A simple welding machine. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / welding equipment

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The semi-automatic welding machine (SAW), considered in [1], has the following disadvantages (see the corrected diagram in Fig. 1).

(click to enlarge)

1. Presence of contactor K3. A contactor of this type is a scarce part. In addition, it tends to burn constantly, which leads to unsatisfactory spa results.

2. The presence of rheostats R2, R5. Since the rheostats are made on the basis of nichrome wire and have large dimensions (especially R2), which means open surfaces, it is dangerous to use the spa in domestic (garage) conditions, due to the fact that it can cause electric shock (although not high voltage).

3. Dependence of the wire feed on the installed current. Since Fusion welding is mainly used for welding thin joints, such as metal instrument cases, car bodies, mufflers, thin-walled metal pipes, some of the requirements for a simple Fusion can be simplified.

Simplicity and reliability. Maintaining performance at an ambient temperature of -30 to +30 ° C and a mains supply voltage of 190-280 V.

The feeder can be placed in the same housing with the welding transformer and controls. Ensure good welding of metals with a thickness of 0,3-1,2 mm.

Work according to a rigid characteristic [2].

Given the above requirements, the main elements of the SPA can be selected from common parts. For example, the author has repeatedly used engine 1 and gearbox 2 of the feeder from the windshield wiper of the car "Volga GAZ-24" (Fig. 2). Since this motor does not have an electric brake and a reverse winding, the author installed an electric brake in the form of a U-shaped core of a solenoid coil 3 (Fig. 2, a), with a gap between the core and the roller of 0,5 mm. The wiper mechanism can be borrowed from trucks, which will favorably affect the electronic circuit, since they have 24 V on-board power.

Schematic diagram of the SPA is shown in Fig.3. The voltage of 220 V through the SА1 packet switch is supplied to the toroidal transformer, which has two primary windings for switching and regulating the voltage on the secondary winding when welding thick metal structures. To increase the control range, a larger number of additional taps are made in the primary winding.

(click to enlarge)

To weld metals with a thickness of 0,7-1 mm, the voltage on the secondary winding must be at least 40 V. The control circuit is powered from a 27 V output. HL14 signals power on. Capacitors C1 and C1 are needed to suppress interference generated by the welding current. In the initial state (SA2 - not pressed), there is no voltage of 2 V at the output of the power rectifier VD1, VD2, VS1, VS2 and on capacitors C5-C10, i.e. there is no voltage at the tip of the sleeve (this factor differs from some of the factory options). The control circuit will be energized and 40/27V is present at C14. When you press the microswitch SA4 (located on the sleeve holder Fig. 2), relay K3 is turned on. Contacts K1 and K1.1 are closed, thyristors VS1.2, VS1 are unlocked by control electrodes (GE) in the circuit: upper output C2, VD2, L1, welding current, K1, R1.1, VD4, UE VS4, KVS2, lower output C2 with a positive half-wave in the secondary winding of the supply voltage transformer; lower terminal C2, VD2, L2, welding current, contacts K1, R1.2, VD3, UE VS3, KVS1, upper terminal C1 with a negative half-wave voltage.

When setting up, instead of welding current, you can connect a nichrome wire with a resistance of 1 ohm. Resistors R1 and R2 are needed to limit the voltage on the control electrodes of thyristors VS1, VS2. Contacts K1.3 are closed, the wire feed and the gas cutter K3 are switched on through the diode VD12. Contacts K1.5 are closed, C11 is charged to a voltage of +27/14 V. At the end of the welding process (SA2 is not pressed), contacts K1.1, K1.2, K1.3, K1.5 open, and K1.4 closes, and C11 is discharged along the circuit: + C11, K1.4, R6, K2, -C11. Relay K2 closes contacts K2.2, K2.1 (thyristors VS1, VS2 are on), K2.4 (gas cutter K3 is on), K2.3 (electric brake is on).

Since the process is mechanically inertial, the wire does not stop immediately, so it is necessary to keep the arc burning and blowing it with carbon dioxide so that the wire burns and the seam has a normal appearance. As soon as the capacitor C11 is discharged, K2 opens its contacts and turns off the thyristors and the gas cutter.

As is known [2], for ignition of an arc on the electrodes, it is necessary to have a large potential difference, and only after ignition, a large current supports the arc. When thyristors VS1, VS2 are unlocked, the voltage at the tip of the sleeve holder does not increase immediately (this is prevented by the choke L1 and the capacitances of capacitors C5-C10. To increase the initial voltage amplitude, resistors R7-R12 with a resistance of 0,1 Ohm are connected in series with each capacitor, and L1 is connected in parallel capacitor C12, which must be selected empirically so that the arc ignites normally and the thyristors are normally (when SA2 is off) locked in. If the thyristors are not locked immediately or unwanted voltage fluctuations occur during the welding process (thyristors can spontaneously lock or unlock at the end of welding), then the capacitance of the capacitor C12 must be reduced or completely removed.

