A simple arc welding machine can be made by anyone at home, without using any specialized equipment or circuits. All we need is just two microwave ovens that can be found in a landfill or two transformers from them.
We disassemble the microwaves and take out the transformers.
These transformers are step-up, that is, they convert 220 Volts into a voltage of about 2.5 kV, necessary for the operation of the magnetron. Therefore, their secondary winding contains a less thick wire and with a larger number of turns. Such a transformer has a power of about 1200 W.
To assemble an arc welding machine, we do not have to disassemble the core of these transformers. We will simply cut down and drill out the secondary high-voltage winding. Usually this winding comes from the top, and the primary winding is 220 V from the bottom.
The tool we need for our work.
Making a simple welding machine from a microwave with your own hands
We take the transformer and secure it so that it does not move. We take a hacksaw and cut off the secondary winding on both sides of both transformers. If you decide to repeat, be careful not to damage the primary winding.
Then we drill the winding with a drill with a metal drill, thereby relieving the internal stress of the metals, making it easier to knock out the remains.
We knock out the remnants of the winding.
We have two transformers with 220 V windings. The transformer on the left, above the winding, has a current shunt that separates the windings. To increase power, they also need to be knocked out. Such manipulation will increase the power of the transformer by 20-25 percent.
There is also a small low-voltage winding made of a pair of wires between the large windings - we also throw that out.
We take a stranded wire in plastic insulation with a cross-section of six squares and a length of 11-12 meters. You can take a more stranded wire, not coarse like in my example.
I wound about 17-18 turns on each transformer, 6 rows high and 3 layers thick.
The windings are connected in series. I wound everything with one wire, but you can wind each transformer separately and then connect it. The entire winding is very tight and should not dangle.
After winding is completed, we connect the high-voltage 220 V windings in parallel. I used automotive grade ferrules, insulated with heat shrink tubing.
I plug in the entire structure and measure the voltage on the secondary that I wound. The result was about 31-32 Volts.
Then I took a wooden board and screwed both transformers with self-tapping screws to make one unit.
When welding, I will use 2.5 mm electrodes and weld two pieces of iron 2 mm thick.
I'm happy with the result; it's quite suitable for household needs, considering that I actually got everything for free.
Watch the video of making an arc welding machine
In stores, spot welding machines are not cheap, but this tool is useful in the household of every real man. Therefore, many decide to make this equipment themselves, using available materials. The finished device will allow you to quickly and reliably connect various metal elements. Thus, repairs of various structures can be carried out at home, saving on the services of a professional. The main advantage of making it yourself is significant cost savings on purchases.
The scope of application is very wide. It can be used both to repair old metal structures and to create new ones. Such a device will allow you to easily cope with the manufacture of gates, stairs, and structural elements made of metal.
The operation of the device directly depends on the electric current, which heats some areas of the steel parts in contact with each other to a certain temperature. At this moment, a welded joint is formed, which experts call a seam. In this case, the metals are joined together by each other’s melts at point contact. The quality of the work performed directly depends on the type of metal and its density.
You must also follow these rules:
- The welding circuit must have a low voltage (up to 10 watts);
- The welding process should last a few seconds;
- High-quality welding is characterized by a minimal melting zone;
- High current strength of the welding pulse;
- The seam obtained after welding must withstand heavy loads.
Compliance with all the above rules guarantees an excellent result. It’s not difficult to make a spot welding machine with your own hands, but you need to carry out all the steps in accordance with the recommendations of specialists.
Manufacturing of the device
A high-quality welding machine consists of two main parts - a contact block and a welding pulse source. The latter gives an impulse automatically. The current should be within 200 A for 0.03-0.1 s when powered from a regular electrical outlet. Some users advise choosing a device that allows you to adjust the current to work with different types of metal of different thicknesses.
The contact block must be characterized by the following basic requirements:
- Good pressing of welding surfaces;
- Using a point electrode, it is necessary to supply a welding signal;
- Holding workpieces after removing the impulse until complete hardening.
Most often you can find the following solutions:
- the workpieces are clamped between the electrodes;
- use 2 different electrodes: point and flat;
- one of the workpieces is the bottom electrode.
