Effect of interlayer rescanning on surface roughness and overhang sinking distance of AlSi10Mg alloy via selective laser melting

Abstract

Laser rescanning technology is usually used to improve the forming quality of 3D printed parts. In order to investigate the relationship between rescanning strategy and forming quality, this paper proposed an interlayer rescanning strategy, which scans once at each odd-number layer and rescans at each even-number layer. In this work, 3D printed parts with inner structures were manufactured via selective laser melting. White light interference profilometry, scanning electron microscope, and three coordinates were used to analyze the surface quality, overhang sinking distance, and therefore the performance of samples with rescanning. White light interference profilometry-based roughness characterization revealed that the minimum surface roughness measured was 8.338 µm with rescanning and 9.676 µm with interlayer rescanning. The range of overhang sinking distance varied to a minimum of 0.146 mm with rescanning and 0.318 mm with interlayer rescanning. Based on the force analysis of the molten pool of overhang layers, the overhang sinking was mainly due to the increasing gravity of the molten pool and the insufficient supporting force provided by lower layers.

Surface Roughness of Interior Fine Flow Channels in Selective Laser Melted Ti-6Al-4V Alloy Components

“…Principal Component Analysis (PCA), a statistical tool, transformed this complex dataset The highest roughness (Ra) at the channel's roof could be caused by the curved surface inducing larger stair-step effects, particularly larger overhang features when the roof is at 0 • orientation, as depicted in Figure 3a. Furthermore, loose powder adhesion and the instability of the molten pool in overhanging layers, lacking solid substrate support, and efficient heat dissipation led to irregular solidification [23,25,26]. As the build angle was increased beyond 0 • , the roughness (Ra) decreased abruptly to 67.3 µm at the roof and 54.8 µm at the floor of the channel at 30 • .…”

“…This results in the deviations in the printed contour relative to the CAD model and increased roughness on the underside of the overhang roof [ 21 , 22 ]. Without a solid substrate to anchor it, the molten pool on an overhanging layer becomes unstable and its surface tension and fluid dynamics cause irregularities and a rougher finish compared to areas with a solid layer beneath [ 23 , 24 , 25 ]. Furthermore, channel roof overhangs lack this heat dissipation pathway, potentially causing inconsistent solidification and increased roughness [ 23 , 25 , 26 ].…”

“…Without a solid substrate to anchor it, the molten pool on an overhanging layer becomes unstable and its surface tension and fluid dynamics cause irregularities and a rougher finish compared to areas with a solid layer beneath [ 23 , 24 , 25 ]. Furthermore, channel roof overhangs lack this heat dissipation pathway, potentially causing inconsistent solidification and increased roughness [ 23 , 25 , 26 ]. The angle at which the laser strikes the overhang can also affects the melt pool’s behavior as non-optimal laser angles result in uneven melting and solidification, leading to a rougher surface texture [ 27 , 28 ].…”