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Acquaintance with the principles of spot welding. Contact spot welding Welding current for spot welding machines

Spot welding is a type of contact welding, during which the parts are to be connected in separate places (points), limiting the size of the heating of the electrodes. They transmit compressive force and conduct electricity. The position of the points depends on how the electrodes are positioned in the spot welding machine being used. At one time, it is possible to weld both one, two, and several points.

By means of resistance spot welding, products from non-ferrous or ferrous metals are traditionally welded, both of the same kind and of dissimilar ones. These can be workpieces of different or identical thicknesses, machined or forged products, rolled or pressed sheets. The most effective spot welding, which is quite affordable, is for welding agricultural machinery components, automotive and tractor elements, railroad cars, microelectronics parts, refrigerators and household items.

Features of spot welding

When welding in this way, the products are overlapped. Then they are clamped with a certain force between a pair of copper electrodes connected to a transformer and conducting electric current to the welding site. With the inclusion of a transformer for spot welding with the help of a short-term pulsed current, the workpieces are heated with the appearance of a molten area or a core of a point in the place of their contract.

The surfaces of the products subjected to welding, in contact with copper electrodes, are not heated as quickly as their inner layers. Therefore, heating lasts until the outer layers reach the state of plasticity with the formation of a volume point of the metal and the state of the melt by the inner layers. After turning off the current, it is necessary to maintain the gain for a certain time, which is necessary for the normal crystallization of the materials subjected to melting and the prevention of such shrinkage defects as looseness with cracks. After turning off the supply of currents with pressure relief, you can see the result of the impact of the spot welding machine - the resulting cast point of the welded joint.

Based on the location of the electrodes relative to the products to be connected, such welding can be performed on one side or be two-sided. In the latter case, two or more workpieces are clamped by the electrodes of the spot welding machine. The method of one-sided welding involves the distribution of current between the lower and upper parts. In this case, part of the current conducted through the lower workpiece provides heating. To increase this current, the use of a special copper gasket is provided. One-way welding allows you to connect products at once with two points at the same time.

How to prepare the elements?

The preparation of blanks for processing by a resistance spot welding machine occupies an important place, since the stability of operations and the quality of the joints obtained depend on it. The product for welding is corrected, cleaned, adjusted, tacked or assembled in a special device. A significant thickness of the oxide film is removed using special rollers with helical notches, flame heating, shot blasting, shot blasting or vacuum fractional processing, and welding zone punching. Workpieces made of low carbon steel must be degreased with gasoline, acetone or other oil solvents, followed by pickling, brushing, abrasive and grinding devices. The treated surfaces are also passivated.

Workpieces can be cleaned only at the overlap or completely. After mechanical cleaning procedures, oxides and dust with abrasive particles should be removed from them. Products coated with metal are usually not subjected to stripping, they are seized by conventional welding. Small assemblies and blanks can be welded without tacks, by rigidly fixing them in spot welding tongs. On large products, tacking by arc welding and subsequent cutting out of areas where tacks are applied are possible.

Spot welding equipment

The most important parameters of the exposure mode of spot welding machines are the time of current conduction with its density, as well as the compressive force. The choice of these characteristics is determined by taking into account the features of the equipment used according to technology maps, tables of exemplary modes and experimental work. This welding is carried out both in soft and hard modes. The first one is distinguished by a relatively low current density, a significant duration of the welding cycle at low pressure. It is most often used for welding low alloy or carbon steel. The harsh modes of the spot welding machine are characterized by high current density, significant pressure, as well as a short duration of the welding cycle. It is applicable for welding work with copper, aluminum alloys and corrosion-resistant steels.

Spot Welding Technology

The connection by welding of dissimilar materials is best done in mild modes. In this case, it is easier to obtain a reliable connection due to the possibility of adjusting the parameters. The increase in heating with a decrease in heat removal to the material contributes to the symmetry of the location of the core. This is achieved due to the lower thermal conductivity and the diameter of the electrodes.

Spot welding schemes provide for the implementation of the entire process in four stages. In the first, the parts to be joined are clamped between the electrodes for spot welding. The second stage involves heating the junction to the melting temperature with the formation of a cast point core at the switched on current. At the third and fourth stages, the compression force at the switched on current is increased to form structures in the weld point, followed by the release of the electrodes from the force. Using this welding method, stamp-welded joints are produced. It is also indispensable in joining individual stamped products with welded points. Both significantly increase the productivity of work and simplify the processes of manufactured entire welding units.

