When performing various repair work sometimes it becomes necessary to securely fasten thin metal sheets or their fragments. Ideal option in this case is the use of electric.
Unlike devices designed for manual electric arc welding, which have long become common attributes of home workshops, devices for resistance spot welding are much less common.
The main thing is that the selected cable passes through the window of the magnetic circuit. Wind two turns with the selected conductor at the site of the removed secondary winding. Now you can carry out the first test of a DIY microwave transformer for spot welding.
The ends of the cable are stripped of insulation. Following safety rules, connect the microwave transformer to a 220 volt network. Using a voltmeter, measure the voltage at the secondary terminals (that is, at the terminals of the welding cable).
If the voltage is between 2 and 4 volts, everything is fine. After this, the operation of the transformer is checked in spot welding mode, that is, in short circuit mode.
To test the operating current of the future spot welding machine from a microwave transformer, the stripped ends of the welding cable are securely connected to each other using a bolted connection.
Cover the secondary conductor with current clamps and briefly turn on the transformer. By indicator current clamp meters monitor the value of the short circuit current. If its value is about 500 amperes or higher, then everything is done correctly.
Assembling the device
In order for a spot welding machine made from a microwave to be used, it must be equipped with a lever for clamping workpieces, contact spot electrodes and a switch.
The lever, which provides point compression of the workpieces, as well as the housing for the transformer, can be made of wood. At the ends of the lever arms there are electrodes made of thick copper rods. The welding cable leads are connected to the reliable bolted electrodes. The switch is located in a convenient, easily accessible place.
Now your DIY microwave spot welding is ready to go. The workpieces to be welded are placed between the electrodes, clamped with a lever and the current is turned on. This is how welding occurs.
In this article we will tell you how to make a welding machine with your own hands using a transformer from microwave oven.
The welding machine is very popular among both professionals and home craftsmen. But sometimes you don’t need to buy an expensive welding machine at home, because you use it a couple of times and in the future it will be idle. Therefore, you can make it yourself and not spend money.
The main part of any welders working on the principle of arc welding is a transformer. You can salvage this part from old household appliances and create a home welding machine. But in most cases, the transformer needs modification.
DIY microwave welding machine
To create mini welding machine you will need a couple of microwave transformers. It is very easy to find an old microwave oven from friends, acquaintances, and neighbors. Most importantly, its power should be up to 650-800 W, and in the transformer it has not changed.
The microwave oven transformer includes 2 coils: primary and secondary.
Transformer from a microwave oven
2 transformer coils: primary and secondary winding.
There are secondary circuits with a small wire cross-section. Therefore, in order for the transformer to be suitable for welding, it must be removed and the old wires replaced with new ones with a larger cross-section. It can be cut on both sides of the device to remove the roll from the transformer.
When you cut a screw, the remaining screw must be removed from the magnetic circuit. This task will be easier if you loosen the metal tension before drilling.
Then use a drill or cutter to break the housing.
Do the same with the other transformer. As a result, you get 2 parts with a 220V winding.
It is important! Be sure to remove current surges (indicated by arrows in the figure below). This process increases the device's power by 30%.
You need to purchase 11-12 meter wire to make spare parts. He must have an area of at least 5 square centimeters.
To create a welding machine, you need to wind 18 transformers (6 in height and 3 in thickness) for each transformer.
Two transformers can be connected with one wire.
The wires must be very tight, in addition, the original packages must be connected in parallel.
If you measure the voltage on the secondary winding of the transformer, it is 31-32 V.
This home welding machine can easily process 2mm thick metal with 2.5mm diameter electrodes.
Cooking material using such an improvised device may cause power outages, since its body will be very hot. On average, after using each electrode, the device should cool for 20-30 minutes.
Home microwave welding machine does not work with thin metal because he cuts it. A ballast resistor or plug can be added to the apparatus to regulate flow. The role of a resistor can be performed by a piece of steel wire of a certain length connected to the low voltage winding.
Resistance welding is increasingly used not only in manufacturing enterprises, but also in home workshops and garages, where it can be successfully used for various works related to metal. Serial equipment for performing such a technological operation is quite expensive, but a device for resistance welding can be made with your own hands from an old microwave.
