Theoretical analysis of cooling mechanism in high-speed ultrasonic vibration cutting interfaces

Cutting temperature has been found as the key factor for the tool life and surface quality during the machining of the difficult-to-cut materials (e.g., titanium and super alloys). To control the cutting temperature, a high-speed ultrasonic vibration cutting (HUVC) method has been proposed by existing research, in which the tool and workpiece have periodic separations and thus open the closed cutting interfaces compared with conventional cutting (CC). On that basis, the coolant can penetrate in the cutting interfaces which is quite different from the cooling methods for CC. Accordingly, in this study, Finite element method (FEM) and experiment methods were used to examine the cooling mechanism in the opened cutting interfaces based on the coolant state, which can guide further scientific research and engineering application of HUVC or even CC. At first, the expanded conventional model and the ultrasonic vibration model used to describe CC and HUVC were developed. Subsequently, FEM was used to examine the transient states of the velocity, pressure, temperature and synergy angle fields in the interfaces opening process. Next, ultrasonic vibration interfaces observation through high-speed visualization was conducted to verify the accuracy of the calculation results using the FEM. Lastly, the cutting experiments on titanium alloys were performed to verify the trends of the FEM results. As revealed by the results, ultrasonic vibration would lead to reversed flows by the negative pressure generated when the interfaces were opening. Subsequently, this reversed flow would lead to the formation of unstable thermal boundary layer, thus increasing the field synergic effect, which directly enhanced the heat flux and convection of the coolant in the opened cutting interfaces. • Cooling mechanism are revealed from the aspect of coolant state. • Coolant state is observed through high-speed visualization. • Unstable thermal boundary layer is the core factor of effective cooling. • Well field synergic effect is the reason of heat transfer enhancement by ultrasonic vibration.