456A MIG/FCAW (GMAW & Flux-Cored Arc Welding) 2 — Questions and Answers
Question 1: What is the difference between FCAW-S (self-shielded) and FCAW-G (gas-shielded) flux-cored welding?
- FCAW-S uses flux in the core to generate its own shielding; FCAW-G requires an external shielding gas in addition to the flux core (Correct answer)
- FCAW-G is used outdoors; FCAW-S requires a welding booth
- FCAW-S requires higher voltage than FCAW-G
- FCAW-G produces more slag than FCAW-S
Correct answer: FCAW-S uses flux in the core to generate its own shielding; FCAW-G requires an external shielding gas in addition to the flux core
FCAW-S electrodes contain flux ingredients that generate all necessary shielding gases and slag without external gas, making them ideal for outdoor/field welding where wind would disperse external shielding. FCAW-G electrodes use a combination of flux core and external shielding gas for better weld quality and lower fume generation.
Question 2: What is the travel angle and work angle convention for GMAW in the flat position?
- Work angle 90° to the joint; travel angle 5–15° drag (backhand) (Correct answer)
- Work angle 45°; travel angle 30° push
- Work angle 60°; travel angle 45° drag
- Both angles must be exactly 90°
Correct answer: Work angle 90° to the joint; travel angle 5–15° drag (backhand)
For flat position GMAW, the work angle is 90° perpendicular to the joint (or split equally for fillet welds at ~45°), and the travel angle is a 5–15° drag (backhand/trailing) angle pointing back toward the completed weld. This provides good visibility of the weld pool and proper penetration.
Question 3: What does 'wire stick-out' (contact tip-to-work distance) affect in GMAW?
- Current draw and deposition rate — longer stick-out reduces current and deposition rate (Correct answer)
- Shielding gas coverage and arc voltage only
- Wire feed speed setting at the machine
- Contact tip wear rate only
Correct answer: Current draw and deposition rate — longer stick-out reduces current and deposition rate
Wire stick-out (the distance from contact tip to workpiece) affects resistance heating of the wire. Longer stick-out increases resistance, preheats the wire, and reduces the actual welding current drawn for the same wire feed speed, lowering penetration and deposition rate. Shorter stick-out increases current and penetration.
Question 4: What is 'spatter' in GMAW and what is the primary cause when using C25 shielding gas?
- Small droplets of metal expelled from the arc; caused by incorrect voltage/amperage settings or contaminated base metal (Correct answer)
- Slag particles on the weld surface from the flux core
- Porosity visible on the weld surface
- Metal oxidation around the weld toes
Correct answer: Small droplets of metal expelled from the arc; caused by incorrect voltage/amperage settings or contaminated base metal
Spatter consists of small molten metal droplets expelled from the arc that solidify on the base metal or nozzle. In GMAW with C25, the primary causes are voltage too low or too high relative to wire feed speed, arc instability from contamination, or improper inductance settings. Spatter is non-fused and does not contribute to weld strength.
Question 5: Which GMAW transfer mode is recommended for welding out-of-position (vertical, overhead)?
- Short-circuit transfer (Correct answer)
- Spray transfer
- Globular transfer
- All transfer modes are equally suitable
Correct answer: Short-circuit transfer
Short-circuit transfer uses lower heat input and produces a smaller, more controllable weld pool that solidifies quickly, making it suitable for out-of-position welding. Spray transfer produces a large, fluid weld pool that is difficult to control in vertical or overhead positions. Pulse spray can also be used out of position.
Question 6: What is the purpose of the inductance setting on a GMAW power source?
- Controls the rate of current rise during short circuits, reducing spatter and smoothing bead appearance (Correct answer)
- Sets the maximum output voltage of the machine
- Controls wire feed speed independently of voltage
- Determines the duty cycle of the welding machine
Correct answer: Controls the rate of current rise during short circuits, reducing spatter and smoothing bead appearance
Inductance (measured in henries) controls how quickly current rises during the short-circuit phase. Higher inductance slows the current rise, reducing spatter and producing a flatter bead. Lower inductance allows faster current rise for more aggressive penetration but increases spatter. It is typically adjusted for the wire diameter and metal thickness.
456A MIG/FCAW (GMAW & Flux-Cored Arc Welding) 2
What is the difference between FCAW-S (self-shielded) and FCAW-G (gas-shielded) flux-cored welding?