Experimental investigation of the mechanics of conventional and ultrasonically-assisted drilling of cortical bone

Bone drilling is an important technique in orthopaedic surgical procedures. Larger bone drilling force and torque may produce unnecessary damage to the surrounding tissue. Previous investigations related to the enhancement of the bone drilling process were performed using conventional drilling (CD). In this paper, an experimental analysis was carried out to investigate the advantages of ultrasonically-assisted drilling (UAD). The paper studies mechanics of the bone drilling process with and without ultrasonic assistance, chip formation mechanisms and chip morphology which affect thrust force, torque and surface quality of the drilled hole. High-speed filming and optical microscopy were performed to visualize the chip formation process in the drill-bone interaction zone and differences in the morphology of bone chips produced by both types of drilling. It was found that UAD produces small and segmented chips and keeps the drill flutes clear from chips and eliminates clogging whereas CD tends to produce longer chips that clog the flutes. UAD resulted smaller drilling thrust force, torque and produced smoother surface.