【摘要】：汽車零部件的高強(qiáng)度不但能夠提高汽車的碰撞性能而且還能減輕汽車的重量，節(jié)能、環(huán)保、輕量化將會(huì)是未來汽車發(fā)展的新方向。高強(qiáng)度鋼熱沖壓技術(shù)能夠?qū)崿F(xiàn)現(xiàn)代汽車輕量化和高強(qiáng)度的要求，這已經(jīng)被國際汽車工業(yè)認(rèn)可并且積極推行運(yùn)用在生產(chǎn)汽車零部件上。 但是，高強(qiáng)度鋼熱沖壓成形技術(shù)是一個(gè)非常復(fù)雜的過程，板料在進(jìn)行熱沖壓過程中，板料與外界發(fā)生熱輻射、熱傳導(dǎo)和熱對(duì)流，材料的降溫速度決定了相變組織并且能夠影響成形件的性能。界面熱交換系數(shù)能夠表征板料與外界的熱量交換能力，但是在熱沖壓成形工藝中板料與模具的界面熱交換系數(shù)的研究還是非常有限的，，能夠參考的資料也不多，所以本文將根據(jù)傳熱學(xué)對(duì)熱沖壓中板料和模具的界面換熱系數(shù)進(jìn)行模擬和實(shí)驗(yàn)研究。 本文通過研制實(shí)驗(yàn)裝置，研究板料在不同壓強(qiáng)下進(jìn)行熱沖壓成形時(shí)板料與模具溫度的變化，利用模擬軟件模擬實(shí)驗(yàn)過程，最后通過優(yōu)化軟件反算出不同壓強(qiáng)下板料和模具的界面熱交換系數(shù)，具體內(nèi)容如下： 1.將高強(qiáng)度硼鋼板料放入加熱爐里加熱到奧氏體化溫度后保溫3分鐘，然后把加熱的板料快速移動(dòng)到模具上，通過電子萬能拉力機(jī)分別施加2MPa、6MPa、10MPa、15MPa和18MPa的載荷對(duì)板料進(jìn)行沖壓淬火，使板料內(nèi)部組織由奧氏體轉(zhuǎn)變成馬氏體，通過熱電偶測(cè)量板料和模具內(nèi)部的溫服變化，處理數(shù)據(jù)得出不同壓強(qiáng)下板料與模具溫度的變化曲線。 通過溫度曲線可以得出：熱沖壓過程中板料溫度逐漸下降，模具溫度先升高，達(dá)到最高點(diǎn)后再下降，最后板料和模具的溫度趨于一致達(dá)到平衡；隨著板料和模具溫差的減小，板料溫度的下降速度也在不斷的改變，進(jìn)而說明板料與模具之間的界面熱交換系數(shù)隨著溫差的改變而改變；在熱沖壓中，板料溫度下降速度隨著施加載荷的增大而增大。 2.利用有限元仿真軟件建立實(shí)驗(yàn)?zāi)Ｐ停?jīng)過計(jì)算獲得模擬結(jié)果。將模擬與實(shí)驗(yàn)數(shù)據(jù)通過優(yōu)化軟件進(jìn)行優(yōu)化，反算出各個(gè)載荷下板料與模具的界面熱交換系數(shù)，繪制出壓強(qiáng)-界面熱交換系數(shù)關(guān)系曲線。 由曲線可以可知：隨著壓強(qiáng)的逐漸增大，板料與模具的界面熱交換系數(shù)逐漸增大。壓強(qiáng)低于10MPa時(shí)，隨著壓強(qiáng)的增大，界面熱交換系數(shù)緩慢的增加，壓強(qiáng)大于10MPa時(shí)，隨著壓強(qiáng)的增大，界面熱交換系數(shù)增加速度明顯加快，壓強(qiáng)與界面熱交換系數(shù)并不是簡單的線性關(guān)系。壓強(qiáng)在2~10MPa時(shí)，界面熱交換系數(shù)平均值為513W/m2K，壓強(qiáng)在10~18MPa時(shí)，界面熱交換系數(shù)平均值為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.
【學(xué)位授予單位】：吉林大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2015
【分類號(hào)】：TG306

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