Research On Multi-scale Simulation And Experiment Of Silicon Nitride Cutting Based On Single Diamond Abrasive Grain

Silicon nitride engineering ceramics have been widely used in the important fields of machinery,chemical,electronics,energy,metallurgy,national defense,and aerospace,due to their high strength,high hardness,wear resistance,high temperature resistance,chemical corrosion resistance,small thermal expansion coefficient and oxidation resistance,and excellent mechanical properties such as low density and toughening modification compared with metal materials.In this paper,the precision grinding of silicon nitride ceramics is taken as the research subject.The microscopic to macroscopic multi-scale simulation of silicon nitride ceramics was carried out by molecular dynamics and finite element method,and the simulation results were verified by experiments.The material removal mechanism of the silicon nitride ceramics,the ductile regime grinding mechanism and the ductility-brittleness transition mechanism were analyzed from the perspective of simulation and experiment,which provide a theoretical basis for the efficient and low-damage ductile grinding of silicon nitride ceramics.The main research contents are as follows:(1)A nano-sphere diamond abrasive particle molecular model and a silicon nitride super crystal cell model were established,and then a single diamond cutting silicon nitride ceramics nanoscale model was constructed on the basis of molecular dynamics method using LAMMPS software.Considering different cutting speeds and cutting depths,the dynamic simulation of the nanoscale removal process of materials was achieved.The nano-cutting process of silicon nitride ceramics was analyzed from the perspective of atomic states,cutting stress,kinetic energy and potential energy.The influence of cutting speed and depth on the ductile deformation of silicon nitride surface was analyzed,and the nano-scale ductile-regime machining mechanism of silicon nitride ceramics was explained..(2)Based on the Johnson-Holmquist brittle material constitutive model,and using truncated octahedron to simulate diamond abrasive grains,the single abrasive grain cutting simulation was put up by finite element method.The influence of the grinding speed on the critical cutting depth of the ductility-brittleness transition of the material was analyzed by means of a single abrasive grain variable depth of cutting simulation.The material removal process and the ductility-brittleness transition process of the workpiece material were analyzed contrasting with the results of molecular dynamics simulation.(3)The cutting experiment of single abrasive grain variable depth of cutting was carrying out on the CNC surface grinder.The influence of the linear velocity of the grinding wheel on the surface scratch morphology of the silicon nitride ceramic was analyzed.The critical cutting depth values obtained by simulation and experiment were compared,and the finite element simulation results were verified.The material removal mechanism and ductility-brittleness transition mechanism of silicon nitride ceramics were analyzed by integrating simulation and experimental results.A ductile regime dynamic critical grindingdepth model which considered the grinding process parameters and material mechanical properties was constructed.The material removal methods of silicon nitride ceramics were predicted by using the maximum undeformed grinding thickness model and the dynamic critical grinding depth model under different grinding process parameters.The correctness of the dynamic critical grinding depth model of the ductile regime grinding of silicon nitride ceramics was verified,which can be used to guide the ductile regime processing of silicon nitride ceramics.