A novel cooling and lubrication approach: Device development and machining performance evaluation of ultrasonic vibration-assisted MQL

Abstract Minimum quantity lubrication (MQL) as a sustainable technology has gained popularity in addressing the conflict between environmental protection and the machining requirements during cutting processes. However, conventional MQL systems employ pneumatic atomization, resulting in the generation of oil droplets with large particle sizes and uneven distribution, eventually leading to the inadequate lubrication performance of the MQL jet. In this case, the present study employed a combination of ultrasonic atomization and MQL technique to propose a novel cooling and lubrication approach and fabricate the ultrasonic vibration-assisted MQL (UVMQL) device. Geometric parameters of the ultrasonic vibrator of this device were designed and optimized using the theoretical design and finite element simulation techniques. Additionally, the impedance and amplitude detected to evaluate the performance of the UVMQL device. Subsequently, the comparative experiments were carried out under five cooling and lubrication conditions in machining of ultra-high strength steels: dry cutting, wet cutting, high-pressure air cooling, MQL and UVMQL. Then, the machining performance of the UVMQL was discussed, in terms of cutting forces, cutting temperature, surface roughness, surface topography and chips. Results demonstrate that in comparison to MQL, UVMQL has a lower cutting force by 5.3N, leading to the formation of a more effective oil film lubrication layer. Due to the excellent penetration of fine oil droplets, UVMQL possesses a slightly higher cutting temperature than that of wet cutting by 43℃, whereas results in optimal surface roughness value and surface topography of the workpiece. Additionally, under UVMQL condition, the length of chip bonding zone is reduced by 39.8%, and the saw-tooth height of chip is decreased by 35.9% compared to dry cutting.