Numerical Research On Polishing Mechanism Of Solid-Liquid Phases Abrasive Flow Based On Molecular Dynamicssimulation

Abrasive flow polishing(AFP)technology,as a way to improve the surface quality of the non-traditional finishing technology,plays an important role in precision machining.Although the study of AFP technology is also increasing,most of the researches is on the macro perspective,and micro perspective researches on AFP mechanism is relatively less.Molecular dynamics(MD)simulation,as a kind of micro scale research methods,has become an important research method for many scholars to study nano-machining mechanism.Based on the friction and wear and crystal plasticity theory,the thesis studies abrasive flow polishing mechanism with molecular dynamics simulation method.Cutting direction of abrasive in liquid is not along with the surface of the workpiece,and in the micro cutting of the workpiece,the cutting direction of abrasive edges is not completely orthogonal to the surface of the workpiece.For analyzing the effect of abrasive types and cutting direction on workpiece material polishing,molecular dynamics simulation model that different types(silicon carbide,boron nitride,alumina and diamond)of abrasive cut single crystal materials(copper,iron,aluminum)is built.The simulation results shows that when the cutting direction is small angle,the number of dislocations produced by cutting is less,the cutting force and energy are relatively low,the internal structure of the workpiece is better than the other cutting angle.In other words,small cutting angel can improve the surface quality of the workpiece and reducing the number of internal defects in the single crystal cutting process.In further study,orthogonal cutting is the preferred cutting means and using abrasive flow finishing polishing technology,abrasive types are selected according to workpiece material.In order to study the mechanism of polishing polycrystalline material workpiece during polishing,the molecular dynamics simulation of orthogonal cutting for three kinds of polycrystalline materials was carried out.The changes of cutting force,energy and friction coefficient in the cutting process show that the atomic adhesion of the abrasive particles and the contact area of the workpiece directly affects the surface quality of the workpiece.Analysis of plastic deformation(including nuclear migration and dislocation,grain boundary shape deformation and deformation twinning)process during polishing shows that the internal defects in the workpiece surface also have the strong competition,and the interaction of dislocations and grain boundaries led to the migration of twin boundaries and twin.Further analyzing numerical results,the cutting depth and abrasive types have different cutting effects on different workpiece materials and appropriate cutting depth and abrasive types can improve abrasive flow polishing quality.In conclusion,molecular dynamics study on abrasive flow polishing single-crystal and polycrystal workpiece material is carried out.After analyzing the results that different types abrasives cut different workpiece in different cutting direction and depth,the solid-liquid two-phase abrasive flow polishing mechanism is obtained.