Collaborative Research: Physical Mechanism of Melt Pool Oscillation and Spatter Formation in Laser Powder Bed Fusion Additive Manufacturing

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Laser powder bed fusion (LPBF) is a widely used additive manufacturing process that can 3D print complex metallic components that can not be produced by conventional manufacturing technologies. Spattering, the uncontrolled eruption of metal droplets, is a critical problem in LPBF systems and is a major cause of poor quality in components printed using the process. In spite of this, the fundamental reasons for spatter formation are not well understood and effective approaches for reducing spatter in LPBF are not available. This award supports fundamental research to understand spatter formation. The research team will perform experiments and computer simulations to observe the dynamic process of spatter formation and model the behavior of the molten metal pool to reveal the spatter formation mechanisms. The outcomes of the research will provide important guidance for optimizing the LPBF process to produce defect-free 3D printed metal parts. This will significantly expedite the applications of 3D printing in aerospace, biomedical, automotive, and other industries and will strengthen the manufacturing capability and competitiveness of U.S. industry. Spatter formation in LPBF is a highly transient process with complex coupling of multi-physics. Due to a limited ability to observe and measure the controlling parameters with adequate spatial and temporal resolution, there is a lack of understanding of the fundamental physics of spatter formation in LPBF. The objectives of this research are to: (i) test the hypothesis that the spatter formation is caused by melt pool oscillation, (ii) test the hypothesis that melt pool oscillation is caused by three physics mechanisms (i.e., non-uniform laser absorption, random powder blocking, and random powder merging), and (iii) evaluate the significance of the three hypothetical mechanisms to melt pool oscillation and spatter formation. A synergistic experimental and numerical investigation will be performed to achieve the research objectives. On the experimental side, a novel two-view high-speed imaging system, including synchrotron-based, side-view, X-ray imaging and a visible-light camera at 45 degrees to the horizontal direction will be used to provide 3-dimensional information on the dynamic behavior of the powder particles, melt pool, depression zone, and spatters. On the numerical side, a multi-physics model will be established to simulate the laser-matter interaction, multi-phase thermofluidic flow, dynamic surface motion, and fluid-solid interaction.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.