As complex ceramic multicomponent materials, the lunar regolith and minerals still challenge people on onsite utilization technology limited to the lunar surface environment. In this paper, we investigate the suitability of lunar regolith simulants and ilmenite powders for 3D printing (aka Additive Manufacturing) of hypothetical brick aimed at lunar habitat construction. The first generation of laser 3D printing equipment (Lunar 1.0) for our experiments has been designed and assembled, which is suitable for selective laser sintering (SLS) process out of many kinds of ceramic powders to manufacturing samples with different geometrical shapes. The lunar regolith simulants and ilmenite powders are demonstrated obvious spectral absorbance from ultraviolet to near-infrared spectra, which are successfully performed during the SLS process in Lunar 1.0. The 3D printing technologies are constantly improved by adjusting the parameters of laser process and mechanical movement. The morphological features of 3D printed samples, including surface and porosity are investigated by using SEM. The evaluation of size and micro-hardness tests are also conducted to reveal the printing qualities of samples. The EDS and XRD results characterize the elements and components of 3D printed samples. Obviously, the strong heating process by laser source in Lunar 1.0 has a great impact on materials, because the complex multicomponent materials and solid state reaction in high temperature by SLS process for regolith simulants and ilmenite. However, this influence of heat treatment by laser source is quite different from continuously thermal treatment for ceramics such as normal high temperature furnace. In the future, the research for 3D printing of lunar regolith simulants and ilmenite powders for hypothetical brick in vacuum and low gravity will carry out for approaching the extreme manufacturing environment on lunar surface.
Multi-photon laser lithography (MPLL) is an economical maskless means for high resolution and intrinsic three-dimensional micro/nanostructures fabrication. Here, we report MPLL of AR-N 4340 photoresist, and a spatial resolution of 40 nm is obtained. The relationships between laser parameters and line morphologies are systematically investigated. In the MPLL process, standing wave interference generated by the reflected light from photoresist/air interface and the incident light could greatly influence the bonding capacity between the fabricated lines and glass substrate. Therefore, lines with width smaller than 150 nm can be easily taken away in the development process. In order to obtain line with higher resolution, two rectangular photoresist plates were fabricated for immobilization of the fabricated lines, and a nanoline with a feature size of 40 nm was achieved between them through carefully adjusting the incident laser power. This work is one of the evidences for high fabricating resolution characteristic of MPLL, and it exhibits the potential for fabricating high resolution semiconductor and electronic micro/nanostructures.
Additive manufacturing of metal parts in space is one of the potential means to realize on-orbit maintenance of aircraft. However, the basic phenomena such as the rapid melting and solidification behavior of metallic materials under the action of high-energy beams in space are unclear. It is necessary to observe those phenomena and reveal basic laws through space experiments. Therefore, an experimental platform for rapid melting and solidification of metal materials is developed. There are two parts included in this platform. A detailed design of the manufacturing system in space is described at first while the in lab experimental system on the ground is introduced also. In order to simulate the vacuum environment in space, a vacuum chamber is used to contain the core unit of the experimental system. Laser is used to melt a metal wire during the experiment while a positioning stage is adopted to shape the melted wire. The melting and solidification process is controlled automatically while it is monitored by a machine vision system at the same time.
Selective Laser Melting is a rapid manufacturing technology which produces complex parts layer by layer. The presence of thermal stress and thermal strain in the forming process often leads to defects in the formed parts. In order to detect fabricate errors and avoid failure which caused by thermal gradient in time. An infrared thermal imager and a high speed CCD camera were applied to build a coaxial optical system for real-time monitoring the temperature distribution and changing trend of laser affected zone in SLM forming process. Molten tracks were fabricated by SLM under different laser parameters such as frequency, pulse width. And the relationship between the laser parameters and the temperature distribution were all obtained and analyzed.
F-theta lens is an important unit for selective laser melting (SLM) manufacture. The dual wavelength f-theta lens has not been used in SLM manufacture. Here, we present the design of the f-theta lens which satisfies SLM manufacture with coaxial 532 nm and 1030 nm~1080 nm laser beams. It is composed of three pieces of spherical lenses. The focal spots for 532 nm laser and 1030 nm~1080 nm laser are smaller than 35 μm and 70 μm, respectively. The results meet the demands of high precision SLM. The chromatic aberration could cause separation between two laser focal spots in the scanning plane, so chromatic aberration correction is very important to our design. The lateral color of the designed f-theta lens is less than 11 μm within the scan area of 150 mm x 150 mm, which meet the application requirements of dual wavelength selective laser melting.
Femtosecond lasers have been found suitable for maskless photolithography with submicron resolution, which is very attractive for solving the problem of high photomask cost. Direct femtosecond laser writing of lithographic patterns is reported with submicron feature width on thin positive photoresist film. We use a scanning electron microscope to investigate the feature sizes of femtosecond laser lithography, which are determined by the incident laser power, the number of scan times and the substrate materials. Submicron T-shaped gates have been fabricated using a two-step process of femtosecond laser lithography where the gate foot and head can be separately defined on positive AZ4620 photoresist film. This work has led to the stable fabrication of sub-300 nm T-gates on the samples of GaN on sapphire substrate and AlGaN/GaN on Si substrate.