Avaliação geométrica, térmica e de porosidade de pré-formas em manufatura aditiva por deposição a arco com resfriamento ativo por quase-imersão

Abstract

In wire + arc additive manufacturing (WAAM), the construction of preforms closer to the final geometry, that is, with a lower “buy-to-sell” ratio, reflects in less post-processing and greater productivity. This factor becomes even more important for materials of high cost, tough machinability and in situations where the heat accumulation becomes a limiting factor (typical of processes with directed energy deposition). Thus, the evaluation of the influence of certain parameters on the final quality of the structure is essential. Therefore, the present work aims at verifying how the deposition speed, wire feed speed and LEWD (layer edge to water distance) influence the geometric quality, porosity level and thermal cycles of the WAAM process by using the CMT technique and applying the NIAC (Near-Immersion Active Cooling) thermal management. Software developed to check geometry based on image analysis were used, one via cross-section analysis and another made use of a non-invasive method with a virtual reconstruction of the surface, along with measurements with a caliper. The Archimedes technique was applied to estimate the volume of voids. The temperature was monitored at a distance of 30 mm ahead of the electric arc. It was observed that lower wire feed speeds, higher deposition speeds and lower LEWDs (with a limit of approximately 8 mm) reduce the heat imposed by the process. These conditions promoted a reduction on the surface waviness, greater height and lower width of the preforms. On the porosity level, a greater volume of voids was observed when the cooling water lamina was closer to the molten pool. Thus, it was possible to conclude the importance of a careful choice of deposition parameters seeking to mitigate the heat imposed by the process and consequently its negative effects on the geometry and porosity.