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

激光粉末床熔融（LPBF）是一种应用广泛的增材制造工艺，可以3D打印传统制造技术无法生产的复杂金属部件。溅射，即金属液滴不受控制的喷发，是LPBF系统中的一个关键问题，也是使用该工艺打印的部件质量差的主要原因。尽管如此，飞溅形成的根本原因尚不清楚，也没有有效的方法来减少LPBF中的飞溅。该奖项支持了解飞溅形成的基础研究。研究小组将通过实验和计算机模拟来观察飞溅形成的动态过程，并对金属熔池的行为进行建模，以揭示飞溅形成的机制。研究结果将为优化LPBF工艺以生产无缺陷的3D打印金属零件提供重要指导。这将大大加快3D打印在航空航天、生物医学、汽车和其他行业的应用，并将加强美国工业的制造能力和竞争力。LPBF中溅射的形成是一个高度瞬态的过程，具有多物理场的复杂耦合。由于观测和测量控制参数的能力有限，具有足够的空间和时间分辨率，因此缺乏对LPBF中飞溅形成的基本物理的理解。本研究的目的是：(1)验证飞溅形成是由熔池振荡引起的假设；(2)验证熔池振荡是由三种物理机制（即激光不均匀吸收、随机粉末阻挡和随机粉末合并）引起的假设；(3)评估三种假设机制对熔池振荡和飞溅形成的意义。为了实现研究目标，将进行协同实验和数值研究。在实验方面，一种新型的双视图高速成像系统，包括基于同步加速器的侧视图，x射线成像和与水平方向45度的可见光相机，将用于提供粉末颗粒，熔池，凹陷区和飞溅的动态行为的三维信息。在数值方面，将建立一个多物理场模型来模拟激光-物质相互作用、多相热流体流动、动态表面运动和流固相互作用。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

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.