Welding is the process of obtaining a permanent connection. Rules and technologies of metal welding

Welding is a technological process in which strong bonds are established between atoms and molecules in the parts being joined. To ensure the connection, the surface of the structures being treated is first cleaned of contaminants, and the oxide film is also removed from the parts. Preparatory work greatly influences the quality of the connection.

The surfaces to be welded are brought together so that the distance between them is minimal. Then the parts are subjected to strong local heating or plastic deformation, after which the workpieces are joined to form a single whole. At the final stage, the weld seam is processed.

There are three classes of welding: mechanical, thermal and thermomechanical. Mechanical types of welding are carried out using pressure energy, for example, processing workpieces by friction, explosion or. Thermal welding uses heat to melt materials. Thermomechanical combines the features of the two described classes.

Main types of welding

Arc welding is one of the most common types of such joining of materials. In this case, welding electrodes are used, which are installed in a special holder and moved along the future seam. An arc is formed between the electrode rod and the workpiece, the metal melts and fills the weld, gradually hardening.

When resistance welding, short-term heating of the joint of parts is performed, which does not imply melting of the edges of the workpieces. In this case, plastic deformation of the metal occurs, which leads to the formation of a welded joint. To heat the joint during contact welding, electric current is used, which is a source of heat. At contact points, the metal becomes very ductile, making it easier to join surfaces.

Gas welding is also widely used in production. In this case, the place where the parts need to be connected is strongly heated with a gas flame having a very high temperature. The edges of the workpieces melt under this thermal influence. A filler material is supplied into the resulting gap, which serves to form a seam. The advantage of gas welding over arc welding is that the workpiece heats up more smoothly under the action of a gas jet. This allows this type of welding to be used for joining workpieces of small thickness.

By heating and melting the edges of the parts being joined. If previously only metals were subjected to it, today other materials, such as plastic, are also joined using this method.

We can say that a welded joint is one that was obtained by melting or pressure welding. Of course, there are a huge number of methods for obtaining the desired result. For example, there is such an element as an electric arc, and it is with its help that welding is carried out. There are a variety of welding methods, we will try to consider them all.

A little history. Classification

Forging metal is the first welding process. The need to repair metal products, as well as the creation of more advanced parts, has become a prerequisite for the development of welding processes. So, in 1800-1802 the electric arc was discovered. Various experiments were done with her. Eventually people learned to make welded joints using an electric arc. In Russia, the training of qualified welders is actively underway, new technologies, fundamentally different approaches, etc. are constantly being developed. A striking example of an excellent theoretical and practical base is the Bauman Training Institute.

Currently, there are about 150 methods by which welding is carried out. Welding methods are divided according to physical, technical, and technological characteristics. Thus, according to physical indicators, three large groups can be distinguished:

• Thermal is a type of welding performed using thermal energy. This includes gas, arc, laser and other welding.
• Thermomechanical- a type of welding that involves the use of not only thermal energy, but also pressure. This can be a contact, diffusion, forge connection, etc.
• Mechanical type of welding. In such cases, mechanical energy is used. The most widespread is cold friction, etc.

Each individual type differs in energy costs, environmental friendliness, and the equipment used during operation.

Gas flame welding

In this case, the main source of heat is the flame, which is released as a result of the combustion of fuel mixed with oxygen. Today, more than a dozen gases are known that can be used. The most popular are acetylene, MAF, propane and butane. The heat generated melts the surfaces along with the filler material.

The operator adjusts the nature of the flame. It can be oxidizing, neutral or reducing, depending on the amount of oxygen and gas in the mixture. In recent years, MAF has been actively used, which provides not only high welding speed, but also excellent seam quality. But at the same time, it is necessary to use more expensive wire with a higher content of manganese and silicon. Today, this is the most relevant mixture for gas welding, due to its safety and high combustion temperature in oxygen (2430 degrees Celsius).

Much depends on the composition of the metal that is planned to be welded. So, depending on this parameter, the number of filler rods is selected, and when taking into account the thickness of the metal, their diameter is selected. With careful preliminary preparation, a perfect weld is obtained.

All welding methods (gas) have a common feature, which is gradual heating of the surface. That is why they are suitable for working with steel sheets of 0.5-5 mm, non-ferrous metals, as well as tool steel and cast iron.

Let's take a closer look at some gas welding methods. There are quite a lot of them.

Left, right and through welding

When the sheet thickness is no more than 5 mm, the left-hand type of gas welding is most often used. Accordingly, the torch moves from right to left, and the filler rod is in front. The flame is directed from the seam and warms up the area being treated and the filler wire well. The technique varies depending on the thickness of the metal. If the sheet is less than 8 mm, then the burner moves only along the seam. If it is more than 8 mm, then it is necessary to simultaneously perform oscillatory movements in the transverse direction to improve the quality of the seam. The advantage of the left method is that the operator has a clear view of the area being treated and can ensure uniformity.

