Forging is mainly classified according to the forming method and deformation temperature. According to the forming method forging can be divided into two categories: forging and stamping; according to the deformation temperature forging can be divided into hot forging, cold forging, warm forging and isothermal forging.

Hot forging

Forging is carried out above the recrystallization temperature of the metal. Increasing the temperature can improve the plasticity of the metal, which is conducive to improving the intrinsic quality of the workpiece and making it less likely to crack. High temperature can also reduce the deformation resistance of the metal, reducing the tonnage of the forging machinery required. However, hot forging and pressing process, workpiece accuracy is poor, the surface is not smooth, forgings are easy to produce oxidation, decarburization and burn damage. When processing large, thick workpieces, high material strength, low plasticity (such as the roll bending of extra-thick plates, high-carbon steel bar drawing length, etc.), are used in hot forging. When the metal (such as lead, tin, zinc, copper, aluminum, etc.) has sufficient plasticity and deformation is not large (such as in most of the stamping process), or the total amount of deformation and the forging process used (such as extrusion, radial forging, etc.) is conducive to the plastic deformation of the metal, often do not use hot forging, but cold forging. In order to make a heating to complete as much forging workload, hot forging and pressing the beginning of the forging temperature and the final forging temperature between the temperature range should be as large as possible. But the beginning of the forging temperature is too high will cause the metal grain growth is too large and the formation of overheating phenomenon, will reduce the quality of forging parts. Temperature close to the melting point of the metal will occur between the crystal low melting point material melting and intergranular oxidation, the formation of overburning. Overburned blanks tend to break during forging. Generally used hot forging temperature: carbon steel 800 ~ 1250 ℃; alloy structural steel 850 ~ 1150 ℃; high-speed steel 900 ~ 1100 ℃; commonly used aluminum alloy 380 ~ 500 ℃; titanium alloy 850 ~ 1000 ℃; brass 700 ~ 900 ℃.

Cold forging

Is lower than the recrystallization temperature of the metal forging, usually referred to as cold forging pressure more specifically at room temperature forging, and will be higher than room temperature, but not more than the recrystallization temperature forging called temperature forging. The precision of warm forging and pressing is higher, the surface is brighter and the deformation resistance is not large.

The workpiece formed by cold forging and pressing at room temperature has high accuracy of shape and size, smooth surface, less processing procedures, and is easy to produce automatically. Many cold forging and cold stamping parts can be directly used as parts or products, and no longer need cutting processing. However, cold forging, because of the low plasticity of the metal, deformation is prone to cracking, deformation resistance, the need for large tonnage of forging machinery.

Warm forging and pressing

Will be higher than room temperature, but does not exceed the recrystallization temperature of the forging is called warm forging press. The metal is preheated, and the heating temperature is much lower than that of hot forging. The precision of warm forging is higher, and the surface is brighter and less resistant to deformation.

Isothermal forging

The temperature of the billet is kept constant during the whole forming process. Isothermal forging is used to take advantage of the high plasticity of certain metals at a constant temperature, or to obtain a specific structure and properties. Isothermal forging requires that the die and the billet be kept together at a constant temperature, is more expensive and is only used for special forging processes such as superplastic forming.