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2021
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What are the classifications of forging?
Author:
Forging is mainly classified by forming method and deformation temperature. According to the forming way forging can be divided into forging and stamping two categories; According to deformation temperature forging can be divided into hot forging, cold forging, warm forging and isothermal forging.
Hot forging
It is forged above the recrystallization temperature of the metal. Increasing the temperature can improve the plasticity of the metal, is conducive to improving 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 reduce the required tonnage of forging machinery. But the hot forging process, the workpiece accuracy is poor, the surface is not smooth, forging is easy to produce oxidation, decarburization and burning. When the workpiece is large and thick, the material strength is high and the plasticity is low (such as the rolling bending of the extra-thick plate, the drawing length of the high carbon steel rod, etc.), the hot forging is used. When the metal (such as lead, tin, zinc, copper, aluminum, etc.) has enough plasticity and deformation is not large (such as in most stamping processing), or the total 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, and use cold forging. In order to complete as much forging work as possible with one heating, the temperature interval between the initial forging temperature and the final forging temperature of hot forging should be as large as possible. However, excessive initial forging temperature will cause excessive growth of metal grains and lead to overheating, which will reduce the quality of forging parts. When the temperature is close to the melting point of metal, the melting and oxidation of intergranular materials with low melting point will occur, resulting in overfiring. Overburned billets often crumble during forging. Generally 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
Is lower than the metal recrystallization temperature forging, usually referred to as cold forging mainly refers to the forging at room temperature, and will be higher than room temperature, but not more than the recrystallization temperature of the forging is called warm forging. The precision of warm forging is higher, the surface is smooth and the deformation resistance is small.
The workpiece formed by cold forging and pressing under normal temperature has high precision of shape and size, smooth surface, fewer processing procedures and easy to automate production. Many cold forging and cold stamping parts can be used directly as parts or products without cutting. But in cold forging, due to the low plasticity of the metal, the deformation is easy to crack, deformation resistance is large, the need of large tonnage forging machinery.
Warm forging
The forging press which is higher than normal temperature but does not exceed recrystallization temperature is called warm forging press. The metal is pre-heated, the heating temperature is much lower than hot forging. The precision of warm forging is higher, the surface is smooth and the deformation resistance is small.
Isothermal forging
The billet temperature remains constant during the whole forming process. Isothermal forging is to make full use of the high plasticity of some metals at the same temperature, or to obtain specific microstructure and properties. Isothermal forging requires to keep the die and blank at a constant temperature together, which requires a high cost and is only used for special forging processes, such as superplastic forming.
Hot forging,Forming mode
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