The fundamental difference between right-hand welding is that it is more economical. This is due to the fact that the burner flame is directed not from the seam, but towards it. This approach allows you to weld metals of maximum thickness, while the opening angle of the edges is small. The torch moves from left to right, followed by the filler rod.

Of course, if we consider gas welding methods, it is definitely worth mentioning through-bead welding. It is used when you need to get a vertical butt joint. The bottom line is that a small through hole is made at the bottom of the joint. When the burner is moved, the upper part of the hole melts, and when the additive is introduced, the lower part is welded. When the sheet thickness is too large, work is carried out on both sides and is carried out by two operators.

Bath method of welding reinforcement

Many of us are familiar with reinforcement, which is actively used in monolithic frame construction. It is used in floor blocks, piles, etc. Let's take a closer look at the features of such welding. Most often it is used for horizontal rods. The essence of the method is that a steel mold is welded at the joint. Then a bath of molten metal is created in it due to the heat of the arc. It turns out that the ends of the welded reinforcement melt and form a common pool. Accordingly, upon cooling, a complete compound is formed.

But before starting welding, it is necessary to prepare the rods. This is done as follows: the surfaces, as well as the ends, are cleaned, and any type of contamination is removed, for example, rust, scale and dirt. A metal brush is suitable for this. By the way, it is important to strip the reinforcement to a length of 30 mm at the welding site. The rods are installed coaxially. In this case, the gap should not exceed one and a half diameters of the electrode (at the end).

The process takes place under high currents. For example, with a 6 mm electrode, the welding unit operates at a current of 450 Amperes. If we are talking about low temperatures, then the current is increased by 10-12%. In addition, work can be performed with several electrodes at once. It is worth paying attention to the fact that this method allows you to reduce the labor intensity of the process, the cost of the product, as well as energy consumption. Today, the bathtub method of welding reinforcement is the most popular and reliable. This is due to low power consumption and high quality connection.

Pressure welding (plastic)

This type of welding is also called cold welding. This is due to the fact that during the connection there is no additional heating of the surface being treated. This method is based on the plastic deformation of metals during compression or sliding. Work is performed at normal or negative temperatures without diffusion. This method is considered one of the oldest.

To obtain a high-quality seam, special devices are used that cause deformation of the treated surfaces, which must first be cleaned. The result is a monolithic and fairly strong connection. There are various types and methods of welding (plastic). Currently there are three of them: point, suture and butt.

Cold welding can be used to join materials such as copper, lead, aluminum, cadmium, iron, etc. Plastic welding is most preferable when it is necessary to work with dissimilar materials that are quite sensitive to heat.

Of course, it should be noted that the main and main advantage of pressure welding is that you do not need to connect a powerful source of electricity to preheat the surface. In addition, the seam obtained in this way is not only strong, but also uniform and resistant to corrosion. However, there are also some disadvantages. They consist in the fact that you can only work with metals of high ductility. While some pipe welding methods can be used, others cannot, and fusion has to be used. This applies to water pipes and gas lines.

Classification of welding methods. Continuation

The process itself proceeds as follows. The parts that need to be connected are installed in close proximity to each other. After this, a powerful heat source is supplied, which melts the parts to be joined.

Molten metal (without any additional mechanical influences) is added to the common weld pool. When the heat source is removed from the welding site, the weld cools and the weld metal forms a very strong joint. The main problem is that the heat source must have high power and temperature. For example, to work with steel, copper or cast iron, you need a device with a temperature of 3 thousand degrees Celsius. If this indicator is deliberately lowered, welding productivity will drop sharply and the process will become ineffective.

The classification of fusion welding methods depending on the heat source is as follows:

• Arc welding. An electric arc is used as a heat source, which burns between the electrode and the surface to be welded.
• The heat source is a compressed electric arc. Gas is blown through it at high speed (supersonic), which acquires the properties of plasma.
• Electroslag- the metal is heated by molten flux through which an electric current flows.
• Electron beam welding- heating is carried out from the kinematic energy of electrons. They move in a vacuum under the influence of an electric field.
• Laser welding produced by heating the metal through the optical beam of a quantum generator. In this case, the radiation range can be light or infrared.
• Gas welding- melting of the treated surface due to the combustion of the gas-oxygen mixture.

Arc welding and its types

Today, electric arc welding is the most important for many industries. If we count the number of operating installations, employment among specialists, as well as the number of products, then this method of producing high-quality seams is leading throughout the world. Let's look at the main methods of arc welding. Today there are several of them.

