What Is The Welding Principle Of TIG?

The core of TIG welding is establishing a high-temperature electric arc between the tungsten electrode and the workpiece.

The arc temperature can reach over 3000℃ (up to 8000℃), sufficient to locally melt most metals to form a molten pool.

The stability of the arc directly affects the weld quality; therefore, a constant current (CC) power supply is typically used, operating in either DC or AC mode.

During welding, an inert gas (commonly argon, but in some cases helium or a mixture) is continuously ejected from the welding torch nozzle.

The main functions of the gas are:

• To isolate the weld pool from air, preventing oxygen, nitrogen, etc., from reacting with the molten pool to produce pores and oxides;
• To stabilize the arc, as monatomic gases like argon have low ionization potentials, helping to maintain a concentrated and stable arc;
• To cool the electrode and welding torch, extending the tungsten electrode's lifespan.

• Tungsten electrodes, as non-consumable electrodes, only undergo slight ablation at extremely high temperatures and do not participate in the composition of the weld metal.
• The electrode tip is typically ground into a conical shape (DC welding) or a hemispherical shape (AC welding) to control the arc concentration.
• To enhance electron emission capability, rare earth oxides such as thorium, cerium, and lanthanum are often added to the tungsten electrode.

• To increase weld thickness or supplement material, filler wire can be added to the molten pool manually or automatically.
• The chemical composition of the filler wire is usually matched to the base metal to avoid metallurgical defects.
• Hot-wire TIG technology preheats the filler wire with an additional power source during wire feeding, improving deposition efficiency.

• DC Positive Polarity (DCEN): Workpiece connected to the negative electrode, tungsten electrode to the positive electrode; arc heat is more concentrated on the workpiece, resulting in greater penetration, suitable for stainless steel, titanium, etc.
• DC Reverse Polarity (DCEP): Workpiece connected to the positive electrode, tungsten electrode to the negative electrode; provides "cathode cleaning," suitable for metals with oxide films on the surface, such as aluminum and magnesium, but the increased heat generated by the tungsten electrode reduces current carrying capacity.
• AC Polarity (AC): Balances cleaning effect and penetration depth, widely used in aluminum and magnesium alloy welding.

• Aerospace: Engine components, fuel tanks;
• Chemical and Nuclear Power: Pipelines, pressure vessels;
• Food and Medical Devices: Stainless steel containers, surgical instruments;
• Automotive and Bicycles: Aluminum alloy body frames, exhaust pipes.