Modern welding technologies. How to make modern welding machines with your own hands

Welding http://weldex.kiev.ua/ is one of the most durable and reliable methods of fastening. This method is widely used in everyday life and industry due to its strength, speed and efficiency. The leading type of welding is electric. Using electric current and an electrode, a permanent connection of parts is created. Welding equipment http://weldex.kiev.ua/ballony/uglekislotnye-ballony/ has been serving humanity for a century.

With the help of modern technologies, it has become possible to join steels of different alloy levels, as well as some non-ferrous alloys. The quality and cost of work are influenced by the methods and type of tasks being solved.

There are many types of welding currently used. Let's look at the most common ones.

Arc welding

In electric arc welding, an electric arc burns between the electrode and the workpiece, which serves as a source of heat. There are different types of arc welding. They differ in the material and number of electrodes, as well as in the method of including the workpiece and electrodes in the electric current circuit. There are electric arc welding with a consumable electrode and a non-consumable electrode, a three-phase arc and an indirect arc.

The arc is powered by alternating and direct current.

Manual arc welding

In this type of welding, welding electrodes are manually fed into the arc and moved along the workpiece. The electrodes for this type of welding are coated rods. The rod itself is a high quality welding wire. Depending on the composition, welding wire is divided into groups: alloyed, high-alloyed and low-carbon. The current during manual welding is limited due to the fact that its increase above the optimal value can lead to overheating of the rod, waste and spattering of the metal, and peeling of the coating.

Automatic Submerged Arc Welding

Submerged arc welding uses flux to protect the weld pool and arc from air, and also uses uncoated electrode wire. The processes of moving and feeding the electrode wire are mechanized, and the processes of igniting the arc and welding the crater at the end of the seam are automated. Submerged arc welding is performed using automatic welding machines, self-propelled tractors that move along the product, or welding heads. This type of welding is used in the manufacture of tanks, boilers, bridge beams, body vessels and other products.

Electroslag welding and fusion

In this type of welding, the electrode and base metals are melted by the heat that is released when electricity passes through the slag bath. When performing electroslag welding, the workpieces to be welded are placed vertically. A slag bath, unlike an electric arc, is a more distributed source of heat. Advantages of an electroslag bath: better macrostructure of the weld, increased productivity, lower costs per meter of weld.

Modern civilization owes a lot to the welding process. Without welding elements, we would not have received transport, huge buildings, technological structures, mobile phones, etc. Despite the fact that this physical process has been used for many centuries, it does not stop its progress. Scientists from many countries continue to research and improve welding mechanisms, apply new techniques and make revolutionary discoveries in this area.

New technologies make it possible to achieve more perfect results using minimal resources. Developments that appear every year make it possible to weld those materials that previously remained beyond the boundaries of this technology.

Main innovative directions

All developments in this area are aimed at improving the main indicators of the process at the lowest cost:

• reduction of corrosion and warping of metals during operation;
• increasing the speed of the welding process;
• facilitating the cleaning of joints or ensuring that there is no such need;
• minimal consumption of materials;
• facilitated and simplified process management;
• the ability to join the thinnest sheets of metal of various grades.

Portable devices

These types of welding machines have made it possible to bring welding to a new – household – level. If before the invention of portable devices, such work was carried out mainly by highly qualified professionals, then portable technology made it possible to use them at home.

Firstly, such devices are very light in weight, making them easy to transport. Secondly, the manufacturers provided them with a complete ready-to-use kit, not forgetting about the electrode supply system (wire weighing up to 10 kg).

The main improvement can be considered that a digital control system is built into the device. On the display, everyone can indicate the basic welding parameters: the diameter of the wire being laid, the type of gas, etc. Based on the entered data, the portable device independently adjusts and performs welding at a level sufficient for non-production welds.

Improved burners

The gas torch is considered the most primitive element during welding, but even small changes to this element have significantly improved the quality of the work performed. Modern burner designs are made not only from new materials, but also have a different outlet diameter, which is capable of working with non-standard temperatures and creating the required pressure.

The gas burners proposed by scientists have become gearless and highly dynamic; with their help, even during a long process at the highest temperatures, you can get a perfectly even flame in which torches, flashes and pops will not appear. Because of such innovations, the welder's work does not require frequent stops, which allows more work to be completed in the same time.

Units have been developed with numerous nozzles that are used to connect large diameter pipes. The flame width when using linear burners can reach several meters. This technology is often used to join parts underwater or in the air, where there is an urgent need to dramatically reduce turnaround times.

Hybrid laser technology

This method was developed for the automotive industry, but has found application in other industrial sectors. A hybrid laser is used to produce high-quality seams when joining refractory steels when combined with carbon dioxide. This allows you to obtain ideal welds with precise control of the laser power within the range of 1.5 - 4.0 kW.

