding current is very convenient for welding, especially in different spatial positions of the weld.

Literature:

1. D. Priymak. To help the radio circle - Radio. 1989. No. 5. With. 79.
2. M.I. Zaks, B.A. Kagansky, A.A. Pechenin. Transformers for arc welding. Leningrad: Energoatomizdat. 1988
3. V.M. Rybakov. Arc and gas welding. - Moscow: "Higher School", 1986

Author: N. Zyzlaev, Samara

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