One of the options for a resistance welding machine from a microwave oven
To manufacture equipment for contact welding at home, you will need the following components, accessories and tools:
- a transformer that can be removed from an old microwave oven (if you need a high-power device, then you will need two such transformers);
- thick copper wire or small diameter wiring harness;
- levers that will be used as clamps;
- lever of the required length;
- a reliable base on which the welding machine will be installed;
- clamping clamps;
- Screwdriver Set;
- cables and winding materials;
- electrodes made of copper, due to which welding will be performed.
Transformer assembly
The main element of any resistance welding machine is a transformer, which can be taken from an old but working microwave. In order for a homemade welding device to be able to connect steel sheets up to 1 mm thick, a transformer with a power of at least 1 kW is required. If you need a more powerful resistance welding machine, you will need two transformers.
Step-up transformer from a microwave oven
To make equipment for contact welding with your own hands, you need to take not the entire transformer from the microwave, but only its magnetic circuit and primary winding. The secondary winding is carefully removed from the transformer, and the shunts that are located on both sides are removed from it.
We cut off the secondary winding with a chisel (chisel) or saw it off with a hacksaw.
Shunts are removed
The new winding for the microwave transformer is made from stranded wire with a cross-section of at least 100 mm 2 (or a diameter of more than 1 cm). It will be enough to make 2-3 turns. If the wire has too thick insulation, you can remove it and replace it with fabric insulating tape. If two transformers are used at once, then the secondary winding for them is made common, but it is very important to correctly connect the leads from their primary windings.
The next stages of making resistance welding from a microwave with your own hands are the installation of controls, the manufacture and connection of electrodes, the installation of the internal part of the equipment in a reliable case, which can also be taken from broken household appliances.
Another great video on the topic:
Selecting Electrodes
The electrodes of equipment for spot welding perform several functions simultaneously: compression of the sheets being joined, supply of current to the welding zone, and subsequent heat removal. Important parameters when choosing an electrode are its shape, dimensions, etc. It is these parameters that directly determine how high-quality the welded joint will be. The geometric shape of the electrodes can be straight or curly, but preference is given to straight models, as they provide better access to the welding area.
When choosing electrodes for a microwave welding machine, you can simply refer to the corresponding GOST (14111-90), which already specifies all possible diameters of these elements (10, 13, 16, 20, 25, 32, 40 mm).
The diameter of the copper rods that will be used as electrodes must be greater than or equal to the diameter of the working wires. To avoid active oxidation of the electrodes during operation, they are connected to the working wires by soldering. The electrodes of a resistance welding device (including one made from a microwave) actively wear out during operation, so they must be regularly sharpened, giving them the shape of a sharpened pencil using a file.
Bottom electrode installed
How to operate a homemade welding machine
Despite the fact that resistance welding is a fairly simple technological operation, it must be properly controlled to achieve the required quality of the joint. It is for these purposes that a homemade microwave oven should be equipped with appropriate controls. The main ones are a switch and a lever, with the help of which the required compression force of the electrodes and connected parts is ensured.
The quality of the resulting connection directly depends on the compression force, so it is advisable to make the lever for the welding machine longer. It is very important that the equipment for resistance welding from the microwave is securely fixed to the surface of the workbench. Clamps are used for these purposes.
You can increase the force transmitted by the electrodes not only using a lever, but also using a lever-screw mechanism, which can also be equipped with a home-made device. It is most convenient to attach such a mechanism directly to the lever so that manipulating it does not take additional time. In addition, this arrangement of controls will free up the operator’s second hand, which can be used to hold the parts being connected.
A special feature of working with a resistance welding machine is that current can be supplied to the electrodes only when they are in a compressed state. If you turn on the current before compressing them, they will spark the moment they come into contact with the parts, and this will lead to their burning and rapid failure.
The switch, also related to the controls for contact welding (including those made from a microwave), must be installed in the primary winding circuit. If you neglect this recommendation and install it in the secondary winding circuit, through which a significant current flows, the switch will create additional resistance, which will lead to welding of the electrodes together.
