Hot forging and cold forging

Forging is one of the oldest metal shaping processes known to man. The process of forging metal involves beating or hammering a workpiece over or into a die, template, or jig, forcing the metal to flow into the desired shape. Forging is generally divided into three process types based on the temperatures to which the metal is heated prior to forging. These are hot, warm, and cold forging, with hot and warm processes employing workpiece temperatures ranging from several hundred degrees to over 2,000° Fahrenheit. Cold forging, on the other hand, sees the working steel heated to no more than three-tenths of its recrystallization temperature.

Cold forging is one variation of the forging metal-shaping process that involves forming or shaping metal parts through a process of applying powerful, localized compressive forces. Cold forging is carried out with the metal generally kept at or slightly above room temperature with the temperature always maintained at or below three-tenths of the recrystallization temperature of the metal being shaped. The compressive forces involved in cold forging may be applied by hand with a hammer or by powered sources, such as dropforge machines. In most cases, the metal is forced into a die in the shape of the finished product or around open templates or jigs. Cold forging offers several distinct benefits over hot forging processes, which include better surface finish, improved dimensional stability, and lower production costs. Cold forging is defined as working a metal below its recrystallization temperature, but usually around room temperature. If the temperature is above 0.3 times the melting temperature (on an absolute scale) then it qualifies as warm forging.

Hot forging is defined as working a metal above its recrystallization temperature. The main advantage of hot forging is that as the metal is deformed the strain-hardening effects are negated by the recrystallization process.