Welding is the production of permanent joints by heating and melting the edges of the parts to be joined. If earlier only metals were subjected to it, then today other materials, for example, plastic, are combined 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, it is with its help that welding is carried out. There are a variety of welding methods, we will try to consider all of them.
A bit of history. Classification
Forging metal is the first welding process. The need for repair of metal products, as well as the creation of more advanced parts, became a prerequisite for the development of welding processes. So, in 1800-1802 an electric arc was discovered. Various experiments were made with her. In the end, people learned to make welds using an electric arc. Qualified welders are being actively trained in Russia, new technologies are being constantly developed, fundamentally different approaches, etc. A striking example of an excellent theoretical and practical base is the Bauman Institute of Education.
Currently, there are about 150 methods for welding. Welding methods are divided by physical, technical, as well as technological characteristics. So, according to physical indicators, three large groups can be distinguished:
- Thermal is a type of welding carried out using thermal energy. These include gas, arc, laser, and other welding.
- Thermomechanical - a type of welding, involving the use of not only thermal energy, but also pressure. This can be a contact, diffusion, forging compound, etc.
- The mechanical type of welding . In such cases, mechanical energy is used. The most widespread cold welding, explosion, friction, etc.
Each individual species is distinguished by energy costs, environmental friendliness, as well as equipment that is used during operation.
Flame welding
In this case, the main source of heat is the flame, which is released as a result of the combustion of fuel in a mixture with oxygen. To date, more than a dozen gases that can be used are known. The most popular are acetylene, MAF, propane and butane. The heat generated melts the surfaces along with the filler material.
The operator controls 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, MAF 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. Today it is the most relevant mixture for gas welding, which is due to the safety and high temperature of combustion in oxygen (2430 degrees Celsius).
Much depends on the composition of the metal to be welded. So, depending on this parameter, the number of filler bars is selected, and when the thickness of the metal is taken into account, their diameter is selected. With careful preliminary preparation, perfect 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 of 0.5-5 mm, non-ferrous metals, as well as tool steel and cast iron.
Let's take a closer look at some methods of gas welding. There are a lot of them.
Left, right and through welding
With a sheet thickness of not more than 5 mm, the left type 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 up the treated area and 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 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 sees the place to be treated well, and he can ensure uniformity.
The fundamental difference between right-hand welding is that it is more economical. This is due to the fact that the flame of the burner is directed not from the seam, but towards it. This approach allows you to weld metals of maximum thickness, while the angle of opening of the edges is small. The burner moves from left to right, followed by a filler rod.
Of course, if we consider methods of gas welding, then it is definitely worth mentioning welding through a 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 brewed. When the sheet thickness is too large, work is done on both sides and performed by two operators.
Bathroom method of welding fittings
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 bars. The essence of the method is that a steel mold is welded at the junction. 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 bath. Accordingly, when cooling, a full-fledged compound is formed.
But before starting the bath welding, it is necessary to prepare the rods. This is done as follows: the surfaces, as well as the ends, are cleaned, while any type of contamination is removed, for example, rust, scale and dirt. For this, a metal brush is suitable. By the way, it is important to strip the reinforcement to a length of 30 mm in the place of welding. The rods are mounted coaxially. In this case, the gap should not exceed one and a half diameter of the electrode (at the end face).
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, work can be performed by several electrodes at once. 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 energy consumption. To date, the bathroom method of welding fittings 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. This is due to the fact that during the connection does not occur additional heating of the treated surface. This method is based on the plastic deformation of metals during compression or sliding. Work is carried out at normal or negative temperatures without diffusion. This method is considered one of the oldest.
To obtain a high-quality weld, special devices are used that cause deformation of the machined surfaces, which must be previously 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: spot, suture and butt.
Cold welding can connect materials such as copper, lead, aluminum, cadmium, iron, etc. The most preferred plastic welding is when you need 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 durable, but also uniform, and also resistant to corrosion. However, there are some disadvantages. They consist in the fact that it is possible to work only with metals of high ductility. If some methods of welding pipes can be applied, then others do not, and you have to use melting. This applies to plumbing and gas pipelines.
Classification of welding methods. Continuation
The process itself proceeds as follows. Parts to be connected 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 influences) is added to the common weld pool. When the heat source is removed from the welding site, the seam 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, a device with a temperature of 3 thousand degrees Celsius is needed. If you deliberately lower this indicator, the 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.
- Plasma welding The heat source is a compressed electric arc. A gas is blown through it at high speed (supersonic), which acquires the properties of a plasma.
- Electroslag - metal is heated by molten flux through which 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 a gas-oxygen mixture.
Arc welding and its types
Today, the most important for many industries is electric arc welding. If you count the number of existing installations, employment among specialists, as well as the number of products, then this method of obtaining high-quality seams is leading around 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 electrode is fed and moved along the seam without human intervention (as opposed 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, which is needed to prevent nitriding and oxidation of the weld during work.
There is also manual welding, which consists in the fact that the melting edges touch and excite an 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 worth paying your attention to the fact that methods of welding with an electrode using 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 on manual arc welding
We have already considered in general terms the principle of obtaining a welded joint in manual mode. 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, in the process various electrodes can be used: melting and non-melting. If the second type is selected, then the seam connection is as follows: the edges are applied to each other, and a graphite or carbon electrode is brought to the surface to be machined and an arc is created. As a result, a bath 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 way is to use a melting electrode with a special coating. This method can be called classic, if we talk about manual welding, since it is the most common and has been used for a long time. The only difference from the above method is that the electrode melts with the surface. The result is a common bath, which hardens after arc removal and forms a high-quality weld. The choice of welding method depends on the specific situation, the material, its composition and much more.
A few important points
We examined the main welding methods. They are conditionally divided into three large groups: cold, hot and gas. However, it is worth noting that sometimes special methods are used to obtain a seam. This is necessary when it comes to reactive metals and their alloys. By the way, such materials are increasingly used in construction for the construction of critical nodes. In such cases, work is carried out at a low oxygen and nitrogen content in the air, and the source should be at a high temperature. A striking 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 about 30-100 kV.
Much more complicated and interesting from the point of view of obtaining high-quality joints is plasma welding. We have already sorted out its essence a little. There are key features in the process, such as plasma electrical conductivity. The gas forming the plasma, in addition to its main task, also protects the joint from oxidative processes and nitriding. It is safe to say that this is a noteworthy 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 complicated.
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. For this, there are various methods of welding with an electrode, for example, melting or not. In addition, the technology may vary depending on the master’s technique. It is convenient for someone to do the work with left welding, for someone - with the right.
Even elementary methods of welding reinforcement should be performed according to the instructions. You must admit that it will not be very pleasant if the partition fails just because the welder faked and decided to save a little.
Today, complex and expensive types of compounds are becoming increasingly common. This is due to some factors. Firstly, technological progress leads to the fact that it is far from always possible to use blacksmith welding due to the fragility of the structure. Secondly, they try to get a high quality seam that would not collapse under prolonged dynamic and vibration loads. This is not difficult to achieve, especially when you consider that shock and vibration are the main enemies of a welded joint. But modern welding (welding methods) is constantly being improved, more and more new approaches are being developed to strengthen and obtain strong and high-quality joints.