650240 Tooling

GTAW Applications 240

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Class Outline

ObjectivesWhat Is GTAW?Pros and Cons of GTAWMetals Welded with GTAWGTAW EquipmentGTAW TorchesParts of the GTAW TorchTungsten ElectrodesElectrode Characteristics Shielding GasesDC or AC SelectionAmperageVoltageGTAW Electrode PreparationGTAW Joint PreparationThe Touch Start MethodThe High-Frequency Start MethodGTAW Torch ManipulationRunning a GTAW BeadSummary


Lesson: 1/20

Objectives

Define GTAW. Distinguish GTAW from other arc welding processes. Identify common metals welded with GTAW. Describe characteristics of common GTAW equipment. Distinguish between gas-cooled and water-cooled torches. Identify parts of the GTAW torch. Describe common types of tungsten electrodes. Describe characteristics of typical tungsten electrodes. Describe the characteristics of shielding gases used for GTAW. Distinguish between using DC or AC for GTAW. Describe GTAW amperage characteristics. Describe the factors that affect voltage for GTAW. Describe common methods for tungsten electrode preparation. Figure 1. A GTAW circuit.Describe common methods for preparing a joint for GTAW. Describe the touch start method. Describe the high-frequency start method. Explain how to manipulate a GTAW torch. Explain how to run a weld bead using GTAW.

Figure 2. In GTAW, electrode extension must be kept as short aspossible.


Lesson: 2/20

What Is GTAW?

GTAW is the American Welding Society’s abbreviation for gas tungsten arc welding. GTAW is a very precise arc welding process often used to weld complex materials. GTAW uses a nonconsumable tungsten electrode to establish the arc, as Figure 1 illustrates. This electrode is nonconsumable because it does not melt or transfer to the weld. Tungsten is good electrode material because it has the highest melting point of all metals and is an excellent conductor. GTAW also uses an inert, external shielding gas to protect the tungsten and molten metal from contamination. For this reason, GTAW is often known as TIG welding, or tungsten inert gas welding.

GTAW can be performed with or without a filler metal. Once the weld puddle begins to form, the welder can add filler metalfrom a separate rod or wire, as Figure 2 shows. The need for filler metal depends on the shape and size of the joint, as well

Figure 1. Gas tungsten arc welding.as the type of material to be welded. However, keep in mind that the filler metal must never touch the electrode or it will contaminate it.

GTAW can be a manual, semi-automatic, or automatic process.In a manual process, the welder controls every part of the process, manipulates the welding torch, and adds filler metalas needed. In a semi-automatic process, the welding torch may be mounted on a special holder. In an automatic process, all of the welding variables are programmed into a welding machine. In this class, you will learn about the characteristicsof manual GTAW and its common applications.

Figure 2. The welder adds filler metal from a separate wire.


Lesson: 3/20

Pros and Cons of GTAW

The main advantage of GTAW is that high-quality welds can be made with almost all weldable metals. One reason is thatthe inert gas surrounding the arc and weld area protects the molten metal. Also, the GTAW process provides the bestcontrol of the weld pool of all the arc welding processes. This is because GTAW produces an intense, highly concentrated arc, which provides more heat control for hard-to-weld metals and thin metals, such as the aluminumin Figure 1.

Another advantage of GTAW is that it is a very clean process, with no spatter, smoke, or slag, as you can see in Figure 2. This makes the weld area highly visible, which also results in better control of the weld pool. Finally, in GTAW, filler metal can be added independently of the electrode.

The main disadvantage of GTAW is that it produces the slowest metal deposition rate of all the arc welding processes. This is because GTAW is a precise process used Figure 1. GTAW is often used to weld thin metals like to weld complex materials. In turn, GTAW often requires aluminum.highly skilled welders and slow welding speeds. Another drawback is that GTAW uses complex equipment and inert gases, which are high in cost.

Figure 2. GTAW is a clean process with no spatter or smoke.


Lesson: 4/20

Metals Welded with GTAW

GTAW can be used to weld almost all metals and alloys. GTAW is especially used for welding reactive metals and some nonferrous alloys. Common reactive metals include titanium, shown in Figure 1, nickel alloys, and magnesium. These metals require high-quality welds, and freedom from atmospheric contamination is critical. Even small amounts of oxygen, hydrogen, or nitrogen react with these metals, causing a loss of ductility and corrosion resistance. GTAW is preferred for welding these metals because it provides the best protection from contamination.

