Orbital Electrode Grinding Method

The Importance of the Tungsten Electrode in Orbital TIG Welding

The tungsten electrode plays a critical role in the orbital TIG welding process because it facilitates the formation of the electric arc, and its geometry directly affects the quality of the weld. There are several important criteria to consider when selecting an electrode: the electrode’s material, diameter, length, size, geometry, and surface condition.

In this article, we will focus specifically on the electrode’s diameter and geometry.

The Effect of Electrode Diameter and Geometry

The electrode diameter and geometry determine the behavior of the electron flow, which in turn affects the outcome of the TIG welding process. A flat tip is essential for ensuring arc stability. So, what is a flat tip, and how do you select an appropriate one?

The Role of a Sharpened Electrode

A sharpened electrode is the most important parameter affecting the characteristics of the welding arc and the geometry of the weld bead. Sharpening facilitates arc initiation; however, it can cause the electrode to wear out quickly and lead to potential tungsten residue during welding.

Therefore, the sharpening process must be an integral part of the welding procedure. To ensure optimal arc stability, sharpening must always be performed along the length of the electrode. Vertical grinding must be strictly avoided, as it can lead to arc instability and unpredictable welding results.

When the electrode tip is sharpened, there is a risk of dulling and tungsten falling into the weld pool. This can cause contamination in the weld and may later be visible as a white spot on an X-ray of the weld.

The Importance of a Flat Tip

A flat tip helps extend the electrode’s life, but it must be carefully shaped to avoid making the arc unstable or channeled, and it should not be too large. Therefore, it is recommended to use an appropriate flat tip to ensure arc stability, good electron transfer, and a long electrode life without risking tungsten inclusion.

This figure illustrates the effect of electrode geometry on electron flow behavior.

As shown, electrons are always emitted perpendicular to the electrode surface. It is important to choose a flat tip at the electrode end, determined based on the current being used. A properly designed flat tip creates an effective flow, providing a linear electron output current.

This flow provides the electrode with a maximum heating zone, resulting in a very small area where the melting zone is formed. The density of the flow and how well it focuses the heat into a limited area ensure optimal fusion. This makes it possible to automatically melt material up to 3 mm thick without the welder having to perform a pendulum motion.

The figures above illustrate the effect of electrode diameter on the electron flow.

The selection of the electrode diameter is a critical factor, as the density of the electron flow within the electrode is proportional to the diameter: more amperes mean a larger flow. For example, when the diameter of the flow is equal to the diameter of the flat tip (as shown in Figure 1), we can assume that the effective flow is optimal as it exits the electrode.

Conversely, in cases where the flow is larger than the straight tip (as shown in Figure 2), the electrons spread vertically, creating a wide heating zone, which reduces efficiency.

Conversely, in the scenario where the flow is smaller than the flat tip (as shown in Figure 3), the effective flow cannot be channeled and “balances out” at the flat tip, increasing the risk of arc drift and instability; in this case, the heating zone spreads out.

Since electrons are not properly channeled at the exit, they will tend to accumulate at the corners and carry the risk of moving sideways during low-current periods, especially in welding applications that require a slope.

Therefore, selecting the appropriate diameter and geometry is crucial for ensuring arc stability, achieving good electron transfer, and guaranteeing a long electrode life without risking tungsten residue.