Several Key Techniques For CAE-based Die-face Design System

The rapid development of China's automobile industry provides a broad space for panel die development of car body, meanwhile it has put forward higher requirements on it. The design of die-face is in the upper reaches of mold design and is also the most important aspect of it for which directly determines the complexicity of die structure and the formability of the die. The traditional reverse-design approach of die-face is overly dependent on the experience of designers, during the period of stamping simulation analysis, this method is still necessary to designers return to the CAD platform to modify the die-face constantly. Since the CAD data of the die-face lacks the corresponding CAE parametric data, which only contains surfaces, curves and other geometric information, therefore, the cyclic process of "design-analysis-design" is not only difficult but also tedious to be achieved. In recent years, the CAE-based die-face design approach which is called forward-design method has been more and more extensive researched and applied. By this method, the die-face of mold is designed in CAE system based on the geometric model of the panel, then designer can import the die-face data into the analysis of the finite element method on CAE directly, and back to the die-face CAD module to modify the design and simulate it again based on the CAE results. The forward-design method can greatly enhance the efficiency of mold development and avoid lots of defects of traditional method, for instance, repetitive design process, lowered the precision of model data and others. Therefore, it is important to study the CAE-based die-face design system for automobile panels.In response to the development of the Tenth National Five-Year Plan for enhancing independent innovation capability of China's auto industry and improving the level of mold design by information technology and digitizing method, supported by the National Outstanding Youth Foundation(No.10125208), the Key Project of the National Natural Science Foundation of China(No.l9832020)and the Project 985-Automotive Engineering of Jilin University, in the development of the automotive panel die-face design system based on the CAE, this paper maked the thorough research on the following several key technical issues:The problem of repairing the geometric models had been studied firstly. CAD models of parts often have some geometric errors, apertures among the surface patches is one of the most common of it. These errors hampered the operation of the various entities of the geometric model in process of die-face design, but also make CAD models unable to generate the mesh models for finite element method. Therefore, the study of healing surfacees of CAD model is important. We presents a new surface healing method based on the geometric model. Firstly, the "Pipeline method" was proposed to judge the matching curves quickly and because without calculating the spacing of large number of discrete points, this searching method resolved inefficient defects of conventional algorithms in this field. To merge the matching-curves effectively, based on the topological characteristics of the matching-curves, we proposed the "Plane intersection method" and "Pipeline intersection method" to calculate the match points, so as to achieve the purpose of the rapid merger of matching-curves and eliminate the gaps between surfaces. Through the treatment by the method we proposed, geometric model can be transformed to B-rep model, but also be leaded directly to the mesh generator to generate seamless finite elements mesh model.The basis of die-face design system CAE-based is finite element mesh model, therefore we studied mesh generation method, local mesh smoothing method and mesh models repairing algorithm. For finite elements mesh generation, An improved grid mesh generation (IGMG) is proposed. The algorithm combines the advantages of grid algorithm and traditional triangulation Delaunay algorithm, it generates quadrilateral/triangle mixed elements that ensured the overall and local performance. For local mesh smoothing, based on the user's need we proposed a smoothing method that we set up a mesh quality function as the objective function of the optimization model for the local mesh region choosed by user and we proposed the "uniform normal law method" to set up nodes move constraint conditions to ensure that the smoothed mesh will not change the space configuration of original CAD model. For repairing mesh model, a method based on triangular finite element mesh is presented in this paper. To any degree, the approach also can repair some defects of the mesh on curve surface. The amelioration can expand the range of the acceptable finite element mesh and is helpful to reduce the difficulty in high quality mesh generation of auto body CAD.After the preparation process, the geometric model of the cover panel is of the drawing die design, which is the key to success of forming panel. The treatment of the stamping direction is the first process factor of the drawing determination, it will not only be able to decide whether or not drawing out satisfied parts by mold, but will also affect the materials consumption of the addendum surface, the shape of the binder surface and some other factors of the next design process. After analyzing the present research situation and the existing problems in this field, this paper proposed an algorithm for computing stamping direction fastly based on the finite element mesh model of panels. To determine the reasonable stamping direction of the panel, we took the stamping direction vector as design variable and established an algorithm model based on the criteria such as avoidance of dead angle, minimization of drawing depth, maximization of initial contact area and the optimal distribution of the initial contact points. Aiming at actual problem of unease expression and calculation of the space vector domain, the unit spherical mesh intersection algorithm was proposed to get the feasible stamping direction vector domain rapidly. The corresponding program module was developed in Visual C++.There are various types of auto panels and some panels' shape are too complex to drawing directly, so in order to create good conditions for drawing, it is necessary to increase the process supplement. The process supplement generally includes two aspects that are addendum surface and binder surface. Parametric modeling method can greatly reduce the time consuming of design and modification. It can change the model design by modifying the size of parameter. Therefore, the repetitive jobs of engineers can be reduced and efficiency of design can be increased enormously by means of introducing the parametric design thinking into the modeling process of addendum and binder surface. Therefore, comparing with the traditional CAD system adopting the method of manual entirely for creating the addendum surface and the binder surface,the parametric design of the addendum surface and the binder surface have become the trend for high efficiency and convenience of modification. In this paper, we studied the parametric design method of the process supplement that "border generation" method was proposed to generate the binder surface and a method based on thin-plate-under-tension model was proposed to generate addendum surface by the section curves and connect-lines, there is the second-order continues between surface-patchs, thus ensure the good smoothing condition of the overall surface.