Design. SPA is assembled in one body: control circuit and feed mechanism. On the back wall of the case 14 (fig. 4) there is a fan 1 (M1 fig. 3), which blows over the toroidal transformer 5 and the power rectifier 9. On top of the case there is a power switch 13 and a fuse 12 (they are also often installed on the front panel of the spa) . The control logic circuit 11 is assembled on the front panel (it is attached to the panel itself), on the front side there is an HL1 lamp 10 and a wire feed regulator 7. The wire feed mechanism and the wire drum 8 are installed above the throttle 6. Carbon dioxide is supplied from the cylinder 2 through the reducer 3 through hose 15 to the gas cutter located next to the wire feeder. After the cutter, the gas is supplied to the sleeve 4, in which the wires from the microswitch 16 also pass and to which the power wire from the throttle L1 is connected. It is desirable to equip the SPA case with turning wheels 17 for ease of movement, the power cord 18 must be taken from power units with a current of at least 10 A.

Figure 2 shows the assembly drawing of the feeder. Since the mechanisms can be used different, the dimensions are not indicated. Engine 1 (Fig. 2, a, connected as shown in Fig. 3) drives gearbox 2 and roller 3, mounted on the shaft of the gearbox (reduction gearbox). From the drum 10 (in Fig. 2, a it is shown schematically, it can be installed both vertically and horizontally) the wire 18 through the square of felt 11 (required for removing dirt), the spring 6 (borrowed from automobile oil seals) and the guide sleeve 19 enters the bearing 9. The bearing, using the bearing holder 5, is pressed against the roller 3, due to the tightening of the screw 20. Next, the wire goes along the guide 7 into the sleeve 8. The sleeve 8 is inserted with the fitting 17 into the clamp 16. The current is supplied to the tip of the sleeve from the choke L1 through the cable through the washer 12, sleeve fitting and inner braid. To brake the wire, a U-shaped electromagnet 3 (the core is made of the stator of the electric motor) is installed in front of the roller 4, which is fixed with screws 15 to the body of the feeder holder 13. The body of the holder 13 is attached to the feeder motor with clamp 14.

The entire feed mechanism must be installed on a dielectric surface (getinaks 10 mm thick). Figure 5 shows the assembly drawing of the initial part of the sleeve.

The wire is passed through the guide sleeve 2 into the working spiral 13. The sleeve is inserted into the clamp of the feeder using the fitting 1. The fitting 1 is screwed onto a hollow screw 3 (inside which there is a working spiral), a cable from the throttle L1 is connected to the fitting 14 using a washer 15 and a lock nut 1. The hollow screw 3 abuts against the helix of the casing 10, inside which the working helix 13 passes. The use of two helixes is necessary for the rigidity of the sleeve. It should be noted that the inner diameter of the working spiral must be at least 0,9 mm so that the wire 4 with a diameter of 0,8 mm passes freely. We solder a copper braid 9 to the hollow screw over the casing spiral to conduct high currents to the tip of the sleeve. A tube passes over the braid, conducting carbon dioxide from the decoupling tube 5 to the sleeve holder, as well as wires from the microswitch. On top of all this, we stretch the sleeve casing 11. Using a special sleeve 8, we fix the wires 12 and the tube 5 with a clamp 7, which also accepts the sleeve casing. The casing can be used from a bicycle camera. Figure 6 shows the counterpart of the sleeve and the holder.

The holder 6 is made of a brass tube with a thread at the outlet (the thread can be cut on the sleeve and soldered to the tube with brass). A conical sleeve made of a dielectric (getinax) is screwed onto the thread. We install nozzle 5 on the sleeve 3 (made of copper or an old solid rubber hose). The working spiral 13, passing along the spiral of the casing 10, enters the guide tube 8 (made of copper), a copper braid 9 is soldered to this tube. In turn, the guide tube 8 is soldered to the holder 6. This is necessary to supply current to the tip 1. To prevent injury current, the holder is insulated with a rubber layer 15. Wires 12 and a carbon dioxide tube 16 (you can use a PVC tube or a tube from medical droppers) pass to the holder 6 under a rubber casing 11. A bushing 6 is screwed inside the holder 2 (made of brass, it should be replaced as it wears out) with holes on the sides (closer to the holder). A working spiral runs inside the sleeve, which rigidly abuts against tip 1. Tip 1 (made of copper) is made in the form of a cylinder with a hole 0,85 mm in diameter drilled to the middle. Using a file at a slight angle, remove the remaining half of the surface of the cylinder so as to reach the tip hole.

We pass the welding wire through the tip and press it on the removed surface of the cylinder. The result is a groove that guides the wire out of the hole. As the groove is actuated, the tip bends upwards, thereby extending the life of the tip by 5-10 times. The length of the sleeve can be up to 2,5 m, which allows welding cars under the lift, but the feeder motor must have enough power to push the wire into the sleeve, and the wire must pass freely inside the spiral and through the ferrule, otherwise it will become tangled in feeding mechanism.

