Drop and hump behaviors in robotic arc-directed energy deposition with vertical position

Arc-directed energy deposition (Arc-DED) with the vertical position offers significant potential for in-situ fabrication of overhang structures. However, the vertical position application is seriously hindered by drop and hump defects since Arc-DED possesses serious heat accumulation resulting from multi-layer depositions. The novelty of this study is to reveal the formation mechanisms of drop and hump defects in vertical Arc-DED of lowcarbon steel walls. Force models of the molten pool in vertical-down and vertical-up Arc-DED are established. Two indicators, i.e., the molten pool area and the molten pool dimensional ratio, are proposed to evaluate the probability of drop and hump occurrence, respectively. Furthermore, how the wire feed speed (WFS), travel speed (TS), and the constant ratio of WFS to TS affect the molten pool behavior is explored and discussed. In the vertical-down deposition, decreasing the TS or increasing the WFS will increase the possibility of drop defects occurring when the molten pool area exceeds 45 mm2. In the vertical-up deposition, increasing the TS or the WFS will increase the possibility of hump defects occurring when the molten pool dimensional ratio exceeds 4.1. Maintaining the WFS/TS constant, the probabilities of hump and drop defects increase as the WFS and the corresponding TS increase. This study offers a better understanding of the formation mechanisms underlying the drop and hump phenomena and lays a solid foundation for the practical application of vertical Arc-DED to fabricate overhang features.