A novel graded laser energy input strategy for fabrication of horizontal overhanging Ti6Al4V metallic structures with PBF-LB method

● Abstract: A graded laser energy input strategy including three fabrication steps involving the optimizations of a single molten track, single-sided cantilevered structure, and horizontal overhanging structure as a bridge-like type was investigated. Results revealed that a defocus distance of 5 mm combined with a low laser power of 20 W and scanning speed of 600 mm/s is suitable for fabricating the 1 st layer, which is slightly sintered to exhibit lower surface roughness and serves as a structural support for the upper layers. For the next two layers, a slightly higher laser power of 40 W was proven to be optimal for minimizing powder adhesion on the bottom surface, forming satisfactory bonding without interlayer delamination and eliminating warpage originating from continuous accumulation of internal stress. Since the 4 th layer, a higher volume energy density ( VED ) with a laser power of 120 W and no defocus distance aimed at additionally remelting the previous three layers was proved to be effective in further reduce the porosity formed due to incomplete melting while maintaining lower warping height. The 30-layer horizontal overhanging structure fabricated using a graded strategy reaches satisfied balance between dimensional accuracy and surface quality, displaying higher density of 99.72±0.21 %, lower thickness deviation of approximately 20 %, top surface roughness of 13.3±1.19 μm and bottom surface roughness of 22.2±2.28 μm.