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%.

Carbon fiber-reinforcement plastics (CFRP) have been widely applied in modern aerospace industry with aluminum alloy in the form of thin-walled stacks due to their superior mechanical and physical properties. However, for CFRP, the heat accumulation occurs easily during countersinking process in consequence of low thermal conductivity. The surface thermal damage of CFRP caused by excessive heat would affect the fatigue and stealth performance of aircraft. Consequently, the countersinking temperature is an important indicator to judge the feasibility of CFRP countersinking process. In this paper, to investigate temperature of countersinking process, the application of rotary ultrasonic machining technology to CFRP/Al thin-walled stacks countersinking process under different stiffness conditions with drilling-countersinking integrated tool is carried out by FEA (Finite element analysis) and experiments. And the influences of cutting temperature on countersunk wall quality are discussed. The results demonstrate that the maximum countersinking temperature increases with the decrease of axial stiffness, and the ultrasonic vibration can effectively reduce maximum countersinking temperature by 22.9%-26.2%. Furthermore, analysis of the surface quality of countersunk wall shows that the countersunk wall roughness and defects gradually deteriorate with the increase of the maximum countersinking temperature. Meanwhile, the ultrasonic vibration can improve countersunk surface quality by reducing maximum countersinking temperature effectively.