WCL Welding Processes & Techniques 2 — Questions and Answers
Question 1: Which shielding gas mixture is most commonly used for MIG welding carbon steel in the US?
- 100% argon
- 75% argon / 25% CO2 (Correct answer)
- 100% CO2
- 50% helium / 50% argon
Correct answer: 75% argon / 25% CO2
A 75/25 argon/CO2 mix (C25) provides good arc stability and weld appearance for carbon steel MIG welding.
Question 2: What is the primary purpose of a backing bar (backing strip) in groove welding?
- To preheat the base metal
- To support the root pass and prevent burn-through (Correct answer)
- To increase travel speed
- To reduce distortion in the weld joint
Correct answer: To support the root pass and prevent burn-through
A backing bar supports the molten weld pool during the root pass to prevent burn-through and achieve full joint penetration.
Question 3: In GMAW, what does 'short-circuit transfer' mean?
- The wire melts before touching the base metal
- The wire contacts the puddle repeatedly, extinguishing and re-igniting the arc (Correct answer)
- The wire is fed in a pulsed pattern
- The arc voltage is set too high
Correct answer: The wire contacts the puddle repeatedly, extinguishing and re-igniting the arc
Short-circuit transfer occurs when the wire electrode contacts the weld puddle, short-circuits, and the arc re-ignites repeatedly at high frequency.
Question 4: Which welding process is best suited for welding thin-gauge aluminum sheet?
- SMAW
- FCAW
- GTAW (Correct answer)
- SAW
Correct answer: GTAW
GTAW (TIG) offers precise heat control and produces clean, high-quality welds ideal for thin aluminum sheet without contamination.
Question 5: What causes porosity in a weld bead?
- Excessive preheat temperature
- Contamination or inadequate shielding gas coverage (Correct answer)
- Too slow a travel speed
- Using an E7018 electrode
Correct answer: Contamination or inadequate shielding gas coverage
Porosity results from gas pockets trapped in the weld, commonly caused by moisture, oil, rust, or loss of shielding gas coverage.
Question 6: When welding in the vertical position (3G), what technique reduces sagging of the weld pool?
- Increasing heat input
- Using a weave or uphill progression with a slight pause at the toes (Correct answer)
- Switching to flat position
- Increasing wire feed speed significantly
Correct answer: Using a weave or uphill progression with a slight pause at the toes
Uphill progression with a slight pause at the weld toes allows the pool to solidify enough to resist gravity-induced sagging.
Question 7: What does 'interpass temperature' refer to in multi-pass welding?
- The temperature at which filler metal melts
- The maximum temperature of the weld joint before depositing the next pass (Correct answer)
- The preheat temperature for the first pass
- The temperature of the shielding gas
Correct answer: The maximum temperature of the weld joint before depositing the next pass
Interpass temperature is the maximum allowable temperature of the weld joint between passes to control heat input and prevent metallurgical damage.
WCL Welding Processes & Techniques 2
Which shielding gas mixture is most commonly used for MIG welding carbon steel in the US?