With the development of Industry 4.0, additive manufacturing will be widely used to produce customized components. However, it is rather time-consuming and expensive to produce components with sound structure and good mechanical properties using additive manufacturing by a trial-and-error approach. To obtain optimal process conditions, numerous experiments are needed to optimize the process variables within given machines and processes. Digital twins (DT) are defined as a digital representation of a production system or service or just an active unique product characterized by certain properties or conditions. They are the potential solution to assist in overcoming many issues in additive manufacturing, in order to improve part quality and shorten the time to qualify products. The DT system could be very helpful to understand, analyze and improve the product, service system or production. However, the development of genuine DT is still impeded due to lots of factors, such as the lack of a thorough understanding of the DT concept, framework, and development methods. Moreover, the linkage between existing brownfield systems and their data are under development. This paper aims to summarize the current status and issues in DT for additive manufacturing, in order to provide more references for subsequent research on DT systems.

In this study, a laser remelting process was applied to the FeCrCoNiTiAl_0.6 high entropy alloy coating in order to improve the density and the surface quality of the coating. The coating was fabricated by high-velocity-oxygen-fuel (HVOF) technology. The microstructure and phase composition of the coating were investigated by scanning electron microscopy (SEM), energy dispersive X-ray spectrometer (EDS), X-ray diffractometer (XRD) and confocal scanning laser microscope (CSLM). Moreover, the wear behavior of the coating was evaluated by use of a ball-on-disc test. The coating was denser after laser remelting treatment by eliminating the previous lamellar structure. The microstructure of the laser-remelted coating exhibits two body-centered cubic (BCC) phases, which is different from the HVOF coating. In addition, aluminum oxide formed during laser remelting. Different from the wear mechanism of the HVOF coating, which comprised abrasion and fatigue, the major wear of the laser remelted coating was abrasion.

In this paper, laser welding Ni to Al using pulsed wave (PW) and continuous wave (CW) lasers was investigated. Weld quality and strength were evaluated in terms of cross-section examination, intermetallic compounds formation, microhardness, shear test and 90-degree peel test. The results show that deep penetration welding Ni to Al causes high melting pool temperature and severe material mixing, which could result in dominant AlNi₃ and AlNi intermetallics (IMCs) in the weld. These IMCs could significantly increase the hardness of the welding zone, but could also lead to the formation of defects, as well as reducing the ability to withstand the shear force and peel force applied to the weld. In comparison, using process optimization to maintain a shallow penetration or form a weld-braze joint, low melting pool temperature and minimum material mixing can be achieved. Hence, low-hardness Al₃Ni IMCs are prevalent in the weld. This helps generate a defect-free dissimilar weld joint to withstand higher shear force and peel force. The findings show promising applications, such as the battery management system of electric vehicles, in which joining a Ni adaptor to an Al bus bar is required.

In this study, deposition of Tribaloy T800 on cobalt-based L605 substrate using micro-laser-aided additive manufacturing (micro-LAAM) was explored. The micro-LAAM process was studied to achieve sound integrity of the deposited layer. The microhardness and microstructure of the deposited Tribaloy T800 layer were investigated. The results showed that the developed micro-LAAM process can achieve single-layer crack-free deposition of Tribaloy T800 onto cobalt-based L605 without pre-heating of the substrate. Surface roughness of Ra 8 μm was obtained, indicating that micro-LAAM can significantly improve the surface quality. Very high microhardness in the range of 818 to 1000 Hv was achieved. Cellular grains with very fine dendritic microstructure and Laves phase were observed in the deposited Tribaloy T800, which contributed to the high hardness. With all the results obtained, it can be concluded that it is feasible to deposit Tribaloy T800 on L605 substrate with micro-LAAM to achieve sound integrity and high hardness.