Manufacturing and characterization of hybrid metal-polymer sandwich structures obtained by foam injection molding process

This Thesis investigates the development and characterization of hybrid polymer–metal sandwich structures produced through foam injection molding, aiming to provide a sustainable, automated, and cost-effective solution for lightweight applications in the automotive and aerospace sectors. Conventional sandwich structures, while offering excellent stiffness-to-weight ratios, are generally manufactured through costly, labour-intensive processes. To address this limitation, the proposed approach combines polymer injection over-molding with the MuCell® foaming process, thereby reducing production steps while maintaining mechanical and functional performance. The study focuses on the effects of two key process parameters mold temperature and the amount of injected supercritical fluid - on the final properties of the hybrid structure. Aluminium face sheets were laser structured to promote mechanical interlocking with a polyamide 6 core reinforced with 30% glass fibers and foamed in-situ. Morphological analyses were conducted via computed tomography and microscopy, while interfacial strength and flexural performance were evaluated respectively through edge shear test and four-point-bending test. Results show that higher mold temperatures improve polymer infiltration and interfacial adhesion, leading to increased shear strength, whereas supercritical fluid injection enhances interface toughness but introduces risks of irregular pore formation at higher contents. The optimized parameter combinations achieved interfacial shear strengths of 18 MPa, with flexural behaviour confirming the dominant contribution of the aluminium face layers. Overall, this work demonstrates that foam injection molding, combined with suitable surface structuring and process control, represents a viable industrial strategy for the production of lightweight and reliable hybrid polymer-metal sandwich structures with strong potential in high performance applications, for example in automotive and aerospace industries.