Mathematical modeling and experimental studies on axial drilling load for rotary ultrasonic drilling of C/SiC composites

Ceramic matrix composites of type C/SiC have great potential in space applications because of their superior properties such as low density, high wear resistance, and high-temperature resistance. However, due to their heterogeneous, anisotropic, and unstable thermal properties, the machining is still challenging to achieve desired efficiency and quality. For advanced materials, rotary ultrasonic machining (RUM) is considered as a highly efficient technology. Predicting mechanical load in RUM can help to optimize input variables and reduce processing defects in composites. In this research, a mathematical axial drilling load (force and torque) model has been developed based on the indentation fracture theory of material removal mechanism considering penetration trajectory and energy conservation theorem for rotary ultrasonic drilling (RUD) of C/SiC. Experiments were conducted on C/SiC composites to validate the model, and experimental results agreed well with model predictions with less than 14% (force) and 10% (torque) error. Therefore, this theoretical model can be effectively applied to predict axial drilling load during RUD of C/SiC. The relationships of axial drilling force and torque with machining process parameters, including spindle speed, feed rate, and ultrasonic power, were investigated. A specific range of experiments was carried out to demonstrate the benefit of ultrasonic vibration in RUD over conventional drilling (CD) on mechanical load for a designed drilling tool. It was noticed that RUD outperformed CD with a maximum of 38.11% and 34.30% in axial drilling force and torque reduction, respectively. The influence of drilling tool flute length on drilling performance was also elucidated based on a set of experiments using several designed drilling tools.