Numerical Simulation Of The Stretch Bending Forming For The Stainless Steel Curved Beam

The rail transportation with a large amount of transportation,energy saving,fast and a series of advantages,our country has rail transit as an important development plan.Stretch bending forming technology is widely used in the production of rail vehicles,the main reason is that the profile has the advantages of small cross section distortion and small springback after stretch bending forming.The stretch bending forming process is mainly composed of analytical calculation,experimental analysis and finite element numerical simulation,in which the use of finite element simulation method can shorten the production cycle,improve the forming quality and material utilization,reduce costs.In this paper,we mainly study the stretch bending forming of the SUS301L-DLT stainless steel curved beam of a rail vehicle body.The influence of process parameters on the distortion and springback of the section is analyzed by using the analytical method and ABAQUS simulation software.The optimal parameters are found and verified by experiment.In this paper,the influence of the vertical depth of the die,the amount of wrap-elongation and the gap of the holder on the distortion of the cross-section is studied.The simulation is carried out in the case of the initial vertical depth of the die is H mm and the amount of wrap-elongation is 7.5%,when the depth of the die is 18 mm,the profile is straight and the side is slightly admit,with an offset of 0.14 mm,which meets the production requirements.The depth of die is too large or too small will have different degrees of influence on the section.After determining the die depth of 18 mm,the effects of the wrap-elongation of 2.5%,5%,7.5%,10%and 12.5% on the cross section distortion are simulated,it is assumed that the excessive amount of the wrap-elongation will cause the profile to be admitted and the string is warped;and too small amount of wrap-elongation can make profile edge eversion,finally,combined with the springback and section distortion,the optimum amount of stretching is 7.5%.Finally the influence of holder gap on cross section distortion is studied,the holder gap is simulated with 0mm,0.5mm,1mm and 2mm respectively,the results shows that the gap is too small to increase the friction during the bending process,and the edge of the profile is collapsed,resulting in a high cross section,the gap is too large to make the profile edge eversion.Finally,the optimum holder gap is determined to be 0.5mm.After the end of the stretch bending,the bending of the beam section of the phenomenon of distortion due to springback.Therefore,the influence of pre-elongation,post-elongation and wrap-elongation on the distortion of the section is analyzed.A series of simulation studies are carried out,the variation law of large arc section,small arc section and side bend of curved beam is analyzed.The results show that the springback of the curved beam decreases with the increase of the amount of pre-elongation,and the distortion of the section is improved,but the effect is not obvious.The springback of the curved beam decreases with the increase of the amount of post-elongation,especially the bending effect of the curved side of the curved beam is improved obviously with the increase of the amount of post-elongation.The springback of the curved beam decreases with the increase of the amount of the wrap-elongation,and the effect of the wrap-elongation is one of the main ways to reduce the springback in the actual production.As a result of further increase the amount of tension will lead to profile cracking,so it is necessary to modify the die through the compensation method,thus correcting the profile accuracy.According to the simulation of the best process parameters and the correction of the die surface compensation,the tension bending test is carried out by using the stretch-wrap CNC bending machine.The bending beam forming precision is very good,and the simulation results are very consistent,and meet the production requirements.The above conclusion provides a clear theoretical guidance and experimental basis for the bending process of the roof curved beam.