Making spot welding from an inverter. How to make a spot welding machine with your own hands How to do spot welding with a conventional inverter

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 consists in heating metal parts in certain places with electric current, 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 high requirements for temperature conditions 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). An online calculator for calculating the inductor coil will help speed up the calculations. 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 insulation, tight laying of turns is of great importance. 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, which is powered by a conventional pneumatic compressor, is best suited. 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 the technical characteristics of the 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 the 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;
• A certain role is played by the indicator of the magnitude of the welding current that the machine produces;
• 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 Supply.

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 perfectly 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. The power should be about 1 kW - this is ideal, but, in the absence of such, it will also work 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 consider 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 the 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 related to one of the types of welding in place.

A spot weld joint is created by local heating of the work with electric current and plastic deformation in the joint area due to the 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.

Airtight Sewing - For Welding Tanks, 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 carried out, 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 with a diameter of up to 20-40 mm 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 an individual 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,

television. 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(FROM)

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 the 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 first provide a heat pump impulse, 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 contact 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, aviation, shipbuilding, mechanical engineering, 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 combine parts, special devices called conductors are used.

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.

In the process of welding, overlapping of points occurs as a result of the correct selection of 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 only in that with continuous supply of parts to the welding zone, a continuous current flows. 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 resistance 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 contact 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 come up with interesting projects sometimes 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 contact 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 be high, 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 contact 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 the preparatory stage, the production of the secondary winding is carried out. 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 output of the power device, the 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 contacts 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 contact 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 call 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. Joint graphic representation of current change 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 workpieces 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), the overlapped workpieces are compressed by electrodes connected to a welding transformer, when turned on, the workpieces at the point of contact 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 when 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 the fig.8 the most common seam welding sequences with continuous current switching are presented (but) 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 intended 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?

THE TASK

For one option, develop a workflow for assembling and spot welding a mild steel beam ( 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 (from).

2. Draw and describe the spot welding cycle.

Do-it-yourself spot welding from an inverter - is it a myth, or a reality? It is not easy to answer this question clearly. On the Internet you can find many articles on this topic. Their authors, as a rule, relate to the problems of reworking electrical and electronic components. The question of how to create the necessary working pressure on the electrodes, as it were, fades into the background. But it is, in fact, the key, since we are talking about an effort of tens, and sometimes hundreds of kilograms. Well, okay, let's get it right.

The advantages of resistance welding are enough to make it attractive for those who intend to establish mass production or repair equipment at a professional level.

• Good weld quality. It is ensured by the stability of the parameters of the welding current and the pressure exerted on the parts to be joined.
• High process speed. It takes seconds to stitch. This is especially important when it comes to performing a large amount of work.
• Operational simplicity. A properly made apparatus for contact welding does not require special skills to use, and even a medium-skilled specialist can master the process.
• The use of a spotter is justified when repairing car bodies. Such a device simplifies not only the welding process, but also the straightening of damaged parts.

The main obstacle to widespread adoption of the technology is the high cost of equipment. It prompts many to think about how to make a resistance welding machine on their own.

Is an inverter needed?

In fact, the use of an inverter for these purposes is unreasonable. After all, for contact welding there is no need for direct current. With a ready-made welding inverter, the task of installing control circuits and manufacturing transformer coils of the required parameters is only somewhat simplified. With the same success, you can make equipment, as they say, from scratch.

What will be required

It is not worth starting to solve such a problem without having the necessary theoretical knowledge and practical skills. It just looks relatively simple in words. But if you know how to solder and know how to properly rewind the coils of a transformer, you can try. To do this, you will need certain materials and tools.

• Copper wire of a certain section. Its cross section and quantity can only be determined by performing preliminary calculations.
• Tire material. At worst, you can get by with the same wire, but it is more expedient to purchase a finished product.
• Varnish to create an insulating layer on the wires and good electrical tape.
• Multimeter for taking the necessary measurements.
• Soldering accessories - soldering iron, flux, solder, etc.

Of course, you will have to purchase a ready-made welding inverter.

Transformer manufacturing

Figure No. 1 schematically shows the possible ratio of turns of the primary and secondary windings of the transformer necessary for resistance welding. A large number of outputs on the secondary winding is necessary in order to be able to roughly adjust the current parameters. But the presented circuit requires adjustment depending on the required current parameters. It is impossible to do without preliminary calculations.

Theoretical and practical assistance

The number of turns can be calculated using this formula: N = 50/S. Where N is the number of turns, S is the core area in cm2. To simplify the task, it is recommended to use a ready-made calculator program. They can also be found online. For example, the OER program. This will help avoid mistakes and simplify the task. Since we are talking about the design of equipment based on a ready-made inverter, you should first measure the parameters of the primary coil, make calculations, and only then proceed to the manufacture of the secondary winding.

Carefully!

Care must be taken to ensure that both windings are grounded. After all, the received current power will be very high, and contact with live parts can be fatal.

Carefully insulate and refrigerate well

When winding the wire on the coil, be sure to apply insulating varnish to its surface and lay the turns as tightly as possible. Otherwise, interturn short circuits and wire burnout due to overheating cannot be excluded. The cooling of the transformer comes to the fore. For some reason, the authors of many articles are silent about this. It is possible that an additional cooling system will be required, consisting of radiators and fans blowing them. If this is not taken care of, the equipment will simply fail from overheating or even become a fire hazard. As an option, it is possible to install ready-made cooling systems used in electrical and electronics.

Control system installation

When installing the control circuit, it is recommended to use ready-made elements. They are already in the factory inverter. This greatly simplifies the assembly process and makes the device easy to use. But the capacity of its regular capacitors may not be enough. In this case, they will have to be replaced with parts that are suitable in terms of parameters. The adjustment of the current parameters in the contact welding machine is carried out in steps. Its accuracy will depend on the number of leads of the secondary winding and their pitch. This is necessary if you need equipment that can operate in different modes.

It is important!

Circuit components should be mounted by soldering. Detachable connections are not able to provide the necessary heat transfer mode. Their use makes sense only in cases where frequent replacement of any parts is expected.

Making pincers

Only when the transformer is ready, it makes sense to start manufacturing contact tongs. Their design primarily depends on the nature of the work for which the equipment will be used. The gripping device will depend on its drive system and the expected size of the parts to be connected. An important part of the pliers are the contact tips. With a small thickness of the sheet to be welded, it is quite acceptable to use copper tips from a soldering iron. It is better if you purchase and install ready-made tips - they are found on sale and are convenient in that they have a special shape that is well suited for work. But if we are talking about a steel sheet of 0.5 mm or more and the imposition of connecting seams of considerable length is expected, it is recommended to equip the tips with rollers.

