Which type of power source is preferred for GMAW and FCAW processes?

• A. Constant current power source
• B. Pulsed power source
• C. Constant voltage power source
• D. Variable resistance power source

Answer: (C)

For GMAW and FCAW, keeping the arc voltage essentially constant while the wire feed controls the current gives the most stable and controllable weld. A constant voltage power source sets the arc voltage, so changes in distance between the torch and the work or minor fluctuations don’t cause large swings in arc behavior. The current then automatically adjusts as you feed more or less wire, which means heat input and bead deposition stay predictable across a range of welding conditions. This stability supports consistent transfer modes (short-circuit, globular, or spray) and smoother beads with less spatter, making it the preferred setup for these processes.

A constant current source would let the current drift with arc length, leading to an unstable arc and poor control as you change standoff or workpiece geometry. A pulsed power source has its uses for certain materials or transfer modes to manage heat input, but it’s not considered the standard setup for routine GMAW and FCAW. Variable resistance power sources don’t provide the necessary arc stability and control these processes rely on.