TIG Welding Process: Shielding Gases and More

Main Applications of TIG Welding

The main target applications of TIG welding include high-quality fabrication of stainless steel, aluminum, copper and nickel alloy structures. It is also ideal for the welding of reactive and refractory metals such as titanium, tantalum and zirconium. The process is used extensively in nuclear and aerospace industries, and in the construction and maintenance/repair of chemical and cryogenic process plants and pipework. Other use cases include the fabrication of tube heat exchangers in petrochemical and power generation plants.

The success of this welding process hinges on various factors such as the choice of shielding gas, welding wire, tungsten electrode and welding technique. Operator skill is also essential, as steady control of the welding torch, the arc and the shielding gas flow plays a key role in optimum welding outcomes.

How Does TIG Welding Work?

The TIG process uses the heat generated by an electric arc, which is struck between a non-consumable tungsten electrode and the workpiece. This arc then fuses metal in the joint area to produce a molten weld pool. The arc area is shrouded in an inert or reducing gas shield to protect the weld pool and the non-consumable electrode. The process may be operated autogenously (i.e. without filler) or with a consumable wire or rod that feeds filler into the established weld pool.

TIG Power Supply

The welding current is normally supplied from a direct or alternating current power source operating at a constant current output. For DC operation, the tungsten may be connected to either output terminal, but the negative pole is the more frequent choice. The output characteristics of the power source can have an effect on the quality of the welds produced.

TIG Welding Methods

Shielding gas is directed into the arc area by the TIG welding torch and a gas lens within the torch distributes this shielding gas evenly over the weld area. In the torch, the welding current is transferred to the tungsten electrode from the copper conductor. The arc is then initiated between the tungsten and the workpiece, typically using one of the following methods:

• Touch or scratch start - a basic gas tungsten arc welding method
• Carbon block - a traditional gas tungsten arc welding method
• High-frequency (HF) power - a more advanced TIG technique
• Lift arc - a modern gas tungsten arc welding approach

TIG Operating Modes

Depending on the parent material being joined, the TIG welding process is operated in one of these three operating modes:

• Direct current electrode negative (DCEN) - also known as straight polarity in the US
  This is the most common mode of operation, using a negatively charged electrode to weld carbon, alloy and stainless steels, nickel and titanium alloys, as well as copper alloys with low aluminum content
• Direct current electrode positive (DCEP) - also known as reverse polarity in the US
  This mode tends to be used for aluminum alloys when welding with pure helium
• Alternating current (AC)
  The AC polarity mode is popular when welding aluminum and its alloys with pure argon or argon/helium mixtures as this leverages the cyclic heating and cleaning action

TIG Welding Process Variants

There are three main process variants in TIG welding, each offering productivity benefits for different tasks.

• The first TIG process variant is orbital TIG. This is an automatic process used primarily to weld pipes. A compact welding torch coupled with a drive mechanism allows the head to move completely around the pipe.
• The second process variant is called hot-wire TIG. Here the filler wire from a small spool is electrically pre-heated and continuously fed via a contact tube into the back of the weld pool. This means the welder doesn't have to manually feed a cold length of filler rod into the molten weld pool. Offering better deposition rates, this method is popular on steel and nickel alloys where the electrical resistance of the wire can have a positive impact on productivity.
• The third, more specialized, TIG process variant is known as narrow-gap TIG. The workpieces are brought together as a square edge joint with a small gap and a backing bar or a 'U' joint. The TIG torch can be lowered into the gap and withdrawn slowly as the weld progresses. Hot-wire filler may be added and pulsed current may be applied to assist the process. The small gap means thicker plates can be welded with fewer weld passes.

Boosting TIG Welding Speeds- with the Right Shielding Gases

During TIG welding, the weld area must be shielded against atmospheric effects. The choice of shielding gas is largely dependent on the material. The inert gases argon (Ar) and helium (He) are commonly used, although mixtures of these gases, such as our ALUSHIELD^® argon-helium shielding gas blend, are also popular.

We deliver a wide range of tried-and-tested TIG welding gases and blends. The names of these shielding gas families vary from one region to another, but the range includes our CORGON^®, CRONIGON^®, VARIGON^®, FORMIER^®, HELISTAR^® and HYDROSTAR^® offerings. Some of these mixes add hydrogen (H₂) or nitrogen (N₂) to argon or helium to achieve superior welding speeds and higher process stability. You will benefit from greater control, higher quality welds, fewer incidents and less rework effort. Some customers have doubled their welding speeds with our dedicated TIG gas mixtures, for instance. Our application experts can advise you on the mixture and operating parameters best suited to your needs, also supporting you with the TIG equipment and gas management services you need.

