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Shielded metal arc weldingShielded metal arc welding (SMAW), also known as manual metal arc welding (MMA or MMAW), flux shielded arc welding[1] or informally as stick welding, is a manual arc welding process that uses a consumable electrode covered with a flux to lay the weld.
An electric current, in the form of either alternating current or direct current from a welding power supply, is used to form an electric arc between the electrode and the metals to be joined. The workpiece and the electrode melts forming a pool of molten metal (weld pool) that cools to form a joint. As the weld is laid, the flux coating of the electrode disintegrates, giving off vapors that serve as a shielding gas and providing a layer of slag, both of which protect the weld area from atmospheric contamination.
Because of the versatility of the process and the simplicity of its equipment and operation, shielded metal arc welding is one of the world's first and most popular welding processes. It dominates other welding processes in the maintenance and repair industry, and though flux-cored arc welding is growing in popularity, SMAW continues to be used extensively in the construction of heavy steel structures and in industrial fabrication. The process is used primarily to weld iron and steels (including stainless steel) but aluminium, nickel and copper alloys can also be welded with this method.[2]
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After the discovery of the short pulsed electric arc in by Humphry Davy[3][4] and of the continuous electric arc in by Vasily Petrov,[4][5] there was little development in electrical welding until Auguste de Méritens developed a carbon arc torch that was patented in .[1]
In , Nikolay Benardos and Stanisław Olszewski developed carbon arc welding,[6] obtaining American patents from showing a rudimentary electrode holder. In , the consumable metal electrode was invented by Nikolay Slavyanov. Later in , C. L. Coffin received U.S. patent 428,459 for his arc welding method that utilized a metal electrode. The process, like SMAW, deposited melted electrode metal into the weld as filler.[7]
Around , Arthur Percy Strohmenger and Oscar Kjellberg released the first coated electrodes. Strohmenger used clay and lime coating to stabilize the arc, while Kjellberg dipped iron wire into mixtures of carbonates and silicates to coat the electrode.[8] In , Strohmenger released a heavily coated electrode, but high cost and complex production methods prevented these early electrodes from gaining popularity. In , the development of an extrusion process reduced the cost of coating electrodes while allowing manufacturers to produce more complex coating mixtures designed for specific applications. In the s, manufacturers introduced iron powder into the flux coating, making it possible to increase the welding speed.[9]
In Karl Kristian Masden described an automated variation of SMAW, now known as gravity welding.[10] It briefly gained popularity in the s after receiving publicity for its use in Japanese shipyards though today its applications are limited. Another little used variation of the process, known as firecracker welding, was developed around the same time by George Hafergut in Austria.[11] In laser welding was developed in Bell Laboratory with the intention of using this technology as a communication tool. Due to the large force of energy coupled with the small area of focus, this laser became a powerful heat source for cutting and tooling.[12]
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SMAW weld area Diagram of arc and weld area, in shielded metal arc welding:To strike the electric arc, the electrode is brought into contact with the workpiece by a very light touch of the electrode to the base metal. The electrode is then pulled back slightly. This initiates the arc and thus the melting of the workpiece and the consumable electrode, and causes droplets of the electrode to be passed from the electrode to the weld pool. Striking an arc, which varies widely based upon electrode and workpiece composition, can be the hardest skill for beginners. The orientation of the electrode to workpiece is where most stumble; if the electrode is held at a perpendicular angle to the workpiece, the tip will likely stick to the metal, which will fuse the electrode to the workpiece, causing it to heat up very rapidly. The tip of the electrode needs to be at a lower angle to the workpiece, which allows the weld pool to flow out of the arc. As the electrode melts, the flux covering disintegrates, giving off shielding gases that protect the weld area from oxygen and other atmospheric gases. In addition, the flux provides molten slag which covers the filler as it travels from electrode to the weld pool. Once part of the weld pool, the slag floats to the surface and protects the weld from contamination as it solidifies. Once hardened, it must be chipped away to reveal the finished weld. As welding progresses and the electrode melts, the welder must periodically stop welding to remove the remaining electrode stub and insert a new electrode into the electrode holder. This activity, combined with chipping away the slag, reduces the amount of time that the welder can spend laying the weld, making SMAW one of the least efficient welding processes. In general, the operator factor, or the percentage of operator's time spent laying weld, is approximately 25%.[13]
The actual welding technique utilized depends on the electrode, the composition of the workpiece, and the position of the joint being welded. The choice of electrode and welding position also determine the welding speed. Flat welds require the least operator skill, and can be done with electrodes that melt quickly but solidify slowly. This permits higher welding speeds.[citation needed]
Sloped, vertical or upside-down welding requires more operator skill, and often necessitates the use of an electrode that solidifies quickly to prevent the molten metal from flowing out of the weld pool. However, this generally means that the electrode melts less quickly, thus increasing the time required to lay the weld.[14]
