Investigation on cutting temperature of CFRP in robotic rotary ultrasonic drilling with minimum quantity lubrication

Carbon fiber reinforced polymer (CFRP) is widely used in aircraft manufacturing field because of superior physical and mechanical properties. Millions of connection holes require to be drilled on CFRP material, the cutting damage of holes has crucial effect on the aircraft performance. Robotic rotary ultrasonic drilling (RRUD) as a potential method is proposed to improve the drilling quality. Nevertheless, it is difficult to control the drilling temperature to avoid exceeding the glass transition temperature of the resin matrix in a dry cutting environment during RRUD. The minimum quantity lubrication (MQL) technology can improve cooling conditions and achieve temperature reduction effectively. In this paper, an investigation on cutting temperature during the processing method combining RRUD and MQL (RRUD&MQL) is carried out and a theoretical prediction model is established. Firstly, analysis on RRUD&MQL coupling friction reduction mechanism is conducted with consideration of periodic kinematics characteristic in RRUD and lubrication property of MQL droplets. After that, based on this friction reduction mechanism, thrust force is calculated and cutting temperature model is established. Finally, validation experiments results indicate that analytical cutting temperatures agree well with the experimental value, and the average of relative prediction error is 9.12 %.