Study On Thermal-Mechanical Coupling Simulation And Prediction Of White Layer Formation Of Hardened Steel In Laser-assisted Turning

GCr15 hardened steel is a typical hard cutting metal material with high strength,high hardness,high wear resistance,and good structure stability,which is widely used in the manufacture of die,bearing,and key parts of the automobile.In order to solve the difficult cutting problem,in recent years,scholars have gradually replaced the traditional grinding technology with dry hard cutting technology,which greatly improves the processing efficiency,but it is still easy to form a white layer on the machined surface.The characteristics of hard and brittle white layer easily lead to the early peeling failure and the formation of fatigue cracks on the surface of parts,which seriously affect the surface integrity and service performance of parts.In order to avoid the formation of white layer and improve the surface integrity of hardened steel,Laser-Assisted Turning(LAT)technology is proposed to replace conventional dry turning technology.The main contents of this paper are as follows(1)Based on the DFLUX user subroutine of ABAQUS finite element software,the finite element prediction model of transient temperature field of hardened steel heated by mobile laser source is established.According to the simulation results,the empirical formula of the maximum temperature and the temperature of the temperature measuring point inside the workpiece is calculated based on the multiple linear regression method,and the influence of different laser preheating parameters on the temperature change trend of the temperature measuring point is studied,which provides data and theoretical basis for the optimization of preheating parameters.(2)Based on VDFLUX user subroutine in ABAQUS,the thermal-mechanical coupling finite element model of Laser-Assisted Turning is established,and the laser moving heat source and tool are loaded simultaneously in one simulation step.Based on the finite element simulation,the influence of laser preheating parameters on the cutting temperature and its change rate,cutting force,stress,and strain in the process of Laser-Assisted Turning is discussed,and the restraining effect of Laser-Assisted Turning technology on the formation of white layer on the machined surface is qualitatively analyzed.At the same time,microstructure observation and analysis experiments show that phase transformation and grain refinement occur in the white layer formed by Laser-Assisted Turning.(3)The data of temperature,stress,and strain energy density in the thermal-mechanical coupling finite element simulation results of Laser-Assisted Turning are extracted,combined with the critical cutting speed of white layer under the influence of laser moving heat source The influence of laser preheating parameters(such as laser power P,laser spot size R and the distance between laser spot and tooltip L)on the critical cutting speed of white layer formation was analyzed,and the prediction results were verified by microscopic observation experiments.The prediction results show that the critical cutting speed of white layer formation can be increased under appropriate preheating parameters in Laser-Assisted Turning,so as to improve the machined surface integrity.Under the optimized laser preheating parameters,the upper limit of critical cutting speed for white layer formation in Laser-Assisted Turning is 26.09%higher than that in conventional dry hard turning.