Gas tungsten arc welding (GTAW), also known as tungsten inert gas (TIG) welding, is an arc welding process that uses a nonconsumable tungsten electrode to produce the weld. The weld area is protected from atmospheric contamination by a shielding gas (usually an inert gas such as argon), and a filler metal is normally used, though some welds, known as autogenous welds, do not require it. A constant-current welding power supply produces energy which is conducted across the arc through a column of highly ionized gas and metal vapors known as a plasma. Manual Metal Arc welding, also known as stick or MMA welding is one of the most common forms of welding. ... For other uses, see Tungsten (disambiguation). ... For other uses, see Electrode (disambiguation). ... Welding is a fabrication process that joins materials, usually metals or thermoplastics, by causing coalescence. ... Shielding gases are inert or semi-inert gases that are commonly used in several welding processes, most notably gas metal arc welding and gas tungsten arc welding. ... An inert gas is any gas that is not reactive under normal circumstances. ... General Name, symbol, number argon, Ar, 18 Chemical series noble gases Group, period, block 18, 3, p Appearance colorless Standard atomic weight 39. ... A filler metal is a metal added in the making of a joint through welding, brazing, or soldering. ... It has been suggested that this article or section be merged with Voltage source. ... A high output constant current welding power supply for use with GTAW and SMAW A welding power supply is an electrical device that provides an electrical current to perform welding procedures which require electricity. ... For other uses, see Plasma. ...

GTAW is most commonly used to weld thin sections of stainless steel and light metals such as aluminum, magnesium, and copper alloys. The process grants the operator greater control over the weld than competing procedures such as shielded metal arc welding and gas metal arc welding, allowing for stronger, higher quality welds. However, GTAW is comparatively more complex and difficult to master, and furthermore, it is significantly slower than most other welding techniques. A related process, plasma arc welding, uses a slightly different welding torch to create a more focused welding arc and as a result is often automated.^[1] The 630 foot (192 m) high, stainless-clad (type 304) Gateway Arch defines St. ... Aluminum redirects here. ... General Name, symbol, number magnesium, Mg, 12 Chemical series alkaline earth metals Group, period, block 2, 3, s Appearance silvery white solid at room temp Standard atomic weight 24. ... For other uses, see Copper (disambiguation). ... Shielded metal arc welding Shielded metal arc welding (SMAW), also known as manual metal arc (MMA) welding or informally as stick welding, is a manual arc welding process that uses a consumable electrode coated in flux to lay the weld. ... Gas metal arc welding Gas metal arc welding (GMAW), sometimes referred to by its subtypes metal inert gas (MIG) welding or metal active gas (MAG) welding, is a semi-automatic or automatic arc welding process in which a continuous and consumable wire electrode and a shielding gas are fed through... Plasma arc welding (PAW) is an arc welding process similar to gas tungsten arc welding (GTAW). ...

Development

After the discovery of the electric arc in 1800 by Humphry Davy, arc welding developed slowly. C. L. Coffin had the idea of welding in an inert gas atmosphere in 1890, but even in the early 1900s, welding non-ferrous materials like aluminum and magnesium remained difficult, because these metals reacted rapidly with the air, resulting in porous and dross-filled welds.^[2] Processes using flux covered electrodes did not satisfactorily protect the weld area from contamination. To solve the problem, bottled inert gases were used in the beginning of the 1930s. A few years later, a direct current, gas-shielded welding process emerged in the aircraft industry for welding magnesium. A 3000 volt electricity arc between two nails Electricity arcs between the power rail and electrical pickup shoe on a London Underground train An electric arc can melt calcium oxide An electric arc is an electrical breakdown of a gas which produces an ongoing plasma discharge, resulting from a current... Sir Humphry Davy, 1st Baronet FRS (17 December 1778 – 29 May 1829) was a British chemist and physicist. ... C.L. Coffin of Detroit was awarded a U.S. patent for an arc welding process using a metal electrode. ... Dross is a mass of solid impurities floating on a molten metal bath. ... An inert gas is any gas that is not reactive under normal circumstances. ... Direct current (DC or continuous current) is the continuous flow of electricity through a conductor such as a wire from high to low potential. ...

This process was perfected in 1941, and became known as heliarc or tungsten inert gas welding, because it utilized a tungsten electrode and helium as a shielding gas. Initially, the electrode overheated quickly, and in spite of tungsten's high melting temperature, particles of tungsten were transferred to the weld. To address this problem, the polarity of the electrode was changed from positive to negative, but this made it unsuitable for welding many non-ferrous materials. Finally, the development of alternating current units made it possible to stabilize the arc and produce high quality aluminum and magnesium welds.^[3] The melting point of a solid is the temperature range at which it changes state from solid to liquid. ... City lights viewed in a motion blurred exposure. ...

Developments continued during the following decades. Linde Air Products developed water-cooled torches that helped to prevent overheating when welding with high currents.^[4] Additionally, during the 1950s, as the process continued to gain popularity, some users turned to carbon dioxide as an alternative to the more expensive welding atmospheres consisting of argon and helium. However, this proved unacceptable for welding aluminum and magnesium because it reduced weld quality, and as a result, it is rarely used with GTAW today. Carbon dioxide (chemical formula: ) is a chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom. ... General Name, symbol, number argon, Ar, 18 Chemical series noble gases Group, period, block 18, 3, p Appearance colorless Standard atomic weight 39. ... General Name, symbol, number helium, He, 2 Chemical series noble gases Group, period, block 18, 1, s Appearance colorless Standard atomic weight 4. ...

In 1953, a new process based on GTAW was developed, called plasma arc welding. It affords greater control and improves weld quality by using a nozzle to focus the electric arc, but is largely limited to automated systems, whereas GTAW remains primarily a manual, hand-held method.^[5] Development within the GTAW process has continued as well, and today a number of variations exist. Among the most popular are the pulsed-current, manual programmed, hot-wire, dabber, and increased penetration GTAW methods.^[6] Plasma arc welding (PAW) is an arc welding process similar to gas tungsten arc welding (GTAW). ...

