Relation between Plasma Electrical Signal Oscillation and Weld Depth in Laser Deep Penetration Welding
(2.Tianjin Key Laboratory of Advanced Joining Technology, Tianjin University, Tianjin, China 300350)
(3.Stainless Cold Rolling Mill, Shanxi Taigang Stainless Steel Co., Ltd., Taiyuan, Shanxi Province, China 030003)
【Abstract】In this study, the relation between keyhole oscillation and depth is analyzed based on the internal pressure balance conditions of the keyhole to allow real-time monitoring of the laser penetration welding process. Then, based on the coupling of keyhole behavior with plasma behavior and consistency of plasma oscillation characteristics with plasma electrical signal fluctuation characteristics, we use a short-time autocorrelation analysis method for the relation between the oscillation period of a plasma electrical signal and weld depth during laser penetration welding of A304 stainless steel and Q235 carbon steel. Results show that the plasma electrical signal’s oscillation period increases with the rise in the weld depth, and the relations between the plasma electrical signal’s oscillation period and weld depth differ when the welding materials are different. Finally, in a verification test of continuous welding with variable heat input, we obtain a good correspondence between the short-time autocorrelation analysis results of plasma electrical signals and weld penetration when the welding process is stable, which is consistent with the characteristic equation of keyhole oscillation in our analysis.
【Keywords】 laser optics; laser penetration welding; weld depth prediction; short-time autocorrelation analysis; plasma electrical signal;
 Peng J, Hu S M, Wang X X, et al. Effect of filler metal on three-dimensional transient behavior of keyholes and molten pools in laser welding [J]. Chinese Journal of Lasers, 2018, 45 (1): 0102003 (in Chinese).
 Yang W X, Xin J J, Fang C, et al. Microstructures and mechanical properties of hundred-millimeter-grade 304 stainless steel joints by ultra-narrow gap laser welding [J]. Chinese Journal of Lasers, 2018, 45 (7): 0702005 (in Chinese).
 Huang Y M, Xu S, Yang L J, et al. Defect detection during laser welding using electrical signals and high-speed photography [J]. Journal of Materials Processing Technology, 2019, 271: 394–403.
 Qiu W C, Yang L J, Liu T, et al. Optic-electrical signal analysis of plasma fluctuation characteristics in laser deep penetration welding [J]. Chinese Journal of Lasers, 2018, 45 (4): 0402001 (in Chinese).
 Buvanashekaran G, Shanmugam S N, Sankaranarayanasamy K, et al. A study of laser welding modes with varying beam energy levels [J]. Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science, 2009, 223 (5): 1141–1156.
 Kawahito Y, Mizutani M, Katayama S. High quality welding of stainless steel with 10 kW high power fibre laser [J]. Science and Technology of Welding and Joining, 2009, 14 (4): 288–294.
 Blecher J J, Galbraith C M, van Vlack C, et al. Real time monitoring of laser beam welding keyhole depth by laser interferometry [J]. Science and Technology of Welding and Joining, 2014, 19 (7): 560–564.
 Tenner F, Brock C, Klämpfl F, et al. Analysis of the correlation between plasma plume and keyhole behavior in laser metal welding for the modeling of the keyhole geometry [J]. Optics and Lasers in Engineering, 2015, 64: 32–41.
 Seto N, Katayama S, Matsunawa A. High-speed simultaneous observation of plasma and keyhole behavior during high power CO2 laser welding: effect of shielding gas on porosity formation [J]. Journal of Laser Applications, 2000, 12 (6): 245–250.
 Mrna L, Sarbort M, Rerucha S, et al. Autocorrelation analysis of plasma plume light emissions in deep penetration laser welding of steel [J]. Journal of Laser Applications, 2017, 29 (1): 012009.
 Sibillano T, Rizzi D, Ancona A, et al. Spectroscopic monitoring of penetration depth in CO2 Nd\:YAG and fiber laser welding processes [J]. Journal of Materials Processing Technology, 2012, 212 (4): 910–916.
 Yang R X, Yang L J, Liu T, et al. Spectral analysis of laser induced plasma electrical signals from Nd\:YAG laser welding of A304 stainless steels [J]. Chinese Journal of Lasers, 2016, 43 (8): 0802008 (in Chinese).
 Zhao S B, Yang L J, Liu T, et al. Analysis of plasma oscillations by electrical detection in Nd\:YAG laser welding [J]. Journal of Materials Processing Technology, 2017, 249: 479–489.
 Qiu W C, Yang L J, Zhao S B, et al. A study on plasma plume fluctuation characteristic during A304 stainless steel laser welding [J]. Journal of Manufacturing Processes, 2018, 33: 1–9.
 Yu G, Yu H J. Laser manufacturing technology [M]. Beijing: National Defense Industry Press. 2012: 205–209 (in Chinese).
 Klein T, Vicanek M, Kroos J, et al. Oscillations of the keyhole in penetration laser beam welding [J]. Journal of Physics D: Applied Physics, 1994, 27 (10): 2023–2030.
 Trappe J, Kroos J, Tix C, et al. On the shape and location of the keyhole in penetration laser welding [J]. Journal of Physics D: Applied Physics, 1994, 27 (10): 2152–2154.
 Kroos J, Gratzke U, Vicanek M, et al. Dynamic behaviour of the keyhole in laser welding [J]. Journal of Physics D: Applied Physics, 1993, 26 (3): 481–486.
 Klein T, Vicanek M, Simon G. Forced oscillations of the keyhole in penetration laser beam welding [J]. Journal of Physics D: Applied Physics, 1996, 29 (2): 322–332.
 Zhao S B, Yang L J, Liu T, et al. Electrical signal characteristics of plasma in YAG laser welding of A304 stainless steels under different modes [J]. Chinese Journal of Lasers, 2016, 43 (12): 1202005 (in Chinese).
 Dowden J, Davis M, Kapadia P. Some aspects of the fluid dynamics of laser welding [J]. Journal of Fluid Mechanics, 1983, 126: 123–146.
 Sabbaghzadeh J, Dadras S, Torkamany J. Comparison of pulsed Nd\:YAG laser welding qualitative features with plasma plume thermal characteristics [J]. Journal of Physics D: Applied Physics, 2007, 40 (4): 1047–1051.