| Ti-5553 titanium alloy has excellent comprehensive mechanical properties because of its low density,high temperature resistance and corrosion resistance.It has been widely used in the manufacture of new aircraft structural parts.Ti-5553 titanium alloy is a ?-?/?-type titanium alloy.Because of its low modulus of elasticity,high chemical activity,adhesion and diffusion,the cutting performance is poor,which is mainly manifested in high temperature in the cutting area,easy burning on the surface of the workpiece,serious tool wear,low tool life,and no breakage of chips.Conventional cooling processing method has poor cooling effect and will cause environmental pollution.Liquid nitrogen cryogenic cooling cutting can effectively reduce cutting tool temperature by increasing heat flow,thus reducing tool wear and improving tool life.At present,there is little research work on tool surface temperature field in cryogenic cooling processing.Therefore,this paper takes Ti-5553 titanium alloy as an object to study tool temperature field in cryogenic cutting with liquid nitrogen.Firstly,the mathematical model of convective heat transfer coefficient under low temperature cooling is established.The liquid movement law near the tool surface during liquid nitrogen injection was analyzed,and the flow boundary layer and thermal boundary layer were defined.The characteristic number equation is established and the dimension is determined.Through the analysis of the influencing factors of convective heat transfer coefficient,the conservation equation is established and solved.The calculation formula of the heat transfer coefficient h on the tool surface is obtained.Thereby,the heat flux on the tool surface is estimated,which provides theoretical support for the determination of the cutting temperature and convective heat transfer coefficient under low temperature cooling.Secondly,convective heat transfer coefficient was determined by the experimental modeling method based on the combination of liquid nitrogen injection experiment and CFD model.The cooling rate measured by liquid nitrogen injection experiment was designed for fluid simulation by use of Star-CCM+ software.The liquid/gas ratio of liquid nitrogen injection process was corrected by experiment and simulation results,and the convective heat transfer coefficient h value of tool surface was finally determined.A polynomial model is established to analyze the influence of injection parameters on the surface heat transfer coefficient,and to optimize the injection parameters for the selection of simulation model parameters for cryogenic cooling turning.Finally,the finite element simulation of liquid nitrogen cryogenic cooling cutting of titanium alloy was carried out by using DEFORM-3D simulation software,and the cutting temperature changing law under dry and cryogenic cooling conditions were compared and analyzed.The experiment of liquid nitrogen cooling cryogenic cutting was carried out with thermocouple temperature measuring device,and the cutting temperature was measured to verify the simulation results of turning. |
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