| Abstract Scope |
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. As the welder knows how to weld and not all the physics behind the process, it is unlikely that an optimum is reached. Due to all the unknown variables, it is difficult to reach an optimum solution and is known to result in faulty welds when applied to new materials, or when attempting to comply with new standards.
This work allows to comprehend a part of the theory behind the droplet temperature at the GMAW process. The development of an energy balance on the electrode is made to understand the power at the anode and by it the droplet temperature. To obtain the value and understand its behavior, it is necessary to understand the mass that evaporates from the droplet. The models that were generated allows to understand the behavior of the droplet, its evaporation, temperature, and deposition rate. The composition of the mass evaporated from the droplet is obtained, and the amount of energy lost in the process. The composition of the mass evaporated varies from one electrode to another, and so the amount of mass that evaporates or stays in the droplet. A relation between the current and the WFS, evaporation rates and anode fall voltages is generated for different wire compositions. These relationships can be used to reduce evaporation and increase deposition rates, as also to study the behavior on new alloys and different conditions of voltage and WFS.
The data then used contained the following variables for each electrode: wire diameter, welding current, WFS, electrode extension, roll temperature, ambient pressure, voltage contact tip, total voltage, and droplet temperature for electrodes ER1100, ER4043, ER5554, ER5183, Pure Fe and ER80S-G. All the material properties were revisited before the calculations were made.
When looking at the rates of evaporation, the amount of mass evaporated in ER5554 or ER5183 electrodes is interesting. The evaporation of ER5183 in some cases reaches 0,22%, where a 30% of it is manganese. This evaporation occurs with a velocity higher than 3,5 mg/min that in the end would be almost 11 mg/min of just Mn. During an hour of continuous welding with ER5183 electrode, out of the droplet is going to evaporate 66 mg that the welder could eventually breathe. To prevent these evaporations on the droplet, the main goal is to have lower droplet temperatures.
With all the work done here, it is possible to understand the consequences of a high droplet temperature. The first impact would be on the evaporation and then the anode fall voltage, that leads to higher energy consumptions. The behavior of the droplet temperature is an important point for the manufacturers because it is what needs to be understood to control and reduce evaporation on the droplet. The main variables to understand the anode fall voltage are the droplet temperatures, droplet evaporation and current. |