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Research On The Initial Guess,Efficiency Optimization And Bending Modification In One-Step Forming Simulation

Posted on:2005-12-25Degree:MasterType:Thesis
Country:ChinaCandidate:J JiaoFull Text:PDF
GTID:2132360122999885Subject:Solid mechanics
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With the fast development of computer technology, CAD/CAE/CAM has been widely used in the designing and making of auto body panels in order to increase the competitive ability effectively with high quality, in a short time and at a low cost. The systemic application of CAD/CAE/CAM has become an important symbol to weigh the level of industry, science and technology of a country.As a significant part of the national key project of nature science fund of china, called the Basic Theories, Simulation Method and Key Technique of Sheet metal Stamping and Tool's Design (19832020), this paper deals with the initial guess arithmetic in one-step forming simulation and the effect of initial blank areas on computing efficiency in this process. What's more, a membrane element is introduced to consider the bending of blank in stamp forming. The main research content is as follows:The introduction of this paper points out the general situation of the development of blank stamp forming technology in auto industry. The necessity of fast simulation technology in the auto body panels' forming process is also presented. Then the introduction analyzes the developing trend and wide use of one-step forming simulation approach which can be applied to the preliminary stage of process design in sheet metal forming. The second chapter of this thesis exploits systemically the basic ideas, hypothesis and character of one-step forming simulation approach, on the basis of which I study the finite forming theory. Then I deduct kinematic relation of large elasto-plastic strains using the sheet metal forming theory and membrane theory. After that, on the basis of Hill's anisotropic yield criterion and ideal deformation theory, I deduct integral constitutive equation of elasto-plastic flat blank by the assumption of proportional loading. Afterwards, I discuss the simplified method as to the contact of blank and tools. Whereafter, using the conception of force's balance and the principle of virtual work, I construct the calculation equation of one-step forming simulation and give the solution by Newton-Raphson method. Finally, the program flow chart of one-step forming is given.In the chapter 3, after reading a lot of literature and discussing their results, I introduce a few of valid and reliable arithmetics of initial guess in view of calculative efficiency and stability. All of them can provide reasonable initial solution for one-step forming simulation and obtain ideal analytic results, which can satisfy the need of engineering project in general. First of all, I introduce a correcting method of vertical plane elements (VPE) and negative plane elements (NPE) on the basis of finite element model's correcting technique. In this method, we create a rotation axis through the upmost node of VPE or NPE. And then we make the other two nodes of this element rotate around the axis for a small angle letting the inclination angle of element's normal and Z axis be less than 90 degree. After that we project the geometry model vertically to get the initial guess avoiding the elements' superposition which can't result in constringency of finite element equation. Secondly, we classify the various complicated auto panels as drawing parts and bending parts by their process. And then we propose two arithmetics of section line spreading schemes considering the mainly forming characters of these two stamped parts. The basic ideas of them are: let the trochoid of the fixed points (or datum points) be the center. Then create a vector from the fixed points (or datum points) to spreaded points. Let this vector's direction be the spreading direction and it's length be the spreading length. Then spread all of the nodes on the part to obtain an initial solution of the blank. The third one: in view of geometry method's being unable to take material performance and deformation into account accurately so that it can't get initial guess which assure solution's stability and constringency. This paper introduces an area's iteration approach to cor...
Keywords/Search Tags:One-step forming simulation, Initial guess, Vertical plane( Negative plane), Section line, Rate of areas, Bending modification
PDF Full Text Request
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