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Gas metal arc welding

Welding is a fabrication or sculptural process that joins materials, usually metals or thermoplastics, by causing coalescence. This is often done by melting the workpieces and adding a filler material to form a pool of molten material (the weld pool) that cools to become a strong joint, with pressure sometimes used in conjunction with heat, or by itself, to produce the weld. This is in contrast with soldering and brazing, which involve melting a lower-melting-point material between the workpieces to form a bond between them, without melting the workpieces.

Many different energy sources can be used for welding, including a gas flame, an electric arc, a laser, an electron beam, friction, and ultrasound. While often an industrial process, welding can be done in many different environments, including open air, under water and in outer space. Regardless of location, however, welding remains dangerous, and precautions are taken to avoid burns, electric shock, eye damage, poisonous fumes, and overexposure to ultraviolet light.

Until the end of the 19th century, the only welding process was forge welding, which blacksmiths had used for centuries to join iron and steel by heating and hammering them. Arc welding and oxyfuel welding were among the first processes to develop late in the century, and resistance welding followed soon after. Welding technology advanced quickly during the early 20th century as World War I and World War II drove the demand for reliable and inexpensive joining methods. Following the wars, several modern welding techniques were developed, including manual methods like shielded metal arc welding, now one of the most popular welding methods, as well as semi-automatic and automatic processes such as gas metal arc welding, submerged arc welding, flux-cored arc welding and electroslag welding. Developments continued with the invention of laser beam welding and electron beam welding in the latter half of the century. Today, the science continues to advance. Robot welding is becoming more commonplace in industrial settings, and researchers continue to develop new welding methods and gain greater understanding of weld quality and properties.



The history of joining metals goes back several millennia, with the earliest examples of welding from the Bronze Age and the Iron Age in Europe and the Middle East. Welding was used in the construction of the iron pillar in Delhi, India, erected about 310 AD and weighing 5.4 metric tons.[1]

The Middle Ages brought advances in forge welding, in which blacksmiths pounded heated metal repeatedly until bonding occurred. In 1540, Vannoccio Biringuccio published De la pirotechnia, which includes descriptions of the forging operation. Renaissance craftsmen were skilled in the process, and the industry continued to grow during the following centuries.[2] Welding, however, was transformed during the 19th century. In 1802, Russian scientist Vasily Petrov discovered the electric arc[3] and subsequently proposed its possible practical applications, including welding. In 1881-82 a Russian inventor Nikolai Bernardos created the first electric arc welding method known as carbon arc welding, using carbon electrodes. The advances in arc welding continued with the invention of metal electrodes in the late 1800s by a Russian, Nikolai Slavyanov (1888), and an American, C. L. Coffin. Around 1900, A. P. Strohmenger released a coated metal electrode in Britain, which gave a more stable arc. In 1905 Russian scientist Vladimir Mitkevich proposed the usage of three-phase electric arc for welding. In 1919, alternating current welding was invented by C. J. Holslag but did not become popular for another decade.[4]

Resistance welding was also developed during the final decades of the 19th century, with the first patents going to 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, oxyfuel welding, became well established. Acetylene was discovered in 1836 by Edmund Davy, but its use was not practical in welding until about 1900, when a suitable blowtorch was developed.[5] At first, oxyfuel welding was one of the more popular welding methods due to its portability and relatively low cost. As the 20th century progressed, however, it fell out of favor for industrial applications. It was largely replaced with arc welding, as metal coverings (known as flux) for the electrode that stabilize the arc and shield the base material from impurities continued to be developed.[6]

World War I caused a major surge in the use of welding processes, with the various military powers attempting to determine which of the several new welding processes would be best. The British primarily used arc welding, even constructing a ship, the Fulagar, with an entirely welded hull. Arc welding was first applied to aircraft during the war as well, as some German airplane fuselages were constructed using the process.[7] Also noteworthy is the first welded road bridge in the world, designed by Stefan Bryła of the Warsaw University of Technology in 1927, and built across the river Słudwia Maurzyce near Łowicz, Poland in 1929.[8]

During the 1920s, major advances were made in welding technology, including the introduction of automatic welding in 1920, in which electrode wire was fed continuously. Shielding gas became a subject receiving much attention, as scientists attempted to protect welds from the effects of oxygen and nitrogen in the atmosphere. Porosity and brittleness were the primary problems, and the solutions that developed included the use of hydrogen, argon, and helium as welding atmospheres.[9] During the following decade, further advances allowed for the welding of reactive metals like aluminum and magnesium. This in conjunction with developments in automatic welding, alternating current, and fluxes fed a major expansion of arc welding during the 1930s and then during World War II.[10]

During the middle of the century, many new welding methods were invented. 1930 saw the release of stud welding, which soon became popular in shipbuilding and construction. Submerged arc welding was invented the same year and continues to be popular today. In 1932 a Russian, Konstantin Khrenov successfully implemented the first underwater electric arc welding. Gas tungsten arc welding, after decades of development, was finally perfected in 1941, and gas metal arc welding followed in 1948, allowing for fast welding of non-ferrous materials but requiring expensive shielding gases. Shielded metal arc welding was developed during the 1950s, using a flux coated consumable electrode, and it quickly became the most popular metal arc welding process. In 1957, the flux-cored arc welding process debuted, in which the self-shielded wire electrode 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 it was followed by its cousin, electrogas welding, in 1961.[11] In 1953 the Soviet scientist N.F. Kazakov proposed the diffusion bonding method.[12]

Other recent developments in welding include the 1958 breakthrough of electron beam welding, making deep and narrow welding possible through the concentrated heat source. Following the invention of the laser in 1960, laser beam welding debuted several decades later, and has proved to be especially useful in high-speed, automated welding. Both of these processes, however, continue to be quite expensive due the high cost of the necessary equipment, and this has limited their applications.[13]




These processes use a welding power supply to create and maintain an electric arc between an electrode and the base material to melt metals at the welding point. They can use either direct (DC) or alternating (AC) current, and consumable or non-consumable electrodes. The welding region is sometimes protected by some type of inert or semi-inert gas, known as a shielding gas, and filler material is sometimes used as well.

Power supplies

To supply the electrical energy necessary for arc welding processes, a number of different power supplies can be used. The most common welding power supplies are constant current power supplies and constant voltage power supplies. In arc welding, the length of the arc is directly related to the voltage, and the amount of heat input is related to 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 relatively constant current even as the voltage varies. This is important because in manual welding, it can be difficult to hold the electrode perfectly steady, and as a result, the arc length and thus voltage tend to fluctuate. Constant voltage power supplies hold the voltage constant and vary the current, and as a result, are most often used for automated welding processes such as gas metal arc welding, flux cored arc welding, and submerged arc welding. In these processes, arc length is kept constant, since any fluctuation in the distance between the wire and the base material is quickly rectified by a large change in current. For example, if the wire and the base material get too close, the current will rapidly increase, which in turn causes the heat to increase and the tip of the wire to melt, returning it to its original separation distance.[14]

The type of current used in arc welding also plays an important role in welding. Consumable electrode processes such as shielded metal arc welding and gas metal arc welding generally use direct current, but the electrode can be charged either positively or negatively. In welding, the positively charged anode will have a greater heat concentration, and as a result, changing the polarity of the electrode has an impact on weld properties. If the electrode is positively charged, the base metal will be hotter, increasing weld penetration and welding speed. Alternatively, a negatively charged electrode results in more shallow welds.[15] Nonconsumable electrode processes, such as gas tungsten arc welding, can use either type of direct current, as well as alternating current. However, with direct current, because the electrode only creates the arc and does not provide filler material, a positively charged electrode causes shallow welds, while a negatively charged electrode makes deeper welds.[16] Alternating current rapidly moves between these two, resulting in medium-penetration welds. One disadvantage of AC, the fact that the arc must be re-ignited after every zero crossing, has been addressed with the invention of special power units that produce a square wave pattern instead of the normal sine wave, making rapid zero crossings possible and minimizing the effects of the problem.[17]


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. Electric current is used to strike an arc between the base material and consumable electrode rod, which is made of steel and is covered with a flux that protects the weld area from oxidation and contamination by producing CO2 gas during the welding process. The electrode core itself acts as filler material, making a separate filler unnecessary.

Shielded metal arc welding

The process is versatile and can be performed with relatively inexpensive equipment, making it well suited to shop jobs and field work.[18] An operator can become reasonably proficient with a modest amount of training and can achieve mastery with experience. Weld times are rather slow, since the consumable electrodes must be frequently replaced and because slag, the residue from the flux, must be chipped away after welding.[19] Furthermore, the process is generally limited to welding ferrous materials, though special electrodes have made possible the welding of cast iron, nickel, aluminum, copper, and other metals. Inexperienced operators may find it difficult to make good out-of-position welds with this process.

Gas metal arc welding (GMAW), also known as metal inert gas or MIG welding, is a semi-automatic or automatic process that uses a continuous wire feed as an electrode and an inert or semi-inert gas mixture to protect the weld from contamination. As with SMAW, reasonable operator proficiency can be achieved with modest training. Since the electrode is continuous, welding speeds are greater for GMAW than for SMAW. Also, the smaller arc size compared to the shielded metal arc welding process makes it easier to make out-of-position welds (e.g., overhead joints, as would be welded 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 setup procedure. Therefore, GMAW is less portable and versatile, and due to the use of a separate shielding gas, is not particularly suitable for outdoor work. However, owing to the higher average rate at which welds can be completed, GMAW is well suited to production welding. The process can be applied to a wide variety of metals, both ferrous and non-ferrous.[20]

A related process, flux-cored arc welding (FCAW), uses similar equipment but uses wire consisting of a steel electrode surrounding a powder fill material. This cored wire is more expensive than the standard solid wire and can generate fumes and/or slag, but it permits even higher welding speed and greater metal penetration.[21]

Gas tungsten arc welding (GTAW), or tungsten inert gas (TIG) welding (also sometimes erroneously referred to as heliarc welding), is a manual welding process that uses a nonconsumable 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 high quality welds, but it requires significant operator skill and can only be accomplished at relatively low speeds.

GTAW can be used on nearly all weldable metals, though it is most often applied to stainless steel and light metals. It is often used when quality welds are extremely important, such as in bicycle, aircraft and naval applications.[22] A related process, plasma arc welding, also uses a tungsten electrode but uses plasma gas to make the arc. The arc is more concentrated than the GTAW arc, making transverse control more critical and thus generally restricting the technique to a mechanized process. Because of its stable current, the method can be used on a wider range of material thicknesses than can the GTAW process, and furthermore, it is much faster. It can be applied to all of the same materials as GTAW except magnesium, and automated welding of stainless steel is one important application of the process. A variation of the process is plasma cutting, an efficient steel cutting process.[23]

Submerged arc welding (SAW) is a high-productivity welding method in which the arc is struck beneath a covering layer of flux. This increases arc quality, since contaminants in the atmosphere are blocked by the flux. The slag that forms on the weld generally comes off by itself, and combined with the use of a continuous wire feed, the weld deposition rate is high. Working conditions are much improved over other arc welding processes, since the flux hides the arc and almost no smoke is produced. The process is commonly used in industry, especially for large products and in the manufacture of welded pressure vessels.[24] Other arc welding processes include atomic hydrogen welding, carbon arc welding, electroslag welding, electrogas welding, and stud arc welding.

