Springback Description And Compensation For Forming Of Doubly Curved Plate Based On Springback Ratio Matrix

Ship hull doubly curved plates are usually formed based on line heating technique,which has the disadvantages of low production efficiency,poor working environment,and high technical requirements for operators.A new approach of hull doubly curved plates forming arose due to the rapid development of discrete reconfigurable molds technique in recent years.This dissertation studies the key technologies of cold stamping for hull plate based on discrete reconfigurable molds with square press head technique,and researches some cores problems during the doubly curved plates forming such as springback description and compensation through the analysis of elastoplastic theory,finite element numerical simulation,and experimental methods,which provides a theoretical guidance for gradually replacing the traditional line heating forming method with the discrete reconfigurable molds technique.the main contents of the dissertation are as follows:（1）Based on the analysis of various sheet forming springback description methods,and according to the springback ratio of single-curvature plates,this dissertation first proposes two new concepts,springback ratio matrix and springback ratio feature value,for describing local points and overall springback of doubly curved plates respectively.The specific approach is to discrete doubly curved plates into grids corresponding to the discrete reconfigurable stamping punch,and use the two discrete directions of the mold to describe the springback of the doubly curved plates in both directions respectively.The springback ratio matrix is a matrix composed by springback ratios of a series of discrete point on the sheet at two discrete directions,which can express all discrete points’ springback in the plate.Springback ratio feature value is a mean value considering the curvature weight of every point based on springback ratio matrix,which describe the springback value of the whole plate.（2）The springback ratio matrix and the springback ratio feature value are proposed in this dissertation to describe the springback data of single curvature plates in the literature,and the conclusions are consistent with the literature.And then,a series of typical doublecurvature plates forming experiments are conducted by a ship hull three-dimensional CNC bending machine with discrete reconfigurable square press,and the springback ratio matrix and springback ratio feature value proposed in this dissertation are used.Comparing the data of sail-type plate and saddle-type plate with the same curvature sizes,it was found that the springback of saddle-type plate is less than that of sail-type plate.The reason is regarded as the coupling effect of doubly curvature during forming.The springback difference between sail-type plate and saddle-type plate were analyzed theoretically.The result consists with the experiment,which also explains the rationality and applicability of the springback ratio matrix and the springback ratio feature value for describing the doubly curved plate.（3）A new springback compensation algorithm based on springback ratio matrix is proposed.The compensation surface is fitted by fitting points which are calculated based on springback ratio matrix.This method is compared with a currently used iterative approximation springback compensation method,and it can be concluded that the springback compensation algorithm proposed had better compensation effect than the existing method.the forming accuracy of the proposed springback compensation algorithm is higher,which improves the accuracy and efficiency of the doubly curved plate forming.