Process–structure relationships in LPBF-fabricated lattice interlocks for injection molded metal–polymer joining

Metal-polymer hybrid structures are increasingly required for lightweight and high-performance applications; however, conventional joining approaches based on chemical surface treatments suffer from poor reproducibility and limited design flexibility. In this study, a process-informed structural interlocking strategy using laser powder bed fusion (LPBF)-fabricated lattice architectures is proposed for injection molded direct joining. Unlike conventional approaches that primarily focus on geometric design, this study incorporates injection molding-induced flow and pressure conditions into the evaluation of lattice performance. Three lattice configurations were designed and fabricated using AlSi10Mg, and their mechanical responses were experimentally assessed through injection molding and tensile testing. In parallel, injection molding simulations were conducted to analyze the pressure distribution and structural deformation of lattice inserts under process-representative conditions. The results show that all lattice configurations achieved stable bonding, while differences in load-bearing capacity were observed depending on lattice geometry. In particular, tensile strength decreased by up to 23.6% with increasing lattice complexity, despite maintained interfacial bonding. Simulation results suggested that lattice density influences both flow behavior and structural response, leading to a trade-off between injection pressure and deformation. The lower-density lattice exhibited lower simulated injection pressure during filling, potentially facilitating polymer penetration, whereas the higher-density lattice exhibited improved structural resistance, accompanied by an increase in von Mises stress of up to 143.3%. This study demonstrates that lattice performance in metal-polymer joining cannot be evaluated solely based on structural design, but should be considered in conjunction with processing conditions. The proposed approach provides a process-structure integrated evaluation framework for LPBF-based lattice interlocking under realistic injection molding environments.