Scheme of resistance welding on an inverter. Contact welding. Typical characteristics of the spotter

What apparatus is used in this case, is it possible to make it yourself - below we will try to answer all these questions.

Spot welding is used not only in production, but also at home.

On an industrial scale, the choice falls on this type of welding when it is necessary to join non-ferrous metal alloys, steels of various grades, when sheets have different thicknesses, when creating profile blanks, for example, corners, etc.

At home, spot welding has found its application in the repair of household appliances, batteries, cables.

To reduce the cost of replacing system batteries, this machine can weld laptop batteries, screwdrivers and other mobile devices.

Batteries are welded according to conventional technology.

The welding process itself consists in heating a metal object to a state of plasticity, after which it is deformed, that is, it is connected.

To create a better seam, it is necessary to ensure the constancy of the process, that is, constantly maintain one speed of processing the object, monitor the pressure.

These requirements are more relevant to manual welding, since in enterprises this process is carried out automatically.

Heating of metal objects occurs due to the passage of an electric current, from which heat is generated on the surface.

In the place where the electrode contacted the surface, a liquid core begins to appear, formed from the melting of two parts.

When the current stops flowing (0.01-0.1 sec), then the core begins to freeze, thus allowing both parts to be held.

To compress a metal sheet, pliers are used, which are divided into manual and suspended.

Hand pliers contribute to the generation of current, which is then fed to the electrodes that clamp the workpiece. Suspension pliers are used in the industry, featuring high performance.

Contact spot welding has a number of advantages:

• The speed of work;
• The safety of work is achieved due to the low voltage;
• The strength of the connection is ensured, but, unfortunately, not tightness;
• You can make a welding machine yourself at home.

Process Features

Resistance spot welding is a simple process: current passes through a spot connection, generating heat.

In this case, the condition of the contacts affects the quality of welding, any roughness or oxide can adversely affect.

See the video for the spot welding process.

When welding, it is necessary to take into account such properties of metals as thermal conductivity, resistance and melting point, since they are different, for example, iron will melt at a temperature of 1300 degrees Celsius, copper - 680, aluminum - 435, zinc - 1115, etc.

Certain requirements are also imposed on the electrodes:

• High rates of heat and electrical conductivity;
• Strength;
• Machining should be easy.

The quality of the weld also depends on the diameter of the electrodes, it determines the current density.

To visually correctly select the diameter of the electrode for the sheet being processed, it is necessary to multiply its thickness by two.

Contact spot welding can be carried out not only on an industrial scale, but also in everyday life.

In order not to have to use bulky equipment at home, manufacturers have released a compact device suitable for minor repairs, for example, household appliances, batteries or a car.

The device is called a spotter. It has two leads, one of which is attached directly to the object, and the second - to the electrode.

Ticks are not needed in this case. To ensure the best workflow, it is desirable to choose a power source in such a way that it is as close as possible to the welding site.

Despite the fact that the spotter is more of a handheld device, it is quite functional.

The simplest devices using single-phase current are reliable and simple, but metal sheets with a thickness of more than 0.8 mm cannot be connected.

More complex and powerful models come with the use of a transformer, it should be noted that they are more expensive. But the most expensive spotter is inverter.

In everyday life, you can get by with a cheaper do-it-yourself device.

Spot welding is characterized by the strength of the seam, which sometimes has to be removed by drilling. The drill is usually used in the case of car repairs.

It should be noted that there is special drill for drilling spot welding. It is better to buy a drill, and not to use some kind of drill that you think is suitable. The price of such a drill is low. These works must be carried out carefully so that the body can be repaired in the future, and not order a new one.

Diagram of a homemade welding machine

Buy for household needs welding machine there will be no reason, especially since you can do it yourself.

The dimensions of such a device will directly depend on the needs. It is more convenient to assemble a medium-sized device. Below is a diagram of a spot welding machine.

1 - transformer OSM-1.0 modified; 2 - conductor (duralumin bar with a diameter of 30, L300, 2 pcs.); 3 - insert (steel bar with a diameter of 10, L30, 2 pcs.); 4 - electrode (copper rod with a diameter of 12, L50, 2 pcs.); 5 - brass washer (2 pcs.); 6.12 - M6 screws; 7 handle; 8 - eccentric; 9 - cheek (2 pcs.); 10 - spring; 11 - output of half of the secondary winding (4 pcs.); 13 - textolite bushing (with a groove for the end loop of the spring); 14 - bolt M8 (6 pcs.); 15 - textolite washer (4 pcs.); 16 - insulating coating (varnished cloth or protective adhesive tape on a fabric basis, 2 pcs.); 17 - transformer casing.

The operation of the welding machine is based on the physical Lenz-Joule law.

The meaning of the law is that the conductor begins to generate heat by passing an electric current through itself, in an amount proportional to the resistance of the conductor material, the square value of the current and the time it takes to "pass" the current.

Wires are selected taking into account this law.

Since contact spot welding occurs due to electrical impulse, then to create the device you will need a transformer, which is not recommended to be connected directly to the power source.

A rectifier bridge with a thyristor is required for correct connection.

The scheme of a home-made device involves the use of another power supply with a transformer and a rectifier bridge for more power.

The current is collected, the pulse is created using a capacitor.

The bridge of the first transformer is closed by a thyristor, which acts as a cathode.

It will remain open until the capacitor is completely discharged. "Impulse" is the beginning and end of the welding machine.

To create a more powerful device, the circuit changes slightly: you need to add a semiconductor thyristor, a time relay.

Homemade welding machine

The circuit is the basis for creating a welding machine, and its “heart” can be considered a transformer that will create the necessary voltage.

It should be noted right away that this element must be powerful with a minimum value of 700-800 watts.

You can make a homemade welding machine using an inverter, but this requires certain knowledge and skills. Using a transformer rather than an inverter is more in a simple way creating a homemade device.

The transformer can be taken from the microwave. Moreover, an old device or a microwave oven can be purchased specially from the hands for this.

The scheme of further actions is as follows:

1. You need to carefully remove the transformer from the microwave, removing all fasteners, disassembling the base;
2. The secondary winding from the microwave transformer must be knocked down. You can use any tool at hand: a hammer, a chisel, pincers, a drill, etc. By the way, the drill should always be at hand when using spot welding. The secondary winding differs from the primary in a thicker wire. It is also necessary to act here carefully so as not to damage the wire used for the primary winding;
3. It is necessary to make two or three turns of a new secondary winding. To obtain a current of 1000A, it is advisable to take a wire whose thickness will be at least 1 cm. Physically, it will not work to make more than three turns, therefore, if necessary, another microwave transformer is added, as mentioned above;
4. The next step is to check the winding for short circuits. A voltmeter is used for this. If none are found, therefore, you can continue to work;
5. Next, the microwave transformer is checked with an ammeter. If the current strength exceeds the value of 2000A, then it is necessary to reduce it in order to avoid further voltage drops.

Copper wire works well for electrodes. The thickness of the wire is selected so that the diameter of the wire does not exceed its diameter.

You can use two soldering irons, or rather their tips, which can be installed as electrodes.

Current losses can be reduced by shortening the length of the wire coming from the electrode.

The wire is connected to the electrode using a copper tip, you can make a hole by drilling, while the drill is used for 8.

If you solder the tip with the wire, then it will be possible to avoid oxidation, which is inevitable when you first turn it on.

When creating levers, the following point must be taken into account: it is necessary to create free movement of the upper lever horizontally and vertically, this can be done using special openings in the body.

If desired, you can do the lower arm in the same way.

It is necessary to provide a place for the switch-switch on the back cover of the device. After installing the toggle switch, the power cable is inserted.

To exclude the possibility of the cable falling out, it must be made thicker, thicker.

The microwave transformer is attached to the base with self-tapping screws. A terminal is put on the mount and grounding is done. All connections must be carefully insulated.

To keep the upper arm in a raised state, you can use a regular rubber band worn on two self-tapping screws.

Watch a video about spot welding with your own hands in our article.

Quite often there is a need to carry out welding work at home. As a rule, these are small volumes performed on a case-by-case basis. Since factory-made welding machines are very expensive, many craftsmen prefer to make them in various ways from scrap materials. A good option for a factory analogue is considered to be do-it-yourself resistance welding from an inverter, which provides high quality work at a relatively low cost.

The device and principle of contact welding

The principle of operation of any spot welding machine is to heat the electric current in certain places metal parts, their subsequent melting, mixing with each other and solidification. As a result, a welding seam is formed in the places of solidification of both metals. During operation, both parts are reliably compressed and fixed by electrodes to which an electric current is supplied.

Resistance welding at home will require powerful power sources, which can lead to overheating and failure of household electrical wiring. In this regard, it is recommended to check the condition of the wiring in advance and replace it if necessary.

When performing spot welding, two workpieces are connected to each other along adjacent edges. This method is very effective for working with small parts, thin metal sheets and bars, up to 5 mm in diameter.

Surface joining is done in one of three ways:

• In the fusion method, all parts to be welded are connected and heated by an electric current until they melt. This technology is widely used in working with non-ferrous metals, low-carbon steels, brass and copper blanks. In other areas, this method is used extremely rarely due to the high requirements for temperature regime and the absence of impurities at the joints. Homemade resistance welding from a welding machine works in the same way.
• Continuous welding of workpieces by the flash method is carried out using welding tongs. The parts are connected at the moment the current is turned on. After the edges of the mounted parts are melted, they are upset, and the current supply is stopped. In this way, thin-walled pipelines and workpieces with different structures are welded. The main disadvantage of this method is the possibility of metal leakage from the weld and the appearance of carbon monoxide.
• The third method is an intermittent melting, during which the workpieces are alternately dense or weakened in contact. The welding line is closed in the connection area with clamping tongs until their temperature rises to 950 degrees. This method is used if the power of the welding device is initially insufficient to perform continuous reflow.

