Thermal equilibrium modeling of cutting zone cooled by supercritical CO2: A case study on Ti-6Al-4V validated with experimental data

Abstract

In recent years, cryogenic cooling techniques such as supercritical carbon dioxide (scCO2) cooling have been widely used for the machining of difficult-to-machine materials. Different from conventional homogeneous flood cooling cutting, the jet field temperature in cryogenic cooling is non-uniform. Additionally, the common modeling of cryogenic cooling describes heat transfer mainly from a transient perspective, making it hard to characterize the time-dependent dynamic impact of gas jet parameters on thermal equilibrium. This limitation set barriers to online monitoring of the thermal equilibrium in the cutting zone, resulting in its poor guidance on industrial applications. Therefore, this study aims to propose a modeling method that can guide industrial practice to evaluate the dynamic impact of gas jet parameters on thermal equilibrium. To consider the balance between model accuracy and industrial usability, the thermal equilibrium model with jet mass flow and cutting parameters as variables was established based on thermodynamic theory, analyzing the input and output of material and energy of the system from a continuous time domain perspective, i.e., enthalpy change of scCO2 and energy change of chips. Considering that the boundary conditions were simplified and assumed in modeling process, the reliability and applicability conditions of the model were further investigated, and the model was verified by experimental data of turning Ti-6Al-4V with scCO2 cooling. The results show that, jet distance affects the applicability of the model and that the model is acceptable within a certain jet distance (e.g. 15 mm). Meanwhile, the model can calculate the theoretical mass flow rate of scCO2 in variable cutting speed machining, where the model errors are less than 1.4 %. In summary, under the jet distance less than 15 mm, the modeling approach proposed in this study can provide a reliable estimate of the dynamic thermal equilibrium in the cutting zone and offer useful instructions for industrial applications.