The history of welding dates back several millennia, with the first examples of welding dating back to the Bronze Age and Iron Age in Europe and the Middle East. Welding was used in the construction of the Iron Pillar of Delhi, India, erected around the year 310 and weighing 5.4 metric tons.[1] The Middle Ages brought advances in forge welding, with which blacksmiths repeatedly struck and heated the metal until a union occurred. In 1540, Vannoccio Biringuccio published De la pirotechnia, which includes descriptions of the forging operation. Renaissance craftsmen were skilled at the process, and the industry continued to develop over the following centuries.[2] However, welding was transformed during the 19th century. In 1800, Sir Humphry Davy discovered the electric arc, and advances in arc welding continued with the inventions of metal electrodes by the Russian Nikolai Slavyanov and the American C. L. Coffin in the late 1800s. Even carbon arc welding, which used a carbon electrode, gained popularity. Around 1900, A. P. Strohmenger" launched a coated metal electrode in Britain, which gave a more stable arc, and in 1919, alternating current welding was invented by C. J. Holslag"), but it did not become popular for another decade.[3]

Resistance welding was also developed during the final decades of the 19th century, with the first patents in the sector held by Elihu Thomson" in 1885, who produced further advances over the next 15 years. Thermite welding was invented in 1893, and around that time, another process, gas welding, was established. Acetylene was discovered in 1836 by Edmund Davy"), but its use in welding was not practical until about 1900, when A convenient torch was developed.[4] At first, gas welding was one of the most popular welding methods due to its portability and relatively low cost. However, as the 20th century progressed, preferences for industrial applications declined. It was largely replaced by arc welding, as metal covers for the electrode (known as flux) continued to be developed, which stabilized the arc and shielded the base material from impurities.[5]​.

World War I caused a major uptick in the use of welding processes, with different military forces seeking to determine which of the various new welding processes would be best. The British primarily used arc welding, even constructing a ship, the Fulagar, with an entirely welded hull. The Americans were more hesitant, but began to recognize the benefits of arc welding when the process allowed them to quickly repair their ships after German attacks in New York Harbor early in the war. Arc welding was also applied for the first time to airplanes during the war, as some German airplane fuselages were built using the process.[6]​.

During the 1920s, important advances were made in welding technology, including the introduction of automatic welding in 1920, in which the electrode wire was fed continuously. Shielding gas became an important issue, as scientists sought to protect welds against the effects of oxygen and nitrogen in the atmosphere. Porosity and fragility were the basic problems arising from this exchange, and the solutions they developed included the use of hydrogen, argon, and helium as welding shielding gases.[7] Over the next decade, further advances allowed the welding of reactive metals such as aluminum and magnesium. This, together with developments in automatic welding, alternating current welding, and fluxes, fueled a significant expansion of arc welding during the 1930s and during World War II.[8]​.

In the mid-20th century, many new welding methods were invented. The 1930s saw the launch of stud welding, which soon became popular in ship manufacturing and construction. Submerged arc welding was invented the same year, and remains popular today. In 1941, after decades of development, tungsten electrode gas arc welding was finally perfected, followed in 1948 by gas metal arc welding, allowing rapid welding of non-ferrous materials but requiring costly shielding gases. Shielded metal arc welding was developed during the 1950s, using a covered consumable electrode flux, and quickly became the most popular. In 1957, the flux-cored arc welding process debuted), in which the self-shielded wire electrode It could be used with automatic equipment, resulting in greatly increased welding speeds, and that same year plasma arc welding was invented. Electroslag welding was introduced in 1958, and was followed in 1961 by its cousin, electrogas welding.

Other recent developments in welding include the important achievement of electron beam welding in 1958, making deep, narrow welding possible by means of the concentrated heat source. Following the invention of the laser in 1960, laser beam welding debuted several decades later, and has proven especially useful in high-speed automated welding. However, both processes remain highly expensive due to the high cost of the necessary equipment, and this has limited their applications.[10]​.

solid state welding

Like the first welding process, forge welding, some modern welding methods do not involve melting the materials being joined. One of the most popular, ultrasonic welding, is used to connect sheets or thin wires made of metal or thermoplastics, making them vibrate at high frequency and under high pressure. The equipment and methods involved are similar to resistance welding, but instead of electrical current, vibration provides the energy source. Welding metals with this process does not involve melting the materials; Instead, the weld is formed by introducing mechanical vibrations horizontally under pressure. When plastics are being welded, the materials must have similar melting temperatures, and vibrations are introduced vertically. Ultrasonic welding is commonly used to make electrical connections from aluminum or copper, and is also a very common polymer welding process.

Another common process, explosive welding, involves joining materials by pushing them together under extremely high pressure. The energy of the impact plasticizes the materials, forming a weld, although only a limited amount of heat is generated. The process is commonly used for welding dissimilar materials, such as welding aluminum to steel in ship hulls or composite plates. Other solid-state welding processes include coextrusion welding, cold welding, diffusion welding, friction welding (including friction stir welding), high-frequency welding, hot pressure welding, induction welding, and roll welding.

Soft and strong welding

Soft soldering and brazing are processes in which the fusion of the base metals does not occur, but only the filler metal. Being the first welding process used by man, already in ancient Sumeria.

Arc welding

These are, in fact, different welding systems, which have in common the use of an electrical power source. This is used to generate an electric arc between an electrode and the base material, which melts the metals at the point of welding. Both direct current (DC) and alternating current (AC) can be used, and they include consumable or non-consumable electrodes, which are covered by a material called coating. Sometimes the weld area is protected by a certain type of inert or semi-inert gas, known as shielding gas), and sometimes a filler material is used.

To provide the electrical energy necessary for arc welding processes, different power sources can be used. The most common classification of these sources is to separate those of constant current and those of constant voltage. In arc welding, the length of the arc is directly related to the voltage, and the amount of heat generated is related to the intensity of the current. Constant current power supplies are most often used for manual welding processes such as gas tungsten arc welding and shielded metal arc welding, because they maintain a constant current even as the voltage varies. This is important in manual welding, as it can be difficult to hold the electrode perfectly stable, and as a result, the arc length and voltage tend to fluctuate. Constant voltage power supplies maintain this and vary the current. As a result, they are most often used for automated welding processes such as gas metal arc welding, flux core arc welding, and submerged arc welding. In these processes, the arc length is kept constant, since any fluctuation in the distance between electrode and base material is quickly rectified by a large change in current. If the wire and the base material become too close, the current will increase rapidly, which, in turn, causes an increase in heat and this causes the end of the wire to melt, thus returning it to its original separation distance.[12]​.