GTAW is also ideally suited for welding aluminum. This is because aluminum has high thermal conductivity, and GTAW’s highly concentrated arc allows for more control of heat input. Also, aluminum contains an oxide film on its surface, which must be removed before welding. GTAW Figure 1. GTAW often welds reactive metals, such as provides a cleaning action on the surface of aluminum to titanium.remove the film. Figure 2 shows a clean GTAW aluminum weld.

GTAW is well suited for welding thin sheets of all weldable metals because it can be controlled at very low amperages. Figure 3 shows welding a thin material with GTAW. However, GTAW should not be used for welding metals with very low melting points, such as zinc-based alloys, because the hightemperature of the arc makes it difficult to control the weld puddle.

GTAW is not commonly used for welding carbon steels. However, it can be used for thin steel sheet and root passeson heavy plate and piping. Other arc welding processes are used for filler passes on thick plate due to GTAW’s slow deposition rate.

Figure 2. A clean GTAW aluminum weld.

Figure 3. GTAW is suitable for welding very thin materials.


Lesson: 5/20

GTAW Equipment

GTAW uses a constant current welder. This means that the machine supplies varying amountsof voltage while the amperage remains constant. This is unlike gas metal arc welding orflux-cored arc welding, which uses a constant voltage welder. GTAW uses three types of current: AC, or alternating current, DCEN, or direct current electrode negative, and DCEP, or direct current electrode positive. The type of metal to be welded and other variables determinethe type of current to use. Figure 1 shows the complete GTAW circuit.

The electrode in GTAW is a nonconsumable tungsten electrode. However, a welder may manually add a filler metal rod or wire to the weld. The welding torch, shown in Figure 2, holds the tungsten electrode, which conducts electricity to the arc. The torch also provides a means for delivering shielding gas to the weld area.

Figure 1. A GTAW circuit.

In GTAW, welders can control welding current withremote controls, like the foot pedal shown in Figure 3. The foot pedal is generally used in an area where the welder can sit down. The welder raises or lowers the pedal for more or less weldingcurrent. However, for out-of-position welds, handcontrols are used to allow the welder more freedom to move.

Finally, a gas cylinder supplies the shielding gas used in GTAW. The cylinder pressure gaugeindicates the amount of gas pressure present in the gas cylinder. The shielding gas flowmetercontrols the amount of shielding gas pressure thatcontinuously flows to the weld area.

Figure 2. The welding torch holds the tungsten electrode and delivers shielding gas to the weld area.


Figure 3. The foot pedal controls welding current.


Lesson: 6/20

GTAW Torches

The GTAW welding torch holds the tungstenelectrode so it can be manipulated along the weld path. Like the welding guns used in other arc welding processes, the GTAW torch is rated according to its duty cycle, which is the maximum current that can be used without overheating. This means that the torch performs work only for a certain amountof time before it must cool. The GTAW torch conducts electricity to the electrode and supplies inert shielding gas to the electrode tip, arc, and weld area. It also insulates the electrode and electrical connections from the welder. Figure 1 shows typical GTAW torches.

The heat generated in the torch during welding is removed by water cooling or gas cooling. A water-cooled torch is cooled by Figure 1. GTAW torches.the passage of water through hoses in the torch, as Figure 2 illustrates. The water exits the system through a line in the power cable. Water-cooled torches are typically used for high-current applications. These torches are larger, and they also require connections to tap water and a drain.

Figure 3 shows a gas-cooled torch and a water-cooled torch. A gas-cooled torch is cooled by the passage of inert shielding gas through the power cable. Unlike water-cooledtorches, these torches are generally used for low-current applications or light-duty field work where water is not available. These torches are also lighter than water-cooled torches.

Figure 2. The interior of a water-cooled welding torch.


Figure 3. The gas-cooled torch is cooled by the passage of gas through the power cable. The water-cooled torch is cooled by the passage of water through a hose.


Lesson: 7/20

Parts of the GTAW Torch

The typical GTAW torch consists of the torch body, a collet set, a torch cap, and a nozzle. Figure 1 shows the parts of a typical welding torch:

