真空微重力环境下表面张力驱动的丝材电阻加热熔积成形

This project is to develop an innovative additive manufacturing method in which the surface tension drives the resistive heat melted wire metal into the work-piece as additive material. In particular, the tip of the current-carrying wire in touch with the substrate is melted by the resistive heat generated at the interface as well as in the liquid metal bridge and un-melted solid wire while the substrate is less melted due to the difference in thermal conductivity. The temperature distribution is controlled as a spatial temporal vector by wire positionwaveform synergistically with current waveform to melt the desired amount of mass from the wire. Such synergic control also assures the fusion of the melted wire with the substrate. The proposed project will study and model the temporal spatial evolution of the surface tension that drives the liquid metal from the wire into the substrate as a function of the temperature gradient. It will also model the behavior of the flow of the highly constrained tiny fluid (melted wire) under the effect of the temperature dependent surface tension and current waveform dependent electromagnetic force in synchronization with the wire motion dependent mechanical force under the space environment as characterized by vacuum and micro-gravity. The project will also study and model how the deposition thickness and width are controlled by the current waveform and wire motion as well as study and model how the solidification is controlled by the synergic control from the surface tension, electromagnetic force and mechanical force. A test platform will be established in a vacuum chamber to conduct deposition experiments at flat, vertical and over-head positions. The effect of the micro-gravity environment on the metallurgical structures will be inversely studied. The controls on the net shape and properties in additive manufacturing will be realized by the current waveform, wire motion and substrate temperature.

本课题面向太空环境增量制造需求，提出一种基于表面张力驱动的丝材电阻加热熔积成形方法。可编程电流利用电阻热加热丝材，配合基材和丝材夹头的不均匀导热，实现熔化温度场的时空域矢量合成；将丝材送进过程中的脉动行为与输出电流波形协同配合，实现丝材端部定量熔化，期间丝材宏观送进保证熔体与基材浸润；研究强温度梯度下熔体表面张力的时空演变特性，建立真空微重力环境下高拘束微流体在与温度强相关的表面张力、与电流波形强相关的电磁力和丝材运动行为强相关的机械力的联合作用下的流动模型；研究电流波形、丝材运动行为（微观脉动、宏观进给、宏观平移）与基体温度场控制对熔敷层几何尺寸的影响，建立表面张力、电磁力和机械力联合作用下的熔体凝固模型；在真空舱内建立上述试验系统，在平、立、仰三种空间位置开展丝材熔敷试验，反向研究微重力环境对熔敷层微观组织的影响，通过电流波形、丝材运动行为及基体热控系统的调控来实现增量制造的控形控性。

本课题面向太空环境增量制造需求，提出一种基于表面张力驱动的丝材电阻加热熔积成形方法。可编程电流利用电阻热加热丝材，配合基材和丝材夹头的不均匀导热，实现熔化温度场的时空域矢量合成；将丝材送进过程中的脉动行为与输出电流波形协同配合，实现丝材端部定量熔化，期间丝材宏观送进保证熔体与基材浸润；研究强温度梯度下熔体表面张力的时空演变特性，建立真空微重力环境下高拘束微流体在与温度强相关的表面张力、与电流波形强相关的电磁力和丝材运动行为强相关的机械力的联合作用下的流动模型；研究电流波形、丝材运动行为（微观脉动、宏观进给、宏观平移）与基体温度场控制对熔敷层几何尺寸的影响，建立表面张力、电磁力和机械力联合作用下的熔体凝固模型；在真空舱内建立上述试验系统，在平、立、仰三种空间位置开展丝材熔敷试验，反向研究微重力环境对熔敷层微观组织的影响，通过电流波形、丝材运动行为及基体热控系统的调控来实现增量制造的控形控性。