Preparing parts and assembling spot welding

The standard design of the contact welding machine consists of a power section, a circuit breaker and a protective device. In turn, the power part includes a welding transformer and a thyristor starter, with the help of which the primary winding is connected. The entire inverter is not needed for a home-made welding machine, it is only necessary to take the main parts from it. This is a transformer with a power supply, a control system and a switch.

In the manufacture of spot welding, first of all, the secondary winding must be removed from the transformer, since it is not used at all during operation. The main thing when removing the winding is to keep the primary winding intact. Instead of a remote secondary winding, another is superimposed, made of thick copper wire, with a cross section of about 2-3 cm. Then it is wrapped with insulating paper and varnished for additional insulation and fixation.

Then the direction of each winding is checked using a conventional voltmeter. There should be no short circuits in the newly created circuit. After that, the current strength is determined. This procedure is mandatory for all such devices with two or more windings. The value of the current strength should not be more than 2 kiloamperes. In case of exceeding the established level, it must be reduced.

During the preparation of the transformer coil and the winding of the secondary winding, it is recommended to follow the mandatory rules. To calculate the number of turns, you can use the formula N = 50 / S, in which N is the number of turns, and S is the core area (cm2). Helps speed up calculations online calculator calculation of the inductor. Since parts from the inverter are used in the design, the parameters of the primary coil are first determined, the necessary calculations are made, and only then can the secondary winding be manufactured.

Pay attention to the grounding of both windings. This is due to the high power of the received current, which can be deadly when in contact with live parts. Along with careful isolation, great importance has a dense stacking of turns. Otherwise, inter-turn short circuits may occur and the wires will burn out as a result of overheating. It is necessary to take care of the cooling of the transformer. It may be necessary to install an additional cooling system, which includes radiators blown by fans.

Additional elements of the welding machine

The next step after the manufacture of the transformer will be the manufacture of contact tongs. The quality of their manufacture largely determines how resistance welding from an inverter will work. The design of the pliers is selected depending on the specifics of future welding work. The gripper is manufactured according to the drive system and the dimensions of the parts to be connected.

The most important part of the pliers are the contact tips. You can use copper tips from a soldering iron or purchase ready-made products. It should also be taken into account that they should not melt during operation, therefore, refractory metal should be used for their manufacture. Usually rods with a diameter of about 15 mm are used. The diameter of the cable to be connected is always smaller than the diameter of the lugs.

The wires are connected to the electrodes using conventional copper lugs. Direct connection is carried out by bolts or soldering, which significantly reduces the likelihood of oxidation at the contact points. Soldering is most often used in low-power devices, eliminating incorrect connections that cause current disturbances at the output of the device.

The main advantage of bolted connections is the ability to quickly replace parts that have failed without additional soldering work. All bolts and nuts must be copper. If it is supposed to impose connecting seams with a large length, in this case the tips are equipped with special rollers.

After the manufacture of the tongs, the time comes to solve an equally difficult task - providing the necessary pressure of the electrodes at the point of welding of the parts. The main difficulty is due to the fact that it is impossible to manually create a high and uniform pressure. If other options are not considered, then it is best to initially abandon the manufacture of spot welding from an inverter, because the efficiency of such an apparatus will be extremely low.

In industry, this problem is successfully solved by using amplifiers based on pneumatic or hydraulic systems. At home, making such devices is almost impossible. For homemade spot welding, a compressed air system that is powered by a conventional pneumatic compressor. The most optimal maximum indicator required for normal operation will be the force at the ends of the electrodes, which is 100 kg or more. The change in pressure occurs with the help of a separate regulator, which can also be built into the overall control system.

At the final stage of the assembly of contact welding from the inverter, it remains only to mount the entire system. For installation, it is recommended to use ready-made elements, which greatly simplifies assembly and improves performance. All the missing parts are in the inverter, from which the transformer has already been taken.

The capacity of the capacitors installed in the inverter may not be sufficient for normal operation. Therefore, if necessary, they are replaced by other parts that are most suitable in their parameters. Next, stepwise current adjustment is performed, the accuracy of which is affected by specifications secondary winding. By such adjustments, it is possible to create equipment capable of operating in various modes.

Welding possibilities in body repair

The need for welding work during body repair is beyond doubt. And so that this process does not take time, and also allows you to fix many problems with your own hands, it is important to choose the appropriate equipment.

Body repair is unthinkable without contact welding

Welding process for body repair

The vast majority of work in the repair of a car body can be done by resistance welding. This type, being rather specific, is used mainly because of its simplicity, lack of consumables and high level of productivity.

More about resistance welding

According to technical definition this type of welding is a process during which an integral connection is formed. Such a connection is a consequence of heating the metal by means of a passing electric current, as well as plastic deformation of the joint zone itself (the latter occurs as a result of compression).

There are several ways to do resistance welding with your own hands, including spot welding. Such a scheme involves the connection of parts in separate sections, which are called points.

To obtain a weld point, the parts to be welded (previously carefully cleaned) are overlapped, compressed with a certain force, after which a current pulse is passed through the place of their contact. At the contact boundary of the parts to be welded, the machine forms a place of melt, called the core of the point. When the current flow is completed, this nucleus will crystallize and form a very strong bond.

Drilling before joining parts

There are a number of factors that can affect quality, i.e. point strength and size:

• We are talking about such a parameter as compression force;
• The quantity index also plays a certain role. welding current which is issued by the machine;
• The duration of the current pulse is also important;
• Finally, the diameter of the contact surface of the electrodes matters.

Applied devices

Do-it-yourself contact welding during body work is carried out using appropriate welding machines. The scheme of their application assumes the following: the machine (in other words, the apparatus) heats up, and as a result of heat release, direct welding occurs in those places where the parts are connected.

It turns out that any apparatus is based on the principle of heating the place of welding with current with simultaneous exposure to pressure.

A stationary machine can be used, as well as a suspended or mobile machine (for manual work). Each such apparatus, in turn, is divided into certain varieties, taking into account the method of welding.

The scheme of each apparatus assumes the presence of a number of parts: electrical, mechanical, hydraulic systems, pneumatic systems (or water cooling systems).

The apparatus for resistance welding may well be designed with your own hands, which we propose to talk about in more detail.

Factory seam pattern

Self-assembly of the device

The apparatus for resistance welding consists of two units:

• Welding remote gun;
• Power unit.

The order of manual assembly is well demonstrated by numerous videos. The process of manufacturing a gun begins with the fact that you should create an adapter and electrodes. For this, a textolite sheet is taken and overlays are cut out of it (dimensions are determined by one's own hand). Then you need to drill channels in the lamp holder for the wires. These wires will lead to the backlight.

A microswitch is attached to the finished pads with screws and two holders. It is possible to bend spacer strips from a strip of plexiglass, taking into account their location on the overlays. We should not forget about the placement of the welding cable passing through the handle.

The end of such a cable is soldered, then inserted into the adapter hole and fixed with a screw. It is recommended to blunt the sharp edges of the overlays. It is important to wrap the handle with electrical tape. The finished version, again, is excellently viewed in the video.

As for the power supply, it is assembled from a relay on a welding transformer and on a thyristor. The electrode is connected to one output of the low-voltage winding using a welding cable. The second terminal during manual welding must be securely connected to the most massive part to be welded.

The primary winding of the transformer is connected to the network by means of a diode bridge and a thyristor included in its diagonal. At the same time, an auxiliary transformer is also needed to ensure the control of thyristors and the backlight.

That is, home-made contact welding is quite possible. After the assembly is completed, the welding machine must be tested. The finished device (how it looks, the video shows) will allow you to perform many works.

Thus, when assembling the corresponding resistance welding machine with your own hands, you need to stock up on the above elements for the gun, as well as for the transformer. Since it is the transformer that affects how the device will end up in size, it is recommended to start the assembly process with it.

How do-it-yourself spot welding is done and what you need to know

Foreword

Do-it-yourself spot welding is made in just a few hours. This is not a high-tech mechanism that should be assembled only at the factory, and soon you will see it! Now we will assemble the device, the technical characteristics of which will not be inferior to those of the purchased goods!

We collect the transformer

The most important detail, the heart of any electrical appliance of this type, is the transformer, with which we will receive the necessary voltage. The transformation ratio must be very large, so we immediately turn our attention to powerful and voluminous microwave ovens - this is where you can get the necessary element. Power should be about 1 kW - this is perfect option, but, in the absence of such, it is also suitable for 700-800 watts. In the microwave, a step-up transformer delivers up to 4 kW to power the magnetron. Exactly what we need. We are considering step by step instructions for the manufacture of the necessary transformer.

Step 1: Remove the transformer from the microwave.

You should not immediately disassemble it with a hammer - it will come in handy in its entirety. We unscrew the base, remove all fasteners, we get it.

Step 2 We knock down the secondary winding.

We only need the primary one (this is the one inside, the wire on it is much thicker and smaller). You can do it with a chisel, a hammer, a hacksaw, even drill corners with an electric drill - anything, as long as the result is the right one. Your task is not to damage the primary winding and the magnetic circuit, and you can do whatever you want with everything else, even for scrap metal.

Step 3 We wind the secondary winding.

We need to get a current of about 1000 A as a result, so we go to the market and buy a wire with a diameter of 1 cm or more. It is expensive, but we can’t do without it. If you want to save money - buy it in a bunch, and not one whole one - this does not affect the course of the case.

Step 4 We make 2-3 turns.

