Lightweight design, achieved through the systematic optimization of topological configuration and material distribution, has become a key approach for reducing weight and improving the performance of modern aircraft structures. However, studies on large components in the lightweight and manufacturing-integrated design of typical pipeline symbiotic body structure components are scarce. Meanwhile, challenges exist, such as the difficulty of achieving synergy between structural optimization and process constraints and the issue of balancing forming accuracy and mechanical properties. Therefore, to meet the lightweight design requirements for the system-tube symbiotic airframe of an aircraft, this study proposes a lightweight design method for typical large-scale sidewall structures based on the constraints of the laser additive manufacturing process to realize structural weight reduction and monolithic high-precision forming.

This study extracts boundary conditions, such as the actual service conditions of the sidewall structure, analyzes the initial strength of the sidewall structure tube before and after adjusting the tube location, and performs envelope design. In this study, based on the variable density method for the topology optimization of the sidewall structure of a typical pipeline symbiotic body, the design parameters are optimized to obtain the optimal distribution of loaded materials with the objective of mass minimization under global stress constraints. This study combines the laser additive process feature constraints to obtain a geometric reconstruction model and checks the structural stress and deformation to determine the optimization scheme. Through selective laser melting (SLM) molding technology, this study integrates the molding of parts that were originally produced separately and examines the molding accuracy.

Initial strength analysis of the simplified sidewall structure (Fig. 1) reveals that the maximum stress (Fig. 3) exceeds the allowable limit and that the displacement primarily concentrates around the smallest tube, indicating significant potential for lightweight structural optimization. Adjusting the tube layout (Fig. 4) indicates that the larger tubes contribute effectively to the load distribution, whereas a reasonable arrangement of support ribs around the smaller tube can mitigate the localized displacement accumulation. Following the envelope design (Fig. 5) and incorporating the SLM process-related geometrical constraints, topology optimization of the rib structure was performed (Fig. 6). The resulting optimized ribs primarily distribute between the tubes and regions connecting the boundary constraints, thereby establishing a more continuous and efficient load transfer path. In contrast, the ribs in the edge regions remain disconnected. The results form localized weak zones that contribute to an optimal material distribution under combined loading and boundary constraints. During the geometric reconstruction phase (Figs. 7 and 8), the same SLM manufacturing constraints were applied. By precisely controlling the cross-sectional thickness, spatial distribution, and joints of the ribs, the stress concentrations are effectively relieved, displacement accumulation is minimized, and the integrity of the load transfer path is preserved. The final reconstruction design achieves simultaneous optimization of the global load-bearing path and local geometric transitions. The calibration results indicate that the structural weight is reduced by 15%, the maximum stress is decreased by 37.2%, the maximum displacement is increased by 44.8%, and the safety factor is improved by 40%, demonstrating that lightweight objectives are achieved without compromising structural integrity. Utilizing SLM technology for integrated fabrication, the comparison between the point cloud data of the printed sidewall and the original CAD model reveals an average dimensional deviation of no more than 0.08 mm, fully satisfying the overall forming accuracy requirements of the sidewall structure.

This paper proposes a lightweight co-design method for typical sidewall structures based on laser additive process constraints to meet the lightweight design requirements of typical tube-symbiotic airframe structures of aircraft. The topology optimization model of the variable density method, which aims at minimizing mass under global stress constraints, integrates the laser additive process feature constraints into the envelope design, shape control selection, and geometric reconfiguration, and adjusts the layouts of the rib, tube, and cylinder to achieve a balance between lightweight and performance. The optimized model of the sidewall structure is achieved using SLM technology for high-precision and rapid preparation, which preliminarily verifies the feasibility of the multisystem symbiotic airframe structure design and integrated manufacturing method.