Spot welding from the microwave oven with your own hands: the instructions for manufacturing

The household often requires a spot welding device, but it is difficult to buy because of the high price. Meanwhile, there is nothing complicated in it, and you can make a device yourself. The basis of the welding machine is a transformer. For personal needs, spot welding from the microwave oven can be made by hand. To better understand the device, you first need to understand how it works.

Principle of operation of the spot welding device

Metal parts are placed between electrodes made of copper or brass, by which they are pressed against each other. After that, an electric current is passed through them, heating the welding site is red-hot. The parts become plastic, and at the junction point a liquid bath with a diameter of about 12 mm is formed. Under the influence of pressure, the joint is welded.

The current supply and the warm-up take place in the form of a pulse, after which the parts continue to be fixed in one position until they cool slightly.

Introducing the principle of work, it's easier to figure out how to make spot welding yourself.

Advantages and disadvantages of spot welding

The main advantages of spot welding are:

• Economy;
• High strength of joint;
• Simplicity of the device;
• The possibility of making your own hands;
• Possibility of process automation in production conditions.

Contact welding does not ensure tightness of the seam, which is a major drawback.

Requirements for the welding machine

• Ability to change the duration of the process.
• Creating a significant pressure at the welding location with a maximum at the end of the heating.
• The presence of electrodes with high electrical and thermal conductivity. For this purpose, electrolytic copper, its alloys with chromium and tungsten, bronze with additions of cadmium and cobalt are suitable. For the home master, copper and its alloy of EV are most accessible. The contact area of the working end of the electrode should be 2-3 times smaller than the weld seam .

Making a welding machine with your own hands

From the description of the principle of operation, it becomes clear that manual spot welding must first ensure the heating of the parts at the point of contact to the melting temperature. The heating power of the apparatus is different, and one must imagine for what purpose the homemade device will be used.

Details for manufacturing:

• transformer;
• Insulated wire with a diameter of 10 mm;
• Electrodes;
• switch;
• Tips;
• Bolts;
• An improvised material for the manufacture of the case and welding pincers (plywood, wooden bars).

Apparatus is mainly made desktop. Portable devices are widely used and often not inferior to stationary ones.

Pliers for spot welding

The electrodes are inserted into the tips, and the latter are attached to the ends of the welding tongs, isolated from each other. The easiest way is to make them from wooden blocks together with a casing made of plywood.

Moves only the upper arm, and the lower one is attached to the base. The compression force is required to provide as much as possible, especially when you need to weld thick sheets of metal. This requires a powerful lever. It needs to be pinned up so that the electrodes in the initial state are open. At home, it is advisable to provide no more than 30 kg of pressure. The handle can be up to 60 cm long, and the electrodes are attached closer to the axis of rotation, so that the arm is 1:10. In the industry, pneumatic and hydraulic devices are used for the necessary pressing of parts with adjustable force.

It is convenient to bring the switch to the handle. It will be connected to the primary winding, over which a small current flows. The device is also controlled by means of a magnetic starter via a foot pedal. The secondary winding and the transformer housing are grounded.

Transformer assembly

When spot welding from the microwave is done by one's own hands, the main part of the device is a 700-1000 W power transformer. The higher it will be, the better. The microwave transformer has a welded construction. He needs to remove only the secondary winding, without damaging the primary one. At the output, it is necessary to obtain a welding current of at least 500 A. To do this, it is necessary to rewind the new winding from the top of the primary winding, from a wire with a diameter of at least 1 cm. For it, in the slits of the transformer there is a gap through which 2-3 turns of thick insulated wire, An opening between the core and the primary winding. The device for 1 kW is suitable for welding plates up to 3 mm thick.

Spot welding from the microwave oven creates a current in the secondary winding up to 2 thousand A by its own hands. With its larger value, the voltage jumps in the network will be noticeable and in the apartment this can have a negative effect on the operation of electronic devices. In a private house, you can use a more powerful device.

How to disassemble a microwave is not a problem. It is important that its transformer provides the necessary power. Often to increase it, two identical voltage converters are used, connected in parallel to each other. For this purpose, the spot welding scheme is created from two identical secondary windings with the connection of the same terminals at the input and output. At the same time, an increase in power of 2 times is achieved without changing the voltage. The welding current will also double. It is important not to confuse the terminals so that a short circuit does not occur. As a result, it will be possible to weld plates up to 5 mm thick.

When the secondary windings are connected in series, the output voltage of each of them is summed. In this case, it is also necessary to avoid the wrong connection in the antiphase. To do this, the output is connected to the load and the voltmeter measures the AC voltage.

Transformers are attached to the base of the housing and grounded.

Manufacture of electrodes

For the manufacture of electrodes, it is easiest to find copper rods. For a small device, they can be made from a sting of a powerful soldering iron. Electrodes quickly lose shape, and they must be periodically undermined. They drill a hole through which the bolts are connected to the wires of the secondary winding.

Requirements for electrodes:

• Strength at operating temperature;
• Ease of machining;
• High thermal and electrical conductivity.

Copper alloys with additions of tungsten and chromium or bronze containing cobalt and cadmium satisfy these requirements to the greatest extent. EV is considered the best alloy.

The lower electrode is fixed, and the upper electrode is fixed to the upper arm. It is important to ensure their reliable isolation.

The device is connected to the mains by a 20 A circuit breaker.

Connecting wires

Connect the wires to the electrodes, the length of which should be as small as possible. They are soldered to the copper tips. Separate cores wire also solder each other, because with a large current contact sites can oxidize, and power is lost. Crimping the tips is not recommended, since additional contact resistance occurs at the contact points.

Contact welding technology

Welding is performed only after pressing the electrodes, otherwise they may burn. The main welding parameters are as follows:

• Current strength;
• pulse duration;
• Force of pressing of electrodes;
• Shape and dimensions of electrodes (sphere, plane).

The maximum compression is created when the current is passed and a short time after it. At the same time the metal has time to crystallize, and the connection is more durable.

It is desirable to cool the unit with a fan. It is necessary to monitor the temperature of the electrodes, wires and windings of the transformer. If they are warmed up, a break takes place.

The time of spot welding depends on the magnitude of the current and is selected experimentally. Usually it's a few seconds. The sheet material is mainly connected, but there may also be rods.

The welding mode can be hard and soft. In the first case, a large current is applied and a large compression force is created with a short pulse duration (no more than 0.5 sec). The hard mode is suitable for welding alloys from copper and aluminum, as well as alloy steels. Soft mode is characterized by a longer pulse duration. It is more suitable for home conditions, where it is not always possible to achieve the required capacity. Billets are welded from ordinary carbon steels.

The pressure, current density and spot size depend on the diameter of the contact surface of the electrode.

In household designs of spot welding machines, the current value is usually not regulated. In general, the orientation is focused on the duration of heating, and the control is performed by changing the color of the parts. If voltage regulation is required, a laboratory autotransformer connected at the input can be used. To ensure that the coil does not burn out when the current is high, when closing with a wheel, devices with step-by-step voltage regulation are used.

Application of spot welding

For home repairers contact welding is needed for minor repairs, when it is necessary to join small sheets of metal. It is used to replace the batteries of power tools, laptops and similar equipment to reduce the cost of replacing batteries. High process speed does not allow parts to overheat.

Conclusion

The choice of spot welding machines on the market is large, but their cost remains high. In addition, it is difficult to find the right parameters. The device can be made independently, and everything you need to find at home or in your workshop. Spot welding from the microwave oven, assembled by its own hands, works reliably and provides the necessary minor repair of parts, if all parameters are correctly selected. It is important here to understand the purpose for which it is manufactured.