The torch body is the plastic part of the GTAW torch that holds the electrode and collet set. The collet set secures the electrode in the torch. This two-piece collet set is made to fit each standard size tungstenelectrode. The collet set is typically made of copper, which isa highly conductive metal. The torch cap is tightened on the back of the torch body. As a result, the collet grips the electrode when the torch cap is tightened in place. Torch caps are designed in varying lengthsto match standard tungsten lengths and adapt the torch for welding in small areas. The nozzle, or cup, fits over the arc end of the torch to direct inert gas over the electrode and weld pool. The inert gas flows through the torch body and through holes in the Figure 1. The parts of a typical welding torch.collet to the arc end of the torch. Nozzles are made of a hard,heat-resistant material, such as ceramic, and are available invarious shapes and sizes. Larger nozzles give more complete inert gas coverage of the weld area, but they may be too big to fit into smaller areas. Smaller nozzles provide adequate gas coverage in smaller areas. The gas lens also may be used in a GTAW torch. The gas lensfits around the collet and produces a longer, undisturbed flowof shielding gas. This allows the welder to use a longer electrode extension than with a standard nozzle. A longer electrode extension improves welders’ ability to see the weld pool and allows them to reach places with limited access, such as inside corners.


Lesson: 8/20

Tungsten Electrodes

Unlike other arc welding processes, GTAW does not use the tungsten electrode as filler metal. The melting point of tungsten is extremely high;it does not easily melt and transfer to the weld like consumable electrodes. However, the tungsten electrode conducts electricity to the arc, which supplies the heat required for welding.

There are three common types of tungsten electrodes. Pure tungsten electrodes, shown in Figure 1, contain at least 99.5 percent tungsten, with no intentional alloying elements. Pure tungsten electrodes have the lowest conductivity and a low resistance to contamination. However, these electrodes are lower in cost and provide good arc stability. Pure tungsten electrodes are primarily used withAC for welding aluminum and magnesium alloys. Consequently, the cleaning action of AC helps remove any possible contamination on the electrode.

Figure 1. Pure tungsten electrodes are primarily used with AC for Thoriated tungsten electrodes, shown in welding aluminum.Figure 2, contain tungsten and small amounts ofthorium. Two percent thoriated tungsten is most commonly used. Thorium is a radioactive element added to tungsten to improve the electrode’s operating characteristics. Thoriated tungsten electrodes are superior to pure tungsten electrodes in many ways. They have higher conductivity and generally last longer. Thoriated tungsten electrodes also have greater resistance to contamination when using either AC or DC. In addition, these electrodes provide greater arc stability, have less tendency to stickto the workpiece, and make arc starting much easier.

Zirconiated tungsten electrodes contain tungsten and small amounts of zirconium oxide. These electrodes are most often used with AC welding because they combine the desirable characteristics of pure tungsten electrodes with the starting characteristics of thoriated electrodes.

Figure 2. Thoriated electrodes have high conductivity and generallylast longer than pure tungsten electrodes.


Lesson: 9/20

Electrode Characteristics

When selecting an electrode for GTAW, you must consider the electrode material, size, tip shape, torch, and nozzle. These factors depend on the welding application, base metal, and joint type. Figure 1 illustrates common GTAW electrode tip shapes.

The total length of the tungsten electrode is limited by the length that the torch can accommodate. Longer electrode lengths allow for more electrode preparation than shorter lengthsand therefore are more economical.

The distance that the electrode extends from the nozzle to the end of the electrode is known as electrode extension. The tungsten electrode must extend enough to reach the joint and allow the welder to see the arc. However, too long of anextension may cause air to mix with inert gas and contaminate the weld. Also, the electrode extension determines the amount of heat in the

Figure 1. When selecting an electrode for GTAW, you must electrode. This heat has no value to the weld consider the shape of the electrode tip.because the heat in GTAW must be concentrated

in the arc and not in the tungsten electrode. Therefore, the electrode extension must be kept as short as possible to provide easy access to the joint. Generally, an extension of 3/8 in. to 1/2 in. is appropriate, as Figure 2 shows.

Figure 2. In GTAW, the electrode extension must be kept as short as possible.


Lesson: 10/20

Shielding Gases

Inert shielding gas surrounds the entire weld area and the tungsten electrode. This inert gas protects the tungsten, molten metal, and heat-affected zone from oxygen, nitrogen, and hydrogen. If the weld is not protected, the atmosphere absorbs into the weld, and it becomes brittle and porous.

Argon is the shielding gas used for most GTAW applications. However, helium and argon-helium mixtures are also often used depending on the type of material and application. These gases are readily available and less costly than other inert gases. Argon has many advantages over helium. It produces a smoother, quieter arc and operates at a lower voltage at any given current. Consequently, the arc is easier to start because of these

Figure 1. Helium transfers more heat from the arc to low voltage characteristics. Also, argon is much heavier the weld pool.than helium. Therefore, argon blankets the weld area and

is more resistant to drafts. Helium instead tends to rise rapidly and cause turbulence. Turbulence occurs when excessive gas creates a whirling motion and mixes with outside air.

