It is one of the most common methods as it guarantees a very high quality of the joints, but requires the use of highly specialized professionals. Let’s find out everything we need to know about this method, which has been used in the aviation industry since the Second World War.
The TIG welding process
TIG welding equipment includes:
- welding machine or current generator
- torch composed of tungsten electrode and its support, gas supply cap, insulating sheath, electrical power supply
- protective gas cylinder
- metal filler rod, where it would be needed
The welding process is based on carrying the electrode, around which the protective gas flows, to the melting bath thanks to the torch. The operator, moving freely and keeping the right distance, is thus able to weld the material: the coin cord is the classic result of this technique that, given the quality and aesthetic value, is used very often when the welding remains visible.
The welding machine
TIG welding does not require any special machinery: to weld some materials you can simply use a direct current generator.
However, this does not apply to all metals: to be able to work on aluminium, magnesium and bronze, a professional welding machine is required, on which you can choose between direct or alternating current.
The TIG welding torch
As we have seen before, the TIG welding torch consists of several parts and is connected directly to the gas cylinder. The gas flow can be adjusted by means of a ceramic cap on the torch itself.
Having to withstand the high temperatures generated by the electric arc, the electrodes are made of tungsten or its alloys: in addition to having better technical and mechanical characteristics than other metals, tungsten is preferred because of its high thermoelectric power that stabilizes the arc.
Generally used in direct current and direct polarity, for example with the positive pole on the workpiece to be welded, electrodes on the market have a diameter ranging from 0.25 mm to 6.4 mm. The reverse polarity, keeping the negative pole on the workpiece, is used on light metals such as aluminium, preferring to work with alternating current.
It is very important to sharpen the tip of the electrode until it becomes conical, increasing the ability to create electrons and direct them to the point to be welded.
Protective gases for TIG welding
For a perfect welding, the protection gas is introduced on both sides of the joint: on the face where the bath is located the toric will bring it directly, while on the back it is blown under controlled conditions to ensure protection from oxidation also at the base of the welding.
The most commonly used gases are argon and helium, separated or mixed with other gases such as hydrogen. Pure argon is preferred because of the advantages of this noble gas:
- makes the welding arc more stable
- has a relatively low cost
- low penetration, very useful when welding very thin pieces
- cleaning on light metals such as aluminium
Argon and helium are mixed in case of welding of thick materials, increasing the thermal conductivity and therefore the penetration power. Hydrogen, on the other hand, is used when welding nickel-based parts.
Conclusion: Advantages and disadvantages of TIG welding
The advantages of this working method are, without a doubt, the great tightness of the welding joints and the aesthetic performance, as well as an excellent penetration. On the other hand, it is not free from defects: it is a slow process and at risk of porosity, as well as having a great difficulty in processing that requires the use of highly qualified personnel.