Gas Metal Arc Welding (GMAW/MIG) Flashcards

The AWS classification for a solid GMAW carbon steel electrode of 70 ksi tensile strength, suitable for welding with CO2 or mixed gas, is:

Answer: ER70S-6

ER70S-6: ER=electrode/rod, 70=70 ksi tensile, S=solid, 6=chemistry designation (higher Mn/Si for deoxidation, works on mill scale/rusty steel).

During GMAW, porosity at the weld start is most often caused by:

Answer: Insufficient preflow of shielding gas before arc initiation

Porosity at the weld start is typically caused by insufficient shielding gas preflow — air is still present in the gun nozzle when the arc initiates, contaminating the first portion of the weld.

In GMAW, what is the purpose of the 'run-in' (slow run-in) setting?

Answer: Feeds wire at reduced speed initially to improve arc starting

Run-in (slow start) feeds wire at a reduced speed initially when the arc fires, allowing a stable arc to establish before ramping to full wire feed speed, reducing the chance of stubbing.

A GMAW welder is welding in the 3G (vertical up) position. Which transfer mode should be used?

Answer: Short-circuit transfer

Short-circuit transfer is preferred for vertical up (3G) GMAW because its low heat input and fast-freezing weld pool resist sagging and allow proper sidewall fusion without molten metal running.

What is 'pulsed GMAW' (GMAW-P) and its primary advantage?

Answer: A process where current alternates rapidly between a high peak and low background current to enable spray transfer at lower average current

Pulsed GMAW alternates between a high peak current (to transfer one droplet per pulse) and a low background current (to maintain the arc), achieving spray transfer characteristics at a lower average heat input.

Contact tip-to-work distance (CTWD) for GMAW with 0.035-inch wire is typically:

Answer: 3/8 to 3/4 inch (10–19 mm)

For 0.035-inch GMAW wire, CTWD is typically 3/8 to 3/4 inch (10–19 mm), balancing adequate resistive preheating with stable arc characteristics.