We make 2-3 turns of the secondary winding, at the output we get about 2V. The more you put into the window, the greater the voltage will be, although after 3 turns there is no more room left in the window. If you need a powerful device, then you can disassemble 1 more microwave or find an additional transformer and connect 2 together. It will be possible to work with metal up to 5 mm thick.

Step 5 Check the direction of the windings.

Using a voltmeter, we check the direction of the windings, as well as the presence of short circuits. If there are none, you can proceed to further work.

Step 6 Check the current.

When connecting 2 or more transformer windings, it is necessary to check the current strength at the output. If it is more than 2000 A, reduce it. This will lead to power surges and you simply will not fight off the neighbors who will run around complaining about you.

Making electrodes

Here everything is simpler than a steamed turnip. We buy electrodes at scrap metal or the market, for this copper twigs with a diameter of 1.5 cm or more are suitable. The main thing to remember is the principle - the diameter of the electrode should not be less than the diameter of the wire and that's it. If your welding is weak, then you can destroy 2 soldering irons and take tips from them - ideal and resistant electrodes that will last a long time!

The wire that goes to the electrode should be as short as possible to reduce current loss. For connection, a copper tip or a hole is used, which can be made with an electric drill and a drill for 8. We tighten the bolted connection and the rod will not run away anywhere. You can solder the tip to the wire to avoid oxidation that will occur when you first start the machine. Unsoldered contacts can create additional resistance, which is very noticeable at low power of the device.

The only advantage of bolted connections is that the electrodes can be removed quickly, otherwise you will have to completely re-solder. This is often done during intensive use, so it makes sense to fasten it that way. Bolts and nuts are easier to buy copper - the result will be much better. Homemade contact welding will turn out to be “fun”, you can remove the electrode in a minute, instead of soldering them for half a day.

Process control and "infrastructure"

This includes levers and switches. You simply cannot do without a good grip, especially when welding thick sheets of metal. That is why you need to take care of a quality lever. On an industrial scale, the force can reach 50-100 and even 1000 kg, but 30 kg will be enough for us, so we make the lever moderately long so that the resistance welding made by our own hands is convenient.

It is best to pull the beginning of the lever arm out of the table so that the emphasis is on it, and not on the machine (suitable for stationary welding devices). The length of the handle should be about 60 centimeters with a ¾ bottom fastening so that the leverage on the clamp is equal to at least 1:10. Then, when exerting 2 kg on the handle, you will press up to 20 kg on the metal leaning against the work surface.

As for the switch, everything is simple here: we put it on the primary winding, since there will be a very large current on the secondary winding, the resistance of the switch will interfere with the operation of the device. You can take out the lever on the handle - original and very practical. You will be able to turn on the device only after metal contact, which will reduce energy costs and protect against sparks.

Homemade spot welding is already ready and now it’s enough just to test it in operation to check that the assembly is correct. It is suitable for welding metal up to 2-3 mm thick when using a 1 kW transformer and up to 5 mm when two or more are connected in series!

Due to the fact that the welding contact for a time that is much less than the melting of the melt, it provides more productivity and less flexibility, because

Contact welding. Types of contact welding.

Because the process is easy to automate and easier to integrate with flow lines, this method is better used for mass production and mass production.

This method has been used in the automotive and aerospace industries.

Since the joints obtained by contact welding are of very high strength and quality, do not depend on the quality of welding, this method finds application in other industries.

With the thickness of the welding seam, connect from hundreds to tens of millimeters as well as tens of mm.

Also welding of oil and gas pipelines.

For robots, systems with an increased frequency of the supply voltage are used, which makes it possible to reduce the size of the transformer.

Classification of welding methods

In accordance with GOST 158-78-77 "Contact welded and welded joints" there are 3 main types:

— spot welding;
- seam welding;
— Direct welding.

However, the series of these methods reaches 300 names.

Spot welding(Kt) is a method in which parts are welded at separate points with two electrodes and welding pressure is applied to them, carrying the welding current.

pulse welding time

Release the pressure, cool the part and get the core casting.

The design of a welded joint (shaped core of a certain size) is determined by two important physical phenomena:

1. Welding of metals by welding current
Q=J^2cRtu
second

Heat transfer from the welding zone λ-thermal conductivity

Sv In the range of electrodes, heat is released during the passage of current and heat, transferred to the mass of work and the action of the electrode.

because

E. Thomson decided to use a copper electrode and λcu >> If the shape of the cast core is lenticular, it is favorable for a welded joint.

If Jcb and Tcc are increased, a molten core begins to develop.

The use of cast electrodes and the increased heat transfer in them compared to the mass of work determine the development of the melting process in the foundry core exactly in the mass of work, and not in the electrode.

In this regard, the probability of failure is reduced by melting in the core, i.e.

Burns are difficult, which determines the effectiveness of spot welding.

Projection Welding - This may be due to one of the types of welding in place.

Spot welding is created by local heating of the work with electric shock and plastic deformation in the joint area due to compressive force.

Q (R) - due to increased stability;
- Q (λ) - metals actively redirect heat.

The connection is created due to two effects:

QI^2R
— Qλ

Protective welding contact(Cylinder)

Rm - The seam seal seals off the welds on the flow line of the cylinders (electrodes), pushing the parts from the side that feed the JSV flow and the moving parts at the welding speed VSV - even through these rollers.

It is used in cases where welded joints must be sealed with welding contacts.

Sealed sewing - for welding containers, gas cylinders, tanks, cavities, etc.

J = I / S - current density
Jš - current

The process is carried out by removing heat and heat.

Seam welding is divided into three processes:

- continuously

With this method, when the flow is constantly continuously performed, a continuous seam is obtained without a distinctive core casting that overlaps.

The disadvantage is the increased heating of the electrode and the need for frequent flow.

- Individual pulses (interrupt)

- Q = f (λ) (tcb + tn)

Changing the amplitude of the current JSV, the duration of its generation - Jc, the duration of the gap - tn and the welding speed - USV can control the amount of overlap LN of cast cores, which is usually sufficient up to 25%, but should not be performed ln>50%.

Due to the better impact of the electrode, their resistance is significantly improved.

When welding heat-resistant steels with low thermal conductivity and high resistance to deformation at high t (thermal resistance), welding forces increase, i.e.

welding stage.

Step welding- the welding current is interrupted, the electrodes stop when the welding current passes.

It provides more reliable contact in the current range when the electrodes stop and the welding pulse passes.

After the current is turned off, the welding forces in the contact area avoid hot cracks.

Contact - welding

There are several types of welding contacts (Ks).

Consider the method resistance to welding, while the parts are first pressed against the electrodes with sponges (prismatic electrodes) to ensure electrical contact and inability to slip through the electrodes.

It is then compressed by the welding force P, the welding current is switched on and the parts in the joint are heated by this current Ic.

Then put the Rozadka 1.5-2 times less than heating, then turn on the current, and the parts are under the influence of precipitation P.

The moment the smallest deformable resistor is used, the force of the deposit is applied and the current is turned off, and the metal layers, heated to high ductility, are compressed from the intersection to the periphery.

At the same time, residual oxide films and honeycombs (metal at the edge of the bonding zone) are removed from the joint.

Thus, small parts up to 20-40 mm in diameter are welded, and the joint is formed in the solid phase without melting the metal. The heated plastic metal is displaced into hail, and the solid heated particles of the working material come into contact.

The disadvantage is the need for careful preparation of the ends of the weld and the need to connect large capacities to the large capacity of the plant.

Another way - flash welding.

It is technologically different from resistive welding, so the voltage in the transformer's primary (and secondary) is guaranteed until the decay ends touch.

As the parts approach contact, individual microscopes enter the contact surface, much fewer in number than if the parts were pressed in advance.

The cays are destroyed, and the contact surface increases. At the first contact, the welding current arises and occurs on several microspheres, therefore the current density in the contact of a separate microspace is so high that the metal heats up in milliseconds and then boils. In this case, explosive destruction of liquid contact bridges occurs.

The new contacts of the microstate are in contact with the metal vapor, i.e.

The increased vapor pressure of the metal in the joint protects the weld area, which heats up to tpl when interacting with the atmosphere.

When melting, the ends of them work in such a state that a thin layer of liquid metal appears on the surface, which provides uniform heating over the entire area of ​​​​the joint, a sediment force is applied to it. The liquid layer from the ends is compressed to the edge of the joint - in hail and under high pressure the compressed parts of the part come into contact,

TV. I next to the liquid layer is not much lower than tpl and was very ductile, and then partially and solid metal is compressed into hail, and under pressure a strong welded joint is formed with the least errors. degradation products and oxide films were extruded into deg.

Fusion welding provides a better connection since the metal on the surface of the ends where contamination can occur is removed during the explosion of the liquid bridges during the reflux process.

The liquid layer and part of the ductile metal are compressed into hail, and completely clean (young) surfaces come into contact.

This does not require careful processing of the weld ends, as is the case with resistance welding.

In addition, if welding parts with different cross sections form a special edge section, the initial contact surface is reduced, the fusion process is more efficient and the process continues, the parts are heated and have a normal shape.

Protective welding with intermediate payment or preheating

When the front welding of large parts: rails, pipes, main pipelines - in order to facilitate the initial phase of the reflow process, the process used includes the first reserves to slowly reduce the occurrence of contact and form liquid and metal vapor.

Then the parts are heated, and the heat generated in the fusion zone is distributed to the work mass and heated.

Then the contact between the switches is recreated until the ends are heated, so that the further process will be continuous, without interruption.

Turn to Lightweight Welding(WITH)

This may be due to the types of spot welding.

It is used for welding parts that occupy a large spatial position.

