Aluminum alloy die-casting has the advantages of high dimensional accuracy, good appearance quality, and high production efficiency. However, due to the high-speed injection of molten metal into the mold cavity during die-casting, gas cannot be discharged and is drawn into the molten metal. After solidification, it remains in the casting in the form of pores. To eliminate the internal pores of die castings and improve the mechanical properties of castings, vacuum die casting is usually used. Metal liquid fills the mold cavity in a vacuum state, and due to the less gas involved, it plays a good role in improving the internal quality of castings, thus it is widely used in the die-casting industry.

        Mechanical vacuum valves are widely used in vacuum die-casting, with the characteristics of large exhaust area, low gas flow resistance, and high vacuum degree. The working principle is to use the inertia impact force of the metal liquid to close the valve core and complete a working cycle. In the actual production process, there is a malfunction caused by the blockage of the vacuum valve core, which affects the vacuum pumping effect. By improving the exhaust system of the oil cooler bracket and using Anycasting software for simulation, it was found that the speed of molten aluminum reaching the vacuum valve reached 68m/s, which was extremely high and had a significant impact on the phenomenon of vacuum valve blockage. There is an urgent need for an effective way to solve the problem of vacuum valve blockage.

Graphic and textual results

     The structure and pouring system of a certain oil cooler bracket are shown in Figure 1. The external dimensions are 411mm x 214mm x 191mm, with a basic wall thickness of 4mm and a mass of 3.4kg. The gate cross-sectional area is 765m ², the exhaust cross-sectional area is 265m ², and the diameter of the injection punch is φ 100mm. The schematic diagram of the vacuum valve core structure is shown in Figure 2. The head of the vacuum valve core (part A) is prone to blockage; In addition, there is a fracture phenomenon at the tail end (part B) of the vacuum valve core.

    Based on the characteristics of high speed and high pressure in the die-casting process, the head of the vacuum valve core is frequently subjected to high-speed and high-pressure aluminum liquid erosion, resulting in blockage of the head of the vacuum valve core (see A in Figure 2); The tail end of the vacuum valve core (see B in Figure 2) is the weakest position, and the molten aluminum frequently impacts the core, causing the tail end to be stressed and prone to fracture.

    By adding a deceleration structure at the end of the exhaust duct, the impact speed of aluminum liquid on the vacuum valve can be effectively weakened, the impact force on the vacuum valve can be reduced, and the problem of fracture and blockage at the tail of the vacuum valve core can be solved, thereby improving the service life of the mechanical vacuum valve core.

Author of this article:

Wang Dongsheng, Li Hua, Wu Yansheng, Zhang Guiquan
Technology Center of Great Wall Motors Co., Ltd. and Hebei Automotive Engineering Technology Research Center
Source of this article: Journal of Special Casting and Nonferrous Alloys