Large forgings are generally used in the key parts of large machinery. Due to the poor working environment and complex and variable forces, large forgings have high quality requirements in the production process. Large forgings are forged directly from ingots. In the production of large forgings, even with advanced metallurgical technology, there are inevitably micro-cracks, looseness, shrinkage, segregation and other defects inside the ingot, which seriously affect the quality of the forgings. In order to eliminate these defects and improve the quality of forgings, the forging process must be improved and reasonable forging process parameters must be selected.

Large forgings forging not only to meet the shape and size of the required parts, but also to break the casting organization, refine the particles, uniform organization, forging shrinkage holes, holes, loose and other defects, to improve the internal quality of forgings. The larger the size of the ingot, the more serious the defects in the ingot, the more difficult it is to forge to improve the defects, thus increasing the difficulty of forging. In the forging process, rolling and stretching is a fundamental and indispensable process, and for forgings with special shapes, tyre die forging is also more commonly used.

　　I. Upsetting process

　　In the free forging production of large forgings, roll heading is a very important deformation process. Reasonable choice of header process parameters plays a decisive role in the quality of large forgings. Repeated head rolls can not only improve the forging ratio of billets, but also break the carbide in the alloy steel to achieve uniform distribution; it can also improve the horizontal mechanical properties of forgings and reduce the anisotropy of mechanical properties.

　　Large cake forgings and wide plate forgings are mainly head deformation, head deformation is very large, but the current ultrasonic flaw detection rate is high, mainly due to internal horizontal internal crack layer defects, but the current process theory can not explain. For this reason, since the 1990s, after a long period of serious research, Chinese scholars have conducted in-depth research on 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 proposed, while a large number of qualitative physical simulation experiments were carried out, the internal stress state of the workpiece was analysed using the generalised slip line method and the mechanical chunking method, and a large amount of data proved the rationality and correctness of the theory, revealing the distribution law of the internal stress of an ordinary flat plate cylinder, proposing a new process of tapered plate rolling, and establishing a rigid plastic machinery model.

　　Second, draw length process

　　Drawing is an essential process in the forging process of large shaft forgings, and is also a major process affecting the quality of forgings. Through the drawing process, the cross-sectional area of the billet can be reduced and the length increased. At the same time, it can also break the coarse crystal, forge internal loose and hole, refine the casting organization, so as to obtain homogeneous and dense forgings. While studying the flat anvil drawing process, people gradually realised the importance of the internal stress and strain state of large forgings to the internal defects of forgings, from ordinary upper and lower flat anvil drawing to upper and lower flat anvil under V anvil drawing and upper and lower V anvil drawing. Later, by changing the shape and process conditions of the drawing anvil, WHF forging, KD forging, FM forging, JTS forging, FML forging, TER forging, SUF forging and the new FM forging were proposed.

　　1. WHF forging method is a forging method of strongly pressing down a wide flat anvil. Its forging principle is to use the upper and lower wide flat anvil with a large pressure rate. The large deformation of the heart during the forging process is conducive to the elimination of internal defects in the ingot and is widely used in the forging of large water presses.

　　2. The KD forging method was developed on the basis of the WHF forging method. The principle is that the ingot has sufficient plasticity under long-term high temperature conditions and can be forged with a wide anvil at a large press rate on limited equipment. The upper and lower V-shaped wide anvil forging helps to improve the metal plasticity of the forging surface, increase the three-way compressive stress state of the heart and effectively forge the internal defects of the ingot.

　　3. FM forging method is to use the upper flat anvil, lower platform forging asymmetric deformation, lower platform forging friction resistance, so that the forging is gradually deformed from top to bottom, so that the tensile stress is transferred to the blank and platform contact surface, increasing the central hydrostatic compressive stress and improving the stress state of the deformed body.

　　4.JTS forging method is to heat the ingot to high temperature before forging, then quickly cool the surface, the ingot surface to form a hard shell, the heart is still in a high temperature state, the hard shell fixed billet deformation, so that the deformation is mainly concentrated in the centre of the forging, improve the heart compaction effect, improve the forging qualification rate.

　　5. The FML forging method is a forging method that reduces the load on the press on the basis of the FM method. The width of the anvil is narrower than the billet, and the length direction is the same as the axial direction of the billet. The following auxiliary tool remains a large platform. In the re-forging process, the pressure and forging ratio are relatively small, under the premise of ensuring effective forging of holes inside the billet and under the premise of loosening defects.

　　6. TER forging method uses a wide flat anvil to elongate in one direction, using the wrong anvil process for multiple strong pressure elongation, so that the billet in one direction to produce large deformation, effective forging of internal hole defects. When using this method of forging, the pressure is small, the forging and forming cycle is short, improving labour productivity, reducing production costs and improving economic efficiency.

　　7. The SUF forging method is a forging method in which the height of the ingot is sufficiently reduced by controlling the anvil width ratio and then the cross-section is forged into a rectangle. It is a forging method that uses a wide flat anvil for flattening. The use of wide flat anvil flattening increases the width of the plastic flow range of the metal near the ingot shaft and is more conducive to forging billets with heart defects.

　　8. The new FM forging method is based on the FM forging method, based on the relationship between the transverse stress in the heart of the forging and the material width ratio, increasing the control of the material width ratio and thus reducing the transverse tensile stress in the heart. Significant economic benefits have been achieved in the production of large forgings using the principles of the new FM forging method.

　　III. Tyre die forging process

Tyre die forging is a forging method in which the billet is pre-forged directly into the required shape and size for tyre forging using either a billet or a free forging, and then the final forging is carried out on a free forging machine using a tyre die. Tyre die forging is not fixed to the forging equipment and is placed on the lower anvil of the equipment when in use, which is easy to use and requires no installation, greatly saving the time for die testing and making the process operation flexible and varied; as the metal deformation is always completed within the die chamber, the shape and size of the forging is mainly ensured by the tyre die, which allows complex shapes and accurate dimensional requirements to be obtained, and the heating fire and deformation process is also reduced, not only improving the The utilization rate of metal materials, but also reduce the processing time, greatly improving labour productivity. In terms of forging quality, due to the role of the die, metal deformation is limited, forging organization is dense, forging quality is better, good surface quality, small machining allowance, material utilization rate is greatly improved, high production efficiency, forging shape is complex; can also produce large forgings on small equipment, partial molding. Based on the above advantages, tyre die forging has received the attention and favour of many manufacturers.