Manufacturing limit and structural scale effect of thin-wall/rod units in lattice structure fabricated by laser powder bed fusion

Abstract

The growing maturity of additive manufacturing (AM) technologies, represented by laser powder bed fusion (LPBF), has greatly facilitated the design and manufacturing of lattice structure. However, the process constraints of the minimum features (thin-wall/rod units) in lattice structure remains poorly understood. This study investigated the manufacturing limits and the relevant failure mechanism of thin-wall/rod units fabricated by LPBF. The effects of structural scale (dimension and inclination angle) on surface morphology, microstructure, and mechanical properties were also studied. Results indicate that the failure of thin-wall/rod units at critical dimension and inclination angle was driven by interlayer molten track mismatch and warping effect in cantilever region, respectively. AM process simulations reveal that rod unit exhibit better manufacturability at small inclination angles compared to thin-wall unit, due to less significant stress deformation. A clear dependence of defect behavior, surface morphology and microstructural characteristics on structural scale is identified. A multi-physics model was created to observe the development of down-skin surface quality of the thin-wall units at small inclination angles. Microstructural analysis reveals transitions between super-refined equiaxed grains, millimeter-long columnar grains, and centimeter-long columnar grains at different scale governed by temperature gradient and grain competitive mechanisms. Additionally, a declining tendency in tensile strength is detected with decreasing feature dimension and inclination angle, primarily because the poor side surface quality and higher porosity accelerated crack initiation and propagation. Moreover, two types of lattice structures were fabricated accordingly. Their characterization results confirm the applicability of the new findings from thin-wall/rod unit experiments, providing insights for the efficient manufacturing of lattice structures endowed with excellent performance.