The most common is automatic welding. Its essence lies in the fact that some operator movements are automated. For example, the supply of the electrode and its movement along the seam are carried out without human intervention (in contrast to the semi-automatic mode). This approach is good in that the quality of the seam and productivity are slightly increased, and the risk of injury is reduced. Shielding gas is often used to prevent nitriding and oxidation of the welded joint during work.

There is also manual welding, which consists in the fact that the consumable edges touch and excite an electric arc (with a non-consumable electrode). After the filler material is heated and melted, a pool is formed, which subsequently creates a weld. It is worth drawing your attention to the fact that methods of electrode welding using an electric arc are classified according to several technical characteristics. For example, by the type of gases used (active and inert), by the degree of mechanization (manual, automatic, etc.) and by other characteristics.

Learn more about manual arc welding

We have already reviewed in general terms the principle of obtaining a welded joint manually. Let's look at this issue in more detail. Today there are methods of manual arc welding, each of which is unique in its own way. For example, different electrodes can be used in the process: consumable and non-consumable. If the second type is chosen, then the seam connection is carried out as follows: the edges are applied to each other, and the graphite one is brought to the surface to be treated and an arc is created. As a result, a pool is formed, which after some time hardens and forms a weld. This method is most relevant for working with non-ferrous metals and their alloys, and is also used for surfacing.

Another method is to use a consumable electrode with a special coating. This method can be called classic when talking about manual welding, since it is the most common and has been used for quite a long time. The only difference from the method described above is that the electrode melts along with the surface. The result is a common pool, which solidifies after the arc is removed and forms a high-quality weld. The choice of welding method depends on the specific situation, material, its composition and much more.

A few important points

We looked at the main welding methods. They are conventionally divided into three large groups: cold, hot and gas. However, it is worth noting that sometimes special methods of obtaining a seam are used. This is necessary when we are talking about chemically active metals and their alloys. By the way, such materials are increasingly used in construction for the construction of critical components. In such cases, work is performed with low oxygen and nitrogen content in the air, and the source must be at a high temperature. A striking example is plasma and beam welding. In the second case, the beam source is similar to a kinescope and has a voltage of about 30-100 kV.

Plasma welding is much more difficult and interesting from the point of view of obtaining a high-quality connection. We have already figured out its essence a little. The process has key features such as the conduction of electrical current by the plasma. The gas that forms the plasma, in addition to its main task, also protects the seam from oxidation processes and nitriding. It's safe to say that this is a worthwhile method, but there are some limitations. For example, the power source must have a voltage of more than 120 V, and the installation is very expensive and complex.

Conclusion

So we figured out what welding is. There are various welding methods. In most cases, the operator is faced with the task of obtaining not only a high-quality, but also a durable seam that will withstand mechanical stress for a long time. To do this, there are various methods of welding with an electrode, for example, consumable or non-consumable. In addition, the technology may differ depending on the technique of the master. Some people find it convenient to do the job with left-hand welding, others with right-hand welding.

Even basic methods of welding reinforcement must be carried out according to the instructions. Agree, it will not be very pleasant if the partition collapses just because the welder cheated and decided to save a little.

Today, complex and expensive types of compound production are becoming increasingly common. This is due to several factors. Firstly, technological progress means that it is not always possible to use forge welding due to the fragility of the structure. Secondly, they try to obtain a high quality seam that would not collapse under prolonged dynamic and vibration loads. This is not difficult to achieve, especially considering that shock and vibration are the main enemies of a welded joint. But modern welding (welding methods) is constantly being improved, and new approaches to strengthening and obtaining durable and high-quality joints are being developed.

Welding

Welder at work

Welding- this is a technological process for obtaining a permanent connection by establishing interatomic and intermolecular bonds between the welded parts of the product when they are heated (local or general) and/or plastic deformation.

Welding is used to join metals and their alloys, thermoplastics in all areas of production and in medicine.

When welding, various energy sources are used: electric arc, electric current, gas flame, laser radiation, electron beam, friction, ultrasound. The development of technology now makes it possible to carry out welding not only in industrial enterprises, but in field and installation conditions (in the steppe, in a field, in the open sea, etc.), under water and even in space. The welding process involves a fire hazard; electric shock; poisoning with harmful gases; damage to the eyes and other parts of the body from thermal, ultraviolet, infrared radiation and splashes of molten metal.

Metal welding classification

The temperature in the welding arc column ranges from 5000 to 12,000 K and depends on the composition of the gaseous medium of the arc, material, electrode diameter and current density. The temperature can be approximately determined by the formula proposed by Academician of the Academy of Sciences of the Ukrainian SSR K.K. Khrenov: Tst = 810 × Uact, where Tst is the temperature of the arc column; Uact is the effective ionization potential, .