Gas welding a steel armature using the oxy-acetylene process.


The most common gas welding process is oxyfuel welding, also known as oxyacetylene 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 widely used for welding pipes and tubes, as well as repair work. It is also frequently well-suited, and favored, for fabricating some types of metal-based artwork. Oxyfuel equipment is versatile, lending itself not only to some sorts of iron or steel welding but also to brazing, braze-welding, metal heating (for bending and forming), and also oxyfuel cutting.

The equipment is relatively inexpensive and simple, generally employing the combustion of acetylene in oxygen to produce a welding flame temperature of about 3100 °C. The flame, since it is less concentrated than an electric arc, causes slower weld cooling, which can lead to greater residual stresses and weld distortion, though it eases the welding of high alloy steels. A similar process, generally called oxyfuel cutting, is used to cut metals.[6] Other gas welding methods, such as air acetylene welding, oxygen hydrogen welding, and pressure gas welding are quite similar, generally differing only in the type of gases used. A water torch is sometimes used for precision welding of small items such as jewelry. Gas welding is also used in plastic welding, though the heated substance is air, and the temperatures are much lower.


Resistance welding involves the generation of heat by passing current through the resistance caused by the contact between two or more metal surfaces. Small pools of molten metal are formed at the weld area as high current (1000–100,000 A) is passed through the metal. In general, resistance welding methods are efficient and cause little pollution, but their applications are somewhat limited and the equipment cost can be high.

Spot welder

Spot welding is a popular resistance welding method used to join overlapping metal sheets of up to 3 mm thick. Two electrodes are simultaneously used to clamp the metal sheets together and to pass current through the sheets. The advantages of the method include efficient energy use, limited workpiece deformation, high production rates, easy automation, and no required filler materials. Weld strength is significantly lower than with other welding methods, making the process suitable for only certain applications. It is used extensively in the automotive industry—ordinary cars can have several thousand spot welds made by industrial robots. A specialized process, called shot 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 metal sheets. However, instead of pointed electrodes, wheel-shaped electrodes roll along and often feed the workpiece, making it possible to make long continuous welds. 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 upset welding.[25]

Energy beam

Energy beam welding methods, namely laser beam welding and electron beam welding, are relatively new processes that have become quite popular in high production applications. The two processes are quite similar, differing most notably in their source of power. Laser beam welding employs a highly focused laser beam, while electron beam welding is done in a vacuum and uses an electron beam. 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 easily automated, making them highly productive. The primary disadvantages are their very high equipment costs (though these are decreasing) and a susceptibility to thermal cracking. Developments in this area include laser-hybrid welding, which uses principles from both laser beam welding and arc welding for even better weld properties, and X-ray welding.[26]


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

Another common process, explosion welding, involves the joining of materials by pushing them together under extremely high pressure. The energy from the impact plasticizes the materials, forming a weld, even though only a limited amount of heat is generated. The process is commonly used for welding dissimilar materials, such as the welding of aluminum with steel in ship hulls or compound plates. Other solid-state welding processes include co-extrusion welding, cold welding, diffusion welding, exothermic welding, friction welding (including friction stir welding), high frequency welding, hot pressure welding, induction welding, and roll welding.[27]


Common welding joint types – (1) Square butt joint, (2) V butt joint, (3) Lap joint, (4) T-joint

Welds can be geometrically prepared in many different ways. The five basic types of weld joints are the butt joint, lap joint, corner joint, edge joint, and T-joint (a variant of this last is the cruciform joint). Other variations exist as well—for example, double-V preparation joints are characterized by the two pieces of material each tapering to a single center point at one-half their height. Single-U and double-U preparation joints are also fairly common—instead of having straight edges like the single-V and double-V preparation joints, they are curved, forming the shape of a U. Lap joints are also commonly more than two pieces thick—depending on the process used and the thickness of the material, many pieces can be welded together in a lap joint geometry.[28]

Often, particular joint designs are used exclusively or almost exclusively by certain welding processes. For example, resistance spot welding, laser beam welding, and electron beam welding are most frequently performed on lap joints. However, some welding methods, like shielded metal arc welding, are extremely versatile and can weld virtually any type of joint. Additionally, some processes can be used to make multipass welds, in which one weld is allowed to cool, and then another weld is performed on top of it. This allows for the welding of thick sections arranged in a single-V preparation joint, for example.[29]

The cross-section of a welded butt joint, with the darkest gray representing the weld or fusion zone, the medium gray the heat-affected zone, and the lightest gray the base material.

After welding, a number of distinct regions can be identified in the weld area. The weld itself is called the fusion zone—more specifically, it is where the filler metal was laid 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 had its microstructure and properties altered by the weld. These properties depend on the base material's behavior when subjected to heat. The metal in this area is often weaker than both the base material and the fusion zone, and is also where residual stresses are found.[30]

Butt welds

Butt welds are welds where two pieces of metal are joined at surfaces that are at 90 degree angles to the surface of at least one of the other pieces.[31] These types of welds require only some preparation and are used with thin sheet metals that can be welded with a single pass (Handbook of welding). When the thickness of a butt weld is defined it is usually measured at the thinner part and does not compensate for the weld reinforcement. Common issues that can weaken a butt weld are the entrapment of slag, excessive porosity, or cracking. For strong welds, the goal is to use the least amount of welding material possible. The square welds are the most economical for pieces thinner than 3/8” because they don’t require the edge to be prepared[32]. Double-groove welds are the most economical for thicker pieces because they use less weld material and time.

Butt welds are prevalent in automated welding processes, such as submerged-arc welding, due to their relative ease of preparation[33]. When metals are welded without human guidance, there is no operator to make adjustments for non ideal joint preparation. Because of this necessity, butt welds can be utilized for their simplistic design to be fed through automated welding machines efficiently.


Butt joint geometries

There are many types of specific butt welds, but each specific kind of butt weld falls into a specific category which consist of single welded butt joints, double welded butt joint, and open or closed butt joints. A single welded butt joint is when it has only been welded from one side. A double welded butt joint is when the weld has been welded from both sides. With double welding the depths of each weld can vary slightly. A closed weld is when the two pieces that will be joined are touching during the welding process. An open weld is when the two pieces have a small gap in between them during welding. Pipes and tubing can be made from rolling and welding together strips, sheets, or plates of material.

The square-groove is simple to prepare, economical to use, and provides satisfactory strength, but is limited by joint thickness. For thicker joints, the edge of each member of the joint must be prepared to a particular geometry to provide accessibility for welding and to ensure the desired weld soundness and strength. The opening or gap at the root of the joint and the included angle of the groove should be selected to require the least weld metal necessary to give needed access and meet strength requirements .There are also many different types of Angle Butt Welds, which are butt welds where the pieces are joined at an angle other than 90 degrees.

Bevel Butt Joints

Single-bevel butt welds are welds where one piece in the joint is beveled and the other surface is perpendicular to the plane of the surface. These types of joints are used where adequate penetration cannot be achieved with a square-groove and the metals are to be welded in the horizontal position (HBW). Double-bevel butt welds are common in arc and gas welding processes. In this type both sides of one of the edges in the joint are beveled.


Single -V -Joint butt welds are similar to a bevel joint, but instead of only one side having the beveled edge, both sides of the weld joint are beveled. In thick metals, and when welding can be performed from both sides of the work piece, a double-V-joint is used. When welding thicker metals, a double-V-joint requires less filler material because there are two narrower V-joints compared to a wider sing V-joint. Also the double-V-joint helps compensate for warping forces. With a single-V-joint, stress tends to warp the piece in one direction when the V-joint is filled, but with a double-V-joint, there are welds on both sides of the material, having opposing stresses, straightening the material.


Single –J- butt welds are when one piece of the weld is in the shape of a “J” that easily accepts filler material and the other piece is square. A J-groove is formed either with special cutting machinery or by grinding the joint edge into the form of a J. Although a J-groove is more difficult and costly to prepare than a V-groove, a single J-groove on metal between a half an inch and three quarters of an inch thick provides a stronger weld that requires less filler material. Double-J-butt welds have one piece that has a “J” shape from both directions and the other piece is square.


Single -U -Joint butt welds are welds that have both edges of the weld surface shaped like a J, but once they come together, they form a U. Double-U-Joints have a U formation on both the top and bottom of the prepared joint. U-joints are the most expensive edge to prepare and weld. They are usually used on thick base metals where a V-groove would be at such a extreme angle, that it would cost too much to fill.

Other Types of Joints

Thin sheet metals are often flanged to produce edge-flange or corner-flange welds. These welds are typically made without the addition of filler metal because the flange melts and provides all the filler needed Flare-groove joints are used for welding metals that, because of their shape, form a convenient groove for welding, such as a pipe against a flat surface.

A closed square butt weld is common with gas and arc welding. With this type of weld the edges being joined are in contact during the welding process and have 90 degree angles.

The Tee Butt Weld is formed when two bars or sheets are joined perpendicular to each other in the form of a “T” shape. This weld is made from the resistance butt welding process.

The square welds are the most economical for pieces thinner than 3/8” because they don’t require the edge to be prepared. Double-groove welds are the most economical for thicker pieces because they use less weld material and time.

The use of fusion welding is common for closed single-bevel, closed single J, open single J, and closed double J butt joints. The use of gas and arc welding is ideal for double-bevel, closed double-bevel, open double-bevel, single-bevel, and open single-bevel butt welds.

Type of Joint Base Metal Thickness
Square-Joint Up to 1/4"
Single-bevel-joint 3/16”- 3/8”
Double-bevel- joint Over 3/8”
Single-V- joint Up to 3/4”
Double-V- joint Over 3/4"
Single-J- joint 1/2” – 3/4”
Double-J- joint Over 3/4"
Single-U- joint Up to 3/4"
Double-U- joint Over 3/4"
Flange (edge of corner) Sheet metals less than 12 gage
Flare-groove All thickness

Plate Edge Preparation

In common welding practices, the welding surface needs to be prepared to ensure the strongest weld possible. Preparation is needed for all forms of welding and all types of joints. Generally, butt welds require very little preparation, but some is still needed for the best results. Plate edges can be prepared for butt joints in various ways, but the five most common techniques are oxyacetylene cutting (oxy-fuel welding and cutting), machining, chipping, grinding, and air carbon-arc cutting or gouging. Each technique has unique advantages to their use.

