Study On The Working Rollers Of Flexible Bending Technology

Bending forming technology, which is also called roll forming technology, is a kind of continuous partial plastic forming technology. It is very common in today's applications means of sheet metal forming. As a novel method of sheet metal forming, the 3-D surface flexible bending forming is being researched by the Jilin University dieless forming technology center. It is a kind of technology which is combined with traditional bending forming machine and multi-point forming after the latter's industrialization. Its basic principle: Firstly, dispersing the forming parts of the bending machine into a number of small discrete cell rollers. Secondly, adjusting the relative position of the cell rollers by regulating device, then the small rollers composed of different curves with various curvatures, so continuous partial forming for different 3-D surfaces of sheet metal can be realized. The technology not only has the multi-point forming technology's characteristic, flexible, but also has bending forming technology's advantage, low-cost and high efficiency.So the dynamic explicit finite element software ANSYS/LS-DYNA is introduced to simulate in the 3D-surface flexible bending forming, and the basic models are created in it. The sheet metals'forming effects, which are influenced by different factors of working rollers have been compared and summed up. The main contents and results of the research are as follows:1. Basic model of 3-D surface flexible bending formingThe finite element analysis aims at the discretization model of the original question; the results'precision is related with the accuracy of the model. It must be able to reflect all the characteristics of 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. In this paper, 3-D surface flexible bending forming process's finite element model are created, and the requirement and points for attention in the choice of element types and material models are explained, the factors which should be considered for importing geometry models and mesh division are introduced, load, contact and friction boundary conditions are discussed. And the purpose and effect of the local coordinate system are described.2. The influence on the sheet metal forming effect by the rollers'rotation speedFor most sheet metal forming process, the forming tools'actual velocity is different from the one in the numerical simulation. If the solution is being done of real time, it is tend to require a large amount of computing time, even up to several hundred hours. Therefore, when use dynamic explicit algorithm to analyse forming problems, the time scale or quality scale should be changed to transform the real problem into a simulation one. For a detailed discussion of the influence on the sheet metal forming effect by the rollers'rotation speed of flexible bending forming. The stress and strain distribution, rollers'force unit, the vertical and horizontal changes of the sheet metals'shape and thickness are discussed in this paper. According to the analysis by simulation, the following conclusions have been made: generally speaking, the flexible working rollers are on the constant accelerated– constant- constant decelerated equally working velocity, the lower the velocity is the better the sheet metal forming effect will be, and the force between the working rollers and sheet metal will be smaller which is beneficial to enlarge the rollers'lives.3. The influence on the sheet metal forming effect by the working roller's discretizationIn the 3-D surface flexible bending process, flexible working rollers'discretization can affect the plates'external quality, internal stress and strain distribution and the device itself. In this paper, three finite element models in different levels of flexible working rollers'discretization have been established. By contrast, The influence on the sheet metal forming effect by the working roller's discretization has been analyzed, the stress and strain distribution, rollers'force unit, the vertical and horizontal changes of the sheet metals'shape and thickness are discussed in this paper. The following conclusions have been made: with the degree of working roller's discretization growing higher, namely the number of the working rollers be more, the sheet metal forming effect will be better, and it is good for the equipment maintenance. But when the working roller's discretization is being higher, the asway machines and adjusting machines should be more too. It will grow the complicacy of the device and the expense greatly, so there is more harm than good. Therefore, for the requirements of different sheet metal forming qualities, the flexible bending machines with different working rollers'discretization should be manufactured. In addition, because some sheet metal's bad quality due to the big gap between the rollers, the machine which rollers are not arranged in one-to-one could be manufactured to improve the sheet metal forming effect. However, the rollers should be adjusted to form different types of products accordingly.4. The influence on the sheet metal forming effect by the distance between the down rollers and the number of working rollersIn the 3-D surface flexible bending process, the sheet is going through the rollers in three rows and is formed by the certain pressure from the up short rollers and the interface friction of the sheet and rollers. So the distance between the down rollers is an important parameter in the 3-D surface flexible bending process, it has a direct impact of the sheet metal's vertical curvature. In this paper, a number of simulation models have been established, the stress and strain distribution, rollers'force unit, the vertical and horizontal changes of the sheet metals'shape and thickness are discussed. The following conclusions have been made: in the same conditions, the distance between the two down roller greater, the deformation is smaller, the influence of end-effect is less obvious. The distance between the two down roller is smaller, the sheet metal forming effect will be better. We can adjust the distance smaller, but according to the differences between actual production and simulation, the rollers may quiver and collide with each other as the spacing is too small, and then the quality of the sheet metal will be debased. Therefore, it is critical to make an appropriate choice of the distance between down rollers to ensure the forming quality and saving resources. At the same time, the feasibility and superiority of the quadplex-row rollers bending machine has also been discussed in the paper. As we know, the quadplex-row rollers bending machine is better than the triple-row one, it could certainly help in some ways to improve the sheet metal forming effect. But if we consider the equipment costs and other factors, in which conditions the quadplex-row rollers bending machine should be used to form sheet metal and which arrangement type of flexible working rollers should be used are still need to discuss further.