What is welding and what types are there

 

What is welding and what types are there

In industry, construction and repair, various methods of joining structural parts are used. The most widespread are various types of portable welding machine, which bind not only the same type and dissimilar metals, but also glass, plastic, ceramics. The popularity of the technology is due to the high strength and reliability of the connections.

Types of welding and their brief description

1 Determination of the welding process

2 Classification of welding types

3 Thermal welding class

3.1 Arc

3.2 Gas

3.3 Radiation

3.4 Thermite

3.5 Electroslag

4 Thermomechanical welding class

4.1 Blacksmith Shop

4.2 Contact information

4.3 Diffusion

5 Mechanical welding class

5.1 By Friction

5.2 Cold

5.3 By Explosion

5.4 Ultrasonic

 

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Determination of the welding process

Regardless of the type, welding is called the technology of creating permanent joints by heating, deforming or combining both methods. The essence of welding is that under the influence of an external energy source (heat, pressure), strong bonds are formed between the materials to be joined at the interatomic level. After crystallization, a welding seam is formed at the joint during the cooling process. Depending on the type of material and working conditions, this is local or general heating and deformation of the joined surfaces.

 Classification of welding types

 Depending on the criteria, the classification of welding methods is performed according to the type of protection of the molten metal from air oxygen, the method of process control, the material, etc. The technological features of welding operations are also taken into account. According to the method of impact on the parts, three main types of welding are distinguished:

 Mechanical work is carried out by external pressure, under the influence of which the surfaces are deformed, which leads to a tight connection.

Thermal processing is performed using additional materials that are melted by heat from an energy source. Liquid metal fills the gap between the workpieces, after cooling, a strong connection is formed.

In thermomechanical (combined) types of welding, the parts are exposed to the combined effects of heat and pressure. To increase the plasticity of the parts, they are preheated, then compressed.

Thermal welding class

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These welding methods are performed with the formation of a welding bath of molten metal parts and an electrode or filler material.

 Arc

The heat for local melting of the metal of the workpieces is released when gorenje electric arc between the electrode and the work pieces. For ignition, the electrode briefly touches the surface, then is withdrawn to a distance of 2-5 mm. The shorter the arc, the higher its temperature.

 Arc welding scheme

The following welding methods are used to connect the parts:

 manual, when all manipulations with the electrode are performed by a welder;

semi-automatic with the supply of an electrode wire by a mechanism installed in the device;

automatic, when the process is performed according to a given algorithm without human intervention.

The arc view is performed by melting and non-melting carbon or tungsten electrodes with the introduction of a filler wire into the working area. To protect the molten metal from contact with air, mechanized methods are carried out under a flux or in an inert gas environment.

 Gas station

In contrast to the arc type, gas welding heats and cools the material more slowly. Therefore, this method is easier to weld thin-walled steel, non-ferrous metals, to conduct surfacing. Independence from electricity allows you to work in the field.

 Gas welding scheme

The joint is heated by the torch of the burner, which is formed when acetylene, propane, hydrogen, gasoline or kerosene vapors are burned in pure oxygen. The seam is formed by melting the filler material. For welding work, acetylene is more often used, the flame temperature of which reaches 3100⁰C. Similar in principle of operation, plasma welding is performed by a jet of ionized gas with a temperature greater than 10000⁰c.

 Radiation therapy

The technology is based on the melting of the material of the parts by a laser light beam or a stream of electrons created by an electron gun. Both methods are used mainly in the radio-electronic industry for connecting and attaching microelements. To prevent the beam from scattering, electron beam welding is carried out in a vacuum chamber.

 See also: The zone of thermal influence

Electron beam welding scheme

Laser welding allows you to apply seams with high accuracy. At the same time, the adjacent surfaces are practically not heated, which eliminates the deformation of even very thin material. To work in hard-to-reach places, change the direction of the beam with prisms. The process is recommended to be carried out in an inert gas environment.

 Thermite

For welding of this type, a powdered mixture (thermite) consisting of aluminum, magnesium, iron oxides is used. During combustion, heat is generated, which melts the edges of the work pieces. The molten thermite is mixed with the metal of the parts, after crystallization, a compound is formed.

 The principle of thermite welding

To start the process, the termite is remotely ignited with a pyropatron, an electric discharge, a Bickford cord. The gorenje temperature of the mixture reaches 2700⁰C, which is sufficient for welding metals of common types. The termite method is used to repair large-sized equipment, rails, and splice wires on power transmission lines.

 Electroslag

This type of thermal welding is used to connect steel with a thickness of 5 cm to 3 m. The workpieces are installed vertically, the gap between them on both sides is closed with movable sliders made of water-cooled copper. From below, a layer of flux is poured onto the pallet, under which an arc is lit.

 Electroslag welding

After melting the flux, the resulting slag becomes electrically conductive. The arc goes out, but the current passing through the slag is enough to melt new portions of the flux, the electrode and the edges. As the melt cools down in the welding bath, the sliders gradually move higher. In this way, the workpieces are connected in one pass, regardless of their thickness, without cracking.

