Effects of ultrasonic vibration-assisted on accuracy of robotic rotary countersinking

Carbon Fiber Reinforced Polymer (CFRP) and aluminum stacked are widely used in aircraft assemble thanks to the high strength-to-weight ratio. Riveting is an important joining technique of stacked structure and requires drilling and countersinking. Robotic machining systems are gradually used in the machining of holes due to their high flexibility. However, weakly rigid stacked structure and low-stiffness industrial robot system bring about complex and diverse countersinking depth errors, which significantly affects the fatigue life of components. In this paper, the influence mechanism of ultrasonic energy on the accuracy of robotic countersinking of stacked structure is investigated. Firstly, a workpiece deformation model is established with the thin-walled plate deformation theory, defined as static error. Then, the vibration of the industrial robot is calculated from the acceleration with the frequency domain integration, defined as dynamic error. The suppression of ultrasonic energy on the two kinds of errors were elucidated, respectively. Base on this, a depth compensation model of robotic ultrasonic countersinking is established. Finally, the feasibility of the accuracy compensation is experimentally verified, and the countersinking depth error can be controlled within ±0.09 mm.