Research On The Mechanism And Deformation Behaviour Of Laser Bending Of Shipbuilding Steel Plate

Presently, a typical technology of plate bending by flame and water is adopted for ship-hull curved plate forming in shipbuilding industry, which is called line heating abroad. It is very difficult to realize controlling the flame accurately. The line heating technology depends on experienced workers by manual work in shipyards. Laser bending is a new and flexible sheet metal forming technology, which utilizes the non-uniform thermal stress induced by laser irradiation to form sheet metal. Because the energy density is high and laser beam is highly controllable, the laser bending technology is more suitable for accomplishing the automatic forming of steel plate. The latent application of laser bending is capacious in shipbuilding field. In recent years, the finite element method (FEM) has become the main means to study the laser bending process. The laser bending process can be analyzed broadly and exactly by simulation. The forming mechanism and deformation behaviour can be studied thoroughly.Ship-hull plate is usually manufactured by line heating using steel plate of 8~20mm thickness. Laser bending of shipbuilding steel plate has been studied by experiment. But the mechanism and deformation behaviour are not investigated thoroughly. In this paper, the numerical simulation method is adopted to investigate the laser bending process, and some experiments are carried out to validate the model. The laser bending of shipbuilding steel plate is simulated by finite element software MSC.Marc. The mechanism and deformation behaviour for different parameters are studied profoundly. And the ANN (artificial neural networks) system is constructed for predicting the bending angle. These investigations can provide theoretical basis for the application of laser bending in the field of shipbuilding. The main research contents and results are as follows:(1) A three-dimensional coupled thermal-mechanical FEM simulation for laser bending of shipbuilding steel plate is presented. The temperature dependency of thermal and mechanical properties of the material is considered. The variation of temperature and bending angle has been obtained from the simulation. The measurement of real-time temperature and bending angle is carried out. The simulation results are in agreement with the experimental results. The validation of the model is testified.(2) The forming mechanism is investigated for laser bending of shipbuilding steel plate under given laser parameters. Based on the analysis of temperature field, stress field and deformation field, the laser bending process of shipbuilding steel plate accords with temperature gradient mechanism. The characteristic of upsetting mechanism can be observed from the distribution of the strain field. It can be concluded that the forming mechanism is the combination of temperature gradient mechanism and upsetting mechanism, named as coupling mechanism. The temperature, stress and strain along the scanning path on the top surface are changed most intensely during laser bending process. The effect of warping deformation, bending deformation along the heating line and thickness increment of heating area is insignificant on the forming accuracy.(3) The deformation behaviour of laser bending for shipbuilding steel plate is investigated under different laser process parameter, geometrical dimension and scanning path. The effect of laser process parameters can be analyzed by energy density and the time of absorbing the energy. Under the limitative temperature, the bending angle is increased with the increase of laser power and decreased with the increase of scanning velocity and laser spot. Amongst the geometric parameters, the thickness of steel plate is the main factor influencing the bending angle. The bending angle is decreased with the increase of the thickness. The deformation behaviour of repeating scanning along the same path is relation to the laser process parameters. The bending angle is affected insignificantly by the scanning space along the different scanning path.(4) Based on the validated simulation results by the FEM model, an improved BP algorithm is used to construct the ANN system for predicting bending angle according to the process parameters and the thickness of the steel plate during the laser bending process. The bending angle and peak temperature are predicted using the trained ANN System, and exact results are obtained.