Analysis of drop transfer in DC and pulsed GMAW

Abstract

The static force balance model (SFBM) has been widely used to analyze drop transfer in gas metal arc welding. Although the SFBM is capable of predicting the detaching drop size in the globular mode with reasonable accuracy, discrepancy between the calculated results and experimental data increases with current. In order to reduce discrepancy, the SFBM is modified in this work by introducing the momentum flux. The momentum flux is generated by the axial flow within the drop, which is induced by the pinch pressure. When the small drop is detached in the high current range, the momentum flux has significant effects on drop transfer and becomes compatible to the electromagnetic force of the SFBM. The modified force balance model predicts the experimental results more accurately than the SFBM, and extends its application to the projected mode. Other then force balance models, wire melting is considered in the globular region and drop detaching criterion is established based on the displacement of drop. A force displacement model FDM is proposed using numerical integration to predict the mass displacement and the calculated results show reasonable agreement with the experimental data. In order to determine the one-drop one-pulse (ODOP) condition of the pulsed GMAW, the FDM is applied. Peak time needed to detach the drop is predicted through numerical integration and closed-form equation, which consists of the time-varying force terms and drop mass coupled with wire melting. While the peak current has significant effects on the drop detaching time, the initial drop mass prior to the peak duration also influences drop transfer. The calculated results show good agreements with the experimental data, which implies that the ODOP condition can be predicted using the proposed method.