| With the rapid development of aviation,electronics,biotechnology and medical technology,the demand for the hollow structure with special properties such as anti-fatigue and explosion-proof light is presented in many fields.The hollow structure has better scalability in the physical and mechanical performance.The high-speed development of 3D printing technology has provided a beneficial tool for the manufacture of the hollow composite structure products.At present,although 3D printing technology can theoretically create any internal composite structure products,but in practice,there is still lack of corresponding modeling methods and tools.Especially for the hollow structure,there is no corresponding CAD modeling method.Based on the structural heterogeneity of products and the complex network theory,the CAD modeling method of hollow structure composite is studied in this thesis.The main contributions of this thesis are briefly depicted as follows:1)Focusing on the characteristics of the hollow structure,the Voronoi diagram is used to build the meta structure for the hollow structure.In order to eliminate the stress concentration in the Voronoi neta structure,Nurbs curves and mesh subdivision algorithm are used to smooth the 2D and 3D meta structure.A rule definition method,which is called VoroSDF,is given to express the irregular shape information inside the hollow structure.Compared with the STP and STL data format,the VoroSDF does not require a precise definition of the facet information,and only the boundary,hole centroid,zoom and combination information are storage in the VoroSDF file,which saves the data storage space.The hollow structure can be edited again by adjusting the hole centroid and the zoom information as required.After converting the defined 3D model into the patch model,the hollow structure can be produced directly through the 3D printing technology.2)The existing CAD modeling methods and tools cannot construct products with non-periodic structure model such as the hollow products.Based on similarity topology between hollow structure and the complex network,the meta structure is mapped to nodes in the complex network,and the connections between the meta-structures is mapped to edges,a modeling method for hollow structure which is called CNCAD(Complex Networks-based CAD)is presented.The method can adjust the parameters of the evolution of complex network model,numbers of holes and porosity to establish different forms of hollow structure with topology map.The non-pneumatic tyre,shark rib structure,and the foam structure are constructed by the proposed method,which verifys the effectiveness of the method.Through the CNCAD method,the product with specific property can be designed with the structure optimization algorithm.The hole number and porosity are treated as design variables,the hybrid encoding adaptive genetic algorithm optimization is adapted for the lightweight design of the product.The force equilibrium preprocessing of the hollow structure is applied based on stress maps to obtain the initial layout of internal voids,which improves the modeling efficiency and get lighter hollow structure.3)When using the FDM(Fused Deposition Modeling)technology to build hollow structure products constructed by the CNCAD method,it is found that the structural support will be enclosed inside the holes,which will lead to failure when removing the support structure after 3D printing.Taking sites in the VoroSDF as the reference point,the Kd tree is used to propose a hollowing model module segmentation method(KDP,KD tree-based Partition method),which ensures the segmented model is approximately ellipse to meet the requirement of tilt angle in the 3D printing process.The separated printable module can be printed in a number of printers in parallel,thus improving the production efficiency of the product.Finally,the simple FDM printing equipment has been successfully used to produce a variety of hollow structure products with complex internal forms. |
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