Springback prediction and compensation method for anisotropy sheet in multi-point forming

Multi-point forming (MPF) is widely used for three-dimensional (3D) curved surfaces, and the multi-point die (MPD) is reconstructed with the desired curvature and the compensated curvature which is caused by springback. Springback is affected by mechanical anisotropy of material in MPF. To predict the springback of anisotropy sheet in MPF process, the finite element models were established based on the three different yield criteria namely; von Mises, Hill's 48 and Yld2004-18p. To compensate the springback of anisotropy sheet, an algorithm with consideration of anisotropy for doubly curved sheet was proposed based on the results of the finite element simulation and the elastic perfect plastic biaxial bending model. The direct curvature adjustment (DCA) method and the Non-Uniform Rational B-Splines (NURBS) method are used to generate the die surface after springback compensation. The final shape of the workpiece is obtained by the execution of iterative compensation. The forming experiments were carried out and the results show that the anisotropic model is closer to the experiment than the isotropic model. Finally, the influences of blank thickness, part shape and forming radius on compensation accuracy were discussed to verify the applicability of the algorithm.

THE EFFECT OF MATERIAL MODELS IN THE FEM SIMULATION ON THE SPRINGBACK PREDICTION OF THE TRIP STEEL

In this work, the influence of material models used in the FEM simulation on the springback prediction is investigated. The interest of this paper is to extend the knowledge base regarding springback predictions in numerical simulation. The springback effect of a V-shaped sheet metal part made of TRIP steel, with a thickness of 0.75 mm was investigated. The bending angle was set to 90°. In the numerical simulation, Hill48 and Barlat yield criteria were used in combination with Ludwik's and Swift's hardening models. Achieved data from the numerical simulations were compared and evaluated with experimental test results. The experimental results showed the relation between springback and calibration force. The effect of specimen cut direction on the springback was smaller in comparison with the calibration force. The numerical results of the springback were not identical with the experimentally achieved springback values in most cases. Particularly, when a calibration force of 1 800 N was used in the simulation. The simulation results showed a good correlation between experimental and numerical results, when Hill48 and Barlat yield criteria were used in combination with Ludwik hardening law and calibration force F with the value 900 N was applied.

Prediction of springback in local bending of hull plates using an optimized backpropagation neural network

Springback is an inevitable problem in the local bending process of hull plates, which leads to low processing efficiency and affects the assembly accuracy. Therefore, the prediction of the springback effect, as a result of the local bending of hull plates, bears great significance. This paper proposes a springback prediction model based on a backpropagation neural network (BPNN), considering geometric and process parameters. Genetic algorithm (GA) and improved particle swarm optimization (PSO) algorithms are used to improve the global search capability of BPNN, which tends to fall into local optimal solutions, in order to find the global optimal solution. The result shows that the proposed springback prediction model, based on the BPNN optimized by genetic algorithm, is faster and offers smaller prediction error on the springback due to local bending.

Springback Prediction for Pure Moment Bending of Aluminum Alloy Square Tube

The springback phenomenon occurring during cold forming is the main problem affecting the dimensional accuracy of bent products, especially when bending thin-walled profiles, where there are significant changes in the cross-section geometry. This article presents the results of the analysis of the springback phenomenon occurring during shaping with a pure bending moment of square tubes with the cross-sectional dimensions of 21.5 × 21.5 × 1.8 mm and 25 × 25 × 2.5 mm made of aluminum alloy 6060. The springback characteristics were determined by defining the dependence of the springback coefficient on the set bending radius of the band. The values of the springback coefficient were provided by means of analytical calculations and numerical modeling, which considered changes in the moment of inertia caused by deformation of the cross-section occurring during bending of the pipes. A good agreement of the calculation results with the results of experimental tests was obtained. In addition, the stress state and the state of deformation, as well as the springback characteristics of square-section pipes were compared with the results obtained during bending of a solid bar with the cross-sectional dimensions of 21.5 × 21.5 mm.