基于自激发静电场驱动的热熔融喷射沉积高分辨率3D打印机理和规律研究

Micro/nano-scale 3D printing is new frontier in additive manufacturing. The emerging technique has shown powerful for fabrication of micro function parts in range of several hundred microns. However, the low print resolution of FDM today hinders the application in micro machining. A new self-excitation electric-jet 3D printing method for FDM has been proposed in this project. The goal of this method is to achieve high-resolution printing through reducing the size of micro droplets or microfilaments. Based on the existing research results of applicants, the project focuses on the issues including the characteristics of self-excited electrical field distribution and the mechanism of stable jet formation. In order to reduce the dimension of the jet from nozzle, a relatively lower voltage will be applied to sustain the continuous jet when the higher voltage with a short pulse duration disequilibrate the electric field force and surface tension on the meniscus. It is beneficial for reducing the jet size and achieving high resolution 3D printing. It mainly includes following several aspects: (1) investigate the forming mechanism and distribution characteristics of self-excited electrostatic field; and the control method for meniscus shape sustain to obtain stable jet; (2) the generation and evolution mechanism of micro/nano-scale micro droplet (microfilaments) under multi-field coupling including temperature field, flow field and electric field; the influencing factors and laws for the accurate deposition of micro droplet; (3) the process of cooling and solidification, surface / interface behavior of molten jet and regulation mechanism; (4) experimental set-up construction, process optimization, and experimental verification for typical applications including micro mould fabrication, biological tissue engineering, micro structures with high aspect ratio and integrate manufacturing with other micromachining means.

微/纳尺度3D打印是当前增材制造的学科前沿、研究难点和亟待突破的关键技术。针对目前阻碍热熔融材料3D打印分辨率提高的技术瓶颈，本项目提出一种基于自激发静电场驱动的热熔融喷射沉积3D打印新方法，旨在进一步降低热熔融材料喷射沉积的微滴/微丝尺寸，实现高分辨率打印。结合课题组前期已有的研究成果，项目重点研究自激发静电场特点及实现射流稳定沉积机理，并利用高压诱导射流协同低压稳定喷射技术解决较低电压下的射流触发和稳定喷射，进一步减小射流尺寸，实现热熔融材料高分辨率、稳定喷射沉积。主要研究内容包括：（1）自激发静电场驱动机理、分布特点及规律，喷嘴弯月面形态控制及射流稳定成形规律；（2）多场耦合作用下热熔融材料微/纳尺度微滴/微丝形成演化机制，微滴/微丝精准按需沉积的影响因素和规律；（3）热熔融喷射沉积中射流冷却、凝固规律及表/界面行为及调控机制；（4）实验平台搭建、工艺优化和典型工程应用研究。

本项目研究了针对自激发静电场驱动的热熔融喷射沉积高分辨率3D打印工艺发展面临的关键问题，通过理论分析和实验研究相结合的方法，对热熔融喷射沉积高分辨3D打印自激发静电场驱动机理、打印喷嘴处弯月面形态及稳定控制、打印材料和打印基底影响规律等进行了系统深度的研究。通过仿真数值模拟，获得了不同打印材料（微晶石蜡、PCL、PMMA、PDMS、导电银浆等）\打印基底（玻璃、金属、聚合物、石蜡等）的空间电场分布特性。打印材料粘度具有大跨度特征，粘度跨度从几十cP到10^7cP。研究了打印喷嘴处弯月面形态规律及稳定控制策略，分别获得了低粘度墨水和高粘度聚合物稳定射流成形规律。搭建了适用于热熔融材料稳定打印的加工平台，开展了相关工艺实验。综合分析了多物理场耦合作用下热熔融材料微米/纳米尺度微滴形成演化机制，通过理论分析和高速摄像机图像分析方法，得到了微滴形成演化机制，获得了直径（丝径）10微米量级的微点阵和微丝结构的精准稳定打印。研究了热熔融喷射沉积中射流冷却、凝固规律、表面/界面行为等，为具体应用提供基础数据。在此基础上，进行了案例研究。利用项目研究获得的微观机理和工艺规律，对多种材料包括低粘度材料（微晶石蜡）、可降解聚合物材料（PCL、PLA），柔性弹性体材料（PDMS、Ecoflex），纳米银浆等进行精准打印。通过三个典型案例（微流体通道模具、石蜡基热驱动微型软机器人、微型管腔支架结构）的设计和制造，验证了本项目理论分析的正确性，获得了良好的加工效果和实际样件。通过以功能为导向的典型案例研究，证明了自激发静电场驱动微尺度3D打印工艺具有打印材料\打印基底取材广泛、打印精度高等突出优势，为该技术的多领域应用和进一步实际应用提供有力的技术支撑。