The need to remove damaged parts during repair work is due to the need for drilling spot welding. It is used whenever you need to carefully drill out the points of connection of a faulty part with the main product. One way to remove welding is to punch and drill with a thin metal drill. Using a special drill for spot welding eliminates these operations. This not only eliminates the need for punching and pre-drilling, but also on the second sheet of the metal joint there are no through holes left from remote weld points. The principle and technology of such drilling is convenient to use in bodywork and any other work when it is necessary to replace an element attached with bolts, self-tapping screws or factory spot welding.

Various welding methods are used to connect parts. One of the widely used types is spot welding. It is especially necessary where it is required to connect parts with a relatively thin wall. This applies to parts of the housing of electrical appliances and various sheet steel structures, the thickness of which is not more than 2 mm.

Welding, performed spot in one or more places of parts, refers to a type of contact welding.

The heating of the metal alloy and its subsequent melting in this technology is carried out due to the heat that occurs due to the passage of current through the electrodes through the overlapped parts in the area of their dense compression. To do this, in parallel with the passage of electric current, mechanical compression of the parts to be connected by the electrodes is carried out. With close contact of the molten areas, their fusion occurs, enhanced by point diffuse penetration during compression of the metal parts.

Contact spot welding is different:

instant connection (a few seconds);
high value of welding current (over 1000A);
low voltage in the working area (from 1 to 10 V);
the use of compressive pressure at the point of welding (from 10 to 100 kg and above);
point area of fusion.

The heating of the metal is explained by the Joule Lenz law, when the low resistance of the electrodes provides good electrical conductivity at the point of contact with the metal surface and increases the current strength in this place. Transferring the maximum possible current to metal parts, the electrode contributes to their heating at the junction due to the high resistance of the metal, which prevents the passage of this current.

The maximum heating at the point of contact of the electrodes with the surface of the part leads to the melting of the metal in this place. At the melting temperature, cast point cores are formed, the diameter of which ranges from 4 to 12 mm. Parts are spot welded in one or more places.

With such a connection, its strength directly depends on the structural structure and size of the point fusion. These characteristics depend on the following factors:

the type of electrodes used;
the nature and strength of the current during welding;
the time of current exposure to the parts to be connected;
the magnitude of the compressive force;
quality, thickness and characteristics of the metal of the welded surfaces.

Stages of work

The welding process takes place in stages:

First, a tight contact of the parts is created using a clamp between the electrodes.
After the current is passed through the electrodes, the metal is heated pointwise to the melting temperature with the formation of a core. As the current continues to flow, the liquid core increases and reaches its maximum value. Inside the molten core, intercrystalline rearrangement of the metal occurs with the formation of new structural bonds.
At the same time, a deformation effect is carried out on the contact zone until the final formation of the desired size of the point connection. Sufficient compressive force provides a tight pressing of the connected parts and due to this, a compacted belt is formed around the liquid core zone, which prevents the melt from splashing out of the resistance welding zone.
The last stage of the welding process is to turn off the current and cool the liquid core of the metal with its gradual final crystallization. At the same time, it becomes smaller in size. During rapid cooling, residual stresses can occur, which adversely affect the quality of the connection. To prevent this, the compression force of the electrodes is reduced gradually, without interrupting immediately, along with the current being turned off after the work has been completed. This ensures the correct structure of the metal without stress in intercrystalline bonds. Sometimes, at the last stage of work, it is advised to increase the compressive force in order to ensure that the metal is completely forged at the junction and its uniformity without the presence of stresses.

Types of spot welding

Parts can be connected in two ways: using soft or hard welding mode.

Performing work using the soft mode is characterized by gradual heating of the metal of the parts to be joined using a moderate current density (no more than 100 amperes / mm 2). Warm-up time from 0.5 to 3 seconds. In this mode, there is less consumption of power consumption and load on the network. Therefore, it does not need increased power requirements. All this leads to a small degree of hardening of the heating zone. This gentle operation is well suited for joining steels that are sensitive to heat treatment and subject to rapid stress quenching under aggressive welding conditions.

The hard mode technology is based on the application of a current with a high density value and a high compression force when squeezing the parts. The current can have a density of up to 300 amperes/mm 2 , and the squeezing force varies in the range of 3-8 kg/mm 2 . The exposure time is much shorter than when performing work in the soft mode, and can last from 0.1 to 1.5 seconds.

