Research On Ship-hull Curved Plate Forming By Pure Line Heating

Presently, ship-hull curved plate forming generally adopts a typical technology of plate bending by flame and water in shipbuilding industry, which is called line heating abroad. Traditional forming method comprises two steps: firstly, the plane plate is rolled to be transverse bending deformation in short edge direction by using the three-roller bending machine. Then, the curved plate is transported to the line-heating workshop to be longitudinal shrinkage deformation by line heating. Thus, the plane plate is formed to 3D surface shape as designed. The two-step forming process including different forming technology is unsuitable for automatic forming process of ship-hull plate, and needs experienced and skillful shipwrights. Because of the spring phenomenon in the rolling process, it is difficult to control the appropriate over-bending magnitude in the rolling process.Based on the above problems, this thesis aims to investigate the process design method of forming plane plate to 3D surface plate by pure line heating technology without the mechanical rolling process. The pure line heating method not only accomplishes the automatic forming of steel plate, but also improves the forming quality by averting the above problems.The purpose of this thesis is to develop an automatic forming design system of ship hull curved plate. The thesis presents a method to change the two-step forming into line heating forming by using curvature analysis. Firstly, the ship hull plate is modeled by B-spline surface. The principal curvature of the plate to be formed can be calculated. The heating lines for bending can be obtained based on the idea of uniform bending angular deformation. Appropriate angular deformation magnitude can be given with the technical parameters of heating and deformation. Thus, the plate obtains the transverse bending forming by line heating. Next step, the plate with desired convex shape can be obtained by heating in the longitudinal edge while the saddle shape, in the middle of the plate. This is the whole forming process by pure line heating.The thesis develops a 3-D FEM simulation model of line heating which includes a nonlinear transient indirect coupled thermal-structural analysis. The results of calculation and experiment are consistent. Based on the analysis of experimental data, the thesis presents the volume power model, which reflects compositive effect of heat source parameters. And the thesis attempts to take this compound variable as independent variable in mathematical modelof technology parameters relation. Numerical simulation is used to analyses the relation between deformation and effect of parameters due to line heating. It is concluded that major effect parameters on transverse bending deformation are combustion gas flow, heating source velocity and plate dimension, while major effect parameters on longitudinal shrinkage forming are combustion gas flow, heating source velocity and heating lines length. Based on parametric study results, technical parametric data of the two kinds of forming process can be obtained by reasonable numeric simulation experiment. Thus, much of experiment measurement work can be saved.Based on technical parametric data, the mathematical model between technical parameters and deformation during line heating process is established. This mathematical model establishment is the core of line heating study. The mechanism of line heating process is complex. There are many factors affecting the ultimate deformation of the plate, and the relation is nonlinear. If each effect parameter participates in mathematical simulation model separately, a serial model needs to be proposed. Therefore, volume power of heat source is adopted as independent variable in line heating mathematical model. The relation between the volume power and residual deformation can cover many forming cases including multiple combustion gas flow and serial plate thickness. Afterwards, suitable heating line arrangement and corresponding deformation magnitude can be given according to these parametric data, and rigorous heating condition of these heating lines can be decided. In this way, an automatic forming design system by pure line heating has been developed for ship hull curved plate.Lastly, the thesis conducts an experiment of a small flat plate to testify the usability of angular deformation simulation equation during transverse bending forming of the plate. Measurement results of angular deformation are consistent with numerical calculation results. With measurement values of angular deformation as known quantity, the heat source velocity can be obtained inversely with the regression model of angular deformation. The calculation results show that the relative error is 5.4% between the calculation velocity and practical heating velocity. So this indicates that the calculated velocity meets the design requirements. Meanwhile, the experiment also explains that the angular deformation has specific scope in line heating process for flat plate. The scope of angular deformation can be obtained for other plate thickness by a serial of numerical calculation. These results show that the pure line heating forming design system of ship hull curved plate can provide the right scope of angular deformation and corresponding heat source velocity, and can acquire the appropriate heating lines arrangement for practical forming requirements. As for longitudinal shrinkage forming, the comparison of the whole heating information, between the values obtained by the regression equation given in this thesis and the technical parameters of the shipyard for real ship-hull plates,is conducted. The comparison results show they are the same. Therefore, the heating parameters given by forming design system by pure line heating in this thesis are feasible, and can be applied in practical ship-hull plate production.