This study investigates the finishing characteristics of internal channels with different cross-sectional geometries using free abrasive grains and evaluates the cooling performance of these channels before and after finishing. Three types of channels with circular, triangular, and hexagram cross-sections were designed and fabricated using laser powder bed fusion (L-PBF). A fluid flow in the channel was evaluated using computational fluid dynamics simulations, and the finishing characteristics and cooling performances of the channels were experimentally investigated. The results indicated that the use of free abrasive grains enabled the improvement in the surface quality as well as the cooling performance of the channel. The cross-section of the channel affected the fluid flow in the channel and finishing progress. The initial surface roughness varied with the cross-section of the channel owing to the limitations of L-PBF, and the triangular section had a relatively uniform surface quality throughout the channel compared with the other cross-sections. The cooling time decreased with the surface area of the channel. To obtain the uniform surface quality, the application of a suitable cross-section is needed for the finishing process. The outcomes of this study demonstrate that a triangular-section channel is suitable for improving both surface quality and cooling performance.

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