For this mode, it is required to use a spot welding machine that consumes significant power. But the process of connecting parts is carried out quickly, providing a high degree of productivity. Hard mode welding is often used to join copper or aluminum alloys, as well as alloyed steel products with high thermal conductivity. Working in this mode helps to maintain their corrosion resistance.

Applied equipment

To perform point-to-point joining of parts, there are many devices that are different in appearance and principle of operation, which differ in technical parameters and have different operating modes.

The spot welding machine differs, first of all, in the power consumed during operation. It can be in the form of a machine with large dimensions and a high level of performance, but at the same time consume a lot of power.

There are also devices that look like a small portable apparatus that can be used for one-time welding work in everyday life.

Existing welding machines differ in the nature of the current in the process of making a welded joint. It depends on the principle of the device and the circuit of an electrical closed circuit.

Welding equipment for spot welding is produced in the form of:

machines that carry out a welded joint on alternating current;
devices using low frequency currents;
machines that weld in condenser mode;
machines that use direct current for welding.

The spot welding machine, which carries out the welding process on alternating current, has the greatest application. In such machines, the voltage for operation is obtained by converting the mains voltage of 220 or 380 volts using a transformer, the operating time of which is regulated by a special module, a control controller and other devices included in the circuit.

A variation of such machines operating on alternating current is the MTP-1210 device, which operates on a pneumatic drive. A modern machine for spot connection on alternating current is the MTP-16053 machine, which has an electronic control of the welding process.

The capacitor welding mode consists in the gradual accumulation of electricity by the capacitor during its charging. Then a rapid consumption of this electricity is carried out during the generation of a large current pulse. This makes it possible to carry out the process very quickly and consume less electricity and power. The impulse power consumption provides the most concentrated heat in a short period of time, which creates a minimum thermal zone for connecting parts. An example of a capacitor machine is the MTK-2002EK spot welding machine.

Machines operating on direct current include the MTVR-19053 device. It has a special design of trunks and electrodes inserted into them. This makes it possible to weld parts of various shapes and sizes.

What electrodes are needed for spot welding

The efficiency of work performance largely depends on the characteristics of the electrodes: their size, shape and material from which they are made. Spot welding electrodes have a dual function: they conduct current to the welding area and provide clamping force.

Electrodes come in straight and curly shapes. Mostly direct devices are used, since they provide free access to the connection point.

The shape of the tip of the electrodes is flat and spherical and is characterized, respectively, by the size of the diameter (d) of the flat section or the radius (R) of the spherical end. The value of the contact area of the electrode with the surface of the metal part depends on these dimensions, which directly affects the density of the supplied current and the force of squeezing the parts. The size of the resulting melt and the size of the core depend on these characteristics.

Electrodes with a spherical tip are more resistant to wear and are not as sensitive if they are incorrectly oriented to the surface of the part during installation. Therefore, they are especially recommended for welding soft alloys based on aluminum or others, because, unlike products with a flat tip, they do not leave dents and damage on the surface. In practice, spherical electrodes are mainly used in spot welding of any alloys.

The dimensions of the electrodes are indicated in GOST 14111-90 and range from 10 to 40 mm. Their choice depends on the size of the thickness of the parts to be joined. The dimensions of the working area of the electrodes recommended for a certain thickness are shown in the table:

* in the new version of GOST, instead of the diameter value D = 12 mm, the size of 10 mm and 13 mm is included.

The material from which the electrode is made also has a significant effect. It determines the characteristics of the electrical resistance, thermal conductivity and strength of the electrode at elevated temperatures. With cyclic changes in high temperature and load, the electrode is subjected to increased wear at the site of the working area. Therefore, this part of the electrode is made of heat-resistant copper alloys with high electrical conductivity and high thermal conductivity.

Application area

Spot welding is used on an industrial scale in the production of structures by stamping with simultaneous spot welding. This connection method is used in the manufacture of parts for cars, aircraft, space, agricultural and other equipment that have profile shapes in the design. Also, such welding is used to create miniature assemblies in the instrument-making industry, including for the production of electronic devices, which use parts with a thin wall.

For more than 150 years, people have known a method of joining metals called spot welding. This method made it possible to automate and mass-produce cars, agricultural machinery, aircraft and thousands of household products. Thanks to a relatively simple principle of operation, spot welding also comes into the life of ordinary amateur craftsmen, car mechanics, and tinsmiths.

