高强度硼钢热冲压界面热交换系数实验与模拟研究
发布时间：2018-07-21 16:03
【摘要】：汽车零部件的高强度不但能够提高汽车的碰撞性能而且还能减轻汽车的重量，节能、环保、轻量化将会是未来汽车发展的新方向。高强度钢热冲压技术能够实现现代汽车轻量化和高强度的要求，这已经被国际汽车工业认可并且积极推行运用在生产汽车零部件上。 但是，高强度钢热冲压成形技术是一个非常复杂的过程，板料在进行热冲压过程中，板料与外界发生热辐射、热传导和热对流，材料的降温速度决定了相变组织并且能够影响成形件的性能。界面热交换系数能够表征板料与外界的热量交换能力，但是在热冲压成形工艺中板料与模具的界面热交换系数的研究还是非常有限的，，能够参考的资料也不多，所以本文将根据传热学对热冲压中板料和模具的界面换热系数进行模拟和实验研究。 本文通过研制实验装置，研究板料在不同压强下进行热冲压成形时板料与模具温度的变化，利用模拟软件模拟实验过程，最后通过优化软件反算出不同压强下板料和模具的界面热交换系数，具体内容如下： 1.将高强度硼钢板料放入加热炉里加热到奥氏体化温度后保温3分钟，然后把加热的板料快速移动到模具上，通过电子万能拉力机分别施加2MPa、6MPa、10MPa、15MPa和18MPa的载荷对板料进行冲压淬火，使板料内部组织由奥氏体转变成马氏体，通过热电偶测量板料和模具内部的温服变化，处理数据得出不同压强下板料与模具温度的变化曲线。 通过温度曲线可以得出：热冲压过程中板料温度逐渐下降，模具温度先升高，达到最高点后再下降，最后板料和模具的温度趋于一致达到平衡；随着板料和模具温差的减小，板料温度的下降速度也在不断的改变，进而说明板料与模具之间的界面热交换系数随着温差的改变而改变；在热冲压中，板料温度下降速度随着施加载荷的增大而增大。 2.利用有限元仿真软件建立实验模型，经过计算获得模拟结果。将模拟与实验数据通过优化软件进行优化，反算出各个载荷下板料与模具的界面热交换系数，绘制出压强-界面热交换系数关系曲线。 由曲线可以可知：随着压强的逐渐增大，板料与模具的界面热交换系数逐渐增大。压强低于10MPa时，随着压强的增大，界面热交换系数缓慢的增加，压强大于10MPa时，随着压强的增大，界面热交换系数增加速度明显加快，压强与界面热交换系数并不是简单的线性关系。压强在2~10MPa时，界面热交换系数平均值为513W/m2K，压强在10~18MPa时，界面热交换系数平均值为1285W/m2K。
[Abstract]:The high strength of automobile parts can not only improve the collision performance of automobile, but also reduce the weight of automobile, save energy, protect environment and reduce weight. It will be a new direction of automobile development in the future. Hot stamping technology of high strength steel can meet the requirements of modern automobile lightweight and high strength, which has been recognized by the international automobile industry and actively applied to the production of automotive parts. However, the hot stamping technology of high strength steel is a very complicated process. During the hot stamping process of sheet metal, heat radiation, heat conduction and heat convection occur between the sheet metal and the outside world. The cooling rate of the material determines the microstructure of the phase change and can affect the properties of the forming parts. The interfacial heat exchange coefficient can represent the heat exchange ability between sheet metal and the outside world, but the research on the interfacial heat exchange coefficient between sheet metal and die in hot stamping process is still very limited. In this paper, the heat transfer coefficient between sheet metal and die is simulated and experimentally studied according to heat transfer theory. In this paper, an experimental device is developed to study the change of sheet metal and die temperature during hot stamping forming under different pressures. The simulation software is used to simulate the experimental process. Finally, the interfacial heat transfer coefficient between sheet metal and die under different pressures is calculated by optimizing software. The specific contents are as follows: 1. The high strength boron steel plate was heated to austenitizing temperature for 3 minutes after heating in a heating furnace, and then the heated plate was moved quickly to the die. The sheet metal was punched and quenched by applying the load of 2MPa1 6MPa10MPa1 15MPa and 18MPa respectively by the electronic universal drawing machine. The internal structure of the plate is changed from austenite to martensite. The temperature change of the plate and die is measured by thermocouple, and the changing curve of the temperature between the sheet and the die under different pressure is obtained by processing the data. Through the temperature curve, it can be concluded that the temperature of the sheet metal decreases gradually during hot stamping, the temperature of the die rises first, then decreases after reaching the highest point, finally the temperature of the sheet metal and the die reaches a balance; with the decrease of the temperature difference between the sheet metal and the die, the temperature difference between the sheet metal and the die decreases. The decreasing rate of sheet metal temperature is changing constantly, which indicates that the interfacial heat exchange coefficient between sheet metal and die changes with the change of temperature difference. The decreasing speed of sheet metal temperature increases with the increase of applied load. 2. 2. The finite element simulation software is used to establish the experimental model, and the simulation results are obtained by calculation. The simulation and experimental data are optimized by optimization software, and the interfacial heat exchange coefficient between sheet metal and die under various loads is calculated, and the relation curve between pressure and interface heat exchange coefficient is drawn. It can be seen from the curve that the interfacial heat transfer coefficient between sheet metal and die increases with increasing pressure. When the pressure is less than 10 MPA, the interfacial heat transfer coefficient increases slowly with the increase of pressure. When the pressure is greater than 10 MPA, the increasing speed of interfacial heat transfer coefficient is obviously accelerated. The relationship between pressure and interfacial heat transfer coefficient is not linear. The average interfacial heat transfer coefficient is 513W / m2K when the pressure is 210MPa, and 1285W / m2K. when the pressure is 100.18MPa.
