Gas Metal Arc Welding (GMAW) is a process where the electrode works as a filler metal and is deposited on the base metal to join the different parts. This welding technique is considered semi-automatic because the filler metal is being deposited in a constant feed rate by the welder, who is responsible to select the voltage and the wire feed speed (WFS) of the process. This electrode deposited in the weld pool, in form of droplets, plays a crucial role in determining the heat from the droplet and eventually the mass that is being deposited.
Experiments were performed using aluminum alloys and steels with different wire diameters and compositions. The measurements of the droplet heat were obtained using a solid-state calorimeter. Thermal cameras were also used to check the heat inside the droplet. The cooling rates of the calorimeter were previously studied to ensure accurate measurements of the droplet heat. A water-cooled copper calorimeter was used, with thermocouples before and after the arc. The cathode allowed the droplet to fall into the solid-state calorimeter, that allowed to separate the heat from the arc and the cathode from the droplet heat. A synchronized data acquisition system with the high-speed videography was used to understand the detachment of the droplets. The videos were studied with machine learning algorithms to obtain values such as the frequency and the arc length. A wide range of current and voltages were used, to study the different transfer modes in the process.
The results show that the droplet temperature is influenced by different factor. Specifically, the wire diameter and the composition of each electrode, with the same base metal, influenced the final droplet heat content. Wire compositions were studied deeply, to understand the effects of the alloying elements. Specifically, alloys with higher amounts of Mn, Mg and Si were studied to understand their effects on the temperature. Evaporation rates were studied with models for the composition, measurements and ICP tests from the droplets obtained. Lower compositions from certain elements were expected.
This study shows the effects of the wire diameter on the droplet temperature, as well as the behaviour of alloys when adding different elements. The results are a clear guide to understand better the evaporation of different elements on the droplet temperature. A double check to the droplet evaporation rates was obtained. Guidelines to the heat behaviour inside the droplet are given. The setup showed in this study could be used and adapted to other different welding processes.