What is the term for a groove cut into the base metal at one or both sides of the weld bead, which may be caused by unbalanced voltage and amperage settings or improper welding gun angles?

• A. Porosity
• B. Crater
• C. Undercut
• D. Overlap

Answer: (C)

Undercut is a groove that forms along the weld toe in the base metal on one or both sides of the bead. It happens when heat input is too high or the arc and filler metal don’t fuse the edge properly, often due to unbalanced voltage and amperage or an improper gun angle. The molten base metal at the toe melts away faster than the filler metal can fill it, leaving a recessed notch that weakens the joint by reducing the weld’s throat thickness. Visually, you’ll see a clean, diagonal groove running beside the weld bead rather than a smooth, continuous fusion with the base metal. To fix it, reduce heat input and adjust the gun angle so filler metal properly deposits into the joint and fills the toe, ensuring the weld rebuilds the thickness of the base metal. This is different from porosity (gas pockets in the weld metal), crater (depression at the end of the weld), or overlap (overhang beyond the edge).