Arc welding

The source of heat is an electric arc that occurs between the end of the electrode and the product being welded when welding current flows as a result of the closure of the external circuit of the electric welding machine. The resistance of the electric arc is greater than the resistance of the welding electrode and wires, therefore most of the thermal energy of the electric current is released into the plasma of the electric arc. This constant flow of thermal energy keeps the plasma (electric arc) from decaying.

The released heat (including due to thermal radiation from the plasma) heats the end of the electrode and melts the welded surfaces, which leads to the formation of a weld pool - a volume of liquid metal. During the process of cooling and crystallization of the weld pool, a welded joint is formed. The main types of electric arc welding are: manual arc welding, non-consumable electrode welding, consumable electrode welding, submerged arc welding, electroslag welding.

Non-consumable electrode welding

In English literature it is known as en:gas tungsten arc welding ( GTA welding, TGAW) or tungsten inert gas welding (TIG welding, TIGW de:wolfram-inertgasschweißen ( WIG).

The electrode is a rod made of graphite or tungsten, the melting point of which is higher than the temperature to which they are heated during welding. Welding is most often carried out in a shielding gas environment (argon, helium, nitrogen and their mixtures) to protect the weld and electrode from the influence of the atmosphere, as well as for stable arc burning. Welding can be carried out both without and with filler material. Metal rods, wire, and strips are used as filler material.

Semi-automatic gas-shielded wire welding

In English-language foreign literature it is referred to as en:gas metal arc welding ( GMA welding, GMAW), in German-language literature - de:metallschutzgasschweißen ( MSG). Separate welding in an inert gas atmosphere ( metal inert gas, MIG) and in an active gas atmosphere ( metal active gas, MAG).

A metal wire is used as an electrode, to which current is supplied through a special device (conductive tip). The electric arc melts the wire, and to ensure a constant arc length, the wire is fed automatically by the wire feeder. For protection from the atmosphere, shielding gases (argon, helium, carbon dioxide and their mixtures) supplied from the welding head along with the electrode wire are used. It should be noted that carbon dioxide is an active gas - at high temperatures it dissociates with the release of oxygen. The released oxygen oxidizes the metal. In this regard, it is necessary to introduce deoxidizing agents (such as manganese and silicon) into the welding wire. Another consequence of the influence of oxygen, also associated with oxidation, is a sharp decrease in surface tension, which leads, among other things, to more intense metal spattering than when welding in argon or helium.

Manual arc welding

In English literature it is called en:shielded metal arc welding ( SMA welding, SMAW) or manual metal arc welding (MMA welding, MMAW).

Manual (TIG) and semi-automatic (MIG, MAG) pulsed welding of aluminum is a more complex process than electric arc welding of ferrous metals. The reason for this is the unique properties of aluminum alloys, for which they are valued.

Submerged arc welding

In English-language foreign literature it is referred to as SAW. In this type of welding, the end of the electrode (in the form of a metal wire or rod) is fed under a layer of flux. Arc combustion occurs in a gas bubble located between the metal and the flux layer, which improves the protection of the metal from the harmful effects of the atmosphere and increases the depth of metal penetration.

Gas flame welding

Flame soldering

Acetylene-oxygen flame (temperature about 3150 °C 2-3 mm from the core)

Welder, 1942

The source of heat is a gas torch formed during the combustion of a mixture of oxygen and combustible gas. Acetylene, MAF, propane, butane, blast gas, hydrogen, kerosene, gasoline, benzene and mixtures thereof can be used as flammable gas. The heat released during the combustion of a mixture of oxygen and combustible gas melts the surfaces being welded and the filler material to form a weld pool. The flame may be oxidative, "neutral" or restorative(carburizing), this is regulated by the ratio of oxygen and combustible gas.

• In recent years [ When?] a new type of fuel is used as a substitute for acetylene - liquefied gas MAF (methyl acetylene-allen fraction). MAF provides high welding speed and high quality of the weld, but requires the use of filler wire with a high content of manganese and silicon (SV08GS, SV08G2S). MAF is much safer than acetylene, 2-3 times cheaper and more convenient for transportation. Due to the high temperature of gas combustion in oxygen (2927 °C) and high heat release (20,800 kcal/m³), gas cutting using MAF is much more efficient than cutting using other gases, including acetylene.

• The use of cyanogen for gas welding is of great interest due to its very high combustion temperature (4500 °C). An obstacle to the expanded use of cyanogen for welding and cutting is its increased toxicity. On the other hand, the efficiency of cyanogen is very high and comparable to an electric arc, and therefore cyanogen represents significant prospects for further progress in the development of gas-flame processing. The flame of cyanogen with oxygen emanating from a welding torch has a sharp outline, is very inert to the metal being processed, is short and has a purplish-violet hue. The metal being processed (steel) literally “flows”, and when using cyanogen, very high speeds of welding and cutting metal are permissible.

