Air jet impingement cooling for hot stamping dies

Abstract

The strength of panel sheets can be increased by 2–3 times after hot stamping, and for high quality of hot stamped sheets, uniform cooling rate on the die face to quench the panel is needed. However, it is difficult for cooling water channels, commonly used for hot stamping dies, to dissipate heat evenly. In addition, dies are easily corroded by contact with water at high temperature. Thus, this study considers air cooling for the quenching process. The airflow can be applied to the sheet directly during the forming stage to cool and quench, eliminating difficulties with cooling channel design and providing more uniform cooling. Simulations and experiments were used to test the feasibility of air cooling for hot stamping with CSC-15B22 steel. A simple hot stamping tool with flat die face and either water or air cooling channels was used for testing, and results show that the both direct and indirect airflow can be used for hot stamping. With indirect air cooling, the cooling rate is sufficient for complete martensite transition, though the cooling rate is 40% lower than with indirect water cooling. To improve cooling efficiency of the air cooling system and obtain more uniform cooling, an air jet impingement cooling system (direct airflow cooling) was also tested. Results show that a similar cooling rate can be obtained in both indirect water cooling and the air jet impingement cooling. Thus, it is possible for air jet impingement cooling to provide hot stamping superior to water cooling. These results can be a reference for the design of new cooling systems for hot stamping dies.