Development of an Interactive Simulation System for Die Cavity Filling and Its Application to the Operation of Low Pressure Casting Process

摘要

The purpose of this study is to develop an interactive die filling simulation system to assist the design and operation of the low pressure casting process. One of the keys to the success for the design and operation of the low pressure casting process is to obtain an optimal pressurization curve to avoid flow related defects while maintaining its productivity. The simulation system is developed based on the incorporation of a computational fluid dynamics technique; named SOLA-MAC, which has the capability of treating transient fluid flow problems with free surfaces. The analytical system incorporated with the necessary pre-processing and post-processing modules is housed on a popular personal computer. The accuracy and reliability of the filling simulation system is then verified by water model experiments which are also conducted in this study. The capability of directly predicting flow related defects such as gas/dross entrapment during the transient filling stage by using an air particle method is added in the simulation system. It is also made interactive by allowing the casting engineer to view the transient filling pattern and the corresponding gas entrapment situation on the computer screen, interrupt the execution of the program, change the casting operation, and restart the program from a previous instant. A process design algorithm is also proposed in this study that the casting is divided into several parts depending on their geometric characteristics and performance requirements. By taking advantage of the interactive capability of the system, the proper gate velocity to fill each and every part of the casting can be determined. In turn, the necessary pressurization curve can be determined. The developed system is tested on an automotive wheel casting made by low pressure casting process. The casting is divided into three distinctive parts. The proper gate velocity to fill each part is interactively determined by directly examining the filling pattern and its resulted gas entrapment condition. With the optimal combination of the gate velocity, the pressurization curve for the whole filling stage can be obtained. It is found that the pressurization curve for the variable gate velocity shows only small deviation from that of employing a constant gate velocity throughout the whole filling stage. It is consistent to the general knowledge in the low pressure casting industry that the casting quality is rather sensitive to the pressurization curve employed in the process.