Providing downforce

Next, you have to solve the most practically difficult problem. The fact is that if you intend to create pressure on the welding tongs manually, it is better to refuse to manufacture contact welding. The efficiency of such a device will be low. The applied force at the welding point must be uniform and very significant.

In industrial environments, hydraulic or pneumatic systems are used for this. It is extremely problematic to make such a device on your own. It is wiser to purchase a ready-made booster, since they are found on sale. When making contact welding with your own hands, it is easier to use amplifiers driven by compressed air. In this case, for their operation it will be enough to connect a conventional pneumatic compressor. It is optimal if the maximum force on the contacts reaches 100 kg and above. To change the pressure, you can use a separate regulator, or integrate it into the overall control system of the apparatus.

Gas supply

To optimize welding conditions and improve the quality of the connecting seam, care should be taken to supply gas to the working area. In the case of steel, it must be carbon dioxide. The selection of the nozzle and its location depend on the size of the pincers, contacts and the working area. The supply hose is fixed so as not to interfere with the operation of other components of the device. It must be made of non-combustible heat-resistant material and equipped with a control valve.

Caring about reliability and safety

For the efficient operation of the equipment, as well as in order to ensure safety standards, all components of the device must be carefully fixed and insulated. As a base, it is recommended to use dielectric materials with good thermal stability and mechanical strength. Care must also be taken to integrate protective fuses into the electrical circuit. It is important to follow all recommended safety precautions when working on the equipment.

0

A spotter is a welding unit used specifically for organizing spot welding, as well as allowing you to work on straightening thin sheet blanks. This type of welding is especially common in workshops, whose employees are engaged in straightening work that requires preliminary disassembly of the body. The use of a spotter allows you to avoid the mandatory dismantling of the bearing parts of the car and straighten surfaces without a reverse hammer (figure below).

In this case, the welding procedure is used for the purpose of spot fixing an additional holder on the surface to be restored, by pulling which it is possible to straighten the existing dent.

Spot welding properties

The design of this device is somewhat different from typical units with a continuously burning arc. It is possible to make a spotter from a welding machine with your own hands only if you know the basic principles of generating a working current. The fact is that with the contact method of welding, heating occurs not by melting the metal, but by concentrating heat in the dotted zone between the workpiece and the electrode.

In the case of an erroneously selected contact welding mode (with a lack of experience from the operator), sticking of the electrode is often observed, which can lead to unpleasant consequences in the form of a short circuit or even to a breakdown of the unit. That is why the spot welding machine is manufactured in such a way that the welding time is strictly limited and does not exceed a second.

In addition, such a device is designed for small values ​​​​of the effective voltage (since ignition of the arc is not required in this case) and for significant operating currents. In this regard, the transformer (CT) included in its composition must also withstand large current loads sufficient for high-quality heating of the welding site.

Rework Features

It is possible to make a spot welding machine with your own hands without undue effort, if you use the option of remaking it from an unnecessary welding device. When preparing for work, it will be necessary to pay attention to the following points:

• For an ordinary CT, the voltage when idling (x.x.), as a rule, is selected no more than 70 volts;
• In a situation with a spot welding unit, this figure should not exceed 6 volts;
• To implement this condition, a new secondary winding is required, designed for a reduced output voltage.

Note! It is also possible to make a new low-voltage coil by winding it over the existing secondary winding (if space permits).

Otherwise, it is better to unwind the old "secondary" and use its wire to form a new working winding.

Before you do spot welding with an updated transformer, it is advisable to familiarize yourself with the existing types of these electrical products and try to choose the most suitable one.

The cores used in welding transformers can have several different designs (figure below).

Among them, the following types of TT stand out:

• With the so-called "W-shaped" or armor core;
• With a rod base (in the form of the letter "O");
• And, finally, with a core made in the form of a torus.

Of all the options listed, the most suitable for the purposes under consideration is a transformer with a toroidal core, which has small dimensions and relatively low weight (see the figure below).

Additional Information. The cross section of such a core in any transformer will be determined by the expected welding current.

In order for do-it-yourself spot welding to work normally, the output current of the unit must be at least 1000 amperes. The latter means that a sufficiently thick wire must be used in the output winding of the CT. This requirement is fully satisfied by the selected version of the toroidal core, since there is plenty of space for placing the output winding in it.

Secondary winding

Choice of options

When modifying a CT, the main attention should be paid to the parameters of the secondary winding, which determine the output characteristics of the device (its load current, in particular). At the same time, it is important to choose a busbar section that would provide a current density of about 8 A / mm² (with a cross-sectional area of ​​\u200b\u200babout 120 mm²). Since it is very difficult to handle such a thick tire when winding on a torus, it is most often limited to 80 mm².

Note! The indicated cross section can be obtained by adding together several wires of a slightly smaller thickness.

To facilitate the conditions for converting a CT to a point unit, it is advisable to pre-calculate the amount of wire required for its rewinding. After that, it will be possible (based on the space occupied by the winding) to decide whether it will enter the free space remaining on the torus or not.

Important! In the event that the new winding does not fit into the torus, the old secondary coil will have to be completely dismantled (dismantled).

For the convenience of handling new wires during the winding process, it is recommended to wrap them with fabric-based insulating tape. To determine the exact number of turns that affect the magnitude of the output voltage, we recommend using the test winding method with a small cross-section wire in insulation.

Since the winding is not connected to the load in this case, the cross section of the test wire does not matter much. Experience has shown that in rough tests it is sufficient to use no more than 10 turns. After winding them, the transformer should be connected to the network and the voltage given out by the test coil should be measured, after which it is divided by the number of turns. The result is a figure showing the number of turns required to produce one volt at the output.

Since in this case it is necessary to obtain 6 Volts, multiplying the number obtained from the test connection by 6, we get the required number of turns.

In order to make a new device with your own hands, you must first calculate the amount of wire needed to rewind the CT. After that, it will be possible (based on the space occupied by the bus winding) to determine whether it will enter the free space remaining on the torus.

Winding schemes and its placement

The switching scheme and the order of placement of the "secondary" depend on the type of the selected core. With the toroidal base of the CT declared by us, it is more convenient to divide it into two half windings connected in series (3 volts each).

In order to increase the load capacity (increase the welding current), you can make two windings of 6 volts each and connect them in parallel. The output voltage in this case will not change, and the load current can be doubled. This embodiment allows solving the issue of a large cross-section of the secondary bus, which can then be reduced by half.

Various types of connections of such windings are shown in the picture below.

