Study Of Temperature Fields In Hot Stamping Of High-strength Steel

With the development of the auto industry, the demands of automotive safety and energy and energy efficiency for people are increasing and high strength steel after hot stamping are used more widely for its high specific strength. Hot stamping technology is that the sheet is heated above to the austenitizing temperature for a period of time to guarantee sufficient austenite transform, then quickly transfer it to a mold for forming and cooling under a certain pressure, and last it is transformed into martensite. Because of the temperature field to join, hot stamping technology is relatively much more complex than cold stamping technology. The heat transfer process between the sheet and the mold is important for stress-strain field, temperature field and phase transformation. So the research of the heat transfer process and the effect of process parameters on the cooling process has important significance for the actual production of hot stamping.Firstly, take BR1500 HS high-strength steel and 5Cr Mn Mo tool steel as the objects, use homemade experimental apparatus to measure the temperature change of sheet and dies, use the least squares method to obtain the heat transfer coefficient of variation interface under certain pressure and a certain degree of oxidation, analysis pressure and oxidation in a separate and interactions situation impact on the mechanism of interface heat transfer coefficient, and finally get the interface heat transfer coefficient and pressure as well as the relational expression under thickness skin of the oxide conditions.Take U-shaped member for the study, based on the design principle of hot stamping die and the cooling system to determine the pipes diameter and the total number of cooling pipes, discuss die gap have an effect on sheet metal forming and cooling determine flow heat transfer coefficient.Based the calculated interface heat transfer coefficient and the convective heat transfer coefficient, according to the design of the U-shaped mold with UG for 3D models, import them into the DEFORM-3D to establish and analyze the temperature field by numerical simulation, discussion the law of the transfer between the sheet and the mold, study the impact of die clearance, cooling time, holding pressure, flow rate and the number of cycles on the cooling effect of the sheet, then initially get the reasonable cooling parameters: the holding pressure is 3MPa, the water flow rate is 3m/s and the holding time is 3s.Take BR1500 HS for material to conduct hot stamping test of U-shaped pieces, by measuring the temperature of the certain locations of mold during forming and cooling to verify the heat transfer law and reasonableness of the cooling parameters.