Hot forging wire and arc additive manufacturing (HF-WAAM)

Abstract

In this study, we propose a new variant of wire and arc additive manufacturing (WAAM) based on hot forging. During WAAM, the material is locally forged immediately after deposition, and in-situ viscoplastic deformation occurs at high temperatures. In the subsequent layer deposition, recrystallization of the previous solidification structure occurs that refines the microstructure. Because of its similarity with hot forging, this variant was named hot forging wire and arc additive manufacturing (HF-WAAM). A customized WAAM torch was developed, manufactured, and tested in the production of samples of AISI316L stainless steel. Forging forces of 17 N and 55 N were applied to plastically deform the material. The results showed that this new variant refines the solidification microstructure and reduce texture effects, as determined via high energy synchrotron X-ray diffraction experiments, without interrupting the additive manufacturing process. Mechanical characterization was performed and improvements on both yield strength and ultimate tensile strength were achieved. Furthermore, it was observed that HF-WAAM significantly affects porosity; pores formed during the process were closed by the hot forging process. Because deformation occurs at high temperatures, the forces involved are small, and the WAAM equipment does not have specific requirements with respect to stiffness, thereby allowing the incorporation of this new variant into conventional moving equipment such as multi-axis robots or 3-axis table used in WAAM.