金属粉末电火花选择性熔化成形新方法研究

In order to achieve additive manufacturing of metal materials with high accuracy and low price, a new 3D printing method is proposed in this program. In this method, a pulse power is applied between the tool electrode and metal powders to ignite consecutive pulse discharges in the air. The discharge column with extremely high power density generated by the discharges is used as the heat source to melt the metal powders. At the same time, the tool electrode scans in a predetermined path during the discharge process so that the movement of the discharge column can decrease the heat flux input into the metal powders, thereby the selective melting of metal powders can be achieved without causing the removal of the metal powders and the 3D metal parts can be manufactured through the layer-by-layer scanning. In the program, the temperature distribution of the metal powders and the flow of molten pool in the discharge process will be simulated through the coupled Thermo-hydraulic coupling analysis to reveal the melting process of the metal powders and the solidifying process of the molten pool under the action of the discharge column. Also, the influencing factors and the acting mechanism of the process parameters in this method will be elucidated. Then, a prototype of experimental equipment will be developed and the servo control system as well as the scanning method of the tool electrode will be investigated so that a stable and efficient forming process can be achieved. Finally, a series of processing experiments will be carried out to study the forming and processing law of this method. The ultimate goal of this program is to achieve the machining of accurate structural metal parts through the reversible EDM method based on the forming machining of different metal powders and the removal machining. This program can not only have high research and application value in the promotion of the additive manufacturing of metal materials but also have high theoretical value for enriching the research content of electrical discharge machining.

针对低成本高精度金属增材制造需求，本项目提出以金属粉末为材料，以工具电极与金属粉末之间的空气介质被放电击穿时产生的具有高能量密度的脉冲火花放电通道为热源，同时使工具电极相对于粉末层表面进行扫描运动，利用放电通道的滑动减少粉末层的输入热流密度，则可在抑制粉末材料放电蚀除的前提下，实现对金属粉末的电火花选择性熔化结合，再经过逐层累加实现三维金属件增材制造。本项目对金属粉末温度场和熔池流场进行热流耦合建模和模拟，揭示火花放电通道作用下金属粉末熔化/熔池凝固过程；明确该方法工艺特性影响因素及作用机制；研制实验装置原型，研究极间伺服控制技术和电极扫描运动方法，实现稳定高效的成形过程；明确该方法成形特性及工艺规律；实现多种金属粉末材料成形及与电火花去除加工结合的可逆加工，实现精密结构金属件成形。本项目对于促进金属增材制造的应用具有迫切的研究和应用价值，同时对于丰富电火花加工内涵具有重要的理论研究价值。

针对低成本高精度金属增材制造需求，本项目提出以金属粉末为成形材料，以工具电极与金属粉末之间的空气介质被放电击穿时产生的具有高能量密度的放电通道为热源，同时使工具电极相对于粉末层表面进行扫描运动，实现对金属粉末的选择性熔化结合，再经过逐层累加实现三维金属件增材制造。本研究通过多物理场耦合有限元仿真和高速摄像观测研究了放电等离子体热源的特性及其对金属粉末材料的作用机制，明确了粉末材料在放电等离子体热源作用下的极间现象、熔池行为、成形过程及表面特征形成机制。研制了金属粉末放电选区熔化增材原型装置，进行了相关的结构设计和成形过程控制方法的研究，实现了稳定高效的成形过程。通过系统的实验研究明确了放电参数选择区间及增材成形工艺过程，通过单层单道成形工艺实验明确了放电极性的影响及工具电极直径的选用原则，明确了放电电流、扫描速度、粉层厚度、保护气流量等参数对成形表面形貌、熔宽、成形精度和成形速度的影响，建立了工艺参数与成形特性之间的关联，明确了该方法的工艺规律，并对成形工艺参数进行了优化，实现了铜粉、镍基高温合金及其复合材料等金属材料单道单层、单道多层、多道单层等零件的精密结构金属件成形，实验中成形得到的单道成形宽度可小至3mm以下，单边成形精度约为0.2mm，最大成形高度约为19mm，成形件微观组织与力学性能的表征与测试结果表明，基于本研究提出的粉末放电选区熔化增材方法实现了金属零件的致密成形。本研究提出的金属增材制造新方法，利用易于生成的放电通道等离子体作为热源，并结合粉床物料进给方式，达到了兼顾降低加工成本和提高成形精度的目标，对于促进金属增材制造的应用具有重要的理论研究意义和实际应用价值。本研究还进而提出了一种以脉冲放电通道为热源的熔丝沉积增材制造新方法，对其成形原理、成形过程和成形质量进行了研究，结果表明该方法为解决传统的电弧熔丝沉积增材制造方法中存在的高水平热输入问题提供了非常有效的解决途径。