Current-independent metal transfer by utilizing droplet resonance in gas metal arc welding

Gas metal arc welding is a widely used welding method owing to its high efficiency and ease of automation. In welding, metal transfer plays a significant role in determining weld stability and quality. In gas metal arc welding, the metal transfer also affects the heat input and the appearance of the welded joints. Metal transfer in the gas metal arc welding process can be classified into three, namely, globular, spray, and short-circuiting. Regardless of the method used, effective control of the metal transfer is necessary. So far, various techniques for controlling the metal transfer in gas metal arc welding have been proposed. However, despite the significant improvement brought about by these methods, they have not resolved the inherent challenge of independent control of heat input and metal transfer, which have been identified as an effective way of obtaining a stable metal transfer. This can be mainly attributed to the fact that the detached forces are majorly provided by the welding current. Therefore, a complete current-independent metal transfer requires a sufficiently large detaching force to substitute that depending on the melting current.

Recently, drop resonance excited by the alternating mechanical force generated by vibrating electrode has exhibited great potential for fully-current independent metal transfer control because it can be achieved at any reasonably low current capable of maintaining the arc. Equipped with this knowledge, a team of researchers at Harbin Institute of Technology: Xiaochao Zhang (PhD candidate), Professor Hongming Gao and Professor Guangjun Zhang studied the current-independent metal transfer, at low current sufficient to sustain the arc, by utilizing droplet resonance in gas metal arc welding. Their main objective was to realize an experimental verification of the droplet transfer control. Their work is currently published in the Journal of Materials Processing Technology.

In their approach, the resonance of the pendant droplet was excited by mechanical means. Metal transfer under reasonable low current was measured as a comparison of the subsequent experiments, without the assistance of active excitation. Also, they examined the droplet oscillation and forced resonance excited by the vibrating electrode. Lastly, the success in achieving a fully current-independent metal transfer was verified by comparing metal transfer under continuous electrode vibration with that without mechanical assistance.

Results showed that the vibrating electrode could induce free oscillations of the droplet from just a small amplitude impact. The natural frequency of the pendant droplet, equal to the free oscillations frequency of the droplet, was negatively correlated with the droplet mass. The oscillation system entered the resonant region and resonance occurred when the natural frequency decreased to close to the excitation frequency, thereby resulting in a significant increase in the oscillation amplitude of the droplet. Larger amplitude resulted in larger inertial forces that induced droplet detachment in the resonant region. Consequently, , a much faster, stable, and more uniform metal transfer than conventional gas metal arc welding was observed under the same welding parameters. Furthermore, it was noted that the current waveform could be designed to freely adjust heat input and other requirements necessary for high-quality welding tasks because the resonance oscillation is current-independent. According to the authors, the study provides useful information that would improve metal transfer processes in different welding conditions.