Analysis of current pulse during short-circuit phase in CMT version of GMAW process under a view of additive manufacturing

The state-of-the-art GMAW processes are those with dynamic feeding, branded as cold metal transfer (CMT) by one of the main developers/suppliers. The metal transfer occurs through the combined action of surface tension force and wire electrode pullback, which is synchronized with the electric current waveform. The forward and pullback movement are generated by a highly dynamic secondary feeder. This process is widely applied to join parts and is currently gaining attention in additive manufacturing, due to its high level of controllability over the metallic transfer and bead geometry. However, there is a lack of studies on the manipulation of the CMT waveform and its influence over the welding process, especially regarding the geometrical control of the deposition and its high stability. This research was focused on investigating the effect of current waveform manipulation on the CMT variant of the GMAW process. Experiments were carried out with two customized CMT waveforms. In case 1, a waveform with a current pulse in the short-circuit phase was used and in case 2, a similar waveform was used, with the same average power, but with no current pulse in the short-circuit phase. High-speed videography and electrical signals analysis revealed a greater striction effect of the metal bridge in case 1. In conclusion, the current waveform manipulation with CMT can not only improve stability but also the geometric aspect of the weld bead, while maintaining a similar power and thermal profile, highlighting the geometric characteristics that can be used for building parts via additive manufacturing.