Usually the Scheme 1 process does not work because the contact with all parts of our work cannot be the same due to the difference in quality of the device, deformation conditions, the location of the contact from the current guide device.

This weld welding method takes place by forming a solid phase joint by extruding a liquid phase to the periphery.

To ensure the same conditions for contacting and deforming a large number of parts, it is necessary to ensure reliable contact with each electrode and parts in the first welding force (or previous pressing force) that compresses all the rods.

This should provide a slight deformation of the parts in contact.

The forces are then removed to the value of the welding force. Since the same conditions for contact with all parts are not guaranteed, but it is better to provide momentum first heat pump, in which the parts are heated in contact and under the influence of the welding force.

Then you can still jop, then turn on the welding current.

Forging force is used to reduce the base, and we get a multi-point connection with high quality.

At the starting point, the current flows along the points, the area is small and the current is high, they start to melt and then deform when welding.

We kill cores and small footprints without any supports and fins.

With a single welding, several welded joints are obtained. However, if the parts have a protective coating that must remain on the surface after welding, only weld welding should be used, since the large surface area between the electrode and the part has a low current density, and the coating will remain.

Physico-chemical conditions for the formation of compounds
The design of the weld in resistance welding.

Welding of metals by welding current
Heating and melting of metals at the point of contact with the release of energy when passing through an electric current. Spot welding current
Replacement of current in contact welding at several points.

Welding in the contact zone and seam welding
Factors affecting the design of a quality weld.

Welding on the floor
Spot contacts in resistance welding. Seam welding
Drain in the form of a seam of successive dots.

relief welding
Welding with contact in the prepared relief. Control circuits for switching welding devices
Electrical circuits for providing welding current and voltage on contact machines. Contactors of contact machines
On and off devices. Welding or secondary circuit of contact machines
Current-carrying elements for high values ​​of current and force of compression.

Transformers for contact welding machines
Characteristics of transformers for resistance welding. Pneumatic equipment for contact machines
Pressure relief devices.
Also on the topic:

Special Methods

Contact welding modes are a set of parameters that are set by the welder before starting work. The parameters of these welding modes depend on the metal product that is planned to be welded, the experience of the welder, and other things. The selected welding modes directly affect the quality of the resulting joint: incorrectly selected parameters can lead to a poor-quality seam, which can subsequently crack.

The main parameters for resistance welding will be:

• The strength of the electric current.
• Reinforcement of compression for welded parts.
• duration of current flow.

We will talk about different welding modes, and specifically the contact method of welding, further.

Welding modes and their influence on the weldability of metals.

Welding modes are divided into two main types:

Both types differ in the duration of the current exposure to the welded part.

The hard mode of welding metal products involves a short exposure to current on the parts, while soft welding modes, on the contrary, involve a long exposure.

The choice of one or another type depends, first of all, on the metal that needs to be welded: its thickness, thermal conductivity indicators, etc. matter.

So, hard welding modes are usually used for metals that have a large thickness, but at the same time lower thermal conductivity. For example, the welding mode for mild steel will be much harder than for aluminum alloys.

The shape of the melting of the metal and the location of the melt zone largely depends on the processes of heat generation and heat removal that occur in the electrode and the workpiece itself.

The duration of current exposure affects heat generation and heat removal, and, accordingly, the welded joint itself.

When welding in soft mode, the shape and location of the cast zone will depend directly on the electrode and the materials being welded. So, in the soft welding mode, the cast core is at the same distance from the surfaces of the part, this contributes to the fact that the irregularities formed during the welding process are shifted into the part with a large thickness.

Note that under mild welding conditions (in which the heating time of the metal product is much longer), the heat-affected zone will also be wider than with hard welding.

With hard welding, this core will be quite symmetrical with respect to both parts to be welded.

During welding, it must be taken into account that the heat removal to the electrodes during hard welding is minimal, which is what makes it possible to obtain a large height of the cast zone in this welding mode (in other words, hard welding modes for parts having the same thickness give a greater penetration depth).

The quality of the obtained welded joints, made under different welding conditions, is evaluated by the following parameters:

• The seam should not have significant softening in the zone of metal joining.
• The formation of rather fragile structures in the joint zone, which can subsequently collapse, is unacceptable.

  This is especially true for the transition zone of the seam.

• The connection zone must be homogeneous and dense, the cast and transition zone must not have visible violations of their complexity.
• The connection must be strong enough.
• Welding work should not reduce the corrosion resistance of the metal product.
• Deformations of parts are allowed within the normal range.

Note that when performing resistance welding, compliance with these conditions depends on the capabilities of your equipment for welding, the actual product that will be welded, and the experience of the welder.

Keep in mind that metals that have good weldability allow welders to use a variety of parameters to set the welding mode, and this, in turn, allows you to get better joints.

Methods of resistance welding and the formation of joints.

All methods and modes of resistance welding are based on heating parts with the help of heat, which is released when an electric current flows through them.

The amount of heat released mainly depends on the strength of the current, the time of its flow through the metal, and also on the resistance of the metal itself in the welding zone.

If two or more parts are welded, compressed together, then an electric current is supplied to them through conventional electrodes.

Spot welding device

In this case, the voltage can be small, from 3 V, but the current strength can reach tens of thousands of amperes. The heat that is necessary for welding is released mainly in the parts, in the zone of contact of the parts with each other and their contact with the electrodes. At the same time, the electrical resistance of metals is of great importance in resistance welding modes.

Thus, we conclude that the choice of welding mode depends directly on the properties of the selected materials.

Resistance welding modes depend on the thermal conductivity and thickness of the parts.

Note that under severe conditions, the amount of heat released is many times greater, so they are used only for metals with low thermal conductivity, for example, for steel.

According to physical features, resistance welding belongs to the thermomechanical class. This means that it is carried out using thermal energy and pressure. Heat is released from special sources during the passage of electric current at the point of contact of the parts to be joined. The metal is heated to a plastic state and at the same time it is combined with significant compression.

This type of welding is used to connect ferrous, non-ferrous and dissimilar metals.

3. Contact welding methods

Depending on the contact welding method, metal up to 20 mm thick can be welded. Contact welding is used in many areas of industry - aircraft, aircraft, ship, mechanical engineering, in the energy industry, agriculture, construction.

Contact welding methods

The main welding methods are:

• point;
• suture;
• butt.

Spot welding is an overlapping connection of parts made of profile, sheet and strip metal.

Parts made of both homogeneous metal and dissimilar ones, as well as having different thicknesses, are connected. Depending on the equipment used, welding can be carried out at one point or simultaneously at several points.

The spot welding process consists of the following steps:

• cleaning parts;
• alignment and placement of parts between the electrodes of the welding machine;
• heating to a state of plasticity;
• compression of the electrodes with the necessary force.

Cleaning of parts is carried out immediately before welding by mechanical or chemical means.

Rust, oxides and other contaminants are removed.
To match parts, use special devices called conductors.

Heating of parts at the welding site is carried out by applying a short-term pulse (0.1 ÷ 3 sec.), Which ensures the melting of the metal.

The current power can reach 100,000A, and the voltage can reach up to 10 V. A liquid core is formed. After the pulse is removed, the parts are compressed to form a point (crystallization and cooling occur). The core diameter, depending on the equipment used and the welding technology, ranges from 4 to 12 mm.

Spot welding can occur in 2 modes:

They differ in the density of welding and the time of passage of electric current.

In soft mode, heating is carried out gradually (0.5 ÷ 3 sec.) With a moderate current strength (does not exceed 100 A \ mm2), and in hard mode, the welding time usually runs in the range of 0.01 - 1.5 sec., And the current density is 120 ÷ 300 A/sec. The compressive force of the electrodes ranges from 3 to 8 kN/mm2.

With seam welding, or it is also called roller welding, the parts are also connected by points, which can either not overlap each other or overlap.

The welding process takes place on special machines with disk rollers-electrodes. During the welding process, they rotate, while tightly squeezing the parts to be welded. The equipment may have one or two roller electrodes. Such welding is used to manufacture containers for various purposes (barrels, pipes, gas tanks, etc.), where tightness requirements are imposed on products.

Seam welding can be performed in 3 ways:

• stepper;
• intermittent;
• continuous.

Step welding welds clad metals, aluminum and its alloys up to 3 mm thick.

Parts are welded with a certain step, while a large welding current is switched on at the moment the rollers stop.

Intermittent seam welding is performed to join metals up to 3 mm thick under the following conditions:

• continuous supply of parts to the welding zone;
• short-term interruption of the current when it passes through the workpieces.

During the welding process, points overlap as a result of correct selection the speed of rotation of the roller electrodes and the frequency of the welding current pulse.

Thanks to this method of welding, both parts and rollers do not overheat, which makes it possible to obtain a high quality sealed seam.

Continuous seam welding differs from intermittent seam welding only in that with continuous supply of parts to the welding zone, a continuous current flow also occurs. This type of welding is used for parts made of low-carbon steels up to 1 mm thick, and parts of non-critical structures are also made in this way.

The quality of the weld is low, because in the process of welding, overheating of the welded parts and roller electrodes occurs.

For resistance seam welding, electrodes Ø 40 ÷ 200 mm are used, made of pure copper (grade M1), bronze (cadmium, beryllium, and other types) and their alloys.

Flash butt welding, depending on the method of its execution, is used to butt butt parts made of a wide variety of materials and their combinations, with an area of ​​up to 1000 cm2.

In this way, rods of any shape (round, rectangular) profiles, rails, corners, wheel rims, etc. are welded. For the implementation of butt welding, a large number of machines and apparatuses for contact welding (spotters) have been developed, differing in power and device.

