Fundamental Research On Ultra-precision Turning Of SiC_p Reinforced Aluminum Matrix Composites

Silicon carbide particle reinforced aluminum matrix composites (SiC_p/Al) have many outstanding properties of high specific stiffness/strength, high wear resistance, low density, high thermal conductivity and low thermal expansion, which make them find inceasing applications in some precision or ultra-precision fields, such as inertial guidance systems, satellite antennae/bearing and laser reflection mirror. Therefore, researchers have paid great attention to the ultra-precision machining of this kind of material. At present, the research about ultra-precision machining of SiC_p/Al composites is still at its initial stage. The present study intends to focus on ultra-precision turning mechanisms and technology for SiC_p/2024Al and SiC_p/ZL101A composites. The following original researches have been performed:1. Chip formation in the ultra-precision turning of SiC_p/Al compositesShear strain/strain rate during the course of serrated chip formation have been calculated. Combined with microhardness measurement on different part of the chip, the deformation characteristics of material in the premier and second shear zone were understood. Chip appearance and chip root metallographic structure were studied and strain, strain rate and local temperature rise were computed to investigate the dynamic generation and spread mechanisms of microcracks in the shear zone. The relationship between this dynamic behavior of microcracks and chip shape/chip formation process was discussed. The mechanisms of semi-periodic variation of chip thickness were discussed, and combining with shear angle changing and dynamic behaviour of microcracks, models of chip forming process were established for SiC_p/Al composites with different reinforcement volume fraction.2. Surface generation mechanisms and machined surface defectsFrom the angle of material swelling and side flow, tool-workpiece relative vibration, feed rate and tool nose radius, SiC particle volume fraction and size, removal mode of SiC particles, surface generation mechanisms when ultra-precision turning SiC_p/Al composites was discussed. Surface generation mechanisms and its relationship with machined surface defects were expounded and the machining induced defects were evaluated comprehensively.3. Factors that affect ultra-precision turning surface roughnessThe influences of cutting tool material, reinforcement volume fraction and size, feed rate and tool nose radius, cooling and tool wear conditions on surface roughness Ra have been investigated when ultra-precision machining of SiC_p/Al composites, which provided important references for selecting the rational machining parameters and tools.4. Diamond tool wear pattern and its mechanismsThe wear pattern and its mechanisms of Single Crystal Diamond (SCD) and Polycrystalline Diamond (PCD) tools have been investigated. The results of this study have offered important rules for selecting rational crystal orientation when SCD tool ultra-precision turning of different SiC_p/Al composites.