Toward understanding the mechanism in ultrasonic cutting of silica aerogel composites using a bionic micro-serrated tool

As a nano porous thermal insulation material, the precision and low damage machining of silica aerogel composite is very challenging due to its mechanical properties of low strength, poor toughness, and easy cracking. This study proposes an ultrasonic cutting method of ultra-low-density silica aerogel composites by using a bionic micro-serrated tool. First, the ultrasonic cutting mechanism of micro-serrated straight tool is expounded. A novel bionic micro-serrated blade is designed and fabricated, inspired by the serrated mouthparts of the leaf-cutting ant. Then, a theoretical cutting force model of ultrasonic cutting of silica aerogel composites using a micro-serrated blade is proposed. The ultrasonic vibration improves the slice/push ratio of the tool, while the micro-serrated blade reinforces the stress concentration. Moreover, the experimental scheme and surface quality evaluation method are provided. The ultrasonic cutting performance in terms of cutting force and surface quality of silica aerogel composite is analyzed by using a micro-serrated blade. Quantitative parameters such as defect ratio and fractal dimension are utilized to evaluate the machined surface quality of silica aerogel composite. Experimental results demonstrate that ultrasonic cutting using a micro-serrated blade has the lowest cutting force and best surface quality among conventional cutting, ultrasonic cutting, micro-serrated blade, or non-micro-serrated blade. Among several micro-serrated blade with micro-serration spacing of 0, 20, 100, 200, and 400 μm, the lowest cutting force and best surface quality is obtained when the micro-serration spacing is 100 μm, and it indicates that there is an optimal micro-serration spacing to minimize the cutting force due to the adverse effects of micro-serration spacing on the number of stress concentration and the tool chip space. The results of cutting experiments show that a higher ultrasonic amplitude (10 μm) and a lower feed rate (50 mm/min), depth of cut (3 mm), and inclination angle (30°) can improve the processing quality.