Aluminum alloy structural parts are widely used in aerospace, but in space, due to the high and low temperature cycle, the internal residual stress of structural parts is easy to relax, which destroys the dimensional stability of the workpiece and can not meet the requirements of long-time accuracy maintenance.
Vibratory stress relief equipment was used to eliminate the residual stress in the bellows. After vibration, the axial and circumferential residual stress of the bellows decreased by 44.6% and 17.6% respectively. In addition, some scholars found that the effect of vibratory stress relief equipment is related to the standing time after forming. The more unstable the structure is, the better the effect of residual stress relief is. In the forming process, the structure and stress state of the material are in an unstable state. If the vibration is introduced into the stamping process, the manufacturing process can be effectively shortened, the production efficiency can be improved, and the residual stress can be reduced.
At present, ultrasonic vibration assisted forming is widely used in vibration assisted forming. Limited by the vibration force, it is mainly used in the field of micro forming. Now, with the development of servo control technology, servo press with large forming force has been widely used. In this study, a high-precision servo press is used as the vibration source, which can produce low-frequency vibration of 0-40 Hz. At the same time, because the distribution of residual stress in the classical three-point bending model can be well calculated by analytical method, and it can easily verify the accuracy of residual stress measurement in the follow-up experiment process, the vibration assisted bending experiment is used in this study, with the vibration frequency, amplitude and pressing rate as variables, The influence of different vibration parameters on the residual stress is studied, and the finite element simulation analysis and micro dislocation theory are used to analyze and explain it.
Conclusion: vibratory stress relief equipment can be used in the forming process
(1) Low frequency vibration assisted forming can reduce the residual stress and dislocation density of the material. Compared with non vibration assisted forming, the residual stress can be reduced by 36.96%.
(2) When the amplitude is in the range of 0-0.15 mm, with the increase of amplitude, the residual stress and dislocation density of the inner bending surface show a trend of first decrease and then increase, and the lowest point of residual stress appears at 0.04-0.07 mm, which is because: with the increase of amplitude, the surface of die and sheet will separate, and then affect the change of dislocation density and residual stress.
(3) When the vibration frequency is in the range of 0-30 Hz, the residual stress first decreases with the increase of frequency, and after the critical frequency is exceeded, the effect of frequency on the residual stress is not obvious.
(4) In the range of 0.1-1.0 mm • s-1, the residual stress increases with the increase of the compression rate.
(5) The average dislocation density of the bending section is consistent with the variation of the residual stresses on the inner and outer bending surfaces with the vibration parameters.
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