Equipment that allows to connect thin-sheet metal parts by the method of resistance spot welding has a very simple device, so it can easily be assembled at home from readily available materials. In the simplest version of such an apparatus, welding is carried out by alternating current, the magnitude of which is not regulated and always remains unchanged - in the range of 800-1000 A. Such current allows to connect metal elements with a thickness of 1-1.5 mm, and the degree of its impact will depend on the duration pulse, which is determined manually or using a relay.
Manual spot welding device: 1 - base, 2 - fixed square, 3 - lever, 4 - hinge, 5 - square, 6 - screw, 7 - electrode.
It should be noted that although the spot welder has an uncomplicated device, the quality of all connections and the chain as a whole must be at the highest level. Otherwise, due to the large amount of current in poorly made contacts, there will be significant heating and significant energy loss.
Where to get a transformer?
The main element of this device is a step-down transformer, the transformation ratio of which will be sufficient to achieve the specified value at the output of the currents. For its manufacture, we need a transformer from an old or broken microwave oven, which will have to be slightly redone. The power supply circuit of the magnetron provides for voltage conversion up to 4000 volts and the step-up transformer provides half of this voltage (hereinafter, the voltage is increased with a doubler). "Microwave" should be powerful enough - not less than 1 kW.
Choosing a stove at a flea market or on the Internet, look for devices with large sizes. Solid dimensions always indicate the same power.
The scheme of capacitor spot welding.
When disassembling a microwave oven, remember that even in the off state, some of its components can cause electric shock. Therefore, during the entire process, care must be taken at all times.
In the extracted transformer it is necessary to dismantle the secondary winding. It differs from the primary wire with a thinner wire and a large number of turns. It is not easy to get rid of this winding, because its coils fill the window of the magnetic circuit tightly enough. For this you have to use a hacksaw or chisel, sometimes you even have to drill the coils. All manipulations should be done with utmost care, since the primary winding of the transformer must remain intact. You must remove the shunts, if any, glue and paper.Back to table of contents
We construct a transformer
"Mined" from the microwave transformer must be converted into a step-down. To do this, it installs a new secondary winding. The scheme of the device of our spot welding machine provides for the use of operating currents up to 1000 A, so the cross section of the wire of the new winding should be large enough. Its diameter is limited only by the lumen of the window of the magnetic circuit, which is usually 7-10 mm. It is not necessary to use one stranded wire, it can be replaced with several thinner ones. To save space, insulation from the wire can be removed by replacing it with a fabric tape. It is important that the resistance of the secondary winding was minimal, so it is recruited from copper wire, the length of which they are trying to make the shortest.
Spot welding scheme.
In total, this winding should have two or three turns, and the output voltage should be about 2 volts. You can try to place more turns, this will make the welding machine more powerful.
If a sufficiently powerful microwave oven could not be obtained, or there is a need to weld parts with greater thickness, it is possible to combine two identical transformers, thus doubling their power. To do this, the same conclusions of their primary windings are connected, and the connections in the secondary winding circuit are performed by means of electrodes. The output voltage will not change, but the rated output current will double. Connection scheme
The connected outputs must be exactly the same, otherwise, when the device is switched on in the network, a short circuit will occur.
It happens that the transformer has enough power, but the gap in the magnetic core does not allow to accommodate the number of turns of the secondary winding, which is necessary to obtain the desired voltage. In this case, you also need to use the second transformer. In this case, one piece of wire is wound first on the magnetic core of the first transformer, then - on the second one. Thus, we get two secondary windings connected in series.
The scheme of the apparatus for the implementation of spot welding with your own hands may include a greater number of transformers. However, it should be remembered that when the power is too high, it will cause a noticeable voltage drop in the network and, as a result, interruptions in the operation of other devices (including lighting sources) in you and in your neighbors.Back to table of contents
Characteristics of spot welding.
The case for the device is the easiest to make of wood. Its size will depend on the number of transformers and their connection scheme. The edges of the body parts after cutting can be slightly rounded with a cutter. Drill holes for wires in the back and front panels. After assembly, the body should be sanded, then coated with a primer and painted. For safety reasons, it is not recommended to use paint of the same color for all elements of the welding machine. For moving parts, a separate color should be selected. They can be painted, for example, in yellow, while the body - in black.
In order to conveniently carry the device, you can attach a simple door handle to the top of its case.Back to table of contents
The diameter of the copper electrodes homemade welding machine must be equal to the diameter of the wire of the secondary winding. The material for their manufacture is a copper rod. In the process, the electrodes are triggered, so they have to periodically sharpen. When the electrodes are very short, they will need to be replaced with new ones.
Modes of spot welding.
To reduce power losses, it is necessary to minimize the length of the wire leading from the transformer to the electrodes, as well as the number of connections in this area. The best option is soldering to both ends of the wire of copper tips (the wires of the wire are also soldered). Crimping with tips in this case is undesirable, since with this method the contact area is reduced, and an oxide film is formed on the copper surface. Losses on it are so great that the welding machine can be absolutely useless.
Tips should be selected tinned, designed specifically for soldering. Soldering the usual tip on such a thick wire will not be easy. Of course, in the ideal case it would be possible to solder the electrodes to the wire, but then their replacement will be difficult.Back to table of contents
For proper quality welding, both parts must be strongly compressed by electrodes, and the magnitude of the force of compression must be the greater, the thicker are the parts to be joined. Of course, if you make a welding machine yourself, it will be difficult to provide a force of 100 kg, as in industrial installations. But for thin-sheet parts, which are designed for a homemade device, such efforts are not needed.
For clamping parts, we will use the lever. It should be strong enough, while the base of the welding machine is better done more massily, equipping it with clamps for attachment to the table. To enhance the effect of the lever can be supplemented with a screw mechanism. It will allow you to develop a significant clamping force and keep it at a constant level during the entire welding cycle.Back to table of contents
Installation of the switch is made in the part of the circuit where the current strength is of minimum value, that is, in the circuit of the primary coil of the transformer. If you put it on the other hand - on the secondary winding, we will get an additional connection and, as a result, additional power loss. Moreover, currents of considerable strength can cause the contacts of the circuit breaker to melt and weld them.
The most convenient way to place the switch on the lever. In this case, the user will be able to control the welding machine (on and off) with the same hand, which presses the lever. Thus, the second hand remains free to manipulate the details.
As a small improvement in the scheme, it is possible to suggest the installation of two switches. One of them - the main one - is mounted on the case of the device, the other - you can use the usual mikrik - on the lever. This solution is more successful in terms of security.Back to table of contents
Starting the welding process can be carried out only if the electrodes are compressed with sufficient force. Otherwise, sparking will occur in the welding zone, which will lead to burnout of the electrodes.
The scheme is the simplest, overheating protection is not provided. Therefore, when operating the device, it is necessary to control the temperature of the transformer, wires and electrodes, if necessary letting them cool down. To improve the working conditions of the equipment will help forced airflow using a fan.
The duration of the pulse should be determined by eye, focusing on the color of the point in the welding zone. After some practice experience will appear, the quality of welding will reach an acceptable level.
Spot welding is not always harmless. If galvanized metal is treated, a large amount of zinc oxide in the form of steam enters the surrounding air. This substance is harmful to human health, so the welding post before carrying out such work should be equipped with strong ventilation.