Experimental And Simulation Study On Heat Transfer Coeiffcient In Hot Stamping Of High Strength Boron Steel

High strength of auto parts can not only improve the car collisionperformance，but also reduce the weight of cars. Energy saving, environmentalprotection and lightweight will be a new direction of the future development tocar manufacturing. High strength steel hot stamping technology can realize therequest of the modern automobile for lightweight and high strength, which hasbeen recognized by the international automobile industry and actively pushed touse in the production of auto parts.But, high strength steel hot stamping technology is a very complicatedprocess. The sheet metal with the outside world will make thermal radiation, heatconduction and heat convection in hot stamping process, cooling speed of whichdetermines the phase change tissue and can affect the performance of the hotforming parts. Interface heat transfer coefficient can do it to characterization ofsheet metal heat exchange with the outside world, but the research of interfaceheat transfer coefficient between sheet metal and die is very limited in hotstamping forming process, and the reference data is relatively low to use. So I willdo experimental and simulation study on interface heat transfer coefficientaccording to heat transfer in hot stamping of high strength boron steel in thisarticle.developing experimental device to study the temperature changes of sheetmetal and mold under different pressure in hot stamping,and simulating processby simulation software, Finally calculating interface heat transfer coefficient between sheet metal and die under different pressure through simulation softwarein this paper. Specific content as follows:1. High-strength boron steel blank was heated to the temperature austenizedin a heating furnace. Then the hotted blank was transferred from the furnace to thetensile machine to be formed, and subsequently quenched by electronic universaltensile machine putting different load of2MPa,6MPa,10MPa,15MPa and18MPa in the closed die to obtain the martensite from austenitic, at the same time,temperature changes of the interior of the sheet metal and die was measured witha thermocouple. Temperature change curve of sheet and mold under differentpressure was obtained after processing data.It can be learned that sheet metal temperature gradually decline, and moldtemperature rise, the temperature of the mold would fall again when it got thepeak, sheet metal and die temperature would get balance finally. With thedecrease of the sheet metal and mould temperature, temperature drop rate of sheetmetal is also changing, then explain the heat transfer coefficient between theblank and mould will change with the change of the temperature difference. Italso can be concluded that temperature drop speed of sheet metal will increasewith the increase of applied load in hot stamping.2. Using finite element simulation software to establish the experimentalmodel and obtain simulation results after calculating. Put the simulation andexperimental results into optimization software to optimize, and inversecalculated interface heat transfer coefficient between the blank and die underdifferent loading. Drawing the pressure-interface heat transfer coefficient curve.From the curve,it can be obtained that interface heat transfer coefficientbetween sheet metal and mold will increase gradually with the pressure increasinggradually. With the increase of the pressure, the interface heat transfer coefficientincreases slowly when the pressure is lower than10MPa, but interface heattransfer coefficient increases accelerated significantly with the increase of thepressure when the pressure is greater than10MPa, the pressure and the interfaceheat transfer coefficient is not a simple linear relationship. The mean value ofinterface heat transfer coefficient was513W/m2K and1285W/m2K when thepressure was during2~10MPa and10~18MPa.