Structural Design And Process Optimization Of Low Pressure Die Casting For Aluminum Alloy Sub-frame

Using aluminum alloy to replace steel is one commonly used method for the lightweight of chassis parts.Aluminum alloy is one of the ideal lightweight materials because of its lower density,higher strength and more various forming methods.Casting is more and more commonly used in forming vehicle structure.Low-pressure casting technology,as a near net shape forming technology,has the advantages of relatively few defects,high density of structure and relatively low cost.Taking the aluminum alloy sub-frame as the research object,based on a traditional steel-made sub-frame,topology optimization and structural design,structure performance analysis,casting process design,numerical simulation of casting process,casting process optimization research have been carried on.The main contents are as follows:(1)Based on the design method of material substitution,the original steel-made subframe structure is redesigned.Considering the layout of vehicle body structure,suspension system,steering system,powertrain and its accessories,the mounting points of sub-frame and other factors,the layout space of sub-frame which meets the condition that the space does not interfere with vehicle's other systems is designed.Based on the structure,OptiStruct software is used to perform topology optimization.The sub-frame structure is designed based both on the results of topology optimization and casting process requirement.Performance analysis of the sub-frame has been performed,including statics analysis and modal analysis,to analyze whether the stiffness and the strength of the aluminum alloy sub-frame meet the requirement,the vibration frequency is reasonable.(2)The casting system for the aluminum alloy sub-frame structure is designed and the numerical simulation of casting process is performed.ProCAST software is used to pretreat the casting and casting system,set the boundary conditions of the casting and virtual mold,and the process parameters of the casting process,etc.Then the numerical simulation of the casting process is conducted,including numerical simulation of the filling process and numerical simulation of the solidification process.The results of filling process,solidification process and defects under the initial filling condition are obtained,which will be the basis for the subsequent process optimization.(3)According to the problems reflected in the numerical simulation of casting process,the casting technology is optimized,including the optimization of casting system and casting process parameters.Taking a typical small thin-walled casting as an example,the effects of different number of internal sprue and different forms of internal sprue on filling,solidification process,final shrinkage and porosity of casting are investigated.Based on the results,the original casting system is optimized,and the optimized casting system is verified.The results show that the optimization of the casting system has a positive correlation with casting quality.Based on the optimized casting system,the influence of process parameters on casting defects is further investigated.The method of orthogonal experiment is used to carry out three factors,including filling pressure,pouring temperature,mold preheating temperature,and three levels orthogonal experiment design.By analyzing the numerical simulation of temperature field,flow field and final casting defects,the optimal parameter combination is determined.The porosity defects are decreased and the quality of the structure is improved.