456A TIG (GTAW - Gas Tungsten Arc Welding) 1

Question 1

What type of tungsten electrode is recommended for AC GTAW welding of aluminum?

Accepted Answer

Pure tungsten (EWP) or zirconiated tungsten (EWZr)

Answer

Pure tungsten (EWP) and zirconiated tungsten (EWZr) are recommended for AC GTAW because they form a rounded, balled tip under AC that provides stable arc characteristics and good cathodic cleaning on aluminum. Thoriated tungsten is used for DC welding and does not ball properly on AC.

Question 2

Why is DCEN (Direct Current Electrode Negative) used for most GTAW applications on steel and stainless steel?

Accepted Answer

DCEN concentrates about 70% of the arc heat at the workpiece, providing deep penetration while keeping the tungsten cool

Answer

With DCEN, electrons flow from the tungsten electrode to the workpiece. This concentrates approximately 70% of the arc heat at the workpiece (for deep penetration) and only 30% at the electrode (keeping the tungsten from overheating). This is opposite to DCEP, which cleans the surface but overheats the tungsten.

Question 3

What is the purpose of the 'high-frequency (HF) arc start' feature on a GTAW power source?

Accepted Answer

Initiates the arc without contact between tungsten and base metal, preventing tungsten contamination

Answer

High-frequency arc starting superimposes a high-voltage, high-frequency spark on the welding circuit that ionizes the shielding gas between the tungsten and workpiece, allowing arc initiation without contact. This prevents tungsten contamination from touching the base metal and maintains electrode tip geometry. HF is also used continuously in AC GTAW to re-strike the arc at each polarity reversal.

Question 4

What shielding gas is standard for GTAW welding of stainless steel?

Accepted Answer

100% Argon

Answer

100% Argon is the standard shielding gas for GTAW on stainless steel and most metals. It provides excellent arc stability, good oxide cleaning in AC mode, minimal reactivity with the weld pool, and good coverage at moderate flow rates. Helium or He/Ar mixtures are sometimes used for deeper penetration but are more expensive.

Question 5

What is 'tungsten inclusion' in GTAW and how is it caused?

Accepted Answer

Tungsten particles embedded in the weld metal; caused by the tungsten tip contacting the weld pool or being contaminated

Answer

Tungsten inclusion occurs when a piece of the tungsten electrode breaks off and becomes embedded in the weld metal. It is caused by: touching the tungsten to the weld pool, excessive current melting the tip, contamination of the tungsten by the base metal, or improper arc starting technique. Tungsten inclusions are rejectable defects and are highly visible on radiographic film.

Red Seal Welder 456A Practice Test

Red Seal Welder 456A Practice Test

456A TIG (GTAW - Gas Tungsten Arc Welding) 1