Spot welding device

  The advantage of spot welding is undeniable when welding small parts. With the same quality of the welded joint, energy costs are reduced several times. The proposed device is indispensable for welding sheet parts up to 1 mm thick or rods, wires up to 4 mm in diameter. These parameters are determined by the geometric dimensions and thermal conductivity of the material.

Functionally, the proposed device consists of three units: 1 - control unit; 2- welding transformer; 3 - contact welding unit.

Main technical parameters

 

Supply voltage. ... ... 220 V, 50 Hz Output voltageтрансформатор в устройстве аппарата точечной сварки

idling ……… .4 - 6 V

Maximum pulse welding current …… .. Up to 1500 A

For the manufacture of the control unit you will need transformer with a power of 10 - 20 W with a voltage of the mains winding of 220 V, 50 kHz and a voltage of the secondary winding of 15 - 25 V; a set of electrolytic capacitors of the K50-35 type; reed relay type RES42; RES43; RES55 or other electromechanical with low operating current and operating voltage 15 - 25; switch button type KM-1 or other; block of switches type P2K for independent switching on for 5-6 positions for connecting capacitors when selecting the welding cycle time; diode bridge for charging capacities with constant voltage, type KTs402 - KTs407; variable resistor with a power of 1 - 3 W of group A or wirewound.
The main part of the control unit is the MTT4K power switch - a single-phase non-contact thyristor starter for a current of 40 - 80 A and a voltage of 600-800 V.
For the manufacture of power welding transformer T2 (Fig. 1) the magnetic circuit is taken from the faulty laboratory autotransformerby 2.5 A. Having removed the old winding, we cut out two washers from electrical cardboard 0.5-1.0 mm thick, which we put on the ends of the magnetic circuit with an overlap of 1-2 mm along the inner and outer diameters, followed by bandaging with varnished cloth or similar material. less than three layers to achieve electrical and mechanical strength, preventing destruction and rubbing of the mains winding on the magnetic circuit during operation. The diameter of the wire of the mains winding is chosen 1.2-1.5 mm, preferably in fabric insulation for better impregnation with varnish.

We lay the wire turn to turn evenly along the entire perimeter of the magnetic circuit according to Fig. 2.

After winding the primary winding, it is bandaged with cotton tape or the like.

The secondary winding contains 4-7 turns of copper stranded wire with a diameter of at least 20 mm and a cross-section of at least 300 mm2 in silicone insulation or a similar bundle. On the ends of the winding, put on the appropriate lugs, followed by soldering to achieve the minimum resistance of the contact transition.

The contact-welding unit is manufactured taking into account the requirements for the technological process. The material for the electrodes can be copper, beryllium bronze and their substitutes. To create a high-quality welding core, the contact area of the electrode should be minimal, and it is also necessary to ensure a tight fit and compression of the parts to be welded with a force of at least 20 kg / cm2 (this force is selected when working out the technological process).

When assembling the device, special attention must be paid to the quality of the connections to obtain minimum losses on the contact resistances.

Operating procedure

When the KN-1 contact or any of the P2K switches is closed, the selected capacitance C1-Cx is charged to a supply voltage of 15-30 V, and after pressing KN-1, the charge circuit is opened, and the K1 - RES discharge circuit is connected. The value of the capacitance, and, consequently, the energy stored by it, determines the holding time of the RES relay in a closed state, i.e. the time of the welding cycle by passing the power current through the MTT4K 80-8 power switch from several to tens of periods of the mains voltage.

In order to reduce the number of capacitors and P2K switches for selecting the welding cycle time, they can be assembled in a parallel circuit. Approximate ratings of capacities C1 and C2 at 47 μF, C3 and C4 at 100 μF, C5 and C6 at 470 μF, all capacities for an operating voltage not lower than a charging voltage of 30 V. A more accurate welding cycle time is selected with a variable resistor R2.

Coarse adjustment of the welding current is carried out by switching the taps of the power transformer T2.

Power switch MTT4K (Fig. 3) is a potential-free thyristor-diode module in a unified MTT4 case. The control current flowing through the relay contacts does not exceed 100 mA.

The MTT4K power switch must be installed on a cooling radiator with an area of 400-600 cm2 or use the heat-dissipating area of the device body, not forgetting that there is a mains voltage on the power contacts and control contacts.

 A.I.Sapronov (Based on the materials of the magazine "Electric")
 
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