TIG Welding

Gas tungsten arc welding (GTAW), also referred to as tungsten inert gas (TIG) welding, is an arc welding process which uses a non-consumable tungsten electrode for creating the weld. The weld area and electrode is protected from oxidation and/or other atmospheric contamination using an inert shielding gas (argon or helium), and a filler metal is commonly made use of, although certain welds, referred to as autogenous welds, don't require it. Whenever helium is used, this is referred to as heliarc welding. A constant-current welding power supply generates electrical energy, that is conducted across the arc via a column of highly ionised gas and metal vapours identified as a plasma. GTAW is typically employed to weld thin sections of stainless steel and non-ferrous metals which includes aluminium, magnesium, and copper alloys. The process permits the operator improved control during the weld as compared to competing processes which include shielded metal arc welding and gas metal arc welding, enabling stronger, higher quality welds. Nonetheless, GTAW is comparatively more complicated and additionally difficult to master, and in addition, it is substantially slower as compared to the majority of welding techniques. A associated process, plasma arc welding, relies on a slightly different welding torch to generate a more focused welding arc and consequently is usually automated.

About GTAW Process

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In TIG welding, a tungsten electrode heats the metal which is being welded and gas (most frequently Argon) protects the weld puddle from airborne contaminants. TIG welding delivers clean, precise welds upon any sort of metal.

TIG welding is highly regarded due to its quality and applicability. Without a doubt, the process can be used on a lot more metals when compared to any other process, effective at welding metals including steel, bronze, nickel, brass, copper, magnesium, aluminium and gold. Welding in a TIG operation is extremely precise and clean, making it possible for a superior appearance. The reason being, a welder is able to increase and reduce the amount of heat which is used in the process, by way of a foot pedal, to be able to better control the weld. With regard to cleanliness, TIG welding doesn’t cause sparks or generate smoke and fumes.

Application of TIG welding

• The TIG process which is used to join a wide range of metal. It can weld aluminium, magnesium, copper, nickel, titanium, etc. and their alloys.
• TIG can be used to weld in any position - flat, horizontal, vertical, overhead position.
• It is employed wherever quality is critical. For example, pipes, vessels, aerospace industry.

Advantages of TIG welding

• Non-consumable electrodes - It facilitates to produce flawless joints since it isn't required to stop for replacing the electrode as with consumable electrode welding. This additionally results in reducing downtime in production.
• No flux becomes necessary due to the fact that inert gas shields the molten metal. Consequently no slag and slag inclusion complications.
• High quality in addition to strong welding is accomplished by means of TIG.
• Cleaner and more appealing joints. In some cases, some sort of finishing process will not be required.
• It is suitable for welding of very thin sections.
• The versatility of the method . It can work with and without filler metal.
• A wide range of metals can be welded. Nonferrous metals including aluminium, copper and dissimilar metals can be welded without any challenge.
• Non-corrosive and ductile joints.
• The minimum amount of flames and spark . Reduced distortion resulting from smaller heat zone.
• It can be executed in both automatic and manual way.

Benefits of TIG Welding

1. Welds more metals and alloys when compared to any other process: TIG welding can be used to weld steel, stainless steel, chromoly, aluminium, nickel alloys, magnesium, copper, brass, bronze, and even gold. TIG is a effective welding process for the purpose of welding wagons, bike frames, lawn mowers, door handles, fenders, and more.
2. Results in high quality, clean welds: With superior arc and weld puddle control, TIG makes it possible to generate clean welds whenever appearances count. Considering that heat input is usually regulated by way of pressing on a foot pedal, akin to driving a vehicle, TIG welding makes it possible to heat up or cool down the weld puddle providing precise weld bead control. The following makes TIG welding ideal for cosmetic welds for instance in sculptures and automotive welds.
3. No sparks or spatter: Since only the essential amount of filler metal is added to the welding puddle, no spatter or sparks are produced, in case the metal being welded is clean.
4. No flux or slag: Considering that the Argon gas protects the weld puddle from contamination, no flux is needed or made use of in TIG welding and additionally there isn't any slag to block the view of the weld puddle. Furthermore, the finished weld won't have slag to remove between weld passes.
5. No smoke or fumes: TIG welding will never generate smoke or fumes, except in cases where the base metal being welded contains contaminants or substances which includes, oil, grease, paint, lead or zinc. The base metal should be cleaned prior to welding.
6. Make use of one shielding gas for all applications: Argon gas is usually used for the majority of TIG welding applications. Considering that Argon can be used to TIG weld all metals and thicknesses, only one variety of gas is necessary to undertake all types of welding projects.
7. Weld in all positions: TIG welds can be produced in all positions - flat, horizontal, vertical or overhead. Ideal for roll cages and inside confined areas.

