Arc Welding Processes Questions and Answers

Answer: C

Flux-cored arc welding employs a continuously fed electrode and uses both an external gas source and a granular flux for protecting the weld pool in the key. The electrode is a tube filled with flux. Gas metal arc welding uses a continuously fed wire and an external gas, but no flux, plasma arc welding uses a tungsten electrode and a plasma gas, and electro gas welding is used for vertical joints with a separate gas shield.

The difference from gas metal arc welding is the flux core in the wire, which forms slag over the weld metal.

Answer: D

The bead cross-section will reduce by 50%.

With all other parameters fixed, the volume of filler deposited per unit time is constant. The bead area times the welding speed equals that deposition rate, so the cross-sectional area is inversely proportional to the travel speed:

\[ A_{2} = A_{1}\frac{v_{1}}{v_{2}} = \frac{A_{1}}{2} \]

The heat input per unit length (VI/v) also halves for the same reason. A 25% reduction would correspond to a speed increase of one third, and the bead cannot grow when the same metal is spread over a longer length.

Answer: C

The shaded weld is a fillet weld.

The figure shows a T-joint, one plate standing on another at right angles, with a triangular weld bead filling the corner between them. A weld of roughly triangular cross-section laid in the corner of a T, lap or corner joint is a fillet weld, the most common type.

A groove weld is laid in a prepared gap between the edges of the parts. Spot welds are small resistance-welded nuggets between overlapping sheets. A plug weld fills a hole in one plate to join it to the plate beneath. None of these forms a triangle in a corner.

Answer: C

The open circuit voltage is 95 V and the short circuit current 950 A.

A longer arc needs more voltage and so draws less current from a drooping source. The two operating points are:

\[ \begin{aligned} l = 5:\ V &= 45\ \text{V},\ I = 500\ \text{A} \\ l = 7:\ V &= 55\ \text{V},\ I = 400\ \text{A} \end{aligned} \]

A linear source characteristic through both points has slope \(-10/100 = -0.1\) V/A:

\[ \begin{aligned} V &= V_{oc} - 0.1I \\ 45 &= V_{oc} - 50 \Rightarrow V_{oc} = 95\ \text{V} \\ I_{sc} &= 95/0.1 = 950\ \text{A} \end{aligned} \]

Pairing the short arc with the low current instead gives a rising line that has no meaningful open circuit voltage, and 45 V is just the arc voltage at 5 mm. 75 V and 150 V do not pass through both operating points.

Answer: C

The most suitable electrode material is low alloy steel.

GMAW (MIG/MAG welding) uses a continuously fed consumable wire electrode, which melts and becomes the filler metal in the joint. For low alloy steels the wire is chosen to match the base metal's composition and strength, so a low alloy steel wire is used.

Tungsten is the non-consumable electrode of gas tungsten arc (TIG) welding, not GMAW. Copper is used for contact tips and resistance-welding electrodes, and cadmium has no use as a welding electrode; neither would give a sound steel weld.