| The automobile industry is one of the pillar industries in national economy all over the world. In the entire of cycle automobile design and manufacture, it`s the key factor of products development speed and quality that the design and manufacture level of automobile panel dies. In fact, it has become the main bottleneck to further shorten the renewal cycle and improve the quality.With rapid development of automobile industry in our country, there`s a huge automobile die`s market. At the same time, it brings forward higher requests to the die corporations. It is learned that the domestic applications of CAD technology for automobile panel still stay on level, which is alternant plotting and modeling and on the popular CAD software system with designers`experiences. It makes CAD software a drawing board barely. However, trial and repair are repeated many times because the design results are lack of evaluation. It`s costly and time consuming in design process.Applying CAE technique, which provides numerical die of CAD in simulation of stamping process, could make die design more reasonable and reduce the debugging cost of die in CAM environment. It must be returned again to CAD environment that modifying the addendum surface when adopting traditional method of stamping die addendum design. There`re a series of steps including mesh, fill hole, flange etc., so the efficiency of simulation will be depressed severely. In order to quicken the speed and improve the quality of die design, Die-Face—surface design of stamping die (generating addendum surface, binder surface and mesh) plays an absolutely necessary role in CAE environment. It is not only a kind of good explorations to the design mode of die in the future, but also applies powerful support for enhancing the competition force of die corporations.Founded by the Key Project of the National Natural Science Foundation of China (No. 19832020), the National Outstanding Youth Foundation (No. 10125208) and the Project 985-Automotive Engineering of Jilin University, an optimized method of generating addendum surface in Die-Face engineering and mesh-based unfolding dimension modification of bending parts of medium & heavy plates are elaborated in this paper.The optimized algorithm of generating addendum surface in automobile panel drawing, which considers a series of requests for technics of addendum and demands for rapid generation and convenient modification, optimizes the generation of interpolation points in the first circle connecting line with the method of moving line to form surface, in which the line mentioned above are parametric section curves in 2D. The local inner sunken or vertical areas of parts can be identified by rolling cylinder algorithm. It results in optimizing the generation arithmetic of interpolation points in the first circle connecting line. The detailed flow is as follows:On the basis of the method and process mentioned above, the patch generation is optimized covering section curves, connecting lines and boundary edges by bi-direction NURBS skinning. By doing this, the phenomenon is avoided in terms of surface curl distortion, self-intersection, etc. The corresponding parametric module is programmed by Language C++.In this way, the designer can change the shape or type of section curves by alternant ways of parameter modification and dragging curves. Consequently, the addendum surface can be generated easily, the design cycle of die-face engineering can be shortened effectively and the quality of addendum surface can be improved. As a result, the manufacturing of stamping parts can be improved and the development circle of products can be reduced.According to pertinent data, there're five driving demands that stimulate the rapid development of medium & heavy product market. Firstly, the demands of the steel, which belongs to high value-added, increase evidently, especially in truck. The structure accessories, such as crossbeams, vehicle axles, wheels and so on, are made of medium & heavy plates. Secondly, the ship-building industry grows in high speed. Moreover, due to growth of steel structure and the rapid development of electric power, bridge construction, urbanization and mining industry, the long-term demands of the engineering machinery give boost to the consumption of medium & heave products.Although there's no explicit definition to medium & heavy plates in our country, the GB/T3880-1997 has classified the plate into that with thickness between 4.5mm and 150mm. Consequently, it's recognized that the plate with thickness more than 4.5mm is named as thick-plate. It is actually named as medium-plate in range from 4.5mm to 10mm, and thick-plate from 10mm to 50mm. In automobile industry, the medium & heavy plates are mostly used in special-purpose vehicles, such as cash truck, dump truck, tank truck, semi trailer or trailer and so on, but rarely in passenger vehicles. Generally speaking, the side panel is made of medium-plates between 9mm and 10mm and the thickness of floor is from 12mm to 18mm. Comparatively speaking, the amount of extra-thick plates is rarely used in truck. Therefore, the study objects of bending parts modification technique, which is mentioned in this paper, belong to category of medium & heavy plates.In blank forming process, the bending forming is a main technique. The blank size is very important to forming precision of the sheet metal products and the accomplishment of subsequent handlings. The parts unfolded by One Step Inverse Forming FEM neglecte the neutral fiber movement towards inner fiber. In particular for medium & thick parts, such kind of errors is obvious in unfolding results if the unfolding process is made directly through the middle fiber.Therefore, the unfolding length of meshed blank needs to be modified in order to assure the accuracy of the final blank length. At present, there`re extremely few papers about mesh based dimension modification. An algorithm, which aims at solving existing problem, is mentioned in this paper.The concrete implement is as follows: Firstly, the least square method is adopted to calculate radius of middle fiber of bending areas, in which the partial points are mapped to a space plane, in which points above are modified by coordinate conversion. In this way, the radius value and the position of circle center in space plane can be calculated precisely. Secondly, the size of the original meshed blank is corrected. Finally, the modification result is compared with original data supplied by manufacturer. The experimental result shows that the final blank length of bending parts can be calculated fastly and precisely. It`s proved that mesh modification method in this paper is feasible and effective. The corresponding parametric module is programmed by Language C++.Compared with the traditional analytic method, there`re several advantages by using mesh modification method, such as reducing time resumption of looking up technical data, enhancing work efficiency and shortening design period. The shape and dimension of final meshed blank with manufacturing are foreshowed very well. This method presented in this paper is of importance in terms of engineering application value.
|
PDF Full Text Request