Page 51 - MSAM-2-2

Materials Science in Additive Manufacturing Biomimetic structures for optical focusing

the laser energy input was further increased, the excessive molten pool incompletely melted, and adhered to the
energy input increased the evaporation of volatile elements formed part surface [39,40] .
in the material, resulting in the increase of gas inside the The optical focusing performance was characterized
melt, which further reduced the relative density of LPBF- to study the focus ability of LPBF-processed BLES
[38]
processed samples (Figure 3C). samples with different UWM to collimate light sources.
Figure 4A depicts a typical upper morphology of a The irregular facula formed by focusing the light of each
microchannel of LPBF-processed BLES with L = 1.0 mm, LPBF-processed BLES sample was regarded as a square
and the white and black dotted lines were used to mark equivalent facula (Figure 5A), and the side length of the
the profile of the designed model and LPBF-processed equivalent facula was used to represent the actual facula
component, respectively. The inset shows the macro- size indirectly. The side length of LPBF-processed BLES
photograph of the LPBF-processed BLES component; the samples with L=1.0 mm, 1.25 mm, 1.5 mm, 1.75 mm, and
upper profile in each microchannel was regular. However, 2.0 mm was 0.72 mm, 0.95 mm, 1.14 mm, 1.32 mm, and
after comparing the black and white dotted lines, it was 1.59 mm, respectively (Figure 5B-F). It can be obtained
found that the forming size of the upper profile was larger that the side length of the corresponding actual facula was
than that of the designed model, which was consistent with increased with the increase of L, implying the focusing
our previous work . The processed profile with “rounded ability of light was weakened. Notably, the light intensity
[9]
chamfer-like” (Figure 4B) was found at the intersection of the facula in the center of the focus plate of samples
area of two thin walls, which was different from the right- with L=1.0 mm and 1.25 mm was obviously higher than
angle shape in the designed model; it may be caused by that of the other three samples (L=1.5 mm, 1.75 mm, and
the overlap of molten pools on two paths which are 2.0 mm), which also proved that samples with small upper
perpendicular to each other during the LPBF process. widths of 1.0 mm and 1.25 mm possessed a good light-
Figure 4C reveals the top surface topography of a thin focusing ability compared with other three samples.
wall, and it can be clearly observed that the scanning trace To further study the optical focusing characteristics
was regular and molten pools were combined well, which of LPBF-processed BLES components, the focusing
illustrates that the LPBF-processed BLES has good forming characteristics of two samples with L=1.0 mm and 1.25 mm
quality. Figure 4D shows the surface roughness and surface were tested with 50% attenuation of light intensity on
morphology of LPBF-processed BLES with L=1.0 mm. the focus plate. Compared with the above results shown
Three tested areas on the surface are shown on the left of in Figure 5B and C, the size of the actual facula after
Figure 4. It can be seen that the surface roughness of the attenuation was smaller and more concentrated (as shown
top, middle, and bottom areas was 9.315 μm, 7.149 μm, in Figure 6A and B), because the stray light and low light
and 10.534 μm, respectively. Adhered powders can be intensity light around the facula were shielded under the
found in all three areas, caused by the particles near the condition of 50% attenuation of light intensity. It can be

A B C

D

Figure 4. (A) The high-magnification SEM images of the laser powder bed fusion-processed bionic lobster eye structure (BLES) component (L = 1.0 mm),
and the insert showing the macro-photograph, (B) the morphology of the intersection area of two thin walls, (C) the morphology of a thin wall, and (D)
diagram of tested positions and surface morphologies on the LPBF-processed BLES component. Ra: surface roughness.

Volume 2 Issue 2 (2023) 6 https://doi.org/10.36922/msam.0361