Mendes Rui, Fanzio Paola, Campo-Deaño Laura, Galindo-Rosales Francisco J
CEFT, Departamento de Engenharia Mecânica, Faculdade de Engenharia da Universidade do Porto, Rua Dr. Roberto Frias, 4200-465 Porto, Portugal.
Ultimaker B.V. Watermolenweg 2, 4191 PN Geldermalsen, The Netherlands.
Materials (Basel). 2019 Sep 3;12(17):2839. doi: 10.3390/ma12172839.
Fused Filament Fabrication is an extrusion deposition technique in which a thermoplastic filament is melted, pushed through a nozzle and deposited to build, layer-by-layer, custom 3D geometries. Despite being one of the most widely used techniques in 3D printing, there are still some challenges to be addressed. One of them is the accurate control of the extrusion flow. It has been shown that this is affected by a reflux upstream the nozzle. Numerical models have been proposed for the explanation of this . However, it is not possible to have optical access to the melting chamber in order to confirm the actual behavior of this annular meniscus. Thus, microfluidics seems to be an excellent platform to tackle this fluid flow problem. In this work, a microfluidic device mimicking the 3D printing nozzle was developed, to study the complex fluid-flow behavior inside it. The principal aim was to investigate the presence of the mentioned back-flow upstream the nozzle contraction. As the microfluidic chip was fabricated by means of soft-lithography, the use of polymer melts was restricted due to technical issues. Thus, the working fluids consisted of two aqueous polymer solutions that allowed replicating the printing flow conditions in terms of Elasticity number and to develop a D e - R e flow map. The results demonstrate that the presence of upstream vortices, due to the elasticity of the fluid, is responsible for the back-flow problem.
熔融长丝制造是一种挤出沉积技术，在该技术中，热塑性长丝被熔化，通过喷嘴挤出并逐层沉积，以构建定制的三维几何形状。尽管它是3D打印中使用最广泛的技术之一，但仍有一些挑战需要解决。其中之一是挤出流量的精确控制。已经表明，这受到喷嘴上游回流的影响。已经提出了数值模型来解释这一现象。然而，无法对熔化腔进行光学观察以确认该环形弯月面的实际行为。因此，微流体似乎是解决这种流体流动问题的一个极好平台。在这项工作中，开发了一种模仿3D打印喷嘴的微流体装置，以研究其内部复杂的流体流动行为。主要目的是研究喷嘴收缩上游是否存在上述回流。由于微流体芯片是通过软光刻制造的，由于技术问题，聚合物熔体的使用受到限制。因此，工作流体由两种聚合物水溶液组成，这两种溶液能够在弹性数方面复制打印流动条件，并绘制出D e - R e流动图。结果表明，由于流体的弹性，上游漩涡的存在是导致回流问题的原因。
