AWS Certified Welding Inspector — FundamentalsWelding ProcessesMedium
A CWI is reviewing a Weld Procedure Specification (WPS) for Gas Metal Arc Welding (GMAW) of a stainless steel component. The WPS specifies spray transfer mode and a shielding gas of 98% Argon / 2% Oxygen. What is the primary purpose of adding 2% Oxygen to the Argon shielding gas for GMAW spray transfer on stainless steel?
- ATo enhance penetration.
- BTo reduce spatter levels.
- CTo increase the welding speed.
- DTo improve arc stability and wetting action.
Show answer & explanationAnswer & explanation
Correct answer: D. To improve arc stability and wetting action.
Small additions of oxygen (typically 1-2%) to argon in GMAW on stainless steel significantly improve arc stability, help with bead wetting, and improve the appearance of the weld bead. It promotes a more fluid puddle and better fusion.
Why the other options are wrong
- A. Oxygen generally has a minor effect on penetration compared to other factors like voltage, current, and travel speed.
- B. Oxygen can sometimes slightly increase spatter compared to pure argon, though its benefits often outweigh this. CO2 is generally better for spatter reduction.
- C. While improved arc characteristics might indirectly allow for faster speeds, it's not the direct primary purpose of the oxygen addition.
GMAW Shielding Gas Additives (Oxygen)
Small amounts of oxygen added to argon in GMAW primarily enhance arc stability and wetting action for certain materials.
- Typically 1-2% oxygen in argon for stainless steel.
- Improves bead appearance and fusion.
- Helps overcome surface tension of molten metal.
Memory trick: Oxygen's a tiny helper, making arcs stable and welds wet.