For steel materials, oxyacetylene cutting is the most common form of preparation. This technique is advantageous because of its speed, low cost, and adaptability. Machining is the most effective in reproducibility and mass production of parts. Preparation of J or U joints is common prepared by machining due to the need for high accuracy. Metal parts that are produced by casting are commonly prepared for welding by the chipping method. The use of grinding to prepare pieces is reserved for small sections that cannot be prepared by other methods. Air carbon arc welding is common in industries that work with stainless steels, cast iron, or ordinary carbon steel[34].


Most often, the major metric used for judging the quality of a weld is its strength and the strength of the material around it. Many distinct factors influence this, including the welding method, the amount and concentration of energy input, the base material, the filler material, the flux material, the design of the joint, and the interactions between all these factors. To test the quality of a weld, either destructive or nondestructive testing methods are commonly used to verify that welds are defect-free, have acceptable levels of residual stresses and distortion, and have acceptable heat-affected zone (HAZ) properties. Welding codes and specifications exist to guide welders in proper welding technique and in how to judge the quality of welds.

Heat-affected zone

The blue area results from oxidation at a corresponding temperature of 600 °F (316 °C). This is an accurate way to identify temperature, but does not represent the HAZ width. The HAZ is the narrow area that immediately surrounds the welded base metal.

The effects of welding on the material surrounding the weld can be detrimental—depending on the materials used and the heat input of the welding process used, the HAZ can be of varying size and strength. The thermal diffusivity of the base material plays a large role—if the diffusivity is high, the material cooling rate is high and the HAZ is relatively small. Conversely, a low diffusivity leads to slower cooling and a larger HAZ. The amount of heat injected by the welding process plays an important role as well, as processes like oxyacetylene welding have an unconcentrated heat input and increase the size of the HAZ. Processes like laser beam welding give a highly concentrated, limited amount of heat, resulting in a small HAZ. Arc welding falls between these two extremes, with the individual processes varying somewhat in heat input.[35][36] To calculate the heat input for arc welding procedures, the following formula can be used:

Q = \left(\frac{V \times I \times 60}{S \times 1000} \right) \times \mathit{Efficiency}

where Q = heat input (kJ/mm), V = voltage (V), I = current (A), and S = welding speed (mm/min). The efficiency is dependent on the welding process used, with shielded metal arc welding having a value of 0.75, gas metal arc welding and submerged arc welding, 0.9, and gas tungsten arc welding, 0.8.[37]


There are many types of defects that can occur depending on the material and welding process. Types of defects include cracks, distortion, gas inclusions (porosity), non-metallic inclusions, lack of fusion, incomplete penetration, lamellar tearing, and undercutting.


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

Unusual conditions

Underwater welding

While many welding applications are done in controlled environments such as factories and repair shops, some welding processes are commonly used in a wide variety of conditions, such as open air, underwater, and vacuums (such as space). In open-air applications, such as construction and outdoors repair, shielded metal arc welding is the most common process. Processes that employ inert gases to protect the weld cannot be readily used in such situations, because unpredictable atmospheric movements can result in a faulty 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, such as flux cored arc welding and gas tungsten arc welding, are also common. Welding in space is also possible—it was first attempted in 1969 by Russian cosmonauts, when they performed experiments to test shielded metal arc welding, plasma arc welding, and electron beam welding in a depressurized environment. Further 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 may be useful for future endeavours similar to the construction of the International Space Station, which could rely on welding for joining in space the parts that were manufactured on Earth.[38]

Safety issues

Arc welding with a welding helmet, gloves, and other protective clothing

Welding, without the proper precautions, can be a dangerous and unhealthy practice. However, with the use of new technology and proper protection, risks of injury and death associated with welding can be greatly reduced. Because many common welding procedures involve an open electric arc or flame, the risk of burns and fire is significant; this is why it is classified as a hot work process. To prevent them, welders wear personal protective equipment in the form of heavy leather gloves and protective long sleeve jackets to avoid exposure to extreme heat and flames. Additionally, the brightness of the weld area leads to a condition called arc eye in which ultraviolet light causes inflammation of the cornea and can burn the retinas of the eyes. Goggles and 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, 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.[39]

Oxyfuel welding with protective eyeware

Welders are also often exposed to dangerous gases and particulate matter. Processes like flux-cored arc welding and shielded metal arc welding produce smoke containing particles of various types of oxides, which in some cases can lead to medical conditions like metal fume fever. The size of the particles in question tends to influence the toxicity of the fumes, with smaller particles presenting a greater danger. Additionally, many processes produce fumes and various gases, most commonly carbon dioxide, ozone and heavy metals, that can prove dangerous without proper ventilation and training. Exposure to manganese welding fumes, for example, even at low levels (<0.2 mg/m3), may lead to neurological problems or to damage to the lungs, liver, kidneys, or central nervous system.[40] Furthermore, because the use of compressed gases and flames in many welding processes poses an explosion and fire risk, some common precautions include limiting the amount of oxygen in the air, keeping combustible materials away from the workplace,[41] or making use of a positive pressure enclosure. Welding fume extractors are often used to remove the fume from the source and filter the fumes through a HEPA filter.

Costs and trends

As an industrial process, the cost of welding plays a crucial role in manufacturing decisions. Many different variables affect the total cost, including equipment cost, labor cost, material cost, and energy cost. Depending on the process, equipment cost can vary, from inexpensive for methods like shielded metal arc welding and oxyfuel welding, to extremely expensive for methods like laser beam welding and electron beam welding. Because of their high cost, they 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 the deposition rate (the rate of welding), the hourly wage, and the total operation time, including both time welding and handling the part. The cost of materials includes the cost of the base and filler material, and the cost of shielding gases. Finally, energy cost depends on arc time and welding power demand.

For manual welding methods, labor costs generally make up the vast majority of the total cost. As a result, many cost-saving measures are focused on minimizing operation time. To do this, welding procedures with high deposition rates can be selected, and weld parameters can be fine-tuned to increase welding speed. Also, removal of welding spatters generated during welding process is highly labor intensive and time consuming. Implementation of Welding Anti Spatter & Flux which is safe and non-polluting is considered as a welcome change in cost cutting and weld joint quality improvement measures. Mechanization and automation are often implemented to reduce labor costs, but this frequently increases the cost of equipment and creates additional setup time. Material costs tend to increase when special properties are necessary, and energy costs normally do not amount to more than several percent of the total welding cost.[42]

In recent years, in order to minimize labor costs in high production manufacturing, industrial welding has become increasingly more automated, most notably with the use of robots in resistance spot welding (especially in the automotive industry) and in arc welding. In robot welding, mechanized devices both hold the material and perform the weld[43] and at first, spot welding was its most common application, but robotic arc welding increases in popularity as technology advances. Other key areas of research and development include the welding of dissimilar materials (such as steel and aluminum, for example) and new welding processes, such as friction stir, magnetic pulse, conductive heat seam, and laser-hybrid welding. Furthermore, progress is desired in making more specialized methods like laser beam welding practical for more applications, such as in the aerospace and automotive industries. Researchers also hope to better understand the often unpredictable properties of welds, especially microstructure, residual stresses, and a weld's tendency to crack or deform.[44]

See also


  1. ^ Cary and Helzer, p 4
  2. ^ Lincoln Electric, p 1.1-1
  3. ^ Lazarev, P.P. (December 1999), "Historical essay on the 200 years of the development of natural sciences in Russia" (Russian), Physics-Uspekhi 42 (1247): 1351-1361, doi:10.1070/PU1999v042n12ABEH000750, archived from the original on 2009-12-04, 
  4. ^ Cary and Helzer, p 5–6
  5. ^ Cary and Helzer, p 6
  6. ^ a b Weman, p 26
  7. ^ Lincoln Electric, p 1.1-5
  8. ^ Sapp, Mark E. (February 22, 2008). "Welding Timeline 1900-1950". Retrieved 2008-04-29. 
  9. ^ Cary and Helzer, p 7
  10. ^ Lincoln Electric, p 1.1-6
  11. ^ Cary and Helzer, p 9
  12. ^ Kazakov, N.F (1985). "Diffusion Bonding of Materials". Pergamon Press. 
  13. ^ Lincoln Electric, 1.1-10
  14. ^ Cary and Helzer, p 246–49
  15. ^ Kalpakjian and Schmid, p 780
  16. ^ Lincoln Electric, p 5.4-5
  17. ^ Weman, p 16
  18. ^ Cary and Helzer, p 103
  19. ^ Weman, p 63
  20. ^ Lincoln Electric, p 5.4-3
  21. ^ Weman, p 53
  22. ^ Weman, p 31
  23. ^ Weman, p 37–38
  24. ^ Weman, p 68
  25. ^ Weman, p 80–84
  26. ^ Weman, p 95–101
  27. ^ Weman, p 89–90
  28. ^ Hicks, p 52–55
  29. ^ Cary and Helzer, p 19, 103, 206
  30. ^ Cary and Helzer, p 401–04
  31. ^ Henderson, 50
  32. ^ James F. Lincoln Foundation, 7-4,7-5
  33. ^ Smith, 473
  34. ^ James F. Lincoln Foundation, 7-7
  35. ^ Lincoln Electric, p 6.1-5–6.1-6
  36. ^ Kalpakjian and Schmid, p 821–22
  37. ^ Weman, p 5
  38. ^ Cary and Helzer, p 677–83
  39. ^ Cary and Helzer, p 42, 49–51
  40. ^ Welding and Manganese: Potential Neurologic Effects. National Institute for Occupational Safety and Health. March 30, 2009.
  41. ^ Cary and Helzer, p 52–62.
  42. ^ Weman, p 184–89
  43. ^ Lincoln Electric, p 4.5-1
  44. ^ ASM International, "Welding Research Trends in the United States", p 995–1005


  • ASM International (2003). Trends in Welding Research. Materials Park, Ohio: ASM International. ISBN 0-87170-780-2. 
  • Blunt, Jane; Nigel C. Balchin (2002). Health and Safety in Welding and Allied Processes. Cambridge: Woodhead. ISBN 1-85573-538-5. 
  • Cary, Howard B; Scott C. Helzer (2005). Modern Welding Technology. Upper Saddle River, New Jersey: Pearson Education. ISBN 0-13-113029-3. 
  • Henderson, J.G. (1953). Metallurgical Dictionary. New York, New York: Reinhold Publishing Corporation. 
  • Hicks, John (1999). Welded Joint Design. New York: Industrial Press. ISBN 0-8311-3130-6. 
  • Kalpakjian, Serope; Steven R. Schmid (2001). Manufacturing Engineering and Technology. Prentice Hall. ISBN 0-201-36131-0. 
  • Lincoln Electric (1994). The Procedure Handbook of Arc Welding. Cleveland: Lincoln Electric. ISBN 99949-25-82-2. 
  • Smith, Dave (1984). Welding Skills and Technology. New York, New York: McGraw-Hill Book Company. ISBN 0-07-000757-8. 
  • The James F. Lincoln Arc Welding Foundation (1978). Principles of Industrial Welding. Cleveland, Ohio: The James F. Lincoln Arc Welding Foundation. 
  • Weman, Klas (2003). Welding processes handbook. New York, NY: CRC Press LLC. ISBN 0-8493-1773-8. 

