Research On Some Key Techniques Of Rapid Prototyping Processing Software

The architecture, the core algorithms and the technical algorithms of rapid prototyping (RP) software have been studied in this dissertation, which include off-line RP software architecture, algorithms of Boolean operations on STL (Stereo Lithography) models, RP technology algorithms and method of improving parts accuracy in selective laser sintering (SLS). The theories and achievements contribute to the development of the RP software and equipment of Huazhong University of Science and Technology, and provide a versatile software tool for the domestic promotion of Rapid Prototyping.In order to meet the development of RP technology and the innovation of RP processing method, this dissertation, in accordance with domain engineering and thought of component-oriented programming, researches and designs a unified architecture of RP software, which is based on hierarchical architecture + support platform and the idea of the domain stepwise refinement, including technical processing software and system control software. The use of the software system can shorten the software development cycle, which is caused by changes in processing methods and equipment types, and at the same time it can improve the quality of software development. At present, the software system has been successfully applied to a variety of RP equipments which are researched and designed by Huazhong University of Science and Technology, and achieved good results.Many advanced and core functions of rapid prototyping softwares for technology processing must be implemented with the aid of algorithms of Boolean operations on STL models. However, the research on this issue by scholars at home stays at a primary stage and the algorithm is of relatively low inefficiency and poor stability. A method of precise space decomposition is employed to limit the scope of searching for candidate triangles that may intersect, which can greatly reduce the times of calculation intersecting triangles and significantly improve the efficiency of the algorithm. A kind of data structure of seven-tuple is choosen to record the intersecting straight-line segment. Based on the topological structure of STL models, the intersection chains/loops can be quickly and accurately determined, and meanwhile the method of tolerance extraction can be avoided. The directional distance between a ray and a triangular facet can be used to determine the locations of different triangular facets and regions. In order to avoid the case of ambiguity when judge the locations, the way of avoiding ambiguous positions has been choosen. Finally, re-triangulate the corresponding regions in order that the Boolean operations can be realized. The efficiency and stability of the algorithm have achieved the level of MagicsRP.According to the needs of development of RP technology, consecutive subsector scan mode with adjustable scan length and direction has been achieved, which can make the parts full melt and improve the forming capability and quality of the parts in selective laser melting (SLM). Based on the algorithm of path tracking, the fractal scanning mode can fill arbitrary two-dimensional contours with fractal curves, which greatly enhance the density of the parts in SLS. Based on the PowerRP software system, the technice processing software for mask Stereo Lithography (SL) has been carried out and the corresponding technical problems have been solved.It is a crucial task to inhibit the curling of the parts, which is a ubiquitous destructive phenomenon in the process of selective laser sintering the polymer materials. Concerning the disadvantages of controlling the preheating temperature by key-layers, the causes of warpage and the development of warpage phenomenon have been analyzed and summarized. In order to prevent parts from warpage, which is caused by the non uniform temperature field and stress field, a method of adding Heat Balance Support (HBS) has been proposed. The selection of styles and parameters of HBS should consider the physical and chemical properties of materials as well as the deformation and heat conduction after the laser sintering the materials; moreover, the HBS should be easily removed from the parts. The method has been successfully used in two kinds of materials which are PS and nylon, and achieved very good results.