Gas Tungsten Arc Welding (GTAW), also known as TIG welding, is a captivating combination of science and craftsmanship. It is considered one of the most precise and versatile methods in the welding industry, capable of producing flawless and superior welds in different materials. In this blog, we will explore the fundamental principles, necessary equipment, essential skills, wide-ranging applications, as well as the pros and cons of GTAW welding.
The original name for the TIG welding process was “heliarc” due to the use of helium as the main shielding gas, although this term is rarely employed in contemporary welding discussions.
Principles of GTAW Welding
GTAW welding is based on the principle of creating an electric arc between a non-consumable tungsten electrode and the workpiece, while a shielding gas (typically argon or helium) protects the weld from atmospheric contamination. The electrode doesn’t melt during the process, ensuring a pure and precise weld bead. It relies on the control of the arc length and the flow of shielding gas to achieve a stable and clean welding process.
Equipment Used in GTAW Welding
A GTAW welding machine provides the electrical current necessary for welding. These machines can be AC or DC, with inverter-based models offering greater control.
TIG welding necessitates the use of a constant current power source, which can be either DC or AC. The importance of this constant current source lies in preventing the occurrence of excessively high currents when the electrode makes contact with the workpiece surface, either intentionally during arc initiation or unintentionally during the welding process. In contrast to MIG welding, which utilizes a flat characteristic power source, TIG welding benefits from a constant current source as it safeguards the electrode tip from damage and prevents it from fusing to the workpiece surface upon contact.
In the case of DC welding, the distribution of arc heat is such that approximately one-third is concentrated at the cathode (negative) while two-thirds are at the anode (positive). This setup ensures that the electrode remains in the negative polarity, preventing overheating and melting. However, there is an advantageous alternative: using a DC electrode with positive polarity. This configuration serves to clean the workpiece surface of oxide contamination when the cathode contacts the surface.
For welding materials with a persistent surface oxide film, such as aluminum, AC is preferred due to its ability to effectively address this issue.
The non-consumable tungsten electrode is used to create the electric arc. It must be sharpened to a point and be the correct type for the job (pure tungsten for AC welding and thoriated or ceriated tungsten for DC welding).
TIG welding possesses distinctive characteristics, notably the absence of physical contact between the tungsten electrode and the metals being joined, as well as the tungsten’s non-consumable nature. This results in a consistent and pristine arc, yielding visually pleasing welds. In contrast, other arc welding methods involve electrodes that physically interact with the metals, often incorporating fluxing agents, which can lead to spattering and reduced arc control.
The tungsten electrode’s remarkable ability to withstand extremely high temperatures, given its melting point of 3422°C, surpassing that of materials like steel (1371-1540°C) and aluminum (660°C), allows it to endure the intense heat while precisely guiding the electrical arc into the weld pool. Furthermore, as the tungsten heats up, its electron emission improves, contributing to an even more stable and cleaner arc.
The versatility of shaping the welding arc and adjusting the cone width is facilitated by grinding the tungsten electrode tip to a fine point. This malleable metal can be easily contoured to maintain the desired shape, allowing for the customization of heat input and concentration. This adaptability is a valuable asset in the realm of TIG welding.
True to its name, the TIG welding process, short for “tungsten inert gas” welding, necessitates the use of an inert shielding gas to shield both the tungsten electrode and the molten metal from oxidation.
Inert gases, by definition, do not engage in chemical reactions with the materials being joined. This protective function is crucial as it guarantees a clean and steady environment for the welding arc and the molten metal pool within the joint.
The two most frequently employed shielding gases in TIG welding are argon and helium. Argon, in most cases, proves to be an ideal choice, meeting the requirements in about 99% of welding scenarios. However, in certain tasks, a mixture of helium and argon can enhance penetration and welding speed, although it may come at the cost of some compromise in arc stability.
The choice of shielding gas in welding depends on the material being joined(Suggestions only). The following guidelines can be considered:
Argon: This is the most commonly used shielding gas, suitable for welding a wide variety of materials, including steels, stainless steel, aluminum, and titanium.
Argon + 2 to 5% H2: The addition of hydrogen to argon introduces a slightly reducing atmosphere, which helps produce cleaner-looking welds without surface oxidation. The hotter and more constricted arc enables higher welding speeds. However, there are potential drawbacks, such as the risk of hydrogen cracking in carbon steels and the possibility of weld metal porosity in aluminum alloys.
Helium and Helium/Argon Mixtures: The inclusion of helium in argon increases the arc temperature, allowing for higher welding speeds and deeper weld penetration. Nonetheless, using helium or a helium/argon blend comes with certain disadvantages, such as the elevated cost of the gas and challenges in initiating the welding arc.
GTAW welding torches are meticulously designed to cater to both automatic and manual operation requirements and are equipped with cooling systems that utilize either air or water. Although the automatic and manual torches share similarities in construction, they exhibit some distinctions in terms of functionality. The manual torch typically features a handle, whereas the automatic torch is commonly accompanied by a mounting rack.
The head angle, which refers to the angle between the centerline of the handle and the centerline of the tungsten electrode, can be adjusted on certain manual torches to align with the operator’s preferences. In practice, air cooling systems are predominantly employed for low-current applications, generally up to around 200 A. In contrast, high-current welding, reaching up to approximately 600 A, necessitates the implementation of water cooling systems.