The type of current used in arc welding also plays an important role. Consumable process electrodes such as those in shielded metal arc welding and gas metal arc welding generally use direct (direct) current, so the electrode can be positively or negatively charged, depending on how the electrode connections are made. In welding, if the electrode is positively charged, more heat will be generated in it, and as a result, the weld will be more superficial (as the base material will hardly melt). If the electrode is negatively charged, the base metal will be hotter, increasing filler penetration and welding speed.[13] Non-consumable electrode processes, such as gas arc and tungsten electrode welding, can use both types of direct current, as well as alternating current. As in the aforementioned case, a positively charged electrode causes superficial welds and a negatively charged electrode also causes deeper welds.[14]​ If alternating current is used, by constantly and quickly reversing the electrical polarity, intermediate penetration welds are achieved. A disadvantage of AC, the fact that the arc cancels out with each polarity reversal, has been overcome with the invention of special power units that produce a square wave pattern, instead of the normal sine wave pattern, generating very rapid zero crossings that minimize the effects of the arc fading problem.[15]​.

One of the most common types of arc welding is shielded metal arc welding (SMAW), which is also known as manual metal arc welding (MMA) or stick welding. Electrical current is used to create an arc between the base material and the consumable electrode rod, which is made of steel and coated with a flux that protects the weld area from oxidation and contamination through the production of CO gas during the welding process. The core of the electrode itself acts as a filler material, making additional filler material unnecessary.

The process is versatile and can be performed with relatively inexpensive equipment, making it suitable for home and field work.[16] An operator can become reasonably competent with a modest amount of training and can achieve mastery with experience. Welding times are somewhat slow, since consumable electrodes must be replaced frequently and because slag, the residue of the flux, must be removed after welding.[17] Additionally, the process is generally limited to ferrous welding materials, although specialized electrodes have made possible the welding of cast iron, nickel, aluminum, copper, stainless steel, and other metals.

Gas Metal Arc Welding (GMAW), also known as MIG (Metal Inert Gas) and MAG (Metal Active Gas) welding, is a semi-automatic or automatic process that uses a continuous feed of wire as an electrode and a mixture of inert or semi-inert gas to protect the weld from contamination. As with SMAW, reasonable operator skill can be achieved with modest training. Since the electrode is injected continuously, welding speeds are higher for GMAW than for SMAW. Also, the smaller arc size, compared to shielded metal arc welding processes, makes it easier to make welds in complicated positions (e.g., overhead splices, as would be the case when welding underneath a structure).

The equipment required to perform the GMAW process is more complex and expensive than that required for SMAW, and requires a more complex preparation procedure. The GMAW is therefore less portable and versatile, and, due to the use of a separate shielding gas, is not particularly suitable for outdoor work. However, the higher average speed than SMAW makes GMAW more suitable for production welding. The process can be applied to a wide variety of metals, both ferrous and non-ferrous.[18]​.

A related process, flux core arc welding (FCAW), uses similar equipment but uses a wire consisting of a steel electrode filled with a powder material. This nucleated wire is more expensive than standard solid wire and can generate fumes and/or slag, but allows for even higher welding speeds and greater metal penetration.[19]​.

Gas tungsten arc welding (GTAW), or tungsten inert gas (TIG) welding (also sometimes mistakenly referred to as heliarc welding), is a manual welding process that uses a non-consumable tungsten electrode, an inert or semi-inert gas mixture, and a separate filler material. Especially useful for welding thin materials, this method is characterized by a stable arc and a high-quality weld, but requires significant operator skill and only gives relatively low working speeds.

GTAW can be used on almost all weldable metals, although it is most often applied to stainless steel alloys and light metals. It is used where quality welds are extremely important, for example in the manufacture of bicycle frames, aircraft, and naval applications. wider range of thick materials than in the case of GTAW, and it is also much faster than this. It is applied to the same materials as GTAW except for magnesium, and the automated welding of stainless steel is a notable application of this system is plasma cutting, an efficient system for cutting steel.[21]​.

Submerged arc welding (SAW) is a high-productivity welding method in which the arc is generated immersed in a fluid. This increases the quality of the arc, since contaminants from the atmosphere are displaced by the fluid. The slag that forms the weld generally comes out on its own, and, combined with the use of a continuous wire feed, the deposition rate of the weld is high. Working conditions are greatly improved compared to other arc welding systems, since the fluid hides The arc and thus almost no smoke is produced. This system is commonly used in industry, especially for large products and in the manufacture of welded pressure vessels.[22] Other arc welding processes include atomic hydrogen welding, carbon arc welding, electroslag welding, electrogas welding, and stud arc welding.

gas welding

The most common gas welding process is oxyacetylene welding, also known as autogenous welding or oxy-fuel welding. It is one of the oldest and most versatile welding processes, but in recent years it has become less popular in industrial applications. It is still used extensively for welding pipes and tubes, as well as for repair work. The equipment is relatively cheap and simple, generally employing the combustion of acetylene in oxygen to produce a welding flame temperature of about 3100 °C. Since the flame is less concentrated than an electric arc, it causes slower cooling of the weld, which can lead to higher residual stresses and weld distortion, although it makes welding of high-alloy steels easier. A similar process, generally called oxyfuel cutting, is used to cut metals.[5] Other methods of gas welding, such as acetylene-oxygen welding, hydrogen-oxygen welding, and pressure gas welding, are very similar, usually differing only in the type of gases used. A water torch is sometimes used for precision welding of items such as jewelry. Gas welding is also used in plastic welding, although the substance is heated. It's air, and the temperatures are much lower.

resistance welding

Resistance welding involves the generation of heat by passing electrical current through two or more metal surfaces. Small pools of molten metal form in the weld area as the high current (1,000 to 100,000 A) passes through the metal. In general, resistance welding methods are efficient and cause little pollution, but their applications are somewhat limited and the cost of the equipment can be high.

Spot welding is a popular resistance welding method used to join together overlapping sheets of metal up to 3mm thick. Two electrodes are used simultaneously to hold the metal sheets together and to pass current through them. Advantages of the method include efficient use of energy, limited workpiece deformation, high production speeds, easy automation, and no requirement for filler materials. The welding strength is significantly lower than with other welding methods, making the process only suitable for certain applications. It is used extensively in the automobile industry. Ordinary cars can have several thousand welded points made by industrial robots. A specialized process, called shock welding, can be used to spot weld stainless steel.

