What process involves heating and shaping metal through plastic deformation?

The process that involves heating and shaping metal through plastic deformation is forging. In forging, metal is typically heated to increase its malleability and then shaped by applying compressive forces using a hammer or a die. This technique changes the metal's internal structure, improving its strength and toughness by refining the grain structure through the deformation process.

In contrast, casting involves pouring molten metal into a mold, where it solidifies into the desired shape, rather than reshaping it through deformation. Molding typically refers to processes that shape materials like plastics or certain types of metals but doesn't specifically refer to the heating and deformation method characteristic of forging. Welding is a joining process where two or more pieces of metal are fused together using heat; it doesn't involve the shaping or forming of the metal itself in the same way that forging does. Thus, forging is the correct answer due to its unique focus on the plastic deformation of heated metal to create durable and strong components.