Operation

GTAW weld area

Manual gas tungsten arc welding is often considered the most difficult of all the welding processes commonly used in industry. Because the welder must maintain a short arc length, great care and skill are required to prevent contact between the electrode and the workpiece. Unlike most other welding processes, GTAW normally requires two hands, since most applications require that the welder manually feed a filler metal into the weld area with one hand while manipulating the welding torch in the other. However, some welds combining thin materials (known as autogenous or fusion welds) can be accomplished without filler metal; most notably edge, corner and butt joints. Image File history File links GTAW.png‎ Gas tungston arc welding schematic en:Gas tungsten arc welding source file: Image:GTAW.svg File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Gas tungsten arc welding ... Image File history File links GTAW.png‎ Gas tungston arc welding schematic en:Gas tungsten arc welding source file: Image:GTAW.svg File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Gas tungsten arc welding ...

To strike the welding arc, a high frequency generator provides a path for the welding current through the shielding gas, allowing the arc to be struck when the separation between the electrode and the workpiece is approximately 1.5–3 mm (0.06–0.12 in). Bringing the two into contact in a "touch start" ("scratch start") also serves to strike an arc. This technique can cause contamination of the weld and electrode. Once the arc is struck, the welder moves the torch in a small circle to create a welding pool, the size of which depends on the size of the electrode and the amount of current. While maintaining a constant separation between the electrode and the workpiece, the operator then moves the torch back slightly and tilts it backward about 10–15 degrees from vertical. Filler metal is added manually to the front end of the weld pool as it is needed.^[7]

Welders often develop a technique of rapidly alternating between moving the torch forward (to advance the weld pool) and adding filler metal. The filler rod is withdrawn from the weld pool each time the electrode advances, but it is never removed from the gas shield to prevent oxidation of its surface and contamination of the weld. Filler rods composed of metals with low melting temperature, such as aluminum, require that the operator maintain some distance from the arc while staying inside the gas shield. If held too close to the arc, the filler rod can melt before it makes contact with the weld puddle. As the weld nears completion, the arc current is often gradually reduced to allow the weld crater to solidify and prevent the formation of crater cracks at the end of the weld.^[8][9]

Operation Modes

GTAW can use a positive direct current, negative direct current or an alternating current, depending on the power supply set up. A negative direct current from the electrode causes a stream of electrons to collide with the surface, generating large amounts of heat at the weld region. This creates a deep, narrow weld. In the opposite process where the electrode is connected to the positive power supply terminal, positively charged ions flow from the tip of the electrode instead, so the heating action of the electrons is mostly on the electrode. This mode also helps to remove oxide layers from the surface of the region to be welded, which is good for metals such as Aluminium or Magnesium. A shallow, wide weld is produced from this mode, with minimum heat input. Alternating current gives a combination of negative and positive modes, giving a cleaning effect and imparts a lot of heat as well. Direct current (DC or continuous current) is the continuous flow of electricity through a conductor such as a wire from high to low potential. ... City lights viewed in a motion blurred exposure. ... Aluminum redirects here. ... General Name, symbol, number magnesium, Mg, 12 Chemical series alkaline earth metals Group, period, block 2, 3, s Appearance silvery white solid at room temp Standard atomic weight 24. ...

Safety

Like other arc welding processes, GTAW can be dangerous if proper precautions are not taken. The process produces intense ultraviolet radiation, which can cause a form of sunburn and, in a few cases, trigger the development of skin cancer. Flying sparks and droplets of molten metal can cause severe burns and start a fire if flammable material is nearby, though GTAW generally produces very few sparks or metal droplets when performed properly. For other uses, see Ultraviolet (disambiguation). ... Skin cancer is a malignant growth on the skin which can have many causes. ...

It is essential that the welder wear suitable protective clothing, including leather gloves, a closed shirt collar to protect the neck (especially the throat), a protective long sleeve jacket and a suitable welding helmet to prevent retinal damage or ultraviolet burns to the cornea, often called arc eye. The shade of welding lens will depend upon the amperage of the welding current. Due to the absence of smoke in GTAW, the arc appears brighter than shielded metal arc welding and more ultraviolet radiation is produced. Exposure of bare skin near a GTAW arc for even a few seconds may cause a painful sunburn. Additionally, the tungsten electrode is heated to a white hot state like the filament of a lightbulb, adding greatly to the total radiated light and heat energy. Transparent welding curtains, made of a polyvinyl chloride plastic film, dyed in order to block UV radiation, are often used to shield nearby personnel from exposure. This article is about welding as a trade. ... Protective clothing is clothing designed to protect either the wearers body or other items of clothing from hazards such as heat, chemicals and infection. ... For other uses, see Leather (disambiguation). ... // Leather gloves A glove (Middle English from Old English glof) is a type of garment (and more specifically a fashion accessory) which covers the hand of a human. ... Welding helmets are typically worn when arc welding. ... Arc eye, also known as arc flash, welders flash, corneal flash burns, or flash burns, is a painful ocular condition sometimes experienced by welders who have failed to use adequate eye protection. ... Shielded metal arc welding Shielded metal arc welding (SMAW), also known as manual metal arc (MMA) welding or informally as stick welding, is a manual arc welding process that uses a consumable electrode coated in flux to lay the weld. ... PVC redirects here. ... Look up dye in Wiktionary, the free dictionary. ...

Welders are also often exposed to dangerous gases and particulate matter. Shielding gases can displace oxygen and lead to asphyxiation, and while smoke is not produced, the arc in GTAW produces very short wavelength ultraviolet light, which causes surrounding air to break down and form ozone. Metals will volatilize and heavy metals can be taken into the lungs. Similarly, the heat can cause poisonous fumes to form from cleaning and degreasing materials. For example chlorinated products will break down producing poisonous phosgene. Cleaning operations using these agents should not be performed near the site of welding, and proper ventilation is necessary to protect the welder.^[10] Particulates, alternatively referred to as particulate matter (PM), aerosols or fine particles, are tiny particles of solid or liquid suspended in a gas. ... Asphyxia is a condition of severely deficient supply of oxygen to the body. ... For other uses, see Ozone (disambiguation). ...