Like spot welding, seam welding relies on two electrodes to apply pressure and current to join sheets of metal. However, instead of point electrodes, wheel-shaped electrodes roll along and often feed the workpiece, making long continuous welds possible. In the past, this process was used in the manufacture of beverage cans, but now its uses are more limited. Other resistance welding methods include flash welding, projection welding, and dump welding.[23]

energy beam welding

Energy beam welding methods, called laser beam welding and electron beam welding, are relatively new processes that have become quite popular in high production applications. The two processes are very similar, differing most notably in their energy source. Laser beam welding employs a highly focused laser beam, while electron beam welding is done in a vacuum and uses a beam of electrons. Both have a very high energy density, making deep weld penetration possible and minimizing the size of the weld area. Both processes are extremely fast, and are easy to automate, making them highly productive. The primary disadvantages are their very high equipment costs (although these are decreasing) and a susceptibility to cracking. Developments in this area include hybrid laser welding), which uses the principles of laser beam welding and arc welding for even better welding properties.[24]​.

Welds can be geometrically prepared in many different ways. The five basic types of solder joints are the end joint, lap joint, corner joint, edge joint, and T-joint. There are other variations, such as the preparation of double-V joints, characterized by two pieces of material each tapering to a single central point at half its height. The preparation of single-U and double-U joints are also quite common—instead of having straight edges like the preparation of single-V and double-V joints, they are curved, having the shape of a U. Lap joints are also commonly more than two thick pieces—depending on the process used and the thickness of the material, many pieces can be welded together in a lap joint geometry.[25]​.

Often, certain welding processes exclusively or almost exclusively use particular joint designs. For example, resistance spot welding, laser beam welding, and electron beam welding are most frequently performed with lap joints. However, some welding methods, such as shielded metal arc welding, are extremely versatile and can weld virtually any type of joint. Additionally, some processes can be used to make multi-pass welds, in which one weld is allowed to cool, and then another weld is made on top of the first. This allows, for example, the welding of thick sections arranged in a single-V joint preparation.[26]​.

After welding, a number of distinct regions can be identified in the weld area. The weld itself is called the fusion zone—more specifically, this is where the filler metal was placed during the welding process. The properties of the fusion zone depend primarily on the filler metal used, and its compatibility with the base materials. It is surrounded by the "heat affected zone", the area that has had its microstructure and properties altered by welding. These properties depend on the behavior of the base material when subjected to heat. The metal in this area is often weaker than the base material and the fusion zone, and is also where residual stresses are found.[27]​.

Contenido

Muy a menudo, la medida principal usada para juzgar la calidad de una soldadura es su fortaleza y la fortaleza del material alrededor de ella. Muchos factores distintos influyen en esto, incluyendo el método de soldadura, la cantidad y la concentración de la entrada de calor, el material base, el material de relleno, el material fundente, el diseño del empalme, y las interacciones entre todos estos factores. Para probar la calidad de una soldadura se usan tanto ensayos no destructivos como ensayos destructivos"), para verificar que las soldaduras están libres de defectos, tienen niveles aceptables de tensiones y distorsión residuales, y tienen propiedades aceptables de zona afectada por el calor (HAZ). Existen códigos y especificaciones de soldadura para guiar a los soldadores en técnicas apropiadas de soldadura y en cómo juzgar la calidad estas.

Heat affected zone

The effects of welding can be detrimental to the material surrounding the weld. Depending on the materials used and the heat input of the welding process used, the heat affected zone (HAZ) can vary in size and strength. The thermal diffusivity of the base material is very important; If the diffusivity is high, the cooling rate of the material is high and the HAZ is relatively small. Conversely, low diffusivity leads to slower cooling and a larger HAZ. The amount of heat injected by the welding process also plays an important role, since processes such as oxyacetylene welding have an input of non-concentrated heat and increase the size of the affected zone. Processes such as laser beam welding have a highly concentrated and limited amount of heat, resulting in a small HAZ. Arc welding falls between these two extremes, with individual processes varying somewhat in heat input.[28]​[29]​ To calculate heat for arc welding procedures, the following formula can be used:.

Distortion and cracking

Welding methods that involve melting the metal at the splice site are necessarily prone to shrinkage&action=edit&redlink=1 "Shrinkage (welding) (not yet redacted)") as the heated metal cools. In turn, shrinkage can introduce residual stresses and both longitudinal and rotational distortion. Distortion can pose a significant problem, since the final product does not have the desired shape. To alleviate rotational distortion, workpieces can be offset so that welding results in a properly formed part.[31] Other methods of limiting distortion, such as clamping workpieces in place, cause residual stress to build up in the heat-affected zone of the base material. These stresses can reduce the strength of the base material, and can lead to catastrophic failure by cold cracking, as in the case of several of the Liberty ships&action=edit&redlink=1 "Liberty (ship) (not yet redacted)"). Cold cracking is limited to steels, and is associated with the formation of martensite as the weld cools. Cracking occurs in the heat affected zone of the base material. To reduce the amount of distortion and residual stress, the amount of heat input should be limited, and the welding sequence used should not be from one end directly to the other, but rather in segments. The other type of cracking, hot cracking or solidification cracking, can occur in all metals, and occurs in the fusion zone of the weld. To decrease the probability of this type of cracking, excess restraint material should be avoided, and an appropriate filler material should be used.[32]​.

Weldability

The quality of a weld also depends on the combination of materials used for the base material and filler material. Not all metals are suitable for welding, and not all filler metals work well with acceptable base materials.

It is necessary to take into account 60% of the smallest base thickness of the plates to be joined for use in one of the welding legs.