Disadvantage of TIG welding

• TIG is a time-consuming process - It is slower compared to almost every other welding process. Lower filler deposition rate.
• More complicated - Highly skilled and experienced personnel are essential to accomplish TIG welding.
• Safety challenges - Welders are exposed to high intensity light that can result in eye damage.
• High preliminary cost.
• It cannot be made use of in thicker sheets of metal.

TIG welding is a remarkably flexible process given its ability to function as a technique of preference for a multitude of metals as well as its extreme precision.

TIG Welding Process

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Most of the time, TIG welding is the process of fusing metal with metal. It entails three factors – heat, a shielding gas, and filler metal.

The heat is generated by way of the electricity passing through the tungsten rod. The shielding is incorporated by using a compressed bottle that delivers gas flow to the weld area. The filler metal is a simple wire which the welder feeds and dips manually, that is subsequently melted into the arc.

In one hand, a TIG welder holds a TIG torch which is aimed toward the area where one needs to start welding. The other hand is reserved for the metal filler rod. Lastly, the foot hovers over a pedal which is used to start everything. By depressing the pedal, an electric current will shoot out of the torch gun and generate an immensely high temperature. Concurrently, the filler wire is fed into the weld pool and melted. Simultaneously, the equipments provide an inert gas with the purpose of creating a barrier bubble designed to, consequently, keep all the impurities from coming into contact with the molten metals. Maintaining everything clean.

There are several components of welding equipment which a TIG welder is required to be familiar with though. The work lead, or the ground cable with a clamp, is attached to the workpiece. The welding lead incorporates a TIG torch at the end. There is a small line along with the cable which supplies the argon gas. Lastly, a gas bottle and a regulator are also essential.

The TIG Welding Torch

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The TIG welding torch consists of various parts. The electrode is the small tungsten rod which is typically available in several sizes. The primary difference is the fact that the electrode doesn't burn up similar to a filler rod. Rather, the tungsten can be sharpened to a point or a ball shape. All this is dependent upon what job is being handled.

There is a copper collet which secures the tungsten which is used to adjust the length that it protrudes from the cup. The cup is constructed of ceramic and it is replaceable in case required. Additionally, there are several cup outlet diameters available.

The collet-body comes with several cross-holes that are used to feed the gas into the cup and surround the tungsten. It is designed to exclude oxygen considering that it can contaminate the weld.

TIG Torch Types

There are two different types of widely used torches meant for TIG welding – Air-cooled and water-cooled TIG torches.

• Air-Cooled TIG Torches: These types of torches are extremely practical and tend to be not as expensive. However, the challenge using it is that, that it can heat excessively. It can also be challenging to grasp and lots of the heat goes wasted.
• Water-Cooled TIG Torches: These types of torches are far more efficient, however, in addition to water coolant, they require a great deal of maintenance. It requires a water cooler and additionally, inside it, there is a radiator that the water passes through.

The Tungsten

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Tungsten is a hard but additionally extremely brittle form of metal. In comparison to other metals, it has applications that are very limited, nonetheless, it has found its use in TIG welding. Tungsten is utilized to produce the non-consumable electrode for the arc meant for TIG welders.

As a consequence of Tungsten’s completely unique properties, the arc has the capacity to sustain a temperature of 6,000 °C. Tungsten boasts a high melting point together with excellent conductivity. Eventhough very strong, it happens to be brittle and can be easily broken using a tap.

