Welding is a manufacturing process which joins together metals and thermoplastics by applying heat, which in turn causes the parts to melt and guide together when cooled. In welding either the base metal is melted and fused together or a filler material is used to fill the gap and join the parts together. This is in short ” what is welding? “
Now before taking a in depth look on TIG welding, let’s understand what is an “electric arc”
What is an electric arc?
An electric arc is a continuous stream of electrons flowing through a medium between two conductors of an electric circuit and accompanied by intense heat generation and radiation.
TIG or GTAW are one of the types of ” electric arc welding “. The electric arc welding is the most extensively used method of joining components of metallic parts using the heat produced due to electric arc.
Gtaw or TIG welding process :
In TIG welding the arc is maintained between the workpiece and the tungsten electrode and is protected by inert gases like Helium, Argon etc. You might be wondering What is the purpose of inert gas used in TIG welding? Let’s see
Inert gases like Argon and helium are used in Tig welding because:
- It helps in producing better and stable arc.
- No slag is produced after welding is completed
- High quality weld can be produced
- The inert gas protects the workpiece from reacting with the gases in the atmosphere by creating a barrier between them.
Tungsten electrode :
Coming back to the topic, In Tig welding as the name suggests a tungsten electrode is used for producing arc. Tungsten is used due to its high melting point of about 3422 degree celsius
. The tungsten electrode is capable of producing an arc of around 10,000K. In tungsten electrode 1-2% of thorium
and zirconium is added to improve current carrying capacity, electron emission, arc stability and increased melting point. Electrode diameters ranging from 0.8mm – 5mm are used commonly.
Welding process of TIG :
As shown in the fig , The welding head (also called as torch or gun) consists of a light in weight handle with provision for holding a tungsten electrode. The shielding gas flows into the welding torch over the electrode through the nozzle at the end of gun into the arc region. The flow of the gas over the electrode helps in better heat dissipation allowing higher currents to be used. Welding torches are provided with water jacket around them for cooling purposes. During welding process, a filler metal may be used or not.
When the current supply is switched ON, current flows through the electrode into the workpiece via the inert gas medium producing a high temperature Arc. This arc melts the filler metal and fuses the parts together when cooled. If filler metal is not used, then depending upon the workpiece metal the current is increased or decreased. The arc melts the base metal and thus joining them together when cooled.
In TIG welding both manual and automatic processes are possible. This method is suitable for welding thinner workpieces (upto 6mm thickness).
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Metals that can be welded using TIG :
- Aluminium and its alloys
- Stainless steel
- Cast iron
- Silicon bronze
- Carbon steels
- Magnesium etc.
When welding metals that have have an oxide film on the surfaces like aluminium or magnesium an high frequency AC current is used to prevent oxidation. However, for others a DC current is used.
Application of TIG welding :
The TIG welding process has a very large area of application due to its many advantages, e.g.:
• It provides a concentrated heating of the workpiece.
• It provides an effective protection of the weld pool by an inert shielding gas.
• It can be independent of filler material.
• The filler materials do not need to be finely prepared if only the alloying is all right.
• There is no need for after treatment of the weld as no slag or spatter are produced.
• Places of difficult access can be welded.
Areas of application TIG welding is often used for jobs that demand high quality welding such as for instance:
• The offshore industry
• Combined heat and power plants
• The petrochemical industry
• The food industry
• The chemical industry
• The nuclear industry
The increasing demands to the weld quality has made TIG welding very popular for welding of smaller tube dimensions as well as root runs in both non-alloyed and alloyed materials in heavier plates.
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