Laser Polishing of Laser Powder Bed Fusion AlSi10Mg Parts—Influence of Initial Surface Roughness on Achievable Surface Quality

Abstract

Laser Powder Bed Fusion (LPBF) is an Additive Manufacturing technique, which allows production of highly complex solid metal parts with good mechanical properties, compared to conventionally manufactured parts. Nevertheless, the layer-by-layer fabrication process also offers several disadvantages, including a relatively high surface roughness depending on the shape of the component, its position and orientation during the fabrication process. This paper deals with investigations on the surface roughness reduction capability, and residual surface structures by laser polishing of LPBF AlSi10Mg parts under varying initial surface roughness in order to investigate the influence of the surface behavior and initial surface roughness to the achievable surface quality by laser polishing. Hereto test specimens with varying fabrication orientations regarding to the built platform are printed and further polished. Thereby the initial arithmetic roughness varies between 19.2 µm and 8.0 µm. It could be shown that the achievable surface roughness by laser polishing with continuous and pulsed laser radiation is increasing with rising initial roughness, but the relative roughness reduction is almost constant in the range of 95% -97.5%. The analyzation of the residual roughness structures shows, that the main roughness differences is found in the middle and long structure wavelength regime, which are directly depending on the initial surface structures of 3D printing.

Laser Polishing of Additive Manufactured Aluminium Parts by Modulated Laser Power

“…In general, laser polishing results in material transport from the centre of the polishing field to the upper and lower turning points of the scanner pendulum movement, similar to pulsed mode polishing [49]. Local immersion of up to −20 µm occur in the centre of the polishing field, Figure 13a.…”

“…Polishing with a CO2 laser (10.6 µm) the highest roughness improvement of 85% from Sa = 22.3 µm to 7.9 µm with the highest tested energy density of 330 J/mm 2 is reached [46]. Pulsed and continuous mode laser polishing of L-PBF surfaces with varying initial roughness by changing fabrication angle revealed a constant relative roughness reduction ability [49]. With decreasing the fabrication angle and thus increasing the initial roughness, the partial roughness regarding to residual long periodic surface structure is increased.…”

“…The orientation, given by the fabrication angle, causes major surface roughness variations of the parts between 8.0 and 19.2 µm, according to Table 2. The common pulsed and continuous laser operation modes have shown a direct influence between initial surface and achievable surface roughness by laser polishing [49]. The roughness reduction rate is almost constant.…”

“…Table 6. Achieved roughness Ra at pulsed [49], continuous [49] and modulated laser operation modes depending on the fabrication angle and initial roughness, measured in sample vertical direction (SVD).…”

“…Furthermore, the process stability, regarding to varying initial roughness is improved. Thus, the roughness variation after polishing ∆Ra polished is reduced from 0.25 µm with pulsed laser radiation [49], and 0.30 µm with continuous laser radiation [49] to 0.13 µm.…”