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The most common quality problems associated with SMAW include weld spatter, porosity, poor fusion, shallow penetration, and cracking.[citation needed]
Weld spatter, while not affecting the integrity of the weld, damages its appearance and increases cleaning costs. Secondary finishing services are often required due to the aesthetic appearance caused by the occurrence of molten splatter.[15] It can be caused by excessively high current, a long arc, or arc blow, a condition associated with direct current characterized by the electric arc being deflected away from the weld pool by magnetic forces. Arc blow can also cause porosity in the weld, as can joint contamination, high welding speed, and a long welding arc, especially when low-hydrogen electrodes are used.[16]
Defects to weld strength make welds prone to cracking. Porosity of the weld bead can cause serious weakening and is often detectable only via advanced nondestructive testing methods. Porosity occurs when the gases produced by the weld flux insufficiently shield the molten weld metal. An overexposed weld bead absorbs nitrogen, oxygen, and hydrogen from the atmosphere; these gases form tiny voids in the weld bead and are released while the weld cools. Poor fusion also affects the strength of the weld and is often easily visible. This is caused by low current, contaminated joint surfaces, or the use of an improper electrode.[citation needed] Shallow welds are weaker and can be mitigated by decreasing welding speed, increasing the current, or using a smaller electrode.
Other factors in cracking propensity include high content of carbon, alloy, or sulfur in the base material, especially if low-hydrogen electrodes and preheating are not employed. Furthermore, workpieces should not be excessively constrained, as this introduces residual stresses into the workpieces (and specifically into the weld) as they expand and contract due to heating and cooling. As the weld cools and contracts, this residual stress can cause cracking in the weld.[17]
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Personal protection equipmentSMAW welding, like other welding methods, can be a dangerous and unhealthy practice if proper precautions are not taken. The process uses an open electric arc, which presents a risk of burns which are prevented by personal protective equipment in the form of heavy leather gloves and long sleeve jackets. Additionally, the brightness of the weld area can lead to a condition called arc eye or flash burn, in which ultraviolet light causes inflammation of the cornea and can burn the retinas of the eyes. Welding helmets with dark face plates are worn to prevent this exposure, and in recent years, new helmet models have been produced that feature a face plate that self-darkens upon exposure to high amounts of UV light. To protect bystanders, especially in industrial environments, translucent welding curtains often surround the welding area. These curtains, made of a polyvinyl chloride plastic film, shield nearby workers from exposure to the UV light from the electric arc, but should not be used to replace the filter glass used in helmets.[18]
In addition, the vaporizing metal and flux materials expose welders to dangerous gases and particulate matter. The smoke produced contains particles of various types of oxides. The size of the particles in question tends to influence the toxicity of the fumes, with smaller particles presenting a greater danger. Additionally, gases like carbon dioxide and ozone can form, which can prove dangerous if ventilation is inadequate. Some of the latest welding masks are fitted with an electric powered fan to help disperse harmful fumes.[19]
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Shielded metal arc welding is one of the world's most popular welding processes, accounting for over half of all welding in some countries. Because of its versatility and simplicity, it is particularly dominant in the maintenance and repair industry, and is heavily used in the construction of steel structures and in industrial fabrication. In recent years its use has declined as flux-cored arc welding has expanded in the construction industry and gas metal arc welding has become more popular in industrial environments. However, because of the low equipment cost and wide applicability, the process will likely remain popular, especially among amateurs and small businesses where specialized welding processes are uneconomical and unnecessary.[20]
SMAW is often used to weld carbon steel, low and high alloy steel, stainless steel, cast iron, and ductile iron. While less popular for non-ferrous materials, it can be used on nickel and copper and their alloys and, in rare cases, on aluminium. The thickness of the material being welded is bounded on the low end primarily by the skill of the welder, but rarely does it drop below 1.5 mm (0.06 in). No upper bound exists: with proper joint preparation and use of multiple passes, materials of virtually unlimited thicknesses can be joined. Furthermore, depending on the electrode used and the skill of the welder, SMAW can be used in any position.[21]
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SMAW system setupShielded metal arc welding equipment typically consists of a constant current welding power supply and an electrode, with an electrode holder, a ground clamp, and welding cables (also known as welding leads) connecting the two. [22]
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The power supply used in SMAW has constant current output, ensuring that the current (and thus the heat) remains relatively constant, even if the arc distance and voltage change. This is important because most applications of SMAW are manual, requiring that an operator hold the torch. Maintaining a suitably steady arc distance is difficult if a constant voltage power source is used instead, since it can cause dramatic heat variations and make welding more difficult. However, because the current is not maintained absolutely constant, skilled welders performing complicated welds can vary the arc length to cause minor fluctuations in the current.
