Abstract
A researching hype upon the Wire and Arc Additive Manufacturing (WAAM) seen in the last decade, has led to a notable increase of the knowledge in how parts built by WAAM are affected by the electrical and thermal parameters, and deposition strategies. In this innovative manufacturing route, the selection of the welding conditions seems to be even more critical than in usual joining and facing applications. The deposition planning in WAAM is highly influenced by these conditions, for example, the feedstock characteristics (composition, form, size), the electric arc (power and density) and metal transfer conditions. A factor that highly influences these parameters is the shielding gas mixture choice. The Gas Metal Arc Welding (GMAW) shielding gas mixtures are mostly based in Argon with parts of Carbon dioxide due to its relatively lower cost. However, the increase of the Carbon dioxide content can negatively influence the stability of the metal transfer and increase the presence of undesirable oxides between the layers. Although, the influence of Carbon dioxide in the formation of these defects during the manufacture of parts via WAAM using the Cold Metal Transfer (CMT), an advanced variant of the GMAW process, is not yet fully described and explained in the literature. To fulfill this gap, this work focuses on the analyses of two types of industrial gas mixtures: 92% Argon + 8% CO2, and 75% Argon + 25% CO2. As feedstock, 1.2 mm ER70S6 filler wire was deposited over 12.7 mm thickness ASTM A36 carbon steel plates. The welding process used in this study was the Fronius CMT, due to its highly usage among WAAM manufacturing and research groups. The influence of CO2 content on the electrical, thermal, and geometrical characteristics of single welding beads, single bead walls and pads was qualitatively and quantitatively analyzed. The results showed a correlation with the increase of CO2 content and the increase in the silicon oxide formation and incidence of pores and lack of fusion between layers. The thermal analysis showed that the thermal profile did not change within the range of 8% to 25% of CO2, even the processes showing a slight difference in electrical power. Furthermore, the geometric profile showed no significant difference between specimens. Therefore, to attenuate inclusions of silicon oxide and to diminish the lack of fusion incidence the mixture with 25 % of carbon dioxide is the most adequate, however this does not discredit the usage of 8% of carbon dioxide in the gas mixture, but it shows the need for the implementation of a more accurate overlapping parametrization.
Keywords: WAAM, gas mixture, CMT, GMAW, additive manufacturing.
Reference:
GALEAZZI, D.; SCHWEDERSKY, M. B.; MACIEL, P. C.; ROCHA , P. C. J.; SILVA, R. H. G.. Analysis of the CO2 Influence in the Gas Mixture for WAAM Using CMT Version of the GMAW Process. 26th ABCM International Congress of Mechanical Engineering. November 22-26, 2021. Florianópolis, SC, Brazil