What could be a cause of weld bead undercut/concave weld?

What could be a cause of weld bead undercut/concave weld?

• A. Voltage too high
• B. Travel speed too slow
• C. Low filler metal
• D. High shielding gas flow

Answer: (A)

When a weld toe is melted back and the bead sits with a groove or a sunken, concave shape, it’s usually due to too much heat being introduced at the weld area. Setting the voltage too high makes the arc longer and injects more heat per unit length, which melts the base metal at the toe faster than the filler metal can fill the joint. The result is an undercut along the edge and a concave appearance because the weld metal doesn’t adequately fill the melted toe. Other options don’t fit as well. Traveling too slowly changes heat input and bead size but doesn’t inherently cause an undercut at the toe. Using too little filler metal can lead to an underfilled or concave bead, but the classic undercut formation is driven by excessive heat input from high voltage. Excessively high shielding gas flow mainly affects porosity and arc stability rather than the weld toe geometry.

When a weld toe is melted back and the bead sits with a groove or a sunken, concave shape, it’s usually due to too much heat being introduced at the weld area. Setting the voltage too high makes the arc longer and injects more heat per unit length, which melts the base metal at the toe faster than the filler metal can fill the joint. The result is an undercut along the edge and a concave appearance because the weld metal doesn’t adequately fill the melted toe.

Other options don’t fit as well. Traveling too slowly changes heat input and bead size but doesn’t inherently cause an undercut at the toe. Using too little filler metal can lead to an underfilled or concave bead, but the classic undercut formation is driven by excessive heat input from high voltage. Excessively high shielding gas flow mainly affects porosity and arc stability rather than the weld toe geometry.