基于超声技术的FDM无支撑悬浮打印基础研究

It is an important solution for 3D printing to reduce supporting or remove supporting, which can improve its manufacturing efficiency, reduce the cost and improve the surface quality of the parts. But the existing 3D printing without support is still a category of structure optimization, the report for pure unsupported printing has not been seen. This project is based on the principle of ultrasonic levitation and combined with molten deposition method (FDM) to study the basic theory for unsupported levitation 3D printing. Multi-phased array acoustic field is build to solve the levitation retention of feeding wire, and the boundary conditions are set to establish the levitation stability theory model of feeding wire; An FDM experimental platform is build for levitation printing. The influence of thermal field on acoustic radiation force is analyzed using thermal imager, which can track the change of heat in the platform. The coordination relationship between dynamic thermal field and acoustic levitation field is decoupled. A high speed camera is used to capture the shape change of the wire in the acoustic field. The deformation and performance change law of feeding wire surface is determined by analyzing the captured images and material property. On the one hand, the research results will break the thinking set that 3D printing must be added supporting, and realize the 3D printing without support in principle. On the other hand, the results will provide theoretical support for the future spatial stereoscopic surface printing, which has important theoretical significance and application value.

为了提高3D打印制造效率，降低成本，提高制件表面质量，减少或实现无支撑打印是一个重要解决方法。但现有的“无支撑”打印仍属工艺结构优化范畴，尚未见纯粹的无支撑悬空打印报道。本项目基于超声波悬浮原理，结合熔融沉积方法（FDM），进行无支撑悬浮3D打印基础理论研究。设计多相阵声场，解决连续送进丝材的悬浮保持性，进而设置边界条件，建立悬浮稳定性理论模型；搭建FDM悬浮打印实验平台，热像仪跟踪热场以分析其对声辐射力影响，解耦打印环境动态热场与声悬浮场之间的协调关系；采用高速相机抓拍丝材在声场中形态变化，结合材料物性，分析并确定连续丝材表面在不均匀声辐射压下的形变及性变规律。研究结果一方面将打破3D打印必须加支撑的思维定势，真正从原理上实现无支撑打印；另一方面为未来空间立体曲面打印的实现提供理论支持，具有重要的理论意义和应用价值。

少无支撑打印是3D打印研究的热点课题之一，本项目提出以超声悬浮力平衡重力，将超声悬浮技术与熔融沉积成型（FDM）打印结合，进行FDM单丝无支撑打印方向的研究。本项目主要进行了以下研究：1）温度场与声场耦合分析，得到了驻波声压随温度的变化规律，进行打印室温度场仿真及实验，获得打印室温度场分布，并且验证了熔融沉积成型过程中打印头及热床温度场对于悬浮稳定性影响较小，可忽略不计。2）搭建了单轴式驻波悬浮设备，实现液滴悬浮及直径1mmPLA丝材悬浮。3）为实现聚焦点的灵活移动，设计并搭建可扩展多通道的声悬浮系统，选择探头400ST160和FPGA型号EP4CE10，进行激励信号发射前端、硬件主控电路、电源系统、存储数据电路等部分设计，相应完成了相控阵聚焦算法控制程序，实现对发射波束合成、聚焦、偏转等功能。4）通过干冰及小球观察声场，并通过麦克风MP401进行驻波场声压测量，验证了圆型活塞换能器声压计算理论对声场数值仿真的正确性，确定相控阵声场分布。5）打印大跨距丝材悬空桥形件，观察悬空丝材、悬空层、悬空件打印过程，进行悬垂量及显微实验，分析得到了影响悬空打印件打印质量的主要因素是丝材在熔融态所受重力发生不可回复的粘弹性变形；提出声悬浮力改变打印质量变形的模型。6）打印单丝悬浮实验。提出链球模型，分析物体（长度大于波长）在驻波声场中受力平衡的条件；采用换能器单聚焦进行圆柱状0.3mm单丝悬浮，搭建两个相控阵设备进行双焦点聚焦实现不同长度层厚0.43mmPLA长方体单层悬浮。7）提出挠度改善理论，进行悬空件单根丝材挠度抬升实验，组合声悬浮设备与熔融沉积成型设备，丝材挠度从5±0.5mm改变为2±0.5mm，悬空丝材变形量得到显著改善。项目证明，超声驻波悬浮技术可有效改善FDM打印过程中的单丝悬垂。