Gas Tungsten Arc Welding (GTAW), also known as Tungsten Inert Gas (TIG) welding, is an arc welding process that produces the weld with a non-consumable tungsten electrode. The process is widely used for joining similar and dissimilar metals due to its good quality outputs. In GTAW, a small intense arc is formed between a pointed tungsten electrode and the workpiece in an inert atmosphere of shielding gas, typically argon or helium. The electrode is not consumed during welding, and when filler metal is required, it must be added separately to the weld pool.
Selecting the Optimal Shielding Gas
The choice of shielding gas is critical to achieving the best results in GTAW. The three most common shielding gas options for GTAW are:
- 100 percent argon
- 100 percent helium
- An argon/helium mix
The optimal gas flow rate for TIG welding varies by the combination of consumables and atmospheric conditions, typically between 10 and 35 cubic feet per hour (cfh). The shielding gas influences heat inputs and arc starting characteristics, and it is critical to adhere to any welding procedure specification (WPS) that is issued.
| Shielding Gas | Typical Flow Rate (cfh) |
|---|---|
| 100% Argon | 10-25 |
| 100% Helium | 15-35 |
| Argon/Helium Mix | 12-30 |
When selecting the shielding gas, consider the following factors:
- Base metal composition
- Desired weld bead profile (width, height, and penetration)
- Arc stability and starting characteristics
- Atmospheric conditions (wind, humidity, etc.)
- Welding position (flat, vertical, overhead, etc.)
Proper shielding gas coverage is essential for achieving high-quality GTAW welds. The shielding gas must completely envelop the weld pool and tungsten electrode to prevent atmospheric contamination.
Preparing the Weld Joint
When preparing the weld joint for GTAW, several different methods can be used, including:
- Oxyfuel cutting
- Plasma cutting
- Shearing
- Machining
- Air carbon arc gouging
- Grinding
- Chipping
The strength of the weld joint is another factor contributing to the weld joint design. Weld joints can be either partial or full penetration, depending on the strength required of the joint. Weld joint design or weldment configuration for GTAW is determined by the type of metal, configuration of the weldment, designated codes and specifications, and the metallurgical analysis.
It is important to ensure that the weld joint is clean and free of any contaminants, such as oil, grease, or rust, to prevent inclusions or other defects in the weld. The joint surfaces should be smooth and free of any sharp edges or irregularities that could disrupt the shielding gas flow.
Welding Procedure Variables
In GTAW, welding procedure variables control the welding process and the quality of the welds produced. Joint configuration is determined by the design of the weldment, the metallurgical analysis, and by the process and procedure required by the weldment.
The fixed welding variables include:
- Type of filler metal
- Electrode type and size
- Type of current (AC or DC)
- Type of shielding gas
The adjustable variables control the shape of the weld by affecting things such as bead height, bead width, penetration, and weld integrity. The primary adjustable variables for GTAW are:
- Welding current
- Arc length
- Travel speed
Proper selection and adjustment of these variables are crucial for achieving the desired weld quality and appearance.
Initiating the Arc
In GTAW, there are a few different methods that can be used for a TIG welding setup, including:
- Scratch Starts: Rely on the welder to scratch the tip of the tungsten on a workpiece to initiate the arc.
- Lift Starts: Use a foot pedal with no arc jumping between tungsten and the metal.
- High-Frequency Starts: Use high voltage sparks of several thousand volts which last for a few microseconds to cause the electrode-workpiece gap to break down or ionise, allowing current to flow from the power source.
The choice of arc starting method will depend on the specific welding application, equipment capabilities, and welder preference.
Conclusion
GTAW is a highly precise welding process that requires a high level of skill and attention to detail. The choice of shielding gas and flow rate, joint preparation, and welding procedure variables are all critical factors that contribute to the quality and integrity of the weld. By following the advanced hands-on details and technical specifications outlined in this guide, you can master the art of GTAW welding and produce high-quality, aesthetically pleasing welds that meet the most demanding specifications.
References:
– https://www.uti.edu/blog/welding/tig-welding-gas-tungsten-arc-welding
– https://www.thefabricator.com/thewelder/article/arcwelding/gas-tungsten-arc-welding-fundamentals-understanding-gtaw
– https://www.twi-global.com/technical-knowledge/job-knowledge/tungsten-inert-gas-tig-or-gta-welding-006
– https://www.sciencedirect.com/topics/engineering/gas-tungsten-arc-welding
– https://www.millerwelds.com/resources/article-library/proper-shielding-gas-coverage-is-key-to-success-in-gtaw
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