Numerical analysis of hot deep drawing of din 27MNCRB5 steel sheets under controlled stretching
Document typeConference report
Rights accessOpen Access
Hot stamping has been widely studied and increasingly applied in the automotive industry. This process is characterized by its ability to stamp high strength steels, yielding products with high mechanical strength, thus reducing the weight of stamped components and therefore the vehicles weight. It also demands less energy because steel sheets are heated by induction, more efficient than electric furnaces. With controlled stretching it is possible to manufacture thinner stamped parts with high mechanical strength, therefore it is necessary to know the formability limits to prevent failure and achieve the largest possible thickness reduction. In this work the hot formability of DIN 27MnCrB5 steel sheets under stretching conditions was evaluated by numerical simulation with the finite element software Forge2008. The numerical results were compared to experimental results. Initially hot tensile tests were simulated to define the strain rate in different regions of the sample and to evaluate the deformation at fracture. For tests at 700, 800 and 900ºC it was found that the strain rates vary from 0.01 to 0.5 s-1. Experimental tensile tests were also carried out with the same conditions as simulated. Both simulation and experiments presented very similar results for the ultimate tensile strength, and therefore it was possible to assume the experimental fracture strain as a consistent input for the numerical models. With the results of the tensile tests, hot Nakazima tests were simulated to evaluate the highest dome which could be formed without failure risks caused by sheet thickness thinning. The simulation results were validated by experimental tests, and as a result, a new numerical strategy was elaborated to define the hot formability based on the plastic instability and necking localization as a function of the stamping temperature and blank dimensions.
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