 Thermomechanical welding class

 Combined types connect small parts, if it is impossible to create a high-quality seam by other methods. The following types of welding belong to the thermostatically class:

•  blacksmith shop
• contact information
• diffusive.

Blacksmith Shop

This method was used to connect iron billets long before the invention of modern welding classes. The blanks are heated in a furnace, put one on top of the other, fastened with hammer blows. A mechanized subspecies, when the workpieces are squeezed by a press, is called press welding.

 The principle of forge welding

The quality of the connection depends on the experience of the master. The list of metals that can be welded by this method is limited to types with good ductility. Due to the low productivity and low reliability of the connection, forging welding is rarely used.

 Contact information

The metal is heated by a current passing through the place of contact of the work pieces, then compressed or deposited. This type is easily automated, so it is widely used at enterprises of the machine-building industry as part of robotic complexes.

 The scheme of butt contact welding

 Depending on the tasks to be solved, the contact type of welding is performed as:

 Pinpoint, clamping the parts between the electrodes. After the current is applied, a point connection is formed at the point of compression.

Butt joint with heating of the entire contact area.

Relief with the preliminary application of protrusions (reliefs) on the connected planes. After the current is applied, the reliefs are deformed, the surface is leveled.

Suture, when the parts are connected by overlapping roller electrodes.

Diffusion

The technology is based on the mutual penetration (diffusion) of atoms of materials, if they are tightly pressed one against the other. When heated, the rate of particle exchange increases. Welding is carried out in a vacuum chamber or an inert gas environment. The parts are compressed with a force of at least 20 MPa, the surface layers are heated by electric current to a temperature close to the melting point. For reliable coupling, the workpieces are left in this position for a while, without turning off the current.

Mechanical welding class

These types of welding are performed due to the energy of friction, explosion, pressure, ultrasound. When exposed to them, heat is released sufficient to melt the material.

By friction

The technology is included in the list of promising developments. One of the connected blanks is fixed motionlessly, the other, pressed against it, rotates. The detailed classification of friction welding includes the following subspecies:

 Mixing is performed on equipment equipped with a rotation tool with two elements ― a base (shoulder) and a tip (pin). The compound is created by squeezing with subsequent mixing.

The pipes are joined radially, placing a rotating ring between the ends.

The pin is sealed with small through-through damage. In place of the hole, a round hole is drilled, into which a rotating pin made of the same metal as the main one is inserted.

The linear one is performed without rotation. The workpieces are rubbed against each other until the joined surfaces begin to melt, then the compression force is increased.

With the inertial type of welding, the work pieces are moved due to the energy of the per-untwisted flywheel.

Method of friction welding with mixing

Cold

The technology is based on the principle of compressing parts with punches with a force of 1-3 GPa. Spot welding is carried out with rods, suture with rollers. The punch is pressed into the workpiece until a plastic deformation is formed, which contributes to the appearance of interatomic bonds and the creation of a connection between the parts. Welding is performed by simple compression or with a shift of the parts after squeezing. The strength of the joint depends on the quality of the joint preparation, the degree of compression, the nature of the impact (vibration or static).

 Types of cold welding of metals

When connecting butt-to-butt, the amount of deformation is limited by the size of the parts of the workpieces protruding from the clamps. To prevent warping of the sheets when overlapping, they are fixed with clamps. After plastic deformation, the metal becomes harder, so the strength of the seam is higher than that of the work pieces.

 

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The cold type of compound is used to work with aluminum, copper, zinc, silver and other metals with a low melting point.

 By explosion

For welding in this way, a movable (throwable) part is installed over a stationary work piece at an angle of 3 — 10⁰ or in parallel with a gap of 2 — 10 mm. A uniform layer of explosives with a detonator is placed on the upper plate. To prevent the lateral spread of the metal, the area of the movable workpiece is made larger than that of the lower one.

 Explosion welding scheme

 After the explosion, the movable part under the influence of a shock wave hits the lower plate at high speed. At the point of contact, a pressure is formed that significantly exceeds the strength of metals, at which the material begins to flow like a liquid. As a result, the surfaces are simultaneously deformed, creating a joint. The duration of the process does not exceed millionths of a second, so the diffusion occurs only in the surface layers.

 Despite the fact that a detailed method of this type has not yet been developed, explosion welding has been widely used in industry for joining dissimilar materials. In this way, bimetallic compounds, parts and blanks of large sizes are obtained, cladding layers up to 45 mm thick are applied.

 Ultrasonic

This type of welding is carried out by a converter of ultrasonic waves into mechanical vibrations in combination with a small pressure. When exposed to the surface, the oxide film is first destroyed due to dry friction, then the material melts. Therefore, there is no need for careful preparation of the joint. To increase the strength of the seam, the parts are preheated.

 Ultrasonic welding

 In addition to metals, including refractory ones, plastic, leather, and fabrics are combined with this type. Welding of glass and ceramics with metal, foil with a thickness of 0.001 mm is also available. If necessary, the parts can be welded with a metal or plastic layer between them.

 In the welding business, something is constantly changing, improving, being finalized. Therefore, to improve your skills, it is useful to get acquainted with new products and test them in practice. Some of them will be useful for professional welders, others for household work.