The resistance welding technology works quite simply - the parts are tightly compressed and a powerful electrical impulse is applied through the shortest distance. The metal is heated, a molten core is formed at the point of contact. Since the parts are compressed, diffusion of metals occurs. The current is turned off, the point cools down, the metal crystallizes. The weld point turns out to be strong, when you try to break the connection, the material near the point bursts. The principle of operation of welding machines is the generation of this pulse and the tight compression of parts.

In order for the current pulse to warm up the metal well, it must be of great strength and low voltage. Industrial devices have characteristics: the voltage at the contacts is only 1 - 3 Volts, they are capable of producing a current of 10 - 15 kiloAmperes.

The device of the spot welding machine

Any spot welding machine consists of two blocks:

power supply;

To get a powerful discharge at low voltage, you need an induction type transformer. The ratio of the primary and secondary windings allows you to get an electrical impulse sufficient to melt the metal.

Clamping pliers consist of two copper or graphite contacts located on different levers and a clamping mechanism. Clamps come with different drives:

Mechanical. They consist of a powerful spring and a lever, the compression of metals occurs due to muscular strength. They are used in home-made or household devices, do not give proper control over the degree of compression, and have low productivity.
Pneumatic. Most popular for portable hand-held devices, easily adjustable by changing the pressure in the air line. The disadvantage is that they are relatively slow, they do not allow pressure changes during the welding process.
Hydraulic. Not so popular, the hydraulic drive is also slow, but has a greater latitude of settings due to the use of bypass adjustable valves.
Electromagnetic. The most "lightning" ones are used both on hand-held devices and on large stationary ones. Allows you to adjust the compression of metals during welding, which allows you to achieve penetration and the absence of "splashes" of the metal.

The complexity of the design is possible when using liquid cooling circuits on loaded devices, using various current and pressure control systems, and robotic movement of electrodes.

Where applicable

Spot welding is used to join various structural metals and alloys. Features of the technology - environmental friendliness, speed, reliability, ease of automation - allow it to be widely used in:

automotive industry for body assembly;
jewelry for connecting parts;
microelectronics for soldering microcircuits;
production of welded reinforcing cages for monolithic slabs;
production of housings, parts of consumer goods.

Advantages and disadvantages

Among the main advantages of spot welding, the following stand out:

connection strength;
manufacturability;
profitability;
the ability to connect both thick and ultra-thin parts;
the possibility of automation and robotization of the welding process;
high culture of production and environmental friendliness;
versatility in materials and scalability.

Among the disadvantages are:

complexity of diagnostics of a welded joint;
requirements for the purity of metals during welding;
the difficulty of setting up the equipment.

Equipment and materials for spot welding

To cook dots you need:

spot welding machine;
welded cleaned parts;
conductive primer or mastic can be used to protect parts from corrosion.

Spot Welding Safety

The main thing when using spot welding machines is compliance with the rules. During the operation of the equipment there should be no bare contacts, violations of cable insulation. All contacts when connecting the device to the network must comply with the nominal parameters, the use of difavtomatov and grounding is mandatory.

When holding metals, use dielectric gloves, the handle of the pliers must be securely insulated.

Means of protection

A standard welder's kit is quite suitable for spot welding work. Thick overalls, cotton or split gloves, a transparent shield or goggles, a respirator or an exhaust hood - that's the whole set of protective equipment.

Security measures

Always check the equipment before starting work! Body parts must be reliably grounded, handles and holders must be insulated.

Maintenance and reconfiguration of the device is performed in the off state.

The pedal or control button should be in a convenient place.

The welder must firmly hold the workpiece or tool, stand firmly and steadily.

Technology and process of spot welding

Depending on the thickness of the metals, their type, conditions, the welding technology may differ in details. But in general, the order of work is the same.

Spot cooking occurs in several stages:

Surface preparation. They must be free of non-conductive paints and oxides and must be tightly connected without tension.
Compression of details. To do this, the pliers drive firmly compresses the surfaces, they are partially deformed. This is necessary for the occurrence of areas of current conduction precisely between the contacts of the tongs.
Heating parts with an electrical impulse. The thicker the parts, the longer you have to keep the heat. The impulse can be both constant and with adjustable current strength, variable.
In automatic machines, there is a stage of easing pressure on the parts - this is necessary to prevent metal from being squeezed out of the molten core. In manual mechanical tongs, this step is skipped.
The current is switched off. By eye, the moment the current is turned off can be determined by heating the area between the electrodes - as soon as the metal begins to turn red, the current is released.
Pressing or forging while the metal is cooling. Needed to form a strong crystalline structure of the weld point.
The detail is ready.

