The Optimization Design Of Cooling System In Hot Stamping Dies

Ultra-high strength steel hot forming technology is an advanced automotive lightweight technology, which can improve the passive safety performance of automotive significantly. This technology is energy efficiently and it has great advantage in producing the complex-shaped auto parts.Due to the requirement of cooling efficiency, temperature uniformity, and thermal fatigue life, the design of cooling system in hot forming dies is very important. The shape of cooling duct, overall arrangement, and the leak tightness are the key factors for cooling system design. This thesis focuses on the optimization design of cooling system. A coupled simulation method for hot stamping process was established and an optimization procedure based on the coupled simulation method was established. This thesis takes a big step forward for the investigation of hot forming simulation and provides an efficient tool for the manufacturing technique.In order to make the simulation and the subsequent optimization procedure reliable, several key physical parameters have been investigated in advance such as the temperature dependent heat transfer coefficient between the blank and the die (take temperature, oxide scale thickness, and contact pressure in to consideration), the convection coefficient between the cooling coolant and the duct wall (take velocity, diameter of duct, and heat flux in to consideration), and the strain-stress relationship of blank under high temperature (take temperature and stain rate in to consideration).Based on the reliable parameters and numerical tools such as ABAQUS and FLUENT, a thermal-mechanical-transformation coupled simulation system was established. A U-shape hot forming die with cooling system was built to verify the temperature evolution and spring-back in hot forming process. The results of coupled simulation and experiment show a good agreement.At last, an integral optimization procedure for cooling system was established. After optimization, the overall cooling efficiency and temperature uniformity show great improvement.