For a homemade welding machine with a microwave transformer, it is necessary to provide the simplest system cooling, also made by hand. An ordinary fan can be used as such a system. Using this device it will be possible to cool the transformer itself, electrodes and other conductive elements. Of course, such cooling will not be very effective, and you will still have to take regular breaks in work necessary to independently cool all heating elements of the equipment.
The welding process performed on a home-made machine is practically no different from a similar technological operation carried out on serial equipment. The first stage of this process is the compression of the parts, during which they undergo plastic deformation at the site of the future connection. In the second stage, current is supplied to the welding zone, passing through copper electrodes.
This stage is characterized by the formation of a liquid welding core, expansion of the weld pool and plastic deformation and sedimentation of the metal of the parts at the connection point. At this moment, molten metal begins to splash out of the weld pool. After the current supply to the connection zone is stopped, it begins to cool, which is accompanied by crystallization of the molten metal.
Finished welding machine (top view)
As a result of the processes described above, a cast core is formed in the joint zone, characterized by high strength. The resulting connection zone is characterized by significant residual stresses, which can be minimized if you do not immediately unclench the electrodes after stopping the current supply, but wait a while. You can even slightly increase the force on the connection area after stopping the current supply, which will also reduce residual stresses and allow you to achieve a forging effect.
By the way, using a transformer from an old microwave and simple components, you can independently assemble a welding machine for arc welding. Of course, such a device can hardly be called complete, but for some species minor works it is quite applicable. An example of creating such a mini-welder can be seen in the video below.
Spot welding, as is known, is performed on specialized equipment, however similar device You can not only find it in a serial version, but you can also make it yourself: for this you will need a transformer taken from an old microwave. The resulting device will give you the opportunity to perform high-quality spot welding with help alternating current, the strength of which is not adjustable.
The transformer is the most important element of any such spot welding device: its task is to increase the input voltage to the required value. To effectively cope with this, the device must have a high transformation ratio. Large microwave ovens are equipped with such transformers, one of which you need to find. When you find such a microwave oven model, you will need to very carefully remove the transformer from it.
The technology for assembling a spot welding machine can be seen in more or less detail in the video below. Example of this homemade device will help us illustrate the process of creating a point. For more details on the assembly details, read the entire article.
Removing the transformer from the microwave oven
If a homemade spot welding machine uses a transformer with a power of 700–800 W, then with its help you can join sheets of metal whose thickness reaches 1 mm. Such a transformer is included in the category of step-up devices; to provide power to the magnetron, it is capable of generating a voltage of 4 kV.
The magnetron that any microwave is equipped with requires high voltage to operate. In this regard, the transformer connected to it has a smaller number of turns on its primary winding and a larger number on the secondary winding. At the latter, a voltage of about 2 kV is created, which is then doubled due to the use of a special doubler. There is no point in checking the performance of such a device by measuring the voltage connected to its primary winding.
The transformer should be removed from the microwave carefully. Do not pick up a hammer or other heavy objects. The base of the microwave is unscrewed, all fastenings are removed, and the transformer is carefully removed from its installation site. In the device removed from the microwave oven, you will need, firstly, its magnetic circuit, and secondly, the primary winding, which, compared to the secondary, is made of thicker wire and has fewer turns.
Due to its uselessness, you will have to dismantle the secondary winding, for which a hammer and chisel will come in handy. It is very important not to damage or crush the primary winding, so you must act with the utmost care. If, when dismantling the secondary winding, you find shunts in the transformer used to limit the current, they must also be removed.
The secondary winding can be cut with a chisel
If the magnetic core of the transformer is not a glued structure, but a welded one, then it is better to remove the secondary winding from it using a chisel or a regular hacksaw. If the winding is very tightly packed into the window of the magnetic circuit, then it will need to be drilled or picked out by cutting the wires. This must be done very carefully, since the magnetic circuit may collapse due to such manipulations.
After dismantling work, a new secondary winding should be wound. To do this, you will need a wire with a diameter of at least 1 cm. If you don’t have such a wire in stock, you will have to buy it. In this case, it is not at all necessary to purchase a solid stranded wire of this cross-section; you can also use a bundle of several individual conductors, which together will provide the required diameter. After installing the new secondary winding, your upgraded transformer will be able to generate current up to 1000 A.
