ABSTRACT

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 (θ). When 0° ≤ θ ≤ 15°, the overhang angle does not affect R_a significantly since only a small area of the melt pool boundaries contacts the powder bed resulting in slight powder adhesion. When 15° < θ ≤ 50°, powder adhesion is enhanced by the melt pool sinking and the increased contact area between the melt pool boundary and powder bed. When θ > 50°, large waviness of the overhang contour, adhesion of powder clusters, severe warp deformation and dross formation increase R_a sharply.

摘要

激光粉末床融合 (L-PBF) 打印悬垂区域的表面粗糙度是导致形状精度/表面质量恶化的主要原因。本研究调查了悬垂区域表面粗糙度 (R _a )演变背后的机制。表面形貌的演变是边界轨迹轮廓、粉末粘附、翘曲变形和浮渣形成共同作用的结果，与悬垂角 ( θ )密切相关。当 0° ≤  θ  ≤ 15° 时，悬垂角不会显着影响 R _a，因为只有一小部分熔池边界接触粉末床，导致粉末轻微粘附。当 15° <  θ ≤ 50°，熔池下沉和熔池边界与粉床接触面积的增加增强了粉末的附着力。当θ  > 50°时，悬垂轮廓的大波纹、粉末团块的粘附、严重的翘曲变形和浮渣形成使R _a急剧增加。