Applications

While the aerospace industry is one of the primary users of gas tungsten arc welding, the process is used in a number of other areas. Many industries use GTAW for welding thin workpieces, especially nonferrous metals. It is used extensively in the manufacture of space vehicles, and is also frequently employed to weld small-diameter, thin-wall tubing such as those used in the bicycle industry. In addition, GTAW is often used to make root or first pass welds for piping of various sizes. In maintenance and repair work, the process is commonly used to repair tools and dies, especially components made of aluminum and magnesium.^[11] Because the weld metal is not transferred directly across the electric arc like most open arc welding processes, a vast assortment of welding filler metal is available to the welding engineer. In fact, no other welding process permits the welding of so many alloys in so many product configurations. Filler metal alloys, such as elemental aluminum and chromium, can be lost through the electric arc from volatilization. This loss does not occur with the GTAW process. Because the resulting welds have the same chemical integrity as the original base metal or match the base metals more closely, GTAW welds are highly resistant to corrosion and cracking over long time periods, GTAW is the welding procedure of choice for critical welding operations like sealing spent nuclear fuel canisters before burial.^[12] Nuclear Fuel Process A graph comparing nucleon number against binding energy Nuclear fuel is any material that can be consumed to derive nuclear energy, by analogy to chemical fuel that is burned to derive energy. ...

Quality

GTAW fillet weld

Engineers prefer GTAW welds because of its low-hydrogen properties and the match of mechanical and chemical properties with the base material. Maximum weld quality is assured by maintaining the cleanliness of the operation—all equipment and materials used must be free from oil, moisture, dirt and other impurities, as these cause weld porosity and consequently a decrease in weld strength and quality. To remove oil and grease, alcohol or similar commercial solvents may be used, while a stainless steel wire brush or chemical process can remove oxides from the surfaces of metals like aluminum. Rust on steels can be removed by first grit blasting the surface and then using a wire brush to remove any embedded grit. These steps are especially important when negative polarity direct current is used, because such a power supply provides no cleaning during the welding process, unlike positive polarity direct current or alternating current.^[13] To maintain a clean weld pool during welding, the shielding gas flow should be sufficient and consistent so that the gas covers the weld and blocks impurities in the atmosphere. GTA welding in windy or drafty environments increases the amount of shielding gas necessary to protect the weld, increasing the cost and making the process unpopular outdoors. Image File history File links 08-TIG-weld. ... Image File history File links 08-TIG-weld. ... The 630 foot (192 m) high, stainless-clad (type 304) Gateway Arch defines St. ... Sandblasting is a generic term for the process of smoothing, shaping and cleaning a hard surface by forcing solid particles across that surface at high speeds. ... Direct current (DC or continuous current) is the continuous flow of electricity through a conductor such as a wire from high to low potential. ... City lights viewed in a motion blurred exposure. ...

Because of GTAW's relative difficulty and the importance of proper technique, skilled operators are employed for important applications. Welders should be qualified following the requirements of the American Welding Society or American Society of Mechanical Engineers. Low heat input, caused by low welding current or high welding speed, can limit penetration and cause the weld bead to lift away from the surface being welded. If there is too much heat input, however, the weld bead grows in width while the likelihood of excessive penetration and spatter increase. Additionally, if the welder holds the welding torch too far from the workpiece, shielding gas is wasted and the appearance of the weld worsens. There are very few or no other articles that link to this one. ...

If the amount of current used exceeds the capability of the electrode, tungsten inclusions in the weld may result. Known as tungsten spitting, it can be identified with radiography and prevented by changing the type of electrode or increasing the electrode diameter. In addition, if the electrode is not well protected by the gas shield or the operator accidentally allows it to contact the molten metal, it can become dirty or contaminated. This often causes the welding arc to become unstable, requiring that electrode be ground with a diamond abrasive to remove the impurity.^[14] A radiograph of a right elbow-joint Radiography is the use of certain types of electromagnetic radiation—usually ionizing—to view objects. ...

Equipment

GTAW torch with various electrodes, cups, collets and gas diffusers

GTAW torch, disassembled

The equipment required for the gas tungsten arc welding operation includes a welding torch utilizing a nonconsumable tungsten electrode, a constant-current welding power supply, and a shielding gas source. Image File history File linksMetadata TIG_torch-accs. ... Image File history File linksMetadata TIG_torch-accs. ... Image File history File linksMetadata TIG_torch_breakdown. ... Image File history File linksMetadata TIG_torch_breakdown. ... For other uses, see Tungsten (disambiguation). ... For other uses, see Electrode (disambiguation). ... A high output constant current welding power supply for use with GTAW and SMAW A welding power supply is an electrical device that provides an electrical current to perform welding procedures which require electricity. ... Shielding gases are inert or semi-inert gases that are commonly used in several welding processes, most notably gas metal arc welding and gas tungsten arc welding. ...

Welding torch

GTAW welding torches are designed for either automatic or manual operation and are equipped with cooling systems using air or water. The automatic and manual torches are similar in construction, but the manual torch has a handle while the automatic torch normally comes with a mounting rack. The angle between the centerline of the handle and the centerline of the tungsten electrode, known as the head angle, can be varied on some manual torches according to the preference of the operator. Air cooling systems are most often used for low-current operations (up to about 200 A), while water cooling is required for high-current welding (up to about 600 A). The torches are connected with cables to the power supply and with hoses to the shielding gas source and where used, the water supply. For other uses, see Ampere (disambiguation). ...

