Analysis of Inverted Y-Shaped Arc Photoelectricity Characteristic of
Flux-Cored Wire Pulsed TIG Additive Manufacturing
HUANG Shi-cheng1, HUANG Yi-ming1, 2*, YANG Li-jun1*, YUAN Jiong1, LIN Zhi-xiong1, ZHAO Xiao-yan1
1. Tianjin Key Laboratory of Advanced Joining Technology，School of Materials Science and Engineering，Tianjin University，Tianjin 300350，China
2. State Key Laboratory of Advanced Welding and Joining, Harbin Institute of Technology, Harbin 150001, China
Abstract：In the process of flux-cored wire pulsed TIG arc additive manufacturing, the phenomenon of the arc riding on both sides of the formed part was found. The arc was called the inverted Y-shaped arc. The inverted Y-shaped arc had a heating effect on both sides of the forming part, and its deviation caused uneven healing on both sides of the forming part, which affected the stability of the cladding process. The electron density of the trailing part of the inverted Y-shaped arc was calculated using Stark broadening according to spectral data measured by the point matrix method. Under the experimental conditions of this study, some areas (about 2 mm outside sidewall, about 1.5 mm below 0 positions in Z direction) conformed to local thermodynamic equilibrium. The electron temperature was calculated using the Boltzmann diagram method of spectral diagnosis, and the complete arc temperature field was obtained by fitting the data of each point. The temperature field parallels to, and perpendicular to the moving direction of the welding torch in the deposition process was analyzed. The results showed that the maximum temperature of the inverted Y-shaped arc at the tungsten electrode tip was about 14 000~16 000 K, distributed in the range of 0.5~1.5 mm below the tungsten electrode the temperature of the trailing part of the arc was about 5 000~8 000 K. In the direction perpendicular to the moving direction of the welding torch, when the tungsten electrode axis coincided with the center of the deposited layer, the normal inverted Y-shaped arc and the temperature field were symmetrically distributed along the tungsten electrode axis. When the tungsten electrode axis shifted by 1 mm to the left of the center of the deposited layer, the inverted Y-shaped arc shifted to the left, and the temperature field also shifted to the left. The temperature on the left side of the deposited layer was significantly higher than that on the right. In the direction parallel to the moving direction of the welding torch, the temperature field distortion of the inverted Y-shaped arc was small. During the deposition process, the welding wire was fed in from the front (left) side of the tungsten electrode, which disturbed and absorbed the arc’s heat. As a result, the size and temperature of the arc’s front (left) side were smaller than those of the rear (right) side, and the arc contraction. By analyzing the electrical signals of the two cases where the tungsten electrode axis coincided with the deposited layer center and shifted by 1mm to the left of the deposited layer center, it was indicated that the mean voltage, the base voltage average and the peak voltage average of the former were less than those of the latter. Based on the analysis by combining the electrical signal and the Gaussian heat source model, it was found that the temperature and heat flux of the normal inverted Y-shaped arc were smaller than those of the offset inverted Y-shaped arc at the same position on the left side of the formed part. In contrast, the opposite results were obtained at the same position of the right side of the formed part, which was consistent with the temperature field distribution obtained by spectral diagnosis. The results of this study were of great significance for establishing a new heat source model and process monitoring in the arc additive manufacturing process.
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