forging

Forging is the blacksmith's craft: you shape metal that is still solid by hammering or squeezing it, the way you would push a lump of clay into a form with your fists. Nothing melts. Instead the metal flows plastically under the blows, spreading and filling the shape you want. Because the metal was never liquid, forged parts avoid the porosity and coarse cast grains of a casting, which is why the parts that must not fail, like crankshafts, connecting rods, and hand-tool heads, are usually forged.

The force can come from a hammer (impact) or a press (slow squeeze), and the dies can be open (simple flat tools) or closed (a shaped cavity the metal is forced to fill). Two things happen inside the metal. First, the deformation breaks up and refines the grains, giving a fine, strong structure. Second, any inclusions and the grain structure get stretched and bent to follow the part outline, producing a grain flow that wraps around corners like the grain in a carved wooden chair leg, so cracks find no straight path to run along.

The upside is strength and reliability: a forged part is typically stronger and tougher than a cast one of the same alloy, with no internal voids. The honest caveat is that the aligned grain flow makes forgings anisotropic, meaning they are strongest along the flow and weaker across it, so the forging must be oriented so the flow lines follow the main load. Forging also needs expensive dies and high forces, so like die casting it favours higher volumes.