铁合金干砂负压消失模铸造气隙形貌动态演变机理及数值模拟研究

Lost Foam Casting is an important green precision forming technology for cast iron with complex structure and parting difficultly. In the process of pouring, the pyrolysis gasification of the foam and negative pressure will form a multi-phase turbulent air gap between the metal front and the foam, which leads to the complex and variable flow of liquid metal, which is easy to produce gas and slag. To this end, numerical simulation of ferroalloy dry sand negative pressure lost foam casting air gap formation and topography dynamic evolution process will be studied to verify the Influence of air gap morphology on the law of liquid metal flow behavior. Firstly, the thermal pyrolysis mechanism of foam is studied, and the foam pyrolysis model under high temperature melt is established. Secondly, the quantitative characterization experiment of the Lost Foam Casting filling process is designed to obtain the temperature and pressure distribution of the air gap under negative pressure and reconstruct the dynamic morphology of air gap. Thirdly, the mathematical model of the multi-phase and multi-physics field of the dynamic evolution of the air gap morphology of the coupled foam pyrolysis model is established. Finally, the numerical simulation system is developed, and the dynamic evolution mechanism of air gap morphology under negative pressure condition is studied. The evolution of metal melt flow behavior during filling process is further elaborated. The results of the project will provide theoretical guidance for the design of defect prevention and casting process optimization for the Lost Foam Casting filling process.

消失模铸造是结构复杂、分型困难铁合金铸件的一种重要绿色精密成形技术。在其浇注过程中，泡沫高温热解气化与负压共同作用会使金属前沿与泡沫间形成多相紊流的气隙区域，导致液态金属流动行为复杂多变，易产生卷气、夹杂等缺陷。为此，本研究拟对铁合金干砂负压消失模铸造充型过程气隙的形成及动态变化过程进行数值模拟研究，以探明负压条件下气隙形貌动态演变机理。首先，研究泡沫多态吸热化学热解机制，建立高温熔体作用下的泡沫热解模型；其次，设计消失模铸造充型过程的定量表征实验，获得负压条件下气隙各相温度和压力分布数据并重构气隙动态形貌；再次，建立耦合泡沫热解模型的气隙形貌动态演变过程多相多物理场数学模型；最后，研发出消失模铸造数值模拟系统，并进一步探究负压条件下气隙形貌动态演变机理，探明其对高温金属熔体流动行为的影响规律。项目成果将为铁合金干砂负压消失模充型过程卷气夹杂等缺陷预防和浇注工艺优化设计提供理论指导。

消失模铸造具有生产结构复杂、分型困难铸件的优势，但浇注时泡沫模样受液态金属高温影响热解吸热，生成大量产物易形成多相紊流区阻碍充型、改变前沿金属成分，导致铸造缺陷的产生。为此，本研究对铁合金干砂负压消失模铸造中的泡沫热解过程进行了研究，通过实验与理论计算对典型泡沫材料EPS（聚苯乙烯）与St-MMA（聚苯乙烯-甲基丙烯酸甲酯共聚料）的热解热力学与动力学特征进行研究，探明了消失模泡沫热解反应机理；对充型过程铸件温度场、气隙的形成及动态变化过程开展了实验研究；对充型过程气隙的形成及动态变化过程进行了数值模拟研究，以探明负压条件下气隙形貌动态演变机理。首先，研究了两种消失模铸造用泡沫在有氧和无氧条件下的多态吸热化学热解机制，建立了高温熔体作用下的泡沫热解模型；其次，设计了消失模铸造充型过程的几种基准平板件并进行了充型过程的定量表征实验，获得了负压条件下气隙各相温度与气隙动态形貌演变规律；进而建立了耦合泡沫热解模型的气隙形貌动态演变过程多相多物理场数学模型；最后，研发出消失模铸造数值模拟系统。基于该系统，对消失模铸造典型箱体件铸造工艺进行了模拟与工艺优化，降低了铸造缺陷，提高了铸件合格率。项目成果为铁合金干砂负压消失模充型过程增碳缺陷预防和浇注工艺优化设计了提供理论指导。