The weldability of steels is inversely proportional to a property known as the hardenability of the steel, which measures the probability of martensite forming during welding or heat treatment. The hardenability of steel depends on its chemical composition, with greater amounts of carbon and other alloying elements resulting in greater hardenability and therefore lower weldability. In order to judge alloys composed of many different materials, a measure known as the carbon equivalent content) is used to compare the relative weldability of steels. different alloys comparing their properties to simple carbon steel. The effect on the weldability of elements such as chromium and vanadium, while not as great as that of carbon, is for example more significant than that of copper and nickel. As the carbon equivalent content increases, the weldability of the alloy decreases.[33]​ The disadvantage of using simple carbon and low alloy steels is their lower strength – there is a trade-off between material strength and weldability. High-strength, low-alloy steels were developed especially for welding uses during the 1970s, and these generally easy-to-weld materials have good strength, making them ideal for many welding applications.[34]

Due to their high chromium content, stainless steels tend to behave differently than other steels with respect to weldability. Austenitic grades of stainless steels tend to be more weldable, but are especially susceptible to distortion due to their high coefficient of thermal expansion. Some alloys of this type are prone to cracking and also have reduced corrosion resistance. If the amount of ferrite "Ferrite (iron)") in the weld is not controlled, hot cracking is possible. To alleviate the problem, an electrode is used that deposits a weld metal containing a small amount of ferrite. Other types of stainless steels, such as ferritic and martensitic stainless steels, are not easily weldable, and often must be preheated and welded with special electrodes.[35]​.

The weldability of aluminum alloys varies significantly depending on the chemical composition of the alloy used. Aluminum alloys are susceptible to hot cracking, and to combat the problem welders increase welding speed to reduce heat input. Preheating reduces the temperature gradient across the weld zone and therefore helps reduce hot cracking, but can reduce the mechanical characteristics of the base material and should not be used when the base material is restricted. The splice design can also be changed, and a more compatible filler alloy can be selected to decrease the likelihood of hot cracking. Aluminum alloys must also be cleaned before welding, in order to remove all oxides, oils, and loose particles from the surface to be welded. This is especially important due to the susceptibility of an aluminum weld to porosity due to hydrogen and slag "Slag (metalworking)") due to oxygen.[36]​.

Although many welding applications take place in controlled environments such as factories and repair shops, some welding processes are frequently used in a wide variety of conditions, such as in open air, underwater, and in vacuums (such as in space). In outdoor uses, such as outdoor construction and repair, shielded metal arc welding is the most common process. Processes that use inert gases to protect the weld cannot easily be used in such situations, because unpredictable atmospheric movements can result in a failed weld. Shielded metal arc welding is also often used in underwater welding in the construction and repair of ships, offshore platforms, and pipelines, but others are also common, such as flux-cored arc welding and gas tungsten arc welding. Welding in space is also possible, first attempted in 1969 by Russian cosmonauts, when they conducted experiments to test shielded metal arc welding, plasma arc welding, and electron beam welding in a depressurized environment. Additional testing of these methods was done in the following decades, and today researchers continue to develop methods for using other welding processes in space, such as laser beam welding, resistance welding, and friction welding. Advances in these areas could prove indispensable for projects such as the construction of the International Space Station, which will likely make extensive use of welding to join parts manufactured on Earth in space.[37]​.

Welding without proper precautions can be a dangerous and harmful practice for your health. However, with the use of new technology and proper protection, the risks of injury or death associated with welding can be virtually eliminated. The risk of burns or electrocution is significant because many common welding procedures involve an open electric arc or flame. To prevent them, welders should wear protective clothing, such as approved footwear, thick leather gloves, and long-sleeved protective jackets to prevent exposure to sparks, heat, and possible flames. In addition, exposure to the glare of the welding area produces an injury called "arc eye" (keratitis) due to the effect of ultraviolet light that inflames the cornea and can burn the retinas. Protective glasses and welding helmets and helmets with dark glass filters are used to prevent this exposure, and in recent years new models of helmets have been marketed in which the glass filter is transparent and allows the work area to be seen when there is no UV radiation, but auto-darkens as soon as UV radiation occurs. To protect spectators, for safety, translucent screens or curtains should be used to surround the welding area. These curtains, made of a polyvinyl chloride plastic film, protect nearby workers from exposure to UV light from the electric arc, but should not be used to replace the glass filter used in welder helmets and face shields.[38]​.

Welders are also often exposed to hazardous gases and fine airborne particles. Processes such as flux-cored arc welding and shielded metal arc welding produce smoke containing particles of various types of oxides, which in some cases can produce medical conditions such as metal vapor fever. The size of the particles in question influences the toxicity of the vapors, with smaller particles presenting a greater danger. In addition, many processes produce vapors and various gases, commonly carbon dioxide, ozone and heavy metals, which can be dangerous without proper ventilation and protection. For this type of work, An FFP3 particulate respirator or welding mask is usually worn. Due to the use of compressed gases and flames, many welding processes pose a risk of explosion and fire. Common precautions include limiting the amount of oxygen in the air and keeping combustible materials away from the workplace.[38]​.

As in any industrial process, the cost of welding plays a crucial role in production decisions. Many different variables affect the total cost, including equipment cost, labor cost, material cost, and electrical energy cost. Depending on the process, the cost of the equipment can vary, from cheap for methods such as shielded metal arc welding and oxyfuel welding, to extremely expensive for methods such as laser beam welding and electron beam welding. Due to their high cost, these are only used in high production operations. Similarly, because automation and robots increase equipment costs, they are only implemented when high production is necessary. Labor cost depends on deposition rate (welding speed), hourly wage, and total operating time, including welding and part handling time. The cost of materials includes the cost of the base and filler material and the cost of shielding gases. Finally, the energy cost depends on the arc time and the energy consumption of the welding.

For manual welding methods, labor costs are generally the vast majority of the total cost. As a result, many cost-saving measures focus on minimizing operating time. To do this, welding procedures with high deposition rates can be selected and the welding parameters can be adjusted to increase the welding speed. Mechanization and automation are frequently implemented to reduce labor costs, but this often increases the cost of equipment and creates additional setup time. Material costs tend to increase when special properties are necessary in them and energy costs normally do not add up to more than a percentage of the total welding cost.[39]​.

