Welding Processes and Equipment
This domain tests whether you can match an arc process to a joint, thickness, position and production rate, and whether you understand the electrical and thermal behaviour behind that choice.
Power-source characteristics
Drooping (constant-current) sources suit manual processes where the welder varies arc length: SMAW, GTAW. Flat (constant-voltage) sources with self-regulating wire feed suit GMAW, FCAW and SAW, where arc length is controlled by wire-feed speed and voltage. Arc efficiency k converts electrical energy into heat in the workpiece: roughly 0.6 for GTAW, 0.8 for SMAW/GMAW/FCAW, close to 1.0 for SAW because the flux blanket retains heat.
Selection drivers
Thickness and joint access, position, material cleanliness, deposition rate, duty cycle and cost. SAW gives very high deposition but is limited to flat/horizontal and high heat input. GTAW gives the cleanest root and best control at low current. FCAW gives high productivity out of position. Equipment items that examiners expect you to know: wire feeders, shielding-gas flowmeters, torches, return clamps, calibration of meters, and interlock/safety devices.
Worked example
A power source is rated 300 A at 60% duty cycle. What duty applies at 400 A? Heating scales with I squared, so allowable duty = 60 × (300/400)² = 33.8%. Reasoning: the thermal limit of the set is fixed, so doubling current squared roughly halves allowable duty. At 400 A the arc must be on for no more than about one third of a 10-minute period (≈3.4 min), or a larger machine must be used. Duty cycle is a thermal rating, not the fraction of a shift spent welding.
Traps
Confusing duty cycle (thermal limit of the equipment) with operating factor (arc-on time as a fraction of paid time). Assuming SAW has 0.8 arc efficiency. Forgetting that constant-voltage behaviour depends on wire-feed speed matching burn-off rate.