If you want to make your spot welder more powerful, then the technical capabilities of one transformer may not be enough for you. Here you need to use two such devices (respectively, by disassembling two microwave ovens).
Subtleties of upgrading a transformer from a microwave oven
To make a secondary winding, you need to wind 2-3 turns on the core, which will ensure an output voltage of about 2 V, and a short-term welding current of more than 800 A. This is quite enough for efficient work spot welding machine. Winding this many turns can be difficult if the wire used has a thick layer of insulation. Solving this problem is quite simple: you need to remove the standard insulation from the wire and wrap it with electrical tape that has fabric base. It is very important that the wire used for the secondary winding has the minimum possible length, which will avoid an unreasonable increase in its resistance and, accordingly, a decrease in current strength.
If you need to weld metal sheets up to 5 mm thick, keep in mind that this will require a spot welder with more power. To make it yourself, you need to use two transformers connected in one circuit. It is imperative to follow the appropriate rules when making such a connection. If you make a mistake and incorrectly connect the terminals of the primary and secondary windings of two transformers, a short circuit may occur. The correct connection of the windings, if there are no markings on their terminals of the same name, is checked using a voltmeter.
After correct connection of the same terminals of two transformers, it is necessary to measure the value of the current that they jointly generate. As a rule, homemade transformers intended for spot welding machines, which are planned to be used in home workshops, are limited in current strength - no more than 2000 A. Exceeding this value will cause interruptions in operation electrical network not only in your home, but also in your immediate neighbors. And this, naturally, will lead to conflicts. The value of the current produced by the connected transformers, as well as the presence of a short circuit in their circuit, is checked using an ammeter.
Another example of spot welding assembly is shown in the video below:
What results can be achieved if, in accordance with the rules, two transformers that are not different are connected? high power? If you take two identical devices with the following characteristics: power - 0.5 kW, input voltage - 220 V, output voltage - 2 V, rated current - 250 A - then by connecting their primary and secondary windings in series, you will get the output double the rated current, that is, 500 A.
Almost the same will increase in short-term welding current, but during its formation significant losses will be observed, which is due to the high resistance of such electrical circuit. Both ends of the secondary winding - wires Ø 1 cm - are connected to the electrodes of the spot welding machine.
Connection of 2 transformers according to scheme No. 1
If you have two powerful transformers at your disposal, but their output voltage is not enough to homemade apparatus, you can connect their secondary windings in series, which should have the same number of turns. This measure is resorted to if it is impossible to simply wind up the turns on the secondary winding due to the insufficiently large size of the window on the magnetic core.
With such a connection, it is necessary to ensure that the direction of the turns on the secondary windings of the connected devices is consistent, otherwise antiphase may result, and the output voltage of such a combined device will be close to zero. To experimentally determine the correctness of the connection, it is advisable to use thin wires.
How to determine the terminals of transformers of the same name
If the terminals of the windings of the connected devices are not marked, then it is necessary to identify among them those of the same name in order to connect them to each other. This problem can be solved in the following way: the primary and secondary windings of two or more transformers are connected in series, voltage is applied to the input of such a combined device, and an alternating voltage voltmeter is connected to the output terminals (terminals from series-connected secondary windings).
Depending on the direction of connection, the voltmeter may behave differently:
- show one or another voltage value;
- show no voltage at all in the circuit.
If the voltmeter produces any voltage, it means that there are opposite terminals in the connection circuit of both the primary and secondary windings. When the windings are connected in such an incorrect way, the following processes occur in them: the voltage supplied to the input of the primary windings of two connected transformers is reduced by half at each of them; The voltage increase occurs on the secondary windings, each of which has the same transformation ratio. The output voltmeter will register the total voltage, the value of which is equal to twice the input value.
If the voltmeter shows a value of "0", then this means that the voltages coming out of each of the series-connected secondary windings are equal in value, but have different signs, thus they compensate each other. In other words, at least one of the pairs of windings combined into a circuit is connected by terminals of the same name. In this case, the correct connection of the circuit elements is achieved by changing the order of connecting the primary or secondary windings, focusing on the readings of the voltmeter.
