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Heavy Duty Equipment Technician Red Seal Exam Prep · Question

A Heavy Duty Equipment Technician is setting up a Gas Metal Arc Welding (GMAW) machine for welding 6 mm thick mild steel, specifically for a fillet weld in the horizontal position. Which shielding gas mixture is generally recommended for optimal results, considering good penetration and minimal spatter?

For GMAW on mild steel, a mixture of 75% Argon and 25% Carbon Dioxide (CO2) is a very common and effective choice. The argon provides a stable arc and good bead

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Question: A Heavy Duty Equipment Technician is setting up a Gas Metal Arc Welding (GMAW) machine for welding 6 mm thick mild steel, specifically for a fillet weld in the horizontal position. Which shielding gas mixture is generally recommended for optimal results, considering good penetration and minimal spatter?

Answer options:

  • 100% Argon ✅ 75% Argon / 25% Carbon Dioxide (CO2)
  • 100% Carbon Dioxide (CO2)
  • 98% Argon / 2% Oxygen

Correct answer: 75% Argon / 25% Carbon Dioxide (CO2)

Explanation: For GMAW on mild steel, a mixture of 75% Argon and 25% Carbon Dioxide (CO2) is a very common and effective choice. The argon provides a stable arc and good bead appearance, while the CO2 adds penetration and helps to reduce spatter. 100% Argon is primarily for aluminum; 100% CO2 provides good penetration but higher spatter; 98% Argon / 2% Oxygen is more common for spray transfer welding on stainless steel.

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