Investigation of thin-wall geometry and hardness of mild steel additive manufacturing using resistance seam welding

Directed energy deposition (DED) is a low-cost method of manufacturing large hollow products and pressure vessels by melting and depositing metal materials using a heat source such as an arc discharge or laser. However, DED has problems with increased bead width and shape variation because of the formation of molten pools and effects of gravity and surface tension. In contrast, resistance seam welding uses Joule heating, in which several kiloamperes of current is applied to melt locally vicinity the bonding interface. Additionally, it is possible to bond continuously. Resistance seam welding can be used for metal additive manufacturing to solve the problems of DED because most of the material can be deposited in the solid phase by forming a localized molten zone. In this study, mild steel wires were deposited using a resistance seam welding machine, and the effects of welding current and downtime on the shape of the deposited part were investigated. Moreover, cross-sections of the deposited parts were observed, and Vickers hardness was evaluated. Finally, we attempted to fabricate a 20-layer thin-walled structure by heat input control. As a result, the resulting structures exhibited an effective width smaller than the wire diameter and achieved hardness equivalent to that achieved using existing DED methods.