A new strategy for eliminating bottom hole defects during aluminum droplet printing within a broad temperature range

Fabrication of hole-free aluminum structures through metal droplet-based 3D printing is an important channel for high-performance aluminum parts in aerospace applications. Unfortunately, completely eliminating bottom hole defects has proven challenging due to the narrow printing temperature range and complex hole defect evolution rules. In this work, by tailoring the overlap ratio (η) and substrate temperature (Ts), we proposed a novel strategy to eliminate bottom hole defects of overlapping droplets in a broad temperature range. Combining the high-speed sequence images and the numerical simulation model, the evolution mechanism of bottom hole defects with distinct overlap ratios was revealed. The result demonstrats that the bottom hole defect evolution is dominated by the droplet spreading order and the competition of inertial and capillary forces. Moreover, a regime map was summarized, where the substrate temperature window for the hole-free region at the valley (η = 0) is expanded by 114% compared to the peak (η = 0.6). Finally, a simple and effective strategy was presented, which could enlarge the printing temperature range for eliminating bottom hole defects. This work might provide theoretical guidance for the low-cost and high-quality droplet printing of multitudinous metal components.