• Significant progress in the development of gas-flame processing using liquid fuels can be achieved by the use of acetylenedinitrile and its mixtures with hydrocarbons due to the highest combustion temperature (5000 °C). Acetylenedinitrile is prone to explosive decomposition when heated strongly, but is much more stable in mixtures with hydrocarbons. Currently, the production of acetylenedinitrile is very limited and its cost is high, but with the development of production, acetylenedinitrile can very significantly develop the areas of application of gas flame processing in all its fields of application.

Electroslag welding

Flash butt welding of plastics

The heat source is a flat heating element coated with PTFE. Welding is divided into 5 stages: heating under pressure, heating the mass, removing the heating element, welding, hardening.

Welding with embedded heaters

Used for welding polyethylene pipes. The source of heat is the resistance elements sealed in the welded coupling. When welding with embedded electric heaters, polyethylene pipes are connected to each other using special plastic connecting parts that have a built-in electric spiral made of metal wire on the inner surface. A welded joint is obtained as a result of the melting of polyethylene on the connected surfaces of pipes and parts (couplings, bends, tees, saddle bends) due to the heat generated when electric current flows through the spiral wire, and the subsequent natural cooling of the joint.

Thermomechanical class

contact welding

When welding, two sequential processes occur: heating of the welded products to a plastic state and their joint plastic deformation. The main types of resistance welding are: resistance spot welding, butt welding, relief welding, seam welding.

Spot welding

When spot welding, parts are clamped in the electrodes of a welding machine or special welding pliers. After this, a large current begins to flow between the electrodes, which heats the metal of the parts at the point of their contact to melting temperatures. Then the current is turned off and “forging” is carried out by increasing the compression force of the electrodes. The metal crystallizes when the electrodes are compressed and a welded joint is formed.

Butt welding

The workpieces are welded along the entire plane of their contact. Depending on the grade of metal, the cross-sectional area of ​​the workpieces and the requirements for the quality of the connection, butt welding can be performed in one of the following ways.

Resistance butt welding

The workpieces, installed and secured in a butting machine, are pressed against one another with a force of a certain magnitude, after which an electric current is passed through them. When the metal in the welding zone is heated to a plastic state, precipitation occurs. The current is turned off until the end of the precipitation. This welding method requires mechanical processing and thorough cleaning of the surfaces of the ends of the workpieces.

Uneven heating and oxidation of the metal at the ends of the workpieces reduce the quality of resistance welding, which limits its scope of application. With an increase in the cross-section of the workpieces, the quality of welding decreases especially noticeably, mainly due to the formation of oxides in the joint.

Continuous flash butt welding

Contact welding by continuous flashing of a gas pipeline pipe with a diameter of 1420 mm in Pskov at the TESO plant

Consists of two stages: melting and precipitation. The workpieces are placed in the clamps of the machine, then the current is turned on and they are slowly brought together. In this case, the ends of the workpieces touch at one or several points. At the points of contact, jumpers are formed, which instantly evaporate and explode. Explosions are accompanied by a characteristic ejection of small drops of molten metal from the joint. The resulting metal vapors act as a protective atmosphere and reduce the oxidation of the molten metal. With further approach of the workpieces, the formation and explosion of bridges occurs in other areas of the ends. As a result, the workpieces are heated in depth, and a thin layer of molten metal appears at the ends, making it easier to remove oxides from the joint. During the melting process, the workpieces are shortened by a specified allowance. Melting must be stable (continuous flow of current without short-circuiting the workpieces), especially before upsetting.

During upsetting, the speed of convergence of the workpieces is sharply increased, thereby causing plastic deformation to a given allowance. The transition from melting to precipitation should be instantaneous, without the slightest interruption. Upsetting begins with the current turned on and is completed when it is turned off.

Continuous flash butt welding ensures uniform heating of workpieces across the cross-section; the ends of the workpieces do not require careful preparation before welding; it is possible to weld workpieces with a cross-section of complex shapes and large areas, as well as dissimilar metals, and allows for stable quality of joints. Its significant advantage is also the ability to automate the process relatively easily.

Flash butt welding is used to connect workpieces with a cross-section of up to 0.1 m². Typical products are elements of tubular structures, wheels, rails, reinforced concrete reinforcement, sheets, pipes.

Relief welding

On parts to be welded, reliefs are first created - local elevations on the surface measuring several millimeters in diameter. When welding, contact of parts occurs along reliefs, which are melted by the welding current passing through them. In this case, plastic deformation of the reliefs occurs, oxides and impurities are squeezed out. After the welding current stops flowing, the molten metal crystallizes and a compound is formed. The advantage of this type of welding is the ability to obtain several high-quality welded joints in one cycle.

