What is undercut in welding, and what causes it?

What is undercut in welding, and what causes it?

• A. A groove at the toe where the weld metal fills too much; caused by excessive filler
• B. A groove at the toe where the weld metal does not fill; caused by excessive heat input or incorrect technique
• C. A deep crack in the base metal
• D. A bulge along the weld due to too rapid cooling

Answer: (B)

Undercut is a groove that forms along the weld toe where the base metal has melted away and the weld metal does not fill the groove, leaving a notch that weakens the joint. The best description matches this: a groove at the toe where the weld metal does not fill, caused by excessive heat input or incorrect technique. When heat is too high or the deposition is not sufficient, the base metal erodes faster than the filler can bridge the gap, creating that notch along the weld edge. This is often due to too much current, an arc that’s too long, or improper travel speed and technique, which prevent proper filling of the joint with weld metal. To prevent it, control heat input, maintain proper travel speed and arc length, ensure adequate filler deposition, and use the correct electrode angle and technique. Other options describe different defects—overfilling, a crack in the base metal, or a bulge from rapid cooling—not undercut.

Undercut is a groove that forms along the weld toe where the base metal has melted away and the weld metal does not fill the groove, leaving a notch that weakens the joint. The best description matches this: a groove at the toe where the weld metal does not fill, caused by excessive heat input or incorrect technique. When heat is too high or the deposition is not sufficient, the base metal erodes faster than the filler can bridge the gap, creating that notch along the weld edge. This is often due to too much current, an arc that’s too long, or improper travel speed and technique, which prevent proper filling of the joint with weld metal. To prevent it, control heat input, maintain proper travel speed and arc length, ensure adequate filler deposition, and use the correct electrode angle and technique. Other options describe different defects—overfilling, a crack in the base metal, or a bulge from rapid cooling—not undercut.