Research On The Three-dimensional Surface Flexible Roll Forming Technologies And Numeircal Simulation

Flexible roll forming technology, as a kind of continuous partial plastic forming，isbeing raised and researched by the Jilin University dieless forming technology center. Thistechnology combines traditional rolling forming and new multi-point forming（MPF）.It notonly has the normal rolling forming technology’s advantage, high efficiency, but also hasthe MPF’ characteristic, flexible and adjustable forming tools. Flexible roll forming uses akind of rollers whose shapes are adjustable. Through these special rollers, the products arenot only limited to flatbed models, but also other complex types such as spericity, saddletype and irregular sections.After introduced the theory of flexible roll forming, this text sets a basic model by thedynamic explicit finite element software and simulates the forming process, After this, wesum the rules by means of comparing the forming result under different press amounts anddifferent radius of rollers. The main contents and results of the research are as follows:1. The basic principles of flexible roll formingFlexible roll forming uses a couple of flexible rollers as forming tool. Throughadjusting regulators, the rollers are bending deflection. At the same time, the space betweenup rollers and down ones is not uniformly distributed. With this model, the sheet will bechanged into non-uniform transformation and the sheet will turn to curve at the direction offorming. The lateral deflection of sheet is come form flexible roller’s itself curve. Finally,the sheet changes into3D-surface.This article analyses the feature of force and deformationat first, and then derived the stress calculation formula by slab method. On this basis, weget the principle of sheet bending forming and the content about resistance of deformation.Finally, the adjustable technology and forming defect are given.2. Finite element model creationIt is a key factor to create a exact and reasonable finite element model when we want acorrect option in the simulation of flexible roll forming. There are two importantparameters in flexible roll forming, one is the space between up and down rollers, another isthe change low of the space along the axis of rollers. In the finite element model, we callthese two parameters press distance and roller radius. In this paper, the model is created at the view of roller bending shape and discretization. After creating the model, we choose theelement types, material models and boundary conditions and so on.3. Flexible roll forming numerical analysisFlexible roll forming is a new technology, the diction and analysis report of formingresult has a direct bearing on the evaluation of this new technology. Since the production offlexible roll forming is3D-surface sheet metal, the evaluation criteria of the surfacemeasure includes two fields as follows: surface feature and stress/strain distribution. Thistext analyses plastic deformation into two ways including elongation and thicknessreduction. Through the ways of coordinate figure fitting, we found the longitudinal curvecan be defined as a circular arc, whose radius can be fixed. Meanwhile, we use reverseengineering to analyze the transverse feature line and get the result that the curve is similarto a circular arc too. Finally, we pick up and calculate the Gaussian Curvature form thehomogeneously deformed local areas which can represent the forming characteristic, theresult is such area has a nearly same value. Therefore, the surface can be attributed tospherical surface. Through the stress/strain distribution and variation tendency of sheet atthe beginning, middle and end of forming process and, it can be summed a formingcharacteristic about flexible roll forming.4. The influence on flexible roll forming by the press distance and roller’s radiusThe two important parameters of flexible roll forming are press distance and roller’sradius. In this paper, these two parameters are relative analyzed dividedly. Through thecomparation of plastic deformation, the character of the formed surface and stress/straindistribution, we can conclude that the press distance is the major parameter of plasticdeformation, which affects the value of deformation and curved character. Meanwhile, thechange of roller radius has little relationship with plastic deformation and the value ofGaussian Curvature. However, the roller’s radius affects the latitude and longitudecurvature distribution. That is to say, as the press distance is a fixed value, the GaussianCurvature of formed spherical surface is foreign to roller’s radius. In addition, the shapedsheet’s stress/strain distribution will be more reasonable and the deformation will be morewell-proportioned.