Different settings apply depending on the type of metal. The quality of the joint depends on the welding technology, the type of pulse, and the modes of compression of the parts.

Defects and their causes in spot welding

Despite the manufacturability, spot welding requires precise settings and constant quality control in production. Among the defects are:

Burnout. It looks like a hole in both parts, the fused edges are easily torn off. If the current is too high, the pulse duration is too long, or the pressure is too strong, the metal overheats and flows. To reduce the risk of burning, it is worth reducing the current or pressure.
Splashes. With strong compression or a long-term weak impulse, the metal leaves the molten core, and a void forms in its place. When working, splashes look like sparks flying out of dots. Up to a certain limit, the splash does not harm, since it is compensated by the compression of parts, but the point will be less reliable - the thickness around the point inevitably decreases.
Lack of fusion A weak impulse, insufficient compression force, weakening of the tongs during welding lead to non-heating of the core. Such a point will be “glued”, but will come off under load. Lack of penetration can occur if the weld points are located nearby - the neighboring point acts as a shunt through which part of the electrical energy passes. Accordingly, it will not be spent on molten metal.
Reducing the welding diameter. If the pulse is short or the parts do not fit snugly, there will be insufficient melt area. In this case, at one point there may be one or several micromelts, which in total are much weaker than a monolithic point.

Cracks and destruction of the base metal. Occur in the absence of compression, the proximity of the point to the edge of the overlapping strip, dirty metal. Visually, with a magnifying glass, this defect is easy to detect.

Correction of welding defects

Diagnosis of spot welding is a rather complicated procedure. Conventional ultrasonic research methods do not give an accurate picture, therefore, in factories with automation, tests are carried out with the destruction of control samples.

Identified defects are corrected by the following methods:

repeated boiling point;
drilling and subsequent semi-automatic welding;
external splashes can be cleaned;
hot spot forging;
installation of a welded or blind rivet.

Spot welding symbols in GOST drawings

The order in production is ensured by the correct technical documentation. Spot welding has its own designation on the drawing, which is supplemented by a special letter code. On the front plane, the contours of the area to be welded are indicated, and the places of the points are marked with crosses. On the side section, the welding point looks like joined hatched planes.

The designation of weld points is made on the drawings in accordance with GOST 15878-79. All symbols and additional data are also specified there.

Buy or do it yourself?

Despite the prevalence of technology, the cost of professional equipment is quite high. Therefore, among home craftsmen, there are schemes for self-manufacturing a device for spot welding from a simple transformer and mechanical tongs. You can make your own hands as a powerful device for connecting 4-5 mm of metal, as well as a jewelry device that can help a radio mechanic. Manual work in the garage does not require expensive equipment.

Such a device is quite capable of cooking irresponsible joints. If a person’s life depends on the strength of welding (for example, body repair), it is better to purchase a factory-made machine spot welding device with a pneumatic tong drive and a customizable controller, or use other types of welding.

The manufacturing quality of factory devices is higher, they are designed for specific tasks, the strength of the connections is higher, there are safety precautions. These devices allow you to cook a lot, and are configured to work in industries.

The very name resistance spot welding indicates that the parts are firmly connected to each other by a point or points as a result of the action of an electric current and the corresponding compressive force.

In this way, it is possible to connect both the thinnest parts, having a thickness of up to 0.02 microns, and parts up to 20 mm thick, made of various metals and alloys, as well as their combinations. This type of welding is used to weld wire, rods of round, cross-section, and other profiles. Most often, structures made of mild and corrosion-resistant steel, as well as all light alloys and brass, are welded.

Spot welding is widely used in the manufacture of structures in the electronics industry, in shipbuilding, aircraft, automotive, agriculture, other industries and everyday life. Welding is used in the straightening and welding of car bodies, in the manufacture of cabinets and cases that are used in the electrical industry, the manufacture of frame-shaped products, and the manufacture of dishes.

Not a single service station and small car service shops can exist without a spot welding machine in their arsenal.

Stages of spot welding

These include:

preparation of product edges for welding;
combining parts in the desired position and placing them between the electrodes;
heating the product to a state of plasticity;
deformation.

