Research On Surface Enhancement Mechanism Of Ultrasonic Deep Rolling With Longitudinal-Torsional Vibration

Ultrasonic deep rolling with Longitudinal-torsional vibration(UDR-LTV) is a newly processing technology, which is used to finish and strengthen the part. UDR-LTV is combined the two-dimensional ultrasonic vibration with ultrasonic deep rolling processing technology. In this thesis, the Q235 steel was processed with UDR-LTV, and the surface enhancement mechanism of UDR-LTV was studied. The main work is as follows:(1) The physical model of the residual stress in the process of UDR-LTV was established based on the processing principle and kinematics analysis of UDR-LTV. It’s found that in the process of UDR-LTV, the residual compressive stress is affected by the physical mechanical properties, the roller radius, the vibration parameters and the rolling process parameters. The influence of vibration parameters and rolling process parameters on the residual compressive stress in the process of UDR-LTV was analyzed by the numerical method. The results showed that the greatest residual compressive stress of surface obtained by UDR-LTV increase with the increment of roller radius, amplitude, frequency and static pressure, and decrease with the increment of rolling speed and rolling depth.(2) The process of ultrasonic deep rolling with longitudinal vibration and the process of UDR-LTV was analyzed with FEM based on kinematics model of DRP-LTV. And the effects of longitudinal vibration and longitudinal-torsional vibration on the residual stress were studied. The distribution of residual stress at the center of the impacted region along the rolling depth was obtained. And the effects of the processing parameter on residual stress were analyzed. The results showed that the influence laws of the longitudinal vibration and longitudinal-torsional vibration on the residual stress are similar with the same rolling processing parameters. The residual stress increases with the increment of the static pressure and the rolling speed, and increases with the increment of the amplitude and the phase angle.(3) Orthogonal experiments of UDR-LTV and conventional deep rolling(CDR) Q235 steel were carried out to study the effects of processing parameters on surface roughness and surface micro hardness. The mathematic models to predict surface roughness and surface micro hardness were constructed. The optimal processing parameters for the lowest surface roughness and the highest surface micro hardness were explored. The results showed that the values of surface roughness obtained by UDR-LTV are smaller than that of CDR with the same processing parameter, and the values of surface micro hardness are higher than that of CDR. The values of surface roughness obtained by UDR-LTV increase and then decrease along with the increasing of the static pressure; and increase with the increasing of the feed-rate, and change a little along with the increasing of the rolling speed. Meanwhile, the feed-rate has a marked effect on surface roughness. The values of surface micro hardness obtained by UDR-LTV increase with the increasing of the static pressure; and increase first then decrease along with the increasing of the feed-rate; and decrease at first then increase along with the increasing of the rolling speed. Meanwhile, the static pressure has a marked effect on surface micro hardness. Finally, the microstructure of the machined surface was observed, and It’s found that the microstructure obtained by UDR-LTV are better than that of turning process and CDR, and processing texture distribution are uniform.The research results may be used to promote the application of the ultrasonic surface strengthening technology with complex vibration mode.