AWS Gas Metal Arc Welding (GMAW/MIG) 5 — Questions and Answers
Question 1: In pulsed GMAW (GMAW-P), what is the primary advantage over conventional spray transfer?
- Eliminates the need for shielding gas
- Allows spray-like transfer at lower average heat input, enabling out-of-position welding (Correct answer)
- Requires no wire feeder calibration
- Works only on carbon steel
Correct answer: Allows spray-like transfer at lower average heat input, enabling out-of-position welding
GMAW-P alternates between peak and background current to achieve spray transfer droplet detachment at a lower average heat input, making out-of-position welding on thinner materials feasible.
Question 2: When qualifying a GMAW procedure per AWS D1.1, changing from ER70S-3 to ER70S-6 wire with the same diameter typically:
- Requires a complete new procedure qualification test
- Is an essential variable change requiring re-qualification
- Is a non-essential variable and does not require re-qualification (Correct answer)
- Voids all previous impact test results only
Correct answer: Is a non-essential variable and does not require re-qualification
Under AWS D1.1, changing between filler metals of the same F-number and A-number classification is a non-essential variable that does not require re-qualification of the WPS.
Question 3: A GMAW gun's liner becomes kinked or contaminated. What is the most likely symptom during welding?
- Excessive spatter from high voltage
- Erratic wire feeding causing arc instability and burn-back (Correct answer)
- Increased deposition rate
- Reduced shielding gas pressure
Correct answer: Erratic wire feeding causing arc instability and burn-back
A damaged or contaminated liner creates friction that causes intermittent wire feeding, leading to arc instability, burn-back, and inconsistent bead quality.
Question 4: What is 'burn-back' in GMAW and what typically causes it?
- Weld metal burning through the base metal due to excessive heat
- The wire fusing to the contact tip when wire feed speed is too low relative to voltage (Correct answer)
- Porosity caused by inadequate shielding gas
- Undercut at the weld toe from excessive current
Correct answer: The wire fusing to the contact tip when wire feed speed is too low relative to voltage
Burn-back occurs when wire feed speed is insufficient relative to the arc voltage, causing the arc to climb up the wire and fuse it to the contact tip.
Question 5: Which shielding gas mixture is generally preferred for GMAW on austenitic stainless steel to minimize carbon pickup and maintain corrosion resistance?
- 100% CO2
- 75% Ar / 25% CO2
- 98% Ar / 2% O2 or 98% Ar / 2% CO2 (Correct answer)
- 100% helium
Correct answer: 98% Ar / 2% O2 or 98% Ar / 2% CO2
A tri-mix or binary argon gas with only 1–2% CO2 or O2 provides arc stability while minimizing carbon introduction that could sensitize the stainless steel HAZ.
Question 6: In a T-joint fillet weld made with GMAW, what is the correct electrode angle to ensure proper fusion to both the web and flange members?
- 10–15° from vertical (mostly pointing at the flange)
- 45° bisecting the joint angle, with 5–15° travel angle (Correct answer)
- Perpendicular (90°) to the web only
- Flat (0°) pointing straight down
Correct answer: 45° bisecting the joint angle, with 5–15° travel angle
For a T-joint fillet, the electrode should bisect the 90° joint angle at approximately 45° with a 5–15° drag or push travel angle to distribute heat evenly to both members.
Question 7: According to AWS standards, what is the minimum preheat temperature typically required for GMAW on A36 steel greater than 1-1/2 inches (38 mm) thick?
- No preheat required
- 150°F (65°C)
- 225°F (107°C) (Correct answer)
- 300°F (150°C)
Correct answer: 225°F (107°C)
AWS D1.1 Table 4.2 requires a minimum preheat of 225°F (107°C) for A36 steel with thickness over 1-1/2 inches to prevent hydrogen-induced cracking.
AWS Gas Metal Arc Welding (GMAW/MIG) 5
In pulsed GMAW (GMAW-P), what is the primary advantage over conventional spray transfer?