Machinability of partition milling stainless steel/Inconel functionally gradient material printed with directed energy deposition

As functionally gradient materials (FGMs) reveal innovative mechanical properties, they have aroused huge interest in multiple industry areas. In this study, a hybrid manufacturing (HM) technique that combines a directed energy deposition (DED)-type additive manufacturing (AM) fabrication process with milling-type machining is investigated. In the DED process examined, Inconel 718 (IN718) and stainless steel 316L (SS316L) metal powders were blown into the molten pool at different and varying respective flow rates to achieve specific composition ratios for different printed layers so that a smooth gradient transition from SS316L to IN718 was achieved. Due to the attendant generation of rough surfaces common to such FGMs, partition milling was employed after fabrication, and the cutting temperatures and forces were simultaneously recorded considering the significant anisotropy in mechanical properties. The surface roughness of each FGM gradient section and tool wear mechanism were also measured after machining. Through analysis of the experimental results, the machining mechanism was revealed, which provides new insights into the machinability of SS316L/IN718 FGMs.