Manufacturing
You can make a high-quality spot welding machine yourself. To do this, you can use a welding pulse source that uses the principle of capacitor discharge. The circuit of such a source is quite simple.
Welding machines with this type of power supply can weld thin sheets of metal (up to 0.5 mm).
The required current is released at the output of the secondary winding. The capacitors are discharged onto the primary winding, which contributes to the generation of the desired signal. Capacitor discharges are controlled by thyristors. The accumulation of charge occurs from the switched on auxiliary circuit of the transformer. It is necessary to use diodes that rectify the electrical signal.
How to make a device?
This device can be assembled from available materials. First of all, you need to assemble it from the inverter. You need to prepare:
- transformer and ;
- diodes and chokes.
Using all of the parts listed will help avoid lengthy setup.
Most often, men make such devices for spot welding batteries from parts of an unnecessary microwave. It may already be at your home, or you can borrow it from friends. The spot welding produced from such parts is characterized by a power of about 800A.
A high-quality spotter guarantees excellent results when working with thin metal. To perform household tasks, this result is often quite sufficient, because metal welding occurs at a certain point.
To make such a machine for resistance spot welding, it is better to choose a large microwave. After all, such models have a powerful transformer. And this is the basis of future equipment.
The transformer is a core with two windings. It is held in place by welded seams, which must be removed with a hacksaw or grinder. Be careful, because the winding should not be damaged. Afterwards, the core needs to be divided into 2 parts, cleaned of glue and paper.
We wind the second winding of the transformer. To do this, use a cable that fits into the slot of the transformer, which is wound into 2 turns.
The transformer is attached to the base with epoxy resin, compressed with a vice.
The secondary winding allows you to increase the power of the device.
If you want to increase the power more, you can use an additional transformer from another microwave. It is attached to the first.
Transformer circuit
After the windings are connected, the current strength can be checked. It should not exceed 200A. If the value is higher, voltage surges may occur, which can lead to negative consequences.
The voltage should go to the first winding. The output voltage should not exceed 2 volts.
To make a battery with your own hands, you need to pay special attention to the body of the future equipment. Wood is used for this. There must be holes in the back of the device that will be responsible for power supply and shutdown.
The body of the welding machine, made of wood, must be sanded and varnished.
Then they make the device with their own hands. Connect all the parts, prepare copper wires that will serve as electrodes. You can use an ordinary screwdriver to secure them. For high-quality fixation, the transformer can be attached to the housing with self-tapping screws. Remember about safety, grounding must be placed on one of the terminals.
The design of this spot welding machine should include an additional switch secured with self-tapping screws to the body. Thus, you can benefit from a welding machine with your own hands. This means saving money on purchasing a new device and earning money from doing simple work.
The easiest to manufacture are AC resistance spot welding machines with unregulated current. The welding process is controlled by changing the duration of the electrical pulse - using a time relay or manually using a switch.
Before considering the designs of homemade devices for resistance spot welding, we should recall the Lenz-Joule law: when an electric current passes through a conductor, the amount of heat generated in the conductor is directly proportional to the square of the current, the resistance of the conductor and the time during which the electric current flowed through the conductor ( Q=I 2 R t). This means that at 1000A current, about 10,000 times more energy is lost on poorly made connections and thin wires than at 10A current. Therefore, the quality of the electrical circuit cannot be neglected.
Transformer. The main component of any equipment for resistance spot welding is a power transformer with a high transformation ratio (to provide high welding current). Such a transformer can be made from a transformer from a powerful microwave oven (the power of the transformer should be about 1 kW or higher) feeding the magnetron.
These transformers are distinguished by their availability and high power. Such a transformer is enough for a precision welding machine capable of welding steel sheets 1 mm thick. If you need a more powerful spot welding machine, you can use two (or more) transformers (how to organize this is described below).
In a microwave oven, the magnetron requires a very high voltage (about 4000V) to operate. Therefore, the transformer feeding the magnetron does not step down, but increases. Its primary winding has fewer turns than the secondary, and the thickness of the winding wire is greater.
