High thermal gradients and complex melt pool instabilities involved in powder bed fusion–based metal additive manufacturing using focused Gaussian-shaped beams often lead to high porosity, poor morphological quality, and degraded mechanical performance. We show here that Bessel beams offer unprecedented control over the spatiotemporal evolution of the melt pool in stainless steel (SS 316L) in comparison to Gaussian beams. Notably, the nondiffractive nature of Bessel beams enables greater tolerance for focal plane positioning during 3D printing. We also demonstrate that Bessel beams significantly reduce the propensity for keyhole formation across a broad scan parameter space. High-speed imaging of the melt pool evolution and solidification dynamics reveals a unique mechanism where Bessel beams stabilize the melt pool turbulence and increase the time for melt pool solidification, owing to reduced thermal gradients. Consequently, we observe a distinctively improved combination of high density, reduced surface roughness, and robust tensile properties in 3D-printed test structures.

中文翻译：

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用于增强金属增材制造中光热控制的非衍射光束整形

使用聚焦高斯形光束的基于粉末床熔融的金属增材制造中涉及的高热梯度和复杂的熔池不稳定性通常会导致高孔隙率、较差的形态质量和降低的机械性能。我们在此展示，与高斯光束相比，贝塞尔光束对不锈钢 (SS 316L) 熔池的时空演变提供了前所未有的控制。值得注意的是，贝塞尔光束的非衍射特性使 3D 打印过程中的焦平面定位具有更大的容差。我们还证明了贝塞尔光束显着降低了在广泛的扫描参数空间中形成小孔的倾向。熔池演化和凝固动力学的高速成像揭示了一种独特的机制，其中贝塞尔光束稳定了熔池湍流并增加了熔池凝固的时间，这是由于热梯度降低。因此，我们观察到 3D 打印测试结构中高密度、降低的表面粗糙度和强大的拉伸性能的明显改进组合。