Page 48 - MSAM-2-2

Materials Science in Additive Manufacturing Biomimetic structures for optical focusing

infrared spectrum range . The reflective materials of long parameters were defined in the meridional plane (y-z
[19]
infrared (metal) are more common and inexpensive than plane). As shown in Figure 1B, h is the wall thickness of
the refractive ones. Therefore, BLES provides a solution for microchannel, L is the upper width of microchannel, t is
reducing the cost of the infrared detector . In the field of the length of microchannel, R is the radius of curvature
[20]
the UV spectrum, researchers proposed to use the BLES of BLES, α is the angle between the axis of two adjacent
to focus UV radiation, which will break down chemical microchannel walls, and C, which is the angle between
bonds and change the molecular structure . Besides, the axis of microchannel walls at both edges of BLES,
[21]
researchers have also performed studies on expanding the also affects the field of view of BLES. Based on the key
applicable spectral range of BLES, for example, exploring parameters described above, the parametric CAD model
the application of BLES in the field of visible light , which of BLES was established (Figure 1C) using the Siemens NX
[22]
is also the focus of this study. software. The structural parameters used in this study are
However, BLES, which was usually made by combining as follows: constant parameters were set as h = 0.2 mm,
a series of thin metal plates [22,23] , was manufactured by t = 10 mm, α = 2° and C = 18°; variables L were set to 1.0,
traditional technology that was prone to warpage and other 1.25, 1.5, 1.75, and 2.0 mm, the corresponding R was set as
defects in processing, reducing the focus performance 35.11, 42.27, 49.44, 56.60, and 63.76 mm.
of BLES. Some researchers use thin glass plates with a 2.2. Laser powder bed fusion processing
metal coating to manufacture BLES [24,25] , but the spherical
surface of which was difficult to realize. BLES can also A self-developed LPBF equipment by Nanjing University
be fabricated by chemical etching technology , but the of Aeronautics and Astronautics was used to manufacture
[26]
microchannel taper of BLES was difficult to process, and BLESs in this study, the schematic of which was illustrated
the etched microchannels were arranged irregularly. The in Figure 1D, and the machine detail could be found
[28]
disadvantages of traditional technology for manufacturing elsewhere . The laser power P was varied from 325 to 425
BLES restrict its development in the optical field. As a kind W in increments of 25 W. The scanning speed v was varied
of laser additive manufacturing technology, laser powder from 1800 to 2600 mm/s in increments of 200 mm/s. For
bed fusion (LPBF) can realize the near-net forming of all the LPBF-processed samples, the hatch spacing was set
[27]
complex components and has unique technical advantages to 50 μm. The layer thickness was controlled at 30 μm by an
in forming bionic components (such as bioinspired automatic powder-spreading device with a flexible scraper
reticulated shell structures [28,29] , bioinspired mantis blade. A gas-atomized AlSi10Mg powder with a mean
shrimp telson structures [3,30] , and bioinspired sandwich particle size of 23 μm was rapidly filled into the powder
structures ). cylinder and then sealed with the door of the building
[31]
chamber. Subsequently, an inert argon gas circulatory
In this study, the BLESs were designed by imitating
the lobster eye. The influence of multiple processing protection system was used to control the oxygen content
in the building chamber to fall below 10 ppm, and the laser
parameters (laser power and scanning speed) on the beam selectively melted powder which was spread by the
densification behavior of LPBF-processed thin walls was flexible scraper according to two-dimensional slice data
investigated. And then, the BLESs with different structural of the CAD model. The long-exposure photograph of this
parameters were processed by LPBF with the optimum LPBF process is shown in Figure 1E. After the LPBF process,
laser parameters, and the forming quality of LPBF- the LPBF-processed samples (Figure 1F) were removed
processed BLES was evaluated. Then, the influence of from the substrate by electrical discharge machining and
different structural parameters on the focus performance ultrasonic cleaned for 5 min with alcohol and dried with
of LPBF-processed BLESs was investigated, and the optical flowing hot air subsequently. An FEI Quanta 200 scanning
focusing mechanism of BLES was revealed by numerical electron microscope (SEM) was used to analyze the
simulation. Finally, an application idea of LPBF-processed forming accuracy and surface morphologies of the LPBF-
BLESs in a light band was proposed.
processed samples, and Olympus FV3000 laser confocal
2. Experimental and simulation methods microscopy was used to test the surface roughness of the
LPBF-processed samples.
2.1. Structural parameters and modeling
2.3. Optical focusing performance testing
Figure 1A shows the morphological characteristics of
lobsters and lobster eyes, and it can be observed that Optical focusing performance testing was conducted on a
the upper surface of the lobster eye microchannel is self-developed optics testing system by Nanjing University
rectangular. To establish computer-aided design (CAD) of Aeronautics and Astronautics; the schematic and
models of BLES with a meridional feature, some key equipment of this system are illustrated in Figure 2A and B.

Volume 2 Issue 2 (2023) 3 https://doi.org/10.36922/msam.0361