Research On Flexible Three-dimensional Stretch-bending Of Multi-point Roller Dies Forming Process

In recent years,three-dimensional profile structural parts have been widely used in rail train,automobile,architecture,aerospace and other fields.The traditional stretchbending forming method has low forming efficiency,long R&D cycle,and high die cost,which cannot realize one-time forming of three-dimensional deformation of profiles.With the continuous improvement of product demand and quality requirements for three-dimensional deformed structural parts in various industries,the traditional stretch bending forming method can not meet the increasing product requirements.The flexible three-dimensional stretch-bending of multi-point roller dies forming technology is a new process for producing three-dimensional deformed structural parts.Using multiple groups of roller dies instead of the traditional overall die can not only quickly reconstruct the die surface,but also realize the forming of profiles with different cross-section shapes and different target shapes.It has the advantages of high forming efficiency,flexible operation and short R&D cycle.Especially in solving the springback problem of stretch bending forming,it only needs to adjust the configuration surface of the die,which greatly saves the manufacturing cost of the die.In this paper,the forming process and forming defects in the flexible three-dimensional stretch bending process of aluminum alloy profiles are systematically studied by means of numerical simulation and experiment.The main research contents are as follows:(1)A flexible three-dimensional stretch-bending of multi-point roller dies forming technology is proposed,which can realize three-dimensional deformation of profiles in one-time forming.The basic principle of flexible three-dimensional stretch bending of multi-point roller dies technology is described.The flexible three-dimensional stretch bending of multi-point roller dies forming equipment and its main structural components are introduced,and the method of adjusting the surface of the die of the equipment and the working process of realizing the three-dimensional deformation of the profile are described.(2)According to the basic principle of flexible three-dimensional stretch bending of multi-point roller dies forming process,the corresponding finite element model and springback analysis model are established based on the elastic-plastic constitutive relationship of the material and the finite element solution algorithm.The problems of element selection,contact and friction,boundary conditions,mass scaling coefficient and mesh size selection in the modeling process are discussed.The rationality of the finite element model is verified by the comparative analysis of numerical simulation and experimental results.(3)The differences between force-displacement loading and displacementdisplacement loading,odd-numbered and even-numbered die arrangement,one-sided forming and two-sided forming are described.The trajectory formula of clamp and dies in the flexible three-dimensional stretch bending of multi-point roller dies process is deduced.Using the numerical simulation method,the profiles with typical crosssectional shapes are selected as the research objects,and the effects of different clamp loading,die arrangement,and clamp clamp moving track on the forming results of flexible three-dimensional stretch bending of profiles are compared and analyzed,and the optimal forming method is determined for subsequent research.(4)The formability of three-dimensional deformed profiles is studied,and the effects of process parameters such as pre-stretching amount,post-stretching amount,number of dies and friction coefficient on the die adhesion and fracture resistance of the profile formed by flexible three-dimensional stretch bending bending are analyzed.The factors affecting the shapeability of three-dimensional deformed profiles are complex.This paper intends to comprehensively study the effects of process parameters,geometric parameters,material properties and profile section shape on the shapeability of profiles formed by flexible three-dimensional stretch bending of multi-point roller dies.(5)A distributed springback compensation method based on variable compensation factor is proposed,which is suitable for solving the springback problem of three-dimensional deformed profile.This method considers the forming principle of flexible three-dimensional stretch bending of multi-point roller dies technology,so that the profile can complete the springback compensation process in the horizontal bending plane and vertical bending plane respectively,so as to reduce the springback error.The method is applied to study the springback compensation of profiles with different lengths,and the optimal springback compensation factor and die surface are determined.The profile formed by the modified die surface is close to the target shape,and the error is small.(6)The measuring equipment and measuring methods used in the experiments are introduced.The profiles with typical section shapes are formed by the flexible threedimensional stretch bending of multi-point roller dies equipment.The forming results show that the experimental parts have good forming effect,which shows that the flexible three-dimensional stretch bending of multi-point roller dies technology has good stability and reliability.