Portable machine for spot welding. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / welding equipment

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The portable small-sized electric welding machine with an external welding gun is designed for welding stainless and ordinary steel sheet with a thickness of 0,08 ... 0,15 mm to massive steel parts, as well as for welding steel wire with a diameter of up to 0,3 mm. It can be used in many sectors of the national economy, for example, in the manufacture of thermocouples, for welding strain gauges pre-glued onto steel foil to metal structures, and in many other cases. The appearance of the welding machine is shown on the 3rd p. tabs (top). The mass of the power unit of the device is about 8 kg, dimensions are 225x135x120 mm.

As can be seen from the circuit diagram, (Fig. 1) the device consists of two main components: an electronic relay on a trinistor V9 and a powerful welding transformer T2.

Fig.1 (click to enlarge)

A welding electrode is connected to one of the terminals of its low-voltage secondary winding, the second terminal is securely connected to the more massive of the two parts to be welded. The mains winding of the welding transformer is connected to the mains through a diode bridge V5-V8, the diagonal of which includes a trinistor V9 of an electronic relay. A low-power auxiliary transformer T1 feeds the SCR control circuit (winding ///) and the HI lamp for welding spot illumination (winding //).

The device works as follows. When the contacts of the switch S1 "On." the supply voltage of 220 V is supplied to the primary winding of the transformer T1 of the SCR control unit. Capacitor C1, connected through the closed contacts of switch S3 "Impulse" to the rectifier bridge V1-V4, is charged. The primary winding of the welding transformer T2 is de-energized, since the trinistor V9 is closed.

When the switch button S3 is pressed, the charged capacitor C1 is connected to the control electrode of the trinistor V9 through a variable resistor R1. The discharge current of the capacitor opens the trinistor, and the mains voltage is supplied to the primary winding of the welding transformer T2. If the secondary winding of the welding transformer is connected to the parts to be welded, then a powerful current pulse arises in it, which causes a strong heating of the metal at the point of contact of the welding electrode. The duration of the current pulse depends on the parameters of the timing circuit R1C1. With the values ​​of the elements of this purpose indicated in the diagram, the maximum pulse duration ti (without taking into account the internal resistance of the trinistor) is approximately equal to 0,1 s. During this time, the current in the secondary winding can reach 300 ... 350 A. This is quite enough for durable welding of foil parts up to 0,15 mm thick to massive structures, for example, from 1Kh18N10T alloy steel.

The device returns to its original state automatically at the end of the discharge of the capacitor C1. The optimal welding mode is set with a tuning resistor R1 "Mode".

Structurally, the welding machine consists of two parts: a power unit and a welding gun, which are connected to each other by a flexible cable using a multi-pin connector. Almost all elements of the device are located on the chassis of the power unit. The design of the chassis and its main dimensions are shown on the masonry.

Fig.2. Power block cover

Fig.3. Power block design

On the basis of chassis 3, a welding transformer 4 and strips with diodes V1-V8 are placed. A bracket 8 is attached to the front panel of the chassis with an auxiliary transformer 5, a capacitor 6 and a trinistor 7 installed on it. On the front panel, one of the connector parts (in a rectangular hole) of the connecting cable, a variable mode setting resistor, a power toggle switch, and a pin part of the power cord connector are mounted. and a clamp for connecting - the more massive of the parts to be welded. The casing 1 is made of duralumin with a thickness of 2,5 mm and is equipped with a handle 2 for carrying.

The device of the welding gun is shown in the figure.

Fig.4. Welding gun device

The body 7 of the gun is made in the form of two parts of the same shape, milled from sheet textolite 12 mm thick. The holder 3 of the welding electrode 2 is mounted in the housing. the lamp 8 of the backlight with a push-button switch 4 "Illumination", a microswitch 6 "Impulse". The connecting cable 5 is a flexible twenty-four-wire rubber-insulated cable with an outer diameter of 11 mm and a cross section of each wire of 0,75 mm square. Five wires of the cable are used to connect the microswitch and the backlight, and the remaining nineteen wires are soldered directly into the holder 3 of the electrode. The holder is made of a copper bar of rectangular or square section. Electrode 2 is a copper bar with a diameter of 8 mm. The electrode must be securely fixed in the holder. At the same time, it should be possible to change the electrode. To weld the foil, the electrode tip is sharpened with a cone turning into a sphere with a diameter of 1 ... 1.5 mm. An electrode with a flat working highlander is used to weld the wire.

Installation of the gun begins with cutting the cable. Nineteen cable conductors are carefully stripped, twisted together, tinned and soldered into the hole of the electrode holder 3. The remaining five wires are cut to the required length and soldered to the microswitch 6 and the backlight lamp 8. The other end of the cable is inserted into a 20-pin type A plug-in connector (cable structure, see photo on the inset). The pistol uses an MPZ-1T microswitch, an SM-34 backlight for 6 V, 0,25 A with an armature equipped with a small lens, a backlight switch button - from a desk lamp.

The mating part of the connecting cable connector is installed on the front panel of the chassis of the power unit. Five corresponding pins of the connector are connected to one or another circuit of the device, and the rest are connected in parallel and connected to one of the outputs of the secondary winding of the welding transformer.

