【作者】 陈飞帆；

【导师】 卢德宏；

【作者基本信息】 昆明理工大学 ， 材料加工工程， 2011， 硕士

【摘要】 锭模是铸造生产过程中重要的设备。在浇注铸锭的过程中,锭模受到高温和热应力的作用,表面容易产生热疲劳裂纹而失效,因而热疲劳是锭模最常见的失效形式。热疲劳开裂不仅缩短了模具寿命,而且还降低了铸锭表面质量。因此,研究锭模在工作过程中的温度场、应力场及其变化情况具有重要的实用价值。仅通过实验的手段得到锭模温度场和应力场是非常困难的。随着计算机数值仿真技术的发展,使得锭模的温度场和应力场的计算机模拟成为可能。本文根据铅锭实际生产过程,首先通过对不同石墨形态的铸铁进行热疲劳实验确定铅锭模的材质,然后利用有限元法对铅锭模工作过程进行热-应力耦合模拟计算,以此为基础,最后对铅锭模的结构进行了优化。不同石墨形态铸铁的冷热循环热疲劳试验的结果表明：铸铁的微裂纹总是起源于石墨相,由微裂纹扩展形成的主裂纹通常是沿着石墨和两石墨相间最近的基体扩展；在20℃-650℃间的冷热循环条件下,球墨铸铁的抗热疲劳性能最好,蠕墨铸铁次之,灰铸铁最差。根据热疲劳性能结果,选择了球墨铸铁作为铅锭模具的材质。文中温度场和应力场数值模拟中锭模的热物性参数和力学性能均按QT600设定。论文分析了有限元数值模拟中关于温度分析和应力计算的有限元理论,并根据实际模型建立了凝固过程中的瞬态温度场及热弹塑性应力场的数学模型。通过ANSYS软件模拟计算出铅锭模工作过程的瞬态温度场,并通过实验验证了铅锭模关键点和铅锭中心位置温度随时间的变化,模拟结果与实验结果较为吻合。通过导入温度场模拟结果作为体载荷,模拟并分析了铅锭模在铅锭凝固过程中应力场的分布及变化,结果表明最大的应力出现在锭模两面相交处,据此推断出锭模在工作过程中容易出现疲劳失效的部位是锭模两面相交处。在斜度为20°的条件下,对壁厚分别为15mm、25mm、35mm和45mm的铅锭模的温度场和应力场进行模拟计算,得出壁厚为25mm的锭模的应力最小。在壁厚为25mm的条件下,对锭模斜度分别为8°、12°和20°三种情况进行应力场模拟,结果表明：在相同壁厚条件下,斜度对铅锭模的应力影响较小。综合考虑铅锭模的使用寿命、铅锭表面质量问题,最终确定铅锭模的壁厚为25mm,斜度为12°。更多还原

【Abstract】 Ingot moulds are important equipment in the production process of casting. The ingot molds are influenced by high temperature and thermal-stress during casting of ingots and easy to fail due to thermal fatigue and hot cracking, so, thermal fatigue is the most common failure modes of ingot molds. It not only shortens the mold life, but also reduces the surface quality of castings. Therefore, to study the variations of the temperature field and stress field of the mold during casting process has important practical value. However, it is difficult to get the temperature field and stress field just through experiment research. With the development of computer numerical simulation technology, it is possible to apply computer simulation technique to calculate the temperature field and stress field of ingot mold, so as to optimize the structure of ingot mold to control and ensure the quality of castings and prolong the service life of ingot mold, reduce production cost and enhance the competitive ability of enterprise. This paper first carried out thermal fatigue tests of different graphite shape of cast iron to determine the lead ingot mold’s material, then simulated the thermal-stress coupling of lead ingot mold in working process using finite element method based on the actual production process of lead ingots. On the base of this analysis, the structure of lead ingot mold was optimization.Thermal fatigue performance of different graphite contained cast iron was investigated by heat-colding recycle tests in the range of 20℃-650℃. The results show that micro-cracks always initiated at graphite phase during the thermal cycle process. The main crack often propagated along graphite and the matrix between two nearest graphite particles. The thermal fatigue resistance of nodular graphite iron is the best, vermicular graphite iron is moderate, and the flake graphite iron is the worst under the same heat-coding recycle condition. According to thermal fatigue test results, nodular graphite iron was choose as lead ingot mold’s material. So the thermal physical parameters of a nodular graphite iron, QT600 were chosen during next numerical simulations of the thermal field and stress field.The finite element theory about thermal analysis and stress calculation in the numerical simulation was reviewed. The mathematical of an ingot mold model of the transient temperature field and thermal elastic-plastic stress field in the solidification process was established according to actual process of a lead ingot product. Then, the transient temperature field of lead ingot mold during casting was simulated using ANSYS software. Temperature and its variation with time of key points of lead ingot mold and the center position of lead ingot were verified by experimental method, and the simulation results are identical with experiment. Furthermore, lead ingot mold’s stress field distribution and its variation in lead ingot solidification process were simulated and analyzed by the import temperature field simulation results as body load. The results shows that the maximum stress appears at two intersect surfaces. And so, it is inferred that the fatigue failure easily occurs at the intersect faces of mold.When the draft is 20 degree, temperature field and stress field of lead ingot molds wall thickness of 15mm,25mm,35mm and 45mm were simulated respectively, the stress of ingot mold whose wall thickness is 25 mm is the minimum. When the wall thickness is 25 mm, stress fields of lead ingot molds draft of 8,12 and 20 degree were simulated respectively. In the same wall thickness, the draft has little influence on the ingot mold stress. Considering the service life of lead ingot mold and ingot surface quality, and finally determined that the wall thickness of lead ingot mould for 25mm, draft of 12 degrees.更多还原