| Silicon carbide particle-reinforced aluminum metal matrix composites (SiCp/AlMMCs) are widely applied in aviation, aerospace and electronic package fields due totheir excellent physical and mechanical properties. When machining high volumefraction SiCp/Al MMCs, the tool wear is serious, machining properties deteriorationbecomes more serious, machining precision and surface quality are poor due to thepresence of hard and brittle SiC particles. Electrical discharge machining, laserprocessing, ultrahigh speed precision processing possess low processing efficiency, highprocessing cost, limited processing range, and the processing demands of the rapidgrowth of components produced by high volume fraction SiCp/Al MMCs can’t besatisfied. There needs a new method to solute the high-speed and high efficientmanufacturing problems of SiCp/Al MMCs. Ultrasonic longitudinal-torsional vibrationhigh-speed milling, together with the advantages of ultrasonic longitudinal-torsionalvibration machining and high-speed milling, provides a new idea for high-speed andhigh efficient machining of high volume fraction SiCp/Al MMCs.In this paper, cutting characteristics of high volume SiCp/Al MMCs with ultrasoniclongitudinal-torsional vibration high-speed milling are studied. The ultrasonic acousticsystem is developed, the movement model of ultrasonic longitudinal-torsional vibrationmilling is established, the basic principle of forming longitudinal-torsional vibrationcausing by diagonal slits in ultrasonic transformers is studied, the ultrasonic transformervibration form is simulated, and the structural parameters of the ultrasonic transformerare optimized. Researches on Chip shapes and formation mechanisms of ultrasoniclongitudinal-torsional vibration milling are carried out, the influence of ultrasoniclongitudinal-torsional vibration on the chip flow is analyzed, and physical model of chipformation is established. The influences of milling parameters and tool deformation onmilling forces are studied, establishing theoretical formulas of milling forces. Theinfluences of milling parameters on surface roughness are analyzed, obtaining theoptimum milling parameters. The removal methods of SiC particles with ultrasoniclongitudinal-torsional vibration milling are analyzed, their influences on machinedsurface are studied, and further study on material removal mechanism is discussed. The results show that ultrasonic transformer with diagonal slits can effectivelychange the longitudinal vibration into longitudinal-torsional vibration, and ultrasonictransformer possesses large amplitude vibration, good stability. The developedultrasonic longitudinal-torsional vibration acoustic system possesses good impedancematching characteristics and excellent vibration stability, it meets the milling demand.The sawtooth chips are primary chips produced by the ultrasonic longitudinal-torsionalvibration high-speed milling due to the changed chip formation mechanism. Becausethe vibration effected on the tool can improve cutting condition, reduce the frictioncoefficient and ensure good tool shape due to improved cutting tool rigidity. At the samemilling conditions, the milling forces of high volume fraction SiCp/Al MMCs withultrasonic longitudinal-torsional vibration high-speed milling are lower than withhigh-speed milling. When machining high volume fraction SiCp/Al MMCs withultrasonic longitudinal-torsional vibration high-speed milling, the particles are directlycut off and less broken, and smoothness of machined surface is good due to changedremoval mechanism. Among the influence of cutting parameters on surface quality,biggest one is milling depth, and least one is milling speed both high-speed milling andultrasonic longitudinal-torsional vibration high-speed milling. |
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