Diffusion welding

Welding is carried out due to diffusion - the mutual penetration of atoms of the welded products at elevated temperatures. Welding is carried out in a vacuum installation, heating the joints to 800 °C. Instead of a vacuum, a protective gas environment can be used. The diffuse welding method can be used to create joints from dissimilar metals that differ in their physical and chemical properties, and to produce products from multilayer composite materials.

The method was developed in the 1950s by N. F. Kazakov.

Forge welding

The first type of welding in history. The joining of materials is carried out due to the formation of interatomic bonds during plastic deformation with a tool (forging hammer). Currently, it is practically not used in industry.

Welding with high frequency currents

The source of heat is a high-frequency current passing between the products being welded. With subsequent plastic deformation and cooling, a welded joint is formed.

Friction welding

There are several friction welding schemes; the coaxial one appeared first. The essence of the process is as follows: on special equipment (friction welding machine), one of the parts to be welded is installed in a rotating chuck, the second is mounted in a stationary support, which can move along the axis. The part installed in the chuck begins to rotate, and the part installed in the caliper approaches the first one and exerts quite a lot of pressure on it. As a result of friction of one end against another, wear of the surfaces occurs and the layers of metal of different parts approach each other at distances commensurate with the size of the atoms. Atomic bonds begin to operate (common atomic clouds are formed and destroyed), resulting in thermal energy that heats the ends of the workpieces in a local zone to the forging temperature. Upon reaching the required parameters, the cartridge stops abruptly, and the caliper continues to press for some time, resulting in a permanent connection. Welding occurs in the solid phase, similar to a forge.

The method is quite economical. Automated friction welding installations consume 9 times less electricity than resistance welding installations. The parts are connected in a matter of seconds, with virtually no gas emissions. With other advantages, high quality welding is obtained, since there is no porosity, inclusions, or cavities. With the constancy of the modes provided by the automation of the equipment, the constancy of the quality of the welded joint is ensured, which, in turn, allows us to eliminate expensive 100% control when ensuring quality. The disadvantages include:

• complexity of the required equipment;
• narrow range of application of the method (bodies of revolution are butt welded);
• impossibility of use in non-production conditions;
• diameters of welded parts from 4 to 250 mm.

The method allows you to weld dissimilar materials: copper and aluminum, copper and steel, aluminum and steel, including those that cannot be welded by other methods.

The idea of ​​welding parts by friction was expressed by turner-inventor A.I. Chudikov. In the 1950s, using a simple lathe, he was able to firmly connect two mild steel rods.

Today, there are several friction welding schemes: such as axial, stir (allowing the welding of stationary parts), inertial, etc.

Mechanical class

Explosion welding

Welding is carried out by bringing the atoms of the welded products closer to the distance of action of interatomic forces due to the energy released during the explosion. Bimetals are often obtained using this welding method.

Ultrasonic welding of metals

Welding is carried out by bringing the atoms of the metal products being welded closer to the distance of action of interatomic forces due to the energy of ultrasonic vibrations introduced into the materials. Ultrasonic welding is characterized by a number of positive qualities, which, despite the high cost of the equipment, determines its use in the production of microcircuits (welding of conductors with contact pads), precision products, welding of different types of metals and metals with non-metals.

Cold welding

Cold spot welding diagram

Cold welding is the joining of homogeneous or inhomogeneous metals at a temperature below the minimum recrystallization temperature; welding occurs due to plastic deformation of the metals being welded in the joint area under the influence of mechanical force. Cold welding can be butt, spot and seam.
The strength of the connection significantly depends on the compression force and the degree of deformation of the parts being welded.

Welding in art

Welding often appears as a subject of socialist realism.

Electric welder. Bust in the Museum of Socialist Art in Sofia	Welding in space on a postage stamp. 2006

see also

Notes

Literature

	Welding on Wikimedia Commons

Nowadays, when it is very often necessary to obtain permanent connections, welding is used. What is welding? It is quite difficult to answer this question unequivocally.

Welding is used to repair complex industrial equipment, heating mains, and is also often used for domestic needs.

Permanent connections of various designs, when general heating is applied, are called welding. The part undergoes plastic deformation due to the formation of interatomic bonds. You can cook:

• metal parts;
• ceramics;
• glass;
• plastic.

Today, several types of welding are known, when metal melts:

• arc;
• electroslag;
• electron beam;
• plasma;
• laser;
• gas.

Fusion welding, when the workpieces are heated and deformed, is divided into contact, high-frequency and gas-press welding. In addition, fusion welding has high-quality performance results.

For deformation without heating, the following is used:

• cold welding;
• explosion;
• diffusion connection using vacuum.

The power source affects the welding process. He can be:

• arc;
• gas;
• electron beam.

