Optimal Design And Modeling Of Variable-Density Cellular Structures For Laser Additive Manufacturing

In the structural design of a product,a lightweight design can not only reduce the energy consumption of manufacturing and operation but also enable improved dynamic and static performance.As a kind of novel multifunctional structure with 2D or 3D pores characterized by low relative density,cellular structures can attain a lightweight design while maintaining the high specific mechanical properties in the solid structures.Focusing on the challenge of finding the optimal design of cellular structures in design object,an optimal design and modeling method of variable-density cellular structures for laser additive manufacturing was proposed.With the cellular cell as design unit,optimization for cell type,cell size,and strut size distribution of cellular structures were specified with mechanical properties analyzed and material model calculated beforehand.Considering laser additive manufacturing constraints,the optimal distribution of topology optimization results were mapped to the strut size distribution of cellular cells,resulting in non-uniform cellular structure.A rapid and automatic CAD modeling auxiliary application for variable-density cellular structure was developed by the parametric definition and assembling of cells.The main contents are as follows:1.The equivalent material models of cellular structures were established: According to the loading condition of structures,the geometric characteristics and mechanical properties of different types of cellular structures were comprehensively analyzed,and the optimal type of uniform cellular structure was selected.According to the structural complexity of different cell types,the expressions with coefficients for effective elastic properties were deduced by the equivalent strain energy method or analytical method.The FEA of cellular structures with different sizes of struts were carried out to fit the coefficients and the equivalent material model was established.Based on the finite element simulation method,the influence of the design domain size and cell size on the equivalent material model was analyzed.The servo frame was taken as an example to analyze the cellular filled structure and the equivalent model.The results were compared to verify the validity of the equivalent performance formula in the engineering structure.2.The manufacturing constraint models for cellular structures were developed: Possible manufacturing constraints were analyzed based on the characteristics of the laser additive manufacturing process.Manufacturing constraint value tests were performed by designing and manufacturing test geometries for specific manufacturing machine and process parameter conditions.Manufacturing constraints were expressed as functions of optimization design variables,so as to be modeled as constraints in topology optimization.According to the manufacturing constraint modeling results,the manufacturable density ranges of cellular structures with different cell types,cell sizes and manufacturing constraint values were obtained,and the optimal design of cell types and cell sizes in variable-density cellular structures were supported.3.A topology optimization and modeling approach for variable-denstiy cellular structures was presented: Based on the equivalent material model,the cellular structure was equivalent to the continuous structure,the manufacturing constraints were modeled as the topology optimization constraints,and the equivalent topology optimization model could be established.The overall stiffness matrix and the flexibility matrix were solved by numerical coding method,so as to perform sensitivity analysis and the density distribution matrix of finite elements was obtained by optimality criteria algorithm.The element density distribution matrix was mapped into aspect ratio distribution matrix of cells.Next,the matrix was analyzed in the CAD auxiliary application to realize the rapid modeling of the cellular structure.4.Structural mechanical properties of designed structures were evaluated by simulations and experiments: The volumetric specific stiffness was defined as the mechanical performance evaluation criterion.FEA simulations for cellular structures with alternative cell types and cell sizes under various working conditions were carried out,and mechanical performance results were compared to provide the information support for the selection of the cell size and cell type under manufacturing constraints.The fabrication and mechanical tests of cellular structures were conducted,the deformation and failure modes were observed,and the test results of optimized structures and uniform structures were compared to validate the effectiveness of the optimal design method.5.A variable-density cellular filling design method for engineering complex structure was presented: Based on the design domain division and FEA for stress and deformation,the cellular filling optimal design method for engineering complex structure was established.Taking the seeker servo base as an example,the variable-density cellular filling optimal design was carried out.The mechanical properties of the cellular filling structures before and after optimization were analyzed and compared with FEA to verify the effectiveness of the design method.