What is the purpose of shielding gas in GMAW and FCAW, and what can happen if coverage is inadequate?

• A. It protects the molten pool from air
• B. It increases cooling rate
• C. It improves arc stability
• D. It reduces shielding gas cost

Answer: (A)

Shielding gas provides a protective blanket around the arc and molten weld pool, keeping air—especially oxygen and moisture—from contacting the hot metal. This prevents oxidation and the formation of porosity, leading to a cleaner, stronger weld with proper metallurgy and bead shape. If coverage is inadequate, air can mix with the molten metal, causing porosity and contamination that weaken the weld, produce an uneven surface, and increase the risk of defects. The other options aren’t the primary purpose: shielding gas isn’t mainly to speed cooling, nor to guarantee arc stability, and shielding gas cost isn’t the intended function.