There are numerous factors to take into consideration in the welding procedure. Tungsten electrode geometry impacts on the arc shape, as a consequence impacting on the weld bead shape and size, the weld penetration, and additionally point longevity of the electrode. Proper electrode grinding procedures together with equipment must be employed in order to ensure that electrodes are dimensionally correct. Ultimately, different tungsten materials possess different characteristics in arc start ability, electrode life, and contamination resistance. This tends to make selecting the suitable material for the application an essential variable in welding performance. The proper preparation of electrodes in every one of these aspects will provide the advantages of consistent welding along with optimum performance.

Tungsten Electrode Types

As the name suggests, Tungsten is the main component of the electrode. However, there are additional elements which are incorporated in order to produce different effects. The most typically incorporated elements tend to be Cerium, Lanthanum, and Zirconium.

• Pure Tungsten: Used in combination with an alternating current exclusively for magnesium and aluminium welding only. It features a green AWS tip and an EWP classification code.
• Zirconium Tungsten: Eventhough it comes with comparable properties to pure Tungsten, it happens to be nevertheless substantially different. The typical combination ranges from ¼% Zirconium Oxide up to ½% Zirconium Oxide, whilst the remainder is pure Tungsten. Additionally, it is generally used in combination with an alternating current to weld aluminum and magnesium. The tip is brown and comes with an AWS classification of EWLa-1.
• Thoriated Tungsten: Typically used in combination with a direct current and an electrode negative polarity (DCEN). The inclusion of Thorium Oxide facilitates the electrode to transport more current along with lower temperatures, making it possible for easier arc starting. Thoriated Tungsten can weld most types of metals with the exception of magnesium and aluminium. 1% mixtures feature a yellow AWS tip and an EWTh-1 classification. 2% mixtures feature a red AWS tip and an EWTh-2 classification.

The selection along with applications with regard to properly ground, cut and prepared Tungsten welding electrodes meant for Gas Tungsten Arc Welding (GTAW), also referred to as Tungsten Inert Gas (TIG) welding and Plasma Arc Welding (PAW), are listed in the table underneath. The different types of GTAW and PAW welding which the following is applicable to comprises of and yet isn't restricted to Orbital Tube and Pipe Welding, Automatic / Mechanised TIG Welding, “Micro-TIG,” Automatic / Mechanised Plasma Welding, “Micro-Plasma,” and Manual Arc Welding.

Choosing the Proper Tungsten

The suitable material to employ for an application is dependent upon several variables, such as the type of weld, the composition of the material getting welded, the amperage level, amongst various other aspects. The quintessential approach to ascertain which tungsten material is most effective for a specific application is by way of testing.

Diameters and Lengths: Tungsten Electrodes are available in an assortment of standard diameters and lengths.

Current Ranges: The American Welding Society document provides a table which illustrates the reccommended current ranges for tungsten working with Direct Current (DC) and Alternating Current (AC). All values listed are based on working with argon as being the shielding gas. Different electrode materials will change slightly from these guidelines. Usage of alternative gases will likewise alter the recommended currents. Consequently, this particular chart must be made use of as a general guide. Additionally take into account that for a specified magnitude of amperage, larger diameter electrodes will last longer, however are going to be harder to arc start. Excessive current will result in the electrode melting and dropping off. Insufficient current is going to result in unstable arc.

Standards: The United States, Europe, and Japan each employ a published standard meant for tungsten. These standards dictate the dimensions, packaging, and manufacturing requirements which tungsten will need to fulfill. On the other hand, meeting these standards doesn't necessarily guarantee that a particular tungsten has been manufactured by a high-quality manufacturer.

Each stick of tungsten carries a colour code applied to one end that identifies the material variety of the tungsten. The American Welding Society document provides a table termed the International Colour Coding Chart which identifies the colour coding employed in United States, Europe, and Japan, that represent the majority of the market share of sold tungsten.

Grain Size and Structure: The molecular structure of the inside of a point of tungsten illustrates the way it is divided into smaller groups called grains. Oxides migrate to the tip of the tungsten, predominantly along the boundaries or borders of these grains. Its much easier for the oxides to migrate from inside the tungsten to the tip on the grain boundaries rather than it's for them to migrate within the crystallised grains. In manufacturing the tungsten, smaller sized grains are better, as they create more paths and consequently the oxides are able to more easily migrate to the tip. Nonetheless, it is a challenging manufacturing process to minimise the size of the grains whilst maximising the consistency of the oxide distribution and additionally maintaining the proper quantity of oxides. This particular difficulty in the manufacturing process is the primary reason behind the differences in tungsten performance quality which is manufactured by the different manufacturers.

