is in the metal recrystallization temperature above the forging. Improving the temperature can improve the plasticity of the metal, which will improve the intrinsic quality of the workpiece and make it not easy to crack. The high temperature can also reduce the metal deformation resistance, reduce the required forging machinery tonnage. But hot forging process, workpiece accuracy is poor, the surface is not smooth, forging easy to produce oxidation, decarbonization and burn loss. When the workpiece is large, thick, the material strength is high, plastic low (such as the special thick plate roll, high carbon steel rod, etc.), are used hot forging. When metals (such as lead, tin, zinc, copper, aluminum, etc. have enough plastic and deformation is not large (such as in most stamping process), or the total deformation of the forging process (such as extrusion, radial forging, etc.) is beneficial to the plastic deformation of metal, often do not use hot forging, but instead of cold forging. The temperature interval between the forging temperature and the final forging temperature should be as large as possible in order to make the heating work as much as possible. However, the high starting temperature will cause the metal grains to grow too large and form overheating phenomenon, will reduce the quality of forging parts. When the temperature is close to the metal melting point, the melting of intergranular low melting point material and intergranular oxidation are formed. The burned blanks often shatter during forging. The hot forging temperature is generally used: carbon steel 800~1250℃, alloy structural steel 850~1150℃, high speed steel 900~1100℃, common aluminum alloy 380~500℃, titanium alloy 850~1000℃, brass 700~900℃.
is under the metal recrystallization temperature under the forging, usually said the cold forging more specifically in the room temperature of the forging, but will be higher than normal temperature, but not more than the recrystallization temperature under the forging called warm forging. The precision of warm forging is higher, the surface is more smooth and the deformation resistance is not big.
The workpiece with cold forging and forming at ambient temperature has high precision in shape and dimension, smooth surface, less processing procedure and convenient for automatic production. Many cold forging, cold stamping parts can be used directly as parts or products, and no longer need cutting processing. But cold, due to the low plasticity of metal, deformation prone to cracking, deformation resistance, need large-tonnage forging machinery.