Electrodes for homemade spot welding
When choosing electrodes for a spot welding machine assembled with your own hands from a microwave, you should pay attention to the fact that their diameter matches the diameter of the wire to which they are connected. Copper rods can be used as such elements, and tips from professional soldering irons are suitable for low-power devices.
During operation, spot welding electrodes wear out actively. To correct their geometric parameters, they must be constantly sharpened. Naturally, over time, such elements will require replacement with new ones.
The wires that connect the electrodes to the spot welding machine must be of a minimum length, otherwise they will lose significant power from the device. Power losses will also become serious if there are many connections in the electrical circuit “electrode - spot welding device”. If you want to increase the efficiency of using your homemade equipment, then it is better to solder copper tips onto the wires that connect the electrodes. Using such lugs, you will avoid power losses at the contact points due to the increased resistance of crimp or any other connections.
The wires connecting the electrodes to the spot welding machine have sufficient large diameter, therefore, special tips, pre-tinned, will help make their soldering easier. Since the electrodes for such a device are removable, soldering is not performed at the points where they are connected to the tips. Of course, there is also a loss of power in such areas, which are constantly exposed to oxidation, but they are much easier to clean than crimped tips.
Installing electrodes on the welding machine
As already mentioned above, the electrode for resistance welding can be made from a copper rod or a tip from a professional soldering iron, if the power of the device is low. The wire from the device is connected to the electrode using a copper tip, which is connected to it by soldering.
The tip is combined with the electrode using a bolted connection, which must be very reliable so that an increase in resistance at the point of unreliable contact does not lead to a loss of power of the spot welding machine. To make such a connection, holes of the same diameter are made in the electrode and tip.
The bolts and nuts with which the electrodes and lugs will be connected to the wires are best chosen from copper or its alloys, which have minimal electrical resistance. Elements of such connections, which greatly simplify the maintenance of the resistance welding machine, are not at all difficult to make with your own hands.
Homemade spot welding controls
Operating a spot welding machine (especially one made from a microwave oven with your own hands) is not particularly difficult. For this, two elements are sufficient: a lever and a switch. The compression force between the electrodes, for which the lever is responsible, must ensure reliable contact of the parts being connected at the welding point. To meet these important requirements, the lever mechanisms of such devices can be supplemented with screw elements, which provide even greater compression force. Naturally, such an element of a spot welding device must have very high reliability.
On serious production equipment, which is used to join sheets of steel of considerable thickness, compression elements are installed that create pressure from 50 to 1000 kg, depending on the need. And on spot welding machines used for irregular and simple work in a home workshop, it is enough for such a mechanism to create a pressure of up to 30 kg. For convenience and ease of operation of the spot welding machine, its clamping lever is made longer; this will also increase the compression force to the required value.
For homemade home device A lever with a length of 60 cm is quite sufficient. Using such a lever, you can increase the applied force by 10 times. Accordingly, if you press the lever with a force of 3 kg, the electrodes and connected parts will be compressed with a force of 30 kg. To prevent such a lever from moving the device itself when pressed, the base of the equipment must be securely fixed to the surface of the desktop using a clamp.
The switch, which is responsible for supplying current to the device, is connected to the circuit of the primary winding of the transformer, the current in which is significantly less than in the secondary. If you connect the switch to the secondary winding, it will create additional resistance, and its contacts will be tightly welded under the influence of strong current.
If a lever is used as a clamping mechanism, then it is better to place the switch directly on it, then the second hand will be free (it can be used to support the parts being welded).
Features of working on homemade equipment for spot welding are that current should be supplied to the electrodes only when they are in a compressed state. Otherwise, you will encounter intense sparking of the electrodes and, as a result, their active burning. You can get initial experience in working with such a device using a training video.
The electrodes of spot welding equipment actively heat up during operation. In addition, the transformer and conductive elements of such a device are subject to intense heating. To avoid too much heat, which can lead to the failure of the spot welding equipment, a simple cooling system should be provided. For this, a regular fan is often used. You can also take breaks in work necessary to cool the elements of the device.
The holding time of the electrodes under current in a compressed state during the welding process can be controlled visually, focusing on the color of the point at the junction, or you can use a special relay for this.
