| Multi-point forming (MPF) is a flexible forming process for 3D sheet metal. It's basic idea is to make traditional mold discrete, using a series of height adjustable elements (little punch) to combine forming surface. By CAD/CAM system, MPF can rapidly achieve required surface, save a lot of modeling time and cost compared with traditional mold, realize the purpose of the equipment for multi-use. Now, the MPF technology can be applied extensively in many fields, such as the skin of high-speed locomotive, ship shell plates, automobile panels and so on.The CAD model of target surface was created by commerce CAD software such as CATIA,UG,Pro/E and so on. It is not advisable to study geometric modeling spending large amount of manpower and material resources. It is a main problem for the application of MPF software to exchange information of CAD model, reconstruct 3D model and study the geometric modeling of element groups. With the application of MPF for sheet metal forming, it is important to explore suitable software for multi-point forming.This paper, according to CAD model of target surface, has applied triangle element to study the geometric modeling of element groups based on finite element technology. The main contents and results are as follows:(1) A method generated triangular mesh of CAD model was studiedThere are several kinds selective way to deal with data interface with commerce CAD model. This paper discussed triangular mesh data of STL file and finite element by means of dispersing. Available information was obtained using CAD software to analyze data format, dislodge redundancy data and topological structure relation. It can blend colors to achieve such effects as making objects appear translucent, create scenes with realistic atmospheric effects, and draw geometry at of near the same depth but avoid unaesthetic artifacts from intersecting geometry by OpenGL, so that the 3D model can be viewed from whatever perspective you wish(2) The geometric modeling of element groups was studied to compute the contact points between surface of part and sphere of elements based on triangular mesh or discrete point clouds and foundation of the math model The geometric modeling of elements is achieved by adjusting the height of elements. The CAD model is scattered by finite triangle element, the contact points between sphere of elements and surface are converted into the construct points between sphere of elements and plan. When the CAD is replaced by point clouds, it is converted that finding the construct points between point clouds and sphere of elements. All above two kinds of method are applicable to any 3D surface, and can fulfill the need of projects.(3) A method to modify the cushion was studiedThe part surface presented by CAD model and cushion is of thickness in the real process of producing. It is not part surface to touch elements but is cushion surface which is the offset surface of the part surface. Now a method is presented to compute the offset surface of finite element nodes based on the theory of surface normal vector. Then it is the substitute for the part surface to computer the contact-point. So the cushion is modified.(4) Develop the software of geometric modeling on triangle element CAD systemThis software, designed by Visual C++6.0, use OpenGL to display 3D model, and improve the capability depend on texture mapping, lighting, and drawing pixels, bitmaps and images. In this software, all pictures can rotate, translate, zoom out or zoom in. We can use keyboard and mouse to manipulate pictures. So we can easily to observe the pictures, and this makes the software easy to manipulate.(5) The algorithm of triangular mesh and discrete point clouds is analyzedAccording to study on analytical solution of the spherical surface and cylindrical surface, the precision of the software was improved with refining triangular mesh. The results show that the software is applicable to model of complex surface, has high precision and fast speed. |
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