[perspective] large forgings are commonly used in key parts of large machinery, due to the harsh working environment and complicated and changeable, so the quality requirements of large forgings in the production process is very high. Large forging ingot directly by forging, the production of large forgings, even with the most advanced metallurgical technology, micro crack, porosity, shrinkage hole, segregation of ingot is inevitable, seriously affecting the quality of forgings, in order to eliminate these defects and improve the quality of the forgings, forging process parameters must be improved and the selection of reasonable forging process.
Forging is not only to meet the required shape and size of the parts, but also important is to break as cast microstructure, grain refinement, uniform structure, forging shrinkage, porosity and shrinkage and other defects, improve the internal quality of forgings. The ingot size becomes larger, the more serious defects in the ingot forging, improve the defects more difficult, thus increasing the difficulty of forging. In the process of forging, upsetting and stretching is the most basic process is an indispensable process, which has special shape forging, die forging is used.
A, upsetting process
In the free forging of heavy forging production, upsetting is a very main deformation process. Reasonable selection of upsetting process parameters, the quality of large forgings plays a decisive role. Repeated upsetting and stretching can not only improve the billet forging ratio, but also can be broken alloy carbide in steel, achieve the aim of uniformly distributed; also can improve the transverse mechanical properties of the forgings, reduce the mechanical properties of anisotropy.
Large forgings and wide plate forgings are the main deformation in upsetting, and upsetting deformation is large, but the ultrasonic testing of the forgings scrap rate is very high, mainly because the internal transverse crack defect layer, however, this theory cannot explain the current process.
From the beginning of 90s, Chinese scholars after careful study of long time, from the main deformation zone and passive deformation zone theory in-depth study of upsetting theory, put forward the plate upsetting rigid plastic mechanical model of the tensile stress theory and hydrostatic stress mechanics model of shear stress theory. At the same time also conducted simulation experiments and a large number of qualitative physics, using generalized slip line method and mechanical block analysis method to solve the workpiece internal stress state, a large amount of data to prove the rationality and validity of the theory, the distribution of the internal stress using ordinary plate upsetting cylinder, and then put forward the new technology of crude cone plate upsetting is established for upsetting a square body rigid plastic mechanical model.
Two, pulling long process
Drawing length is a process that must be in the forging process of large shaft forgings, and it is also the main working procedure that affects the quality of forgings. By pulling long working procedure, the blank section area decreases, the length increases, and also plays the role of breaking the coarse grain, the internal loose and the hole, and the fine as cast structure, so as to obtain the homogeneous and compact high quality forgings. In the study of flat anvils stretching process at the same time, people gradually began to realize large forging internal stress on the importance and strain of forging internal defects, from the ordinary on the flat anvil to a long, flat anvil type V anvils and anvil type V, and then to then by changing the anvil shape and process conditions, this paper puts forward WHF forging method, KD forging method, FM forging method, JTS forging method, FML forging method, TER method, SUF forging method and forging new FM forging method of these methods have been applied to the production of large forgings, and achieved good results.
1, WHF forging method
Forging method of flat anvil under strong pressure, the forging principle is the use of the upper and lower flat anvil, and using a large reduction rate, the heart of forging deformation is conducive to the elimination of internal defects of steel ingot, widely used in large forging hydraulic press.
2, KD forging method
Developed based on WHF forging method, its principle is to use steel ingot in high temperature long time under adequate ductility, can in the limited equipment, with a wide anvil with large forging rate. The upper and lower V type wide die forging is beneficial for metal surface plasticity increase, increase of the core of the three direction compressive stress state, thus effectively combined the internal defects of steel ingot forging.
3, FM forging method
The use of flat anvil, asymmetric platform forging deformation, and under the platform on the friction force of forging deformation, the forging deformation gradually from top to bottom, so that the tensile stress transferred to the contact surface of the billet and the platform on the central part of the hydrostatic stress has been increased, thereby improving the state the stress and deformation of the body.
4, JTS forging method
Before forging ingot heated to a high temperature, and then make the surface rapid cooling the ingot surface and form a layer of crust, the heart still at high temperature, the shell fixing on the blank deformation, the deformation is mainly concentrated in the center of the forging, thus increasing the compaction effect of the core, improve the qualified the rate of forging.
5, FML forging method
To reduce a load press forging method based on the FM method, the upper anvil width than the blank narrow length direction and blank axial direction consistent, auxiliary tool is still below the big platform, then the forging process and forging pressure volume ratio is relatively small, is a prerequisite for effective combination of forging billet the internal hole and porosity defects reduce compressor load.
6, TER forging method
Draw out the use of wide flat anvil in a direction of stretching, and the use of the wrong process repeatedly forced anvil stretching, the maximum deformation of the billet produced in one direction, effectively closure hole type defect inside. When the method is used, the pressure is small, and the forging process is shorter, and the labor productivity is improved, the production cost is reduced, and the economic benefit is increased.
7, SUF forging method
Based on the control of the ratio of anvil width, forging ingot height to decrease, finally a kind of rectangular section forging forging method, is a kind of wide flat anvil forging method using flat anvil compressed, compressed, thus increasing the ingot axis near the metal plastic flow width, more conducive to the heart defects of forging with the blank.
8, the new FM forging method
According to the center of the forgings transverse stress and blank width ratio, on the basis of FM forging method increased to control the ratio of blank width, transverse tensile stress and to reduce the care department, applying the principle of new FM forging method of large forgings, has achieved remarkable economic benefits.
Three, die forging process
1, definition
Die forgingIt is the shape and size of the blank for the direct use of the blank or the first through the free forging, and then in the free forging equipment, the die forging process is carried out. In addition to the need for a flat anvil and general forging tools, but also need to use a special model.
2, advantages
(1) the tire mold is not fixed on the forging equipment, when the use of the device on the flat anvil, do not need to be unloaded; easy to use does not need to install, greatly saving the time of the test mode, the process is flexible and diverse
(2) because of the metal deformation in die cavity always in the shape and size of the main forging mould guarantee, so can obtain complicated shape and size requirements of precise forging, and the required heating fire and deformation process is also reduced, thus not only improves the material utilization rate and reduce machining time, greatly improve labor productivity
(3) from the forging quality, the forming process of the mould, metal deformation limit, forged forging structure compact, forging quality is relatively good, good surface quality, machining allowance is also very small, greatly improve the utilization of materials, the production efficiency is high, and can shape forging complex forging
(4) the production of large forgings on small devices can be done locally.
Based on the above advantages, forging die forging has been the attention and favor of many manufacturers.
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