Choon Man Lee

In underwater laser beam machining (ULBM), water provides a cooling effect by reducing the influence of the laser heat source, which makes ULBM more suitable for marking, cutting, and postprocessing than laser beam machining (LBM). Because the laser heat source not only affects the substrate temperature, but also heats the water, this study analyzes how the cooling effect occurs when water is heated. In this study, the heat-transformed zones in ULBM and heated underwater laser beam machining (HULBM) were improved by approximately 33% and 24%, respectively, compared to LBM at 400 W. In addition, the heat-affected zones in ULBM and HULBM improved by approximately 15% and 9%, respectively, compared to LBM. The hardness of ULBM and HULBM was higher than that of LBM. Based on these results, it was confirmed that water can reduce the effect of the laser heat source and improve the mechanical properties. Experiments will be conducted on the underwater laser beam machining of various substrates, such as Inconel718 and Ti-6Al-4V, in a future study. In addition, experiments will be conducted on the underwater laser beam machining of various substrates using a cooling system that can lower the temperature of water.

The superior deposition rates of Wire Arc Additive Manufacturing (WAAM) allow for the production of a substantial number of parts while reducing the time and cost associated with machining, and have attracted significant attention. This study focused the microstructural and mechanical properties of a bimetallic thin-wall composed of SS308L and Inconel625, manufactured using variable-pressure rolling WAAM. A detailed analysis of the cross-sectional microstructure of the bi-metallic wall of non-pressure cases revealed a columnar solidification structure. In contrast, the pressured case was dominated by equiaxed structures. The microhardness tests conducted on the bimetallic interface revealed a hardness range of 139–188 HV within the SS308L region, and a 187–222 HV hardness spectrum within the Inconel625 region. The bimetallic interface displayed no unexpected hardness variations. Tensile tests carried out in the vertical direction across the bi-metallic interface resulted in a localized failure at the 308L region. The range of ultimate tensile strength was between 539 and 585 MPa, the yield strength varied from 344 to 377 MPa, and the elongation measurements were found to be within the range of 37 to 44%. All test specimens showed a consistent pattern of ductile rupture upon fractographic inspection, with fracture occurring in the SS308L region.