Why is undercutting considered a defect in welding?

Undercutting is a defect characterized by a groove or notch that forms at the edges of the weld metal, where the base metal is melted away and not adequately filled with weld material. This defect results in weaker areas in the weld, which can compromise the overall strength and integrity of the welded joint.

When undercutting occurs, the load-bearing capacity of the weld is diminished, making it vulnerable to failure, particularly under stress or fatigue. Such weak spots can be critical in applications where structural integrity is paramount, leading to potential safety issues. This is why the identification and correction of undercuts are crucial during the welding process, as they can significantly affect the performance and reliability of the finished product.

While undercutting does not contribute positively to the welding process—such as increasing weight, enhancing aesthetics, or supporting penetration—its presence poses a direct threat to weld quality, emphasizing the importance of maintaining proper welding techniques and settings to avoid this defect.