【学位授予单位】：吉林大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TG306
本文编号：2136046
[Abstract]:The high strength of automobile parts can not only improve the collision performance of automobile, but also reduce the weight of automobile, save energy, protect environment and reduce weight. It will be a new direction of automobile development in the future. Hot stamping technology of high strength steel can meet the requirements of modern automobile lightweight and high strength, which has been recognized by the international automobile industry and actively applied to the production of automotive parts. However, the hot stamping technology of high strength steel is a very complicated process. During the hot stamping process of sheet metal, heat radiation, heat conduction and heat convection occur between the sheet metal and the outside world. The cooling rate of the material determines the microstructure of the phase change and can affect the properties of the forming parts. The interfacial heat exchange coefficient can represent the heat exchange ability between sheet metal and the outside world, but the research on the interfacial heat exchange coefficient between sheet metal and die in hot stamping process is still very limited. In this paper, the heat transfer coefficient between sheet metal and die is simulated and experimentally studied according to heat transfer theory. In this paper, an experimental device is developed to study the change of sheet metal and die temperature during hot stamping forming under different pressures. The simulation software is used to simulate the experimental process. Finally, the interfacial heat transfer coefficient between sheet metal and die under different pressures is calculated by optimizing software. The specific contents are as follows: 1. The high strength boron steel plate was heated to austenitizing temperature for 3 minutes after heating in a heating furnace, and then the heated plate was moved quickly to the die. The sheet metal was punched and quenched by applying the load of 2MPa1 6MPa10MPa1 15MPa and 18MPa respectively by the electronic universal drawing machine. The internal structure of the plate is changed from austenite to martensite. The temperature change of the plate and die is measured by thermocouple, and the changing curve of the temperature between the sheet and the die under different pressure is obtained by processing the data. Through the temperature curve, it can be concluded that the temperature of the sheet metal decreases gradually during hot stamping, the temperature of the die rises first, then decreases after reaching the highest point, finally the temperature of the sheet metal and the die reaches a balance; with the decrease of the temperature difference between the sheet metal and the die, the temperature difference between the sheet metal and the die decreases. The decreasing rate of sheet metal temperature is changing constantly, which indicates that the interfacial heat exchange coefficient between sheet metal and die changes with the change of temperature difference. The decreasing speed of sheet metal temperature increases with the increase of applied load. 2. 2. The finite element simulation software is used to establish the experimental model, and the simulation results are obtained by calculation. The simulation and experimental data are optimized by optimization software, and the interfacial heat exchange coefficient between sheet metal and die under various loads is calculated, and the relation curve between pressure and interface heat exchange coefficient is drawn. It can be seen from the curve that the interfacial heat transfer coefficient between sheet metal and die increases with increasing pressure. When the pressure is less than 10 MPA, the interfacial heat transfer coefficient increases slowly with the increase of pressure. When the pressure is greater than 10 MPA, the increasing speed of interfacial heat transfer coefficient is obviously accelerated. The relationship between pressure and interfacial heat transfer coefficient is not linear. The average interfacial heat transfer coefficient is 513W / m2K when the pressure is 210MPa, and 1285W / m2K. when the pressure is 100.18MPa.
【学位授予单位】：吉林大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TG306
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