456A GMAW MIG

Question 1

What are the two main modes of metal transfer in GMAW (MIG) welding?

Accepted Answer

Short-circuit (short arc) transfer and spray transfer — with globular and pulsed spray as additional modes

Answer

The primary GMAW transfer modes are: short-circuit (wire touches the puddle, metal transfers during short circuits — used for thin material and all positions) and spray transfer (fine droplets are propelled across the arc — used for thicker material in flat and horizontal positions). Globular and pulsed spray are intermediate and advanced modes.

Question 2

What shielding gas or gas mixture is most commonly used for GMAW welding of carbon steel?

Accepted Answer

75% argon / 25% CO₂ (C25) or 90% argon / 10% CO₂

Answer

The most common shielding gas mixture for GMAW on carbon steel is 75% argon / 25% CO₂ (often called C25). This mixture provides good arc stability, minimal spatter, good weld appearance, and adequate penetration. Pure CO₂ is cheaper and provides deeper penetration but produces more spatter. Higher argon ratios (90/10) give smoother transfer.

Question 3

What is wire feed speed (WFS) in GMAW and what does it control?

Accepted Answer

The rate at which the filler wire is fed to the arc; it directly controls the welding amperage in constant-voltage systems

Answer

Wire feed speed (WFS) is the rate (in m/min or in/min) at which the consumable electrode wire is fed from the spool through the gun to the arc. In constant-voltage (CV) GMAW systems, WFS is the primary control for welding current — increasing WFS increases amperage, and decreasing WFS decreases amperage.

Question 4

What is the function of the contact tip in a GMAW gun?

Accepted Answer

To transfer welding current to the wire and guide it precisely to the weld joint

Answer

The contact tip is a copper or copper-alloy tube inside the GMAW gun nozzle that serves two functions: it transfers welding current from the power cable to the moving wire electrode, and it guides the wire to maintain a consistent stick-out and arc location. Contact tips are consumable and must be replaced when worn.

Question 5

What is the correct contact-tip-to-work distance (CTWD) or stick-out for GMAW on carbon steel?

Accepted Answer

10 to 19 mm (3/8 to 3/4 in.)

Answer

The recommended CTWD for GMAW on carbon steel is typically 10 to 19 mm (3/8 to 3/4 inch). Too short a stick-out causes excessive spatter and can damage the contact tip. Too long a stick-out reduces shielding effectiveness, increases resistance (preheating the wire), and can cause irregular arc behaviour.

Red Seal Welder 456A Practice Test

Red Seal Welder 456A Practice Test

456A GMAW MIG