Variable density lattice filling method for structure shelling based on topology optimization by additive manufacturing

Purpose The purpose of this paper is to address the limitations of traditional selective laser melting structures when filling shell lattices. First, these structures do not adequately consider the mechanical properties under actual external loads. Second, they overlook the constraints imposed by the selective laser melting process for metal materials. Design/methodology/approach This paper proposes a variable density lattice filling optimization method based on topology optimization. The internal space remaining after shell extraction is designated as the design domain, while the external loads applied to the structure serve as the design loads. In addition, a transition zone between the lattice and the shell is incorporated. A dual-criteria density mapping method is used to map the lattice structure, enabling variable density lattice filling design. The structural stiffness and deformation characteristics of shell extracted and lattice filled structures are analyzed through quasi-static crushing simulations, additive manufacturing process simulations, forming experiments and quasi-static crushing experiments on specific examples. Findings The results show that introducing a transition region between the lattice and the shell reduces the maximum deformation in the additive forming process by 14.3%, and decreases the maximum displacement in the quasi-static crushing process by 6.5% and 12.6%, respectively. In addition, the peak crushing force is reduced by 23.4%. The overall mass of the structure is also reduced by 8.5% and 12.0%, respectively. Originality/value This study demonstrates that the proposed method offers advantages over traditional lattice filling in terms of structural mechanical properties, the additive manufacturing process and lightweight design. It provides a more scientific and rational approach for designing shell lattice fillings in additive manufacturing.