来自Department of Energy’sBrookhaven National Laboratory（BNL）设计了一种更好地了解融合细丝制造（FFF）3D打印过程的方法。
Working with a team fromStony Brook University，布鲁克黑文科学家开发了一种双扫描方法，使他们能够实时监视3D打印过程中的材料沉积。在测试他们的方法时，该小组发现喷嘴诱导的剪切物可以在聚丙烯（一种常用的半晶热塑性聚合物）聚丙烯中产生“ shish kebab”结构。“ shish”组件是连接“烤肉串”的长纤维结构，外观上类似磁盘。Utilizing their new technique, the researchers not only discovered the cause of the irregularities, but now believe it could also be used to provide an insight into how other polymers behave during FFF manufacturing.
“添加剂制造是一项快速新兴的技术，直到最近，经验方面的改进仍在进行，而且通常效率低下。这是技术的狂野西部。” Stony Brook大学教授Miriam Rafailovich说。“该领域现在正在成熟，参与其中的人意识到，量化程序和结果很重要，以确保印刷设备之间的可重复性（例如，它们符合大小的标准），并使这些标准能够得到验证。”
Better understanding FFF 3D printing
During the FFF 3D printing process, materials are extruded in a way that exposes them to a high level of heat and mechanical stress. The pressure caused on the filament during this process makes the layer want to distort, and as the layers build, the potential for irregularities to occur increases in equal measure. If the polymer deforms too much as it’s extruded from the printer’s nozzle, this can even lead to structural failures within the part.
According to the researchers, some materials are especially vulnerable to this type of structural irregularity. Semi-crystalline plastics for instance, feature polymer chains that are highly-organized and tightly packed, making them more susceptible to collapse. In order to better understand why failures happen, the team developed a simultaneous system which involved taking X-ray scattering readings along with temperature checks of the printing process in real-time.
The researchers’ fabrication monitoring method
To capture the necessary data, the research team leveraged their Soft Matter Interfaces (SMI) beamline system, housed at the Brookhaven lab’s National Synchrotron Light Source II (NSLS-II) facility. Using the scanner’s X-ray microbeam technology, the scientists were able to measure the structural details of 3D printed parts, right down to a resolution of several micrometers, or several millionths of a meter.
The SMI system also allowed the team to examine the interior structures of filaments during layer formation, while the machine’s infrared camera enabled them to monitor temperature throughout the process too. Yuval Shmueli, lead author and Stony Brook researcher explained the complicated procedure worked: “The X-ray microbeam combined with three detectors—for small, medium, and wide scattering angles—enabled us to gather high-resolution spatial morphological data on the printed structure as it was being printed.”
他补充说：“我们面临的最大挑战之一是将3D打印机直接安装在X射线梁的路径中，以及略微偏移的红外热摄像机，以便可以同时测量温度和高分辨率散射频谱。”。
研究小组挥舞着新发现的技术，发现在FFF过程中由打印机喷嘴引起的剪切力有时会在广泛使用的聚丙烯丝中创建“ shish kebab”结构。地层的“ shish”成分似乎是长纤维结构，它们附着在类似盘子的“烤肉串”部分上，以产生类似捐赠者的偏差。
Subsequent X-ray scattering tests revealed that the shish-like structures nucleated at the surface of the filament, and then propagated inward, towards the filament core. Summarily, when the second layer was printed, the polymer chains relaxed and diffused across the interface between the already-printed layer and that being-printed. The overall process caused the filaments to nearly completely fuse together.
Correlating the X-ray scattering results with subsequent mechanical measurements, the team found that the finished products featured excellent strength properties, rivaling those of products created using molds. As a result, the researchers considered their new scanning approach to be a success, and concluded that new applications of the method could lead to further discoveries about FFF 3D printing. “We hope that, following this work, more materials can be investigated in this manner for improving the 3D printing process and having better and more comprehensive insights on it,” concluded Shmueli.
X射线增材制造业
While the Brookhaven team’s combination of imaging methods may constitute a novel approach, X-ray technology itself has already been applied in many ways to improve the performance of 3D printed parts.
Auburn University’sCenter for Additive Manufacturingfor instance, has installed a$1.5 million X-ray CT system对于3D打印零件的无损测试（NDT）。该系统被描述为大学航空航天行业生产计划的“真正的游戏规则”。
同样，科学家在Lawrence Livermore National Laboratoryare researching the use ofX-ray imaging to examine metal parts在激光粉床融合（LPBF）过程中。该研究旨在确定金属3D印刷零件中缺陷的原因，并了解如何减轻这些缺陷。
来自南特大学另一方面，已经使用IR成像调查传热和粘附between layers during FFF 3D printing. The team set out to find the optimal set of print parameters, with which to maximize mechanical properties of the 3D printed parts produced.
The researchers’ findings are detailed in their paper titled “In Situ Time-Resolved X‑ray Scattering Study of Isotactic Polypropylene in Additive Manufacturing” in the Applied Materials and Interfaces journal. The report was co-authored by Yuval Shmueli, Yu-Chung Lin, Sungsik Lee, Mikhail Zhernenkov, Rina Tannenbaum, Gad Marom and Miriam H. Rafailovich.
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特色,研究小组将展示形象ir 3D printer into the chamber of the Soft Matter Interfaces (SMI) beamline at Brookhaven Lab’s NSLS-II. Photo via BNL。
