The Research On Hot Forming Tool’s Cooling System Of HSS

Due to the demand for efficient, energy saving and improved safety inautomotive industry, high strength steel (HSS) is becoming more popular based on itspotential to reduce vehicle weight without affecting the structural performance of finalproducts. Hot stamping technology is used to form HSS,especially for ultra highstrength steel (UHSS). Hot stamping is a relatively new sheet metal forming processwhere the blank is heated above the austemitiaztion temperature to lead to theformation of austenitic microstructure, and then formed and quenched in the tool at acontrolled cooling rate. At the end of the cycle, the formed part has a fully martensiticmicrostructure with strength above1500MPa.The car body parts formed by hotforming technology is increasingly popular in automotive industry. Thanks to the finalhigh strength, the good adequate formability that blank exhibits at elevatedtemperatures, thinner and more complex sheet metal parts can be produced.Hot stamping is a complex manufacturing process where the microstructure andproperties of the final component are strongly affected by the cooling rate. A coolingrate of over27℃/s is necessary for a full martensite of HSS after forming. Thecooling rate which influence the final properties of the formed blank is dependence onwhether the design of cooling system is reasonable or not. In the quenching process,the fluid coolant which flows through cooling ducts in the die take away heat of die,which transfer from the formed blank to the tool, so the heat transfer efficiencybetween die and blank at high temperature and die and fluid coolant is very importentto get the full harden parts. The contact state and temperature difference betweenblank and die, the quenching pressure, and thermal conductivity of material will affectthe heat transfer from sheet to die.In this paper, cooling process of built-in cooling system of die was researched,based on relevant principles of heat transfer and fluid dynamics, and taking intoaccount the efficiency of the numerical simulation and calculation accuracy.Numerical model of high-strength steel hot forming process and quenching processwas established. Based on this numerical model and the key factors influencing the design of cooling system of hot forming die such as: flow velocity, the initialtemperature field of mold, the number of strokes on continuous forming condition,pressure, was studied. This work can provide an instructive advice about the design ofcooling system of hot forming and numerical simulation analysis of cooling process.