A team of international researchers is taking a deeper dive into the fundamental physics behind metal 3D printing, all in the hopes of better understanding defects in printed parts.
Since its invention, laser powder bed fusion (LPBF) has proven itself to be an excellent tool for industry, enabling engineers to fabricate complex metal geometries that would otherwise be impossible. However, the process isn’t perfect as the heat generated by the high-power laser beams can often result in pores being formed in components. These defects are detrimental to the density of a part and lead to overall poor mechanical properties in a structure.
In critical industries where part performance is paramount, pores can pose a limitation on the types of parts that can be printed. As such, there’s an ongoing need to develop better defect detection and mitigation techniques in 3D printing.
Using advanced imaging tech, the team comprising scientists fromHeriot-Watt University,卡内基·梅隆大学, andArgonne 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?
在金属添加剂制造过程中，将激光束应雷电竞充值用于粉末材料床。这导致一小池熔融金属称为熔体池，粉末颗粒融合在一起。
在熔体池内部，少量金属蒸发并压在液体上，这在池的中心形成了一个空腔。如果被称为“钥匙孔”，如果它变得不稳定，则可以自身崩溃，从而导致在3D打印部分中形成孔。
Additionally, in the event of a collapse, vapor is shot upwards out of the keyhole and forms a plume. This can impact some of the unfused particles in the powder bed, potentially disturbing the top layer of material.
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.”
结合X射线和Schlieren成像
该团队结合了X射线和Schlieren成像的组合来检查和表征熔体池中存在的气体，蒸气，液体和实心相之间的相互作用。
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.
By modifying some of the parameters of the laser such 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.
该研究的合着者安德鲁·摩尔教授补充说：“迄今为止，研究重点是根据液态金属或颗粒的行为来检测和预测缺陷，通常俯瞰熔体池上方产生的蒸气射流的影响。我们认为，这项工作将能够创建改进的过程监控和分析工具，以识别和防止金属添加剂制造中的缺陷。”雷电竞充值
该研究的进一步详细信息可以在标题的论文中找到‘The interplay between vapor, liquid, and solid phases in laser powder bed fusion’。
Although important, defect prevention is just one area of metal additive manufacturing research. Just recently, researchers fromTsinghua大学and theNational University of Singaporeinvestigated theeffects of fluid flow on the mechanical propertiesof 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.
在其他地方，在Tallinn University of Technologyand theEstonian University of Life Sciences，工程师正在研究如何3D printing can be used to produce soft magnetic cores。就很难保留核心效率而言，打印磁芯一直是一个重大挑战，但是该团队现在提出了基于激光的增材制造业工作流程，他们声称，它们可以为软磁复合材料产生出色的磁性特性。雷电竞充值
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Featured image shows a time evolution of a plume shooting out of a melt pool’s keyhole. Image via Heriot-Watt University.