In recent years, to minimize labor costs in high-production manufacturing, industrial welding has become increasingly automated, most notably with the use of robots in resistance spot welding (especially in the automotive industry) and arc welding. In robotic welding, mechanical devices hold the material and perform the welding,[40]​ and initially, spot welding was its most common use. But robotic arc welding has increased in popularity as technology has advanced. Other key areas of research and development include welding of dissimilar materials (such as steel and aluminum) and new welding processes. In addition, progress is being made to make specialized methods such as laser beam welding practical for more applications, for example in the aerospace and automotive industries. Researchers also hope to better understand the often unpredictable properties of welds, especially microstructure, residual stresses, and the tendency of a weld to crack or deform.[41]

The history of welding dates back several millennia, with the first examples of welding dating back to the Bronze Age and Iron Age in Europe and the Middle East. Welding was used in the construction of the Iron Pillar of Delhi, India, erected around the year 310 and weighing 5.4 metric tons.[1] The Middle Ages brought advances in forge welding, with which blacksmiths repeatedly struck and heated the metal until a union occurred. In 1540, Vannoccio Biringuccio published De la pirotechnia, which includes descriptions of the forging operation. Renaissance craftsmen were skilled at the process, and the industry continued to develop over the following centuries.[2] However, welding was transformed during the 19th century. In 1800, Sir Humphry Davy discovered the electric arc, and advances in arc welding continued with the inventions of metal electrodes by the Russian Nikolai Slavyanov and the American C. L. Coffin in the late 1800s. Even carbon arc welding, which used a carbon electrode, gained popularity. Around 1900, A. P. Strohmenger" launched a coated metal electrode in Britain, which gave a more stable arc, and in 1919, alternating current welding was invented by C. J. Holslag"), but it did not become popular for another decade.[3]

Resistance welding was also developed during the final decades of the 19th century, with the first patents in the sector held by Elihu Thomson" in 1885, who produced further advances over the next 15 years. Thermite welding was invented in 1893, and around that time, another process, gas welding, was established. Acetylene was discovered in 1836 by Edmund Davy"), but its use in welding was not practical until about 1900, when A convenient torch was developed.[4] At first, gas welding was one of the most popular welding methods due to its portability and relatively low cost. However, as the 20th century progressed, preferences for industrial applications declined. It was largely replaced by arc welding, as metal covers for the electrode (known as flux) continued to be developed, which stabilized the arc and shielded the base material from impurities.[5]​.

World War I caused a major uptick in the use of welding processes, with different military forces seeking to determine which of the various new welding processes would be best. The British primarily used arc welding, even constructing a ship, the Fulagar, with an entirely welded hull. The Americans were more hesitant, but began to recognize the benefits of arc welding when the process allowed them to quickly repair their ships after German attacks in New York Harbor early in the war. Arc welding was also applied for the first time to airplanes during the war, as some German airplane fuselages were built using the process.[6]​.

During the 1920s, important advances were made in welding technology, including the introduction of automatic welding in 1920, in which the electrode wire was fed continuously. Shielding gas became an important issue, as scientists sought to protect welds against the effects of oxygen and nitrogen in the atmosphere. Porosity and fragility were the basic problems arising from this exchange, and the solutions they developed included the use of hydrogen, argon, and helium as welding shielding gases.[7] Over the next decade, further advances allowed the welding of reactive metals such as aluminum and magnesium. This, together with developments in automatic welding, alternating current welding, and fluxes, fueled a significant expansion of arc welding during the 1930s and during World War II.[8]​.

In the mid-20th century, many new welding methods were invented. The 1930s saw the launch of stud welding, which soon became popular in ship manufacturing and construction. Submerged arc welding was invented the same year, and remains popular today. In 1941, after decades of development, tungsten electrode gas arc welding was finally perfected, followed in 1948 by gas metal arc welding, allowing rapid welding of non-ferrous materials but requiring costly shielding gases. Shielded metal arc welding was developed during the 1950s, using a covered consumable electrode flux, and quickly became the most popular. In 1957, the flux-cored arc welding process debuted), in which the self-shielded wire electrode It could be used with automatic equipment, resulting in greatly increased welding speeds, and that same year plasma arc welding was invented. Electroslag welding was introduced in 1958, and was followed in 1961 by its cousin, electrogas welding.

Other recent developments in welding include the important achievement of electron beam welding in 1958, making deep, narrow welding possible by means of the concentrated heat source. Following the invention of the laser in 1960, laser beam welding debuted several decades later, and has proven especially useful in high-speed automated welding. However, both processes remain highly expensive due to the high cost of the necessary equipment, and this has limited their applications.[10]​.

solid state welding

Like the first welding process, forge welding, some modern welding methods do not involve melting the materials being joined. One of the most popular, ultrasonic welding, is used to connect sheets or thin wires made of metal or thermoplastics, making them vibrate at high frequency and under high pressure. The equipment and methods involved are similar to resistance welding, but instead of electrical current, vibration provides the energy source. Welding metals with this process does not involve melting the materials; Instead, the weld is formed by introducing mechanical vibrations horizontally under pressure. When plastics are being welded, the materials must have similar melting temperatures, and vibrations are introduced vertically. Ultrasonic welding is commonly used to make electrical connections from aluminum or copper, and is also a very common polymer welding process.

Another common process, explosive welding, involves joining materials by pushing them together under extremely high pressure. The energy of the impact plasticizes the materials, forming a weld, although only a limited amount of heat is generated. The process is commonly used for welding dissimilar materials, such as welding aluminum to steel in ship hulls or composite plates. Other solid-state welding processes include coextrusion welding, cold welding, diffusion welding, friction welding (including friction stir welding), high-frequency welding, hot pressure welding, induction welding, and roll welding.

Soft and strong welding

Soft soldering and brazing are processes in which the fusion of the base metals does not occur, but only the filler metal. Being the first welding process used by man, already in ancient Sumeria.

Arc welding

These are, in fact, different welding systems, which have in common the use of an electrical power source. This is used to generate an electric arc between an electrode and the base material, which melts the metals at the point of welding. Both direct current (DC) and alternating current (AC) can be used, and they include consumable or non-consumable electrodes, which are covered by a material called coating. Sometimes the weld area is protected by a certain type of inert or semi-inert gas, known as shielding gas), and sometimes a filler material is used.

To provide the electrical energy necessary for arc welding processes, different power sources can be used. The most common classification of these sources is to separate those of constant current and those of constant voltage. In arc welding, the length of the arc is directly related to the voltage, and the amount of heat generated is related to the intensity of the current. Constant current power supplies are most often used for manual welding processes such as gas tungsten arc welding and shielded metal arc welding, because they maintain a constant current even as the voltage varies. This is important in manual welding, as it can be difficult to hold the electrode perfectly stable, and as a result, the arc length and voltage tend to fluctuate. Constant voltage power supplies maintain this and vary the current. As a result, they are most often used for automated welding processes such as gas metal arc welding, flux core arc welding, and submerged arc welding. In these processes, the arc length is kept constant, since any fluctuation in the distance between electrode and base material is quickly rectified by a large change in current. If the wire and the base material become too close, the current will increase rapidly, which, in turn, causes an increase in heat and this causes the end of the wire to melt, thus returning it to its original separation distance.[12]​.

