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 this study, design for additive manufacturing (DfAM) of release agent injection manifold for hot forging has been performed to achieve weight reduction and flow path optimization. The weight reduction of 53.5% was achieved, thereby enabling the application of stainless steel 316L, which has high strength and corrosion resistance. Lightweight manifolds using Al-Mg-10Si and SUS316L materials were fabricated by PBF-type metal 3D printer. The feasibility test showed that mold life was improved by 14% by solving residual release agent problem. In addition, the flow path optimization results suggested that the flow standard deviation of each outlet dropped sharply from 264 to 75 ㎤/s. This approach demonstrated that DfAM for release agent manifold could be applied to increase mold life and improve product quality and productivity for hot forging.

Chemical mechanical polishing achieves surface planarity through combined mechanical and chemical means. The role of the chemical reaction is very important in a metal CMP like aluminum. The slurry used in aluminum CMP typically consists of oxidizers, a chelating agent, corrosion inhibitors, and abrasives. This study investigates the effect of oxalic acid as a chelating agent for aluminum CMP with H2O2. To study the chemical effect of the chelating agent, the two methods of a polishing experiment and an electrochemical analysis were used. Lastly, it was confirmed that the optimum concentration of oxalic acid significantly improved the removal rate and surface roughness of aluminum.