How Does GTAW Welding Works: A Comprehensive Guide

Gas Tungsten Arc Welding (GTAW), also known as Tungsten Inert Gas (TIG) welding, is a highly precise and versatile arc welding process that produces high-quality welds using a non-consumable tungsten electrode. The process utilizes an inert gas shield to protect the weld pool from atmospheric contamination, resulting in exceptional weld quality and precision. In this comprehensive guide, we will delve into the intricate details of how GTAW welding works, covering everything from the fundamental principles to the advanced techniques and equipment required for successful GTAW welding.

The Fundamentals of GTAW Welding

At the core of GTAW welding is the formation of an arc between a pointed tungsten electrode and the workpiece, all within an inert gas atmosphere, typically argon or helium. This inert gas shield serves to protect the weld pool from atmospheric contaminants, ensuring a clean and high-quality weld. The arc itself is small and intense, providing precise control and heat input, making GTAW an ideal choice for welding a wide range of metals, including steel, stainless steel, aluminum, and copper.

Power Source Selection: AC vs. DC

GTAW welding can be operated using either Direct Current (DC) or Alternating Current (AC) power sources. The choice between DC and AC depends on the specific metal being welded:

• Direct Current (DC): DC is commonly used for welding metals like steel and copper. In DC GTAW, the electrode is always negative polarity, which helps prevent overheating and melting of the tungsten electrode.
• Alternating Current (AC): AC is preferred for welding metals with a tenacious surface oxide film, such as aluminum and magnesium. The AC waveform helps to clean the oxide contamination on the surface of the workpiece, improving the weld quality.

Electrode Selection and Preparation

The selection and preparation of the tungsten electrode are crucial in GTAW welding. Factors to consider include the electrode diameter, tip shape, and the addition of alloying elements:

• Electrode Diameter: The electrode diameter typically ranges from 0.8 mm (0.032 inches) to 6.4 mm (0.250 inches), with the smaller diameters used for thinner materials and the larger diameters for thicker materials.
• Tip Shape: The tungsten electrode can be ground to various tip shapes, such as pointed, balled, or tapered, depending on the application and the desired arc characteristics.
• Alloying Elements: Tungsten electrodes can be alloyed with elements like thorium, zirconium, or lanthanum to improve the electrode’s performance, such as increased electron emission, higher current-carrying capacity, and better arc stability.

Proper electrode preparation, including grinding and sharpening, is essential to maintain a consistent arc and prevent tungsten inclusions in the weld.

Initiating the GTAW Arc

Image source: flickr

Initiating the GTAW arc is a critical step in the welding process, as it can significantly impact the quality of the weld and the lifespan of the tungsten electrode. There are several methods for starting the GTAW arc, each with its own advantages and considerations:

Scratch Start Technique

The scratch start technique involves physically touching the tungsten electrode to the workpiece, then quickly lifting it to establish the arc. This method is simple and straightforward but can lead to tungsten inclusions in the weld if not done properly.

Lift Arc Technique

The lift arc technique involves creating a short-circuit between the tungsten electrode and the workpiece at a very low current level, then quickly lifting the electrode to initiate the arc. This method is gentler on the electrode and helps to prevent tungsten inclusions.

High-Frequency (HF) Start

The high-frequency (HF) start method uses a high-voltage spark to ionize the gap between the tungsten electrode and the workpiece, allowing the current to flow from the power source and establish the arc. HF starts are the most controlled and consistent method, but they require specialized equipment.

Regardless of the starting method used, it is crucial to follow proper procedures to avoid damaging the tungsten electrode or causing tungsten inclusions in the weld.

Controlling the GTAW Weld Pool

GTAW welding requires a high degree of precision and control, similar to welding with an oxy-acetylene torch. The welder must carefully manage the weld pool, the filler metal addition, and the electrical current to achieve the desired weld quality and appearance.

Weld Pool Manipulation

The welder holds the GTAW torch in one hand and uses the other hand to feed the filler metal into the weld pool. By carefully controlling the movement of the torch and the addition of filler metal, the welder can manipulate the shape and size of the weld pool, ensuring a consistent and high-quality weld.

Filler Metal Selection and Addition

The filler metal used in GTAW welding is typically composed of the same material as the workpiece, ensuring a strong and compatible weld. The welder must carefully control the addition of the filler metal, matching the rate of filler metal addition to the size and shape of the weld pool.

Electrical Current Control

The welder controls the electrical current to the weld puddle using a foot pedal or other device. By adjusting the current, the welder can fine-tune the heat input and the weld pool characteristics, ensuring optimal weld quality and appearance.

Advanced GTAW Techniques

GTAW welding is a highly versatile process, and there are several advanced techniques that can be employed to address specific welding challenges or requirements:

Pulsed GTAW

Pulsed GTAW involves the use of a pulsed current waveform, which alternates between a high-current peak and a low-current background. This technique can be used to improve weld penetration, reduce distortion, and enhance the appearance of the weld.

Automated GTAW

Automated GTAW systems use robotic or computer-controlled equipment to perform the welding process, providing consistent and repeatable welds with minimal operator intervention. These systems are often used in high-volume production environments or for complex welding applications.

Orbital GTAW

Orbital GTAW is a specialized technique used for welding pipes and tubes. The GTAW torch is mounted on a rotating mechanism that travels around the circumference of the pipe, allowing for a consistent and uniform weld.

Conclusion

Gas Tungsten Arc Welding (GTAW) is a highly versatile and precise welding process that produces exceptional weld quality and appearance. By understanding the fundamental principles of GTAW, including power source selection, electrode preparation, arc initiation, and weld pool control, welders can master this technique and tackle a wide range of welding challenges. Additionally, the advanced GTAW techniques, such as pulsed welding, automation, and orbital welding, provide even greater flexibility and capabilities for specialized applications. With the comprehensive information provided in this guide, you are now equipped with the knowledge and understanding to successfully apply GTAW welding in your projects.

References

1. TWI Global. (n.d.). Tungsten Inert Gas (TIG) welding, also known as Gas Tungsten Arc Welding (GTAW). Retrieved from https://www.twi-global.com/technical-knowledge/job-knowledge/tungsten-inert-gas-tig-or-gta-welding-006
2. WeldingHub. (2017, April 19). What is TIG Welding? (GTAW) – YouTube. Retrieved from https://www.youtube.com/watch?v=uO5pVLOAmD4
3. ScienceDirect. (n.d.). Gas Tungsten Arc Welding – an overview. Retrieved from https://www.sciencedirect.com/topics/engineering/gas-tungsten-arc-welding
4. Universal Technical Institute. (2019, June 27). WHAT IS TIG (GTAW) WELDING? – Universal Technical Institute. Retrieved from https://www.uti.edu/blog/welding/tig-welding-gas-tungsten-arc-welding
5. Wikipedia. (2022, October 15). Gas tungsten arc welding. Retrieved from https://en.wikipedia.org/wiki/Gas_tungsten_arc_welding