External links

Study guide

Up to date as of January 14, 2010

From Wikiversity

Please see Directions for use for more information.


Learning Project Summary

  • Project code:
  • Suggested Prerequisites: Basic understanding of metal and electricity (but not required)
    • ...
  • Time investment: approximately 275 working hours.
  • Assessment suggestions: Apprentice or Journeyman inspection.
  • Portal:
  • School:
  • Department: Technology
  • Stream
  • Level: One

Content summary

The Welding Learning Project exists to provide a program of study and a network of feedback and support for beginning welders.


By the time this project reaches maturity, it should:

  • describe the various processes of modern welding
  • relate essential metallurgical and technical concepts
  • prepare students to work safely in a metal shop
  • provide a course of self-study exercises that develop essential skills, harbor methodical understanding, and train ones muscles for the demanding task of joining metal
  • present comprehensive photographic and textual weld analysis tools for the independent learner
  • foster a community of mutually-supportive learners

Skills to learn include:

  • Job Safety
  • Oxy-Fuel Welding & Cutting
  • SMAW (Stick Welding)
  • GMAW (Mig Welding)
  • GTAW (Tig Welding)
  • Basic Blueprint Reading
  • Basic Metallurgy

Concerning Safety

It is essential that Shop Safety be the first topic to be developed in this course. Welding involves bare electricity, molten metal and explosive gasses, so before any projects are attempted, the student should thoroughly understand how to interact with these elements with minimal risk.

Also, a disclaimer should be prepared and posted.

This site contains a good introduction to welding safety, including links to OSHA publications.

Learning materials

The Internet teems with welding-related resources, and one purpose of this Learning Project is to pool them together into a useful, indexed directory.

Printed Texts

Process Guides

  • Oxyacetylene Welding: Basic Fundamentals by Ronald J. Baird.
  • Arc Welding: Basic Funamentals by John R. Walker
  • Flux Cored Arc Welding Handbook by William H. Minnick
  • Gas Metal Arc Welding Handbook by William H. Minnick
  • Gas Tungsten Arc Welding Handbook by William H. Minnick

Blueprint Reading

  • Blueprint Reading for Welders (7th Ed.) by A.E. Bennett & Louis J. Siy


  • Metallurgy Fundamentals by Daniel A. Brandt & J.C. Warner
    • A basic text for beginning welders that deals almost exclusively with ferrous metallurgy.
  • Welding Metallurgy by Sindo Kou
    • An advanced text for experienced welders, or those students who have previously studied chemistry and physics.

Comprehensive Texts

  • Welding Skills and Practices by Joseph W. Giachino & William Weeks
    • NOTE: This title is several decades out of print, but remains well worth reading for its clear and coherent discussion of both welding theory and practicalities.


  • Welding Fabrication and Repair: Questions & Answers by Frank Marlow
    • From the Preface: "Beginning welding students learn how to make weld beads- and nothing else... [This book] goes beyond the classroom, to real life practical applications such as vehicle frame repairs, building tables, rectangular and box frames, and brackets."

Electronic Texts

Other Internet Resources

  • The Miller and Lincoln welding equipment companies have each prepared an impressive array of free educational materials, including how-to articles, setting calculators and interactive, flash-animated tutorials.


  1. Introduction to the Processes of Welding
  2. General Shop Safety
  3. Math & Measurement for Welding
  4. Joint Design & Terminology
  5. Basic Welding Metallurgy
  6. Oxy-Acetylene Welding
    1. Oxy-Acetylene Equipment
      1. Cylinders
      2. Regulators
      3. Torches
      4. Filler Materials & Fluxes
      5. Other Tools
    2. Welding in the Flat Position
      1. Square (Butt) Joint w/o Filler Material
      2. Square Joint w/ Filler Rod
      3. Lap Joint
      4. T-Joint
      5. Corner Joint
      6. ...
    3. Welding in the Horizontal Position
      1. Square (Butt) Joint w/o Filler Material
      2. Square Joint w/ Filler Rod
      3. Lap Joint
      4. T-Joint
      5. Corner Joint
      6. ...
    4. Welding in the Vertical Position
      1. Square (Butt) Joint w/o Filler Material
      2. Square Joint w/ Filler Rod
      3. Lap Joint
      4. T-Joint
      5. Corner Joint
      6. ...
    5. Welding in the Overhead Position
      1. Square (Butt) Joint w/o Filler Material
      2. Square Joint w/ Filler Rod
      3. Lap Joint
      4. T-Joint
      5. Corner Joint
      6. ...
    6. ...
  7. Introduction to the Arc Welding Processes
  8. Shielded Metal Arc Welding
    1. SMAW Welding Equipment
      1. Personal Protective Equipment
      2. Welding Machines
      3. Leads
      4. Electrode Holders
      5. Ground Connections
      6. Cleaning Tools
      7. Electrodes
        1. Functions of Electrodes
        2. Electrode Identification
        3. Correct Electrode Selection
        4. Types of Electrodes
    2. Striking an Arc
    3. Running Short Beads
    4. Restarting the Arc
    5. PROJECT 1: Padding a 1/2 plate with 7018 DCRP



  • Activity 1.
  • etc.


Each activity has a suggested associated background reading selection.


Additional helpful readings include:

Active participants

Active participants in this Learning Group

  • Lordcorvid (Currently in Welding School)
  • JeremyP
  • AtlantisEndevour

Related news

1911 encyclopedia

Up to date as of January 14, 2010

From LoveToKnow 1911

WELDING (i.e. the action of the verb "to weld," the same word as "to well," to boil or spring up, the history of the word being to boil, to heat to a high degree, to beat heated iron; according to Skeat, who points out that in Swedish the compound verb uppvalla means to boil, the simple vdlla is only used in the sense of welding), the process of uniting metallic surfaces by pressure exercised when they are in a semi-fused condition. It differs therefore from brazing and soldering, in which cold surfaces are united by the interposition of a fused metallic cementing material. The conditions in which welding is a suitable process to adopt are stated in the article Forging. The technique of the work will be considered here.

The conditions for successful welding may be summed up as clean metallic surfaces in contact, a suitable temperature and rapid closing of the joint. All the variations in the forms of welds are either due to differences in shames of material. or to the practice of different craftsmen. The typical weld is the scarf. If, for instance, a bar has to be united to another bar or to an eye, the joint is made diagonally (scarfed) because that gives a longer surface in contact than a weld at right angles (a butt weld), and because the hammer can be brought into play better. Abutting faces for a scarfed joint are made slightly convex; the object is to force out any scale or dirt which might otherwise become entangled in the joint at the moment of closing and which would impair its union. The ends are upset (enlarged) previous to welding, in order to give an excess of metal that will permit of slight corrections being effected around the joint ("swaging") without reducing the diameter below that of the remainder of the bar. These principles are seen in other joints of diverse types, in the butt, the vee and their modifications. Joint faces must be clean, both chemically, i.e. free from oxides, and mechanically, i.e. free from dust and dirt, else they will not unite. The first condition is fulfilled by the use of a fluxing agent, the second by ordinary precautions. The flux produces with the oxide a fluid slag which is squeezed out at the instant of making the weld. The commonest fluxes are sand, used chiefly with wrought iron, and borax, used with steel; they are dusted over the joint faces both while in the fire and on the anvil. Mechanical cleanliness is ensured by heating the ends in a clean hollow fire previously prepared, and in brushing off any adherent particles of fuel before closing the weld. The scarf, the butt and the vee occur in various modifications in all kinds of forgings, but the principles and precautions to be observed are identical in all. But in work involving the use of rolled sections, as angles, tees, channels and joists, important differences occur, because the awkwardness of the shapes to be welded involves cutting and bending and the insertion of separate welding pieces ("gluts"). Welds are seldom made lengthwise in rolled sections, nor at right angles, because union is effected in such cases by means of riveted joints. But welding is essential in all bending of sections done at sharp angles or to curves of small radius. It is necessary, because a broad flange cannot be bent sharply; if the attempt be made when it is on an outer curve it is either ruptured or much attenuated, while on an inner curve it is crumpled up. The plater's smith therefore cuts the flanges in both cases, and then bends and welds them. If it is on an inner curve, the joint is a lap weld; if it is on an outer one, a fresh piece or glut is welded in. Gluts of rectangular section are used for cylindrical objects and rings of various sections. The edges to be united may or may not be scarfed, and the gluts, which are plain bars, are welded against the edges, all being brought to a welding heat in separate furnaces. The furnace tubes of boilers and the cross tubes are welded in this way, sometimes by hand, but often with a power hammer, as also are all rings of angle and other sections on the vertical web.

The temperature for welding is very important. It must be high enough to render the surfaces in contact pasty, but must not be in excess, else the metal will become badly oxidized (burnt) and will not adhere. Iron can be raised to a temperature at which minute globules melt and fall off, but steel must not be heated nearly so much, and a moderate white heat must not be exceeded. Welds in steel are not so trustworthy nor so readily made as those in iron.

Thermit Welding

The affinity of finely powdered aluminium for metallic oxides, sulphides, chlorides, &c., may be utilized to effect a reduction of metals with which oxygen, sulphur or chlorine combine. C. Vautin in 1894 found that when aluminium in a finely divided state was mixed with such compounds and ignited, an exceedingly high temperature, about 3000 C., was developed by the rapid oxidation of the aluminium. He found that metals which are ordinarily regarded as infusible were readily reduced, and in a very high degree of purity. These facts were turned to practical account by Dr H. Goldschmidt, who first welded two iron bars by means of molten iron produced by the process, to which the name of "thermit" is now commonly applied. The method has also been applied to the production of pure metals for alloying purposes, as of chromium free from carbon, used in the manufacture of chrome steel, of pure manganese for manganese steel, of molybdenum, ferro-vanadium, ferro-titanium and others used in the manufacture of high speed steels.

