Study Of Springback For Ship Hull Plate In Cold Forming

Traditional line-heating forming combined with rolling forming model is the popular way for 3D ship hull plate forming in shipyards at home and abroad, which depends largely on manual operation and restricts the production efficiency. The CNC ship plate machine based on reconfigurable loose mould forming mechanism with square press heads, can be used to achieve effectively the hull plate of 3D surface by cold forming, which would make the automation and numerical control of ship plate forming come true. Springback is the main factor to decreasing shape accuracy in cold forming, so the springback prediction method and appropriate springback control technology are import ways to improve the forming accuracy, which are also needed by CNC ship plate machine.Based on the structural characteristics and cold-pressing forming load mode of SKWB-400 model prototype CNC ship plate machine, numerical simulation model for cold forming process is established, which is used to predict the springback of formed parts. In this work the key issues of the numerical model are discussed, such as equivalent transformation of square press head, material constitutive model, forming loading mode, solving algorithm, etc.The cold forming of spherical parts and saddle surface is taken as research object, the processes of forming are analyzed by the finite element method, the influence laws of plate thickness and curvature of formed plate, chosen as variables, to springback are presented, and the reliability of the simulation results is verified by the plate cold forming test accordingly. The research result shows that springback of hull plate is effected by thickness and curvature of formed plate significantly, and the laws of springback are different between spherical parts and saddle surface pieces. For spherical parts, springback values decrease with the increase of plate thickness and the increase of forming deformation, and the velocity of decrease turns to be reducing gradually. For saddle surface pieces, the springback tendency varies with the point location at the plate, which is depending on the co-action of forming deformation and gather order of the mold. Changing trend of springback obtained by research would be used as basis and reference of determination of springback control method.According to characteristic of adjusting figuration rapidly of modular surface and the springback rule obtained forward, trial and error method is presented. The related saddle surface cold forming experiment is carried out to checking the feasibility of trial and error method.The test results show that the accuracy of final shape of saddle surface satisfies the code requirement, after twice approximation bending. Finally, the relationship between plate springback tendencies and gradually approximation coefficient C used in trial and error method is to be discussed based on the springback simulation results of the spherical surface parts forward, and then an expression has been presented to calculate the optimized C based on the slope of springback trend line.