Multi-material additive manufacturing

Hybrid Material Extrusion (MEX) System

• Initial G-code to print the closed cell structure is generated using the slicing software such as Simplify 3D.

• The generated G-code is later post-processed, and a piece of G-code (a G-code sample) is added that commands the secondary nozzle to the filling position, travel speed, dispensing amount (based on the internal CAD volume), and rate of filling.

Hybrid lattice metamaterials (HLMs)

In this work, a novel dual-phase metamaterial, named “hybrid lattice metamaterial (HLM),” is designed and fabricated by combining reentrant and sea-urchin (SU)-based surface-lattice (SL) structures with polyamide 12 (PA12) material via the material extrusion (MEX) process. Four different designs with varying reentrant truss thicknesses of 0.8 mm (H1), 1.0 mm (H2), 1.2 mm (H3), and 1.5 mm (H4) have been modified to assemble seamlessly with the empty spaces within the SL structure. Quasistatic compression tests were conducted to evaluate the deformation modes and compression characteristics. The findings from quasistatic experiments were subsequently validated using numerical simulations. The H4 metamaterial exhibited superior structural properties, with a 42% increase in stiffness and a 35% enhancement in specific energy absorption compared to only SL structure. Additionally, dynamic sinusoidal compression tests were conducted to evaluate the dynamic elastic ratio (DER), hysteresis work, and viscoelastic properties using the tan δ. The H4 metamaterial outperformed the SL in all dynamic properties, with a 50% increase in elastic modulus and a 36% increase in hysteresis work. This study shows metamaterial properties can be tailored for specific requirements. SL structure facilitates elastic recovery, while H4 metamaterials offer superior energy absorption and stability, making them well-suited for protective equipment and impact-resistant components. 

Biphasic architectured structure (Quasistatic compression analysis) 

This research introduces a new method for fabricating biphasic-architectured structures using a self-developed hybrid material extrusion (MEX) process. This approach involves filling the voids of closed-cell structures with a powder material in a single process. The architectured structures were 3D-printed using thermoplastic polyurethane (TPU) and subsequently filled with polyamide 12 (PA12) powder in two distinct configurations: partially filled (50%) and fully filled (100%), named as biphasic architectured structures. Experimental and numerical uniaxial quasistatic compression tests were conducted on partially-filled and fully-filled local and global closed-cell architectured structures, and their results were compared with those of empty architectured structures. The comparative analysis revealed that the partially filled structures, representing a transitional phase, exhibit enhanced properties, which are influenced by the amount of powder filling within the structure. A substantial enhancement in stiffness and specific energy absorption (SEA) was observed in the consolidation phase. The fully-filled architectured structures exhibit a rapid increase in their loading response, characterized by high stiffness and SEA. Furthermore, this study paves the way for future exploration into strategic filling of multiple powders in different regions, thereby tailoring the mechanical and functional responses. Potential applications include manufacturing components and equipment that absorb energy, provide impact protection, and offer vibration damping and soundproofing capabilities.

Biphasic architectured structure (Dynamic Impact analysis) 

This research investigates biphase lattice structures fabricated through hybrid material extrusion (MEX), combining TPU lattices with polyamide (PA)-12 powder filler. This filling methodology was applied to both local and global closed lattice structures. A systematic layered approach was implemented to examine the effect of varying powder fill levels, ranging from 0% (unfilled local closed lattice structure: ULS-L, unfilled global closed lattice structure: ULS-G) to completely-filled 100% (biphase local closed lattice structure: BLS-L100, biphase global closed lattice structure: BLS-G100), with intermediate levels of 25% (BLS-L25, BLS-G25), 50% (BLS-L50, BLS-G50), and 75% (BLS-L75, BLS-G75). Experimental and numerical drop-weight impact tests have been performed to investigate the impact performance along with impact force, CFE, and energy absorption. Results indicate that the BLS-L100 exhibited superior mechanical properties among all structures. Powder-filled lattice structures demonstrated remarkable impact performance, with BLS-L100 and BLS-G100 configurations exhibiting significant increases in both peak impact force (142% and 144%, respectively) and impulse absorption capacity (34% and 46%, respectively) compared to their unfilled counterparts. These dual improvements in impact resistance suggest a synergistic interaction between the powder fill and the lattice structure, leading to enhanced dynamic mechanical performance compared with single-phase lattice structure. This study also concludes that the dynamic impact response can be tuned through appropriate selection of biphase lattice structures. 

Interpenetrating Phase Composite (IPC) Metamaterials 

Interpenetrating phase composite (IPC) is a unique type of material that may exhibit tunable mechanical and functional properties. This study introduces a novel hybrid material extrusion (MEX) technique to fabricate lattice-based IPC metamaterials. This approach aims to functionally tune mechanical properties by incorporating diverse material phases within the lattice voids. Two different designs—sea urchin (SU) and hybrid (H) lattice were 3D printed using thermoplastic polyurethane (TPU) as the outer material. The lattice voids were filled with combinations of polyamide (PA)-12 powder, 316L stainless steel-based slurry, and polyurethane (PU) foam, resulting in three IPC configurations (IPC- type I: foam-powder-powder, IPC- type II: foam-slurry-powder, and IPC- type III: foam-slurry-slurry). Comprehensive static and dynamic compression tests were conducted to evaluate the mechanical properties of the resulting IPC metamaterials. Hybrid lattice-based IPC metamaterials demonstrated superior mechanical properties compared to their SU counterparts. IPC-type I demonstrated a substantial improvement in mechanical performance, exhibiting a compressive strength up to 5 times higher and an energy absorption per unit volume up to 2.5 times greater than empty or single-phase metamaterials. Under dynamic conditions, both designs showed distinct properties in hysteresis work, tan δ, and dynamic elastic recovery (DER). The study also explores the effects of varying loading rates and frequencies on the IPC metamaterials' mechanical behavior. Overall, this study presents an innovative fabrication technique for IPC metamaterials, revealing how the strategic placement and stacking sequence of secondary materials within the primary structure significantly influences their mechanical properties.