Study On Chip Formation Mechanism Of Cutting SiCp/Al Composites

The SiCp/Al composite is a metal matrix composite reinforced with SiC particles in an aluminum matrix with high specific strength,high specific stiffness,low coefficient of thermal expansion,good thermal stability and also with excellent thermal conductivity,electrical conductivity and wear resistance,corrosion resistance and other characteristics,which makes it widely used in aerospace,advanced weapon systems,automotive industry,and electronics packaging and other fields.However,the addition of SiC particles into the aluminum matrix causes severe wear of the cutting tools of the SiCp/Al composites,which deteriorates the machinability,and the chip formation mechanism is also different from that of the conventional continuous metal materials.Therefore,it is very important to study the chip formation mechanism of SiCp/Al composites to guide its cutting process.In this paper,the SiCp/Al composites with different particle size ratios and particle sizes were used to study the formation process of SiCp/Al composites by orthogonal cutting tests.The influencing factors of cutting force,cutting temperature and deformation zone parameters were studied.The main works and conclusions are as follows:1.The chip roots was obtained by using a Self-made spring-loaded quick-stop device.For workpieces with different material parameters,it was found that chip shapes were changed due to the difference of matrix plasticity and the degree of crack propagation under different cutting parameters.The force and torque generated by plastic sliding of matrix causes the particles to be aligned along the shear bands.The fracture of particles mainly occur in the shear zones,the chip separation surface,the second deformation zone and the machined surface near the tool nose.The microcracks initiated from the outside free surface and interior of shear zone propagate along the shear plane and thread together.As the cracks propagate along the shear bands,the force subjected by the chips is unbalanced,which causes the chips to speed up to flow,and the malposition along the shear planes on both sides of the cracks leads to the formation of irregular saw-tooth chip.2.The variation of the cutting forces and cutting temperature when cutting samples of different material parameters under different cutting parameters were measured experimentally.It was found that the main cutting force of cutting composite SiCp/Al was slightly larger than that of cutting aluminum alloys,but the feed force was far greater.As the cutting speed increased,the cutting power increased,resulting in the cutting temperature increasing.Both the cutting force and the cutting temperature increased with the increasing of the feed rate,but decreased when the tool rake angle increased.The particle volume fraction and particle size had no significant effect on cutting force,but the cutting temperature increased with increasing the particle size.3.By using the cutting force and chip thickness measured experimentally,the shear deformation zone parameters were calculated and analyzed,and the influence of cutting parameters on the parameters of the deformation zone was analyzed.The relation between shear and friction angles of the SiCp/Al composites was obtained by fitting.The results show that the parameters of shear deformation zone of SiCp/Al composites are greatly affected by the cracks and the particles at the cutting edge.With the increase of cutting thickness and cutting speed,chip deformation coefficient,shear strain and friction angle decrease,and the shear angle increases.With the increase of volume fraction ratio,the number of cracks in the shear zone increases,and the relative sliding of the chip along the shear surface increases,which leads to the increase of the deformation coefficient and shear strain.The B value of ?=B-C(?-?)in the SiCp/Al composite is greater than 2024 Al,and the slope-C(negative value)is less than 2024 Al.