Welding: Welding methods and technology. Classification of welding methods

Welding is the production of permanent joints by heating and melting the edges of the joined parts. If earlier only metals were subjected to it, then today other materials, for example, plastics, are connected by this method.

It can be said that a welded joint is one that was obtained by melting or welding with pressure. Of course, there are a huge number of methods for obtaining the required result. For example, there is such an element as an electric arc, it is with its help that welding is carried out. Ways of welding are very different, we will try to consider them all.

A bit of history. Classification

Metal forging is the first welding process. The need to repair metal products, as well as the creation of more sophisticated parts, was a prerequisite for the development of welding processes. Thus, in 1800-1802 an electric arc was opened. Various experiments were carried out with her. In the end, people learned how to make welded joints by means of an electric arc. On the territory of Russia, the training of qualified welders is actively conducted, new technologies are constantly being developed, fundamentally different approaches, etc. A vivid example of an excellent theoretical and practical base is the Bauman Institution of Education.

At present, there are about 150 methods for welding. Welding methods are divided into physical, technical, and technological features. Thus, according to physical indicators, there are three large groups:

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

Each individual species is characterized by energy costs, environmental friendliness, and equipment that is used during operation.

Flame welding

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

The operator regulates the nature of the flame. It can be oxidative, neutral or reducing, depending on the amount of oxygen and gas in the mixture. In recent years, the LFA has been actively used, which provides not only high welding speed, but also excellent weld quality. But at the same time, it is necessary to use a more expensive wire with a high content of manganese and silicon. For today it is the most actual mixture for gas welding, which is caused by safety and high temperature of combustion in oxygen (2430 degrees Celsius).

Much depends on the composition of the metal, which is planned to be welded. Thus, depending on this parameter, the number of filler rods is selected, and when the thickness of the metal is taken into account, their diameter is chosen. With careful preliminary preparation, an ideal welding is obtained.

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

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

Left, right and through welding

When the sheet thickness is not more than 5 mm, the left-most kind of gas welding is most often used. Accordingly, the burner moves from right to left, and the filler rod is in front. The flame is directed from the seam and warms the workpiece and the filler wire well. The technique varies depending on the thickness of the metal. If the sheet is less than 8 mm, the burner moves only along the seam. If more than 8 mm, then it is necessary to perform in parallel the oscillatory movements in the transverse direction to improve the quality of the seam. The advantage of the left-hand method is that the operator can clearly see the work area and it can provide uniformity.

The fundamental difference between right welding is that it is more economical. The reason is that the flame of the burner is not directed from the seam, but to it. This approach allows to weld metals of maximum thickness, with the angle of opening of the edges small. The burner moves from left to right, followed by a filler rod.

Of course, if we consider the methods of gas welding, then it is worth mentioning welding through the roller. 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 moving the burner, the upper part of the hole melts, and when the additive is introduced, the lower part is welded. When the thickness of the sheet is too large, the work is done on both sides and is performed by two operators.

Bathroom fittings welding method

Many of us are familiar with the armature, which is actively used in monolithic frame construction. It is used in blocks of overlapping, 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 lies in the fact that a steel mold is welded at the junction. Then it creates a bath of molten metal at the expense of the heat of the arc. It turns out that the ends of the welded armature are melted and form a common bath. Accordingly, when cooling, a full connection is formed.

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

The process proceeds under high currents. For example, with an electrode of 6 mm, 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, the work can be performed simultaneously with several electrodes. It is worth paying attention to the fact that this method allows you to reduce the complexity of the process, the cost of the product, as well as electricity consumption. To date, the bathing method of welding armature is the most popular and reliable. This is due to low power consumption and high quality connections.

Pressure welding (plastic)

This type of welding is also called cold welding. Due to the fact that during the execution of the connection, there is no additional heating of the treated surface. This method is based on 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 be previously cleaned. As a result, a monolithic and rather strong connection is formed. There are different types and methods of welding (plastic). At present there are three of them: spot, suture and butt.

Cold welding can be combined with materials such as copper, lead, aluminum, cadmium, iron, etc. The most preferred plastic welding is when it is necessary to work with heterogeneous materials that are quite sensitive to heat.