The output of such transformers is up to 2000V (a double voltage is supplied to the magnetron), so you should not check the performance of the transformer by connecting it to the network and measuring the voltage at the output.
Such a transformer requires a magnetic core and a primary winding (the one with fewer turns and a thicker wire). The secondary winding is cut off with a hacksaw or chopped off with a chisel (if the magnetic core is securely welded and not glued), knocked out with a rod or drilled out and picked out. The need for drilling arises when the winding is packed very tightly into the window and an attempt to knock it out can lead to destruction of the magnetic circuit.
When removing the secondary winding, care must be taken not to damage the primary winding.
In addition to two windings, shunts that limit the current can be built into the transformer; they must also be removed.
After removing unnecessary elements from the transformer, a new secondary winding is wound. To provide a large current close to 1000A, a thick copper wire with a cross-sectional area of more than 100 mm 2 (wire with a diameter of more than 1 cm) is required. This can be either a single stranded wire or a bundle of several wires of small diameter. If the wire insulation is thick and prevents you from making a sufficient number of turns, then it can be removed and the wire wrapped with fabric insulating tape. The length of the wire should be as short as possible so as not to create additional resistance.
2-3 turns are made. The output should be about 2V, this will be enough. If you manage to cram more turns into the transformer windows, then the output voltage will be greater, therefore the current will be longer (in comparison with fewer turns of wire of the same diameter) and the power of the device.
If there are two identical transformers, then they can be combined into one, more powerful current source. This may be required when there are two transformers with insufficient power or when you want to make your own spot welding machine to work with thicker metal.
For example, in the case of insufficiently powerful transformers, each of the 0.5 kW transformers has an input voltage of 220V, the output voltage is 2V at nominal current 250A (the value is taken as an example, let the short-term welding current be 500A). By connecting namesake conclusions of the primary and secondary windings, we get a device in which, at the same voltage value (2V) nominal the output current value will be 500A (the welding current will almost double, and there will be more losses due to resistances).
At the same time, the connections in the circuit of secondary windings shown in the diagram must be on electrodes, that is, in the case of two transformers with a power of 0.5 kW there will be two identical wires with a diameter of 1 cm, the ends of which are connected to the electrodes.
If you make a mistake in connecting the terminals of the primary or secondary windings, there will be a short circuit.
If there are two sufficiently powerful transformers and you need to increase the voltage, and the dimensions of the magnetic circuit window do not allow you to make the required number of turns with a thick wire on one transformer, then the secondary windings of the two transformers are connected in series (one wire is pulled through two transformers), with the same number of turns on each transformer . The direction of the turns must be consistent so that there is no antiphase and, as a result, the output voltage is close to zero (you can experiment with thin wires first).
Typically, in transformers, winding terminals of the same name are always marked. If for some reason they are unknown, then they can be determined by performing a simple experiment, the diagram of which is shown below.
Here, the input voltage is supplied to the series-connected primary windings of two identical transformers, and an alternating voltage voltmeter is connected at the output formed by the series connection of the secondary windings. Depending on the direction in which the windings are turned on, there can be two cases: the voltmeter shows some voltage or the output voltage is zero. The first case indicates that in both the primary and secondary circuits the opposite terminals of the corresponding windings are interconnected. In fact, the voltage on each of the primary windings is equal to half the input and is transformed in the secondary windings with the same transformation ratios. When the secondary windings are turned on as indicated, the voltages on them are summed up and the voltmeter gives twice the voltage value of each winding. A zero voltmeter reading indicates that equal voltages on the secondary windings of transformers connected in series have opposite signs and, therefore, any pair of windings is connected by terminals of the same name. In this case, by changing, for example, the sequence of connecting the terminals of the primary windings as shown in Figure (b), we will obtain at the output twice the value of the output voltage of each of the secondary windings and we can assume that the windings of the transformer are connected different names conclusions. Obviously, the same result can be obtained by changing the sequence of connecting the terminals of the secondary windings.