A high output welding power supply for SMAW, GTAW, MIG, Flux-Cored, & GougingThe preferred polarity of the SMAW system depends primarily upon the electrode being used and the desired properties of the weld. Direct current with a negatively charged electrode (DCEN) causes heat to build up in the parent material, increasing the electrode melting rate and decreasing the depth of the weld. Reversing the polarity so that the electrode is positively charged (DCEP) and the workpiece is negatively charged increases the weld penetration. With alternating current the polarity changes over 100 times per second, creating an even heat distribution and providing a balance between electrode melting rate and penetration.
Typically, the equipment used for SMAW consists of a step-down transformer and for direct current models a rectifier, which converts alternating current into direct current. Because the power normally supplied to the welding machine is high-voltage alternating current, the welding transformer is used to reduce the voltage and increase the current. As a result, instead of 220 V at 50 A, for example, the power supplied by the transformer is around 17'45 V at currents up to 600 A. A number of different types of transformers can be used to produce this effect, including multiple coil and inverter machines, with each using a different method to manipulate the welding current. The multiple coil type adjusts the current by either varying the number of turns in the coil (in tap-type transformers) or by varying the distance between the primary and secondary coils (in movable coil or movable core transformers). Inverters, which are smaller and thus more portable, use electronic components to change the current characteristics.
Electrical generators and alternators are frequently used as portable welding power supplies, but because of lower efficiency and greater costs, they are less frequently used in industry. Maintenance also tends to be more difficult, because of the complexities of using a combustion engine as a power source. However, in one sense they are simpler: the use of a separate rectifier is unnecessary because they can provide either AC or DC. However, the engine driven units are most practical in field work where the welding often must be done out of doors and in locations where transformer type welders are not usable because there is no power source available to be transformed.[citation needed]
In some units the alternator is essentially the same as that used in portable generating sets used to supply mains power, modified to produce a higher current at a lower voltage but still at the 50 or 60 Hz grid frequency. In higher-quality units an alternator with more poles is used and supplies current at a higher frequency, such as 400 Hz. The smaller amount of time the high-frequency waveform spends near zero makes it much easier to strike and maintain a stable arc than with the cheaper grid-frequency sets or grid-frequency mains-powered units.[citation needed]
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Various accessories for SMAWThe choice of electrode for SMAW depends on a number of factors, including the weld material, welding position and the desired weld properties. The electrode is coated in a metal mixture called flux, which gives off gases as it decomposes to prevent weld contamination, introduces deoxidizers to purify the weld, causes weld-protecting slag to form, improves the arc stability, and provides alloying elements to improve the weld quality.[28] Electrodes can be divided into three groups'those designed to melt quickly are called "fast-fill" electrodes, those designed to solidify quickly are called "fast-freeze" electrodes, and intermediate electrodes go by the name "fill-freeze" or "fast-follow" electrodes. Fast-fill electrodes are designed to melt quickly so that the welding speed can be maximized, while fast-freeze electrodes supply filler metal that solidifies quickly, making welding in a variety of positions possible by preventing the weld pool from shifting significantly before solidifying.[29]
The composition of the electrode core is generally similar and sometimes identical to that of the base material. But even though a number of feasible options exist, a slight difference in alloy composition can strongly impact the properties of the resulting weld. This is especially true of alloy steels such as HSLA steels. Likewise, electrodes of compositions similar to those of the base materials are often used for welding nonferrous materials like aluminium and copper.[30] However, sometimes it is desirable to use electrodes with core materials significantly different from the base material. For example, stainless steel electrodes are sometimes used to weld two pieces of carbon steel, and are often utilized to weld stainless steel workpieces with carbon steel workpieces.[31]
