Rapid Prototyping Journal ( IF 3.9 ) Pub Date : 2021-02-08 , DOI: 10.1108/rpj-05-2019-0142 Easir Arafat Papon , Anwarul Haque , Muhammad Ali Rob Sharif
Purpose
This paper aims to develop a numerical model of bead spreading architecture of a viscous polymer in fused filament fabrication (FFF) process with different nozzle geometry. This paper also focuses on the manufacturing feasibility of the nozzles and 3D printing of the molten beads using the developed nozzles.
Design/methodology/approach
The flow of a highly viscous polymer from a nozzle, the melt expansion in free space and the deposition of the melt on a moving platform are captured using the FLUENT volume of fluid (VOF) method based computational fluid dynamics code. The free surface motion of the material is captured in VOF, which is governed by the hydrodynamics of the two-phase flow. The phases involved in the numerical model are liquid polymer and air. A laminar, non-Newtonian and non-isothermal flow is assumed. Under such assumptions, the spreading characteristic of the polymer is simulated with different nozzle-exit geometries. The governing equations are solved on a regular stationary grid following a transient algorithm, where the boundary between the polymer and the air is tracked by piecewise linear interface construction (PLIC) to reconstruct the free surface. The prototype nozzles were also manufactured, and the deposition of the molten beads on a flatbed was performed using a commercial 3D printer. The deposited bead cross-sections were examined through optical microscopic examination, and the cross-sectional profiles were compared with those obtained in the numerical simulations.
Findings
The numerical model successfully predicted the spreading characteristics and the cross-sectional shape of the extruded bead. The cross-sectional shape of the bead varied from elliptical (with circular nozzle) to trapezoidal (with square and star nozzles) where the top and bottom surfaces are significantly flattened (which is desirable to reduce the void spaces in the cross-section). The numerical model yielded a good approximation of the bead cross-section, capturing most of the geometric features of the bead with a reasonable qualitative agreement compared to the experiment. The quantitative comparison of the cross-sectional profiles against experimental observation also indicated a favorable agreement. The significant improvement observed in the bead cross-section with the square and star nozzles is the flattening of the surfaces.
Originality/value
The developed numerical algorithm attempts to address the fundamental challenge of voids and bonding in the FFF process. It presents a new approach to increase the inter-bead bonding and reduce the inter-bead voids in 3D printing of polymers by modifying the bead cross-sectional shape through the modification of nozzle exit-geometry. The change in bead cross-sectional shape from elliptical (circular) to trapezoidal (square and star) cross-section is supposed to increase the contact surface area and inter-bead bonding while in contact with adjacent beads.
中文翻译:
改进的喷嘴几何形状在聚合物增材制造中改善微珠铺展结构的数值研究
目的
本文旨在建立具有不同喷嘴几何形状的熔融长丝制造(FFF)过程中粘性聚合物的微珠铺展结构的数值模型。本文还着重介绍了喷嘴的制造可行性以及使用已开发的喷嘴进行3D打印熔融珠粒的可行性。
设计/方法/方法
使用基于FLUENT的流体体积(VOF)方法基于计算流体动力学代码,可以捕获来自喷嘴的高粘度聚合物的流动,熔体在自由空间中的膨胀以及熔体在移动平台上的沉积。材料的自由表面运动记录在VOF中,这由两相流的流体动力学控制。数值模型涉及的阶段是液态聚合物和空气。假定为层流,非牛顿流和非等温流。在这种假设下,用不同的喷嘴出口几何形状模拟了聚合物的扩散特性。遵循瞬态算法,在规则的固定网格上求解控制方程,其中聚合物和空气之间的边界通过分段线性界面构造(PLIC)进行跟踪,以重建自由表面。还制造了原型喷嘴,并使用商用3D打印机在平板上沉积了熔融的珠子。通过光学显微镜检查检查沉积的珠子横截面,并将横截面轮廓与在数值模拟中获得的横截面轮廓进行比较。
发现
数值模型成功地预测了挤出珠的铺展特性和横截面形状。珠子的横截面形状从椭圆形(带圆形喷嘴)到梯形(带方形和星形喷嘴)不等,其中顶部和底部表面显着变平(希望减少横截面中的空隙空间)。数值模型产生了良好的珠子横截面近似值,与实验相比,以合理的定性协议捕获了珠子的大多数几何特征。横截面轮廓与实验观察结果的定量比较也表明了良好的一致性。使用方形和星形喷嘴在珠子横截面中观察到的显着改进是表面变平。
创意/价值
所开发的数值算法试图解决FFF过程中空隙和键合的基本挑战。它提出了一种新方法,可通过修改喷嘴的出口几何形状来修改珠子的横截面形状,从而在聚合物的3D打印中增加珠子间的粘合力并减少珠子间的空隙。珠子横截面形状从椭圆形(圆形)到梯形(正方形和星形)的变化被认为会增加与相邻珠子接触时的接触表面积和珠间键合。