To make a more powerful spot welding machine with your own hands, you can connect more transformers in the same way, if only the network allows it. A transformer that is too powerful will cause a large voltage drop in the network, causing fuses to trip, light bulbs to flicker, neighbors to complain, etc. Therefore, the power of homemade spot welding machines is usually limited to values that provide a welding current of 1000-2000A. The lack of current is compensated by increasing the welding cycle time.
Electrodes. Copper rods (rods) are used as electrodes. The thicker the electrode, the better; it is desirable that the diameter of the electrode is not less than the diameter of the wire. Tips from powerful soldering irons are suitable for low-power devices.
The electrodes must be sharpened periodically, because they lose their shape. Over time, they wear down completely and require replacement.
As already written, the length of the wire running from the transformer to the electrodes should be minimal. There should also be a minimum of connections, because There is a loss of power on every connection. Ideally, copper lugs are placed on both ends of the wire, through which the wire is connected to the electrodes.
The tips must be soldered to the wire (the wire cores must also be soldered). The fact is that over time (possibly at the very first start), oxidation of copper occurs at the contacts, leading to an increase in resistance and a large loss of power, which is why the device may stop welding. Plus, when crimping tips, the contact area is smaller than when soldering, which also increases the contact resistance.
Due to the large diameter of the wire and its tip, it is not easy to solder them, but sold tin-plated solder tips can make this task easier.
Unsoldered connections between tips and electrodes also create additional resistance and oxidize, but since The electrodes must be removable; it is inconvenient to unsolder the old ones and solder in the new ones each time you replace them. Moreover, this connection is much easier to clean from oxides than the end of a stranded wire crimped with a ferrule.
Controls. The only controls may be a lever and a switch.
The compression force between the electrodes must be sufficient to ensure contact of the parts being welded with the electrodes, and the thicker the sheets being welded, the greater the compression force must be. On industrial devices, this force is measured in tens and hundreds of kilograms, so the lever should be made longer and stronger, and the base of the device should be more massive and can be attached to the table with clamps.
A large clamping force for homemade spot welding machines can be created not only with a lever clamp, but also with a lever-screw clamp (a screw tie between the lever and the base). Other methods are possible, requiring different equipment.
The switch must be installed in the primary winding circuit, because there is a very large current in the secondary winding circuit and the switch will create additional resistance, in addition, the contacts in a regular switch can be tightly welded.
In the case of a lever clamping mechanism, the switch should be mounted on the lever, then with one hand you can press on the lever and turn on the current. The second hand will remain free to hold the parts being welded.
Exploitation. It is necessary to turn the welding current on and off only when the electrodes are compressed, otherwise intense sparking occurs, leading to burning of the electrodes.
It is advisable to use forced cooling of the device using a fan. In the absence of the latter, you need to constantly monitor the temperature of the transformer, conductors, electrodes and take breaks to prevent them from overheating.
The quality of welding depends on the experience gained, which comes down mainly to maintaining the required duration of the current pulse based on visual observation (by color) of the weld point. More information about performing spot welding is written in the article Contact spot welding.
Video:
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Having your own welding machine is the dream of any home craftsman. Moreover, it does not have to be a bulky block weighing 20-30 kg. You don't have to weld a garage door every day, do you?
As a rule, when performing home plumbing work, spot welding is the most popular.
There are ready-made samples of welding machines on the market, but their cost is too high for the home budget. For regular welding of small parts, you can make a compact spot machine with your own hands from an old microwave oven.
Of course, such a device cannot weld a water pipe or a corner 4 mm thick. But it’s easy to perform minor body repairs on a car, or assemble a metal structure from sheet metal.
It is spot welding machines that are used on the conveyors of automobile factories when assembling the car body. Metal frames of household appliances (washing machines, refrigerators, etc.) are also welded using similar electrical appliances.
Video example of making a small welding machine from an old microwave oven
Working principle of a spot welding machine
To heat a metal to the melting point, a large current is required, hundreds of amperes. The voltage value does not matter, therefore, to save wire and work safety, 2-3 volts are usually used.
You can learn about the principles of spot welding from this video:
There is no point in experimenting with current strength. All described options have been tested numerous times and you don’t have to waste time on calculations. The power is selected based on the thickness of the metal being welded.
