AWS Certified Welding Inspector — FundamentalsWelding ProcessesMedium
A CWI is observing a Gas Metal Arc Welding (GMAW) operation using a CO2 shielding gas. The welder is complaining about excessive spatter and an unstable arc. Given these symptoms, which of the following adjustments would be the most appropriate first step to resolve the issue, assuming the wire feed speed and voltage are initially set correctly for the desired transfer mode?
- AChange to an Argon-CO2 gas mixture.
- BIncrease the stick-out length.
- CDecrease the shielding gas flow rate.
- DIncrease the wire feed speed.
Show answer & explanationAnswer & explanation
Correct answer: A. Change to an Argon-CO2 gas mixture.
Pure CO2 shielding gas often results in a harsher arc and more spatter compared to Argon-CO2 mixtures. Switching to a mixture with Argon improves arc stability and reduces spatter due to Argon's lower ionization potential.
Why the other options are wrong
- B. Increasing stick-out length generally increases resistance heating of the wire, reducing current and potentially causing an even more unstable arc or lack of fusion, especially if already experiencing issues.
- C. Decreasing shielding gas flow rate could lead to porosity and lack of shielding, exacerbating arc instability.
- D. Increasing wire feed speed (without adjusting voltage) would likely increase current, potentially worsening spatter or causing burn-through.
GMAW Shielding Gas Effects
The choice of shielding gas in GMAW significantly impacts arc stability, penetration, spatter, and weld bead characteristics.
- CO2: Deep penetration, more spatter, harsher arc.
- Argon: Stable arc, good for spray transfer, less spatter.
- Argon-CO2 mixtures: Balance of penetration, arc stability, and reduced spatter.
Memory trick: Gas makes the arc smooth or rough, like a calm or stormy sea.