Views:35 Author:Site Editor Publish Time: 2018-08-08 Origin:Site
1. Natural aging elimination of residual stress
Natural aging is a method to stabilize the dimensional accuracy of parts by exposing them outdoors for several months to several years. A large number of experiments and production practice have proved that natural aging has good effect in stabilizing the dimensional accuracy of castings.
However, after natural aging, the change of residual stress is not obvious. As shown in Figure 3-1, the residual stress of the castings is only reduced by 2-10% after one year. The result of the residual stress of the machine tool bed shows that the maximum residual stress is reduced from 80N/mm to the average residual stress of 70N/mm after a year of natural aging. The force dropped from 38N/mm to 30N/mm, or only about 10-20%. It can be seen that the castings that have stopped deformation after natural aging are still left with considerable residual stress. For castings that need to be loaded with heavy loads, the use of stress on high residual stresses may affect the performance of the castings. Therefore, it is necessary to consider whether this kind of aging method should be used.
2. Thermal time validity
The most traditional and popular method, thermal aging, is to put the workpiece into a thermal aging furnace for heat treatment and gradually eliminate stress. The shortcomings of this approach are also significant, for example, the satellite manufacturing plant, which has very strict temperature control requirements for aluminum alloy pieces and ten meters long or larger, can not be treated in this way. And this method also brings a lot of pollution and energy consumption. With the further requirements of environmental protection in China and the world, the treatment of hot aging furnace is immediately facing the situation of full withdrawal.
3. The use of subresonance to eliminate stress
Although this method solves the environmental problem of thermal aging, it is very cumbersome to use. It is necessary to make different aging processes for different shapes. If there are hundreds of thousands of workpieces, hundreds of thousands of processes will be made, and the operation is quite complex in production. The operators need to determine the processing parameters and complex workpieces. It must be skilled professionals to operate. What is more regrettable is that this method can only eliminate 23% of the workpiece stress and can not achieve the purpose of processing all workpieces.
4. Vibration aging removal of stress
The vibration aging technology, known as "Vibrating Stress Relief" ("VSR"), aims to make the processed workpiece resonate through a special vibration aging equipment, and transfer certain vibration energy to all parts of the workpiece through this resonance mode, and make the micro plastic deformation in the interior of the workpiece - the distorted crystal. The lattice gradually resumed the state of balance. The dislocation slips and pins again, eventually eliminating and homogenizing the residual stress, thus ensuring the stability of the dimensional accuracy of the workpiece.
5. The essence of the vibration aging is to apply the additional dynamic stress to the workpiece in the form of resonance. When the additional dynamic stress and residual stress are superimposed to reach or exceed the yield limit of the material, the workpiece occurs micro or macroscopic plastic deformation, thus reducing and homogenizing the residual stress inside the workpiece and making its dimensional precision stable.