The technological process of creating an inseparable connection of homogeneous materials due to the formation of atomic bonds is called welding. In this case, at the point of contact, a 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 whole process of metal welding proceeds in two stages. First, the surfaces of the materials must be brought closer to each other by the distance of the forces of interatomic cohesion. At room temperature, standard metals are not able to join even when compressed with significant force. The reason for this is their physical hardness, so contact when approaching such materials 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, and layers of impurity atoms are always present in natural conditions.
Therefore, creating contact between the edges of the partscan be achieved either due to plastic deformations that occur as a result of applied pressure, or in the case of melting of the material.
At the next stage of metal welding, electron diffusion is carried out between the atoms of the joined surfaces. Therefore, the interface between the edges disappears and either a metallic atomic bond, or ionic and covalent bonds (in the case of semiconductors or dielectrics) is obtained.
Classification of types of welding
Welding technology is constantly improving and becoming more diverse. To date, there are about 20 types of metal welding, which are classified into three groups:
- Pressure welding is carried out by the application of mechanical energy, when the bonds between the crystals are obtained by the method of plastic deformation of the material. As a result, the metal begins to flow, moving along the line of joining parts, taking with it a layer of contaminated impurities. The process of deformation and connection of surfaces without preheating is called cold welding for metal. In this case, interatomic bonds are formed, which leads to a tight docking of parts.
- Fusion welding is carried out by connecting products without applying pressure. Heat sources in such metal welding are gas flame, electric arc, beam-type energy. During welding, the surfaces heat up and melt, forming interatomic bonds between the two metals and the electrode, uniting into a common weld pool. After cooling and solidification of the composition, a continuous castseam.
- Thermomechanical welding of metal is carried out using heat and pressure. The place of joining of the material is first heated and then pressed. Heating the part gives it the necessary plasticity, and mechanical action combines the parts of the product into a monolithic connection.
Fusion welding
This type of welding is widely used both in industrial conditions and in everyday life. Fusion joining of metals includes:
- Arc welding. It is produced by creating a high-temperature electric arc between the metal and the electrode.
- In plasma bonding, the heat source is ionized gas that passes at high speed through an electric arc.
- Slag welding is carried out by heating the molten flux (slag) with electric current.
- Laser bonding occurs by processing the metal surface with a laser beam.
- In electron beam welding, the joint is heated by the kinetic energy of moving electrons in a vacuum under the influence of an electric field.
- Gas welding of metals is based on heating the connection point with a stream of fire, which is formed during the combustion of oxygen and gas.
Arc welding joint
Arc welding involves the use of a current source with a large nominal value, while the machine has a small voltage. The transformer is connected simultaneously to the metalworkpiece and welding electrode.
As a result of metal welding with an electrode, an electric arc is formed, due to which the edges of the workpieces to be joined are melted. In the zone of action of the arc, a temperature of about five thousand degrees is created. Such heating is enough to melt any metal.
During the melting of the metal of the parts to be joined 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 introduce a special wire into the area of the electric arc. The consumable electrodes weld form 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 may be elements with a high degree of ionization (potassium, sodium).
Arc connection methods
Arc welding is carried out in three ways:
- Manual method. In this case, all joining steps are performed manually, using simple electric arc welding.
- More productive is semi-automatic metal welding. With this method, the weld is made manually, and the filler wire is fed automatically.
- Automatic welding is supervisedoperator, and all the work is done by the welding machine.
Gas welding technology
This type of welding allows you to connect various metal structures not only at industrial enterprises, but also at home. The metal welding technology is not very complicated, the gas mixture during combustion melts the surface edges, which are filled with filler wire. When cooling, the seam crystallizes and creates a strong and reliable connection of materials.
Gas welding has many positive aspects:
- The ability to connect various parts offline. Moreover, this work does not require a powerful source of energy.
- Simple and reliable gas welding equipment is easy to transport.
- The ability to carry out an adjustable welding process, as it is easy to manually change the angle of the fire and the surface heating speed.
But there are also disadvantages of using such equipment:
- The heated area has a large area, which negatively affects the neighboring elements of the part.
- Inability to automate the welding process.
- The need to strictly observe security measures. Working with a gas mixture has a high degree of explosion hazard.
- The thickness of the metal for a quality connection should be no more than 5 mm.
Slagwelding
This type of connection is considered a fundamentally new way to obtain 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 the base metal.
At the initial stage, welding is similar to submerged arc welding. Then, after the formation of a weld pool of liquid slag, the arc stops burning. Further melting of the edges of the part is carried out due to the heat that is released during the flow of current. A feature of this type of metal welding is the high productivity of the process and the quality of the weld.
Pressure welding joint
The joining of metal surfaces by mechanical deformation is most often carried out in industrial production, as this technology requires expensive equipment.
For pressure welding include:
- Ultrasonic docking of metal parts. Performed by vibrations of ultrasonic frequency.
- Cold welding. It is carried out on the basis of the interatomic connection of two parts by creating a large pressure.
- Forge-forge method. Known since ancient times. The material is heated in a furnace and then welded by mechanical or manual forging.
- Gas pressure welding. Very similar to the blacksmith method, only gas equipment is used for heating.
- Contact electrical connection. It is considered one of the most popular types. With such welding, the heating of the metal is carried out by passing an electric current through it.
- In diffusion welding, the pressure force on the metal is low, but a high heating temperature of the joint is required.
Spot welding
The surfaces to be joined in such welding are between two electrodes. Under the action of the press, the electrodes compress the parts, after which voltage is applied. The welding site is heated by the passage of current. The diameter of the welding spot depends entirely on the size of the contact pad of the electrode.
Depending on how the electrodes are located in relation to the parts to be joined, resistance 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
Working with welding equipment is associated with many factors hazardous to the he alth of the operator. High temperatures, explosive environments and harmful chemical fumes require a person to strictly observe safety measures:
- All electrical equipment and devices must be properly grounded and insulated.
- It is necessary to work in dry overalls and gloves. To protect the skin of the face and eyes, be sure to use a mask with dark glass.
- A first-aid kit and a fire extinguisher must be at the welder's workplace.
- The room where welding work is carried out must be well ventilated.
- Work must not be carried out in close proximity to flammable objects.
- Do not leave gas bottles unattended.
There are a large number of types of metal welding, which one the welder decides to choose, based on the availability of equipment and the ability to achieve the desired result of work. The welder must know the device and the principles of work on certain equipment.
