Numerical Simulation Of Beads Filling Process In Lost Foam Casting

Lost foam casting, the new generation of precision casting process, is called to be the representation of advanced casting technology of 21th century. In lost foam casting (LFC) ,the foam pattern is the key qualification, and the beads filling process is quite crucial to ensure the high quality of the foam pattern. Filling without uniformity and denseness will cause various defects and affect the quality of the surface of the casting. The influential factors of beads filling process are realized in this research. And optimizing beads filling process, enhancing efficiency, decreasing waster and so on are obtained by the numerical simulation of beads filling process using computer. All of these are profoundly valuable for the theory and practical application.Based on molecular dynamics simulation, the Discrete Element Method (DEM) is established to simulate the flow of discrete particles. In the high dense particle phase, the collision processes of discrete particles are simulated by rigid sphere model which uses the optimized technology to reduce computer workload on the occurrences of searching collision. An universal program of simulating LFC beads filling process based on rigid sphere model is developed which can forecast movement law and character of foam beads in die cavity.By comparing the result of visual experiments with simulation results, the rationality of such physics concept and correctness of computational method can be tested, and further more, the force distribution on beads and movement mechanism of filling process will be analyzed. Since the movement flow of simulations is quite in accord with that of experiments, such numerical simulation then can be taken as a kind of effective method to analyze the filling process. What's more, using the existing software Arena-flow to simulate the process, and on the condition of two inlet to fill cavity, we can find that the simulation result of Arena-flow is also close to that of the method in this paper, which further ensures the correctness of DEM.In fact, the factors which affect the quality of foam patterns include molds, process control of expanding beads. Besides, bead filling process is also a crucial factor for the quality of patterns, for that the filling process is the basis of molding, and different molds should match respective filling process. Therefore, adopting numerical simulation method rather than conventional repeated experiment to optimize the filling process can improve efficiency and reduce cost greatly. Factors which may influence the filling process include the position of beads inlets, the amount and position of outlets, the filling pressure, choosing beads etc. In this paper, different filling processes are tested by numerical simulation adopting DEM, the results and analysis provide evidences of deciding the technological parameters in practical production.Cylinder with the complicated structure, large dimension, and uneven thickness of wall (the thinest thickness can be 3～5mm) is one of the most important part of an engine, and then the most difficult casting product. Thus, the best casting process to product engine cylinder should be LFC which uses several foam patterns glued to form a cylinder pattern for casting. How to rationally parting the pattern is then to be the key of gaining high quality products.In this paper, vertical parting and horizontal parting are combined to make sure that the structure of cylinder will not be deformed and the weight of the casting can also be reduced. When producing the foam pattern, some defeats such as inadequate filling, insufficient comapction of beads are apt to occur in the thin-wall part, which will surely affect the surface quality of casting products. By analyzing the factors of bead filling and optimizing technological parameters, the practical production is improved, and good filling process is acquired, especially in the thin-wall part and some corners of the mold. The improved process can gain qualified patterns and greatly reduce times of test, thus has a profound meaning on foam pattern production in LFC.