Local and global influencing factors on support-free manufacturability in powder bed fusion of metals using a laser beam

Powder bed fusion of metals using a laser beam (PBF-LB/M) enables the fabrication of complex geometries but is often constrained by the need for support structures, particularly in overhanging regions of the part. This study presents a systematic investigation of local and global factors affecting the support-free manufacturability using Inconel 718. In the first substudy, the effect of the downskin laser power on steep overhangs was analyzed. While conventional strategies reduce the energy input to improve the overhang manufacturability, this study shows that increasing the downskin laser power beyond 380% of the standard value enables the successful fabrication of overhang angles as low as 25°, revealing a previously unexplored process window, though with increased surface roughness. A second, quasi-in situ substudy examined the progression of overhang failures. Part manufacturing was interrupted at predefined heights to assess the deformation evolution. A nonlinear accumulation of the top-layer distortion prior to failure was revealed, emphasizing that the overhang angle alone is insufficient to determine the support necessity. In the third substudy, global geometric constraints were investigated using bottleneck structures with varying diameters. While all geometries were built successfully, optical tomography data showed localized heat accumulations in specimens with narrower bottlenecks, indicating impaired heat dissipation and reduced process stability. Overall, the results demonstrate that both local melt pool dynamics and global thermal effects must be considered to reliably enable support-free fabrication. These findings challenge traditional angle-based rules and motivate thermally informed design approaches, advancing the robustness and industrial applicability of PBF-LB/M.