The essence of welding - parts in the process of heating are connected along the entire plane of their contact.

Welding can be done in 2 ways:

• reflow;
• resistance.

Flash welding is widely used because does not require preliminary preparation of the product for welding. It can be of two types - with preheating of parts before welding and without it (continuous flash welding).

For the implementation of butt resistance welding, a wide range of machines is produced that have special clamps in which parts are fixed before welding.

The clamps are installed as follows - one on a fixed plate, and the second on a movable one. When the parts come close to contact, a current is turned on that melts the metal to a plastic state, then compression occurs under the action of a force, the magnitude of which depends on the thickness of the product and metal.

Thus, a strong connection of parts occurs.

Flash welding with preheating is carried out for metals that are capable of being hardened during the welding process. This heating promotes uniform heating of the metal and its slow cooling, which has a positive effect on welding.

Welding tongs

Welding tongs are suspended type devices.

Used in industry and small repair shops, as well as in service centers. The thickness of metal parts welded using such devices does not exceed 4 mm.

The pliers are connected to the welding transformer using flexible wires, which allows you to work in the right place. And allows you to weld products of large dimensions.

Various manufacturers produce a wide range of welding guns.

Some of them allow you to remotely select welding programs, change the welding position during operation, auto-repeat welding, monitor the condition of the electrodes, and even display a message about the need to replace the electrodes or the need to clean them.

Do-it-yourself resistance welding

A country house always requires special care from the owner. There are many more of them than in an apartment. Repair and reconstruction of the house, the construction of decorative bridges and arbors, the construction of foundations and ceilings, all these works require the ability to work not only with wood, but also with metal. Tools and fixtures for such work need appropriate.

Skill and experience, the ability to work and invent interesting projects sometimes it rests on only one thing: not all the work the owner can do on his own. And this very often stops interesting creative ideas.

As a rule, this happens when it comes to welding. It is believed that it is impossible to weld metal structures without a specialist with a special apparatus. Yes, of course, not every welder will make a neat seam.

Of course, welding of bridge structures and ceilings of buildings should be carried out by professionals. But to make a garden gate or a frame for a decorative composition out of metal rods is within the power of an amateur. If he has a special device.

It turns out that making such a home-made welding unit is quite simple and craftsmen have come up with a design for a long time.

Do-it-yourself contact welding is made quickly enough if a person has elementary knowledge and skills in electrical engineering.

For the manufacture of the unit will require the following materials and fixtures:

• power transformer;
• switch;
• timer;
• copper rod with a diameter of 1.5 cm;
• copper wire with a diameter of one centimeter.

A timer in the absence of skills in radio engineering is best purchased at a specialized store.

Production of a transformer for resistance welding

The most important part of the apparatus intended for resistance welding is the transformer. This unit allows you to get the required voltage for welding.

The transformation ratio should have a high value, for this reason, for the manufacture of this element of the welding machine, it is best to use the devices that are included with microwave ovens. The power of this component of the unit must be at least one kilowatt. IN microwave ovens, as a rule, a unit with a power of up to 4 kW is used.

The transformer is removed from the microwave, the secondary winding is removed from it.

For the manufacture of a welding transformer, only the primary winding of the unit is required. When removing the wire, all disassembly operations should be carried out very carefully.

Types and characteristics of resistance welding

This is required in order not to damage the copper wire of the primary winding and the magnetic circuit during the manufacturing process.

After holding preparatory phase production of the secondary winding. At the output of the unit, you need to get a current of 1000 A. For this purpose, a copper wire with a diameter of 1 cm is used. When made from such a copper wire, 2-3 turns are obtained in the device. At the exit from power device voltage is about 2 volts.

The use of such a transformer in the device of a welding machine for resistance welding allows you to work with metal up to 5 mm thick. After winding the copper wire, the direction of the windings is checked, in addition, at this stage of manufacture, the presence of short circuits in the transformer is checked. In the absence of the latter, proceed to the further manufacturing process. When using two or more transformers in the design of the welding device, the output current is checked - it should not be more than 2000 A.

If this value is exceeded, the current strength should be reduced, since a high current strength provokes significant drops in the household electrical network during the operation of the device. After winding the copper wire and checking the parameters of the transformer, it is ready for use.

Production of electrodes for contact welding apparatus

The manufacture of electrodes is carried out from thick copper rods, the diameter of which is 1.5 cm.

In the manufacture of electrodes, one must strictly adhere to the rule that the thickness of the electrode must be no less than the wire used in the secondary winding of the device.

In the case of using a low-power transformer, tips from a pair of soldering irons can be used as welding electrodes. Tips from soldering irons have one undoubted advantage - they are resistant and thanks to this they will last for a long time.

The wires connected to the electrodes should have a minimum length, this is required in order to reduce current losses. To connect the wire to the electrode, a copper tip or a hole in the electrode made with a drill is used.

The wire is attached to the electrode with a bolted connection. For better contact, it is best to solder the wire with the tip, this will prevent the oxidation process and current losses during the oxidation process.

The advantage of a bolted connection is the ability to quickly remove the electrodes. When making a connection by soldering, if it is necessary to replace the electrodes, soldering of the joints will be required, which takes a lot of time.

Welding process control and welding machine infrastructure

Do-it-yourself resistance welding made requires equipment with a control lever and switches.

The quality of welding of metal products is ensured not only by the current strength, but also by the compression force. For this purpose, the device is equipped with a lever. The compression force, especially a huge role, plays when welding thick sheets of metal.

When welding at home, the compression force must be at least 30 kg, for this reason the lever must be made of the appropriate length. This will provide convenience in working with the welding machine and high quality welding of parts. The length of the lever handle to ensure the degree of compression must be equal to 60 cm.

The lever is mounted 3/4 from the bottom. Thus, the ratio of shoulder to clip is 1:10. With this design of the lever, in the case of pressure exerted on the lever by one kilogram, a pressure of ten kilograms is applied to the metal.

The switch is installed on the primary winding of the transformer, since a large current circulates in the secondary winding of the device, and the resistance of the switch in the secondary winding circuit will lead to current loss.

For ease of operation, the switch is placed on the handle of the lever, this allows the supply of electrical energy to the device only after the metal has come into contact with the electrodes of the device. This arrangement of the switch allows you to save energy to a large extent due to the absence of idle operation of the device.

When working with thin metal, it is best to mount a timer in the control circuit of the welding device.

The timer allows you to adjust the operating time of the unit, you can use a cooler from an old desktop computer to cool the device and its components.

After completing the assembly of the device, it should be tested.

METHODS OF CONTACT WELDING

There are butt, spot and seam welding.

Butt welding

Butt resistance welding is a method of resistance welding in which workpieces are welded over the entire contact area.

The scheme of flash butt welding is shown on fig.1. Workpieces to be welded 1 fixed in the clamps of the butt machine. clamp 3 mounted on a fixed plate 2 , clamp 4 - on a movable plate 5 . welding transformer 6 connected to the boards by flexible busbars and powered by an alternating current mains through a switching device. With the help of the pressure mechanism, the movable plate 5 moves, the workpieces to be welded 1 are compressed under the force R.

Distinguish butt welding resistance and flashing.

resistance welding - butt welding with heating of the joint to a plastic state and subsequent upsetting. Flash welding called butt welding with heating of the joint until flashing and subsequent upsetting.

The parameters of the flash butt welding mode are the current density j(A / mm2), specific compression force of the ends of the workpieces p (MPa), current flow time t(c) and installation length L(mm).

installation length L called the distance from the end of the workpiece to the inner edge of the electrode of the butt machine, measured before welding.

For the correct formation of a welded joint and high mechanical properties of the joint, it is necessary that the process proceed in a certain sequence. A joint graphic image current changes I and pressure R when welding is called a cycle or contact machine cyclogram .

Resistance butt welding.

The resistance butt welding cycle is shown in Fig.2.

In resistance welding, the cleanly machined ends of the workpieces to be welded are brought into contact and squeezed by force R.

Then turn on the welding current I. After heating the metal in the contact zone to a plastic state, the force is increased (the blanks are upset) and the current is turned off at the same time. In this case, plastic deformation of the metal in the joint and the formation of a joint in the solid state occur.

When welding with resistance, it is difficult to ensure uniform heating of the workpieces over the cross section and sufficiently complete removal of oxide films. Therefore, resistance welding is used to a limited extent.

This method welds identical blanks of simple shape (circle, square, rectangle with a small aspect ratio) of small cross section (up to 250 mm2) from low-carbon and low-alloy structural steels and non-ferrous metals and alloys.

Flash butt welding unlike resistance butt welding, it does not require preliminary preparation of the ends of the workpieces.

Flash butt welding has two varieties: continuous and intermittent flashing.

With continuous melting workpieces are brought together with the welding current on and very little effort. At the beginning, the workpieces come into contact over separate small areas through which a high-density current passes, causing the workpieces to melt as a result of the continuous formation and destruction of contacts - jumpers between their ends.

As a result of melting, a layer of liquid metal is formed on the end face. Then produce a draft and turn off the current. During precipitation, liquid metal, together with impurities and oxide films, is squeezed out of the joint, forming a burr.

The compound is then formed in the solid state. The flash welding cycle is shown in fig.3.

With intermittent melting clamped workpieces are brought together under current, brought into short-term contact and again separated for a short distance.

Repeating approach and separation one after another, the entire section is melted. Then the current is turned off and the workpieces are upset.

Flash butt welding can weld workpieces with various sections, both simple and complex shapes, from homogeneous or dissimilar metals. Continuous flash welding is used to connect workpieces with a cross section of up to 1000 mm2, and intermittent melted welding - up to 10,000 mm2.

