Research On FLD Of IF Steel

As the third generation of deep drawing steel, IF steel is widely used in automobile industry for manufacturing some kinds of difficult forming parts with high deformation degree because of its excellent plastic deformation ability. The use of IF steels represents the level of a country's automobile industry to some extent. Although automobile industry in our country has had the fastest growing period, but it's still in a stage of rapid development, which means the automobile industry remained a larger demand on IF steel. The research of forming limit of IF steel helps make full use of the plastic forming properties, thus optimize the forming processing, it is of significance in improving the quality of automobile stamping parts.Forming limit is limit strain state under the premise of stability in the process of plastic deformation. It's one of the most important indicator measuring formability of steel sheet. Experiments for forming limit diagram are specified by the corresponding standard both at home and abroad, but it took huge amout of time and energy to design and preparation for samples, measurement of true strain. It's not convenient for application. Taking DX54D+Z as an example, through the study of forming limit, experimental and theoretical analysis and forming simulation, this paper discusss the a new way to get FLD efficiently through theoretical analysis and numerical simulation.In the aspect of theoretical analysis, the theory of the M-K groove, Logan-Hosford yield criterion and Rossard hardening equation are used to establish the mathematical model to predict the forming limit. Combined with Secant Method, programs are written in MATLAB to predict the forming limit of DX54D+Z. On this basis, this paper analyzed the impacts of different yield criterion, strain-hardening index, strain rate sensitivity and thickness inhomogeneity factor on result of theoretical predictions.In the aspect of forming simulation, using professional sheet forming finite element analysis software, DYNAFORM, to simulate standard experiment of Erichsen Test. The software doesn't have a criterion for instability so it can't tell when to stop the virtual FLD experiment. This paper analyzed different criteria and their scope of application, and the impact of process parameters are discussed.At last, the prediction of theoretical analysis and numerical simulation are compared with experimental FLD, it verify the feasibility of theory and simulation method and the correctness of the results. Providing a new way for parts manufacturers to get FLD efficiently in the production.