Welding processes and equipment
This domain examines how fusion processes are chosen, how power sources behave and how equipment ratings constrain real welding. The IWE candidate is expected to reason from arc physics and duty cycle to process suitability, not merely list process acronyms.
Process families and selection
Arc processes dominate industrial fabrication: SMAW for site and root work, GTAW for precision and reactive metals, GMAW/FCAW for semi-automatic productivity, SAW for flat high-deposition butt and fillet welds. Selection balances thickness, position, joint access, required quality (EN ISO 5817 level), deposition rate and automation potential.
Power source characteristics
SMAW and GTAW use drooping (constant-current) sources: arc-length variation changes voltage far more than current. GMAW uses a flat (constant-voltage) characteristic so that wire-feed speed sets current through self-regulation. Duty cycle is rated over a 10-minute period at 40 °C ambient.
Worked example: duty cycle
A source is rated 350 A at 60% duty cycle. The permissible continuous current at 100% follows the thermal limit I²t = constant: I₁₀₀ = 350 × √(60/100) = 350 × 0.775 ≈ 271 A. Linear scaling (350 × 0.6 = 210 A) is wrong because heating depends on current squared.
Traps that cost marks
- Applying duty cycle linearly instead of by square root.
- Claiming GMAW is constant current; wire-feed speed, not voltage setting, controls current.
- Ignoring process efficiency when comparing energy use: SMAW ≈ 0.7, GTAW ≈ 0.6, SAW ≈ 0.9.
- Forgetting that SAW is essentially limited to flat or horizontal-vertical positions and needs flux handling and recovery.