A welder is using an FCAW-G process with a 75/25 Ar/CO2 shielding gas on 10 mm (0.4 in) mild steel. They notice excessive spatter and an unstable arc, despite correct voltage and wire feed speed settings. The gas flow rate is set to 14 L/min (30 CFH). What is the most likely cause for these symptoms?

Question: A welder is using an FCAW-G process with a 75/25 Ar/CO2 shielding gas on 10 mm (0.4 in) mild steel. They notice excessive spatter and an unstable arc, despite correct voltage and wire feed speed settings. The gas flow rate is set to 14 L/min (30 CFH). What is the most likely cause for these symptoms?

Answer options:

• The wire stick-out is too short ✅ The polarity is set to DC- (DC Electrode Negative)
• The travel speed is too slow
• The welding gun nozzle is partially blocked

Correct answer: The polarity is set to DC- (DC Electrode Negative)

Explanation: FCAW, especially FCAW-G, typically requires DC+ (DCEP or DC Electrode Positive) polarity for proper arc characteristics, penetration, and smooth metal transfer. Using DC- would result in an unstable arc, excessive spatter, and poor penetration. Short stick-out typically leads to a hotter arc, not necessarily unstable, and slow travel speed would increase heat input, but not cause arc instability in this manner.