The order in which they are connected is very important to obtain the required output parameters, and mistakes made in this case can lead to completely different indicators. So, in particular, if you make a mistake during installation and turn on two windings in opposite directions, as a result they will be closed to one another and will give out zero voltage at the output, which is equivalent to a short circuit.

At the ends of ready-made secondary windings, special tips should be equipped by crimping.

Control scheme

To control the welding process, short pulses are used, which are generated in a special electronic circuit. When manufacturing a spotter based on an old unit, it is also necessary to provide a control unit that allows switching a significant output current.

To solve this problem, manually generated pulses are applied to the primary winding of the CT (the simplest control circuit is shown in the figure below).

The disadvantages of such management include:

• By means of the button shown in the figure, the mains voltage is switched, which is extremely dangerous;
• When mechanical contacts open, strong sparking occurs;
• Even if you replace the mains switch with a traction relay from a starter controlled by a push-button mechanism, then such a circuit, despite the improvement, will still be unfinished.

Note! To implement the traction principle, it is allowed to use a combination of “powerful starter plus automotive relay” (and the latter can be of any brand).

When this combination is selected, the relay is activated when a voltage of 12 volts is applied, and its switching causes the power contactor to operate. However, this control option is not without drawbacks, since in this case it is not possible to accurately suppress the exposure interval (pulse width).

For those who know the basics of electronics and know how to handle a soldering iron, a more complex, but reliable electronic control circuit is suitable (see photo below).

Here, the working pulses are supplied to the input winding of the CT from an electronic device - a thyristor, which opens when voltage is applied to its control electrode. The capacitor (C1) included in its circuit, when the push-button contact is open, is charged through the elements V1-V4 of the diode bridge. When the button is pressed, the capacitance is discharged through the resistor R1 and directly through the control electrode circuit of the thyristor, which turns it on.

The electronic device will be in the on state until the capacitor is completely discharged (this interval can be adjusted with a variable resistor R1). For the next start operation, the button must first be released and then pressed again (its shutter speed determines the welding interval).

Transformer T1 can be of any type (with a secondary voltage of 12 volts). The thyristor parameters must satisfy the operating conditions, that is, allow it to operate at voltages up to 400 volts and currents of at least 50 amperes. For these purposes, an electronic product of the T132-50 brand is quite suitable.

In the final part of the review, we recall that spotter-type welding equipment is most often in demand in body repair and similar work with sheet metal. In this regard, when choosing the output power of a home-made unit, it is necessary to take into account the thickness of the sheet material with which you will mainly work.

Video

Spot welding can be found not only in production, but also in domestic conditions. The advantage of choosing this type of welding lies in its reliability. This way of fastening is easy to connect different-carbon steels, non-ferrous metal. At the same time, it is possible to build almost any configuration and combination with metals.

Allows you to create a product for any fantasies and needs.

Application spectrum

Most often, spot welding has been widely used in the repair of cables and household appliances. allows you to repair batteries and other mobile portable devices.

Welding technology

The battery welding technology is quite simple, an example can be seen in the video below.

The whole welding process consists in heating the working metal surface to a plastic state. In this state, the products are easily deformed and connected.

Continuous melting is required to ensure quality. Continuity and a certain speed of the working pace, pressing force are key in the work. In the future, these parameters characterize the quality of products.

The basis of the principle of operation of this welding is the conversion of electrical energy into thermal energy. Under the influence of heat, the metal surface undergoes melting.

The electrode contact should be placed at the junction of 2 working surfaces of the parts required for fixing.

The solidification of the molten mass occurs at the moment the current is turned off. This eliminates the effect of spreading the surface of the seams. Therefore, this type of welding is called spot welding.

Ticks

Attachment of parts of parts is carried out by fixing the surface with the help of special pliers. Which are divided into suspended and manual.

• Suspended. Have received wide application in the conditions of the plant and industrial enterprises, are subject to repeated use.
• Manual. The main function is the transmission of electric current to the electrodes.

Several advantages

• High speed of work;
• The highest degree of electrical safety;
• Ensuring a quality connection;
• You can make a device for welding manually.

Technical process

The whole system is built on elemental heat transfer in order to melt the metal at the fixing points. Welding quality can be affected by poor surface cleaning, visible oxides.

Using the law of thermal conductivity, this parameter should be taken into account for most common metals. The thermal conductivity parameters for some of them are presented in the table below.

Metal name	Melting point, Сᵒ
Iron (low carbon steel)
Aluminum

The electrodes must also meet certain parameters:

• Thermal conductivity;
• electrical conductivity;
• Mechanical strength;
• Processing speed.

The electrodes are short-lived and require careful handling. With constant exposure to temperature conditions, it is necessary to interrupt. This feature allows the electrodes and the welded surface to cool down. Thus, the service life of the electrodes is extended.

The diameter of the electrodes affects the characteristic of the current strength, and, accordingly, the quality of the seam. The diameter of the electrode section is selected based on the thickness of the working surface. The electrode should be approximately twice as thick as the workpieces to be fixed.

contact welding

Contact welding and allows you to work in normal home conditions. But, most often, this method is widely used in industry.

Manufacturers have made sure that bulky spot welding machines are not present at home. Compact mobile devices have long been invented. Their purpose is to repair household appliances.

Such a device is called a spotter. The device is equipped with two terminals designed to secure one of them to the working surface of the product. The second output is connected to the electrode.

In this configuration, it is not necessary. The power source should be located at a sufficiently close distance from the place of work.

You should not pay attention to a small-sized device, it is quite functional for its size.

The simplest devices use single-phase current. But you should not hope to fix the part by more than one millimeter. Fastening of more complex parts is carried out with the involvement of an additional transformer.

Price

The cost of spotters is quite low. In the most expensive category are inverter.

As a rule, household devices do not require large capacities. Therefore, you can get by with a homemade device.

Spot welding is distinguished by its quality of the seam. In most cases, in order to destroy it, the use of serious mechanical influences is required. Most often, drills are used for this.

Apparatus scheme

If there is such a need, there is a desire to make the device yourself, then it is quite possible to assemble it at home.

The size of the spot welding machine depends primarily on the needs. The most convenient are devices with medium dimensions.

Picture. The scheme of the welding machine for spot welding.

The operation of the device is based on the Lenz-Joule principle. The requirement of physical law states that the conductor must generate heat in an amount equal to the proportion of the resistance of the conductor, as well as the square of the current and the elapsed time.

Such a circuit solution requires the installation of a rectifier bridge. The capacitor is charged through the thyristor bridge. The first thyristor acts as a cathode.

