Optimization of Downskin Surface Quality in Laser Powder Bed Fusion of IN718 for Supportless Manufacturing

Support structures remain a major limitation of laser powder bed fusion (LPBF), particularly for downward-facing surfaces prone to powder adhesion, dross formation, melt-pool instability, and staircase effects. This study investigates the downskin optimization of Inconel 718 (IN718), fabricated at a 35° inclination using a Renishaw RenAM 500S Flex. A Taguchi L25 orthogonal array was employed to evaluate three process parameters: hatch power (225–425 W), remelting times (0–4), and printing velocity (1100–1900 mm/s). Surface topography was characterized using an Alicona InfiniteFocus G5, with Sa and Sz selected as surface-quality indicators. Remelting was identified as the dominant factor for both responses, followed by hatch power and printing velocity. The response deltas for Sa were 22.70, 7.86, and 5.22 μm, respectively, while those for Sz were 68.9, 46.8, and 37.2 μm. The optimum mean responses were obtained at 375 W, one remelting operation, and 1700 mm/s for Sa, and 275 W, one remelting operation, and 1100 mm/s for Sz. The lowest measured Sa and Sz were 50.75 and 500.7 μm, respectively. The results demonstrate the potential of controlled remelting for improving downskin surface quality and reducing support requirements in LPBF.