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Due to the poor working environment and complex and changeable forces, the quality requirements of large-scale fittings in the production process are very high. Large forgings are directly forged from steel ingots. In the production of large forgings, even if advanced metallurgical skills are used, there are inevitably defects such as micro-cracks, slack, shortening, and segregation inside the ingot, which seriously affect the quality of the forgings. In order to eliminate these shortcomings and improve the quality of forgings, it is necessary to improve the forging process and select reasonable forging process parameters.
The forging of large forgings not only needs to satisfy the shape and size of the required parts, but also breaks the casting structure, refines the particles, distributes them evenly, shortens the defects such as holes, holes, and looseness, and improves the internal quality of the forgings. The larger the size of the ingot, the more severe the defects in the ingot, the more difficult it is for forging to improve the defects, and then the difficulty of forging is added. In the forging process, rolling and stretching is a basic process and an indispensable process, and tire die forging is also more commonly used for forgings with special shapes.
1. Rolling process.
In the free forging production of large forgings, the coil head is a very important deformation process. Reasonable selection of coil head process parameters plays a decisive role in the quality of large forgings. The repeated coil head can not only improve the forging ratio of the billet, but also break down the carbides in the alloy steel to achieve the purpose of uniform distribution; it can also improve the horizontal mechanical properties of the forgings and reduce the anisotropy of the mechanical properties.
Large cake forgings and wide plate forgings are mainly deformed by the head, and the deformation of the head is very large, but now the ultrasonic flaw detection rate is very high, mainly because of the defect of the crack layer at the internal level, but the current process theory cannot explain it. For this reason, since the 1990s, after a long period of serious research, Chinese scholars have carried out in-depth research on the head theory starting from the theory of the main deformation zone and the passive deformation zone. The tensile stress theory of the rigid plastic mechanical model and the shear stress theory of the hydrostatic stress mechanical model were put forward, and the qualitative physical simulation experiment of Daxing was carried out together. The generalized sliding line method and the mechanical block method were used to analyze the internal stress of the workpiece. A large number of data proved that The rationality and correctness of the theory are presented, the distribution rules of the internal stress of the general plate column are reminded, a new technology of conical tumbling is proposed, and a rigid plastic mechanical model is established.
Second, the elongation process.
Elongation is an indispensable process in the forging process of large shaft forgings, and it is also the primary process that affects the quality of forgings. Through the elongation process, the cross-sectional area of the blank can be reduced and the length can be increased. At the same time, it can also crush coarse crystals, forge internal slack and holes, fine-tune the casting arrangement, and obtain uniform, dense forgings. While studying the process of plate cutting and elongation, people gradually realized the importance of the internal stress and strain conditions of large forgings to the internal defects of forgings, from general plate cutting and elongation to upper and lower plate cutting V cutting and elongation and upper and lower V cutting Cut to elongate. Later, after changing the shape and process conditions of the elongated incision, WHF forging, KD forging, FM forging, JTS forging, FML forging, TER forging, SUF forging and new FM forging were proposed.
1. WH forging method is a forging method of strong pressing and wide flat anvil. The forging principle is to use the upper and lower wide flat anvils, and the pressure rate is high. The large deformation of the heart during the forging process is conducive to eliminating the internal defects of the steel ingot, and is widely used in the forging of large hydraulic presses.
2. The KD forging method is developed on the basis of the WHF forging method. The principle is to use steel ingots that have sufficient plasticity under long-term high temperature conditions, and can be cast with wide anvils and large reduction rates on limited equipment. The upper and lower V-shaped wide anvil casting is conducive to improving the metal plasticity of the forging surface, increasing the three-way compressive stress state of the heart, and eliminating the internal defects of cast ingots.
The 3FM forging method is to use the upper flat anvil, the lower channel forging asymmetric deformation, and the lower channel forging frictional resistance to gradually deform the forging from top to bottom, transfer the tensile stress to the contact surface between the blank and the channel, add the central hydrostatic stress, and improve. The stress state of the deformed body.
4. The JTS forging method is to heat the ingot to a high temperature before forging, and then rapidly cool the surface. The surface of the steel ingot forms a hard shell, and the heart is still at a high temperature. The deformation of the hard shell fixed billet is mainly concentrated in the center of the forging, which improves the heart pressure effect and improves the qualification rate of the forging.
5. The FML forging method is a forging method that reduces the load of the press on the basis of the FM method. The width of the cutting board is narrower than that of the blank, and the length direction is consistent with the axial direction of the blank. The following aids are still a big channel. During the recasting process, the pressure and forging ratio are relatively small. On the premise of ensuring the effective casting of the inner hole of the billet, and on the premise of loose defects.
6. The TER forging method uses a wide flat anvil to elongate in one direction, and chooses the wrong anvil process to carry out multiple strong pressure elongation, so that the blank is deformed greatly in one direction, which has the disadvantage of casting inner hole. When using this method for forging, the pressure is small, the casting cycle is short, the labor productivity is improved, the production cost is reduced, and the economic benefit is improved.
7.SUF forging method is a forging method. After controlling the anvil width ratio, the height of the steel ingot is fully lowered, and then the section is forged into a rectangle. This is a casting method of flattening with a wide flat anvil. Wide flat anvil flattening increases the width of the ingot axis adjacent to the metal plastic activity range, which is more conducive to the core defect of casting billets.
8 The new FW forging method is based on the FM forging method. According to the relationship between the transverse stress of the forging heart and the material width ratio, the control of the material width ratio is added, and then the transverse tensile stress of the heart is reduced. When using the new FM forging method to produce large forgings, obvious economic benefits have been achieved.
Third, the tire mold forging process.
Tire die forging is a forging method that directly uses blanks or free forging to pre-forge the blanks into the shape and size required for tire forging, and then uses tire molds on free forging equipment for final forging. The tire die forging is not fixed on the forging equipment, and it is placed on the cutting board of the equipment during use. It is easy to use and does not need to be installed. The size is mainly guaranteed by the tire mold, which can achieve complex shapes and precise size requirements, reduce heating fires and deformation processes, not only improve the utilization rate of metal materials, but also reduce the processing time and greatly improve labor productivity. In terms of the quality of forgings, due to the function of the mold, the metal deformation is limited, the forgings are densely arranged, the quality of the forgings is good, the surface quality is good, the machining allowance is small, the material utilization rate is greatly improved, the production efficiency is high, and the shape of the forgings is complex; it can also Produced on small devices.