| Stainless steel plays an important role in the railway vehicle.As an important component of the roof structure,the hat-shaped curved beam can not only reduce the weight of the car body,but also enhance the strength of the car body structure and reduce the maintenance cost.Four-roll bending is one of the forming methods of stainless steel curved profile because of its low cost and high efficiency.However,the strength of stainless steel is large,and the spring back is also large during roll bending.In this paper,the finite element simulation method is used to study the four-roll bending of the stainless steel hat-shaped curved profile,analyze the dynamic springback of the bending,explore the springback compensation method and the analysis of the forming factors.In order to provide a reference for the roll forming of stainless steel hat-shaped curved beams.The main research contents of this paper are as follows:(1)Establishing a four-roll bending finite element model of stainless steel hat-shaped curved profile with constant and variable curvature,analyzing the causes of roll-bending spring back and the characteristics of dynamic spring back of four-roll bending.(2)Through the comparative analysis of different springback compensation methods,the over bending method is used for compensation.The formula of curvature radius based on over bend compensation is derived,and the springback of each arc segment after discretization is corrected.The numerical simulation of the roll bending is carried out with the corrected radius of curvature to reduce springback,and improved the forming accuracy of rolled parts.The simulation results show that the error of the forming radius after the rebound of each arc segment does not exceed 2%,and the springback compensation effect is good.(3)Analyze the influence of four-roller bending springback,cross section distortion and wrinkling by simulations.The results show that the springback is larger if the roll-bending's radius is longer,The springback is smaller if the up-roller press more,The springback is smaller if the wall of the profile is thicker,The springback is larger if the coefficient of friction is bigger;When the gap between the roller and side wall profile is 0.2 mm,the gap between the roller and brim is 0.5 mm,the cross section distortion is smallest.When the vertical gap between the profile and roller is 0.5 mm,the pressing force is 4 kN,the profile is not easy to wrinkle.(4)Based on the compensation method of four-roll bending springback of stainless steel hat-shaped curved beam,simulations were carried out on four-roller bending springback compensation studying.The results show that the calculation method of curvature radius based on over-bending compensation,it can reduce the springback of stainless steel roof camber beam parts,and can be applied to the springback compensation of variable curvature roof curved beam parts. |
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