Another feature inherent in hybrid laser technology is the highest speed of the melting electrode and the work performed - from 40 to 450 m/hour. With the same performance, it is possible to process the thinnest sheets made of automotive steel, which became the reason for the financial support and improvement of this development by leading automobile corporations.

Twin arc welding

This technique was developed for large-sized structures, the manufacture of which involves thick sheets of hardening steel of grades such as 30KhGSA. The method is based on the fact that during double-arc exposure, two different types of wires containing alloying (heavy-duty) components are simultaneously used. The diameter of such electrodes is 5 mm.

To ensure stable arc burning during double-arc welding, a ceramic flux based on ANK-51A ceramics is required. It is with ceramic flux that this method shows the highest results and the formation of an ideal welded surface.

Gentle technique

For certain work, a new gentle technology has been developed, which is very highly effective, but has a low cost. During the process, special mixtures of protective gases are used: carbon dioxide combined with argon or a mixture of argon, carbon dioxide and oxygen. Compared to the traditional use of separated carbon dioxide, the resulting seam is smoother and more flawless.

Another positive point is the significant reduction in cost of the welding process: fewer wire electrodes are consumed for the same volume of connections made. The savings are about 20%, which is a significant amount on an industrial scale. Additionally, during the welding process, the transition to weldable parts becomes very gradual and smooth. Professional welders who were involved in the initial tests of the gentle technique emphasized that spattering of electrode metals with a multi-component gas mixture is significantly reduced.

Two-component technique

This new method, which has become widespread in developed countries in a short period of time, owes its appearance to the launch of new high-speed trains on the railways. Two-component technology is a modified version of the injection molding method. It made it possible to achieve results that were previously considered mutually exclusive: to ensure the highest ductility of the seam joint without compromising the wear resistance of the metal at the weld site.

Technically, the two-component method is difficult to perform because it requires special preparation: there must be molten steel at the work site, which is carefully placed in liquid form into the gap between the rails. In order to give the compound impressive viscosity, a melt with low-alloy components is used. Wear resistance is increased through the use of ceramic fluxes, which allow alloying additives to be removed from the process after filling the weld joint. Ceramics are destroyed under the influence of high temperature, and additives that strengthen the connection harden on the surface, ensuring long-term operation without cracks or deformations.

Orbital argon arc technology

This technology has found applications in the aerospace, automotive and semiconductor industries. This technique is highly specific and is used for objects with a complex structural contour. It was first developed 50 years ago, but it was significantly improved by using a tungsten electrode.

The main advantage of orbital argon-arc tungsten welding is that the consumption of activating flux with this method is record low: only 1 g of flux is consumed per 1 m of weld. This makes it possible to carry out the process at a reduced current, which reduces not only the volume, but also the weight of the weld pool. In this case, the quality of the connection is regulated in real time by adjusting the arc pressure.

This technique is successfully used when it is necessary to connect heat-resistant, high-strength alloys, carbon steels, titanium, copper and nickel.

SMT technology

This technique is based on cold metal transfer. When they talk about cold transfer, they don’t mean a really low temperature, it’s just much lower than with the classic options.

The main difference is that the workpieces and the area of ​​the future weld are not heated to maximum values, so the heat input in the processing area is reduced significantly. Due to the fact that the metal does not overheat pointwise, severe deformation does not occur. The operation of the electrode is based on a controlled short circuit, which is terminated by quickly moving the wire away from the discharge zone and quickly returning it (up to 70 times per second).

The use of SMT welding is carried out through automated systems that produce very uniform and high-quality seams at the junction of galvanized or steel sheets with aluminum alloys.

In this case, welding is carried out with a short-circuited arc with systematic interruptions. As a result of this system, the seam is attacked by hot and cold pulses, which reduces the pressure in the area where the arc enters. The same principle reduces splashing when transferring metals.

Thus, with the help of CMT welding, a standard that was previously considered only theoretical has been achieved. This is made possible by short-circuit control and the complete absence of spatter, which dramatically reduces the need for post-weld machining.

This method makes it possible to weld metals of different thicknesses, from the thinnest sheets to a seam depth of up to 20 cm. Plasma technology allows cutting to be carried out simultaneously with welding work.

The plasma method is based on ionized gas, which completely fills the space between two electrodes. It is through this gas that an electric arc of a certain power passes, providing a very strong effect.

Using a plasma generator is a complex process that requires high professionalism and professional skills, so it will not be possible to use it for domestic purposes. Inside the generator there is a multifunctional welding system that can be used in highly specialized areas.

Computer simulation technology

The most modern direction in welding technologies is rightfully given to computer modeling. It is equally suitable for making connections between the smallest parts with complex contours and for large-scale work where it is necessary to manage huge areas and many welding machines.

If previously voluminous work was carried out using many devices or an entire welding complex, then computer modeling allows you to have one functional unit with branched periphery, equipped with many torches and nozzles.