The capacitor bank is a kind of protection and serves as a current releaser. A swing principle is created, constant charging and discharging of capacitors. This principle allows you to create the effect of spot soldering. The seam cools evenly and in a timely manner, preventing the metal from spreading.

To increase the power in the circuit, an additional thyristor with a shutdown relay is also added.

Homemade apparatus

An important part of the welding machine is the transformer. The minimum power value should be 750 watts.

Video on creating your own device.

You can create a device using an inverter. Before proceeding to the goal, it is necessary to have some skills in the field of electrical engineering.

A circuit using a transformer instead of an inverter is considered simpler. But such devices are not powerful enough to work with metals of sufficient thickness of more than 1 mm.

Device Creation Steps

• Remove the transformer from an unnecessary microwave;
• Get rid of the secondary winding, fasteners, shunts;
• Make the secondary winding with a thicker wire than in the primary;
• Check the assembled device for current leakage;
• Leaks should be repaired with insulation using tape;
• Check current strength. The value should be no more than 2 kA.

Copper wire of considerable thickness is most suitable as tips or electrodes. The tips are sharpened and fixed.

Do-it-yourself welding in this case does not mean welding technology, but home-made equipment for electric welding. Work skills are acquired through work experience. Of course, before going to the workshop, you need to learn the theoretical course. But it can only be put into practice if you have something to work on. This is the first argument in favor of, independently mastering the welding business, first take care of the availability of appropriate equipment.

The second - a purchased welding machine is expensive. Rent is also not cheap, because. the probability of its failure with unskilled use is high. Finally, in the outback, getting to the nearest point where you can rent a welder can be just long and difficult. All in all, it is better to start the first steps in metal welding with the manufacture of a welding machine with your own hands. And then - let him stand in a barn or garage until the case. It's never too late to spend money on branded welding, if things go well.

What will we be about

This article discusses how to make equipment at home for:

• Electric arc welding with alternating current of industrial frequency 50/60 Hz and direct current up to 200 A. This is enough to weld metal structures up to about a fence from a corrugated board on a frame from a professional pipe or a welded garage.
• Microarc welding of strands of wires is very simple, and useful when laying or repairing electrical wiring.
• Spot pulse resistance welding - can be very useful when assembling products from a thin steel sheet.

What we won't talk about

First, skip the gas welding. Equipment for it costs pennies compared to consumables, gas cylinders cannot be made at home, and a home-made gas generator is a serious risk to life, plus carbide is now, where it is still on sale, expensive.

The second is inverter arc welding. Indeed, a semi-automatic welding inverter allows a novice amateur to cook quite important structures. It is light and compact and can be carried by hand. But the retail purchase of inverter components, which allows you to consistently conduct a high-quality seam, will cost more than a finished device. And with simplified homemade products, an experienced welder will try to work, and refuse - “Give me a normal device!” Plus, or rather minus - to make a more or less decent welding inverter, you need to have a fairly solid experience and knowledge in electrical engineering and electronics.

The third is argon-arc welding. From whose light hand the assertion that it is a hybrid of gas and arc went for a walk is unknown. In fact, this is a kind of arc welding: the inert gas argon does not participate in the welding process, but creates a cocoon around the working area, isolating it from the air. As a result, the welding seam is chemically clean, free from impurities of metal compounds with oxygen and nitrogen. Therefore, non-ferrous metals can be boiled under argon, incl. heterogeneous. In addition, it is possible to reduce the welding current and arc temperature without compromising its stability and to weld with a non-consumable electrode.

It is quite possible to make equipment for argon-arc welding at home, but gas is very expensive. It is unlikely that you will need to cook aluminum, stainless steel or bronze in the order of routine economic activity. And if you really need it, it’s easier to rent argon welding - compared to how much (in money terms) the gas will go back into the atmosphere, these are pennies.

Transformer

The basis of all "our" types of welding is a welding transformer. The procedure for its calculation and design features differ significantly from those of power supply (power) and signal (sound) transformers. The welding transformer operates in intermittent mode. If you design it for maximum current like continuous transformers, it will turn out to be prohibitively large, heavy and expensive. Ignorance of the features of electrical transformers for arc welding is the main reason for the failure of amateur designers. Therefore, we will walk through the welding transformers in the following order:

1. a little theory - on the fingers, without formulas and zaumi;
2. features of the magnetic circuits of welding transformers with recommendations for choosing from randomly turned up ones;
3. testing of available second-hand;
4. calculation of a transformer for a welding machine;
5. preparation of components and winding of windings;
6. trial assembly and fine-tuning;
7. commissioning.

Theory

An electrical transformer can be likened to a water storage tank. This is a rather deep analogy: the transformer operates due to the energy reserve of the magnetic field in its magnetic circuit (core), which can many times exceed that instantly transferred from the power supply network to the consumer. And the formal description of losses due to eddy currents in steel is similar to that for water losses due to infiltration. Electricity losses in copper windings are formally similar to pressure losses in pipes due to viscous friction in a liquid.

Note: the difference is in evaporation losses and, accordingly, magnetic field scattering. The latter in the transformer are partially reversible, but they smooth out the peaks of energy consumption in the secondary circuit.

An important factor in our case is the external current-voltage characteristic (VVC) of the transformer, or simply its external characteristic (VX) - the dependence of the voltage on the secondary winding (secondary) on the load current, with a constant voltage on the primary winding (primary). For power transformers, the VX is rigid (curve 1 in the figure); they are like a shallow vast pool. If it is properly insulated and covered with a roof, then the water loss is minimal and the pressure is quite stable, no matter how the consumers turn the taps. But if there is a gurgle in the drain - sushi paddles, the water is drained. With regard to transformers, the power engineer must keep the output voltage as stable as possible up to a certain threshold, less than the maximum instantaneous power consumption, be economical, small and light. For this:

• The steel grade for the core is chosen with a more rectangular hysteresis loop.
• Constructive measures (core configuration, calculation method, winding configuration and arrangement) in every possible way reduce dissipation losses, losses in steel and copper.
• The induction of the magnetic field in the core is taken less than the maximum allowable for the transfer of the current form, because. its distortion reduces the efficiency.

Note: transformer steel with "angular" hysteresis is often referred to as magnetically hard. This is not true. Hard magnetic materials retain strong residual magnetization, they are made by permanent magnets. And any transformer iron is magnetically soft.

