Gas Tungsten Arc Welding (GTAW)


What is Gas Tungsten Arc Welding (GTAW)?

The designation TIG comes from the USA and is an abbreviation of Tungsten Inert Gas. Tungsten – also called wolfram – is a metal with a fusion point of more than 3300 degree C, which means more than double the fusion point of the metals which are usually welded.

Inert Gas is the same thing as inactive gas, which means a type of gas that will not combine with other elements. In Germany, this method is called WIG welding, the W meaning wolfram.

TIG welding is the international standardized designation for this welding method. According to DS/EN 24063, this welding process has number 141.

Gas Tungsten Arc Welding (GTAW) is also known as Tungsten Inert Gas (TIG) Welding. It is a manual welding process. In this process, a non-consumable tungsten electrode is used to generate heat. An externally supplied filler metal is added manually. As the name suggests, shielding gas such as Argon and Helium or a mixture of these inert gases are used for gas shielding. These gases shield the solidifying weld pool from atmospheric contamination to avoid weld oxidation and porosity.

To know and learn more about TIG welding, watch our detailed classroom Training Video on YouTube.

TIG Welding Process Principle

TIG welding one of the important welding processes in fusion welding processes. This process is very versatile and make it suitable to weld both thin sheets and thick sections, especially root run in pipeline welding. Welding can be performed in all positions although with low productivity rate.

The TIG process uses the heat generated by an electric arc between the base metals to be joined and an non-consumables tungsten-based electrode as shown in figure 1. The arc area is shrouded in an inert gas shield to protect the weld pool and the tungsten electrode. The filler metal as a rod is applied manually by the welder into the weld pool. TIG welding is especially suited to weld sheet-metal/ thin materials with thicknesses up to about 10 mm.

gas-tungsten-arc-welding

TIG Welding Equipment Setup

The welding process works on constant current characteristics (CC) or called dropping characteristics. The work piece is connected to the positive terminal and welding torch to the negative terminal. The on/off switch is located on the welding torch. The process in manual in operation. The TIG torch is moved manually and same time filler rod is added manually with other hand to the weld puddle.

Equipment Setup

                                                                                      Figure 2 Equipment setup

  1. Solid wire (AWS A 5.18 for carbon steel electrodes)
  2. Metal cored wire (AWS A 5.36 for carbon steel electrodes and low alloy steel)

Different size of filler wires is used ranging from 0.8 mm to 2.4 mm in the industries according to the requirements. A higher diameter offers more deposition although less suitable to weld thin sheet metals.

The equipment needed for GTAW set up are as shown in figure 2 are:

  • Power Source
  • Welding Gun
  • Shielding Gas
  • Welding cables / leads and gas hoses

Figure 3 shows the different types of TIG welding torches.

GTAW welding torch is having two variants:

  • Air cooled welding torch
  • Water cooled welding torch.

An air-cooled welding torch is used for normal duty welding activities. Welding requiring a high duty cycle and high welding current normally uses water-cooled torched. The air-cooled torches due to their simple construction are cheaper than water-cooled torches. They are also easy to repair compared to the latter ones.

Figure 3 TIG Welding Torches

A TIG welding torch construction is shown in figure 4.

Equipment Setup

Power Source for TIG Welding

TIG welding is carried out with a drooping, constant current power source – either DC or AC. A constant current power source is important to avoid excessively high currents on the electrode when it is short-circuited on to the workpiece surface. This can happen either purposely during arc starting or due to carelessness during welding. Like in MIG-MAG welding, a constant voltage power source is used, any contact with the workpiece surface will damage the electrode tip or gives tungsten inclusion to the workpiece surface. But in DC types, because arc heat is distributed approximately one-third at the cathode (negative) which is tungsten electrode in TIG welding and two-thirds at the anode (positive) i.e. work piece prevent overheating and melting of the tungsten electrode. AC has the advantage in TIG welding as when the cathode is on the workpiece, the surface is cleaned of oxide contamination. For this reason, AC is used when welding materials with a firm surface oxide film, such as aluminum welding.

Method of arc starting in TIG

There are three methods of arc starting in TIG welding as given below:

  1. Scratch method
  2. High frequency arc starting
  3. Contact method

The three methods are shown in figure 5 below.

