Research On The Ultrasonic Extrusion Strengthening Technology For Hollow Axle Material Of High Speed Train

Conventional finishing processes such as extrusion are usually used to improve the work-surface quality in production process. However, the conventional extrusion force is relatively large, thus, the deformation of the work-surface is not ideal. Grinding is a widely used method to obtain high accuracy of the train axle. But cracks are easily generated in the work-surface of the train axle after grinding, leading to the reduction of the life of the train axle. Therefore, a novel work-surface finishing method using ultrasonic vibration (UV) is proposed in this study to strengthen the work-surface of the train axle.In this study, the effect of ultrasonic vibration extrusion strengthening (UVES) technique on the ordinary axle steel40and30CrMoA axle steel used for train are confirmed, using a combination of experimental and simulation method. The work-surface appearance, roughness, hardness, friction and wear, corrosion resistance, cross organizational, tensile properties, residual stress, and half height to width, etc., after UVES are compared with those before UVES. The results found that the work-surface appears to be mirror after UVES while cloudy before strengthening; The work-surface is smooth and a metallic luster can be seen after UVES. Surface roughness is decreased about94%compared to that before UVES. The surface corrosion resistance is improved, thus the corrosion is not easy to penetrate into subsurface. The investigation into the work-surface microstructure shows that the work-surface becomes even and dense, and a nanocrystalline layer is formed after UVES. In addition, the original residual stress changes to compressive stress, the depth of compressive residual stress layer reaches nearly2mm after UVES. This could prevent the generation of fatigue crack and help to improve fatigue strength and service life of metal material.The thesis discussed the optimal parameters in UVES based on the basic theory. To obtain the high strengthening quality and high efficiency, the process parameters in the UVES are optimized. The investigation into UVES mechanism using a finite element modeling (FEM) method by ABAQUS found that UV plays an ironing role in the UVES process. These findings could provide a comprehensive understanding of the UVES process and severe as a useful springboard for development of more sophisticated UV equipment.