SkyDrill

Purpose of shielding gas in GMAW

Aviation Mechanic Airframe (AMA) practice question 3 of 20 on Metallic Structures. ACS element AM.II.A.K13 · difficulty: recall. Want to answer it in a timed quiz? Use the Aviation Mechanic Airframe (AMA) practice mode.

Question bank updated 2026-09-22

QUESTIONIn gas metal arc welding, what is the purpose of the gas that flows out around the wire electrode?

  1. ATo cool the wire electrode as it feeds
  2. BTo protect the puddle from oxygen
  3. CTo raise the current flowing in the arc
Show the answer and explanation

Correct answer: B. To protect the puddle from oxygen

  • A — incorrect The gas is described as a shield against oxygen; cooling the consumable wire is not its stated function.
  • B — correct The handbook states that an inert gas flows out around the wire to protect the puddle from oxygen.
  • C — incorrect Current comes from the power supply connected to the torch and the work, not from the shielding gas.

BACKGROUND

Gas metal arc welding, formerly called metal inert gas or MIG welding, is an improvement over stick welding in which an uncoated wire electrode is fed into and through the torch. An inert gas such as argon, helium, or carbon dioxide flows out around the wire to protect the puddle from oxygen, taking the place of the flux coating used in shielded metal arc welding. The power supply is connected to the torch and the work, and the arc supplies the intense heat that melts both the work and the electrode; low-voltage, high-current direct current is typically used. The same shielding principle appears in TIG welding, where argon or helium envelopes the arc to prevent oxides from forming in the molten puddle. Argon and helium are both colorless, odorless, tasteless, non-toxic inert gases, meaning they cannot combine with other elements.

STUDY TIP

Keep the shielding gases straight by process: argon, helium, or carbon dioxide for GMAW, and argon or helium for TIG, with argon preferred for manual titanium and magnesium work.

KEY POINTS

  • Shielding gas in GMAW keeps oxygen away from the molten puddle.
  • Argon, helium, or carbon dioxide may be used, replacing the flux of stick welding.
  • Inert gases cannot combine with other elements, which is what makes them suitable shields.

SOURCES

  • sources/ama-airframe/ch05.txt "Gas Metal Arc Welding (GMAW)"
  • sources/ama-airframe/ch05.txt "Welding Gases — Argon"
Practice the Aviation Mechanic Airframe (AMA) test →Timed 100-question exam, by ACS area, or review your misses. Free.
MORE ON METALLIC STRUCTURES

SkyDrill is not affiliated with the FAA. This is an original practice item based on FAA-H-8083-31B Aviation Maintenance Technician Handbook – Airframe, and 14 CFR part 43. Regulations and handbooks are revised; confirm details against the current edition.