456A GMAW MIG 2 — Questions and Answers
Question 1: What is the difference between push (forehand) and pull (backhand) gun angle in GMAW?
- There is no difference in technique
- Push angle tilts the gun in the direction of travel for less penetration and wider bead; pull angle tilts away from travel direction for deeper penetration and narrower bead (Correct answer)
- Push is for vertical; pull is for horizontal
- Push is for thick metal; pull is for thin metal
Correct answer: Push angle tilts the gun in the direction of travel for less penetration and wider bead; pull angle tilts away from travel direction for deeper penetration and narrower bead
Push (forehand) technique tilts the gun 10-15° in the direction of travel, placing the arc ahead of the puddle. This produces less penetration, a wider/flatter bead, and better visibility. Pull (backhand) tilts the gun 10-15° away from the direction of travel, producing deeper penetration, a narrower/more convex bead, and more spatter.
Question 2: What is the purpose of anti-spatter compound in GMAW welding?
- To improve the weld's mechanical properties
- To coat the nozzle, workpiece surface, and fixtures to prevent spatter from adhering, making cleanup easier (Correct answer)
- To reduce the shielding gas consumption
- To lubricate the wire feed mechanism
Correct answer: To coat the nozzle, workpiece surface, and fixtures to prevent spatter from adhering, making cleanup easier
Anti-spatter compound is applied to the inside of the gas nozzle, the workpiece surface near the weld, and fixtures/clamps. It prevents molten spatter from welding onto these surfaces, reducing cleanup time and preventing nozzle blockage. It must not be applied to the weld joint itself as it can contaminate the weld.
Question 3: What causes excessive spatter in GMAW welding?
- Using too much shielding gas
- Voltage set too high or too low for the wire feed speed, contaminated base metal, wrong shielding gas, excessive stick-out, or moisture on the wire (Correct answer)
- The room temperature is too high
- Using the correct parameters
Correct answer: Voltage set too high or too low for the wire feed speed, contaminated base metal, wrong shielding gas, excessive stick-out, or moisture on the wire
Excessive spatter results from: voltage too low (unstable short-circuit transfer), voltage too high (long arc, excessive droplet spray), contaminated or rusty base metal, wrong or depleted shielding gas, excessive stick-out, moisture on the wire or base metal, or worn/wrong-sized contact tip. Proper parameter balance minimizes spatter.
Question 4: What is pulsed GMAW and what are its advantages?
- A manual on-off technique by the welder
- An electronically controlled process that alternates between high peak current (for droplet transfer) and low background current (to maintain the arc), allowing spray-type transfer at lower average heat input (Correct answer)
- A process using pulsed shielding gas
- The same as short-circuit transfer
Correct answer: An electronically controlled process that alternates between high peak current (for droplet transfer) and low background current (to maintain the arc), allowing spray-type transfer at lower average heat input
Pulsed GMAW uses a power source that rapidly switches between high peak current (which detaches a single droplet per pulse in a spray-like manner) and low background current (which maintains the arc without metal transfer). This provides the quality of spray transfer with lower average heat input, enabling use on thinner materials and in all positions.
Question 5: What is the correct procedure for setting up a GMAW machine for a new welding job?
- Just turn it on and start welding
- Select correct wire size and type, install matching drive rolls and contact tip, set gas type and flow rate, adjust wire feed speed and voltage per the manufacturer's chart, and make test welds (Correct answer)
- Only adjust the voltage
- Only change the wire spool
Correct answer: Select correct wire size and type, install matching drive rolls and contact tip, set gas type and flow rate, adjust wire feed speed and voltage per the manufacturer's chart, and make test welds
Proper GMAW setup includes: (1) selecting the correct wire type and diameter for the application, (2) installing matching drive rolls, liner, and contact tip, (3) selecting the correct shielding gas and setting the flow rate (typically 15-20 L/min), (4) setting wire feed speed and voltage using the manufacturer's parameter chart, (5) adjusting stick-out, and (6) making test welds to fine-tune.
Question 6: In GMAW, what does a constant voltage (CV) power source do differently from a constant current (CC) source?
- CV provides constant amperage; CC provides constant voltage
- CV maintains a set voltage and allows amperage to vary with arc length changes (self-regulating); CC maintains set amperage and allows voltage to vary — GMAW uses CV (Correct answer)
- There is no difference for GMAW
- CV is for AC only; CC is for DC only
Correct answer: CV maintains a set voltage and allows amperage to vary with arc length changes (self-regulating); CC maintains set amperage and allows voltage to vary — GMAW uses CV
A CV power source maintains a relatively constant output voltage while allowing the amperage to fluctuate in response to changes in arc length. This creates a self-regulating arc: if stick-out decreases (shorter arc), current increases, melting wire faster to restore the arc length. This self-regulation is essential for the continuous wire-feed GMAW process.
456A GMAW MIG 2
What is the difference between push (forehand) and pull (backhand) gun angle in GMAW?