Application Of Numerical Simulation In The Bending Of Magnesium Alloy Extruded Profiles

The light-weighting of vehicle is one of the important developing directions in automobile industry, and the reduction weight of vehicle body plays a key role in the processes of light-weighting of vehicle. In order to lighten the vehicle body as well as improve the security conditions of vehicle, a new type of vehicle body, called the space frame structure, is being paid more and more attention by car manufactures. The key technology of producing space frame structure lies in how to achieve the high precision bending process of the profile. This paper dealt with elastic-plastic finite element analyses of the bending of magnesium alloy AZ31B square extrusions applying software ANSYS/LS-DYNA.Due to the great influences of constitutive model on the accuracy of the numerical simulation, the major work of this paper is to set up the constitutive model of the material. At room temperate, slipping dominates the magnesium alloy deformation in tension; while twinning dominates the magnesium alloy deformation in compression. Thus the mechanical property of magnesium alloy in tension does not coincide with that in compression. Therefore, setting constitutive models in tension and compression respectively is necessary.The three-point bending processes of extrusions were simulated by applying the constitutive models set up. It was found that the top part of square extrusion was compressed; while the bottom part was tensed. Consequently, two different constitutive models were applied. The accuracy of FEM simulations were validated through comparisons with experimental results. The research showed that the forming force, the collapse of the outside wall and the springback angle fit very well with results of laboratorial tests and simulations; the deviation of the sagging of the inside wall was significant due to ignorance of the anisotropy of the extrusions. The simulation results also showed that the fracture position can be forecasted effectively through analyzing the maximum shear stress in the forming process. In three-point bending process, the fracture zone was around the corner between the inside wall and the side wall.The most important factor of stretch bending, which is widely used in extrusion bending, is the magnitude of pre-stretch force. Thus, the extrusions under different pre-stretch forces were studied by applying the constitutive models, which were validated by three-point bending processes previously. The results showed that with the increasing of pre-stretch force the deformation of cross-section was severe and the angle of springback decreased. Simultaneously, the maximum shear stress also increased but the increment was slight.