Simulation Of Low-Pressure Die Casting Process Of A Fan Impeller And Mold Design

In this paper,the aluminum alloy impeller casting on the traction motor fan of a rail car is taken as the research object.The casting defects in the actual production process of the impeller casting are analyzed.The casting simulation software ProCAST is used to simulate the filling and solidification process of the impeller casting.In view of the main casting defects that appear in the current process using castings,corresponding improvements are proposed.Through the orthogonal test of four factors and four levels,the effects of pouring temperature,filling pressure,mold preheating temperature and metal mold wall thickness on the filling and solidification process of the impeller casting were studied,and a set of optimal process parameters was obtained.The three-dimensional modeling software UG10.0 was used to design the low-pressure casting mold of the impeller casting.The impeller casting adopts the current technology.The main casting defects in actual production are:there are shrinkage holes with a diameter of about 1~2mm in the thick wall of the blade.Such shrinkage defects are the main reason for the scrapping of the impeller casting,accounting for about 80%of the waste products;Some castings have insufficient casting defects at the sharp corners of the blades;oxidized slag may sometimes appear at the junction of the thin-walled sharp corners of the blades and the wheel cover.In this paper,the filling and solidification processes of impeller castings using the current low-pressure casting process are simulated and analyzed.The simulation results of filling process show that the risk of underpouring defect is high at the thin-wall cusp of the blade;in the process of mold filling,the metal liquid has a long contact time with the air and tends to produce oxidized slag.The analysis results of the solidification process show that the temperature of the sand core is higher during the solidification process,the solidification time of the thick part of the blade is longer,and the isolated liquid phase area is formed in the later period of solidification.The metal liquid at the gate cannot be effectively compacted through the wheel.The simulation extraction results of shrinkage defects show that there are shrinkage defects of different degrees in the wheel cover between the impeller wheel and the blade.Shrinkage occurs at the maximum wall thickness of the blade about 40mm upward from the impeller wheel.The total shrinkage volume is 61.4 cm~3,the average shrinkage volume of each blade is about 5.13 cm~3.The simulation results of microstructure and performance show that the secondary dendrite arm spacing SDAS of the main part of the impeller casting is 21.6 um to 39.5 um,and the tensile strength of the main part is above 286MPa.The simulation analysis results are basically consistent with the problems in actual production.According to the simulation analysis results,three improvement schemes of the process system are proposed for the shrinkage defects of the thick-walled parts of the blade.According to the actual production implementation,the scheme with less improvement of the mold but better effect is selected.The thickness of the channel wheel is reduced,the solidification sequence is adjusted,and the exhaust system and cold iron structure are improved.The simulation analysis results show that the degree of air entrainment during the filling process is significantly improved,and the risk of insufficient casting defects at the sharp corners of the blade is reduced.The shrinkage hole defect in the center of the thick wall of the blade disappeared,and there was a small shrinkage hole defect in the lower part.The total shrinkage hole volume was reduced from the original 61.4cm3 to 2.02cm3.The shrinkage defects of the impeller wheel and the blade part were significantly reduced.The shrinkage defects of the wheel cover were not alleviated.The results of the trial production show that the thick-walled parts of the blade are basically free of shrinkage defects,indicating that this scheme is feasible.The orthogonal test was used to simulate and optimize the four important parameters affecting the low-pressure filling and solidification process of the impeller casting.The pouring temperature,filling pressure,mold preheating temperature,and metal mold wall thickness determined three evaluation indicators:one is the pore volume The second is the grade of slag inclusion in gas oxidation,and the third is the SDAS of secondary dendrite arm spacing.The results show that:(1)The process parameter that has the greatest influence on the pore volume of the impeller casting is the mold preheating temperature,and the remaining order is the metal wall thickness,pouring temperature,and filling pressure;(2)The process parameter that has the greatest impact on the rating of the gas oxidation slag inclusions in impeller castings is the filling pressure,and the remaining order is the mold preheating temperature,pouring temperature,and metal mold wall thickness;(3)The biggest influence on the secondary dendrite arm of the impeller casting is the pouring temperature,and the remainder is the mold preheating temperature,filling pressure,and metal mold wall thickness;(4)The optimized set of process parameters are:pouring temperature 700?,filling pressure 0.025MPa,left and right half preheat temperature 200?,bottom preheat temperature 240?,and metal mold wall thickness 35mm.The optimized process parameters were used to simulate and analyze the filling and solidification process of the impeller casting.The results showed that there were no shrinkage defects in the thick wall of the blade,and there were small shrinkage defects in the lower part.The total volume was 0.55cm~3,which was compared with the process parameters2.04cm~3 before the improvement,a reduction of 90.69%,the degree of shrinkage of the casting is significantly reduced;the air volume at the wheel is reduced to a certain extent.According to the optimized plan for actual production,there are no obvious shrinkage shrinkage defects,pores and slag inclusion defects in the X-ray detection of the blade part,no insufficient casting defects at the tip of the blade tip,and no significant pinholes and shrinkage in the fluorescence detection at the bottom of the wheel hole defects.