Modification of pinch instability theory for analysis of spray mode in GMAW

While the pinch instability theory (PIT) has been widely used to analyse the spray mode in gas metal arc welding (GMAW), it assumes an infinite cylinder and no current leakage on the cylinder surface. The PIT is modified in this work to predict the spray mode more accurately by considering reduction of the molten tip radius, the finite cylinder geometry and current leakage. The effective cylinder radius is formulated as a function of current to consider the tapered cone shape of the molten tip, and the critical wavelength of the modified PIT is derived considering a finite cylinder with a hemispherical end and current leakage. The effective radius is found to have most significant effects on drop transfer followed by the finite cylinder geometry and current leakage, and the predicted results of the modified PIT are in reasonable agreement with the experimental data of the spray mode.