Drop forging is a metal shaping process in which a heated work piece is formed by rapid closing of a punch and die forcing the work piece to conform to a die cavity. A work piece may be forged by a series of punch and die operations (or by several cavities in the same die) to gradually change its shape. Drop forging is also called impression die or closed die forging, or rot forging. The advantage of forging is that it improves the strength of the metal by aligning and stretching the grain structure. A forged part will normally be stronger than a casting or a machined piece. Information provided is from Manufacturing Processes Reference Guide by Robert H. Todd, Dell K. Allen, and Leo Alting.--1st ed. Published by Industrial Press Inc., 1994.