De Rosa Stefano, Tammaro Daniele, D'Avino Gaetano
Dipartimento di Ingegneria Chimica, dei Materiali e Della Produzione Industriale, Università Degli Studi di Napoli Federico II, P.le Tecchio 80, 80125 Napoli, Italy.
Micromachines (Basel). 2023 Jan 27;14(2):329. doi: 10.3390/mi14020329.
Fused deposition modelling is one of the most widely used additive manufacturing techniques and the diffusion of 3D printers has increased in popularity even further in recent times. Since high precision is required in 3D printing, a good control over the extrusion process is necessary. In this regard, a crucial phenomenon to be accounted for is the die or extrudate swell, i.e., the enlargement of the cross-section of the strand when coming out of the printer nozzle. While this phenomenon has been studied in large scale extruders, it has not yet been investigated in depth for 3D printing processes. In this work, the die swell phenomenon observed in a printed PLA filament is studied by experiments and fluid dynamic simulations. A novel, easy-to-use, accurate and fast procedure for measuring the value of the die swell ratio during the printing process is developed, accounting for typical errors related to a non-constant strand diameter and possible oscillations of the filament with respect to the extrusion direction. As the printing velocity is increased, a linearly increasing swelling ratio is observed at low printing speeds. The trend flattens at moderate speed values. A sudden increase is found at high printing velocities. The swelling ratio measured with the proposed technique is compared with the results of multi-mode viscoelastic simulations at different temperatures. A fair agreement between the experimental measurements and the numerical predictions is found for printing velocities that are typically employed in commercial 3D printers, supporting the reliability of the developed procedure.
熔融沉积建模是应用最为广泛的增材制造技术之一，近年来3D打印机的普及程度进一步提高。由于3D打印需要高精度，因此必须对挤出过程进行良好的控制。在这方面，一个需要考虑的关键现象是模头或挤出物膨胀，即当丝条从打印机喷嘴出来时其横截面的增大。虽然这种现象在大型挤出机中已经得到研究，但在3D打印过程中尚未进行深入研究。在这项工作中，通过实验和流体动力学模拟研究了在打印的聚乳酸（PLA）长丝中观察到的模头膨胀现象。开发了一种新颖、易于使用、准确且快速的程序，用于在打印过程中测量模头膨胀比的值，该程序考虑了与丝条直径不恒定以及长丝相对于挤出方向可能的振荡相关的典型误差。随着打印速度的增加，在低打印速度下观察到膨胀比呈线性增加。在中等速度值时趋势变平。在高打印速度下发现突然增加。将用所提出的技术测量的膨胀比与不同温度下的多模式粘弹性模拟结果进行比较。对于商业3D打印机通常采用的打印速度，实验测量结果与数值预测结果之间发现了良好的一致性，这支持了所开发程序的可靠性。