The internal metal parts of a torch are made of hard alloys of copper or brass in order to transmit current and heat effectively. The tungsten electrode must be held firmly in the center of the torch with an appropriately sized collet, and ports around the electrode provide a constant flow of shielding gas. Collets are sized according to the diameter of the tungsten electrode they hold. The body of the torch is made of heat-resistant, insulating plastics covering the metal components, providing insulation from heat and electricity to protect the welder. For other uses, see Copper (disambiguation). ... Brazen redirects here. ... A collet is a holding device that forms a collar around the object to be held and exerts a strong clamping force on the object when it is tightened. ...

The size of the welding torch nozzle depends on the amount of shielded area desired. The size of the gas nozzle will depend upon the diameter of the electrode, the joint configuration, and the availability of access to the joint by the welder. The inside diameter of the nozzle is preferably at least three times the diameter of the electrode, but there are no hard rules. The welder will judge the effectiveness of the shielding and increase the nozzle size to increase the area protected by the external gas shield as needed. The nozzle must be heat resistant and thus is normally made of alumina or a ceramic material, but fused quartz, a glass-like substance, offers greater visibility. Devices can be inserted into the nozzle for special applications, such as gas lenses or valves to improve the control shielding gas flow to reduce turbulence and introduction of contaminated atmosphere into the shielded area. Hand switches to control welding current can be added to the manual GTAW torches.^[15] Aluminium oxide (or aluminum oxide) (Al2O3) is a chemical compound of aluminium and oxygen. ... A sphere manufactured by NASA out of fused quartz for use in a gyroscope in the Gravity Probe B experiment. ...

Power supply

Gas tungsten arc welding uses a constant current power source, meaning that the current (and thus the heat) remains relatively constant, even if the arc distance and voltage change. This is important because most applications of GTAW are manual or semiautomatic, requiring that an operator hold the torch. Maintaining a suitably steady arc distance is difficult if a constant voltage power source is used instead, since it can cause dramatic heat variations and make welding more difficult.^[16]

GTAW power supply

The preferred polarity of the GTAW system depends largely on the type of metal being welded. Direct current with a negatively charged electrode (DCEN) is often employed when welding steels, nickel, titanium, and other metals. It can also be used in automatic GTA welding of aluminum or magnesium when helium is used as a shielding gas. The negatively charged electrode generates heat by emitting electrons which travel across the arc, causing thermal ionization of the shielding gas and increasing the temperature of the base material. The ionized shielding gas flows toward the electrode, not the base material. Direct current with a positively charged electrode (DCEP) is less common, and is used primarily for shallow welds since less heat is generated in the base material. Instead of flowing from the electrode to the base material, as in DCEN, electrons go the other direction, causing the electrode to reach very high temperatures. To help it maintain its shape and prevent softening, a larger electrode is often used. As the electrons flow toward the electrode, ionized shielding gas flows back toward the base material, cleaning the weld by removing oxides and other impurities and thereby improving its quality and appearance. Image File history File links Download high resolution version (2272x1704, 808 KB) // Overview This is a picture of the front of a Miller Syncrowave 350LX welding power source for Gas Tungsten Arc Welding and Shielded Metal Arc Welding. ... Image File history File links Download high resolution version (2272x1704, 808 KB) // Overview This is a picture of the front of a Miller Syncrowave 350LX welding power source for Gas Tungsten Arc Welding and Shielded Metal Arc Welding. ... Direct current (DC or continuous current) is the continuous flow of electricity through a conductor such as a wire from high to low potential. ... For other uses, see Steel (disambiguation). ... For other uses, see Nickel (disambiguation). ... General Name, symbol, number titanium, Ti, 22 Chemical series transition metals Group, period, block 4, 4, d Appearance silvery grey-white metallic Standard atomic weight 47. ...

Alternating current, commonly used when welding aluminum and magnesium manually or semi-automatically, combines the two direct currents by making the electrode and base material alternate between positive and negative charge. This causes the electron flow to switch directions constantly, preventing the tungsten electrode from overheating while maintaining the heat in the base material. Surface oxides are still removed during the electrode-positive portion of the cycle and the base metal is heated more deeply during the electrode-negative portion of the cycle. Some power supplies enable operators to use an unbalanced alternating current wave by modifying the exact percentage of time that the current spends in each state of polarity, giving them more control over the amount of heat and cleaning action supplied by the power source. In addition, operators must be wary of rectification, in which the arc fails to reignite as it passes from straight polarity (negative electrode) to reverse polarity (positive electrode). To remedy the problem, a square wave power supply can be used, as can high-frequency voltage to encourage ignition.^[17] City lights viewed in a motion blurred exposure. ... Aluminum redirects here. ... General Name, symbol, number magnesium, Mg, 12 Chemical series alkaline earth metals Group, period, block 2, 3, s Appearance silvery white solid at room temp Standard atomic weight 24. ... Rectification is the conversion of ac current into dc current. ... A square wave is a kind of basic waveform. ...

Electrode

The electrode used in GTAW is made of tungsten or a tungsten alloy, because tungsten has the highest melting temperature among pure metals, at 3,422 °C (6,192 °F). As a result, the electrode is not consumed during welding, though some erosion (called burn-off) can occur. Electrodes can have either a clean finish or a ground finish—clean finish electrodes have been chemically cleaned, while ground finish electrodes have been ground to a uniform size and have a polished surface, making them optimal for heat conduction. The diameter of the electrode can vary between 0.5 millimeter and 6.4 millimeters (0.02–0.25 in), and their length can range from 75 to 610 millimeters (3–24 in). ... Lanthanum(III) oxide is La2O3, a chemical compound containing the rare earth lanthanum and oxygen. ... Thorium dioxide (ThO2), also called thorium(IV) oxide (IUPAC) is a white, crystalline powder. ... Yttrium oxide is Y2O3. ... Zirconia (ZrO2) is a white crystalline oxide of zirconium. ... For other uses, see Electrode (disambiguation). ... For other uses, see Tungsten (disambiguation). ... For other uses, see Celsius (disambiguation). ... For other uses, see Fahrenheit (disambiguation). ... An inch (plural: inches; symbol or abbreviation: in or, sometimes, ″ - a double prime) is the name of a unit of length in a number of different systems, including English units, Imperial units, and United States customary units. ...