These torches are interconnected with cables that link to the power supply and hoses that connect to the shielding gas source. In cases where water cooling is utilized, hoses also facilitate the supply of water to the system.
The TIG welding process offers the versatility to join metals both with and without the use of filler metal. The welding arc generated by the tungsten electrode achieves the fusion of the two base metals by melting them together. Nevertheless, welders often opt to introduce filler metal to reinforce the joints and prevent potential cracking.
Incorporating filler metal is considered one of the more intricate aspects of GTAW welding. Welders face the challenge of delicately adding the filler wire to the weld pool with one hand while concurrently managing the TIG torch with the other. A key concern is preventing any contact between the filler metal and the tungsten electrode, as this can lead to electrode contamination, necessitating a pause in the process for the tungsten tip to be regrinded.
Therefore, the art of adding filler metal involves a skillful coordination, ensuring that the tungsten tip and the filler wire tip remain in close proximity and move harmoniously in the same direction, all while avoiding direct contact.
Skills Required for GTAW Welding
GTAW welding is a precise and challenging process that requires a high level of skill and attention to detail. Some essential skills include but not limited to below:
Arc Control: Maintaining a stable and consistent arc length is crucial for producing quality welds.
Heat Control: Properly controlling the heat input is necessary to avoid overheating or warping the workpiece.
Weld Joint Preparation: Adequate cleaning and preparation of the weld joint, including beveling, is essential for strong and reliable welds.
Filler Rod Control: If used, precise control of the filler rod is necessary to ensure it melts into the weld joint smoothly.
Applications of GTAW Welding
GTAW welding is commonly chosen for the precise joining of exotic metals such as stainless steel, aluminum, Chromoly, nickel alloys, and magnesium. Yet, it finds application even in the welding of ordinary mild steel when the utmost joint quality is imperative. In cases where speed and simplicity take precedence over absolute joint quality, MIG welding tends to be the more suitable option for mild steel.
Pipe Welding: GTAW welding is used to join pipes in industries like petrochemical, pharmaceutical, and food processing, ensuring leak-free joints.
Aerospace: GTAW welding is used to join critical components such as aircraft frames and engine parts due to its precision and clean welds.
Automotive: It is employed in exhaust systems, intake manifolds, and other components where weld quality is paramount.
Art and Craft: The process is popular among artists and craftsmen due to its ability to create intricate and detailed welds.
Advantages & Disadvantages Of TIG Welding
While GTAW welding offers numerous advantages, it is not exempt from certain limitations.
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GTAW Welding Faqs
What is GTAW welding?
GTAW welding is a welding process that uses a non-consumable tungsten electrode to create an electric arc for welding. A shielding gas, typically argon, is used to protect the weld area from atmospheric contamination.
What materials can be welded with GTAW?
GTAW is versatile and can be used to weld a wide range of materials, including steel, stainless steel, aluminum, copper, and exotic alloys like titanium.
What are the advantages of GTAW welding?
Some advantages of GTAW welding include precise control, a high-quality weld with minimal spatter, and the ability to weld thin materials. It’s also suitable for welding in various positions.
What are the disadvantages of GTAW welding?
GTAW can be a slower welding process compared to others like MIG or stick welding. It requires a high skill level and is not as suitable for high-volume production.
What equipment is needed for GTAW welding?
GTAW welding equipment includes a power source, a TIG torch, a non-consumable tungsten electrode, shielding gas (usually argon), filler material (if necessary), and appropriate safety gear.
How do I choose the right tungsten electrode for GTAW welding?
Tungsten electrodes come in various compositions (e.g., pure tungsten, thoriated, ceriated). The choice depends on the material you’re welding and the type of current you’re using (AC or DC). Consult the welding equipment manufacturer’s recommendations.
What is the purpose of the shielding gas in GTAW welding?
The shielding gas (typically argon) is used to protect the weld area from atmospheric contamination. It prevents oxidation and ensures a clean, strong weld.
How do I set the right welding parameters for GTAW?
Welding parameters, such as amperage, voltage, and travel speed, depend on the material, thickness, and joint configuration. Consult the welding procedure specifications or guidelines provided by the material manufacturer or welding equipment manufacturer.
Can GTAW welding be used for pipe welding?
Yes, GTAW welding is commonly used for pipe welding, particularly for materials like stainless steel and high-purity pipes in industries like food and pharmaceuticals.
Can GTAW weld aluminum?
Yes, GTAW welding is an excellent choice for aluminum welding. It offers precise control and minimizes heat distortion.
What safety precautions should I take when GTAW welding?
Safety precautions include wearing protective gear like a welding helmet, gloves, and appropriate clothing. Ensure proper ventilation to remove fumes and avoid inhaling them. Be aware of electrical hazards and follow safety guidelines.
Can GTAW be automated?
Yes, GTAW welding can be automated using robotic systems for high-volume production and precision welding applications.
What are common joint configurations for GTAW welding?
Common joint configurations in GTAW welding include butt joints, lap joints, T-joints, and corner joints.
Can GTAW welding be used for root passes in pipe welding?
Yes, GTAW is often used for root passes in pipe welding because of its ability to provide a high-quality, low-porosity weld.