WELDING RESEARCH CurrentIndependent Metal Transfer by Using Pulsed Laser Irradiation Part 1: System and Verification A novel process involving the use of a pulsed fiber laser to control the metal transfer in MARCH 2016 / WELDING JOURNAL 93-s KEYWORDS • LaserEnhanced Gas Metal Arc Welding (GMAW) • Metal Transfer • Pulsed Laser Irradiation Introduction For decades, innovations in the gas metal arc welding (GMAW) process have been primarily focused around the metal transfer, recognized for its most critical role in determining spatters, arc stability, and bead formation (Ref. 1). A major barrier that affects the ability to achieve desirable metal transfer is the dependence of metal transfer on the welding current. For instance, drop spray transfer, the preferred transfer mode (Ref. 2), would not be achieved unless the welding current exceeds the so-called spray transition current (Refs. 3, 4). Even in pulsed GMAW, the peak current still needs to be higher than the transition current (Refs. 5, 6). Another point is the welding current also determines the force (arc pressure), heat, and mass inputs in GMAW (Ref. 7). Achieving desired metal transfer may thus compromise the abilities to achieve and control other critical variables of the welding process. Ideally for next-generation manufacturing, a novel GMAW process with currentindependent metal transfer would be greatly appreciated. Its ultimate goal is to detach the droplet at a preferred diameter at any (reasonable low) current below the transition current as preferred by the application for other critical variables. Up-to-date, impressive innovations in control of metal transfer have been made in electrical, magnetic, mechanical, or irradiant ways (Refs. 8–18). Surface tension transfer (STT), a very representative electrical method, is able to reduce/minimize spatters in shortcircuiting transfer, but its current waveform has been strictly plotted without the freedom to meet other applicationdependent requirements (Ref. 8). The active droplet oscillation method uses a multipulse current waveform to excite droplet oscillation and then utilize that oscillation to enhance droplet detachment. The pulse peak can be reduced to be quite lower than the transition current through waveform optimization (Refs. 19–22). Cold metal transfer (CMT), a typical mechanical way, oscillates the wire feed direction (Ref. 9). It successfully minimizes spatters but at the expense of the use of a complex wire feed system. In addition, it is only suitable for short-circuiting transfer and the current waveform, although not as strictly determined as in STT, cannot be as free as desired. In another effort, Fan et al. proposed an ultrasonic-assisted GMAW process (Refs. 12, 13). An ultrasonic wave is coaxially coupled in the arc GMAW is investigated BY J. XIAO, S. J. CHEN, G. J. ZHANG, AND Y. M. ZHANG ABSTRACT Currentindependent metal transfer that allows the droplet to be detached at any reasonable small diameter and low current will provide the gas metal arc welding (GMAW) process with entirely new abilities to better meet possible needs from different applications. To this end, a novel GMAW process involving the use of a pulsed fiber laser to irradiate droplets is proposed as a significant evolution from the previous laserenhanced GMAW. The laser is focused to a tiny spot to maximize the laser power density and aimed at the liquid droplet. It is expected the irradiation of a pulsed laser with a relatively large peak power would generate an adequate recoil force to dominate the droplet detachment. Laserinduced vaporization is first observed and analyzed. The metal transfer under continuous wave (CW) and pulsed laser irradiation are then experimentally observed/ analyzed. The results demonstrate that the currentindependent metal transfer is successfully realized by using the pulsed laser, since the selected laser allows much higher peak power in pulsed mode. The desirable one drop per pulse (ODPP) transfer is obtained. Therefore, a pulsed fiber laser not only avoids waste of laser energy but also achieves the desired controllability on the metal transfer. The verified currentindependent metal transfer ensures free design or optimization of current waveform without constraint from the metal transfer. J. XIAO and S. J. CHEN are with the Engineering Research Center of Advanced Manufacturing Technology for Automotive Components, Ministry of Education, Beijing University of Technology, Beijing, China. J. XIAO is also with the Institute for Sustainable Manufacturing, University of Kentucky, Lexington, Ky. G. J. ZHANG is with the State Key Laboratory of Advanced Welding and Joining, Harbin Institute of Technology, China. Y. M. ZHANG (yuming.zhang@uky.edu) is with the Institute for Sustainable Manufacturing and Department of Electrical and Computer Engineering, University of Kentucky, Lexington, Ky.
Welding Journal | March 2016
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