Experiment And Simulation Research On Surface Performance In Rolling Processing Of High Strength Steel

Torsion bar spring is widely used as a kind of elastic element with good performance in various vehicle suspension systems.When the vehicle is driving,the torsion bar spring absorbs and releases energy through elastic torsion,reaching the purpose of cushioning and shock absorption.During the working,the torsion bar spring is often affected by large stress,strain,impact and alternating torque load.It is easy to crack on the surface of the torsion bar and seriously affect the service life of the vehicle.Rolling processing can reduce the surface roughness of torsion bar spring,increase the surface hardness and residual compressive stress.If the rolling processing parameters are controlled properly,a good surface properties can be obtained,the anti-fatigue performance of the torsion bar spring can be improved to prolong its service life.At present,the research on the surface performance of the torsion bar spring rolling processing is not perfect,resulting in the lack of theoretical support and guidance for the torsion bar spring rolling technology,and affecting its production efficiency and product qualification rate.Therefore,it is urgent to carry out the research on the surface performance of high Strength steel rolling processing,and optimize the control of the surface performance of rolling processing to improve the anti-fatigue performance of the torsion bar spring.The main research content is as follows:(1)Based on the elastic-plastic mechanics theory,the surface smoothing mechanism of high Strength steel rolling is studied.The surface smoothing experiment of high Strength steel rolling processing is carried out.The experiment results show that the roller presses the wave metal on the workpiece surface to reduce the roughness of the workpiece surface.And increased rolling depth and the number of rolling times or reduced feed rate and workpiece rotation speeds give better surface processing quality.Combined with orthogonal experiment,the empirical formula of power exponent prediction for surface roughness is obtained by linear multiple regression method.(2)Surface strengthening mechanism of high Strength steel rolling processing is studied.The results of SEM and EBSD analysis show that the rolling processing can refine the surface martensite grains.The average grain size of the surface layer is reduced from0.8129?m to 0.4736?m,and the martensite grains slide along the rolling direction.The surface strengthening experiment of high Strength steel rolling is carried out.The experiment results show that the rolling processing can improve the surface hardness and residual compressive stress of the workpiece.The surface microhardness and residual compressive stress increase with the increase of the rolling depth and the number of rolling times,and decrease with the increase of the feed rate and the workpiece rotation speed.Combined with orthogonal experiment,the empirical formula of power exponent prediction for surface microhardness and residual compressive stress are obtained by linear multiple regression method.(3)Through the finite element simulation,a prediction model for the residual stress field of the high Strength steel rolling processing surface is established.The simulation results show that the residual compressive stress appears on the surface of high Strength steel.With the increase of depth,the compressive stress increases first and then decreases.The influence depth of surface residual compressive stress and compressive stress increase with the increase of the roll pressure and the feed rate,and decreases with the increase of the rotational speed of the workpiece,the radius of the roller,and the fillet radius of the roller.Through the rolling processing experiment,it was found that the error between the simulated value and the experiment value of the residual compressive stress on the rolling surface of the workpiece was less than 20%,and the two are consistent with the trend of rolling processing parameters,which verified the correctness of the prediction model.(4)The mechanism of ultrasonic rolling processing of high Strength steel and the trajectory equation of the rolling ball are analyzed.A single point ultrasonic impact model was established by finite element simulation.The results show that the plastic strain of the workpiece surface increases with the increase of the number of vibrations.After the number of impacts exceeds 41 times,the amplitude tends to be stable.A prediction model for the residual stress field of the high Strength steel ultrasonic rolling processing surface was established.The influence depth of residual compressive stress and compressive stress increases with the increase of static pressure,amplitude and frequency.