Investigation on shape deviation of horizontal interior circular channels fabricated by laser powder bed fusion

Abstract

Abstract The fabrication of horizontal interior circular channels poses some unique challenges to the laser powder bed fusion (L-PBF) process. The engineering challenge is to be able to print horizontal interior channels using L-PBF without using support structures, while the scientific challenge is to predict the shape deviation in the horizontal channel. This paper studies the geometric fidelity (roundness and shape deviation) of L-PBF printed horizontal interior circular channels (diameters 1−3 mm) by developing experiment-based regression models and a preliminary computational fluid dynamics (CFD) simulation model. The roundness error is found to be affected by the shape/size of the melt pool, thermal stresses, beam offset, and the slicing algorithm. It is recommended that to decrease the roundness error, in addition to choosing a proper beam offset, the width/depth of the melt pool should be minimized by minimizing the volumetric energy density (smaller laser power or higher scanning speed). Shape deviation in overhanging structures is determined by the thermo-mechanical driven molten flow in the melt pool. Hanging structures with irregular profiles (dross) are formed due to the sinking of the melt pool on an unconsolidated powder bed under the effect of gravity, surface tension, and poor thermal conductivity. (Partially) unmelted powder randomly adheres to the edges of the melt pool enlarging the hanging structure and roughening the profile. Small laser power or large scanning speed benefits reducing the roundness error and hang-diameter ratio. 0° or 45° rotational linear scanning strategy can be selected for minimizing the roundness error or the hang-diameter ratio, respectively.