Robust control of pulsed gas metal arc welding

A system is developed to control the pulsed gas metal arc welding process. To achieve controlled detachment of the droplet, the welding current is switched from a peak level to a background level to induce droplet oscillation. When the droplet moves downwards, the current is switched hack to peak level. The combination of downward momentum of the oscillating droplet and increased electromagnetic force guarantees detachment of the droplet. Instead of adjusting duration of the background current, the waveform of the current is adjusted to control the melting rate of the electrode wire without having to change the transfer frequency. It is found that the dynamic model of the process depends on welding operational parameters, which vary with applications, and therefore it is unrealistic for operators to provide welding machines these parameters as inputs. Hence, welding operational parameters are considered as unfixed and their ranges are used to quantify the resultant uncertainty in the dynamic model. As a result, the process is controlled using a single algorithm at different operational parameters. Experiments verified the effectiveness of the system in overcoming two common variations in welding operational parameters, wire speed and contact tube-to-work distance.