WCL Welding Processes & Techniques 2

Question 1

Which shielding gas mixture is most commonly used for MIG welding carbon steel in the US?

Accepted Answer

75% argon / 25% CO2

Answer

A 75/25 argon/CO2 mix (C25) provides good arc stability and weld appearance for carbon steel MIG welding.

Question 2

What is the primary purpose of a backing bar (backing strip) in groove welding?

Accepted Answer

To support the root pass and prevent burn-through

Answer

A backing bar supports the molten weld pool during the root pass to prevent burn-through and achieve full joint penetration.

Question 3

In GMAW, what does 'short-circuit transfer' mean?

Accepted Answer

The wire contacts the puddle repeatedly, extinguishing and re-igniting the arc

Answer

Short-circuit transfer occurs when the wire electrode contacts the weld puddle, short-circuits, and the arc re-ignites repeatedly at high frequency.

Question 4

Which welding process is best suited for welding thin-gauge aluminum sheet?

Accepted Answer

GTAW

Answer

GTAW (TIG) offers precise heat control and produces clean, high-quality welds ideal for thin aluminum sheet without contamination.

Question 5

What causes porosity in a weld bead?

Accepted Answer

Contamination or inadequate shielding gas coverage

Answer

Porosity results from gas pockets trapped in the weld, commonly caused by moisture, oil, rust, or loss of shielding gas coverage.

(WCL) Welding Certification Los Angeles Practice Test