Forging is mainly classified by 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 performed above the recrystallization temperature of the metal. Increasing the temperature can improve the plasticity of the metal, which is beneficial to improve the internal quality of the workpiece and make it difficult to crack. High temperature can also reduce the deformation resistance of the metal and reduce the tonnage of the required forging machinery. However, there are many hot forging processes, the workpiece accuracy is poor, the surface is not smooth, and the forgings are prone to oxidation, decarburization and burning. When the workpiece is large and thick, the material is high and the plasticity is low (such as the roll bending of the extra thick plate, the stretching of the high carbon steel rod, etc.), hot forging is used. When the metal (such as lead, tin, zinc, copper, aluminum, etc.) has sufficient plasticity and deformation is not large (such as in most stamping processing), or the total amount of deformation is large and the forging process used (such as extrusion, Radial forging, etc.) is conducive to the plastic deformation of the metal, hot forging is often not used, and cold forging is used instead. In order to complete as much forging work as possible by one heating, the temperature range between the initial forging temperature and the final forging temperature of hot forging should be as large as possible. But the initial 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. When the temperature is close to the melting point of the metal, the melting of intergranular low melting point substances and intergranular oxidation will occur, forming overburning. Burned blanks tend to crumble during forging. The commonly used hot forging temperature is: 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

It is forged at a temperature lower than the recrystallization temperature of the metal. The cold forging usually refers to the forging at room temperature, and the forging at a temperature higher than room temperature but not exceeding the recrystallization temperature is called warm forging. The precision of warm forging is high, the surface is smooth and the deformation resistance is not great.

The workpiece formed by cold forging at room temperature has high shape and size accuracy, smooth surface, few processing procedures, and is convenient for automatic production. Many cold forging, cold stamping parts can be directly used as parts or products, and no longer need to cut. However, when cold forging, due to the low plasticity of the metal, it is easy to crack during deformation, and the deformation resistance is large, which requires large tonnage forging machinery.

warm forging

The forging at a temperature higher than normal temperature but not exceeding the recrystallization temperature is called warm forging. The metal is pre-heated and the heating temperature is much lower than that of hot forging. The precision of warm forging is high, the surface is smooth and the deformation resistance is not great.

isothermal forging

The blank temperature is maintained at a constant value throughout the forming process. Isothermal forging is to make full use of the high plasticity of certain metals at equal temperatures, or to obtain specific structures and properties. Isothermal forging needs to keep the mold and blank at a constant temperature, which is expensive and is only used for special forging processes, such as superplastic forming.