Fig.5. Appearance of the device

The magnetic core of this transformer is assembled from Sh40 plates, the thickness of the set is 70 mm. The primary winding contains 300 turns of PEV-2 0,8 wire. The secondary winding of this transformer consists of 10 turns of insulated wire or bus with a cross section of at least 20 sq. mm (in the described design, this winding is made of two stranded conductors with a diameter of 4 mm, wound simultaneously). The "grounding" connecting conductor of the secondary winding is made of the same section. Its length should not be chosen greater than 2 ... 2,5 m.

Transformer T1 can be any one that provides 8 ... 10 V on the secondary windings (to charge the capacitor C1) and 3 ... 6 V (to power the lamp). In this design, a magnetic circuit was used from the transformer of the children's railway (section 10x10, L-shaped plates). A network winding / containing 8000 turns of wire PEV-2 0,08, a winding //-330 turns of wire PEV-2 0,3 and a winding ///-350 turns of wire PEV-2 0,2 are placed on it.

The clamp connected to the lower (according to the diagram) output of the secondary winding of the transformer T2 is mounted on the chassis without insulating gaskets.

When manufacturing transformers, it must be borne in mind that the safety of the person working with the device depends on the quality of the insulation of their windings. Therefore, over the primary (network) windings of transformers, at least 4-6 layers of varnished cloth or paraffin-impregnated paper should be applied.

The welding machine uses a trimming resistor PPZ-11, a K50-3 capacitor, and a TP1-2 network toggle switch. It should be noted that the use of the PTL-50 trinistor is due solely to the desire to ensure the high reliability of the device and trouble-free operation in difficult climatic conditions and with large fluctuations in the mains voltage. With some deterioration in the quality of welding, trinistors of the KU202 series with indices K, L, M or N can be used in the apparatus. In this case, it is necessary to reduce the resistance of the resistor R1 to 50 Ohms, and double the capacitance of the capacitor C1.

A properly assembled device starts working immediately, without any adjustment. The quality of the weld (points) is checked as follows. A strip of steel foil 10 ... 12 mm wide is welded to the surface of the steel bar cleaned of scale with three to five points, and then torn off with pliers. Holes with a diameter of 0,5 ... 0,8 mm should remain at the welding points on the foil, which indicates that the separation does not occur at the welding site, but around it. If the foil is torn off at the welding site, the welding current is selected with the trimming resistor "Mode". When selecting the current, it must be taken into account that the quality of the weld deteriorates with increasing pressure on the electrode.

It should also be noted that, according to reference data, the constant voltage that must be applied to the control electrode of the PTL-50 trinistor to open it is 8 V. However, the quality of the seam improves significantly if this voltage is increased to 12 ... 15 V (charged capacitor voltage C1).

How to use the device

First of all, they “ground” the casing of the welding machine and the structure to which the part must be welded. The person working with the welding machine must wear protective rubber gloves and stand on a rubber mat. The apparatus is turned on, the part to be welded is applied to the structure and firmly pressed with the tip of the welding electrode of the gun in the place where the weld point is to be obtained. They press the "trigger" of the pistol (on the microswitch button), after 1 ... 1.5 s they remove the pistol from the part and set the sting to the next point. In cases where necessary, turn on the backlight.

When operating the machine in production, it must be approved by the local safety committee.

In conclusion, it should be noted that the capabilities of the apparatus can be significantly expanded. If you use, for example, a copper-plated graphite electrode with a diameter of 6 ... 8 mm, you can weld tinned copper conductors with a diameter of up to 0,3 mm. Very well, such conductors are welded to any tinned and silver-plated parts, as well as to untinned copper foil. It is possible, for example, to weld thin conductors to printed circuit board foil without the use of flux. Good results have been obtained when welding sheets of very thin copper foil. In this case, it is necessary to experimentally select the length and shape of the graphite electrode tip.

If it is necessary to weld parts from thicker sheet metals, the welding transformer will have to be replaced with a more powerful one. For example, to connect steel sheets with a thickness of 0,5 ... 0,7 mm, a transformer with a magnetic circuit cross section of at least 65 ... 70 sq. cm is required. The primary winding of such a transformer should contain 160-165 turns of PETV wire with a diameter of 1,62 ... 1,7 mm, and the secondary - 4,5 turns of a copper bus with a cross section of at least 90 sq. mm (based on a welding current of 1400 ... 1800 A). The electrode diameter must be increased to 18...20 mm. At the same time, a current of about 45 A flows in the primary winding of the transformer at the time of the welding pulse. Therefore, the V5-V8 diodes will need to be replaced with more powerful ones, for example, VL-50.

The trinistor V9 must also be designed for a direct current of at least 50 A. Experience, however, shows that for welding steel sheets up to 0,5 ... the pulse is very short.

In order to ensure the nominal mode when welding metals of various thicknesses (from 0,08 to 0,7 mm), it is necessary to provide for a wider regulation of the welding current in the device. It is most advisable instead of capacitor C1 to use a set of three capacitors with a capacity of 1000 microfarads each, switched by a switch either in series (for sheet metals) or in parallel.

Author: V. Papenin; Publication: N. Bolshakov, rf.atnn.ru

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