Multi-material additive manufacturing with lightweight closed-cell foam-filled lattice structures for enhanced mechanical and functional properties

This work studies the novel concept of multi-material additive manufacturing by filling closed-cell lattice structures with secondary material. Filling closed cells incorporate new functional properties that unfilled or open-cell lattice structures cannot otherwise achieve. Filled closed cells also prevent materials from escaping the cellular cavity that can prove advantageous while combining dissimilar materials. For this, a hybrid 3D printing and foaming process is developed, which involves simultaneous 3D printing and foam-filling of closed-cell lattice structures on an open-source fused filament fabrication (FFF) 3D printer. This hybrid system targets direct digital manufacturing (DDM) by combining two separate processes into a single process, eliminating post-process operations. Here, the global closed-cell sea-urchin (SU) lattice structure is 3D printed with thermoplastic polyurethane (TPU), and the secondary functional material filled in the lattice structures is polyurethane (PU) foam. The load vs. deformation responses of the composite of PU foam and TPU lattice structures has shown higher stiffness, energy dissipation, and damping characteristics which otherwise could not have been achieved by the lattice structure alone. Possible applications for these could be protective equipment, shoe midsoles, and other energy absorbing and damping devices.