Three-objective Pareto optimization of GMAW process parameters using a modified force balance model

Abstract

In this paper, a three-objective optimization model was developed for the preliminary selection of welding current and electrode wire extension length in the gas metal arc welding (GMAW) process, to achieve a droplet size characteristic for the projected spray metal transfer mode. The model is based on a modified force balance model, i.e., the MFBM approach, in which the droplet detachment condition is determined from the balance between the total detaching force and the surface tension force. A correction of the effective electrode wire neck radius, based on the balance between the pressure due to surface tension and the electromagnetic pinch pressure, was introduced to account for the tapering/necking effect at higher current values. The optimization variables are the welding current and electrode wire extension length, while the objective functions are defined to maximize the melting rate, minimize the deviation of the normalized droplet diameter from the target value, and minimize the normalized Joule/stick-out index. The obtained Pareto front indicates a clear compromise between productivity, droplet size control, and thermal loading of the electrode wire extension. A dynamic diagnostic layer was also introduced to verify the regularity of the droplet growth and detachment cycle for selected Pareto solutions.