What is the principal cause of undercut in welding?

• A. Excessive amperes
• B. Excessive volts
• C. Excessive travel speed
• D. Inadequate shielding gas

Answer: (A)

The principal cause of undercut in welding is excessive amperes. When the current (amperage) is too high, it can lead to melting of the base metal beyond the weld puddle, creating a groove along the edges of the weld joint. This excessive heat results in a high rate of melting that can exceed the width of the weld bead, ultimately causing the base metal to erode or “undercut” as it cools, leading to a weakened joint.

While issues like excessive voltage or travel speed can also influence weld quality, they tend to manifest in different ways such as porosity or insufficient penetration rather than the specific undercutting seen with high amperage. Inadequate shielding gas can contribute to other welding defects like oxidation or porosity but does not primarily cause undercutting. Therefore, focusing on controlling the amperage is crucial to prevent this defect.