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Types and Characteristics of Forging
Publish：2019-05-18 15:08:07 Source：Kinglongly company
When the temperature exceeds 300-400 ("blue brittle zone") and reaches 700-800 ("blue brittle zone"), the deformation resistance decreases sharply and the deformation energy improves greatly. According to the forging in different temperature regions, according to the quality of forgings and the different requirements of forging process, it can be divided into three forming temperature regions: cold forging, warm forging and hot forging. In general, forging in the recrystallized temperature region is called hot forging, and forging without heating at room temperature is called cold forging.
When forging at low temperature, the size of the forgings changes little. When forged below 700 C, less oxide scales are formed and no decarbonization occurs on the surface. Therefore, as long as the deformation energy is within the range of forming energy, cold forging can easily obtain good dimensional accuracy and surface finish. As long as temperature and lubrication cooling are well controlled, warm forging below 700 C can also achieve good accuracy. In hot forging, large forgings with complex shapes can be forged because of the small deformation energy and resistance. In order to obtain forgings with high dimensional accuracy, hot forging can be used in the temperature range of 900-1000 C. In addition, attention should be paid to improving the working environment of hot forging. Forging die life (hot forging 2-5,000, warm forging 12-20,000, cold forging 20-50,000) is shorter than that of other forgings in the temperature range, but it has higher freedom and lower cost.
In cold forging, the blank must be deformed and hardened to make the forging die bear high load. Therefore, it is necessary to use high strength forging die and use hard lubrication film to prevent wear and adhesion. In addition, in order to prevent billet cracking, intermediate annealing is needed to ensure the required deformation capacity. In order to maintain good lubrication, the billet can be phosphated. When bar and wire rod are processed continuously, the section can not be lubricated at present. The possibility of using phosphating lubrication method is being studied.
According to the moving mode of billet, forging can be divided into free forging, upsetting, extrusion, die forging, closed die forging and closed upsetting. Closed die forging and closed upsetting have high material utilization rate because they have no flying edge. It is possible to finish complex forgings with one or more processes. Because there is no flying edge, the force area of forgings decreases and the load required decreases. However, it should be noted that the blank can not be completely limited. Therefore, the volume of the blank should be strictly controlled, the relative position of the forging die should be controlled and the forgings should be measured, so as to reduce the wear of the forging die.
According to the movement mode of forging die, forging can be divided into rotary forging, rotary forging, roll forging, cross wedge rolling, ring rolling and cross rolling. Rotary forging, rotary forging and ring forging can also be used for precision forging. In order to improve the utilization rate of materials, roll forging and cross rolling can be used as the preceding process of slender materials. Rotary forging, like free forging, is also locally formed. Its advantage is that compared with the size of forgings, it can also be formed with less forging force. This forging method, including free forging, expands the material from the die surface to the free surface during processing, so it is difficult to guarantee the accuracy. Therefore, the movement direction of the forging die and the rotary forging process can be controlled by computer, and the products with complex shape and high precision can be obtained with lower forging force. For example, forgings such as steam turbine blades with many varieties and large sizes are produced.
When forging at low temperature, the size of the forgings changes little. When forged below 700 C, less oxide scales are formed and no decarbonization occurs on the surface. Therefore, as long as the deformation energy is within the range of forming energy, cold forging can easily obtain good dimensional accuracy and surface finish. As long as temperature and lubrication cooling are well controlled, warm forging below 700 C can also achieve good accuracy. In hot forging, large forgings with complex shapes can be forged because of the small deformation energy and resistance. In order to obtain forgings with high dimensional accuracy, hot forging can be used in the temperature range of 900-1000 C. In addition, attention should be paid to improving the working environment of hot forging. Forging die life (hot forging 2-5,000, warm forging 12-20,000, cold forging 20-50,000) is shorter than that of other forgings in the temperature range, but it has higher freedom and lower cost.
In cold forging, the blank must be deformed and hardened to make the forging die bear high load. Therefore, it is necessary to use high strength forging die and use hard lubrication film to prevent wear and adhesion. In addition, in order to prevent billet cracking, intermediate annealing is needed to ensure the required deformation capacity. In order to maintain good lubrication, the billet can be phosphated. When bar and wire rod are processed continuously, the section can not be lubricated at present. The possibility of using phosphating lubrication method is being studied.
According to the moving mode of billet, forging can be divided into free forging, upsetting, extrusion, die forging, closed die forging and closed upsetting. Closed die forging and closed upsetting have high material utilization rate because they have no flying edge. It is possible to finish complex forgings with one or more processes. Because there is no flying edge, the force area of forgings decreases and the load required decreases. However, it should be noted that the blank can not be completely limited. Therefore, the volume of the blank should be strictly controlled, the relative position of the forging die should be controlled and the forgings should be measured, so as to reduce the wear of the forging die.
According to the movement mode of forging die, forging can be divided into rotary forging, rotary forging, roll forging, cross wedge rolling, ring rolling and cross rolling. Rotary forging, rotary forging and ring forging can also be used for precision forging. In order to improve the utilization rate of materials, roll forging and cross rolling can be used as the preceding process of slender materials. Rotary forging, like free forging, is also locally formed. Its advantage is that compared with the size of forgings, it can also be formed with less forging force. This forging method, including free forging, expands the material from the die surface to the free surface during processing, so it is difficult to guarantee the accuracy. Therefore, the movement direction of the forging die and the rotary forging process can be controlled by computer, and the products with complex shape and high precision can be obtained with lower forging force. For example, forgings such as steam turbine blades with many varieties and large sizes are produced.
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