Thermit as a welding agent is produced by mixing iron oxides with finely granulated aluminium, in a special crucible lined with magnesia. On ignition, the chemical reactions proceed so rapidly that the contents would be lost over the edges unless the crucible were closed with a cover. The result of the reaction is that two layers are produced, the bottom one of pure iron, the top one of oxide of alumina or corundum. If the contents are poured over the edge, the slag follows first, and is followed by the metal. But in welding the metal is poured first through the bottom upon the joint. It is practically pure wrought iron in a molten state, at 3000° C., or 5400° F. The heat is so intense that it is possible thus to burn a clean hole through a i in. wrought iron plate. The joints are prepared by abutting them, and provision is made with clamps to grip and retain them in correct positions. Often, but not always, the part to be welded is enclosed in a mould, into which the thermit is tapped from the crucible. The applications of thermit welding are numerous. A wide field is that of tramway rails, of which large numbers have been successfully welded. Steel girders have been welded, as also have broken and faulty steel and iron castings, broken shafts, broken sternposts (for which crucibles 6 ft. in height with a capacity of 7 cwt. have been constructed), and wrought iron pipes. Another application is to render steel ingots sound, by introducing thermit in a block on an iron rod into the mould, which prevents or greatly lessens the amount of piping in the head, due to shrinkage and occlusion of gases. (J. G. H.) Electric Welding. - In electric welding and metal working the heat may be communicated to the metal by an electric arc, or by means of the electric resistance of the metal, as in the Thomson process. Arc welding is the older procedure, and it appears to have been first made use of by de Meritens in 1881 for uniting the parts of storage-battery plates. The work-piece was placed upon a support or table, and connected with the positive pole of a source of current capable of maintaining an electric arc. The other pole was a carbon rod directed by the hand of the operator so as first to make contact with the work-piece, and then to effect the proper separation to maintain the arc. The heat of the arc was partly communicated to the work and partly dissipated in the hot gases escaping into the surrounding air. The result was a fusion of the metallic lead of the storage-battery plate which united various parts of the plate. The process was somewhat similar to the operation of lead-burning by the hydrogen and air blowpipe, as used in the formation of joints in chemical tanks made of sheet-lead. The method of de Meritens has been modified by Bernardos and Olszewski, Slavienoff, Coffin and others.

In the Bernardos and Olszewski process the work is made the negative pole of a direct current circuit, and an arc is drawn between this and a carbon rod, to which a handle is attached for manipulating. As this rod is the positive terminal, particles of carbon may be introduced as a constituent of the metal taking part in the operation, making it hard and brittle, and causing cracks in the joint or filling; the metal may, in fact, become very hard and unworkable. The Slavienoff modification of the arc-welding process consists in the employment of a metal electrode in place of the carbon rod. The metal electrode gradually melts, and furnishes fused drops of metal for the filling of vacant spaces in castings, or for forming a joint between two parts or pieces.

In arc welding, with a current source at practically constant potential, a choking resistance in series with the heating arc is needed to secure stability in the arc current, as in electric arc lighting from constant potential lines. Little effective work can be done by the Bernardos and Olszewski method with currents much below 150 amperes in the arc, and the value in some cases ranges above 500 amperes. The potential must be such that an arc of 2 to 3 in. in length is steadily maintained. This may demand a total of about 150 volts for the arc and the choking resistance together. In the Slavienoff arc the potential required will be naturally somewhat lower than when a carbon electrode is used, and the current strength will be, on the other hand, considerably greater, reaching, it appears, in certain cases, more than 4000 amperes. In some recent applications of the arc process the polarity of the work-piece and the arccontrolling electrode has, it is understood, been reversed, the work being made the positive pole and the movable electrode the negative. More heat energy is thus delivered to the work for a given total of electric energy expended.

Arc welding. The arc method is essentially a fusing process, though with due care it is used for heating to plasticity the edges of iron sheets to be welded by pressure and hammering. It has been found applicable in special cases to the filling of defective spots in iron castings, by fusing into blow-holes or other spaces small masses of similar metal, added gradually, and melted into union with the body of the piece by the heat of the arc. Similarly, a more or less complete union between separate pieces of iron plate 4 to 2 in. in thickness has been effected by fusing additional metal between them. The range of operations to which the arc process is applicable is naturally somewhat limited, and depends to a large extent upon the skill acquired by the operator, who necessarily works with his eyes well screened from the glare of the large arc. Unless the space in which the work is carried on is large, the irritating vapours which rise from the arc stream add to the difficulty. Strong draughts of air which would disturb the arc must also be avoided. These factors, added to the relative slowness of the work and the uncertainty as to its result, have tended to restrict the application of arc welding in practice. Moreover, much heat-energy is dissipated in the arc flame and passes into the air, while, owing to the time required for the work, the metal undergoing treatment loses much heat by radiation. Yet the method requires little special machinery. The current may be taken from existing electric lighting and power circuits of moderate potential without transformation, and may be utilized with simple appliances, consisting chiefly of heavy wire leads, a carbon or metal electrode with a suitable handle for its manipulation, a choking or steadying resistance, and screen of dark glass for the operator's eyes.

In 1874 Werdermann proposed to use, as a sort of electric blowpipe, the flame gases of an electric arc blown or deflected by an air jet or the like - a suggestion subsequently revived by Zerener for arc welding. The arc in this instance is deflected from the space between the usual carbon electrodes by a magnetic field. The metal to be heated takes no part in the conduction of current, the heat is communicated by the gases of the arc, and, to a small extent, by the radiation from the hot carbon electrodes between which the arc is formed. The process is scarcely to be called electric in any true sense. Another curious operation, resembling in some respects the arc methods, has been proposed for the heating of metal pieces before they are brought under the hammer for forging or welding. The end of a metal bar is plunged into an electrolytic bath while connected with the negative pole of a lighting or other electric circuit having a potential of ioo to 150 volts. The positive pole is connected with a metal plate as an anode immersed in the electrolyte, or forming the side of the containing vat or tank. A solution of sodium or potassium carbonate is a suitable electrolyte. That part of the bar which is immersed acts as a cathode of limited surface, and is at once seen to be surrounded by a luminous glow, with gas bubbles arising from it. The immersed end of the bar rapidly heats, and may even melt under the liquid of the bath. It is probable that an arc forms between the surface of the metal and the adjacent liquid layer, the intense heat of which is in part communicated to the metal and in part lost in the solution, causing thereby a rapid heating of the bath. This singular action appears to have been first made known by Hoho and Lagrange. It is distinctly a form of electric heating, having no necessary relation to such subsequent operations as welding, and is, moreover, wasteful of energy, as the heat is largely carried off in the liquid bath.

The process of Elihu Thomson first brought to public notice in 1886, has since that time been applied commercially on a large scale to various metal-welding operations. The usual laminated iron-transformer core, I, constituting a closed iron. magnetic circuit threading both primary and secondary electric circuits. The terminals of the single-turn secondary serve as connexions and supports for the welding clamps C D, which hold the work. The clamps are variously modified to suit the size, shape and character of the metal pieces, MN, to be welded, and the proportions of the transformer itself are made proper for the conditions existing in each case. The potential of the primary circuit may be selected at any convenient value, provided the winding of the coil P P is adapted thereto, but usually 300 volts is employed, and the periodicity is about 60 cycles. Inasmuch as only the proposed joint and a small amount of metal on each side of it are concerned in the operation, the delivery of energy is closely localized. The chief electrical resistance in the welding circuit is in the projections between the clamps, where the electric energy is delivered and appears as heat. A portion of the energy is, as usual, lost in the transformation and in the resistance of the circuits elsewhere, but, by proper proportion FIG. I. - Thomson Welding Transformer.

ing, the loss may be kept down to a moderate percentage of the total, as in other electric work.

The pieces are set firmly in the welding clamps, with the ends to be joined in abutment and in electric contact. The projection of each piece from the clamp varies with the section of the pieces, their form and the nature of the metal, and the time in which a joint is to be made; but it rarely exceeds the thickness or diameter of the pieces, except with metals of high heat conductivity such as copper. When the pieces are in place the current is turned into the primary coil of the transformer, sometimes suddenly and in full force, but more often gradually. Switches and regulating devices in the primary circuit permit complete and delicate control. At least one of the clamps, D (fig. I), is movable through a limited range towards and from the other, and is thus the means of exerting pressure for forcing the softened metal into complete union. In large work the motion is given by a hydraulic cylinder and piston, under suitable control by valves. At about the time the current is cut off, it is usual to apply i ncreased pressure. The softened metal is upset or pressed outwards at the joint and forms a characteristic burr, which may be removed by filing or grinding, or be hammered down while the metal is still hot. Sometimes the burr is not objectionable, and is allowed to remain. Lap welds may be made, but butt welds are found to be satisfactory for most purposes. The appearance of round bars in abutment before welding is shown in fig. 2 at A; and at B they are represented as having been joined by an electric butt weld, with the slight upset or burr at the j oint. Before the introduction of the Thomson process a few only of the metals, such as platinum, gold and iron, were regarded as weldable; now nearly all metals and alloys may be readily joined. Such combinations as tin and lead, copper and brass, brass and iron, iron and nickel, brass and German silver, silver and copper, copper and platinum, iron and German silver, tin and zinc, zinc and cadmium, &c., are easily made; even brittle crystalline metals like bismuth and antimony may be welded, as well as different metals and alloys whose fusing or softening temperatures do not differ too widely.

If the meeting ends conduct sufficiently to start the heating, it is not necessary that they should fit closely together, nor is it necessary that they should be quite clean, the effect of the incipient heating being to confer conductivity upon the scale and oxide at the joint.

metal pieces to be united are held in massive clamps and process. pressed together in firm contact; and a current is made to traverse the proposed joint, bringing it to the welding temperature. The union is effected by forcing the pieces together mechanically. The characteristic feature of the process is the fact that the heat is given out in the body of the metal.

The voltage does not usually exceed two or three, though it may reach four or five volts; but as the resistance of the metal pieces to be joined is low, the currents are of very large values, sometimes reaching between 50,000 and 100,000 amperes. Even for the joining of small wires the current is rarely less than ioo amperes. Such currents cannot, of course, be carried more than a few feet without excessive loss, unless the conductors are given very large section. With alternating currents, also, the effectiveness of the work speedily diminishes, on account of the inductive drop in the leads, if they are of any considerable length. The carrying of the welding currents over a distance of several feet may, in fact, lead to serious losses. These difficulties are overcome in the Thomson welding transformer, which resembles the step-down transformers used in electric lighting distribution by alternating currents, with the exception that the secondary coil or conductor, which forms part of the welding circuit, usually consists of only one turn of great section, S S (fig. I). This is often made in the form of a copper casing, which surrounds or encloses the primary coil P P in whole or in part. The primary coil is of copper wire of many turns. The secondary casing, with the primary enclosed, is provided with the FIG. 2.

