STUDY OF HEAT INPUT IN ADVANCED GMA WELDING SHORT CIRCUIT VARIANTS

Due to its ample range of applications, the short circuit GMAW process mode is intensively used in the industry. Among the welding processes available in the market, this one stands out for delivering low cost and high productivity, being commonly used in in naval field for root pass welds and thinner sheet welding. More recently, advanced applications in additive manufacture for turbines production have been developed. Nevertheless, the heat input applied for this process is one of the main challenges, regarding applications where sensitive materials are used and precision is required, since high temperatures imply residual stress and possible structural damages. Therefore, the short-circuiting metal transfer technologies developed by different companies are tested to study their methods to control the temperature in the welding process. This knowledge may help to understand the influences of the parameters and, then, to parameterize the process and select a technology among so many available in the market. The processes divided in standard, electrically controlled and retractable wire feed short circuit are used to produce a weld bead with similar geometry and have their performance analyzed developing the same task. The electrical parameters of each process are measured and the theoretical heat input is calculated and compared. A macrograph of the result weld beads is made to analyze the penetration and its relation with the deposition. It was observed throughout the comparison between the heat input number and penetration areas that the theoretical heat input does not describe the physical performance of the processes. Several samples showed higher theoretical heat input and smaller penetration than others. With this, it was concluded that the physical performance can be predicted better by observing the electric waveform shown by the processes, where drop detachment frequency, power peak and low current intervals are very influential. The standard short circuit processes showed the highest penetrations, followed by the electrical controlled processes. The retractable wire feed processes showed the lowest penetration values. The theoretical heat input measurement showed some variations, however it was not possible to observe significant advantages between the electrical controlled and standard processes, with exception for the STT technology. The retractable wire feed processes, on the other hand, had the best results in all the metrics, showing the lowest theoretical heat input and penetration numbers.