Research On The Stretch Bending Forming Process Of Railway Vehicle Stainless Steel Curved Beam With Variable Curvature

With the rapid development of economy and the fast growing of the urban population of china,rail transportation has become an important industry for the country’s priority development.Because of the advantages of large transport capacity,environment protection,rail transportation can effectively alleviate a series of problems caused by the increasing of private cars in cities,such as environmental pollution,traffic jams and energy shortage.Stainless steel profile has high corrosion resistance,the strength,stiffness and other performance of stainless steel are significantly better than that of ordinary carbon steel,so stainless steel profile is widely used in manufacture of new type of railway bending beam and curved beam.Stretch bending forming process can improve the precision of forming parts,reduce the forming defects,therefore it is widely used in the manufacture of rail structural profile.In this paper,numerical simulation and experimental method were combined to analyze the stretch bending forming process of bottleneck beam,the main research and conclusions are as follows:(1)For the wrinkle defects in the small arc region done numerical simulation during the stretch bending process of the variable curvature beam.Results showed that wrinkling height in small arc region decreases with the reducing of the die-clearance,but the reduction of die-clearance can not completely eliminate the wrinkling defects,and when the die-clearance is extremely small,the resistance between die-clearance and the vertical edge of profile is large,leading to poor section contour accuracy.With the increasing of amounts of stretching,the wrinkling defects of profiles get better,and when the amount of stretching is more than 7.5%,the wrinkling defects of profiles almost disappear.The height of profiles vertical edge also affects the wrinkling defects,in the premise of fixing the length of flange,the wrinkling defects become more serious as the vertical height of the profile increases.(2)For the section distortion defects done numerical simulation during the stretch bending process of the variable curvature beam.Results showed that the depth of diestanding seam heights has a great influence on cross section distortion,the depth should be lower than appropriate height of profile vertical edge.when the depth of die standing seam heights is too small,vertical edge will twist and flange will collapse because profile flange side lacks of the support from broadside of die;when the depth is excessive large,vertical edge will twist and flange will wrap because profile vertical side lacks of the support from bottom of the die.Simulations were carried out on 5 sets of different stretching amounts.The results showed that the profile has the best cross-section accuracy when the stretching amount is 10%.The distribution of the stretching amounts has a great influence on the cross-section distortion.Under the premise of a fixed total stretching amount,it is best to appropriately distribute stretching amounts in the small arc region.Multi-distribution of the stretching amounts in the remaining arc regions or excessive distribution of the stretching amounts in the small arc region will cause a certain cross-sectional distortion.(3)Established stretch bending springback analysis model of curved beam,studied the influencing factors on the springback,the results showed that increasing pre-elongation and post-elongation will reduce the springback of bending beam,but the effect is not obvious.In the case of fixed total stretch amounts,the different distributions of the stretching amounts have a great influence on the springback,in which the more distribution of the stretching amounts in transition arc region,the less the springback.Mold surface modification based on springback compensation can effectively improve the accuracy of bending beam profile.(4)Based on the the optimal process parameters and moulding surface compensation after the design of curved beam,developed and manufactured the stretch bending die and carried out forming experiment.After measuring,the profile had high contour accuracy and without wrinkling and cross section defects.The result verified the predictive accuracy of the simulation and provided guidance for actual manufacturing.