How does wire diameter affect deposition rate and the required current in GMAW?

• A. A smaller diameter wire deposits less metal and uses lower current.
• B. A larger diameter wire yields higher deposition per pass and requires higher current.
• C. Wire diameter has no effect on deposition rate or current.
• D. A larger diameter wire deposits less metal and uses lower current.

Answer: (B)

In GMAW, how much metal ends up in the weld (the deposition rate) depends on how much wire is melted and transferred to the weld per unit time. A wire with a larger diameter has more metal per unit length, so if you feed it at the same rate, more metal can be melted and deposited each second. Melting more metal also needs more heat, which means higher arc current to maintain a stable arc and proper transfer of that larger amount of metal. So, a larger diameter wire delivers higher deposition per pass and requires higher current.

The other ideas don’t fit because changing diameter does affect deposition and heat input. A smaller diameter generally deposits less metal (and can use lower current, but not universally, depending on the target deposition rate), and saying a larger diameter deposits less metal or that diameter has no effect contradicts the basic relationship between wire cross-section, melt rate, and current.