Finite Element Analysis Of Springback In The Flexible Roll-bending Process

Flexible roll-bending forming technology is a new technology for sheet metal forming. When this technology is used, the horizontal and vertical shapes of the sheets are adjustable, so the sheets can be processed into 3D-sheet parts with different shapes. Flexible roll-bending forming will have great market potential bacause now the sheet parts are produced diversely and the quantity become smaller. However, just like traditional rolling process, the springback of flexible roll-bending forming is very serious, which can reduce the forming precision relatively. As flexible roll-bending forming is very complex and changeable, meanwhile, the horizontal and vertical deformation can influence with each other, it is hard to use traditional methods like empirical formula to control the springback. The efficiency and accuracy are restricted. So exploring the laws and controling methods of springback to instruct the practice is a core for the development of flexible roll-bending forming.The finite element simulation method of springback in flexible roll-bending forming process is proposed and verified and the corresponding parameters are optimized. Then the research focus on analyzing the factors which influence springback and finding methods to control springback. Besides, the effects to springback of different equipments are also discussed. The main contents and results of the research are as follows:1. The simulation scheme determination of springback in flexible roll formingFirst, the mechanisms of flexible roll forming and springback process are analyzed, the results indicate that the mechanisms are the same with bending process basically and the orientation of springback in two directions are different between the saddle parts and spherical parts. Second, the dynamic relaxation method of springback simulation in flexible roll-bending forming process is proposed and verified. In this method, the forming process is first simulated by dynamic explicit simulation, then the damping is added for the secondary analysis. Under the present computer level, this method can be used to simulate the process of springback efficiently. If the simulation results are correct, they can instruct the practical production. As for experimental validation, by using three-dimensional optical scanner equipment the point-cloud datas of experimental parts are attained and the comparation of the fitting datas of simulation and experiment shows the reliability of simulant datas.2. Finite element simulation of springback and parameter optimization in the flexible roll-bending process.Elaborating the procedure in which ANSYS / LS-DYNA software is used to simulate the flexible roll forming and springback process. The accordance between the simulation model and the actual model is assured by analyzing the foundation of finite element model and boundary conditions. Moreover, the choice and control of damping are introduced to get accurate simulation results. Finally, dicussing the effect of the inertial effect and the element roller width to the horizontal and vertical curvature of the final forming. The results are as follows: the effect of the inertial effect can be avoided efficiently when the rollers are at the rotating speed of 1300r/min. If the gap among rollers is kept in a small value range, the effect of the element roller width is tiny, but for assuring the accuracy of simulation and analyzing springback conveniently, the element roller width is set to four millimeters according to the experimental parts.3.The finite element analysis of the factors which influence springback in the flexible roll-bending processThe influence of sheet thickness, material, up-roller's decline value and the horizontal sheet width are analyzed and the results are as follows: as the plate's thickness increases, the springback values become smaller because of the greater deformation resistance; the contrast between 10steel and 15steel shows the springback values reduce as the up-roller's decline value become greater because the vertical forces and the proportion of plastic deformation increased; increasing the horizontal sheet width has a certain effect to springback and make the springback values rise to some extent.4.The law of double-curvature parts'springback in the flexible roll-bending processThe saddle piece and sphericity piece respectively belong to one-way and two-way double-curvature parts. Under the same conditions, the forming quality and springback values'contrast of different kinds of pieces show that the saddle piece's forming quality is better and the springback values are relatively smaller. Then, the relationship between horizontal and vertical deformation is analyzed. The results of the analysis show that the increase of deformation in one direction will lead to reduced deformation in another direction which means its springback values increase.when the deformation continue increasing to be absolutely dominant, the deformation in another direction will be weak.5.The control of springback in the flexible roll-bending processThe control of springback is analyzed from rolling times and springback compensation. First, as the rolling times increase, the horizontal and vertical springback values reduce but the decrease become very weak when rolling times increase to a certain value which can be defined as the reasonable rolling times.In springback compensation, an example is given to analyze the relationship between the up-roller's decline value and the curvature formed. This can be used to get the desired shape by adding the up-roller's decline values but the effect to forming qualities should be considered.6.The finite element analysis of four-roll and six-roll flexible bending processesFirst, four-roll flexible bending process is analyzed which could eliminate the defect of straight edge. Then the finite element model is established. The contrast of simulation results show that the forming quality of four-roll bending is better than that of three-roll bending but the defect of springback is not improved.Finally, the finite element model of six-roll flexible bending is also established and the simulation results show that using six-roll flexible bending equipment can get better forming quality and reduce the springback values, so the six-roll flexible bending is the best way for the 3D-sheet parts if the cost is suitable.