A novel experimental approach to exploring process parameters for fabricating support-free horizontal overhangs in LPBF of Inconel 718

The design freedom of Laser Powder Bed Fusion (LPBF) components has been confined by the minimum allowable overhang angle of 45°. It remains unclear how to achieve multiple layers of overhang at zero-degree overhang angle, which is the fundamental basis of overhang. Here, we have confirmed the possibility of manufacturing three layers of support-free 0° overhang, but also demonstrated the robustness of the present approach via the successful manufacture of an overhang with 18 mm span. The stable dross thickness reveals that the laser drilling effect did not penetrate beyond the three-layer overhang. Furthermore, this research also demonstrates that the failure to manufacture long bridge overhangs was caused by severe consolidation rather than the conventional understanding of residual stress of the first few layers. The high correlation between porosity and surface roughness, and the etched melt pool reveal the underlying mechanism for low surface roughness for the horizontal overhang.HighlightsAn experimental approach is proposed to efficiently explore the parameter space.The present approach enables the manufacture of three layers of support-free overhang.The mechanisms for the successful and failed prints are elucidated.The relationship of Ra and porosity is proposed to further refine the parameters.