Gas Metal Arc Welding (GMAW/MIG) Flashcards

What metal transfer mode is used in GMAW short-circuit transfer?

Answer: The wire physically touches and short-circuits into the weld pool at low voltage

In short-circuit transfer (SCT), the wire tip contacts the molten pool, causing a short circuit; the current surges, melts the wire tip, and breaks the short — repeating 20–200 times per second at low voltage.

In GMAW spray transfer, what gas mixture is most commonly used for carbon steel?

Answer: Ar/CO2 blend (typically 75-95% Ar)

Spray transfer requires a high-argon shielding gas (typically 75–95% Ar with 5–25% CO2) to maintain the stable axial spray arc; 100% CO2 doesn't support true spray transfer.

The 'burnback' setting on a GMAW welding machine controls:

Answer: The rate at which the wire retracts after the arc extinguishes

Burnback (also called burn-back time or retract) is the brief delay between wire feed stopping and the power source shutting off, which burns back the wire to prevent it from freezing in the puddle.

Globular transfer in GMAW is characterized by:

Answer: Large, irregular droplets that fall off the wire due to gravity — high spatter

Globular transfer produces droplets larger than the electrode diameter that detach irregularly due to gravity, resulting in high spatter levels, and is generally avoided in production welding.

What is the purpose of the inductance setting on a GMAW CV power source?

Answer: Smooths the arc by controlling the rate of current rise during short circuits

Inductance controls how quickly current rises during short-circuit events in GMAW. Higher inductance slows the current rise, producing a softer arc with less spatter and a flatter bead.

For GMAW on austenitic stainless steel, the recommended shielding gas is typically:

Answer: Ar/He/CO2 trimix or Ar/CO2 with ≤2% CO2

Stainless steel welding requires very low CO2 content (≤2%) or tri-mix (Ar/He/CO2) to minimize carbon pickup (sensitization) and carbide precipitation in the HAZ.