2012 Volume 30 Issue 1 Pages 1-8
Metal transfer modes in GMA welding process are different from welding variables: current, voltage, shielding gas, electrode wire and etc. Essentially they are influenced by physical properties of molten metal and electro-magnetic force. Then we numerically investigated the time-change of liquid transfer process using calculation model developed. The numerical result agreed very well with experimental result of water drop transfer from cylindrical nozzle. Numerical analysis shows that liquid transfer modes depend on the pressure balance at the tip of drop. When the dynamic pressure induced by liquid flow is lower than capillary pressure due to surface tension, globular transfer occurs. In contrast, when the dynamic pressure of liquid flow is higher, spray transfer occurs. In the case that the electrical current flows in the liquid, electro-magnetic force significantly influences on the transfer mode and the drop detachment. As for liquid flow-out from the nozzle of 1.2 mm in diameter, calculated results with use of physical properties of molten mild steel show that electro-magnetic force induced by higher current than 250 A changes the transfer mode from globular to spray. Whereas in real GMAW with pure argon gas shielding the transfer mode changes at around 230 A. The behavior of drop detachment is varied by both spatial distribution and time-change of the electro-magnetic force.