Tungsten Inert Gas Welding -TIG

The Tungsten Inert Gas (TIG) welding is a type of a arc welding process.This process is also widely known as the Gas Tungsten Arc Welding (GTAW). TIG welding was developed in the 1930's as a joining method for aluminum and magnesium components in the aircraft industry, to replace the riveting type of joining methods. This process was then called Heli Arc process as helium was used as the inert shielding gas.

In this type of welding process a high temperature arc produced between a tungsten electrode (non consumable) and the work piece is used to melt the base metal. A inert gas is used to sustain the arc and protects the molten metal from atmospheric contamination. The inert gas normally used is argon, helium or a combination of argon and helium. The process may be used with or without the addition of a filler metal.TIG welding has been a popular welding process in the fabrication industry due to the higher quality of welds produced by this type of welding.

TIG welding process Explained:

A non consumable  tungsten (or a tungsten alloy) electrode held within a torch, with the shielding gas fed through the torch is used to produce an electric arc by the passage of current through the conductive, ionized shielding gas.The arc is produced between the tip of the electrode and the workpiece. The heat generated by the arc melts the based metal. Once the arc and the weld pool is established the torch is moved along the joint and the arc progressively melts the surfaces of the plates to be joined.As the base metal is still in the molten stage a filler wire is added in the leading edge of the weld pool to fill the joint being welded.

The components of a TIG welding setup are :

1. Welding torch

2. Electrode

3. Welding power source

4. Shielding gas

Process Variables affecting TIG welding :

The main process variables in TIG welding are :

Arc Current - Arc current is directly proportional to the weld penetration required. Either direct current or alternating current can be used in the TIG welding process. The choice largely depends on the metal that needs to be welded. Using direct current with the electrode as negative, helps in producing deep penetration and faster welding speeds. Whereas use of Alternating current provides a cathodic cleaning (sputtering) which can remove refractory oxides from the joint surfaces of Aluminium and magnesium which helps in getting a superior weld quality.

Arc Voltage - The voltage measured between the tungsten electrode and the work piece is called the arc voltage. Arc voltage depends on the following factors :

a.   Arc Current

b.   Shape of the tungsten electrode tip

c.   Distance between the tungsten electrode and the workpiece.

d.   Type of the shielding gas used in the Process.

Arc voltage is used to control the arc length, which is important because pool width is proportional to the arc length. Due to this reason in most of the applications other than those involving sheet, the desired arc length is as short as possible. However great care needs to be taken to avoid the possibility of shot circuiting the electrode into the pool or filler wire when the arc used is too short which may lead to a weld defect.

Travel speed - Travel speed affects both the width and penetration of a TIG weld. While using a mechanised welding process the welding travel speed is normally given priority and other variables like current or voltage are adjusted accordingly. In the other cases, the travel may be a dependent variable alongwith other variables to obtain the required weld quality and uniformity.

Shielding Gas- Shielding Gas is used to protect the electrode and the molten weld metal from atmospheric contamination. Argon and Helium or their mixtures are the most commonly used inert gases for shielding purpose. Argon-hydrogen mixture are also used but for some special applications.

Each type of shielding gas or their mixtures are used in the TIG welding process based on the type of application.

Advantage of TIG Welding Process :

1.   Produces a high quality welded joint, hence used in applications which need the highest weld quality and reliability.

2.   The weld is free from spatter.

3.   Can be used with or without using a filler wire.

4.   Welding can be carried out with almost all type of metals.

5.   Gives precise control over the heat produced during the welding.

6.   Allows excellent control of root pass weld penetration.

Application of TIG welding process :

TIG welding process can be used with almost all metals. It is especially used for joining aluminium and magnesium which form refractory oxides and also for joining reactive metals like titanium and zirconium. This process is extensively used to join stainless steels, copper, aluminium-brass(Yorcalbro),conifer, alloy steel and carbon steels.

 

While using it for carbon steels, it is primarily used for root-pass welding with the application of consumable inserts or open root techniques on pipes. This process is used in applications that demands quality and reliability of the welded joint, where the quality and reliability is more important than the cost factor. Due to this reason it has been widely used in aerospace and nuclear industries.


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