Metal welding: types and technology

The technological process of creating an integral connection of homogeneous materials due to the formation of atomic bonds is called welding. In this case, at the point of contact there is a dense fusion of two materials into one. 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 allows the joining of various products with increased reliability and quality.

Features of surface welding

The whole process of welding metals proceeds in two stages. First, the surfaces of the materials must be brought closer to each other by the distance of interatomic adhesion forces. At room temperature, standard metals are not able to combine even when compressed with considerable force. The reason for this is their physical hardness, so contact with the approach of such materials occurs only at some points, regardless of the quality of the surface treatment. It is surface contamination that significantly affects the adhesion of materials, because films, oxides, and also layers of impurity atoms are always present in natural conditions.

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

At the next stage of metal welding, electron diffusion between the atoms of the surfaces to be joined is carried out. 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

The technology of welding is constantly being improved and becomes more diverse. Today, there are about 20 types of metal welding, which are classified into three groups:

1. Pressure welding is carried out by the application of mechanical energy, when the bonds between the crystals are obtained by plastic deformation of the material. As a result, the metal begins to flow, moving along the joining line of the parts, taking with it a layer of contaminated impurities. The process of deforming and joining surfaces without preheating is called cold welding for metal. In this case, interatomic bonds are formed, which leads to a dense joining of parts.
2. Fusion welding is carried out by joining products without applying pressure. Sources of heat in such metal welding are gas flame, electric arc, beam type energy. When welding, the surfaces heat up and melt, forming interatomic bonds between two metals and the electrode, uniting into a common weld pool. After cooling and solidification of the composition, a continuous cast seam is formed.
   
3. Thermomechanical welding of metal is carried out using heat and pressure. The junction of the material is first heated, and then pressed. Heating a part gives it the necessary plasticity, and mechanical impact combines parts of the product in a monolithic connection.

Fusion welding

This type of welding is widely used both in industrial conditions and in everyday life. Melting metal compounds include:

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 an ionized gas that passes through the electric arc at high speed.
3. Slag welding is carried out by heating the molten flux (slag) with electric current.
4. Laser connection occurs due to the processing of a metal surface by a laser beam.
5. In electron beam welding, the junction is heated 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 during the combustion of oxygen and gas.

Arc welding connection

Arc welding involves the use of a current source with a large nominal value, while the apparatus has a small voltage. The transformer is connected simultaneously to a metal billet and a welding electrode.

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

During the melting of the metal of the connected parts and the electrode, a weld pool is formed, in which all the adhesion processes occur. 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-consumable;
• melting.

When using a non-consumable electrode, it is necessary to introduce a special wire into the zone of operation of the electric arc. Melting 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 can be elements with a high degree of ionization (potassium, sodium).

Arc Connection Methods

Arc welding is carried out in three ways:

1. Manual method. In this case, all the connection steps are performed manually, using simple electric arc welding.
2. Semi-automatic welding is more productive. With this method, the weld is done manually, and the filler wire is fed in automatically.
3. Automatic welding is carried out under the supervision of the operator, and all work is done by a welding machine.
   

Gas welding technology

This type of welding allows you to connect various metal structures, not only in industrial enterprises, but also in domestic conditions. The technology of welding metal is not very complicated, the gas mixture during combustion melts the edges of the surface, 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:

1. The ability to connect various 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, since it is easy to manually change the angle of inclination of the fire and the heating rate of the surface.

But there are also disadvantages of using such equipment:

1. The heating place has a large area, which negatively affects the neighboring elements of the part.
2. The inability to automate the welding process.
3. The need to strictly observe safety measures. Work with the gas mixture has a high degree of explosion hazard.
4. The thickness of the metal for a good connection should be no more than 5 mm.
   

Slag welding

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 a submerged arc connection. Then, after the formation of a weld pool of liquid slag, the arc ceases to burn. 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

The connection of metal surfaces through mechanical deformation is most often carried out in industrial production, as this technology requires expensive equipment.

Pressure welding includes:

1. Ultrasonic docking of metal parts. It is performed due to fluctuations in ultrasonic frequency.
2. Cold welding. It is carried out on the basis of the interatomic connection of two parts by creating a lot of pressure.
3. Forge furnace method. Known since ancient times. The material is heated in the furnace and then welded by mechanical or manual forging.
4. Press gas welding. It is very similar to the blacksmithing method, only gas equipment is used for heating.
5. Contact electrical connection. It is considered one of the most popular species. In such welding, the metal is heated by passing electric current through it.
6. In diffusion welding , the pressure force on the metal is not high, but a high temperature of heating the joint is necessary.

Spot welding

The surfaces to be joined in this welding are between two electrodes. Under the action of the press, the electrodes compress the parts, after which voltage is applied. The welding spot is heated by the passage of current. The diameter of the welding site is completely dependent on the size of the electrode pad.

From how the electrodes are located in relation to the parts to be joined, contact welding can be one-sided or two-sided.

There are many types of resistance welding, working on a similar principle. These include: butt welding, seam welding, condenser.

Safety precautions

Work with welding equipment is associated with many hazards to the health of the operator. High temperature, explosive atmospheres and harmful chemical fumes require strict adherence to safety measures from a person:

1. All electrical units and devices must be reliably grounded and insulated.
2. It is necessary to work in dry overalls and mittens. To protect the skin of the face and eyes, it is necessary to use a mask with dark glass.
   
3. Be sure to be at the welder's workplace first aid kit and fire extinguisher.
4. The room where welding is carried out must have good ventilation.
5. Work is forbidden to be carried out in close proximity to flammable objects.
6. It is forbidden to leave gas cylinders unattended.

There are a large number of types of metal welding, which one is decided by the welder himself, based on the availability of equipment and the ability to achieve the desired result. The welder must know the device and the principles of operation on certain equipment.