It is impossible to cook from a transformer with a rigid VX: the seam is torn, burnt, the metal is splashed. The arc is inelastic: I almost moved the electrode in the wrong way, it goes out. Therefore, the welding transformer is already made similar to a conventional water tank. Its VC is soft (normal dissipation, curve 2): as the load current increases, the secondary voltage drops smoothly. The normal scattering curve is approximated by a straight line falling at an angle of 45 degrees. This allows, due to a decrease in efficiency, to briefly remove several times more power from the same iron, or, respectively. reduce the weight and size of the transformer. In this case, the induction in the core can reach the saturation value, and even exceed it for a short time: the transformer will not go into a short circuit with zero power transfer, like a “silovik”, but will begin to heat up. Quite long: thermal time constant of welding transformers 20-40 min. If you then let it cool down and there was no unacceptable overheating, you can continue to work. The relative drop in the secondary voltage ΔU2 (corresponding to the range of arrows in the figure) of normal dissipation gradually increases with an increase in the range of oscillations of the welding current Iw, which makes it easy to hold the arc in any type of work. These properties are provided as follows:

1. The steel of the magnetic circuit is taken with a hysteresis, more "oval".
2. The reversible scattering losses are normalized. By analogy: the pressure has dropped - consumers will not pour out a lot and quickly. And the operator of the water utility will have time to turn on the pumping.
3. The induction is chosen close to the limiting overheating, this allows, by reducing cosφ (a parameter equivalent to efficiency) at a current that is significantly different from sinusoidal, to take more power from the same steel.

Note: reversible scattering loss means that part of the lines of force penetrates the secondary through the air, bypassing the magnetic circuit. The name is not entirely successful, as well as "useful scattering", because. "Reversible" losses are no more useful for the efficiency of a transformer than irreversible ones, but they soften the VX.

As you can see, the conditions are completely different. So, is it necessary to look for iron from a welder? Optional, for currents up to 200 A and peak power up to 7 kVA, and this is enough on the farm. By calculation and constructive measures, as well as with the help of simple additional devices (see below), we will obtain, on any hardware, a BX curve 2a that is somewhat more rigid than the normal one. In this case, the efficiency of welding energy consumption is unlikely to exceed 60%, but for episodic work, this is not a problem for yourself. But on thin work and low currents, it will not be difficult to hold the arc and welding current, without having much experience (ΔU2.2 and Ib1), at high currents Ib2 we will get an acceptable weld quality, and it will be possible to cut metal up to 3-4 mm.

There are also welding transformers with a steeply falling VX, curve 3. This is more like a booster pump: either the output flow is at the nominal value, regardless of the feed height, or it does not exist at all. They are even more compact and light, but in order to withstand the welding mode at a steeply falling VX, it is necessary to respond to fluctuations ΔU2.1 of the order of a volt within a time of about 1 ms. Electronics can do this, so transformers with a "cool" VX are often used in semi-automatic welding machines. If you cook from such a transformer manually, then the seam will go sluggish, undercooked, the arc is again inelastic, and when you try to light it again, the electrode sticks every now and then.

Magnetic circuits

Types of magnetic circuits suitable for the manufacture of welding transformers are shown in fig. Their names begin with a letter combination respectively. size. L means tape. For a welding transformer L or without L, there is no significant difference. If there is M in the prefix (SLM, PLM, SMM, PM) - ignore without discussion. This is iron of reduced height, unsuitable for a welder with all other outstanding advantages.

The letters of the nominal value are followed by numbers denoting a, b and h in fig. For example, for Sh20x40x90, the cross-sectional dimensions of the core (central rod) are 20x40 mm (a * b), and the window height h is 90 mm. Cross-sectional area of ​​the core Sc = a*b; window area Sok = c * h is needed for accurate calculation of transformers. We will not use it: for an accurate calculation, you need to know the dependence of losses in steel and copper on the value of induction in the core of a given size, and for them - the steel grade. Where will we get it if we wind it on random hardware? We will calculate according to a simplified method (see below), and then we will bring it up during the tests. It will take more work, but we will get welding, on which you can actually work.

Note: if the iron is rusty from the surface, then nothing, the properties of the transformer will not suffer from this. But if there are spots of tarnishing colors on it, this is a marriage. Once this transformer overheated very much and the magnetic properties of its iron deteriorated irreversibly.

Another important parameter of the magnetic circuit is its mass, weight. Since the specific gravity of the steel is unchanged, it determines the volume of the core, and, accordingly, the power that can be taken from it. For the manufacture of welding transformers, magnetic cores with a mass of:

• O, OL - from 10 kg.
• P, PL - from 12 kg.
• W, WL - from 16 kg.

Why Sh and ShL are needed harder is understandable: they have an “extra” side rod with “shoulders”. OL can be lighter, because it does not have corners that require excess iron, and the bends of the magnetic lines of force are smoother and for some other reasons, which are already in the next. section.

Oh OL

The cost of transformers on tori is high due to the complexity of their winding. Therefore, the use of toroidal cores is limited. A torus suitable for welding can, firstly, be removed from LATR - a laboratory autotransformer. Laboratory, which means it should not be afraid of overloads, and the LATR iron provides a VX close to normal. But…

LATR is a very useful thing, first. If the core is still alive, it is better to restore the LATR. Suddenly you don’t need it, you can sell it, and the proceeds will be enough for welding suitable for your needs. Therefore, it is difficult to find “bare” LATR cores.

The second is that LATRs with a power of up to 500 VA for welding are weak. From iron LATR-500, it is possible to achieve welding with an electrode 2.5 in the mode: cook for 5 minutes - it cools down for 20 minutes, and we heat up. As in the satire of Arkady Raikin: mortar bar, brick yok. Brick bar, mortar yok. LATRs 750 and 1000 are very rare and fit.

Another torus suitable for all properties is the stator of an electric motor; welding from it will turn out at least for an exhibition. But finding it is no easier than LATR's iron, and winding it up is much more difficult. In general, a welding transformer from an electric motor stator is a separate issue, there are so many complexities and nuances. First of all - with the winding of a thick wire on a "donut". Having no experience in winding toroidal transformers, the probability of damaging an expensive wire and not getting welding is close to 100%. Therefore, alas, it will be necessary to wait a little with the cooking apparatus on a triad transformer.

SH, SHL

Armor cores are structurally designed for minimal scattering, and it is practically impossible to normalize it. Welding on a regular Sh or ShL will be too hard. In addition, the cooling conditions of the windings on Sh and ShL are the worst. The only armored cores suitable for a welding transformer are of increased height with spaced biscuit windings (see below), on the left in fig. The windings are separated by dielectric non-magnetic heat-resistant and mechanically strong gaskets (see below) with a thickness of 1/6-1/8 of the core height.

