Otimização da seleção de parâmetros através do método de taguchi para soldagem em aço DIN EN 10025-2 S275JR-AR pelo processo GMAW robotizado

Abstract

Gas metal arc welding (GMAW) is one of the most used welding methods in the metalworking industry, due to its high productivity and the possibility of welding different thicknesses components. The increase in performance and reduction of waste has been a constant challenge for industries. Such challenge is directly related to welding parameters selection processes, which significantly affects welding consumables consumption, such as welding wire and shielding gas, in addition to being linked to a welded joint mechanical properties. In view of this, this work focus on optimize welding parameters selection through Taguchi’s method aiming at greater thermal efficiency in the Robotic GMAW process. DIN EN 10025-2 S275JR-AR steel, used as base metal, contains 0.12% of carbon with a microstructure formed by a ferritic matrix with dispersed pearlite grains. As variable parameters, shielding gases C10, C25 and F36 were used with flow rates of 15 and 20 liters per minute, stick-out of 15, 20 and 25 millimeters, welding speeds of 250, 300 and 350 millimeters per minute and feed of 7, 9 and 11 meters per minute. Taguchi’s method with L18 experimental matrix was used and 3 welds were performed for each combination. Aiming to attest with 95% reliability the hierarchy of influence on the result, analysis of variance (ANOVA) was performed, with experimental confirmation through the one-factor-at-a-time (OFAT) method. Following the statistical analysis, experimental proof was carried out using the one-factor-at-a-time (OFAT) method, where the greatest influence parameter was kept constant, while changing the others. OFAT method resulting combinations were submitted to deposited yield, dilution, hardness and microscopy analyses. The constituent phases and impacts on the heat-affected zone (HTA) hardness resulting from the heat input optimization were also evidenced. Results showed shielding gas composition as results greatest influence parameter, with 76% influence on the ANOVA. Taguchi's method optimized combination consisted of using C10 gas, 15 liters per minute flow rate, 20 millimeters stick-out and 350 millimeters per minute welding speed. Optimized combination provided a thermal efficiency of 62%, 36,7% dilution and 88,6% deposited yield, however a reduction in hardness was observed in the HAZ, in the order of 10.2 HV in relation to base metal hardness. Metallographic analyzes showed aligned second-phase ferrite and granular bainite in the HAZ-GG and grain refining with pearlite and ferrite phases in the HAZ-GR.