456A MIG/FCAW (GMAW & Flux-Cored Arc Welding)

Question 1

What type of power source characteristic is used for GMAW (MIG) welding?

Accepted Answer

Constant voltage (CV)

Answer

GMAW uses a constant voltage (CV) power source. The arc self-regulates: if the arc shortens, current increases and melts the wire faster; if the arc lengthens, current decreases and the wire catches up. This maintains a stable arc length automatically with a constant wire feed speed.

Question 2

What is the function of the shielding gas in GMAW welding?

Accepted Answer

Protects the weld pool from atmospheric oxygen and nitrogen, affects arc characteristics and bead profile

Answer

Shielding gas in GMAW protects the molten weld pool and arc from atmospheric contamination (oxygen causes porosity and oxidation; nitrogen causes porosity and embrittlement). The gas type also affects arc stability, penetration profile, and spatter levels.

Question 3

Which shielding gas mixture is most commonly used for GMAW on carbon steel in Canada?

Accepted Answer

75% Argon / 25% CO2 (C25)

Answer

C25 (75% Ar / 25% CO2) is the most widely used shielding gas for carbon steel GMAW in Canada. It provides a good balance of arc stability, low spatter, good penetration, and bead appearance. Pure CO2 gives deeper penetration but more spatter; pure Ar is used for aluminum and some stainless applications.

Question 4

What is 'wire burnback' in GMAW and what causes it?

Accepted Answer

The wire fuses to the contact tip; caused by the wire feed stopping while the arc is still active

Answer

Burnback occurs when the wire feed slows or stops while the arc remains active, causing the wire to melt back and fuse to the contact tip. Causes include wire feed drive roll slippage, a kinked liner, or releasing the gun trigger too slowly. It requires contact tip replacement.

Question 5

In GMAW short-circuit transfer mode, what happens during the 'short circuit' phase of metal transfer?

Accepted Answer

The wire touches the weld pool, current surges, and surface tension pulls molten metal from the wire into the pool

Answer

In short-circuit transfer, the wire periodically contacts (shorts to) the weld pool, extinguishing the arc momentarily. Current surges, and a combination of surface tension and electromagnetic forces (pinch effect) detaches the molten droplet into the pool. The arc then re-establishes and the cycle repeats 20–200 times per second.

Red Seal Welder 456A Practice Test

Red Seal Welder 456A Practice Test

456A MIG/FCAW (GMAW & Flux-Cored Arc Welding)