FAN Hanjing, CHEN Haoming, ZHAN Zhiyuan, FENG Bocong, WANG Liang, WU Shanghua

(Guangdong University of Technology, School of Mechanical and Electrical Engineering,

Guangzhou 510006, Guangdong, China)

Extended abstract:

[Significance] In the face of high Earth-Moon transportation costs, the utilization of lunar in-situ resources is an important strategy to achieve long-term exploration of the Moon and the construction of lunar bases. The key to this strategy is to obtain local materials and in-situ transformation. However, real lunar regolith samples are scarce and precious, while it is difficult to be used in a large number of experiments. Therefore, domestic researchers have developed simulated lunar regolith materials based on the chemical composition and physical properties of real lunar regolith. The traditional molding process, such as dry pressing, injection molding, hot pressing and so on, are difficult to meet the preparation requirements of complex components. They not only have low molding accuracy, limited model freedom and long preparation cycle, but also cannot adapt to the special environment of the Moon. However, additive manufacturing technology has the advantages of high forming precision, complex and peculiar shapes and high material utilization rate, which provides key support for human beings to achieve the goal of long-term residence on the Moon and promote the breakthrough of deep space exploration technology.

[Process] This review was aimed to systematically summarize the research results of lunar soil simulant materials in the field of additive manufacturing, including Powder bed Melting (PBF), Fused Deposition Modeling (FDM), Direct Ink Writing (DIW) and Binder Jetting (BJ). PBF is formed by laser selective melting of lunar soil simulant powder. The laser process parameters, powder bed spreading uniformity and printing process are studied to solve the problems of insufficient melting and low sintering density. FDM takes the composite wire prepared by mixing the simulated lunar soil powder and thermoplastic polymer as the core raw material and focuses on the mechanical and thermal processing properties of the composite wire, the suitable extrusion temperature range and the continuous and stable extrusion process, so as to ensure the continuous forming and structural integrity of the simulated lunar soil green body. DIW takes the lunar soil simulant composite slurry as the forming medium, with the core focuses on the rheological properties of the slurry to solve the problems of easy sedimentation of lunar soil simulant particles and slurry extrusion. BJ focuses on the selection of adhesives and the matching of injection parameters, focusing on improving the structural strength of the green body and optimizing the subsequent post-treatment processes, such as degreasing and sintering. In addition, the research progress and advantages of VPP were summarized. VPP overcomes the problem that the powder is easy to float and difficult to capture in the weightless environment of the Moon. However, this technology leads to the problems of easy sedimentation of lunar soil simulant powder, uneven dispersion of slurry, low solid content, low mechanical properties of molded parts and the presence of ceramic defects. In order to solve these problems, researchers used ball milling process to reduce particle size of the powders, the powder modification to improve the compatibility of the powder and the resin, the introduction of dispersant to improve the dispersion of the powder and the sedimentation behavior of the slurry, the adjustment of the printing process to improve the dimensional accuracy and molding quality, and the optimization of the degreasing and sintering process to solve the defects of the ceramic parts and improve the performance, which well alleviated the difficulties faced by the light curing technology of the simulated lunar soil materials.

[Conclusion and prospects] At present, additive manufacturing has become the core technology for the mutual transformation of lunar in-situ resources and functional components, which can be used to prepare complex structural parts that cannot be produced by using the traditional forming methods. The continuous progress of VPP, as well as the in-depth exploration of powder properties, slurry formulation, printing parameters and debinding sintering process, has laid a solid foundation for the application of lunar soil simulant additive manufacturing. However, in order to give full play to the potential of additive manufacturing on the Moon, some key problems must be solved. Future research needs to focus on the following aspects: (1) strengthen the research of multiple environments and break the bottleneck of adaptation of the real lunar environment, (2) break through the technical shortcomings and realize the integration of material innovation and technology and (3) constructing a system that combines the performance and life required for Moon.

Key words: in situ resource utilization; lunar soil; additive manufacturing technology; vat photopolymerization