Oxide distribution is a key indicator of quality. Oxides ought to be distributed homogeneously throughout the tungsten. Uneven distribution leads to poor performance: areas having minimal oxides will typically suffer from grain growth, as opposed to areas with an excessive amount of oxide will tend to “bottleneck” preventing the oxides from progressing to the point. Higher quality oxides are smaller in size, that enables them to migrate to the tip easier.

Physical Characteristics of Different Oxides

Electron Work Function (eV): Work function is the energy required to remove an electron from an atom, and it is measured in electron volts (eV). The lower the work function of an electrode, the lower the voltage required to strike an arc, consequently the easier the arc starts. The oxides combined with a tungsten serve to promote the electron emission by means of reducing the work function of the tungsten. The table underneath lists thr different oxides and metals together with their respective work functions. The lower the eV for the oxide, the easier it's going to start. The metal work function is crucial, considering that upon emitting an oxide, the metal is left as a film on the tip. The lower the eV of the metal at the tip, the lower the temperature is going to be at the tip which will decrease grain growth and provides a constant flow of oxides and longer service life.

The more of an oxide included in tungsten, the lower the work function which tungsten will have, thereby the better it will arc start. A 2% Lanthanated tungsten will arc start more easily than a 1% Lanthanated tungsten.

Density: Each oxide possesses a distinct density. Consequently a 2% by weight thorium, cerium, or lanthanum electrode will all possess varied amounts of oxides by volume. The table underneath details the difference between density and weight with regard to different materials.

Despite the fact that each material possesses 2% by weight of the oxides, a 2% Lanthanated tungsten possesses a considerably higher volume of oxides as compared to 2% Thoriated tungsten to feed to the tip.

Despite the fact that electrodes are the same type, electrodes from different manufacturers cannot be compared only using the work function and volume of oxides, considering that this kind of comparison wouldn't consider the important manufacturing variables for instance grain size and structure of the oxide size and distribution. Consequently, the work function and oxide density numbers ought to only be used as a general guide. Testing is invariably the best way to ascertain which tungsten is going to be most effective.

Migration and Evaporation Rates: The migration rate, or diffusion rate as it is normally termed, is the rate at which each of the different oxides naturally moves from inside the tungsten to the heat at the tip of the electrode. The evaporation rate is the rate at which the oxides separate from their metal component and are emitted at the tip of the electrode. The optimum-performing electrode is the one that possesses a balance of good migration and evaporation rates. In the event the migration rate is slower compared to evaporation rate, in that case there will be an inadequate amount of oxides coming to the tip to maintain a consistent arc and the tungsten could be reduced to the performance level of pure tungsten. In case the evaporation rate is slower ın comparison to the migration rate, the oxides are going to be crowded at the point. If both of the rates are very high, welding properties at the start of welding are going to be great, however all of the oxides could be consumed quickly.

Tungsten Oxide Types

The subsequent gives a description of the general characteristics involving typical oxide types. Remember that testing is the only method to ascertain which tungsten is optimal for a specific application.

Thoriated
(EWTh-1 Yellow Stripe Electrode Classifications: Yellow Stripe; and EWTh-2 Electrode Classifications: Red Stripe)

Thoriated tungsten incorporates thorium oxide (ThO₂ or thoria), and it is the most commonly utilised tungsten in America. It has become the standard for comparison. Nonetheless, since it is a low-level radioactive hazard, many end users have switched to other alternatives. 2% Thoriated constitutes a general use tungsten. It includes one of the lowest work functions, and it also functions effectively whenever overloaded by using extra amperage. On the other hand, it doesn't maintain its point when compared to various other non-radioactive tungstens which have been launched.