Full automation makes it possible to introduce fundamentally new methods of welding work that are inaccessible to most welders. In this case, the welders themselves functionally turn into operators who set the computer all the necessary parameters, based on which the program sets the optimal values ​​and controls the process. This approach significantly improves the results of the work performed.

New technologies have brought welding to a completely new level, which allows the welding process to be completed in record time with minimal labor costs and maximum results. At the same time, progress does not stand still, so it is quite possible that in the near future there will be systems that will work autonomously, with virtually no human intervention. Development of such projects is already underway, and if the tests are successful, humanity will soon be able to achieve new scales and concepts of welding production.

Chapter 1
A little history
1.1. Invention of electric welding
1.2. Development of electric welding in the 20th century

Chapter 2
Arc Welding Basics
2.1. Electric arc
Physical entity
Current-voltage characteristic
Manual DC welding
Semi-automatic DC welding
AC Welding
2.2. Welding process
Non-consumable electrode welding
Consumable electrode welding
Metal transfer
2.3. Main characteristics of welding arc power sources

Chapter 3
Simulator LTspice IV
3.1. Simulation of power supply operation
Simulation capabilities
Electronic circuit simulation programs
Features of the LTspice IV program
3.2. How LTspice IV works
Starting the program
Drawing a circuit of a simple multivibrator on a PC
Defining numerical parameters and types of circuit components
Simulation of multivibrator operation
3.3. Simulation of a simple power supply
Low Voltage DC Power Supply
Test node

Chapter 4
AC Welding Power Sources
4.1. Features of terminology
4.2. Basic requirements for a welding source
4.3. AC Electric Arc Model
4.4. Welding source with ballast rheostat (active resistance)
4.5. Welding source with linear choke (inductive reactance)
4.6. Welding transformer
4.7. How to calculate leakage inductance?
Leakage inductance of a transformer with cylindrical windings
Leakage inductance of a transformer with windings spaced apart
Leakage inductance of a transformer with disc windings
4.8. Requirements for a welding transformer
4.9. Classic AC power source
Calculation of a welding transformer with developed magnetic leakage

Design of AC Welding Power Source
4.10. Budyonny welding source
Ways to reduce the amount of current consumed
Structural electrical diagram of Budyonny's welding source
General principles for designing a welding source
Budyonny welding source model
Overcoming the design limitations of the Budenny welding source
Determining the overall power of a transformer
Core selection
Winding calculation
Magnetic shunt calculation
Leakage inductance calculation
Simulation of calculation results
Welding source design with alternative transformer design
4.11. Welding source with resonant capacitor
Calculation of a welding source with a resonant capacitor
Calculation of a welding transformer
Checking the placement of windings in the welding transformer window
Leakage inductance calculation
Welding source simulation
4.12. AC Arc Stabilizers
Features of AC welding arc
Operating principle of the arc stabilizer
First version of arc stabilizer
Details
Second version of the arc stabilizer
Details

Chapter 5
Welding source for semi-automatic welding
5.1. Basics of semi-automatic welding
5.2. Calculations of circuit elements
Determination of parameters and calculation of the source power transformer
Model setup procedure
Calculation of ohmic resistance of windings
Calculation of inductance and resistance of transformer windings
Calculation of overall dimensions of the transformer
Completing the transformer calculation
Calculation of the feed current source choke
5.3. Description of the design of a simple source for semi-automatic welding
Diagram of a simple source for semi-automatic welding
Parts for semi-automatic welding machine
Design and manufacture of welding transformer
Throttle design
Source connection

Chapter 6
Welding source for semi-automatic welding with thyristor regulator
6.1. Adjusting the welding current
6.2. Ensuring continuity of welding current
6.3. Calculation of a welding transformer
6.4. Control unit
6.5. Description of the design of a welding source with a thyristor regulator
Electrical circuit diagram
Details
Welding transformer design
Throttle design
Source connection

Chapter 7
Electronic welding current regulator
7.1. Multi-station welding
Multi-station welding with connection
through an individual ballast rheostat
Electronic analogue of the ballast rheostat ERST
7.2. Calculation of the main components of ERST
7.3. Description of ERST
Basic protection options
Purpose of the main components of ERST
Operating principle
Operating principle and configuration of block A1
Details
Operating principle and configuration of block A2
The principle of operation of the stabilizer
Details
Settings
Formation of external characteristics of ERST
Operating principle of the ERST control unit
Operating principle of the key transistor driver unit
Final setup of ERST

Chapter 8
Inverter welding source
8.1. A little history
8.2. General description of the source
8.3. Recommendations for self-production of ISI
8.4. Calculation of a forward converter transformer
8.5. Transformer manufacturing
8.6. Calculation of power losses on converter transistors
8.7. Calculation of the welding current filter choke
8.8. Simulation of converter operation
8.9. Current transformer calculation
8.10. Calculation of galvanic isolation transformer
8.11. PWM controller TDA4718A
8.12. Schematic diagram of the control unit of the inverter welding source “RytmArc”
8.13. Formation of the load characteristic of the source
8.14. Methodology for setting up the control unit
8.15. Remote control panel (modulator)
8.16. Using an alternative PWM controller
8.17. Transformer driver
8.18. Damping chain that does not dissipate energy

