In welding terminology, what does 'undercutting' refer to?

In welding terminology, 'undercutting' refers to a groove or notch that is created in the base metal adjacent to the weld, where the weld metal is lower than the surface of the base metal. This defect occurs during the welding process when the heat causes local melting of the base metal, which can lead to a weak area that may compromise the integrity of the joint. When the weld is complete, if the weld metal does not completely fill in the area where the undercut occurred, it will appear as if there is a cavity or dip below the surface of the surrounding material.

Understanding undercutting is essential because it can significantly affect the strength and fatigue resistance of the weld joint. It is important for welders to recognize the causes of undercutting, such as excessive heat, incorrect travel speed, or improper torch angle, in order to produce a strong and sound weld without this defect.