Ensuring the repeatability and stability of printing process is significant for the 3D Concrete Printing (3DCP). However, the diversity of printers often leads to unpredictable printing journeys. Hence, in this study the printer head was dimensionally characterized by three factors: channel diameter, neck height, and nozzle diameter. The effects of printer head and process parameters (travel speed, extrusion flow rate, and nozzle height) on the geometry stability and shape of printed filament were investigated with computational fluid dynamics method. The results indicated that, for printing materials without coarse aggregates, extrusion methods had a negligible impact on 3DCP process. For the printer head, the nozzle diameter dominated the geometry stability while the neck height and channel diameter had little effects. A dimensionless parameter was proposed to quantitatively analyze the influences of travel speed, extrusion flow rate, and nozzle diameter. The systematic mechanical analysis indicated that the geometry instability (tearing and meandering) was controlled by the and nozzle height. Based on the above analysis, the selection principle for printing parameters was proposed to ensure a stable and repeatable printing. The research results regarding printer heads and printing parameters can greatly promise the large-scale application of 3DCP.

中文翻译：

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打印头和打印过程的3D混凝土打印数值模拟

确保打印过程的可重复性和稳定性对于3D混凝土打印（3DCP）具有重要意义。然而，打印机的多样性往往会导致不可预测的打印旅程。因此，在本研究中，打印机头的尺寸由三个因素表征：通道直径、颈部高度和喷嘴直径。采用计算流体动力学方法研究了打印头和工艺参数（行进速度、挤出流量和喷嘴高度）对打印长丝几何稳定性和形状的影响。结果表明，对于不含粗骨料的打印材料，挤出方法对3DCP工艺的影响可以忽略不计。对于打印机头，喷嘴直径决定几何稳定性，而颈部高度和通道直径影响不大。提出了无量纲参数来定量分析行进速度、挤出流量和喷嘴直径的影响。系统的力学分析表明，几何不稳定性（撕裂和曲折）是由喷嘴高度控制的。基于上述分析，提出了打印参数的选择原则，以保证打印的稳定和可重复性。有关打印头和打印参数的研究成果可以极大地保证3DCP的大规模应用。