Chapter 9
Inverter welding source COLT-1300
9.1. General description
What is this chapter about?
Purpose
Main Features
9.2. Power part
Winding unit data
9.3. Control unit
Functional diagram
Operating principle
Schematic diagram
Implementation of the Anty-Stick function
Implementation of the Arc Force function
9.4. Settings

Chapter 10
Useful information
10.1. How to test unknown hardware?
10.2. How to calculate a transformer?
10.3. How to calculate a choke with a core?
Calculation features
Example of calculation of throttle No. 1
Example of calculation of throttle No. 2
Example of calculation of throttle No. 3
10.4. Calculation of chokes with powder core
Advantages of Powder Cores
Inductor Design Software address and installation
Automatic calculation functions of Inductor Design Software
Additional Features of Inductor Design Software
Inductor Design Software menu bar
Example of choke calculation in Inductor Design Software
Magnetics Inductor Design Using Powder Cores
Example of inductor calculation in Magnetics Inductor Design Using Powder Cores
10.5. How to calculate a radiator?
10.6. Hysteresis model of nonlinear inductance of the LTspice simulator
Brief description of the hysteresis model of nonlinear inductance
Selection of parameters of the hysteresis model of nonlinear inductance
10.7. Modeling complex electromagnetic components using LTspice
Modeling problem
The principle of similarity of electric and magnetic circuits
Duality of physical circuits
Model of an unbranched magnetic circuit
Simulation of a branched magnetic circuit
Simulation of a complex magnetic circuit
Adaptation of the model for magnetic circuits operating with partial or full magnetization
Creating an Integrated Magnetic Component Model
10.8. How to make welding electrodes?

Connecting optical fibers using the welding method is the highest quality, most durable and reliable. Welding machines are complex high-tech devices. They combine precision mechanics to ensure fiber alignment to within 0.1 microns, high-quality optics to evaluate fiber position, and software to control the fiber alignment, splicing process and machine control.

This article will review welding machines from leading manufacturers.

At the moment, devices from Fujikura, Sumitomo, Fitel (Furukawa), Ericsson and Corning have gained the greatest popularity in the domestic market. Separately among the modern welding machines is the OptiSplice LID model produced by Corning. A characteristic feature of this device is the ability to measure real losses at the point of the welded joint, which is carried out directly during the welding process. The device is also equipped with a global positioning system (GPS), which, if necessary, makes adjustments to the welding program.

Splicers can be divided into two classes based on the method of fiber alignment during the welding process - sheath alignment and core alignment. When using the core alignment method, a higher connection quality is achieved, which is extremely important when working with single-mode fibers, as well as when installing long-distance optical communication lines.

Devices that use the fiber-to-cladding method are primarily used for splicing multimode fibers or single-mode fibers where the line length is not long.

All modern machines can splice both single-mode and multimode fibers, as well as fibers with a shifted dispersion region. Losses at the welding site, regulated by the manufacturer, do not exceed 0.02 dB. Welding work can be carried out both in stationary and field conditions. For this purpose, almost all devices have the ability to be powered by a battery. A number of welders come with cords for connecting to car cigarette lighters.

In addition to reducing the weight and size of the device and reducing welding time, manufacturers are making other changes to the design of welding machines. For example, the latest models from Fujikura - FSM-60S and FSM-18S - have increased dust and moisture resistance and an impact-resistant housing, which guarantees the device’s performance under mechanical stress (for example, when dropped from a height of 70 cm).

Let's look at the lines of welding machines from leading manufacturers.

Table 1. Core-aligned welding machines

Table 2. Shell-aligned welding machines

1. Physical foundations of welding

Welding is a technological process of obtaining a permanent connection of materials due to the formation of an atomic bond. The process of creating a welded joint occurs in two stages.

At the first stage, it is necessary to bring the surfaces of the materials being welded closer to the distance of action of interatomic interaction forces (about 3 A). Ordinary metals at room temperature do not bond when compressed even with significant forces. The joining of materials is hampered by their hardness; when they come together, actual contact occurs only at a few points, no matter how carefully they are processed. The joining process is strongly influenced by surface contamination - oxides, fatty films, etc., as well as layers of absorbed impurity atoms. Due to these reasons, it is impossible to fulfill the condition of good contact under normal conditions. Therefore, the formation of physical contact between the joined edges over the entire surface is achieved either due to the melting of the material or as a result of plastic deformations resulting from the applied pressure. At the second stage, electronic interaction occurs between the atoms of the surfaces being connected. As a result, the interface between the parts disappears and either atomic metal bonds are formed (metals are welded) or covalent or ionic bonds are formed (when welding dielectrics or semiconductors). Based on the physical essence of the process of formation of a welded joint, three classes of welding are distinguished: fusion welding, pressure welding and thermomechanical welding (Fig. 1.25).

