Combination of Hot Forming with CRP and Rapid Cooling to Obtain Enhanced Formability in Thermomechanical Treatment
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Combination of Hot Forming with CRP and Rapid Cooling to Obtain Enhanced Formability in Thermomechanical Treatment Peter Birnbaum1, Markus Baumann1, Andreas Kunke1, Verena Kraeusel1 and Dirk Landgrebe1,2 1 Professorship for Forming and Joining, Technische Universität Chemnitz, Chemnitz, Germany. 2 Fraunhofer Institute for Machine Tools and Forming Technology IWU, Chemnitz, Germany. ABSTRACT In sheet metal forming, rapid cooling of austenitized steel and CRP (cushion-ram pulsation) results in an optimized formability. An analysis is conducted regarding the influence of a stepwise deep drawing process of manganese-boron steel 22MnB5, using an oscillating ramcushion motion at simultaneous cooling. The stops occurring in stepwise forming provide sufficient time for softening and recovery of forming properties. The microstructure can be adjusted by controlled cooling. In order to examine the newly developed process in more detail, FE simulation is applied. Thus, relevant process and material parameters can be determined. The considered values are required for profound experiments using the forming simulator BAEHR DIL 805 A/D. The softening behavior at defined forming temperatures due to CRP are examined. The experimental results of softening at distinctive temperatures provide a basis for the combined processes of stepwise hot sheet metal forming and simultaneous cooling. INTRODUCTION In metal forming, the combination of materials engineering and innovative press technology offers the opportunity of enhanced formability and adjusted component properties. In the considered case, the new press technology of cushion-ram pulsation (CRP) interacts with hot sheet metal forming. This kind of novel thermomechanical treatment becomes significantly relevant with regard to the production of high-strength structural parts of complex shape. The hot sheet metal is formed by new press motion profiles into its final shape while simultaneously increasing in strength due to quenching as a result of martensitic transformation. THEORY Innovative forming technologies The considered forming technology is based on the advantage of the new servo-driven spindle press technology which allows a high variability in motion of the punch and the cushion. The agility and precision in motion are essential benefits in comparison to conventional mechanical presses and hydraulic presses. The motion and speed of cushion and punch are individually programmable which enables the adjustment of a variable flange gap during the forming process. In the press hardening process the specimen is heated up to 950 °C with 10 min soaking time and subsequent transfer to the press. During forming the austenitized circular blank cools down which mainly depends on the temperature of the forming tool. A superposition of drawing and rapid cooling takes place. The ongoing development of the press hardening process considers an adjusted motion profile of the press. The developed process of cushion and ram pulsation (CRP) [1] consists of several steps in cushion and ram motion.
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