In this study, we investigated characteristics and mechanical properties of SKD61 repaired using the direct energy deposition (DED) process. Mechanical properties of the repaired product can vary depending on the base material and powder used in the DED process. To prepare for DED repairing for a damaged part, we conducted experiments using two different powders (H13 and P21). Experimental results showed that both powders were deposited without defects in the surface or interface between the deposited zone and the substrate. Hardness measurements indicated that the repaired region of the Repaired-H13 sample exhibited higher hardness than the base material, while the Repaired-P21 sample showed a sharp increase in hardness in the heat-affected zone (HAZ). Additionally, tensile test results revealed that the Repaired-H13 sample had lower tensile strength and elongation than the base material, whereas the Repaired-P21 sample demonstrated higher tensile strength and yield strength with a higher elongation than the Repaired-H13 sample. In case of Repaired-H13, it was confirmed that interfacial crack occurred due to a high hardness difference between the repaired part and the substrate.

Exteriors of structures (apartments, buildings, bridges, dams, power plants, etc.) are subject to deterioration and damage (cracks, rust, etc.), mainly due to thermal expansion/contraction and environmental humidity. The damages shorten the lifespan of structures and cause unnecessary reconstruction, increasing social costs. The existing damage maintenance methods, which are directly constructed by the workers, have problems such as reduced work efficiency, increased work cost, lack of timely maintenance, and high work risks. In this paper, a spraying device attached to a drone for active and flexible maintenance of structures is developed. To simplify maintenance, the device consists of a solenoid motor, detachable parts for maintenance agent, and a lightweight-designed frame, manufactured with a 3D printer. In particular, the lever mechanism that amplifies the pushing force of the solenoid motor is designed to spray the maintenance agent when a switch comes into contact with the exterior of the structure. The prototype of a spraying device is attached to a commercial drone (Mavic3, DJI) and tested for effectiveness in structure maintenance. It demonstrates successful, cost-effective maintenance of structural damages in less than 10 minutes.

In order to maintain parts critical to using 3D printing technology, it is necessary to provide the user with information about powders, equipment, processing conditions, and inspection methods, as well as 3D CAD models used as input files for 3D printing operations. In order to address this issue, this paper proposes a manufacturing condition retrieval system that provides the information necessary for the maintenance of parts important to using 3D printing technology. To accomplish this, we define a data structure that stores manufacturing condition information for 3D printers. Then, after analyzing the user"s requirements, we design the manufacturing condition retrieval system. Finally, we implement a prototype system, construct a database using sample manufacturing condition sheets, and perform data retrieval experiments.