The core Ш is shifted (assembled from plates) for welding necessarily overlapped, i.e. yoke-plate pairs are alternately oriented back and forth relative to each other. The method of normalizing scattering by a non-magnetic gap for a welding transformer is unsuitable, because the loss is irreversible.

If a laminated Ш turns up without a yoke, but with a punching of the plates between the core and the jumper (in the center), you are in luck. The plates of signal transformers are mixed, and the steel on them, to reduce signal distortion, goes giving a normal VX initially. But the probability of such luck is very small: signal transformers for kilowatt power are a rare curiosity.

Note: do not try to assemble a high W or WL from a pair of ordinary ones, as on the right in fig. A continuous direct gap, albeit a very thin one, is irreversible scattering and a steeply falling VX. Here, the dispersion losses are almost similar to the losses of water due to evaporation.

PL, PLM

Rod cores are most suitable for welding. Of these, they are laminated in pairs of identical L-shaped plates, see Fig., Their irreversible scattering is the smallest. Secondly, the windings of P and Plov are wound in exactly the same halves, half turns for each. The slightest magnetic or current asymmetry - the transformer buzzes, heats up, but there is no current. The third thing that may seem non-obvious to those who have not forgotten the school rule of the gimlet is that the windings on the rods are wound in one direction. Does something not seem right? Does the magnetic flux in the core have to be closed? And you twist the gimlets according to the current, and not according to the turns. The directions of the currents in the half-windings are opposite, and the magnetic fluxes are shown there. You can also check if the wiring protection is reliable: apply the network to 1 and 2 ', and close 2 and 1 '. If the machine does not immediately knock out, then the transformer will howl and shake. However, who knows what you have with the wiring. Better not.

Note: you can still find recommendations - to wind the windings of the welding P or PL on different rods. Like, VX softens. That's how it is, but for this you need a special core, with rods of different sections (secondary on a smaller one) and notches that release lines of force into the air in the right direction, see fig. on right. Without this, we get a noisy, shaky and gluttonous, but not a cooking transformer.

If there is a transformer

A 6.3 A circuit breaker and an AC ammeter will also help determine the suitability of an old welder lying around God knows where and the devil knows how. An ammeter is needed either a non-contact induction (current clamp), or a 3 A electromagnetic pointer. the shape of the current in the circuit will be far from sinusoidal. Another is a liquid household thermometer with a long neck, or, better, a digital multimeter with the ability to measure temperature and a probe for this. The step-by-step procedure for testing and preparing for further operation of the old welding transformer is as follows:

Calculation of the welding transformer

In Runet, you can find different methods for calculating welding transformers. With apparent inconsistency, most of them are correct, but with full knowledge of the properties of steel and / or for a specific range of magnetic core ratings. The proposed methodology was developed in Soviet times, when there was a shortage of everything instead of a choice. For the transformer calculated from it, the VX drops a little steeply, somewhere between curves 2 and 3 in Fig. at the beginning. This is suitable for cutting, and for thinner work, the transformer is supplemented with external devices (see below), which stretch the VX along the current axis to curve 2a.

The calculation basis is usual: the arc stably burns under voltage Ud 18-24 V, and its ignition requires an instantaneous current 4-5 times greater than the nominal welding current. Accordingly, the minimum open-circuit voltage Uxx of the secondary will be 55 V, but for cutting, since everything possible is squeezed out of the core, we take not the standard 60 V, but 75 V. Nothing more: it’s unacceptable according to TB, and the iron will not pull out. Another feature, for the same reasons, is the dynamic properties of the transformer, i.e. its ability to quickly switch from a short circuit mode (say, when shorted by metal drops) to a working one, is maintained without additional measures. True, such a transformer is prone to overheating, but since it is our own and in front of our eyes, and not in the far corner of a workshop or site, we will consider this acceptable. So:

• According to the formula from paragraph 2 before. the list we find the overall power;
• We find the maximum possible welding current Iw \u003d Pg / Ud. 200 A are provided if 3.6-4.8 kW can be removed from the iron. True, in the 1st case, the arc will be sluggish, and it will be possible to cook only with a deuce or 2.5;
• We calculate the operating current of the primary at the maximum network voltage allowed for welding I1rmax \u003d 1.1Pg (VA) / 235 V. In general, the norm for the network is 185-245 V, but for a home-made welder at the limit, this is too much. We take 195-235 V;
• Based on the found value, we determine the tripping current of the circuit breaker as 1.2I1рmax;
• We accept the current density of the primary J1 = 5 A/sq. mm and, using I1rmax, we find the diameter of its copper wire d = (4S / 3.1415) ^ 0.5. Its full diameter with self-isolation D = 0.25 + d, and if the wire is ready - tabular. To work in the "brick bar, mortar yok" mode, you can take J1 \u003d 6-7 A / sq. mm, but only if the required wire is not available and is not expected;
• We find the number of turns per volt of the primary: w = k2 / Sс, where k2 = 50 for W and P, k2 = 40 for PL, SHL and k2 = 35 for O, OL;
• We find the total number of its turns W = 195k3w, where k3 = 1.03. k3 takes into account the energy losses of the winding due to leakage and in copper, which is formally expressed by a somewhat abstract parameter of the winding's own voltage drop;
• We set the stacking factor Ku = 0.8, add 3-5 mm to a and b of the magnetic circuit, calculate the number of winding layers, the average length of the coil and the wire footage
• We calculate the secondary in the same way at J1 = 6 A/sq. mm, k3 \u003d 1.05 and Ku \u003d 0.85 for voltages of 50, 55, 60, 65, 70 and 75 V, in these places there will be taps for rough adjustment of the welding mode and compensation for fluctuations in the supply voltage.

Winding and finishing

The diameters of the wires in the calculation of the windings are usually obtained more than 3 mm, and varnished winding wires with d> 2.4 mm are rare in wide sale. In addition, the welder's windings experience strong mechanical loads from electromagnetic forces, so finished wires are needed with an additional textile winding: PELSh, PELSHO, PB, PBD. Finding them is even more difficult, and they are very expensive. The footage of the wire per welder is such that cheaper bare wires can be insulated on their own. An additional advantage is that by twisting several stranded wires to the desired S, we get a flexible wire, which is much easier to wind. Anyone who has tried to manually lay a tire on the frame at least 10 squares will appreciate it.

isolation

Let's say there is a wire of 2.5 square meters. mm in PVC insulation, and the secondary needs 20 m per 25 squares. We prepare 10 coils or coils of 25 m each. We unwind about 1 m of wire from each and remove the standard insulation, it is thick and not heat-resistant. We twist the bare wires with a pair of pliers into an even tight braid, and wrap it around, in order of increasing cost of insulation:

1. Masking tape with an overlap of turns of 75-80%, i.e. in 4-5 layers.
2. Muslin braid with an overlap of 2/3-3/4 turns, i.e. 3-4 layers.
3. Cotton tape with an overlap of 50-67%, in 2-3 layers.