Rice. 1.25.

For fusion welding These are types of welding carried out by fusion without applied pressure. The main sources of heat in fusion welding are the welding arc, gas flame, beam energy sources and “Joule heat”. In this case, the melts of the metals being joined are combined into a common weld pool, and upon cooling, the melt crystallizes into a cast weld.

For thermomechanical welding thermal energy and pressure are used. The joining of connected parts into a monolithic whole is carried out through the application of mechanical loads, and heating of the workpieces ensures the required plasticity of the material.

For pressure welding refers to operations carried out with the application of mechanical energy in the form of pressure. As a result, the metal becomes deformed and begins to flow like a liquid. The metal moves along the interface, taking the contaminated layer with it. Thus, fresh layers of material come into direct contact, which enter into chemical interaction.

2. Main types of welding

Manual electric arc welding. Electric arc welding is currently the most important type of metal welding. The heat source in this case is an electric arc between two electrodes, one of which is the workpiece being welded. An electric arc is a powerful discharge in a gaseous environment. 

The arc ignition process consists of three stages: short circuit of the electrode to the workpiece, withdrawal of the electrode by 3-5 mm and the occurrence of a stable arc discharge. A short circuit is performed in order to heat the electrode (cathode) to the temperature of intense exo-emission of electrons.

At the second stage, electrons emitted by the electrode are accelerated in the electric field and cause ionization of the cathode-anode gas gap, which leads to the occurrence of a stable arc discharge. An electric arc is a concentrated source of heat with temperatures up to 6000 °C. Welding currents reach 2-3 kA at arc voltage (10-50) V. Covered electrode arc welding is most often used. This is manual arc welding with an electrode coated with an appropriate composition that has the following purpose:

1. Gas and slag protection of the melt from the surrounding atmosphere.

2. Alloying the weld material with the necessary elements.

The composition of the coatings includes substances: slag-forming substances - to protect the melt with a shell (oxides, feldspars, marble, chalk); forming gases CO2, CH4, CCl4; alloying - to improve the properties of the weld (ferrovanadium, ferrochrome, ferrotitanium, aluminum, etc.); deoxidizers - to eliminate iron oxides (Ti, Mn, Al, Si, etc.) Example of a deoxidation reaction: Fe2O3+Al = Al2O3+Fe.

Rice. 1.26. : 1 - parts to be welded, 2 - weld seam, 3 - flux crust, 4 - gas protection, 5 - electrode, 6 - electrode coating, 7 - weld pool

Rice. Figure 1.26 illustrates coated electrode welding. According to the above diagram, a welding arc is ignited between the parts (1) and the electrode (6). When melted, the coating (5) protects the weld from oxidation and improves its properties by alloying. Under the influence of the arc temperature, the electrode and the workpiece material melt, forming a weld pool (7), which subsequently crystallizes into a weld seam (2), on top of which the latter is covered with a flux crust (3), intended to protect the seam. To obtain a high-quality seam, the welder places the electrode at an angle of (15-20)0 and moves it downward as it melts to maintain a constant arc length (3-5) mm and along the axis of the seam to fill the seam groove with metal. In this case, the end of the electrode usually makes transverse oscillatory movements to obtain rollers of the required width.

Automatic submerged arc welding.

Automatic welding with a consumable electrode under a layer of flux is widely used. The flux is poured onto the product in a layer (50-60) mm thick, as a result of which the arc burns not in the air, but in a gas bubble located under the flux melted during welding and isolated from direct contact with air. This is enough to eliminate splashing of liquid metal and disruption of the shape of the seam, even at high currents. When welding under a layer of flux, a current of up to (1000-1200) A is usually used, which is impossible with an open arc. Thus, in submerged arc welding it is possible to increase the welding current by 4-8 times compared to open arc welding, while maintaining good welding quality and high productivity. In submerged arc welding, the weld metal is formed by melting the base metal (about 2/3) and only about 1/3 by the electrode metal. The arc under a layer of flux is more stable than with an open arc. Welding under a layer of flux is carried out with bare electrode wire, which is fed from a reel into the arc burning zone by the welding head of an automatic machine, which is moved along the seam. Ahead of the head, granular flux enters the weld through the pipe, which, melting during the welding process, evenly covers the seam, forming a hard slag crust.

Thus, automatic welding under a layer of flux differs from manual welding in the following indicators: stable quality of the seam, productivity is (4-8) times greater than with manual welding, thickness of the flux layer - (50-60) mm, current strength - ( 1000-1200) And, the optimal arc length is maintained automatically, the seam consists of 2/3 of the base metal and 1/3 of the arc burns in a gas bubble, which ensures excellent welding quality.

Electroslag welding.

