Ultrasonic-assisted micro-milling of cortical bone: An experimental study

Bone machining is a critical aspect of orthopedic surgeries, where excessive heat generation can cause thermal necrosis and hinder patient recovery. Ultrasonic-assisted micro-milling (UAM) offers advantages by reducing cutting forces and heat generation. This study examines the effects of feed rate, rotational speed, tool diameter, depth of cut, and vibration amplitude on cutting force and temperature in UAM of cortical bone. 64 experiments were performed on fresh bovine cortical bone specimens prepared to consistent dimensions and stored to prevent moisture loss. Repeated central points in the design quantified experimental error and repeatability. Precision, calibrated instruments ensured accurate force and temperature measurements. Data were analyzed using regression modeling and statistical methods. Results showed that increasing rotational speed and vibration amplitude generally reduced cutting force and temperature, while feed rate and tool diameter had complex interactive effects. Multi-objective optimization using NSGA-II identified optimal conditions: for the X-axis, 1047 rpm, 63 mm/min feed, 1.5 mm diameter, 0.6 mm depth, and 30 μm amplitude; for the Y-axis, 990 rpm, 22 mm/min, 0.8 mm diameter, 0.2 mm depth, and 20 μm amplitude. Predictive models achieved temperature errors of 1.6% (X) and 7.6% (Y), and force errors of 12.9% (X) and 14.5% (Y). These models can help surgeons anticipate cutting conditions preoperatively, reducing surgical risks and preserving bone integrity. The findings support optimization of orthopedic machining processes, improving surgical outcomes and advancing bone-milling techniques.