Forging is mainly classified according to forming method and deformation temperature. According to the forming method, forging can be divided into free forging, die forging, cold head forging, radial forging, roller forging, rotary forging and rolling. The deformation of blank under pressure is basically not subject to external restrictions, which is called free forging or open forging; The blank deformation of other forging methods is limited by the die, which is called closed die forging. Roll forging, rotary forging, rolling expansion and other forming tools have relative rotary movement with blank. Blank is pressed and formed point by point, line by line, also known as rotary forging.
According to the motion mode of the blank, forging can be divided into free forging, seesaw, extrusion, die forging, closed die forging and closed rolling. As there is no flash, the utilization rate of materials is very high. The finishing of complex forgings can be completed through one or several processes. Since there is no flash, the stress area of forgings is reduced, and the required load is also reduced. However, it should be noted that the blank cannot be completely restricted. Therefore, it is necessary to strictly control the blank volume, control the relative position of the forging die, measure the forging, and try to reduce the wear of the forging die. According to the motion mode of forging die, forging can be divided into swing forging, swing forging, rolling forging, wedge cross rolling, rolling ring and cross rolling. Swing, rotary forging and rolling ring can also be processed by fine forging. In order to improve the utilization rate of materials, rolling forging and cross wedge rolling can be used as the previous working procedure of slender materials. The same as the free forging, the rotary forging is also locally formed. The advantage is that compared with the forging size, the forging force can also be smaller. This forging method, including free forging, is difficult to ensure the accuracy because the material extends from the die surface to the free surface during the processing. Therefore, through the computer control of the direction of motion of the forging die and the rotary forging process, products with complex shape and high precision can be obtained, and the forging force is low. For example, many kinds of large turbine blades and other forgings are produced.
According to the deformation temperature, forging can be divided into hot forging, cold forging, warm forging and other temperature forging. Hot forging is carried out above the metal recrystallization temperature. Increasing the temperature can improve the plasticity of the metal, help to improve the internal quality of the workpiece, so that it is not easy to crack. High temperature can also reduce the deformation resistance of metal and the tonnage of forging machinery required. However, there are many hot forging processes, poor precision of the workpiece, and the surface is not smooth. The forgings are easy to be oxidized, decarburized, and burned. Cold forging is carried out below the metal recrystallization temperature. Cold forging usually refers to forging at room temperature, and it is called warm forging when the recrystallization temperature is not exceeded. Temperature forging has high precision, smooth surface and small deformation resistance. At room temperature, cold forging has high shape and size accuracy, smooth surface, less processing technology and easy automatic production.