The most typical products welded by butt welding are elements of tubular structures, wheels, rings, rails, reinforced concrete reinforcement, etc.

SELF-CHECK QUESTIONS

7. What is called butt welding?

8. What is the sequence of technological operations in welding

resistance and reflow?

What is the difference between resistance butt welding and flash butt welding?

10. What is the difference between continuous flash butt welding and intermittent flash butt welding?

When is it advisable to use resistance butt welding? And when by reflow (continuous or intermittent)?

Contact spot welding

Spot welding is a type of resistance welding in which workpieces are joined at separate points.

Before welding, the surfaces of the workpieces are thoroughly cleaned of dirt, oil and oxide films (with an emery wheel, a metal brush or etching).

In spot welding (Fig. 4), overlapped workpieces are compressed by electrodes connected to a welding transformer, when turned on, the workpieces at the contact point are heated by electric current until a molten zone (dot core) appears.

Then the current is turned off, and the compression forces are kept constant for some time so that the crystallization of the molten metal of the point takes place under pressure. This prevents the formation of shrinkage defects - cracks, looseness, etc. In some cases, to improve the structure of the weld point, the compression force is increased before turning off the current (point forging).

Spot welding according to the number of simultaneously welded points can be one-, two- and multi-point.

According to the method of current supply, spot welding can be two-sided ( fig.4a) and one-sided ( fig.4b)

With double-sided welding, the current is supplied to the upper and lower workpieces, with one-sided welding, to one of them.

To increase the current density in the connection zone with a one-sided current supply, the workpieces are placed on a current-carrying copper lining. One-sided welding is used when access to one of the workpieces is difficult, as well as when it is necessary to increase the productivity of the process, since in this case two points can be welded simultaneously.

One of the spot welding cycles - the forging cycle is presented on pic 5.

The entire welding cycle consists of four periods: compression of the workpieces to be welded by electrodes, switching on the current and heating the contact point to the melted temperature with the formation of a cast core of the point; turning off the current and increasing the compression force (point forging); removal of force from the electrodes.

The spot welding mode can be soft or hard.

Soft mode is characterized by a relatively low current density (j=80...160A/mm2) and a long time of its flow (T=0.5...3s) at a relatively low specific pressure (p=15...40MPa). Hard mode is characterized by high current density (j=160…350А/mm2), high specific pressure (р=40…150MPa) and short current flow time (t=0.001…0.1s). Soft modes are used mainly for welding carbon and low-alloy steels, hard modes are used for corrosion-resistant steels, aluminum and copper alloys.

Spot welding can weld sheet blanks of the same or different thicknesses, intersecting rods, sheet blanks with rods or profile blanks (corners, channels, etc.) made of low-carbon, carbon, low-alloy and corrosion-resistant steels, aluminum and copper alloys.

The thickness of the welded metals is 0.5-6 mm, and in some cases it can reach 30 mm.

Multi-point resistance welding - a kind of resistance welding, when several points are welded in one cycle.

Multi-spot welding is performed on the principle of one-sided spot welding. Multi-point machines can have from one pair to 100 pairs of electrodes, respectively, you can weld 2 - 200 points at the same time. Multi-point welding is used mainly in mass production;

A variation of spot welding is relief welding ,

relief welding

Relief welding - a method of spot resistance welding, in which the location of the points is determined by pre-prepared protrusions (reliefs) in the workpiece 2 .

In relief welding ( fig.6) blanks 2 And 4 clamped between flat electrodes 5 And 1 (contact plates). Connection occurs at points 3 (defined by protrusions), which is obtained by stamping in one of the blanks.

When the current is turned on, the upper electrode compresses the blanks and compresses them until the protrusions are completely destroyed. Thus, in one stroke of the machine, as many weld points are made as there are protrusions between the electrodes; This method is highly productive.

The disadvantage is the significant power consumption.

SELF-CHECK QUESTIONS

What is called spot welding?

13. What is the sequence of technological operations in spot welding?

14. What is the difference between two-sided spot welding and one-sided?

15. In what modes is spot welding performed?

What is the difference between soft mode and hard mode?

17. For welding of which products is spot welding used?

18. What is called multi-spot welding?

19. What is called relief welding?

Contact seam welding

Seam welding - a type of resistance welding, in which the weld is formed by setting a successive series of overlapping points, which determines its density and tightness.

For seam welding, the current supply i transmission of force R to blanks 1 and their movement is carried out through rotating disk electrodes - rollers 2 (fig.7).

Before welding, workpieces with cleaned surfaces from dirt, oil and oxide films are overlapped. Smooth welding, as well as spot welding, can be performed with two-sided ( fig.7a) and one-sided ( fig.76) current supply.

On fig.8 the most common seam welding sequences with continuous current switching are presented (A) and with discontinuous (b) with continuous rotation of the rollers.

The sequence of operations is the same as for spot welding.

The first cycle is designed for welding short seams and metals and alloys that are not prone to grain growth and do not undergo noticeable structural transformations when the heat-affected zone is overheated (low-carbon and low-alloy steels); the second cycle for welding long seams and metals and alloys for which overheating of the heat-affected zone is dangerous (stainless steels, aluminum alloys).

The main parameters of the seam welding mode are: current density j in A/mm2" specific pressure R in MPa and welding speed vst m /h

Seam welding is widely used in mass production for the manufacture of various containers, tanks, car fuel tanks, etc.

from low-carbon, alloy structural steels, as well as non-ferrous metals and alloys, the thickness of the welded sheets is 0.3 ... 3 mm.

SELF-CHECK QUESTIONS

20. What is called seam welding?

21. What is the sequence of technological operations in seam welding?

Description of the process of self-assembly of spot welding

When is intermittent seam welding used, and when is continuous?

23. For what structures is it advisable to use seam welding?

EXERCISE

For one of the options, develop technological process assembly and spot welding of mild steel beams ( fig.9).

Dot pitch t=3dt. Large scale production.

1. Specify the preparation of workpieces for welding. According to the thickness of the workpieces to be welded, select the type of machine and indicate its technical data.

Calculate the contact surface area of ​​the electrode. By current density valuesj (A/mm2) and pressure R(MPa) determine the welding currentJ (A) and effort R(MN) applied on the electrodes. Determine the welding time of the productt (With).

2. Draw and describe the spot welding cycle.

Home locksmith work is a part of the life of an economic person. One of the most popular home devices is spot welding. It assumes the presence of a factory or home-made welding device. It is not difficult to create such an apparatus, which will carry out spot welding with your own hands, you only need desire and some improvised means.

Features and principle of spot welding

Studying the question of how to do spot welding with your own hands, let's start with the principle of operation.

Today, spot welding is in demand not only in everyday life, but also in production, as it is able to solve even the most difficult tasks. In industry, as a rule, devices operating in automatic mode are used; in domestic conditions, a semi-automatic welding machine is used for spot welding.

Spot resistance welding in production is necessary to weld sheet blanks from ferrous and non-ferrous metals. With the help of it, products from a profile of different thicknesses and configurations, intersecting metal blanks are welded. Under certain conditions, it is possible to achieve a high-speed operating mode of up to 600 points per minute.

Many people are interested in the question of how to do spot welding at home? In a domestic environment, spot welding is used to repair household utensils and, if necessary, weld electrical wires.

The spot welding procedure includes several steps:

• workpieces are combined in the required position;
• make fastener parts directly between the clamping electrodes of the installation;
• surfaces are heated, during which the parts are deformed and they are interconnected.

There is another technology of point connection - laser welding. It is capable of performing tasks related to high precision work and ultimate soldering strength.

It turns out that the principle of spot welding is the excessive heating of the working metal surfaces, which results in their fusion and a single structural neoplasm.

The main role in the welding process is played by the impulse response of the current, which creates the necessary heating of the metal area. No less important characteristic is the exposure time and the force of holding parts. Due to these parameters, the metal structure crystallizes.

The main advantages of electrocontact welding from a welding machine are:

• profitability of use;
• strong seam;
• simplicity of equipment;
• homemade spot welding can be created at home;
• the possibility of automation in the enterprise.

The only flaw in the point connection of parts is the leakage of the connection.

The main requirements for welding equipment are:

• the ability to change the process time;
• creating pressure in the working area, reaching the limit at the end of the heating process;
• the presence of electrodes with high conductivity of energy and heat.

For domestic use, electrolytic copper and its mixture of the EV brand are suitable. It should be noted that the area of ​​the contacted area of ​​the electrode should exceed the welded joint (seam) by 2.5 times.

Do-it-yourself welding machine assembly

For spot welding of parts, it is necessary to create appropriate equipment. Do-it-yourself spot welding installation, made at home, can have any shape - from portable varieties to large-sized models. In practice, desktop options are usually used to connect various metals. Before you create spot welding from an inverter, you should familiarize yourself with the materials that will be needed in the manufacture.

• an energy converter, i.e. a transformer;
• electric cable with insulation with a cross section of 10 mm;
• copper electrodes;
• breaker;
• tips;
• bolts;
• improvised means and materials for creating a hull base or welding tongs (wood bars, recycled materials, plywood).

1 - modified transformer OSM-1.0; 2 - conductor (duralumin rod with a diameter of 30, L300, 2 pcs.); 3 - insert (steel bar with a diameter of 10, L30, 2 pcs.); 4 - electrode (copper rod with a diameter of 12, L50, 2 pcs.); 5 - brass washer (2 pcs.); 6.12 - M6 screws; 7 handle; 8 - eccentric; 9 - cheek (2 pcs.); 10 - spring; 11 - output of half of the secondary winding (4 pcs.); 13 - textolite bushing (with a groove for the end loop of the spring); 14 - M8 bolt (6 pcs.); 15 - textolite washer (4 pcs.); 16 - insulating coating (varnished cloth or protective adhesive tape on a fabric basis, 2 pcs.); 17 - transformer casing.

