Feasibility of Multipoint Press with Continuously Divisional Forming for Double Curvature Plates in Shipbuilding

Abstract

This article introduces a mechanical forming technique using a set of multipoint press forming (MPF) steps to obtain a curved hull plate. Given only the geometry of the desired surface, the integrated MPF system can generate the punch strokes required by various geometries of hull surfaces without the need for solid dies. The divisional MPF-forming technique can form double-curvature surfaces since the discrete die surface is constructed by changing the strokes of the double-sided reconfigurable multiple presses. The spring-back phenomena after unloading can be successfully compensated for by a combination of finite element analysis (FEA) and the displacement adjustment method. The deformation history of a moving plate on each division was simulated while carefully considering the movement toward a contacting boundary. The displacement adjustment iterates the calculation of punch strokes based on the deformed geometry simulated by FEA, which was used to simulate the spring-back of the plate. The strokes are determined by an iterative process of sequential pressing. A nonlinear shell element was used to deal with the elasto-plastic state and contact problems at the tool-metal interfaces. The appropriate stroke is calculated for each punch for both the initial and corrective forming processes. Experiments were performed to validate the configuration of the spring-back compensation, divisional forming and the integrated system. The predicted punch stroke in the displacement adjustment shows good agreement with the experimental results. 1. Introduction The bow and stern sections of a ship have double-curvature surfaces, whereas the parallel midship section is characterized by flat and cylindrical plates. Double-curvature surfaces are currently formed using the line heating method, in which the forming quality and geometrical precision depend on the thermal elasto-plastic deformation behavior. Gas-flame and high-frequency induction heating have been successfully used to provide the heat needed for thermal bending (Shin et al. 2003; Shin & Lee 2002; Nomoto et al. 1990; Jang et al. 2002). However, it is difficult to control the residual deformation of thermal bending because it is not easy to control the plastic strain distribution, which is coupled with the heat input.