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

激光粉床熔化是一种广泛使用的添加剂制造工艺，可以对传统制造技术无法生产的复杂金属零件进行三维打印。飞溅，即金属液滴的不受控制的喷发，是LPBF系统中的一个关键问题，也是使用该工艺印刷的部件质量较差的主要原因。尽管如此，飞溅形成的根本原因还不是很清楚，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。研究小组将进行实验和计算机模拟，以观察飞溅形成的动态过程，并对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工艺生产无缺陷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、汽车等行业的应用，并将增强美国工业的制造能力和竞争力。LPBF中飞溅的形成是一个多物理复杂耦合的高度瞬变过程。由于在空间和时间分辨率上观测和测量控制参数的能力有限，人们对LPBF中溅射形成的基本物理缺乏了解。本研究的目的是：(I)检验熔池振荡引起飞溅形成的假设，(Ii)检验熔池振荡是由三种物理机制(即非均匀激光吸收、随机粉末阻塞和随机粉末合并)引起的假设，以及(Iii)评估这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，将进行协同的实验和数值研究。在实验方面，将使用一种新型的双视高速成像系统，包括基于同步加速器的侧视X射线成像和与水平方向成45度角的可见光相机，以提供关于粉末颗粒、熔池、凹陷区和飞溅的动态行为的三维信息。在数值方面，将建立一个多物理模型来模拟激光-物质相互作用、多相热流体流、动态表面运动和流固相互作用。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.