Numerical simulation of lost foam casting process for ductile iron shell

Using proe software for three-dimensional modeling and ProCAST software as simulation analysis means, the casting process of ductile iron shell parts in lost foam casting was analyzed, and its lost foam casting process was optimized. Firstly, the mold filling and solidification process of nodular iron shell is simulated and analyzed, and the simulation results are compared with the actual production to verify the accuracy of the simulation results. Then, on this basis, the lost foam casting process of the shell is optimized. The following conclusions are obtained:

1) the existence of foam pattern makes the mold filling process of lost foam casting much different from traditional casting. Through the simulation analysis of mold filling process of lost foam casting ductile iron shell, it is known that the air gap pressure formed by the foam product pyrolysis product at the filling front of liquid metal hinders the flow and filling of molten metal, so that the filling speed of lost foam casting is obviously lower than that of conventional sand casting. On the other hand, the pyrolysis process of the foam pattern is an endothermic process, which makes the temperature drop of the liquid metal at the filling front more than that of the conventional sand casting.

2) the original lost foam casting process adopts the step gating system, which is divided into two layers to introduce metal liquid, the upper one gate and the lower layer two. It is hoped that the lower gate will introduce more metal liquid, so that the foam pattern will burn from bottom to top. The rising direction of the metal liquid is consistent with the direction of the gasification product of foam plastics, which is favorable for filling. Through the simulation and analysis of the mold filling process of the original lost foam casting process, it is found that the lower inner gate starts to fill when the mold filling is 50%, so the stepped gating system does not achieve the expected effect.

3) The original process adopts no riser design, and uses nodular cast iron graphite expansion effect and gating system for feeding. In the analysis of the solidification process of the original process, combined with the solid phase rate distribution diagram, solidification time distribution diagram and shrinkage porosity and shrinkage cavity distribution diagram, it is found that there are shrinkage porosity and shrinkage cavities on one side and large rotation parts of lost foam castings. Therefore, the feeding capacity of the original process is insufficient, and the feeding riser needs to be designed. It shows that although nodular cast iron has a certain self feeding ability, it is still necessary to design riser feeding for some small and medium-sized nodular cast iron castings.

4) Comparing the simulation results with the actual production results, it is found that the simulation results are basically consistent with the actual production results, indicating that the setting of initial conditions, boundary conditions, heat transfer conditions and other parameters is reasonable.

5) The original lost foam casting process was improved according to the simulation results and actual production results. The new process adopts top pouring system, cylindrical concealed riser, two pieces in one box, and the process yield is 67%.

6) The solidification process of the new process is simulated and analyzed. It is found that the lost foam castings gradually solidify from the bottom to the center of the riser, and the feeding effect of the riser is good. After solidification, there is no shrinkage cavity defect in the lost foam castings, and only a small amount of shrinkage cavity exists in the riser. Using the optimized process for actual production, the castings produced are of good quality and can meet the application requirements, which shows that it is feasible to optimize the lost foam casting process by using numerical simulation technology.

7) Analyzing the process of lost foam casting with ProCAST and guiding the actual production with the analysis results can not only shorten the trial production cycle of new products, save the manpower and material resources of trial production, but also improve the quality of lost foam casting and bring great economic and social benefits to the enterprise.

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