Research On The Tool-Chip Friction Characteristics In Ultra-Precision Diamond Cutting Of Copper

Precision physics experiment of inertial confinement fusion of nuclear puts forward a very high requirement for the ultra-smooth surface of high purity metal copper parts.Due to the high stress and temperature of tool-chip contact surface near tool edge,the friction state between the bottom of metal material and tool rake is always sticking in process of metal cutting.So the tool-chip friction behavior is significantly different from the constant Coulomb friction.In addition,the two friction states of sticking and sliding can be transformed mutually with the evolution of cutting temperature,stress and other cutting factors,which leads to unstable cutting force and poor machining surface quality and tool wear.At the same time,the friction heat generation in the second deformation zone leads to the increase of cutting temperature,material thermal softening and the change of tool-chip contact properties.Especially for ultra-precision diamond cutting,the high thermal conductivity and low friction coefficient of tool lead to the difference of tool-chip friction characteristics in the cutting process.Therefore,it is of great significance to accurately characterize the frictional state between tool and chip in metal cutting and to clarify the influence law of technological parameters on the friction state between tool and chip for deeply exploring the frictional behavior between tool and chip and optimizing the machining process.In this paper,the diamond orthogonal cutting process of crystal copper is taken as the research object,the friction behavior between tool and chip and the influence law of different parameters on the friction state between tool and chip with the micron cutting scale are deeply analyzed through the combination of finite element simulation and cutting experiment.The specific research contents of this paper are as follows:The theoretical analytical study of tool-chip friction behavior in metal copper of diamond cutting is carried out.The tool-chip friction behavior is in-depth analyzed in the process of cutting,based on the sticking-sliding friction theory,the improved friction analytical model is set up containing the dynamic evolution of the process parameters to accurately describe the tool-chip fricition state in the cutting process with full consideration of thermodynamically coupled interaction.The FE simulation model of two-dimensional diamond orthogonal cutting process of crystal copper is established.Firstly,the key characteristicses of modeling are improved,the failure criterion based on fracture energy is introduced to prevent the influence of mesh size on element failure.In order to ensure the accuracy of heat transfer between tool and chip,the gap heat exchange coefficient between tool and chip is introduced.To prevent the calculation interference of temperature field and stress field during cutting process,the adaptive mesh technology is introduced to modeling of chip during thermodynamic coupling simulation.In addition,the improved tool-chip friction model is subprogrammed by Fortran language through VFRIC and associated with ABAQUS explicit solver,in which the effectiveness of the improved friction model is verified by the comparison with velocity field,stress field and other state parameters under the constant Coulomb friction model,which provides the technical basis for studying the tool-chip friction characteristics in diamond cutting.The simulation study on the characteristic and correlation of technological parameters in diamond orthogonal cutting process of metal copper is conducted.Firstly,the manufacturability in diamond orthogonal cutting of crystal copper is studied by the above FE model,and the influence of DOC,cutting speed,tool rake angle and tool edge radius on the tool-chip friction state,cutting temperature field and the residual stress of the machining surface are analyzed.The verification experiment in regard to tool-chip relative motion state and cutting force in diamond orthogonal cutting process of metal copper is carried out.The diamond orthogonal cutting experiments of crystal copper are carried out,the special fixture for high-speed camera is designed and the processing platform is set up.The influence of depth of cutting and tool rake angle on the friction state between tool and chip and the cutting force are studied to verify the predictive accuracy of the above simulation model.In addition,the chip morphology and relative motion state between tool and chip with different crystal orientations are compared in diamond orthogonal cutting of copper,and the influence of different crystal orientations on the tool-chip friction state is verified.Finally,based on the results of finite element simulation and experiment,the optimal process parameters in the diamond orthogonal cutting of copper are obtained.