Preparation of edges for welding consists in cleaning them to a metallic sheen and degreasing. The parts must fit snugly against each other during the welding process. To do this, use a hand vise or clamps.

The benefits include:

high speed (some devices allow you to make 600 connections per minute);
lack of deformations and warping;
there is no need to use a highly qualified welder;
profitability;
the possibility of automating the welding process.

The disadvantages include the high complexity of welding, the inability to obtain a tight connection and the inability to apply this type of welding for loaded and power products.

Welding machine device

The main parts of any spot welding machine are:

current transformer (the secondary winding is connected to the electrodes);
a special mechanism designed to compress the electrodes;
welding clamp;
a device that allows you to turn the welding current on and off;
control cabinet (regulates the strength of the current and the time of its flow).

Welding machines of low power may not have a control cabinet, then the current flow time and the necessary compression force of the electrodes are adjusted by the welder himself, relying on his experience and skills.

Typically, welding machines are regulated by the following main parameters:

current strength;
current passage time;
compression force of the electrodes.

In the process of working on any welding machine, it is necessary to monitor the condition of the electrodes. The electrode diameter must not increase. This leads to a decrease in the concentration of heat at the junction of the parts. The electrode diameter must be the same as the subsequently obtained welding spot. The plane of contact of the electrode with the metal is cleaned with a flat file or sandpaper.

It must be remembered that the electrodes are made of special materials - copper and heat-resistant bronzes, which are able to retain their size and shape at high temperatures (up to 600 0C), but during operation they quickly wear out and lose their shape. Therefore, it is necessary not only to monitor the state of the shape of the electrodes, but also to replace them in time.

All devices can be classified according to the following main features:

appointment;
the location of the electrodes;
movement;
way of automation.

According to the purpose, the devices are divided into general-purpose machines and those intended for specific work (specialized). General purpose devices are used for domestic and industrial purposes when performing one-time work. They are characterized by small size and weight, are easily transported and operate, as a rule, from a household electrical network.

Specialized devices are used for production purposes in large-scale and mass production of the same type of products. This maximizes performance. They are characterized by large dimensions, they are often powered by a 380 V electrical network. These include special spotters and machines designed specifically for the production of bodywork.

The electrodes of the machines can be located as follows:

opposite each other;
next to each other (parallel).

In the first case, the electrodes on both sides simultaneously compress the parts to be welded, and in the second case, the electrodes rest on one side of the parts. Such ticks are called two-point.

According to the method of movement, devices can be of 3 types:

stationary;
suspended;
mobile.

In stationary machines for spot welding, the parts are moved under the machine, while in suspended and mobile machines, the machine is installed in the welding position. Usually, welding tongs are used for repair purposes. They are small in size and allow spot welding at the place of repair work.

According to the method of automation, equipment can be:

manual;
automatic.

The main parameter when choosing the machine necessary for one purpose or another is the strength of the welding current and the length of the levers with electrodes. This is what determines what thickness of parts can be welded, what metal and with what dimensions. Usually the manufacturer indicates this in the passport for a specific model of the spot welding machine. The simplest machine for turning welding is quite possible.

The procedure for the operation of spot welding machines

The parts to be connected overlap each other. Then they are installed between the electrodes and fixed. Next, a large current (about 5000 A) and a small voltage (4V) are passed. These values \u200b\u200bdepend on the thickness of the parts being welded. This will cause rapid heating of the metal at the point of contact for the entire thickness of the parts. It will melt.

Heating is carried out by applying a pulse of welding current. Its duration is not more than 0.1 sec, or even less, depending on the welding conditions. During this time, it will melt the metal in the joint zone and form liquid metal. After removing it, the parts are held under pressure for some time. This is done so that the metal cools down and crystallizes. The parts are pressed at the moment of action of the welding pulse. This helps to prevent splashing of metal from the dot formation zone.

Resistance spot welding defects

All defects that can occur during resistance spot welding can be divided into visible and invisible (internal). Visible defects include:

cracks;
burns;
metal breaks;
dot breaks;
dark surface of dots;
dents;
irregular dots.

Invisible defects include:

lack of fusion:
internal cracks, splashes, shells and pores.

This is facilitated by an incorrectly selected welding technology, improper preparation of the metal for welding, insufficient cooling of the electrodes during the welding process, wear of the electrode surface and other factors that adversely affect the quality of the product. It is possible to identify external defects immediately, and internal ones only by special non-destructive testing methods, which are used in industries that produce critical products.

