456A GTAW TIG

Question 1

What type of electrode is used in GTAW (TIG) welding and why is it called 'non-consumable'?

Accepted Answer

A tungsten electrode that creates the arc but does not melt into the weld pool; it is 'non-consumable' because it has a much higher melting point than the base metal

Answer

GTAW uses a tungsten electrode with a melting point of approximately 3,422°C, far higher than the melting point of steel (~1,500°C) or aluminium (~660°C). The tungsten creates and sustains the arc but does not melt into the weld pool. Filler metal, when needed, is added separately by hand-feeding a filler rod.

Question 2

What shielding gas is most commonly used in GTAW welding?

Accepted Answer

Pure argon (100%) or argon-helium mixtures

Answer

Pure argon is the most common shielding gas for GTAW because it provides excellent arc stability, good shielding effectiveness, and is suitable for most metals. Argon-helium mixtures are used when more heat input is needed (such as for thick aluminium), as helium increases arc energy. CO₂ and oxygen are never used in GTAW as they would destroy the tungsten electrode.

Question 3

What polarity is used for GTAW welding of carbon steel and stainless steel?

Accepted Answer

DCEN (DC Electrode Negative / Straight Polarity) for maximum penetration and minimal electrode heating

Answer

DCEN (straight polarity) is used for GTAW welding of steel, stainless steel, copper, and most metals. With DCEN, about two-thirds of the arc heat is directed at the workpiece (deeper penetration) and only one-third at the tungsten electrode (extending electrode life). AC is used for aluminium and magnesium to provide cathodic cleaning.

Question 4

Why is AC polarity used for GTAW welding of aluminium?

Accepted Answer

The electrode-positive (EP) half-cycle provides a cathodic cleaning action that breaks up the aluminium oxide layer, while the electrode-negative (EN) half-cycle provides penetration

Answer

AC alternates between DCEP and DCEN. The DCEP portion provides cathodic cleaning action that breaks up the tenacious aluminium oxide layer (which melts at 2,072°C — far higher than aluminium at 660°C). The DCEN portion provides penetration and reduces electrode heating. Modern inverters allow balance control between EP and EN portions.

Question 5

What is the purpose of post-flow gas in GTAW welding?

Accepted Answer

To continue shielding the cooling tungsten electrode and weld pool after the arc is extinguished, preventing oxidation

Answer

Post-flow continues the shielding gas flow after the arc is terminated, protecting both the hot tungsten electrode and the solidifying weld pool from atmospheric contamination. Without adequate post-flow (typically 1 second per 10 amps), the tungsten tip oxidizes and the weld crater can develop porosity or discolouration.

Red Seal Welder 456A Practice Test

Red Seal Welder 456A Practice Test

456A GTAW TIG