Unstructured Quadrilateral Mesh Generation Algorithm Based On Discretized Model & Parametric Modeling Method For Sheet Metal Forming

Construction of a mesh model is one of the key techniques in the finite element analysis (FEA). Because of the inevitable and tedious modification problems for the model introduced by using CAD model as the source for a mesh generation, the mesh generation process is inefficient, costly and time consuming, so the efficiency of CAE is greatly affected. We attempted to find a new way for mesh generation. In this article, some key techniques in the mesh generation field have been investigated1. An algorithm of generating all-quadrilateral element mesh from discretized models was proposed and programmed. By this method, discretized models, such as scattered points or STL file format model, were the source for mesh generation, and model fix was no longer necessary. The original mesh generation paving method was modified to handle discretized models. For the purpose of controlling mesh size and enhancing element quality, several mesh adjustment strategies were studied. The first one was the control of mesh size by using the discretized model as background mesh, the second one was the adjustment of mesh density distribution by mesh refinement and coarsening operation; the third one was automatic identifying surface features and preserving it in mesh model; the last one was a new method to detect collisions between paving boundaries.2. The element refinement method is a key point for adjusting mesh density. A modified structured quadrilateral mesh refinement procedure and a new mesh refinement strategy are proposed, and this method was extended to handle unstructured quadrilateral meshes and hybrid meshes. The two main categories of mesh improvement are smoothing and clean-up. Several mesh topology clean-up operations were proposed to improve the mesh's quality. Comparing several modified Laplacian smoothing methods, a smoothing approach of combining Laplacian and micro Genetic algorithm for quadrilateral meshes was proposed.3. The successful application of computer simulation techniques in sheet metal forming raises an urgent requirement for more rapid and automatic die surface modeling method, a new parametric design method of mould addendum surfaces and drawbead was proposed. Using this method, the design of die face was completed in CAE preprocessor instead of in CAD systems as ordinary methods do, and the mold models could be used in sheet forming simulation directly. It makes the design and change of die surface more convenient, and the efficiency of design process is improved greatly. 4. A pre-process software for sheet metal forming simulation named STLMesher was programmed. Its main functions included facet model repairing, optimal drawing direction defining, model flange unfolding, contour smoothing, and addendum surface and geometric drawbead parametric modeling. Most of these functions were completed automatically. Also a post-process software with GUI named StampPost was programmed. It dealt with simulation result, and its main features included deformed part displaying, animation of stamping process, stress/strain color mapping and Forming Limit Diagram (FLD). It improved the understanding of the simulation result.