Machinability Improvements Through Active Thermal Conductive Medium Coated On Workpiece Surface To Be Machined

While nickel-based superalloy GH4169 exhibits excellent fatigue and impact resistance,its remarkable mechanical and chemical properties also result in poor machinability.The low thermal conductivity and specific heat of GH4169 lead to slow heat transfer during cutting,causing high thermal stresses to accumulate between the tool and workpiece.Consequently,this leads to elevated temperatures and severe tool wear,as well as compromised surface integrity of the workpiece.Therefore,reducing the cutting temperature during the processing of GH4169 has been a focal point of research.This study aims to investigate the mechanochemical effect and enhanced heat transfer effect produced by the application of an active thermal conductive medium on the machined surface of the workpiece.By employing cutting theory analysis and establishing a temperature model for cutting,the study examines the cutting forces,cutting temperature,and workpiece surface integrity when using a surface-coated active thermal conductive medium.Furthermore,the influence of the thermal conductivity of the surface-coated active thermal conductive medium on cutting forces and cutting temperatures during the processing of GH4169 is explored.The study reveals the multi-physical field mapping relationship between the thermalmechanical load during cutting with the coated thermal conductive medium and surface integrity indicators.The research findings contribute to improving the machinability of challenging materials and optimizing the selection of active thermal conductive media.To begin,first principles and material plastic deformation theory are utilized to analyze the adsorption mechanism of the active thermal conductive medium during the cutting process,including the induction of micro-crack formation,dislocation accumulation,and plastic deformation.Orthogonal cutting experiments are conducted on GH4169 surfaces coated with the active thermal conductive medium,enabling observations of dislocation accumulation,cutting forces,chip thickness,and chip morphology in the shear deformation zone.The effects of surface coating with the active thermal conductive medium on the machinability of GH4169 are analyzed.The research indicates that the chemical bonds formed by the active thermal conductive medium exhibit good affinity,facilitating surface adsorption.The chemical bonds formed between the active thermal conductive medium and the coated material surface reduce the surface free energy of the interface,thereby mitigating the mechanical-chemical effects.The reduction in surface free energy leads to dislocation accumulation and stress concentration,ultimately lowering the critical stress required for crack nucleation.Cutting forces and maximum chip thickness decrease with an increase in the thermal conductivity of the active thermal conductive medium.When cutting with the active thermal conductive medium,microcracks appear on the free surface of the chip,accompanied by a reduction in chip thickness.Furthermore,the enhanced heat conduction mechanism resulting from the surface coating of the active thermal conductive medium is elucidated.Based on interface thermal conduction and Fourier heat transfer theory,a numerical analytical model for heat conduction of the active thermal conductive medium is established to simulate and analyze the enhancement of heat conduction.The study unveils the influence of the active thermal conductive medium on heat conduction.The findings show that the influence of the thermal conductivity of the active thermal conductive medium on the temperature difference on both sides of the cutting shear deformation zone in GH4169 increases with an increase in its thermal conductivity.During the stage where the thermal conductivity of the active thermal conductive medium increases from 0 to 40 W/(m·℃),the heat dissipation enhanced by the active thermal conductive medium rapidly increases.As the thermal conductivity changes from 40 W/(m·℃)to 80 W/(m·℃),the growth of the temperature difference becomes gradual.After the thermal conductivity reaches 80 W/(m·℃),the temperature difference tends to flatten.Moreover,the enhanced heat transfer effect of the active thermal conductive medium is more significant at high temperatures.Next,based on the theory of heat generation,dissipation,and heat conduction in cutting,models for predicting the chip temperature and instantaneous temperature field of the workpiece after the application of the active thermal conductive medium on the workpiece surface are established.The study reveals the influence of the enhanced heat transfer effect of the active thermal conductive medium on the chip temperature during cutting and the transient temperature field of the workpiece.The research indicates that the active thermal conductive medium enhances the dissipation of heat on the chip backside and workpiece surface,reducing the accumulation of heat in the workpiece and lowering the cutting temperature.A larger thermal conductivity of the active thermal conductive medium results in higher heat dissipation efficiency.The application of a surface-coated active thermal conductive medium,specifically graphene,exhibits the most pronounced decrease in chip temperature and workpiece surface temperature.The accuracy of the theoretical models is validated through practical applications.Finally,the study investigates the impact of the thermal-mechanical load during cutting with the surface-coated active thermal conductive medium on the surface integrity of GH4169,including surface roughness,microhardness,and residual stresses.The research reveals that the reduction in cutting forces and cutting temperatures due to the surface-coated active thermal conductive medium leads to a decrease in residual thermal and mechanical stresses within the workpiece.This alteration results in changes to the grain size in the processed surface layer and a corresponding variation in microhardness.The improvement of surface roughness in the machined surface is observed.