Study On Uniform Wall Thickness Of T-shaped Tube Formed By Hydroforming Based On Parameter Optimization

To meet the demands for increased safety in cars and aircraft that are also lightweight and low-cost,new manufacturing processes are required.Compared with traditional forming technologies such as traditional casting,forging and welding,hydroforming technology has been applied more and more widely in the field of aviation and automobile due to its core technology of lightweight structure,advantages of low mold cost,high structure strength and stiffness,avoiding secondary processing and low scrap rate.This paper had analyzed the effect of die radius,friction coefficient,the loading paths of the internal pressure and axial feeding,balance punch feed on hydroforming of T-shaped tube by finite element simulation software Dynaform.It is found that the thinnest wall is at the top of the branch pipe and the thickest wall is at both ends of the main tube.The thickening rate of the main tube decreased continuously from both ends of the tube to the center.Under the premise of satisfying the uniform wall thickness of the T-shaped tube,the mold with a large radius of the transition fillet should be selected for testing.The friction coefficient between the tube blank and mold should be reduced as far as possible to strengthen the flow of pipe material.For the internal pressure loading and the axial feed loading trajectory,four kinds of loading trajectories are given in this paper,and finally the multi-linear loading path of the axial feeding is used.The balance punch rise speed should be slightly faster than the branch pipe forming speed to ensure that the punch and the top of the branch pipe are in relative contact.According to the limit of wall thickness and the height of branch tube to comprehensive select the suitable loading path plan.Taking each point in the loading path and friction coefficient as the influencing factors that may affect the thickening rate and thinning rate of the wall thickness.By means of orthogonal experiment design and range analysis,the influence of forming process parameters on forming minimum wall thickness was sorted,and the key forming parameters were obtained.Using the experimental design of Box-Behnken Design,the minimum wall thickness reduction ratio and the center wall thickness increase ratio of the bottom of the supervisor are taken as the design objectives.The response surface formula between the design objective and the key factors is obtained,and the response surface model is established.The minimum wall thickness reduction rate and the thickness increase rate of the center wall at the bottom of the main pipe are taken as the design objectives.Using variance and regression analysis,the optimal parameter set was obtained.Theradius of the mold fillet is 8mm,the friction coefficient is 0.1,the first change of the internal pressure is 0.01 s,the start time of the second internal pressure change is 0.02 s,and the start time of the third internal change is 0.06 s.The pressure is 1.01 MPa,the first internal pressure is increased by 10.37 MPa,the second internal pressure is 17.69 MPa,the final internal pressure is 20.27 MPa,and the axial feed is 44.01 mm.The relative error was within 1% compared with the numerical simulation analysis.The optimized loading path can improve the uniformity of the wall thickness of the T-shaped tube hydroforming parts.Finally,a comparative study on the T-shaped tube hydroforming before and after optimization is carried out.It is found that the experimental results of the wall thickness data of the T-shaped tube with optimized parameters are basically consistent with the predicted results.The maximum wall thickness thickening rate is 41.33%,the minimum wall thickness reduction rate is 28%,the ultimate wall thickness difference is0.94 mm.It shows that the optimized parameters can better reduce the wall thickness thickening rate and thinning rate,and improve the overall wall thickness uniformity of the T-shaped tube.