In stores, including online stores, you can purchase devices from leading global and domestic manufacturers of welding equipment.

G.I.Kraft devices from Germany, BlueWeld welding machines manufactured in Italy, Forsage companies from Ukraine, CRAB mobile devices from a manufacturer from Ukraine and others are especially popular and in good demand. All of them are distinguished by excellent quality characteristics, innovative manufacturing technologies and high productivity. A huge assortment range allows you to choose a device for specific needs with excellent characteristics, which will last a long time.

Resistance spot welding has a number of advantages - the ability of the seams to withstand significant mechanical loads, the low cost of equipment, the ability to create an automated process, etc.

A welding machine of this type is relatively easy to assemble, which is also its advantage and makes it possible to make the machine yourself. The only drawback of this type of welding is the inability to create a sealed weld.

How to make a transformer for spot welding

The main component of the welding machine is the transformer. Ensuring an increased indicator of welding current is achieved by a large transformation ratio. The transformer must have a power of at least 1 kW. For this purpose, transformers from microwave ovens with sufficient power are excellent.

It is easy to find such a transformer, and a welding machine of this type can be used to weld 1 mm steel sheets. For the manufacture of an apparatus with greater power, several transformer installations can be used.

The transformer contains the primary winding and the magnetic circuit, which you will need. The secondary winding should be cut with a hacksaw or any other tool. In this case, it is very important to prevent damage to the magnetic circuit and the primary winding. If the transformer has current limiting shunts, they must be removed.

Having removed all unnecessary (in this case) elements, a secondary winding (new) should be created. In order to provide a large current, a copper thick wire is required, the diameter of which should be at least 1 cm. Three turns will be enough, make sure that the output is approximately 2 V.

More powerful do-it-yourself welding will turn out if you connect two (or more) transformers together. The main thing at the same time is to take into account the capabilities of your network, otherwise, including spot welding, you will have to deal with various troubles when lights flash, fuses work, etc.

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Do-it-yourself spot welding assembly and electrode manufacturing

Electrodes are a very important element in welding, so they should be made taking into account all recommendations. For the manufacture of these elements, you will need copper rods. It is better to choose rods of large diameter (at least the thickness of the wire). If your plans include making a welding machine that has a low power, you can use tips that contain powerful soldering irons.

Depending on how often resistance spot welding is used, over time the shape of the electrodes is lost. After some time of use, they can be sharpened, and if necessary, replaced with new ones.

It is desirable that the wire that goes from the electrodes to the transformer be of a minimum length and with a minimum number of connections. The fact is that at the junction, power is partially lost. Copper tips should be put on the ends of the wire and the wire and electrodes should be connected through them.

Each tip should be soldered to the wire. Such measures are necessary for the reason that during welding, copper contacts can gradually oxidize. This explains the significant loss of power and failure of the do-it-yourself welding machine. Soldering the wire and the tip is a rather difficult task, due to the large diameter. For this purpose, you can use tin-plated solder tips, which can be purchased at any specialized store.

The reason for the additional resistance that spot welding can cause may be in the non-soldered connections of the tips to each of the electrodes. However, this drawback cannot be corrected, because the electrodes must be periodically removed for sharpening or for the purpose of complete replacement. But here it is worth noting that these connections are quite easy to clean from oxide, unlike stranded wires that are crimped with a ferrule.

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Spot welding and how to manage it

Spot welding is controlled by a switch and a lever. In order to ensure proper contact of the parts that are being welded, it is necessary to provide sufficient compressive force between the electrodes.

If it is necessary to weld thick sheets of iron, it is required to use more powerful resistance spot welding (with a greater compression force between the electrodes). It is desirable that the lever is not short, while it must be strong enough. The welding machine must have a massive base, make sure in advance that it can be fixed to the table.

For a large clamping force, which do-it-yourself resistance spot welding should have, both the lever described above and the lever-screw clamp in the form of a screw tie located between the base and the lever itself can be used. If desired, you can use other methods, but they may require special equipment.

To install the switch, you must select the primary winding, or rather, its circuit. The fact is that the secondary winding circuit has too much current, which can cause additional resistance and welding of the contacts.

If you decide to use a lever clamping mechanism, it is better to choose a lever for mounting the switch. In this case, during operation, switching on the current and operating the lever can be performed with one hand. Thus, holding the parts to be welded will be as convenient as possible.