TIG Welding Torches

Shielded Gases for TIG Welding

Shielding gases is TIG welding are selected according to the material to be welded. Most commonly used gases are:

  • Argon – is the most commonly used shielding gas in TIG. Argon can be used for welding a wide range of materials such as carbon steel, low alloy steel, stainless steel, Nickel alloys, aluminum, and titanium, etc.
  • Argon + 2 to 5% H2 – By adding the hydrogen to argon, it makes the shielding gas slightly reducing, which produces clean look welds without surface oxidation. Mixing hydrogen gives a hotter and more constricted arc, which allows higher welding speeds. Hydrogen brings adverse effects such as the risk of hydrogen cracking in carbon steels if hydrogen level exceeds the limits and weld metal porosity in aluminum.
  • Helium and helium/argon mixtures – Adding helium to argon raises the temperature of the welding arc. This supports higher welding speeds and wide, deep weld penetration compare to argon alone. The disadvantages of using helium or a helium/argon mixture are the high cost of gas and difficulty in starting the arc as the helium arc Ionisation rate is low.

Advantages of GTAW (TIG Welding)

  1. TIG can be used to join almost all metals, with superior weld quality, generally free of defects.
  2. Free from spatter that occurs with other arc welding processes.
  3. Can be used with or without filler metal as required for the specific application.
  4. Provides excellent control of root pass weld penetration.
  5. Best welding process for welding pipeline root run and hot pass.
  6. Can be used to produce inexpensive autogenous (fusion) welds with good penetration.
  7. Provides for separate control over the heat input and filler metal additions.
  8. This process can be easily automated for robotic welding and for special purpose machines (SPM).

Limitations of GTAW (TIG Welding)

  1. Travel speeds and deposition rates are relatively low, increasing weld cost.
  2. A high degree of operator skill is required to produce quality welds.
  3. The process is not easily automated.

TIG Welding parameters for Aluminum

Material Thickness (in, mm)PositionPasses RequiredTravel Speed (ipm)AC (amp)Cup Diameter (in, mm)Cup SizeGas Flow (cfh)Gas Volume per 100 ft of weld (cft)Tungsten Diameter (in, mm)Filler Rod Diameter (in, mm)Pounds Deposited per 100 ft (lb)
1/16 (1.5)Flat18751/2(12)820501/16 (1.6)0.030 (0.8)1/2
1/16 (1.5)H & V18753/8 (10)620501/16 (1.6)0.030 (0.8)1/2
1/16 (1.5)OH18703/8 (10)625621/16 (1.6)0.030 (0.8)1/2
1/8 (3.2)Flat1101401/2(12)820401/8 (3.2)1/8 (3.2)2
1/8 (3.2)H & V181203/8 (10)620503/32 (2.4)1/8 (3.2)2
1/8 (3.2)OH181403/8 (10)625623/32 (2.4)1/8 (3.2)2
3/16 (5)Flat182103/4 (19)1225625/32 (4)5/32 (4)4.5
3/16 (5)H & V181801/2(12)825621/8 (3.2)5/32 (4)4.5
3/16 (5)OH181701/2(12)830755/32 (4)5/32 (4)4.5
1/4 (6)Flat182503/4(19)1230753/16 (5)3/16 (5)7
1/4 (6)H & V182403/4(19)1230753/16 (5)3/16 (5)7
1/4 (6)OH181403/4(19)1235873/16 (5)3/16 (5)7

TIG Welding parameters for stainless steel

Material Thickness (in, mm)PositionPasses RequiredTravel Speed (ipm)DCEN (Amp)Cup Diameter (in, mm)Cup SizeGas Flow (cfh)Tungsten Diameter (in, mm)Filler Rod Diameter (in, mm)
0.018 (0.5)Flat114205/16 (2)5100.040 (1)0.035 (0.8)
0.030 (0.8)Flat110303/8 (10)6101/16 (1.6)0.045 (1.2)
0.062 (1.6)Flat18603/8 8 (10)6101/16 (1.6)0.045 (1.2)
0.093 (2.4)Flat18703/8 8 (10)6151/16 (1.6)1/16 (1.6)
0.125 (3)Flat181303/88 (10)6153/32 (2.4)1/16 (1.6)
0.250 (6)Flat382401/2(12.5)8151/8 (3.2)3/32 (2.4)

Applications of TIG Welding

TIG welding is used in all industries but is especially suitable for high quality welding. In manual welding, it is ideal for thin sheet material or controlled penetration (in the root run of pipe welds). Because deposition rate can be quite low (using a separate filler rod) MMA or MIG may be preferable for thicker material and for fill passes in thick-wall pipe welds.

TIG welding is also widely applied in mechanized systems either autogenously or with filler wire. The systems require no manipulative skill, but the operator must be well trained. Because the welder has less control over arc and weld pool behavior, careful attention must be paid to edge preparation (machined rather than hand-prepared), joint fit-up and control of welding parameters.

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