Gas Metal Arc Welding (MIG/MAG) and Flux Cored Arc Welding
What this domain tests
Transfer modes, shielding-gas selection, polarity, parameter relationships, deposition rate, and where FCAW beats GMAW.
Core rules
- Transfer modes. Short-circuiting (low current, CO2-rich gas, thin sheet, high spatter), globular (unstable, avoid), spray (argon-rich gas and current above the transition value, high deposition, low spatter), and pulsed spray which gives spray-like transfer at lower average current.
- Gases. CO2 gives deep penetration, good tolerance to mill scale but spatter; Ar + 15–25% CO2 is the general MAG mix; Ar + 2–3% O2 suits stainless; pure argon is used for aluminium.
- Polarity. GMAW runs DCEP. Gas-shielded flux-cored wires run DCEP; self-shielded wires run DCEN.
- Parameters. Wire-feed speed sets current; voltage sets arc length; inductance shapes short-circuit behaviour. Contact-tip-to-work distance 10–15 mm - increasing it raises resistance and current falls.
- FCAW. Higher deposition and penetration than solid wire, tolerant of wind when self-shielded, but produces slag that must be cleaned between passes.
Worked example
Deposition rate for 1.2 mm wire at 8 m/min with 92% efficiency, steel density 7.85 g/cm³. Wire area = π(0.06 cm)² = 0.01131 cm². Feed 8 m/min = 800 cm/min. Volume = 0.01131 × 800 = 9.05 cm³/min. Mass = 9.05 × 7.85 = 71.0 g/min. Deposited = 71.0 × 0.92 = 65.3 g/min. Doubling the wire-feed speed roughly doubles deposition, but only if the power source can supply the corresponding current without voltage collapse.
Traps
Using DCEN for solid-wire GMAW; assuming the same wire-feed speed gives the same current on a different machine; forgetting to clean slag between FCAW passes; judging MIG parameters by sound alone.