| Automotive lightweight is of great benefit to the endurance mileage,control stability and safety of electric vehicles.Battery pack is the energy source of electric vehicles,and the battery box plays the role of protecting of battery pack.Therefore,the research on battery box needs to pay attention to lightweight and safety.The lightweight of battery box can be achieved mainly by two methods:one is using new lightweight materials,the other is optimizing the structure of battery box.Magnesium alloys are the lightest structural materials for engineering applications,but there are still technical difficulties in structural redesign and forming process optimization.In order to realize the large-scale application of magnesium alloy in battery box,the substitution structure of magnesium alloy material for battery box was redesigned.Through simulation analysis,the static strength and stiffness characteristics of battery box under two extreme conditions of"bump+brake"and"bump+sharp turn"were studied.According to the structural characteristics and numerical simulation results of magnesium alloy battery box,the vacuum die casting process was designed and optimized,the optimal vacuum die casting process parameters were determined,and the engineering verification and sample trial production were carried out.This paper has made some achievements in the following aspects:(1)Under the two extreme conditions of"bump+brake"and"bump+sharp turn",the stress concentration areas of magnesium alloy battery box are the same,which are all in the connection between stiffeners and the side wall.The statics properties of the optimized magnesium alloy battery box can meet the requirements.In terms of static strength,the maximum equivalent stresses are 124.83 MPa and 114.69 MPa under the two extreme conditions,and in terms of static stiffness,the maximum deformation is2.32 mm and 1.87 mm under the two extreme conditions.(2)The magnesium alloy battery box mass is 14.06kg and the steel battery box mass is 38.23kg.Therefore,the weight is reduced by 63.2%,and the lightweight effect is obvious.(3)According to the structure characteristics of battery box and the forming technology of magnesium alloy material,the calculation and design of pouring system and discharge system were completed.The optimum vacuum die casting parameters were obtained by numerical simulation:the vacuum degree was 5×10~4Pa,the rapid injection rate was 3.2 m/s,the pouring temperature and preheat temperature of die were680℃and 220℃,respectively.(4)According to the optimum process,the design and manufacture of the die have been completed,and the sample has been trial-produced.The effect of die casting is very good. |
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