药芯焊丝脉冲TIG电弧增材制造电弧特性研究

对药芯焊丝脉冲TIG电弧增材制造电弧特性展开研究。利用高速摄像拍摄不同熔敷层脉冲电流条件下的电弧与熔滴过渡图片，对高速摄像图片进行分析，发现焊丝熔化过程存在“滞熔”现象，导致熔滴过渡存在渣桥过渡与液桥过渡两种接触过渡方式，在脉冲峰值电流较小的50/100 A电流参数下，出现熔滴断续的渣桥过渡的频率最高。熔滴过渡影响电弧温度场与药粉成分在电弧中的分布，利用光谱诊断分析熔敷过程中在不同脉冲峰值电流与脉冲基值电流条件下电弧温度场及药粉成分在电弧中的分布。利用点阵法测量得到各点光谱数据，根据Boltzmann图法计算各点温度，将各点温度拟合得到完整电弧温度场，结果表明，焊丝从钨极轴线前（左）侧送入，吸收电弧热量并且对电弧有扰动作用，电弧前侧温度低于电弧后（右）侧，电弧前侧尺寸稍小于后侧；随着熔敷层数增加，降低峰值电流，电弧收缩，高温区面积相对减小，低温区面积相对增大。电弧最高温度区域出现在钨极下方1~2 mm的范围，大约为13 000~15 000 K，脉冲峰值电流越大则最高温度区域面积越大。在脉冲基值电流时期，由于电流小，电弧面积相比于峰值时期要小得多，焊丝与电弧相互作用减弱，电弧温度场基本关于钨极轴线对称分布。选择药芯焊丝中特有的Na元素的NaⅠ589.6 nm谱线对其分布点进行标记，拟合绘出不同脉冲峰值电流与基值电流下药粉元素在电弧中的分布情况，结果表明，电流越小，药粉运动高度越低，在不同的脉冲峰值电流下药粉均没有沾染到钨极上，在不同的脉冲峰值电流与脉冲基值电流下 Na元素均偏电弧后侧分布，说明焊丝自电弧前侧送入熔池后，在电弧前侧的电弧中没有出现药粉强烈的喷发现象，而是进入熔池进行冶金反应。接触过渡解决了碱性焊丝工艺性差的问题，电弧较为稳定，避免药粉喷发损伤钨极，熔敷过程稳定进行。

Study on Arc Characteristic of Flux-Cored Wire Pulse TIG Arc Additive Manufacturing

The arc characteristic of flux-cored wire pulsed TIG arc additive manufacturing was studied. The images of arc and droplet transition under different pulsed current were taken using high speed camera. High-speed camera images were analyzed. The results showed that the lagging melt phenomena in the wire melting process resulted in two contacting transition modes: slag bridge transition and liquid bridge transition, in addition, under the current parameters of 50/100 A, the frequency of slag bridge transition with intermittent droplets is the highest. Droplet transfer modes affected the arc temperature field and the distribution of flux composition in the arc. The characteristics of flux-cored wire pulsed TIG arc additive manufacturing were studied by spectral diagnosis, and the distribution of the arc temperature field under the conditions of different pulsed peak current and pulsed base current during additive manufacturing was analyzed. The spectral data of each point was measured by the lattice method, the temperature of each point was calculated according to the Boltzmann diagram method, finally the temperature of each point was fitted to obtain a complete arc temperature field. The result showed that the arc was disturbed and arc heat was absorbed by wire when the wire was fed from the front (left) side of the tungsten electrode axis. The temperature on the front side of the arc is lower than the back (right) side of the arc, and the size of the front side of the arc is slightly smaller than the back side. As the number of additive layers increased, the peak current was reduced, the arc shrunk. Also the proportion of the high- temperature region was relatively reduced, the proportion of low-temperature region is relatively enlarged. The highest temperature region of the arc appeared in the range of 1~2 mm below the tungsten electrode, which is about 13 000~15 000 K. The larger the pulse peak current, the larger the proportion of the highest temperature region. Due to the small current, the arc size was much smaller than the peak period in the pulse base current period, the interaction between the wire and the arc weakened, and the arc temperature field was basically symmetrical about the tungsten axis. The Na Ⅰ 589.5 nm spectrum line of the unique Na element in the basic flux-cored wire was selected to mark its distribution points, and the distribution of flux composition in the arc under different pulse peak currents and base currents was drawn by fitting. The results showed that the smaller the current, the lower the movement height of the powder. The flux composition was not contaminated on the tungsten electrode under different pulse peak currents, and the Na element was distributed in the back of the arc under different pulse peak currents and pulse base current. It showed that after the wire was fed into the molten pool from the front side of the arc, there was no strong spraying phenomenon of flux composition in the arc but it entered the molten pool for metallurgical reaction. The contact transition solves the problem of poor manufacturability of the flux-cored wire, the arc was relatively stable, and the tungsten electrode was prevented from being damaged by the spraying flux composition, the deposition process was stable.