一组国际研究人员正在深入研究金属3D印刷背后的基本物理，以期更好地理解印刷零件中的缺陷。
自发明以来，激光粉床融合（LPBF）已证明自己是行业的绝佳工具，使工程师能够制造复杂的金属几何形状，否则这是不可能的。但是，该过程并不完美，因为高功率激光束产生的热量通常会导致组件中形成毛孔。这些缺陷不利于零件的密度，并导致结构中的总体机械性能较差。
在零件性能至关重要的关键行业中，毛孔可以对可以打印的零件类型构成限制。因此，持续需要在3D打印中开发更好的缺陷检测和缓解技术。
Using advanced imaging tech, the team comprising scientists fromHeriot-Watt University,Carnegie-Mellon University， 和Argonne National Laboratoryhas now examined the material states present during metal 3D printing. The work offers new insights into how and why defects form.
Dr. Ioannis Bitharas, a research associate at Heriot-Watt’s Institute of Photonics and Quantum Sciences, explains, “Our research visualizes the interplay between all states of matter present when a laser interacts with metallic particles.”
How are pores formed in LPBF?
During the metal additive manufacturing process, a laser beam is applied to a bed of powder material. This results in a small pool of molten metal called the melt pool where the powder particles fuse together.
Inside the melt pool, a small amount of metal evaporates and presses against the liquid, which creates a cavity right at the center of the pool. Named a ‘keyhole’, this cavity can collapse on itself if it becomes unstable, leading to the formation of a pore in the 3D printed part.
此外，如果发生崩溃，蒸气会从钥匙孔向上射击并形成羽流。这可能会影响粉末床中的某些未连接的颗粒，可能会干扰材料的顶层。
Bitharas adds, “Such events create tiny imperfections scattered throughout the component and, consequently, an unacceptable level of material porosity to many manufacturers. The images we have captured provide, for the first time, a complete picture of such interactions and we can now tell with certainty what is happening.”
Combining X-ray and schlieren imaging
The team used a combination of X-ray and schlieren imaging to examine and characterize the interactions between the gas, vapor, liquid, and solid phases present in a melt pool.
Analyzing the images, they found that the vapor plume’s behavior had a direct impact on the overall stability of the melt pool’s keyhole. Specifically, the more dynamic and active the plume, the less stable the keyhole was, leading to more porosity.
通过修改一些参数的激光uch as power, spot size, and scan speed, Bitharas’ team also found that they could adequately control the dynamism of the plume and stability of the melt pool. The researchers believe they’re the first to use the keyhole plume as a process signature that can be monitored, and expect their findings to have major implications in sectors such as aerospace, automotive, and defense.
Professor Andrew Moore, co-author of the study, adds, “Research has so far focused on detecting and predicting defects based on the behavior of the liquid metal or particles, often overlooking the effects of the vapor jet and plume generated above the melt pool. We believe that this work will enable the creation of improved process monitoring and analytic tools that identify and prevent defects in the additive manufacturing of metals.”
Further details of the study can be found in the paper titled‘The interplay between vapor, liquid, and solid phases in laser powder bed fusion’.
尽管很重要，但预防缺陷只是金属添加剂制造研究的一个领域。就在最近，来自Tsinghua Universityand theNational University of Singaporeinvestigated the流体流对机械性能的影响of metal 3D printed parts. Carefully controlling the formation of new grains and dendrites in printed parts is crucial for tuning the final grain structure, but the effects of fluid flow in the melt pool hadn’t yet been explored until now.
Elsewhere, at the塔林技术大学and theEstonian University of Life Sciences, engineers are looking into how3D打印可用于产生软磁芯. Printing magnetic cores has been a major challenge so far as it’s so difficult to preserve core efficiency, but the team has now proposed a laser-based additive manufacturing workflow that they claim can yield superior magnetic properties to soft magnetic composites.
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特色图像显示了羽毛池的钥匙孔中羽流射击的时间演变。图片通过赫奥特瓦特大学。
