Numerical Simulation Study On Force-energy Parameters Of Flexible Bend-forming For 3-D Surface

Flexible bend-forming is a simple, practical and flexible new sheet forming technology for 3-D surfaces, which is developed by Jilin University Dieless Forming Technology Center. It's the organic combination of traditional roll bending technology and multi-point forming technology. It has the advantages of low cost, high production efficiency, easy automation, and flexibility. Its application prospect is very extensive. It's an important part of development for the 3-D surface flexible bend-forming to study on the force-energy parameters, including the down force, the drive torque, and the shear force, which the rolls apply on the forming sheet. It's an economical and effective way to using the numerical simulation software to study on the force-energy parameters of flexible bend-forming for 3-D surface.So the finite element analysis software ABAQUS is introduced to study on the force-energy parameters of flexible bend-forming for 3-D surface ,including the down force, the drive torque and the shear force, so as to provide guidance for the design and actual production of the flexible bending equipment. The main contents and results of the research are as follows:1,The set up of the finite element model for the 3-D surface flexible bending-formingFirstly, establish the finite element model for the 3-D surface flexible bend-forming in the finite element analysis software ABAQUS .Introduce the process of setting up the finite element model in detail. Among it, emphasize highly the treatment of contacts, the selection of algorithm, the output of force, the set up of local coordinate system and the determination of the virtual speed .Then compare on the two methods of setting up the flexible rollers in the finite element model. As a result, the discrete short roll model with equal radius is adopted because it's more realistic. At last, discuss the influence of the discretization of the flexible rollers on the distribution of the down force.2,The numerical analysis on the force-energy parameters of single curvature rolling formingThe finite element model must be able to reflect all the characteristics of the problem-solving, while at the same time as simple as possible in order to avoid unnecessary waste of computing resources or increasing the complexity of the issues. There are certain requirements on the accuracy of the simulation results. So set up the finite element model for the single curvature rolling forming. With the numerical simulation results, study on the down force, shear force, and the drive torque which the rolls apply on the sheet. Then compare with the computing results of theoretical formula. The comparison shows that, the finite element models can reflect the actual situation very well , and the obtained force-energy parameters are relatively accurate. Verify the feasibility of numerical simulation. And that also lay the foundation for the study on force-energy parameters of 3-D surface flexible bending technology.3,Numerical simulation study on the down force of 3-D surface flexible bend-formingThe deformation of the sheet is very complex during the 3-D surface flexible bending forming. The down force which the up flexible roll applies on the sheet not only has a important influence on the distribution of the moment, the stress, and the strain on the forming sheet, but also greatly affects the final forming curvature of the sheet. Besides, it has a relation with the design and actual production of the bending equipment. With the numerical simulation results of the 3-D surface flexible bending forming, output the down force which the up flexible roll applies on the forming sheet. Analyze the down force and the distribution of the discrete short rolls. Then discuss the influence of the sheet material, thickness, deformation amount on the down force. The distribution curves of the down force which the discrete short rolls apply on the forming parts along the transverse and longitudinal direction is given out. Obtain the history curves of the down force which the up flexible roll applies on the forming sheet, when different sheet materials, different thicknesses, different transverse deformation and different longitudinal deformation. Then analyze the variation rule among them. Finally, make a comparison of the down force provided by the upper roll between the single curvature plates, the saddle parts and the spherical parts. The results show that: The required down force of the 3-D surfaces is much greater than that of the single curvature plates. Furthermore, the saddle parts need a little more down force than the spherical parts, and their distributions of the down force are different.4,Numerical simulation study on the shear force and torque of 3-D surface flexible bend-formingTorque has a close relationship with the drive power of the bending machine, so it's one of the most important force-energy parameters, which must be taken into account when the bending machine is designed. The finite element numerical simulation is extended to apply to the 3-D surface flexible bending forming, so as to study on the shear force and torque which the discrete short rolls apply on the forming sheet. Then discuss the influence of the friction coefficient, the sheet size, and the sheet feeding speed on the shear force and the torque. The following conclusions have been made: Because it's pure rolling friction between the rolls and the sheet, changing the sliding friction coefficients has no effect on the friction and torque. But the greater the friction coefficient is, the higher the forming capacity limit of the rolling machine is. The history curves of the shear force and the data tables of the necessary drive torque ,which the three flexible rolls apply on the forming sheet, are given out ,when different sheet size, different sheet feeding speed. Then analyze the variation rule and the size relationship among them. Finally, make a comparison of the required shear force and drive torque between the single curvature plates, the saddle parts and the spherical parts. The results show that: The required friction and drive torque of the 3-D surfaces is much greater than that of the single curvature plates. Furthermore, the saddle parts need a little more friction and torque than the spherical parts.