Abstract:

In order to ensure the stability and controllability of the pulsed MIG welding, a self-developed soft-switching inverter was used to change the control waveform, and a droplet transfer phase was added in the falling edge of pulse waveform. The instantaneous current, the transient voltage, the dynamic resistance, the instantaneous energy, and the probability density distribution of current ＆ voltage were then acquired and analyzed using a wavelet analyzer. Moreover, the effects of the droplet transfer current and its duration on the welding quality were investigated. Experimental results show that  adding a droplet transfer phase may result in a stable and controllable welding process;  the energy shortage due to a small droplet transfer current may cause a short circuit transfer and an unstable welding process;  when the transfer current is close to the peak value, the welding process is similar to the ordinary pulsed MIG welding process, which deviates from the goal of controlling the waveform;  at a constant transfer current, the welding quality improves with the increase of droplet transfer duration, attaining an ideal state when the duration reaches 7ms;  with further increase in transfer duration, the welding quality lowers due to the irregular droplet transfer caused by excessive energy; and  the optimal droplet transfer current and the transfer duration in experiments are found to be 160A and 7ms, respectively.

Key words: pulsed MIG welding, droplet transfer, wavelet analysis, instantaneous energy, dynamic resistance