AWS Gas Tungsten Arc Welding (GTAW/TIG) Fundamentals 4 — Questions and Answers
Question 1: When welding aluminum with GTAW using AC power, what phenomenon helps produce a quality weld?
- Cathodic cleaning action removes the oxide layer (Correct answer)
- Anodic cleaning increases penetration depth
- High-frequency stabilization prevents arc blow
- Reverse polarity increases filler deposition rate
Correct answer: Cathodic cleaning action removes the oxide layer
AC current's electrode-positive half-cycle provides cathodic cleaning that blasts away the refractory aluminum oxide layer, enabling fusion.
Question 2: Which tungsten electrode type is most commonly recommended for welding aluminum with AC GTAW?
- 2% thoriated (red band)
- Pure tungsten (green band) (Correct answer)
- 2% ceriated (gray band)
- Lanthanated (gold band)
Correct answer: Pure tungsten (green band)
Pure tungsten forms a clean hemispherical ball on its tip under AC current, which is optimal for aluminum welding.
Question 3: What is the purpose of the high-frequency (HF) component in a GTAW power source?
- It increases amperage during welding
- It initiates the arc without contact and stabilizes AC arcs (Correct answer)
- It controls the shielding gas flow rate
- It preheats the base metal before welding
Correct answer: It initiates the arc without contact and stabilizes AC arcs
High-frequency current allows non-contact arc starting and continuously re-establishes the arc during the zero-crossing points of AC welding.
Question 4: In GTAW, what does 'walking the cup' technique involve?
- Moving the torch in a circular pattern without a gas cup
- Resting the ceramic cup on the workpiece and pivoting the torch forward (Correct answer)
- Rapidly alternating between forehand and backhand positions
- Dragging the tungsten tip along the joint for consistent arc length
Correct answer: Resting the ceramic cup on the workpiece and pivoting the torch forward
Walking the cup involves rocking the ceramic nozzle on the workpiece to maintain a consistent arc length and travel angle, often used in pipe welding.
Question 5: Which condition causes tungsten contamination in GTAW and results in a 'spitting' arc?
- Using argon shielding gas at too high a flow rate
- Touching the tungsten electrode to the weld puddle or filler metal (Correct answer)
- Welding with DCEN polarity on stainless steel
- Setting amperage below the minimum for the tungsten diameter
Correct answer: Touching the tungsten electrode to the weld puddle or filler metal
When tungsten contacts the molten puddle or filler rod, weld metal contaminates the electrode, causing an erratic, spitting arc and weld inclusions.
Question 6: What is the correct method to restore a contaminated pure tungsten electrode used for AC aluminum welding?
- Grind the tip to a point on a bench grinder
- Strike an arc on a copper block at high amperage to re-ball the tip
- Snap off the contaminated end and re-ball on a scrap piece of the base metal (Correct answer)
- Polish the tungsten with fine-grit emery cloth
Correct answer: Snap off the contaminated end and re-ball on a scrap piece of the base metal
Breaking off the contaminated portion and then striking an arc on scrap base metal allows the tungsten to re-form the clean hemispherical ball needed for AC welding.
Question 7: When GTAW welding titanium, what additional shielding measure beyond the standard gas cup is typically required?
- A water-cooled copper backing bar
- A trailing shield and back purge to protect hot metal from atmospheric contamination (Correct answer)
- Flux coating applied to the filler rod
- A preheat of at least 400°F (204°C)
Correct answer: A trailing shield and back purge to protect hot metal from atmospheric contamination
Titanium absorbs oxygen and nitrogen above ~800°F (427°C), so trailing shields and back purging with inert gas are essential to prevent embrittlement.
AWS Gas Tungsten Arc Welding (GTAW/TIG) Fundamentals 4
When welding aluminum with GTAW using AC power, what phenomenon helps produce a quality weld?