Argon-helium mixtures are often used for welding thick sections and for materials with high thermal conductivity and high melting temperatures, such as aluminum and copper. This is because helium transfers more heat to the weld pool causing deeper penetration, as Figure 1 illustrates.


Lesson: 11/20

DC or AC Selection

GTAW uses three types of current: direct current electrode negative (DCEN), direct current electrode positive (DCEP), or alternating current (AC). The type of current used depends on the metal to be welded.

GTAW uses DCEN for welding most metals. In DCEN, electricity flows from the tungsten electrode to the workpiece. In turn, DCEN generates the greatest amount of heat in the workpiece, as Figure 1 illustrates. This produces deeper weld penetration. However, one disadvantage is that DCEN does not provide a cleaning action on the surface of the metal. This is generally acceptable except for when welding aluminum. Aluminumhas an oxide film on its surface, which must be removed before welding.

In DCEP, electricity flows from the workpiece to the tungsten electrode. In turn, the tungsten electrode receives most of the heat, as Figure 2 illustrates. This produces shallow weld penetration. DCEP has limited use in GTAW because it directs most of the heat toward the

Figure 1. DCEN generates the greatest amount of heat in tungsten, taking away the heat required in the the workpiece.workpiece. However, one advantage of DCEP is that it

provides a cleaning action to remove the oxide film from the metal’s surface.

AC combines the deep penetration characteristic of DCENwith the cleaning action of DCEP, as Figure 3 illustrates. Aluminum and magnesium are generally welded using ACbecause, during the DCEP part of the cycle, weld penetration is reduced and more heat is directed at the tungsten electrode. As a result, the arc removes the oxides from the surface of the material, making welding easier. During the DCEN part of the cycle, most of the heat accumulates in the workpiece.

Figure 2. DCEP generates heat in the tungsten electrode.


Figure 3. AC combines characteristics of DCEN and DCEP.


Lesson: 12/20

Amperage

The amount of amperage determines the amount of heat in the arc. GTAW uses a constant current welder,like the one in Figure 1. This means that amperage is pre-set before welding begins, and the welder calculates voltage automatically. In GTAW, the constant current welder must provide enough amperage for melting the metal at a low voltage. However, GTAW typically uses constant current with a drooping characteristic. With a drooping characteristic, the welder may vary the current level slightly by changing the arc length. Welders can change the current level with the use of hand or foot controls. Figure 2 shows a welding torch with a hand control. These controls allow the welder to apply additional current for deeper penetration, or reduce current levels for bridging gaps. Welders can also apply current slowly to prevent burnthrough on thin material.

GTAW has a wide range of amperage capabilities. It can use 2-3 amps to weld 0.005 in. metal sheet, or Figure 1. GTAW uses a constant current welder.use 1000 amps to weld 1 in. metal plate. In other words, each 0.001 in. of metal generally requires about 1 amp of welding power.

Figure 2. The welder may use a torch with a hand control to change current levels.


Lesson: 13/20

Voltage

In GTAW, the amperage is pre-set on the welder, and the welder calculates the voltage automatically. Voltage is a dependent variable and is affected by other variables such as current, tip shape, arc length, and type of shielding gas.

Voltage varies in proportion to the amperage. For this reason, to keep a fixed arc length, if the amperage changes, it is also necessary to change the voltage settings. Arc length is important because it affects the width of the weld pool. A shorter arc length yields a narrower weld pool, as you can see in the narrow weldin Figure 1. A narrow weld is essential in GTAW.

High-voltage is generally used to start the arc. However, using excessive voltage, shown in Figure 2,

Figure 1. A narrow weld is essential in GTAW.can cause porosity, spatter, and undercut. In addition, the welder may lose control of the weld pool.On the other hand, using insufficient voltage, shown inFigure 3, can cause an erratic, popping arc that will not melt the base metals. This may also cause the tungsten to stick to the workpiece.

Figure 2. Excessive voltage may cause the welder to lose control of the weld pool.

Figure 3. Insufficient voltage may cause the electrode to stick to the workpiece.


Lesson: 14/20

GTAW Electrode Preparation

Preparing the tungsten electrode tip is an important variable in the GTAW process. The shape of the electrode tip affects the size and shape of the weld bead. Tungsten tips are generally prepared by balling or grinding. Ballingforms a hemispherical ball on the end of the tungsten electrode, as Figure 1 illustrates. To create a ball:

1. Sharpen the tungsten electrode to a long taper with a point.

2. Insert the pointed electrode in a torch so that the tip extends about ½ in. beyond the nozzle and tighten the cap.

3. Start the arc on a test piece of steel or copper with a low current, and then increase the current to form the desired ball diameter.