Details. A toroidal transformer was chosen as the welding transformer. Its core is made of thin permalloy electrical steel with an oxidized surface (to eliminate eddy currents). The winding ratio is typically 1 V/turn. Overall power 2 kW. The remaining design characteristics depend on the quality of the core, and they are selected empirically. The author chose a toroidal transformer, because it has a high efficiency, small dimensions and weight, excellent parameters when working on a rigid characteristic. These advantages are essential for the considered SPA. Choke L2 is similar to the previous version of the CPA [1]. As a rule, the choke is designed according to the readings of the variable component at the time of welding: 1-1 V, but the metal to be welded must melt immediately at the moment the wire touches. If this condition is not met, then the number of turns in the inductor is reduced or the resistance of resistors R2-R3 is increased. If the metal does not melt, then it is necessary to carry out tests without capacitors C5-C7, in the case of the previous result, without the inductor L12. If in this case the metal does not melt, then it is necessary to increase the power of the transformer (of course, check the power rectifier).

Indicative throttle data: core from a transformer 1 kW 50 Hz, number of turns 60, non-magnetic gap 2-5 mm (getinaks), the larger the gap, the greater the inductance (up to certain sizes).

Diodes VD1 and VD2 (Fig. 3) VL-100-90 (or any others with a direct maximum current of 100 A, without a radiator), VD3-VD6, VD12 type D226 or others with a direct current of at least 1 A. VD7-VD11 type D232, D246 or any other with a direct current of at least 10 A on an aluminum radiator with a dissipation area of ​​60 cm2 each. Fan M1 from a mini-computer for ? 220 V, M2 - a windshield wiper from cars. Package switch SA1 for 380 V, 15 A or two paired types VDS-632075 for 15 A. Fuse FU1 for 15 A, microswitch SA2 of any type for a current of 0,5 A. Capacitors: C1-C3 0,1 microns x 400 V; C4 - 1000 x 50 V type K50-18; C5-C10 - 10000 x 100 V of the same type, C11 - 200 x 50 V of the K50-32 type; C12 - 0,1 x 700 V high voltage. Resistors R1-R4 type MLT-0,5; R5 - variable rheostat 47 Ohm, R6 - 100 Ohm PZ-75, HL1 - 40 V x 10 W. Core K4 from el. steel, the number of turns is ?200 PEV-0,1, if it heats up, increase the number of turns.

Relay K1, K2 of any type for a current between contacts of at least 2 A (contacts include paired) type TKE-54 PD1. Connector X1 any for a current between contacts of at least 5 A (contacts to pair). The wires indicated in the diagram by a thickened line must have a cross-sectional area of ​​at least 10 mm2. SPA setup. The welding transformer is wound according to the method [3], after which it is checked using conventional electrodes with a diameter of 2 mm. Then the control circuit and the feed mechanism are assembled. From the power rectifier, you can immediately supply current through the cables to the feeder (attention! The mechanism must be well isolated from the housing). As the wire moves, it must melt, and a large amount of scale will occur (for this you need to have a suit that covers all parts of the body). If the wire does not melt, it is necessary to rewind the transformer, increase the core and the thickness of the turns of the secondary winding. Reduce the winding factor to 0,9-1 V/turn. This operation is done with the capacitors C5-C10 turned off, otherwise the electrolytes may burst. In the case of a positive result, C5-C10 and the L1 choke are connected. If there is no voltage at the output of the power rectifier, R3 and R4 are selected, for some thyristors parallel to R3, R4, capacitors of 0,22 x 100 V of any type are connected. The power rectifier is checked at the time of welding or the switched on load with a resistance of 1-10 ohms from a nichrome wire with a diameter of 3 mm.

Better results can be achieved by selecting C12 and R7-R12, as well as changing the gap in the throttle. With the help of R5, the wire is fed so that it has time to melt the metal being welded and at the same time does not get tangled at the feeder roller. R6 is adjusted so that the wire has time to stop and peek out of the tip by no more than 5 mm. When using conical mouthpieces 3 (Fig. 6), the pressure at the outlet of the carbon dioxide reducer can be adjusted by 0,3 atm. If the mouthpiece is cylindrical, then by 0,5 atm., on an open windy area - up to 1 atm. The mouthpiece should protrude beyond the tip no more than 2-3 mm. Attention! All high voltage parts (220 V) must be carefully insulated. Do not use the device in a damp place! For safety, the author recommends that all adjustment operations be carried out with rubber gloves on a rubber mat away from flammable substances. In no case should you weld gas tanks, canisters (in operation) or near them. During operation, a large amount of scale (splashes of hot metal) is formed.

References:

1. Pronsky I.N. Simple semi-automatic welding // Radioamator.-1998.-№10.- P.38.
2. Pronsky I.N. Secrets of the welding transformer // Radioamator.-1998. -Number 3.
3. Pronsky I.N. Welding transformer // Radioamator.-1999.-№7.

Author: I.N. Pronsky

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