Research On The Electric-assisted Bending Forming Law Of Ti55 Integral Panel

Because of its high strength,light weight,long life and other advantages,integral panel is widely used in modern advanced aircraft and high-speed aircraft fuselage,wing and other parts.High-temperature titanium alloy grid-rib panel is more efficient than traditional aluminum alloy grid-rib panel,but it is difficult to form titanium alloy grid-rib panel at room temperature.The use of current electroplastic effect and Joule heating effect can effectively reduce the forming load,increase the forming limit,and can avoid the serious problem of titanium alloy heating and oxidation.Therefore,this paper proposes an electric pulse-assisted bending forming for Ti55 integral panelBased on the ABAQUS finite element analysis software,a coupled finite element model of the electric-thermal-structure of Ti55 alloy grid-rib panel with electric pulse-assisted bending is established.The temporal and spatial distribution of temperature,stress and strain during the forming process of the wall panel are analyzed,and it is found that the main reason for the instability of the transverse ribs is the compressive stress in the Y direction generated during the bending process.In this paper,the influence of different process parameters(current density,bending radius,current loading direction)on the quality of electric-assisted bending of grid-rib panel is studied.The current density affects the instability and rebound of the integral panel through the temperature distribution of the integral panel;the instability of the ribs increases with the increase in the amount of deformation.The greater the amount of deformation,the proportion of elastic deformation decreases,and the rebound rate of the integral panel decreases;Changing the direction of the current can effectively control the temperature of the transverse ribs so as to slow down the instability of the ribs,and the rebound is only slightly improved.By controlling the distribution of electric field,the instability and the rebound of integral panels can be effectively controlled when the temperature of transverse ribs is low and the temperature of web is high.Under the same process parameters,the degree of instability of the integral panel increases with the height of the ribs.The higher the ribs,the lower the critical load required for instability and the worse the stability of the ribs;When the thickness of the web is small,the temperature effect brought by it is greater than that of its own structure on the forming of the wall.When the thickness of the web is large,the temperature change is not obvious,mainly because its structure has an impact on the forming process of the wall;The smaller the spacing of the longitudinal ribs,the better the stability of the ribs,the ribs are less prone to instability,and the rebound will not increase due to the decrease in temperature.Taking rib height,web thickness and rib spacing as design variables,and aiming at the best combination of rib instability and integral panel springback,a multi-objective optimization mathematical model for the structural parameters of the panel under the limit ratio of height to thickness is established.The BP neural network prediction model is used as the knowledge source of the optimization algorithm,and the artificial neural network is combined with the modified genetic algorithm to optimize the structural parameters of the integral panel.The optimal combination of the structural parameters of the grid-rib integral panel is obtained as the rib height 9mm,the web thickness2.4mm,and the longitudinal rib spacing 11 mm.The electric-assisted press-bending insulation mold tooling was designed,the press-bending process test of the grid-rib integral panel was carried out,and the metallographic and micro-hardness test of the samples were carried out.The pulse current promotes the recrystallization of Ti55 alloy,the grain is refined,and the hardness of the material is higher.