Figure 1. Balling occurs when a hemispherical ball is formed on the end of the tungsten electrode.Too much current used during balling can cause

the tungsten to separate from the electrode, contaminating the weld. If this happens, use a larger diameter electrode that carries more amperage. AC and DCEP welding require a hemispherical electrode tip. This shape tends to increase the width of the weld bead and decrease penetration. Keep in mind that the size of the ball must not exceed 1 1/2 times the electrode diameter.

Grinding uses an abrasive to wear away at the surface of the tungsten electrode tip, changing its shape. The electrode must be perpendicular to the axis of the grinding wheel. The electrode contacts the wheel's outer surface. The grinding wheel used for tungsten electrodes must be used only for tungsten to prevent contamination of the tip. Figure 2 shows a grinding wheel exclusively

Figure 2. Grinding wheels used for tungsten electrodes must onlyused for tungsten. In DCEN welding, the tungsten be used for tungsten.tip is ground to a taper point. This is generally no


more than 2-3 times the diameter in length. This tip should be cone-shaped instead of a sharp point, as Figure 3 illustrates. A sharp point promotes easy arc starting, but it can melt and form a small ball on the end. The flatter tip end will maintain its shape within the current range.

Figure 3. In DCEN, the electrode should have a conical tip.


Lesson: 15/20

GTAW Joint Preparation

Almost all joints must be prepared before welding. Joint preparation often involves thoroughly cleaning the basemetals before welding as well as machining them to remove any possible surface defects. Grinding is often used to remove impurities from the metal’s surface. Keepin mind that grinding wheels must be cleaned and used only for the material being welded. Grinding wheels, like the one in Figure 1, may contain abrasive particles, which can cause porosity in the weld if they are not removed.

GTAW is used to weld most standard joint types. Nevertheless, a major consideration in GTAW joint designis proper accessibility. The groove angle, like the one inFigure 2, must permit manipulation of the torch to obtainadequate fusion of the groove face. In addition, the characteristics of the weld metal must be considered when preparing a joint. For example, high-nickel alloys

Figure 1. Grinding wheels are often used in joint move very slowly when molten, and the weld metal does preparation.not wet the groove face well. Therefore, groove angles

must be wider to provide space for manipulation.

Finally, the choice of whether or not to use filler metal must be considered. For example, consider the square-edge butt joint in Figure 3. If you are not using a filler metal, and the joint requires complete penetration, make sure that the joint edges are preparedso that they align properly with a minimum gap.

Figure 2. The groove angle must permit proper torch accessibility.


Figure 3. The edges of a butt joint must align properly when using GTAW.


Lesson: 16/20

The Touch Start Method

The GTAW arc is commonly started using the touch start method. The touch start method occurs when the welder lowers the torch toward the workpiece until the tungsten electrode makes contact. This creates a short circuit and an arc, which allows current to flow. The torch is then quickly withdrawn a short distance to establish the arc.

The touch start method is a simple arc starting method. However, this method is generally not used for critical work because the electrode may stick to the weld if the torch is not pulled away quickly. If the tungsten electrode dips into the molten weld pool, it will be contaminated. Contaminated electrodes may cause tungsten inclusions in the weld metal, as Figure 1 shows. To avoid contamination, you must break off the contaminated section with a pair of wire cutters or pliers and regrind the electrode to the required shape. Figure 1. Contaminated electrodes may cause tungsten

inclusions in the weld metal.


Lesson: 17/20

The High-Frequency Start Method

The most common method for starting the arc in GTAW is the high-frequency start method. High-frequency start can be used with both DC and AC. This start uses high voltage to generate a spark when the tungsten electrode nears the workpiece. The high voltage ionizesthe gas between the electrode and the work, and the gas conducts the welding current. When using DC, the welder starts the high frequency until an arc is established and then turns it off. When using AC, high frequency remains continuous during welding.

High frequency is maintained by a control, like the button on the torch in Figure 1. If the high frequency remains on for a long time, it may create tracking marks on the weld surface. Therefore, some machines use "hot start." This causes high current to start the arcquickly and reduce the duration of high frequency. However, this method may cause problems for thin materials that melt easily. Nevertheless, high-frequencystart avoids tungsten contamination because the Figure 1. The control on this welding torch generates the tungsten does not touch the workpiece. high-frequency start.


