Drawing length is a necessary process in the forging process of large forgings, and it is also the main process that affects the quality of large forgings. Through drawing length, the billet cross-sectional area is reduced, the length is increased, and it also plays the role of breaking coarse crystals, forging the internal porosity and holes, and refining the organization, so as to obtain homogeneous dense high-quality forgings.
At the same time of studying the drawing process of flat anvil, people gradually began to realize the importance of the stress and strain state inside the large forgings on the internal defects of forging, from the ordinary drawing length of the flat anvil, to the drawing length of the V-shaped anvil under the flat anvil and the drawing length of the V-shaped anvil above and below the flat anvil, and then to the later by changing the drawing anvil shape and process conditions. WHF forging method, KD forging method, FM forging method, JTS forging method, FML forging method, TER forging method, SUF forging method and new FM forging method are put forward. These methods have been applied to the production of large forgings and achieved good results.
WHF forging method is a wide flat anvil strong pressing forging method, its forging principle is to use the upper and lower wide flat anvil, and adopt large pressing rate, the large deformation of the heart during forging is conducive to eliminating the internal defects of the ingot, and is widely used in large hydraulic press forging.
KD forging method is developed on the basis of WHF forging method, the principle is the use of ingot in a long time of high temperature conditions have enough plasticity, can be in limited equipment, with wide anvil large compression rate forging, the use of upper and lower V-type wide anvil forging is conducive to the improvement of metal plasticity on the surface of the forging, increase the heart of the three-way compressive stress state, Then the ingot internal defects can be forged effectively.
FM forging method is to use the upper flat anvil, the asymmetric deformation of the lower platform forging, and the friction resistance of the lower platform to the forging deformation, so that the forging gradually deforms from top to bottom, so that the tensile stress is transferred to the contact surface between the blank and the platform, the hydrostatic stress in the center is increased, and the stress state in the deformation body is improved.
JTS forging method is to heat the ingot to high temperature before forging, and then make the surface cool quickly, the surface of the ingot and then form a layer of hard shell, the core is still in a high temperature state, this layer of hard shell plays a fixed role in the deformation of the billet, so that the deformation is mainly concentrated in the center of the forging, thereby increasing the compaction effect of the heart and improving the pass rate of the forging.
FML forging method is a forging method to reduce the load of the press on the basis of FM method. The width of the upper anvil is narrower than that of the billet, and the length direction is consistent with the axial direction of the billet. The following auxiliary tools are still large platforms, and the pressing amount and forging ratio in the process of reforging are relatively small. It is to reduce the load of the press on the premise of ensuring the effective forging of the internal holes and loose defects of the billet.
TER forging method uses wide flat anvil to draw length in one direction, and adopts the cross-anvil process to press and draw length several times, so that the maximum deformation of the blank is produced in one direction, and the internal cavity defects are effectively forged. When the forging method is used, the required pressure is small, and the forging forming cycle is short, so as to improve labor productivity, reduce production costs, and increase economic benefits.
SUF forging method is a forging method in which the height of the ingot is fully reduced during forging by controlling the width ratio of the anvil, and the section is finally forged into a rectangle. It is a forging method by flattening the ingot with a wide flat anvil, and then the width of the metal plastic flow range near the ingot axis is increased by using a wide flat anvil, which is more conducive to forging the defects in the billet core.
The new FM forging method is based on the relationship between the transverse stress of the heart of large forgings and the ratio of material to width. On the basis of the FM forging method, the control of the ratio of material to width is increased to reduce the transverse tensile stress of the careful part.