Improving the GMAW process through current control

TL;DR

This work targets the quality of Gas Metal Arc Welding by precisely controlling the electrical current waveform. It introduces a closed-loop switched PID controller designed from a data-driven switched equivalent circuit model, implemented on a microcontroller, and tuned via Root Locus to meet stringent phase-specific ramp requirements. The model combines short-circuit and arc phase dynamics, with parameters identified through Prediction Error Identification from experimental data, enabling realistic simulation and control design. Experimental validation on manual and robotic welding demonstrates improved current regulation, reduced spatter, and higher-quality joints, supported by metallographic analysis. The approach holds promise for adaptive, data-driven control and the enforcement of more complex current waveforms in welding applications.

Abstract

A control strategy for the electrical current in GMAW processes is proposed. The control is in closed-loop, designed by formal methods, based on a mathematical model of the electrical behavior of the GMAW process, and implemented in C+ language in a microcontroller. The model consists of a switched equivalent electrical circuit whose parameters are obtained in a data-driven manner. The strategy is tested in numerous experiments with both manual and robot welding, showing improvements in the overall welding process.

Figures (11)

• Figure 1: Schematics of the GMAW process
• Figure 2: Metal transfer cycle in the GMAW process
• Figure 3: SUMIG Intellimig500 inverter welding power source
• Figure 4: Typical operation in open-loop; $I_W$ is the current through the joint, $E_W$ is the source's voltage and $U_{arc}$ is the voltage drop in the joint
• Figure 5: Switched circuit model proposed in Gohr:2002.