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Laser powder bed fusion (LPBF) allows the fabrication of complex parts with high resolution. In the process of manufacturing complex parts, overhanging structures with unique mechanical properties are inevitable. The mechanical properties are relevant to the microstructure that are severely influenced by the support structures and build orientation. In this study, a three-dimensional finite element model was established to numerically investigate the thermal behavior of the melt pool in the overhanging structures, and the effects of different forming conditions on tensile behavior were analyzed through the microstructure of overhanging specimens and fracture surfaces of failed specimens. The simulation results show that the change trend of the melt pool size is the same as that of the maximum temperature. Moreover, the melt pools closer to the down-facing surface of overhanging structures carry higher temperature and larger size. The application of the support structures effectively reduces the temperature of the melt pool in the starting layer by 5.3%. With the increase of inclination angle, the melt pool temperature in the starting layer decreases slightly. The experimental results indicate that the mechanical properties of 45° specimens fabricated above the entity are stronger than those of 45° specimens with support structures, and the mechanical properties of 45° specimens with support structures are stronger than those of 45° specimens without support structures. Moreover, the mechanical properties of the specimens deteriorate when the build orientation of the overhanging structures varies from 0° to 45°. The mechanical properties of different specimens with 45° build orientation are mainly affected by the thickness of defect area, and the mechanical properties of the specimens with different build orientations are mainly affected by fracture path. The results will facilitate the understanding and application of the LPBF manufacturing technique for overhanging structures in complex parts. [ABSTRACT FROM AUTHOR]

• A finite element model used to study the influence of the block support structures on the starting layer is established. • The thermal behavior of the melt pool in the starting layer is numerically investigated. • The average dimension of the melt pool in the starting layer is related to the thickness of porous defect area. • The results of simulation and experiment are used to obtain the optimal dimension parameters of block support structure. Support structures are necessary for laser powder bed fusion (LPBF) especially when overhanging structures are fabricated. In this study, in order to understand the heat dissipation effect of the block support structures on the overhanging structures, a three-dimensional finite element model including the starting layer of the overhanging structure and the block support structures with different dimension parameters was established to numerically investigate the thermal behavior during the LPBF process. The results revealed that the support structures could dissipate the excessive heat of the melt pool in the starting layer, thus formed smaller melt pool and denser area. Different morphological characteristics of melt pool were observed at different positions above the support structures. Compared with increasing the thickness of the support structures, decreasing the distance of the support structures caused the obvious reduction of the average dimension of the melt pool. Samples and the block support structures with different dimension parameters fabricated by AlSi10Mg powder were also experimentally performed and the microstructures of the bottom section of the sample with starting and subsequent layers were investigated to verify the reliability of the numerical model. The minimum porous defect area was achieved at the optimal dimension parameters of the block support structures with 1.0 mm distance and 0.15 mm thickness. [ABSTRACT FROM AUTHOR]

• The design method of hierarchical structure is proposed. • The proposed hierarchical structure has a dual function of stretching and bending. • The specific component ratio and size ratio can enhance energy absorption. With the development of additive manufacturing technology, lattice structures with complex topological shapes can be manufactured. In order to combine the advantages of stretch dominance and bend dominance, a hierarchical lattice structure composed of variable unit cell is proposed. The hierarchical lattice structures are manufactured by laser powder bed fusion (LPBF). Five different cell arrangement combinations are designed based on face centered cubic (FCC) with octet truss structure (OTS) at the macro scale. The mechanical performance and deformation behavior of the hierarchical lattice was investigated systematically through compressive experiments and numerical simulations. The deformation modes were captured with a digital camera. Then, the crashworthiness design on the Row layered structure parametric analysis was performed to discuss the effect of geometrical parameters including component ratio and size ratio. The results indicated that the hierarchical structure exhibits a mixed deformation mode among those the Row layered structure has the best energy absorption characteristics. And the specific ratios of these geometrical parameters significantly enhance the energy absorption of hierarchical structure. Overall, this work not only provides a novel solution for designing hierarchical structures, but also highlights the advantages of additive manufacturing techniques for manufacturing complex structures. [ABSTRACT FROM AUTHOR]