Fully dense structures of high solids loaded polymer composites printed via material extrusion additive manufacturing are of interest across many applications, including biomedical scaffolds and energetic materials. It is common to observe defects such as interfilament voids in space-filling structures, particularly during material extrusion printing with high solids inks, which exit the nozzle in a circular structure and require applied forces to deform. An understanding of the impact of process parameters on the void volume and structure, which can ultimately affect material performance, is necessary. Here we examine the effects of four key process parameters, layer height, extrusion rate, print speed and nozzle diameter, on the filament geometry and interfilament void formation. The layer height, extrusion rate and print speed all impact the width of the printed lines, but the layer height plays the most significant role in the line aspect ratios and void formation in printed structures. We find that in material extrusion of high solids loaded inks there is a critical layer height; below the critical height, the ink will spread to fill in gaps between filaments, and above it the filament will maintain a rounded shape and lead to formation of interfilament voids. The results illuminate a pathway to control porosity of fully dense structures with high solids loaded inks using the layer height parameter while maintaining geometric accuracy in the printed design.

通过材料挤出增材制造打印的高固体负载聚合物复合材料的完全致密结构在许多应用中受到关注，包括生物医学支架和高能材料。通常会观察到缺陷，例如空间填充结构中的丝间空隙，特别是在使用高固体份墨水进行材料挤出打印期间，这些缺陷以圆形结构从喷嘴中排出并需要施加力才能变形。必须了解工艺参数对空隙体积和结构的影响，这最终会影响材料性能。在这里，我们检查了四个关键工艺参数，层高、挤出速率、打印速度和喷嘴直径对灯丝几何形状和灯丝间空隙形成的影响。层高，挤出速率和印刷速度都会影响印刷线条的宽度，但层高在印刷结构中的线条纵横比和空隙形成中起着最重要的作用。我们发现在高固体含量油墨的材料挤出中存在一个临界层高；在临界高度以下，墨水将扩散以填充细丝之间的间隙，而在临界高度之上，细丝将保持圆形形状并导致形成细丝间空隙。结果阐明了使用层高参数控制具有高固体负载油墨的完全致密结构的孔隙率的途径，同时保持印刷设计的几何精度。我们发现在高固体含量油墨的材料挤出中存在一个临界层高；在临界高度以下，墨水将扩散以填充细丝之间的间隙，而在临界高度之上，细丝将保持圆形形状并导致形成细丝间空隙。结果阐明了使用层高参数控制具有高固体负载油墨的完全致密结构的孔隙率的途径，同时保持印刷设计的几何精度。我们发现在高固体含量油墨的材料挤出中存在一个临界层高；在临界高度以下，墨水将扩散以填充细丝之间的间隙，而在临界高度之上，细丝将保持圆形形状并导致形成细丝间空隙。结果阐明了使用层高参数控制具有高固体负载油墨的完全致密结构的孔隙率的途径，同时保持印刷设计的几何精度。