Surface roughness and image analyses of contour scanning offset effects on sloping topography in laser powder bed fusion
摘要
The variability in surface quality of laser powder-bed fusion (L-PBF) parts may negatively affect part mechanical performance, particularly under dynamic loading. Inconsistent surface quality is primarily caused by sophisticated process-induced surface formation as well as partially melted particles attached to the surfaces. One potentially effective way to improve the surface quality of L-PBF parts is through contour scanning around the boundary. This study investigates the effect of contouring parameters, including the contour offset, on the inclined surface characteristics of L-PBF parts. Ti6Al4V samples were designed with different inclination angles and fabricated with a post-contouring strategy using an L-PBF machine. The part surface morphology was measured by white-light interferometry to evaluate both upskin and downskin surfaces, including the average surface roughness (Sa) and skewness (Ssk). The results show that upskin surfaces are the presence of either the outer contour alone or the interaction between both the outer and inner contours, depending on the angle and the offset distance. Increasing the contour offset distance and decreasing the inclination angle will reduce the Sa of upskin surfaces. On the other hand, the downskin surface roughness is dominated by the amount of partially melted particles attached. A simplified melt-pool size analysis qualitatively supports the argument that the surface roughness of downskin is largely affected by particle attachment. In addition, the upskin surface characteristics highly depend on the contour scan linear energy density (LED). The highest LED (0.26 J/mm) resulted in the best upskin of 8.00 µm Sa but generated the roughest downskin of 40.6 µm Sa. Moreover, the offset strategy also has an impact on upskin surface skewness, but to a much lesser extent on downskin skewness.