Research On Mesh Generation And Nesting Optimization Involving With CAE Project Of Sheet Metal Forming

Automobile industry has been ranked as one of the pillar industries of national economies for the industrialized countries in the world, and the competition is getting increasing fierce. Independent R&D of car models and die design capacities are an important indicator of the development of auto industry. In the entire cycle of automobile designing and manufacturing, automobile panel die has become the"bottle-neck"for the development of new car models for its large size, complexity of work surface, high machining precision and long period of designing and manufacturing. Its quality directly influences the follow-up vehicle production, and becomes an important guarantee for automobile individuality and upgrading.The traditional die design is a complicated process of conception design– analysis– sample manufacturing– analysis– design– analysis– manufacturing, thus the prime die is formed. With the development of computer science, CAD/CAE technology gradually replaced the traditional way of die design concepts and design methods, which enable the precise structural design, structural analysis and formation simulation possible before real manufacturing through computer software. Via computer simulation of formation process, we can repeatedly amend the local structure of die through computer, and optimize the improved die structure to enable the formation of die only one time, as a result, shortening the debug time and reducing the cost, at the same time, accelerating the generation updating and enhancing competitiveness in the international market.Supported by the Key Project of the National Natural Science Foundation of China named"Fundamental Theories, Computation Algorithm and Key Technology of Stamping Forming and Die Design", this paper aims to give an in-depth research of the key technologies of KMAS mesh generator and nesting system from theoretical description to program design, to meet the requirements of"Sheet Metal Stamping CAE Simulation Software KMAS".Many modules in the KMAS system have to rely on finite element mesh. To further improve the KMAS mesh generator this paper researches on the mainstream automatic mesh generation algorithm—Delaunay triangulation method. Based on the traditional Delaunay algorithm and the needs of KMAS software, in combination of practical engineering problems, we propose several algorithms to improve mesh quality, including the treatment of missing edges, the optimization of strip elements and the smoothing algorithm of the mesh. In the end, an algorithm has been proposed to delete small element, which will improve the quality of the entire mesh. The programme module developed based on this method has been applied successfully in commercial software KMAS/One-step.In view of the high demand of the tool mesh for precision and simplicity, we have developed in the paper a fast, simple and precise mesh production algorithm—scan line algorithm. Through the internal mesh generation—border region division—generating border mesh, we can promptly and precisely get the finite element mesh in conformity with KMAS/Incremental. The key to the algorithm lies in reasonable division of the border region according to the shape of the internal mesh, making the generation of high-quality mesh possible to fit for the original CAD curve.In the car design area, the spending on material constitutes a relatively large proportion of the cost of products. Automatic optimal nesting is one of the principal means to improve material utilization, lessen material losses, reduce product cost and enhance competitiveness of the products. The thesis also aims at the following research regarding the blank boundary extension, regularization, blank margin analysis, nesting parameter optimization technology.The spread method of product part by inverse FEM neglected the blank area except for the part itself. The blank mesh of product part needs to be extended to make sure of the right size of the final blank. A non-isometric extension algorithm based on the discrete boundary points of blank mesh is presented. After that, an optimized algorithm for complex boundary is provided to reduce the complexity of the industry production. The algorithm has an advantage on computing efficient and optimized result. Finally, an actual example is provided to show the validity of the algorithm.The so-called optimization of nesting is to distribute material for parts of specified size and number by using specified sheet metal, thus, making full use of the metal under the requirement of a complete set. This will inevitably involves the related issues such as the placement and orientation of parts, and the calculation of the distance between adjacent parts. In the paper we have proposed an analytic algorithm of part gap and given an overall measurement of the distance between adjacent parts, as a result a reasonable calculation can be reached. We have also developed the corresponding design module and successfully applied it to KMAS nesting system.The substantive issue of nesting is one-dimensional or two-dimensional layout, i.e. the question of optimization. In the thesis, we design an optimized method based on genetic algorithm to optimize the important parameters such as orientation, position and distance.