Research On Thermal-mechanical Coupled Analysis And Work Hardening On Micro-milling Nickel-base Superalloy

The development of high-tech industries has placed a greater demand on processing technology for precision components.The components not only should be precision but also can work reliably under the terrible working conditions.Micro-milling technology,which can be used to fabricate precise three-dimensional complex structures on micro-parts with millimeter or less dimensions,meets the requirements of manufacturing micro parts.Nickel-base superalloy Inconel 718 still maintains the high strength under high temperature and has excellent comprehensive mechanical properties,which satisfies the requriements of those parts working under high temperature.However,nickel-base superalloy is a typical difficult-to-machine material,and the work hardening occurs during the the micro-milling process.Work hardening affects the quality of the parts and the tool life of the micro-milling cutter.So,study on work hardening of micro-milled nickel-base superalloy is necessary.Work hardening on the micro-milled surface is affected by cutting force and temperature.Accurate micro-milling force prediction model is the foundation of building a work hardening prediction model.Most of the existed micro-milling force models had not considered the effect of cutting temperature.During the micro-milling process,cutting force and temperature affect mutually.Therefore,the interaction between cutting force and temperature should be considerated,which is the prerequisite to predict micro-milling force and temperature accurately.The main contents of this paper are as follows:Based on the earlier established model of the instantaneous undeformed chip thickness by our research group,a prediction model of micro-milling force considering cutting temperature was built.According to Fourier's law,the temperature model was built then.Coupled calculation of micro-milling force and temperature was conducted to achieve the accurate prediction of mechanical-thermal condition.The influence rules of the spindle speed,the feed per tooth and the axial cutting depth on micro-milling force and temperature were studied through experiments.A three-dimensional micro-milling Inconel 718 model was established by utilizing Deform-3D.The effects of tool nose corner radius and main cutting edge radius on cutting temperature were studied through the simulation model.Inconel 718 stress-strain curve was acquired through quasi-static tensile tests.The strain hardening properties of Inconel 718 were obtained by fitting Hollomon equation according to the experimental data.Then,the microhardness of Inconel 718 on different residual strain was measured.The relationship between microhardness and residual strain was obtained by studying microhardness and the corresponding strain.Based on the built micro-milling force model,which considers the effect of cutting temperature,the stress on a point in workpiece during micro-milling was deduced.Through the relationship among the stress,strain and microhardness of Inconel 718 acquierd by tensile tests,the prediction model of the micro-hardness on the micro-milled surface was built.A 3D micro-milling simulation model of micro-milling Inconel 718 was built to investigate the distribution of the work hardening on the micro-milled surface of Inconel 718.