Obviously, making a spot welding machine based on a transformer from a microwave is not at all difficult, after carefully studying the presented videos and photos of the assembly process and taking into account the recommendations voiced.
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It is important for motorists and homestead owners to have on hand a device for welding metal parts. Industrial goods in the retail chain are not cheap - from 3,000 rubles. Do-it-yourself microwave welding will completely replace it.
The main element of the welding machine
The basis of the homemade product will be a transformer from an old microwave oven.
It provided power to the magnetron and generated up to 4 kilowatts due to the high transformation ratio. IN large ovens its power is 700–800 watts. The unit created on it will be able to connect thin metal.
You will need:
- Transformer (if you need a larger power unit, you will need two).
- Installation platform.
- Large gauge copper wire.
- Long lever.
- Clamp.
- Cable and insulating material.
- Electrodes.
- Chisel or hacksaw.
- Ampere-voltmeter.
Removing the microwave oven
The electromagnetic emitter and inverter in it required high voltage. Therefore, the converter has fewer turns on the primary winding and more on the secondary. The latter generates a voltage of 2 kilovolts, which is then increased using a doubler.
To make a spot welding machine from a transformer:
- Carefully remove it by removing the housing and disconnecting the fasteners.
- We remove the secondary winding without damaging the primary.
- We remove the shunts that limit the current.
- Using a stranded wire with a cross-section of 1 cm or assembled into a bundle of several thin ones to the same diameter, we wind two or three turns of a new winding.
To prevent thick insulation from complicating the winding operation, remove it and wrap it with fabric insulating tape. To ensure that the resistance does not increase and the current does not decrease, the wire must be as short as possible.
Rework
The converted converter will provide the required output voltage and current of up to 1,000 amperes, which will allow micro-spot resistance welding of thin sheet metal.
For more powerful unit you will need two parts, upgraded as described above, connected in series in a chain. Such a welding machine will be able to weld five-millimeter metal fragments.
Identical windings of both converters and their correct combination will avoid the formation of antiphase, as well as short circuits!
Check the assembly accuracy and mark the pins. The serial connection is shown in the diagram.
Measure the values of the “spark” indicators with an ampere-voltmeter.
If the original devices had a power of 0.5 kilowatts, then with an input voltage they gave an output of 2 kilovolts and 250 amperes. In a pair, the latter will increase to 500. In order not to create interruptions in the power grid, it should be no higher than 2,000 amperes.
The same process occurs during welding. But due to the increasing resistance, when the ends of the secondary winding with a large cross-section are connected to the electrodes, significant losses are created.
Electrode preparation
For them, use copper rods or soldering iron tips.
Their diameters strictly correspond to the cross-section of the wires, which should be as short as possible to avoid power losses. It is more effective to solder electrodes to reduce the resistance at the crimp point on the contacts.
To make them replaceable, do not solder the wire-to-tip connections themselves. Connect them with a bolt method by drilling holes of the same size. It is better to use copper nuts and bolts, which have less resistance.
Control
It is enough to make a switch and levers that ensure a sufficient fit of the welded parts. To increase the pressing force, add screws to the mechanism. For convenience, equip the 60 cm long clamping lever with a durable rubber ring. It will lighten the load force, and the elastic band will fix it.
This is usually enough for work in a home workshop. To prevent the device from moving on the work table when pressed, its platform is secured with a clamp.
The switch is connected to the primary winding so that additional resistance and overheating do not appear at the contacts. For convenience, it is better to place it on the upper arm.
Attention! The equipment should only be turned on with the electrodes compressed, otherwise strong sparking will occur and the contacts will burn!
During operation of the transformer installation, the wires and tips become hot. So think about how to cool them down. A household fan will do. And while working, take breaks periodically.
Work principles
They are almost no different from the processes when using a welding machine industrial production. After compressing the workpieces and touching the electrodes, voltage is applied, and a voltage appears at the welding site. electric arc. Its plasma melts metal, connecting parts.
A residual voltage remains at the bonding site for some time, which can be reduced by not immediately disconnecting the contacts after the process is completed.
As you can see, with the necessary skills, the availability of initial elements and tools, it is quite possible to make a welder yourself. It will be an excellent help in the household and will save your money.