- sheets up to 1 mm – power 1 kW;
- sheets up to 1.8 mm – power 2 kW;
- sheets up to 3 mm – power 5 kW.
The primary winding of the welding machine is calculated according to the total power of the device. Since making a transformer yourself is troublesome and costly, you can use a ready-made design.
The best option– a power transformer from an old microwave oven. The electrical circuit works according to the following principle:
- To operate the magnetron (the radiating element of the furnace), a voltage of several thousand volts is required, and the current strength does not matter;
- The power on the primary and secondary windings of the transformer is the same, therefore, when the number of turns on the secondary winding increases, the voltage increases in the same proportion, at the cost of losses in current strength;
- Microwave oven transformers are designed for power up to 3 kW. This value is quite sufficient for the manufacture of a spot welding machine.
The required spare parts can be purchased on the radio market, at service centers for repairing household appliances, or simply buy a faulty microwave oven from an advertisement for a symbolic price.
Secondary windings usually burn out (due to thinner wires), so the chances of purchasing a transformer with a working primary are quite high.
Current strength up to 1000 Amperes (with a power of 3 kW and a voltage on the secondary winding of 2 volts) allows you to easily melt the metal at the point of contact, thereby ensuring reliable spot welding.
In this brain project I want to tell you how with your own hands make a resistance spot welder from old microwave oven components. I plan to use it to weld nickel plates to an 18650 battery, but depending on the position of the electrode holder, the machine can be used to weld sheet metal and other metal objects. Now let's start making the device!
Step 1: Disassembling the microwave
Warning!
There is a danger inside the microwave oven. A large capacitor may be charged and is a potential source of dangerous or fatal electrical shock. Therefore, you should discharge it as quickly as possible by short-circuiting the capacitor terminals using the metal blade of a screwdriver.
So, remove the microwave cover to get to the electronic components of the device. Discharge the capacitor as stated earlier and begin dismantling the microwave parts. Find a transformer that should look something like the one shown in the photo. Unscrew the nuts and it should come out quite easily. I also removed some limit switches that will be used later and some power cables.
Step 2: Removing the secondary winding
It is necessary to rewind the secondary winding if we need to get more current and less voltage. The primary winding is where the power is supplied and the secondary has a thinner winding wire with red wires attached.
Fewer turns of wire increases the current but decreases the voltage, and more turns increases the voltage but decreases the current. We do not need the secondary winding of the transformer, so it must be carefully removed. Be careful not to damage the primary winding.
Step 3: Adding a New Winding
The new winding will provide the necessary current for the operation of our welding machine. Choosing a thick cable will reduce the number of turns from thousands to just a few and still provide the required current load. A thick cable has good insulation, which will not melt when heated, as in a thin cable.
First install the primary winding, followed by 2 shunts on each side and then wrap a couple of turns of blue cable on top. Be sure to leave enough cable length to attach the welding electrodes.
Step 4: Completing the Transformer Fabrication
Our super powerful transformer is almost ready. The top part needs to be welded back. Alternatively, you can use a 2-part epoxy to glue it in place. There is a choice, use the method that suits you best!
Step 5: Electrode Leads
Now we need to attach the ends of the cable to the copper bushings that will be used for welding. I turned the copper bushings on a lathe. But you can use copper clamps from a hardware store for this purpose. I have also included instructions for making a clamp for the electrode.
Step 6: Welding Holder
I will use a welder to weld the nickel plates to the battery. For this purpose, I will place two welding electrodes side by side, although you can easily place them opposite, like in a traditional welder. I designed and laser cut a fiberboard base for the holder that will hold the switch and electrode leads.
Step 7: Completing the Project
The transformer is supplied with a dangerous voltage of 230 V, so it is very important to close the transformer. A laser cut enclosure can be perfect for this purpose. Make sure all live parts are covered. This will ensure your safety when working with the device.
To connect the phase and neutral to the primary winding of the transformer, use the existing contact plates. I recommend installing a switch between one of the power cables to easily turn the device on and off. I used the switch from the microwave.
Your device is now ready. It's time to start spot welding!