Design of hot stamping tools and blanking strategies of ultra high strength steels

In recent years, the automotive industry is making an effort to reduce the vehicle weight in order to reduce the CO2 emission while maintaining high strength properties of vehicle components. For lightweight construction, the demand of ultra high strength steels is drastically increased. To increase the formability and reduce the high spring back, hot stamping with ultra high strength steel is becoming more popular in automotive industry. In hot stamping, blanks are hot formed and press hardened in a water-cooled tool to achieve high strength. Hence, design of the tool with active cooling system significantly influences the final properties of the blank and the process time. However, the achieved high strength causes severe tool wear at the blanking of the hardened parts in a serial production with conventional mechanical cutting methods. Because of high costs for repairing of the blanking tools, laser cutting has been necessarily used in almost all automotive industries as alternatives in spite of the high costs and long process time. In this paper, the systematic design method of the hot stamping tool is introduced. Subsequently, some latest results on the blanking of the hardened steels after hot stamping are presented.