In some cases the application of a flux, such as borax, enables the welding to be accomplished at a lower temperature, thus avoiding risk of injury by excessive heating. While the pieces are heating, the increase of temperature may raise the specific resistance of the metal so that the current required will be lessened per unit of area, while on the other hand the growing perfection of contact during welding, by increasing the conducting area at the joint, compensates for this in that it tends to the increase of current. With some alloys like brass and German silver, which have a low temperature coefficient, this compensating effect is nearly absent. The increase of specific resistance of the metals with increase of temperature FIG. 3.-Automatic Welder.

has another valuable effect in properly distributing the heating over the whole section of the joint. Any portion which may be for the moment at a lower temperature than other portions will necessarily have a lower relative resistance, and more current will be diverted to it. This action rapidly brings any cooler portion into equality of temperature with the rest. It also prevents the overheating of the interior portions which are not losing heat by radiation and convection. The success of the electric process in welding metals which were not formerly regarded as weldable is probably due in a measure to this cause, and also to the ease of control of the operation, for the operator may work within far narrower limits of plasticity and fusibility than with the forge fire or blowpipe. The mechanical pressure may be automatically applied and the current automatically cut off after the completion of the weld. In some more recent types of welders the clamping and releasing of the pieces are also accomplished automatically, and nothing is left for the operator to do but to feed the pieces into the clamps. Repetitionwork is thus rapidly and accurately done. The automatic welder represented in fig. 3 has a capacity of nearly woo welds per day. The pressure required is subject to considerable variation: the more rigid the material at the welding temperature, the greater is the necessary pressure. With copper the force may be about 600 pounds per square inch of section; with wrought iron, 1200 pounds; and with steel, 1800 pounds. It is customary to begin the operation with much lighter pressure than that used when all parts of the pieces at the joint have come into contact. The pressure exerted in completing the weld has the effect of extruding from the joint all dross and slag, together with most of the metal which is rendered plastic by the heat. The strongest electric welds are those effected by this extrusion from the joint, in consequence of heavy pressure quickly applied at the time of completion of the weld. The unhammered weld, as ordinarily made by the electric process, has substantially the same strength as the annealed metal of the bar, the break under tensile strain, when the burr at the weld is left on, usually occurring a little to one side of the joint proper, where the metal has been annealed by'heating. Hammering or forging the joint while the metal cools, in the case of malleable metals such as iron or copper, will usually greatly toughen the metal, and it should be resorted to where a maximum of strength is desired. The same object is partially effected by placing the weld, while still hot, between dies pressed forcibly together so as to give to the weld some desired form, as in drop-forging.

The amount of electric energy necessary for welding by the Thomson process varies with the different metals, their electric conductivity, their heat conductivity, fusibility, the shape of the pieces, section at the joint, &c. In the following table are given some results obtained in the working of iron, brass and copper. The figures are of course only approximate, and refer to one condition alone of time-consumption in the making of each weld. The more rapidly the work is done, the less, as a rule, is the total energy required; but the rate of output of the plant must be increased with increase of speed, and this involves a larger plant, the consequent expense of which is often disadvantageous. If in the following table the watts for a given section be multiplied by the time, the relation between the total energy required for different sections of the same metal, or for the same section of the different metals, is obtained. These products are given under the head of watt-seconds. It will be seen that the energy increases more rapidly than the sections of the pieces-doubtless because the larger pieces take a longer time in welding, with the result of an increased loss by conduction of heat along the bars back from the joint. If the time of welding could be made the same for various sections, it is probable that the energy required would be more nearly in direct proportion to the area of section for any given metal. This relation would however, only hold approximately, as there is a greater relative loss of heat by radiation and convection into the air from the pieces of smaller section. The total energy in watt-seconds for any given section of copper will be found to be about half as much again as that for the same section of iron, while the amounts of energy required for equal sections of brass and iron do not greatly differ.

Iron and Steel.

Section, Sq. In.

Watts in Prim-

ary of Welder.

Time in



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Energy Used In Electric Welding In practice, joints in solid bars or in wires are the most common but the process is applicable to pieces of quite varied form. Joints in iron, brass, or lead pipe are readily made; strips of sheet metal are joined, as in band saws; bars or tubes are j oined at various angles; sheet metal is joined to bars, &c. One of the more interesting of the recent applications of electric welding is the longitudinal seaming of thin steel pipe. The metal or skelp is in long strips, bent to form a hollow cylinder or pipe, and the longitudinal seam moves through a special welder, which passes a current across it. The work is completed by drawing the pipe through dies. The welding of a ring formed by bending a short bar into a circle affords an excellent illustration of the character of the currents employed in the Thomson process. Notwithstanding the comparatively free path around the ring through the full section of the bent bar, the current heats the abutted ends to the welding temperature. In this way waggon and carriage wheel tyres, harness rings, pail and barrel hoops, and similar objects are extensively produced. The process is also largely applied to the welding of iron and copper wires used for electric lines and conductors, of steel axles, tyres and metal frames used in carriage work, and of such parts of bicycles as pedals, crank hangers, seat posts, forks, and steel tubing for the frames. The heat, whether it be utilized in welding or brazing, is so sharply localized that no damage is done to the finish of surfaces a short distance from the weld or joint. Parts can be accurately formed and finished before being joined, as in the welding of taper shanks to drills, the lengthening of drills, screw taps, or augers, and the like. Electric welding is applicable to forms of pieces or to conditions of work which would be impracticable with the ordinary forge fire or gas blowpipe. A characteristic instance is the wire bands which hold in place the solid rubber tyres of vehicles. The proximity of the rubber forbids the application of the heat of a fire or blowpipe, but by springing the rubber back from the proposed joint and seizing the ends of wire by the electric welding clamps, the union is rapidly and easily made. When the rubber of the tyre is released, it covers the joint, regaining its complete form. Special manufactures have in some cases arisen based upon the use of electric welding. The welding clamps, and the mechanical devices connected with them, vary widely in accordance with the work they have to do. A machine for forming metal wheels is so constructed that thethubs are made in two sections, which when brought together in the welder are caused to embrace the radiating iron or steel spokes of the wheel. The two sections are then welded, and hold the spokes in solid union with themselves. Another machine, designed for the manufacture of wire fences,makes several welds automatically and simultaneously Galvanized iron wires are fed into the machine from reels in several parallel lines about a foot apart, and at intervals are crossed at right angles by wire sections cut automatically from another reel of wire. As the wire passes, electric welds are formed between the transverse and the parallel lines. The machine delivers a continuous web of wire fencing, which is wound upon a drum and removed from time to time in large rolls. In the United States, street railway rails are welded into a continuous metal structure. A huge welding transformer is suspended upon a crane, which is borne upon a car arranged to run upon the track as it is laid. The joint between the ends of two contiguous rails is made by welding lateral strap pieces, covering the joint at each side and taking the place of the ordinary fish-plates and bolts. The exertion of a greatly increased pressure at the finish of the welding seems to be decidedly favourable to the permanence and strength of the joints. When properly made, the joint is strong enough to resist the strains of extension and compression during temperature changes. For electric railways the welded joint obviates all necessity for "bonding" the rails together with copper wires to convert them into continuous lines of return conductors for the railway current. In railway welding the source of energy is usually a current delivered from the trolley line itself to a rotary converter mounted on the welding car, whereby an alternating current is obtained for feeding the primary circuit of the welding transformer. Power from a distant station is thus made to produce the heat required for track welding, and at exactly the place where it is to be utilized. In this instance the work is stationary while the welding apparatus is moved from one joint to the next. Welding transformers are sometimes used to heat metal for annealing, for forging, bending, or shaping, for tempering, or for hard soldering. Under special conditions they are well adapted to these purposes, on account of the perfect control of the heating or energy delivery, and the rapidity and cleanliness of the operation.

Divested of its welding clamps, the welding transformer has found a unique application in the armour-annealing process of Lemp, by means of which spots or lines are locally annealed Armouri n hard-faced ship's armour, so that it can be drilled or plate cut as desired. Before the introduction of this process, it was practically impossible to render any portion of the hardened face of such armour workable by cutting tools without detriment to the hardness of the rest. A very heavy electric current is passed through the, spot or area which it is desired to soften, so that, notwithstanding the rapid conduction of heat into the body of the plate, the metal is brought to a low red heat. In order that the spot shall not reharden, it is requisite that the rate of cooling shall be slower than when the heating current is cut off suddenly, the current therefore undergoes gradual diminution, under control of the operator. The welding transformer has for its secondary terminals simply two copper blocks fixed in position, and mounted at a distance of an inch or more apart. These are placed firmly against the face of the armour plate, with the spot to be annealed bridging the contacts, or situated between them. As in track welding, the transformer is made movable, so that it can be brought into any position desired. When the annealing is to be done along a line, the secondary terminals, with the transformer, are slowly and steadily slid over the face of the plate, new portions of the plate being thus continually brought between the terminals, while those which had reached the proper heat are slowly removed from the terminals and cool gradually. (E. T.)

<< Friedrich Gottlieb Welcker

Walter Weldon >>


Up to date as of January 23, 2010

From Wikibooks, the open-content textbooks collection



Welding. One of the most important trades of the world in which we live. Welding is defined as 'the fusing of two or more pieces of metal or plastic'. It binds the office buildings in which we work, the malls where we hang out, and in every car that we will ever drive. Welding is a 'skilled trade', which means that not everyone can pick up a welding torch and build something, it must be learned. Because of this, welders are often paid well or above average wages. Interested? It actually doesn't take too long to learn, in some cases a journey person status can be reached in as little as 3 years. The skilled welder has a steady hand, good hand-eye coordination, and good working ethics.


Safety is a key player in all types of welding. The human body is mostly made up of water, and water and metal don't usually go together well. Make proper use of safety goggles/glasses, gloves, leather clothing, work boots and welding helmets. Welding is HOT, so keep around a metal pail of cooling oil or water, and, just in case, a can of instant-freeze for yourself. Wear earplugs if you are sensitive to loud noise, as it can get pretty loud while welding and grinding. Make proper use of and KNOW the tools you are using, if you don't know what something is or does, ask... it may save a limb or even a life. Be wary of sparks and weld flashing, eyes are extremely sensitive, and if extreme or prolonged enough, damage can lead to permanent blindness.


Welding has been around in some form or another ever since people realized that metal could be useful. One of the oldest methods of welding was actually forging. A metal ore would be retrieved by mining, smelted in a hot fire, collected into a large quantity of almost pure metal, and hammered into shape by using different fire techniques. Different methods of kindling, stocking and airing a fire could control the heat that it would produce. For example, to forge a sword a fire would need to heat the metal (likely copper or bronze), to a red-orange glow. Eventually, mixed metals (alloys) were used for higher strength and a range of new uses.



There are several different ways in which to weld. The most common in industrial workplaces is 'SMAW', or "Shielded Metal Arc Welding". The 'stick' or 'rod' is placed into a 'stick holder' (gun or clamp style) which is then scraped or tapped onto the grounded weld piece to produce an 'electric arc', which produces enough heat to melt the 'rod' and form it into the weld piece. This process utilizes electricity to push out a "glob" of molten metal onto a plate(s) of metal, the 'workpiece'. Pipeline and structural welders use this method the most because of its deep 'penetration' (how much it digs into the base metal), and pressure handling capabilities.


The next most common method of welding is Gas Metal Arc Welding(GMAW) also called MIG or MAG welding (MIG- Metal Inert Gas and MAG- Metal Active Gas), GMAW utilizes the same principal as SMAW, but the electrode is not a 'rod', but a wire on a spool, which is fed through a 'gun'. The welder may prefer this method because of its ability to travel along the weld surface faster, and has a similar outcome in quality of the weld. However, spools of wire can be expensive, and the use of a 'shielding gas' is needed to keep the weld free of contaminants (oxidization, particles, bubbles, etc.).

