AWS Welding Processes 2 — Questions and Answers
Question 1: In GMAW (MIG welding), what does the term 'short-circuit transfer' describe?
- The wire melts and transfers droplets across the arc without touching the base metal
- The wire electrode periodically contacts the weld pool, causing the arc to extinguish and re-ignite (Correct answer)
- Electrons flow from the electrode to the base metal in a straight path
- The shielding gas short-circuits and stops protecting the weld pool
Correct answer: The wire electrode periodically contacts the weld pool, causing the arc to extinguish and re-ignite
Short-circuit transfer occurs when the wire electrode touches the molten pool, extinguishing the arc momentarily before re-igniting as the wire burns back.
Question 2: Which shielding gas is most commonly used for GMAW of carbon steel in the US?
- 100% argon
- 100% helium
- 75% argon / 25% CO₂ (Correct answer)
- 50% argon / 50% oxygen
Correct answer: 75% argon / 25% CO₂
A 75% Ar / 25% CO₂ mixture (C25) is the most widely used shielding gas for GMAW on carbon steel, providing good arc stability and penetration.
Question 3: What is the primary advantage of the flux-cored arc welding (FCAW) process over solid-wire GMAW?
- Lower fume generation
- Higher deposition rates and better performance in outdoor/windy conditions (Correct answer)
- Eliminates the need for any shielding gas
- Produces no slag, requiring less post-weld cleanup
Correct answer: Higher deposition rates and better performance in outdoor/windy conditions
FCAW provides higher deposition rates than solid-wire GMAW and, with self-shielded variants, can be used outdoors where wind would disrupt external shielding gas coverage.
Question 4: During GTAW (TIG welding), what is the purpose of the high-frequency (HF) start?
- To preheat the base metal before welding begins
- To initiate the arc without the tungsten electrode touching the workpiece (Correct answer)
- To clean the oxide layer from the filler wire
- To increase amperage during the welding pass
Correct answer: To initiate the arc without the tungsten electrode touching the workpiece
HF start ionizes the shielding gas to initiate the arc while the tungsten is still held away from the base metal, preventing tungsten contamination.
Question 5: In submerged arc welding (SAW), what covers the arc and molten metal during welding?
- An inert gas blanket of argon and helium
- A granular flux that completely submerges the arc (Correct answer)
- A flux-cored wire that burns internally
- A ceramic backing tape applied under the joint
Correct answer: A granular flux that completely submerges the arc
SAW uses a granular flux that covers and submerges the arc, protecting the weld metal, reducing spatter, and allowing very high deposition rates.
Question 6: Which welding process is best suited for joining thin sheet metal (under 1/8 inch) with minimal distortion?
- Submerged arc welding (SAW)
- Shielded metal arc welding (SMAW)
- Gas tungsten arc welding (GTAW) (Correct answer)
- Electroslag welding (ESW)
Correct answer: Gas tungsten arc welding (GTAW)
GTAW provides precise heat control and low heat input, making it ideal for thin materials where distortion and burn-through must be minimized.
Question 7: What is 'spray transfer' in GMAW and at what current level does it typically occur?
- Low current mode where droplets fall into the puddle under gravity
- A high-current, high-voltage mode where fine droplets are propelled axially across the arc (Correct answer)
- Transfer that occurs only with flux-cored wire above 150 amps
- A pulsed mode used exclusively for aluminum welding below 100 amps
Correct answer: A high-current, high-voltage mode where fine droplets are propelled axially across the arc
Spray transfer occurs above a threshold current (the transition current) where fine droplets are propelled rapidly and axially across the arc, producing high deposition rates and a smooth bead.
AWS Welding Processes 2
In GMAW (MIG welding), what does the term 'short-circuit transfer' describe?