Nature of tig welding machine and advantages?

Outstanding advantages of TIG welding method

TIG welding uses Tungsten electrodes combined with a protective inert gas environment, allowing applications on a variety of materials such as stainless steel, aluminum, magnesium, copper, copper alloys, nickel and nickel alloys, as well as like low carbon steels with a variety of thicknesses.

A special feature of this method is the ability to perform welding in many spatial positions without causing splashes. The filler metal melts directly in the weld pool without participating in creating the arc, ensuring a smooth and safe process.

TIG welds have the advantage of not being trapped in slag, because slag is not created during the welding process. This method is also especially effective with difficult-to-weld metals, helping to easily combine filler metal and base metal, creating high-quality welds. Notably, scrap metal pieces can be used for welding, and the completed weld usually does not require further machining because the protrusion is adjusted during the process.

Current used on Tig welding machine

TIG welders are divided into two main types based on current: direct current (DC) and alternating current (AC). Each type is individually designed to suit the material and specific arc characteristic requirements.

Direct current (DC):

With DC current, there are two main types of wiring: forward polarity and reverse polarity, according to the convention of arc welding. However, reverse polarity is rarely applied in TIG welding due to the disadvantages of a less stable arc, low penetration depth and rapid electrode wear. However, the advantage of the reverse polarity method is the ability to clean the oxide layer on the surface, helping to effectively treat easily oxidized metals such as aluminum and magnesium.

Forward polarity is more commonly used in TIG welding because it provides a stable arc, good penetration depth and reduces stress and deformation in the weld joint. This is suitable for most metals, especially where surface cleaning is not required.

Alternating current (AC):

AC current is a combination of forward bias and reverse bias in each cycle. During the reverse bias half cycle, the AC current aids in cleaning the oxide layer on the surface of the material, which is important for metals such as aluminum, magnesium or beryllium bronze. Thanks to this ability, the AC line is often preferred when welding metals with thick oxide layers that require a clean and aesthetically pleasing weld surface..

Features of TIG welding machine:

DC welders often use high-frequency current to initialize the arc, while AC welders maintain a continuous high-frequency current to stabilize the arc. Typical TIG welders operate at a current range of 3 to 350A, with a voltage of 10 to 35V and a load factor of about 60%. Some high-frequency welding machines are also compatible with both AC and DC power sources, as long as the AC source ensures a minimum no-load voltage of 75V.

Protective gas in TIG welding

The arc and molten metal are protected by an inert gas environment such as Argon, Helium or a mixture of these two gases. Among them, Argon is more commonly used thanks to its low price, ease of production and higher density than Helium. This gives Argon better protection even at low injection air flow rates. When Helium is mixed with Argon, this mixture increases the heat of the arc, even though the current and arc size do not change. Thanks to this, Argon-Helium mixture is often preferred when welding thick materials.

There are five main types of shielding gases and gas mixtures commonly used in TIG welding:

1. Pure CO₂

2. Pure Argon

3. Pure helium

4. Argon + CO₂ mixture

5. Argon + Helium mixture

TIG welding torch

The TIG welding torch is responsible for holding the Tungsten electrode, ceramic cap, electrical conductor and protective gas.

a. Cooling:

During the welding process, the TIG welding torch must endure a large amount of heat, so it needs to be cooled to ensure safety and increase longevity.

- The welding torch uses low current and can be cooled by air.

- High capacity soldering irons (up to 500A) need to be cooled with water.

- The "soft sheath" welding torch has a special design, with a flexible soldering tip that bends at angles, suitable for specific jobs.

b. Electrode holder:

The electrode is held in place in the welding torch by means of a screwed cone. The cone bush is a screw with a hole in the middle, with a size appropriate to the electrode diameter. The direction and flow of shielding gas are adjusted using an air cup or nozzle mounted on the tip of the welding torch.

TIG welding electrode

Unlike other types of arc welding, TIG electrodes do not melt during the welding process. Therefore, the electrode must be made from a material with a high melting temperature, enough to withstand the welding current without deformation.

1. Pure Tungsten electrode:

The first type of electrode used, with a melting temperature of up to 3400°C (6170°F). However, the disadvantages of this electrode have been improved with Tungsten alloys. Pure Tungsten electrodes usually have a green painted tip, symbol EWP.

2. Tungsten alloy electrode:

Tungsten alloy is more popular due to its superior properties in various applications. Two common types are:

- Zirconi-Vonfram:

This type is mainly used to weld aluminum. Zirconium-Tungsten electrodes are more durable than pure Tungsten, often used with AC current and create high quality welds. This electrode has a brown painted tip, symbol EWZr.

- Thorium-Tungsten:

This type is often used to weld low alloy steel with forward-biased DC current. Thorium-Tungsten electrodes are less susceptible to deformation when using low currents and reduce the impact on weld quality if an interruption occurs. There are two types with thorium content of 1% and 2%:

- 1% thorium type: yellow painted tip, symbol EWTh 1.

- 2% thorium type: red painted tip, symbol EWTh 2.

Pressure relief valve and flow meter in TIG welding

Pressure relief valves used in TIG welding are a little different from those used for gas welding such as Oxy-Acetylene.

- Gas welding (Oxy-Acetylene): Gas pressure is measured at the tip of the welding torch using a pressure gauge, with the common measurement unit being PSI (Anglo-American system) or MPa (1 PSI ≈ 0.007 MPa).

- TIG welding: Shielding gas flow is measured not by pressure but by flow, using units such as CFH (Anglo-American system) or m³/h (1 CFH ≈ 0.0283 m³/h).

The shielding gas flow is checked with a flowmeter, with a ball indicator. As the air flow increases, the ball is pushed higher on the scale, making it easier for the user to determine the exact amount of air being supplied.