Welding Processes and Equipment
Process families
Know the main arc processes and their characteristics: SMAW (stick), GMAW (MIG/MAG), FCAW, GTAW (TIG), SAW, and their typical applications. Be able to match process to material, position, thickness and productivity. Understand transfer modes in GMAW: short circuit, globular, spray, and pulsed, and how shielding gas and current affect them.
Power sources and characteristics
Distinguish constant-current (drooping) sources used for SMAW and GTAW from constant-voltage sources used for GMAW and FCAW. Know that CC holds current steady as arc length varies, while CV holds voltage steady so current varies with wire feed. Understand duty cycle: a 60% duty at 200 A means 6 minutes welding in 10 at that current; questions often ask for derating at higher current.
Equipment setup and care
Cover electrode holders, earth clamps, leads, regulators, flowmeters, wire feeders, torches, and gas supply. Know correct polarity (DCEN, DCEP, AC) and its effect on penetration and cleaning. Understand the roles of shielding gas composition and flow rate, and the consequences of too little (porosity) or too much (turbulence, porosity).
Traps
- Mixing up CC/CV with process.
- Assuming duty cycle is a time limit rather than a thermal rating at a stated current.
- Confusing electrode positive and negative effects on penetration.
- Forgetting that gas flow too high also causes porosity.
Rule of thumb
For duty cycle, use the square-root rule: allowable current scales as the square root of the duty ratio. Going from 60% to 35% duty allows roughly 0.76 times the current (√(35/60) ≈ 0.76).