forge

To forge is to heat metal to a plastic state, then shape it by striking with a hammer or press. The heat makes the metal malleable without melting it; the blows compress the grain structure and move material into the required form. A smith heats stock in a furnace or forge fire until it glows red or yellow (typically 1100 to 1300 degrees Celsius for steel), then places it on an anvil and strikes with hand tools or powered equipment. The metal cools as work proceeds, so it must return to the fire repeatedly during a single piece.

Forging differs fundamentally from casting and machining. Cast metal is poured into a mold and has a coarse, brittle grain structure with internal voids. Machined parts are cut from solid stock, which wastes material and leaves surface stress. Forged metal is compressed and refined; grain flows along the shape of the finished part, making it stronger and tougher. Forgings can withstand shock loads that would fracture castings of the same size. This is why critical parts like connecting rods, crankshafts, and tool shanks are forged rather than cast.

The process divides into hand forging and power forging. Hand forging uses a hammer, tongs, and an anvil; the smith controls timing and placement of each blow. Power forging uses a drop hammer or hydraulic press to deliver predetermined force. Drop hammers fall from a height (often 2 to 10 meters) and strike with impact; hydraulic presses apply steady squeezing force. Power methods are faster and more consistent for production runs, but hand forging offers precision and adaptability for one-off work and complex shapes.

Common faults and limits

Overheating causes grain growth and brittleness; the metal becomes soft and mushy and may crack when struck. Underheating leaves it stiff and difficult to shape; the hammer bounces rather than deforming the metal. Surface scaling (oxidation that flakes off) removes material and creates defects. Internal cracks and voids can form if cooling is too rapid or if the metal is worked when too cold. Forging cannot produce sharp internal corners or fine details; the metal must flow smoothly around the anvil or die.

The term derives from the Latin fabrica, meaning workshop or smithy. In English it became forge, the noun for the hearth and tool collection, then the verb for the act of shaping. Forge work remains a foundation of metalworking; even modern shops that rely on CNC machining and casting still use forging for high-stress parts and for straightening, bending, and local shaping during repair and modification.