Note: the wire for the secondary winding is prepared and wound after winding and testing the primary, see below.

winding

A thin-walled home-made frame will not withstand the pressure of thick wire turns, vibrations and jerks during operation. Therefore, the windings of welding transformers are made frameless biscuit, and on the core they are fixed with wedges made of textolite, fiberglass or, in extreme cases, impregnated with liquid varnish (see above) bakelite plywood. The instruction for winding the windings of the welding transformer is as follows:

• We are preparing a wooden boss with a height in winding height and with dimensions in diameter 3-4 mm larger than a and b of the magnetic circuit;
• We nail or fasten temporary plywood cheeks to it;
• We wrap the temporary frame in 3-4 layers with a thin plastic film with a call on the cheeks and a twist on their outer side so that the wire does not stick to the tree;
• We wind a pre-insulated winding;
• After winding, we impregnate twice until it flows through with liquid varnish;
• after the impregnation dries, carefully remove the cheeks, squeeze out the boss and tear off the film;
• we tightly tie the winding in 8-10 places evenly around the circumference with thin cord or propylene twine - it is ready for testing.

Finishing and domotka

We shift the core into a biscuit and tighten it with bolts, as expected. The winding tests are carried out in exactly the same way as those of the dubious finished transformer, see above. It is better to use LATR; Iхх at an input voltage of 235 V should not exceed 0.45 A per 1 kVA of the overall power of the transformer. If more, the primary is homemade. Winding wire connections are made on bolts (!), insulated with a heat-shrinkable tube (HERE) in 2 layers or cotton tape in 4-5 layers.

According to the test results, the number of turns of the secondary is corrected. For example, the calculation gave 210 turns, but in reality Ixx got back to normal at 216. Then we multiply the calculated turns of the secondary sections by 216/210 = 1.03 approx. Do not neglect the decimal places, the quality of the transformer largely depends on them!

After finishing, we disassemble the core; we tightly wrap the biscuit with the same masking tape, calico or “rag” electrical tape in 5-6, 4-5 or 2-3 layers, respectively. Wind across the turns, not along them! Now once again impregnate with liquid varnish; when dry - twice undiluted. This biscuit is ready, you can make a secondary one. When both are on the core, we once again test the transformer for Ixx (suddenly it curled somewhere), fix the biscuits and impregnate the entire transformer with normal varnish. Phew, the most dreary part of the work is over.

Pull VX

But he is still too cool with us, remember? Needs to be softened. The simplest way - a resistor in the secondary circuit - does not suit us. Everything is very simple: at a resistance of only 0.1 ohms at a current of 200, 4 kW of heat will be dissipated. If we have a welder for 10 or more kVA, and we need to weld thin metal, a resistor is needed. Whatever the current is set by the regulator, its emissions when the arc is ignited are inevitable. Without an active ballast, they will burn the seam in places, and the resistor will extinguish them. But to us, low-powered ones, he will not be of any use to him.

The reactive ballast (inductor, choke) will not take away excess power: it will absorb current surges, and then smoothly give them to the arc, this will stretch the VX as it should. But then you need a choke with dissipation control. And for him - the core is almost the same as that of the transformer, and rather complex mechanics, see fig.

We will go the other way: we will use an active-reactive ballast, colloquially referred to as the gut by old welders, see fig. on right. Material - steel wire rod 6 mm. The diameter of the turns is 15-20 cm. How many of them are shown in fig. it can be seen that for power up to 7 kVA this gut is correct. The air gaps between the turns are 4-6 cm. The active-reactive choke is connected to the transformer with an additional piece of welding cable (hose, simply), and the electrode holder is attached to it with a clip-clothespin. By selecting the connection point, it is possible, together with switching to secondary outlets, to fine-tune the operating mode of the arc.

Note: an active-reactive inductor can get red hot in operation, so it needs a fireproof, heat-resistant, non-magnetic dielectric lining. In theory, a special ceramic lodgment. It is acceptable to replace it with a dry sand cushion, or already formally with a violation, but not rough, the welding gut is laid on bricks.

But other?

This means, first of all, an electrode holder and a connection device for the return hose (clamp, clothespin). They, since we have a transformer at the limit, need to be bought ready-made, but such as in fig. right, don't. For a 400-600 A welding machine, the quality of the contact in the holder is not very noticeable, and it will also withstand simply winding the return hose. And our self-made, working with an effort, can go wrong, it seems to be unclear why.

Next, the body of the device. It must be made from plywood; preferably Bakelite impregnated as described above. The bottom is from 16 mm thick, the panel with the terminal block is from 12 mm, and the walls and cover are from 6 mm, so that they do not come off when carrying. Why not sheet steel? It is a ferromagnet and in the stray field of a transformer it can disrupt its operation, because. we get everything we can out of it.

As for the terminal blocks, the very terminals are made from bolts from M10. The basis is the same textolite or fiberglass. Getinax, bakelite and carbolite are not suitable, they will crumble, crack and delaminate pretty soon.

Trying a constant

DC welding has a number of advantages, but the VX of any DC welding transformer is tightened. And ours, designed for the minimum possible power reserve, will become unacceptably tough. The inductor-gut will not help here, even if it worked on direct current. In addition, expensive 200 A rectifier diodes must be protected from current and voltage surges. We need a return-absorbing filter of infra-low frequencies, Finch. Although it looks reflective, you need to take into account the strong magnetic connection between the halves of the coil.

The scheme of such a filter, known for many years, is shown in Fig. But immediately after its introduction by amateurs, it turned out that the operating voltage of the capacitor C is small: voltage surges during ignition of the arc can reach 6-7 values ​​of its Uxx, i.e. 450-500 V. Further, capacitors are needed to withstand the circulation of large reactive power, only and only oil-paper (MBGCH, MBGO, KBG-MN). About the mass and dimensions of single "cans" of these types (by the way, and not cheap) gives an idea of ​​the following. fig., and the battery will need 100-200 of them.

With a magnetic circuit, the coil is simpler, although not quite. For it, 2 PLA of the TS-270 power transformer from old tube TVs-“coffins” (the data is available in reference books and in Runet), or similar, or SL with similar or large a, b, c and h. From 2 PLs, a SL is assembled with a gap, see Fig., 15-20 mm. Fix it with textolite or plywood gaskets. Winding - insulated wire from 20 sq. mm, how much will fit in the window; 16-20 turns. They wind it in 2 wires. The end of one is connected to the beginning of the other, this will be the middle point.

