TIG Welding – Gas Tungsten Arc Welding [GTAW]

GTAW (Gas Tungsten Arc Welding) is also called as TIG Welding (Tungsten Inert Gas Welding). It comes under Fusion Welding section.

TIG Welding Equipments:

Figure shows the basic setup for TIG welding.

1. Welding Gun: It is the assembly that loads electrode, electric connections and ports for gas connecting tubes.
2. Power Supply: DC or AC power supply.
3. Gas Cylinder and Connecting Tubes: Gas cylinder for shielding gas supply (argon, helium etc.). Connecting tubes for carrying gas from cylinder to welding gun.
4. Tungsten Electrode: Arc is created between workpiece and tungsten electrode. Tungsten have the highest melting point of all of the metals hence tungsten is used.
5. Filler Rod: Depending upon type of welded joint filler rod may be needed or not. Generally made of base metal.

TIG Welding Operation Overview:

TIG welding is performed in very similar manner as that of other arc welding processes. DC or AC power supply is used. Arc is stuck between workpiece and electrode under the cover of shielding gas like argon, helium or similar combination etc. This results in heating of the workpiece and the electrode. Temperature of 35000 F or 19000 C can be achieved. As electrode is made of tungsten it does not melt but workpiece does. Molten metal pool is created at welding zone. Depending upon the need and type of the welded joint, filler metal can be used. Care must be taken to keep the tip of the filler metal within the shield of the gas. If molten tip comes out of the gas then atmospheric contents may contaminate the metal causing contaminated welded joint.

Arc Strike-Start Methods for TIG Welding:

1. Scratch Start: Easy but contaminates the electrode.
2. Touch Start or Lift Arc: Best method but needs additional equipment to control the electric properties.
3. High Frequency Generator: Good method but can cause harm to workpiece having some electric circuitry on board.

Power Supply – DC, AC, Electrode Polarity:

GTAW with AC – Alternating Current:

Current flow occurs due to flow of electrons in the conductor. In AC power source this current keeps on changing its direction continuously. This switching of direction of current per second is called as frequency, which is measured in Hz (Hertz). Most of places in world this is kept at 50Hz or 60Hz.

AC is can be used for TIG welding operation. More is the frequency, better is the arc stability and focus.

Round tip electrode is used for TIG when using AC.

GTAW with DC – Direct Current:

Direct current is simpler to understand. Here, flow of electrons does not change its direction. So, there is no term called frequency in direct current. But there is another term comes in picture, Polarity.

Electrode Negative or Straight Polarity:

• Negative end of power supply is connected to electrode.
• Flow of positive ions is from workpiece to electrode.
• Arc is stable.
• More, about 70%, heat is concentrated on workpiece.
• Deeper penetration is achieved.

Electrode Positive or Reverse Polarity:

• Positive end of power supply is connected to electrode.
• Arc goes erratic at times.
• More, about 70%, heat is concentrated on electrode.
• Longer electrode is needed.
• Penetration is not deep as straight polarity.
• Positive ions flow from electrode to workpiece. These ions can break the oxide coating on non ferrous materials giving cleaning of work.
• Has excellent oxide cleansing property of non ferrous materials like aluminum.

Shielding Gas:

Shielding gas shields the other atmospheric gases, mainly oxygen and impurities, from being the part of weld. Inert gas does not react with either electrode or work even at very high temperatures.

When arc is stuck, circuit completes through the gap between electrode and work. So, shielding gas must have very good ionization capabilities.

Argon and Helium are mostly used in TIG. But argon has excellent properties for this process. It is heavier than air. It ionizes faster than helium.

Advantages:

1. Arc welding is good at making strong joints. But it falls short on some very strong or reactive metals such as stainless steel, bronze, brass, aluminum, magnesium, titanium etc. TIG welding works very well with all these metals.
2. No harmful fumes are produced.
3. Heat affected zone is small or lesser.
4. Here inert gas (which is totally transparent) shields atmospheric gases from hot metals very well so flux is less needed. This allows welder to see the actual welding zone and welding with very high accuracy can be achieved.
5. Quality of welds can be controlled through electric supply. DC, AC both can be used. When using DC, Electrode polarity can be swapped which changes welds quality.
6. Process can be automated.
7. Gases used here are not explosive, as they are in gas welding operations.

Disadvantages/Limitations:

1. Hard to learn. Skilled welder needed for crucial job.
2. Care must be taken to keep filler rod within the shield of gas. If it is taken out then atmosphere may contaminate the tip of rod which is in molten state.
3. Very bright arc rays are produced. Ultraviolet light is also emitted from arc. This also results in ozone and NOx formation. Proper care must be taken to cope up with these.
4. Due to ozone, NOx formation and shield gas itself it may be dangerous to work in compact areas. Ventilation is must to avoid potential hazards.

Where To Go From Here:

1. TIG Welding Resources From Miller

2. TIG Welding on Wikipedia

3. Check MIG Welding Article

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