Electrode coatings can consist of a number of different compounds, including rutile, calcium fluoride, cellulose, and iron powder. Rutile electrodes, coated with 25%'45% TiO2, are characterized by ease of use and good appearance of the resulting weld. However, they create welds with high hydrogen content, encouraging embrittlement and cracking. Electrodes containing calcium fluoride (CaF2), sometimes known as basic or low-hydrogen electrodes, are hygroscopic and must be stored in dry conditions. They produce strong welds, but with a coarse and convex-shaped joint surface. Electrodes coated with cellulose, especially when combined with rutile, provide deep weld penetration, but because of their high moisture content, special procedures must be used to prevent excessive risk of cracking. Finally, iron powder is a common coating additive that increases the rate at which the electrode fills the weld joint, up to twice as fast.[32]
To identify different electrodes, the American Welding Society established a system that assigns electrodes with a four- or five-digit number. Covered electrodes made of mild or low alloy steel carry the prefix E, followed by their number. The first two or three digits of the number specify the tensile strength of the weld metal, in thousand pounds per square inch (ksi). The penultimate digit generally identifies the welding positions permissible with the electrode, typically using the values 1 (normally fast-freeze electrodes, implying all position welding) and 2 (normally fast-fill electrodes, implying horizontal welding only). The welding current and type of electrode covering are specified by the last two digits together. When applicable, a suffix is used to denote the alloying element being contributed by the electrode.[33]
Common electrodes include the E, a fast-freeze, all-position electrode with a minimum tensile strength of 60 ksi (410 MPa) which is operated using DCEP, and provides deep weld penetration with a forceful arc capable of burning through light rust or oxides on the workpiece. E is similar except its flux coating allows it to be used with alternating current in addition to DCEP. E is a fast-fill electrode, used primarily to make flat or horizontal fillet welds using AC, DCEN, or DCEP. Examples of fill-freeze electrodes are the E, E, and E, all of which provide a compromise between fast welding speeds and all-position welding.[34]
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Though SMAW is almost exclusively a manual arc welding process, one notable process variation exists, known as gravity welding or gravity arc welding. It serves as an automated version of the traditional shielded metal arc welding process, employing an electrode holder attached to an inclined bar along the length of the weld. Once started, the process continues until the electrode is spent, allowing the operator to manage multiple gravity welding systems. The electrodes employed (often E or E) are coated heavily in flux, and are typically 71 cm (28 in) in length and about 6.35 mm (0.25 in) thick. As in manual SMAW, a constant current welding power supply is used, with either negative polarity direct current or alternating current. Due to a rise in the use of semiautomatic welding processes such as flux-cored arc welding, the popularity of gravity welding has fallen as its economic advantage over such methods is often minimal. Other SMAW-related methods that are even less frequently used include firecracker welding, an automatic method for making butt and fillet welds, and massive electrode welding, a process for welding large components or structures that can deposit up to 27 kg (60 lb) of weld metal per hour.[11]
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Welding has been around since ancient times. Read this article for a brief overview of welding history throughout the years.
Welding can trace its historic development back to ancient times. The earliest examples of welding come from the Bronze Age. Small gold circular boxes were made by pressure welding lap joints together. It is estimated that these boxes were made more than 2,000 years ago. During the Iron Age the Egyptians and people in the eastern Mediterranean area learned to weld pieces of iron together. Many tools were found that were made in approximately B.C.
During the Middle Ages, the art of blacksmithing was developed and many items of iron were produced that were welded by hammering. It was not until the 19th century that welding as we know it today was invented.
Historians credit Edmund Davy of England with the discovery of acetylene in . Sir Humphry Davy produced an arc between two carbon electrodes using a battery in . In the mid-19th century, the electric generator was invented and arc lighting became popular. Gas welding and cutting developed during the late s. Arc welding with the carbon arc and metal arc was developed and resistance welding became a practical joining process.
Auguste De Meritens, working in the Cabot Laboratory in France, used the heat of an arc for joining lead plates for storage batteries in the year . It was his pupil, a Russian, Nikolai N. Benardos, working in the French laboratory, received a patent for welding. He, with a fellow Russian, Stanislaus Olszewski, secured a British patent in and an American patent in . The patents show an early electrode holder. This was the beginning of carbon arc welding. Benardos restricted his efforts to carbon arc welding, although he was able to weld iron as well as lead. Carbon arc welding became popular during the late s and early s.