A similar method of GMAW is available, Flux Cored Arc Welding(FCAW) can either be self shielded, or gas shielded just like GMAW welding. The welder must chip slag off the face of the weld, as it stays on the cooled metal surface once the weld is completed. The main difference can be seen in the selection of the electrode wire for this process. GMAW uses a soild wire and will be listed on the spool as for example ER70S. S standing for solid wire. Flux cored is tubular and will be listed as ER71T. T standing for tubular wire.

Gas selection can also vary. 100% CO2, 75% Argon/25% CO2(75/25), and Argon/Helium/CO2 (Trimix). CO2 is commonly used for FCAW as it causes the arc to be hotter, increasing penetration. 75/25 is the most common shielding gas for GMAW as it is relatively inexpensive, and has excellent welding characteristics. Trimix is only used for GMAW-SS or MIG weling stainless steel.

The reader should note that the processes talked about in this chapter are the most commonly used methods that a welder may use. There are however, other methods that will be discussed in a later chapter.

Oxy-Fuel Cutting and Welding

OxyFuel cutting and welding is a skill all in itself. The terms, oxy- (standing for oxygen,) and fuel (the assortment of gases that produce combustion) speak for themselves. Oxy-Acetylene welding is the most common fuel to use, but others can include natural gas, propane, MAPP gas, gasoline or any number of 'hot' gases.
Generally, the principal for oxy-fuel welding or cutting is the same. Oxygen is supplied in ratio to the fuel gas, and is then lit by a sparking lighter. Valves on the torch handle control the flame (more oxygen to make an oxidizing flame, or more gas to make a carbonizing flame, or in between to make a neutral flame). Welding with oxy-fuel usually desires a 'neutral flame', with no 'feather'. A 'feather' is cooler then the 'cone', the flame at the very tip of the torch. 'Feathers' can be used to determine how carbonizing a flame is. A slightly carbonizing flame is desirable when welding with brass rod, or 'brazing', thus, the 'feather' should be present, but only slightly above the 'cone', about a half of an inch. For direct welding of steel and mild steels, no 'feather' should be present, but use of a hot 'cone' is efficient. For steel, the welder may desire to apply the use of a 'filler rod', or a long, skinny rod of metal similar to the base metal. This helps to build up a weld face and strengthen the joint. This is done by heating the base metal into a molten puddle at the base of the joint, and then 'dipping' or adding the filler rod directly to the puddle.
Cutting involves the same principal, but requires (in most cases) a special torch handle and head. In a regular torch head, there is only one 'orifice', or hole, for which the gas and oxygen can pass through. In a cutting torch, however, there is the one 'orifice' in the center, and a circle of orifices around it. The purpose for this is simple. The torch is lit regularly, and adjusted to a hot neutral flame. The flame is wider, more forceful and louder (although not much). The torch handle has a lever on it that allows the welder to have an extra "burst" of oxygen when he or she desires. This burst blows the hot metal out of the way, allowing a gap to be created, thus the cut is formed. This burst of oxygen is easier to be applied if there is more room to push the oxygen through, thus the extra orifices are essential.

TIG (GTAW) Welding

TIG welding is a form of arc welding, with the same principal to that of MIG/MAG or SMAW. An electric current is supplied, and is fed through a handle. TIG stands for 'tungsten inert gas' and GTAW for 'Gas Tungsten Arc Welding', both meaning the same thing. Tungsten is used as an 'electrode', which is semi-permanent in the torch. It carries the electric current and is used to establish and keep an arc. Tungsten is used because of its conductivity, versatility and high melting temperature. The electrode will become contaminated, however, if accidentally dipped into the weld pool. TIG is preferred by many because of its ability to weld "almost any metal". As long as a filler material (rod) is available, that particular type of metal can be welded with TIG. TIG welding is achieved by operating the torch in a similar manner to oxy-fuel welding, but the operator controls the heat by means of electricity. There are 'remotes' that the welder can use for this task, or it can be set directly on some machines, so it will not fluctuate. Fluctuation is desired in some cases, where the base metal must be cooled sufficiently at regular intervals so as to not burn a hole.

For other, more advanced welding techniques, see the "Welding" article.


Introductory arc welding

Stick Metal Arc Welding is often the first welding technique that a welder learns. A machine supplies a negative electrical circuit to the work-piece via a clip and a welding rod is attached to the positive end of the circuit. When the rod is brought close to the work-piece the current connects creating sparks and heat which melts the metal and the rod together. It requires a very steady hand and patience. It is possibly the oldest electrical welding technique still in use. Pre-electrical techniques included 'soldering', 'forging' and 'oxy-acetylene (flammable gas) welding'. It is difficult at first to weld solid bonds without creating bubbles and SMAW is important for this skill as it is easier to feel what the weld is doing (welding is only possible when the eyes are protected by darkened glass so feeling is important). SMAW is preferred in high-strength structure welding, such as construction or pipeline. It generally takes more time and patience to stick weld than it does to MIG or gas weld. SMAW should be the method spent the most time on learning for a beginner welder. Welding practice should begin with an 'E6013' 3mm rod. This is a simple rod to manipulate, and has a medium heat range, with a medium penetration. Amperage for this rod should be set in AC current, working around 85-95 amps. This is an all position rod, suitable for many general applications.

To practice as a beginner, start with a 1/4 inch thickness metal plate around 1ft x 1ft. Do not forget to wear gloves and welders eye protection. If you are right handed start on your left, working to the right, and vis-versa for left handed (MIG welding goes the opposite direction). Try to weld straight lines across your one foot metal plate until it is covered in stripes. Chip off the black residue (slag) with a Chipping Hammer each time you pause and use a wire brush for any smaller pieces of residue. If you allow the plate to cool down (try keeping a container of water nearby to dip your hot work-piece in), you can use both sides of the same plate repeatedly until you are comfortable and steady with the rod. You should learn to hold the tip of the rod around 2mm or less from the work piece and at a 45 degree angle. It is also nessecary to change rods in the middle of a weld without affecting its quality but this should become easy when you get your pace and angle comfortably. The rod will stick to the work-piece a lot at first. You will soon find that arc welding is like blowing hot liquid from a straw in the dark (sounds complicated but is really a matter of a steady hand). You need to learn to make straight, smooth lines (beads).

When you are convinced that your welds are smooth and can maintain the tip of the rod at 2mm from the work-piece, move on to joints. The basic welding joints are T-joints (in the shape of a T, also known as fillet-joints) and lap-joints (overlapping edges, one resting on top of the other). To practice, use metal strips, 1/4 inch thickness, 2 inches wide and 8 - 12 inches long. Place two metal strips together in a T shape or overlapping and 'spot' weld at each end to keep them in place. Now weld from one side of the joint to the other in a careful, small circle motion of the rod, with an angle of 45-65 degrees (in both the up-down direction and left-right direction) keeping a distance of 1-2mm between the rod and the work-peiece. It is important to hold the tip of the rod so close to the joint as a good weld will melt and fuse the edges of the original work-piece. The finished weld should look almost smooth and the slag should break off effortlessly (will take at least a few hours practice for most people). The most important part of the weld is inside. Break your finished welds open with a heavy hammer and a vice. Be careful! A good weld is not easy to open and fingers are easily removed against a piece of steel! Try weakening the spot welds with a hacksaw on difficult pieces. A good weld will have decently fused the original edges together. The bead should not cut a groove into the face of the work-piece or leave bubbles and gaps in the weld (the bond should be complete inside leaving no visible straight edge under the weld). This is the requirement to pass a welding examintaion. Note that a welded piece will lean toward the joint as it cools. Although enough heat is required to fuse the work pieces together, too much heat will make the whole piece red hot, worsening the distortion when it cools so practice is important.

Slightly more difficult to weld correctly without warping is the end-to-end-joint (two pieces beside each other end to end or side by side). This is only slightly more difficult than the previous joints. Practice on two 1/4 inch strips as before but this time take the edges off the strips with a file or rasp so that you are welding into a V-shape. Place together at the edges and weld along the gap. The weld should be done in a careful, small circle motion of the rod, at a slightly more raised angle than before around 60-80 degrees. The finished weld should look like a "stack of dimes" or evenly spaced ripples in the weld. The sides of the weld should be evenly flushed with the base plate raising to a bump in the middle. If the weld looks "stretched", the travel speed should be slower and the tip closer. There will be significant 'slag' and 'spatter' on the sides of the weld, and will be just generally ugly looking. If the build up of the finished weld is higher than about an sixth of an inch, the travel speed was likely too slow. Slightly more difficult again is the corner-joint (end to end in a V or L shape). Do not remove the edges of a corner joint. Instead, weld the inside first which will leave a small "V" shape on the outside for the final weld. The requiremets for these welds are the same, properly fused without any bubbles or gaps.

Once these welds have been mastered, play around with welding a plate in a vertical position. Weld vertical beads going up, not down. This is significantly more difficult than a flat position, and can be frustrating to learn, but patience is important. Use a counter-clockwise circle motion, spiraling upwards, pausing at the top of each motion. It may feel more comfortable to pause at the bottom of this motion, but this will cause bad 'undercut', where the sides are not filled in with weld material.

Once this has been mastered, one may choose to continue in SMAW, or move into oxy-fuel welding for a time.

  • Remember that most arc welds shouldn't be cooled in water or cooling oil, but by allowing air access around the whole joint. Cooling, in most cases, changes the way the metal atoms retract and can weaken the weld.