The type of current used in arc welding also plays an important role. Consumable process electrodes such as those in shielded metal arc welding and gas metal arc welding generally use direct (direct) current, so the electrode can be positively or negatively charged, depending on how the electrode connections are made. In welding, if the electrode is positively charged, more heat will be generated in it, and as a result, the weld will be more superficial (as the base material will hardly melt). If the electrode is negatively charged, the base metal will be hotter, increasing filler penetration and welding speed.[13] Non-consumable electrode processes, such as gas arc and tungsten electrode welding, can use both types of direct current, as well as alternating current. As in the aforementioned case, a positively charged electrode causes superficial welds and a negatively charged electrode also causes deeper welds.[14]​ If alternating current is used, by constantly and quickly reversing the electrical polarity, intermediate penetration welds are achieved. A disadvantage of AC, the fact that the arc cancels out with each polarity reversal, has been overcome with the invention of special power units that produce a square wave pattern, instead of the normal sine wave pattern, generating very rapid zero crossings that minimize the effects of the arc fading problem.[15]​.

One of the most common types of arc welding is shielded metal arc welding (SMAW), which is also known as manual metal arc welding (MMA) or stick welding. Electrical current is used to create an arc between the base material and the consumable electrode rod, which is made of steel and coated with a flux that protects the weld area from oxidation and contamination through the production of CO gas during the welding process. The core of the electrode itself acts as a filler material, making additional filler material unnecessary.

The process is versatile and can be performed with relatively inexpensive equipment, making it suitable for home and field work.[16] An operator can become reasonably competent with a modest amount of training and can achieve mastery with experience. Welding times are somewhat slow, since consumable electrodes must be replaced frequently and because slag, the residue of the flux, must be removed after welding.[17] Additionally, the process is generally limited to ferrous welding materials, although specialized electrodes have made possible the welding of cast iron, nickel, aluminum, copper, stainless steel, and other metals.

Gas Metal Arc Welding (GMAW), also known as MIG (Metal Inert Gas) and MAG (Metal Active Gas) welding, is a semi-automatic or automatic process that uses a continuous feed of wire as an electrode and a mixture of inert or semi-inert gas to protect the weld from contamination. As with SMAW, reasonable operator skill can be achieved with modest training. Since the electrode is injected continuously, welding speeds are higher for GMAW than for SMAW. Also, the smaller arc size, compared to shielded metal arc welding processes, makes it easier to make welds in complicated positions (e.g., overhead splices, as would be the case when welding underneath a structure).

The equipment required to perform the GMAW process is more complex and expensive than that required for SMAW, and requires a more complex preparation procedure. The GMAW is therefore less portable and versatile, and, due to the use of a separate shielding gas, is not particularly suitable for outdoor work. However, the higher average speed than SMAW makes GMAW more suitable for production welding. The process can be applied to a wide variety of metals, both ferrous and non-ferrous.[18]​.

A related process, flux core arc welding (FCAW), uses similar equipment but uses a wire consisting of a steel electrode filled with a powder material. This nucleated wire is more expensive than standard solid wire and can generate fumes and/or slag, but allows for even higher welding speeds and greater metal penetration.[19]​.

Gas tungsten arc welding (GTAW), or tungsten inert gas (TIG) welding (also sometimes mistakenly referred to as heliarc welding), is a manual welding process that uses a non-consumable tungsten electrode, an inert or semi-inert gas mixture, and a separate filler material. Especially useful for welding thin materials, this method is characterized by a stable arc and a high-quality weld, but requires significant operator skill and only gives relatively low working speeds.

GTAW can be used on almost all weldable metals, although it is most often applied to stainless steel alloys and light metals. It is used where quality welds are extremely important, for example in the manufacture of bicycle frames, aircraft, and naval applications. wider range of thick materials than in the case of GTAW, and it is also much faster than this. It is applied to the same materials as GTAW except for magnesium, and the automated welding of stainless steel is a notable application of this system is plasma cutting, an efficient system for cutting steel.[21]​.

Submerged arc welding (SAW) is a high-productivity welding method in which the arc is generated immersed in a fluid. This increases the quality of the arc, since contaminants from the atmosphere are displaced by the fluid. The slag that forms the weld generally comes out on its own, and, combined with the use of a continuous wire feed, the deposition rate of the weld is high. Working conditions are greatly improved compared to other arc welding systems, since the fluid hides The arc and thus almost no smoke is produced. This system is commonly used in industry, especially for large products and in the manufacture of welded pressure vessels.[22] Other arc welding processes include atomic hydrogen welding, carbon arc welding, electroslag welding, electrogas welding, and stud arc welding.

gas welding

The most common gas welding process is oxyacetylene welding, also known as autogenous welding or oxy-fuel welding. It is one of the oldest and most versatile welding processes, but in recent years it has become less popular in industrial applications. It is still used extensively for welding pipes and tubes, as well as for repair work. The equipment is relatively cheap and simple, generally employing the combustion of acetylene in oxygen to produce a welding flame temperature of about 3100 °C. Since the flame is less concentrated than an electric arc, it causes slower cooling of the weld, which can lead to higher residual stresses and weld distortion, although it makes welding of high-alloy steels easier. A similar process, generally called oxyfuel cutting, is used to cut metals.[5] Other methods of gas welding, such as acetylene-oxygen welding, hydrogen-oxygen welding, and pressure gas welding, are very similar, usually differing only in the type of gases used. A water torch is sometimes used for precision welding of items such as jewelry. Gas welding is also used in plastic welding, although the substance is heated. It's air, and the temperatures are much lower.

resistance welding

Resistance welding involves the generation of heat by passing electrical current through two or more metal surfaces. Small pools of molten metal form in the weld area as the high current (1,000 to 100,000 A) passes through the metal. In general, resistance welding methods are efficient and cause little pollution, but their applications are somewhat limited and the cost of the equipment can be high.

Spot welding is a popular resistance welding method used to join together overlapping sheets of metal up to 3mm thick. Two electrodes are used simultaneously to hold the metal sheets together and to pass current through them. Advantages of the method include efficient use of energy, limited workpiece deformation, high production speeds, easy automation, and no requirement for filler materials. The welding strength is significantly lower than with other welding methods, making the process only suitable for certain applications. It is used extensively in the automobile industry. Ordinary cars can have several thousand welded points made by industrial robots. A specialized process, called shock welding, can be used to spot weld stainless steel.