Electroslag welding is a fundamentally new type of metal joining process, invented and developed at the Electric Welding Institute named after. Paton. The parts to be welded are covered with slag, heated to a temperature exceeding the melting point of the base metal and electrode wire.

At the first stage, the process proceeds in the same way as with submerged arc welding. After the formation of a bath of liquid slag, the burning of the arc stops and the melting of the edges of the product occurs due to the heat released when current passes through the melt. Electroslag welding allows you to weld large thicknesses of metal in one pass, provides greater productivity, and high quality welds. 

Rice. 1.27. :

1 - parts to be welded, 2 - weld seam, 3 - molten slag, 4 - sliders, 5 - electrode

The electroslag welding diagram is shown in Fig. 1.27. Welding is carried out with a vertical arrangement of parts (1), the edges of which are also vertical or have an inclination of no more than 30 o to the vertical. A small gap is installed between the parts to be welded, into which slag powder is poured. At the initial moment, an arc is ignited between the electrode (5) and the metal strip installed below. The arc melts the flux, which fills the space between the edges of the parts being welded and the water-cooled copper forming slides (4). Thus, a slag bath (3) appears from the molten flux, after which the arc is shunted by the molten slag and goes out. At this point, electric arc melting turns into an electroslag process. When current passes through molten slag, Joule heat is released. The slag bath is heated to temperatures (1600-1700) 0C, exceeding the melting point of the base and electrode metals. The slag melts the edges of the parts being welded and the electrode immersed in the slag bath. The molten metal flows to the bottom of the slag pool, where it forms a weld pool. The slag pool reliably protects the weld pool from the surrounding atmosphere. After removing the heat source, the metal of the weld pool crystallizes. The formed seam is covered with a slag crust, the thickness of which reaches 2 mm.

A number of processes contribute to improving the quality of the weld in electroslag welding. In conclusion, we note the main advantages of electroslag welding.

Gas bubbles, slag and light impurities are removed from the welding zone due to the vertical position of the welding device.

High weld density.

The weld seam is less susceptible to cracking.

The productivity of electroslag welding for large material thicknesses is almost 20 times higher than that of automatic submerged arc welding.

It is possible to obtain seams of complex configuration. 

This type of welding is most effective when joining large parts such as ship hulls, bridges, rolling mills, etc.

Electron beam welding.

The heat source is a powerful beam of electrons with an energy of tens of kiloelectronvolts. Fast electrons, penetrating into the workpiece, transfer their energy to the electrons and atoms of the substance, causing intense heating of the material being welded to the melting point. The welding process is carried out in a vacuum, which ensures high quality seams. Due to the fact that the electron beam can be focused to very small sizes (less than a micron in diameter), this technology is exclusive to welding micro parts.

Plasma welding.

In plasma welding, the source of energy for heating the material is plasma - ionized gas. The presence of electrically charged particles makes plasma sensitive to the effects of electric fields. In an electric field, electrons and ions are accelerated, that is, they increase their energy, and this is equivalent to heating the plasma up to 20-30 thousand degrees. Arc and high-frequency plasma torches are used for welding (see Fig. 1.17 - 1.19). For welding metals, as a rule, direct plasma torches are used, and for welding dielectrics and semiconductors, indirect plasma torches are used. High-frequency plasma torches (Fig. 1.19) are also used for welding. In the plasmatron chamber, the gas is heated by eddy currents created by high-frequency currents of the inductor. There are no electrodes, so the plasma is highly pure. A torch of such plasma can be effectively used in welding production.

Diffusion welding.

The method is based on the mutual diffusion of atoms in the surface layers of contacting materials under high vacuum. The high diffusivity of atoms is ensured by heating the material to a temperature close to the melting point. The absence of air in the chamber prevents the formation of an oxide film that could impede diffusion. Reliable contact between the surfaces being welded is ensured by mechanical processing to a high class of cleanliness. The compressive force required to increase the actual contact area is (10-20) MPa.

The diffusion welding technology is as follows. The workpieces to be welded are placed in a vacuum chamber and compressed with slight force. Then the workpieces are heated with current and kept for some time at a given temperature. Diffusion welding is used to join poorly compatible materials: steel with cast iron, titanium, tungsten, ceramics, etc.

Contact electric welding.

In electric resistance welding, or resistance welding, heating is achieved by passing an electric current from a sufficient needle through the weld site. Parts heated by electric current to a melting or plastic state are mechanically compressed or upset, which ensures the chemical interaction of metal atoms. Thus, resistance welding belongs to the group of pressure welding. Resistance welding is one of the high-performance welding methods; it can easily be automated and mechanized, as a result of which it is widely used in mechanical engineering and construction. Based on the shape of the connections being made, there are three types of resistance welding: butt, roller (suture) and spot welding.

Butt contact welding.