Of course, it should be noted that the main and main advantage of welding with pressure lies in the fact that it is not necessary to connect a powerful source of electric power to preheat the surface. In addition, the seam thus obtained is not only strong, but also uniform, and also resistant to corrosion. Nevertheless, there are some drawbacks. They are concluded that it is possible to work only with metals of high plasticity. If some methods of welding pipes can be applied, others - no, and you have to use melting. This applies to water pipes and gas mains.

Classification of welding methods. Continuation

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

The molten metal (without any additional mechanical effects) is added to the overall weld pool. When the heat source is removed from the welding location, the seam is cooled, 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 3,000 degrees Celsius. If this indicator is deliberately reduced, the welding productivity will drop sharply, and the process will become inefficient.

The classification of welding methods for melting, depending on the heat source, is as follows:

• Arc welding. An electric arc is used as a source of heat, which burns between the electrode and the surface to be welded.
• Plasma welding. The source of heat is a compressed electric arc. Through it at high speed (supersonic), a gas is blown, which acquires the properties of plasma.
• Electroslag - metal is heated from a 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 is performed 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, the most important for many industries is electric arc welding. If we calculate the number of existing installations, employment among professionals, and the number of products, this way of obtaining high-quality seams leads the world. Let's look at the basic methods of arc welding. To date, there are several.

The most common is automatic welding. Its essence lies in the fact that some of the operator's movements are automated. For example, the supply of the electrode and its movement along the seam are carried out without human intervention (unlike the semi-automatic mode). This approach is good because the quality of the seam and the productivity are somewhat increased, and the trauma danger is reduced. Often a protective gas is used, which is needed to prevent nitriding and oxidation of the welded joint during the work.

There is also manual welding, which consists in the fact that the melting edges come into contact and excite the electric arc (with a non-consumable electrode). After the filler material is heated and melted, a bath is obtained, which subsequently creates a seam. It is worthwhile to draw your attention to the fact that the methods of welding an electrode with an electric arc are classified according to several technical features. For example, by the type of gases used (active and inert), by the degree of mechanization (manual, automatic, etc.) and by other signs.

More about manual arc welding

We have already examined in general terms the principle of obtaining a welded connection in manual mode. Let's look at this issue in more detail. To date, there are methods of manual arc welding, each of which is unique in its own way. For example, various electrodes can be used in the process: melting and non-melting. If a second view is selected, the joint is made as follows: the edges are applied to each other, and the graphite or carbon electrode is brought to the surface to be treated and an arc is created. As a result, a bath is formed, which after a while hardens and forms a weld seam. This method is the most relevant for working with non-ferrous metals and their alloys, and is also used for surfacing.

Another way is to use a melting electrode with a special coating. This method can be called classical, if we are talking about manual welding, since it is the most common and used for a long time. The only difference from the above described method is that the electrode melts together with the surface. As a result, a common bath is obtained, which solidifies after removing the arc and forms a high-quality welded seam. The choice of the welding method depends on the specific situation, the material, its composition and much more.

A few important points

We examined the basic methods of welding. 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 it comes to chemically active metals and their alloys. By the way, such materials are increasingly used in construction for the construction of critical sites. In such cases, work is performed with a low content of oxygen and nitrogen in the air, and the source must be at a high temperature. A vivid example is plasma, as well as beam welding. In the second case, the beam source is similar to a kinescope and has a voltage of the order of 30-100 kV.

Where it is more difficult and more interesting from the point of view of obtaining a qualitative compound plasma welding. With its essence we have already sorted out a little. In the process there are such key features as the conductivity of an electric current by plasma. The gas forming the plasma, in addition to its main task, also protects the seam from oxidation processes and nitriding. We can say with confidence that this is a worthy method, but there are some limitations. For example, the power supply 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. Welding methods are different. In most cases, the operator is faced with the task of obtaining not only a high-quality, but also a strong weld that will withstand mechanical stress for a long time. To do this, there are different ways of welding the electrode, for example, melting or not. In addition, the technology may differ depending on the technique of the master. It is convenient for someone to do the job with the left welding, someone - the right one.

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

Today, increasingly complex and expensive forms of obtaining compounds. This is due to some factors. First, technological progress leads to the fact that it is far from always possible to use forging welding because of the fragility of the structure. Secondly, they try to obtain a high quality of the seam, which would not break down under long dynamic and vibrational loads. This is not difficult to achieve, especially if one considers that shock and vibration are the most important enemies of a welded joint. But modern welding (welding methods) is constantly being improved, new approaches to strengthening and obtaining strong and high-quality joints are being developed.