Like spot welding, seam welding relies on two electrodes to apply pressure and current to join sheets of metal. However, instead of point electrodes, wheel-shaped electrodes roll along and often feed the workpiece, making long continuous welds possible. In the past, this process was used in the manufacture of beverage cans, but now its uses are more limited. Other resistance welding methods include flash welding, projection welding, and dump welding.[23]

energy beam welding

Energy beam welding methods, called laser beam welding and electron beam welding, are relatively new processes that have become quite popular in high production applications. The two processes are very similar, differing most notably in their energy source. Laser beam welding employs a highly focused laser beam, while electron beam welding is done in a vacuum and uses a beam of electrons. Both have a very high energy density, making deep weld penetration possible and minimizing the size of the weld area. Both processes are extremely fast, and are easy to automate, making them highly productive. The primary disadvantages are their very high equipment costs (although these are decreasing) and a susceptibility to cracking. Developments in this area include hybrid laser welding), which uses the principles of laser beam welding and arc welding for even better welding properties.[24]​.

Welds can be geometrically prepared in many different ways. The five basic types of solder joints are the end joint, lap joint, corner joint, edge joint, and T-joint. There are other variations, such as the preparation of double-V joints, characterized by two pieces of material each tapering to a single central point at half its height. The preparation of single-U and double-U joints are also quite common—instead of having straight edges like the preparation of single-V and double-V joints, they are curved, having the shape of a U. Lap joints are also commonly more than two thick pieces—depending on the process used and the thickness of the material, many pieces can be welded together in a lap joint geometry.[25]​.

Often, certain welding processes exclusively or almost exclusively use particular joint designs. For example, resistance spot welding, laser beam welding, and electron beam welding are most frequently performed with lap joints. However, some welding methods, such as shielded metal arc welding, are extremely versatile and can weld virtually any type of joint. Additionally, some processes can be used to make multi-pass welds, in which one weld is allowed to cool, and then another weld is made on top of the first. This allows, for example, the welding of thick sections arranged in a single-V joint preparation.[26]​.

After welding, a number of distinct regions can be identified in the weld area. The weld itself is called the fusion zone—more specifically, this is where the filler metal was placed during the welding process. The properties of the fusion zone depend primarily on the filler metal used, and its compatibility with the base materials. It is surrounded by the "heat affected zone", the area that has had its microstructure and properties altered by welding. These properties depend on the behavior of the base material when subjected to heat. The metal in this area is often weaker than the base material and the fusion zone, and is also where residual stresses are found.[27]​.

Contenido

Muy a menudo, la medida principal usada para juzgar la calidad de una soldadura es su fortaleza y la fortaleza del material alrededor de ella. Muchos factores distintos influyen en esto, incluyendo el método de soldadura, la cantidad y la concentración de la entrada de calor, el material base, el material de relleno, el material fundente, el diseño del empalme, y las interacciones entre todos estos factores. Para probar la calidad de una soldadura se usan tanto ensayos no destructivos como ensayos destructivos"), para verificar que las soldaduras están libres de defectos, tienen niveles aceptables de tensiones y distorsión residuales, y tienen propiedades aceptables de zona afectada por el calor (HAZ). Existen códigos y especificaciones de soldadura para guiar a los soldadores en técnicas apropiadas de soldadura y en cómo juzgar la calidad estas.

Heat affected zone

The effects of welding can be detrimental to the material surrounding the weld. Depending on the materials used and the heat input of the welding process used, the heat affected zone (HAZ) can vary in size and strength. The thermal diffusivity of the base material is very important; If the diffusivity is high, the cooling rate of the material is high and the HAZ is relatively small. Conversely, low diffusivity leads to slower cooling and a larger HAZ. The amount of heat injected by the welding process also plays an important role, since processes such as oxyacetylene welding have an input of non-concentrated heat and increase the size of the affected zone. Processes such as laser beam welding have a highly concentrated and limited amount of heat, resulting in a small HAZ. Arc welding falls between these two extremes, with individual processes varying somewhat in heat input.[28]​[29]​ To calculate heat for arc welding procedures, the following formula can be used:.

Distortion and cracking

Welding methods that involve melting the metal at the splice site are necessarily prone to shrinkage&action=edit&redlink=1 "Shrinkage (welding) (not yet redacted)") as the heated metal cools. In turn, shrinkage can introduce residual stresses and both longitudinal and rotational distortion. Distortion can pose a significant problem, since the final product does not have the desired shape. To alleviate rotational distortion, workpieces can be offset so that welding results in a properly formed part.[31] Other methods of limiting distortion, such as clamping workpieces in place, cause residual stress to build up in the heat-affected zone of the base material. These stresses can reduce the strength of the base material, and can lead to catastrophic failure by cold cracking, as in the case of several of the Liberty ships&action=edit&redlink=1 "Liberty (ship) (not yet redacted)"). Cold cracking is limited to steels, and is associated with the formation of martensite as the weld cools. Cracking occurs in the heat affected zone of the base material. To reduce the amount of distortion and residual stress, the amount of heat input should be limited, and the welding sequence used should not be from one end directly to the other, but rather in segments. The other type of cracking, hot cracking or solidification cracking, can occur in all metals, and occurs in the fusion zone of the weld. To decrease the probability of this type of cracking, excess restraint material should be avoided, and an appropriate filler material should be used.[32]​.

Weldability

The quality of a weld also depends on the combination of materials used for the base material and filler material. Not all metals are suitable for welding, and not all filler metals work well with acceptable base materials.

It is necessary to take into account 60% of the smallest base thickness of the plates to be joined for use in one of the welding legs.

