SIMULATION OF SQUEEZE CASTING FOR FIBER REINFORCED CASTINGS

挤压铸造是生产纤维增强金属复合材料铸件最经济、最具发展前景的方法。研究的最终目的是开发一种能够模拟铸造过程的计算机软件，以节省开发复合铸件的时间和成本。主要研究结果如下：(1)利用CCD相机可以通过耐热玻璃模具直接观察金属模具的充型行为。研究发现，即使在对称型腔内，流动也不总是对称的。筒体和浇口内的流动对腔内的流动影响很大。当熔体温度较低且发生凝固时，流动比未凝固情况下的估计流动有相当大的变化。(2)利用低压型机器和水、汞、蜡直接观察了预坯填充模腔过程中的流体流动情况。结果表明，排气孔的位置对充填性能有重要影响。(3)开发了一种计算机模拟程序，分别假设在腔体和预制体中存在层流和达西流。该程序能较好地模拟观测结果。(4)虽然原计划考察纤维增强铝复合铸件的铸造组织，但由于预坯加热和防止预坯与模具之间的流动，很难生产出良好的铸件。此外，由于冷却速度非常快，因此不容易测量充模期间的温度变化。这项工作将在我们的实验室进一步进行。

The squeeze casting is the most economical and promising method to produce fiber reinforced metallic composite casting. The final research aim is to develop a computer software which can simulate the casting process to save time and cost of development of composite castings. Main results are as follows:(1) Mold filling behavior in a metallic mold could be observed directly through a heat-resistant glass mold by using CCD camera. It was found that the flow is not always symmetry even in a symmetric mold cavity. The flow in the cylinder and gate affects considerably the flow in the cavity. When melt temperature is low and solidification occurs, the flow considerable changes from estimated one for the case without solidification.(2) Fluid flow during filling a mold cavity with a preform was directly observed by using a low pressure type machine and water, mercury and wax. It was found that the position of vent is very important, affecting the filling behavior.(3) A computer simulation program where laminar and D'Arcy flows are assumed in the cavity and preform, respectively, has been developed. The program can rather well simulate the observed results.(4) Although it was planned to examine the cast structure of fiber reinforced aluminum composite casting, it was difficult to produce sound castings, because heating of the preform and preventing from the flow between the preform and mold. Further, it is not easy to measure temperature change during mold filling, because the cooling is very fast. This work will be continued further in our laboratory.