AWS Gas Tungsten Arc Welding (GTAW/TIG) 4 — Questions and Answers
Question 1: When welding aluminum with GTAW, which current type is typically used to achieve the cleaning action needed to break up the oxide layer?
- DCEN (direct current electrode negative)
- DCEP (direct current electrode positive)
- AC (alternating current) (Correct answer)
- High-frequency DC pulsed current
Correct answer: AC (alternating current)
AC current is used for aluminum GTAW because the electrode-positive half-cycle provides the cathodic cleaning action that breaks up the tenacious aluminum oxide layer.
Question 2: In GTAW, what is the primary purpose of the high-frequency (HF) arc starting feature?
- To increase heat input at the weld puddle
- To initiate the arc without touching the tungsten to the workpiece (Correct answer)
- To stabilize the shielding gas flow
- To preheat the base metal before welding
Correct answer: To initiate the arc without touching the tungsten to the workpiece
High-frequency arc starting allows the welder to establish an arc without contact, preventing tungsten contamination and workpiece damage.
Question 3: What condition is indicated when a GTAW weld bead shows excessive porosity on stainless steel?
- The arc length was too long
- Inadequate shielding gas coverage or contamination (Correct answer)
- The travel speed was too fast
- The tungsten diameter was too large
Correct answer: Inadequate shielding gas coverage or contamination
Porosity in stainless steel GTAW welds is most commonly caused by insufficient or contaminated shielding gas allowing atmospheric gases to enter the weld pool.
Question 4: Which tungsten electrode geometry is recommended for use with DC welding of steel and stainless steel?
- Balled tip
- Flat tip
- Pointed or truncated tip (Correct answer)
- Split tip
Correct answer: Pointed or truncated tip
A pointed or slightly truncated tungsten tip concentrates the arc for precise control and deep penetration when welding steel and stainless steel with DCEN.
Question 5: During GTAW, a welder notices the tungsten electrode turning black. What is the most likely cause?
- Excessive amperage
- Inadequate post-flow shielding gas (Correct answer)
- Too short an arc length
- Wrong filler metal alloy
Correct answer: Inadequate post-flow shielding gas
A blackened tungsten indicates oxidation caused by insufficient post-flow time, where the hot electrode is exposed to atmosphere before it cools sufficiently.
Question 6: What is the correct technique for adding filler metal in GTAW to avoid contaminating the tungsten electrode?
- Dip the filler rod directly into the arc
- Feed the filler rod at a low angle into the leading edge of the weld pool (Correct answer)
- Hold the filler rod perpendicular to the workpiece
- Touch the filler rod to the tungsten to transfer metal
Correct answer: Feed the filler rod at a low angle into the leading edge of the weld pool
The filler rod should be fed at a shallow angle into the front of the weld puddle, never entering the arc zone, to prevent tungsten contamination.
Question 7: Which shielding gas or mixture is commonly used when GTAW welding titanium to prevent embrittlement?
- Carbon dioxide (CO₂)
- Argon/CO₂ mix (75/25)
- Pure argon with trailing shields (Correct answer)
- Helium/argon mix at 50/50
Correct answer: Pure argon with trailing shields
Pure argon with trailing shields (and often back purging) is required for titanium GTAW because any oxygen or nitrogen contamination causes severe embrittlement.
AWS Gas Tungsten Arc Welding (GTAW/TIG) 4
When welding aluminum with GTAW, which current type is typically used to achieve the cleaning action needed to break up the oxide layer?