Contact your local Linde representative to check availability of our TIG shielding gases and welding supplies in your region.

TIG vs MIG - The Low-down

The TIG process is often compared to metal inert gas (MIG) welding as both methods use an electric arc and a shielding gas, and are popular across a wide range of fabrication and manufacturing applications.

Similarities between TIG and MIG

• Both TIG and MIG can be carried out either manually or automatically
• Both welding methods use an electric arc and a shielding gas

Differences between TIG and MIG

• TIG tends to be faster and produces welds of higher quality with less spatter
• The defect rate of TIG welding is usually lower than with MIG
• Skill levels for TIG welding are generally higher than those required for MIG
• Welding speeds for TIG, with the exception of hot-wire TIG, are generally slower than those possible with MIG
• Weld costs per unit length are higher with TIG than with MIG

TIG vs MMA Welding / Stick Welding - How Do They Compare?

The TIG welding process is also frequently compared with the manual metal arc (MMA) welding process (also known as shielded metal arc welding (SMAW) or stick welding).

Similarities between TIG and MMA

• Both TIG and MMA welding are gas metal arc welding (GMAW) variants and thus require a power supply
• Both arc welding processes use filter metal to produce a weld pool

Differences between TIG and MMA

• TIG can be used manually or automatically, whereas MMA is predominantly a manual process
• TIG is suited to virtually all metals and alloys whereas MMA electrodes are generally restricted to ferrous materials, stainless steels and nickel alloys
• Due to its inert gas shield, TIG can be used to weld refractory metals
• TIG filler compositions are restricted but MMA electrodes can be tailored to the composition of the parent material
• TIG is prone to the effect of drafts, which can disrupt the gas shield, whereas MMA is ideally suited to rugged outdoor environments and on-site work as it does not require a shielding gas
• Consumable usage is more efficient with TIG welding as almost all of the consumable is converted into weld metal, compared with only 65% or so in the case of MMA
• TIG doesn't create a slag cover and needs limited post-weld cleaning, but stick welders must remove the slag

FAQs

What does TIG stand for?

TIG stands for tungsten inert gas. According to the American Welding Society, the official term is gas tungsten arc welding or GTAW.

Does TIG require shielding gas?

Yes, the TIG welding process must be operated with a shielding or reducing gas to protect the weld area. The type of shielding gas depends on the material being welded. The right shielding gas and flow rate impact welding outcomes.

What shielding gases are most commonly used for TIG?

The inert gases argon (Ar) and helium (He) are commonly used for TIG welding. We offer these gases along with dedicated blends that include gases such as hydrogen (H₂) or nitrogen (N₂) to accelerate welding and increase process stability.

What equipment is needed for TIG?

The basic equipment requirements for TIG welding are a power supply, a welding torch plus a tungsten electrode, leads and connectors, a gas supply system and, normally, an arc initiation and re-ignition system.

What electrodes are used with TIG welding?

Originally, pure tungsten was used as the electrode material. Over time, experience showed that arc stability, tip shape retention and arc initiation could be improved by adding small amounts of thorium oxide (thoria) or zirconium oxide (zirconia) to the tungsten electrode. More recently, it has been found that improved performance can be obtained by alloying the electrodes with oxides of lanthanum, yttrium or cerium, particularly in automatic or orbital TIG welding where consistency of operation is important.

Is TIG a safe welding method?

In general, TIG welding is associated with lower fume emission rates (FER) than metal inert gas (MIG) or metal active gas (MAG) welding processes. TIG welding is nonetheless capable of generating ozone in appreciable amounts as a result of the action of ultraviolet light and heat on atmospheric oxygen and nitrogen. General ventilation is normally sufficient to control exposure to fume although fume extraction equipment and personal protective equipment (PPE), such as respiratory devices, may also be required.

The composition of shielding gases used in TIG welding can have a bearing on the level of ozone generated. Helium or helium-argon shielding gas blends tend to generate less ozone than pure argon or argon-rich gases. Complementing our broad PPE offering, our COMPETENCE, PERFORMANCE and PREVENTION Lines of shielding gases can help increase productivity and lower occupational health and safety risks through less-emissive welding gases with the ability to reduce FER directly at the source.