Research On Springback Compensation Control Of Cold Forming Of Square Indenter For Hull Plate

With the continuous progress of China's comprehensive national strength,the development of science and technology plays a major role.With the continuous improvement of China's manufacturing standards,the shipbuilding industry also ushered in unprecedented innovation and soaring.At present,the production and processing of hull outer plate still adopts the mode of combination of water fire bending technology and manual control press,which is not only inefficient in production and processing,but also highly dependent on the production experience of workers,so the product quality standard is difficult to be unified.Multi-point forming is one of the main methods of sheet metal forming.In this paper,the finite element numerical simulation is established based on the "movable square non counter pressure head curved surface forming device",and the accuracy of the numerical simulation is verified by experiments.The theory of metal elastic-plastic forming,the theory of neutral layer movement,the theory of plate thickness reduction are discussed.The constitutive relation model,the basic equation of finite element,energy principle,algorithm model and other theories of plate are elaborated in detail.At the same time,the numerical simulation of the non opposite forming method of square indenter is studied,including the establishment of the model,the analysis of the mechanical properties of materials,the contact friction,the type of elements and the mesh division.The numerical simulation results are compared with the experimental results,and the model is improved and improved.Through theoretical research and numerical simulation,the influencing factors of sheet springback are analyzed,including sheet material,sheet forming shape,sheet thickness,foraming process and forming mode.Some rules are summarized and the influencing factors of sheet springback are classified into positive and negative ones.For two-dimensional cylindrical plate,according to the bending forming theory of medium thick plate and based on the stress-strain mathcmatical model of power function material,the curvature change before and after springback is obtained by using stress,strain,elastie modulus,plate thickness and target curvature radius;the curvature correction coefficient is determined by precise numerical simulation technology,and the curvature radius before springback is obtained by using numerical simulation and experiment The method is verified.For the shell with variable curvature,it is discretized into several cylindrical surfaces according to the curvature gradient of its geometric profile,and the compensation algorithm of springback curvature correction is used to obtain the array of compensation curvature.The discrete points are determined by the differential geometry algorithm of surface curvature based on the curvature data.A new envelope surface is formed by using the non-uniform rational B-spline curve(NURBS)surface reconstruction technology,and the algorithm is verified by numerical simulation.For the springback problem of three-dimensional sheet metal,this paper uses BP neural network to train the springback curvature calculated by numerical simulation and verify the accuracy.BP neural network can accurately predict the overprcssure curvature of the target curvature,so that the sheet can be formed once.The predicted shapes include ball plate,sail plate and saddle plate.The accuracy of the three shapes can be verified.The method used in this chapter improves the efficiency and precision of forming,and lays the foundation for the digital forming of sheet metal.