The2021 3D Printing Industry Awards候选名单愿意投票，现在就有发言权。
研究ers atLawrence Livermore National Laboratory(LLNL) are seeking to address the drawbacks of laser beams traditionally used in metal 3D printing.
By exploring alternative shapes to the Gaussian beams commonly used in laser-based 3D printing processes such as laser powder bed fusion (LPBF), the researchers hope to reduce porosity and defects in metal parts that can lead to poor mechanical performance.
To overcome such issues, the researchers are exploring how exotic optical beam shapes, known as Bessel beams, can reduce the likelihood of pore formation and “keyholing”, where bubbles are created in the melt pool that then form pores in finished parts.
使用高斯光束”是很多like using a flamethrower to cook your food; you don’t have a lot of control over how heat is deposited around the material,” said Thej Tumkur Umanath, LLNL Research Scientist and lead author of the study. “With a Bessel Beam, the fact that we redistribute some of that energy away from the center means we can engineer thermal profiles and reduce thermal gradients to aid microstructural grain refinement and, ultimately, result in denser parts and smoother surfaces.”
常规激光束的缺点
大多数现成的高功率激光系统都利用高斯光束形状。虽然这种基于激光的3D打印技术具有advanced design complexitywithin the production of metal parts, they can also lead to undesirable levels of porosity and potentially poor mechanical performance.
In recent years, a fair amount of research has been undertaken in this area toimprove LPBF 3D printing technologies和avoid defects in metal printed parts. Such attempts have involved the use ofLED代替激光器to melt powder, the development of“smart” baseplates, and betterbalancing heat within the build chamberto reduce a component’s residual stress and distortion.
Now, the LLNL team is investigating how the comparatively low-cost method of laser beam shaping could further enhance the LPBF printing process and reduce porosity in printed metal parts.
Gaussian vs Bessel beams
根据LLNL研究人员的说法，在LPBF 3D打印过程中使用高斯光束会导致大型热梯度和复杂的熔体池的不稳定性，激光符合金属粉末。高斯梁也可能导致钥匙孔，从而导致成品零件的机械性能降解。
Unlike Gaussian beams, Bessel beams are non-diffracting and do not diverge when they propagate. The beam shape is reminiscent of a bullseye pattern, and in addition to being non-diffracting possesses other unique properties such as self-healing.
贝塞尔束的非裂纹特性提供了更大的焦点，并增加了对工件在激光焦点方面的放置的容忍度。结果，每当将一层金属粉末存放在激光器的深度内，公司可能会放弃重新定位在激光器深处所需的昂贵技术。
These properties prompted the LLNL researchers to experiment with Bessel beam shapes to see if they could overcome some of the most pressing concerns in LPBF 3D printing.
“Bessel beams have been used extensively in imaging, microscopy and other optical applications for their non-diffractive and self-healing properties, but beam-shape engineering approaches are rather uncommon in laser-based manufacturing applications,” continued Tumkur. “Our work addresses the seeming disconnect between optical physics and materials engineering in the metal additive manufacturing community by incorporating designer beam shapes to achieve control over melt pool dynamics.”
Experimenting with beam shaping
To achieve the Bessel beam shape, the LLML researchers ran a laser through two conical lenses to produce a donut shape, and then passed it through additional optics and a scanner to create rings around the central beam. The setup was installed in a commercial 3D printer in LLNL’s Advanced Manufacturing Laboratory and was used to fabricate cubes and other shapes from stainless steel powder.
为了研究其激光束塑形实验的影响，研究人员使用了高速成像。对熔体池动力学的观察显示，熔体池的湍流显着降低，而Spater（在构建过程中从激光路径飞行的熔融金属颗粒）得到了显着缓解。它的飞溅倾向于导致金属3D印刷零件中的孔形成，因此减少这种效果的事实可能是改善LPBF工艺的正向一步。
“Industry has long sought the ability to increase control of the LPBF process to minimize defects,” said Ibo Matthews, Principal Investigator for the study. “Introducing complex structure to the laser beam adds increased flexibility to precisely control the laser-material interaction, heat deposition and ultimately the quality of the prints.”
该团队还进行了各种机械研究和模拟，发现使用贝塞尔束建造的零件比使用常规高斯梁制造的零件更密集，更强，并且具有更强的拉伸性能。
研究人员模拟两者的互动Gaussian and Bessel beam laser shapes with single tracks of metal powder, within which the Bessel beam demonstrated improved thermal gradients over Gaussian beams. As a result, this was estimated to encourage better microstructure formation while avoiding the generation of “hot spots”.
The benefits of beam shaping
研究人员试图探索光束塑形如何通过低成本与替代扫描策略相比，如何改善LPBF 3D印刷金属零件的质量。通过合并简单的光学元素，该方法可以几乎不需要成本执行，同时否定了使用高斯横梁建造的零件所需的昂贵且耗时的后处理技术。
“有一个巨大的需要robu生产零部件st and defect-free, with the ability to print very large structures in a cost-effective fashion,” said Tumkur. “To make 3D printing truly compatible with industrial standards and move beyond conventional manufacturing approaches, we need to address some fundamental issues that occur at very short temporal regimes and microstructural scales.”
The LLNL team is also experimenting with other beam shaping techniques as part of the laboratory’s ongoing partnership with GE Global Research. Going forward, the researchers will look to develop complex laser beam and polarization-shaping techniques to improve control over the quality of printed parts.
Tumkur continued: “I think beam shaping is really the way to go because it can be applied to print a wide range of metals ubiquitously and be incorporated into commercial printing systems without posing significant integrability challenges as other alternate techniques tend to do.”
Further information on the study can be found in the paper titled:“Nondiffractive beam shaping for enhanced optothermal control in metal additive manufacturing,”发表在《科学进步杂志》上。该研究由T. Voisin，R。Shi，P。Decond，T。Roehling，S。Wu，M。Crumb，J。Roehling和G. Guss，T。Tumkur，S。Kairallah和M马修斯。
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特色图片显示LLNL researchers are experimenting with Bessel beams to address porosity and defects in metal 3D printing. Photo via Veronica Chen/LLNL.
