【作者】 赵永美；

【导师】 史金飞；

【作者基本信息】 东南大学 ， 机械电子工程， 2006， 硕士

【摘要】 某铝合金气缸盖铸造生产中,常产生开裂缺陷,为解决此问题,首先基于传热学理论和弹塑性理论,用ANSYS软件对缸盖建模,然后对铸造凝固过程进行仿真,最后根据仿真实验结果对冷却工艺进行优化。根据传热学理论和弹塑性理论,该铸件凝固过程中系统的温度和系统内能随时间有明显的变化,凝固过程的相变问题需要考虑凝固潜热,铝合金铸件凝固过程热分析属于非线性的瞬态的问题。在凝固过程中产生的铸造应力残余在铸件内,当残余应力值大于铸件的屈服极限时,就会产生裂纹。缸盖三维实体建模时,对关键部位计算影响很小的一些孔道、凸台等结构作了简化处理,通过布尔运算完成缸盖、浇冒口和砂芯之间的连接。利用ANSYS热分析功能,对铝合金气缸盖进行瞬态非线性温度场分析和计算机模拟仿真。选用热单元SOLID70对实体模型进行网格划分。假设铝合金固液两相密度不变,忽略由于固液两相容积变化而引起的对流,采用热焓法处理相变过程中的凝固潜热问题。忽略对系统影响很小且高度非线性的热辐射散热,考虑空气对流和砂子的热传导。热-力耦合过程的分析中,选用结构分析单元SOLID45,采用间接法,将温度场分析的结果作为体载荷施加在结构分析中,进行铸造应力场的分析,对凝固过程铸造应力进行计算机模拟仿真。根据温度场和应力场的分析结果,以落砂时间和对流系数为设计变量,以铸造残余应力为目标函数,对铸造过程进行了冷却工艺优化,提出采用合适的冷却方式和适当延迟落砂时间可以防止铸件裂纹的产生。更多还原

【Abstract】 During the casting process of Aluminum cylinder head, crack defect is often appeared. To solve the problem, entity model of cylinder head is established using the ANSYS software. Then the casting solidification process is simulated based on thermal theory and elastic-plastic theory. At last, optimization of the solidification process is conducted according to the result of simulation.According to the thermal-delivering theory and elastic-plastic theory, the temperature and internal energy of the system are significantly variant during the casting solidification process. Considering the latent heat of solidification, the thermal analysis about casting solidification process of the aluminum cylinder head is non-linear and transient. The casting stress is generated during the process. When the residual stress exceeds the yield stress, the bull crack is easily generated.The bulge and some holes which have little influence to the structure are predigested. According to casting technology diagram, the 3-D models of the cylinder head and the sand mould are established. Parts of the model are connected through Boolean operation.FEM(Finite Element Method)mesh is set up, using the SOLID70 element of ANSYS. The loads of air conduction and radiation are ignored. Taking the air convection, sand conduction, and the latent heat into consideration, the nonlinear-transient thermal analysis is solved. And the distribution of temperature field during the solidification process is obtained.The result of thermal analysis is set as the body loads. Using the SOLID45 element, the thermal stress analysis is solved. The distribution of stress field is obtained.Optimization of the solidification process is also done with ANSYS. The time of sand-removing and the convection coefficient are set as design variables. The thermal-stress is set as object function. The result shows that the generation of defect would be avoided if the time of sand-removing were postponed and the convection coefficient was increased.更多还原