The use of protective materials requires the use of other welding methods:

• using flux;
• in the protective gas zone;
• in a vacuum.

Depending on the mechanization used, welding can be:

• manual;
• semi-automatic;
• automatic.

Let's look at the main types of fusion welding.

Manual technology

Currently, EMF has become the basis for performing. Welding theory primarily studies EMF. The heat source is an electric arc formed by two electrodes, one of which is the part being welded. An electric arc can be defined as the strongest discharge that occurs in a gas zone.

In order for the arc to ignite, several criteria must be present:

• short circuit when the electrode touches the workpiece;
• quick removal of the electrode;
• the appearance of stable combustion.

A short circuit is required to warm up the electrode. It must reach a temperature where electron emission occurs.

The resulting electrons receive strong acceleration, and ionization of the gas gap between the anode and cathode appears. As a result, the arc discharge obtains stable combustion.

An electric arc is a powerful source of heat, reaching temperatures of 6000°. At this time, the maximum welding current is 3 kA. The arc voltage during operation can reach 50 V.

The most commonly used emf is with coated electrodes. Manual welding, when such electrodes are used, is intended for:

• gas protection of liquid metal from ambient air;
• doping.

Return to contents

Welding using flux

It is widely used when a consumable electrode is used, and the operation takes place under a layer of special flux.

It is poured onto the part, the layer thickness reaches 50 mm. This prevents arcing in the air space. A gas bubble is formed, which is located under the liquid flux, where the arc burns, completely isolated from direct contact with oxygen.

When automatic welding is performed, there is no spattering of hot metal, and the shape of the seam is not disrupted, even when a high current is supplied. When parts are welded using flux, the current strength is adjusted, the maximum current is set to 1200 A. When parts are welded with an open arc, it is impossible to achieve this value.

Flux arc welding allows you to increase the welding current. Moreover, excellent seam quality is maintained and high productivity is observed. For such welding, it is necessary to have a clean electrode wire, which is supplied by the welding head. It rotates slowly, and at this time the wire moves along the seam.

Granular flux is fed into the welding head through a special tube directly into the weld area. It melts and seals the seam evenly. The result is a hard slag crust.

The main differences between automatic welding using flux and manual arc:

• excellent seam quality;
• increased productivity;
• size of the flux layer;
• current power;
• automatic exposure of the required arc length.

Return to contents

Welding using slag

This type of electroslag technique is considered a completely new technology for joining metals. It was invented and completely developed by scientists from the Paton Institute.

During operation, all workpieces are covered with slag, the heating temperature of which is higher than the melting point of the workpiece, as well as the electrode wire.

First, the process repeats operations similar to using flux. When liquid slag is formed, the arc is completely extinguished. The edges of the product begin to melt due to the heat that is released when current is passed through the melt. This type can be used to weld workpieces of large thickness, and one pass is sufficient.

This option is characterized by high productivity and excellent seam quality.

Return to contents

Induction welding

This type of welding is considered a new method that began to be used several years ago. Typically, longitudinal seams are welded using this method when pipes are manufactured with continuous feeding. This method is used for:

• surfacing of hard alloys;
• manufacturing cutting tools.

In this case, the metal begins to heat up due to the use of high frequency current and strong compression. Induction welding is performed without contact. Localization of high frequency currents occurs near the surface of heated parts.

The operation of these installations is carried out in the following order. The current from the high-frequency generator is transmitted to the inductor. Eddy currents begin to appear in the workpiece, and the pipe becomes very hot.

Such mills are designed for welding pipes with a maximum diameter of 60 mm. The processing speed is 50 m/min. A 260 kW tube generator provides power. The frequency used is 880 kHz.

It is possible to weld pipes of very large diameters, the wall thickness of which exceeds 7 mm. The maximum pipe diameter is 426 mm, welding speed is 30 m/min.

Homogeneous materials due to the formation of atomic bonds is called welding. In this case, at the point of contact, dense fusion of two materials into one occurs. Despite the fact that such a connection has been used for a long time, modern metal welding, the types and technology of its implementation are constantly being improved, which makes it possible to join various products with increased reliability and quality.

Features of surface welding

The entire process of welding metals occurs in two stages. First, the surfaces of the materials must be brought closer to each other at a distance of interatomic adhesion forces. At room temperature, standard metals are unable to bond even when compressed with significant force. The reason for this is their physical hardness, so contact when such materials come together occurs only at some points, regardless of the quality of surface treatment. It is surface contamination that significantly affects the possibility of adhesion of materials, because films, oxides, as well as layers of impurity atoms are always present in natural conditions.

Therefore, the creation of contact between the edges of parts can be achieved either due to plastic deformations that arise as a result of applied pressure, or in the event of melting of the material.

