Research On The Fracture Criteria And Numerical Simulation Of The Magnesium Alloy In Electromagnetic Sheet Forming

AZ31 is one of the magnesium-based alloys that are commercially produced and most commonly used. Although the ductility itself is not so bad, the press-forming of the AZ31 sheet is difficult at room temperature. The plastic formability of magnesium alloy sheet can be improved effectively by warm & electromagnetic hybrid forming. It is necessary to indicate the effects of the electric-force factors, the temperature and die parameters on the magnesium alloy sheet forming properties and the failure modes. As formability of magnesium alloys is highly dependent upon temperature and strain rate at elevated temperatures, a new approach of incorporating strain rate and temperature effects into a failure criterion needs to be developed, to correctly predict the fracture initiation in sheet forming processes. In sheet metal forming, the forming limit is generally determined by the onset of localized necking and predicted by the analyses of tensile instability or bifurcation phenomena. However, the conventional analytical methods are not applicable to AZ31 sheet. In the forming processes of AZ31 sheet, fracture occurs suddenly without any obvious necking phenomenon preceding the forming limit. AbstractThis article described the principle of electromagnetic sheet forming and research progress.Some failure models today used for determine failure in thin sheets were analyzed to compare their applicability and reliability in order to get the appropriate Fracture Criteria for electromagnetic forming of AZ31 sheet. According to the dynamic tension testing, quasi-static tensile testing and the FLD of AZ31,the fracture strain was taken into consideration in Johnson-Cook Fracture model based on J-C constitutive equations. The two failure criteria were developed based on the effective strain or damage parameters and both could be formulated as a function of Zener-Holloman parameter.Electromagnetic forming of magnesium alloy is a multi-parameter coupling process. the effects of those parameters on the deforming and sheet accuracy differ. Coils were distinguished and expatiated based on their configurations。and their typical applications were presented by demonstrations. Establish appropriate tooling model based on the research of this article. The uniform pressure coil was selected as tool coil and specifically designed. Electromagnetic forming process was analyzed based on loosely coupled method. ANSYS was used to calculate the transient magnetic forces acting on the sheet, which was then used as boundary conditions to model the high velocity deformation. The results showed the uniform distribution of magnetic forces in the most regions of the sheet, except for a slightly divergent appear due to the sheet edge effects.