The mode of deformation is tangential compression. Because forging stock may assume complex shapes, it is rare that only a single die impression is needed. Gains in productivity, die life, and forging quality often outweigh the fact that preforming adds an operation and attendant costs. Forging in one final die impression may be practical for extremely small part runs. Since bending of larger parts requires a machine of long stroke, special mechanical or hydraulic presses are often necessary.
Simple shapes can be bent in one operation, but more complex contours take successive steps.
If complex shapes are to be formed in a single operation, the tool must contain moving elements. After deformation, forged parts may undergo further metalworking. Flash is removed, punched holes may be needed, and improved surface finish or closer dimensional accuracy may be desired. Occasionally, especially with crack-sensitive alloys, this may be done by grinding, milling, sawing, or flame cutting. Coining is usually done on surfaces parallel to the parting line, while ironing is typified by the forcing of a cup-shaped component through a ring to size on outer diameter.