Research On Multi-scale Simulation Of Multi-field Coupling Effects During Electrically-assisted Micro-forming In Titanium Alloy

Because of its high efficiency and cleanness,electrically-assisted forming has a promising application space in the field of micro-forming.A large amount of joule heat will be generated when the current flows through the conductor material,which will change the mechanical properties of the material.Therefore,as a new hot forming process,it has been widely concerned by researchers.It is necessary to carry out experimental and simulation research on the basic experiment of electrically-assisted forming because the plastic deformation of metal materials under current density will produce different deformation behavior from that in conventional hot forming.In this paper,the coupling effect of electric current is simulated at macro and meso scale.At the same time,the experiment of electrically-assisted compression and the simulation of current assisted upsetting process were studied.At the macro scale,the influence of electric current on the internal microstructure of the material is not taken into account.The material is considered as a homogeneous medium,and the average resistivity and thermal conductivity of the material are taken as the overall electrothermal physical property parameters for the electrothermal multi-field coupling simulation.Using DEFORM-3D finite element software,the changes of Joule heat temperature,stress field and strain field in the process of current-assisted micro-tension were simulated and predicted.The effects of electric pulse frequency,amplitude,duty ratio and sample size on current-assisted micro-tension were studied.At the mesoscopic scale,it is considered that there are defects such as grain boundary and holes in the material,and the influence of uneven resistivity distribution on current flow direction is considered.On the MATLAB platform,maxwell equations and Kirchhoff’s law were used to solve the distribution of electric field intensity and current density in the characteristic space,and the mesoscopic electrothermal coupling was obtained by finite difference method.The effects of current loading direction,grain size and micropore shape on the electrothermal distribution at mesoscopic scale were studied.The electrically-assisted micro-compression experiment and simulation study of TC4 titanium alloy were conducted.The deformation behavior of the micro-compression samples with diameters of 0.5mm,1mm,1.5mm and 2mm under different current densities was studied.It was found that the higher the current density,the better the softening effect of the material,and the martensitic transformation of the material occurred under the high current.In addition,it is found that the softening degree of the material is related to the size of the sample,and the relationship between the shape of the sample and the temperature is deduced theoretically.The finite element simulation of electrically-assisted microcompression was carried out,and the relationship between the compression deformation drum degree,current density and sample size was studied.Further,the current-assisted microupsetting process was simulated,and the advantages and disadvantages of the three forming schemes of end upsetting,a quarter part upsetting and center upsetting were studied.It was found that the improved current flow path could effectively improve the deformation capacity of the material.Under the same current density,the center upsetting was the best,followed by a quarter part upsetting,and the end upsetting was the worst.