In , C.L. Coffin of Detroit received the first U.S. patent for an arc welding process using a metal electrode. This was the first record of the metal melted from the electrode carried across the arc to deposit filler metal in the joint to make a weld. About the same time, N.G. Slavianoff, a Russian, presented the same idea of transferring metal across an arc, but to cast metal in a mold.
Approximately , Strohmenger introduced a coated metal electrode in Great Britain. There was a thin coating of clay or lime, but it provided a more stable arc. Oscar Kjellberg of Sweden invented a covered or coated electrode during the period of to . He produced stick electrodes by dipping short lengths of bare iron wire in thick mixtures of carbonates and silicates and allowing the coating to dry.
Meanwhile, resistance welding processes developed, including spot welding, seam welding, projection welding and flash butt welding. Elihu Thompson originated resistance welding. His patents dated -. In , a German named Goldschmidt invented thermite welding that was first used to weld railroad rails.
Gas welding and cutting were perfected during this period as well. The production of oxygen and later the liquefying of air, along with the introduction of a blow pipe or torch in , helped the development of both welding and cutting. Before , hydrogen and coal gas were used with oxygen. However, in about a torch suitable for use with low-pressure acetylene was developed.
World War I brought a tremendous demand for armament production, growing the need for welding. Many companies sprang up in America and in Europe to manufacture welding machines and electrodes to meet the requirements.
Immediately after the war in , 20 members of the Wartime Welding Committee of the Emergency Fleet Corporation, under the leadership of Comfort Avery Adams, founded the American Welding Society as a nonprofit organization dedicated to the advancement of welding and allied processes.
C.J. Holslag invented alternating current in ; however, it did not become popular until the s when the heavy-coated electrode found widespread use.
In , P.O. Nobel of the General Electric Company invented automatic welding. It utilized bare electrode wire operated on direct current and used arc voltage as the basis of regulating the feed rate. General Electric used automatic welding to build up worn motor shafts and worn crane wheels. The automobile industry also used it to produce rear axle housings.
During the s, various types of welding electrodes were developed. There was considerable controversy during the s about the advantage of the heavy-coated rods versus light-coated rods. In , Langstroth and Wunder of the A.O. Smith Company developed heavy-coated electrodes. Then in , Lincoln Electric Company produced extruded electrode rods and sold them to. the public. By , covered electrodes were widely used. Welding codes appeared that required higher-quality weld metal, which increased the use of covered electrodes.
During the s there was considerable research in shielding the arc and weld area by externally applied gases. The atmosphere of oxygen and nitrogen in contact with the molten weld metal caused brittle and sometimes porous welds. Researchers tested welds utilizing gas shielding techniques. Alexander and Langmuir did work in chambers using hydrogen as a welding atmosphere. They utilized two electrodes, starting with carbon electrodes but later changing to tungsten electrodes. The hydrogen was changed to atomic hydrogen in the arc. It was then blown out of the arc forming an intensely hot flame of atomic hydrogen turning to the molecular form and liberating heat. This arc produced half again as much heat as an oxyacetylene flame. This became the atomic hydrogen welding process. Atomic hydrogen never became popular but was used during the s and s for special applications of welding and later on for welding of tool steels.
H.M. Hobart and P.K. Devers were doing similar work but using atmospheres of argon and helium. In their patents applied for in , arc welding utilizing gas supplied around the arc was a forerunner of the gas tungsten arc welding process. They also showed welding with a concentric nozzle and with the electrode being fed as a wire through the nozzle. This was the forerunner of the gas metal arc welding process.
Welders at the New York Navy Yard developed stud welding in , specifically for attaching wood decking over a metal surface. Stud welding became popular in the shipbuilding and construction industries.
The automatic process that became popular was the submerged arc welding process. The National Tube Company developed this under powder, or smothered arc, welding process for a pipe mill at McKeesport, Pennsylvania. the company designed the process to make the longitudinal seams in the pipe. Robinoff patented the process in and later sold it to Linde Air Products Company. Linde renamed it to Unionmelt welding. Shipyards and ordnance factories used submerged arc welding during the defense buildup in . It is one of the most productive welding processes and remains popular today.
Gas tungsten arc welding (GTAW) had its beginnings in welding history from an idea by C.L. Coffin to weld in a nonoxidizing gas atmosphere, which he patented in . H.M. Hobart and P.K. Devers further refined the concept in the late s using helium and argon for shielding, respectively. This process was ideal for welding magnesium and also for welding stainless and aluminum. It was perfected in , patented by Meredith, and named Heliarc welding. It was later licensed to Linde Air Products, where the water-cooled torch was developed. The gas tungsten arc welding process has become one of the most important.