Mounting diagrams

The main varieties of welding device assembly schemes are simple projects with a minimum amount of required materials. It is worth noting that the manufactured equipment will not be powerful, that is, this spot welding scheme is intended only for domestic use. Its purpose is to weld small sheets of iron and electrical wires.

To understand how to do resistance welding, remember the course of the school curriculum, namely the physical rule "Joule-Lenz Law": when electricity passes through a conductor, the amount of thermal energy created in it is directly proportional to the resistance of the conductor, the exposure time and the square of the electric current. Conclusion, if the current was initially large (for example, 1000 A), then with a weak connection and small wires, more energy will be consumed (several thousand times) than with a smaller electric current (10 A). That is, the quality of the collected electrical circuit plays an important role.

The formation of an electrical pulse between two sections of metal products is considered the basic part of the operation of the welding installation. This will require a small power converter. The workpiece to be welded must be connected to the lower winding of the device, and the metal electrode to the secondary.

It is worth noting that It is unacceptable to directly combine the converter with the power supply. For this, a bridge with an electronic switch (thyristor) is provided in the electrical circuit. To create the required impulse, the device must be supplied with auxiliary power, which includes an energy rectification bridge and a transformer. The electric current will be concentrated in the capacitor, whose role is to form an impulse.

In order for the do-it-yourself contact welding machine to work, you need to press the "pulse button" on the pistol handle to open the capacitor-resistor circuit. As a result of these manipulations, a discharge will occur through a metal rod. To consolidate the theoretical material, it is recommended that you familiarize yourself with the training video, which talks in detail about spot welding. This allows you to visually understand how all this is done correctly.

Homemade microwave oven

Since it is not always possible to allocate an extra amount of money for spot welding machines, you can make it on your own. This will require a fairly powerful microwave oven.

Transformer assembly

From the microwave, only one part is required - this is a high-voltage transformer for spot welding. This part requires only a core (magnistor) and a primary (lower) winding. To remove unnecessary areas, you can use a hammer, grinder or hacksaw. After removing the transformer secondary winding, it is necessary to create a home-made transformer for resistance welding. To do this, you should use a copper cable with a diameter equal to the opening of the transformer. It is necessary to make two turns. In order to connect the two parts of the core, epoxy resin is required.

The basis has been made, now it is necessary to deal with the case of a home-made installation. For this, various polymers are used, for example, plastic or wood. The back area of ​​the body of the spot installation must contain several openings. One opening will serve as the device's key, and the other will supply electricity.

If wood is used instead of plastic, then first you need to perform several preparatory operations, namely sanding, impregnating and varnishing. To create a home-made working apparatus for spot welding with your own hands, you will need:

• welding installation power cable;
• Door knob;
• switch;
• copper holders;
• large diameter electrical wire;
• Consumables(screws, nails).

After drying the body section, it is necessary to assemble the installation and combine all related parts. After that, the copper wire is cut into 2 parts, each of which is approximately 25 mm. These elements will act as electrodes. To fix them, it is enough to use a standard screwdriver. Then you need to install the system key, a thick electric cable will prevent it from slipping out. To fix the transformer on the body of the structure, you can use self-tapping screws, but do not forget about grounding one of the terminals.

To increase the safety of using the welding device, it is recommended to install an auxiliary switch. Small nails and other fasteners are also used to fasten the working levers. Contact metal rods are attached to the end parts of the handles. For the ascension of the upper handle, a standard polymer is used - rubber.

Creating electrodes

Elements used for do-it-yourself spot welding must meet certain requirements, namely resistance to operating temperatures, good electrical conductivity and ease of machining.

Copper wires with a cross section of 15 mm are perfect for this. The basic principle is that the cross section of the electrode should not be less than the diameter of the wire. If it’s not a pity, then you can use the tips of 2 soldering irons, which will definitely last a long time.

Governing bodies

The do-it-yourself resistance welding created has a simple device. There are only two control systems - a switch and a handle. The spot welding switch is fixed in the primary circuit. This is necessary due to the fact that the current in the secondary winding is greater, and the switching system will create additional resistance. The switch is mounted on the lever, so it will be more convenient to work. That is, it will be possible to turn on the electricity with one hand, and hold the materials to be welded with the other.

It is worth noting that turning the welding current on and off must be carried out only with compressed electrodes, because otherwise a spark will appear, leading to their burning. It is also recommended to use a fan to cool the machine.

If such a cooling system is not available, then the temperature of the energy converter, metal electrodes, electrical wires should be constantly monitored and additional breaks should be created to prevent overheating.

Today, the purchase of a spot welding machine is not a problem if there is cash. In any specialized store they will offer a number of installations for point-to-point connection of parts, with different capacities and manufacturers. But for home craftsmen it is not always possible to select the required parameters, so making a spot welding machine with your own hands will be optimal solution. All necessary supplies can be borrowed and found at home. Collected with my own hands the spot welding unit does not fail and works perfectly, thereby providing the required minor repairs of metal products.

It differs from the usual arc in that the metal does not melt when high temperature electric arc that occurs between the electrode and the metal to be welded, but due to the passage of current through the contact of two parts to be welded. These parts can be thin sheets of metal, wire, plates. They are firmly compressed by special mechanical devices and a pulsed current is passed through the junction high strength(1000 or more amperes) at a voltage of several volts.

Do-it-yourself spot welding assumes that at least 5 kW of power falls on 1 mm 2 of contact area, which corresponds to a current strength of up to 50A / mm 2. In this case, the mechanical pressure on the same square millimeter should be at least 3-8 kg. To achieve such parameters, a special design of the working tool in the form of pincers is required.

The working body is two conductive electrodes that compress the parts to be connected with the required force when the handles are pressed. After compression, a current pulse with a duration of 01–1 s is applied to the electrodes, which melts the metal to a plastic state. After the current supply is stopped, the mechanical effect is maintained and the molten metal merges into one whole and so solidifies, forming a strong connection that is not inferior to electric arc welding.

The welding scheme looks like this:

The main difficulty in the manufacture of a spot welding machine with your own hands is the assembly of a power source. It must provide short pulses of low voltage and high current, exceeding 1000A. The pulse duration is regulated by a thyristor circuit or manually by a conventional switch on the primary winding. For low-alloy steels, a longer pulse is needed, stainless steel is welded with short pulses so that the upper part does not have time to warm up and oxidize, which significantly reduces the anti-corrosion properties.

In the second case, welding with such an apparatus requires a certain skill - it is very difficult to guess the required pulse duration the first time, especially on different metals. But by trial and error on scraps of sheet steel or non-ferrous alloys, it is quite possible to achieve welding quality no worse than on industrial machines.

Do-it-yourself spot welding, assembled from an old welding machine, works quite efficiently and is quite able to solve a number of problems with joining sheet metal with a thickness of several tenths to 2-3 mm. For a thicker sheet, it is difficult to create the required force with homemade pliers or a lever device.

Why is the old transformer chosen? A do-it-yourself spot welding machine involves its complete re-equipment, which, however, concerns only the secondary winding. After the alteration, ordinary MMA welding with such an apparatus becomes impossible, therefore an old, but still working apparatus is selected, at least the primary winding should be, if not in ideal, then in acceptable condition.

The secondary winding is removed completely and another is installed in its place, from a copper insulated bundle or busbar. It is necessary to isolate the wire very carefully, in several layers of non-combustible insulation. Fabric electrical tape is convenient for these purposes, which alternates with winding with ordinary automotive tape, which is used when painting the body.

The cross section of the wire of the secondary winding must be at least 1.8 cm 2. If you can find a suitable factory-made cable insulated, then it is better to use it. A good result is given by both cables with a monolithic core, and stranded ones from twisted into a bundle. copper wires. Several turns of a cable or bus go to the secondary winding so that when 220V is supplied to the primary circuit, a current of 6-8 V arises in the secondary. In this case, the current strength will reach 800-1000 A. This is quite enough for welding individual parts in the home workshop.

How to choose electrodes

For spot contact welding, it is best to use industrial electrodes made in accordance with GOST 14111-69. These can be bought on the Internet sites or in welding equipment stores. When used on homemade equipment, they will last almost forever. But they are quite expensive, especially with pressed tips made of tungsten or other refractory material.

In most cases, craftsmen make electrodes on their own. Depending on the welding power, copper rods with a diameter of 5 to 15 mm are suitable. On the one hand, they are inserted into a metal sleeve with clamping bolts, fixed on the cable from the transformer. Like the cable, the electrodes are firmly clamped with bolts.

The second option for attaching the electrode is soldering. It is also quite reliable and effective method, providing reliable electrical contact, but changing the electrode in this case is more difficult. This does not affect productivity too much - the electrodes wear out very slowly, especially when amateur welding.

Reliable contact is much more important. If the connection is loose, then the wire and electrode will oxidize and overheat, and the current strength will be less than required. It is also necessary to make all connecting cables as short as possible - the diameter of the electrode and cable must be the same, otherwise there may be surprises in the form of burning insulation or burning of the rods.

It would be useful to recall that the same copper wires are selected for copper electrodes. Aluminium/copper combinations are unreliable and result in unreliable welding.

The working ends of the electrodes can be pointed (conical), oval or flat. In household home-made devices, it is most convenient to use a flat lower and conical upper electrodes. This combination will provide high density current at the point of welding, and a reliable support for pressing parts.

