Welding Processes and Equipment
Domain 1: Welding processes and equipment
This domain tests whether you can choose a process for a joint, material and production context and defend the equipment settings from first principles. Expect quantitative items on power-source characteristics, duty cycle, deposition rate, heat input and process efficiency.
Power sources and process families
SMAW and GTAW use constant-current (drooping) sources: a change in arc length changes voltage much more than current. GMAW and FCAW use constant-voltage sources and self-regulating wire feed. SAW combines high current with granular flux, giving high deposition and deep penetration, but it is restricted mainly to flat and horizontal positions. Selection depends on position, thickness, material, required quality and productivity.
Heat input
Arc energy is Q = (60 × U × I) / (1000 × v), with U in volts, I in amperes and v in mm/min; the result is kJ/mm. Thermal efficiency differs: roughly 0.9–0.95 for SAW, 0.8 for GMAW and 0.6–0.7 for GTAW. Net heat input is arc energy divided by efficiency.
Worked example
A GMAW procedure runs at 26 V, 220 A and 300 mm/min. Q = (60 × 26 × 220) / (1000 × 300) = 343,200 / 300,000 = 1.14 kJ/mm. If travel speed falls to 200 mm/min at the same settings, Q becomes 1.72 kJ/mm, a 50% increase, which may exceed the WPS limit and reduce HAZ toughness. The trap is to treat this arc energy as net heat input without dividing by efficiency.
Traps
Duty cycle is a 10-minute rating, not a production utilisation figure. A CV source is not appropriate for SMAW. Polarity changes penetration and hydrogen behaviour. Comparing processes on current alone ignores voltage and travel speed.