WELDING RESEARCH CurrentIndependent Metal Transfer by Using Pulsed Laser Irradiation Part 2: Affecting Factors Experiments were conducted to examine the effects of laser positioning, laser pulse waveform, and arc parameters on successful pulse transfer and deflection minimization Introduction In conventional gas metal arc welding (GMAW), the metal transfer mode is dominantly determined by the welding current. Relatively low currents produce short-circuiting or large drop globular transfer, which typically generates spatter and unstable arcs. To produce more desirable drop spray transfers, a current higher than the spray transition current is needed. Unfortunately, such currents cause significant 194-s WELDING JOURNAL / JUNE 2016, VOL. 95 increases in heat input and arc pressure (Refs. 1–4). In particular, as found by Mendez and his associates, droplet temperature reaches a minimum at the transition from globular to spray transfer by currents slightly lower than the transition current (Ref. 5). As such, the properties of the resultant process, including, but not limited to, metal transfer, arc, and heat input, strongly depend on the current that is used to detach the droplet. An ideal GMAW process calls for an ideal metal transfer controllability (droplet detachment ability) that is current independent, i.e., can detach the droplet at any current in the reasonable range as demanded by the application. Such ideal current-independent metal transfer control is especially crucial for advanced applications like welding of ultrathin sheets and additive manufacturing that demand precise process controls. As has been reviewed in the first part of this study, many innovations, such as surface tension transfer (STT), cold metal transfer (CMT), and ultrasonic assisted GMAW, have achieved significant improvements on metal transfer control by electrical, magnetical, mechanical, and radiating ways (Refs. 6–19). However, they all are still far away from the ultimate/ideal goal: current-independent metal transfer, i.e., detaching droplets of the desired size at any current in the reasonable range especially at reasonably low current for free flight transfer. A recent innovation having the potential toward this ultimate goal for the ideal metal transfer control is laserenhanced GMAW, proposed and continuously studied at the University of Kentucky. Huang explored the use of a direct diode laser (862 W, 14 × 1-mm focus line) to irradiate the droplet (Refs. 20–22). However, the enhancement on the metal transfer controllability is quite weak due to the very low BY J. XIAO, S. J. CHEN, G. J. ZHANG, AND Y. M. ZHANG ABSTRACT The ideal currentindependent metal transfer characterized by ensured robust droplet detachment at a relatively small size at any reasonable low current, which can sustain the arc, has been successfully realized in the first part of this study by applying a highpowerdensity pulsed fiber laser to irradiate the droplet neck. The desired onedropletperlaserpulse (ODPP) mode was ensured. The droplet flying trajectory deflected from the wire axial due to the use of a single laser. This second part of the study focuses on how relevant parameters influence the metal transfer behavior, especially the droplet deflection that affects the controllability of bead formation. To facilitate the study, the relevant parameters were categorized into three major types: laser positioning, laser pulse waveform, and arc parameters. A series of experiments was conducted to examine their effects on successful ODPP transfer and deflection minimization. In particular, the optimal laser incident point and angle for most submissive droplet detachment and smallest droplet deflection were first determined. Secondly, the minimums of the laser peak power and duration for stable ODPP were determined. Finally, the droplet deflections under different welding currents in the desirable low range, as well as different torch orientations and arc lengths, were measured and analyzed. KEYWORDS • Gas Metal Arc Welding (GMAW) • Process Control • Metal Transfer • Droplet • Laser Irradiation J. XIAO and S. J. CHEN (sjchen@bjut.edu.cn) 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 | June 2016
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