Experimental Investigation on Acoustic Control Droplet Transfer in Ultrasonic-Wave-Assisted Gas Metal Arc Welding
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INTRODUCTION
GAS metal arc welding (GMAW) is an arc welding method that uses a consumable electrode and protects the metal droplet, weld pool, and high-temperature metal in the welding zone using shielding gases. Owing to its advantages such as low cost, good adaptability, and easy automation, GMAW is currently more suitable for all welding positions.[1–3] There are three basic metal droplet transfer modes: short-circuiting, globular, and spray transfer.[4] The choice of droplet transfer mode affects the arc stability and spatter degree, which greatly influence the weld formation.[5] Droplet transfer is an exciting research topic in the field of welding, and researchers have proposed many methods to control metal droplets. For example, by using the oscillation characteristics of the droplet before it falls from the wire end, the downward momentum of the droplet can be used to promote droplet transfer. An experiment on pulsed GMAW showed that its peak current was lower than its transition current, and that accidental droplet
XIE WEIFENG is with the School of Mechanical Engineering, Northeast Electric Power University, Jilin 132012, China. Contact e-mail: [email protected] FAN CHENGLEI, YANG CHUNLI, and LIN SANBAO are with the State Key Laboratory of Advanced Welding and Joining, Harbin Institute of Technology, Harbin 150001, China. Manuscript submitted January 20, 2016.
METALLURGICAL AND MATERIALS TRANSACTIONS B
transfer was also prevented.[6] Mechanically assisted droplet deposition synchronizes the power source and the welding wire feeder to obtain optimized droplet transfer, controlling the short-circuiting transfer by retracting the welding wire, which causes spray transfer below the transition current.[7] Pulsed-laser-enhanced droplet transfer, which uses laser recoil pressure to increase the detaching force against the droplet, produces free droplet transfer at low welding current.[8] These methods can realize highly efficient, stable welding and produce a favorable weld. However, for some special materials or welding positions, droplet transfer can be easily influenced by various parameters, particularly the large, heavy welding gun is inconvenient for welding positions other than flat welding. In arc welding, using an ultrasonic wave—a mechanical vibration with a frequency of 20 kHz or more— gives excellent directivity and high energy density, causing several interesting ultrasonic effects on the weld pool. The weld structure produced by ultrasonic action is more uniform, and the thick dendritic grains could be Moreover, ultrasonic-wave-assisted refined.[9–12] GMAW (U-GMAW) is designed to control the droplet using acoustic radiation force. Similar to a single-axis acoustic levitator, this welding gun ignites an arc in the acoustic field between the ultrasonic radiator and the workpiece. Compared with the droplet in conventional GMAW, the droplet in U-GMAW is longer in the axial direction of the welding wire, and the droplet is smaller.[13] However, it is not yet known how the ultrasonic action affects the droplet tra
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