Correct Response: D. Hot forging is a metal part manufacturing process involving the pounding of a heated piece of metal into a desired shape. A major advantage of this process is that, as the part is pounded into shape, the internal metal grains are deformed to become aligned along the contours of the part. This results in greater material strength. Therefore less material is required, and the resulting part is both stronger and lighter. Machining (A) involves the cutting away of metal from a blank, typically a rectangular block of metal. Since the metal is not deformed, there is no altering of the internal grain. Hence there are none of the associated improvements in strength and weight. Investment casting (B) and molding (C) involve the pouring of molten metal into a mold. The internal grain alignment resulting from these processes tends to be random, resulting in a weak, brittle part. This would not be appropriate for a high-stress application such as a connecting rod in an engine.
