Analysis of Forming Regularity in Line Heating Process for Curved Hull Plate by Considering the Plate Deflection

Abstract

Nowadays in most shipyards, line heating techniques are widely used in the forming process of hull plates. The precision and efficiency of the process are greatly influenced by the determination of technical parameters, including heating length, heating velocity, and the arrangement of heating line. Previous studies on this, which considered only local shrinkage, produced large errors in the calculation of thick and large curvature plates because the whole deformation was ignored. In this article, new mathematical formulas are proposed to indicate the relationship between the whole deflection and shrinkage during the plate-forming process by line heating. The numerical models were established based on the thermoelastic plastic finite element method considering the deflection. The reliability of the numerical models was verified by the comparison of temperature fields and displacement. Based on the analysis of forming regularity, a new concept named influence factor of deflection (IFD) was proposed from the analysis between deflection and shrinkage. The formulas were derived, which establishes the relation between the IFD and technical parameters. Finally, the experimental results showed that the relative percentage error is 5.13% for IFD, and the forming formulas were verified. The research lays a foundation for the technique of parameter prediction of thick and big curvature plates considering the deflection. 1. Introduction The procedure of lofting, marking-off, pretreatment of steel plates, cutting, and welding has been automated in shipbuilding. Hull plate forming is the bottleneck of shipbuilding. There are numerous curved hull plates that need to be formed within the shipbuilding industry. Precision and efficiency are the technical difficulties in hull plate forming. It is very important to realize the automatic forming of curved hull plate. Line heating is an important method in hull plate forming, which mainly relies on the experience of the workers (Seong et al. 2013). The general processes are as follows. First, the technical parameters of hull plate forming are obtained based on the workers' experience. Then, hull plate forming is carried out manually by the workers. Last, plate forming quality is detected by using detection templates or a detection box. If plate forming cannot meet the requirements of the standards, the workers need to reform the plate, until it can meet the requirements. These procedures cause low efficiency and great fluctuation in forming quality. Therefore, it is essential to perform automatic line heating research.