A number of tungsten alloys have been standardized by the International Organization for Standardization and the American Welding Society in ISO 6848 and AWS A5.12, respectively, for use in GTAW electrodes, and are summarized in the adjacent table. Pure tungsten electrodes (classified as WP or EWP) are general purpose and low cost electrodes. Cerium oxide (or ceria) as an alloying element improves arc stability and ease of starting while decreasing burn-off. Using an alloy of lanthanum oxide (or lanthana) has a similar effect. Thorium oxide (or thoria) alloy electrodes were designed for DC applications and can withstand somewhat higher temperatures while providing many of the benefits of other alloys. However, it is somewhat radioactive. Inhalation of the thorium grinding dust during preparation of the electrode is hazardous to one's health. As a replacement to thoriated electrodes, electrodes with larger concentrations of lanthanum oxide can be used. Electrodes containing zirconium oxide (or zirconia) increase the current capacity while improving arc stability and starting and increasing electrode life. In addition, electrode manufacturers may create alternative tungsten alloys with specified metal additions, and these are designated with the classification EWG under the AWS system. “ISO” redirects here. ... There are very few or no other articles that link to this one. ... General Name, Symbol, Number cerium, Ce, 58 Chemical series lanthanides Group, Period, Block n/a, 6, f Appearance silvery white Standard atomic weight 140. ... ... General Name, Symbol, Number lanthanum, La, 57 Chemical series lanthanides Group, Period, Block 3, 6, f Appearance silvery white Atomic mass 138. ... Lanthanum(III) oxide is La2O3, a chemical compound containing the rare earth lanthanum and oxygen. ... General Name, Symbol, Number thorium, Th, 90 Chemical series Actinides Group, Period, Block n/a, 7, f Appearance silvery white Standard atomic weight 232. ... Thorium dioxide (ThO2), also called thorium(IV) oxide (IUPAC) is a white, crystalline powder. ... The radiation warning symbol (trefoil). ... General Name, Symbol, Number zirconium, Zr, 40 Chemical series transition metals Group, Period, Block 4, 5, d Appearance silvery white Standard atomic weight 91. ... Zirconia (ZrO2) is a white crystalline oxide of zirconium. ...

Filler metals are also used in nearly all applications of GTAW, the major exception being the welding of thin materials. Filler metals are available with different diameters and are made of a variety of materials. In most cases, the filler metal in the form of a rod is added to the weld pool manually, but some applications call for an automatically fed filler metal, which often is stored on spools or coils.^[19]

Shielding gas

GTAW system setup

As with other welding processes such as gas metal arc welding, shielding gases are necessary in GTAW to protect the welding area from atmospheric gases such as nitrogen and oxygen, which can cause fusion defects, porosity, and weld metal embrittlement if they come in contact with the electrode, the arc, or the welding metal. The gas also transfers heat from the tungsten electrode to the metal, and it helps start and maintain a stable arc. Image File history File links GTAW_setup. ... Image File history File links GTAW_setup. ... Gas metal arc welding Gas metal arc welding (GMAW), sometimes referred to by its subtypes metal inert gas (MIG) welding or metal active gas (MAG) welding, is a semi-automatic or automatic arc welding process in which a continuous and consumable wire electrode and a shielding gas are fed through... Shielding gases are inert or semi-inert gases that are commonly used in several welding processes, most notably gas metal arc welding and gas tungsten arc welding. ... General Name, symbol, number nitrogen, N, 7 Chemical series nonmetals Group, period, block 15, 2, p Appearance colorless gas Standard atomic weight 14. ... This article is about the chemical element and its most stable form, or dioxygen. ...

The selection of a shielding gas depends on several factors, including the type of material being welded, joint design, and desired final weld appearance. Argon is the most commonly used shielding gas for GTAW, since it helps prevent defects due to a varying arc length. When used with alternating current, the use of argon results in high weld quality and good appearance. Another common shielding gas, helium, is most often used to increase the weld penetration in a joint, to increase the welding speed, and to weld metals with high heat conductivity, such as copper and aluminum. A significant disadvantage is the difficulty of striking an arc with helium gas, and the decreased weld quality associated with a varying arc length. General Name, symbol, number argon, Ar, 18 Chemical series noble gases Group, period, block 18, 3, p Appearance colorless Standard atomic weight 39. ... General Name, symbol, number helium, He, 2 Chemical series noble gases Group, period, block 18, 1, s Appearance colorless Standard atomic weight 4. ... For other uses, see Copper (disambiguation). ... Aluminum redirects here. ...

Argon-helium mixtures are also frequently utilized in GTAW, since they can increase control of the heat input while maintaining the benefits of using argon. Normally, the mixtures are made with primarily helium (often about 75% or higher) and a balance of argon. These mixtures increase the speed and quality of the AC welding of aluminum, and also make it easier to strike an arc. Another shielding gas mixture, argon-hydrogen, is used in the mechanized welding of light gauge stainless steel, but because hydrogen can cause porosity, its uses are limited.^[20] Similarly, nitrogen can sometimes be added to argon to help stabilize the austenite in austentitic stainless steels and increase penetration when welding copper. Due to porosity problems in ferritic steels and limited benefits, however, it is not a popular shielding gas additive.^[21] This article is about the chemistry of hydrogen. ... The 630 foot (192 m) high, stainless-clad (type 304) Gateway Arch defines St. ... Iron-carbon phase diagram, showing the conditions under which austenite (γ) is stable in carbon steel. ...

