Limited research has attempted to reveal the different modes of the melt pool formation in additive manufacturing. This paper aims to study the mechanisms of surface roughness formation, especially on the aspect of melt pool formation which determine the surface profile and consequently significantly influence the surface roughness.,In this study, the conditions under which different modes of melt pool formation (conduction mode and keyhole mode) occur for the case of as-fabricated Hastelloy X using direct metal laser solidification (DMLS) are derived and validated experimentally. Top surfaces of uni-directionally built samples under various processing conditions are cut, grinded, polished and etched to reveal their individual melt pool morphologies. Similarly, up-skin (slope angle 90°) melt pool morphologies are also investigated to compare the differences. Surface tension gradients and resultant Marangoni flow, which dominate the melt flow in the melt pool, is also calculated to help better evaluate the melt pool shape forming.,Two types of melt pool formation modes are dominating in DMLS: conduction mode and keyhole mode. Melt pool formed by conduction mode generally has an aspect ratio of 1:2 (depth vs width) and is in elliptical shape. Appropriate selection of scanning laser power and speed are required to maintain a low characteristic length and width ratio to prevent ballings. Melt pool formed by keyhole mode has an aspect ratio of 1:1 or less. High-energy contour promotes formation of key-hole-shaped melt pool which fills the gaps between layers and smoothens the up-skin surface roughness. Low-energy contour scan is necessary for down-skin surface to form small melt pool profiles and achieve low Ra.,This paper provides valuable insight into the origins of surface quality problem of DMLS, which is a very critical issue for upgrading the process for manufacturing real components. This paper helps promote the understanding of the attributes and capabilities of this rapidly evolving three-dimensional printing technology and allow appropriate control of processing parameters for successful fabrication of components with sound surface quality.

中文翻译：

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Hastelloy X 金属直接激光凝固熔池形貌与表面粗糙度关系

有限的研究试图揭示增材制造中熔池形成的不同模式。本文旨在研究表面粗糙度的形成机制，特别是在熔池形成方面，它决定了表面轮廓并因此显着影响表面粗糙度。在本研究中，不同模式的熔池形成（传导）的条件模式和锁孔模式）在使用直接金属激光凝固 (DMLS) 制造的哈氏合金 X 的情况下发生的情况得到了推导出和实验验证。在各种加工条件下单向构建的样品的顶面被切割、研磨、抛光和蚀刻，以显示它们各自的熔池形态。相似地，还研究了表皮（倾斜角 90°）熔池形态以比较差异。还计算了在熔池中主导熔体流动的表面张力梯度和由此产生的 Marangoni 流动，以帮助更好地评估熔池形状的形成。两种类型的熔池形成模式在 DMLS 中占主导地位：传导模式和小孔模式。导电方式形成的熔池一般长宽比为1:2（深宽比），呈椭圆形。Appropriate selection of scanning laser power and speed are required to maintain a low characteristic length and width ratio to prevent ballings. 由锁孔模式形成的熔池的纵横比为 1:1 或更小。高能轮廓促进形成钥匙孔状熔池，填充层间间隙并平滑上皮表面粗糙度。低能量轮廓扫描对于下皮表面形成小的熔池轮廓并实现低Ra是必要的，本文提供了对DMLS表面质量问题起源的宝贵见解，这是升级工艺的一个非常关键的问题制造真正的组件。本文有助于促进对这种快速发展的 3D 打印技术的属性和功能的理解，并允许适当控制加工参数以成功制造具有良好表面质量的组件。