Study On Geometric Modeling Of Element Groups Based On Triangle Element

Multi-point forming (MPF) is a new means for sheet metal forming. Its main idea is dividing the curved surface of the traditional stamping dies into many pairs of matrices of elements, and then the three-dimensional shape of sheet metal is formed by the curved surface of elements. Relative to the traditional stamping technique, the MPF has saved a lot of time for die designing, die manufacturing and debugging. It has shortened the exploiting cycle and reduced the costs. 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 large sculpture pieces in the city. Geometric modeling of element's matrices is very important to the application of MPF.With the application of MFP, more and more parts are created by the commerce CAD software. Study the geometric modeling of element groups for CAD math model is of important mening.This paper, based on finite element technology, according to CAD model of target surface, apply triangle element to study the geometric modeling of element groups. The main contents and results are as follows:1) Introduction the method to generate the geometric modeling of element groups of MFP software, this method is offset surface of NURBS.This method treats sheet metal as equal thickness metal and translates the geometric description of part to how to generate the 3D surface of the part. This method applies NURBS to define the surface of the part, and according to theoffset surface of NURBS to work out the contact points between the surface of part and sphere of elements.2) The study on the method to generate the geometric modeling of element groups based on triangle element and foundation for the math model to compute the contact points between surface of part and sphere of elements.The CAD model is replaced by finite element model made up of triangle elements after meshed by FE software. According to the nodes on triangle elements a plane can be created. Then, the contact points between sphere of elements and surface are converted into the contact points between sphere of elements and plane. This makes it simple to compute the position of elements. This method is suit to any 3D surface, and can fulfill the need of projects.3) The study on orientation of finite element model.The finite element model of CAD model is composed of lots of triangle elements, the nodes on of elements make these elements a integer. On the whole, these nodes can be regards as a graphics, we can compute the corners of the graphics and use of the coordinate switch in CAGD to orientate the finite element model according to the corners.4) A method to modify the cushion is presented.As the part surface presented by CAD model is of no thichness, the cushion and sheet metal are of thickness. The contact-points are between elements and cushion surface, not between elements and part surface. The cushion surface is the offset surface of the part surface, so a method is presented to compute the offset surface of finite element nodes. Then it is the substitute for the part surface to compute the contact-point. So the cushion is modified.to observe the pictures, and this makes the software easy to manipulate.This software, explored by Visual C++6.0, include geometric modeling of stumping die and geometric modeling of stretch forming die, and use of OpenGL to display the picture. 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 5) The exploitation of geometric modeling software...