Lesson: 18/20

GTAW Torch Manipulation

The GTAW torch is usually held like a pencil, as Figure 1 shows. This angle allows the welder to move the torch easily and change angles if necessary. When welding in the flat position, hold the torch with your favored hand at an angle of about 15° from the vertical, and place your other hand lightly ona surface, so your welding hand moves across the joint evenly. If you move the torch using only your fingers, this may cause incorrect torch angles and a poor weld. Figure 2 illustrates the proper torch and fillermetal angles.

The angle at which the filler metal enters theweld is critical. When adding filler metal, grip the wire or rod in your fingers. Keep thishand as close as possible to the arc to hold

Figure 1. The GTAW torch is usually held like a pencil.the filler metal steady. Move the filler metal in conjunction with the torch movement. Always maintain a flat entrance angle of the filler metal into the weld pool. This angle should be about 15 to 20° from the workpiece to the filler metal.

Figure 2. The welding torch must be held about 15° from vertical, and the filler metal must be moved in conjunction with the torch.


Lesson: 19/20

Running a GTAW Bead

Manual GTAW requires a highly skilled welder to manipulate the torch with one hand while controlling the weld current with a foot pedal and feeding filler metal with the other hand. Figure 1 illustrates how to begin a GTAW weld bead. To begin the GTAW process:

1. Hold the torch in one hand with the tungsten about ¼ in. away from the base metal.

2. If you are using the high-frequency start, step on the foot pedal and push down about part way to initiate the high frequency.

3. Move the torch slowly toward the plate until you establish an arc, and then increase the current to the required amperage by pushing the foot pedal all the way down.

4. Hold the pedal down until a weld pool is established. 5. Next, hold a length of the proper filler wire in the

other hand with about a 10 in. extension and feed into the front end of the weld pool at about a 15° angle from the plate.

6. Pull the wire back out of the pool slightly and melt the Figure 1. This process illustrates how to begin a GTAW added metal into the pool with a forward motion of theweld bead.torch.

To prevent the hot end from oxidizing, the filler wire must not be pulled back out of the inert gas shield. When adding filler wire, you must avoid touching the wire to the tungsten electrode. This will cause tungsten contamination and an unstable arc. If this occurs, the electrode must be removed and either ground down or replaced.


Lesson: 20/20

Summary

GTAW is the American Welding Society’s abbreviation for gas tungsten arc welding. GTAW uses a nonconsumable tungsten electrode to establish an arc and an inert shielding gas to protect the electrode and weld area. GTAW is often known as TIG welding and can be performed with or without a filler metal.

GTAW is a precise process often used to weld complex materials. GTAW produces a highly concentrated arc, which provides more heat control for hard-to-weld metals. GTAW is also a clean process, with no spatter, smoke, or slag. However, GTAW requires highly skilled welders and produces the slowest deposition rate.

GTAW uses a constant current welder, a tungsten electrode, a welding torch, shielding gas, and remote controls. The type of metal to be welded determines the type of current to use for GTAW: alternating current (AC), direct current electrode negative (DCEN), or direct current electrode positive (DCEP). The GTAW torch can be water-cooled or gas-cooled. The parts of the torch consist of the torch body, a collet set, torch cap, and nozzle.

The most common tungsten electrodes used in GTAW are pure Figure 1. Balling is typically used with AC tungsten and thoriated tungsten. The shape of the electrode tip welding.affects the size and shape of the weld. Tungsten tips are generally

prepared by balling or grinding. Balling is used only with AC welding and grinding is typically used with DCEN welding.

The GTAW arc is commonly started using the touch start method or the high-frequency start method. Touch start may cause the electrode to stick, which causes tungsten inclusions. High-frequency start avoids tungsten contamination because the tungsten does not touch the workpiece.

Figure 2. A GTAW weld bead.


Class VocabularyTerm Definition

A material consisting of hard particles used to wear down, rub away, or machine material.abrasiveCurrent that regularly reverses the direction of its flow. AC is often used in GTAW to weld ACaluminum and magnesium alloys.

A silvery white metal that is soft, light, and an effective conductor. GTAW is sometimes the first aluminumchoice for welding aluminum.

A measurement that indicates the amount of current flowing in a circuit, which is measured in amperageamperes. FCAW amperage is determined by wire speed.

An inactive gas commonly used as shielding. Argon is much heavier than air, so it effectively argonshields the weld area.