This is a type of resistance welding in which the connection of the parts being welded occurs along the surface of the butt ends. The parts are clamped in sponge electrodes, then pressed against each other by the surfaces to be joined and the welding current is passed through. Butt welding is used to connect wire, rods, pipes, strips, rails, chains and other parts over the entire area of ​​their ends. There are two methods of butt welding:

Resistance: plastic deformation occurs at the joint and the joint is formed without melting the metal (the temperature of the joints is 0.8-0.9 from the melting temperature).

By melting: the parts come into contact at the beginning at separate small contact points through which a high-density current passes, causing the parts to melt. As a result of melting, a layer of liquid metal is formed at the end, which, during sedimentation, along with contaminants and oxide films, is squeezed out of the joint.

Table 1.4

Parameters of Butt Welding Machines

Column designations: W - machine power, Uwork - operating voltage, productivity, F - compression force of the parts being welded, S - area of ​​the welded surface.

Heating temperature and compressive pressure during butt welding are interrelated. As follows from Fig. 1.28, the force F decreases significantly with increasing heating temperature of the workpieces during welding.

Seam resistance welding.

A type of resistance welding in which the elements are overlapped with rotating disk electrodes in the form of a continuous or intermittent seam. In seam welding, the formation of a continuous joint (seam) occurs by sequentially overlapping points one after another; to obtain a hermetic seam, the points overlap each other by at least half their diameter. In practice, seam welding is used:

Continuous;

Intermittent with continuous rotation of the rollers;

Intermittent with periodic rotation.

Rice. 1.28.

Seam welding is used in mass production in the manufacture of various vessels. It is carried out using alternating current with a force of (2000-5000) A. The diameter of the rollers is (40-350) mm, the compression force of the welded parts reaches 0.6 tons, the welding speed is (0.53.5) m/min.

Spot resistance welding.

In spot welding, the parts to be joined are usually placed between two electrodes. Under the action of a pressure mechanism, the electrodes tightly compress the parts to be welded, after which the current is turned on. Due to the passage of current, the parts being welded quickly heat up to the welding temperature. The diameter of the molten core determines the diameter of the weld spot, usually equal to the diameter of the electrode contact surface.

Depending on the location of the electrodes in relation to the parts being welded, spot welding can be double-sided or single-sided.

When spot welding parts of different thicknesses, the resulting asymmetrical core is shifted towards the thicker part and, if there is a large difference in thickness, does not capture the thin part. Therefore, various technological methods are used to ensure the displacement of the core to the mating surfaces, increase the heating of a thin sheet due to overlays, create a relief on a thin sheet, use more massive electrodes on the side of a thick part, etc.

A type of spot welding is relief welding, when the initial contact of parts occurs along previously prepared protrusions (reliefs). The current, passing through the place where all the reliefs touch the lower part, heats them and partially melts them. Under pressure, the reliefs are deformed, and the upper part becomes flat. This method is used for welding small parts. In table 1.5 shows the characteristics of machines for spot welding.

Table 1.5

Characteristics of Spot Welding Machines

Column designations: W - machine power, irab - operating voltage, D - electrode diameter, F - compression force of welded parts, welds per hour - productivity.

Spot capacitor welding.

One of the common types of resistance welding is capacitor welding or welding with stored energy stored in electric capacitors. Energy in capacitors is accumulated when they are charged from a constant voltage source (generator or rectifier), and then, during the discharge process, is converted into heat used for welding. The energy stored in capacitors can be regulated by changing the capacitance of the capacitor (C) and the charging voltage (U). 

There are two types of capacitor welding:

Transformerless (capacitors are discharged directly onto the parts being welded);

Transformer (the capacitor is discharged onto the primary winding of the welding transformer, in the secondary circuit of which there are pre-compressed parts to be welded).

The schematic diagram of capacitor welding is shown in Fig. 1.29.

Rice. 1.29. : Tr - step-up transformer, B - rectifier, C - capacitor with a capacity of 500 μF, Rk - resistance of the parts being welded, K - key switch

In switch position 1, the capacitor is charged to voltage U0. When the switch is moved to position. 2, the capacitor is discharged through the contact resistance of the parts being welded. This creates a powerful current pulse.

The voltage from the capacitor is applied to the workpiece through point contacts with an area of ​​~ 2 mm. The resulting current pulse, in accordance with the Joule-Lenz law, heats the contact area to the operating temperature of welding. To ensure reliable pressing of the welded surfaces, a mechanical stress of about 100 MPa is transmitted to the parts through point electrodes.

The main application of capacitor welding is to join metals and alloys of small thicknesses. The advantage of capacitor welding is its low power consumption.

To determine the efficiency of welding, we estimate the maximum temperature in the area of ​​​​contact of the parts being welded (Tmax).

Due to the fact that the duration of the discharge current pulse does not exceed 10 -6 s, the calculation was carried out in the adiabatic approximation, that is, neglecting heat removal from the region of current flow. 

The principle of contact heating of parts is shown in Fig. 1.30.