Materials

Gas tungsten arc welding is most commonly used to weld stainless steel and nonferrous materials, such as aluminum and magnesium, but it can be applied to nearly all metals, with notable exceptions being lead and zinc. Its applications involving carbon steels are limited not because of process restrictions, but because of the existence of more economical steel welding techniques, such as gas metal arc welding and shielded metal arc welding. Furthermore, GTAW can be performed in a variety of other-than-flat positions, depending on the skill of the welder and the materials being welded.^[22] General Name, Symbol, Number lead, Pb, 82 Chemical series Post-transition metals or poor metals Group, Period, Block 14, 6, p Appearance bluish gray Standard atomic weight 207. ... General Name, symbol, number zinc, Zn, 30 Chemical series transition metals Group, period, block 12, 4, d Appearance bluish pale gray Standard atomic weight 65. ... Gas metal arc welding Gas metal arc welding (GMAW), sometimes referred to by its subtypes metal inert gas (MIG) welding or metal active gas (MAG) welding, is a semi-automatic or automatic arc welding process in which a continuous and consumable wire electrode and a shielding gas are fed through... Shielded metal arc welding Shielded metal arc welding (SMAW), also known as manual metal arc (MMA) welding or informally as stick welding, is a manual arc welding process that uses a consumable electrode coated in flux to lay the weld. ...

Aluminum and magnesium

A TIG weld showing an accentuated AC etched zone

Closeup view of an aluminium TIG weld AC etch zone

Aluminum and magnesium are most often welded using alternating current, but the use of direct current is also possible, depending on the properties desired. Before welding, the work area should be cleaned and may be preheated to 175 to 200 °C (350 to 400 °F) for aluminum or to a maximum of 150 °C (300 °F) for thick magnesium workpieces to improve penetration and increase travel speed. AC current can provide a self-cleaning effect, removing the thin, refractory aluminium oxide (sapphire) layer that forms on aluminium metal within minutes of exposure to air. This oxide layer must be removed for welding to occur. When alternating current is used, pure tungsten electrodes or zirconiated tungsten electrodes are preferred over thoriated electrodes, as the latter are more likely to "spit" electrode particles across the welding arc into the weld. Blunt electrode tips are preferred, and pure argon shielding gas should be employed for thin workpieces. Introducing helium allows for greater penetration in thicker workpieces, but can make arc starting difficult. Image File history File linksMetadata TIG_Weld_low_magnification. ... Image File history File linksMetadata TIG_Weld_low_magnification. ... Image File history File linksMetadata Download high-resolution version (1024x768, 777 KB) Summary A closeup micrograph of a TIG weld etch zone on 6061 aluminium (pulsed at 200 amps peak current, 5 amps sustain current, 50% pulse duty cycle, AC, 65% electrode negative, pure argon shield gas). ... Image File history File linksMetadata Download high-resolution version (1024x768, 777 KB) Summary A closeup micrograph of a TIG weld etch zone on 6061 aluminium (pulsed at 200 amps peak current, 5 amps sustain current, 50% pulse duty cycle, AC, 65% electrode negative, pure argon shield gas). ... Aluminum is a soft and lightweight metal with a dull silvery appearance, due to a thin layer of oxidation that forms quickly when it is exposed to air. ... General Name, symbol, number magnesium, Mg, 12 Chemical series alkaline earth metals Group, period, block 2, 3, s Appearance silvery white solid at room temp Standard atomic weight 24. ... City lights viewed in a motion blurred exposure. ... Direct current (DC or continuous current) is the continuous flow of electricity through a conductor such as a wire from high to low potential. ... For other uses, see Sapphire (disambiguation). ...

Direct current of either polarity, positive or negative, can be used to weld aluminum and magnesium as well. Direct current with a positively charged electrode (DCEP) allows for high penetration, Short arc length (generally less than 2 mm or 0.07 in) gives the best results, making the process better suited for automatic operation than manual operation. Shielding gases with high helium contents are most commonly used with DCEN, and thoriated electrodes are suitable. Direct current with a negatively charged electrode (DCEN) is used primarily for shallow welds, especially those with a joint thickness of less than 1.6 millimeters (0.06 in). A thoriated tungsten electrode is commonly used, along with a pure argon shielding gas.^[23]

Steels

For GTA welding of carbon and stainless steels, the selection of a filler material is important to prevent excessive porosity. Oxides on the filler material and workpieces must be removed before welding to prevent contamination, and immediately prior to welding, alcohol or acetone should be used to clean the surface. Preheating is generally not necessary for mild steels less than one inch thick, but low alloy steels may require preheating to slow the cooling process and prevent the formation of martensite in the heat-affected zone. Tool steels should also be preheated to prevent cracking in the heat-affected zone. Austenitic stainless steels do not require preheating, but martensitic and ferritic chromium stainless steels do. A DCEN power source is normally used, and thoriated electrodes, tapered to a sharp point, are recommended. Pure argon is used for thin workpieces, but helium can be introduced as thickness increases.^[24] Plain-carbon steel is a metal alloy, a combination of two elements, iron and carbon, where other elements are present in quantities too small to affect the properties. ... The 630 foot (192 m) high, stainless-clad (type 304) Gateway Arch defines St. ... Martensite in AISI 4140 steel 0. ... 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. ... Tool steel refers to a variety of carbon and alloy steels that are particularly well-suited to be made into tools. ...

Copper alloys

TIG welding of copper and some of its alloys is possible, but in order to get a seam free of oxidation and porosities, shielding gas needs to be provided on the root side of the weld. Alternatively, a special "backing tape", consisting of a fiberglass weave on heat-resistant aluminum tape can be used, to prevent air reaching the molten metal. Bundle of fiberglass Fiberglass (also called fibreglass and glass fibre) is material made from extremely fine fibers of glass. ...

