A Parametric Study on the Stability, Geometry and Hardness of AISI 308LSi WAAM-GMAW

Wire arc additive manufacturing (WAAM) has been established to be an efficient and cost-effective additive manufacturing technique for fabricating functional metallic parts from scratch. However, there is need to determine optimal processing condition for each material system to produce high-quality parts. In this work, a parametric study of WAAM of AISI 308LSi was performed to determine the processing condition(s) at which single tracks of high dimensional accuracy, excellent geometry, no visible crack and pore, and high hardness required for high-quality multi-track deposition can be achieved. The track geometries were investigated using a combination of optical microscopy and image processing software. The microstructure and hardness of the deposited single tracks were examined using optical microscopy and Vickers hardness tester respectively. A process map predicting the process stability of WAAM of AISI 308LSi was developed within a process window. Continuous single tracks of high dimensional accuracy were produced from a stable deposition process. The process becomes unstable whenever the wire deposition volume per unit length of track is in excess of the available heat energy per unit length of track. The wire feed rate and traverse speed significantly influence the stability and geometry of the single tracks. The processing conditions at which single tracks of low wetting angle (<90◦), high aspect ratio (>1.5), high surface quality, and high hardness (close to the as-received material) can be deposited were determined. These processing conditions were considered suitable for the fabrication, surface modification and repair of functional engineering parts made of 308LSi stainless steel.