Fundamental Study On High Speed Milling Of High Volume Fraction SiCp/Al Composite

High volume fracrion silicon carbide reinforced aluminum matrix(SiCp/Al) composites have superior physical and mechanical properties, such as high strength to weight ratios, low thermal expansion coefficient and low thermal conductivity coefficient, which make them as the ideal material for high power density electronic packaging shell and thermal control components. They have promising prospects in the field of advanced weapon systems and precision instruments, such as military communications satellite, airborne fire control radar and electronic equipment. However, due to the presence of hard and wear-resistant SiC particles in the aluminum matrix, machining SiCp/Al composites is encountered with extremely rapid tool wear and poor surface quality, thereby impeding their widespread application greatly. Therefore, exploring the method to solve the problems during the machining process of SiCp/Al composites appears to be quite necessary and urgent, which can promote the application of these material in the national high-tech field. This paper conducts fundamental study on high speed milling of high volume fraction(65%), small size(average size 10μm) SiCp/Al composite and the main research contents are as follows:(1) The study of micro-structure and mechanical properties of SiCp/Al compositeThe statistic analysis of the size, shape factor and fractal dimension distribution of the SiC are conducted on Matlab platform; the constants of Johnson-Cook constitutive model of matrix material Al6063 is identified by inverse identification method based on the results from the quasi-static compression, orthogonal cutting tests and cutting simulation; utilizing universal compression testing machine and split Hopkinson pressure bar, the strain-stress curves of SiCp/Al composite under the quasi-static and dynamic condition are obtained, and the influence of stain rate on the mechanical properties and failure mechanism of the material are investigated; an axisymmetric unit cell model is established, in which the interface between SiC particle and matrix is modeled as cohesive element, to investigate the influence of interfacial fracture energy, strength and volume fraction on the strain-stress curve of the SiCp/Al composite under tensile condition.(2) The study of milling process of SiCp/Al compositeBased on the platform of Abaqus/Explicit finite element software, a simplified round particles cutting model and a polygonal particles cutting model with SiC fracture parameters are established according to the milling geometry analysis to investigate the SiC fracture during cutting process; a new modeling methodology is proposed to build a microstructure-based cutting model by Python which consists of particle edges information extracted by Matlab; finally, the new model is utilized to investigated the formation process of the typical defects on the milled surface, such as the SiC fracture, a shallow cavity, a deep cavity and a swell, which are experimentally verified by 2D profile on milled surface.(3) The study of milled surface integrity of SiCp/Al compositeThe chip morphology is examined by Confocal Scanning Laser Microscope and Scanning Electron Microscopy, and the cutting mechanism is analyzed based on the dislocation theory; milling tests are carried out on SiCp/Al composite by PCD tool on central composite rotatable designs consisting of 31 experiments, and the significant main factors and interaction factors are investigated by response-surface methodology and analysis of variance, and the optimized milling parameters for minimum surface roughness are obtained by using genetic algorithm; speed and feed rate single factor test are designed to investigate the difference between 2D and 3D surface roughness parameters which is measured by Talysurf CCI non-contact surface profiler system; the influence of milling parameters on the residual stress of the milled surface of SiCp/Al composite and the corresponding matrix material are investigated.(4) The study of tool wear during milling SiCp/Al compositeIn order to solve the high tool wear rate during high speed milling of SiCp/Al composite, the PCD tool with different grain size are utilized to conduct high-speed milling tool wear tests. Utilizing Optical Microscopy, Confocal Scanning Laser Microscope, Scanning Electron Microscopy, Energy Dispersive X-ray Spectroscopy and Energy Dispersive X-ray Spectroscopy, the main tool wear pattern and mechanism, appropriate tool blunt criterion, main influencing factors on the tool cutting performance and the influence of tool wear on surface roughness are investigated.