Module 3: TIG GTAW Operation Assessment Quiz

Module: U6M3 - TIG GTAW Operation Duration: 25 minutes Passing Score: 70% Format: Multiple choice and scenario-based

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What is the purpose of the tungsten electrode in TIG welding?

To create and maintain the arc — it does not melt or become part of the weld

To provide filler metal to the weld pool

To ground the electrical circuit

To generate shielding gas through decomposition

Submit

Explanation: The tungsten electrode is non-consumable — its melting point (6,170°F / 3,410°C) is far above the temperatures needed to melt steel or aluminum. It provides the electrical pathway for the arc while remaining solid. Filler metal is added separately by hand via a filler rod.

What type of tungsten electrode is recommended for welding mild steel with DC?

2% Thoriated (red band) or 2% Lanthanated (blue band)

Pure tungsten (green band)

Zirconiated (brown band)

Any type works equally well on all materials

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Explanation: Thoriated (red) and Lanthanated (blue) tungsten electrodes provide excellent arc starting and stability on DC (used for steel and stainless). Pure tungsten (green) is used for AC welding of aluminum. Lanthanated is increasingly preferred over thoriated due to health concerns about thorium's low-level radioactivity during grinding.

How should a tungsten electrode be prepared (ground) for DC TIG welding of steel?

Ground to a sharp point with a taper length of 2-3 times the electrode diameter, with grinding marks running lengthwise

Left with a flat end — no grinding needed

Ground to a ball shape

Cut with wire cutters for a flat end

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Explanation: For DC welding, the tungsten is ground to a conical point. The taper affects arc focus: sharper point = narrower, more focused arc (better for thin material). Grinding marks must run lengthwise (along the electrode axis) to direct the arc straight down. Cross-grinding causes the arc to wander. Grind on a dedicated wheel (not one used for steel) to prevent contamination.

What is the correct polarity for TIG welding mild steel and stainless steel?

DCEN (DC Electrode Negative) — current flows from tungsten to workpiece

DCEP (DC Electrode Positive)

AC (Alternating Current)

Either polarity works for steel

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Explanation: DCEN concentrates approximately 70% of the heat at the workpiece and 30% at the electrode, providing good penetration while keeping the tungsten cool (extending its life). DCEP would put 70% of the heat on the tungsten, causing it to overheat and ball up. AC is used for aluminum (the EP half-cycle provides oxide cleaning).

What is the function of the foot pedal in TIG welding?

To control the welding amperage in real-time — press harder for more amps, release to reduce

To control the shielding gas flow rate

To start and stop the wire feed

To activate the cooling water for the torch

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Explanation: The foot pedal gives the TIG welder real-time amperage control. This is essential because different areas of a weld need different heat: more amps to establish the pool, steady amps during welding, and ramped-down amps at the end (crater fill) to prevent cracking. The foot pedal is what makes TIG welding so precise — and what makes it challenging.

When TIG welding, how should the filler rod be introduced to the weld pool?

Dip the rod into the leading edge of the weld pool at a low angle (15°-20° to the workpiece), then withdraw

Hold the rod in the arc continuously

Push the rod through the backside of the joint

Melt the rod on the surface ahead of the pool

Submit

Explanation: The filler rod is dipped into the front (leading edge) of the molten pool, where it melts and flows into the puddle. The dip-and-withdraw rhythm creates the characteristic stacked-dime appearance. The rod should be kept close to the pool (within the gas shield) but should NOT be held in the arc — this causes the rod to ball up, creates spatter, and contaminates the tungsten.

A student notices their tungsten electrode has a gray, contaminated tip. What is the most likely cause?

The tungsten touched the weld pool or the filler rod during welding

The shielding gas flow is too high

The amperage is too low

The base metal is too thick

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Explanation: Tungsten contamination occurs when the electrode touches the molten weld pool (picks up base metal) or when the filler rod touches the hot tungsten. The contaminated tungsten must be re-ground to a clean point — welding with a contaminated tip causes an erratic arc and introduces tungsten inclusions into the weld.

What is the purpose of post-flow (gas after the arc stops) in TIG welding?

To continue shielding the hot tungsten and weld pool with argon as they cool, preventing oxidation

To cool the inside of the torch

To purge moisture from the gas line for the next weld

Post-flow has no practical purpose

Submit

Explanation: After the arc stops, the tungsten and weld pool are still hot enough to oxidize in air. Post-flow continues the argon shield for 5-15 seconds (1 second per 10 amps is a common rule), allowing cooling below oxidation temperature. Without adequate post-flow, the tungsten discolors and degrades, and the weld crater oxidizes (turns gray/black).

When TIG welding aluminum, why is AC polarity required instead of DC?

The electrode-positive half of the AC cycle breaks up the aluminum oxide layer (cleaning action), which melts at 3,700°F — far above aluminum's melting point (1,220°F)

AC provides more heat for the higher melting point of aluminum

DC would melt the tungsten when welding aluminum

AC is required by electrical code for aluminum welding

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Explanation: Aluminum oxide (Al₂O₃) forms instantly on aluminum surfaces and melts at 3,700°F. Without removing it, the base aluminum underneath melts but the oxide shell prevents fusion. The DCEP half of the AC cycle (electrode positive) creates a "cleaning action" that disrupts the oxide layer. The DCEN half provides the heat for penetration. Modern inverter TIG machines allow AC balance adjustment to control the ratio of cleaning to penetration.

What is "arc length" in TIG welding and how should it be controlled?

The distance between the tungsten tip and the workpiece — it should be approximately equal to the electrode diameter

The total length of the weld bead

The length of the arc cable from the machine to the torch

The time the arc is maintained during one weld pass

Submit

Explanation: Arc length in TIG is the gap between the tungsten tip and the workpiece/weld pool. Ideal arc length ≈ tungsten diameter (e.g., 3/32" electrode → 3/32" arc gap). Too short risks contamination (tungsten touching pool). Too long causes a wide, unfocused arc with poor gas coverage. Consistent arc length is essential for bead quality.

What is a "gas lens" and when should it be used?

A screen/mesh inside the TIG cup that creates laminar gas flow, extending shielding coverage and allowing longer arc lengths

A magnifying lens built into the welding helmet for TIG precision

A filter that removes moisture from the shielding gas

A specialized lens for inspecting TIG welds

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Explanation: A gas lens replaces the standard collet body and uses a mesh screen to straighten the argon flow into smooth, laminar columns instead of turbulent jets. This extends effective gas coverage by 2-3× the distance, allowing the cup to be set back for better visibility and enabling longer electrode extension for reaching into tight joints.

A student's TIG weld on stainless steel shows rainbow discoloration (heat tint) on the backside of the joint. What does this indicate?

The backside was not shielded from the atmosphere — oxidation occurred, which weakens corrosion resistance

The weld was done correctly — rainbow colors indicate proper heat control

The wrong filler rod was used

The tungsten was contaminated

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Explanation: Heat tint (temper colors) on stainless steel indicates oxidation. While light straw color is often acceptable, dark blue/purple/rainbow colors indicate significant chromium depletion, reducing the stainless steel's corrosion resistance. For critical applications, a purge gas (argon) must be applied to the backside of the joint to prevent oxidation. The discolored area must be removed (ground or pickled) for corrosion-sensitive applications.

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Last Updated: 2026-03-19