Die forging is the integral forming of metal in an approximately closed model, which is often used in mass forging production. Because the metal flows integrally in the die forging process, it needs a lot of equipment capacity. For example, the die forging of the six-crank crankshaft of Jiefang automobile engine requires a 12500 ton press. If the size is large, such as die forgings on an airplane, it needs a press of 30,000 tons or even 80,000 tons to achieve it.
Free forging is local deformation. Metal is gradually forged into the required shape through the upper and lower anvils and related accessories of the press, which is often used in the production of single piece, small batch and large forgings. Such as steam turbine rotors, large backup rollers, large marine crankshafts, pressure shells in nuclear power, evaporators, nozzle sections, etc. These heavy forgings cannot be produced by die forging, but only by free forging press.