At the next stage of metal welding, electron diffusion occurs between the atoms of the surfaces being joined. Therefore, the interface between the edges disappears and either a metallic atomic bond or an ionic and covalent bond (in the case of semiconductors or dielectrics) is obtained.

Classification of welding types

Welding technology is constantly improving and becoming more diverse. Today there are about 20 types of metal welding, which are classified into three groups:

Fusion welding

This type of welding work is widely used both in industrial conditions and in everyday life. The joining of metals by melting includes:

1. Arc welding. It is produced by creating a high-temperature electric arc between the metal and the electrode.
2. In a plasma connection, the heat source is ionized gas that passes at high speed through an electric arc.
3. Slag welding is carried out by heating molten flux (slag) with an electric current.
4. Laser bonding occurs by treating the metal surface with a laser beam.
5. In electron beam welding, heating of the joint is carried out due to the kinetic energy of moving electrons in a vacuum under the influence of an electric field.
6. Gas welding of metals is based on heating the connection point with a stream of fire, which is formed by the combustion of oxygen and gas.

Electric arc welding joint

Arc welding involves the use of a current source with a high nominal value, while the machine has a low voltage. The transformer is connected simultaneously to the metal workpiece and the welding electrode.

As a result of welding metal with an electrode, an electric arc is formed, due to which the edges of the joined workpieces melt. In the area of ​​the arc, a temperature of about five thousand degrees is created. This heating is quite sufficient to melt any metals.

During the melting of the metal of the parts being connected and the electrode, a weld pool is formed, in which all adhesion processes take place. The slag rises to the surface of the molten composition and forms a special protective film. In the process of metal arc welding, two types of electrodes are used:

• non-melting;
• melting.

When using a non-consumable electrode, it is necessary to insert a special wire into the area of ​​the electric arc. Consumable electrodes form the weld independently. Special additives are added to the composition of such electrodes, which do not allow the arc to go out and increase its stability. These can be elements with a high degree of ionization (potassium, sodium).

Arc connection methods

Electric arc welding is carried out in three ways:

Gas welding technology

This type of welding work allows you to connect various metal structures not only in industrial enterprises, but also in domestic conditions. The technology of metal welding is not very complicated; during combustion, the gas mixture melts the edges of the surface, which are filled with filler wire. When cooled, the seam crystallizes and creates a strong and reliable connection of materials.

Gas welding has many positive aspects:

1. Ability to connect different parts offline. Moreover, this work does not require a powerful source of energy.
2. Simple and reliable gas welding equipment is easy to transport.
3. The ability to carry out an adjustable welding process, as it is easy to manually change the angle of the fire and the speed of heating the surface.

But there are also disadvantages to using such equipment:

Slag welding

This type of connection is considered a fundamentally new way of producing a weld. The surfaces of the parts to be welded are covered with slag, which is heated to a temperature exceeding the melting of the wire and base metal.

At the initial stage, welding is similar to submerged arc joining. Then, after the formation of a weld pool from liquid slag, the arc stops burning. Further melting of the edges of the part is carried out due to the heat that is released when current flows. A feature of this type of metal welding is the high productivity of the process and quality

Pressure welding joint

The joining of metal surfaces by means of mechanical deformation is most often carried out in industrial production conditions, since this technology requires expensive equipment.

Pressure welding includes:

1. Ultrasonic joining of metal parts. It is carried out thanks to ultrasonic frequency fluctuations.
2. Cold welding. It is carried out on the basis of the interatomic connection of two parts by creating high pressure.
3. Forge-forge method. Known since ancient times. The material is heated in a forge and then welded by mechanical or manual forging.
4. Gas welding with pressing. It is very similar to the blacksmith method, only gas equipment is used for heating.
5. Contact electrical connection. It is considered one of the most popular species. In this type of welding, the metal is heated by passing an electric current through it.
6. When the pressure on the metal is low, it requires a high heating temperature at the joint.

Spot resistance welding

During this type of welding, the surfaces to be joined are located between two electrodes. Under the action of the press, the electrodes compress the parts, after which voltage is applied. Heating of the welding site occurs due to the passage of current. The diameter of the welding site completely depends on the size of the electrode contact pad.

Depending on how the electrodes are positioned in relation to the parts being joined, contact welding can be one-sided or two-sided.

There are many types of resistance welding that work on a similar principle. These include: butt welding, seam welding, capacitor welding.

Safety precautions

Working with welding equipment involves many factors hazardous to the health of the operator. High temperatures, explosive atmospheres and harmful chemical fumes require a person to strictly adhere to safety measures:

There are a large number of types of metal welding; the welder himself decides which one to choose, based on the availability of equipment and the ability to achieve the required work result. The welder must know the structure and principles of operation of certain equipment.