Study On Subsurface Defects Evolution Of Aluminum And Its Effect On Surface Cleanliness In Ultra-precision Cutting

The subsurface defect characteristics have a direct impact on the machining quality and service life of the workpiece while the removed material achieve nano-scale rate during the ultra-precision cutting process.Aluminum material is widely used in the components of high energy laser system based on its advantages,the machining surface quality and cleanliness of the workpiece are highly required.Therefore,the study of the subsurface defects evolution from molecular and atomic level has theoretical and practical significance for improving the surface quality and explaining the surface contamination of the workpiece.Based on the theory of molecular dynamics simulation,the aluminum cutting simulation models under vacuum are carried out to study the cutting mechanism and cutting phenomenon.The evolution of the subsurface defect structure and the mechanism of stress-induced dislocation nucleation and expansion are studied.The influence of cutting depth on the subsurface crystal structure is also investigated by counting the number of subsurface defect atoms and calculating the atomic ratio.For the cutting simulation of polycrystalline aluminum,the block affecting of the grain boundaries on the dislocation slip propagation is selective analyzed,the influence of grain boundaries and dislocations on the cutting force fluctuation and stress distribution are explored.The cutting simulation models of aluminum in water medium are established,the effect of water medium on the subsurface crystal structure change is investigated,it is found that the dislocation accumulation time in the water medium is longer by comparing with the simulation results in vacuum under the same parameters.Through observing the water distribution between tool and workpiece during the cutting process and analyzing the distribution of stress and temperature on the machining surface,it reveals that the water medium can effectively weaken the sticking phenomenon of the tool flank to the material and reduce the overall temperature of the workpiece.The influence of water medium on the variation of cutting force and the fluctuation amplitude are further analyzed.The cutting simulation models of single crystal aluminum in organic medium are established,the evolution of subsurface dislocations in three environments are analyzed in detail,the cooling and lubrication properties of organic and water media are further studied.The influence regularities of cutting depths on subsurface crystal structure,surface quality and surface cleanliness are discussed by analyzing the change of different crystal structure atoms in the subsurface,the arrangement of surface atoms,the stress distribution and the residual amount of organic on surface.Rectangular grooves with different widths are built on surface to simulate the influence of existing defects on the surface quality and surface cleanliness,the generation process of pollution sources inside the workpiece is analyzed from the microscopic level.Finally,ultra-precision turning experiments of aluminum under different cutting depths are performed,the surface roughness and surface composition of the specimen are detected to analyze the relationship between the surface quality and the surface cleanliness.