Battery Spot Welding

There is information on the Internet on how to do spot welding with your own hands using a regular 12 V car battery. You can use it to connect small parts that are usually connected by soldering. But in many cases, welding gives the best result in terms of strength and is more convenient for joining dissimilar metals.

Do-it-yourself spot welding from a battery is a simple design and can be done in a garage for several hours, with all the parts and tools, of course. It does not require any special tools or sophisticated equipment for installation.

There are three types of welding with a battery. The first, the simplest, one might say primitive, requires only a battery and two copper wires, the bare ends of which act as electrodes. As a rule, this method is used most often, but only for welding non-ferrous metals. It is with good reason that it can be called a point.

The other two methods - and with the help of an inverter - require batteries from several batteries and additional equipment. They are also used in domestic and camping conditions, but buying several batteries of the same type to make a welding machine out of them is quite expensive. Any battery that can be removed from the car can be used for spot welding.

A simple device for performing welding work consists of two copper wires with a cross section of at least 1.5 mm 2, fixed in a terminal block. The distance between the stripped ends of the electrodes is 2-3 mm. Of course, as in any home-made design, there can be many options, but as a base it is best to use this particular type of design. How such a mini installation works is shown in the video:

Battery welding is designed to connect small pieces of thin sheet metal, but even with this, the battery is discharged quite intensively. If you removed it from the car, then it is advisable to have it in the garage and Charger to return the batteries to their previous charge.

The examples given are the simplest. homemade designs spot welding machines. If you have your own developments - write to us on the site. We and our readers are very interested in the real development of amateur designers. We will certainly publish the most interesting schemes.

Resistance welding, in addition to the technological advantages of the application, has another important advantage - simple equipment for it can be made independently, and its operation does not require specific skills and initial experience.

1 Principles of design and assembly of contact welding

Contact welding, assembled with one's own hands, can be used to solve a fairly wide range of non-serial and non-industrial tasks for the repair and manufacture of products, mechanisms, equipment from various metals both at home and in small workshops.

Resistance welding ensures the creation of a welded joint of parts by heating the area of ​​their contact with an electric current passing through them while simultaneously applying a compressive force to the joint zone. Depending on the material (its thermal conductivity) and the geometric dimensions of the parts, as well as the power of the equipment used for their welding, the resistance welding process should proceed with the following parameters:

• low voltage in the power welding circuit - 1–10 V;
• in a short time - from 0.01 seconds to several;
• high welding pulse current - most often from 1000 A or higher;
• small melting zone;
• the compressive force applied to the welding site must be significant - tens to hundreds of kilograms.

Compliance with all these characteristics directly affects the quality of the resulting welded joint. You can only make devices for yourself, as in the video. The easiest way is to assemble an alternating current welding machine with unregulated power. In it, the process of connecting parts is controlled by changing the duration of the supplied electrical impulse. To do this, use a time relay or cope with this task manually "by eye" using a switch.

Home-made spot welding is not very difficult to manufacture, and to make its main unit - a welding transformer - you can pick up transformers from old microwaves, TVs, LATRs, inverters, and the like. The windings of a suitable transformer will need to be rewound in accordance with the required voltage and welding current at its output.

The control circuit is selected ready-made or developed, and all other components, and, in particular, for the contact welding mechanism, are taken based on the power and parameters of the welding transformer. The contact welding mechanism is made in accordance with the nature of the upcoming welding work according to any of the known schemes. Usually make welding tongs.

All electrical connections must be of good quality and have good contact. And connections using wires - from conductors with a cross section corresponding to the current flowing through them (as shown in the video). This is especially true of the power part - between the transformer and the clamp electrodes. If the circuit contacts are poor, there will be large energy losses at the joints, sparking may occur, and welding may become impossible.

2 Scheme of a device for welding metal up to 1 mm thick

To connect parts by contact, you can assemble according to the diagrams below. The proposed apparatus is designed for welding metals:

• sheet, the thickness of which is up to 1 mm;
• wire and rods, the diameter of which is up to 4 mm.

The main technical characteristics of the device:

• supply voltage - alternating 50 Hz, 220 V;
• output voltage (at the electrodes of the contact welding mechanism - on tongs) - variable 4–7 V (idle);
• welding current (maximum pulsed) - up to 1500 A.

Figure 1 shows the circuit diagram of the entire device. The proposed contact welding consists of a power unit, a control circuit and an automatic switch AB1, which serves to turn on the power of the device and protect it in case of emergencies. The first unit includes a welding transformer T2 and a non-contact thyristor single-phase starter type MTT4K, which connects the primary winding T2 to the mains.

Figure 2 shows the winding diagram of the welding transformer indicating the number of turns. The primary winding has 6 outputs, by switching which it is possible to carry out stepwise coarse adjustment of the output welding current of the secondary winding. At the same time, output No. 1 remains permanently connected to the network circuit, and the remaining 5 serve for adjustment, and only one of them is connected to power for operation.

Scheme of the MTT4K starter, commercially available, in Fig.3. This module is a thyristor key, which, when its contacts 5 and 4 are closed, switches the load through contacts 1 and 3 connected to the open circuit of the primary winding Tr2. MTT4K is designed for a load with a maximum voltage of up to 800 V and a current of up to 80 A. Such modules are produced in Zaporozhye at Element-Converter LLC.

The control scheme consists of:

• power supply;
• direct control circuit;
• relay K1.

Any transformer with a power of not more than 20 W, designed to operate from a 220 V network and outputting a voltage of 20–25 V on the secondary winding, can be used in the power supply. It is proposed to install a diode bridge of the KTs402 type as a rectifier, but any other with similar parameters or assembled from individual diodes.

Relay K1 is used to close contacts 4 and 5 of the MTT4K key. This happens when voltage is applied from the control circuit to the winding of its coil. Since the switched current flowing through the closed contacts 4 and 5 of the thyristor key does not exceed 100 mA, almost any low-current electromagnetic relay with a response voltage in the range of 15–20 V is suitable as K1, for example, RES55, RES43, RES32 and the like.

3 Control chain - what does it consist of and how does it work?

The control circuit performs the functions of a time relay. Turning on K1 for a given period of time, it sets the duration of the effect of an electric pulse on the parts to be welded. The control circuit consists of capacitors C1-C6, which must be electrolytic with a charging voltage of 50 V or higher, switches of the P2K type with independent fixation, a KN1 button and two resistors - R1 and R2.

The capacitance of the capacitors can be: 47 uF for C1 and C2, 100 uF for C3 and C4, 470 uF for C5 and C6. KH1 should be with one normally closed and the other normally open contacts. When AB1 is turned on, the capacitors connected via P2K to the control circuit and power supply start charging (in Fig. 1 it is only C1), R1 limits the initial charging current, which can significantly increase the service life of the tanks. Charging occurs through the normally closed contact group of the KN1 button, which was switched at that time.

When KN1 is pressed, the normally-closed contact group opens, disconnecting the control circuit from the power supply, and the normally open contact group closes, connecting the charged containers to relay K1. The capacitors are then discharged and the discharge current triggers K1.

The open normally closed contact group KN1 prevents the relay from being powered directly from the power supply. The greater the total capacitance of the discharging capacitors, the longer they discharge, and, accordingly, K1 closes contacts 4 and 5 of the MTT4K key longer, and the longer the welding pulse. When the capacitors are completely discharged, K1 will turn off and resistance welding will stop. To prepare it for the next impulse, KH1 must be released. The capacitors are discharged through the resistor R2, which must be variable and serves to more accurately control the duration of the welding pulse.

4 Power section - transformer

The proposed contact welding can be assembled, as shown in the video, on the basis of a welding transformer made using a magnetic circuit from a 2.5 A transformer. These are found in LATRs, laboratory instruments and a number of other devices. The old winding must be removed. At the ends of the magnetic circuit, it is necessary to install rings made of thin electric cardboard.

They are folded along the inner and outer edges. Then the magnetic circuit must be wrapped over the rings with 3 or more layers of varnished fabric. To perform the windings, wires are used:

• For primary 1.5 mm in diameter, it is better in fabric insulation - this will contribute to good impregnation of the winding with varnish;
• For a secondary diameter of 20 mm, stranded in organosilicon insulation with a cross-sectional area of ​​at least 300 mm 2.

The number of turns is shown in Fig.2. Intermediate conclusions are drawn from the primary winding. After winding, it is impregnated with varnish EP370, KS521 or similar. A cotton tape (1 layer) is wound over the primary coil, which is also impregnated with varnish. Then the secondary winding is laid and varnished again.

5 How to make pincers?

Resistance welding can be equipped with tongs that are mounted directly into the body of the device itself, as in the video, or remote in the form of scissors. The first ones, from the point of view of performing high-quality, reliable insulation between their nodes and ensuring good contact in the circuit from the transformer to the electrodes, are much easier to manufacture and connect than remote ones.

However, the clamping force developed by such a design, if the length of the movable arm of the tongs is not increased after the electrode, will be equal to the force created directly by the welder. Remote tongs are more convenient to use - you can work at some distance from the device. And the effort developed by them will depend on the length of the handles. However, it will be necessary to make sufficiently good insulation from textolite bushings and washers in the place of their movable bolted connection.

When making tongs, it is necessary to foresee the necessary reach of their electrodes in advance - the distance from the body of the apparatus or the place of the movable connection of the handles to the electrodes. This parameter will determine the maximum possible distance from the edge of the sheet metal to the place where welding is performed.

Tick ​​electrodes are made from copper bars or beryllium bronze. You can use the tips of powerful soldering irons. In any case, the diameter of the electrodes must be no less than that of the wires supplying current to them. To get welding cores the right quality, at the contact pads (electrode tips) the size should be as small as possible.