Research Of Molecular Dynamics-Based SiCp/Al Composites Ultra-Precision Cutting Mechanism

Particle-reinforced metal matrix composites(SiCp/Al),with aluminum as the matrix and SiC as the reinforcing phase,are widely used in many fields such as aerospace,automotive industry,electronic packaging,and optical instruments because of their superior properties such as high strength,high rigidity,high wear resistance,high thermal conductivity,and high oxidation resistance.However,there are still some difficulties in the processing of such composite materials,such as high surface roughness,high cutting force,high cutting temperature and severe tool wear.Therefore,it is necessary to conduct a detailed study on the cutting mechanism of particle-reinforced metal matrix composites in the ultraprecision cutting process in order to obtain a more reasonable processing method.Firstly,the method of establishing the molecular dynamics simulation model and the setting of simulation parameters are described to establish a nano-cutting molecular dynamics model with three potential functions,EAM,Morse and Tersoff,to assign the interactions between different kinds of atoms.The established model is applied to the study of the ultra-precision cutting mechanism of SiCp/Al composites.Secondly,the mechanism of strengthening and hardening of the SiCp/Al composite workpiece during cutting is discussed from the viewpoint of the slip expansion of dislocations and the interaction between different types of dislocations.It is found that the cutting force on the tool after completely cutting through the first SiC ball is higher than that on the first contact with the workpiece,which proves that the aluminum matrix between the two SiC balls is strengthened during the cutting process,mainly because the interaction between dislocations forms dislocation entanglement,stacking layer dislocations and dislocation locking during the cutting process,which hinders the slippage and expansion of dislocations and thus increases the strength of the aluminum matrix.The strength of the aluminum substrate is increased.By analyzing the stress distribution inside the workpiece during the cutting process,it is found that the internal stress of the workpiece is mainly concentrated in the area where the rear tool surface is in contact with the workpiece,which is the main reason for the machining hardening of SiCp/Al composites.Finally,the cutting process of SiCp/Al composites was investigated by a combination of experiments and molecular dynamics simulations to further investigate the mechanism of machined surface formation,brittle-plastic transformation and tool wear mechanism of SiCp/Al composites.It was found that: when diamond tools cut SiCp/Al composites in ultraprecision,due to the presence of SiC-Al interface and Al phase in SiC/Al composites,coupled with the high-pressure phase change in the contact area between the tool and the workpiece due to high temperature and pressure during the cutting process,the removal mode of SiC particles undergoes a transformation process from plasticity to mixed plasticity and brittle-plasticity to pure brittle removal,which is the cause of This is a fundamental factor in the reduction of cutting performance of composite materials.Due to the effect of shearing and squeezing of the tool,a large number of microscopic cracks are generated at the parts where the SiC balls are in contact with the tool,and these microscopic cracks continue to extend and expand with the cutting,which eventually lead to the brittle fracture of the SiC balls.Diamond tool wear is mainly caused when cutting SiC balls,and the cause of wear is mainly the graphitization phenomenon due to the destruction of the dense structure of diamond.