The weldability of steels is inversely proportional to a property known as the hardenability of the steel, which measures the probability of martensite forming during welding or heat treatment. The hardenability of steel depends on its chemical composition, with greater amounts of carbon and other alloying elements resulting in greater hardenability and therefore lower weldability. In order to judge alloys composed of many different materials, a measure known as the carbon equivalent content) is used to compare the relative weldability of steels. different alloys comparing their properties to simple carbon steel. The effect on the weldability of elements such as chromium and vanadium, while not as great as that of carbon, is for example more significant than that of copper and nickel. As the carbon equivalent content increases, the weldability of the alloy decreases.[33]​ The disadvantage of using simple carbon and low alloy steels is their lower strength – there is a trade-off between material strength and weldability. High-strength, low-alloy steels were developed especially for welding uses during the 1970s, and these generally easy-to-weld materials have good strength, making them ideal for many welding applications.[34]

Due to their high chromium content, stainless steels tend to behave differently than other steels with respect to weldability. Austenitic grades of stainless steels tend to be more weldable, but are especially susceptible to distortion due to their high coefficient of thermal expansion. Some alloys of this type are prone to cracking and also have reduced corrosion resistance. If the amount of ferrite "Ferrite (iron)") in the weld is not controlled, hot cracking is possible. To alleviate the problem, an electrode is used that deposits a weld metal containing a small amount of ferrite. Other types of stainless steels, such as ferritic and martensitic stainless steels, are not easily weldable, and often must be preheated and welded with special electrodes.[35]​.

The weldability of aluminum alloys varies significantly depending on the chemical composition of the alloy used. Aluminum alloys are susceptible to hot cracking, and to combat the problem welders increase welding speed to reduce heat input. Preheating reduces the temperature gradient across the weld zone and therefore helps reduce hot cracking, but can reduce the mechanical characteristics of the base material and should not be used when the base material is restricted. The splice design can also be changed, and a more compatible filler alloy can be selected to decrease the likelihood of hot cracking. Aluminum alloys must also be cleaned before welding, in order to remove all oxides, oils, and loose particles from the surface to be welded. This is especially important due to the susceptibility of an aluminum weld to porosity due to hydrogen and slag "Slag (metalworking)") due to oxygen.[36]​.

Although many welding applications take place in controlled environments such as factories and repair shops, some welding processes are frequently used in a wide variety of conditions, such as in open air, underwater, and in vacuums (such as in space). In outdoor uses, such as outdoor construction and repair, shielded metal arc welding is the most common process. Processes that use inert gases to protect the weld cannot easily be used in such situations, because unpredictable atmospheric movements can result in a failed weld. Shielded metal arc welding is also often used in underwater welding in the construction and repair of ships, offshore platforms, and pipelines, but others are also common, such as flux-cored arc welding and gas tungsten arc welding. Welding in space is also possible, first attempted in 1969 by Russian cosmonauts, when they conducted experiments to test shielded metal arc welding, plasma arc welding, and electron beam welding in a depressurized environment. Additional testing of these methods was done in the following decades, and today researchers continue to develop methods for using other welding processes in space, such as laser beam welding, resistance welding, and friction welding. Advances in these areas could prove indispensable for projects such as the construction of the International Space Station, which will likely make extensive use of welding to join parts manufactured on Earth in space.[37]​.

Welding without proper precautions can be a dangerous and harmful practice for your health. However, with the use of new technology and proper protection, the risks of injury or death associated with welding can be virtually eliminated. The risk of burns or electrocution is significant because many common welding procedures involve an open electric arc or flame. To prevent them, welders should wear protective clothing, such as approved footwear, thick leather gloves, and long-sleeved protective jackets to prevent exposure to sparks, heat, and possible flames. In addition, exposure to the glare of the welding area produces an injury called "arc eye" (keratitis) due to the effect of ultraviolet light that inflames the cornea and can burn the retinas. Protective glasses and welding helmets and helmets with dark glass filters are used to prevent this exposure, and in recent years new models of helmets have been marketed in which the glass filter is transparent and allows the work area to be seen when there is no UV radiation, but auto-darkens as soon as UV radiation occurs. To protect spectators, for safety, translucent screens or curtains should be used to surround the welding area. These curtains, made of a polyvinyl chloride plastic film, protect nearby workers from exposure to UV light from the electric arc, but should not be used to replace the glass filter used in welder helmets and face shields.[38]​.

Welders are also often exposed to hazardous gases and fine airborne particles. Processes such as flux-cored arc welding and shielded metal arc welding produce smoke containing particles of various types of oxides, which in some cases can produce medical conditions such as metal vapor fever. The size of the particles in question influences the toxicity of the vapors, with smaller particles presenting a greater danger. In addition, many processes produce vapors and various gases, commonly carbon dioxide, ozone and heavy metals, which can be dangerous without proper ventilation and protection. For this type of work, An FFP3 particulate respirator or welding mask is usually worn. Due to the use of compressed gases and flames, many welding processes pose a risk of explosion and fire. Common precautions include limiting the amount of oxygen in the air and keeping combustible materials away from the workplace.[38]​.

As in any industrial process, the cost of welding plays a crucial role in production decisions. Many different variables affect the total cost, including equipment cost, labor cost, material cost, and electrical energy cost. Depending on the process, the cost of the equipment can vary, from cheap for methods such as shielded metal arc welding and oxyfuel welding, to extremely expensive for methods such as laser beam welding and electron beam welding. Due to their high cost, these are only used in high production operations. Similarly, because automation and robots increase equipment costs, they are only implemented when high production is necessary. Labor cost depends on deposition rate (welding speed), hourly wage, and total operating time, including welding and part handling time. The cost of materials includes the cost of the base and filler material and the cost of shielding gases. Finally, the energy cost depends on the arc time and the energy consumption of the welding.

For manual welding methods, labor costs are generally the vast majority of the total cost. As a result, many cost-saving measures focus on minimizing operating time. To do this, welding procedures with high deposition rates can be selected and the welding parameters can be adjusted to increase the welding speed. Mechanization and automation are frequently implemented to reduce labor costs, but this often increases the cost of equipment and creates additional setup time. Material costs tend to increase when special properties are necessary in them and energy costs normally do not add up to more than a percentage of the total welding cost.[39]​.

In recent years, to minimize labor costs in high-production manufacturing, industrial welding has become increasingly automated, most notably with the use of robots in resistance spot welding (especially in the automotive industry) and arc welding. In robotic welding, mechanical devices hold the material and perform the welding,[40]​ and initially, spot welding was its most common use. But robotic arc welding has increased in popularity as technology has advanced. Other key areas of research and development include welding of dissimilar materials (such as steel and aluminum) and new welding processes. In addition, progress is being made to make specialized methods such as laser beam welding practical for more applications, for example in the aerospace and automotive industries. Researchers also hope to better understand the often unpredictable properties of welds, especially microstructure, residual stresses, and the tendency of a weld to crack or deform.[41]