Experimental and numerical investigation of the origin of surface roughness in laser powder bed fused overhang regions

Surface roughness of laser powder bed fusion (L-PBF) printed overhang regions is a major contributor to deteriorated shape accuracy/surface quality. This study investigates the mechanisms behind the evolution of surface roughness (R-a) in overhang regions. The evolution of surface morphology is the result of a combination of border track contour, powder adhesion, warp deformation, and dross formation, which is strongly related to the overhang angle (theta). When 0 degrees <= theta <= 15 degrees, the overhang angle does not affect FL significantly since only a small area of the melt pool boundaries contacts the powder bed resulting in slight powder adhesion. When 15 degrees < theta <= 50 degrees, powder adhesion is enhanced by the melt pool sinking and the increased contact area between the melt pool boundary and powder bed. When theta > 50 degrees, large waviness of the overhang contour, adhesion of powder clusters, severe warp deformation and dross formation increase R-a sharply.