6010 and 6011 Rods

E6010 Rods are the most preferred rod for deep 'root' passes, or where a lot of penetration is required. Often, this root pass is covered with two hot passes and a cap or 'face' pass with E7018 rods. This rod has been said to be one of the hardest rods to use, due to the constant attention to rod manipulation, travel speed, and 'arc length'. E6010 is a 'fast-freeze' rod, meaning it is suitable for use in all positions. It is best used with the positive polarity on the rod, or 'reverse polarity', (DC+) with amperage from 75 to 95 being the best (depending on the application). Practice using this rod by cutting (or buying) two 1/4 inch plates with about a 35.5 degree bevel on either side. The bottom of the bevel should be a sharp edge, which will be ground down to about a 3/16 of an inch lands, with either a 3/16 inch gap or 3/32, which ever is more comfortable. Start by simply running a bead down a plain 1/4 inch scrap plate to get the feel of the rod. The flux is cellulose, and is ugly looking at the end; use a wire brush and chipping hammer to clean off. Once comfortable manipulating a straight bead, place the two beveled plates together with the lands facing each other. Make sure that they are perfectly even, as this will cause less grief for the root pass. Use 80 or 85 amps to run the root pass, and start with tacking the two plates together. Weld the root with a 'backhand' motion, (pushing the rod from the base of the weld to the top). Once the root is finished, flip the plate over and wire brush off the bottom; the weld should have fallen through the gap and sealed along both sides evenly if done correctly. If this looks shallow or pitted, turn the amperage up by 5 (but to no more than 90 amps,) and try again, pitching the rod into a sharp 85 to 90 degree angle to the plates. While welding, try to 'dig' the rod into the sides of the bevel, pausing on the sides. If done right, a loud crackling-hissing noise will be heard. This is simply the 'wind' as the weld falls through the bottom of the root. Remember to keep a short arc length with this rod, no longer than the thickness of the rod itself. Otherwise, the weld will be weak, insufficient and contain excessive spatter. Also, consistently weave the rod back and forth, pausing slightly off center, both sides. Once cleaned off, the root pass should be shiny and smooth on the face side, and evenly deep on the bottom. Continue to practice the root weld until it comes naturally and comfortably, as this is a main strength of the whole weld.
Next, a weld will be placed over top the root; a 'hot pass'. Turn the amperage up to 90 or 95 amps (+10% comparing to the root amperage). Weld over top of the root, digging into the sides of the bevel by weaving and pausing on each side momentarily. Minor undercut is normal in this case, and will be filled in by a second hot pass.
The second hot pass should be conducted the same as the first, but the welder may choose to turn the heat down by 5 amps, depending on the joint to be produced. After this, finish with a 'cap' or 'face weld', which must have no undercut on either side. This pass should be done around 85 amps. Use a weaving motion, something like upside down "U's", pausing on either side to allow filler metal to fill in any undercutting. The 6011 rod is essentially the same as a 6010, but is used in AC instead.

6010 and 7018

The next thing to practice is a 6010 root pass, with 7018 hot and face passes. This is a common method used often in pipeline and boiler welding. The 6010 will dig into the root pass and cause it to have a higher tensile strength. The 7018 will add more strength to the top than would a 6010 alone. It also has a lesser chance of undercutting the side, which would cause a weaker weld. For the most part, a 7018 rod is easy to manipulate, and deposits nicely. Use DC straight (DC-) polarity around 105 to 115 amps. The flux on this rod is strange in how it reacts to moisture and humidity. A 'rod oven' is essential if these rods are going to be used in large quantities. The flux must be thoroughly dried out to be used properly, otherwise it will not protect well enough and the weld may look sloppy and weak. If only being used for a personal project, find an old baking sheet, turn up the kitchen oven to around 350 degrees, and bake the required amount of rods for about fifteen minutes. This is far cheaper than a rod oven. To practice with this rod, simply run several beads in the flat, vertical and horizontal position. If control of the 6010 rod has been achieved already, this will not be a big problem. Remember to make small cursive 's' motions on the horizontal weld, pausing at the top, and continuing through quickly on the lower area. Vertical welds should be done in a sort of 'z' motion, pausing on either side, and going quickly over the middle, zigzagging upwards. Once this has been accomplished, practice some more on the 1/4 inch plates in all these positions, welding the root with the 6010. Don't forget to grind lands into the beveled sides (about 3/16 of an inch). Once the root has been cleaned and satisfactory, use the 7018 at 105 amps DC-. For the third pass, turn it up to 115 amps DC-, and finally, for the cap weld use 105 amps again. Remember to clean between each pass, otherwise strength will be decreased. Cool slowly by leaning it somewhere that is not affected by a draft, but where room temperature is stable. Make sure that air has access to the whole plate. You can test these bevel welds by cutting each one down the middle, crossing the weld path. Grind each edge smooth, and the welds should be ground flush to the rest of the plate; both root and face sides. Place in a 50 or 25 ton press, pressing slowly into 'U' shapes. To test the root pass, place the face weld upwards. To test the face weld, simply face the root weld upwards. If there is more than a quarter inch of cracking anywhere on either weld, the weld should be retried.

From here on, any other type of rod can be tried by 'playing around', although if you are unsure, check the rod number on the internet to find the correct voltage and any other applicable setting. This includes travel speed and angle. The next thing to move onto would be MIG welding, but if at all possible (assuming the equiptment is available) one should at least understand how to use oxy-fuel welding and cutting methods.

Oxy Fuel

Oxy fuel refers to an oxygen and fuel gas mixture being burned rapidly from compressed sources, such as large acetylene cylinders or more commonly, a propane tank (one you may find on a barbeque). A variety of fuel gasses can be used in this task, such as propane, acetylene, natural gas, compressed gasoline fumes or anything else easily combustible. However, each type of gas has its own unique pro's and con's of usage.

Simple English

Welding is a way of heating pieces of metal using electricity or a flame so that they melt and stick together. There are many kinds of welding, including arc welding, resistance welding, and gas welding. The most common type is arc welding. Anyone who is near arc welding needs to wear a special helmet or goggles because the arc is so bright. Looking at the arc will hurt your eyes, maybe forever. It is also important to cover all your skin because it can give you something like a sunburn. Hot sparks from the weld can burn any skin that is showing. One kind of welding that does not use an arc is Oxy-fuel welding (OFW), sometimes called gas welding. OFW uses a flame to heat up the metal. There are other kinds of welding that do not use an arc.


Arc Welding

Any welding process that utilizes an electrical arc is known as arc welding. The common forms of arc welding include:

Shielded metal arc welding (SMAW): SMAW is also known as "stick" welding.

Gas metal arc welding (GMAW): GMAW is also known as MIG (metal/inert gas welding).

Gas tungsten arc welding (GTAW): GTAW is also known as TIG (tungsten inert gas welding).

Arc welding heats metals by making a high-current electric arc between pieces of metal to be joined and an electrode.

Use of the electrode varies based on the type of welding process. In SMAW, GMAW, and related welding processes, the electrode is consumed and becomes part of the weld. The electrode is usually made of the same kind of metal to be welded. Because the electrode is consumed by the welding process, the electrode must constantly be fed into the weld. The SMAW welding process features an "stick" electrode impregnated with a weld promoter known as flux, clamped to the end.

The GMAW welding process features a continuous electrode as a thin wire on a rotating spool. The size of this electrode varies from around 0.635 millimeters to about 4 millimeters. The welding machine has a motor-driven spool inside that feeds the wire electrode into the weld.

The TIG welding (GTAW) process features an electrode that is not consumed by the welding process as the metal that makes up the weld does not have any electricity flowing through it. The electrode is made of Tungsten, so used as it will not melt while immersed in the electrical arc. A filler metal, in the form of a rod, can be used to add metal to the weld area.

Almost all welding uses filler metal to fill in the small gap between the metal. The extra metal helps to make the weld strong. Sometimes welds need to be made without any filler metal. Welding with no filler metal is called autogenous welding.

Shielding in arc welding

All types of welding require that the hot metal have protection. Dirt, rust, grease, and even the oxidation of the metal under the weld process can prevent a proper weld joint. As such all weld processes use one of two protection methods: flux, and shielding gas.

Welding flux may be used in a solid, liquid, or paste form. During welding, the flux will melt and some of it will evaporate. This creates a small pocket of gas around the weld. This pocket of gas prevents oxidation of the metal under weld. Melted flux, through a corrosive reaction, cleans contaminants that prevent a proper weld. After welding, the flux solidifies. This layer of solid flux is called slag, and must be removed from the weld. The SMAW weld process most commonly uses flux, and is most commonly used on steel.

Shielding gas protects the weld by being a pocket of gas around the weld. The purpose of this gas is to keep normal air out, especially oxygen. It is different from flux because there is no liquid on the weld. There is only a gas around the weld. Because there is no liquid, it will not clean up dirt and other things on the metal. This means that the metal has to be clean before it is welded. If it is not, the dirt and other things could cause problems. The gases that are usually used are argon, helium, and a mixture that is 3 parts argon and one part carbon dioxide. Other mixtures of gases can have nitrogen, hydrogen, or even a little bit of oxygen in them. One kind of welding that uses shielding gas is gas metal arc welding. It is usually used in factories to make things.

Welding that uses flux is easier to do outside when it is windy. This is because the liquid flux is protecting the hot metal and it will not blow away. Also, the flux is always making the pocket of gas which keeps the electric arc from going out. Welding that uses shielding gas usually cannot be used outside because the gas would blow away if there were any wind.

Other kinds of welding

Some kinds of welding do not use an electric arc. They might use a flame, electricity without an arc, an energy beam, or physical force. The most common type of welding that does not use an arc is called gas welding. In gas welding, a flammable(meaning it will burn) gas and oxygen are combined and burn at the end of a torch. Gas welding does not need any special shielding because a flame which is adjusted right has no extra oxygen in it. It is still important to make sure the metal is clean. The flame heats up the metal so much that it melts. When both the pieces of metal are melted at the edge, the liquid metal becomes one piece.

The other kind of welding that does not use an arc still uses electricity. It is called resistance welding. With this kind, two pieces of thin metal are pinched together and then electricity is made to go through them. This makes the metal get really hot and melt where it is pinched together. The two pieces melt together at that place. Sometimes this is called spot welding because the welding can only happen at one small place(or spot) at a time.

Forge welding is the first kind of welding that ever was used. Forge welding needs the two pieces of metal to so hot that they almost melt. Then they are beat together with hammers until they are one piece.

The other kinds of welding that do not use an arc are hard to do, and usually new. They are expensive too. Most of these kinds of welding are only done where specially needed. They might use an electron beam, laser, or ultrasonic sound waves.

Energy for welding

Every kind of welding needs to use energy. This energy is usually heat, but sometimes force is used to make a weld. When heat is used, it can be from electricity or from fire.

Power supplies for arc welding

A lot of electricity is used in arc welding. Some kinds of welding use alternating current like the electricity that buildings use. Other kinds use direct current like the electricity in a car or most things with a battery. Almost all kinds of welding use a lower voltage than the electricity that comes from a power plant. Arc welding requires using a special power supply that makes the electricity from the power plant usable for welding. A power supply lowers the voltage and controls the amount of current. The power supply usually has controls on it that allow these things to be changed. For kinds of arc welding that use alternating current, sometimes the power supply can do special things to make the electricity alternate differently. Some power supplies do not plug into a power plug, but instead generate their own electricity. These kind of power supplies have an engine that turns a generator head to make the electricity. The engine might run on gasoline, diesel fuel, or propane.

Energy for other kinds of welding

OFW uses a flame from burning fuel gas and oxygen to heat up the metal. This fuel gas is almost always acetylene. Acetylene is a flammable gas that burns very hot, hotter than any other gas. That is why it is used most of the time. Other gases like propane, natural gas, or other industrial gases can be used too.

Some kinds of welding do not use heat to make the weld. These kinds of welding can get hot, but they do not make the metal melt. Forge welding is an example of this. Friction stir welding is a special kind of welding that does not use heat. It uses a very powerful motor and a special spinning bit to mix the metals together at the edge. This seems odd because metals are a solid. this is why it takes a lot of force to do and is very hard. The energy for this kind of welding is mechanical energy from the spinning bit.

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