Welding Processes and Equipment
Core Concepts
You must compare SMAW, GMAW (short-circuit, globular, spray, pulsed), FCAW (self-shielded vs. gas-shielded), GTAW (AC vs. DCEN vs. DCEP), SAW, and resistance welding by their electrode, shielding, current type, deposition rate, and typical applications. Know power-source characteristics: constant-current (drooping) for SMAW and GTAW, constant-voltage for GMAW and FCAW, and the volt-ampere curve shape. Understand duty cycle and how to derate amperage, polarity effects (DCEP deeper penetration in GMAW; DCEN for GTAW), and gas flow rates. Equipment knowledge includes wire feeders, regulators, flowmeters, torches, and the difference between transformer, inverter, and engine-driven machines.
Traps
Frequent distractors swap polarity effects or confuse constant-voltage with constant-current. Duty cycle questions often hide a derating calculation: a 60% duty-cycle machine at 200 A cannot run 200 A continuously. Self-shielded FCAW needs no external gas - a common trick. Remember AC GTAW is used for aluminum to combine cleaning and penetration.
Worked Example / Rule of Thumb
Duty-cycle derating: if a machine is rated 200 A at 60%, the allowable current at 100% duty is roughly I = 200 × √(0.60/1.00) ≈ 155 A. Rule of thumb: constant-current for stick and TIG, constant-voltage for wire-feed processes.