TIG welding is a precise and versatile welding technique that uses an electric arc between a tungsten electrode and the workpiece to melt and fuse the metal. The tungsten electrode is a crucial component of the TIG welding process, as it determines the shape, stability, and quality of the arc. Therefore, it is important to know how to shape the tungsten electrode correctly for different welding applications.
I. What is the tungsten electrode and why does it need to be shaped?
The tungsten electrode is a thin rod of tungsten or tungsten alloy that is inserted into the TIG torch and connected to the negative terminal of the power source. The tungsten electrode acts as a non-consumable electrode, meaning that it does not melt or become part of the weld. Instead, it creates an arc that heats and melts the filler metal and the base metal.
The tungsten electrode needs to be shaped or sharpened to a certain tip angle and geometry, depending on the type of metal, current, and polarity used for welding. The shape of the tungsten electrode affects the arc characteristics, such as the arc length, width, direction, and stability. The shape of the tungsten electrode also influences the weld quality, such as the penetration, bead profile, spatter, and porosity.
II. Advantages of Pulse Spray Transfer GMAW
The first step in shaping the tungsten electrode is to choose the right type and diameter of the electrode for the welding application. There are different types of tungsten electrodes, classified by the alloying elements and the color codes. The most common types are:
Pure tungsten (green): This type has no alloying elements and has the lowest melting point and highest conductivity. It is suitable for AC welding of aluminum and magnesium, as it forms a balled tip that provides a stable arc and good cleaning action. However, it is not recommended for DC welding, as it has poor arc stability and low resistance to contamination.
Thoriated tungsten (red): This type contains 1.7% or 2% of thorium oxide, which increases the electron emission and the arc stability. It is suitable for DC welding of steel, stainless steel, nickel, and copper alloys, as it forms a pointed tip that provides a narrow arc and deep penetration. However, it is not recommended for AC welding, as it has poor arc starting and cleaning action. It is also radioactive and requires proper handling and disposal.
Ceriated tungsten (orange): This type contains 1.8% or 2% of cerium oxide, which enhances the arc starting and stability. It is suitable for both AC and DC welding of various metals, especially at low amperages. It forms a pointed or slightly balled tip that provides a stable arc and good cleaning action. It is also non-radioactive and has a longer service life than thoriated tungsten.
Lanthanated tungsten (gold or blue): This type contains 1.5% or 2% of lanthanum oxide, which improves the arc starting, stability, and resistance to contamination. It is suitable for both AC and DC welding of various metals, especially at high amperages. It forms a pointed or slightly balled tip that provides a stable arc and good cleaning action. It is also non-radioactive and has a longer service life than thoriated and ceriated tungsten.
The diameter of the tungsten electrode depends on the welding current and the material thickness. Generally, the higher the current and the thicker the material, the larger the diameter of the electrode. The following table shows the recommended electrode diameters for different welding currents and materials.
| Electrode Diameter | Welding Current (A) | Material Thickness (mm) |
|---|
| 1.0 mm | 5-15 | 0.5-1.5 |
| 1.6 mm | 10-80 | 1-3 |
| 2.4 mm | 70-150 | 2-6 |
| 3.2 mm | 140-250 | 5-10 |
| 4.0 mm | 200-400 | 8-16 |
II. How to shape the tungsten electrode tip?
The second step in shaping the tungsten electrode is to sharpen the electrode tip to a certain angle and geometry, depending on the type of current and polarity used for welding. The shape of the electrode tip affects the arc characteristics, such as the arc length, width, direction, and stability. The shape of the electrode tip also influences the weld quality, such as the penetration, bead profile, spatter, and porosity.
The most common shapes of the electrode tip are:
Pointed: This shape is achieved by grinding the electrode tip to a sharp point with a 15 to 30-degree angle. This shape is suitable for DC welding of steel, stainless steel, nickel, and copper alloys, as it provides a narrow arc and deep penetration. It is also suitable for AC welding of aluminum and magnesium at low amperages, as it provides a stable arc and good cleaning action. However, this shape is prone to erosion and contamination, especially at high amperages and frequencies.
Balled: This shape is achieved by heating the electrode tip to a hemispherical ball with a high positive current. This shape is suitable for AC welding of aluminum and magnesium at high amperages, as it provides a stable arc and good cleaning action. However, this shape is not suitable for DC welding, as it provides a wide arc and shallow penetration.It is also not suitable for welding thin materials, as it may cause burn-through and distortion.
Truncated: This shape is achieved by grinding the electrode tip to a pointed cone and then flattening the tip slightly. This shape is suitable for both AC and DC welding of various metals, as it provides a stable arc and moderate penetration. It is also resistant to erosion and contamination, especially at high amperages and frequencies. The width of the flat tip should be about 10% of the electrode diameter.
The following table shows the recommended electrode tip shapes for different types of current and polarity.
| Current Type | Polarity | Electrode Tip Shape |
|---|
| AC | Balanced | Pointed or balled |
| AC | High DCEP | Balled |
| AC | High DCEN | Pointed |
| DC | DCEN | Pointed or truncated |
| DC | DCEP | Not recommended |
III. How to grind the tungsten electrode?
The third step in shaping the tungsten electrode is to grind the electrode using a proper tool and technique. The grinding of the electrode affects the surface finish, alignment, and consistency of the electrode tip. The grinding of the electrode also affects the weld quality, such as the arc stability, spatter, and porosity.
The most common tools for grinding the tungsten electrode are:
Bench grinder: This is a stationary machine that has a grinding wheel that rotates at high speed. It is suitable for grinding large quantities of electrodes with a consistent angle and geometry. However, it may produce sparks, dust, and noise, which may pose safety and health hazards. It may also contaminate the electrode with other metals, which may affect the arc quality and weld performance.
Hand-held grinder: This is a portable machine that has a grinding wheel that rotates at high speed. It is suitable for grinding small quantities of electrodes with a flexible angle and geometry. However, it may produce sparks, dust, and noise, which may pose safety and health hazards. It may also contaminate the electrode with other metals, which may affect the arc quality and weld performance.
Tungsten grinder: This is a dedicated machine that has a diamond wheel that rotates at low speed. It is suitable for grinding any quantity of electrodes with a precise angle and geometry. It does not produce sparks, dust, or noise, which reduces the safety and health hazards. It also does not contaminate the electrode with other metals, which improves the arc quality and weld performance.
The most common techniques for grinding the tungsten electrode are:
Longitudinal grinding: This is the preferred technique, as it produces a smooth and even surface finish on the electrode tip. It also aligns the grinding marks with the direction of the current flow, which reduces the arc wandering and improves the arc stability. To perform this technique, the electrode should be held at a right angle to the grinding wheel and rotated along its axis while moving back and forth.
Circumferential grinding: This is an alternative technique, as it produces a rough and uneven surface finish on the electrode tip. It also misaligns the grinding marks with the direction of the current flow, which increases the arc wandering and reduces the arc stability. To perform this technique, the electrode should be held at a right angle to the grinding wheel and rotated around its circumference while moving back and forth.
IV. Conclusion
TIG welding is a precise and versatile welding technique that requires proper shaping of the tungsten electrode. The tungsten electrode needs to be chosen and sharpened according to the type of metal, current, and polarity used for welding. The shape of the tungsten electrode affects the arc characteristics and the weld quality. The tungsten electrode also needs to be ground using a proper tool and technique. The grinding of the tungsten electrode affects the surface finish, alignment, and consistency of the electrode tip. By following the guidelines and tips in this article, you can shape your tungsten electrode correctly for TIG welding and achieve optimal results in your welding projects.
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