Abstract Droplet-based 3D printing is very promising for the fabrication of complex thin-wall microwave devices such as antenna horns and waveguide tubes since it can print a shell by utilizing only several layers of droplets. However, due to the naturally scalloped shape of metal droplets, conventional droplet-based 3D printing methods cannot produce thin-wall tubes with high-quality inner surfaces that can meet the requirement of electromagnetic transmission. Here, combining the conventional casting procedure and droplet printing, a hybrid printing process is proposed. Uniform aluminum droplets were first rotationally deposited on a soluble core, and then the core was dissolved and left behind a tube with a high-quality inner surface. The deposition parameters (i.e., number of layers and deposition frequency) were adjusted according to the rotation of the core to form a dense shell over its surface. A hexagonal metal tube was fabricated by using the proposed method to prove its effectiveness. The standard Archimedes test shows that the density of the formed part was up to 98.89%. The industrial CT scanning results also prove a porosity-free inner structure. The inner surface roughness (Ra) was measured to be 4.38 μm by using a laser confocal microscope scanning, and the roughness is only 0.37% of the droplet diameter.

中文翻译：

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通过可溶芯上的液滴沉积直接制造具有高质量内表面的金属管

摘要 基于液滴的 3D 打印技术在制造复杂的薄壁微波器件（如天线喇叭和波导管）方面非常有前景，因为它可以仅利用几层液滴来打印外壳。然而，由于金属液滴的自然扇贝形状，传统的基于液滴的 3D 打印方法无法生产具有满足电磁传输要求的高质量内表面的薄壁管。在这里，结合传统的浇铸程序和液滴印刷，提出了一种混合印刷工艺。均匀的铝液滴首先旋转沉积在可溶核上，然后核溶解并留下具有高质量内表面的管子。沉积参数（即 层数和沉积频率）根据核的旋转进行调整，以在其表面形成致密的壳。使用所提出的方法制造了六边形金属管以证明其有效性。标准的阿基米德测试表明成型件的密度高达98.89%。工业 CT 扫描结果也证明了无孔隙的内部结构。使用激光共聚焦显微镜扫描测得的内表面粗糙度（Ra）为4.38 μm，粗糙度仅为液滴直径的0.37%。工业 CT 扫描结果也证明了无孔隙的内部结构。使用激光共聚焦显微镜扫描测得的内表面粗糙度（Ra）为4.38 μm，粗糙度仅为液滴直径的0.37%。工业 CT 扫描结果也证明了无孔隙的内部结构。使用激光共聚焦显微镜扫描测得的内表面粗糙度（Ra）为4.38 μm，粗糙度仅为液滴直径的0.37%。