In production process of aluminum alloy die-casting parts, metal liquid is quickly ejected into cavity and hits mold wall, which will inevitably produce vortices and air rolls. If overflow system is not designed reasonably, it will cause gas dissolved in aluminum liquid to be difficult to discharge from cavity, resulting in pore defects inside and on the surface of casting. Based on requirements of weight reduction, parts of new energy vehicles mostly use aluminum alloy die-casting parts with complex structures and thin walls. In order to ensure mechanical properties of castings, heat treatment processes must be used. If gas content of casting is high, bubbles will be formed on the surface of casting during heat treatment, and mechanical properties will be poor, which cannot meet technical requirements, resulting in scrapping and great waste for enterprise.
Due to weight reduction requirements of new energy vehicles, their battery housings generally use aluminum alloy die-casting parts with light weight, easy processing and molding, high high temperature corrosion resistance, good heat transfer and electrical conductivity. Casting has high technical requirements, die-casting machine tonnage is too large, and many problems occur during die-casting trial production. Taking a new energy vehicle battery shell as an example, CAE is used to simulate original plan, and casting simulation software MAGMA Software is used to analyze causes of defects in battery shell during die-casting process. Use of a reasonable overflow system and vacuum process can effectively avoid cold shut and pore defects.
Graphic results
Structure of a battery shell is shown in Figure 1, with a weight of 14.1kg and a material of AlSi10MgMn. Outer contour size of casting is 801 mm×726mm×145.5mm, wall thickness is relatively uniform, maximum is 5mm, minimum is 2mm, main wall thickness is 3.5mm, and inner cavity is regularly arranged with reinforcing ribs.

 

Figure 1 Structural diagram of battery shell

 

Figure 2 Cold shut defect picture

 

Figure 3 B and C zone pore defect picture

 

Figure 4 C zone threaded through hole defect

 

Figure 5 CAE analysis of casting filling
Cold shut in zone A is due to fact that this position is end of casting filling, which is prone to gas entrainment. Improvement plan is: add slag bag 2 and thicken slag bag mouth 3 by 1mm. Pore exposure defect after machining of large planes in zones B and C is caused by gas entrainment in mold wall. Improvement plan is: widen slag bag mouth 4 by 5mm and thicken 1mm; widen and deepen overflow channel 5, see Figure 6a. For rotten teeth after machining of threaded through hole 1 in zone C, improvement plan is: accelerate filling of this area, change casting structure without affecting use function, and add two ribs at the front end of this area, see Figure 6b.

 

Figure 6 Improved solution

 

Figure 7 CAE analysis comparison of original solution and improved solution for area A

 

Figure 8 CAE analysis comparison of original solution and improved solution for areas B and C

 

Figure 9 Appearance of casting after mold modification