Online measurement of droplet size by actively exciting droplet oscillation in GMAW and GMAW-AM

Metal transfer plays a significant role in determining the process stability and deposition quality in GMAW and GMAW-AM. Predetermined parameters for controlling metal transfer may fail because of changes in applications or external disturbances. To obtain droplets of target sizes as expected and personalize control parameters for every single droplet, a low-cost method is proposed for the online measurement of the size of the droplet before being detached. The natural frequencies of droplets of different sizes are experimentally measured. The free oscillation of the droplet is actively excited first, during which the voltage falls as the droplet moves upward and rises as the droplet moves downward, with almost the same frequency as that of the droplet. By performing a frequency domain analysis of the voltage, the droplet size is able to be determined online from the oscillation frequency. This technique contributes to the feedback control of the transfer of every single droplet. The fluctuation of the voltage during the droplet oscillation is believed related to the variation of arc structure, the underlying mechanism still needs further study.