EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

In recent years advanced high-strength steels (AHSS) including dual phase (DP) and complex phase (CP) steels have been increasingly used in automotive lightweight design, as these steel grades may improve the crashworthiness without increasing the weight of car bodies. The good formability of AHSS makes them particularly suitable for deep-drawing applications. Hence, the present work investigates the influence of the drawing velocity and of the blankholder force on the formability of different AHSS grades with sheet thicknesses of 1-2 mm. Five typical drawing velocities in the range of 10-120 mm/s and five blankholder forces in the range of 0-1200 kN were considered. Deep-drawing experiments at semi-industrial scale were performed using a standard cross tool consisting of the punch, the die and the blankholder. The cross tool was equipped with a load cell, a distance sensor and an accelerometer for measuring the forming force and the die displacement as well as for detecting the crack initiation at the deep-drawn component during the process. The maximum drawing depth achieved without cracking of the component was considered as characteristic parameter that quantifies the formability. Thinning and strain distributions of crack-free components were determined using optical 3D scanning and forming analysis systems. The results of the experimental investigations were utilized for validating a numerical model of the deep-drawing process, which was built using the AutoForm R8 finite element (FE) software. This model included the actual elastoplastic properties of the investigated AHSS grades. In general, the maximum drawing depth was observed to decrease with increasing tensile strength, drawing velocity or blankholder force, respectively, but with decreasing sheet thickness. For drawing velocities below 60 mm/s, however, the investigated DP steels did not show any significant velocity influence.