Electrostatic atomization minimum quantity lubrication (EMQL) technology has been developed to address the need for environmentally friendly, efficient, and low-damage grinding of challenging titanium alloy materials. EMQL leverages multiple physical fields to achieve precise atomization of micro-lubricants, enabling effective lubrication in high temperature, high pressure, and high-speed grinding environments through the use of electric traction. Notably, the applied electric field not only enhances atomization and lubrication capabilities of micro-lubricants but also significantly impacts heat transfer within the grinding zone. In order to explore the influence mechanism of external electric field on spatial heat transfer, this paper first comparatively analyzes the grinding heat under dry grinding, MQL, and EMQL conditions and explores the intensity of the effect of external electric field on the heat transfer behavior in the grinding zone. Furthermore, the COMSOL numerical calculation platform was used to establish an electric field-enhanced (EHD) heat transfer model, clarifying charged particles’ migration rules between poles. By considering the electroviscous effect, the study reveals the evolution of heat transfer structures in the presence of an electric field and its impact on heat transfer mechanisms.

The machining of Ti-6Al-4V thin-walled parts is characterized by high cutting temperatures, significant force fluctuations, and complex thermomechanical coupling. Cryogenic Minimum Quantity Lubrication Technology (CMQL) uses bio-lubricant as the lubrication carrier, combined with the cooling characteristics of cryogenic temperature medium, showing good cooling and lubrication performance and environmental friendliness. However, the cooling and lubrication mechanism of different cryogenic media in synergy with bio-lubricants is still unclear. This paper establishes convective heat transfer coefficient and penetration models for cryogenic media in the cutting zone, based on the jet core theory and the continuum medium assumption. The model results show that cryogenic air has a higher heat transfer coefficient, while cryogenic CO₂ exhibits a better penetration ability in the cutting zone. Further milling experiments show that compared with cryogenic air, the average temperature rise, average cutting force and surface roughness of workpiece surface with cryogenic CO₂ as cryogenic medium are reduced by 23.6%, 32.8%, and 11.8%, respectively. It is considered that excellent permeability is the key to realize efficient cooling and lubrication in the cutting zone by Cryogenic CO₂ Minimum Quantity Lubrication Technology. This study provides a theoretical basis and technical reference for efficient precision machining of titanium alloy thin-walled parts.

Abstract: In recent years, a large number of patents have been devoted to developing minimum quantity lubrication (MQL) grinding techniques for environment friendly, energy saving, and cost-effective grinding fluid alternatives. One patent involves the nanoparticle jet flow in the MQL of grinding lubricant supply systems. An MQL grinding lubricant is prepared by adding nanoscale solid particles into a degradable grinding liquid. The lubricant is turned into pulse liquid drops with fixed pressure, variable pulse frequency, and invariant liquid drop diameter. The pulse liquid drops are sprayed into a grinding region in the form of jet flow by an air-isolating layer formed by high-pressure gas. The system has the advantages of MQL technology, has high cooling performance and excellent tribological characteristic, and plays an important role in effectively avoiding grinding burn, thus enhancing the surface quality of the workpiece and realizing an efficient, low consumption, environment friendly, economic, low carbon, and clean production. The temperature field model of surface grinding with a nanoparticle jet flow of MQL and the proportionality coefficient model of the energy input workpiece were established. The surface grinding temperature fields of 45 Steel and 2Cr13 were numerically simulated. Results show that the surface temperature of the workpiece is significantly higher than the subsurface temperature, thus presenting a relatively large temperature gradient along the direction of workpiece thickness. Grinding depth significantly affects grinding temperature. The values of grinding temperature increase with increasing cutting depth. The uniform distribution rules of the 2Cr13 temperature field are observed in four cooling and lubrication approaches: dry grinding, flood grinding, MQL, and nanoparticle MQL jet flow. Experiments are conducted to verify the simulation results. The results show that grinding temperature increases significantly with the increasing peripheral velocity of the grinding wheel. Furthermore, the movement speed of a workpiece is inversely proportional to the grinding temperature and a larger cutting depth contributes to higher grinding temperature. These results are consistent with theoretical analysis and show the effectiveness of the simulation method.