The influence of power source dynamics on wire melting rate in pulsed GMA welding

The welding wire melting rate during conventional direct current (DC) gas metal arc (GMA) welding may be modeled empirically by a simple expression relating material constants, current and electrode extension. The resultant equation is found to be in good agreement when welding at moderate or high currents. In the case of pulsed GMA welding, it has already been shown that a good approximation to the observed melting behavior may be obtained by assuming that the DC equation is instantaneously valid and integrating over one pulse cycle. This article extends earlier work to consider the influence of power source dynamics on the integrated expression. Calculations have been made for two cases: an idealized trapezoidal waveform and a more representative exponential form. Predictions indicate that under certain circumstances response rate can have a significant influence over the wire melting rate at a given mean current. The validity of this prediction has been tested experimentally for the idealized trapezoidal waveform and results are presented for comparison. The significance of power source dynamics is discussed with reference to static output characteristics and the resultant influence on metal droplet detachment.