Aluminum alloy die-casting has advantages of high dimensional accuracy, good appearance quality, and high production efficiency. However, because molten metal fills mold cavity in a high-speed jet state during die-casting, gas cannot be discharged and is drawn into molten metal. After solidification, it remains in casting in the form of pores. In order to eliminate pores inside die casting and improve mechanical properties of casting, vacuum die casting is usually used. Molten metal fills mold cavity in a vacuum state. Since less gas is involved, it has a good effect on improving internal quality of casting, so it is widely used in die-casting industry.
Mechanical vacuum valves are widely used in vacuum die-casting. They have characteristics of large exhaust area, small gas flow resistance, and high vacuum degree. Working principle is to use inertial impact force of molten metal to close valve core to complete a working cycle. In actual production process, vacuum valve core may be clogged, causing malfunction and affecting vacuuming effect. By improving exhaust system of oil cooler bracket and using Anycasting software for simulation, it was found that when molten aluminum reaches vacuum valve, speed reaches 68m/s, which is extremely high and has a significant impact on clogging of vacuum valve. An effective way to solve problem of vacuum valve clogging is urgently needed.
Graphics Results
An oil cooler bracket, its structure and pouring and drainage system are shown in Figure 1. The overall dimensions are 411mm×214mm×191mm, basic wall thickness is 4mm, weight is 3.4kg, gate cross-sectional area is 765mm2, exhaust cross-sectional area is 265mm2, and injection punch diameter is φ100mm. Structural diagram of vacuum valve core is shown in Figure 2. Head of vacuum valve spool (Part A) is easily clogged; in addition, tail part of vacuum valve spool (Part B) is broken.
Due to high-speed and high-pressure characteristics of die-casting process, head of vacuum valve core is frequently washed away by high-speed and high-pressure aluminum liquid, causing head of vacuum valve core (see A in Figure 2) to become clogged; tail of vacuum valve core (see point B in Figure 2) is the weakest position. Molten aluminum liquid frequently impacts valve core, which concentrates force on tail, causing tail to easily break.

 

Figure 1 Oil cooler bracket and pouring overflow system

 

Figure 2 Schematic diagram of vacuum valve core structure

 

Figure 3 Simulation analysis of initial plan

 

Figure 4 Different forms of reduction mechanisms

 

Figure 5 Adding rear oil cooler bracket of triangular reduction mechanism
Pouring overflow system

 

Figure 6 Schematic diagram of speed detection through simulation analysis after setting up deceleration mechanism
By adding a deceleration structure at the end of exhaust duct, impact speed of aluminum liquid on vacuum valve can be effectively weakened, impact force on vacuum valve can be reduced, problem of fracture of tail of vacuum valve core and problem of vacuum valve clogging can be solved, thereby improving service life of mechanical vacuum valve core.