In the household, a spot welding device is often required, but it is difficult to buy it due to the high price. Meanwhile, there is nothing complicated in it, and you can make a device with your own hands. The basis of the welding machine is a transformer. For personal needs, do-it-yourself spot welding from a microwave can be made. To better understand the device, you first need to understand how it works.
The principle of operation of the spot welding device
Metal parts are placed between electrodes made of copper or brass, with which they are pressed against each other. After that, an electric current is passed through them, heating the welding spot red-hot. The parts become plastic, and a liquid bath with a diameter of about 12 mm is formed at the junction. Under the action of pressure, the joint is welded.
The supply of current and heating occur in the form of an impulse, after which the parts continue to remain fixed in oneposition until cool slightly.
Introducing the principle of operation, it is easier to figure out how to do spot welding yourself.
Advantages and disadvantages of spot welding
The main advantages of spot welding are:
- economy;
- high bond strength;
- simplicity of the device;
- do it yourself;
- possibility of automating the process in production conditions.
Resistance welding does not ensure the tightness of the seam, which is the main disadvantage.
Welding Machine Requirements
- Possibility to change the duration of the process.
- Creating significant pressure at the welding point, reaching a maximum at the end of heating.
- The presence of electrodes with high electrical and thermal conductivity. Electrolytic copper, its alloys with chromium and tungsten, bronze with the addition of cadmium and cob alt are suitable for this. For a home craftsman, copper and its alloy of the EV brand are the most accessible. The contact area of the working end of the electrode should be 2-3 times less than the size of the weld.
Making a welding machine with your own hands
From the description of the principle of operation, it becomes clear that manual spot welding, first of all, should ensure that the parts at the point of contact are heated to the melting temperature. The heating power of the devices is different, and you need to imagine for what purposes the home-made device will be used.
Details for making:
- transformer;
- insulated wire with a diameter of 10 mm or more;
- electrodes;
- switch;
- tips;
- bolts;
- handy material for the manufacture of the body and welding tongs (plywood, wooden blocks).
Devices are made mostly desktop. Portable devices are widely used and are often on par with stationary devices.
Spot welding pliers
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 along with a body made of plywood.
Only the upper arm moves, while the lower arm is attached to the base. The compression force must be provided as much as possible, especially when thick sheets of metal are to be welded. This requires a strong leverage. It must be spring-loaded so that the electrodes in the initial state are open. At home, it is advisable to provide a pressure of no more than 30 kg. The handle can be up to 60 cm long, and the electrodes are attached closer to the axis of rotation so that the leverage is 1:10. In industry, pneumatic and hydraulic devices are used to achieve the necessary pressing of parts with adjustable force.
It is convenient to bring the switch on the handle. It will be connected to the primary winding, through which a small current flows. The device is also controlled by a magnetic starter through a foot pedal. The secondary winding and the transformer case are grounded.
Transformer assembly
When donedo-it-yourself spot welding from a microwave oven, the main part of the device is a 700-1000 W transformer. The higher it is, the better. The microwave transformer has a welded design. He needs to remove only the secondary winding, without damaging the primary. At the output, it is necessary to obtain a welding current of at least 500 A. To do this, you need to wind a new one on top of the primary winding, from a wire with a diameter of at least 1 cm. For it, a gap remains in the slots of the transformer, through which 2-3 turns of a thick insulated wire pass tightly opening between the core and the primary winding. A 1 kW device is suitable for welding plates up to 3 mm thick.
Do-it-yourself spot welding from a microwave creates a current in the secondary winding up to 2 thousand A. With a larger value, voltage surges in the network will be noticeable and in the apartment this can have a negative impact on the operation of electronic devices. In a private house, you can use a more powerful device.
How to disassemble the 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. To do this, a spot welding circuit is created from two identical secondary windings with a connection of the same outputs at the input and output. In this case, an increase in power by 2 times is achieved without changing the voltage. The welding current will also double. It is important not to confuse the leads so that a short circuit does not occur. ATAs 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 up. In this case, erroneous connection in antiphase should also be avoided. To do this, a load is connected to the output and an alternating voltage is measured with a voltmeter.
Transformers are attached to the base of the housing and grounded.
Production of electrodes
Copper rods are the easiest to find for making electrodes. For a small device, they can be made from the tip of a powerful soldering iron. The electrodes quickly lose their shape and need to be sharpened periodically. A hole is drilled in them, through which bolts are connected to the wires of the secondary winding.
Electrode requirements:
- strength at operating temperature;
- ease of machining;
- high thermal and electrical conductivity.
To the greatest extent these requirements are met by copper alloys with additions of tungsten and chromium or bronze containing cob alt and cadmium. EV is considered the best alloy.
The lower electrode is installed motionless, and the upper one is attached to the upper arm. It is important to ensure that they are well insulated.
The device is connected to the network by a 20 A circuit breaker.
Wiring
Wires are connected to the electrodes, the length of which should be as short as possible. They are soldered to copper tips. The individual cores of the wire are also soldered together, because with a largecurrent, the contact points can oxidize and power is lost. It is not recommended to crimp the lugs, as there is additional resistance at the points of contact.
Resistance welding technology
Welding is done only after pressing the electrodes, otherwise they may burn. The main welding parameters are as follows:
- current strength;
- pulse duration;
- electrode pressing force;
- shape and size of electrodes (sphere, plane).
Maximum compression is created when the current is passed and a short time after it. In this case, the metal has time to crystallize, and the connection is stronger.
It is desirable to cool the device 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 is made.
The time of spot welding depends on the magnitude of the current and is selected empirically. Usually it's a few seconds. Mostly sheet material is connected, but there may be rods.
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). Hard mode is suitable for welding copper and aluminum alloys, as well as alloy steels. Soft mode has a longer pulse duration. It is more suitable for home conditions, where it is not always possible to achieve the required power. Workpieces are welded from conventional carbon steels.
From the diameter of the contactThe surface of the electrode depends on pressure, current density and the size of the weld spot.
In home designs of spot welders, the current is usually not regulated. Basically, an orientation is made to the duration of heating, and control is carried out by changing the color of the parts. If voltage regulation is required, a laboratory autotransformer connected at the input can be used. So that at high current its winding does not burn out when closed with a wheel, devices with stepped voltage regulation are used.
Application of spot welding
A home craftsman needs resistance welding for minor repairs when small sheets of metal need to be joined. It is used to replace the batteries of power tools, laptops and similar equipment in order to reduce the cost of replacing batteries. The high speed of the process prevents the parts from overheating.
Conclusion
The choice of spot welding machines on the market is large, but their cost remains high. In addition, it is difficult to choose the right parameters. You can make the device yourself, and find everything you need at home or in your workshop. Do-it-yourself spot welding from a microwave oven works reliably and provides the necessary minor repairs of parts if all parameters are correctly selected. Here it is important to understand for what purposes it is made.
