Aluminum hulls, which are preferred in the marine industry due to their durability, corrosion resistance, and lightweight properties, face serious challenges due to thermal deformation during welding. This study aims to predict and minimize transverse deformations due to welding sequences for a transverse model in the lower part of an aluminum hull. To predict deformations, heat source dimensions obtained from actual weld beads were used as simulation conditions, and various welding sequence conditions were simulated through the developed finite element method (FEM). The simulation results were compared with actual deformation measurements to verify their reliability, and the optimal welding sequence which minimized deformation was derived. The simulation results show that by changing the welding sequence conditions, the maximum displacement can be reduced from a maximum of 52.1% to a minimum of 39.1%, and the effective plastic strain can be reduced from a maximum of 19.6% to a minimum of 4.8%. These results show that adjusting the welding sequence conditions can significantly improve structural integrity by minimizing deformation. The results of this study suggest that the control of the welding sequence can be used to reduce the deformation of aluminum hulls and promote a more sustainable marine industry with improved quality.

High-density polyethylene (HDPE) has emerged as a promising alternative to fiber-reinforced plastic (FRP) for small vessel manufacturing due to its durability, chemical resistance, lightweight properties, and recyclability. However, while thermoplastic polymers like HDPE have been extensively used in gas and water pipelines, their application in large, complex marine structures remains underexplored, particularly in terms of joining methods. Existing techniques, such as ultrasonic welding, laser welding, and friction stir welding, are unsuitable for large-scale HDPE components, where extrusion welding is more viable. This study focuses on evaluating the impact of key process parameters, such as the preheating temperature, hot air movement speed, and nozzle distance, on the welding performance of HDPE. By analyzing the influence of these variables on heat distribution during the extrusion welding process, we aim to conduct basic research to derive optimal conditions for achieving strong and reliable joints. The results highlight the critical importance of a uniform temperature distribution in preventing defects such as excessive melting or thermal degradation, which could compromise weld integrity. This research provides valuable insights into improving HDPE joining techniques, contributing to its broader adoption in the marine and manufacturing industries.

To effectively use aluminum, which is inherently weak under heat, as a material for hull construction, it is crucial to precisely predict the thermal deformation in the weld zone. Most studies employing finite element (FE) methods to predict thermal deformation due to welding typically use estimated heat source conditions based on the results of the weld. However, these estimated values can differ significantly from the actual welding conditions. In this study, we investigated whether using the actual shape of the heat source, rather than an estimated value, can serve as a reliable condition for analysis in predicting thermal deformation. This prediction is essential for minimizing deformation in the fillet welds of an aluminum hull. To compare deformation outcomes, Al 5083, commonly used in hull construction, was selected as the base material. The thermal deformation of aluminum hull fillet welds, welded using the Cold Metal Transfer (CMT) welding method, which reduces heat input, was measured. The simulation results demonstrated similar deformation trends, with discrepancies ranging from a minimum of 0.02 mm to a maximum of 1.4 mm when using actual welding conditions and heat source shapes. The results of this study confirm that the actual heat source shape can be utilized as a reliable condition for predicting thermal deformation in aluminum hull welds. The aim is to contribute to the improvement of aluminum hull manufacturing quality by providing essential data for establishing welding conditions and minimizing deformation.

High-density polyethylene (HDPE) has attracted attention as an alternative material for marine structures because of its chemical resistance, processability, and recyclability. However, internal pores formed during extrusion welding can reduce weld quality and mechanical performance. This study investigated pore formation mechanisms in HDPE extrusion welds by considering material throughput, filler wire storage condition, and artificial defect volume fraction. Porosity increased from 0.06% to 0.37% as material throughput increased from 0.96 to 2.00 kg/h and slightly decreased to 0.33% at 2.60 kg/h. Under these process conditions, tensile strength changed within approximately 1.49%, whereas elongation decreased more clearly with increasing porosity. In contrast, residual surface moisture on the filler wire caused severe pore formation and reduced tensile strength by approximately 55.53%. Artificial defect tests also confirmed that increasing internal defect volume directly reduced tensile strength. Overall, controlling material throughput and removing surface moisture are essential for improving HDPE extrusion weld quality.