Avaliação da influência da vazão de gás utilizada no processo GMAW nas tensões residuais utilizando ondas LCR

Abstract

Welding is a manufacturing process widely used in industry to join metal parts permanently. However, at the end of the process, due to the high temperatures involved, residual stresses (RS) appear, making the welded region highly susceptible to failure. This is because such stresses overlap the applied stresses. Therefore, it is important to know the RS present inside the material, so that the real efforts to which the component is being submitted can be determined, guaranteeing safety, and avoiding unexpected failures. The measurement of these stresses can be done through destructive or non-destructive methods. Non-destructive methods (NDT) do not cause damage to the part, and one of the most recent one is ultrasonic method, which uses critically refracted longitudinal waves (LCR waves), a type of wave sensitive to the presence of stress in the medium in which it propagates. However, the biggest challenge in using LCR waves is the fact that there are some factors that influence their propagation, such as temperature, coupling force and applied amount of coupling liquid, among others. However, some of these can be monitored and used to correct the LCR wave travel time. In welding, the welding parameters influence the TRs and the weld quality. One of these parameters is the gas flow, which interferes with the geometry and mechanical properties of the weld. The objective of this work is to study the influence of the gas flow rate, used in the gas metal arc welding (GMAW) robotized, in the RS of specimens of DIN EN 10025-2 S275JR steel using LCR waves. For this, TOF measurements were performed on nine welded steel plates using gas flow rates of 12, 15 and 20 l/min. The other welding parameters were kept fixed. Thus, distribution profiles of longitudinal RS to the weld bead were obtained for each specimen. The results allowed determining the influence of the gas flow rate on the generated RS, with the highest RS values obtained for the specimen welded with a gas flow rate of 15 l/min. It can be concluded that the gas flow rate influences the RS of steel plates welded by the robotic GMAW process.