Two types of Thoriated tungsten electrodes are available. The EWTh-1 and EWTh-2 electrodes contain 1 percent and 2 percent, respectively, evenly distributed evenly through their entire lengths. Thoriated tungsten electrodes are superior to pure electrodes in numerous aspects. The thoria delivers approximately 20 percent higher current-carrying capacity, characteristically longer life, together with increased resistance to contamination of the weld. With these electrodes, arc starting is easier, plus the arc is more stable compared with pure tungsten or Zirconiated tungsten electrodes. The EWTh-1 and EWTh-2 electrodes were designed for DCEN applications. They sustain a sharpened tip configuration in the course of welding, which is suitable for welding steel. They are infrequently used in combination with AC since it is difficult to maintain the balled end, which is necessary with AC welding, without splitting the electrode.

Ceriated
(EWCe-2 Electrode Classification: Grey/ Formerly Orange Stripe)

Ceriated tungsten was introduced as being the first non-radioactive replacement of the Thoriated. It is typically available as 2% Ceriated, also it is conveniently available. The EWCe-2 electrodes are tungsten electrodes containing 2 percent cerium oxide (CeO₂), termed as ceria. It is considered specifically suitable for DC welding using low amperage since it starts effortlessly at low amps and typically requires approximately 10% less amps compared to Thoriated material to operate. Consequently it is the preferred material employed for orbital tube and pipe welding, along with being also widely used for welding very small parts. In comparison to pure tungsten, the Ceriated electrodes demonstrate a reduced rate of vaporisation or burn-off. These advantages of ceria enhance with an increase of ceria content. Cerium in addition has the highest migration rate therefore it provides it good welding properties at the beginning, nevertheless it provides a significantly reduced migration rate over time as a consequence of grain growth. On the other hand, at lower amperage it will last longer compared to Thoriated. As a consequence of these properties, it is typically suitable for short welding cycles or whenever a specific number of welds are needed thereafter the electrode is to be replaced. Higher amperage applications are best left to Thoriated or Lanthanated material. EWCe-2 electrodes will operate successfully with AC or DC; nevertheless, it is made use of typically for DC welding as it could split if used for AC welding.

Lanthanated Tungsten
(EWLa-1 Electrode Classification: Black, EWLa-1.5 Electrode Classification: Gold; and EWLa-2 Electrode Classification: Blue)

The commonest Lanthanated tungsten incorporates 2 percent lanthanum oxide (La₂O₃), termed as lanthana. In Europe and Japan, Lanthanated tungsten has been the most popular alternative to 2% Thoriated tungsten for the majority of applications. It is obtainable as 2%, 1.5%, and 1% Lanthanated tungsten. Lanthanum Trioxide offers the lowest work function of any of the materials as a result it typically starts easiest and possesses the lowest temperature at the tip, which resists grain growth and promotes longer service life. Testing of 2% Lanthanated material has demonstrated that it provides a much longer life than Thoriated if not overloaded and better arc starting in most applications.

Additionally, it is particularly good at

1. resisting the “Thermal shock” of pulsing,
2. working with welding in situations wherever there are numerous re-ignitions with a short weld cycle, and
3. resisting contamination.

Welders having tube mill applications are particularly satisfied with this particular material considering that its longer life reduces down time. Moreover, in general it will in all probability require approximately 15% less amps to get started and sustain low current arcs. The Lanthanum in this tungsten is a “rare earth” material and is not radioactive. It hasn't been as intensively promoted and made use of in the United States as in Europe or Japan. This particular tungsten is predominantly intended for DC welding, although will in addition demonstrate good results for AC welding. The EWLa-1 electrodes have been developed about the same time as the Ceriated electrodes and, for the same reason, that lanthanum is not radioactive. These electrodes incorporate 2 percent lanthanum oxide (La₂O₃).

Zirconiated Tungsten
(EWZr-1 Electrode Classification: Brown Stripe; and EWZr-8 Classification: White Stripe)

Zirconiated tungsten electrodes (EWZr) contain a small amount of zirconium oxide (ZrO₂). Zirconiated tungsten electrodes possess welding characteristics which typically fall around those of pure and Thoriated tungsten. Zirconiated tungsten is typically utilized for AC welding since it balls up properly in AC welding and possesses a more stable arc when compared to pure tungsten. In addition, it resists contamination effectively in AC welding. On the other hand, although it offers improved current carrying and arc starting characteristics compared to pure tungsten, generally speaking it's the worst non-radioactive tungsten from a performance standpoint.

