Numerical Simulation Research Of Aluminum Alloy Piston Defects

Casting is the process which liquid metal fill the cavity, and then solidify with cold. Filling process and solidification process play a crucial role on the final casting quality, and have a direct impact on shrinkage, porosity, slag and other casting defects. Therefore, CAE software can simulate the casting mold filling and solidification processes, explore the liquid metal filling order and temperature changes in the filling process, explore solidification sequence in the solidification process and temperature distribution at various locations, do the analysis of defects formation mechanism and distribution situation in order to optimize the process parameters to improve the casting process, reduce the casting defect rates, and improve production efficiency.This topic uses gravity casting pump piston for solidification simulation study by Intecast CAE software, through analyzing shrinkage distribution and parameter change effect, to find the best gating system, pouring temperature and mold temperature. This topic uses die casting mower piston for filling simulation study by Flow-3D numerical simulation software, to find the best filling velocity parameter through analyzing porosity, slag formation and distribution mechanism.Considering the structural characteristics of the pump piston, the gating system, the top risers and side risers size were designed, bottom-gating system with riser and middle-gating system with riser is simulated, and the simulation results shows the best system was middle-gating system with riser. Based on the middle-gating system with riser, mold preheating temperature was selected 200℃,pouring temperature was chosen between 700-800℃, and then shrinkage distribution and volume was simulated. The simulation result shows the best pouring temperature is 780℃; pouring temperature was selected as 780℃,mold preheating temperature was chosen between 160～260℃,and then shrinkage distribution and volume was simulated.The simulation result shows the optimum mold temperature was 200℃.Based on the middle-gating system with riser, the mold preheating temperature 200℃,and the pouring temperature 780℃,we do the practical production, getting casting with good surface quality, no internal voids, and after three batches production cycle, shrinkage defect rate was always less than 5%, which achieves the desired objective.Considering the structural characteristics of mower piston, the process parameters were pouring temperature 680℃, mold preheating temperature 200℃, the filling speed selected six variables between 50～500cm, and then volume of entrained air and slag inclusion concentration was simulated on different filling velocity. Through analyzing the simulation results we found that, the smaller filling speed, the longer filling time, the more oxide produced by mold and high temperature alloy fluid reaction, and more importantly, the slag inclusion cannot be routed along the flow to slag package, so the more casting surface slag. The greater the filling velocity, the more liquid alloy filling the cavity when the gas involved, the more gas fell after a collision-type wall above the parcel, and cannot be discharged from the exhaust slot so the more pores appear inside the casting. When the test done die-casting experiments selectively on the filling velocity 100cm/s,200cm/s,400cm/s, results obtained from the piston can be found that, filling velocity varies from 100cm/s to 200cm/s, slag defects mostly were eliminated, and filling velocity varies from 400cm/s to 200cm/s, the porosity defects decreased a lot, consistent with the trends of the simulation results.