Dissimilar metals

Welding dissimilar metals often introduces new difficulties to GTAW welding, because most materials do not easily fuse to form a strong bond. However, welds of dissimilar materials have numerous applications in manufacturing, repair work, and the prevention of corrosion and oxidation. In some joints, a compatible filler metal is chosen to help form the bond, and this filler metal can be the same as one of the base materials (for example, using a stainless steel filler metal with stainless steel and carbon steel as base materials), or a different metal (such as the use of a nickel filler metal for joining steel and cast iron). Very different materials may be coated or "buttered" with a material compatible with a particular filler metal, and then welded. In addition, GTAW can be used in cladding or overlaying dissimilar materials. For the hazard, see corrosive. ... The most fundamental reactions in chemistry are the redox processes. ... For other uses, see Nickel (disambiguation). ... Cast iron usually refers to grey cast iron, but can mean any of a group of iron-based alloys containing more than 2% carbon (alloys with less carbon are carbon steel by definition). ... The term cladding can have a number of meanings: Regarding optical fiber in telecommunication, cladding is one or more layers of material of lower refractive index, in intimate contact with a core material of higher refractive index. ...

When welding dissimilar metals, the joint must have an accurate fit, with proper gap dimensions and bevel angles. Care should be taken to avoid melting excessive base material. Pulsed current is particularly useful for these applications, as it helps limit the heat input. The filler metal should be added quickly, and a large weld pool should be avoided to prevent dilution of the base materials.^[25]

Process variations

Pulsed-current

In the pulsed-current mode, the welding current rapidly alternates between two levels. The higher current state is known as the pulse current, while the lower current level is called the background current. During the period of pulse current, the weld area is heated and fusion occurs. Upon dropping to the background current, the weld area is allowed to cool and solidify. Pulsed-current GTAW has a number of advantages, including lower heat input and consequently a reduction in distortion and warpage in thin workpieces. In addition, it allows for greater control of the weld pool, and can increase weld penetration, welding speed, and quality. A similar method, manual programmed GTAW, allows the operator to program a specific rate and magnitude of current variations, making it useful for specialized applications.^[26]

Dabber

The dabber variation is used to precisely place weld metal on thin edges. The automatic process replicates the motions of manual welding by feeding a cold filler wire into the weld area and dabbing (or oscillating) it into the welding arc. It can be used in conjunction with pulsed current, and is used to weld a variety of alloys, including titanium, nickel, and tool steels. Common applications include rebuilding seals in jet engines and building up saw blades, milling cutters, drill bits, and mower blades.^[27] A Pratt and Whitney turbofan engine for the F-15 Eagle is tested at Robins Air Force Base, Georgia, USA. The tunnel behind the engine muffles noise and allows exhaust to escape. ... Milling cutters are cutting tools used in milling machines or machining centres. ... Drill bits are cutting tools used to create cylindrical holes. ...

Hot Wire

Welding filler metal can be resistance heated to a temperature near its melting point before being introduced into the weld pool. This increases the deposition rate of machine and automatic GTAW welding processes. More pounds per hour of filler metal is introduced into the weld joint than when filler metal is added cold and the heat of the electric arc introduces all of the heat. This process is used extensively in base material build up before machining, clad metal overlays, and hardfacing operations.

Advantages

• Concentrated Arc - Permits pin point control of heat input to the workpiece resulting in a narrow heat-affected zone
• No Slag - No requirement for flux, therefore no slag to obscure the welder’s vision of the molten weld pool
• No Sparks or Spatter - No transfer of metal across the arc. No molten globules of spatter to contend with and no sparks produced if material being welded is free of contaminants
• Little Smoke or Fumes - Compared to other arc-welding processes like stick or flux-cored welding, few fumes are produced. The base metals being welded may contain coatings or elements such as lead, zinc, copper, nickel that may produce hazardous fumes, however
• Welds more metals and metal alloys than any other process
• Good for welding thin material ^[28]

Disadvantages

• Slower travel speeds than other processes
• Lower filler metal deposition rates
• Hand-eye coordination is a required skill
• Brighter UV rays than other processes
• Equipment costs can be higher than other processes
• Concentrations of shielding gas may build up and displace oxygen when welding in confined areas^[29]

References

• ASM International (2003). Trends in Welding Research. Materials Park, Ohio: ASM International. ISBN 0-87170-780-2
• Cary, Howard B. and Scott C. Helzer (2005). Modern Welding Technology. Upper Saddle River, New Jersey: Pearson Education. ISBN 0-13-113029-3.
• Jeffus, Larry (2002). Welding: Principles and Applications. Thomson Delmar. ISBN 1-4018-1046-2.
• Lincoln Electric (1994). The Procedure Handbook of Arc Welding. Cleveland: Lincoln Electric. ISBN 99949-25-82-2.
• Minnick, William H. (1996). Gas Tungsten Arc Welding handbook. Tinley Park, Illinois: Goodheart-Willcox Company. ISBN 1-56637-206-2.
• Weman, Klas (2003). Welding processes handbook. New York: CRC Press LLC. ISBN 0-8493-1773-8.
• American Welding Society (2004). Welding Handbook, Welding Processes Part 1. Miami Florida: American Welding Society. ISBN 0-87171-729-8.
• Messler, Robert W. (1999). Principles of Welding. Troy, New York: John Wiley & Sons, Inc. ISBN 0-471-25376-6

This article is about the U.S. State. ... This article is about the U.S. state. ... Cleveland redirects here. ... Tinley Park is a village located in Cook County, Illinois. ... This article is about the U.S. State. ... This article is about the U.S. State of Florida. ... This article is about the state. ...

