Abstract: Due to the great hardness of SiC reinforcements, high volume fraction silicon carbide-reinforced aluminum matrix composites (SiCp/Al) are considered as one of the most difficult-to-machine materials. Rotary ultrasonic machining (RUM) is considered to be an effective method for machining such materials. The material removal mechanism of SiCp/Al composites in RUM is studied by ultrasonic vibration-assisted scratch tests. The experimental results reveal that under ultrasonic vibration, the plastic deformation of aluminum matrix occurs in the material and the surface of the aluminum matrix is compacted; SiC reinforcements are hammered into small particles and are easy to be removed away. Because most of the defects are produced in the process of removing SiC particles, the removal mode of SiC reinforcements plays a decisive role in the formation of the machined surface of SiCp/Al composites. The machining quality of SiCp/Al composites can be improved effectively through selecting appropriate machining parameters. Experiments on process characteristics show that ultrasonic vibration can effectively reduce the cutting force; the spindle speed has the greatest effect on normal cutting force, followed by the feed rate, and finally the depth of cut; the effect of spindle speed on the surface quality is also the largest and the surface roughness increases with the spindle speed. Therefore, in the machining process, in order to obtain better machining surface quality and machining efficiency, the larger depth of cut can be chosen properly, the larger feed rate can be selected on the basis of ensuring the machining surface quality and the appropriate spindle speed should be adopted in the premise of ensuring tool life.

Key words: material removal mechanism, process characteristics, rotary ultrasonic machining, SiCp/Al, ultrasonic scratching