All around Tig Welding Process with Detailed Explanation

This article gives an overview of Tig welding process with explaining all minute details. So you can expect a better grip of this process after finishing this read. 

Tungsten Inert Gas Welding (TIG) is known as one of the two types of gas shielded arc welding process (the other one is Metal Inert Gas Welding (MIG)). Also, in the dual-shield mode of Flux Core Arc Welding (FCAW), a gas supply is added along with self-shielding of core flux. That’s why FCAW is also listed in the gas shield arc processes. The principle of Tig welding process is based on the production of arc using the high melting and non-consumable tungsten electrode. That reasons why this process is referred to as tungsten arc gas-shielded (TAGS) (also, argon arc welding, tungsten inert gas, gas tungsten arc welding). Gas shielding is applied to protect the weld puddle from atmospheric contamination. Because those gases are transparent, the weld puddle is made visible to the welder. Tig process features:

Distinct features

• In Tig welding, no flux is used, then you don’t have to fear about corrosion due to flux entrapment. 

• No slagging, which helps with elimination of post weld cleaning.

• Because there is no spark and fumes, you can produce sound welds with perfect definition.

Non-consumable tungsten electrodes are used to produce an arc of substantial high temperature that helps melt the work metal. Air is driven out owing to the envelope of inert gas that averts the weldment, tungsten electrode and heat affected zone (HAZ) from oxidation. Unlike Mig welding, tungsten electrode isn’t consumed; rather, it gives arc to melt the additional filler metal. Filler metal is fed to the weld puddle. 

Normally, there are 2 modes of Tig welding: semi-automatic, automatic. In semi-automatic, the operator has to configure the current and gas flow settings, and then manually deal with the torch and filler road. Still, in automatic mode, the operator sets the speed of travel, arc length, gas flow rate, filler rod position, and then observes the operation and controls where it’s needed. 

First, Tig was introduced to weld magnesium to mitigate rapid corrosion problems. The technique was successfully applied to attain best results with no consequent corrosion. This process was introduced with distinct characteristics as opposed to other arc processes. For shielding, the gas flow rate can be controlled by flow rate and manifold. During welding, the gas flow not just shields the weld and filler metal but protects the torch. There is also a gas delay feature allowing gas to flow in the preset time, after the current has been shut off. 

Tig is used in both welding ferrous and non-ferrous metals with a wide range of thickness not beyond 8mm. Both AC and DC current supplies are used with the range from 15 to 350 amps. Using small diameter electrodes and suitable current range, this process is also applied in repair work and new manufacturing. Though it’s relatively slower than other arc processes, it creates high-quality welds with perfect definition in carbon steel, stainless steel, aluminum. The DC source is used for welding stainless steel, carbon steel, nickel, copper alloy. Meanwhile, AC source is suited for welding aluminum and its alloys. 

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Equipment

Tig torch

Different sizes of torches are available for different current-carrying capacities. The assembly of Tig torch includes a switch for different welding operations. The torch casting holds electrode and gas nozzles. 

Additional features

Water cooling system

As you weld with high amperages, cooling is required. A water cooling system is installed where water is circulated through the torch to keep it cool. In the past, systems were connected with additional cooling system, but nowadays, it’s installed inside the modified equipment. The water flow is controlled either by torch or by foot pedal.

DC suppression

In aluminum and magnesium alloy welding, the surface oxide formation is the major concern. In aluminum welder, because the arc is formed between tungsten and aluminum, chances are that AC is converted to DC. That’s why a DC suppressor is employed to avert the conversion from AC to DC mode. 

Contactor

It puts the arc to be extinguished when delay shielding is needed for cooling purposes. This way, it not just protects weld but give means of safety to your welder. This process is also controlled by foot pedal and torch. 

Arc initiation

Arc initiation by touching the electrode with base metal can induce serious contamination problems and arc unstability. Clearly, tungsten inclusion can lead to localized hard spots. The transfer of the base metal to tungsten electrode can also induce contamination and consequently unstabilize the arc. In order for the electrode not to touch with your work piece, high frequency spark is created, which causes some ionization in spark gap. The current continues to flow as a result of this ionized spark gap. This feature also helps enhance the life span of tungsten electrode. Below are arc initiation methods that are often used in modern equipment:

   • Scratch start
In this method, the electrode is brought down to work piece, and gently scratched for arc initiation. As stated above, the slight contact can lead to the contamination problems. This method is taken only in the applications that contamination isn’t serious.

   • Lift up
Here the electrode is brought down to contact with work piece at the initial point of welding. Torch switch is pressed, creating contact, and still no current is generated. When the electrode is lifted up, the current continues to flow and quickly increase to the pre-set value. This rapid rise is referred to as slope up.

   • Slope up
Slope up is the rapid increase of welding current to the pre-set current on the power source. Using the switch, the welder can set the time required for the increase of current to the selected amperage. This feature makes less contamination and reduces the risk of burning thin sheets at the initial point of welding.

   • Slope down
Slope down is the gradual drop of welding current to zero. It is defined as the time taken to decrease the current until the arc is extinguished. This feature is used for filling the crater at the end of the weld. Often, this function is operated with the support of torch switch and foot pedal.  

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Defects in welding

Electrode used in Tig welding

Tungsten is the high melting point metal around 3000 degree Celsius. In the Tig welding process, pure tungsten with its best thermal and electrical conductivity is employed. Nowadays, alloyed tungsten with 1-2% thorium and zirconium is used for better arc stability and enhanced electrode life. There are 2 types of alloyed tungsten electrodes: thoriated electrodes for DC mode and zirconiated electrode for AC mode. Also, noticeably, electrode diameter is determined by current polarity.

Electrode grinding is one of main concerns in attaining consistent performance in welds. Electrodes are ground as per application. There are 2 ways of electrode grinding: manual grinding and machine grinding. Machine grinding leads to consistent grinding. Care must be taken while manual welding. 

As with electrode shape, electrode is often ground to the required vertex angle. For the DC usage, the electrode is ground to the length of 1-3 x the diameter of electrode.

Point length of electrode = 1-3 x diameter of electrode

This way, the lower the current is, the longer the point length will be. Electrodes are normally available with the diameter range of 0.8, 1.6, 3.2, 4.0 and 6.4 mm.

For the AC usage, the electrode side is ground to 45 degree, remaining the front side to be flat. This offers the spherical shape as shown in the below image.

Electrode installation in torch is simple. The electrode is installed in torch, and held tightly thanks to grippers known as sockets. They can grip and hold electrodes of various diameters.

Gas nozzles

Those nozzles are made of high temperature ceramic materials for bearing high welding temperature. As stated above, some nozzles are equipped with water cooling system. Only the right choice of gas nozzle size gives better protection of weldment, weld pool as well as filler material. Different shapes of nozzles are available for different types of jobs. Small-size nozzles are available for confined areas while long shapes are available for deep-groove joints.

Gas lens

Gas lens are offered to prevent the turbulence of gas flow. Poor gas flow may not give quality shielding service; that’s why gas lens are used to give consistent and smooth gas flow, well shielding the weld puddle. Thanks to gas lens, electrode extension can also be attained for access to complicated areas.