The filter is adjusted along the arc at the minimum and maximum Uхх values. If the arc is sluggish at the minimum, the electrode sticks, the gap is reduced. If the metal burns at the maximum, increase it or, which will be more efficient, cut off part of the side rods symmetrically. So that the core does not crumble from this, it is impregnated with liquid, and then with normal varnish. Finding the optimum inductance is quite difficult, but then welding works flawlessly on alternating current.

microarc

The purpose of microarc welding is said at the beginning. The “equipment” for it is extremely simple: a step-down transformer 220 / 6.3 V 3-5 A. In tube times, radio amateurs were connected to the filament winding of a standard power transformer. One electrode - the twisting of wires itself (copper-aluminum, copper-steel can be used); the other is a graphite rod like a lead from a 2M pencil.

Now more computer power supplies are used for microarc welding, or, for pulsed microarc welding, capacitor banks, see the video below. At direct current, the quality of work, of course, improves.

Video: homemade twist welding machine

Video: do-it-yourself welding machine from capacitors

Contact! There is a contact!

Contact welding in industry is mainly used for spot, seam and butt welding. At home, primarily in terms of energy consumption, a pulsed point is feasible. It is suitable for welding and welding thin, from 0.1 to 3-4 mm, steel sheet parts. Arc welding will burn through a thin wall, and if the part is a coin or less, then the softest arc will burn it entirely.

The principle of contact spot welding is illustrated in Fig: copper electrodes compress parts with force, a current pulse in the steel-steel ohmic resistance zone heats the metal to the point where electrodiffusion occurs; metal does not melt. This requires approx. 1000 A per 1 mm thickness of the parts to be welded. Yes, a current of 800 A will grab sheets of 1 and even 1.5 mm. But if this is not a craft for fun, but, say, a galvanized corrugated fence, then the very first strong gust of wind will remind you: “Man, the current was rather weak!”

Nevertheless, resistance spot welding is much more economical than arc welding: the open-circuit voltage of the welding transformer for it is 2 V. It is the sum of 2-contact steel-copper potential differences and the ohmic resistance of the penetration zone. A transformer for contact welding is calculated similarly to it for arc welding, but the current density in the secondary winding is 30-50 or more A / sq. mm. The secondary of the contact-welding transformer contains 2-4 turns, it cools well, and its utilization factor (the ratio of welding time to idling and cooling time) is many times lower.

In RuNet there are many descriptions of home-made pulsed spot welders from unusable microwaves. They are, in general, correct, but in repetition, as it is written in "1001 Nights", there is no use. And old microwave ovens don't lie around in heaps. Therefore, we will deal with less well-known designs, but, by the way, more practical.

On fig. - the device of the simplest apparatus for pulsed spot welding. They can weld sheets up to 0.5 mm; for small crafts, it fits perfectly, and magnetic cores of this and larger sizes are relatively affordable. Its advantage, in addition to simplicity, is the clamping of the welding tongs running rod with a load. A third hand would not hurt to work with a contact welding impulse, and if one has to squeeze the tongs with force, then it’s generally inconvenient. Disadvantages - increased accident and injury hazard. If you accidentally give an impulse when the electrodes are brought together without the parts to be welded, then plasma will strike from the tongs, metal splashes will fly, the wiring protection will be knocked out, and the electrodes will fuse tightly.

The secondary winding is made of a 16x2 copper bus. It can be made from strips of thin sheet copper (it will turn out flexible) or made from a segment of a flattened refrigerant supply pipe for a domestic air conditioner. The tire is isolated manually, as described above.

Here in fig. - drawings of a pulsed spot welding machine are more powerful, for welding a sheet up to 3 mm, and more reliable. Thanks to a fairly powerful return spring (from the armored mesh of the bed), accidental convergence of the tongs is excluded, and the eccentric clamp provides a strong stable compression of the tongs, which significantly affects the quality of the welded joint. In which case, the clamp can be instantly reset with one blow on the eccentric lever. The disadvantage is the insulating knots of the pliers, there are too many of them and they are complex. Another one is aluminum pincer bars. Firstly, they are not as strong as steel ones, and secondly, these are 2 unnecessary contact differences. Although the heat dissipation of aluminum is certainly excellent.

About electrodes

In amateur conditions, it is more expedient to isolate the electrodes at the installation site, as shown in fig. on right. There is no conveyor at home, the apparatus can always be allowed to cool down so that the insulating sleeves do not overheat. This design will make it possible to make rods from a durable and cheap steel professional pipe, and also extend the wires (up to 2.5 m is acceptable) and use a contact welding gun or remote tongs, see fig. below.

On fig. on the right, one more feature of electrodes for resistance spot welding is visible: a spherical contact surface (heel). Flat heels are more durable, so electrodes with them are widely used in industry. But the diameter of the flat heel of the electrode must be equal to 3 thicknesses of the adjacent welded material, otherwise the penetration spot will burn out either in the center (wide heel) or along the edges (narrow heel), and corrosion will go from the welded joint even on stainless steel.

The last point about the electrodes is their material and dimensions. Red copper quickly burns out, so purchased electrodes for resistance welding are made of copper with a chromium additive. These should be used, at current copper prices it is more than justified. The electrode diameter is taken depending on the mode of its use, based on a current density of 100-200 A/sq. mm. The length of the electrode according to the conditions of heat transfer is at least 3 of its diameters from the heel to the root (beginning of the shank).

How to give impetus

In the simplest home-made pulse-contact welding machines, a current pulse is given manually: they simply turn on the welding transformer. This, of course, does not benefit him, and welding is either lack of fusion, or burnout. However, it is not so difficult to automate the feed and normalize the welding pulses.

A diagram of a simple, but reliable and long-term practice-tested welding pulse shaper is shown in fig. Auxiliary transformer T1 is a conventional power transformer for 25-40 watts. Winding voltage II - according to the backlight. Instead of it, you can put 2 LEDs connected in anti-parallel with a quenching resistor (normal, 0.5 W) 120-150 Ohms, then the voltage II will be 6 V.

Voltage III - 12-15 V. It can be 24, then capacitor C1 (ordinary electrolytic) is needed for a voltage of 40 V. Diodes V1-V4 and V5-V8 - any rectifier bridges for 1 and from 12 A, respectively. Thyristor V9 - for 12 or more A 400 V. Optothyristors from computer power supplies or TO-12.5, TO-25 are suitable. Resistor R1 - wire, they regulate the pulse duration. Transformer T2 - welding.