In order to ensure the validity of the test data, all test pieces are made of the same material (same batch of raw materials), the same processing equipment, the same tool, and the same cutting parameters. In the two states of heat treatment to eliminate stress and vibration to eliminate stress, respectively, the test piece was taken in each state, and the test piece was processed into rough machining (5 mm margin on one side) and semi-finishing (2 mm on one side). Process), finishing and other processes.
a. Heat treatment stress relief processing test (test piece 2-1)
The processing flow of test piece 2-1 is as follows:
Figure 6 Test piece 2-1 (finishing)
b. Vibration stress relief test (test piece 2-2)
The processing flow of the test piece 2-2 is as follows:
Figure 7 Test piece 2-2 (finishing)
The effect of stress relief was reflected by measuring the amount of deformation (flatness) of the free-form test piece after processing. The test results are shown in Table 2.
Table 2 Comparison table of deformation of large bearing members under different conditions
Table 2 Comparison table of deformation of large bearing members under different conditions
Deformation state | Heat treatment to eliminate stress / mm | Vibration relief stress / mm |
Roughing state | 7 | 2 |
Semi-finished state | 15 | 1.5 |
Finishing state | 13 | 0.5 |
It can be seen from Table 2 that the vibration stress relief effect is significantly better than the heat treatment stress relief.
3.5 Test conclusion
Based on the test results and analysis, the following conclusions can be drawn:
a. The effect of vibration stress relief is significantly better than the heat treatment to eliminate stress;
b. Vibration relief stress can effectively control the processing deformation of small thin-walled structural members;
c. Vibration relief stress can effectively control the processing deformation of large structural parts;
d. Vibration relief stress can replace or partially replace the heat treatment aging stress relief process.
4 vibration stress relief process application
4.1 Application of vibration stress relief technology in large castings
Large-scale casting magnesium alloys and aluminum alloy parts are often used in spacecraft structures such as satellites and spacecraft, such as: camera girders of remote sensing satellites, load compartment floor plates, bottle brackets, and momentum wheel brackets. Among the large number of ground tooling required for spacecraft development, large aluminum alloy castings are more common. These parts will produce a large internal stress after casting. If these stresses are not treated in time, they will have a tendency to crack, and during the machining process, large deformation will occur, and the products will be stored and used. Reduced accuracy and structural distortion.
The use of vibration-relieving stress technology is not limited by the size and weight of the casting, and the equipment and site requirements are greatly reduced. Figure 8 is a high-strength cast aluminum alloy part, the material is ZL205, the outer dimension is Ф1500mm×800mm, and the wall thickness is 25mm. During the machining process, vibration relief stress treatment is arranged in the state of casting blank, after rough machining and after semi-finishing. After the machining is completed, the flatness of the workpiece reaches 0.02 mm.
a casting blank vibration treatment b semi-finished product processing vibration treatment
c processed products
Figure 8 Vibration blank stress relief casting blank workpiece
4.2 Application of vibration stress relief technology in precision parts processing
There are a large number of precision components in the spacecraft structure and mechanism, such as: solar wing deployment mechanism, gyro, camera, etc. The materials are mostly made of high-strength aluminum alloy materials such as LY12CZ and LD10CS. Such materials are extremely easy to deform during processing, especially the processing deformation of thin-walled complex parts is difficult to control. The main reason is that the material has large and uneven distribution of residual stress before processing. Due to cutting, material residual stress Partially released and redistributed, causing processing distortion. This deformation is largely due not to the deformation caused by the cutting force, but more due to the residual stress in the material before processing.
The vibration relieving stress technology is not limited by the temperature and the number of treatments, and multiple vibrations can be used to eliminate stress and achieve the purpose of controlling deformation. Figure 9 shows a typical thin-walled precision part with an outer dimension of 300 mm × 280 mm × 140 mm, a wall thickness of 2 mm, and a material of LD10CS. After vibration is used to eliminate stress, the machining deformation is well controlled. The verticality after machining is less than 0.10 mm and the flatness is 0.08 mm.
a semi-finished product in vibration processing
Figure 9 Thin-walled precision workpieces with vibration stress relief
4.3 Application of vibration stress relief technology in the processing of large parts of spacecraft
In order to meet the requirements of lightweight, the large parts in the spacecraft are designed as a typical weak rigid structure with a diameter of 5m and a wall thickness of 3 to 5mm. In order to ensure the dimensional accuracy and shape position accuracy of the product before and during processing, the product needs to be relieved of stress. For large parts, the volume of heat treatment aging equipment is difficult to meet.
The vibration relieving stress technology is not limited by the size of the product, which is beneficial to ensure the dimensional accuracy and shape position accuracy of the product. At the same time, it will greatly improve the stability of the product precision and prolong the storage period of the product. Figure 10 shows a large frame-type thin-walled workpiece treated with vibration-relieving stress technology.
Figure 10 Large frame type thin-walled workpiece with vibration stress relief treatment
5 Conclusion
Through the process test and application practice, the advantages of the vibration stress relief technology are fully demonstrated, which can largely replace the conventional heat treatment aging stress relief process. For large workpieces, high-strength aluminum alloy thin-wall structural parts, and heat treatment, vacuum environment is required. The advantages of titanium alloy workpieces are particularly obvious, and it has a good promotion value in the development of spacecraft structures and mechanisms.
In addition, the vibration relieving stress technique is also well applied to the welding deformation control of ferrous materials and the stress relief of welded parts after welding, but the application of stress relief for welded structures of non-ferrous metals such as aluminum alloys is rarely applied in spacecraft welding. In the application of the structure, a large number of reliability process verification and test work are also required.
references
1Vibratory stress relieving–It's advantages as an alternative to thermal treatment. J. S Hornsey VSR(Africa)cc 2004,12
2 Shi Dezhen. Dislocation and material strength. Xi'an: Xi'an Jiaotong University Press, 1998, 11
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