Research And Experiment On Eliminating Residual Stress By Ultrasonic Vibratory

The metal parts will exist residual stress after pressure processing or hot working, the existence of the residual stress is easy to make workpiece cracks, deformation or warp etc, at the same time, the strength and fatigue limit of workpieces is reduced greatly. So the elimination of residual stress in workpieces has become a major problem in manufacturing technology. Usually there are three kinds of methods which can eliminate residual stress, including natural stress relief, thermal stress relief and vibratory stress relief. Natural stress relief need long time period of work and the effect of eliminating stress s not obvious; Thermal stress relief consume energy greatly and pollute the environment, and the influence to the stability of the size of the part. So the vibration stress relief shows a good application prospect.Traditional low frequency vibration stress relief equipment has been applied greatly in factory and market, and achieved good results. But it has a certain limitations, such as can’t meet the miniature parts with high first intrinsic frequency’s stress relieving. Ultrasonic vibration stress relief have low amplitude and high frequency, per unit time of the input energy is larger, eliminate the residual stress in short time, and it have little effect on dimension stability of parts. At present, there is few research on ultrasonic vibration stress relief. It still need to further research mechanism research, equipment and application aspects.In order to solve the above problems, the main research about several aspects of the problem in this paper:(1) To compare vibration stress relief microscopic mechanism of eliminating residual stress. Through the changeability of the yield strength, movability of dislocation and high-cycle fatigue strength theory making a microscopic explanation for the mechanism of ultrasonic vibration stress relieving. First proposed it can eliminate residual stress inside the workpiece when meet the component within the residual stress and dynamic stress superposition is greater than the sum of material fatigue strength limit in the ultrasonic vibration stress relieving, and is verified through experiments(2) This topic to explore the effect of eliminating residual stress by the ultrasonic vibration stress relief evaluation. Using residual curvature calculation method and the cut seam measurement of residual stress before and after stress relief, and compare the two way of measurement results.(3) According to the actual requirements and the characteristics of a variety of products to choose equipment, including ultrasonic generator and transducer and set the ultrasonic vibration device. At the same time, set up a press machine and round rod deflection measurement devices, and design the amplitude and bar that used in the experiment. Calculated the residual stress in the bar, and simulated the vibration force in the bar during ultrasonic vibration stress relief.(4) Through a set of comparative tests to determine the effect of vibration time and vibration amplitude in eliminating residual stress, the test results show that the ultrasonic vibration can reduce the residual stress in the workpiece. The optimal vibration time is10min-15min. Blind extension of the excitation time has little effect on the stress relief performance, they may also lead to fatigue damage of workpieces. The elimination rate of residual stress in the workpiece increases with the increase of amplitude.