Rice. 1.30.: 1 - parts to be welded with thickness d = 5*10 -2 cm, 2 - electrodes with area S = 3*10 -2 cm, C - capacitor with a capacity of 500 μF, Rk - contact resistance

The advantage of capacitor welding is its low power consumption, which is (0.1-0.2) kVA. The duration of the welding current pulse is thousandths of a second. The range of welded metal thicknesses is from 0.005 mm to 1 mm. Capacitor welding allows you to successfully join thin metals, small parts and micro parts that are poorly visible to the naked eye and require the use of optical instruments during assembly. This progressive welding method has found application in the production of electrical measuring instruments and aircraft instruments, clock mechanisms, cameras, etc.

Cold welding.

The connection of workpieces during cold welding is carried out by plastic deformation at room and even at negative temperatures. The formation of a permanent connection occurs as a result of the emergence of a metallic bond when the contacting surfaces approach each other to a distance at which the action of interatomic forces is possible, and as a result of a large compression force, the oxide film breaks and clean metal surfaces are formed. 

The surfaces to be welded must be thoroughly cleaned of adsorbed impurities and fatty films. Cold welding can be used to make spot, seam and butt joints.

In Fig. Figure 1.31 shows the cold spot welding process. Sheets of metal (1) with a thoroughly cleaned surface at the welding site are placed between punches (2) having projections (3). The punch is compressed with some force P, the projections (3) are pressed into the metal to their entire height until the supporting surfaces (4) of the punches rest against the outer surface of the workpieces being welded.

Rice. 1.31.

Cold welding is used to make overlapped and butt joints of wires, busbars, and pipes. The pressure is selected depending on the composition and thickness of the material being welded; on average it is (1-3) GPa.

Induction welding.

This method is used primarily to weld longitudinal seams of pipes during their manufacture on continuous mills and to deposit hard alloys on steel bases in the manufacture of cutters, drill bits and other tools.

With this method, the metal is heated by passing high-frequency currents through it and is compressed. Induction welding is convenient because it is non-contact; high-frequency currents are localized near the surface of the heated workpiece. Such installations work as follows. The high-frequency generator current is supplied to the inductor, which induces eddy currents in the workpiece, and the pipe heats up. Mills of this type are successfully used for the production of pipes with a diameter of (12-60) mm at speeds of up to 50 m/min. The current is supplied from tube generators with a power of up to 260 kW at a frequency of 440 kHz and 880 kHz. Pipes of large diameters (325 mm and 426 mm) with a wall thickness of (7-8) mm, with a welding speed of up to (30-40) m/min are also manufactured.

Features of welding various metals and alloys

Weldability is understood as the ability of metals and alloys to form a compound with the same properties as the metals being welded, and not to have defects in the form of cracks, pores, cavities and non-metallic inclusions.

When welding, residual welding stresses almost always occur (usually tensile stresses in the weld and compressive stresses in the base metal). To stabilize the properties of the connection, it is necessary to reduce these voltages.

Welding carbon steels.

Electric arc welding of carbon and alloy steels is carried out with electrode materials that provide the necessary mechanical properties. The main difficulty in this case lies in the hardening of the heat-affected zone and the formation of cracks. To prevent the formation of cracks, it is recommended:

1) heat products to temperatures (100-300) 0C;

2) replace single-layer welding with multi-layer welding;

3) use coated electrodes (welding is carried out using direct current of reverse polarity);

4) temper the product after welding to a temperature of 300 0C.

Welding of high chromium steels.

High-chromium steels containing (12-28)% Cr have stainless and heat-resistant properties. Depending on the content of chromium and carbon, high-chromium steels are divided according to their structure into ferritic, ferritic-martensitic and martensitic.

Difficulties in welding ferrite steels are due to the fact that during cooling in the region of 1000 0C, chromium carbide may precipitate at the grain boundaries. This reduces the corrosion resistance of steel. To prevent these phenomena it is necessary:

1) use reduced current values ​​in order to ensure high cooling rates during welding;

2) introduce strong carbide formers (Ti, Cr, Zr, V) into the steel;

3) anneal after welding at 900 0C to level the chromium content in the grains and at the boundaries.

Ferrite-martensitic and martensitic steels are recommended to be welded with heating to (200-300) 0C.

Welding cast iron.

Welding of cast iron is carried out with heating to (400-600) 0C. Welding is carried out with cast iron electrodes with a diameter of (8-25) mm. Good results are obtained by diffusion welding of cast iron to cast iron and cast iron to steel.

Welding of copper and its alloys.

The weldability of copper is negatively affected by impurities of oxygen, hydrogen, and lead. The most common is gas welding. Arc welding with carbon and metal electrodes is promising.

Aluminum welding.

Welding is hampered by the Al2O3 oxide film. Only the use of fluxes (NaCl, RCl, LiF) makes it possible to dissolve aluminum oxide and ensure normal formation of the weld. Aluminum is welded well by diffusion welding.