Pure Tungsten
(EWP Electrode Classification: Green Stripe)

Pure tungsten electrodes (EWP) includes minimum of 99.5 percent tungsten, without having any intentional alloying elements. Pure tungsten possesses a very high work function, thereby it is more difficult to start and produce a stable arc compared to other materials. Furthermore, as a consequence of the high work function, the temperature at the tip is higher and grain growth occurs. The following results in an unstable arc, starting difficulty, and a shorter service life. Pure tungsten is only utilized for AC welding; having said that; better alternatives are available.

Other Options

Besides the materials in the above list, there are additional less widespread materials, including 1% Thoriated, 4% Thoriated, 2% Yttriated, in addition to combinations of different oxides in the same tungsten. A particular variety of tungsten electrodes combines three non-radioactive materials into one tungsten to produce the best possible tungsten by balancing the migration and evaporation rates whilst preserving the work function lower. It starts and re-ignites very well, and it also comes with a notably excellent service life in welding situations wherever welding cycles of at a minimum 15 minutes are employed.

Electrode Sizes and Current Capacities

Selecting the correct electrode for specific applications will need to consider the different current levels and power supplies. Current levels which are greater than those recommended for specific electrode size and tip configuration will result in the tungsten being eroded or melting. Tungsten particles might fall into the weld pool and turn into defects in the weld joint. Current levels which are too low for a particular electrode diameter can result in arc instability. Direct current with the electrode positive requires a much larger diameter to support a given level of current, considering that the tip isn't cooled by the evaporation of electrons but heated by their impact. Typically, specific electrode diameter on DCEP would be expected to handle only 10 percent of the current possible with the electrode negative. With alternating current, the tip is cooled during the electrode negative cycle and heated when positive. Consequently, the current carrying capacity of an electrode on AC is in between that of DCEN and DCEP. Generally speaking, it is approximately 50 percent lower than that of DCEN.

Determining Electrode to Use

Testing is the easiest way to ascertain which material is the most suitable for a specific application and/or which manufacturer manufactures a superior quality tungsten. The following properties of the different tungsten must be documented when testing in order to compare products.

Making use of materials which last longer and enhance arc starting can reduce costs and improve the welding process. Additionally, minimized down-time in replacing and preparing new electrodes is a significant savings to take into consideration.

Shielding Gases

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Similarly to other welding processes including gas metal arc welding, shielding gases are essential in GTAW to protect the welding area from atmospheric gases which include nitrogen and oxygen, which could result in fusion defects, porosity, and weld metal embrittlement should they come in contact with the electrode, the arc, or the welding metal. The gas additionally transfers heat from the tungsten electrode to the metal, therefore helps start and maintain a stable arc.

Selecting a shielding gas is dependent upon several factors, including the type of material being welded, joint design, and desired final weld appearance. Argon is the most frequently utilized shielding gas for GTAW, considering that it aids in preventing defects caused by a varying arc length. Whenever used in combination with alternating current, argon shielding results in high weld quality and good appearance. An additional preferred shielding gas, helium, is usually employed to increase the weld penetration in a joint, to increase the welding speed, and also to weld metals with high heat conductivity, including copper and aluminium. A significant disadvantage will be difficulty of striking an arc with helium gas, along with the decreased weld quality associated with a varying arc length.

Argon-helium mixtures are also commonly made use of in GTAW, given that they can increase control of the heat input at the same time maintaining the main advantages of using argon. Ordinarily, the mixtures are prepared using primarily helium (typically approximately 75% or higher) and a balance of argon. These mixtures increase the speed and quality of the AC welding of aluminium, and in addition enable it to be easier to strike an arc. Yet another shielding gas mixture, argon-hydrogen, is commonly employed in the mechanised welding of light gauge stainless steel, however considering hydrogen can lead to porosity, it's purposes are limited. Likewise, nitrogen can occasionally be combined with argon to help stabilise the austenite in austenitic stainless steels and increase penetration whenever welding copper. As a result of porosity problems in ferritic steels and limited advantages, however, this isn't a popular shielding gas additive.