Study of the effect of the combination of protective gases on the structure of the weld bead for the GMAW process using pulsed arc and short circuit

Abstract

A weld bead's geometry directly influences the welded joint's physical characteristics and mechanical performance. The composition of the shielding gas directly affects the form of metal transfer during the welding process and, therefore, modifies the geometry of the weld seam obtained. In addition, metal transfer methods also influence the configuration of the weld bead profile. The objective is to analyze the geometry of the weld bead with different combinations of  shielding gases and metal transfer modes in the continuous wire electric arc welding process with gas shielding (GMAW). To achieve this objective, a methodology is proposed to analyze the weld bead's penetration and other geometric parameters. This is achieved by varying the percentages of the gas mixture between Ar and CO2 and by employing different types of metal  transfer, such as short circuit, pulsed, and PMC multi-control pulsed. Generally, when using only CO2 as shielding gas, a wide, round weld bead is obtained. If Ar alone is used, the weld bead profile has a very thin shape and deep penetration. With the mixture of Ar and CO2, a bead is  obtained with good penetration and sufficient width to cover the two test tubes without empty spaces between the base and filler materials. The macrographic analysis of the chords with their respective measurements is presented, and the geometric parameters of the obtained chords are tabulated. The penetration of the bead is directly proportional to the percentage of CO2 present in the mixture. In a comparison between the three transfer modes used with the  same gas composition, it is found that  the pulsed spray mode produces greater penetration.