What factors can lead to undercut in GTAW?

Excessive travel speed combined with high amperage can indeed lead to undercut in Gas Tungsten Arc Welding (GTAW). When the travel speed is too rapid, the molten puddle does not have sufficient time to properly fuse the base metals together and can lead to a V-shaped groove or undercut along the edges of the weld. High amperage, on the other hand, increases the heat input into the weld area, which can further exacerbate the problem by causing rapid melting and solidification, making it more difficult for the molten metal to flow smoothly and fill in properly. This combination results in incomplete fill and undesirable undercutting along the edges of the weld.

In contrast, while low filler material quality, insufficient torch angle, and inadequate shielding gas can contribute to various welding defects, they do not directly cause undercut in the specific manner that excessive travel speed and high amperage do. These other factors might lead to issues like porosity, lack of fusion, or contamination but do not inherently create the characteristic undercut found with improper travel speed and amperage settings.