Forging is characterized by which of the following processes?

Forging is a manufacturing process that primarily involves shaping metal through the application of compressive forces. This process typically involves heating the metal to a plastic state and then using tools such as hammers or presses to deform it into the desired shape. The key aspect of forging is the force applied to manipulate the metal's structure, which results in improved strength and integrity of the material.

The focus on compressive forces distinguishes forging from other metalworking processes. While melting metal (as mentioned in the first choice) involves changing the physical state rather than shaping it, and pressing sheets of metal into specific shapes (the third choice) typically relates more to techniques like stamping or die-cutting, forging aims to enhance the characteristics of the material by working with its solid form. Additionally, reducing thickness by passing metal through machinery, like in rolling processes, is a different operation that does not involve the same level of compaction and shaping associated with forging. Therefore, the defining feature of the forging process is indeed its emphasis on shaping metal through compressive forces.