A turning point in welding history came when the Battelle Memorial Institute ' under the sponsorship of the Air Reduction Company ' successfully developed the gas metal arc welding (GMAW) process in . This development utilized the gas shielded arc similar to the gas tungsten arc but replaced the tungsten electrode with a continuously fed electrode wire. One of the basic changes that made the process more usable was the small-diameter electrode wires and the constant-voltage power source. H.E. Kennedy patented this principle earlier. The initial introduction of GMAW was for welding nonferrous metals. The high deposition rate led users to try the process on steel. The cost of inert gas was relatively high, and the cost savings were not immediately available.
In , Lyubavskii and Novoshilov announced the use of welding with consumable electrodes in an atmosphere of carbon dioxide gas. The CO2 welding process immediately gained favor since it utilized equipment developed for inert gas metal arc welding but could now be used for economically welding steels. The CO2 arc is a hot arc and the larger electrode wires required fairly high currents. The process became widely used with the introduction of smaller-diameter electrode wires and refined power supplies. This short-circuit arc variation was known as Micro-wire, short-arc and dip transfer welding, all of which appeared late in and early in . This variation allowed all-position welding on thin materials and soon became the most popular of the gas metal arc welding process variations.
Another variation was the use of inert gas with small amounts of oxygen that provided the spray-type arc transfer. It became popular in the early s. A recent variation is the use of pulsed current. The current switches from a high to a low value at a rate of once or twice the line frequency.
Soon after the introduction of CO2 welding, a variation utilizing a special electrode wire was developed. This wire, described as an inside-outside electrode, was tubular in cross section with the fluxing agents on the inside. The process was called Dualshield, which indicated that external shielding gas was utilized as well as the gas produced by the flux in the core of the wire for arc shielding. This process, invented by Bernard, was announced in , but was patented in , when the National Cylinder Gas Company reintroduced it.
In , an inside-outside electrode was produced that did not require external gas shielding. The absence of shielding gas gave the process popularity for noncritical work. This process was named Innershield®.
The Soviets announced the electroslag welding process at the Brussels World Fair in Belgium in . It had been used in the Soviet Union since but was based on work done in the United States by R.K. Hopkins, who was granted patents in . The Hopkins process was never used to a very great degree for joining. The Paton Institute Laboratory in Kiev, Ukraine, and the Welding Research Laboratory in Bratislava, Czechoslovakia, perfected the process and developed the equipment. The Electromotive Division of General Motors Corporation in Chicago used the process in production for the first time in the U.S. They called it the Electro-molding process and used it for the fabrication of welded diesel engine blocks. Manufacturers use the process and its variation, using a consumable guide tube, for welding thicker materials.
The Arcos Corporation introduced another vertical welding method, called Electrogas, in . It utilized equipment developed for electroslag welding but employed a flux-cored electrode wire and an externally supplied gas shield. It is an open arc process since a slag bath is not involved. A newer development uses self-shielding electrode wires and a variation uses solid wire but with gas shielding. These methods allow the welding of thinner materials than allowed with the electroslag process.
Gage invented plasma arc welding in . This process uses a constricted arc or an arc through an orifice, which creates an arc plasma that has a higher temperature than the tungsten arc. It is also used for metal spraying, gouging and cutting.
Developed in France, the electron beam welding process uses a focused beam of electrons as a heat source in a vacuum chamber. J.A. Stohr of the French Atomic Energy Commission made the first public disclosure of the process on Nov. 23, . In the United States, the automotive and aircraft engine industries are the major users of electron beam welding.
Developed in the Soviet Union, friction welding uses rotational speed and upset pressure to provide friction heat. It is a specialized process and has applications only where a sufficient volume of similar parts is to be welded because of the initial expense for equipment and tooling. This process is called inertia welding.
Laser welding is one of the newest processes. The Bell Laboratories originally developed the laser as a communications device. Because of the tremendous concentration of energy in a small space, it proved to be a powerful heat source. Operations use lasers or cutting metals and nonmetals. Continuous pulse equipment is available. The laser is finding welding applications in automotive metalworking operations.
Welding history information courtesy of Hobart Institute of Welding Technology. This article was excerpted from Modern Welding Technology, 4th edition, , by Howard B. Cary. Published by Prentice-Hall.
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