Numerical Simulation Of Filling Pattern Of Vacuum Counter-pressure Casting Aluminum Alloy Based On The Fluent Software

Vacuum counter-pressure casting (VCPC) is an advanced anti-gravity precision forming method, which realizes the controllable mold filling in the vacuum and solidification under high pressure; and has great advantage in the foundry of large complex thin-walled non-ferrous alloy precise castings. During the filling process in vacuum counter-pressure, the liquid metal flow pattern has a large impact on the forming quality of the thin wall casting. To master and control the filling process of vacuum counter-pressure casting is one of the key to obtain high quality castings. But during the filling process of vacuum counter pressure casting, especially the filling flow pattern is difficult to monitor. The numerical simulation methods can provide better forecast for filling pattern. Therefore, the numerical simulation of filling pattern of aluminum alloy vacuum counter-pressure has a certain theoretical and practical significance.This thesis bases on Fluent software platform, uses the Scheme language and UDF, achieves the vacuum counter-pressure filling module upon Fluent, and does numerical simulation to the vacuum counter-pressure casting filling pattern, to find out the influencing rules of vacuum and pressurization rate to vacuum counter-pressure casting filling pattern. The simulation results show that the vacuum degree has great influence on aluminum alloy casting filling pattern:with the vacuum pressure decreases, the molten aluminum alloy will has stronger filling ability and smoother filling pattern; with the vacuum pressure increases, misrun easily occurred and there were roll gas n wrapped gas and other defects in the casting. The effect of vacuum degree to the thin-walled aluminum alloy casting pattern increases gradually with decrease of the wall thickness; when the wall thickness is less than5mm, vacuum degree will produce very significant influence to the vacuum counter-pressure casting filling pattern. Pressurization rate also has a large impact on filling pattern of aluminum alloy vacuum counter-pressure castings. As the increase of pressurization rate, vacuum counter-pressure castings filling pattern of molten aluminum alloy gradually turning to reverse direction from forward direction and shifting to turbulent flow instead of smoothly filing. For these reasons, the writer establishes below mathematical model to indicate the influence rules of vacuum degree to vacuum counter-pressure castings:At the same time, the writer applies the vacuum counter-pressure castings technology to make a trial production of the complicated thin-walled aluminum alloy housing castings. The result indicates that when the vacuum degree is80Kpa and60PKa, the casting has many defects, such as misrun、roll gas、wrapped gas and so no; when the vacuum degree is20PKa, the aluminum alloy castings can be filled completely and defects such as roll gas and wrapped gas are obviously reduced, which satisfies the quality requirement of complicated thin wall casting.The numerical simulation predicted outcome of the mold filling is consistent with the actual result, which manifests the result of numerical simulation can provide efficient reference and basis to vacuum counter-pressure casting for the practical production and the forming process optimization of complicated thin-walled aluminum alloy casting.