AWS Gas Metal Arc Welding (GMAW/MIG) 4 — Questions and Answers
Question 1: In GMAW, what is the primary purpose of using a push angle (forehand) technique compared to a drag angle (backhand) technique?
- Produces deeper penetration and narrower bead
- Produces shallower penetration and wider, flatter bead (Correct answer)
- Increases wire feed speed automatically
- Reduces shielding gas consumption
Correct answer: Produces shallower penetration and wider, flatter bead
A push (forehand) angle directs heat forward, resulting in shallower penetration and a wider, flatter bead profile.
Question 2: Which GMAW transfer mode is characterized by the wire tip never actually touching the base metal, with metal crossing the arc as fine droplets?
- Short-circuit transfer
- Globular transfer
- Spray transfer (Correct answer)
- Pulsed spray transfer
Correct answer: Spray transfer
Spray transfer occurs above a critical current threshold where metal transfers as a fine axial spray across the arc without contact with the base metal.
Question 3: What condition causes 'cold lapping' (lack of fusion) at the toes of a GMAW weld?
- Excessive travel speed with insufficient heat input (Correct answer)
- Too slow a travel speed
- Excessive wire stick-out
- High shielding gas flow rate
Correct answer: Excessive travel speed with insufficient heat input
Cold lapping occurs when travel speed is too fast or heat input is too low, preventing the weld metal from properly fusing with the base material at the toes.
Question 4: When welding aluminum with GMAW, which polarity and shielding gas combination is standard practice?
- DCEN with 100% CO2
- DCEP with 100% argon (Correct answer)
- DCEP with 75% Ar/25% CO2
- DCEN with 100% argon
Correct answer: DCEP with 100% argon
DCEP (electrode positive) with 100% argon is standard for GMAW on aluminum because DCEP provides cathodic cleaning action that removes the oxide layer.
Question 5: A welder notices the weld bead has excessive spatter and an irregular, convex profile. Which parameter adjustment is most likely needed?
- Increase wire feed speed
- Decrease voltage
- Increase voltage (Correct answer)
- Decrease shielding gas flow
Correct answer: Increase voltage
Excessive spatter and a convex bead profile typically indicate voltage is too low; increasing voltage widens and flattens the bead while reducing spatter.
Question 6: What is the recommended contact tip-to-work distance (CTWD) for most standard GMAW applications?
- 1/4 to 1/2 inch (6–13 mm)
- 5/8 to 7/8 inch (16–22 mm) (Correct answer)
- 1 to 1-1/2 inches (25–38 mm)
- 1/16 to 1/8 inch (1.6–3.2 mm)
Correct answer: 5/8 to 7/8 inch (16–22 mm)
A CTWD of approximately 5/8 to 7/8 inch (16–22 mm) is typical for standard GMAW, balancing electrical stick-out resistance heating and arc stability.
Question 7: Which type of weld discontinuity is most associated with excessive moisture in GMAW shielding gas or on the base metal surface?
- Undercut
- Overlap
- Porosity (Correct answer)
- Incomplete fusion
Correct answer: Porosity
Moisture dissociates in the arc and releases hydrogen, which becomes trapped in the solidifying weld metal and causes porosity.
AWS Gas Metal Arc Welding (GMAW/MIG) 4
In GMAW, what is the primary purpose of using a push angle (forehand) technique compared to a drag angle (backhand) technique?