An electrode preparation process in which the tip of the tungsten electrode is formed into a ballinghemispherical ball. This shape is required for AC and DCEP welding.

Excessive melt through or a hole in the base metal. Extremely high welding temperatures can burnthroughcause burnthrough.

A type of joint between two metal parts that lie in the same plane. A butt joint is the most butt jointcommon joint type.

A steel that is made up of iron and carbon, without any additional materials.carbon steelA nonmetallic material made from clay and hardened by firing at a high temperature. GTAW ceramicnozzles are often made of ceramic because of its resistance to high temperatures.

A two-piece set, usually made of copper, which secures the electrode in the torch. Standard collet collet setsizes are made to fit each standard size tungsten electrode.

A material that allows for the flow of electricity. For a successful arc weld, electrodes and base conductormetals must be good conductors.

A welder that uses current that varies slightly with changes in voltage. Constant current, or CC, is constant current often used in gas tungsten arc welding (GTAW) and shielded metal arc welding (SMAW).welderA welder that uses voltage that varies slightly with changes in current. Constant voltage, or CV, is constant voltage often used for gas metal arc welding (GMAW) and flux-cored arc welding (FCAW).welderA reddish metal that is very ductile, thermally and electrically conductive, and corrosive resistant. copperCopper is often used to make electrical wire.

A metal's ability to resist attack by other elements and chemicals.corrosion resistanceAnother name for the nozzle in GTAW.cup

cylinder pressure The device that indicates the amount of shielding gas present in the gas cylinder.gauge

An abbreviation for direct current electrode negative. DCEN is another way of expressing direct DCENcurrent with straight polarity.

An abbreviation for direct current electrode positive. DCEP is another way of expressing direct DCEPcurrent with reverse polarity.

The rate at which an electrode melts into the molten weld puddle to form a weld.deposition rateA characteristic of welding current that occurs when using a constant current welder. Even though droopingcurrent is constant in GTAW, when the welder raises or lowers the welding torch, current varies slightly.

A metal's ability to be drawn, stretched, or formed without breaking.ductilityThe amount of time in a ten-minute period that an electrical device can perform work without duty cycleoverheating. If a welding gun has a 30% duty cycle, it can operate for three consecutive minutes and must rest for seven.

The distance from the end of the contact tip to the end of the electrode.electrode extensionThe use of processes that prepare the tungsten electrode before welding. Grinding and balling are electrode preparationcommon electrode preparation processes.

Metal deposited into the weld that often adds strength and mass to the welded joint. GTAW filler metalsometimes uses filler metal that is added independently of the tungsten electrode.

A single progression of welding with the purpose of filling the joint with metal. GTAW is generally filler passesnot used for filler passes due to its slow deposition rate.

An arc welding process that uses a continuously fed consumable electrode that contains flux in a flux-cored arc weldinghollowed-out center. It is also referred to as FCAW.

A type of control that, when pressed by the welder, initiates frequency. Pushing the pedal all the foot pedalway down increases amperage.


The rate at which an electrical current alternates, expressed as the number of cycles per unit of frequencytime. Frequency is typically measured in Hertz (Hz) or cycles per second.

An external device used to house shielding gas. Shielding gas flows from the gas cylinder, to the gas cylindergas hose, to the welding gun.

A specially designed screen assembly that attaches to the welding torch and gas nozzle to maintaingas lensa longer shielding gas flow.

An arc welding process in which a bare wire electrode and inert or active shielding gas is fed to thegas metal arc weldingweld through a welding gun. It is also referred to as GMAW or MIG welding.

A very precise arc welding process that uses a nonconsumable tungsten electrode. It is also gas tungsten arc referred to as GTAW or TIG welding.weldingA type of welding torch that uses shielding gas to cool the torch. Gas-cooled torches are often usedgas-cooled torchfor low-current applications.

The use of an abrasive to wear away at the surface of metal and change its shape. Grinding is grindingoften used for tungsten electrodes to maintain the required shape.

A wheel coated with an abrasive that is used to grind a workpiece.grinding wheelThe total angle of the groove in between workpieces. GTAW joints must have wide groove angles groove angleto accommodate for torch manipulation.

The exposed surface of the groove weld in between workpieces.groove faceThe American Welding Society abbreviation for gas tungsten arc welding.GTAWA type of control mounted on the welding torch, which initiates frequency. Hand controls allow the hand controlwelder more freedom to move.

The portion of the base metal that has not been melted, but its mechanical properties have been heat-affected zonealtered by the heat of welding.

