Gas tungsten arc welding (GTAW)
The Gas tungsten arc welding (GTAW) is also known as Tungsten inert gas (TIG) welding or Heliarc welding. It is a welding process that joins metals by heating them with an arc between a tungsten electrode (also called a non-consumable electrode) and the workpiece. The tungsten electrode and the weld pool are shielded by an inert gas, normally gas uses helium and argon, for preventing the weld pool from oxidation and other atmospheric contamination. Argon gas is most commonly used in gas tungsten arc welding for shielding weld pool. In argon gas 2% to 5% hydrogen gas addition to make the gas slightly traduction assisting the production of the clear looking weld without surface oxidations. As the arc is hotter and more constricted, its permitted higher welding speed.
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| TIG welding process |
The Tungsten electrode is the core of tungsten inert gas welding. The Tungsten electrode has the highest melting point that is about 3300-degree Celsius temperature of the tungsten electrode. This means the electrode can emit an arc that heats and liquified the workpiece without itself melting away. Tungsten inert gas welding is a slow but quiet and precise form of welding and it is most suitable for joining thin workpieces. It is suitable for most metals like stainless steel, non-ferrous metals, such as aluminum, magnesium, and copper alloy. The Gas tungsten arc welding (GTAW) process grants the welding operator greater control over the welding than other welding processes like shielded metal arc welding (SMAW) and much more.
Process
GTAW welding is a difficult welding method due to the coordination required by the welder. In this method normally two hands engaged properly because most of the applications require that welder manually feed a filler metal into the weld area with one hand manipulating the welding torch in the other hand maintaining short arc length after spark generation, it is about 1.5 to 3 mm between workpiece and electrode welding holder for continuing arc generation or avoid any contact with the workpiece surface would damage the electrode tip or fuse the electrode to the workpiece surface.
In the GTAW welding process, the welding arc is formed between a pointed tungsten electrode and the workpiece in an inert gas of argon or helium, scratching the job surface, forming a short circuit is broken that main welding current will flow. Once the arc is struck, the welders move the torch in small circles to create welding pools, the size of which depends on the size of the electrodes and amounts of the current. When maintaining a constant separation between electrode and workpiece, then operators move the touchback slightly and tilts it backward about 10 degrees to 15 degrees from vertical. The small intense arc provided by the pointed electrodes is ideal for high quality and precise welding. Because the electrode is not consumed during welding, the welder does not have to balance the heat inputs from the arc as the metal is deposited from the melting electrodes. When filler metals are required, it will be must be added separately to the weld pool.
click this link to know about variables in Gas tungsten arc welding (GTAW) for Welding procedure specification (WPS).
Power source
Gas tungsten arc welding (GTAW) must be operated with a constant current power source, it may either Direct current (DC) or alternating current (AC). GTAW welding power source has two terminals one terminal connected to the base metal and another terminal connected to the welding holder which holds the electrode and also gives the power supply to the electrode. When a positive terminal connected with the electrode then it is called Direct current electrode positive or reverse polarity (DCEP). It has about 70% heat, which gives good penetration so it is mainly used for thin material. DCEP is the electron flow close to the electrode. And when the negative terminal connected with the electrode then it is called direct current electrode negative or straight polarity (DCEN). It has about 30% of heat on the electrode hence penetration is less so it is mainly used for thinner steel. DCEN is the electron flow from the tip of the electrode, the electrode is always negative polarity to prevent overheating and melting.
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| TIG welding process |