Arc Welding Fundamentals Questions and Answers

Answer: A

The three elements are current, voltage and speed of travel.

These are the three variables in the heat input of an arc weld, the energy delivered per unit length of weld:

\[ \text{heat input} = \frac{V \times I}{\text{travel speed}} \]

Too much heat input burns through or distorts the work; too little gives poor fusion. Controlling current, voltage and travel speed controls the weld.

Arc length is not a separate element: the arc voltage rises and falls with the arc length, so the two describe the same variable. Every option that lists arc length alongside voltage, or in place of one of the three, is therefore wrong.

Answer: B

In reverse polarity, the electrode holder is connected to the positive and the work to the negative.

In DC arc welding, 'straight polarity' (DCEN) makes the electrode negative and the work positive. Reverse polarity (DCEP) swaps them, so the electrode becomes positive. More heat is released at the positive side, so reverse polarity puts more heat into the electrode and less into the work, which suits thin sheet and many coated electrodes.

The first option describes straight polarity. The 'earthed' options are not polarity arrangements at all: in DC welding one terminal goes to the holder and the other to the work.

Answer: C

The keyed answer is width of weld to depth.

In welding practice the shape of a fusion bead is described by comparing its width with the depth to which it penetrates the base metal. Welding institutes quote this as a width-to-depth ratio, the weld form factor, and warn that a bead much deeper than it is wide (a ratio below about 1 : 1.2) is prone to centre-line cracking. The paper follows that convention and keys option C.

Depth to length and length to depth compare the bead with its run along the joint, which says nothing about how the bead is shaped. Depth to width is the same ratio written the other way up; the sources are not consistent about which way round it is quoted, but the key takes width over depth, so C is the answer to give here.

Answer: B

The keyed answer is welding with light coated electrodes.

With straight polarity the electrode is negative and the work is positive, so more of the arc heat goes into the work and the electrode melts more slowly. In the trade-school convention this paper follows, bare and lightly coated electrodes are run on straight polarity, while heavy coatings are paired with reverse polarity.

Heavy and super heavy coated electrodes, and sheet metal work where deep penetration would burn through, are the cases the convention assigns to the other arrangement. Polarity in practice depends on the electrode class and the maker's data sheet, so this item is a textbook rule rather than a universal one.

Answer: A

The arc length should be about equal to the diameter of the electrode (d).

A normal arc is roughly as long as the core wire of the electrode is thick; with a 3.15 mm electrode, for example, the arc should be about 3 mm. At that length the arc is stable, the metal transfers cleanly and the shielding from the coating is effective.

An arc of 1.5d, 2d or 3d is a long arc: the voltage rises, the arc wanders, spatter increases, penetration falls and air reaches the molten metal, giving porosity. So the longer options are wrong.