Notes

External links

• GTAW handbook
• Selection and Preparation Guide for Tungsten Electrodes

v • d • e Welding in metalworking Arc welding Shielded metal (MMA) · Gas metal (MIG/MAG) · Flux-cored · Submerged · Gas tungsten (TIG) · Plasma · Atomic hydrogen Image File history File links Blacksmith-hammer-anvil-50x50. ... Welding is a fabrication process that joins materials, usually metals or thermoplastics, by causing coalescence. ... Turned chess pieces Metalworking is the craft and practice of working with metals to create structures or machine parts. ... Manual Metal Arc welding, also known as stick or MMA welding is one of the most common forms of welding. ... Shielded metal arc welding Shielded metal arc welding (SMAW), also known as manual metal arc (MMA) welding or informally as stick welding, is a manual arc welding process that uses a consumable electrode coated in flux to lay the weld. ... Gas metal arc welding Gas metal arc welding (GMAW), sometimes referred to by its subtypes metal inert gas (MIG) welding or metal active gas (MAG) welding, is a semi-automatic or automatic arc welding process in which a continuous and consumable wire electrode and a shielding gas are fed through... A wire feeder configured for . ... A submerged arc welder used for training. ... Plasma arc welding (PAW) is an arc welding process similar to gas tungsten arc welding (GTAW). ... Atomic Hydrogen Welding (AHW) is an arc welding process that uses an arc between two metal tungsten electrodes in a shielding atmosphere of hydrogen and without the application of pressure. ... Other processes Oxyfuel · Resistance · Spot · Forge · Ultrasonic · Electron beam · Laser beam · Laser-hybrid · Electrogas · Electroslag This is a list of welding processes, separated into their respective categories. ... “Oxyacetylene” redirects here. ... Resistance welding refers to a group of welding processes that produce coalescence of the faying surfaces with the heat obtained from resistance of the workpieces to the flow of the welding current in a circuit of which the workpieces are part, and by the application of pressure. ... A miller spot welder Spot welding is a type of resistance welding used to weld various sheet metals. ... Forge welding is a welding process of heating two or more pieces of wrought iron or steel until their surfaces are malleable and then hammering them together. ... Ultrasonic welding is an industrial technique whereby high-frequency ultrasonic acoustic vibrations are used to weld objects together, usually plastics, and especially for joining dissimilar materials. ... Electron beam welding is a welding process where the energy to melt the material is applied by an electron beam. ... Laser beam welding is a technique in manufacturing whereby two or more pieces of material (usually metal) are joined by together through use of a laser beam. ... Laser-hybrid welding is a new type of welding process that combines the principles of laser beam welding and arc welding. ... Electrogas welding (EGW) is a continuous vertical position arc welding process developed in 1961, in which an arc is struck between a consumable electrode and the workpiece. ... Electroslag welding is a highly productive welding process for thick materials. ... Equipment Power supply · Electrode · Filler metal · Shielding gas · Robot · Helmet A high output constant current welding power supply for use with GTAW and SMAW A welding power supply is an electrical device that provides an electrical current to perform welding procedures which require electricity. ... For other uses, see Electrode (disambiguation). ... A filler metal is a metal added in the making of a joint through welding, brazing, or soldering. ... Shielding gases are inert or semi-inert gases that are commonly used in several welding processes, most notably gas metal arc welding and gas tungsten arc welding. ... Spot welding: KUKA industrial robots welding a car body in the white section of a production line. ... Welding helmets are typically worn when arc welding. ... Related features Heat-affected zone · Weldability · Residual stress · Arc eye · Underwater 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. ... Welding is a fabrication process that joins materials, usually metals or thermoplastics, by causing coalescence. ... Residual stresses are stresses that remain after the original cause of the stresses (external forces, heat gradient) has been removed. ... Arc eye, also known as arc flash, welders flash, corneal flash burns, or flash burns, is a painful ocular condition sometimes experienced by welders who have failed to use adequate eye protection. ... Underwater welding Underwater welding refers to a number of distinct welding processes that are performed underwater. ... Related areas Brazing · Soldering · Fabrication · Casting · Machining · Metallurgy · Jewelry This article is about the metal joining process. ... (De)soldering a contact from a wire. ... A typical steel fabrication shop Fabrication, when used as an industrial term, applies to the building of machines , structures, process equipment for chemical, fertilizer sector by cutting, shaping and assembling components made from raw materials. ... This article is about the manufacturing process. ... A lathe is a common tool used in machining. ... Georg Agricola, author of De re metallica, an important early book on metal extraction Metallurgy is a domain of materials science that studies the physical and chemical behavior of metallic elements, their intermetallic compounds, and their compounds, which are called alloys. ... Jewelry (the American spelling; spelled jewellery in Commonwealth English) consists of ornamental devices worn by persons, typically made with gems and precious metals. ... Metalworking topics Casting · CNC · Cutting tools · Drilling and threading · Fabrication · Forging · Grinding · Jewellery · Lathe · Machining · Machine tooling · Measuring · Metalworking · Hand tools · Metallurgy · Milling · Occupations · Press tools · Pipe and tube bending · Smithing · Turning · General terminology · Welding This article is about the manufacturing process. ... For other uses, see CNC (disambiguation). ... a Cutting Tool, in the context of Metalworking is any tool that is used to remove metal from the workpiece by means of shear deformation. ... Drilling is the process of using a drill bit in a drill to produce holes. ... A typical steel fabrication shop Fabrication, when used as an industrial term, applies to the building of machines , structures, process equipment for chemical, fertilizer sector by cutting, shaping and assembling components made from raw materials. ... This article is about smithing. ... Rotating abrasive wheel on a bench grinder. ... For the Korean music group, see Jewelry (group). ... Center lathe with DRO and chuck guard. ... A lathe is a common tool used in machining. ... A machine tool is a powered mechanical device, typically used to fabricate metal components of machines by the selective removal of metal. ... The examples and perspective in this article or section may not represent a worldwide view. ... Turned chess pieces Metalworking is the craft and practice of working with metals to create structures or machine parts. ... Metalworking hand tools are hand tools that are used in the metalworking field. ... Georg Agricola, author of De re metallica, an important early book on metal extraction Metallurgy is a domain of materials science that studies the physical and chemical behavior of metallic elements, their intermetallic compounds, and their compounds, which are called alloys. ... Endmills for a milling machine. ... It has been suggested that this article or section be merged with Smith (metalwork). ... Power press with a fixed barrier guard A press, or a machine press is a tool used to work metal (typically steel) by changing its shape and internal structure. ... A smith, or metalsmith, is a person involved in the shaping of metal objects. ... Turning, CNC turning, or manual turning is the process used to produce cylindrical components in a lathe. ... This article needs to be wikified. ... Welding is a fabrication process that joins materials, usually metals or thermoplastics, by causing coalescence. ...