Heat Transfer Mechanism And Experimental Rasearch Of Cryogenic Air Nanofluid Minimal Quantitity Lubrication Grinding On Titanium Alloy

Grinding is one of the most basic and indispensable machining methods in machining,and also plays an important role in the field of advanced manufacturing.The relatively high–speed motion between grinding wheel and workpiece will consume a lot of energy.The processing of grinding abrasive is generally negative rake angle processing,so material grinding consumes higher amounts of energy to remove a unit volume of materials compared with other processing techniques.Most of the energy consumed in the grinding process is converted into heat which accumulates in the grinding zone to form local high temperature,which leads to surface thermal damage?surface oxidation and burns?,even cracks and residual stress,and reduces the surface quality and integrity of the workpiece,thus the processing difficulty is increased greatly,especially for titanium alloys with high hardness and low thermal conductivity.At the same time,the agglomeration of high temperature will aggravate the wear of the grinding wheel and reduce the fatigue resistance of the grinding wheel,thereby reducing the processing accuracy and service life of grinding wheel.Therefore,how to achieve effective cooling and lubrication in grinding area is of great significance.“Made in China2025”clearly points out that green sustainable manufacturing and cleaner production are the inevitable requirement and development trend of manufacturing industry.Nanofluids minimum quantity lubrication technology possesses excellent lubrication effect,and also can effectively improve the utilization rate of cutting fluid and the surface quality of the workpiece.But there is still a bottleneck in the overall heat transfer capacity of this technology.Cryogenic air technology can effectively take away the heat in the processing area to reduce the temperature of the processing area and control the grinding damage.However,due to the lack of lubricantion,the surface quality of the workpiece is difficult to guarantee under cryogenic air.Combining the strong cooling and heat transfer performance of cryogenic air with the excellent lubrication effect of Nanofluids minimum quantity lubrication,it is expected to further improve the grinding performance.In view of this,this paper combines the two green processing technologies to further boost the cooling and heat transfer capability of the grinding zone while ensuring excellent lubrication effect,so as to achieve the effect of reducing the temperature of the grinding zone and improving the processing quality of the workpiece.In this paper,the theoretical analysis and experimental study of cryogenic air nanofluids minimum quantity lubrication are carried out.The main research contents are as follows:?1?On the basis that different boiling heat transfer states corresponds to different heat transfer capacity in grinding zone,the mathematical model of heat transfer coefficient of grinding temperature field is established.?2?The heat transfer performance in the grinding area of the grinding of titanium alloy under the condition of cryogenic air nanofluids minimum quantity lubrication was studied.A finite difference model of grinding temperature field is established.Based on the model,the temperature field in grinding zone under different cooling modes is numerically simulated and then experimentally verified.Furthermore,the cooling and heat transfer performance under different cooling modes is analyzed from the cooling and heat transfer mechanism in the grinding zone.?3?The effect of cryogenic air nanofluids minimum quantity lubrication on specific grinding energy and friction coefficient of the grinding of titanium alloy is investigated.The specific grinding energy and friction coefficient under different lubrication modes are obtained,and the lubrication mechanism of the grinding zone under cryogenic air nanofluids minimum quantity lubrication and nanofluids minimum quantity lubrication is analyzed in terms of viscosity,contact angle,stability of lubricating oil film,atomization effect of droplets and surface morphology of workpiece.?4?The effect of different cold air fraction of vortex tube on the heat transfer mechanism of cryogenic air nanofluids minimum quantity lubrication grinding is studied.Finite difference numerical simulation and verification experiments for the temperature field in grinding zone under different cold air fraction of vortex tube are carried out,and the simulation and experimental results are compared.Furthermore,the cooling and lubrication mechanism of grinding zone under different cold air fraction of vortex tube is analyzed from the aspects of specific grinding energy,viscosity of nanofluids,surface tension and contact angle of nanofluids,atomization and boiling heat transfer effectin grinding zone,and the optimum old air fraction for cooling and heat transfer effect in grinding zone is obtained.?5?The effect of Al₂O₃ nanofluid concentration on the heat transfer performance of cryogenic air nanofluids minimum quantity lubrication grinding is studied.The effects of specific grinding energy,viscosity and contact angle of nanofluids,dispersion of nanoparticles and atomization effect on cooling and heat transfer are analyzed and discussed.And then the optimal concentration of nanofluid for cooling and heat transfer in the grinding area are determined.