Production design based on strain as direct boundary method in ship block

Abstract

The shipbuilding industry is a large assembly with on-demand manufacturing and a consumer-leading technology development state. Therefore, it is impossible to create a standardized production process like general machine manufacturing. In addition, as a labor-intensive industry with a large proportion of human judgment and work, immediately responding to problems such as residual distortion occurring is necessary for the shipbuilding industry. Also, ship blocks are gradually heavier and larger to increase manufacturing efficiency by increasing dock efficiency. Therefore, an analysis procedure for huge structures is required to consider these characteristics of the shipbuilding industry. Since ship blocks gradually become thinner, standards for determining temperature boundary conditions of the strain as direct boundary (SDB) method are needed. Therefore, this work determined the heat-affected zone area for local and global welding deformation simulation by comparing the deformation prediction results according to the heat-affected zone consideration area with the experiment. In addition, ship blocks have many weld lines, and differences in final deformation occur due to differences in structural rigidity according to welding sequence. Therefore, this work decided the welding sequence by considering plastic properties in the welding area. Blocks that have been welded are assembled with other blocks at the target location through lifting, and line heating is performed before lifting for the assembly process. Line heating is a procedure that removes out-of-plane deformation by generating a residual strain in the area symmetrical to the welded area. However, as there is no standard for determining the magnitude of line heating for the assembly process, it depends on the judgment of the field worker. Therefore, this work determined the magnitude of line heating by comparing the local and global out-of-plane deformations according to the magnitude of line heating. Finally, after the lifting, the effect of removing the out-of-plane deformation according to the previously performed line heating disappears, and the line heating is performed again, which affects the entire process. Therefore, it is necessary to install stiffener materials to maintain the line heating effect. The design method of these materials is decided by considering the change in mechanical properties due to phase transformation and the plate theory.