Numerical Simulation And Process Optimization Design Of Investment Casting For Large Complex Heavy Haul Freight Coupler

Railway freight car coupler is the key component to connect vehicles,transfer traction and ensure the safe operation of trains.It needs to ensure that the connected carriages at both ends do not move laterally and longitudinally.As the core bearing component of train set connection,the stress state of coupler is complex and changeable,and it is affected by large impact,tension,compression and torque during operation.Therefore,the coupler casting needs to have excellent comprehensive performance.In order to solve the problem of frequent cracks and shrinkage cavities and low yield in the actual production of investment casting of a locomotive coupler casting using the original gating system scheme,through computer simulation analysis and Research on the actual casting and performance inspection in the investment casting process,in order to improve the quality and yield of coupler casting,the main research contents are as follows:(1)The structure,size and working conditions of coupler casting are analyzed,and the initial gating system scheme is numerically simulated.The results showed that under the original gating system scheme,the coupler casting did not follow the principle of sequential solidification and simultaneous solidification in the solidification process,resulting in a large area of isolated liquid phase area at the end of solidification,and shrinkage cavity,porosity and crack defects concentrated in the key parts such as the intersection of coupler head and coupler tongue,which seriously affected the quality and yield of the casting.(2)The gating system of coupler casting is optimized.The horizontal single side gate gating system is modified to vertical symmetrical gating system to increase the number of gates and the volume of gating system.The simulation results of the optimization scheme show that the shrinkage cavity and shrinkage porosity defects in the key parts of the casting disappear,and only sporadic shrinkage cavity and shrinkage porosity defects appear in the non important parts of the casting,and the effective stress in the key parts is small.The solidification of the casting roughly follows the principle of sequential solidification.(3)Taking the shrinkage cavity and porosity volume of the casting body and the average value of effective stress at the selected point of key parts as the reference index,and taking the pouring temperature,mold shell temperature and pouring time as the influencing factors,the orthogonal experiment was designed.The orthogonal experiment shows that the optimal pouring parameters are as follows: pouring temperature 1570℃,mold preheating temperature 425℃ and pouring time 29 s.The range analysis shows that the pouring temperature has the greatest influence on the casting quality,followed by the pouring time and the mold shell temperature.(4)Through the actual pouring production,the actual performance of the optimized pouring system and the optimal pouring process parameter combination is verified.The wax mold and shell of the optimized pouring system are made,and the optimal pouring process parameters are used for pouring forming.After cooling and finalization,random samples were taken for fluorescent magnetic particle flaw detection and X-ray flaw detection,and no cracks,shrinkage cavities and other defects were found.Take samples to prepare metallographic samples for official microscope(OM)and scanning electron microscope(SEM)microstructure observation,and take samples to prepare tensile test and hardness test samples for mechanical property test.The results show that the room temperature tensile strength of the coupler casting samples after heat treatment is between 850～1500 MPa,up to 1450 MPa,and the elongation is up to 4.5%.After heat treatment,the hardness value of the casting remains in the range of 352～375 HBW,and its tensile strength and hardness meet the service requirements.This shows that the coupler castings with good surface quality and service performance can be obtained through the combination of optimized gating system and optimal gating process parameters.