Beam Shaping in LPBF of IN718: Top-Surface Morphology and Defect Mechanisms — Doubling Build Rate via Small Hatch Spacing and High Scan Speed Process Window
Robin Prudlik, Jonas Grünewald, Simon Sankaré, and Katrin Wudy from the Laser Additive Manufacturing team at the Technical University of Munich published a paper in Additive Manufacturing (October 2026 issue, DOI: 10.1016/j.addma.2026.105402) systematically investigating the effects of laser power, scan speed, and hatch spacing on the top-surface morphology and defect formation in IN718 processed by laser powder bed fusion (PBF-LB/M), comparing Gaussian and ring beam profiles. The study shows that surface tension-driven melt pool instability is the core factor limiting productivity, particularly at high scan speeds (≳1600 mm/s) and large hatch spacings (≳0.15 mm). Hatch spacing is the primary trigger of surface irregularity, acting through control of inter-track remelting and transverse melt pool confinement; scan speed determines the morphology type and characteristic wavelength. Increasing hatch spacing reduces inter-track overlap, suppresses remelting-induced planarization, and induces unstable surface features; increasing scan speed shrinks the melt pool size, driving the surface from continuous to discontinuous states. Using ISO 25178 areal roughness parameters and a regularized classification framework, process maps were constructed: a planar top surface is achieved only at small hatch spacings, independent of beam shape; however, the combination of small hatch spacing and high scan speed maintains a planar top surface while increasing build rate by more than twofold compared to typical existing processes. Value for powder buyers: This study provides a new process window for IN718 powder under beam-shaping processes that balances surface quality and productivity. The small hatch spacing and high scan speed strategy imposes higher demands on powder batch consistency—sphericity, particle size distribution, and flowability directly affect melt pool stability at high scan speeds. When purchasing, verify the supplier's batch data and quality traceability documentation.