Finite Element Polycrystalline Modeling And Surface Formation Mechanism Research Of Austenitic Stainless Steel Cuttin

AISI 304 is a typical polycrystalline austenitic stainless steel material with good mechanical strength,wear resistance and corrosion resistance.It is an important structural material for nuclear power,petroleum and marine equipment.Due to the non-uniform distribution and anisotropy of the internal microstructure of the material,the cutting process is affected by the size effect and microstructure effect,which makes it difficult to control the surface burr,residual stress and work hardening,and restricts its efficient production and service ability.Therefore,combining the microscopic characteristics of polycrystalline materials to explore the formation mechanism of the cutting surface quality is the key to improve the surface quality of AISI 304.By constructing the polycrystalline cutting model of AISI 304,considering the grain factors(such as grain size,orientation and grain boundary,etc.),the plastic deformation behavior of the material at the mesoscopic scale during the cutting process is analyzed,and the influence of cutting parameters,grain size and tool structure parameters on the formation mechanism of burr,residual stress and work hardening is explored,which provides a theoretical basis and scientific basis for the processing optimization of AISI 304.(1)The material constitutive model subroutine based on dislocation density theory was developed by Fortran language,and then the Voronoi model was used to describe the microstructure of polycrystalline non-uniform distribution of AISI 304 material.Based on the ABAQUS/Explicit solver,a right-angle cutting simulation model considering microdislocation density evolution and grain morphology distribution was constructed.Through the experimental observation of cutting force,chip morphology and burr morphology,the accuracy and credibility of AISI 304 cutting finite element polycrystalline model are verified,which provides a reliable model basis for exploring the formation mechanism of burr and surface quality.(2)Based on the constructed polycrystalline microscopic cutting model considering grain factors,the plastic flow of materials,the formation of surface folds and the plastic deformation of single grains in the cutting process were simulated.By analyzing the plastic deformation behavior of grain and grain boundary in the deformation zone from steady-state cutting to burr formation,the formation processes of outlet burr and lateral burr were described.Combined with the finite element simulation and experimental law of burr,the influences of cutting speed,cutting thickness,grain size and geometric parameters of circular and chamfered cutting tools on burr formation size were investigated.The cutting model established in this study and related experimental data can provide technical support for the burr control of AISI 304.(3)Combined with the formation mechanism of residual stress and work hardening,it was found that different sizes of bumps and holes would be formed on the machined surface after cutting.The polycrystalline finite element cutting process of AISI 304 was divided into three stages: steady cutting,boundary condition conversion and cooling,and the simulation of surface residual stress was realized.The results show that the distribution of residual stress on the surface of the workpiece is fishhook in both directions.However,due to the existence of grain boundary effect,there will be obvious gradient and uneven distribution of stress at the grain boundary.According to the relationship between the dislocation density and work hardening,the formation and distribution of microhardness were simulated.The effects of cutting parameters,grain size and tool structure parameters on the formation mechanism of residual stress and work hardening were investigated,which provided a theoretical reference for further understanding of the physical and mechanical properties of AISI 304 cutting surface.