An inactive gas commonly used as shielding. Helium is much lighter than air and can escape the heliumweld area quickly.

A half circle of molten metal formed on the tip of the tungsten electrode. The hemispherical ball is hemispherical ballformed during the balling process.

An arc starting method in which high voltage is used to generate a spark between the electrode high-frequency start and the workpiece to establish an arc. With this method, the electrode does not touch the methodworkpiece.

A type of gas that does not react with other elements. Argon and helium are inert gases.inert gasTo convert something into ions, which are atoms that carry positive and negative electrical ionizecharges. With high-frequency start, high voltage ionizes the gas, which conducts the current.

A variety of processes that prepare base metals before welding. This can involve preheating, joint preparationcutting, or other preparations.

The process of removing metal by producing chips through the use of cutting tools.machiningA grayish white, extremely light metal that is also brittle and has poor wear resistance.magnesiumA metal that contains nickel, which is a hard, malleable, silvery white metal used in various alloys nickel alloyto add strength, toughness, and impact resistance to metals.

An electrode made of tungsten that is not melted by welding heat and does not become part of nonconsumable the molten weld metal.tungsten electrodeA metal that does not contain iron. Aluminum and copper are common nonferrous metals.nonferrous alloyA device attached to the front of the torch body that directs inert shielding gas over the weld area.nozzleGTAW nozzles are typically made of ceramic.

A chemical compound that contains oxygen, which forms a thin layer on the surface of metals oxide filmwhen exposed to air. Oxide film should be removed before welding.

A type of tungsten electrode made with at least 99.5 percent tungsten. Pure tungsten electrodes pure tungsten are primarily used with AC for welding aluminum and magnesium.electrodeA type of metal that undergoes a chemical reaction when combined with elements such as oxygen, reactive metalhydrogen, or nitrogen. Reactive metals include titanium, nickel, and magnesium.

A device used to control a welding sequence or welding current. GTAW uses hand controls and footremote controlcontrols to control current.

A single progression of welding in the root of a joint.root passesA gas that protects the weld puddle and arc from reacting negatively with the atmosphere. GTAW shielding gasshielding gas is supplied by a cylinder and flows through the welding torch.

shielding gas The device that controls the amount of shielding gas that flows to the weld area.flowmeter

A gradual decrease in the width of an object. Tungsten electrodes are tapered to a point.taper


The rate at which heat flows through metal.thermal conductivityA type of tungsten electrode that contains approximately 2 percent thorium. Thoriated tungsten thoriated tungsten electrodes have higher conductivity and generally last longer.electrodeA heavy, radioactive element used in tungsten electrodes.thoriumAnother name for gas tungsten arc welding or GTAW.TIG weldingA silver-gray, strong, but lightweight metal known for its corrosion resistance. Titanium is often titaniumused in the aerospace industry.

The metallic part of the welding torch that holds the electrode and collet set.torch bodyA cap on the back of the torch body that allows the collet to grip the electrode when tightened. torch capTorch caps are designed to match standard tungsten electrode lengths.

An arc starting method in which the tungsten electrode contacts the workpiece to create a short touch start methodcircuit and an arc. This method is not used for critical work because it may cause electrode contamination.

A gray metal that is very strong at elevated temperatures. Tungsten is used to make tungstennonconsumable electrodes.

A piece of tungsten entrapped in the weld metal. Tungsten inclusions contaminate the weld.tungsten inclusionAn upset in the even flow of shielding gas to the welding area. Turbulence causes gas to swirl, andturbulenceas a result, mix with outside air. Turbulence is often the result of excessive shielding gas.

A groove melted into the base material, usually along the toes of the weld, that produces a weak undercutspot in the weld.

The electrical force or pressure that causes current to flow in a circuit.voltageA type of welding torch that uses water to cool the torch and power cable. Water-cooled torches water-cooled torchare often used for high-current applications.

Equipment used to perform the welding operation. A welding machine is used in an automatic welding machinewelding process.

The device that holds the tungsten electrode, delivers shielding gas to the weld area, and insulateswelding torchthe welder from the welding current.

An alloy that contains zinc, a bluish-white metal most often used in brass and bronze.zinc-based alloyA type of tungsten electrode, which contains small amounts of zirconium oxide. Zirconiated zirconiated tungsten tungsten electrodes combine the characteristics of pure tungsten and thoriated tungsten electrodeelectrodes.

A white, crystalline powder used in zirconiated tungsten electrodes.zirconium oxide


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650240 Tooling