1. College of Mechanical and Electrical Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China;
2. JITRI Jiangsu Industrial Technology Research Institute, Nanjing 210016, China
To reduce drilling temperatures and improve the machining quality of CFRP/Ti6Al4V laminates, this study proposed a cryogenic minimum quantity lubrication (CMQL) technique, utilizing the high solubility of lubricant in supercritical carbon dioxide (ScCO2). Tests were conducted on the droplet atomization performance and output temperature of the CMQL system, followed by low-frequency vibration drilling experiments under CMQL conditions for CFRP/Ti6Al4V laminates. The influence of CO2 pressure on laminate drilling was analyzed. The results demonstrate that increasing CO2 pressure enhances the atomization and cooling capability of the CMQL system. When the pressure increases to 8 MPa, CO2 presents as supercritical state, and the output temperature drops to below –80 ℃. As the system pressure rises from 5 MPa to 9 MPa, the drilling temperatures of CFRP and Ti6Al4V layers decrease by 15.91% and 50.78%, axial forces increase by 65.22% and 20.26%, and torques decrease by 23.33% and 16.77%, respectively. Moreover, the burr height at the Ti6Al4V layer exit decreases by 42.04%, the delamination factor at the CFRP layer exit is reduced by 5.41% and a low roughness of borehole wall of CFRP/Ti6Al4V laminates is achieved at pressures of 7 MPa, 8 MPa and 9 MPa.